Research, Competition-based Low-latency Mac Protocol

Medium access control protocol is an important part of the wireless sensornetwork protocol stack. The MAC protocol mainly solves the problem hownodes access the common medium. It plays a major role in determining networkthroughput, latency, bandwidth utilization and energy consumption. SMAC is atypical and contention-based medium access control protocol for wireless sensornetworks. This protocol is based on IEEE802.11and the low-duty-cycle schemeof periodic listen and sleep is able to significantly reduce the energyconsumption of wireless sensor networks. However, there are many virtualclusters in SMAC. When one node in one virtual cluster receives a data packetfrom its previous-hop node, it cannot retransmit the packet to its next-hop nodein another virtual cluster right now. It has to wait until the next listen time forthe next-hop node comes. That is to say, low-duty-cycle operation of SMACreduces energy consumption at the cost of increased latency and decreasedthroughput.This thesis not only introduces concepts and features of wireless sensornetworks, but also discusses design principles and key technical problems ofMAC. On the basis of the research and analysis of SMAC, this thesis proposesLDSMAC, a contention-based and low-latency MAC protocol for wirelesssensor network, and then simulates it on NS2. In order to improve the latencycaused by the periodic sleep between different virtual clusters, LDSMACapplies a global synchronization mechanism to follow the same schedule for allnodes in the whole network through fusing the information of neighbor nodes.Therefore all nodes owning the same schedule can be active at the same timeand do not need to establish the distributed listen and sleep scheme. Themechanism can solve the forward pause problem of data transmission. SoLDSMAC can reduce latency and increase throughput.Finally this thesis implements the improved MAC protocol based on NS2and designs a simulation experiment. The simulation results show that although LDSMAC achieves no less than10%in energy consumption compared to theSMAC, its transmission delay is reduced at most50%and an improvement ofabout50%in throughput.