A Reliable and Flexible Transmission Method in Wireless Sensor Networks

Abstract

Recent advances in wireless communication have enabled multifunctional tiny nodes to construct a wireless network by themselves Akyildiz et al. (2002). The network is called a wireless sensor network. The tiny sensor nodes are densely deployed in a physical space. They monitor physical phenomena, deliver information, and cooperate with neighbor nodes Akyildiz et al. (2002); Culler et al. (2004); Hac (2003); Zhao and Guibas (2004); Chong and Kumar (2003). The communication systems in end-to-end data transmission of wireless sensor networks employ a recovery mechanism for lost data during data transmissions because reliable data transmissions are required for various sensor network applications. Two types of retransmission have been proposed for the recovery, namely end-to-end loss recovery (E2E) and hop-by-hop loss recovery (HBH). In these mechanisms, lost packets are retransmitted from a source node or an intermediate node. If a retransmit request for lost packets is sent to a source node, the end-to-end delay may increase because channel error accumulates exponentially over multi-hops Wan et al. (2002). The well-known HBH mechanisms are PSFQ Wan et al. (2002) and RMST Stann & Heidemann (2003). PSFQ is based on ACKmessage and RMST is on NACKmessage. In HBH, when intermediate nodes cache data packets into storage, retransmissions can be requested to an intermediate relay node to reduce end-to-end delays. Because sensor nodes have limited resources, however, it is difficult for all sensor nodes to find sufficient space in their routing paths to cache data packets. There is therefore a tradeoff between end-to-end delays and memory requirements. Because data traffic on sensor networks requires a variety of levels of communication reliability (CR) depending on the application, a loss recovery method to guarantee the desired CR should be provided. Traditional loss recovery mechanisms consider only 100% reliability. In this letter, we propose a flexible loss recovery mechanism to guarantee various CRs and we discuss the tradeoff between end-to-end delays and memory requirements for various CRs. The proposed method can be widely used for the design of wireless sensor networks that require a variety of CRs.