Due to the WBAN's channel instabili

Due to the WBAN's channel instability, fixed power communication protocols cannot achieve high performance in terms of energy efficiency, interference mitigation, and communicationreliability because: (a) a fixed-low transmission power can save energy and reduce interference but possibly produce very poor communication reliability; and (b) a fixed-hightransmission power improves communication reliability at the cost of more energy consumption and more significant interference. Accordingly, a power-adaptive communication protocolfor WBANs is required. To justify the necessity of such an adaptive communication protocol, we have carried out a set of experiments using the TelosB hardware platform. The CC2420radio chip in this platform has 31 different transmission power levels. In our setup, a sensor mote is attached to the wrist of a subject and can directly communicate with a gateway attachedto the chest. During the experiment, the subject stays in fivepostures of a gait cycle of walking as depicted in Fig. 1