Research On Coded Cooperation Technology In Wireless Communication Systems

Multipath fading is an important factor in wireless channel which still seriously degrades the efficiency and reliability of wireless communication systems in the future. Multiple input multiple output (MIMO) technology is an effective way to combat fading over wireless channels, which can improve the spectral efficiency and reliability of wireless communication systems without additional power and bandwidth consumption. In order to take full advantage of MIMO technology on mobile terminals which may not have multiple antennas, cooperation diversity has been proposed as a promising solution in recent years. This technology creates a virtual antenna array through sharing terminal's antennas, which can obtain space diversity on single antenna terminals. It is particularly attractive in wireless communication filed as it can be viewed as an effective complement of MIMO technology at low hardware cost. This dissertation intends to focus on some key technologies in cooperative diversity systems. Specifically, we mainly investigate the applications of channel coding and network coding technologies in wireless communication systems. The main contribution of our works can be summarized as follows:1. Outage probability analysis and power allocation scheme of coded cooperationAn optimum power allocation (OPA) approach is proposed base on the outage probability analysis of coded cooperation over Rayleigh fading channels. An approximation method is proposed for simplifying the outage integral, and a simple expression of the outage probability approximation bound is derived. Then, the closed-form expression of OPA coefficient is obtained based on the approximation bound. Simulation results demonstrate the validity of the theoretical analysis and the tightness of the approximation bound. In addition, the OPA method can improve the outage performance substantially with a better channel condition between relay and destination. Based on the approximation method mentioned above, the outage probability of coded cooperation over Nakagami fading channel is investigated, and then, the closed-form expression of outage probability approximation bound is derived. With the analysis of the closed-form expression, the diversity order is obtained in terms of full cooperation case at high average signal to noise ratio region. Moreover, the relationships of outage probability with cooperation level and power allocation are discussed through simulations.2. Relay selection scheme of coded cooperation For the rate reduction induced by using cyclic redundancy check (CRC) in coded cooperation, an improved threshold selection relaying scheme is proposed for coded cooperation. The upper bound of the bit error rate is derived when the rate-compatible punctured convolutional codes are used, and an optimum threshold (OT) is obtained by minimizing the bit error rate. The relay node decides whether to relay or not by comparing the estimated signal to noise ratio with the threshold. Simulations show that with the OT and power allocation method, the scheme has a better improvement over the CRC scheme.3. Joint network-channel coding cooperation schemeA high-order diversity scheme is proposed for relay cooperation with the network-channel coding approach. The information received by the relay node in different time slots is encoded with a channel coding method, and all the codes are then forwarded after network coding. With iterative maximum a posteriori decoding method, the information can be obtained at the destination node by decoding the codes received in different time slots. The pairwise error probability analysis under Rayleigh fading channel show that the proposed scheme can increase time diversity gain by forwarding the information several times in different time slots. Simulation results show that the scheme can obtain higher diversity gain in both fast and slow fading channels. Furthermore, the bit error rate performance can be improved when increasing the received signal to noise ratio of the relay node.4. Multiple-access relay cooperation schemeAs for the conventional multiple-access relay cooperation scheme, the coding redundancy is not fully utilized. In order to solve this problem, a novel cooperative scheme based on network and channel coding is proposed over ideal user-relay channel. In this scheme, the coding redundancy of different users is simultaneously forwarded through network coding at the relay node, and once the codes of one user are correctly decoded at the destination, the coding redundancy of other users can be retrieved. The approximation of outage probability and bit error rate of the proposed scheme are then deduced by analyzing the error event probability. Simulation results show that the proposed scheme is of better performance than the coded cooperation in terms of outage probability and bit error rate when the signal to noise ratio is getting higher.In addition,an improved cooperative scheme is proposed for non-ideal user-relay channel. The error event is investigated through analyzing the decoding process at the destination node. Then, the approximation of bit error rate over Nakagami channel is deduced. Simulation verified the validity of the theoretical analysis, and also analyzed the relationship between user-relay channel and the bit error rate of this scheme.