Research On Broadcast Efficiency In Asynchronous Wireless Sensor Networks

Broadcast routing is a widely applied and fundamental service in wireless sensor networks (WSNs), which can support upper layer services such as network configuration, code updating and route discovery by broadcasting a packet to the whole network. In order to reduce energy consumption, the asynchronous sleep scheduling mechanism (each node independently determines its sleep/wake schedules) is commonly adopted by nodes in WSNs. Moreover, the wireless links are usually unreliable. These two factors above keep traditional broadcast protocols with nodes always-awake in ad-hoc networks and with links reliable in wired networks cannot be used to asynchronous WSNs. In the efficient broadcast protocol’s designing in asynchronous WSNs, sleep scheduling and link unreliability are two important factors should be taken into consideration to optimize the broadcast protocol’s performance.Existing research works in asynchronous WSNs with static sink generally consider link quality information, coverage order of nodes and sleep schedule factors to optimize the broadcast performance such as broadcast delay, number of transmissions and energy consumption, and trade-off between delay efficiency and energy efficiency. One of the conventional broadcast protocols’designing ideas only utilize the information of one or two hop to perform status based broadcast, which can adapt to the dynamic changing of network. However, they make decisions based on incomplete information, which will induce inefficient transmissions and conflicts. In data dissemination strategies with mobile sink, existing research works are not designed to broadcast a packet to the whole network, but the sensor nodes transmit information to the sink node, or the sink node disseminates its real-time location to all nodes in the network via flooding. The main methods are virtual grid based strategies and cluster based strategies. However, these mechanisms cannot be used for broadcast in asynchronous WSNs with mobile sink.In this paper, we jointly consider and analyze the asynchronous sleep scheduling, unreliable wireless links, node position information and the coverage order of neighboring nodes. Then we propose two efficient broadcast protocols respectively for the asynchronous WSNs scenario with static sink and mobile sink:(1) Static sink scenario:In broadcast for asynchronous WSNs, delegation refers to a sender node delegating an uncovered node to a neighbor node already received the broadcast packet. Conventional delegation has problems for that it makes the delegation decision based on incomplete information and does not change the decision anymore even a better delegater appears. Moreover, sometimes an uncovered node is delegated by two or more nodes, which may not take advantage of the most appropriate delegation. In this paper, we propose a dynamic delegation based efficient broadcast protocol (DDEB). DDEB jointly considers the link quality information and broadcast process to delegate an uncovered node to the best covered one so far from the view of both the sender and the uncovered node. DDEB can avoid transmissions over poor links by dynamic delegation if a better sender appears to be energy efficient, and take advantage of the early covered neighbor to accelerate the broadcast process. Thus, broadcast delay efficiency and energy efficiency are improved.(2) Mobile sink scenario:We investigate the broadcast scenario that the sink node disseminating broadcast packet while moving in the network, which can benefit the network lifetime’s prolonging and the reducing of broadcast delay if the moving pattern and speed of mobile sink are appropriately set. However, the moving of the mobile sink in the network will induce the unbalance of the broadcast area, which makes the broadcast protocols in static sink scenario cannot be directly applied or inefficient if applied. This paper proposes a fast and efficient broadcast protocol (Fast and Efficient Broadcast Protocol, FEBP). We analyze the challenges after the introduction of mobile sink and the moving pattern and speed of mobile sink. Moreover, we jointly consider the broadcast process, the node location and the neighbor coverage knowledge then propose three efficient schemes of density adapted opportunistic forwarding, different delivery deferring under different broadcast process and different delivery deferring time under different neighbor knowledge. The three mechanisms solve the problem of unbalance of broadcast area and reduce the number of transmissions and energy consumption, thus improving the efficiency of the broadcast. So as to achieve the unified optimization of delay efficiency and energy efficiency.