Self Organized, Flexible, Latency and Energy Efficient Protocol for Wireless Sensor Networks

摘要

This paper presents Self Organized, Flexible, Latency and Energy Efficient (SOFLEE) Protocol, a cross-layer protocol for Wireless Sensor Networks that uses TDMA based medium access scheme combined with multi-hop routing information during time slot allocation. Time slot allocation is done centrally by Master Station (MS) to provide a collision-free and fair media access. MS allocates same transmission slot to nodes that are two hops apart to increase channel spatial reuse and decrease data latency. For data gathering at MS, SOFLEE uses parenthood willingness to forward data to MS through unidirectional tree rooted at MS. Parenthood willingness of a node is decided using: (ⅰ) its location with respect to MS, to forward data in correct direction; (ⅱ) its number of children, to prevent local congestion; (ⅲ) its residual energy, to uniformly distribute energy load of being a parent node and (ⅳ) its parent-child communication link reliability to guarantee consistent data delivery. The parenthood willingness requires simple comparisons against thresholds, and thus, is very simple to implement on memory and computationally constrained nodes. Unlike a conventional TDMA-based protocol, SOFLEE provides flexibility to transfer data slots among nodes and priority based slot scheduling to adapt to dynamic traffic patterns of various Wireless Sensor Network applications. Finally, simple, memory and energy efficient techniques for: (ⅰ) hop-by-hop congestion control; (ⅱ) catering to orphan nodes, link breakdowns and node deaths are incorporated in SOFLEE. A comparative analysis of SOFLEE, FlexiTP, self organized TDMA protocol, energy efficient fast forwarding and D-MAC show that SOFLEE is 25 to 61 % more energy efficient compared to FlexiTP. Data latency of SOFLEE is 32 to 68 % less, delivery ratio is 7 to 19 %, goodput is 3 % and network lifetime is 253.784 s to 448.440 s more compared to FlexiTP.