KR200216084Y1 - Partial Response Signaled - Orthogonal Frequency Division Multiplexing Apparatus - Google Patents

Abstract

The present invention provides a novel PRS-OFDM (partial response signaled-OFDM) scheme that significantly improves data transmission performance of a conventional orthogonal frequency division multiplexing (OFDM) scheme. In case of transmitting uncoded data in 4-QAM complex symbol, PRS-OFDM scheme of the present invention The signal-to-noise ratio at the receiving end to maintain the transmission bit error probability of is improved by about 10dB or more compared to the conventional OFDM scheme. Coded data When transmitting in QAM complex symbol, the larger the code rate is, and The larger the PRS-OFDM scheme of the present invention provides a significantly improved data transmission performance compared to the conventional OFDM scheme. The data transmission system using the PRS-OFDM scheme of the present invention has a PRS signal processing at the transmitting end of the conventional data transmission system using the OFDM method, so that the signal processing has a frequency diversity transmission function and is equalized at the receiving end. Implemented by obtaining a frequency diversity transmit gain by means of an equalizer.

Description

Partial Response Signaled-Orthogonal Frequency Division Multiplexing Apparatus}

The present invention introduces a new frequency diversity scheme that requires little spread of the frequency band in Orthogonal Frequency Division Multiplexing (OFDM), which significantly improves data transmission performance. It relates to the field of devices.

The OFDM method first transmits data to be transmitted. -QAM ( Convert complex complex symbols in the form of -ary quadrature amplitude modulation and convert the complex symbol sequence, which is a sequence of complex symbols, into multiple parallel complex symbols through serial-to-parallel conversion. Multi-Carrier Modulation (SRC) is a rectangular pulse shaping and sub-carrier modulation. Here, each of the square wave shaped parallel complex symbols is promised to be referred to as a parallel square wave signal, and in the multicarrier modulation scheme, a frequency interval between subcarriers so that all sub-carrier modulated parallel square wave signals are orthogonal to each other. Is set.

Over a wireless fading channel without using OFDM When transmitting a QAM modulated signal, if the delay spread of the channel caused by the multipath delay is greater than the symbol period of the modulated signal, inter-symbol interference occurs and Correct signal recovery is not possible at. Therefore, an equalizer that compensates for random delay spread should be used. However, the equalizer is not only complicated to implement, but also has a disadvantage in that transmission performance deteriorates due to input noise at the receiving end.

On the other hand, the OFDM scheme can make the symbol period of each parallel square wave signal much longer than the delay spread of the channel, thereby making it possible to relatively reduce symbol interference. In particular, by setting the guard interval longer than the delay spread, there is an advantage that the interference between symbols can be completely eliminated. Of course, there is no need to implement an equalizer that compensates for random delay spread due to multipath delay. Accordingly, the OFDM scheme is very effective for data transmission over a wireless fading channel and is currently adopted as a standard transmission scheme for terrestrial digital television and audio broadcasting systems in Europe. In addition, data transmission system through wired channels such as digital subscriber loop (DSL) and powerline communication eliminates degradation of transmission performance due to multipath reflection occurring in line network environment. It is used a lot.

The transmitting end of the data transmission system using the OFDM scheme first converts the data to be transmitted into coded data through channel encoding means and the encoded data through a mapper. -Convert to complex symbols in the form of QAM, phase shift keying (PSK), and differential PSK (DPSK), and convert them to multiple parallel complex symbols through serial-to-parallel conversion, then shape each parallel complex symbol into a square wave and subcarrier modulation Then, it consists of a modulation means for carrier-modulating the sum of all subcarrier-modulated signals, and a transmission end channel matching means composed of an amplifier and an antenna for transmitting the carrier-modulated signal through wireless and wired channels. In contrast to the transmitting end, the receiving end comprises a receiving end channel matching means, a demodulation means, a channel decoding means and the like.

As the channel encoding means, a number of methods including a convolutional encoding, a block encoding, a turbo encoding, or the like, or a suitable combination thereof are used. The square wave shaping and subcarrier modulation means of a plurality of parallel complex symbols among the transmitter modulation means are implemented as an inverse fast Fourier transform (IFFT) signal processing means based on a sampling theorem. Fast Fourier transform (FFT) signal processing means is used.

The structure of the present invention is to generate a partial response signal (hereinafter referred to as PRS) in order to have a new frequency diversity transmission function that requires almost no spread of a frequency band in the configuration of a data transmission system using a conventional OFDM scheme. It is an object to remarkably improve data transmission performance by adding means to the transmitting end and adding equalizing means for processing the diversity gain obtained by PRS signal processing to the receiving end.

Therefore, in order to mainly describe the PRS signal processing means added to the modulation means of the conventional data transmission system using the OFDM scheme, the encoded data, which is the output of the channel encoding means, is regarded as input data to be transmitted by the transmitting end. The configuration and operation of a data transmission system using the OFDM scheme will be briefly described.

1 and 2 are conventional configuration diagrams of a transmitting end and a receiving end of a data transmission system using an OFDM scheme.

Referring to Figure 1, the configuration of the transmitter

Encoded data to be transmitted A mapper 100 for converting into complex symbols such as QAM, PSK and DPSK forms,

A frequency interleaver 101 for properly rearranging the order of the output complex symbol sequences of the mapper 100,

A serial and parallel converter 102 for making a series of complex symbol sequences, which are outputs of the frequency loom 101, into a plurality of parallel complex symbols;

IFFT signal processor 103 for processing IFFT signal by inputting a plurality of outputs of the serial and parallel converter 102,

A parallel and serial converter 104 for converting a plurality of outputs of the IFFT signal processor 103 into a series complex symbol sequence and outputting the same;

A guard section inserter 105 for inserting a guard section at the output of the parallel-serial converter 104;

A real part selector 106 for selecting a real part of an output complex symbol of the guard interval inserter 105 and an imaginary part selector 107 for selecting an imaginary part,

Waveform shaping filters 108, 109 for shaping the outputs of the real part selector 106 and the imaginary part selector 107, respectively;

The waveform shaping filter 108, 109 output signals respectively carrier And A carrier modulator (110) for generating a carrier modulated signal by multiplying and multiplying the multiplied results by

It consists of transmission stage channel matchers 111 for matching the output signal of the carrier modulator 110 to the channel.

The thick lines represent the paths of complex signals and the thin lines represent the paths of real signals.

The IFFT signal processor 103 is responsible for the core function of subcarrier modulation, and as the number of subcarriers to be used increases, the serial / parallel converter 102, the IFFT signal processor 103, and the parallel-serial converter 104 are used. Difficult to implement However, if the IFFT signal processor 103 is implemented with a pipeline structure (E.Bidet, D.Castelain, C.Joanblanq, and P.Senn: 'A Fast Single-Chip Implemenation of 8192 Complex Point FFT,' IEEE , Jour. Of Solid-State Circuit, pp300-306, Vol. 30, No. 3, Mar. 1995), by implementing a serial input / output signal to implement the serial-to-parallel converter 102 and the parallel-to-parallel converter 104 and the like. Can be omitted.

2, the configuration of the receiving end is

Receiving end channel matcher 200 for receiving a signal through a channel,

A carrier demodulator 201 for reproducing a complex symbol from an output of the receiving end channel matcher 200,

A guard interval remover 202 for removing complex symbols within the guard interval from the output of the carrier demodulator 201,

Serial-to-parallel converter 203 for making the output of the guard interval remover 202 into a plurality of parallel complex symbols,

An FFT signal processor 204 for inputting a plurality of outputs of the serial-to-parallel converter 203,

Parallel to parallel converter 205 for converting a plurality of parallel outputs of the FFT signal processor 204 into a series complex symbol sequence;

A frequency deinterleaver 206 for arranging the output complex symbol sequences of the parallel-sequencer 205 in the original order;

And an inverse mapper 207 for outputting a soft decision or hard decision estimate of the input encoded data of the transmitter from the output of the frequency reversal loom 206.

The carrier demodulator 201 carries the output signal of the receiving end channel matcher 200, respectively. And After multiplying by, we extract two sample values through matched filtering process and convert them into one complex symbol.

The FFT signal processor 204 may implement a parallel / parallel converter 203, a parallel-to-parallel converter 205, and the like by implementing a pipeline structure having a serial input / output structure similar to the IFFT signal processor 103 of the transmitting end. Can be.

Input coded data at the transmitter referred to in FIG. 1 is generally input to the mapper 100 after time interleaving signal processing, and is caused by various types of causes including Doppler frequency shift. Prevents burst errors due to time selective fading. On the other hand, in the frequency shifter 101 of the transmitter referred to in FIG. 1, the sequential output complex symbols of the mapper 100 are different from each other at intervals larger than the coherence bandwidth of the wireless fading channel. By being modulated by the subcarrier, it copes with frequency selective fading.

The theoretical basis for using the IFFT signal processing and the FFT signal processing means in the transmitting end of FIG. 1 and the receiving end of FIG. 2 and the operations of the transmitting end and the receiving end will be described in more detail.

The output signal of the carrier modulator 110 at the transmitting end of FIG. Is expressed as

here Is the sum of the subcarrier modulated all parallel square wave signals.

here Is the symbol period index of the parallel square wave signals, Is the total number of subcarriers ( Is excellent), Each parallel square wave signal, Is During the first symbol interval Parallel complex symbols on the first subcarrier, and Is defined as

Also ( ) Is the symbol period of the parallel square wave signal, Is the length of the effective symbol interval of the parallel square wave signal, Denotes the length of the guard interval of the parallel square wave signal. Any two subcarriers And The two parallel square wave signals modulated by are orthogonal to each other for the effective symbol interval.

Is the baseband signal and frequency bandwidth is weak. More than twice the sampling bandwidth (In other words, Using the sampled sampled as), we can express

here Is In Is a sample of, Is the impulse response of the waveform shaping filters 108 and 109. to be. (For reference, in real data transmission system applications, the parallel to parallel conversion ratio of the serial and parallel converters is large enough, and the parallel square wave signal of the symbol period including the protection period is generated to insert the protection interval. No signal distortion due to

Sampling cycle Is usually ( , m is a natural number) Select Set to. In addition, the length of the protective section ( Is set to any natural number). Therefore, in (Equation 3) Is full It is represented by two sample values. Sample in the range ( ) From (Equation 2) ( Is obtained by an inverse discrete Fourier transform (IDFT).

sign Is defined as a value of 0, As defined above, Equation 4 may be expressed by a more general IDFT equation as follows.

For reference, the IDFT expression referenced in Equation 5 is

There is no scaling factor, but in the application of communication system, the function of this scaling factor only increases or decreases the signal by a constant factor and has no effect on the performance interpretation such as transmission error probability of the transmission system.

The cyclic prefix signal transmitted during the protection period of the parallel square wave signal plays an auxiliary role such as properly operating the AGC (automatic gain control) function at the receiving end or preventing signal loss due to delay spread. The sample values in are given by Eq. (2).

The above-described configuration of the transmitting end of FIG. 1 is based on (Equation 3), (Equation 5) and (Equation 6), and the subcarrier modulation function includes the IFFT signal processor 103 and the waveform shaping filter 108, 109. And so on.

3 illustrates subcarriers in order to conceptually show each parallel square wave signal conceptually. instead Is considered, , , Taking into account the complex symbol ( ) And a subcarrier waveform diagram. Parallel square wave signal during the first symbol interval Is Modulated on the first subcarrier. For your reference, Signal of the subcarrier (i.e., DC component) Because it changes the reference level of, the complex symbol is usually not subcarrier modulated.

Figure 4 is referred to in Figure 3 above from Equation 5 A parallel complex symbol applied to each input terminal of the IFFT signal processor 103 to generate a modulated signal on the first subcarrier, { , , , } Are respectively applied to the input terminals {1, 2, 3, 4} of the IFFT signal processor 103, and { , , , } Are applied to the input terminals {12, 13, 14, 15} of the IFFT signal processor 103, respectively.

At the receiving end, the complex symbol is recovered from the signal during the effective symbol interval, The power spectral density function, or power spectrum, is

FIG. 5 illustrates a subcarrier modulated full parallel square wave signal referred to in FIG. ) Shows the power density function. The frequency spacing between each subcarrier is the inverse of the effective symbol interval length. Is given by if, To Double If set to (the length of the protective section ), The frequency interval between subcarriers satisfying orthogonal And thus Within the baseband frequency bandwidth of Subcarriers may be transmitted. However, the amount of encoded data that can be transmitted per unit time within the same frequency bandwidth The same is true regardless of the value of.

The channel encoding means generates encoded data by adding redundancy data to the information data to be transmitted. The channel encoding means expresses the ratio of the amount of information data to the amount of encoded data as a code rate, and is smaller than 1. to be. In the case of data transmission using channel encoding means, the amount of data information that can be transmitted through a given frequency band is reduced by the coding ratio used. Despite the disadvantage that the spectral efficiency of the expensive frequency band is deteriorated, however, channel encoding means are widely used to compensate for the degradation of data transmission performance in poor radio fading channels. In the transmitting end of the data transmission system using the OFDM scheme referenced in FIG. 1, the encoded data is converted into a complex symbol through a mapper, and the complex symbol is a frequency demultiplexer 206 of the receiver referred to in FIG. ), Adjacent complex symbols are affected by independent fading. Therefore, the coded data reconstructed by the receiver referred to in FIG. 2 is prevented from severe performance deterioration due to a loss of a burst form. However, the probability of loss of information due to fading is still very high, which results in a severe degradation of transmission performance compared to data transmission through an unfaded channel.

Accordingly, the present invention provides a novel method of improving data transmission performance by reducing the amount of fading applied to each complex symbol by introducing a frequency diversity scheme that requires little spread of the frequency band to solve this problem. do. That is, in the conventional data transmission system using the conventional OFDM scheme, each parallel complex symbol is modulated to one subcarrier during the symbol period, whereas in the present invention, one parallel complex symbol is modulated to a plurality of subcarriers. The frequency diversity effect obtained by changing the transmission structure reduces the amount of fading that affects each complex symbol, thereby significantly improving data transmission performance. In particular, the configuration of the present invention has a great feature in that the frequency diversity technique is used under the condition of using a frequency band which is almost the same as that used in the conventional OFDM scheme.

Several attempts have been made to improve the data transmission performance of the conventional OFDM scheme using the frequency diversity scheme. For example, a scheme called frequency hopped OFDM (FH-OFDM) divides an OFDM symbol period into a plurality of sections, and each parallel complex symbol is divided into a plurality of subcarriers farther than the coherence bandwidth in each divided section. By alternating with each other, each parallel complex symbol achieves a frequency diversity effect transmitted over multiple independent fading channels. In the receiver, the estimated values of the respective parallel demodulation symbols are restored by accumulating the subcarrier demodulated values by the same subcarrier in each of the divided sections for the entire symbol period. However, by dividing the intervals of the OFDM symbol period, the orthogonal condition between subcarrier signals is not satisfied in each interval, which inevitably causes deterioration of data transmission performance, and its magnitude cancels the gain obtained by the frequency diversity transmission effect. It is so large that it is difficult to achieve its intended purpose of improving data transfer performance.

1 is a block diagram of a transmitting end of a data transmission system using a conventional OFDM scheme;

2 is a block diagram of a receiving end of a data transmission system using a conventional OFDM scheme;

3 is a diagram showing an embodiment of a parallel square wave signal in which a subcarrier is modulated in the conventional OFDM scheme;

4 is an embodiment showing an input sequence of a complex symbol in the IFFT signal processor referenced in FIG. 1;

5 is a power density function of a subcarrier modulated all-parallel square wave signal in the conventional OFDM scheme;

6 is a configuration diagram of a transmitting end of a data transmission system using a PRS-OFDM scheme according to the present invention;

7 is a block diagram of a receiving end of a data transmission system using a PRS-OFDM scheme according to the present invention;

8 is a typical configuration diagram of a PRS signal processor playing a key role of the PRS-OFDM scheme of the present invention;

9 is a configuration diagram in which the transmitter is reconfigured by changing the PRS signal processor and the frequency interleaver of the transmitter in the data transmission system using the PRS-OFDM scheme of FIG.

FIG. 10 is a block diagram illustrating in detail an input and output complex symbol centering on a DB-PRS signal processor, a frequency shifter, and an IFFT signal processor including parallel input and output stages with reference to FIG.

FIG. 11 is a block diagram illustrating in detail the input and output complex symbols centering on an RC-PRS signal processor, a frequency shifter, and an IFFT signal processor including parallel input and output stages with reference to FIG.

12 is a comparison diagram of data transmission performance of the PRS-OFDM scheme and the conventional OFDM scheme of the present invention using RC-PRS signal processing when each subcarrier modulates 4-QAM complex symbols.

Fig. 13 is a comparison diagram of overall data transmission performance including coding means of the PRS-OFDM scheme of the present invention and the conventional OFDM scheme in the case of using convolutional coding with a coding ratio of 1/2 and a constraint length of 3.

The scheme provided by the present invention has the effect of modulating each complex symbol by a plurality of subcarriers farther than the coherence bandwidth by transmitting the frequency complex after outputting the complex symbol sequence of the transmitter mapper 100 after processing the PRS signal. Is the way to get. At the receiving end, the frequency diversity effect is obtained by signal processing the frequency-reversed complex symbols by an equalizer. The equalizer is completely different from the role of the equalizer used to compensate for the random delay spread in that it completely recovers information from the controllable PRS signal.

Since the scheme provided by the present invention is characterized in achieving a frequency diversity function by adding PRS signal processing to the conventional OFDM scheme, the scheme of the present invention is referred to as Partial Response Signaled-Orthogonal Frequency Division Multiplexing. (Hereinafter referred to as PRS-OFDM) method.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

6 and 7 are configuration diagrams of a data transmission system using a PRS-OFDM scheme according to an embodiment of the present invention. The coded data, which is the output of the channel encoding means, is regarded as the input data to be transmitted by the transmitting end and illustrated.

Referring to Figure 6, the configuration of the transmitting end of the PRS-OFDM scheme

Encoded data to be transmitted Mapper 100 for converting to complex symbols such as QAM, PSK and DPSK forms,

A PRS signal processor 112 for converting an output complex symbol sequence of the mapper 100 into a PRS signal;

A frequency loom 101 for properly rearranging the order of the output complex symbol sequences of the PRS signal processor 112,

A serial and parallel converter 102 for making a series of complex symbol sequences, which are outputs of the frequency loom 101, into a plurality of parallel complex symbols;

IFFT signal processor 103 for processing IFFT signal by inputting a plurality of outputs of the serial and parallel converter 102,

A parallel and serial converter 104 for converting a plurality of outputs of the IFFT signal processor 103 into a series complex symbol sequence and outputting the same;

A guard section inserter 105 for inserting a guard section at the output of the parallel-serial converter 104;

A real part selector 106 for selecting a real part of an output complex symbol of the guard interval inserter 105 and an imaginary part selector 107 for selecting an imaginary part,

Waveform shaping filters 108, 109 for shaping the outputs of the real part selector 106 and the imaginary part selector 107, respectively;

A carrier modulator 110 for generating a carrier modulated signal from the waveform shaped filter 108, 109 output signal,

It consists of transmission stage channel matchers 111 for matching the output signal of the carrier modulator 110 to the channel.

Referring to Figure 7, the configuration of the receiving end of the PRS-OFDM scheme

Receiving end channel matcher 200 for receiving a signal through a channel,

A carrier demodulator 201 for reproducing a complex symbol from an output of the receiving end channel matcher 200,

A guard interval remover 202 for removing complex symbols within the guard interval from the output of the carrier demodulator 201,

Serial-to-parallel converter 203 for making the output of the guard interval remover 202 into a plurality of parallel complex symbols,

An FFT signal processor 204 for inputting a plurality of outputs of the serial-to-parallel converter 203,

A parallel-to-serial converter 205 for converting a plurality of parallel outputs of the FFT signal processor 204 into a serial complex symbol,

A frequency reverse weaving machine 206 for arranging the output complex symbol sequences of the parallel-sequencing converter 205 in the original order;

An equalizer 214 which achieves frequency diversity transmission gain by PRS signal processing at the transmitting end from the output of the frequency reverse weaving machine 206,

An inverse mapper 207 outputs a soft decision or hard decision estimate of the input encoded data of the transmitter from the output of the equalizer 214.

Referring to FIG. 6, the PRS-OFDM transmission end configuration according to the present invention merely adds the PRS signal processor 112 to the conventional OFDM transmission configuration, which is referred to in FIG. The receiver configuration of the PRS-OFDM scheme of the present invention is an addition of the equalizer 208 in the receiver configuration of the conventional OFDM scheme referred to in FIG.

A typical configuration of the PRS signal processor 112, which plays a key role in the PRS-OFDM scheme of the present invention, is configured in the form of a linear tapped delay line as shown in FIG. S. Pasupathy: 'Partial Response Signaling,' IEEE, Tr. Comm. Pp921-934, Vol. 23, No9, Sep. 1975), the relationship between input and output is expressed as:

here Enter complex symbol, Output complex symbol, Is the number of taps, Is the tab polynomial, and Is defined as In this design Is for Duobinary (hereinafter referred to as DB-PRS) signal, Modified duobinary signal, Various forms of PRS signal processing can be considered, including raised cosine (hereinafter referred to as RC-PRS) signal. For reference, the conventional OFDM scheme PRS-OFDM can be considered. A typical feature of the PRS signal processing is that there is no increase in the output complex symbol relative to the speed of the input complex symbol. Therefore, it is very advantageous in terms of utilization of the frequency band. But, The larger this is, the higher the level number of the output complex symbols is. For example, in the case of a DB signal, the output has a ternary output value for a binary input. This causes a deterioration of the signal-to-noise ratio at the receiver, but this degradation can be minimized by using a maximum likelihood sequence detection (MLSD) technique.

9 is a reconfigured transmitter by changing the PRS signal processor 112 and the frequency loom 101 of the transmitter of the data transmission system using the PRS-OFDM scheme of FIG. . Compared to the transmitter configuration shown in FIG. 6, the PRS signal processor 112 and the frequency shifter 101 are moved to a position between the output of the serial and parallel converter 102 and the input of the IFFT signal processor 108. see.

FIG. 10 specifically illustrates input and output complex symbols based on the DB-PRS signal processor 112, the frequency shifter 101, and the IFFT signal processor 107 configured as parallel input and output stages with reference to FIG. It is shown. The parallel input / output stage is referred to as Fig. 4 = 16 pieces. The configuration of the frequency weaving machine 101 is possible in a number of embodiments, but shows a configuration in the form of a perfect shuffle as one embodiment. In particular, the number of effective complex symbols of the output terminal is one more than the number of effective complex symbols of the input terminal of the DB-PRS signal processor 112. In general, the frequency bandwidth of each parallel carrier modulated subcarrier is Will increase slightly, but this increase is the FFT size (i.e. The larger the), the smaller the negligible ratio.

Next, the effect of improving the data transmission performance of the data transmission system using the PRS-OFDM scheme of the present invention will be described.

Data transmission performance is generally the ratio of signal energy and noise power density, or signal-to-noise ratio, required to send a bit of information at the receiver to obtain a specified data transmission bit error probability under constant noise reception. to noise ratio). Symbol sequence processed by one PRS signal at transmitter ( ), The receiver equalizer selects a complex symbol sequence that maximizes the value obtained from the following equation based on the MLSD technique.

here Is First received complex symbol, ( ) Denotes a complex symbol sequence trained with an arbitrary PRS signal, And Are each And of Complex Symbol, Is a complex additive white gaussian noise signal. Assuming that the phase of the complex symbol is completely restored at the receiving end so that the real part and the imaginary part can be independently processed, only the detection of the real part is sufficient. In this case, Equation (9) is changed as follows.

here , , Is an additive white Gaushan noise signal. In Equation (10), the data transmission performance is determined by the distance, in particular, the minimum distance, of each of the PRS signal-processed real symbol sequences. And A street of love Is defined as

It is very difficult to theoretically completely calculate the data transmission performance of the conventional OFDM scheme and the PRS-OFDM scheme of the present invention. Therefore, on the basis of the above Equation (10), a rough comparison will be made first in terms of bound performance, and then the comparison will be made in detail through computer simulation.

First, the data transmission performance using the conventional OFDM scheme, which is the basis of performance comparison, will be described. Arbitrary random sequence in the transmitting end In the case of transmitting the random random punctuation sequence that minimizes the value obtained by using Equation (10). Is Compared with, only one symbol has a different value, and the remaining symbols are actual symbol sequences composed of the same symbol. Therefore, the signal to noise ratio at the receiver (here silver The probability of transmission bit error over the non-fading channel is (JG Proakis; Digital Communications, 1995, pp 593-601). This result is consistent with the fact that when the PRS signal is received in the non-fading channel using the MLSD technique, there is no degradation in transmission performance. In case of data transmission through fading channel, the transmission bit error probability is (here Is a random variable of the centralized chi-square distribution.

Next, the transmission performance in the PRS-OFDM scheme of the present invention using the DB-PRS signal processing referred to in FIG. 10 will be described. In this case (Equation 10) Is an output symbol string of the PRS signal processor 112, unlike the OFDM scheme. Arbitrary hollow row to minimize the above (Equation 10) We need to consider only a few cases to get. For example, in the case of two input symmetric sequences, in which only one symbol is different and all other symbols are the same, the difference between the symbol sequence and the output symmetric sequences of the PRS signal processor 112 is represented by the PRS signal processor (Equation 8). Using the fact that the input / output of 112) has a linear relationship, it is obtained as shown in the left side of Equation (12) below.

In this case, the energy of the signal Noise variance Signal-to-noise ratio due to actual distance of minimum distance As a result, the transmission bit error probability is the same as that of the conventional OFDM scheme. In another case, when the two generate a state in which the difference between the actual symbol sequences is continuously changed, the difference between the PRS signal processor 112 output the actual symbol sequences is given as the left side of Equation (13) below.

This case also has the same signal-to-noise ratio as obtained in (12).

However, this result does not hold for data transmission on a fading channel. For example, consider a case in which data is transmitted using a DB-PRS-OFDM scheme through a fading channel capable of using two frequency diversity. In this case, the frequency output of the DB-PRS signal processor 112 is completely shuffled by the frequency shifter 102 in order to obtain a frequency diversity effect. , , Also ) To be affected. In Equation 12, the average signal energy of the odd numbered signal is And noise variance Therefore, the average signal to noise ratio is Becomes Similarly, the average signal-to-noise ratio for even-numbered signals Is determined. Therefore, the transmission energy is divided into odd-numbered and even-numbered signals affected by independent fading, thereby obtaining frequency diversity effects. On the other hand, in Equation 13, the average signal energy of the odd numbered signal is And noise variance So the average signal to noise ratio is On the other hand, the average signal to noise ratio for the even signal is zero. Therefore, since the transmission energy is not dividedly transmitted to the even-numbered signal, the frequency diversity effect is not obtained at all. Equations (12) and (13) are included in all the possibilities for determining the marginal performance, so in the case of data transmission over a fading channel with frequency diversity 2 using the DB-PRS signal processor The improvement in data transmission performance cannot be achieved as compared with the conventional OFDM scheme.

In order to solve this problem, other types of PRS signals, for example, The case of using the RC-PRS signal is shown in FIG. In the same way as described above, only a few cases can be examined to easily estimate the marginal performance. The difference between the output symbol sequences of the RC-PRS signal processor 112 for two input symbol sequences that differ only in one symbol and all the other symbols are obtained as shown in the left side of Equation (14).

When frequency shifting is performed so that the odd-numbered and even-numbered outputs are affected by independent fading, the average signal-to-noise ratio of each of the odd-numbered and even-numbered symbols is received at the receiving end. And There is no loss of signal-to-noise ratio as a whole. However, there is a loss because each transmit power is not evenly divided into two independent fading channels. As another case, when the two generate a state in which the difference between the actual symbol sequences is continuously changed, the difference between the output actual symbol sequences of the PRS-PRS signal processor 112 is obtained as shown in the left side of Equation 15 below.

In this case, the average signal-to-noise ratio of each of the odd and even symbols is The overall loss of signal-to-noise ratio That is, there is a loss of 1.7609 dB. However, since the gain obtained by diversity transmission cancels them sufficiently, even in view of such a loss, a significantly improved data transmission performance can be obtained compared to a data transmission system using a conventional OFDM scheme that does not use PRS signal processing. .

FIG. 12 compares the data transmission performance of the PRS-OFDM scheme and the conventional OFDM scheme of the present invention using RC-PRS signal processing when each subcarrier modulates 4-QAM complex symbols through computer simulations. The vertical axis represents the data transmission bit error probability, and the horizontal axis represents the average signal-to-noise ratio required to transmit one bit of information data to maintain a given transmission bit error probability. Referring to FIG. 12, the PRS-OFDM scheme of the present invention has a significant transmission performance improvement effect, for example, compared to the conventional OFDM scheme. The signal-to-noise ratio is improved by more than about 10dB to maintain the transmission bit error probability. In addition, the greater the frequency selectivity determined in the channel, the greater the effect of performance improvement. Instead of 4-QAM complex symbol When sending a QAM complex symbol It is well known by the cutoff rate theory that the larger the value, the more the difference in transmission performance increases.

As described above, in the case of the uncoded data transmission (that is, the coding ratio is 1), the effect of improving the data transmission performance of the PRS-OFDM scheme of the present invention has been described.

Next, the transmission performance of the PRS-OFDM scheme of the present invention and the conventional OFDM scheme for the case where the coding ratio is smaller than 1 will be compared. Fig. 13 shows the results obtained by computer simulation of the overall data transmission performance including the PRS-OFDM and OFDM coding means in the case of using convolutional coding with a coding ratio of 1/2 and a constraint length of 3. Shown. The dotted line indicates the OFDM scheme, and the solid line indicates the data transmission performance of the PRS-OFDM scheme. Referring to FIG. 13, the PRS-OFDM scheme of the present invention is based on the number of diversity that can be used in a fading channel compared to the conventional OFDM scheme. A gain of about 2-3 dB is obtained at For reference The PRS signal processor is used, and the equalizer and channel encoder for PRS signal processing are regarded as a finite state machine at the receiving end.

The PRS-OFDM method of the present invention can be directly applied to complex symbols in the form of not only QAM but also PSK (Phase Shift Keying) in the mapper, and can also be used for baseband signal processing when used in a wired communication channel. Do. In addition, the configuration of the present invention can also be used in the ISDN-OFDM method under study in Japan, etc. It is obvious.

In the PRS-OFDM scheme of the present invention, in the data transmission system using the conventional OFDM scheme, multiple symbol interferences that can be controlled so as to have a frequency diversity transmission function under the condition of using a frequency band almost identical to that of the OFDM scheme at the transmitting end are multiplexed. By adding the PRS signal processing means to be given during the symbol period and the equalizer means for obtaining the frequency diversity transmission performance gain at the receiving end, the data transmission performance is remarkably improved compared with the conventional OFDM scheme.

The PRS-OFDM method of the present invention is a conventional OFDM application field, that is, DSL (Asynchronous Digital Subscriber Loop), VDSL (Very High Rate Digital Subscriber Loop), powerline communication system, terrestrial digital TV broadcasting system, B Widely applicable to Broadband-Wireless Local Loop (WLL) systems, HomePNA systems, Multi Carrier-Code Division Multiple Access (MC-CDMA) systems, and the like.

Claims (1)

Mapper for converting the coded data to be transmitted to complex symbols such as QAM form, A PRS signal for converting the intersymbol interactions that can be controlled according to a predetermined rule by adding the output complex symbol sequence of the mapper as an input signal to the remaining complex symbols and converting the complex symbol sequence into a new complex symbol sequence. Handler, By inputting the output complex symbol sequence of the PRS signal processor, adjacent complex symbols within the complex symbol sequence are modulated by subcarriers farther from each other than the coherence bandwidth to rearrange the complex symbol sequence to obtain a frequency diversity effect. Frequency Loom, IFFT signal processor for processing the output of the frequency loom IFFT signal, A guard section inserter for inserting a guard section at the output of the IFFT signal processor; A carrier modulator for inputting the output of the guard interval inserter into a carrier modulated signal, A PRS-OFDM transmitter comprising a transmitter end channel matcher for matching an output signal of the carrier modulator to a channel; A receiver end channel matcher receiving a signal through a channel, A carrier demodulator for reproducing a complex symbol from an output of the receiving end channel matcher, A guard interval eliminator for removing complex symbols within the guard interval from the output of the carrier demodulator, An FFT signal processor having an output of the guard section remover as an input, A frequency reverse weaving machine for arranging the FFT signal processor output complex symbol sequences in the original order; an equalizer for restoring the input complex symbols of the PRS signal processor at the transmitting end from the output of the frequency reverse weaving machine; A PRS-OFDM receiver comprising an inverse mapper for outputting a (soft decision or hard decision) estimate of the input encoded data of the transmitter from the output of the equalizer, And a PRS-OFDM transceiver comprising the transmitter and the receiver.