JP2003348041A - Transmitter for ofdm signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmitter for an OFDM (orthogonal frequency division multiplexing) signal which reduces computational quantity regarding window function processing for suppressing discontinuity between symbols of an OFDM modulation signal and which is effective for reduction of costs and power consumption. <P>SOLUTION: The transmitter for the OFDM signal is constituted so as to perform the window function processing by providing a window function processing part 1 with an adder 2, a shift register 3 and a switching device 5 and storing control information in a window function W (n) control table 6 in order to control the devices by associating them with sample numbers (n), thus, the very small quantity of computation is required in comparison with the case of using a multiplier. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM signal transmitting apparatus and, more particularly, to a technique for reducing the amount of calculation related to window function processing for suppressing spurious due to discontinuity between symbols.

[0002]

2. Description of the Related Art For example, in power line communication, information is transmitted using a power line provided to supply electric power such as an outdoor power distribution line or an indoor power line, and it is necessary to newly lay a communication line. Various methods have been studied so far because communication costs can be reduced without the need. In power line communication, while having the above advantages, a power line having poor transmission characteristics due to noise or the like is used. Therefore, it is necessary to use a communication method that is resistant to noise.

[0003] Orthogonal frequency division multiplexing (Orthogonal Frequen
The cy Division Multiplexing (hereinafter abbreviated as OFDM) communication system is a type of multi-carrier modulation system in which data of one channel is dispersed over a plurality of carriers and transmitted. It is known as a communication method suitable for the above-mentioned power line communication because the probability of loss is low. Note that OFDM communication is also used for wireless LAN, digital television broadcasting, and the like, but here, power line communication will be described as an example.

FIG. 3 shows a conventional O in a power line communication device.
FIG. 4 is a functional block diagram illustrating a configuration example of an FDM signal transmission device. The OFDM signal transmitting apparatus shown in FIG. 1 includes a symbol mapper 10 which divides transmission data into a plurality of orthogonal carrier waves with each frequency component partially overlapping to generate a predetermined modulated signal, and converts serial data into parallel data. S / P conversion circuit 20 for converting the data into an inverse fast Fourier transformer (Inverse Fast Fourier Transfo
rm, hereinafter referred to as IFFT) 30, a P / S conversion circuit 40 for converting parallel data to serial data, and a guard interval (guard interval, which reduces the effect of multipath due to reflected waves from the transmission line (power line) branch). G below
I) are sequentially connected to the additional circuit 50, and further, the output from the GI additional circuit 50 is route-divided between the switches 60a and 60b, and a window function processing unit 100 provided on one of the routes is provided. And a control unit 70 that performs overall control of the transmission device.

The window function processing section 100 has a multiplier 101 and a window function W _(n) coefficient table 102. The multiplier 101 has two inputs and one output. One input is connected to the output of the GI addition circuit 50 arriving via the switch 60a, and the other input is a window function W _(n).
The output of the coefficient table 102 is connected. And multiplier 1
The output of 010 is connected to the switch 60b. Further, the control unit 70 includes a sample counting unit 71 that counts the number of samples (s) described below, and a window generation unit 72 that generates a time window for applying a window function to a head portion and a tail portion of a symbol time region described later. And an s / n converter 73 for replacing the number of samples (s) counted by the sample counter 71 with a sample number (n) determined in advance.

[0006] The OFDM signal transmitting apparatus shown in this figure functions as follows. Since the outline of the OFDM system is described in detail in, for example, "Makoto Itami, OFDM Modulation Technique, Trikeps, March 2000", only the main points will be described here. FIG. 6 is a diagram illustrating a spectrum of a signal output by the symbol mapper 10. In this example,
FIG. 4 shows a spectrum when an OFDM signal using n carriers is generated, and each spectrum is arranged so as to overlap with a part of an adjacent spectrum in order to increase frequency use efficiency. That is, the symbol mapper 10 divides the transmission data into a plurality of carrier waves having frequency components as shown in FIG. 6 and orthogonal to each other, and divides the data into predetermined modulated signals (for example, quadrature amplitude modulation (QAM) or phase modulation (QAM)). PSK))
Is generated and output, the S / P conversion circuit 20 converts it into a parallel signal.

Although the orthogonality of the modulated signal is not guaranteed due to a shift in the generation timing (phase shift) of each carrier, each carrier is converted into a signal in the time domain by the IFFT converter 30. As a result, it is known that the occurrence timing deviation is corrected, and an ideal OFDM signal is output as a multiplexed waveform. Then, the OFDM signal is returned to a serial signal by the next P / S conversion circuit 40, and is processed by the GI addition circuit 50 into a signal that is less affected by multipath.

Here, an output signal from the GI addition circuit 50 and an output signal from the window function processing section 100 will be described. FIG. 4A is an image diagram showing an example of an output signal from the GI addition circuit 50, and FIG. 4B is an image diagram showing an example of an output signal from the window function processing section 100. That is, the GI addition circuit 5
At 0, a period called a guard interval is provided for each symbol to prevent deterioration due to intersymbol interference, as shown in FIG. The signal in this period is a signal obtained by copying a predetermined portion at the end of the symbol and adding it to the beginning, so that the guard interval and the effective symbol are continuous signals. As a result, if the delay time due to the reflection is within the guard interval, there is no interference from the previous symbol and only interference within the same symbol. In this case, each of the plurality of carriers corresponds to a case where the carrier has undergone flat fading, but the deterioration is smaller than that in a case where the carrier has undergone inter-symbol interference with the previous symbol.

The output signal from the GI addition circuit 50 is
By the switches 60a and 60b, the case of through output and the case of passing through the window function processing unit 100 are separated.
Switching signals to the switches 60a and 60b are transmitted to the control unit 70.
Supplied from Here, FIG. 4A shows an example of 100 samples per symbol, and the operation of the control unit 70 will be described using this example. That is, in the control unit 70, the sample counting unit 71 counts the number of symbol samples, and this count value is supplied to the window generation unit 72. When the count value (S) of the number of samples is 1 to 8 and 93 to 100, the window generator 72
A contact signal is selected so as to select the contact 2 side for 0a and 60b and to select the contact 1 side between 9 and 92. In other words, the window function processing unit 100
Via the route through which the OFDM modulated signal is output.

The s / n converter 73 replaces the number of samples (S) in the window period by the window generator 72 with a sample number (n) defined in advance and uses this as the n information. The function processing unit 100 gives the window function W _{(n) to the} coefficient table 102. For example, when (S) is "1" at the head, (n) is replaced with "8", and when (S) is "2", (n) is replaced with "7". When (S) at the center is "9" to "92", (n) is replaced with "0". In the tail part, (n) is set to "7" when (S) is "99", and (n) is set to "8" when (S) is "100", contrary to the head part. And so on.

Next, the window function processing section 100 will be described. Since the OFDM modulation signal is discontinuous between symbols, spurious components appear. Therefore, a window function is applied to prevent discontinuity before and after the temporally cut data section. In other words, a predetermined weighting coefficient is applied to the samples at the head and tail of the symbol so that both sides of the symbol smoothly approach "0", thereby suppressing discontinuity between symbols and suppressing spurious. Various window functions are considered, for example, Hanning window, H
There are amming windows and Blackman-harris windows. Here, taking a Hanning window as an example of a frequently used window function, it is expressed by the following equation.

(Equation 1)

Next, FIG. 5 is a table showing an example of the window function stored in the window function W _(n) coefficient table 102. This Ha
Using the nning window, the multiplier 101 multiplies the coefficient W (n) obtained by the above equation 1 for each sample of the leading part and the trailing part of the output signal from the GI adding circuit 50 in advance. Is used to suppress discontinuity between symbols. Thereby, the output of the OFDM modulated signal from the switch 60 is smoothly “0” on both sides as shown in the image shown in FIG.
Will be closer to.

[0013]

However, the above-mentioned conventional OFDM signal transmitting apparatus has the following problems. That is, the window function coefficient W
A multiplier for multiplying (n) is required. The multiplier has a large amount of calculation for multiplication, and the data transmission speed by the OFDM signal is limited by the calculation processing speed of the multiplier, so that a calculation device with a high calculation processing speed is used. This has led to an increase in cost and power consumption of the transmission device.

The present invention has been made in order to solve such a problem, and OFD is performed without using a multiplier.
An object of the present invention is to provide an OFDM signal transmitting apparatus in which discontinuity between symbols of an M-modulated signal is suppressed.

[0015]

According to a first aspect of the present invention, there is provided an OFDM signal transmitting apparatus according to the present invention. A symbol mapper for generating a predetermined modulated signal dispersed in a carrier wave; and an inverse Fourier transform unit for multiplexing the modulated signal in a time domain and outputting an OFDM signal, and suppressing spurious suppression due to discontinuity between symbols. Signal transmitting apparatus comprising: a window function processing means for performing an addition operation of a predetermined addition amount on an input signal to be subjected to a window function processing; A shift register for holding an input signal to be subjected to a shift operation, and a sign inversion of an output from the shift register to the adder as a predetermined addition amount. A sign inverter to be supplied, a switch for selectively switching the output of the adder or the shift register, and a window function value corresponding to a sample in the input signal to be subjected to the window function processing, which is previously replaced by an approximate operation expression and shifted. An OFDM signal transmitting apparatus, comprising: a window function control table represented by an amount and a switch selection destination.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a functional block diagram showing an embodiment of an OFDM signal transmitting apparatus according to the present invention. Note that the same reference numerals are given to the same functional blocks as those shown in FIG. 3 described above, and description thereof will be omitted.

The transmitting apparatus of the OFDM signal shown in this example includes:
The configuration of the window function processing unit differs from that shown in FIG. 3 described above. That is, the window function processing unit 1 performs the sign inversion of the output of the adder 2 and the shift register 3 to which the output signal of the GI addition circuit 50 is input via the contact 2 of the switch 60a, and A sign inverter 4 for supplying the other input of the adder; a switch 5 (switch means) for connecting the output of the adder 2 to the contact 1 and connecting the output of the shift register 3 to the contact 2; A window function W (n) control table 6 for controlling the adder 2, shift register 3, and switch 5 based on n information from the control unit 70 is provided.

The window function W (n) control table 6
Stores the following information in advance. FIGS. 2A and 2B are diagrams for explaining information stored in the window function W (n) control table. FIG. 2A shows a numerical example of the window function according to the present invention, and FIG. It is storage information (control table) corresponding to the numerical value of (a). Here, shown in FIG.
Using an example of the Hanning window, a method of obtaining information to be stored in the window function W (n) control table of the OFDM signal transmitting apparatus according to the present invention will be described. First, the coefficient value of the window function shown in the example of the Hanning window is approximated to a value expressed by adding 2- ^k and 1 or 0. For example, in the Hanning window example, n
The coefficient value W (n) at the time of = 1 is “0.95677272”
"Is a, which 1 + (- ^{2 -5)} expressed value" 9 defined approximates 0.96875 ", the shift amount and the switch selecting destination switch 5 to the shift register 3 in the control table 6 In this manner, the shift amount of the shift register 3 is determined from the value of k, and when the value to be added to the shift amount is 1, the selection destination of the switch 5 is the adder 2,
When it is 0, it is determined that the selection destination is the shift register 3.

The OFDM signal transmitting apparatus shown in FIG.
It works as follows. That is, the transmission data is transmitted to the symbol mapper 10, the S / P conversion circuit 20, the IFFT 30,
OFD via the S conversion circuit 40 and the GI addition circuit 50
An M modulation signal (symbol) is used. Next, the control unit 70
The window generator 72 outputs a switching signal to the switches 60a and 60b based on the value counted by the sample coefficient unit 71.
In the example shown in FIG. 4A, the switches 60a and 60b determine that the first part (s is 1 to 8) and the last part (s is 93 to 100) of the symbol are the window coefficient processing unit 1 , The contact 2 side is selected, and the central part of the symbol (s is 9 to 9)
2) selects the contact 1 side.

Further, the control unit 70 converts the counted number of samples (s) into a sample number (n) associated with the sample number (s) in advance by the s / n conversion unit 73 and supplies the sample number (n) to the window function processing unit 1. . Specifically, the s / n conversion unit 73 determines (s1 / n8), (s2 / n7),
(S3 / n6), (s4 / n5), (s5 / n4),
(S6 / n3), (s7 / n2), and (s8 / n1) are associated with each other. Also, at the tail of the symbol (s9
3 / n1), (s94 / n2), (s95 / n3),
(S96 / n4), (s97 / n5), (s98 / n
6), (s99 / n7), and (s100 / n8). Note that when s is from 9 to 92, n may be associated with 0.

That is, in the window function processing unit 1, the control unit 70
The window function W (n) control table 6 controls the adder 2, shift register 3 and switch 5 based on n information from The same processing is performed. For example, when n = 1, the shift register 3 outputs the output signal from the GI addition circuit 50 to 5
The value is shifted right (5 bits), and the shifted value is sign-inverted by the sign inverter 4 and supplied to one input of the adder 2. The adder 2 is provided with a GI addition circuit 50.
And the output signal from the sign inverter 4 are added. The switch 5 operates to select the contact 1 side and supply the output of the adder 2 to the contact 2 of the switch 60b.
When n = 7, the shift register 3 right-shifts the output signal from the GI addition circuit 50 five times (by 5 bits),
The switch 5 operates to select the contact 2 side and supply the output of the shift register 3 to the contact 2 of the switch 60b. When n = 8, the shift register 3 resets the value to "0", and the switch 5 selects the contact 2 side to supply the output of the shift register 3 to the contact 2 of the switch 60b. I do.

Since the window function processing section 1 functions as described above, the output of the OFDM modulated signal from the switch 60 is
As shown in the image shown in (b), both sides smoothly approach "0". Thus, using the multiplier, Hannin
A window function processing effect almost equivalent to the conventional one obtained by multiplying the coefficient of the g window can be obtained.

As described above, in the ODFM signal transmitting apparatus according to the present invention, the window function processing unit 1 is provided with the adder 2, the shift register 3, and the switch 5, which correspond to the sample number (n). Since control information is stored and configured in the window function W (n) control table 6 to perform the window function processing, the amount of calculation can be significantly reduced as compared with the case where a multiplier is used. .

[0024]

As described above, the transmitting apparatus for an ODFM signal according to the present invention comprises an adder for performing an addition operation of a predetermined addition amount on an input signal (symbol head and tail) to be subjected to window function processing. A shift register that holds an input signal to be subjected to window function processing in a shiftable manner, a sign inverter that inverts the sign of the output from the shift register and supplies the result as a predetermined addition amount to the adder, and the adder or the shifter. A switch means for selectively switching the output of the register; and a coefficient value W (n) to be subjected to the window function processing for the sample is set to 2
^-K is approximated to a value that can be expressed by adding 1 or 0, and is configured using a window function processing unit having a window function control table storing a shift amount and a switch selection destination according to the approximate value, It operates so as to obtain the same OFDM modulation signal output as that obtained by applying a window function without using a multiplier. Therefore, even if the transmission speed of data to be transmitted is increased, the cost and power consumption of the transmission device are increased. OFDM without inviting
An OFDM signal transmitting apparatus in which discontinuity between symbols of a modulated signal is suppressed can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an OFDM signal transmitting apparatus according to the present invention.

FIG. 2 is a diagram illustrating an example of a control table in a window function processing unit according to the present invention. (A) shows a coefficient value W (n) corresponding to a symbol number n and an example in which the coefficient value is represented by an approximate operation expression, and (b) shows control information corresponding to the coefficient value of (a). FIG. 9 is a diagram showing contents actually stored in a table.

FIG. 3 is a block diagram illustrating a configuration example of a conventional OFDM signal transmitting apparatus.

FIG. 4 is an image diagram for explaining window function processing; (A) shows the output from the GI addition circuit, (b)
Indicates an output from the window function processing unit.

FIG. 5 is a diagram illustrating an example of a coefficient value of a Hanning window.

FIG. 6 is a diagram illustrating an example of an output signal of a symbol mapper.

[Explanation of symbols]

1: Window function processing unit 2 ... Adder 3. Shift register 4 Sign reverser 5 ... Switch 6. Window function W (n) control table 10 ... Symbol mapper 20 ... Serial / parallel (S / P) conversion circuit 30 Inverse fast Fourier transformer (IFFT) 40 ... Parallel / serial (P / S) conversion circuit 50: Guard interval (GI) addition circuit 60a, 60b ... switch 70 ... Control unit 71: Sample number (s) counting unit 72... Window generation unit 73 ... sample number / sample number (s / n) conversion unit 100 Window function processing unit 101 Multiplier 102: Window function W (n) coefficient table

Claims (1)

[Claims] 1. A symbol mapper for generating a predetermined modulated signal by dispersing at least transmission data to a plurality of orthogonal carriers while partially overlapping each frequency component, and multiplexing the modulated signal in a time domain to OFDM. An OFDM signal transmitting apparatus comprising: an inverse Fourier transform unit for outputting a signal; and a window function processing unit for suppressing spurious due to discontinuity between symbols, wherein the window function processing unit performs a window function process. An adder for performing an addition operation of a predetermined addition amount on an input signal to be applied; a shift register for holding an input signal to be subjected to window function processing so as to be shiftable; and an adder for inverting the sign of the output from the shift register. A sign inverter for supplying a predetermined addition amount to the switch, a switch means for selectively switching the output of the adder or the shift register, and a window function. An OFDM signal transmission characterized by comprising a window function control table in which a window function value corresponding to a sample in an input signal to be processed is preliminarily replaced with an approximate operation expression and a shift amount and a window function control destination are displayed. apparatus.