Research On Synchronization In Network Coding Based Two-way Relay Systems

Both the bidirectional relaying technology and the network coding technology can improve the throughout and the bandwidth efficiency of wireless networks. The combination of the two has been a hot topic in the research of wireless communications. In the thesis, the synchronization in the two-way relay system based on network coding is studied, including carrier synchronization of PNC, the phase ambiguity of PNC based two-way relaying and improved synchronization techniques of TNC.In the carrier synchronization of PNC, since the issue has not been adequately studied, we propose a non-data aided carrier synchronization algorithm using a differential mode loop. Firstly, we extract the users' signals. Then the two signals are fed to a differential mode loop to make the frequency and phase become the same. In the differential mode loop, the design of the phase detector is the key. Simulation results show that, the designed loop can track the frequency and phase differences between two signals well, which accomplishs the carrier sychronization between users.In the phase ambiguity of PNC based two-way relaying, we study the use of differential encoding to resolve this ambiguity and discuss it in the case of BPSK?QPSK and precoded MSK, respectively. For each modulation, we give two schemes and compare them in the respect of BER performs and device complexity. In order to deepen the understanding of differential decoder, we also study the double error probability. Finally, the correctness of the theoretical calculation is verified by Matlab simulation.In improved synchronization techniques of TNC, we apply the CPM which has good power and bandwidth efficiency to the TNC based two-way relay system and investigate problems of carrier frequency synchronization and timing synchronization. To solve the contradiction between acquisition rapidity and tracking accuracy in the traditional closed-loop frequency control system, we propose that the prior frequency discrimination by FFT can be used to control the initial frequency difference so that the acquisition performance will be improved and the tracking performance remain unchanged. Besides, the timing synchronization algorithm which adopts a closed-loop structure can track the symbol timing offset steadily. This is very suitable for continious mode transmission.