Study On Cooperative Relay Communication System With Turbo Codes

Multiple Input Multiple Output (MIMO) is one of the key techniques for the next generation mobile communication system. However, it is difficult to configure MIMO technique on the present mobile terminals because of its rigorous demand for the distance between the antenna units. Cooperative communication provides a way to realize the diversity function of MIMO through the mutual cooperation among single-antenna terminals with large spatial distance. With the excellent performance near Shannon limit at low signal to noise ratio, Turrbo codes, as a kind of channel code, have attracted a great deal of attention since it was proposed. Therefore, the cooperative communication system combined with Turbo codes will take the advantages both from the diversity gain of cooperative communication and the coding gain of Turbo codes.In this thesis, we first introduce the model of cooperative diversity system and the three cooperative modes: amplify forward(AF), decode forward(DF) and coded cooperation(CC), including the analysis and simulations of their outage probability. Then we present the encoding and decoding theory of Turbo codes, and the discussion with different factors on bit error probability rate (BER) performance. Finally, we combine Turbo codes with cooperative diversity system to construct cooperative Turbo coding systems, and analyze the BER performance of the system. Furthermore, we discuss the influence of the location of cooperative node on the system performance. The simulation results show that the closer for the cooperative node to the user, the lower BER is.To address the issue that AF can not provide the channel coding gain and DF can not get signal soft information, we propose a decode and amplify forward (DAF) cooperative Turbo codes scheme and analyze the system BER performance. It is shown that the performance of this scheme has greatly improved compared with AF Turbo codes scheme, and the system has obtained a lower bit error rate than DF Turbo codes scheme at low signal-to-noise (SNR) rate. Further more, we combined DAF with CC to propose a mixture of DAF and CC scheme using Turbo codes. The simulation results show that the BER performance is better than all of the above discussed schemes, and the decoding success rate of cooperative node increased dramatically due to the improvement of inter-user channel status.