Research Of Coded Cooperation In Wireless Communication

Cooperative diversity enables single-antenna mobiles to share their antennas and generate a virtual multiple-antenna transmitter that could achieve transmit diversity to combat the multipath fading in wireless channels, and improve the uplink channel performance efficiently. The thesis mainly investigates on coded cooperation in wireless communication.First, the principle and main protocols of cooperative diversity are outlined, of which coded cooperation protocol is investigated on the system model and performance simulation. In order to avoid channel estimation, a differential modulation scheme for coded cooperation is presented, the BER (Bit Error Rate) expressions of cooperation system are analyzed, and with a CRC (Cyclic Redundant Check) method implemented at the destination, the performance can be improved under the asymmetric uplink channel conditions.Next, the cooperative diversity models based on network coding are considered. On one hand, in the foundation of network coding DF (Decode and Forward) protocol, a network coded cooperation model based on convolutional codes is presented, which would transmit more information with algebraic superposition of codes and without increasing power or channel resources; on the other hand, the LDGM (Low-Density Generator Matrix) codes are introduced to establish a cooperative diversity model based on network coding, and decoding algorithm at the destination is improved corresponding to the new codes. The LDGM scheme provides a potential application for cooperation system with long codes, which have good performance near the Shannon Limit. For the purpose of increasing the diversity order gain further, an improved network coding scheme at the relay is proposed, the diversity order in full cooperative case can be improved to three with an additional diversity path.Finally, a multi-user coded cooperation scheme is proposed, in which each cooperative user transmits different parts of source codeword to increase diversity gain. An analysis of outage probability for the multi-user cooperative system is presented, which demonstrated that the scheme can obtain high-order diversity under full cooperative condition. The optimization of cooperative level and power allocation in the system are discussed through the simulation to improve the cooperation performance further.