Intentional Forwarding: Providing reliable and real-time delivery in the presence of body shadowing in breadcrumb systems

The primary goal of breadcrumb trail sensor networks is to transmit in real-time users' physiological parameters that measure life critical functions to an incident commander through reliable multihop communication. In applications using breadcrumb solutions, there are often many users working together, and this creates a well-known body shadowing effect (BSE). In this paper, we first measure the characteristics of body shadowing for 2.4 GHz sensor nodes. Our empirical results show that the body shadowing effect leads to severe packet loss, and consequently very poor real-time performance. Then we develop a novel Intentional Forwarding solution. This solution accurately detects the shadowing mode and enables selected neighbors to forward data packets. Experimental results from a fully implemented testbed demonstrate that Intentional Forwarding is able to improve the end-to-end average packet delivery ratio (PDR) from 58% to 93% and worst-case PDR from 45% to 85%, and meet soft real-time requirements even under severe body shadowing problems.