Research On Two-way Differential Coding Schemes In Distributed Wireless System With Multiple Relays

Cooperative communication technology can not only avoid the defect of traditional MIMO systems that small communication terminals are difficult to install multiple antennas in practice, but also improve the reliability of communication. Two-way communication network is equivalent to the organic integration of two unidirectional cooperative communication systems, which can be used to achieve a high rate and a high reliability in wireless communication. Unfortunately, the channel of wireless communication is so complex and changeable that it will take up a great part of the precious channel bandwidth to estimate the channel parameters correctly. Studies have found that distributed differential transmission can obtain the potential diversity gain of distributed system without channel status information at every node. But unfortunately, the existing two-way distributed differential transmission methods with low spectrum efficiency have the defects that it is difficult to design the transfer matrix and the process of detecting is complicated. The main content of this dissertation includes:(1) Introducing the method of using the linear complex field (LCF) coding technology to obtain the full diversity gain of system. Although LCF can improve the BER performance of differential transmission, the detection complexity will an grow exponentially with the increase of the number of relay node, resulting it the hardness to achieve a real-time communication.(2) In order to reduce the detection complexity at the receiving node, cyclic delay diversity (CDD) technology was introduced, which can simplify the coding and detecting process. As to the receiving end, CDD takes the multiplex channels as a one-dimension channel, which can not only decrease the number of joint detection symbol, but also significantly reduce the detection complexity.(3) Finally, based on the deep research of the integrating point of LCF and CDD, a two-way cooperative differential transmission scheme which could be adapted to arbitrary number of relay nodes is proposed. The scheme pre-codes the transmission message using LCF before transmitting. After modulating the pre-coded signals in a differential way, the two source nodes broadcast the processed data to the relays respectively. To eliminate the self-interference of differential two-way transmission, the source nodes broadcast signals to all the relay nodes in the adjacent two different time slot respectively. Then the relay nodes merge the data from the two source nodes using Hadamard operation. Finally, the relay nodes amplify and forward the received data and to the source nodes using distributed cyclic delay encoding. The experiment results indicate that the scheme proposed in this essay has a low detection complexity and is applicable for the scenarios containing arbitrary number of relay nodes. The scheme can increase encoding gain and enhance spectral efficiency, has high practical value.