KR20070096443A - Apparatus and method for transmitting/receiving a signal in a communication system - Google Patents

Abstract

An apparatus and a method for transmitting and receiving a signal in a communication system are provided to minimize a feedback channel overhead due to FBI(Feedback information) feedback by transmitting and receiving the signal with the minimized quantity of FBI. A method for transmitting and receiving a signal in a communication system includes the steps of: estimating a channel frequency response of a received signal; detecting at least one MCS(Modulation and Coding Scheme) level which has a bit error rate below a target bit error rate which is a target in the communication system in correspondence to the estimated channel frequency response; selecting the MCS level which has the minimum bit error rate among the MCS levels; and generating an MCS level index corresponding to the MCS level which has the minimum bit error rate as feedback information of a terminal.

Description

A device and method for transmitting and receiving signals in a communication system {APPARATUS AND METHOD FOR TRANSMITTING / RECEIVING A SIGNAL IN A COMMUNICATION SYSTEM}

1 is a diagram illustrating a base station structure of an adaptive BIC-OFDM communication system according to an embodiment of the present invention.

2 is a diagram illustrating a terminal structure of an adaptive BIC-OFDM communication system according to an exemplary embodiment of the present invention.

3 is a view showing constellations when using a general 16 QAM method

4 is a flow chart illustrating an operation of generating an FBI by the controller 227 of FIG. 2.

The present invention relates to an apparatus and method for transmitting and receiving signals in a communication system, and in particular, to adaptive bit-interleaved coded (BIC), orthogonal frequency division multiplexing (OFDM). The present invention relates to a device and a method for transmitting and receiving signals in a communication system (hereinafter, referred to as an adaptive BIC-OFDM communication system) using frequency division multiplexing (hereinafter, referred to as 'OFDM').

In the next generation communication system, active researches are being conducted to provide users with services having high speed and quality of service (QoS). In particular, in the current generation communication system, a wireless local area network (WLAN) will be referred to as a communication system and a wireless metropolitan area network (WMAN). Researches are being actively conducted to support high-speed services in the form of guaranteeing mobility and quality of service (QoS) in a broadband communication system such as a communication system. Institute of Electrical and Electronics Engineers) 802.16a / d communication system and IEEE 802.16e communication system. The IEEE 802.16a / d communication system and the IEEE 802.16e communication system are orthogonal frequency division multiplexing (OFDM) to support wideband signal transmission and reception on a physical channel of the WMAN communication system. And an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, and the like.

As described above, next-generation communication systems are actively considering using broadband for high-speed services. As such, in order to use broadband, problems caused by using the broadband must be solved. Among the problems caused by using the broadband, one of the most serious problems is caused by a frequency selective channel. Interference problem. In general, when the OFDM scheme is used, wideband transmission and reception through frequency selective fading channels is possible without using an equalizer.

In addition, the bit-interleaved coded modulation (BICM) scheme is a high order modulation scheme using binary convolutional codes. By using these methods, a high diversity gain can be obtained. The BCM-OFDM scheme is a combination of the BICM scheme and the OFDM scheme, and the BIC-OFDM scheme has already been applied to the IEEE 802.11a communication system, which is a WLAN communication system, and the IEEE 802.16 communication system, a WMAN communication system.

On the other hand, assuming that the indoor wireless environment with a relatively low mobility of the user can be assumed that the channel has a quasi-static (hereinafter referred to as "quasi-static") characteristics. In this quasi-static channel environment, adaptive modulation and coding (AMC) is used as an efficient way to improve link performance. In addition, in a communication system using a single carrier (hereinafter, referred to as a 'single carrier communication system'), a constrained bit error rate (BER) will be referred to as BER. There has been proposed a method of using a variable rate variable power quadrature amplitude modulation (M-QAM) modulation scheme (hereinafter referred to as 'constrained BER-variable rate variable power M-QAM modulation scheme'). . Here, the constrained BER refers to a target BER that is a target in the corresponding communication system. In the case of using the constrained BER-variable rate variable power M-QAM modulation scheme, a signal-to-noise ratio (SNR) range is obtained by applying different modulation levels to each transmission. It is divided into regions.

On the contrary, when the OFDM scheme is used, BER performance is affected not only by the SNR of the received signal but also by the frequency selectivity of the channel. Hereinafter, for convenience of description, the SNR of the received signal will be referred to as a 'receive SNR'. For example, for the same reception SNR, the BER is reduced correspondingly to an increase in delay spread of a root mean square (RMS). Accordingly, in a communication system using the OFDM scheme (hereinafter, referred to as an 'OFDM communication system'), a fixed link table in which SNR ranges for spectral efficiencies that can be supported in the OFDM communication system are defined. If the efficiency is lowered. Here, the spectral efficiency refers to a transmission rate, and it should be noted that the terms spectral efficiency and transmission rate are used interchangeably in the following description. Therefore, in the OFDM communication system, it is already known that the BER performance efficiency is optimal when using water-filling (hereinafter, referred to as 'water-filling') using adaptive modulation schemes.

In addition, an adaptive BIC-OFDM scheme using full feedback information (hereinafter referred to as FBI) has been proposed. Herein, the entire FBI includes FBIs for each of all sub-carriers used in a communication system using the adaptive BIC-OFDM scheme (hereinafter, referred to as an 'adaptive BIC-OFDM communication system'). Include. In the adaptive BIC-OFDM scheme, a capacity-approaching throughput is calculated by using a bit loading scheme and a power adaptation scheme based on the water-filling scheme. The bit loading method and the power adaptation method based on the water-filling method will be referred to as a water-filling AMC (hereinafter, referred to as a 'WF-AMC' method).

On the other hand, when using the OFDM scheme as described above, BER performance is affected by the frequency selectivity of the channel as well as the reception SNR. Also, for the same average received SNR, the BER decreases with increasing RMS delay spread. As an example, the received SNR required to obtain a BER of 10 ⁻⁴ varies from 5 [dB] when the RMS delay is changed from 50 [ns] to 250 [ns]. This indicates that a different link table should be used whenever channel conditions, such as delay spread, change, which is practically impossible to determine for each of all possible channels in the OFDM communication system.

When the WF-AMC scheme is used in the OFDM communication system, the terminal transmits channel state information (CSI) for each subcarrier to a base station (BS), or The traffic overhead is very large due to the feedback of the entire FBI including the FBI, such as the bit loading information, i.e., the feedback of the entire FBI through the feedback channel. In general, in a wireless communication system, it is advantageous in terms of resource efficiency of the wireless communication system to minimize the bandwidth allocated for the feedback channel. Therefore, the general wireless communication system limits the bandwidth that can be allocated to the feedback channel.

However, since the OFDM communication system basically uses a plurality of subcarriers, the amount of FBI to feed back is larger than that of the single carrier communication system, and thus the bandwidth to be used as the feedback channel is also larger than that of the single carrier communication system. In particular, as the number of subcarriers used in the OFDM communication system increases, the amount of FBI to feed back increases so that the bandwidth to be allocated to the feedback channel must also increase. As the number of subcarriers increases in the OFDM communication system, the total FBI amount also increases, so it is difficult to feed back the entire FBI using only a limited bandwidth that can be allocated to a feedback channel. As such, when it is difficult to feed back the entire FBI in the OFDM communication system, it becomes difficult to use the adaptive BIC-OFDM scheme in the OFDM communication system, so that the BER performance is degraded. The degradation of the BER performance results in deterioration of the quality of the entire OFDM communication system.

Accordingly, an object of the present invention is to provide an apparatus and method for transmitting and receiving signals in an adaptive BIC-OFDM communication system.

Another object of the present invention is to provide an apparatus and method for transmitting and receiving signals by minimizing the amount of FBI in an adaptive BIC-OFDM communication system.

The apparatus of the present invention for achieving the above objects; A terminal of a communication system, comprising: a signal receiving apparatus for receiving a signal and a signal transmitting apparatus for transmitting feedback information to a base station, wherein the signal receiving apparatus; A channel estimator for estimating a channel frequency response of the received signal of the received signal received from the base station, and at least one having a bit error rate less than a target bit error rate targeted by the communication system corresponding to the estimated channel frequency response; Detects Modulation and Coding Scheme (MCS) levels, selects an MCS level having a minimum bit error rate among the at least one MCS levels, and corresponds to an MCS level having the minimum bit error rate And a controller for generating a level index as feedback information of a terminal and controlling the feedback information to be transmitted to the base station.

Another apparatus of the present invention for achieving the above objects; A base station of a communication system, comprising: a signal transmitting apparatus for transmitting a signal and a signal receiving apparatus for receiving feedback information from a terminal, the signal transmitting apparatus; When an information vector to be transmitted to the terminal is generated, an encoder for encoding the information vector by a coding scheme according to a predetermined control to generate a codeword vector, and interleaving the codeword vector according to a preset interleaving scheme. An interleaver for generating an interleaved vector, a modulator for modulating the interleaved vector with a modulation scheme according to a predetermined control to generate a modulation vector, a controller for controlling the coding scheme and the modulation scheme in accordance with the feedback information, And a reference signal inserter for inserting a reference signal into a modulation vector, and a transmitter for transmitting the modulation vector into which the reference signal is inserted.

The method of the present invention for achieving the above objects; A method of transmitting feedback information in a terminal of a communication system, the method comprising: estimating a channel frequency response of a received signal and a bit error rate less than a target bit error rate targeted by the communication system corresponding to the estimated channel frequency response; Detecting at least one Modulation and Coding Scheme (MCS) level having a minimum value; selecting an MCS level having a minimum bit error rate among the at least one MCS level; And generating, as feedback information of the terminal, an MCS level index corresponding to an MCS level having a rate.

Another method of the present invention for achieving the above objects is; A method for transmitting a signal in a base station of a communication system, when an information vector to be transmitted to a terminal is generated, encoding the information vector into an encoding scheme corresponding to feedback information previously fed back from the terminal to generate a codeword vector. Generating an interleaved vector by interleaving the codeword vector according to a predetermined interleaving scheme, and generating a modulation vector by modulating the interleaved vector using a modulation scheme corresponding to the feedback information; And inserting a reference signal into the modulation vector and transmitting it to the terminal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

The present invention is adaptive bit-interleaved coded (BIC: referred to as 'BIC')-Orthogonal Frequency Division Multiplexing (OFDM). An apparatus and method for transmitting / receiving signals in a communication system (hereinafter, referred to as an adaptive BIC-OFDM communication system) using a scheme are provided. In addition, the present invention proposes an apparatus and method for transmitting and receiving signals by minimizing the amount of feedback information (FBI) in an adaptive BIC-OFDM communication system.

The present invention does not use the full FBI including the FBI for each of all sub-carriers used in the adaptive BIC-OFDM communication system as in the conventional BIC-OFDM communication system. In the adaptive BIC-OFDM communication system, an FBI generated in units of OFDM symbols is used. In general, the received signal received through each of the subcarriers used in the adaptive BIC-OFDM communication system is different from the signal-to-noise ratio (SNR) due to the frequency selectivity of the channel. Hereinafter referred to as 'SNR'). Hereinafter, for convenience of description, the SNR of the received signal will be referred to as a 'receive SNR'. The BIC-OFDM communication system can reduce the fluctuation due to the frequency selectivity by using an adaptive modulation and coding (AMC) scheme for the OFDM symbol. Can be.

Hereinafter, the AMC scheme proposed in the present invention will be referred to as a block AMC scheme. Here, the reason why the AMC scheme proposed in the present invention is called a block AMC scheme is because it is not based on each of the subcarriers but is based on an OFDM symbol unit. When transmitting and receiving a signal using the block AMC scheme, the terminal satisfies a constraint bit error rate (BER), which is required by the BIC-OFDM communication system. The maximum spectral efficiency is calculated, and the modulation and coding scheme (MCS: Modulation and Coding Scheme (MCS)) corresponding to the maximum spectral efficiency is selected. Here, the constrained BER refers to a target BER that is a target in the BIC-OFDM communication system. In addition, the terminal reports the selected MCS level to a base station (BS). In addition, the spectrum efficiency refers to a transmission rate, and it should be noted that the terms spectral efficiency and transmission rate are used interchangeably in the following description.

As described above, in order for the terminal to report the MCS level corresponding to the maximum spectrum efficiency to the base station, in the new BER estimation scheme and the corresponding channel state information (CSI: Channel State Information, hereinafter referred to as 'CSI'), The new MCS level selection method using the new BER estimation method must be used. In particular, the new BER estimation method and the MCS level selection method do not use water-filling (hereinafter, referred to as 'water-filling'). The procedure required for using the block AMC scheme is only a procedure for calculating an error range for candidate spectral efficiencies by averaging symbol error probabilities in each subcarrier, and thus a computational complexity compared to using the water-filling scheme. Will be much reduced.

Next, a description will be given of a base station structure of an adaptive BIC-OFDM communication system according to an embodiment of the present invention with reference to FIG. 1.

1 is a diagram illustrating a base station structure of an adaptive BIC-OFDM communication system according to an embodiment of the present invention.

Referring to FIG. 1, the base station includes a signal transmission device and a signal reception device, and the signal transmission device of the base station includes an encoder 111, an interleaver 113, and a modulator. 115, controller 117, serial to parallel converter 119, pilot symbol inserter 121, and inverse fast Fourier transform (IFFT) Transform (hereinafter referred to as IFFT) group 123, parallel to serial converter 125, and transmitter 127. In addition, although not separately illustrated in FIG. 1, the signal reception apparatus of the base station receives an FBI fed back by a terminal corresponding to the base station.

라고 칭하기로 하며, 상기 부호어 벡터

는

라고 가정하기로 하며, c_k는 상기 부호어 벡터

를 구성하는 k번째 엘리먼트(element), 즉 k번째 부호화된 비트(coded bit)를 나타낸다. 또한, 상기 제어기(117)는 상기 단말기로부터 피드백되는 FBI에 상응하게 상기 부호화기(111)에서 사용할 부호화 방식을 제어하며, 상기 제어기(117)가 상기 부호화기(111)에서 사용할 부호화 방식을 제어하는 동작에 대해서는 하기에서 설명할 것이므로 여기서는 그 상세한 설명을 생략하기로 한다. 여기서, 상기 단말기로부터 피드백되는 FBI는 OFDM 심벌을 기반으로 하여 선택된 MCS 레벨 인덱스가 되며, 이 역시 하기에서 설명할 것이므로 그 상세한 설명을 생략하기로 한다.Before describing FIG. 1, it is assumed that the adaptive BIC-OFDM communication system uses a plurality of subcarriers, for example, N subcarriers. When an information vector to be transmitted from the base station is generated, the information vector is transmitted to the encoder 111. The encoder 111 encodes the information vector by a coding scheme according to the control of the controller 117 to generate a codeword vector, and outputs the codeword vector to the interleaver 113. Here, the codeword vector

And the codeword vector

Is

And c _k is the codeword vector.

A k-th element constituting the, i.e., k-th coded bit (coded bit). In addition, the controller 117 controls the encoding scheme to be used by the encoder 111 in accordance with the FBI fed back from the terminal, and the controller 117 controls the encoding scheme to be used by the encoder 111. Since it will be described later, the detailed description thereof will be omitted. Here, the FBI fed back from the terminal becomes the MCS level index selected based on the OFDM symbol, which will be described later, and thus, detailed description thereof will be omitted.

라고 칭하기로 하며, 상기 인터리빙된 벡터

는

라고 가정하기로 하며, d_k는 상기 인터리빙된 벡터 를 구성하는 k번째 엘리먼트, 즉 k번째 인터리빙된 비트(interleaved bit)를 나타낸다. 상기 변조기(115)는 상기 인터리버(113)에서 출력한 인터리빙된 벡터를 입력하여 상기 제어기(117)의 제어에 따라 해당 변조 방식으로 변조하여 변조 벡터로 생성한 후 상기 직렬/병렬 변환기(119)로 출력한다. 여기서, 변조 벡터를

라고 칭하기로 하며, 상기 변조 벡터

는

라고 가정하기로 하며, x_n는 상기 변조 벡터

를 구성하는 n번째 엘리먼트, 즉 n번째 변조 심볼을 나타낸다. 또한, 상기 제어기(117)는 상기 단말기로부터 피드백되는 FBI에 상응하게 상기 변조기(115)에서 사용할 변조 방식을 제어하며, 상기 제어기(117)가 상기 변조기(115)에서 사용할 변조 방식을 제어하는 동작에 대해서는 하기에서 설명할 것이므로 여기서는 그 상세한 설명을 생략하기로 한다.The interleaver 113 is a bit-level interleaver. The interleaver 113 inputs a codeword vector output from the encoder 111 into an interleaved vector by interleaving in a predetermined interleaving scheme. After the generation, it outputs to the modulator 115. Here, the interleaved vector

The interleaved vector, referred to as

Is

And _k is the interleaved vector. The k-th element constituting the, i.e., the k-th interleaved bit. The modulator 115 inputs an interleaved vector output from the interleaver 113, modulates the modulated vector according to a modulation method under the control of the controller 117, and generates a modulated vector, and then converts it into the serial / parallel converter 119. Output Where modulation vector

And the modulation vector

Is

Where x _n is the modulation vector.

N-th element, that is, n-th modulation symbol constituting a. In addition, the controller 117 controls the modulation scheme to be used in the modulator 115 according to the FBI fed back from the terminal, and the controller 117 controls the modulation scheme to be used in the modulator 115. Since it will be described later, the detailed description thereof will be omitted.

The serial / parallel converter 119 inputs a modulation vector output from the modulator 115 to perform parallel conversion and outputs the same to the pilot symbol inserter 121. The pilot symbol inserter 121 inserts a pilot symbol into a signal input from the serial / parallel converter 119 and outputs the pilot symbol to the IFFT unit 123. The IFFT unit 123 inputs the signal output from the pilot symbol inserter 121 to perform an N-point IFFT and then outputs the parallel / serial converter 125. The parallel / serial converter 125 inputs a signal output from the IFFT device 123, converts the signal in series, and outputs the serial signal to the transmitter 127. The transmitter 127 inputs a signal output from the parallel / serial converter 125 to perform guard signal insertion, analog conversion, and the like, and then transmits the signal to the terminal through an antenna. .

Next, a description will be given of a terminal structure of an adaptive BIC-OFDM communication system according to an embodiment of the present invention with reference to FIG.

2 is a diagram illustrating a terminal structure of an adaptive BIC-OFDM communication system according to an embodiment of the present invention.

Referring to FIG. 2, the terminal includes a signal transmitter and a signal receiver, and the signal receiver of the terminal includes a receiver 211, a serial / parallel converter 213, and a fast Fourier transform (FFT: Fast). Fourier Transform (hereinafter referred to as 'FFT') 215, pilot symbol extractor 217, parallel / serial converter 219, demodulator 221, and deinterleaver an interleaver 223, a decoder 225, a controller 227, and a channel estimator 229. In addition, although not separately illustrated in FIG. 2, the signal transmission apparatus of the terminal feeds back the FBI to a base station corresponding to the terminal.

First, when a signal is received through an antenna, the received signal is transmitted to the receiver 211. The receiver 211 performs the received signal processing on the received signal, and then outputs the serial / parallel converter 213 after performing digital conversion, guard interval signal extraction, and the like. The serial / parallel converter 213 converts the signal output from the receiver 211 in parallel and outputs the same to the FFT unit 215. The FFT unit 215 inputs the signal output from the serial / parallel converter 213 to perform an N-point FFT and then outputs the signal to the pilot symbol extractor 217.

The pilot symbol extractor 217 inputs a signal output from the FFT unit 215 to extract a pilot symbol, and outputs the extracted pilot symbol to the channel estimator 229, and the signal from which the pilot symbol is extracted Output to the parallel / serial converter 219. The parallel / serial converter 219 inputs the signal output from the pilot symbol extractor 217 to serially convert the signal and outputs the serial signal to the demodulator 221. The demodulator 221 inputs a signal output from the parallel / serial converter 219, demodulates the demodulation method according to the control of the controller 227, and outputs the demodulated signal to the deinterleaver 223. Here, the controller 227 receives and recognizes a modulation scheme used in the modulator 115 of the base station from the base station in advance, and thus the demodulator 221 is parallel to the demodulation scheme using a demodulation scheme corresponding to the modulation scheme. Control to demodulate the signal output from the / serial converter 219.

The deinterleaver 223 deinterleaves a signal output from the demodulator 221 by a deinterleaving scheme corresponding to a deinterleaving scheme set in advance, that is, an interleaving scheme applied by the interleaver 113 of the base station. Output to the decoder 225. The decoder 225 receives a signal output from the deinterleaver 223, decodes the signal in a corresponding decoding scheme under the control of the controller 227, and restores the information vector. Here, the controller 227 receives and recognizes an encoding scheme used by the encoder 111 of the base station from the base station in advance. Therefore, the decoder 225 uses the decoding scheme corresponding to the encoding scheme. Control to decode the signal output from the interleaver 223.

Meanwhile, the channel estimator 229 estimates a channel frequency response using the pilot symbols extracted by the pilot symbol extractor 217, and then outputs the channel frequency response to the controller 227. The controller 227 inputs a channel frequency response output from the channel estimator 229 to determine the MCS level that the terminal intends to use, and generates the determined MCS level index as an FBI. Then, the controller 227 controls to feed back the generated FBI to the base station through the signal transmission device of the terminal. The controller 227 determines the MCS level according to the channel frequency response, which will be described in detail later, and thus the detailed description thereof will be omitted.

Now, the BER estimation scheme and the block AMC scheme proposed by the present invention will be described.

(1) BER estimation method

를 가지는 순시(instantaneous) BER을 추정하는 것이 굉장히 중요한데, 그 이유는 상기 블록 AMC 방식 사용을 사용함에 있어 계산 복잡도를 감소시킬 수 있기 때문이다. First, in the BER estimation method, CSI, that is, channel frequency response, for variable constellation sizes and coding rates.

It is very important to estimate the instantaneous BER with, since the computational complexity can be reduced in using the block AMC scheme.

는 채널 부호화 레이트를 나타내며,

는 최소 해밍 거리(minimum Hamming distance)를 나타낸다. 본 발명에서는 레이트 호환 천공 컨벌루셔널(RCPC: Rate Compatible Punctured Convolutional, 이하 'RCPC'라 칭하기로 한다) 부호를 사용하고, 높은 레이트의 RCPC 부호들은 해당 천공 주기에 상응하게 1/2 레이트 모 부호(mother code)를 천공하여 생성된다고 가정하기로 한다. 이 경우, 상기 순시 BER은 하기 수학식 1과 같이 추정된다.For any code C,

Represents the channel coding rate,

Denotes a minimum Hamming distance. In the present invention, a Rate Compatible Punctured Convolutional (RCPC) code is used, and the high rate RCPC codes are 1/2 rate model codes corresponding to the corresponding puncturing periods. It is assumed to be generated by drilling the mother code). In this case, the instantaneous BER is estimated as in Equation 1 below.

In Equation 1, N (d) represents the total input weight of error events at the Hamming distance of the RCPC code, and P (d, H) is between codewords having a Hamming distance d. Represents an average codeword pairwise error probability (PEP: Pairwise Error Probability, hereinafter referred to as 'PEP').

Next, an operation of calculating the average codeword PEP will be described.

를

라고 가정하고, 상기 복호기(225)가 복원한 부호어 벡터를

라고 칭하기로 한다. 이하, 설명의 편의상 상기 복호기(225)가 복원한 부호어 벡터를 복원 부호어 벡터라고 칭하기로 하며, 상기 복원 부호어 벡터

는

라고 가정하기로 한다. 상기 복원 부호어 벡터

는 상기 부호어 벡터

와 d개의 비트들에서 차이가 존재한다고 가정하기로 한다. 여기서, 상기 부호어 벡터

가 포함하는 K개의 부호화된 비트들중 첫 번째 부호화된 비트, 즉 부호화된 비트 c₁부터 연속된 총 d개의 부호화된 비트들, 즉 부호화된 비트 c₁부터 부호화된 비트 c_d까지의 연속된 d개의 부호화된 비트들이 상기 복원 부호어 벡터

와 상이하다고 가정하기로 한다. 결국, 상기 부호어 벡터

와 복원 부호어 벡터

간에는

이고,

의 관계를 가진다.First, the codeword vector

To

Suppose that the codeword vector restored by the decoder 225 is

It will be called. Hereinafter, for convenience of description, the codeword vector reconstructed by the decoder 225 will be referred to as a reconstructed codeword vector, and the reconstructed codeword vector

Is

Let's assume. The reconstructed codeword vector

Is the codeword vector

Assume that there is a difference between and bits. Where the codeword vector

The first coded bit of the K coded bits, i.e., coded bit c ₁ through a total of d consecutive coded bits, that is, the continuous _d from coded bit c ₁ to coded bit c _d . Coded bits include the reconstructed codeword vector.

Assume that is different from. Finally, the codeword vector

And restore codeword vector

Liver

ego,

Has a relationship with

라고 정의하기로 한다. 상기 가변 시퀀스

는

이며, i_k는 상기 부호어 벡터

가 포함하는 k번째 부호화된 비트 c_k가 매핑된 비트 위치를 나타낸다. 그리고, 상기 부호어 벡터

와 복원 부호어 벡터

각각의 첫 번째 비트부터 d번째 비트까지의 총 d개의 비트들 각각에 의해 선택된 신호 서브 집합(subset)의 데카르트 곱을

와

라고 정의하기로 한다. 여기서, 상기

는 i_k번째 비트가 c_k인 신호 포인트 (signal point)들에서의 서브 집합을 나타낸다. 따라서, 그레이 매핑(Gray mapping)에 의해 상기 P(d,H)는 하기 수학식 2와 같이 나타낼 수 있다.In addition, the Cartesian product of the consecutive _d coded bits from the coded bit c ₁ to the coded c _d in the OFDM symbol after the interleaving is a variable sequence.

Let's define. The variable sequence

Is

I _k is the codeword vector

Indicates a bit position to which the k-th coded bit c _{k included in} is mapped. And the codeword vector

And restore codeword vector

The Cartesian product of the signal subset selected by each of the total of d bits from each first bit to the dth bit

Wow

Let's define. Where

Denotes a subset at signal points where the i _k th bit is c _k . Accordingly, P (d, H) may be represented by Equation 2 by gray mapping.

의 계산은 채널의 주파수 선택도로 인해 굉장히 복잡해진다. 여기서, 상기

는 심볼 천이 확률을 나타낸다. 상기 심볼 천이 확률

계산의 복잡도를 감소시키기 위해서, 대부분의 심볼 에러 이벤트는 인접 신호 포인트들중 1개의 인접 신호 포인트가 송신된 심벌(transmitted symbol)로서 검출될 경우 발생한다고 가정하기로 한다. 또한, 각 심벌 에러 이벤트는 그레이 매핑으로 매핑된 1개의 부호화된 비트 에러를 발생시키기 때문에, 상기 부호어 벡터

가 포함하는 첫 번째 부호화된 비트 c₁부터 d번째 부호화된 비트 c_d까지의 d개의 부호화된 비트들은 서로 다른 서브 캐리어들에 매핑된다고 가정하기로 한다. 또한, 상기 부호화된 비트 에러 이벤트들 각각은 상기 인터리빙에 의해 서로 독립적이라고 가정하기로 한다. 그래서, d개의 부호화된 비트 에러 이벤트들에서의 결합(union)은 d개의 독립적인 에러 이벤트들로 분할될 수 있다. 따라서, 상기 부호어 벡터

의 d개의 부호화된 비 트들 c₁, c₂, ... , c_d이 모두 영(zero) 값을 갖는다고 가정하기로 한다. 그러면 상기 수학식 2는 하기 수학식 3과 같이 간략화된다.In the adaptive BIC-OFDM communication system,

The computation of is complicated by the frequency selectivity of the channel. Where

Represents the symbol transition probability. The symbol transition probability

In order to reduce the complexity of the calculation, it is assumed that most symbol error events occur when one of the adjacent signal points is detected as a transmitted symbol. In addition, since each symbol error event generates one coded bit error mapped to gray mapping, the codeword vector

It is assumed that _d coded bits from the first coded bit c ₁ to the d-th coded bit c _d which are included are mapped to different subcarriers. In addition, it is assumed that each of the encoded bit error events is independent of each other by the interleaving. Thus, the union in d coded bit error events may be divided into d independent error events. Thus, the codeword vector

It is assumed that all of the d encoded bits c ₁ , c ₂ ,..., And c _d of have a zero value. Then, Equation 2 is simplified as in Equation 3 below.

Assuming that the encoded bits are uniformly distributed to each of the subcarriers by the interleaver 113, Equation 3 is decomposed into d identical events as shown in Equation 4 below.

은 하기 수학식 5와 같이 나타낼 수 있다.Symbol Transition Probability in Equation 4

May be expressed as in Equation 5 below.

In Equation 5, Q (x) may be expressed as Equation 6 below.

계산을 최소화시키기 위해 인접 신호 포인트들만을 고려하기로 한다. 상기 심볼 천이 확률

을 계산할 경우, 해당 신호 포인트가 상기 인접 신호 포인트들이 아닌 다른 신호 포인트들로 천이되는 경우는 높은 SNR을 제외하고는 거의 발생되지 않는다.Here, the symbol transition probability

In order to minimize the calculation, only adjacent signal points are considered. The symbol transition probability

When the signal is calculated, the signal point transitions to other signal points other than the adjacent signal points is rarely generated except for high SNR.

Next, with reference to FIG. 3, a constellation of 16 quadrature amplitude modulation (QAM) schemes will be described when i = 1.

3 is a diagram illustrating constellations when using a general 16 QAM scheme.

Referring to FIG. 3, the black circles shown represent a set of signal points whose first bit position is 1, and the characteristics of each error event are classified into three types of transitions. Signal point A1 has two adjacent signal points that are different at the first position, whereas signal point A2 has three different adjacent signal points at the first position. In contrast, signal point A3 has no different adjacent signal points at the first position. In addition, Q ₁ and Q ₂ will be defined as Equation 7 and Equation 8 below.

The transition probabilities for each of signal point A1 and signal point A2 are Q ₁ + Q ₂ and Q ₁ + 2Q ₂ . By using the left and right symmetry of gray labeling, when using the 16 QAM method, B _M (H _n ) of Equation 4 may be expressed as Equation 9 below.

In addition, Q (x) can be simplified as shown in Equation 10 below.

If in a similar way to the 16 QAM system to calculate the B _M (H _n) for QPSK (Quadrature Phase Shift Keying) scheme and the 64 QAM scheme, respectively, B _M (H _n) of using the QPSK scheme is Q ₁ + Q ₂ is obtained, and B _M (H _n ) in the case of using the 64 QAM system is (28Q ₁ + 49Q ₂ ) / 48. As a result, the B _M (H _n ) is simply calculated as a function of H _n , so that the BER estimation is also very simple.

(2) Block AMC Method

The present invention proposes a rate adaptation scheme based on OFDM symbols, that is, a block AMC scheme, using an instantaneous BER estimated by the BER estimation scheme. The block AMC scheme has an advantage of reducing the amount of FBI while minimizing performance loss compared to the WF-AMC scheme. In general, the purpose of adaptive transmission is to obtain an average BER lower than the constraint BER by varying the transmission rate according to the current CSI. Therefore, the block AMC scheme transmits a signal at high speed in good channel conditions, and provides high spectral efficiencies by decreasing the transmission rate as the channel conditions worsen.

인 컨벌루셔널 부호화 방식과

인

변조 방식을 포함한다고 가정하기로 한다. 상기 MCS 레벨 l에 의해 지원되는 스펙트럼 효율은

이다. 상기 구속 BER이 Pe라고 가정할 경우, 상기 블록 AMC 방식을 사용하여 송신 레이트를 최대화시키기 위해서는 하기 수학식 11과 같은 최적화 문제를 해결해야만 한다.First, each MCS level l (l = 1, ..., I _max )

In-convolutional coding scheme

sign

It is assumed that the modulation scheme is included. The spectral efficiency supported by the MCS level l is

to be. Assuming that the constrained BER is Pe, an optimization problem such as the following Equation 11 must be solved in order to maximize a transmission rate using the block AMC scheme.

는 레이트

RCPC 부호의 천공 주기를 나타내며,

는 상기 RCPC 부호

의 해밍 거리에서 에러 이벤트들의 총 입력 웨이트를 나타낸다. In Equation 11,

The rate

Represents the puncturing period of the RCPC code,

Is the RCPC code

It represents the total input weight of error events at Hamming distance of.

를 무시할 경우, 상기 수학식 7과 수학식 8에서의

이 임의의 레벨 이상을 유지하는한 적정 BER 성능을 획득할 수 있다. 이는 결과적으로 양호한 채널 조건에서는 높은 차수의 MCS 레벨을 사용될 수 있음을 나타내는 것이다. 여기서, 상기 MCS 레벨은 다수개 존재하며, MCS 레벨이 낮을수록, 즉 MCS 레벨 인덱스가 작을수록 그 송신 레이트가 작은 부호화 레이트(coding rate)를 가지는 부호화 방식과 낮은 차수의 변조 방식의 조합을 포함한다. 일 예로, 상기 적응적 BIC-OFDM 통신 시스템에서 사용하는 MCS 레벨들의 개수가 6개라고 가정할 경우 상기 MCS 레벨들은 하기 표 1과 같이 나타낼 수 있다.Using the block AMC scheme maintains a constant average transmission energy for all sub-channels while using the transmission rate in the channel conditions without reducing the BER Pe at the terminal. remind

In the case of ignoring Equations 7 and 8,

Appropriate BER performance can be obtained as long as it remains above this arbitrary level. This in turn indicates that higher order MCS levels can be used under good channel conditions. Here, a plurality of MCS levels exist, and a lower MCS level, that is, a smaller MCS level index includes a combination of a coding scheme having a lower coding rate and a lower order modulation scheme. . For example, assuming that the number of MCS levels used in the adaptive BIC-OFDM communication system is six, the MCS levels may be represented as shown in Table 1 below.

MCS level index (l) Transmission rate (R _T ) Coding Rate (R _c ) Modulation method One One 1/2 QPSK 2 2 1/2 16 QAM 3 3 3/4 16 QAM 4 4 2/3 64 QAM 5 4.5 3/4 64 QAM 6 5 5/6 64 QAM

라고 가정할 경우, 상기 수학식 7 및 수학식 8은 하기 수학식 12 및 수학식 13과 같이 나타낼 수 있다.Also,

If it is assumed that, the equations (7) and (8) can be represented by the following equations (12) and (13).

Next, the cost function of the spectral efficiency R _T (l) will be defined as the following equation (14). Here, the spectral efficiency R _T (l) represents the spectral efficiency when MCS level l is used.

을 만족하는 상기 수학식 11에서 스펙트럼 효율을 최대화시키는 MCS 레벨을 결정하고, 그 결정한 MCS 레벨의 인덱스를 상기 기지국으로 보고한다. 일반적으로 지원 가능한 스펙트럼 효율들의 집합은 상기 BIC-OFDM 통신 시스템의 특성에 의해 미리 결정된다.Here, it is assumed that an error region using Gaussian approximation, which provides a narrower region than the standard Bhattacharyya union bound, is used. And the terminal

In Equation 11 that satisfies the MCS level maximizing the spectral efficiency is determined, and the index of the determined MCS level is reported to the base station. In general, the set of supportable spectral efficiencies is predetermined by the nature of the BIC-OFDM communication system.

개의 비트들이 된다. 여기서,

는 α보다 작은 정수를 나타낸다. 이는 종래의 상기 BIC-OFDM 통신 시스템에서 water-filling AMC(이하, 'WF-AMC'라 칭하기로 한다) 방식을 사용할 경우 모든 서브 캐리어들에 대한 전체 FBI를 피드백하는 경우에 비해 그 FBI 양이 굉장히 작아진 것으로서, 상기 FBI 피드백으로 인한 피드백 채널 오버헤드를 최소화시킨다. 즉, 상기 WF-AMC 방식을 사용할 경우에는 단말기는 총

비트를 포함하는 FBI를 상기 기지국으로 피드백해야만 하지만, 상기 블록 AMC 방식을 사용할 경우에는 단말기는 총

비트를 포함하는 FBI를 기지국으로 피드백해야만 하므로 그 FBI 양이 굉장히 작아져 피드백 채널 오버헤드가 감소되는 것이다. As described above, when using the block AMC scheme proposed by the present invention, the terminal may feed back the FBI including the index for the MCS level determined by the terminal to the base station. Thus, the amount of FBI that the terminal feeds back to the base station may indicate the MCS level indexes.

Bits. here,

Represents an integer smaller than α. In the conventional BIC-OFDM communication system, when the water-filling AMC (hereinafter, referred to as 'WF-AMC') scheme is used, the amount of the FBI is significantly higher than that of feeding back the entire FBI for all subcarriers. As small as possible, the feedback channel overhead due to the FBI feedback is minimized. That is, when using the WF-AMC method, the terminal is a total

The FBI including the bit must be fed back to the base station, but when the block AMC scheme is used, the terminal is

Since the FBI containing the bits must be fed back to the base station, the amount of the FBI is so small that the feedback channel overhead is reduced.

Next, an operation of generating the FBI by the controller 227 of FIG. 2 will be described with reference to FIG. 4.

4 is a flowchart illustrating an operation of generating an FBI by the controller 227 of FIG. 2.

을 검출한 후 413단계로 진행한다. 상기 413단계에서 상기 제어기(227)는 MCS 레벨 인덱스 l을 0으로 초기화시키고(l = 0) 415단계로 진행한다. 상기 415단계에서 상기 제어기(227)는 l+1의 인덱스를 가지는 MCS 레벨을 사용하였을 경우의 송신 레이트(R_T(l+1))에 대한 비용 함수 f(H,l+1)을 계산하고 417단계로 진행한다. 상기 417단계에서 상기 제어기(227)는 상기 비용 함수 f(H,l+1)가 상기 BIC-OFDM 통신 시스템의 구속 BER Pe 미만인지 검사한다. 상기 검사 결과 상기 비용 함수 f(H,l+1)가 상기 구속 BER Pe 미만이 아닐 경우 상기 제어기(227)는 421단계로 진행한다.Referring to FIG. 4, first, in step 411, the controller 227 estimates the channel frequency response estimated by the channel estimator 229.

After detecting the process, the process proceeds to step 413. In step 413, the controller 227 initializes the MCS level index l to 0 (l = 0) and proceeds to step 415. In step 415, the controller 227 calculates a cost function f (H, l + 1) for the transmission rate R _T (l + 1) when the MCS level having an index of l + 1 is used. Proceed to step 417. In step 417, the controller 227 checks whether the cost function f (H, l + 1) is less than the constraint BER Pe of the BIC-OFDM communication system. The controller 227 proceeds to step 421 if the cost function f (H, l + 1) is not less than the constrained BER Pe.

On the other hand, if the cost function f (H, l + 1) is less than the restrained BER Pe as a result of the test in step 417, the controller 227 proceeds to the system 419. In step 419, the controller 227 checks whether the MCS level index l + 1 is equal to the maximum value of the MCS level index used in the BIC-OFDM communication system, that is, l _max . If the MCS level index l + 1 is not equal to l _max , the controller 227 proceeds to step 423. In step 423, the controller 227 increases the MCS level index 1 by 1 and proceeds to step 415.

If the MCS level index l + 1 is equal to l _max in step 419, the controller 227 proceeds to step 421. In step 421, the controller 227 determines l + 1 as the MCS level index and ends. In this way, after the controller 227 determines the MCS level index, the controller 227 generates the determined MCS level index as an FBI and controls the signal transmission apparatus of the terminal to feed back the FBI to a base station.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention has the advantage of minimizing the amount of FBI in a BIC-OFDM communication system to transmit and receive signals, thereby minimizing feedback channel overhead due to FBI feedback. Minimizing the feedback channel overhead eventually has the advantage of increasing the resource efficiency of the BIC-OFDM communication system.

Claims (13)

A method for transmitting feedback information in a terminal of a communication system, Estimating a channel frequency response of the received signal; Detecting at least one modulation and coding scheme (MCS) level having a bit error rate less than a target bit error rate targeted by the communication system corresponding to the estimated channel frequency response; Selecting an MCS level having a minimum bit error rate among the at least one MCS level; And generating feedback information of the terminal from the MCS level index corresponding to the MCS level having the minimum bit error rate. The method of claim 1, And transmitting the generated feedback information to a base station. The method of claim 1, Detecting the at least one MCS level; A first step of initializing the MCS level index to a preset initial value; A second step of setting a first value, which is a value obtained by adding an increase value preset to the initial value, to a current value; Setting the current value to the MCS level index; A fourth step of calculating a cost function of a transmission rate when the MCS level corresponding to the MCS level index having the current value is used; A fifth process of returning to the third process by setting the MCS level index to the first value as the current value until the cost function becomes equal to or greater than the target bit error rate; and, And detecting the MCS level indexes as the at least one MCS level indexes until the cost function is equal to or greater than the target bit error rate. The method of claim 3, The cost function is expressed by Equation 15 below.

In Equation 15, f (H, l) represents a cost function of the transmission rate when using the MCS level index l in the estimated channel frequency response H,

The rate

Represents the puncturing period of Rate Compatible Punctured Convolutional (RCPC) code,

RCPC code

Represents the channel coding rate of,

RCPC code

Represents the minimum Hamming distance of,

Is the RCPC code

It represents the total input weight of the error events at the Hamming distance of, Q (x) is expressed as in Equation 16 below.

A method for transmitting a signal at a base station of a communication system, When the information vector to be transmitted to the terminal is generated, encoding the information vector into a codeword vector by encoding the information vector corresponding to the feedback information previously fed back from the terminal, Generating an interleaved vector by interleaving the codeword vector according to a predetermined interleaving scheme; Generating a modulation vector by modulating the interleaved vector by a modulation scheme corresponding to the feedback information; And inserting a reference signal into the modulation vector and transmitting the signal to the terminal. The method of claim 5, And the feedback information is an MCS level index indicating a modulation and coding scheme (MCS) level determined to be used by the terminal. The method of claim 6, The MCS level index is at least one modulation and coding scheme (MCS) level having a bit error rate less than a target bit error rate targeted by the communication system corresponding to the channel frequency response estimated by the terminal. A method of transmitting a signal in a base station, characterized in that the MCS level index corresponding to the MCS level having a minimum bit error rate. In a terminal of a communication system, A signal receiving device for receiving a signal, and a signal transmitting device for transmitting feedback information to a base station, The signal receiving device comprises; A channel estimator for estimating a channel frequency response of the received signal of the received signal received from the base station; Detect at least one Modulation and Coding Scheme (MCS) levels having a bit error rate less than a target bit error rate targeted by the communication system corresponding to the estimated channel frequency response; Selecting an MCS level having a minimum bit error rate among MCS levels, generating an MCS level index corresponding to the MCS level having the minimum bit error rate as feedback information of a terminal, and controlling the feedback information to be transmitted to the base station; A terminal comprising a controller. The method of claim 8, The controller; Initialize the MCS level index to a preset initial value, A first value, which is a value obtained by adding an increase value preset to the initial value, is set as a current value. Set the current value to the MCS level index, When using the MCS level corresponding to the MCS level index having the current value calculates the cost function of the transmission rate, The MCS level index setting and the present value are set by setting the MCS level index to the current value until the cost function becomes equal to or greater than the target bit error rate. Continuously use the cost function of the transmission rate when using the MCS level corresponding to the MCS level index, And detect the MCS level indexes as the at least one MCS level indexes until the cost function is greater than or equal to the target bit error rate. The method of claim 9, The cost function is a terminal characterized in that represented by the following equation (17).

In Equation 17, f (H, l) represents a cost function of a transmission rate when using the MCS level index l in the estimated channel frequency response H,

The rate

Represents the puncturing period of Rate Compatible Punctured Convolutional (RCPC) code,

RCPC code

Represents the channel coding rate of,

RCPC code

Represents the minimum Hamming distance of,

Is the RCPC code

It represents the total input weight of the error events at the Hamming distance of, Q (x) is expressed as in Equation 18 below.

In a base station of a communication system, A signal transmission device for transmitting a signal, and a signal reception device for receiving feedback information from a terminal, The signal transmission device; An encoder for generating the codeword vector by encoding the information vector by an encoding method according to a predetermined control when an information vector to be transmitted to the terminal is generated; An interleaver for interleaving the codeword vector according to a predetermined interleaving scheme to generate an interleaved vector; A modulator for modulating the interleaved vector by a modulation method according to a predetermined control to generate a modulation vector; A controller for controlling the encoding method and the modulation method according to the feedback information; A reference signal inserter for inserting a reference signal into the modulation vector; And a transmitter for transmitting the modulation vector inserted with the reference signal to the terminal. The method of claim 11, The feedback information base station, characterized in that the MCS level index indicating the modulation and coding scheme (MCS) level determined to be used by the terminal. The method of claim 12, The MCS level index is at least one modulation and coding scheme (MCS) level having a bit error rate less than a target bit error rate targeted by the communication system corresponding to the channel frequency response estimated by the terminal. The base station, characterized in that the MCS level index corresponding to the MCS level having the minimum bit error rate.

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