A Study On The Adaptive Modulation Technique In Wireless Cooperative Communication Networks

Cooperative communication technique can be used to improve the capacity and transmission reliability of wireless communication systems by sharing the antennas of mobile terminals, which can effectively combat the adverse impact of channel fading and reduce the outage probability of service. Adaptive transmission technique can improve the spectral efficiency of wireless communication systems under a target bit error rate(BER) by changing the mode of modulation adaptively. Antenna diversity is a powerful technique to combat channel fading, which can be used to improve the capacity and transmission reliability of wireless communication systems. The common antenna diversity technique includes receive diversity, transmit diversity, multiple-input multiple-output (MIMO) maximal ratio combining (MRC) and so on. For further improving the performance of cooperative wireless communication system, this thesis investigates the theory and technique of cooperative wireless communication system using adaptive transmission technique and several antenna diversity techniques.Chapter 1 presents a brief review of the transmission manners of cooperative communication and several common cooperative system models, adaptive modulation technique in cooperative communication systems, and MIMO antenna diversity technique and its application in cooperative systems.Chapter 2 derives the average channel capacity of single relay decode-and-forward(DF) cooperative system, multiple relay amplify-and-forward(AF) cooperative system, and multi-hop relay cooperative system which uses diversity reception technique under variable rate and variable power(VRVP), variable rate with constant power(VR), and truncated channel inversion with fixed rate(TIFR) adaptive transmission strategies, respectively. The closed-form expressions of outage probability, spectral efficiency, and the average BER of the above adaptive cooperative systems using constant power M-ary quadrature amplitude modulation(MQAM) are derived. Simulation results verify the accuracy of theoretical analysis. Numerical and simulation results show that the performance of adaptive cooperative communication systems can be improved by using diversity reception, but the distinction of performance will be getting smaller with the increase of the number of receive antenna.Chapter 3 investigates the performance of two-hop DF cooperative communication system using MIMO MRC and adaptive transmission. The exact closed-form expressions of outage probability and average channel capacity of the above system under VRVP, VR, and TIFR adaptive transmission strategies are derived. The closed-form expressions of outage probability, average spectral efficiency, and average BER of MIMO MRC two-hop DF system using constant power MQAM are also presented. Numerical and simulation results show that the performance of MIMO MRC two-hop DF cooperative communication system can be improved by increasing the number of transmit and receive antennas of the nodes.Chapter 4 investigates the performance of two-hop DF adaptive cooperative communication system using space time block codes(STBC) on transmit terminal of the communicate nodes, and MRC on receive terminal. The exact closed-form expressions of outage probability and average channel capacity of the above system under VRVP, VR, and TIFR adaptive transmission strategies are derived, respectively. The closed-form expressions of outage probability, average spectral efficiency, and average BER of STBC two-hop DF system using constant power MQAM are also obtained. We also compared the above system with the adaptive cooperative systems with MIMO MRC. Numerical and simulation results show that the performance of two-hop DF adaptive cooperative system can be effectively improved by using STBC, and that the performance of MIMO MRC adaptive cooperative system is superior to that of adaptive cooperative system with STBC.Chapter 5 concludes the thesis.