Study On Time Synchronization And Network Optimization In Wireless Sensor Networks

Wireless sensor networks (WSN), which is integrated by sensor, embedded computing and wireless communication technologies, is a novel technology for acquiring and processing information. Time synchronization is a critical supporting technique of WSN, a synchronized network essential for TDMA scheduling, coordination dormant, localization, data fusion and many other applications of WSN. Transmission quality and network lifetime is of great importance for the performance of energy-constrained multi-hop wireless sensor networks, in which transmission quality is measured by network utility function and network lifetime is constrained by the energy of the sensor node. Sensor nodes are energy constrained, reducing energy consumption is one of the most important conditions in design of WSN protocols. Proper MAC protocol can reduce energy consumption and extend network lifetime.First, we carry out an extensive and thorough investigation on the basic time synchronization theory and the existing synchronization mechanisms for WSN. Advantages and disadvantages of the typical synchronization mechanisms are analyzed and summarized. Traditional time synchronization mechanisms are classified into three types: the receiver-receiver based mechanisms such as RBS; the sender-receiver based mechanisms such as TPSN, LTS; the sender based mechanisms such as DMTS, FTSP.Second, based on the typical synchronization mechanisms, a new Low-power Cluster-based Time Synchronization (LCTS) protocol is proposed for multi-hop wireless sensor networks. Our mechanism combines unidirectional reference broadcast synchronization mechanism and pair-wise synchronization mechanism, reduces the consumption of synchronization packets significantly without causing synchronization lag. At the basis of hierarchical network structure, we propose a new clustering algorithm so LCTS can extend to multi-hop networks, we also compensate the clock drift to ensure high synchronization accuracy. According to packet delay decomposition in transmission, synchronization error and energy consumption analysis of LCTS are carried out, LCTS is evaluated on the Simsync platform and compared with other typical algorithms.In the end, based on cross-layer framework, we consider joint congestion, contention and energy control for multi-hop wireless sensor networks, where the goal is to find optimal end-to-end source rates at the transport layer, per-link persistence probabilities at the medium access control (MAC) layer and lifetime of the sensor nodes at the network layer to achieve the tradeoff between the maximization of the aggregate source utility and network lifetime. By applying appropriate variable transformations, we transform the non-convex and non-separable primal problem to a dual-decomposable convex problem. And through the vertical and horizontal dual decomposition, we derive a distributed sub-gradient algorithm to arrive at the global optimum. Simulations illustrate the convergence and effectiveness of our algorithm.