JPH10247897A - Diversity reception method, transmitter and receiver therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the circuit with a small sale to discriminate propriety of reception quality in a plurality of reception systems in the diversity reception system of a selection system, adopting an orthogonal frequency division multiplex system for the radio transmission system. SOLUTION: A transmitter multiplexes a known P-N signal on a specific carrier. The receiver uses low-pass filters 14, 24 to extract the specific carrier and uses demodulation circuits 15, 25 to demodulates the carrier. Comparator circuits 16, 26 compare the demodulation output with a P-N signal, an output of a P-N signal generating circuit 34 to obtain number of errors. A system with few number of error is selected by controlling a changeover circuit 32, depending on the number of errors and the entire band is demodulated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiving method, a transmitting apparatus and a receiving apparatus employing a selection method used for receiving a radio transmission signal of broadcasting or communication, and more particularly to a system for transmitting a digital signal by an OFDM method. The present invention relates to a diversity receiving method, a transmitting device, and a receiving device provided for a mobile terminal.

[0002]

2. Description of the Related Art As a conventional spatial diversity receiver, for example, as disclosed in Japanese Patent Laid-Open No. 2-19042, signals received by a plurality of antennas are demodulated, and the number of errors in the demodulated data is demodulated. There is known a method of detecting using an error detection code included in data and selecting demodulated data having a small number of errors.

FIG. 8 shows a simplified version of FIG. 1 described in the above publication. In FIG. 8, signals received by a plurality of (two in FIG. 2) antennas 81a and 81b are demodulated by demodulators 82a and 82b, respectively.
a, 83b. These error detectors 83a,
83b detects the number of errors included in the demodulated data by using an error detection code for each of the input demodulated data. Demodulated data output from each of the error detectors 83a and 83b is supplied to a switching circuit 86, and information on the number of errors is supplied to an error number comparing circuit 84.

The error number comparison circuit 84 includes an error detection unit 83
The information on the number of errors from a and 83b is compared, and the comparison result is supplied to the switching control circuit 85. The switching control circuit 85 selects the demodulated data having the smaller number of errors from the comparison result of the error number comparing circuit 84 so as to select the demodulated data having the smaller number of errors.
6 is switched. As a result, the demodulated data having less error among the outputs of the error detectors 83a and 83b can be selectively extracted from the switching circuit 86 as output data.

[0005]

However, in the conventional spatial diversity receiver as described above, the first
The problem is that a plurality of demodulation units must be provided. In particular, when the OFDM scheme, which is one of the multi-carrier schemes, is used as the transmission scheme, the receiver has a plurality of demodulation units compared to the case where the single-carrier scheme is adopted. The increase is remarkable.

That is, in the OFDM system, FFT (Fast Fourier Transform) processing is required for demodulation, but when transmitting a video signal and an audio signal by the OFDM system, hundreds to thousands of carriers are required. For use, a large-scale FFT circuit of several hundred to several thousand points is required. Therefore, if the number of demodulation units is plural, the number of FFT circuits is also plural, and the overall circuit scale is greatly increased.

[0007] The second problem is that a plurality of error correction code decoding circuits and deinterleave circuits must be provided. In particular, in the case of terrestrial broadcasting, a large increase in circuit scale is required.

That is, in the case of terrestrial broadcasting, there are fading and multipath. In order to compensate for the deterioration in transmission quality by error correction, a method having a high error correction capability is required, and it is assumed that a concatenated code of a convolutional code and a Reed-Solomon code is adopted. in this case,
The receiver requires a Viterbi decoder and a Reed-Solomon decoder for error detection. Furthermore, since a deinterleave circuit is usually inserted between these correction code decoding circuits, a plurality of large-capacity memories are required for the deinterleave, and the overall circuit scale is greatly increased.

[0009] The present invention solves the above-mentioned problems and provides an OFD
It is an object of the present invention to provide a diversity system capable of diversity receiving a transmission signal by the M system with a relatively small configuration, and a transmitter and a receiver thereof.

[0010]

In order to solve the above-mentioned problems, a diversity receiving system according to the present invention is configured as follows.

(1) A diversity receiving system used for a system for wirelessly transmitting information by an OFDM (Orthogonal Frequency Division Multiplexing) system, wherein a transmitting apparatus transmits a known digital signal sequence to one or more specific carriers. A known digital signal sequence multiplexing means for multiplexing and transmitting by hierarchical modulation,
The receiving device includes a plurality of receiving units that receive OFDM signals transmitted from the transmitting device independently of each other, and extracts the specific carrier from each of the OFDM signals received by the plurality of receiving units, and performs hierarchical modulation. A plurality of error number detection means for demodulating the multiplexed and transmitted known digital signal sequence and detecting the number of errors included in the digital signal sequence; and Selecting means for selecting the output of the receiving means having the least number of errors by comparing the number of errors obtained by the number detecting means, and extracting information from the OFDM reception signal of the receiving means selected by the selecting means. The demodulation is performed.

(2) In particular, in a transmitting apparatus for transmitting information by an OFDM (orthogonal frequency division multiplexing) method, a known digital signal sequence generating means for generating a known digital signal sequence, and information based on the OFDM method are transmitted. A hierarchical modulation unit that specifies one or more carriers from a plurality of carriers for transmission and multiplexes the known digital signal sequence generated by the known digital signal sequence generation unit by hierarchical modulation. It is characterized by the following.

(3) In the configuration of (2), the known digital signal sequence generating means performs generation of the known digital signal sequence in synchronization with a frame synchronization signal.

(4) In the configuration of (2), the hierarchical modulation means uses non-uniform 16QAM.

(5) In the configuration of (4), the hierarchical modulation means performs differential conversion on the known digital signal sequence, and then multiplexes the signal sequence by hierarchical modulation.

(6) In the configuration of (2), the hierarchical modulation means uses one of 8DAPSK and 8APSK.

(7) In any one of (4) and (6), the non-uniform 16QAM, 8
When using either DAPSK or 8APSK, non-uniform 16QAM, 8DAPSK
Alternatively, the minimum inter-symbol distance when QPSK demodulating an 8APSK signal is equal to the minimum inter-symbol distance when demodulating another QPSK modulated signal that does not perform hierarchical modulation.

(8) A known digital signal sequence is OFDM
OFDM wirelessly transmitted along with information to be transmitted on one or more specific carriers of the (orthogonal frequency division multiplexing) method
A diversity receiving method receiving apparatus for receiving a signal, comprising: carrier extraction means for receiving the wirelessly transmitted OFDM signal and extracting the specific one or more carrier components; and a carrier component extracted by the carrier extraction means. Demodulating means for demodulating the known digital signal sequence multiplexed by hierarchical modulation, known digital signal sequence generating means for generating the known digital signal sequence, and demodulating the known digital signal sequence obtained by this means and the demodulation means. A plurality of receiving systems including a comparing unit that detects the number of errors included in the demodulated output by comparing the known digital signal sequence with the received digital signal sequence, and compares the number of errors obtained by the comparing unit of each of the plurality of receiving systems. Error number comparing means, receiving system selecting means for selecting the receiving system having a small number of errors based on the comparison result of the means, Characterized by comprising a demodulation means for demodulating the information to be transmitted from the output of-option reception system.

(9) In the configuration of (8), the known digital signal sequence generating means generates the same known digital signal sequence as that on the transmitting side in synchronization with a frame synchronization signal.

(10) In the configuration of (9), the selection means performs switching for selecting a reception system having a small number of errors in units of frames.

That is, in the diversity receiving method according to the present invention, the transmitting apparatus has means (1, 3 in FIG. 1) for multiplexing the PN signal by hierarchical modulation, and the receiver receives the PN signal received by the diversity receiving. It has means (16, 26 in FIG. 1) for comparing the signal sequence with the PN signal generated in the receiver, and means (31, 32 in FIG. 1) for selecting a receiving system with less error from the comparison result.

Accordingly, in the diversity receiving system of the present invention, the frequency of occurrence of errors in a plurality of receiving systems can be grasped by demodulating an OFDM signal by a small-point FFT or demodulating an OFDM signal by a single carrier demodulation circuit. As a result, it is possible to simplify the circuit of the demodulation system of the diversity receiving apparatus of the system that selects the system according to the frequency of occurrence of errors in each reception system.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS.

(First Embodiment) FIGS. 1A and 1B
1 shows a configuration of an OFDM transmitting apparatus and an OFDM receiving apparatus using a diversity scheme according to the present invention as a first embodiment.

In the OFDM transmission apparatus shown in FIG. 1A, the mapping circuit 1 synchronizes with the output of the frame synchronization signal generation circuit 2 together with the video and audio digital signals, and
The PN signal generated by the signal generation circuit 3 is input and symbolized to correspond to one of a plurality of carriers. A plurality of signals output from the mapping circuit 1 and arranged in the frequency axis direction are converted into signals on the time axis by an IFFT (Inverse Fast Fourier Transform) circuit 4, and then output to an OFDM signal by a quadrature modulation circuit 5. Become. The OFDM signal output from the quadrature modulation circuit 5 is frequency-converted and power-amplified by a transmitter 6, and then transmitted to a space through an antenna 7.

In the OFDM receiving apparatus shown in FIG. 1B, the antennas 11 and 21 receive signals transmitted from the OFDM transmitting apparatus. After being amplified and frequency-converted by 22 to be an OFDM signal of an intermediate frequency, it is supplied to quadrature demodulation circuits 13 and 23.

The quadrature demodulation circuits 13 and 23 perform quadrature demodulation of the reception signals from the reception high frequency circuits 12 and 22, respectively. The demodulation signals are both supplied to the switching circuit 32 and the low pass filters 14 and , 24. Each of the low-pass filters 14 and 24 passes a carrier in a frequency band in which a PN signal is applied by hierarchical modulation on the OFDM transmission device side. The output of each filter is supplied to demodulation circuits 15 and 25, respectively.

The demodulation circuits 15 and 25 demodulate the PN signal from the carriers extracted by the low-pass filters 14 and 24, respectively.
6, 26. The comparison circuits 16 and 26 respectively convert the PN signals demodulated by the demodulation circuits 15 and 25 into internal P
The PN signal generated by the N signal generation circuit 34 is compared with the PN signal to detect the number of errors, and each error number detection result is supplied to the error comparison circuit 31 together. The error comparison circuit 31 compares the error number detection results of the two systems, and controls the switching of the switching circuit 32 so as to select the system with the smaller number of errors.

The switching circuit 32 includes the quadrature demodulation circuit 1
The OFDM signal orthogonally demodulated in 3 and 23 is selectively derived according to the switching control of the error comparison circuit 31, and the selected output is supplied to the frame synchronization circuit 33 and the FFT 35.

The frame synchronization circuit 33 detects a frame synchronization signal in the OFDM signal and generates a frame synchronization signal.
4 is supplied. The PN signal generating circuit 34 generates the same PN signal as that on the transmitting side according to the frame synchronizing signal from the frame synchronizing circuit 33, and the PN signal generated here is supplied to the above-mentioned comparing circuits 16 and 26. You.

The FFT 35 converts the orthogonally demodulated OFDM signal into data on the frequency axis by performing a fast Fourier transform. The output of the FFT 35 is demodulated by a demodulation circuit 36 to become a video or audio digital signal. Is output.

In order to simplify the explanation, FIG.
In (B), the description of circuits relating to error correction and interleaving is omitted.

Next, the operation of the embodiment of the present invention will be described in detail with reference to FIGS.

FIGS. 2A and 2B show examples of the arrangement of carriers of an OFDM signal. FIG. 2 (A)
FIG. 2B shows a case where a transmission carrier of a signal obtained by multiplexing a PN signal with video and audio data by hierarchical modulation is arranged at a position indicated by a solid line in the center of the band, and FIG. 2 shows a case where transmission carriers of signals obtained by multiplexing a PN signal with video and audio data by hierarchical modulation are arranged at two positions indicated by solid lines.

Here, the embodiment shown in FIGS. 1A and 1B corresponds to the carrier arrangement shown in FIG. 2A.
The PN signal generation circuit 3 in FIG.
A PN signal that is multiplexed and transmitted by hierarchical modulation on a carrier indicated by a solid line in the center is generated,
The video and audio data transmitted on the carriers indicated by the dashed line and the solid line in FIG. 2A are allocated to each carrier by the mapping circuit 1 in FIG.

A PN signal transmitted by hierarchical modulation on a carrier indicated by a solid line in FIG. 2 (A) is a known code sequence, and the receiving device generates a PN signal generated by the receiving device and a received PN signal. Is used to know the number of errors contained in the received PN signal.

The frame synchronization signal generating circuit 2 shown in FIG.
Generates a frame synchronization signal. OFD
When transmission is performed by the M system, a frame configuration is generally adopted for synchronization on the receiving side. A frame is composed of a plurality of data symbols and synchronization symbols.

The data symbol is an array of digital data to be transmitted, and the synchronization symbol is a null signal (no signal) or a chirp signal (frequency sweep signal).
Is used. The receiving apparatus can establish frame synchronization by detecting these null signals and chirp signals. FIG. 3 shows a frame configuration of the OFDM system described above.

The PN signal generating circuit 3 shown in FIG.
Generates a PN signal based on the frame synchronization signal generated by the frame synchronization signal generation circuit 2. P
The PN signal output from the N signal generation circuit 3 is shown in FIG.
The carrier is hierarchically multiplexed by the mapping circuit 1 on the carrier indicated by the solid line in FIG.

On the other hand, the video and audio digital signals to be transmitted are input to the mapping circuit 1, and similarly, as shown in FIG.
Are assigned to a plurality of carriers indicated by broken lines and solid lines in accordance with a predetermined procedure. The PN signal is hierarchically multiplexed with the data allocated to the center carrier.

The input of the IFFT 4 is the output of the mapping circuit 1 corresponding to each carrier, and these signals are converted by the IFFT 4 from signals arranged on the frequency axis to signals arranged on the time axis. The signal converted to a signal on the time axis by the IFFT 4 is quadrature-modulated by the quadrature modulation circuit 5, frequency-converted and amplified by the transmitter 6, and transmitted by the antenna 7.

On the other hand, in the receiving device, the signals are received by a plurality of antennas 11 and 21 and received by high-frequency circuits 12 and 22.
The signal is amplified and frequency-converted to obtain an intermediate frequency signal, and then orthogonally demodulated by the orthogonal demodulation circuits 13 and 23 to obtain an OFDM signal. The output of the quadrature demodulation circuit 13 is input to the switching circuit 32 and the low-pass filter 14
Is input to

The low-pass filter 14 extracts the carrier at the center frequency of the quadrature demodulation circuit 13, that is, the carrier indicated by the solid line in FIG. The carrier extracted by the low-pass filter 14 is single-carrier demodulated in the demodulation circuit 15, and only the PN signal multiplexed by the hierarchical modulation is output to the comparison circuit 16 among the demodulated signals. The details of multiplexing by hierarchical modulation will be described later.

The comparison circuit 16 compares the PN signal output from the demodulation circuit 15 with the PN signal output from the PN signal generation circuit 34. The PN signal generation circuit 34 generates the same PN signal sequence as the PN generation circuit 3 in the above-described transmission device with reference to the output signal of the frame synchronization circuit 33.

Therefore, it is possible to detect the number of errors included in the received PN signal sequence in the comparison circuit 16. At this time, the comparison circuit 16 outputs, for example, the number of errors that have occurred in one frame. The number of errors is supplied to an error comparison circuit 31.

The same processing as described above is performed on the output signal of the orthogonal demodulation circuit 23 in the low-pass filter 24, the demodulation circuit 25, and the comparison circuit 26. In an error comparison circuit 31 to which the outputs of the comparison circuits 16 and 26 are input, the number of errors obtained by the comparison circuits 16 and 26 is compared, and a signal of a system with a small number of errors is selected in a switching circuit 32. Output to the frame synchronization circuit 33 and the FFT 35.

The frame synchronization circuit 33 detects the frame synchronization signal, and the PN signal generation circuit 34 generates a predetermined PN signal based on the synchronization signal. On the other hand, FFT3
At 5, the OFDM demodulation is performed by converting the output of the switching circuit 32 from the signal on the time axis to the signal on the frequency axis by the fast Fourier transform, and the output is demodulated by the demodulation circuit 36 based on the threshold value. As a result, digital signals of video and audio can be obtained.

As described above, the diversity receiving system according to the first embodiment has means (1 and 3 in FIG. 1A) for multiplexing PN signals by hierarchical modulation in the transmitting device, and in the receiver. Means for comparing the PN signal sequence received by the diversity reception with the PN signal generated in the receiver (16 and 26 in FIG. 1B), and means for selecting a reception system with less error from the comparison result ( FIG.
(B) 31, 32).

According to this configuration, it is possible to grasp the frequency of occurrence of errors in a plurality of reception systems by demodulating an OFDM signal by single carrier demodulation. Therefore, diversity reception in a method of selecting a system based on the frequency of occurrence of errors in each reception system. The circuit of the demodulation system of the device can be simplified.

(Second Embodiment) FIG. 4 is a block diagram showing a second embodiment of the present invention. Since the transmitting device used in the second embodiment has the same block diagram as the transmitting device used in the first embodiment, its display is omitted in FIG. In FIG. 4, FIG.
The same parts as those shown in (B) are denoted by the same reference numerals, and duplicate description is omitted here.

The difference between the second embodiment shown in FIG. 4 and the first embodiment shown in FIG. 1 is that in the first embodiment,
While the PN signal is transmitted by the center carrier of the band, the second embodiment is characterized in that the PN signal is transmitted by two carriers in the band.

The second embodiment shown in FIG. 4 is similar to that of FIG.
This corresponds to the case where carriers for transmitting PN signals are arranged at two places in the band shown in FIG. As in the first embodiment, the outputs of the reception high-frequency circuits 12 and 22 are output from the quadrature demodulation circuits 13 and 23.
However, in the second embodiment, they are also supplied to the band-pass filters 41 and 42 or 51 and 52 at the same time.

The band-pass filter 41 and the band-pass filter 42 are filters that pass signals in different frequency bands, and correspond to two frequency bands in which the PN signal shown in FIG. 2B is multiplexed and transmitted. Pass the signal.
The band-pass filters 41 and 51 and the band-pass filters 42 and 52 allow signals in the same frequency band to pass.

These band-pass filters 41, 42, 5
The carriers to which the PN signals extracted by 1 and 52 are transmitted are demodulated with respect to a single carrier by demodulation circuits 43, 44, 53 and 54, and a PN signal is output as in the first embodiment. These outputs are supplied to comparison circuits 17 and 27 and are compared with a PN signal generated by a PN signal generation circuit 34.
The number of errors contained in the signal sequence is detected.

Thereafter, as in the first embodiment, the number of errors in both systems is compared by the error comparison circuit 31, and the quadrature demodulation output of the system with a small number of errors is selected by the switching circuit 32. The signal is converted into a signal on the frequency axis and demodulation processing is performed by the demodulation circuit 36, whereby a video and audio digital signal can be obtained.

As described above, the diversity receiving system in the second embodiment employs means for multiplexing a PN signal by hierarchical modulation in the transmitting device (1, 3 in FIG. 1A), as in the first embodiment. Means for comparing the PN signal sequence received by the diversity reception with the PN signal generated in the receiver (17, 27 in FIG. 4), and the reception with less error from the comparison result. Means for selecting a system (31, 32 in FIG. 4).

According to this configuration, OFD by single carrier demodulation for two carriers in each receiving system
Since demodulation of the M signal is performed and the frequency of occurrence of errors in each receiving system is grasped for each demodulated output,
The circuit of the demodulation system of the diversity receiver of the system of selecting the system according to the frequency of occurrence of errors in each reception system can be simplified.

Further, even when errors are concentrated in one of the carriers, the influence is reduced by the other carrier. Therefore, the error occurrence situation in the entire transmission band is reduced as compared with the case where the comparison is performed by one carrier. Information on the number of close errors can be obtained, and reliability can be improved.

(Third Embodiment) FIG. 5 is a block diagram showing a third embodiment of the present invention. Since the transmitting device used in the third embodiment has the same block diagram as the transmitting device used in the first embodiment, the display is omitted in FIG. In FIG. 5, FIG.
The same parts as those described above are denoted by the same reference numerals, and redundant description is omitted here.

The difference between the third embodiment shown in FIG. 5 and the second embodiment shown in FIG. 4 is that in the second embodiment,
Although a demodulation circuit for a single carrier is used for demodulating a PN signal, the third embodiment is that OFDM demodulation is performed by using a small number of FFTs.
For this reason, in the third embodiment, a plurality of quadrature demodulation circuits are provided in each receiving system, and the output signals thereof are output by an FFT.
FDM demodulation.

That is, the third embodiment shown in FIG.
Similar to the second embodiment shown in FIG. 4, this corresponds to a case where carriers for transmitting PN signals are arranged at two places in the band shown in FIG. 2B. However, in the third embodiment,
Since demodulation means for OFDM is adopted for demodulation,
A plurality of carriers for transmitting the PN signal can be arranged at each of two places in the band.

In FIG. 5, the receiving high-frequency circuits 12, 22
The received signals converted to the intermediate frequency signals by the quadrature demodulation circuits 13, 45, 46 and the quadrature demodulation circuits 23, 5,
5, 56. Quadrature demodulation circuits 45, 46, 5
At steps 5 and 56, quadrature demodulation is performed around the band in which the PN signal is transmitted.

At this time, the orthogonal demodulation circuit 45 and the orthogonal demodulation circuit 46 have different bands as center frequencies, and the orthogonal demodulation circuit 45 and the orthogonal demodulation circuit 55 and the orthogonal demodulation circuit 46 and the orthogonal demodulation circuit 56 respectively An equal frequency is set as a center frequency.

In the quadrature demodulation circuits 45, 46, 55, and 56, the carrier for transmitting the PN signal is output as a signal near DC. , 50, 59, 6
0 and are OFDM demodulated by FFTs 49, 50, 59, 60. The following processing is the same as in the above-described embodiment.

The FFTs 49, 50, 59, and 60 may be FFTs with a small number of points, such as 4 points when transmitting a PN signal using one carrier and 8 points when transmitting a PN signal using three adjacent carriers. FFT
Is enough.

As described above, in the diversity receiving method according to the third embodiment, as in the first embodiment, the transmitting device multiplexes the PN signal by hierarchical modulation (1, 3 in FIG. 1A). Means for comparing the PN signal sequence received by the diversity reception with the PN signal generated in the receiver (17 and 27 in FIG. 5), and the reception with few errors is determined from the comparison result. Means for selecting a system (31, 32 in FIG. 5).

According to this configuration, in each receiving system, the OFDM signal is demodulated by the FFT processing of a small number of points of the two carriers, and the frequency of occurrence of errors in each receiving system is grasped for each demodulated output. Therefore, it is possible to simplify the circuit of the demodulation system of the diversity receiving apparatus of the system that selects the system according to the frequency of occurrence of errors in each receiving system.

Further, even when errors are concentrated on one of the carriers, it is possible to obtain information on the number of errors closer to the error occurrence situation in the entire transmission band than when comparison is made with the other carrier. , Reliability can be improved.

In the first embodiment shown in FIG. 1, one or a plurality of carriers are OFDM-demodulated using the small-point FFT shown in the third embodiment instead of the demodulation circuits 15 and 25. It is clear from the present embodiment that the same effect can be obtained even if the above operation is performed.

Embodiment Next, an embodiment of the present invention will be described in detail with reference to the drawings.

In FIGS. 2 (A) and 2 (B), digital data of audio and video is transmitted on the carriers shown as video and audio data, and the modulation format of each of these carriers is QPSK, DQPSK (difference Dynamic QPSK) and multi-value Q
AM or the like is adopted. These modulation formats are determined in consideration of the transmission speed, C / N required for reception, and the like. Digital data of audio and video and a PN signal are transmitted on the carrier indicated by video and audio data + carrier indicated by PN signal, but digital data of audio and video is QPSK or DPN.
Modulated by QPSK.

FIG. 6A shows this QPSK or DQPS
FIG. 6 (B) shows a constellation of K.
Indicates a constellation of non-uniform 16QAM.

The non-uniform 1 shown in FIG.
In 6QAM, information can be transmitted depending on which quadrant of each quadrant divided by each axis of the IQ has a signal, and information can also be transmitted based on the position within each quadrant. Therefore, transmitting information according to which quadrant the signal is in is similar to QPSK or DQPSK, and this information can be demodulated by a demodulation circuit for QPSK or DQPSK.

From the above, this non-uniform 1
In a 6QAM signal, information in each quadrant is hierarchically multiplexed on a QPSK or DQPSK signal.
As described above, digital data of audio and video depends on which quadrant the signal is in, that is, QPSK or DQP.
By SK modulation, the PN signal is multiplexed and transmitted according to where in the quadrant the signal is located, that is, by hierarchical modulation.

The information based on the position in each quadrant can be demodulated by, for example, a demodulation circuit for multi-level QAM. Furthermore, in the case where the PN signal to be transmitted is differentially converted in advance and multiplexed by hierarchical modulation, it is possible to perform differential detection between symbols in the receiving apparatus even for information multiplexed by hierarchical modulation. This allows video and audio data to be DQ
In the case of transmission by PSK, these images transmitted by other carriers where the PN signal is not multiplexed,
It is possible to determine the transmission quality of audio data more faithfully.

To avoid deterioration of the transmission quality of video and audio data due to multiplexing of PN signals,
The minimum inter-symbol distance in the carrier where the PN signal is not multiplexed and the carrier in which the PN signal is multiplexed are QPSK.
The minimum inter-code distance in the case of demodulation may be made substantially equal.

As a method of hierarchical modulation, in addition to non-uniform 16QAM, 8APSK or 8DAPSK (differential 8
APSK). FIG. 6C shows 8APSK or 8D.
FIG. 4 is a diagram showing a constellation of APSK.

The 8APSK or 8DA shown in FIG.
PSK is obtained by multiplexing information in the amplitude direction on the constellation of QPSK shown in FIG. 6A, and it is possible to multiplex and transmit a PN signal using the information in the amplitude direction.

The 8DAPSK multiplexes and transmits a PN signal differentially converted to a DQPSK signal. 8AP
In the case of SK or 8DAPSK, QPSK or DQPSK is used similarly to the case of non-uniform 16QAM.
By equalizing the minimum inter-symbol distance in demodulation, PN
Deterioration of transmission quality of video and audio data due to multiplexing of signals can be avoided.

Digital transmission of video and audio data depends on the strength of the error correction code, but the practical error rate before error correction is about 10 −2 to 10 −3. Therefore, when transmitting a PN signal in the same modulation format as that of a carrier transmitting these data, a PN signal of at least about 1000 bits is required for selecting a receiving system.

However, since this PN signal does not contribute to information transmission, it is not efficient to transmit many PN signals. Since the PN signal is used only for judging the quality of the reception quality (error rate) of a plurality of reception systems, the received PN signal has a reception quality within a range where the reception quality (error rate) can be compared. It is desirable that the (error rate) be low. That is, it is desirable that the error rate of the PN signal is higher than the error rate of the video and audio data.

In the case of the non-uniform QAM shown in FIG. 6B, the inter-code distance of the constellation in each quadrant is smaller than the inter-code distance of the constellation between quadrants. I have. Therefore, the error rate of the PN signal multiplexed by the hierarchical modulation is higher than the error rate of the video and audio data, and is suitable for comparing the reception quality.

FIGS. 7A and 7B each show a specific configuration of the PN signal generation circuit. FIG. 7A shows an example using a delay element, and FIG. Shows an example using a memory element.

The PN signal generation circuit shown in FIG. 7A has a plurality of (six in the figure) delay elements (D) 91 to 96 connected in series, and any two of the delay elements (94 and 96 in the figure) are connected. )
Is input to an exclusive-OR (EX-OR) gate 97, and its operation output is input to a first-stage delay element 91 to obtain a PN signal from the output of the last-stage delay element 96. It is.

In the case of using this delay element, an initial value is given to each delay element by a data set signal synchronized with the frame synchronization signal. At this time, if the same initial value is given in transmission and reception, the same PN signal synchronized with the frame synchronization signal can be obtained in transmission and reception. Note that a flip-flop can be used as the delay element, which can cause a delay of a clock cycle.

The PN signal generating circuit shown in FIG. 7B is provided with a ROM (read only memory) 98 in which a PN signal sequence is recorded in advance, and obtains a PN signal by sequentially reading data by an address counter 99. Things.

In the case of using this memory element, an address counter 99 is reset by a reset signal synchronized with a frame synchronization signal, and a PN signal output from a memory (ROM) 98 in which a PN signal sequence is recorded in advance is used. Transmission and reception can be the same.

In the diversity receiving apparatus according to the present invention, switching for selecting a plurality of receiving means is desirably performed in frame units. The reason for this is that the reference signal for synchronous detection is generally transmitted in frame units, and the differential conversion for delay detection is performed in frame units, so that switching in frame units can reduce the circuit scale. That's why. Further, when switching is performed on a frame basis, the receiving apparatus can use a frame synchronization signal to determine a period for integrating the number of errors.

In the above description, the case where the PN signal is allocated to a plurality of carriers and transmitted is described as an example.
In a plurality of carriers, the same P
It is also possible to transmit N signals.

A first effect of the present invention is that the circuit scale of the receiving device can be reduced.

The reason is that a demodulation circuit using an FFT with a small number of points or a single-carrier demodulation circuit can be used to detect the reception quality. Further, it does not have a plurality of error correction code decoding circuits and a deinterleave circuit. It depends.

A second effect of the present invention is that the amount of information of a PN signal to be transmitted for detecting reception quality can be reduced.

The reason is that a modulation format having a high required C / N can be used for the PN signal transmitted for discriminating the reception quality, and the reception quality is compared with a small number of bits.

[0094]

As described above, according to the present invention, OFDM
It is possible to provide a diversity system capable of diversity receiving a transmission signal by the system with a relatively small configuration, and a transmission device and a reception device thereof.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first embodiment of a transmission device and a reception device of a system using a diversity reception scheme according to the present invention.

FIG. 2 is a diagram showing a carrier arrangement of the diversity receiving system of the embodiment.

FIG. 3 is a diagram showing an example of an OFDM frame configuration according to the embodiment;

FIG. 4 is a block diagram showing a second embodiment of the receiving apparatus of the system according to the diversity receiving system of the present invention.

FIG. 5 is a block diagram showing a third embodiment of the receiving apparatus of the system according to the diversity receiving system of the present invention.

FIG. 6 is a diagram showing an example of a constellation that can be used in an embodiment of the present invention.

FIG. 7 is a diagram illustrating a specific configuration example of a PN signal generation circuit used in the embodiment of the present invention.

FIG. 8 is a block diagram illustrating a configuration of a receiving apparatus using a conventional diversity receiving method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mapping circuit 2 frame synchronization signal generation circuit 3 PN signal generation circuit 4 IFFT 5 orthogonal modulation circuit 6 transmitter 7 antenna 11, 21 antenna 12, 22 reception high-frequency circuit 13, 23 orthogonal demodulation Circuits 14, 24 Low band pass filters 15, 25 Demodulation circuits 16, 26 Comparison circuits 17, 27 Comparison circuits 31 Error comparison circuits 32 Switching circuits 33 Frame synchronization circuits 34 PN signal generation circuits 35 FFT 36 demodulation circuit 41, 42, 51, 52 band-pass filter 43, 44, 53, 54 demodulation circuit 45, 46, 55, 56 quadrature demodulation circuit 47, 48, 57, 58 low-pass filter 49 , 50, 59, 60 FFT 91-96 delay element 97 EX-OR gate 98 PN signal string storage ROM 99 address counter

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroo Takeda 1-10 Nisshinmachi, Fuchu-shi, Tokyo Inside the Fuchu Office of NEC Corporation

Claims (10)

[Claims] 1. A diversity receiving system provided to a system for wirelessly transmitting information by an OFDM (Orthogonal Frequency Division Multiplexing) system, wherein a transmitting device has a known digital signal sequence hierarchically arranged on one or more specific carriers. A known digital signal sequence multiplexing means for multiplexing and transmitting the modulated digital signal by a modulation; a receiving apparatus receiving a plurality of OFDM signals transmitted from the transmitting apparatus independently of each other; A plurality of error numbers for extracting the specific carrier from each of the obtained OFDM signals, demodulating the known digital signal sequence multiplexed and transmitted by hierarchical modulation, and detecting the number of errors included in the digital signal sequence Detecting means, and comparing the number of errors obtained by the plurality of error number detecting means from the outputs of the plurality of receiving means to determine And selecting means for selecting an output of less receiver, a diversity receiving method characterized by demodulating the information from the OFDM reception signal of the receiving means selected by said selecting means. 2. A transmitting apparatus for transmitting information according to an OFDM (Orthogonal Frequency Division Multiplexing) method, comprising: a known digital signal sequence generating means for generating a known digital signal sequence; and transmitting information by the OFDM method. Transmitting means for identifying one or more carriers from among the plurality of carriers and multiplexing the known digital signal sequence generated by the known digital signal sequence generating means by hierarchical modulation. . 3. The transmitting apparatus according to claim 2, wherein said known digital signal sequence generation means generates a known digital signal sequence in synchronization with a frame synchronization signal. 4. The non-uniform 1
3. The transmitting apparatus according to claim 2, wherein 6QAM is used. 5. The transmitting apparatus according to claim 4, wherein said hierarchical modulation means performs differential conversion on said known digital signal sequence and thereafter multiplexes said signal sequence by hierarchical modulation. 6. The transmitting apparatus according to claim 2, wherein said hierarchical modulation means uses one of 8DAPSK and 8APSK. 7. The non-uniform 1
When using any of 6QAM, 8DAPSK or 8APSK, non-uniform 16QAM,
7. The method according to claim 4, wherein a minimum inter-symbol distance when demodulating an 8DAPSK or 8APSK signal by QPSK is equal to a minimum inter-symbol distance when demodulating another QPSK modulated signal that is not subjected to hierarchical modulation. The transmitting device according to any one of the above. 8. A diversity receiving system receiving a known digital signal sequence on one or more specific carriers of an orthogonal frequency division multiplexing (OFDM) system and receiving an OFDM signal wirelessly transmitted together with information to be transmitted. A carrier extracting means for receiving the wirelessly transmitted OFDM signal and extracting the specific one or more carrier components; and the known digital signal multiplexed from the carrier components extracted by the carrier extracting means by hierarchical modulation. Demodulating means for demodulating a sequence, a known digital signal sequence generating means for generating the known digital signal sequence, comparing the known digital signal sequence obtained by this means with the known digital signal sequence demodulated by the demodulating means, A plurality of receiving systems including a comparing unit for detecting the number of errors included in the demodulated output; Error number comparing means for comparing the number of errors obtained by the comparing means, receiving system selecting means for selecting the receiving system having a small number of errors based on the comparison result of the means, and receiving system selected by the means And a demodulating means for demodulating information to be transmitted from the output of the receiver. 9. The receiving apparatus according to claim 8, wherein said known digital signal sequence generating means generates the same known digital signal sequence as that of the transmitting side in synchronization with a frame synchronization signal. 10. The receiving apparatus according to claim 9, wherein said selecting means performs switching for selecting a receiving system having a small number of errors on a frame basis.