KR20030023525A - Method and apparatus for transferring channel information in OFDM communications - Google Patents

Abstract

PURPOSE: A method and an apparatus for sending channel information in an orthogonal frequency division multiplexing communication system are provided to reduce data of a channel transmitted to a transmitting part, thereby efficiently using up-link channel and easily obtaining adaptability according to time variation used by the transmitting side. CONSTITUTION: A prefix remover(200a) removes a prefix applied to a transmission signal by a transmitting part transmitting orthogonal frequency division multiplexed signals. A Fourier transformer(200b) transforms the prefix-removed receiving signal of a time area into a signal of a frequency area. A channel meter(200e) measures a channel value from the transformed frequency information. A compensator(200c) compensates the output data of the Fourier transformer by using the measured channel value. A parallel-to-serial converter(200d) converts serial signals output from the compensator into serial signals. A signal processor(210) processes the measured channel value before sending to the transmitting part, with compressing the channel value.

Description

Method and apparatus for transmitting channel information in orthogonal frequency division multiplexing communication system {Method and apparatus for transferring channel information in OFDM communications}

The present invention relates to a communication system using a frequency division transmission scheme in an orthogonal frequency division multiplexing method, and more particularly, to a method and apparatus for measuring information on a channel at a receiving side, compressing the information about a channel, and transmitting the compressed information to a transmitter.

Orthogonal Frequency Division Multiplexing (OFDM) is widely used for digital communications such as asymmetrical Digital Access Line (ADSL), Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), etc. have.

When multiple antennas are used in a transmitter of a communication system employing the OFDM scheme, the transmission speed can be increased by increasing the channel capacity. When using such a multi-antenna, when the transmitting end transmits in a state in which transmission channel information is known, more data can be transmitted than when transmitting without knowing channel information, thereby improving transmission performance. As such a method for improving the transmission performance, a single value decomposition (SVD), a beam forming machine, a transmission diversity antenna selection, and the like can be cited.

1 shows a general block diagram of a transmission and reception apparatus to which an OFDM scheme according to the prior art is applied. In Figure 1 the signal is transmitted from left to right. The serial / parallel converter 100a of the transmitter 100 converts a serially connected signal in parallel to perform an inverse Fourier transform. The signal processor 100b performs signal processing before modulating the parallel-converted signal by the serial / parallel converter 100a. Various methods can be used here to improve the performance of transmission and reception. Examples include SVD, beamformer, and transmission diversity antenna selection when the multi-antenna system is used in the transmitter. Among them, the SVD method can separate the channel H by SVD, such as H = UAV ^{H. Thus} , the transmitter multiplies the eigenvector U ^H and the receiver 110 multiplies the eigenvector V again to zoom the channel ^H. It is a method of increasing the transmission performance, and the beam former multiplies the multi-antenna response vector obtained by the transmission channel at the transmitting side to produce a highly directional transmission signal at the receiver. Get the effect of improving. The inverse Fourier transformer 100c is an apparatus for inverse Fourier transform (IFFT) and corresponds to a modulator that modulates an OFDM signal. In the inverse Fourier transformer 100c, the signal is converted from the frequency domain to the time domain. The parallel / serial converter 100d is a device that converts the signal converted into the time domain into serial data again because the signal converted into the time domain is parallel data. Data output from the parallel / serial converter 100d has an additional prefix CP to overcome channel fading. The final data is transmitted to the receiving end through the transmitting antenna 102. In this case, although the Tx1, Tx2, ..., TxN are represented as N transmit antennas 102, one may be used. Channel path 104 represents an example of a channel path between transmit antenna 102 and receive antenna 106. The receiving antenna 106 receives a signal transmitted through the channel path 104. Although the antennas displayed on the receiving antenna 106 are represented by M antennas as Rx1, Rx2, ..., RxM, etc., one antenna may be used similarly to the transmitting antenna 102. The serial / parallel converter 110a of the receiver 110 removes the additional prefix CP from data received by the receiving antenna 106 and then converts the additional prefix CP into parallel data. The Fourier transformer 110b performs a Fourier transform on a portion corresponding to a demodulator for demodulating an OFDM signal. The signal processor 110c is a portion that is symmetrical with the signal processor 100b in the transmitter 100. The signal processor 110c of the receiver 110 may include a device for measuring a channel. The parallel / serial converter 110d converts the parallel data into a serial.

In case of transmitting / receiving by the orthogonal frequency division multiple frequency division duplexing (OFDM / FDD) method according to the prior art, when the transmission unit cannot measure the transmission channel, the transmitter tries to increase the transmission efficiency by using a signal processing method. In the OFDM / FDD system, when the transmitter transmits the information of the channel measured by the receiver to the transmitter, channel information corresponding to each subcarrier of OFDM is transmitted. Will be sent. Therefore, when the number of transmit / receive antennas increases, the amount of information transmitted becomes too large as the number of antennas increases, so that system performance may be impaired.

The technical problem to be achieved by the present invention is to transmit the information of the channel measured by the receiver in the OFDM / FDD system to the transmitter, converts the information in the frequency domain into information in the time domain of the CP length to perform signal compression, and transmits Orthogonal Frequency Division Multiple Frequency Division (OFDM / FDD) is used to restore the channel information by decoding the information transmitted from the receiver again, thereby minimizing the loss of channel information transmitted from the receiver to the transmitter and effectively reducing the amount of channel transmission. An apparatus for transmitting channel information of a system is provided.

Another object of the present invention is to provide a channel information transmission method using the transmission device.

1 is a block diagram illustrating a transmitter / receiver of a conventional orthogonal frequency division multiple communication system.

2 is a block diagram illustrating a receiver of an orthogonal frequency division multiplexing system according to an embodiment of the present invention.

3 is a block diagram illustrating a transmitter of an orthogonal frequency division multiplexing system according to an embodiment of the present invention.

* Description of Signs of Major Parts of Drawings *

200: OFDM receiver 210: channel information transmitter

300: OFDM transmitter 310: channel information receiver

In order to achieve the above technical problem, the present invention provides a receiver of a channel information transmitter of an OFDM communication system, wherein the receiver is a prefix remover for removing a prefix added to a transmission signal from a transmitter, and a received signal in a time domain in which the prefix is removed. Fourier transformer for converting the signal of the region, a channel meter for extracting the channel value from the frequency information converted by the Fourier transformer, a compensator for compensating the output data from the Fourier transformer using the channel value measured by the channel meter And a parallel / serial converter converting the parallel signal compensated by the compensator to a serial signal and a channel value measured by the channel measurer to be transmitted to the transmitter by processing the channel value in the process of processing the channel value. And a signal processor for compressing the To provide a channel information transmission apparatus of the OFDM communication system.

The present invention also provides a serial / parallel converter for converting a serially input signal into a parallel signal in a transmitter of a channel information transmitter of an orthogonal frequency division multiplex communication system in order to achieve the above technical problem. A signal processor for converting a signal in accordance with a transmitter to process the signal before modulating the signal converted in parallel in a parallel converter, an inverse Fourier transformer for converting a signal in a frequency domain that has passed through the signal processor into a time domain signal, and the inverse Fourier A parallel / serial converter for converting the parallel signal converted into the time domain through the converter into a serial signal, and a cyclic prefix (CP) adder and receiver for adding an additional prefix to the signal output through the parallel / serial converter. Error correction decoding and signal processing of the fed back channel information signal is performed on the receiver. Recovering the measured value channel, and then provides an orthogonal frequency division multiplexing communication system, channel information transmission apparatus comprising a receiver to send the channel information to the recovered signal to the signal processor.

In order to achieve the above object, the present invention provides a first step of removing a prefix from a received signal in a time domain, a second step of converting a received signal from which the prefix has been removed into a signal in a frequency domain, and the converted frequency domain. A third step of measuring a channel value from a signal of a fourth step of compensating the output data obtained in the second step by using the measured channel value, a fifth step of converting the compensated output data into a serial signal, and And a sixth step of performing signal processing for transmitting the measured channel value to the transmitter.

In this case, the sixth step may further include converting the measured channel value of the frequency domain into a channel value of the time domain and compressing the channel value converted into the time domain.

The channel value is compressed with run length coding, ZIP coding, bit quantization coding or arithmetic coding.

The compressed channel value is converted into an error correction code and transmitted to the transmitter.

The received signal from which the prefix is removed is converted into a signal in the frequency domain by using a Fourier transformer.

The measured channel value in the frequency domain is converted to a channel value in the time domain using Least Squares.

In order to achieve the above technical problem, the present invention also provides a first step of converting a serially input signal into a parallel signal, a second step of signal processing the signal converted into the parallel signal, and time processing the signal processed signal. A third step of converting the signal into a region, a fourth step of converting the parallel signal converted into the time domain into a serial signal, and a fifth step of adding an additional prefix to the serially converted signal, wherein the second step is performed. In the step, the channel information transmission method, characterized in that the error correction decoding and signal processing of the channel information signal compressed and fed back to the receiving unit is given a signal recovered to the channel value measured by the receiving unit.

In this case, the signal processed signal is converted into a signal in the time domain using an inverse Fourier transformer.

If the channel information is compressed and then transmitted using the present invention, the number of data of the channel transmitted to the transmitter can be reduced while minimizing the loss of channel information. In addition, it is possible to efficiently use an uplink channel, and in a channel that changes frequently, data of a transmission channel can be transmitted with only a small number of data transmissions. Relatively easy.

Hereinafter, a method and apparatus for transmitting channel information in an orthogonal frequency division multiplexing communication system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram illustrating a receiver of an orthogonal frequency division multiplex (OFDM) communication system according to an embodiment of the present invention. The channel information transmitter 210 compresses an OFDM receiver 200 and received channel information and transmits the received channel information to a transmitter. It consists of. The OFDM receiver 200 includes a prefix remover 200a, a Fourier transformer 200b, a compensator 200c, a parallel / serial converter 200d and a channel meter 200e. The prefix remover 200a removes the periodic prefix from the received data. The Fourier transformer 200b is a Fourier transformer corresponding to OFDM demodulation and converts channel information in the time domain into channel information in the frequency domain. The channel measurer 200e extracts a channel value from the channel information of the Fourier transformed frequency domain. The compensator 200c compensates the output data of the Fourier transformer 200b using the channel value obtained here. The parallel / serial converter 200d converts the parallel output signal from the compensator 200c into series. The channel information transmitter 210 includes a signal processor 210a. The signal processor 201a compresses and processes the signal output from the channel measurer 200e of the OFDM receiver 200. In the signal processor 210a, when the channel value extracted from the channel measurer 200e, that is, channel information, is sent in the frequency domain as it is, the amount of information becomes very large as the number of OFDM subcarriers. Therefore, it is converted to time domain and then compressed.

The method of compressing the channel information is as follows. In the case of OFDM, the length of the CP is usually longer than the length of the channel. In other words, the CP information in time includes all the frequency information of the channel, and the length of the information CP in time is shorter than the length of the transmission signal. Therefore, when channel information on the frequency domain is converted to channel information on the time domain and sent to the transmitter, the amount of data transmitted to the transmitter is reduced.

An inverse Fourier transform may be used to convert channel information in the frequency domain into channel information in the time domain. However, the OFDM signal sent from the transmitter sets a guard band to prevent transmission of signals other than the frequency bands available by radio laws and sends 0 signals to them. Therefore, if the data received at the receiver is directly inverse Fourier transformed, the exact channel information can not be obtained by converting the channel information in the frequency domain using the exact information. Accordingly, it is preferable to use the least square method in order to efficiently change the channel information in the frequency domain to the channel information in the time domain. That is, the time domain data h '(n) that minimizes the square of the error between the Fourier transformed frequency domain data of the signal corresponding to the length of CP in the time domain and the frequency domain data obtained from the received signal is given by the following equation. Obtained as

Where N is the number of OFDM subcarriers, H (m) is frequency domain channel data of m subcarriers, and h '(n) is data in the time domain to be estimated. And n is a time index in the time domain, and its value has the length of CP. This is transmitted through a general coding method, that is, compression coding method such as run length coding or arithmetic coding, thereby further minimizing the amount of transmitted signals and converting them into error correction codes and transmitting them to the transmitting end. If so, the transmission error is minimized. The transmitted data becomes channel information in the frequency domain through error correction decoding, compression decoding, and Fourier transform in the channel information receiver (see 310 of FIG. 3) of the transmitter. The h '(n) is transmitted to the transmitter.

As a result, the channel information compression process in the signal processing process can be summarized as the step of converting the channel information in the frequency domain to the channel information in the time domain and compressing the converted result.

Subsequently, when the signal processor 210a compresses the channel value to be transmitted from the receiver to the transmitter, all possible signal processing schemes are used. For example, non-loss coding or loss coding is used. Run length coding, ZIP coding, and the like may be used for the non-lossy coding, and all domain transform coding may be used for the lossy coding, and bit quantization and arithmetic coding methods may be included. . The coded data is converted into an error correction code and then transmitted to the transmitter.

3 is a block diagram illustrating a transmitter of an orthogonal frequency division multiplexing system according to an exemplary embodiment of the present invention. The channel information compressed from the OFDM transmitter 300 and the receiver is signal-processed and transmitted to the OFDM signal processor 300b. The channel information receiver 310 is configured. OFDM transmitter 300 includes serial / parallel converter 300a, signal processor 300b, inverse Fourier transformer 300c, parallel / serial converter 300d and prefix adder 300e. The serial / parallel converter 300a converts input serial data into parallel data. The channel information receiver 310 performs error correction decoding on the data output from the receiver, and inversely processes the signal back (decoding) to restore the channel value measured by the receiver. The signal processor 300b performs signal processing on the data output from the channel information receiver 310 to improve transmission performance. The inverse Fourier transformer 300c converts the frequency domain data into the time domain through an inverse Fourier transform in a portion corresponding to the modulation of OFDM. The parallel / serial converter 300d converts the data output from the inverse Fourier transformer 300c in parallel and converts them in series. The prefix adder 300e transmits an additional prefix obtained from the data converted by the parallel / serial converter 300d before the serially converted data in order to overcome fading of the channel before transmitting the converted data.

Next, a channel information transmission method using the above-described transmission apparatus will be described.

First, the channel information transmission method in the receiver will be described.

Specifically, a prefix added to the transmission signal is removed by the transmitter which transmits the orthogonal frequency-divided signal using the prefix remover 200a. The received signal in the time domain from which the prefix is removed is converted into a signal in the frequency domain by using a Fourier transformer 200b. Subsequently, the channel measurer 200e is used to measure the channel value from the frequency information converted by the Fourier transformer 200b. The channel data measured by the channel meter 200e is used to compensate the output data of the Fourier transducer 200b. At this time, the compensator 200c is used to compensate the output data. Since the compensated output data is a parallel signal, it is converted into a serial signal using the parallel / serial converter 300d. Subsequently, the signal processor 210a performs signal processing for transmitting the channel value measured by the channel measurer to the transmitter.

Next, a method of transmitting channel information at the transmitter will be described.

Specifically, the signals input in series are converted into parallel signals. Subsequently, a signal processor performs signal processing before modulating the signal converted into the parallel signal. The signal processed in the frequency domain is converted into a signal in the time domain, and then the parallel signal converted in the time domain is converted back into a serial signal. An additional prefix is added to the serially converted signal again.

At this time, an error correction decoding and signal processing of the channel information signal compressed and fed back by the receiver and a signal recovered to the channel value measured by the receiver are given to the signal processing process.

When transmitting frequency channel data in an orthogonal frequency division multiplex (OFDM) communication system, the amount of data of a channel to be transmitted increases as the number of orthogonal frequency division multiplex (OFDM) subcarriers increases. In addition, when using multiple antennas, the amount of data to be transmitted increases as the number of antennas increases. However, if the channel information is compressed and transmitted using the present invention, the number of data of the channel transmitted to the transmitter can be reduced. Therefore, it is possible to effectively use an uplink channel, and in the case of a frequently changing channel, it is possible to send data of a transmission channel only by transmitting a small number of data, so that adaptability according to time variation used by a transmitter is relatively high. There is an effect to facilitate.

Claims (15)

In the receiving unit of the channel information transmitting apparatus of the orthogonal frequency division multiplexing communication system, The receiving unit, A prefix remover for removing a prefix added to a transmission signal by a transmitter for transmitting an orthogonal frequency-divided signal; A Fourier transformer for converting the received signal in the time domain from which the prefix is removed to a signal in the frequency domain; A channel measurer measuring a channel value from the frequency information converted by the Fourier transformer; A compensator for compensating output data from the Fourier transformer using the channel value measured by the channel meter; A parallel / serial converter converting the parallel signal compensated by the compensator into a serial signal; And Transmitting the channel value measured by the channel measurer and transmitting the signal value to a transmitter, wherein the signal processor compresses the channel value in the process of processing the channel value. Device. 2. The apparatus of claim 1, wherein the compressed channel value is compressed by run length coding. The apparatus of claim 1, wherein the compressed channel value is compressed by ZIP coding. The apparatus of claim 1, wherein the compressed channel value is compressed by bit quantization coding. The apparatus of claim 1, wherein the channel value is compressed by arithmetic coding. The apparatus of any one of claims 2 to 5, wherein the compressed channel value is converted into an error correction code and transmitted to the transmitter. In the transmitting unit of the channel information transmitting apparatus of the orthogonal frequency division multiplexing communication system, The transmitting unit, A serial / parallel converter for converting a serially input signal into a parallel signal; A signal processor which processes the signal changed in parallel in the serial / parallel converter; An inverse Fourier transformer for converting a signal in the frequency domain that has passed through the signal processor into a time domain signal; A parallel / serial converter for converting the parallel signal converted into the time domain through the inverse Fourier transformer into a serial signal; A periodic prefix (CP) adder for adding an additional prefix to the signal coming out of the parallel / serial converter; And Orthogonal frequency, comprising: a channel information receiver compressed and fed back by the receiver to error correction decoding and signal processing to recover channel values measured by the receiver, and then send the recovered signal to the signal processor; Channel information transmission apparatus of a split multiple communication system. Removing the prefix from the received signal in the time domain; Converting the received signal from which the prefix has been removed into a signal in a frequency domain; A third step of measuring a channel value from the converted frequency domain signal; A fourth step of compensating the output data obtained in the second step by using the measured channel value; Converting the compensated output data into a serial signal; And And a sixth step of performing signal processing for transmitting the measured channel value to the transmitter. The method of claim 8, wherein the sixth step is Converting the measured channel value of the frequency domain to a channel value of the time domain; And And compressing the channel value converted into the time domain. 10. The method of claim 9, wherein the channel value is compressed by run length coding, ZIP coding, bit quantization coding, or arithmetic coding. 10. The method of claim 9, wherein the compressed channel value is converted into an error correction code and transmitted to the transmitter. 9. The method of claim 8, wherein the prefixed signal is converted into a signal in a frequency domain by using a Fourier transformer. 10. The method of claim 9, wherein the measured channel value of the frequency domain is converted into a channel value of a time domain using a least square method. A first step of converting a serially input signal into a parallel signal; Signal processing the signal converted into the parallel signal; A third step of converting the signal processed signal into a signal in a time domain; A fourth step of converting the parallel signal converted into the time domain into a serial signal; And A fifth step of adding an additional prefix to the serially converted signal, And in the second step, error correction decoding and signal processing of the channel information signal compressed and fed back by the receiver to give a signal restored to the channel value measured by the receiver. 15. The method of claim 14, wherein the signal processed signal is converted into a signal in a time domain by using an inverse Fourier transformer.