Research On MAC Protocol For Cognitive Radio Wireless Sensor Networks

In recent years, wireless sensor network (WSN) has been widely used and got afast development. Meanwhile, the unlicensed band, 2.4GHz band where WSN worksis becoming overcrowded. In order to solve the problem of spectrum shortage, the con-ceptofcognitiveradiosensornetworkhasbeensuggestedasanewdirectioninwirelesscommunication, andcognitiveMACis ahottopic inthis ffeld. Ourthesisproposestwocognitive MAC protocols for centralized and distributed WSNs separately.Firstly, this thesis has made research on the centralized WSN with star topologyand proposed a cluster network based cognitive MAC. By making different clusters us-ingdifferentdatachannels, sensornodeswithsingletransceivercanaccessthelicensedchannels opportunistically without causing harmful interference to primary users. Ourproposed MAC controls the medium access from cluster level and network level, anddesign a reasonable superframe structure based on IEEE 802.15.4 superframe to co-ordinate the communications between common nodes, cluster head and coordinator.SimulationresultsshowthattheproposedcognitiveMACcanimprovetheperformanceof such centralized networks.Then, for distributed WSN, our thesis proposes a single transceiver and networkcharacteristics based MAC Protocol (STNC-MAC), a cognitive MAC that can makewirelesssensornodeswithsingletransceiveropportunisticallyaccessthelicensedspec-trum. STNC-MAC takes the network characteristics of both primary users (PUs) andsecondary users (SUs) into consideration suffciently. By deffning the concepts of DataTransmission Unit and Maximum Channel Occupation Period, STNC-MAC develope-d its data transmission pattern and available channel table management mechanism tosolve the multi-channel hidden terminal problem and blind state problem. Addition- ally, packets transmission of different lengths is supported by using the channels ofdifferent PUs utilizations, causing no or limited interference to PUs. NS2 simulationresults have shown that STNC-MAC outperforms STDCA-MAC and the original IEEE802.11 MAC in terms of throughput and average transmission delay.