Studies On Coded Cooperation Techniques For Multi-user Communication System

Cooperative communication combines diversity techniques with relay transmission techniques, in which multiple communication entities share the limited resource. Because of cooperation, wireless resources can be utilized efficiently. Coded cooperation integrates channel coding with diversity techniques, which can enhance the transimission reliability. In wireless communication network, relay coding integrates channel coding with cooperative relay, which can enlarge the scope of communication and improve the transmission quality. Forasmuch as forementioned advantages, we emphasize the research on diversity techniques of coded cooperation and relay coding techniques for multi-user system. The main research work is as follows:1. Cooperation level is defined as the percentage of the total bits per each source block that the user transmits for its partner, which can influence the bit error rate(BER) weightily. In this thesis, cooperative transmission scheme for multi-user is investigated, and the optimal transmission problem for the slow fading channel is discussed. In order to achieve the lowest BER, the optimal transmission rule based on “water fill” is proposed, in which the optimal cooperation level is the key. Simulation results show that the proposed optimal transmission can achieve lower BER compared with the uniform transmission under the slow fading channel.2. Signal space diversity(SSD) techniques can obtain space diversity gain efficiently, which is adapted to cooperative transmission. In this thesis, multidimensional SSD techniques are investigated, and the scheme integrated SSD with BICM-ID(bit-interleaved coded modulation with iterative decoding) is discussed. For multi-user system, the coded cooperation transmission scheme based on BICM-ID-SSD is proposed, which combine constellation dimension with the number of partners. Compared with the scheme without SSD, the proposed scheme can achieve higher diversity order under the fast fading channel.3. Compared with traditional two-dimensioal constellation, hypercube constellation can enhance the transmission BER performance. For relay-assisted multi-user system, the scheme using hypercube constellation techniques at relay can improve transmission reliability, which combines the number of users with mapping dimensions. In this thesis, basic theory and demapping algorithm with lower complexity of hypercube constellation are investigated. The relay coding based on hypercube constellation is proposed, which can improve the transmission performance on the premise of fixed users’ transmission code rate. For some traditional modulations such as QPSK, 8PSK and 16 QAM etc, the universal relay-coding matrixes with the optimal design are shown. The theoretical performance of user is derived under the slow and fast fading channel. And the performance comparision between two cases, one is with relay coding, and the other is without relay coding. Both the theoretical analysis and simulation results show that user can achieve better transmission performance with the aid of relay coding.4. Because of flexible code structure and better performance, multi-dimensional product codes are popular in cooperation. At the present time, two-dimensional product codes are mainly applicated in relay coded coopation. In this thesis, the code construction method and decoding algorithm with lower complexity are investigated. For relay-assisted multi-user system, the relay coding based on multi-dimensional product codes is proposed, which utilizes the structure of two-dimensional and three-dimensioal product codes. Considering the number of users and code words, check bits are distributed at each dimension reasonably. With the aid of relay coding, higher diversity order can be achieved on the premise of fixed users’ transmission code rate. In the text, the relay-coding matrixes are shown. Furthermore, the theoretical performance is derivated, and the simulation results are analyzed. Compared with existing researches, the relay coding based on multi-dimensional product codes can achieve higher diversity order, for the sufficient usage of the multi-dimensional structure character.5. Network coding(NC) is preferred for the efficient transmission. Joint network and fountain coding(JNFC) schemes give attention to both efficient transmission and channel adaptability. For relay-assisted multi-user system, two kinds of JNFC schemes are devised according to the channel condition of direct transmission. Based on the main idea of distributed Luby transform(DLT) codes and multi-dimensional LT(MD-LT) codes, the united degree distribution design method for JNFC schemes is proposed, which is adapted to short-length fountain codes. Considering both user and relay, the united degree distribution can debase decoding overhead and increase the transmission efficiency. Compared with existing researches, the proposed relay coding based on JNFC schemes can achieve better adaptability to the number of users and the channel condition of uplinks.