Research On CDMA-Based Ad Hoc Networks

The main research areas involved in this dissertation include following aspects for CDMA-based Ad Hoc networks:the interference analysis;the dual reservation MAC protocol;the least-mean-square routing with load balancing;spreading code selection and a physical layer implementation scheme with a set of phase-shift codes.Due to its anti-multipath capability,good security and large capacity, CDMA technology is widely used in wireless networks.Firstly,this dissertation introduces briefly the features of Ad Hoc networks and key technologies for CDMA-based Ad Hoc networks,and followed by the research meanings.On the physical layer,the interference in CDMA-based Ad Hoc networks is analyzed in this dissertation and the relationship between SIR with the transmitting node distribution density,code set normalized crosscorrelation is given under the poisson distribution model. Theoretically,the results show that it is necessary for CDMA-based Ad Hoc networks to detect multiple access interference on the physical layer, avoid collision on the MAC layer and select the code set with less normalized crosscorrelation.On the MAC layer,the channel allocation,contention and collision avoidance should be solved for a CDMA-based Ad Hoc network.A dual-reservation MAC protocol for a CDMA-based Ad Hoc network is presented in this dissertation,the purpose is to provide better channel sharing capability and real-time service transmission,improve the network performance in further,the simulation results show that the presented DRC protocol can degrade collision effectively under heavy load condition,the throughput is improved greatly and the transmission delay half less than that for IEEE802.11 DCF.On the network layer,a feasible way to solve congestion problem, avoid hot-spot area in networks and prolong the existing span of an Ad Hoc network is to adopt a routing protocol with load balancing capability. A least-mean-sqare routing protocol is given in this dissertation and the simulation results show it has better load balancing performance in the routing finding process.Under the same load condition,the load variance for LMSR is only half of that for DLAR and only one-sixth of that for ADOV,that result shows LMSR is an effective load balancing routing protocol.For a CDMA-based Ad Hoc network,spreading code set selection and the physical layer implementation are two of the most important factors which decide the performance of a network.In the dissertation, several common code sets are analyzed for Ad Hoc networks,and on this basis,a new physical layer implementation scheme,which uses the phase-shift code set of a sequence as the spreading code set,is presented and the feasibility is analyzed.Finally,under the preposed signal model, the MAI is analyzed for a phase-shift code set of a m sequence,the result shows its MAI is much less than those which uses other code sets such as GOLD or WALSH code sets.