Reliable Data Forwarding in Wireless Sensor Networks: Delay and Energy Trade Off

Abstract

Wireless sensor networks (WSNs) are currently the topic of intense academic and industrial studies. Research is mainly devoted to the exploitation of energy saving techniques, able to prolong as much as possible the lifetime of these networks composed of hundreds of battery driven devices[1] [2]. Many envisioned applications for wireless sensor networks require immediate and guaranteed actions; think for example of medical emergency alarm, fire alarm detection, intrusion detection [3]. In such environments data has to be transported in a reliable way and in time through the sensor network towards the sink, a base station that allows the end user to access the data. Thus, besides the energy consumption, that still remains of crucial importance, other metrics such as delay and data reliability become very relevant for the proper functioning of the network [4]. These reasons have led us to investigate a very interesting trade off between the delay required to reliably deliver the data inside a WSN to the sink and the energy consumption necessary to the achievement of this goal. Typically WSNs consist of many sensor nodes scattered throughout an area of interest that monitor some physical attributes; local information gathered by these nodes has to be forwarded to a sink. Direct communication between any node and the sink could be subject only to just a small delay, if the distance between the source and the destination is short, but it suffers an important energy wasting when the distance increases. Therefore often multihop short range communications through other sensor nodes, acting as intermediate relays, are preferred in order to reduce the energy consumption in the network [5]. In such a scenario it is necessary to define efficient techniques that can ensure reliable communications with very tight delay constraint. In this work we focus our attention on the control of data transport delay and reliability in multihop scenario. Reliable communications can be achieved thanks to error control strategies: typically the most applied techniques are forward error correction (FEC), automatic repeat request (ARQ) and hybrid FEC-ARQ solutions. A simple implementation of an ARQ is represented by the Stop and Wait technique, that consists in waiting the acknowledgment of each transmitted