Research Of MAC Protocols In Wireless Sensor Networks

Wireless sensor networks are considered promising infrastructures to change the physical environment,and hence our life in this environment.It has been an active research area in the past few years.Wireless sensor networks are presumed to be deployed using battery-powered stationary sensor nodes equipped with sensing, computing and wireless communicating modules.In a broad range of potential applications,inexpensive sensors can be embedded into buildings or scattered into spaces to collect,process and send out relevant information for various civilian or military purposes.Media access control(MAC) protocols are fundamental protocols and key techniques in the research of wireless sensor networks.The research on MAC protocols has the deep and broad influences to other important techniques in wireless sensor networks,including networks deployment,topology control,routing,synchronization, orientation,and even security management.Traditional MAC protocols in wireless networks can not be applied to wireless sensor networks directely.Hence,a great deal of MAC protocols has been presented,which aim at adapting the new characters and application requirement in wireless sensor networks.However,current MAC protocols are concerned with different networks character,optimize different performance target, adopt different technique,and different application.They exists different shortage and there are still many fundamental and important problems to be solved.Focusing on the performance optimization of MAC protocol in wireless sensor networks,the thesis deeply analyzes the inbeing causation which influences the performance of MAC protocol.Considering the insufficiencies in current work,for example,the optimization of energy consumption and end to end delay is not satisfied enough,the communication model is too simple,energy efficiency and load balance cannot be unified considered,theory production is difficult to be efficiently validated. The thesis presents alternative means to solve them and meanwhile do many useful attempt.The major contributions of this thesis include:1) Summarizes the design principles and classification methods for MAC protocols in wireless sensor networks;analyzes the fundamental mechanism of each recent representative MAC protocol in detail;adequately compares the characteristics, performance,and application areas of various MAC protocols in wireless sensor networks;concludes the status of current research development and points out open research issues,strategies,and emphases on MAC layer design in the future.2) Presents a Ladder Pattern Wakeup Schedule based MAC protocol-LP-MAC and its enhanced version-ELP-MAC.By arranging the nodes in multi-hop path to forward data continuously,wakeup delay is eliminated;by conflict avoiding scheme and the temporary wakeup mechanism based on link counters,conflicts between sibling nodes are decreased and the sleeping time of nodes is increased,which further improves the protocol's energy efficiency.Theoretic analysis and simulation results show that, LP-MAC protocol has both low energy consumption and stable low end-to-end delay. Based on LP-MAC,ELP-MAC improves on Ladder Pattern Wakeup Schedule and temporary wakeup mechanism.ELP-MAC adopts centralized algorithm which calculates the minimal conflict scale receiving schedule to further reduce energy cost in communication.Simulation results show that ELP-MAC can further improve energy efficiency without increasing LP-MAC delay.3) Presents a Minimal Spatial Reuse TDMA Link Scheduling(MSRLS) centralized algorithm-MSRLS-C and its distributed implementation-MSRLS-D.In common topology WSN,given a collection of link bandwidth assignment,given a collection of source-destination pairs {(s_i,t_i)},how to find the minimal scale link scheduling to make the bandwidth efficiently used,and at the same time there might be channel disturbing among nodes.In this thesis,channel interference model is studied and on the basis of which,the formalized depiction is given for MSRLS;based on the NP-Complete proving for vertex-coloring problem,we conclude that the problem of finding the optimal solution for MSRLS is also NP-Complete;the centralized approximate algorithm MSRLS-C for problem MSRLS is designed and the approximation of the algorithm is analyzed;the distributed implementation MSRLS-D for the centralized algorithm is presented,meanwhile,an upper bound of the conflict-label number and the algorithm executing time are analyzed.Simulation validates the performance of MSRLS-C and MSRLS-D,and results show that less time slots assignment and higher space reusing can be required.4) Presents a Forwarding Election-based cross-layer MAC protocol-FE-MAC. FE-MAC belongs to a kind of contention-based protocols,and also has the routing capability of the networks layer protocols.FE-MAC aims at prolonging WSN lifetime by means of improving energy efficiency and enhancing load balance.By adopting an adaptive listening method aiming in further increasing the sleeping time of sensor nodes, the energy efficiency is improved.By organizing nodes to contend packet relaying right, nodes with more residual energy have more chance to relay packets for sender, consequently,load balance and routing are achieved.The thesis analyzes the operating principle of forwarding election and discusses its correctness.Priority assignment algorithm is given and the value of time parameter is discussed.Simulation results show that the load balance of FE-MAC has obvious effect,which can efficiently extend networks life time with the cost of the increasing of transmission delay.Experiments validate that pursuing energy efficiency or load balance separately cannot acquire the maximum networks life time.We points out that load balance should be emphasized in large scale networks deploying.5) Realizes B-MAC and its improved protocol SP-MAC based on MOS.Utilizing current WSN experiment platform,we construct real networks scenery to carry out the protocol testing and comparison.Experiments show that in three different traffic load conditions,the shorten preamble frame receiving mechanism adopted SP-MAC protocol is superior to B-MAC protocol in delay and energy consumption,which validates the theoretic analysis.