Research On Cross Layer Optimization Design In Device-to-Device Communication System

In the trend of high speed development for mobile communication, people are pursuing more and more stringent requirements of mobile communication technology. In particular, the system capacity, rate and reliability of data transmission, the quality of service and diversified communication services all make the cellular networks bear a great deal of pressure. Just under such a background, Device-to-Device(D2D) technology has gained much attention with advantages of improving system capacity and expanding communication coverage area. This thesis mainly focuses on introducing cross layer approach to improve the performance of D2 D communication.Firstly, the cross layer optimization method based on hybrid automatic repeat request(HARQ) technology is studied for D2 D system in this thesis, which combines HARQ at data link layer with adaptive modulation and coding(AMC) at physical layer. On the one hand, the method can satisfy requirements of maximum transmission time delay and packet loss rate for data link layer. On the other hand, it makes packet transmission more reliable according to the channel quality status at physical layer. In addition, the thesis also applies three different types of HARQ into cross layer scheme and gives performance comparison. Simulation results illustrate that the method obtains a substantial system throughput gain and reduces packet loss rate. Meanwhile the cross layer scheme based on Type-III HARQ has better performance than other counterparts.Then a cross layer relay selection algorithm is proposed in D2 D system. Based on single cell of one pair of D2 D users, the channel state information at physical layer and the buffer queue state information at data link layer are both considered because of different types of services for Qo S requirements in this thesis. Seen from simulation results, the method has good feasibility to improve system throughput, reduce average transmission time delay and packet loss rate, which leads to the purpose of optimizing system performance.Finally, another cross layer relay selection strategy is optimized and could be more practicable, which is aimed at researching coexistence of several pairs of D2 D users in single cell for D2 D system. Meanwhile, the quality of service(QoS) requirement of various users is represented by a time delay factor. Satisfying time delay and packet loss rate of different QoS requirements, the best relays are chosen for all D2 D users respectively by taking channel state information and queue state information into consideration. Simulation results show that in terms of the average transmission delay, the packet loss rate and the system throughput, the method can get suitable performance optimization.