Energy-Aware and Time-Critical Geo-Routing in Wireless Sensor Networks

Yingqi Xu, Wang-Chien Lee, Jianliang Xu, Gail Mitchell
2008 International Journal of Distributed Sensor Networks  
Volunteer forwarding, as an emerging routing idea for large scale, location-aware wireless sensor networks, has recently received significant attention. However, several critical research issues raised by volunteer forwarding, including communication collisions, communication voids, and time-critical routing, have not been well addressed by the existing work. In this paper, we propose a priority-based stateless geo-routing (PSGR) protocol that addresses these issues. Based on PSGR, sensor nodes
more » ... are able to locally determine their priority to serve as the next relay node using dynamically estimated network density. This effectively suppresses potential communication collisions without prolonging routing delays. PSGR also overcomes the communication void problem using two alternative stateless schemes, rebroadcast and bypass. Meanwhile, PSGR supports routing of time-critical packets with different deadline requirements at no extra communication cost. Additionally, we analyze the energy consumption and the delivery rate of PSGR as functions of the transmission range. Finally, an extensive performance evaluation has been conducted to compare PSGR with competing protocols, including GeRaf, IGF, GPSR, flooding, and MSPEED. Simulation results show that PSGR exhibits superior performance in terms of energy consumption, routing latency, and delivery rate, and soundly outperforms all of the compared protocols. These stateless routing protocols leverage the key idea of volunteer forwarding in which the next relay node is not chosen by the packet holder (the node presently holding the packet), but instead by a set of volunteering neighbor nodes based on their geographical locations. Volunteer forwarding avoids the communication overhead of exchanging state information among sensor nodes, which in turn effectively reduces communication collisions and improves the energy efficiency of a routing protocol. Figure 1 illustrates the volunteer forwarding steps. Specifically, the packet holder broadcasts a forwarding probe message to its neighbors (Fig. 1a) . Since georouting is expected to make geographical progress towards the destination, we define the nodes eligible for forwarding the packet (called potential forwarders) as those neighbors that are closer to the destination than the holder, and the area where PFs reside is called a forwarding region. Upon receiving the probe, the potential forwarders acknowledge according to some pre-designated priority (Fig. 1b) . The first acknowledger receives the packet and becomes a new packet holder (Fig. 1c) . This process is repeated until the delivery succeeds or fails. The probe message and acknowledgement message can be integrated with RTS/CTS messages from MAC layers for further reducing the communication overhead, as suggested by [2, 13] . There are two fundamental research issues involved in volunteer forwarding based geo-routing: In this paper, we present an in-depth study into the above research issues of volunteer forwarding. A novel protocol, called priority-based stateless geo-routing (PSGR), is proposed to achieve the following design objectives: Stateless architecture. The physical constraints of a wireless sensor network (e.g., large scale, error-prone wireless communications, fragile sensor nodes, limited network resources) necessitate its protocols require minimal state requirements. By employing a volunteer forwarding scheme, PSGR relieves the sensor nodes from caching and maintaining network states required by stateful approaches [20, 28, 29] . Collision restraints. Communication collisions widely exist in wireless networks. They deteriorate network performance by increasing network traffic and prolonging communication delays. In PSGR, a priority-based autonomous acknowledgment mechanism consisting of a. dynamic forwarding zone formation based on the sensor node density estimated on-the-fly, and b. autonomous acknowledgement, is proposed to avoid the contention for the wireless broadcast channel among potential forwarders. Resilience to communication void. Similarly to all geo-routing protocols, PSGR faces the communication void problem, in which a routing protocol fails to find a path to the destination, even when one actually exists. We overcome this problem by considering two complementary approaches, i.e., stateless rebroadcast and bypass, which favor different network scenarios. Differentiated time-critical control. Multiple levels of communication criticalness are supported by PSGR. Unlike stateful time-critical routing protocols that may suffer from re-routing when packets are relayed to nodes incapable of meeting routing deadlines, the nature of PSGR (i.e., volunteer forwarding) allows unqualified sensor nodes to independently disqualify themselves from being the next relay node at no communication overhead. Transmission range control. The transmission range of sensor nodes has significant impacts on energy consumption and delivery rate. We develop an analytical model with these two metrics as functions of the transmission range. The analysis provides insights on selecting radio transmission range and is important for planning and deployment of large-scale wireless sensor networks. An extensive simulation is conducted to evaluate the performance of PSGR, against state-of-the-art geo-routing protocols including GeRaf [39, 40] , IGF [2], GPSR [20], and flooding, and a time-critical routing protocol, i.e., MSPEED [7]. PSGR exhibits superior performances (in measured metrics of energy consumption, routing latency, and delivery rate) under various network conditions, and soundly outperforms all compared protocols. The rest of the paper is outlined as follows. Section 2 presents the preliminaries and examines the related work, including stateful routing protocols and stateless volunteer forwarding based routing protocols. Section 3 presents the basic design of PSGR. Section 4 analyzes the appropriate transmission range for use in PSGR. Section 5 reports our performance evaluation and simulation results. Finally, Section 6 concludes the paper with a summary and discussion of future work. Volunteer Forwarding in WSNs 317 324 Y. Xu et al. 346 Y. Xu et al.
doi:10.1080/15501320701260410 fatcat:ic763df2wzhd5eugvpt4mbmi4m