JP3538098B2 - OFDM modulation / demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to orthogonal frequency division multiplexing (OFDM) used in digital wireless communication.
O to process frequency division multiplexing signals
The present invention relates to an FDM modulation / demodulation circuit, and more particularly to adaptive modulation for changing a transmission signal modulation method, a symbol rate, an error correction coding rate, and the like according to a transmission path environment in order to maximize a transmission speed.

[0002]

2. Description of the Related Art In land mobile communications, for example, the transmission path environment changes constantly with time. In such an environment, the effective data transmission speed can be maximized by changing the transmission conditions according to the transmission path environment at that time. That is, when the transmission path environment is bad,
The transmission rate is reduced by lowering the symbol rate, error correction coding rate, etc., and when the transmission path environment is good, the modulation multi-level number,
The transmission rate is increased by increasing the symbol rate, the error correction coding rate, and the like. Such a technique of changing the modulation condition according to the transmission path environment is called an adaptive modulation scheme.

Conventionally, a signal transmitted between each terminal station (mobile station) and a radio base station in mobile communication is shown in FIG.
It is configured as shown in FIG. In FIG. 15, a signal BC arranged at the head of the frame format is a downlink control signal, and signals BD (1) to BD (N
1) are downlink bursts for the first to N1st users, respectively, and subsequent signals BU (1) to BU
(N2) is an uplink burst for each of the first to N2th users.

The downlink signal is a signal transmitted from the base station to the terminal station, and the uplink signal is a signal transmitted from the terminal station to the base station. In the case of performing adaptive modulation, as shown in FIG. 15, a known PN in the time domain is used as a preamble signal at the beginning of each burst.
A (pseudo noise) signal is arranged, followed by a data signal (DATA).

[0005] A modulation / demodulation circuit of a communication terminal that performs adaptive modulation is configured as shown in FIG. In this example,
It is assumed that a single carrier system is used. The operation of the circuit illustrated in FIG. 14 is described below. On the reception side, the reception signal input from the transmission path
At 0, it is converted to a baseband signal. This baseband signal is input to the fading compensation circuit 340 and the transmission path characteristic estimation circuit 320.

[0006] The transmission line characteristic estimating circuit 320 calculates a delay profile from the baseband signal input in the preamble section. That is, since the preamble included in the received signal is a known PN signal, the delay profile is calculated based on the known signal and the received signal held by the transmission path characteristic estimation circuit 320 itself.

The transmission path characteristic estimating circuit 320 calculates a delay spread and CNR (Carr (Carr) from the obtained delay profile.
ier to Noise Ratio). Further, the modulation condition is determined according to the obtained delay spread and CNR.
The determination of the modulation condition is performed based on, for example, a predetermined modulation control chart as shown in FIG. This modulation control chart is created under the constraint that constant transmission quality is always maintained.

In this example, the modulation condition is selected from four types according to the division of the area to which the coordinates corresponding to the delay spread and the CNR belong. Further, a symbol rate and a modulation multi-level number are controlled as modulation conditions. The transmission path characteristic estimating circuit 320 inputs a control signal corresponding to the determined symbol rate and modulation multilevel number to the adaptive modulation circuit 300. Further, the transmission path characteristic estimating circuit 320 simultaneously outputs a carrier signal necessary for demodulating the received signal to the fading compensation circuit 340.

[0009] Fading compensation circuit 340 demodulates the received signal using the carrier signal input from transmission path characteristic estimating circuit 320. On the transmission side, the adaptive modulation circuit 300
Modulates the transmission data. The symbol rate and the number of modulation levels, which are the conditions for modulation, are controlled so as to match the symbol rate and the number of modulation levels determined by the transmission path characteristic estimation circuit 320. The signal modulated by the adaptive modulation circuit 300 is
The signal is converted into a radio frequency by the transmission circuit 310 and transmitted.

The above prior art is disclosed in the following document: "Matsuoka, Kami, Sanbe, Morinaga," Transmission characteristic analysis of symbol rate / modulation multilevel variable adaptive modulation system ", IEICE Tech.
CS94-64 ".

[0011]

As described above, when a modulation / demodulation circuit employing an adaptive modulation method is used, a desired modulation method and symbol rate corresponding to fluctuations in the characteristics of a transmission line are automatically selected. Is possible.

By the way, it is known that the OFDM system used in digital radio communication is not easily affected by multipath fading. If the modulation and demodulation circuit that modulates the OFDM system adopts the adaptive modulation system as described above, the following problem occurs. In the case of the OFDM system, a large number of subcarriers having different frequencies are used at the same time, so that a known signal in the frequency domain must be used as a preamble signal used for carrier estimation or the like.

On the other hand, in order to realize the conventional adaptive modulation method, it is necessary to use a known signal in the time domain as a preamble signal for estimating a transmission path. Therefore, O
In order to adopt the conventional adaptive modulation scheme for the FDM scheme,
It is necessary to insert both a known preamble signal in the frequency domain and a known preamble signal in the time domain into a signal to be transmitted.

[0014] When an extra preamble signal is inserted in this way, a reduction in transmission efficiency is inevitable. In addition, since an existing system cannot add a time domain preamble signal, it is not possible to employ an adaptive modulation scheme.
Also, when the uplink and downlink are asymmetric due to transmission power control or the like, the terminal station sends a signal of the modulation scheme determined by the terminal station to the base station so that the base station transmits the signal to the terminal station. It is necessary to transmit a request signal for designating a modulation method. If such a request signal is transmitted for each burst, the transmission efficiency decreases.

In an environment where the optimum modulation method or the like cannot be uniquely determined, the modulation method or the like is changed for each burst, so that a portion (such as a scheduler) other than the modulation / demodulation unit is burdened.

The present invention relates to an OFDM modulation / demodulation circuit,
It is necessary to make it possible to estimate the state of the transmission path without adding an extra signal to the OFDM preamble signal used for carrier estimation, etc., and to transmit a request signal for specifying modulation conditions for each burst. And to reduce the number of times of changing the modulation scheme as much as possible.

[0017]

An OFDM demodulation circuit for inputting an orthogonal frequency multiplexed signal in which the same known preamble signal appears at least twice, and detecting received data included in the input signal, A receiving circuit that converts a received signal of a radio frequency into a baseband signal, a fast Fourier transform circuit that performs a fast Fourier transform after serial-to-parallel conversion of the baseband signal output from the receiving circuit, and a fast Fourier transform circuit. A reception data extraction circuit that extracts reception data from a plurality of signals separated for each output frequency, and a plurality of signals separated for each frequency output from the fast Fourier transform circuit in a preamble section of the reception signal. A modulation component removing circuit for generating a signal from which the modulation component has been removed as a first signal; A carrier signal generation circuit for generating, as a second signal, a carrier signal representing the amplitude characteristic and the phase characteristic of the transmission line for each frequency from a plurality of signals separated for each frequency output from the fast Fourier transform circuit in the reamble section; And estimating the characteristics of the transmission path based on the first signal generated by the modulation component removal circuit and the second signal generated by the carrier signal generation circuit, and adapting the transmission path to the estimated characteristics of the transmission path. And a transmission path characteristic estimating circuit for outputting a signal indicating the modulation condition.

According to the first aspect of the present invention, the modulation component removing circuit converts a signal obtained by removing a modulation component from a plurality of signals separated for each frequency output from the fast Fourier transform circuit into a first signal in a preamble section of the received signal. Is generated as Further, the carrier signal generation circuit converts the carrier signal representing the amplitude characteristic and the phase characteristic of the transmission path for each frequency from a plurality of signals separated for each frequency output from the fast Fourier transform circuit in the preamble section of the received signal. 2 is generated. Further, the transmission line characteristic estimating circuit estimates the characteristics of the transmission line based on the first signal generated by the modulation component removing circuit and the second signal generated by the carrier signal generation circuit. A signal indicating a modulation condition suitable for the characteristics of the road is output.

Even if the signal in the preamble section is a known signal in the frequency domain, the first signal from which the modulation component has been removed can be obtained using the known signal. Also, for example, by smoothing the first signal for each subcarrier frequency, a carrier signal (second signal) representing the amplitude characteristics and the phase characteristics of the transmission path for each frequency can be obtained.
Since the transmission line characteristic estimating circuit estimates the characteristics of the transmission line based on the first signal and the second signal, a known preamble signal in the time domain is not required.

Therefore, it is not necessary to transmit a known preamble signal in bursts in the time domain, and a decrease in transmission efficiency is prevented. Further, since it is not necessary to change the preamble signal, it is possible to add an adaptive modulation function to an existing system that handles OFDM signals. Claim 2 provides that the same known preamble signal is at least 2
An OFDM modulation / demodulation circuit that inputs orthogonal frequency multiplexed signals that appear twice, detects received data contained in the input signals, modulates data to be transmitted, and outputs the data, converts the received signals of radio frequencies to baseband signals. A fast Fourier transform circuit that performs a fast Fourier transform after serial-to-parallel conversion of a baseband signal output from the receive circuit, and a plurality of frequency bands separated for each frequency output from the fast Fourier transform circuit. A reception data extraction circuit for extracting reception data from a signal,
A modulation component elimination circuit for generating, as a first signal, a signal obtained by removing a modulation component from a plurality of signals separated for each frequency output from the fast Fourier transform circuit in a preamble section of the reception signal; and a preamble of the reception signal. In the section,
A carrier signal generation circuit for generating, as a second signal, a carrier signal representing amplitude characteristics and phase characteristics of a transmission line for each frequency from a plurality of signals separated for each frequency output from the fast Fourier transform circuit; Based on the first signal generated by the component elimination circuit and the second signal generated by the carrier signal generation circuit, the characteristics of the transmission path are estimated, and a modulation condition suitable for the estimated transmission path characteristic is determined. A transmission path characteristic estimating circuit for outputting a signal indicative of the signal, and a modulation circuit having at least one of a modulation scheme, an error correction coding rate and a symbol rate variable, and a modulation condition determined according to the signal output by the transmission path characteristic estimating circuit. An adaptive modulation circuit that modulates data to be transmitted with the adaptive modulation circuit, and an inverse fast Fourier transform that performs an inverse fast Fourier transform on the signal modulated by the adaptive modulation circuit And road, characterized in that a signal processed by the inverse fast Fourier transform circuit is provided and a transmission circuit for converting the radio frequency signals.

According to a second aspect, as in the first aspect, the transmission line characteristic estimating circuit is based on the first signal generated by the modulation component removing circuit and the second signal generated by the carrier signal generating circuit. The characteristic of the transmission path is estimated, and a signal indicating a modulation condition suitable for the estimated characteristic of the transmission path is output. Also,
The adaptive modulation circuit modulates data to be transmitted under the modulation condition determined according to the signal output from the transmission path characteristic estimation circuit. The inverse fast Fourier transform circuit performs an inverse fast Fourier transform process on the signal modulated by the adaptive modulation circuit. The transmission circuit converts the signal processed by the inverse fast Fourier transform circuit into a radio frequency signal.

That is, according to the second aspect, modulation suitable for the characteristics of the transmission path detected on the receiving side is automatically performed and transmitted. Therefore, when this OFDM modulation / demodulation circuit is provided in, for example, both the base station and the terminal station, there is no need to transmit a request signal for designating a modulation scheme between the base station and the terminal station, and the transmission efficiency is reduced. Can be avoided. According to a third aspect of the present invention, in the OFDM demodulation circuit of the first aspect, the modulation component elimination circuit is provided with inverse modulation means for calculating a known preamble signal and a reception signal for each subcarrier, and the carrier signal generation circuit is provided. Filter means for smoothing the first signal output from the modulation component removal circuit with respect to a plurality of preambles is provided, and the reception data extraction circuit uses the second signal output from the carrier signal generation circuit as a carrier signal to receive the reception signal. Is provided with synchronous detection means for detecting.

According to a third aspect of the present invention, the modulation component elimination circuit calculates a known preamble signal and a reception signal for each subcarrier and inversely modulates the reception signal to generate a first signal from which the modulation component has been eliminated. . Further, the carrier signal generation circuit generates a second signal by smoothing the first signal output from the modulation component removal circuit with respect to a plurality of preambles. Further, the reception data extraction circuit performs synchronous detection using the second signal output from the carrier signal generation circuit as a carrier signal.

Therefore, a circuit for generating a carrier signal required for synchronous detection and a circuit for generating a signal required for estimating a transmission path can be shared, thereby preventing the circuit configuration from becoming complicated. . Claim 4 is the OFD of claim 1
In the M demodulation circuit, an amplitude calculation circuit for calculating and outputting the magnitude or amplitude of the second signal for each subcarrier to the transmission path characteristic estimating circuit, and a signal output from the amplitude calculation circuit for all sub-carriers. A sub-carrier amplitude summation circuit for adding a carrier, a signal output from the amplitude calculation circuit, an inter-subcarrier difference calculation circuit for calculating and outputting a difference between signal amplitudes of adjacent subcarriers, A correlation calculation circuit that calculates and outputs the magnitude or amplitude of the difference signal output by the inter-carrier difference calculation circuit, and a subcarrier correlation summation circuit that adds the signal output by the correlation calculation circuit for all subcarriers; ,
A first division circuit for dividing a signal output from each of the subcarrier correlation summation circuits by a signal output from each of the subcarrier amplitude summation circuits; and calculating a difference between the first signal and the second signal. A difference calculation circuit for calculating the difference between the received signal and the carrier signal, an error calculation circuit for calculating and outputting the magnitude or amplitude of the signal output from the difference signal between the received signal and the carrier signal, A sub-carrier error summation circuit that adds signals to be processed for all subcarriers, and a second division circuit that divides a signal output by each of the subcarrier amplitude summation circuits by a signal output by each of the subcarrier error summation circuits. A modulation control signal generation circuit for generating a signal corresponding to a characteristic of a transmission path detected according to a signal output from the first division circuit and a signal output from the second division circuit. Characterized in that a and.

According to a fourth aspect, the amplitude calculation circuit calculates and outputs the magnitude or amplitude of the second signal for each subcarrier by calculating the absolute value or calculating the square. Further, each subcarrier amplitude summation circuit obtains the sum by adding the signals output from the amplitude calculation circuit for all the subcarriers. The inter-subcarrier difference calculation circuit receives the signal output from the amplitude calculation circuit, calculates a difference between signal amplitudes of adjacent subcarriers, and outputs the difference.

The correlation calculating circuit calculates and outputs the magnitude or amplitude of the difference signal output from the inter-subcarrier difference calculating circuit by calculating the absolute value or calculating the square. Each subcarrier correlation summation circuit obtains the sum by adding the signals output from the correlation calculation circuit for all the subcarriers. The first division circuit divides a signal output from each of the subcarrier correlation summation circuits by a signal output from each of the subcarrier amplitude summation circuits.

Further, the reception signal-carrier signal difference calculation circuit calculates and outputs the difference between the first signal and the second signal. The error calculation circuit calculates and outputs the magnitude or amplitude of the signal output by the reception signal-carrier signal difference calculation circuit. Each subcarrier error summation circuit obtains the sum by adding the signal output from the error calculation circuit for all the subcarriers. The second division circuit is
A signal output from each of the subcarrier amplitude summation circuits is divided by a signal output from each of the subcarrier error summation circuits. The modulation control signal generation circuit generates a signal corresponding to the detected characteristic of the transmission line according to the signal output from the first division circuit and the signal output from the second division circuit.

According to a fifth aspect of the present invention, in an OFDM demodulation circuit for inputting an orthogonal frequency multiplexed signal in which the same known preamble signal appears at least twice and detecting received data contained in the input signal, the received signal of a radio frequency is A receiving circuit that converts the signal into a baseband signal and generates the baseband signal as a first signal in a preamble section, a noise removing circuit that removes noise of a signal output from the receiving circuit only in the preamble section, A fast Fourier transform circuit that performs a fast Fourier transform after serial-to-parallel conversion of a baseband signal output from the circuit and the receiving circuit; and a plurality of signals separated for each frequency output from the fast Fourier transform circuit. And a reception data extraction circuit for extracting the A modulation component elimination circuit for generating, as a second signal, a signal obtained by removing a modulation component from a plurality of signals separated by frequency output from the fast Fourier transform circuit, and a second signal generated by the modulation component elimination circuit And a transmission path characteristic estimating circuit that estimates a characteristic of the transmission path based on the first signal generated by the receiving circuit and outputs a signal indicating a modulation condition suitable for the estimated characteristic of the transmission path. It is characterized by having been provided.

According to the fifth aspect, the receiving circuit converts a radio frequency received signal into a baseband signal, and generates the baseband signal as a first signal in a preamble section. The noise removing circuit removes noise of the signal output from the receiving circuit only in the preamble section. The fast Fourier transform circuit performs a fast Fourier transform after serial-to-parallel conversion of the baseband signal output from the noise elimination circuit and the receiving circuit. The reception data extraction circuit
Received data is extracted from a plurality of signals separated for each frequency output from the fast Fourier transform circuit.

Further, the modulation component elimination circuit generates, as a second signal, a signal obtained by removing a modulation component from a plurality of signals output from the fast Fourier transform circuit and separated for each frequency in a preamble section of the received signal. . The transmission path characteristic estimating circuit estimates a characteristic of the transmission path based on the second signal generated by the modulation component removing circuit and the first signal generated by the receiving circuit, and A signal indicating a modulation condition suitable for the characteristic is output.

A receiving circuit for converting a received signal of a radio frequency into a baseband signal and generating the baseband signal as a first signal in a preamble section, and a noise of a signal output from the receiving circuit. And a baseband signal output from the noise elimination circuit and the reception circuit.
A fast Fourier transform circuit that performs a fast Fourier transform after parallel conversion, a received data extraction circuit that extracts received data from a plurality of signals separated for each frequency output from the fast Fourier transform circuit, and a preamble section of the received signal A modulation component elimination circuit that generates a signal obtained by removing a modulation component from a plurality of signals separated for each frequency output from the fast Fourier transform circuit as a second signal, and a modulation component elimination circuit generated by the modulation component elimination circuit. Channel characteristic estimation that estimates a characteristic of a transmission line based on the second signal and the first signal generated by the receiving circuit, and outputs a signal indicating a modulation condition suitable for the estimated characteristic of the transmission line. Circuit and modulation method,
At least one of an error correction coding rate and a symbol rate
One includes a variable modulation circuit, an adaptive modulation circuit that modulates data to be transmitted under a modulation condition determined according to a signal output from the transmission path characteristic estimation circuit, and an inverse high-speed signal with respect to the signal modulated by the adaptive modulation circuit. An inverse fast Fourier transform circuit for performing a Fourier transform process and a transmission circuit for converting a signal processed by the inverse fast Fourier transform circuit into a radio frequency signal are provided.

According to a sixth aspect, in the same manner as in the fifth aspect, the transmission path characteristic estimating circuit performs transmission based on the second signal generated by the modulation component removing circuit and the first signal generated by the receiving circuit. Channel characteristics are estimated, and a signal indicating a modulation condition suitable for the estimated transmission line characteristics is output. Further, the adaptive modulation circuit modulates data to be transmitted under modulation conditions determined according to the signal output from the transmission path characteristic estimation circuit.

The inverse fast Fourier transform circuit performs an inverse fast Fourier transform process on the signal modulated by the adaptive modulation circuit. The transmission circuit converts the signal processed by the inverse fast Fourier transform circuit into a radio frequency signal.
That is, in the sixth aspect, modulation suitable for the characteristics of the transmission path detected on the receiving side is automatically performed and transmitted. Therefore, when this OFDM modulation / demodulation circuit is provided in, for example, both the base station and the terminal station, there is no need to transmit a request signal for designating a modulation scheme between the base station and the terminal station, and the transmission efficiency is reduced. Can be avoided.

According to a seventh aspect of the present invention, in the OFDM demodulation circuit according to the fifth aspect, the noise elimination circuit includes filter means for smoothing the first signal output from the reception circuit in a preamble section, and the modulation component elimination is performed. The circuit is provided with inverse modulation means for calculating a known preamble signal for each subcarrier and the received signal output by the noise elimination circuit, and the reception data extraction circuit includes an output from the modulation component elimination circuit. Synchronous detection means for detecting a received signal using the second signal as a carrier signal is provided.

In the present invention, in the preamble section, the first signal output from the receiving circuit is smoothed by the filter means to extract the preamble. The inverse modulator calculates a known preamble signal for each subcarrier and the received signal output by the noise elimination circuit to remove a modulation component. The synchronous detection means detects a received signal using the second signal output from the modulation component elimination circuit as a carrier signal.

According to an eighth aspect of the present invention, in the OFDM demodulation circuit according to the fifth aspect, an amplitude calculation circuit for calculating and outputting the magnitude or amplitude of the second signal for each subcarrier to the transmission path characteristic estimating circuit; A sub-carrier amplitude summation circuit that adds the signals output by the amplitude calculation circuit for all subcarriers; and a sub-input circuit that receives a signal output by the amplitude calculation circuit and calculates a difference between signal amplitudes of adjacent subcarriers. An inter-carrier difference calculation circuit, a correlation calculation circuit that calculates and outputs the magnitude or amplitude of a difference signal output by the inter-subcarrier difference calculation circuit, and a signal output by the correlation calculation circuit for all subcarriers. Each subcarrier correlation summation circuit to be added, and each subcarrier amplitude summation circuit outputs a signal output from each subcarrier correlation summation circuit. A first divider circuit for dividing the items,
An averaging circuit for averaging the first signal, a delay circuit for delaying the first signal by a processing delay of the averaging circuit and outputting the signal, a signal output from the averaging circuit, and an output A difference calculation circuit for calculating a difference from a signal to be processed;
An error calculation circuit that calculates and outputs the magnitude or amplitude of a signal output by the difference calculation circuit, an error summation circuit that adds the signal output by the error calculation circuit in a preamble section, and an error summation circuit that outputs A second division circuit for dividing a signal by a signal output from each of the subcarrier error summation circuits, and a transmission path detected according to a signal output from the first division circuit and a signal output from the second division circuit And a modulation method determining circuit for generating a signal corresponding to the characteristic of (1).

[0037] According to claim 8, the amplitude calculation circuit includes the second circuit.
Is calculated and output for each subcarrier. Each subcarrier amplitude summation circuit adds the signal output from the amplitude calculation circuit for all subcarriers. The inter-subcarrier difference calculation circuit receives the signal output from the amplitude calculation circuit and calculates a difference between signal amplitudes of adjacent subcarriers.

The correlation calculation circuit calculates and outputs the magnitude or amplitude of the difference signal output by the inter-subcarrier difference calculation circuit. Each subcarrier correlation summation circuit adds the signal output by the correlation calculation circuit for all subcarriers. The first division circuit divides a signal output from each of the subcarrier correlation summation circuits by a signal output from each of the subcarrier amplitude summation circuits.

Further, the averaging circuit averages the first signal. The delay circuit delays the first signal by a processing delay of the averaging circuit and outputs the delayed signal. The difference calculation circuit calculates a difference between the signal output by the averaging circuit and the signal output by the delay circuit. The error calculation circuit calculates and outputs the magnitude or amplitude of the signal output by the difference calculation circuit. The error summation circuit adds the signals output by the error calculation circuit in a preamble section.

The second divider divides the signal output by the error summation circuit by the signal output by each of the subcarrier error summation circuits. The modulation scheme determination circuit generates a signal corresponding to the characteristic of the transmission path detected according to the signal output from the first division circuit and the signal output from the second division circuit. A ninth aspect of the present invention is the OFDM demodulation circuit according to the first or fifth aspect, wherein the receiving circuit, the fast Fourier transform circuit, the received data extracting circuit and the modulation component removing circuit, and the carrier signal generating circuit or the carrier signal generating circuit according to the first aspect. Item 5
And a plurality of the second signals generated by the carrier signal generating circuit of claim 1 or the noise removing circuit of claim 5 are input to the transmission path characteristic estimating circuit, respectively. A comparison / selection circuit for selecting and outputting a signal having a larger amplitude for each subcarrier and outputting information indicating the selected state; and an amplitude calculation for calculating the magnitude or amplitude of the signal output by the comparison / selection circuit. Circuit, a subcarrier amplitude summation circuit that adds the signals output by the amplitude calculation circuit for all subcarriers and outputs the sum as a carrier reception signal, and inputs the signals output by the amplitude calculation circuit, An inter-subcarrier difference calculation circuit that calculates the difference between the signal amplitudes of the signals, and the magnitude of the difference signal output by the inter-subcarrier difference calculation circuit or A correlation calculation circuit for calculating a width, each subcarrier correlation summation circuit for adding a signal output from the correlation calculation circuit for all subcarriers, and a signal output from each subcarrier correlation summation circuit for each subcarrier amplitude. A first dividing circuit for dividing by a signal output from the summing circuit.

According to the ninth aspect, since a plurality of receiving systems are provided, the receiving circuit, the fast Fourier transform circuit, the received data extracting circuit and the modulation component removing circuit, the carrier signal generating circuit according to the first aspect, or the carrier signal generating circuit according to the first aspect. A plurality of the noise removing circuits of item 5 are provided. The comparison and selection circuit inputs a plurality of the second signals generated by the carrier signal generation circuit of claim 1 or the noise removal circuit of claim 5 and selects a signal having a larger amplitude for each subcarrier. And outputs information indicating the selected state. The amplitude calculation circuit calculates the magnitude or amplitude of the signal output from the comparison and selection circuit. Each subcarrier amplitude summation circuit adds the signal output from the amplitude calculation circuit for all subcarriers and outputs the result as a carrier reception signal.

The inter-subcarrier difference calculation circuit receives a signal output from the amplitude calculation circuit and calculates a difference between signal amplitudes of adjacent subcarriers. The correlation calculation circuit calculates the magnitude or amplitude of the difference signal output by the inter-subcarrier difference calculation circuit. Each subcarrier correlation summation circuit adds the signal output by the correlation calculation circuit for all subcarriers. The first division circuit divides a signal output from each of the subcarrier correlation summation circuits by a signal output from each of the subcarrier amplitude summation circuits.

A tenth aspect of the present invention relates to the first or fifth aspect.
In the FDM demodulation circuit, a plurality of the receiving circuit, the fast Fourier transform circuit, the received data extracting circuit, the modulation component removing circuit, the carrier signal generating circuit of claim 1 or the noise removing circuit of claim 5 are provided, respectively. A plurality of the second signals generated by the carrier signal generation circuit according to claim 1 or the noise removal circuit according to claim 5 are input to the transmission path characteristic estimating circuit, and a magnitude or amplitude of an input signal is input for each subcarrier. , A sub-carrier amplitude summation circuit that adds the signals output by the addition amplitude calculation circuit for all subcarriers and outputs the sum as a carrier reception signal, and a signal output by the addition amplitude calculation circuit. A sub-carrier difference calculating circuit for inputting and calculating a difference between signal amplitudes of adjacent sub-carriers; A correlation calculating circuit rear differencing calculation circuit for calculating the magnitude or amplitude of the difference signal output,
A sub-carrier correlation summation circuit that adds the signal output by the correlation calculation circuit for all subcarriers; and a signal output by the subcarrier correlation summation circuit is divided by a signal output by the subcarrier amplitude summation circuit. First
And a dividing circuit.

In the tenth aspect, since a plurality of receiving systems are provided, the receiving circuit, the fast Fourier transform circuit,
A plurality of the reception data extraction circuit and the modulation component elimination circuit, a plurality of the carrier signal generation circuit of the first aspect, and a plurality of the noise elimination circuits of the fifth aspect are provided. The added amplitude calculation circuit is a carrier signal generation circuit according to claim 1 or claim 5.
A plurality of the second signals generated by the noise elimination circuit are input, and the magnitude or amplitude of the input signal is added for each subcarrier. Each subcarrier amplitude summation circuit adds the signal output by the addition amplitude calculation circuit for all subcarriers and outputs the result as a carrier reception signal. The inter-subcarrier difference calculation circuit receives the signal output from the addition amplitude calculation circuit and calculates a difference between signal amplitudes of subcarriers adjacent to each other.

The correlation calculation circuit calculates the magnitude or amplitude of the difference signal output by the inter-subcarrier difference calculation circuit. Each subcarrier correlation summation circuit adds the signal output by the correlation calculation circuit for all subcarriers. The first division circuit divides a signal output from each of the subcarrier correlation summation circuits by a signal output from each of the subcarrier amplitude summation circuits.

According to an eleventh aspect of the present invention, in the OFDM demodulation circuit according to the first aspect, the receiving circuit, the fast Fourier transform circuit, the received data extracting circuit, the modulation component removing circuit, and the carrier signal generating circuit are provided in plurality, respectively. A comparison and selection circuit that inputs a plurality of the second signals to a transmission path characteristic estimating circuit, selects and outputs a signal having a larger amplitude for each subcarrier, and outputs information indicating the selected state; A selection circuit that receives a plurality of first signals output by the modulation component removal circuit and selects one first signal according to a selection state of the comparison selection circuit for each subcarrier; A signal-to-carrier signal difference calculation circuit for calculating a difference between a signal to be output and a signal output from the comparison / selection circuit;
An error calculation circuit for calculating the magnitude or amplitude of the signal output by the difference calculation circuit between carrier signals; a subcarrier error summation circuit for adding the signal output by the error calculation circuit for all subcarriers; A second division circuit for dividing a signal output from the carrier amplitude summation circuit by a signal output from each of the subcarrier error summation circuits is provided.

In the eleventh aspect, since a plurality of receiving systems are provided, the receiving circuit, the fast Fourier transform circuit,
A plurality of reception data extraction circuits, modulation component removal circuits, and carrier signal generation circuits are provided. The comparison and selection circuit inputs a plurality of the second signals, selects and outputs the signal having the larger amplitude for each subcarrier, and outputs information indicating the selected state.

The selection circuit inputs a plurality of first signals output from the modulation component removal circuit, and for each subcarrier,
One first signal is selected according to the selection state of the comparison and selection circuit. The reception signal-carrier signal difference calculation circuit calculates a difference between the signal output by the selection circuit and the signal output by the comparison selection circuit. The error calculation circuit calculates the magnitude or amplitude of the signal output by the reception signal-carrier signal difference calculation circuit. Each subcarrier error summation circuit adds the signal output from the error calculation circuit for all subcarriers. The second division circuit divides a signal output from each of the subcarrier amplitude summation circuits by a signal output from each of the subcarrier error summation circuits.

According to a twelfth aspect of the present invention, in the OFDM demodulation circuit according to the first aspect, the receiving circuit, the fast Fourier transform circuit, the received data extracting circuit, the modulation component removing circuit, and the carrier signal generating circuit are provided in plurality, respectively. A plurality of received signal-carriers for inputting a plurality of first signals and a plurality of second signals to a transmission path characteristic estimating circuit and calculating a difference between the first signal and the second signal for each corresponding subcarrier A signal difference calculation circuit, and a plurality of error calculation circuits for calculating the magnitude or amplitude of the signal respectively output by the plurality of received signal-carrier signal difference calculation circuit,
Each of the subcarrier error summation circuits for adding the signals output by the plurality of error calculation circuits for all the subcarriers, and the signal output by each of the subcarrier amplitude summation circuits is a signal output by each of the subcarrier error summation circuits. A second division circuit for performing division.

In the twelfth aspect, since a plurality of receiving systems are provided, the receiving circuit, the fast Fourier transform circuit,
A plurality of reception data extraction circuits, modulation component removal circuits, and carrier signal generation circuits are provided. Also,
A plurality of reception signal-carrier signal difference calculation circuits and error calculation circuits are also provided. Each subcarrier error summation circuit,
Signals output from the plurality of error calculation circuits are added for all subcarriers. The second division circuit divides a signal output from each of the subcarrier amplitude summation circuits by a signal output from each of the subcarrier error summation circuits.

According to a thirteenth aspect, in the OFDM demodulation circuit according to the fifth aspect, the receiving circuit, the fast Fourier transform circuit, the received data extracting circuit, the modulation component removing circuit, and the noise removing circuit are provided in plurality, respectively. A plurality of averaging circuits for averaging the plurality of first signals generated by the plurality of noise elimination circuits, respectively; and a delay of the plurality of first signals by a processing delay of the averaging circuit. A plurality of delay circuits, and a plurality of difference calculation circuits for calculating a difference between a signal output from the averaging circuit and a signal output from the delay circuit; and a magnitude of a signal output from the difference calculation circuit. A plurality of error calculation circuits for calculating and outputting amplitudes; a plurality of error summation circuits for adding signals output from the error calculation circuits in a preamble section; A signal averaging circuit that calculates an average of a plurality of signals respectively output by the summation circuit; and a second division circuit that divides a signal output by the signal averaging circuit by a signal output by each of the subcarrier error summation circuits. It is characterized by having.

According to the thirteenth aspect, since a plurality of receiving systems are provided, the receiving circuit, the fast Fourier transform circuit,
A plurality of the reception data extraction circuit, the modulation component elimination circuit and the noise elimination circuit are provided. A plurality of averaging circuits, delay circuits, difference calculation circuits, error calculation circuits, and error summation circuits are provided. The signal averaging circuit is
An average of a plurality of signals respectively output from the plurality of error sum circuits is calculated. The second divider divides the signal output from the signal averaging circuit by the signal output from each of the subcarrier error summation circuits.

According to a fourteenth aspect of the present invention, in the OFDM demodulation circuit according to the thirteenth aspect, the signal averaging circuit calculates the average by adding the results of weighting a plurality of input signals. Claim 15 is the OF of claim 5
In the DM demodulation circuit, the reception circuit, the fast Fourier transform circuit, the reception data extraction circuit, the modulation component elimination circuit, and the noise elimination circuit are provided in plurality, respectively, and the transmission line characteristic estimation circuit includes the plurality of noise elimination circuits. A plurality of averaging circuits each for averaging a plurality of first signals generated by the circuit, a plurality of delay circuits for delaying the plurality of first signals by a processing delay of the averaging circuit, and outputting the plurality of averaging circuits; A plurality of difference calculation circuits for calculating a difference between the signal output by the circuit and the signal output by the delay circuit,
A plurality of error calculation circuits that calculate and output the magnitude or amplitude of the signal output by the difference calculation circuit; a plurality of error summation circuits that add a signal output by the error calculation circuit in a preamble section; A signal selection circuit for selecting one signal having a large integrated value from a plurality of signals respectively output by the error summation circuit, and dividing a signal output by the signal selection circuit by a signal output by each of the subcarrier error summation circuits And a second dividing circuit for performing the operation.

According to the fifteenth aspect, since a plurality of receiving systems are provided, the receiving circuit, the fast Fourier transform circuit,
A plurality of the reception data extraction circuit, the modulation component elimination circuit and the noise elimination circuit are provided. A plurality of averaging circuits, delay circuits, difference calculation circuits, error calculation circuits, and error summation circuits are provided. The signal selection circuit
One signal having a large integrated value is selected from a plurality of signals output from the plurality of error summing circuits. The second division circuit divides the signal output from the signal selection circuit by the signal output from each of the subcarrier error summation circuits.

The sixteenth aspect of the present invention relates to the first or fifth aspect.
In the FDM demodulation circuit, the space representing the estimated characteristics of the transmission path is divided into a plurality of regions, and information indicating the relationship between each of the divided regions and the modulation conditions is used as conversion means by the transmission line characteristic estimation circuit. Holding and providing an intermediate region having a width at a boundary portion between a plurality of regions adjacent to each other in the space, and when the estimated characteristic of the transmission line is located in the intermediate region, the transmission line characteristic estimation circuit Selects one of the modulation condition assigned to the first region adjacent to the intermediate region and the modulation condition assigned to the second region adjacent to the intermediate region as time passes. It is characterized by doing.

According to a sixteenth aspect, information indicating the correlation between each of the divided regions in the space representing the estimated characteristics of the transmission path and the modulation condition is held in the transmission path characteristic estimating circuit. An intermediate region having a width is provided at a boundary between a plurality of regions adjacent to each other. When the intermediate region does not exist, if the estimated characteristics of the transmission path change across the boundaries of the plurality of divided regions, the modulation condition on the transmission side may change immediately. However, when the characteristic change of the transmission path is temporary, switching of the modulation condition on the transmission side is useless, and it is necessary to return to the original modulation condition again.

By providing an intermediate area between adjacent areas, and in the intermediate area, the modulation conditions of the first area and the second area adjacent to each other are selectively selected in accordance with the passage of time, so that there is no waste. Switching of the modulation condition is less likely to occur. According to a seventeenth aspect, in the OFDM demodulation circuit according to the first or fifth aspect, the space representing the estimated characteristics of the transmission path is divided into a plurality of regions, and the relation between each of the divided regions and the modulation condition is determined. While holding the information shown in the transmission path characteristic estimating circuit as conversion means, providing an intermediate region having a width at the boundary between a plurality of regions adjacent to each other in the space,
When the estimated characteristics of the transmission path are located in the intermediate region, the previous modulation condition is maintained as it is.

By maintaining the previous modulation condition in the intermediate region as it is, useless switching of the modulation condition is less likely to occur.

[0059]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment)
One embodiment of the FDM modulation / demodulation circuit will be described with reference to FIGS. This form corresponds to claims 1 to 4, claim 16 and claim 17.

FIG. 1 is a block diagram showing the configuration of an OFDM modulation / demodulation circuit according to this embodiment. FIG. 2 is a block diagram showing the configuration of the transmission line characteristic estimating circuit of this embodiment. FIG. 3 is a time chart showing a signal configuration according to the embodiment of the present invention. FIG. 4 is a modulation control chart showing the correspondence (1) between the characteristics of the transmission path and the modulation conditions. FIG. 5 is a modulation control chart showing the correspondence (2) between the characteristics of the transmission path and the modulation conditions.

In this embodiment, the receiving circuit, the fast Fourier transform circuit, the received data extracting circuit,
The modulation component elimination circuit, the carrier signal generation circuit, and the transmission path characteristic estimation circuit include a reception circuit 40, an FFT circuit
0, a modulation signal detection circuit 67, a modulation component removal circuit 63, a low-pass filter 65, and a transmission path characteristic estimation circuit 70. Further, the adaptive modulation circuit, the inverse fast Fourier transform circuit and the transmission circuit of the second aspect are respectively adapted to the adaptive modulation circuit 10,
It corresponds to the IFFT circuit 20 and the transmission circuit 30.

Further, an amplitude calculation circuit, a summation circuit for each subcarrier amplitude, a difference calculation circuit between subcarriers, a correlation calculation circuit, a summation circuit for each subcarrier correlation, a first division circuit, and a circuit between a received signal and a carrier signal are provided. The difference calculation circuit, the error calculation circuit, the respective subcarrier error summation circuits, the second division circuit, and the modulation control signal generation circuit each include an amplitude calculation circuit 7.
2. Each subcarrier amplitude summation circuit 74, a difference calculation circuit between subcarriers 73, a correlation calculation circuit 75, a summation circuit for each subcarrier correlation 76, a division circuit 77, a difference calculation circuit 83 between a received signal and a carrier signal, and an error calculation circuit 84 , The subcarrier error summation circuit 85, the division circuit 86, and the modulation control signal generation circuit 87.

In this example, a communication terminal having the OFDM modulation / demodulation circuit shown in FIG.
It is assumed that wireless communication is performed with a wireless base station using a signal. The base station also includes a transmitting unit 101 and a receiving unit 102 having the same configuration as in FIG. However, when the uplink and downlink are symmetrical, the transmitting unit 101 and the receiving unit 102 as shown in FIG. 1 may be provided in only one of the base station and the mobile station (communication terminal). Good.

In FIG. 3, signal BC arranged at the head of the frame format is a downlink control signal,
Subsequent signals BD (1) to BD (N1) are first to
Signals BU (1) to BU (N2) subsequent to the N1st user (communication terminal) are bursts in the downlink, and uplink BUs for the first to N2th users.

Note that the downlink signal is a signal transmitted from the base station to the communication terminal, and the uplink signal is a signal transmitted from the communication terminal to the base station.
In this example, as shown in FIG. 3, two preambles PRE each having a length of 1 OFDM symbol are arranged continuously over 2 OFDM symbols at the head of each burst. These preambles PRE are known signals in the frequency domain. The two preambles PRE are the same signal.

Further, a guard interval GI is added before the first preamble. Subsequent to the preamble PRE, an OFDM symbol composed of a guard interval GI and data DATA repeatedly appears in the burst. Referring to FIG. 1, the transmission unit 101 includes an adaptive modulation circuit 10, an IFFT circuit 20, and a transmission circuit 30. Adaptive modulation circuit 10 modulates input transmission data and outputs a modulated signal. The adaptive modulation circuit 10 can perform modulation under various modulation conditions.

For example, BPSK, QPS
K, 16QAM, 64QAM and the like can be selected. When a convolutional code is used, 1/2, 3/4, or the like can be selected as a coding rate at the time of modulation. Of course, the configuration of the adaptive modulation circuit 10 may be changed so that another modulation condition such as a symbol rate can be selected.

In this example, the adaptive modulation circuit 10
The modulation condition is determined in accordance with the control signal SG7 output from the control signal 02. When the control signal SG7 changes, the modulation condition is changed from the next transmission start timing (next frame) to the changed modulation condition.

The signal modulated by the adaptive modulation circuit 10 is I
The signal is input to the FFT circuit 20 and subjected to inverse Fourier transform. I
The signal subjected to the inverse Fourier transform by the FFT circuit 20 is input to the transmission circuit 30 and subjected to a process of adding a guard interval and the like, then converted into a radio frequency and transmitted as a radio wave to a transmission path. On the other hand, the receiving unit 102 includes the receiving circuit 4
0, an FFT circuit 50, a detection circuit 60, and a transmission path characteristic estimation circuit 70.

The signal input as a radio wave from the transmission line is
The signal is received by the receiving circuit 40, converted into a baseband signal, and output from the receiving circuit 40. Further, the receiving circuit 40 performs processing such as removal of a guard interval on the baseband signal. The baseband signal output from the receiving circuit 40 is Fourier-transformed by the FFT circuit 50, detected by the detection circuit 60, and output as received data.

The detection circuit 60 includes an S / P circuit 61, a delay circuit 62, a modulation component removal circuit 63, a P / S circuit 64, a low-pass filter 65, a P / S circuit 66, a modulation signal detection circuit 67, and a P / S A circuit 68 is provided. The S / P circuit 61 performs serial-parallel conversion in order to input a serial signal in which signals of many subcarriers are arranged in time series from the FFT circuit 50 and generate a parallel signal separated for each subcarrier. .

The parallel signal for each subcarrier output from the S / P circuit 61 is input to a delay circuit 62 and a modulation component removing circuit 63. The signal delayed by the delay circuit 62 is input to the modulation signal detection circuit 67. The modulation signal detection circuit 67 converts the signal output from the delay circuit 62 into
Carrier signal SG output from low-pass filter 65
3 for synchronous detection for each subcarrier.

A delay circuit 62 is provided to compensate for the time delay of the carrier signal SG3 output from the low-pass filter 65. The parallel signal SG4 detected by the modulation signal detection circuit 67 is converted into a parallel signal by the P / S circuit 68.
The data is output as received data in the form of a serial signal that is serially converted and arranged in time series. Modulation component removal circuit 63
Is S / S in the section where the preamble PRE appears in the received signal.
The signal SG1 output from the P circuit 61 is input, and a signal SG2 from which a modulation component has been removed is generated. Specifically, the received signal is inversely modulated for each subcarrier component using a known signal (the same signal as the preamble PRE) held in advance by the modulation component removing circuit 63. The signal SG2 from which the modulation component has been removed is obtained by the inverse modulation.

Here, the component of the n-th subcarrier of the known signal is represented by d (n), and the component of the n-th subcarrier of the i-th preamble of the received signal SG1 is SG1.
Expressed as (i, n), the component SG2 (i, n) of the n-th subcarrier of the i-th preamble of the signal from which the modulation component has been removed
n) is represented by the following equation. SG2 (i, n) = (SG1 (i, n) · d (n) ^* ) / | d (n) | ^2, where i = 1 to 2, n = 1 to N, N: the received OFDM signal Number of subcarriers, *: The signal SG2 output from the complex conjugate modulation component removal circuit 63 is P / S
The signal is input to the circuit 64 and the low-pass filter 65.

The low-pass filter 65 performs signal smoothing in order to reduce noise components included in the signal SG2. In practice, the preamble appearing first and the preamble appearing second are averaged for each subcarrier. That is, the signal component SG3 (n) of the n-th subcarrier output from the low-pass filter 65 is represented by the following equation.

SG3 (n) = (SG2 (1, n) + SG2 (2, n)) / 2, where n = 1 to N. The signal SG3 output from the low-pass filter 65 is composed of N sets including no modulation component. It is a carrier signal. This carrier signal SG3 is used as a modulation signal detection circuit 6 for synchronous detection.
7 is applied. Further, the carrier signal SG3 is also input to the P / S circuit 66.

The P / S circuit 64 converts N sets of parallel signals SG2 that are independent for each subcarrier into a serial signal SG5 arranged in time series by parallel-serial conversion. Similarly, the P / S circuit 66 converts N sets of parallel signals SG3 that are independent for each subcarrier into serial signals SG6 arranged in time series by parallel-serial conversion. These serial signals SG5 and SG6 are applied to the transmission path characteristic estimation circuit 70.

The transmission path characteristic estimating circuit 70 estimates the characteristics of the transmission path based on the signals SG5 and SG6 generated from the components of the preamble section of the received signal as described above, and sets a modulation condition suitable for the estimated characteristic. select. The transmission line characteristic estimating circuit 70 of FIG. 1 is actually configured as shown in FIG. Referring to FIG. 2, the transmission path characteristic estimating circuit 70 includes an S / P circuit 71, an amplitude calculating circuit 72, an inter-subcarrier difference calculating circuit 73, a sub-carrier amplitude summing circuit 74,
Correlation calculation circuit 75, each subcarrier correlation summation circuit 76,
A division circuit 77, an S / P circuit 81, a difference calculation circuit 83 between a received signal and a carrier signal, an error calculation circuit 84, a subcarrier error summation circuit 85, a division circuit 86, and a modulation control signal generation circuit 87 are provided.

The S / P circuits 71 and 81 perform serial / parallel conversion, respectively, and output N sets of parallel signals independent for each subcarrier. Inside the transmission path characteristic estimating circuit 70 of FIG.
And a value p of a CNR (carrier-to-noise ratio) estimation function is calculated.

(Equation 1) The amplitude calculation circuit 72 calculates an absolute value or calculates a square to obtain the magnitude or amplitude of the input carrier signal. This corresponds to obtaining the absolute value of C (n) in the above equation (1).

Each subcarrier amplitude summation circuit 74 obtains the sum of the amplitudes by adding the amplitude of the carrier signal output from the amplitude calculation circuit 72 for all the subcarriers. This corresponds to calculating the denominator of the above equation (1). The inter-subcarrier difference calculation circuit 73 calculates a difference between adjacent subcarriers for the amplitude of the carrier signal output from the amplitude calculation circuit 72. That is, the difference between the absolute value of C (n) and the absolute value of C (n + 1) in Equation (1) is calculated.

The correlation calculation circuit 75 calculates the absolute value or the square of the input signal in order to obtain the correlation which is the magnitude or amplitude of the difference for each subcarrier obtained by the inter-subcarrier difference calculation circuit 73. This is because (| C of the above equation (1)
(n) │-│C (n + 1) │). Each subcarrier correlation summation circuit 76 calculates the sum by adding the correlation values output from the correlation calculation circuit 75 for all the subcarriers. This corresponds to calculating the denominator of the above equation (1).

The division circuit 77 divides the value of the signal output from each subcarrier correlation summation circuit 76 by the value of the signal output from each subcarrier amplitude summation circuit 74. That is, this corresponds to performing the division of the denominator and the numerator in the above equation (1).
The difference calculation circuit 83 between the received signal and the carrier signal calculates the S / P
The difference between the signal output from the circuit 81 and the signal output from the S / P circuit 71 is calculated. This corresponds to calculating the difference between S (n, i) and C (n) of the denominator of the above equation (2).

The error calculation circuit 84 calculates the absolute value or the square of the difference signal output from the reception signal-carrier signal difference calculation circuit 83 in order to obtain the magnitude or amplitude. This is because (S (n, i) -C (n)) of the denominator of the above equation (2)
Is equivalent to calculating the absolute value of.

Each subcarrier error summation circuit 85 adds the signal output from the error calculation circuit 84 for all the subcarriers to obtain the sum. This corresponds to calculating the denominator of the above equation (2). The division circuit 86 divides the value of the signal output from each subcarrier amplitude summation circuit 74 by the value of the signal output from each subcarrier error summation circuit 85. This corresponds to the division of the numerator and the denominator in the above equation (2).

A large value f of the carrier correlation function of the above equation (1) means a large delay spread,
The fact that the value p of the CNR estimation function of the above equation (2) is large indicates that C
It means that NR is large. That is, the value f output from the division circuit 77 and the value p output from the division circuit 86 represent the characteristics of the transmission path. Therefore, the modulation control signal generation circuit 8
In 7, a desired modulation condition can be determined based on the value f output from the division circuit 77 and the value p output from the division circuit 86.

Actually, the information of the modulation control chart as shown in FIG. 4 which defines the correspondence between the values f and p of each function and the modulation condition is stored in the internal memory (RO) of the modulation control signal generation circuit 87.
M), the modulation condition is determined according to the modulation control chart. This modulation control chart is
It is obtained under the constraint condition of (PER (Packet Error Rate) = 1e-1).

In the modulation control chart of FIG. 4, the two-dimensional coordinate space specified by the value of p and the value of f is divided into four areas A, C, E, and G in advance, and each area has A modulation method (modulation multi-level number) and a coding rate are assigned as modulation conditions. That is, when the coordinates (p, f) representing the estimated characteristics of the transmission path belong to the area A, the BPSK modulation method and the coding rate of (R = 1/2) are selected, and the coordinates (p, f) are selected. Belongs to the area C, the modulation scheme of QPSK and the coding rate of (R = 1/2) are selected, and the coordinates (p,
If f) belongs to the area E, a modulation method of 16QAM and a coding rate of (R = 1/2) are selected, and the coordinates (p, f) are selected.
If belongs to the region G, the modulation method of 16QAM and the coding rate of (R = 3/4) are selected.

Therefore, the modulation control signal generation circuit 87 converts the signal representing the modulation scheme and the coding rate selected according to the area to which the coordinates (p, f) representing the estimated characteristics of the transmission path belong into S.
Output as G7. By the way, when control is performed using the modulation control chart shown in FIG. 4, when the state of the transmission path changes and the area to which the coordinates (p, f) belong moves to an adjacent area, the change is temporarily changed. However, the change will be reflected as a change in the modulation scheme or the coding rate.

However, when the characteristics of the transmission path temporarily change and immediately return to the original characteristics, even if the modulation method or the coding rate is changed immediately in response to the temporary change, the change is not changed. Unnecessary changes will be made because they are canceled. Therefore, in this embodiment, the modulation control chart shown in FIG. 5 is actually used. Referring to FIG. 5, in this modulation control chart, an intermediate area B having a width is formed between an area A and an area C, and an intermediate area D is similarly formed between an area C and an area E. An intermediate region F is formed between E and the region G.

When the modulation control chart of FIG. 5 is used, if the area to which the coordinates (p, f) representing the estimated characteristics of the transmission path belong enters the intermediate area, the modulation control signal generation circuit 87
Determines the modulation condition as follows. For example, the area to which the coordinates (p, f) belong due to the deterioration of the characteristics of the transmission path is the area G
To the intermediate region F, the first x frame (x, x, y) of the y frames of the signal frames to be transmitted thereafter
For y> x), among the areas E and G adjacent to the intermediate area F, the condition of the area G to which the modulation condition with the higher transmission rate is assigned is applied. Then, (y-
x) For frames, areas E,
Among the G, the condition of the region E to which the modulation condition of the lower transmission speed is assigned is applied.

Conversely, when the characteristics of the transmission path are improved and the area to which the coordinates (p, f) belong transitions from the area E to the intermediate area F, the first x frame of the y frames of the signal frames transmitted thereafter is changed. As for the frame, of the areas E and G adjacent to the intermediate area F, the condition of the area E to which the modulation condition of the lower transmission rate is assigned is applied. Then, for the subsequent (y-x) frame, of the areas E and G adjacent to the intermediate area F, the condition of the area G to which the modulation condition with the higher transmission rate is assigned is applied.

With this control, the number of changes in the modulation multi-level number and the coding rate in the intermediate area is limited to once for every y frame, so that useless switching of modulation conditions is unlikely to occur. Although the example of FIG. 1 illustrates a case where the modulation of the transmitting unit 101 is actually switched according to the modulation condition selected by the transmission path characteristic estimating circuit 70, for example, a signal transmitted by a partner (a radio base station in this example) is transmitted. The transmission path characteristic estimating circuit 70 may be configured to transmit information on the selected modulation condition as a request signal for switching the modulation condition.

Further, the contents of the modulation control chart shown in FIG. 5 may be changed as necessary. The present invention can be similarly applied to a case where not only the modulation multi-level number and the coding rate but also other parameters such as a symbol rate are changed. It should be noted that, instead of the expressions (1) and (2), the following expression
Equations (3) and (4) may be used.

(Equation 2) When these equations are used, the configuration of the transmission line characteristic estimation circuit shown in FIG. 2 may be changed as follows. A circuit for calculating power is used instead of the amplitude calculation circuit 72. That is, the square of the amplitude of the input signal is calculated so as to correspond to Expressions (3) and (4). In addition, each subcarrier amplitude sum circuit 74 calculates not the sum of the amplitude but the sum of the power.

(Second Embodiment) Another embodiment of the OFDM modulation / demodulation circuit of the present invention will be described with reference to FIGS. This embodiment corresponds to claims 5 to 8, claim 16, and claim 17. FIG. 6 is a block diagram showing the configuration of the OFDM modulation / demodulation circuit of this embodiment. FIG. 7 is a block diagram showing the configuration of the transmission line characteristic estimating circuit of this embodiment. This embodiment is a modification of the first embodiment. 6 and 7, elements corresponding to those in the first embodiment are denoted by the same reference numerals. The format of the assumed OFDM signal is the same as that of FIG. In the following description, the description of the already described elements will be omitted.

In this embodiment, the receiving circuit, the noise removing circuit, the fast Fourier transform circuit, the received data extracting circuit, the modulation component removing circuit, and the transmission path characteristic estimating circuit of the fifth and sixth aspects are respectively composed of the receiving circuit 40B, the low-pass Filter 4
5, corresponding to the FFT circuit 50, the modulation signal detection circuit 67, the modulation component removal circuit 63, and the transmission path characteristic estimation circuit 70B. The adaptive modulation circuit, the inverse fast Fourier transform circuit, and the transmission circuit according to claim 6 are adaptive modulation circuits 10, I, respectively.
It corresponds to the FFT circuit 20 and the transmission circuit 30.

Further, an amplitude calculation circuit, a sub-carrier amplitude sum circuit, an inter-subcarrier difference calculation circuit, a correlation calculation circuit, a sub-carrier correlation sum circuit, a first division circuit, an average circuit, a delay circuit, The difference calculation circuit, the error calculation circuit, the error summation circuit, the second division circuit, and the modulation scheme determination circuit include an amplitude calculation circuit 72, each subcarrier amplitude summation circuit 74, an intersubcarrier difference calculation circuit 73, and a correlation calculation circuit 75, respectively. , The subcarrier correlation summation circuit 76, the division circuit 77, the averaging circuit 92, the delay circuit 91, the difference calculation circuit 93, the error calculation circuit 94, the error summation circuit 95, the division circuit 86, and the modulation control signal generation circuit 87.

Referring to FIG. 6, the OFDM modulation / demodulation circuit includes a transmission unit 101 and a reception unit 102.
The configuration of the transmitting unit 101 is the same as that of FIG. Receiver 102
Has a receiving circuit 40B, a low-pass filter 45, an FFT
Circuit 50, detection circuit 60, and transmission path characteristic estimation circuit 70B
Is provided.

The signal input as a radio wave from the transmission path is
The signal is received by the receiving circuit 40B. The receiving circuit 40B converts the received signal into a baseband signal and outputs it. Further, the receiving circuit 40B performs processing such as guard interval removal on the baseband signal. The receiving circuit 40B
The preamble section of the received signal is distinguished from other sections, and the baseband signal of the preamble section is output to the transmission path characteristic estimation circuit 70B as the signal SG8.

The baseband signal output from the receiving circuit 40B is a low-pass filter 4 for the preamble section.
5 and is applied to the FFT circuit 50 in a section other than the preamble. This baseband signal is Fourier-transformed by the FFT circuit 50, detected by the detection circuit 60, and output as received data.

The low-pass filter 45 performs signal smoothing to remove noise components included in the preamble section of the received signal. Actually, smoothing is performed between a signal component at an arbitrary position of the baseband signal and a signal component at a position shifted from the signal component by an interval corresponding to the number of points of the Fourier transform in the FFT circuit 50. As a result, noise components other than the preamble are removed.

The signal subjected to the Fourier transform by the FFT circuit 50 is converted into a parallel signal for each subcarrier by the S / P circuit 61 and input to the delay circuit 62 and the modulation component removing circuit 63. The signal delayed by the delay circuit 62 is input to the modulation signal detection circuit 67. Modulation signal detection circuit 67
Performs synchronous detection of the signal output from the delay circuit 62 for each subcarrier using the signal SG3 output from the modulation component removal circuit 63. The delay circuit 62 is provided to compensate for a time delay of the signal SG3 output from the modulation component removing circuit 63.

The parallel signal SG4 output from the modulation signal detection circuit 67 as a detection output is converted by the P / S circuit 68 into a serial signal arranged in time series and output as received data. The modulation component elimination circuit 63 receives the signal output from the S / P circuit 61 in a section where the preamble PRE appears in the received signal, and generates a signal SG3 from which the modulation component has been eliminated. Specifically, the received signal is inversely modulated for each subcarrier component using a known signal (the same signal as the preamble PRE) held in advance by the modulation component removing circuit 63. Signal SG3 from which the modulation component has been removed by the inverse modulation
Is obtained.

In the preamble section of the signal input to the modulation component elimination circuit 63, since the low-pass filter 45 has already smoothed the signal, the modulation component elimination circuit 63 in FIG.
Output signal SG3 is the same as the signal SG3 of FIG. The signal SG3 is a parallel signal for each of N sets of subcarriers corresponding to the number of subcarriers of the received OFDM signal. This signal SG3 is converted by the P / S circuit 66 into a serial signal arranged in time series, and input to the transmission path characteristic estimating circuit 70B as a signal SG6.

The transmission path characteristic estimating circuit 70B outputs signals SG8, SG generated from the components of the preamble section of the received signal.
It estimates the characteristics of the transmission path based on G6, and outputs a control signal SG7 for selecting a modulation method suitable for the characteristics. As shown in FIG. 7, the transmission path characteristic estimating circuit 70B
S / P circuit 71, amplitude calculation circuit 72, difference calculation circuit between subcarriers 73, each subcarrier amplitude summation circuit 74, correlation calculation circuit 75, each subcarrier correlation summation circuit 76, division circuit 77, delay circuit 91, averaging circuit 92, a difference calculation circuit 93, an error calculation circuit 94, an error summation circuit 95, a division circuit 86, and a modulation control signal generation circuit 87.

The transmission path characteristic estimating circuit 70B calculates the value f of the above-mentioned carrier estimation function and the value C of the following equation (5).
The value p ′ of the NR estimation function is calculated. In this example, the number of preambles is 2 symbols.

[Equation 3] The circuit for calculating the value f of the carrier estimation function in the transmission path characteristic estimation circuit 70B in FIG. 7 is the same as that in FIG. Further, the value of the numerator of the equation (5) is obtained at the output of each subcarrier amplitude summation circuit 74 as in the case of FIG.

The averaging circuit 92 is included in the average of two symbols of the received signal SG8, that is, included in the denominator of the formula (5) ((1/2)
Σr (n, j)). The delay circuit 91 includes an averaging circuit 9
The delay corresponding to the processing time in the received signal SG8
(R (n, i)). The difference calculation circuit 93 calculates the difference between the signal output from the delay circuit 91 and the signal output from the averaging circuit 92.

The error calculation circuit 94 calculates the absolute value or the square value of the signal output from the difference calculation circuit 93. The error summation circuit 95 adds the signals output from the error calculation circuit 94 in all the sections of the preamble of two symbols, and obtains the sum. The result of the calculation corresponds to the denominator of the above equation (5). The dividing circuit 86 includes a sub-carrier amplitude summing circuit 74.
Is divided by the value of the signal output by the error summation circuit 95 (the denominator of the expression (5)). Therefore, the value of p 'in the equation (5) is obtained at the output of the division circuit 86. Note that the power calculation as shown in the above-described equation (4) may be performed instead of the equation (5).

The modulation control signal generation circuit 87 determines a desirable modulation condition based on the value f output from the division circuit 77 and the value p ′ output from the division circuit 86, as in the first embodiment. (Third Embodiment) Another embodiment of the present invention will be described with reference to FIGS. This mode is defined in claims 1 to 4, claim 9, claim 11, and claim 1.
6 and Claim 17.

In this embodiment, the comparison / selection circuit of claim 9
The amplitude calculation circuit, each subcarrier amplitude summation circuit, the difference calculation circuit between subcarriers, the correlation calculation circuit, each subcarrier correlation summation circuit, and the first division circuit respectively include a comparison selection circuit 78, an amplitude calculation circuit 72, and each subcarrier. This corresponds to the amplitude summation circuit 74, the inter-subcarrier difference calculation circuit 73, the correlation calculation circuit 75, each subcarrier correlation summation circuit 76, and the division circuit 77.

The comparison selection circuit, selection circuit, received signal-carrier signal difference calculation circuit, error calculation circuit, each subcarrier error summation circuit, and the second division circuit according to claim 11 are a comparison selection circuit 78, Selection circuit 82, reception signal-carrier signal difference calculation circuit 83, error calculation circuit 8
4. Each subcarrier error summation circuit 85 and division circuit 86
Corresponding to

FIG. 8 is a block diagram showing the configuration of the OFDM demodulation circuit of this embodiment. FIG. 9 is a block diagram showing the configuration of the transmission line characteristic estimating circuit of this embodiment. This embodiment is a modification of the first embodiment. 8 and 9,
Elements corresponding to those in the first embodiment are denoted by the same reference numerals. In FIG. 8, the transmitting unit 101 of FIG.
Are omitted. In the following description, the description of the already described elements will be omitted.

In this embodiment, it is assumed that two systems of received signals are input from transmission lines. For example, this embodiment can be applied to a case where received signals from a plurality of antennas are input in parallel, such as a diversity antenna.
Therefore, as shown in FIG. 8, two reception circuits 40, two FFT circuits 50, and two detection circuits 60 are provided. The configuration and operation of each of the receiving circuit 40, the FFT circuit 50, and the detection circuit 60 are the same as those in FIG.

The transmission path characteristic estimating circuit 70C includes the signals SG5 and SG6 output from the one detection circuit 60 (1) and the signals SG5 'and SG6' output from the other detection circuit 60 (2).
Are respectively input. As shown in FIG. 9, the transmission path characteristic estimating circuit 70C includes a comparison / selection circuit 78, an S / P circuit 71, an amplitude calculation circuit 72, an inter-subcarrier difference calculation circuit 73, a sub-carrier amplitude summation circuit 74, and a correlation calculation. Circuit 75, each subcarrier correlation summation circuit 76, division circuit 7
7, a selection circuit 82, an S / P circuit 81, a reception signal-carrier signal difference calculation circuit 83, an error calculation circuit 84, each subcarrier error summation circuit 85, a division circuit 86, and a modulation control signal generation circuit 87. .

Signals SG6 and SG6 'from the two detection circuits 60 (1) and 60 (2) are input to the input of the comparison and selection circuit 78, respectively. The comparison selection circuit 78 receives the input 2
The amplitude or power of the system signals SG6 and SG6 'is compared for each subcarrier, and the larger signal is selected and output to the S / P circuit 71. The comparison and selection circuit 78 outputs information indicating which of the two signals SG6 and SG6 'has been selected as the selection information signal SG9.

On the other hand, signals SG5 and SG5 'from the two detection circuits 60 (1) and 60 (2) are input to the input of the selection circuit 82, respectively. The selection circuit 82 includes a comparison selection circuit 7
8 according to the selection information signal SG9 from the two signals SG9
5 and SG5 'are selected and output to the S / P circuit 81. The configuration and operation of the transmission path characteristic estimating circuit 70C of FIG. 9 are the same as those of the transmission path characteristic estimating circuit 70 of FIG. 2 except that a comparison selection circuit 78 and a selection circuit 82 are added. Therefore, similarly to the first embodiment, a control signal SG7 for selecting a modulation method and a coding rate can be generated.

(Fourth Embodiment) Another embodiment of the present invention will be described with reference to FIGS. This form corresponds to claims 1 to 4, claim 10, claim 12, claim 16, and claim 17.

In this embodiment, the added amplitude calculation circuit, each subcarrier amplitude summation circuit, the difference calculation circuit between subcarriers, the correlation calculation circuit, each subcarrier correlation summation circuit, and the first division circuit are respectively added to each other. Amplitude calculation circuit 7
2B, each subcarrier amplitude summation circuit 74, an intersubcarrier difference calculation circuit 73, a correlation calculation circuit 75, each subcarrier correlation summation circuit 76, and a division circuit 77.

The received signal-carrier signal difference calculating circuit, the error calculating circuit, the respective subcarrier error summing circuits and the second dividing circuit according to the twelfth aspect respectively comprise the received signal-carrier signal difference calculating circuit 83, It corresponds to the calculation circuit 84, each subcarrier error summation circuit 85B, and the division circuit 86. FIG. 10 is a block diagram showing the configuration of the transmission line characteristic estimating circuit of this embodiment. This embodiment is a modification of the first embodiment and the third embodiment, and the configuration of the OFDM demodulation circuit is the same as that of FIG. 8 already described. However, the configuration of the transmission path characteristic estimating circuit 70C is changed as shown in FIG. In FIG. 10, elements corresponding to those in the first embodiment are denoted by the same reference numerals. In the following description, the description of the already described elements will be omitted.

Signals SG5 and SG6 output from one detection circuit 60 (1) and signals SG5 'and SG6' output from the other detection circuit 60 (2) are provided to transmission path characteristic estimating circuit 70C.
Are respectively input. In this embodiment, two sets of S / P circuits 71, S / P circuits 81, a difference calculation circuit 83 between a received signal and a carrier signal, and an error calculation circuit 84 are provided in the transmission path characteristic estimation circuit 70C as shown in FIG. And the addition amplitude calculation circuit 72B and the difference calculation circuit 7 between subcarriers
3. Each subcarrier amplitude summation circuit 74, correlation calculation circuit 7
5, each subcarrier correlation summation circuit 76, division circuit 77,
Each subcarrier error summation circuit 85B, division circuit 86, and modulation control signal generation circuit 87 are provided.

The two sets of signals SG6 and SG6 'are converted into parallel signals by S / P circuits 71 (1) and 71 (2), respectively, and are input to the addition amplitude calculation circuit 72B and the difference between the received signal and the carrier signal is calculated. Applied to the input of circuit 83. The added amplitude calculation circuit 72B receives the two signals SG
6, the amplitude or power of SG6 'is calculated, and the amplitude or power of signal SG6 and signal SG6 are calculated for each subcarrier.
6 'amplitude or power.

The two sets of signals SG5 and SG5 'are converted into parallel signals by S / P circuits 81 (1) and 81 (2), respectively, and applied to the input of a received signal-carrier signal difference calculation circuit 83. Is done. The configuration and operation of the two sets of received signal-carrier signal difference calculation circuits 83 and the two sets of error calculation circuits 84 are the same as those in FIG. Each subcarrier error summation circuit 85B calculates the error by adding the signals for each subcarrier output by the error calculation circuits 84 (1) and 84 (2) over the entire section of the preamble of two symbols, and calculates the error. The error obtained for the signal from the signal 84 (1) and the error obtained for the signal from the error calculation circuit 84 (2) are added, and the sum of the errors is obtained.

The operations of the divider 77, divider 86 and modulation control signal generator 87 in FIG. 10 are the same as those in FIG. Therefore, similarly to the first embodiment, a control signal SG7 for selecting a modulation method and a coding rate can be generated. (Fifth Embodiment) Another embodiment of the present invention will be described with reference to FIGS. This mode corresponds to claims 5 to 7, claim 9, claim 13, claim 14, claim 16, and claim 17.

In this embodiment, an averaging circuit, a delay circuit, a difference calculation circuit, an error calculation circuit, an error summation circuit,
The signal averaging circuit and the second division circuit correspond to the averaging circuit 92, the delay circuit 91, the difference calculation circuit 93, the error calculation circuit 94, the error summation circuit 95, the signal averaging circuit 96, and the division circuit 86, respectively. FIG. 11 is a block diagram showing a configuration of the OFDM demodulation circuit of this embodiment. FIG. 12 is a block diagram showing the configuration of the transmission line characteristic estimating circuit of this embodiment. This embodiment is a modification of the second embodiment. 11 and 12, elements corresponding to those of the second embodiment are denoted by the same reference numerals. In FIG. 11, the description of the transmission unit 101 in FIG. 6 is omitted. In the following description, description of the already described elements will be omitted.

In this embodiment, it is assumed that two systems of received signals are input from transmission lines. For example, this embodiment can be applied to a case where received signals from a plurality of antennas are input in parallel, such as a diversity antenna.
Therefore, as shown in FIG. 11, two reception circuits 40, two FFT circuits 50, and two detection circuits 60 are provided. Receiving circuit 40, low-pass filter 45, FFT circuit 50,
The configuration and operation of each of the detection circuits 60 are the same as those in FIG.

The transmission path characteristic estimating circuit 70D includes the signals SG8 and SG6 output from one detection circuit 60 (1) and the signals SG8 'and SG6' output from the other detection circuit 60 (2).
Are respectively input. As shown in FIG. 12, the transmission path characteristic estimation circuit 70D includes a comparison selection circuit 78, an S / P circuit 71, an amplitude calculation circuit 72, an inter-subcarrier difference calculation circuit 73, a subcarrier amplitude summation circuit 74, and a correlation calculation. Circuit 75, each subcarrier correlation summation circuit 76, division circuit 7
7, two sets of averaging circuit 92, delay circuit 91, difference calculation circuit 93, error calculation circuit 94, and error summation circuit 95, respectively.
And a signal averaging circuit 96, a division circuit 86, and a modulation control signal generation circuit 87.

The signals SG6 and SG6 'from the two detection circuits 60 (1) and 60 (2) are input to the input of the comparison and selection circuit 78, respectively. The comparison selection circuit 78 receives the input 2
The amplitude or power of the system signals SG6 and SG6 'is compared for each subcarrier, and the larger signal is selected and output to the S / P circuit 71. Two sets of averaging circuit 92, delay circuit 91,
The configurations and operations of the difference calculation circuit 93, the error calculation circuit 94, and each subcarrier error summation circuit 85 are the same as those in FIG. The signal averaging circuit 96 includes two error summation circuits 9
The average of two signals output from 5 (1) and 95 (2) is calculated, and the calculation result is output. When calculating the average, the signal averaging circuit 96 performs independent weighting on the signal from the error summation circuit 95 (1) and the signal from the error summation circuit 95 (2).

The operations of the divider 77, divider 86 and modulation control signal generator 87 in FIG. 12 are the same as those in FIG. Therefore, similarly to the second embodiment, the control signal SG7 for selecting the modulation method and the coding rate can be generated. (Sixth Embodiment) Another embodiment of the present invention will be described with reference to FIGS. This embodiment corresponds to claims 5 to 7, claim 9, and claims 15 to 17.

In this embodiment, an averaging circuit, a delay circuit, a difference calculation circuit, an error calculation circuit, an error summation circuit,
The signal selection circuit and the second division circuit correspond to the averaging circuit 92, the delay circuit 91, the difference calculation circuit 93, the error calculation circuit 94, the error summation circuit 95, the signal selection circuit 97, and the division circuit 86, respectively. FIG. 13 is a block diagram showing the configuration of the transmission line characteristic estimating circuit of this embodiment. This embodiment is a modification of the fifth embodiment. 13, elements corresponding to those in FIG. 12 are denoted by the same reference numerals. In the following description, the description of the already described elements will be omitted.

The OFDM demodulation circuit of this embodiment is configured as shown in FIG. 11, similarly to the fifth embodiment. However, the configuration of the transmission path characteristic estimating circuit 70D is changed as shown in FIG. 13, a signal selection circuit 97 is provided instead of the signal averaging circuit 96 in FIG. The signal selection circuit 97 compares the signal input from the error summation circuit 95 (1) with the signal input from the error summation circuit 95 (2), selects the larger signal, and outputs the larger signal to the division circuit 86. I do.

The operations of the division circuit 77, the division circuit 86 and the modulation control signal generation circuit 87 in FIG. 13 are the same as those in FIG. Therefore, similarly to the second embodiment, the control signal SG7 for selecting the modulation method and the coding rate can be generated.

[0131]

As described above, according to the present invention, the OF
When dealing with a DM signal, it is possible to estimate the characteristics of a transmission path without transmitting a known preamble in the time domain. For this reason, it is possible to avoid a decrease in transmission efficiency, and it is possible to adopt an adaptive modulation scheme in an existing system.

By estimating the characteristics of the transmission path using the signal used for detection, it is possible to avoid complication of the circuit configuration or increase of the processing amount. Furthermore, when the modulation conditions on the transmission side are automatically changed when the characteristics of the transmission line change, there is no need to transmit a request signal for switching the modulation conditions for each burst, preventing a decrease in transmission efficiency. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an OFDM modulation / demodulation circuit according to a first embodiment.

FIG. 2 is a block diagram illustrating a configuration of a transmission path characteristic estimation circuit according to the first embodiment.

FIG. 3 is a time chart illustrating a signal configuration according to the first embodiment;

FIG. 4 is a modulation control chart showing the correspondence (1) between the characteristics of the transmission path and the modulation conditions.

FIG. 5 is a modulation control chart showing the correspondence (2) between the characteristics of the transmission path and the modulation conditions.

FIG. 6 is a block diagram illustrating a configuration of an OFDM modulation / demodulation circuit according to a second embodiment;

FIG. 7 is a block diagram illustrating a configuration of a transmission line characteristic estimation circuit according to a second embodiment.

FIG. 8 shows an OF according to a third embodiment and a fourth embodiment;
FIG. 3 is a block diagram illustrating a configuration of a DM demodulation circuit.

FIG. 9 is a block diagram illustrating a configuration of a transmission path characteristic estimation circuit according to a third embodiment.

FIG. 10 is a block diagram illustrating a configuration of a transmission line characteristic estimation circuit according to a fourth embodiment.

FIG. 11 is a diagram illustrating O of the fifth embodiment and the sixth embodiment;
FIG. 3 is a block diagram illustrating a configuration of an FDM demodulation circuit.

FIG. 12 is a block diagram illustrating a configuration of a transmission path characteristic estimation circuit according to a fifth embodiment.

FIG. 13 is a block diagram illustrating a configuration of a transmission path characteristic estimation circuit according to a sixth embodiment.

FIG. 14 is a block diagram illustrating a configuration of a main part of a conventional communication terminal.

FIG. 15 is a time chart showing a configuration of a signal in a conventional example.

FIG. 16 is a modulation control chart of a conventional example.

[Explanation of symbols]

10 Adaptive modulation circuit 20 IFFT circuit 30 transmission circuit 40, 40B receiving circuit 45 Low-pass filter 50 FFT circuit 60 Detection circuit 61 S / P circuit 62 delay circuit 63 Modulation component removal circuit 64, 66, 68 P / S circuit 65 Low-pass filter 67 Modulation signal detection circuit 70, 70B, 70C, 70D Transmission line characteristic estimation circuit 71,81 S / P circuit 72 Amplitude calculation circuit 72B Addition amplitude calculation circuit 73 Difference calculation circuit between subcarriers 74 Each subcarrier amplitude summation circuit 75 Correlation Calculation Circuit 76 Each subcarrier correlation summation circuit 77,86 division circuit 78 Comparison selection circuit 81 S / P circuit 82 selection circuit 83 Received Signal-Carrier Signal Difference Calculation Circuit 84 Error Calculation Circuit 85, 85B Each subcarrier error summation circuit 87 Modulation control signal generation circuit 91 Delay circuit 92 Average circuit 93 Difference calculation circuit 94 Error Calculation Circuit 95 Error summation circuit 96 signal averaging circuit 97 signal selection circuit 101 transmission unit 102 Receiver

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masahiro Umehira 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-10-257013 (JP, A) JP-A-11-17642 (JP, A) JP-A-11-163822 (JP, A) JP-A-11-163823 (JP, A) JP-A-10-303849 (JP, A) JP-A-10-247955 (JP JP, A) WO 99/001956 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04J 11/00

Claims (17)

(57) [Claims] An OFDM that receives an orthogonal frequency multiplexed signal in which the same known preamble signal appears at least twice and detects received data included in the input signal.
A demodulation circuit, a reception circuit for converting a radio frequency reception signal to a baseband signal, a high-speed Fourier transform circuit for performing a high-speed Fourier transform after serial-to-parallel conversion of the baseband signal output from the reception circuit, and A reception data extraction circuit that extracts reception data from a plurality of signals separated for each frequency output from the Fourier transform circuit; and a preamble section of the received signal, which is separated for each frequency output from the fast Fourier transform circuit. A modulation component elimination circuit for generating a signal obtained by removing a modulation component from the plurality of signals as a first signal; and a plurality of signals separated for each frequency output from the fast Fourier transform circuit in a preamble section of a reception signal. A carrier signal representing the amplitude characteristic and phase characteristic of the transmission line for each frequency is used as a second signal. A carrier signal generation circuit, a first signal generated by the modulation component elimination circuit, and a second signal generated by the carrier signal generation circuit. An OFDM demodulation circuit, comprising: a transmission line characteristic estimating circuit that outputs a signal indicating a modulation condition suitable for a characteristic of a transmission line. 2. An OFDM modulator / demodulator for inputting an orthogonal frequency multiplex signal in which the same known preamble signal appears at least twice, detecting received data contained in the input signal, modulating data to be transmitted, and outputting the modulated data. A circuit for converting a received signal of a radio frequency into a baseband signal; a fast Fourier transform circuit for performing a fast Fourier transform after serial-to-parallel conversion of the baseband signal output from the receive circuit; and the fast Fourier transform. A reception data extraction circuit for extracting reception data from a plurality of signals separated for each frequency output from the conversion circuit; and a plurality of reception signals extracted for each frequency output from the fast Fourier transform circuit in a preamble section of the reception signal. Modulation signal for generating a signal obtained by removing the modulation component from the signal A carrier signal representing the amplitude characteristic and the phase characteristic of the transmission line for each frequency from a plurality of signals output from the fast Fourier transform circuit and separated for each frequency in a preamble section of the received signal. A carrier signal generation circuit that is generated as follows: a first signal generated by the modulation component elimination circuit; and a second signal generated by the carrier signal generation circuit. A transmission line characteristic estimating circuit for outputting a signal indicating a modulation condition suitable for the characteristics of the transmission line, and a modulation circuit in which at least one of a modulation scheme, an error correction coding rate, and a symbol rate is variable. An adaptive modulation circuit that modulates data to be transmitted under modulation conditions determined according to a signal output by the estimation circuit; and an inverse modulation circuit for the signal modulated by the adaptive modulation circuit. OFDM modulation and demodulation circuit, wherein the inverse fast Fourier transform circuit which performs the processing of Fourier transform, that the processed signal by the inverse fast Fourier transform circuit is provided and a transmission circuit for converting the radio frequency signals. 3. The OFDM demodulation circuit according to claim 1, wherein
The modulation component elimination circuit is provided with inverse modulation means for calculating a known preamble signal and a reception signal for each subcarrier, and the carrier signal generation circuit converts a first signal output from the modulation component elimination circuit into a plurality of signals. A filter means for smoothing a preamble is provided, and the reception data extraction circuit is provided with a synchronous detection means for detecting a reception signal using the second signal output from the carrier signal generation circuit as a carrier signal. OFDM demodulation circuit. 4. The OFDM demodulation circuit according to claim 1,
An amplitude calculation circuit that calculates and outputs the magnitude or amplitude of the second signal for each subcarrier to the transmission path characteristic estimating circuit; and adds a signal output by the amplitude calculation circuit for all subcarriers. A subcarrier amplitude summation circuit, a signal output from the amplitude calculation circuit, an intersubcarrier difference calculation circuit that calculates and outputs a difference between signal amplitudes of adjacent subcarriers, and the intersubcarrier difference calculation circuit A correlation calculation circuit that calculates and outputs the magnitude or amplitude of the difference signal output by the sub-carriers; a sub-carrier correlation summation circuit that adds the signals output by the correlation calculation circuit for all sub-carriers; A first division circuit for dividing a signal output from the correlation summation circuit by a signal output from each of the subcarrier amplitude summation circuits; A reception signal-carrier signal difference calculation circuit that calculates and outputs a difference from the second signal; and calculates and outputs the magnitude or amplitude of the signal output by the reception signal-carrier signal difference calculation circuit. An error calculation circuit, each subcarrier error summation circuit that adds the signal output by the error calculation circuit for all subcarriers, and each subcarrier error summation circuit outputs a signal output by each subcarrier amplitude summation circuit A second division circuit for dividing by a signal to be divided, and a modulation control for generating a signal corresponding to a characteristic of a transmission path detected according to a signal output from the first division circuit and a signal output from the second division circuit. An OFDM demodulation circuit comprising a signal generation circuit. 5. An OFDM for inputting an orthogonal frequency multiplex signal in which the same known preamble signal appears at least twice, and detecting received data included in the input signal.
A demodulation circuit for converting a radio frequency reception signal into a baseband signal and generating the baseband signal as a first signal in a preamble section; A noise removing circuit that removes the signal; a fast Fourier transform circuit that performs fast Fourier transform after serial-to-parallel conversion of the baseband signal output from the noise removing circuit and the receiving circuit; and a frequency output from the fast Fourier transform circuit. A reception data extraction circuit that extracts reception data from a plurality of signals separated into a plurality of signals, and in a preamble section of the reception signal, a modulation component is removed from a plurality of signals separated for each frequency output from the fast Fourier transform circuit. A modulation component removing circuit for generating a signal as a second signal; and the modulation component removing circuit. A transmission for estimating characteristics of a transmission path based on the generated second signal and the first signal generated by the reception circuit, and outputting a signal indicating a modulation condition suitable for the estimated characteristics of the transmission path. An OFDM demodulation circuit comprising a road characteristic estimation circuit. 6. An OFDM modulator / demodulator for inputting an orthogonal frequency multiplexed signal in which the same known preamble signal appears at least twice, detecting received data included in the input signal, modulating data to be transmitted, and outputting the modulated data. A circuit configured to convert a radio frequency reception signal into a baseband signal and generate the baseband signal as a first signal in a preamble section; and remove noise of a signal output from the reception circuit only in the preamble section. A noise removing circuit, a fast Fourier transform circuit that performs a fast Fourier transform after serial-to-parallel conversion of the baseband signal output from the noise removing circuit and the receiving circuit, and a frequency output from the fast Fourier transform circuit. Received data extraction circuit for extracting received data from a plurality of separated signals A modulation component removal circuit that generates, as a second signal, a signal obtained by removing a modulation component from a plurality of signals separated for each frequency output from the fast Fourier transform circuit in a preamble section of a reception signal; Based on the second signal generated by the removing circuit and the first signal generated by the receiving circuit, a characteristic of a transmission path is estimated, and a signal indicating a modulation condition suitable for the estimated characteristic of the transmission path is calculated. A transmission path characteristic estimating circuit to output, and a modulation circuit in which at least one of a modulation scheme, an error correction coding rate and a symbol rate is variable, and a transmission target under a modulation condition determined according to a signal output from the transmission path characteristic estimating circuit. An adaptive modulation circuit that modulates the data of the adaptive modulation circuit; an inverse fast Fourier transform circuit that performs an inverse fast Fourier transform process on the signal modulated by the adaptive modulation circuit; OFDM modulation and demodulation circuit which is characterized in that a transmission circuit for converting the signals processed by the Fourier transform circuit into a radio frequency signal. 7. The OFDM demodulation circuit according to claim 5,
The noise elimination circuit includes filter means for smoothing the first signal output from the reception circuit in a preamble section. The modulation component elimination circuit includes a known preamble signal for each subcarrier and the noise elimination circuit. A demodulation means for calculating a received signal output from the receiver, wherein the received data extracting circuit uses the second signal output from the modulation component removing circuit as a carrier signal to detect a received signal. An OFDM demodulation circuit comprising means. 8. The OFDM demodulation circuit according to claim 5,
An amplitude calculation circuit that calculates and outputs the magnitude or amplitude of the second signal for each subcarrier to the transmission path characteristic estimating circuit; and adds a signal output by the amplitude calculation circuit for all subcarriers. A subcarrier amplitude summation circuit, a signal output from the amplitude calculation circuit, a difference calculation circuit between subcarriers for calculating a difference between signal amplitudes of adjacent subcarriers, and a difference calculation circuit between the subcarriers. A correlation calculation circuit that calculates and outputs the magnitude or amplitude of the difference signal; a subcarrier correlation summation circuit that adds the signal output by the correlation calculation circuit for all subcarriers; and the subcarrier correlation summation circuit A first divider that divides the signal output by the sub-carrier amplitude summation circuit by a signal output by each of the subcarrier amplitude summation circuits; and averaging the first signal. An averaging circuit, a delay circuit that delays the first signal by the processing delay of the averaging circuit and outputs the same, and calculates a difference between a signal output by the averaging circuit and a signal output by the delay circuit. A difference calculation circuit, an error calculation circuit that calculates and outputs the magnitude or amplitude of a signal output by the difference calculation circuit, an error summation circuit that adds a signal output by the error calculation circuit in a preamble section, and the error A second division circuit that divides a signal output by the summation circuit by a signal output by each of the subcarrier error summation circuits, according to a signal output by the first division circuit and a signal output by the second division circuit An OFDM demodulation circuit, comprising: a modulation scheme determination circuit that generates a signal according to the detected characteristic of the transmission path. 9. The OFDM demodulation circuit according to claim 1, wherein the reception circuit, the fast Fourier transform circuit, the reception data extraction circuit, the modulation component removal circuit, and the modulation component removal circuit.
A plurality of the carrier signal generating circuits or the noise removing circuits according to claim 5, respectively, and the transmission path characteristic estimating circuit includes the carrier signal generating circuit according to claim 1 or the noise removing circuit generated by the noise removing circuit according to claim 5. 2, a comparison and selection circuit that selects and outputs a signal having a larger amplitude for each subcarrier, and outputs information indicating the selected state, and a signal output by the comparison and selection circuit. An amplitude calculation circuit that calculates the magnitude or amplitude; a subcarrier amplitude summation circuit that adds a signal output by the amplitude calculation circuit for all subcarriers and outputs the sum as a carrier reception signal; and a signal output by the amplitude calculation circuit. And an inter-subcarrier difference calculation circuit for calculating a difference between signal amplitudes of adjacent subcarriers, and the inter-subcarrier difference meter A correlation calculation circuit that calculates the magnitude or amplitude of the difference signal output by the circuit; a subcarrier correlation summation circuit that adds the signals output by the correlation calculation circuit for all subcarriers; and the subcarrier correlation summations An OFDM demodulation circuit comprising: a first division circuit for dividing a signal output from the circuit by a signal output from each of the subcarrier amplitude summation circuits. 10. The OFDM demodulation circuit according to claim 1, wherein said reception circuit, said fast Fourier transform circuit, said reception data extraction circuit, said modulation component removal circuit, and said modulation component removal circuit.
A plurality of the carrier signal generating circuits or the noise removing circuits according to claim 5, respectively, and the transmission path characteristic estimating circuit includes the carrier signal generating circuit according to claim 1 or the noise removing circuit generated by the noise removing circuit according to claim 5. 2, a sum amplitude calculation circuit for adding the magnitude or amplitude of the input signal for each subcarrier, and a signal output from the sum amplitude calculation circuit for all subcarriers to obtain a carrier reception signal. Each subcarrier amplitude summing circuit to be output, a signal output from the addition amplitude calculation circuit, and an intersubcarrier difference calculation circuit that calculates a difference between signal amplitudes of adjacent subcarriers, and the intersubcarrier difference calculation A correlation calculation circuit for calculating the magnitude or amplitude of the difference signal output by the circuit; and A sub-carrier correlation summation circuit for adding a subcarrier, and a first division circuit for dividing a signal output from each of the subcarrier correlation summation circuits by a signal output from each of the subcarrier amplitude summation circuits. OFDM demodulation circuit. 11. The OFDM demodulation circuit according to claim 1, wherein said reception circuit, said fast Fourier transform circuit, said reception data extraction circuit, said modulation component elimination circuit, and a carrier signal generation circuit are provided in plurality, respectively, and said transmission path characteristics are provided. A comparison / selection circuit that inputs a plurality of the second signals to an estimation circuit, selects and outputs a signal having a larger amplitude for each subcarrier, and outputs information indicating the selection state; A selection circuit that receives a plurality of first signals output by the removal circuit and selects one first signal according to a selection state of the comparison selection circuit for each subcarrier; and a signal output by the selection circuit. A reception signal-carrier signal difference calculation circuit for calculating a difference from the signal output by the comparison / selection circuit; and the reception signal-carrier signal difference calculation circuit An error calculation circuit for calculating the magnitude or amplitude of a signal to be output; a subcarrier error summation circuit for adding the signal output by the error calculation circuit for all subcarriers; and an output from each of the subcarrier amplitude summation circuits. An OFDM demodulation circuit comprising: a second division circuit for dividing a signal by a signal output from each of the subcarrier error summation circuits. 12. The OFDM demodulation circuit according to claim 1, wherein a plurality of said reception circuits, said fast Fourier transform circuits, said reception data extraction circuits, said modulation component removal circuits, and a carrier signal generation circuit are provided respectively, and said transmission path characteristics are provided. A plurality of received signal-carrier signal differences for inputting a plurality of first signals and second signals to an estimating circuit and calculating a difference between the first signal and the second signal for each corresponding subcarrier A calculation circuit; a plurality of error calculation circuits for calculating the magnitudes or amplitudes of the signals respectively output by the plurality of received signal-carrier signal difference calculation circuits; A subcarrier error summation circuit for adding a carrier; and a signal output from the subcarrier amplitude summation circuit, the subcarrier error summation circuit. OFDM demodulation circuit characterized in that a second divider circuit for dividing the output signal. 13. The OFDM demodulation circuit according to claim 5, wherein said reception circuit, said fast Fourier transform circuit, said reception data extraction circuit, said modulation component elimination circuit, and said noise elimination circuit are provided in plurality respectively, and said transmission line characteristic is provided. A plurality of averaging circuits for averaging the plurality of first signals generated by the plurality of noise removing circuits, respectively; and an estimating circuit, the plurality of first signals being delayed by a processing delay of the averaging circuit and output. A plurality of delay circuits, a plurality of difference calculation circuits that calculate a difference between the signal output by the averaging circuit, and a signal output by the delay circuit, and the magnitude or amplitude of the signal output by the difference calculation circuit. A plurality of error calculation circuits for calculating and outputting; a plurality of error summation circuits for adding signals output by the error calculation circuit in a preamble section; and the plurality of error summations. A signal averaging circuit that calculates an average of a plurality of signals output from the respective paths; and a second division circuit that divides a signal output by the signal averaging circuit by a signal output by each of the subcarrier error summation circuits. An OFDM demodulation circuit, characterized in that: 14. The OFDM demodulation circuit according to claim 13, wherein said signal averaging circuit calculates the average by adding the results obtained by weighting a plurality of input signals. 15. The OFDM demodulation circuit according to claim 5, wherein said reception circuit, said fast Fourier transform circuit, said reception data extraction circuit, said modulation component elimination circuit, and said noise elimination circuit are provided in plurality, respectively, and said transmission line characteristics are provided. A plurality of averaging circuits for averaging the plurality of first signals generated by the plurality of noise removing circuits, respectively; and an estimating circuit, the plurality of first signals being delayed by a processing delay of the averaging circuit and output. A plurality of delay circuits, a plurality of difference calculation circuits that calculate a difference between the signal output by the averaging circuit, and a signal output by the delay circuit, and the magnitude or amplitude of the signal output by the difference calculation circuit. A plurality of error calculation circuits for calculating and outputting; a plurality of error summation circuits for adding signals output by the error calculation circuit in a preamble section; and the plurality of error summations. A signal selecting circuit for selecting one signal having a large integrated value from a plurality of signals output from the respective paths; and a signal selecting circuit for dividing a signal output from the signal selecting circuit by a signal output from each of the subcarrier error summing circuits. An OFDM demodulation circuit, comprising: a division circuit of 2. 16. The OFDM demodulation circuit according to claim 1, wherein the space representing the estimated characteristics of the transmission path is divided into a plurality of regions, and the relation between each of the divided regions and the modulation condition is determined. The transmission line characteristic estimation circuit is held as the conversion information, and an intermediate region having a width is provided at a boundary portion between a plurality of regions adjacent to each other in the space, and the estimated characteristic of the transmission line is within the intermediate region. When the transmission path characteristic estimating circuit is located in the first region adjacent to the intermediate region and the modulation condition allocated to the second region adjacent to the intermediate region, An OFDM demodulation circuit characterized in that both are selectively selected according to the passage of time. 17. The OFDM demodulation circuit according to claim 1, wherein the space representing the estimated characteristics of the transmission path is divided into a plurality of regions, and the relation between each of the divided regions and the modulation condition is determined. The transmission line characteristic estimation circuit is held as the conversion information, and an intermediate region having a width is provided at a boundary portion between a plurality of regions adjacent to each other in the space, and the estimated characteristic of the transmission line is within the intermediate region. , The modulation condition before that is maintained as it is.