Multimedia applications have different QoS requirements such as, bounded latency or delay, throughput, jitter, availability, and energy consumption. Since energy efficiency is considered as the main goal of most WSNs routing protocols, the majority of these protocols does not perform well when applied to QoS-constrained WMSN. Routing techniques in WMSN can be classified similarly to those of WSNs. In [4] another categorization for WMSN routing protocols is presented. Protocols are classified based on the handled data types, data delivery model types, classes of algorithms adopted, and the used hole-bypassing approach.
Many routing schemes [4] and [5] have been proposed to address QoS requirements. In most of these schemes, only one of the desired objectives is optimized, while others are assumed as problems’ constraints [6]. In certain applications, a meta-heuristic approach [7] and [8] using a multi-objective optimization (MO) algorithms that can provide several optimal solutions may be preferred, since single design objective algorithms ignore other relevant objectives. By considering all objectives simultaneously, a set of optimal solutions can be generated, also known as the Pareto solutions [9] of the multi-objective problem. It is also known from [10] that finding optimal routes for multiple objectives in networks (multi-constrained QoS routing), is a NP-complete problem, hence efficient heuristic search algorithms based on reduced-complexity Evolutionary Algorithms (EAs) [11] are necessary.
The Expected Transmission Count (ETX) [12] metric is an estimation of the expected total number of transmissions (including retransmissions) required to deliver a packet to the destination node successfully. ETX allows finding high throughput paths on a multi-hop wireless network, and incorporates the effects of link loss ratios, asymmetry in the loss ratios between the two directions of each link, and the interference among the successive links of a path.
This paper proposes a new multi-objective approach for the WMSN routing problem that takes into account QoS parameters such as delay and ETX. A comparison of the proposed approach with two alternative routing protocols was also presented.