KR100897363B1 - SFTC-OFDM telecommunication system and receiver of the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Space-Frequency Trellis Code (SFTC) -Orthogonal Frequency Division Multiplexing (OFDM) communication system and a receiver thereof. In the apparatus, a plurality of receive antennas are grouped to define reception symbols and fading coefficients for each group, and a codeword that minimizes a branch metric is selected for Viterbi decoding.

SFTC-OFDM, Viterbi decoding, receive antennas, grouping, branch metric

Description

SFT-OFDM communication system and its receiving apparatus {SFTC-OFDM telecommunication system and receiver of the same}

1 is a configuration diagram of a conventional SFTC-OFDM communication system,

2 is a diagram for explaining an embodiment of grouping receiving antennas in K in an SFTC-OFDM communication system according to the present invention;

3 is a block diagram of an embodiment of a receiving apparatus grouping K receiving antennas in an SFTC-OFDM communication system according to the present invention;

4 is a configuration diagram of an embodiment of a SFTC-OFDM communication system according to the present invention.

The present invention relates to a Space-Frequency Trellis Code (SFTC) -Orthogonal Frequency Division Multiplexing (OFDM) communication system and a receiver thereof, and more particularly, to the complexity of a receiver in a multiple-input multiple-output (MIMO) -OFDM communication system. The present invention relates to an SFTC-OFDM system and a receiver thereof capable of satisfying a Quality of Service (QoS) while reducing the cost.

Recently, orthogonal frequency division multiplexing (OFDM) techniques and space-time encoding techniques have been actively researched to support high data rates required in next generation wireless communication services.

OFDM divides one serial data stream into N parallel data streams and transmits them on N subcarriers simultaneously to support high-speed data traffic. A sufficiently large value of N and a sufficient guard interval are provided. In this case, each subchannel has a frequency non-selective characteristic (frequency flat), so that it is possible to apply a modulation scheme having a relatively high modulation order.

As such, due to its high bandwidth efficiency and strong resistance to a multipath channel environment, OFDM has been adopted as a standard for a wireless LAN system such as IEEE 802.11a and ETSI HIPERLAN type2, and a broadcasting system such as DAB and DVB-T. .

Meanwhile, the space-time encoding technique is a technique for obtaining spatial diversity using a plurality of transmitting antennas in a fading channel environment, and is a space-time trellis code (STTC: Space-) in a frequency non-selective fading channel environment. Much research has been published on Time Trellis Code and Space-Time Block Code (STBC).

Recently, a MIMO-OFDM system based on space-time code has been proposed.

In particular, when a high-speed data is to be transmitted in a multipath fading channel, the complexity of the receiver increases greatly in a single carrier method, whereas the MIMO-OFDM system can easily implement a receiver while greatly improving a link budget. Recently, it has been actively researched as a high speed transmission method.

Such MIMO-OFDM includes a Space-Time Block Code (STBC) -OFDM system using a space-time block code, and a Space-Frequency Trellis Code (SFTC) -OFDM system using a space-time trellis code.

1 is a configuration diagram of a conventional SFTC-OFDM communication system.

As shown in FIG. 1, when the space-time trellis code (STTC) is applied to the OFDM scheme, the encoding process is performed in the frequency domain, thereby becoming SFTC-OFDM. The encoder of the SFTC-OFDM system encoded in symbol units is initialized to a zero state and then encoding is started. After the last information bit is encoded, the encoder is again in a zero state. To this end, since the information bits per symbol input to the encoder having the total s state need S / 2 0 bits at the end, the bits transmitted per symbol have S / 2 surplus bits.

Thereafter, the encoded series of symbols are sequentially loaded on an OFDM subcarrier and are OFDM modulated through the IFFT stage of each transmitter and finally output to the RF stage.

On the other hand, the decoding of the SFTC-OFDM system is performed using a Viterbi decoder. The Viterbi Decoder finds the path with the smallest distance from the frequency domain to zero state and then separates on the trellis and then merges again.

Assuming that the receiver knows the channel information, the path metric value for Viterbi decoding in the receiver operating with Maximum Likelihood (ML) decoding indicates the distance between the received symbol and any transmitted signal. Obtain by using In the case of having N transmit antennas and M receive antennas, a path metric value for Viterbi decoding is given by Equation 1 below.

와

는 s번째 OFDM 심볼의 k번째 부반송파로서, i번째 송신 안테나에서 전송된 심볼과 j번째 수신안테나로 수신된 신호를 각각 나타내며,

는 i번째 송신 안테나로부터 j번째 수신 안테나에 이르는 채널의 주파수 응답의 추정치를 나타낸다.here,

Wow

Is a kth subcarrier of the s-th OFDM symbol, and represents a symbol transmitted by the i th transmit antenna and a signal received by the j th reception antenna, respectively

Denotes an estimate of the frequency response of the channel from the i th transmit antenna to the j th receive antenna.

As described above, the ML decoding method is used in the receiver of the conventional SFTC-OFDM communication system. When using the ML decoding method, it shows the best performance, while the ML metric shows that the complexity of the receiver is further increased because the decoder is proportional to the number of transmitting and receiving antennas. Therefore, there is an urgent need for a technique capable of improving performance while reducing complexity of a receiver in an SFTC-OFDM communication system.

The present invention has been proposed to meet the above requirements, and can reduce the complexity of the receiver in a multiple-input multiple-output (MIMO) -OFDM communication system, while satisfying the Quality of Service (QoS), and the SFTC-OFDM system and Its purpose is to provide its receiving device.

The objects of the present invention are not limited to the above-mentioned objects, and other objects which are not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention for achieving the above object, in the receiving apparatus of the space-frequency frequency code multiplexing (SFTC) -OFDM (Orthogonal Frequency Division Multiplexing) communication system, by grouping a predetermined number of receive antennas, each received symbol and fading for each group Viterbi decoding by selecting a codeword that defines the coefficients and minimizes the branch metric (branch metric).

와

를 계산한 후, 이로부터

와

를 계산하고, 하기 [수학식 1]의 경로 메트릭을 최소화하는 부호어로서

를 선택하여 하기의 [수학식 1]과 같이 비터비 복호화를 위한 경로 메트릭(branch metric)을 구하는 것을 특징으로 한다. In particular, the present invention relates to a receiving apparatus of a space-frequency frequency code multiplexing (SFTC) -OFDM communication system, wherein the number of receiving antennas is m (m is a natural number). Group by a certain number K (K is a natural number), for each symbol of each group

Wow

After calculating

Wow

As a codeword to minimize the path metric of Equation 1

Select to obtain a path metric (branch metric) for Viterbi decoding as shown in Equation 1 below.

[Equation 1]

In the present invention, in the Space-Frequency Trellis Code (SFTC) -Orthogonal Frequency Division Multiplexing (OFDM) communication system, a receiver groups a predetermined number of receive antennas to define received symbols and fading coefficients for each group. Viterbi decoding is performed by selecting a codeword that minimizes the branch metric.

Specific details of other embodiments are included in the detailed description and the drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be embodied in various forms, and the present embodiments are merely provided to make the disclosure of the present invention complete and the general knowledge in the art to which the present invention belongs. It is provided to fully inform the person having the scope of the invention, the invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

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

FIG. 3 is a diagram illustrating an exemplary embodiment of a reception apparatus in which k reception antennas are grouped in an SFTC-OFDM communication system according to the present invention.

In the SFTC-OFDM communication system according to the present invention, as shown in FIG. 2, the receiving antennas are grouped into K to reduce the complexity of the receiver.

In this case, the grouping rule for determining the number of antennas of each group that exhibits optimal performance is m / K when m / K is an integer in the case of having m reception antennas. However, if m / K is not an integer, the number of antennas in each group is the nearest integer to m / K, and the excess (or lack) is evenly distributed.

By determining the number of receiving antennas included in each group in this way, it is possible to implement the SFTC-OFDM communication system having the best performance while reducing the complexity.

가 단위길이

인

로 나눠진다. 이때,

,

그리고 x=1,2,...,K이다. 그리고, 수신 신호

과 모든

를 선형 컴바이닝하면 다음의 [수학식 2]와 같이 새로 수신된 신호를 얻 을 수 있다.vector

Unit length

sign

Divided by. At this time,

,

And x = 1,2, ..., K. And the received signal

And all

By linearly combining, we can obtain a newly received signal as shown in Equation 2 below.

는 다음의 [수학식 3]과 같다. In Equation 2 above

Is shown in Equation 3 below.

를 새로운 수신 심벌로 다루게 되고, 새로운 페이딩 계수는 다음의 [수학식 4]와 같다.Thus, the receiver

Is treated as a new received symbol, and the new fading coefficient is given by Equation 4 below.

을 최대화하는

계산 을 통해서, 에너지 관점에서

는

에 대해 가능한 많은 정보를 포함한다. 이때

로 계산하므로 잡음 전력은 일정하다. In the GPRC receiver proposed in the present invention

To maximize

Through calculation, from an energy point of view

Is

Include as much information as possible about. At this time

Noise power is constant.

,

라 하면, 다음과 같은 [수학식 5]를 얻을 수 있다. therefore,

,

Then, the following [Equation 5] can be obtained.

는

의 공액전치(conjugate transpose) 벡터이다. 그러면, 위 [수학식 5]를 최대화하는

를 선택하는 연산은 행렬

의 최대 고유값(eigenvalue)에 대응되는

의 고유벡터(eigenvector)를 선택하는 것이다. At this time,

Is

Is the conjugate transpose vector of. Then, to maximize the above [Equation 5]

Operation to select the matrix

Corresponding to the maximum eigenvalue of

Is to choose the eigenvector of.

와

를 계산한 후에

와

를 계산한다. 그러므로, 모든 가능한 부호어에 대하여, 다음의 [수학식 6]과 같은 경로 메트릭을 최소화하는 부호어로서,

을 선택한다.At the receiver x = 1,2, ..., K, i = 1,2, ..., n and t = 1,2, ... l

Wow

After calculating

Wow

Calculate Therefore, for all possible codewords, as a codeword that minimizes the path metric as shown in Equation 6,

Select.

As can be seen from the GPRC (Generalized Principal Ratio Combining) metric proposed by the present invention as shown in [Equation 6], it can be seen that the complexity of the receiver according to the receiving antenna has disappeared. Not proportional to). In addition, the GPRC decoding method (see Equation 6) proposed by the present invention is m / K compared with the conventional SFTC-OFDM communication system using the ML (Maximum Likelihood) decoding method (see Equation 1). The complexity of the decoder is reduced by twice. In other words, when the parameter calculation amount of the metric is ignored, the complexity of the decoder is reduced by m / K times as compared with the conventional ML decoding method.

When K = 1, the branch metric for Viterbi decoding is equal to PRC (Principal Ratio Combining), and when K = m, it is equal to ML. Therefore, all the decoding methods used in the conventional SFTC-OFDM are included. can do.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that. Therefore, the embodiments described above are to be understood in all respects as illustrative and not restrictive.

The present invention as described above, when ignoring the parameter calculation amount of the metric, there is an effect that can reduce the complexity of the decoder by m / K times compared to the conventional ML decoding method.

In addition, in the present invention, by using the GPRC decoding method, it is possible to design an optimal decoder that satisfies the QoS of the SFTC-OFDM communication system using a flexible trade-off relationship in terms of decoder performance and complexity.

Claims (9)

delete In the reception apparatus of a Space-Frequency Trellis Code (SFTC) -Orthogonal Frequency Division Multiplexing (OFDM) communication system, In this case, the receiving antennas (where the number of receiving antennas are m (m is a natural number)) are grouped by a predetermined number K (K is a natural number) for each symbol of each group.

Wow

After calculating

Wow

As a codeword to minimize the path metric of Equation 1

Select to obtain a branch metric for Viterbi decoding as shown in [Equation 1] below, remind

Is defined as in Equation 2 below, remind

Is defined as in Equation 3 below, Grouping the receiving antennas to a predetermined number, When the number of receiving antennas is m (m is a natural number) and the predetermined number is K (K is a natural number), when m / K is an integer, the number of antennas in each group is m / K, and m If / K is not an integer, the number of antennas in each group is the nearest integer to m / K, and the spare (or lack) is evenly distributed. [Equation 1]

[Equation 2]

[Equation 3]

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