Opportunistic relaying protocols for human monitoring in BAN

Body Area Networks (BAN) offer amazing perspectives to instrument and support humans in many aspects of their life. Among all possible applications, this paper focuses on body monitoring applications having a body equipped with a set of sensors transmitting in real-time their measures to a common sink. The underlying network topology is a star topology which is quite usual in the broad scope of wireless sensor networks. Therefore, a classical superframe structure as proposed in 802.15.3 or 802.15.4 seems to comply with the needs of such an application. Basically however, the specificities of the BAN channel can reduce the performance of such protocol. Indeed, channel time variations make the star structure unstable and temporary subject to a high packet error rate. A multi-hop mesh topology cannot counteract this problem efficiently, since the pathloss attenuation in a BAN environment is almost independent with the emitter-receiver distance. In this paper, we address this issue by considering the topology of a BAN network as a time-varying fully connected network instead of a star structure. We then show how an opportunistic cooperative mechanism based on a decode-and-forward protocol can address this issue. We derive a performance criterion based on a packet error rate outage and we discuss the implementation of this scheme in the classical superframe structure.