Research On The Adaptive And Enhanced Technologies Of Wireless Cooperative Relaying System

Improving the efficiency of available resource has always been one of the main drives to the development of communication technology. It is even more important for wireless communication systems with limited resource and an ever increasing demand. In the new wireless communication technologies, cooperative relaying can significantly improve system performance under low network deployment cost. Therefore, wireless cooperative relaying has received more and more concerns. However, studies have shown that spectal efficiency and energy efficiency of the wireless communication system will decrease after introduing the relay to help transmission. The reason is that the relay node needs additional orthogonal channels to transmit information. For this reason, we concerntrate on the adaptive and enhanced technologies to improve the spectral efficiency and energy efficiency of the wireless cooperative relaying system. This work was carried out on the basis of analyzing a large number of wireless cooperative relaying transmission characteristics.Firstly, the problem of improving system spectral efficiency by introducing the adaptive modulation into the wireless cooperative relaying system is studied. Selective receive mode is adapted in the system. In wireless cooperative relaying system, the source information can be transmited to destination by direct or relay mode. In the independent but not identical Rayleigh fading channel, we dirive the probability density function (PDF) and cumulative distribution function (CDF) of the receiver SNRs under different transmission modes. The system spectral efficiencies of different modes are not same, which occurs because of the wireless channel randomness. Further, average spectral efficiency and outage probability of the wireless cooperative relaying system using adaptive modulation are derived, and the operating mode selection criteria is to maximize the spectral efficiency. The analysis results are verified by using Monte Carlo simulation. The results indicate that the proposed scheme not only has simplified receiver architecture, but also can offer good performances.Secondly, the performance of amplify-and-forward (AF) relaying with adaptive modulation and selection receiver over Nakagami-m fading channels are investigated. Nakagami-m channel can be used as a general model to represent fading channel, including Rayleigh fading and Rician fading. The closed-form expressions of average spectral efficiency and outage probability of the proposed scheme over independent and non-identical Nakagami-m fading channels are derived. The simulation results demonstrate the correctness of analysis result and the superiority of the system using adaptive modulation.Thirdly, the problem of adaptive modulation using in wireless two-way relay system is analyzed. Two-way relay is an enhanced transmission technology, which employ network coding in wireless cooperative relay system. The average spectral efficiency and outage probability of two-way relay system is provided. The information exchange can be completed in two time slots, three time slots or four time slots. The simulation results show the correctness and rationality of the analysis, which can be conveniently used to evaluate the two-way relay system with adaptive modulation.Finally, the power allocation problem of two-way relay system using two time slots over Nakagami-m fading channels is discussed. Assume that the total transmission power is limited, we get the optimal power allocation schemes to minimize the system outage probability, when the instantaneous channel information or statistical channel information are known. Simulation results verify the optimality of the obtained allocation scheme.