KR101233281B1 - Transmitter and Receiver thereof - Google Patents

Abstract

The transmitter is initiated. In a multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) system, a transmitter for transmitting an OFDM signal through a plurality of transmit antennas includes a modulator for modulating an input signal and a space-time block coding for the modulated signal. STBC coding unit for performing Space Time Block Code (STBC), inverse fast Fourier transform for output of first and second multiplexer and first and second multiplexer for placing block coded signals in Comb form First and second IFFT units for performing Inverse Fast Fourier Transform (IFFT), and first and second coding units for performing coding using codes orthogonal to each other for the outputs of the first and second IFFT units. And first and second transmitters for transmitting the outputs of the second coding unit, respectively. As a result, the channel length limitation of the Comb Type Pilot Aided channel estimation can be overcome to minimize channel interference and to obtain accurate channel information.

Description

Transmitter and Receiver

The present invention relates to a transmitter and a receiver, and more particularly, to a transmitter and a receiver according to a MIMO Multi-Input Multi-Output (OFDM) Orthogonal Frequency Division Multiplexing (OFDM) system.

Multi-Input Multi-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems increase the throughput by using multiple antennas. However, as the number of antennas of the transmitting and receiving end increases, the number of channels increases, so that channel information to be compensated for increases. In addition, the long channel length causes inter-symbol interference. In order to equalize properly, it is important to minimize such channel interference and to find out accurate channel information.

A basic channel estimation method is to arrange a pilot, which is a signal known to both the transmitting and receiving end, between the transmission signals and to estimate the degree of distortion of the pilot passing through the channel. At this time, there are various methods of arranging pilots, and among them, a method of arranging pilots by a comb method may be used.

Comb arrangement inserts pilots into transmission signals at regular intervals in the frequency domain. Receiving the signal transmitted through the channel, the receiver applies a time domain averaging algorithm.

This algorithm has the advantage of high channel estimation even at low signal-to-noise ratio (SNR). However, there is a restriction that the length of the channel should be less than 1/2 of the interval between the peaks of the OFDM symbols.

Therefore, if the channel length is longer, there is a problem in that channel estimation is virtually impossible in the case of distortion in which several channels are overlapped.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a transmitter and a receiver for coding a sample interval of a signal in a time domain using an orthogonal code.

In the multi-input multi-output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system according to an embodiment of the present invention for achieving the above object, a transmitter for transmitting an OFDM signal through a plurality of transmit antennas, the input signal Modulator for modulating; An STBC coding unit performing space time block code (STBC) on the modulated signal; First and second multiplexing units for disposing the block coded signals in a Comb form; First and second IFFT units which perform an Inverse Fast Fourier Transform (IFFT) on the outputs of the first and second multiplexers; First and second coding units configured to perform coding using codes orthogonal to each other on the outputs of the first and second IFFT units; And first and second transmitters for transmitting the outputs of the first and second coding units, respectively.

Here, the orthogonal codes may be [1 1 1 1] and [1 -1 1 -1].

In addition, the first multiplexer may arrange one pilot every four out of 1024 symbols in the OFDM symbol in the frequency domain in a Comb form, and the first IFFT unit may convert the OFDM symbol in the frequency domain into an OFDM symbol in the time domain. The first coding unit may multiply and code 1, 1, 1, and 1 codes for four sample intervals having a length of 256 separated by the four pilots.

The second multiplexer may arrange one pilot every four out of 1024 symbols in the OFDM symbol in the frequency domain in a Comb form, and the second IFFT unit may convert the OFDM symbol in the frequency domain into an OFDM symbol in the time domain. The second coding unit may multiply and code four sample intervals divided by the four pilots, respectively, by 1, -1, 1, and -1 codes.

In addition, the pilot signal Pilot 1 provided to the first multiplexer and the pilot signal Pilot 2 provided to the second multiplexer are characterized by the following equations.

Here, A is a constant, M is the number of samples per section divided by the pilot signals, and k 'is a pilot index.

Meanwhile, in a MIMO Multi-Input Multi-Output (OFDM) Orthogonal Frequency Division Multiplexing (OFDM) system according to an embodiment of the present invention, a receiver for receiving an OFDM signal transmitted through a plurality of antennas through one antenna may include a frequency. A receiver configured to receive an OFDM signal, which is divided into a plurality of sample intervals of a time domain by a plurality of pilot signals arranged in a Comb form in a region, and is coded through codes orthogonal to each other; A channel estimator for averaging samples at the same distance with respect to the OFDM signal received through the receiver and estimating a channel through a code orthogonal to each other; First and second FFT units performing fast Fourier transform on the output of the channel estimator; An interpolator for performing frequency interpolation on the outputs of the first and second FFT units; And an STBC decoding unit for performing a space time block code (STBC) decoding on the output of the interpolator.

Here, the orthogonal codes may be [1 1 1 1] and [1 -1 1 -1].

In addition, in the OFDM signal received through the receiver, one pilot every four out of 1024 symbols is arranged in a Comb form in the OFDM signal in the frequency domain, so that four sample intervals having 256 lengths between peaks in the time domain are provided. And are coded by multiplying 1, 1, 1, and 1 codes by, respectively, and the channel estimator may estimate a channel by multiplying the four sample intervals by 1, 1, 1, and 1 codes, respectively.

In addition, in the OFDM signal received through the receiver, one pilot every four out of 1024 symbols is arranged in a Comb form in the OFDM signal in the frequency domain, so that four sample intervals having 256 lengths between peaks in the time domain are provided. Is multiplied by 1, -1, 1, and -1 codes, respectively, and the channel estimator may estimate the channel by multiplying the four sample intervals by 1, -1, 1, and -1 codes, respectively. .

In addition, the plurality of pilot signals Pilot 1 and Pilot 2 are characterized by the following equation.

Here, A is a constant, M is the number of samples per section divided by the pilot signals, and k 'is a pilot index.

As described above, according to the present invention, it is possible to overcome the channel length constraint of the Comb Type Pilot Aided channel estimation to minimize the channel interference and to find the correct channel information.

1A and 1B are block diagrams illustrating a transmitter configuration according to various embodiments of the present disclosure.
2 is a view for explaining a Comb Type Pilot Aided channel estimation system according to an embodiment of the present invention.
3A and 3B are diagrams for describing a coding method according to an embodiment of the present invention.
4 is a diagram for describing a channel estimation method according to an exemplary embodiment.
5A and 5B are block diagrams illustrating a receiver configuration according to various embodiments of the present disclosure.
6 is a diagram for describing a channel estimation method of a receiver according to an embodiment of the present invention.
7A and 7B are diagrams illustrating the shape of an OFDM signal according to the prior art and the present invention.
8 is a view showing the form of the OFDM signal at the receiving end according to an embodiment of the present invention.
9 is a diagram illustrating an experimental result of a time domain channel estimation method according to an embodiment of the present invention.
10A and 10B, and FIGS. 11A and 11B are diagrams for comparing the performance of the channel estimation method according to an exemplary embodiment of the present invention with the prior art.
12 shows a channel estimation MSE according to the prior art and the present invention.
FIG. 13 is a diagram for describing a method of applying the proposed algorithm in channel estimation of a MIMO system having four transmitting antennas.

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

1A and 1B are block diagrams illustrating a transmitter configuration according to various embodiments of the present disclosure.

Referring to FIG. 1A, a transmitter according to an embodiment of the present invention may include a modulator 110, an STBC coding unit 120, first and second multiplexers 131 and 132, and first and second IFFT units 141. 142, first and second coding units 151 and 152, and first and second transmitters 161 and 162.

The modulator 110 modulates an input signal (or data). In detail, the modulator 110 may perform quadrature phase shift keying (QPSK). Here, QPSK refers to a method of transmitting power in four types of 45 degrees, 135 degrees, 225 degrees, and 315 degrees with the same power level during data transmission.

The STBC coding unit 120 performs a space time block coding (STBC) space time block coding on the output of the modulator 110. STBC is a coding method defined in the 3GPP WCDMA-based IMT-2000 air interface specification, and has the effect of achieving diversity gain that can reduce the effects of multipath fading without requiring additional bandwidth in a multi-antenna system.

The first and second multiplexers 131 and 132 mix the pilot signals provided with respect to the output of the STBC coding unit 120. In this case, the first and second multiplexers 131 and 132 may arrange pilots in a COMB manner.

In detail, the first and second multiplexers 131 and 132 may insert pilots into the signal at regular intervals in the frequency domain. Here, it is assumed that 1024 OFDM signals of subcarriers.

For example, the first multiplexer 131 may arrange one pilot every four out of 1024 symbols in the OFDM signal in the frequency domain in a COMB scheme.

In addition, the second multiplexer 132 may arrange one pilot every four out of 1024 symbols in the OFDM signal in the frequency domain in a COMB scheme.

Here, the pilot signals Pilot 1 and Pilot 2 input to the first multiplexer 131 and the second multiplexer 132 may be in the form of Equations 1 and 2 below.

Here, A is a constant and M is the number of samples per interval divided by the pilot signals. If pilot 1 = A = t ₁ (p _{k '} ), then pilot 2 = t ₂ (p _k' ). Here, p _{k '} ∈ P; k' = 1, 2, ..., M can be. Here, k 'may be a pilot number, that is, a pilot index. For example, if there are 1024 subcarriers in the frequency domain, if pilots are inserted at four symbol intervals, a total of 256 pilots may be inserted, in which case k 'may be 1 to 256, and M may be 256. Can be.

The first and second IFFT units 141 and 142 perform an Inverse Fast Fourier Transform (IFFT) on the outputs of the first and second multiplexers 131 and 132 to actually generate a signal in a frequency domain. Convert to an OFDM signal in the time domain that can be transmitted.

Specifically, the first IFFT unit 141 performs an inverse fast Fourier transform on the output of the first multiplexer 131 to convert the OFDM signal to a time domain, and the second IFFT unit 142 is a second multiplexer. An inverse fast Fourier transform is performed on the output of 132 to convert an OFDM signal in a time domain.

The first and second coding units 151 and 152 perform encoding on the outputs of the first and second IFFT units 141 and 142.

In detail, the first coding unit 151 may apply Code 1 = [1 1 1 1] to the output of the first IFFT unit 141.

For example, the first coding unit 151 is 1, 1, 1 for each of four sample intervals in the time domain generated by the pilot mixed by the first IFFT unit 141 to the OFDM signal in the frequency domain. Can be coded by multiplying by one code.

The second coding unit 152 may apply Code 2 = [1 -1 1 -1] to the output of the second IFFT unit 142.

For example, the second coding part 152 for each of the first four sample intervals in the time domain are generated by the pilot mixing the OFDM signal in the frequency domain by the second IFFT unit 142 1, -1 Can be coded by multiplying by 1, -1 code.

The first and second transmitters 161 and 162 transmit a signal coded by the first and second coding units 151 and 152. Here, the first and second transmitters 161 and 162 may be implemented as antennas, respectively.

FIG. 1B is a block diagram illustrating an example of more concrete implementation of the transmitter configuration shown in FIG. 1A. A detailed description of components overlapping with those shown in FIG. 1A among those shown in FIG. 1B will be omitted.

IFFT / G.I. Blocks 141 ′ and 142 ′ insert a guard interval (GI) in addition to the functions of the first IFFT unit 141 and the second IFFT unit 142 of FIG. 1B.

That is, IFFT / G.I. The blocks 141 'and 142' insert a guard interval (GI) on the input signal and perform inverse fast Fourier transform to convert the signal in the frequency domain into an OFDM signal in the time domain that can be actually transmitted.

The P / S blocks 171 and 172 convert the OFDM signals in the time domain in series and output the serial signals.

On the other hand, in the channel estimation algorithm according to the present invention using the structure of the transmitter 100 described above, the estimation of overlapping samples during channel estimation is solved through coding in the time domain. That is, coding is performed on four sample intervals of the OFDM symbol in the time domain. Specifically, OFDM symbols transmitted to the first transmitter 161 (ie, antenna 1) and the second transmitter 162 (ie, antenna 2) are respectively C1 = [1 1 1 1] and C2 = [1 -1. 1 -1]. These are codes that are orthogonal to each other, and the correlation between them is zero.

Pilots are planted at four intervals out of 1024 symbols in an OFDM signal in the frequency domain. In total, four peaks appear in the time domain. And if the interval between the peak of the OFDM symbol is taken as one section, a total of four sections appear.

Here, the length of one section is 256 samples, which means that a channel having a length of 256 samples or less can be accommodated.

The symbol transmitted from antenna 1 is coded as C1 = [1 1 1 1]. That is, four codes are multiplied by each code and transmitted. Therefore, at antenna 1, the same signal as before coding is transmitted.

The sample between the first and second peak value of the symbol transmitted by antenna 2 is multiplied by the first value 1 of the code C2 = [1 -1 1 -1]. The samples between the second and third peaks are then multiplied by the second value -1 in the code. That is, compared with the original signal is transmitted in an inverted state. The samples between the third and fourth peaks are multiplied by 1, the third value of the code, and the 256 samples between the fourth and the first peak of the next OFDM multiply by the fourth value -1 of the code. do. That is, the interval 2 and the interval 4 are inverted compared with the original signal and transmitted.

The receiving end estimates the average of samples having the same location based on the peak values of four zones. This eliminates the influence of channel 2 when channel 1 is obtained. This allows the extraction of signals that have passed through channels longer than 128 samples. Through simple coding of the time domain of the transmitter and receiver, the complexity is hardly increased, and even a long channel of 256 samples or less can be estimated. A detailed configuration of the receiver will be described later with reference to the drawings.

2 is a view for explaining a Comb Type Pilot Aided channel estimation system according to an embodiment of the present invention.

The channel estimation algorithm according to the present invention is a system of two transmit antennas and one receive antenna using a Comb-based pilot structure based on ST-OFDM (Space Time Coded OFDM) ([1] SM Alamouti, "A simple transmitter diversity scheme for wireless communications, "IEEE J. Select. Areas Commun., vol. 17, pp. 1451-1458, Oct. 1998.), and the received signal is expressed as in Equation 3 below. Can be.

Where h _i is the channel impulse response between the i th antenna and the receiver, x _i is the transmitted signal, and ω is AWGN (Additive White Gaussian Noise). And n and l mean time block and channel length.

The channel estimation algorithm according to the present invention is basically based on ST-OFDM and can use two transmit antennas and one receive antenna.

A pilot of a constant value of A is planted in the signal transmitted from antenna 1, and a pilot of the signal transmitted from antenna 2 is multiplied by an exponent term to design a pilot such that time delay and inversion occur in the time domain. 2 is a diagram illustrating a pilot design process.

In addition, the channel may be estimated through the average of the intervals of the signals received at the receiver. In this case, there is an advantage that the channel estimation is relatively accurate even in a low SNR environment. However, there is also a limitation that, due to its nature, there must be an assumption that it passes through channels less than one-half of the interval between peaks in the time domain ([2] Bowei Song, Lin Gui, and Wenjun Zhang, “Comb Type Pilot Aided Channel Estimation in OFDM Systems With Transmit Diversity ”IEEE Trans. On Broadcast, vol. 52, no. 1, March, 2006).

In addition, a detailed description of the channel estimation method of the receiver will be described later with reference to the drawings.

3A and 3B are diagrams for describing a coding method according to an embodiment of the present invention.

According to FIG. 3A, the first coding unit 151 outputs a signal as shown on the right by multiplying the code C = [1 1 1 1] by each section divided by four pilot signals as shown on the left. can do.

In addition, according to FIG. 3B, the second coding unit 152 multiplies the code C = [1 -1 1 -1] by each section divided by four pilot signals as shown on the left side, as shown on the right side. The same signal can be output.

4 is a diagram for describing a channel estimation method according to an exemplary embodiment.

According to FIG. 4, an OFDM signal having four sections having a length of 256 samples in one section can be configured using the coded signals shown in FIGS. 3A and 3B.

5A and 5B are block diagrams illustrating a receiver configuration according to various embodiments of the present disclosure.

Referring to FIG. 5A, a receiver 200 according to an exemplary embodiment may include a receiver 210, a channel estimator 220, first and second FFT units 231 and 232, and first and second interpolators. 241 and 242, an STBC decoding unit 250 and a pilot removing unit 260.

The receiver 210 serves to receive an OFDM data signal from a plurality of antennas. Here, the receiver may be implemented with at least one antenna. Specifically, the receiver 210 may be divided into a plurality of sections in the time domain by a plurality of pilot signals arranged in a Comb form in the frequency domain, and may receive an OFDM data signal coded through codes that are orthogonal to each other. Specifically, one pilot every four out of 1024 symbols in an OFDM signal in the frequency domain is arranged in a Comb form to receive an OFDM data signal having four sample intervals having a length of 256 between peaks in the time domain. have.

The channel estimator 220 averages samples at the same distance based on each pilot signal with respect to the OFDM data received through the receiver 210 and estimates a channel through a code that is a code orthogonal to each other.

Specifically, since the channel estimator 220 knows that the peaks are spaced at 256 sample intervals, it is divided into four sections 1-256, 257-512, 513-768, and 769-1024 under the assumption that the synchronization is correct. The channel can be estimated by averaging samples over the same distance.

In particular, when channel 2 is obtained, starting with the sample delayed by 128 samples in these four zones, that is, 129th sample, C = [1 -1 1 -1] is multiplied by each zone and averaged. In other words, the samples indicated in red in FIG. 7B are samples of the signal transmitted at antenna 2. FIG.

The sample between the first and second peak is multiplied by the first value 1 of the code C2 = [1 -1 1 -1].

The samples between the second and third peaks are then multiplied by the second value -1 in the code.

The samples between the third and fourth peaks are multiplied by 1, the third value in the code, and the 256 samples between the fourth and the first peak of the next OFDM multiplied by the fourth value, -1. .

The channel is estimated by averaging samples at the same distance from each peak.

That is, in order to estimate channel 1, the first sample having the maximum length of 256 samples can be obtained by averaging the first blue peak value and the second and third fourth peak values. Then, the second sample of the first section, the second section, the third section, and the second sample of the fourth section are averaged to obtain the second sample of the channel. Thus all 256 samples are averaged to estimate all 256 samples of the channel with a maximum length of 256 samples.

The first and second FFT units 231 and 232 may perform fast Fourier transform on the output of the channel estimator 220.

The first and second interpolators 241 and 242 perform frequency interpolation on the outputs of the first and second FFT units 231 and 232.

The STBC decoding unit 250 performs a space time block coding (STBC) decoding on the outputs of the first and second interpolators 241 and 242.

The third FFT unit 260 may perform fast Fourier transform on the received signal.

The pilot remover 270 removes the pilot signal from the signal on which the fast Fourier transform has been performed and provides the STBC decoder 250 to the STBC decoder 250.

FIG. 5B is a block diagram illustrating an example of implementing the receiver configuration illustrated in FIG. 5A in more detail. A detailed description of components overlapping with those shown in FIG. 1A among those shown in FIG. 5B will be omitted.

The removing G.I./S/P block 250 removes a guard interval (GI) and converts an OFDM signal in series.

That is, IFFT / G.I. The blocks 141 'and 142' insert a guard interval (GI) on the input signal and perform inverse fast Fourier transform to convert the signal in the frequency domain into an OFDM signal in the time domain that can be actually transmitted.

6 is a diagram for describing a channel estimation method of a receiver according to an embodiment of the present invention.

Equations 4 to 6 below represent a process of estimating a channel by obtaining an average value of the received OFDM signal.

Δf is the interval between pilots, and r and M are the peak-to-peak intervals of the time domain and the number of samples per interval, respectively. The algorithm estimates the channel by averaging the samples between the peaks of the received signals. The first channel and the second channel are represented by Equations 5 and 6 below, respectively.

7A and 7B are diagrams illustrating the shape of an OFDM signal according to the prior art and the present invention.

FIG. 7A illustrates a form of an OFDM signal according to the prior art, in which blue is a signal component of channel 1 and red is a signal component of channel 2. FIG.

FIG. 7B illustrates a form of an OFDM signal according to the present invention, and the signal of FIG. 7A is a signal multiplied by a code proposed by the present invention. It can be seen that the red signal components of the second and fourth zones are reversed.

When the OFDM signal of the type shown in FIG. 7B is transmitted, the signal received at the receiving end has the form as shown in FIG. 8.

9 is a diagram illustrating an experimental result of a time domain channel estimation method according to an embodiment of the present invention.

In this experiment, the following conditions were applied.

Constellation: QPSK

# of bits: 10240 [bit] = 5120 symbols

Range of SNR: 15, 20 [dB]

On the other hand, an experiment was conducted to compare the channel estimation performance with the channel length of 128 samples or more and 256 samples or less of the conventional algorithm. Table 1 shows the environment in which the experiment was conducted.

Modulation level QPSK Symbol count 51200 SNR range 15, 20 [dB] channel Rayleigh Delay 1 [10 22 64 200] Delay 2 [10 + 128 22 + 128 64 + 128 219] Delay 256

The channel used in the experiment is a Rayleigh channel with four paths. The delays are shown in Table 1 as delay 1 and delay 2. The reason is that the component of channel 1 and the component of channel 2 are delayed to overlap. That is, since channel estimation is the most difficult case when channel 2 and channel 1 overlap, the delay is arbitrarily set as shown in Table 1 above.

10A and 10B, and FIGS. 11A and 11B are diagrams for comparing the performance of the channel estimation method according to an exemplary embodiment of the present invention with the prior art.

10A and 10B show channel estimation results at SNR 15 dB.

According to FIG. 10A, when the channel 1 is estimated, the channel 2 is mixed and the value of the channel 1 is not properly found. In addition, in the case of channel 2, it can be confirmed that accurate channel estimation is difficult.

10B illustrates a channel estimation result of the channel estimation method according to an embodiment of the present invention.

According to FIG. 10B, channel 1 found the channel size and position almost accurately, and channel 2 was able to estimate the channel relatively accurately. Also, when estimating channel 1, channel 2 did not mix, and so did when estimating channel 2.

11A and 11B show a channel estimation result at 20dB SNR, FIG. 11A shows a channel estimation result different from the prior art, and FIG. 11B shows a channel estimation method according to an embodiment of the present invention. The results are shown.

In the case of 20dB SNR, the same result can be seen through FIGS. 11A and 11B.

12 shows a channel estimation MSE according to the prior art and the present invention.

As shown in FIG. 12, the mean square error of SNR 0 to 24 dB was obtained by averaging the channels estimated by 100 OFDM symbols in order to obtain a difference from the present channel after channel estimation.

Here, the reason why the experiment was performed with 100 symbols is that performance is not constant when the number of symbols is small, and when 100 symbols, it is sufficient to obtain an average square error performance curve for SNR.

As described above, the channel estimation method according to an embodiment of the present invention has a constraint that the channel length should be less than 128 samples (1/8 of the OFDM symbol length) in an OFDM symbol having 1024 samples of the conventional channel estimation method. Is increased to 256 samples (1/4 of the OFDM symbol length) and the interference between the channels is reduced. In particular, it can be seen that the channel estimation performance of each channel well appears even in the overlapping section of the sample of the OFDM symbol.

On the other hand, four orthogonal codes having a correlation value of 0 with each other having a code length of 4 are four. Therefore, in the channel estimation of the MIMO system having 4 transmit antennas with a code length of 4, the proposed algorithm can be applied as shown in FIG.

FIG. 13 is a diagram for describing a method of applying the proposed algorithm in channel estimation of a MIMO system having four transmitting antennas.

In systems with four transmit antennas, channel estimation is possible regardless of the number of receive antennas.

In the time domain, a method of multiplying and transmitting an element value of a code for each interval in a sequence and a channel estimation for multiplying and averaging at a receiving end can be performed. In this case, the codes applied to each antenna are orthogonal to each other.

As described above, according to the present invention, the channel length limitation of the Comb Type Pilot Aided channel estimation can be overcome to minimize the channel interference and to determine the correct channel information.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the above-described specific embodiment, the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be understood from the technical spirit or the prospect of the present invention.

110: modulator 120: STBC coding unit
131: first multiplexer 132: second multiplexer
141: first IFFT unit 142: second IFFT unit
151: first coding unit 152: second coding unit
161: first transmitting unit 162: second transmitting unit
210: receiver 220: channel estimator
231: first FFT unit 232: second FFT unit
241: first interpolator 242: second interpolator
250: STBC decoding unit 260: third FFT unit
270: pilot remover

Claims (10)

A transmitter for transmitting an OFDM signal through a plurality of transmit antennas in a multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) system,
A modulator for modulating the input signal;
An STBC coding unit performing space time block code (STBC) on the modulated signal;
First and second multiplexing units for arranging a pilot signal provided in the block coded signal in a Comb form;
First and second IFFT units which perform an Inverse Fast Fourier Transform (IFFT) on the outputs of the first and second multiplexers;
First and second coding units configured to perform coding using codes orthogonal to each other on the outputs of the first and second IFFT units; And
And first and second transmitters for transmitting the outputs of the first and second coding units, respectively.
The second coding unit,
And multiply and code 1, -1, 1, -1 codes for four sample intervals having a predetermined length separated by the pilot signals arranged in the Comb form. delete The method of claim 1,
The first multiplexer,
Pilots are arranged in a Comb form at predetermined number intervals among a predetermined number of symbols in the OFDM signal in the frequency domain,
The first IFFT unit,
Converts the OFDM signal in the frequency domain into an OFDM signal in the time domain,
The first coding unit,
And multiply and code 1, 1, 1, and 1 codes for four sample intervals each having a predetermined length divided by the pilot. The method of claim 3,
The second multiplexer,
One pilot is arranged in a Comb form at predetermined number intervals among a predetermined number of symbols in the OFDM signal in the frequency domain,
The second IFFT unit,
And converting the OFDM signal in the frequency domain into an OFDM signal in the time domain. The method of claim 1,
The pilot signal Pilot 1 provided to the first multiplexer and the pilot signal Pilot 2 provided to the second multiplexer may be represented by the following equations;

Here, A is a constant, M is the number of samples per section divided by the pilot signals, and k 'is a pilot index. A receiver for receiving an OFDM signal transmitted through a plurality of transmit antennas through one antenna in a multi-input multi-output (MIMO OFDM) orthogonal frequency division multiplexing (OFDM) system,
A receiver configured to receive an OFDM signal, which is divided into a plurality of sample intervals of a time domain by a plurality of pilot signals arranged in a Comb form in a frequency domain, and coded through codes that are orthogonal to each other;
A channel estimator for averaging samples at the same distance with respect to the OFDM signal received through the receiver and estimating a channel through a code orthogonal to each other;
First and second FFT units performing fast Fourier transform on the output of the channel estimator;
An interpolator for performing frequency interpolation on the outputs of the first and second FFT units; And
A STBC decoding unit for performing a space time block code (STBC) decoding on the output of the interpolator;
In addition,
OFDM signal received through the receiver,
One pilot is arranged in a Comb form at a predetermined number interval among the predetermined number of symbols in the OFDM signal in the frequency domain, so that 1 and -1 for each of four sample intervals having a predetermined length between peaks in the time domain. Is multiplied by a code of, 1, -1,
The channel estimator,
And estimating a channel by multiplying each of the four sample intervals by 1, -1, 1, -1 codes. The method according to claim 6,
The orthogonal codes are
[1 1 1 1] and [1 -1 1 -1]. The method of claim 7, wherein
OFDM signal received through the receiver,
One pilot is arranged in a Comb form at a predetermined number interval among the predetermined number of symbols in the OFDM signal in the frequency domain, so that 1, 1, and 4 samples are respectively provided for a predetermined length between peaks in the time domain. Is multiplied by one and one code,
The channel estimator,
And estimating a channel by multiplying each of the four sample intervals by 1, 1, 1, 1 codes. delete The method according to claim 6,
The plurality of pilot signals Pilot 1 and Pilot 2 is a transmitter, characterized in that the following equation;

Here, A is a constant, M is the number of samples per section divided by the pilot signals, and k 'is a pilot index.

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