Research On Cooperative Diversity Transmission Techniques In Land Mobile Satellite Communications

In order to satisfy the needs of multi-service transmission, the next-generationland mobile satellite communication system is required to achieve higher data ratesand spectral efficiency. Being able to fully exploit the resources of space domain,Multiple Input Multiple Output (MIMO) technology has become very important forthe further improvement of system performance, under the circumstances of limitedtransmission power and spectrum resources. However, due to the limitation ofpower consumption, size and hardware complexities at both ends, especially at theground terminal, the installation of multiple antennas on a single terminal remainsdifficult, thus tremendously hampering the development of MIMO technology. Atthis point, cooperative diversity is able to achieve virtual MIMO through thecooperation between single-antenna terminals. So, it is necessary to focus on theresearch of satellite cooperative diversity transmission technology, in order toenhance the reliability and effectiveness of signal transmission of land mobilesatellite system.First, the model of hybrid satellite-terrestrial cooperative diversitycommunication system is established, and also the signal transmissioncharacteristics of land mobile satellite channel and terrestrial wireless channel areintroduced. The appropriate channel models for the system channel modeling areselected, and the simulation is carried out. Then, the cooperative diversitytransmission technologies are introduced and suitable schemes are adopted in thesystem. Two relaying modes: Amplify-and-Forward (AF) and Decode-and-Forward(DF) is applied in the cooperative diversity system after the other transmissiontechnologies are chosen. The system outage probability and BER (Bit Error Rate)are investigated and compared in terms of the two relaying modes. Combing thesimulation results and characteristics of the cooperative diversity system, it isshown that, the optimal relaying mode is the DF mode. However, the system usingDF mode has the following disadvantages: poor outage probability performance,and low spectral efficiency due to the cooperation.And then, in order to lower the outage probability of the DF mode, CodedCooperation (CC) model is utilized in the cooperative diversity system as aimproved version of the DF mode. Theoretical analysis and computer simulationresults are consistent, showing that CC The model is able to reduce system outageprobability dramatically. As for the characteristics of poor spectral efficiency ofcooperative diversity systems, a new adaptive DF relaying strategy is proposed,incorporating the DF relaying mode, AMC（Adaptive Modulation and Coding）and adaptive relaying strategy. Simulation results show the system the new strategy hasa higher average spectral efficiency, as well as guarantee the target BER.Finally, this article is summarized and conclusions are given.