Efficient Time-division Mechanism Of Energy-constrained Wireless Sensor Networks Research

A wireless sensor network(WSN) is a wireless network consisting of spatiallydistributed nodes with capabilities of sensing, wireless communicating, data processing, andeven executing, aiming to moniter or collect environmental conditions such as temperature,humidity and light. Due to the special properties of WSNs, protocols are expected to beenergy efficient, self-oragizing, delay guaranteed and fault tolerant, among which energyefficiency is of the most concern as it directly determines the life-time of the network.We point out that widely adopted random access scheme is far from energy efficientwhile the scheduled-based scheme, especially the time-division access scheme, has greatpotential in reducing the idle listening and overhearing which are the major sources ofenergy wastage. From the perspective of improving energy efficiency, we dedicates onstudying high performance time-division access scheme and its application in periodicaldata gathering scenarios in this dissertation. The research mainly includes three parts: slotallocation scheme, time synchronization protocol and time frame design.Firstly, we propose a distributed auto-negotiation slot allocation scheme whichaccomplishes the slot allocation in a distributed and parallel way by means of contentionaccess ideas used in CSMA, what's more important, without local topology information andpacket exchanging. The key contributions are:●The confronted challenges and available problems in slot allocation are discussed.●A distributed and parallel slot allocation scheme that does not depend on localtopology information and packet exchanging is proposed.●The advantages of our auto-negotiation slot allocation scheme in energycomsuption, convergence time and adaptive ability are validated.Secondly, we summarize the relavant concepts, basic synchronization approaches,corresponding parameter estimation algorithms and available protocols in timesynchronization. Then, an energy efficient time-division flooding time synchronizationprotocol(TDFS) is proposed, which employs the one-way delay estimation method tosynchronize nodes within one hop, adopts auto-negotiation slot allocation scheme to floodsynchronization packets and introduces new global clock model that tailored for resourceconstrained sensor nodes to manage time resources. The key contributions are:●The fundamental principles of time synchronization protocols are introduced.●The specific characteristics of data flows in network-wide time synchronization protocols are summarized.●An energy efficient time-division flooding time synchronization protocol based onauto-negotiation slot allocation scheme is proposed.●A ready-to-go global clock model that supports clock tuning, frequencycompensation and global clock timer is proposed.●The protocol has been implemented with the off-the-shelf hardware and thesynchronization errors as well as the packet delay statistics are measured.●Through both real-world testing and simulation, we have proved that TDFS hashigher energy efficiency, lower synchronization error, faster convergence speedand stronger adaptive ability than FTSP.Thirdly, to further improve the synchronization precision, we claim to utilize globalclock informations provided by multiple parents and combine these observations withKalman Filter. The key contributions are:●It's the first time as we know to introduce the idea of reducing synchronizationerrors using global clock informations from multiple parents.●The state and measurement models of global clock in multihop sensor networksare derived.●The Kalman Filter is introduced to jointly estimate clock offset and frequencydifference.●It's validated through both real-world testing and simulation that our algorithm canlargerly reduce the synchronization error especially for nodes longer hops away.Finally, considering the fact that time frame design is strongly associated withapplications, we illustrate how to design a practical MAC protocol for periodical datagathering scenario with auto-negotiation slot allocation scheme and TDFS synchronizationprotocol, which is the major application model of wireless sensor networks. The keycontributions are:●The specific characteristics of data flows in periodical data gathering scenario aresummarized.●A high efficient auto-negotiation MAC protocols based on auto-negotiation slotallocation scheme dedicated for periodical data gathering is proposed.●The advantages of our protocol in delivery ratio, energy efficiency and maximumdata latency are validated through intensive simulation.