Research Of MAC Protocol For Large-scale Distributed Antenna System

The large-scale distributed antenna system(LDAS)is formed by some geographically distributed remote antenna unites(RAUs)connected to the central processing element(CPE)through low-loss optical fiber link.It has ability to cover enormous nodes.RAUs do not perform signal processing,but convert between optical signals and radio frequency signals.Owning to its evenly distributed signal power,LDAS achieves extra macro diversity gain than traditional centralized multi-antenna system,and it has higher spectral efficiency and energy efficiency.LDAS is one of key technologies in 5G communication,and the main structures to achieve indoor coverage in the future.This paper studied the performance of IEEE 802.11 point coordination function(PCF)when applied to the distributed antenna system with two main parameters varying.Then an improved PCF protocol has been provided.Moreover,a novel medium access control(MAC)protocol designed for DAS has been proposed.There are three main contributions in this paper.1)The relation between the retransmission times and the parameter CFPPeriod and CFPMaxDuration was analyzed while PCF is applied to DAS.CFPPeriod and CFPMaxDuration are two main parameters of PCF,the former is the length of a super frame and the latter is the max length of contention free period.A model of DAS with PCF has been built on OPNET platform firstly.Then the relation between the retransmission times and the parameter has been tested and explained.2)An improved PCF protocol CRP-MAC(Contention Reduced Protocol)which can improve the border nodes' performance is designed.As there is no backoff mechanism in the PCF which may cause the boder nodes to be interfered by other RAUs,the CRP-MAC protocol is designed in this paper.In addition,the performance of the protocol such as network retransmission,latency and throughput of the boder nodes is tested by OPNET,and the validity and cost of the protocol are verified.3)TP-MAC(Token based PCF MAC)protocol is designed to improve the overall network throughput.As the frequent interaction with CPE in DAS system limits the growth of network throughput,TP-MAC is designed based on routing information and drawed the idea of token ring.And a simple and efficient ID allocation algorithm is designed to solve the problem caused by improper ID assignment.The node and process model of TP-MAC are built in the OPNET platform,and the performance of the protocol is verified.The simulation results show that the TP-MAC can achieve better throuput performance than the more fiber used distributed coordination function(DCF),PCF,and time division multiple access(TDMA),which can achieve both the orderliness and efficient access,especially in the heavy load network scene.