Cross-layer Design Based On Adaptive Modulation And Coding In Wireless System

With the rapid development of modern wireless communication technology and the rapid growth in demand for wireless data services, high-speed wireless data transmission needs urgently a kind of intelligent communication technology, which can resist channel fading effectively, and also has high spectrum efficiency and reliability. The issue that how to make a fine compromise between the transmission rate and reliability of wireless system and improve the spectrum utilization of the communication system in the fading channel, has become a hotspot of the research on wireless communication technology. With its intelligent transport mechanism and efficient spectrum utilization, Adaptive Modulation and Coding technology gets extensive attention and research, and becomes one of the key technologies of wireless communication systems.Modern communication network uses the layered model of Open System Interconnection, and admits data transfer between adjacent layers, but it does not exchange the information about the parameters and states of each layer. When designing the protocols of each layer, system designers don't consider the whole situation of adjacent layers jointly, which leads to that the designed system isn't able to adapt to rapidly changing mobile channel characteristics or cannot effectively use the limited radio spectrum resources. In order to solve this problem, the idea of cross-layer design arises at the historic moment.This paper mainly studies the cross-layer design which is based on AMC, on the basis of analyses and studies of the existing cross-layer scheme based on the fixed threshold AMC, and gives two kinds of improved cross-layer schemes, the maximum throughput cross-layer scheme and the cross-layer scheme combining the link layer retransmission mechanism and AMC, and makes a theory analysis and simulation of three cross-layer schemes in aspects of packet-loss-rate, packet-loss-rate and average spectrum efficiency. The simulation results show that, under the condition that the Poisson arrival rate of data packets in the link layer is high, the system packet-loss-rate of the improved maximum throughput cross-layer scheme is significantly lower than the existing high reliability cross-layer scheme, and that under the condition that the Poisson arrival rate of data packets in the link layer is low, the improved cross-layer scheme combining the retransmission mechanism and AMC can decrease the packet-error-rate and packet-loss-rate without affecting the system packet-drop-rate, and further improve the throughput and the average spectral efficiency of the system. Finally, this paper gives the packet-loss-rate curves of the high reliability cross-layer scheme and the improved maximum throughput cross-layer scheme under the different maximum Doppler frequency shift, and the stability of the performance of the designed system are verified.