Throughput vs. Resilience in Multi-hop Wireless Sensor Networks with Periodic Packet Traffic

In this paper we consider multi-hop wireless sensor networks using time division multiple access to radio channel. It is assumed that packets, periodically generated at the sensors at the beginning of each consecutive time frame, are to be delivered to (Internet) gateways. Although in the nominal network condition it is sufficient when the packet streams produced by each sensor reach one of the gateways, from resilience viewpoint it would be advantageous to deliver them to multiple gateways, preferably using the broadcast capability of wireless nodes. Clearly, under the assumption of periodic packet traffic, a longer frame must be used when packets are to be delivered (without losses) to multiple gateways rather to single gateways. Since traffic throughput (one packet per stream per frame) is inversely proportional to the frame length, a clear tradeoff between resilience and traffic throughput arises. In the paper we present a numerical study, using a modification of our previous optimization model for frame length minimization in the considered kind of networks, that illustrates the relation between the frame length and the number of gateways each packet stream is supposed to reach. A general conclusion is that the frame length increase is non-negligible when multiple gateways are assumed, and depends heavily on the way the resulting multicast traffic is handled and how the particular subsets of gateways are selected for particular streams.