Characterization of the Body-Area Propagation Channel for Monitoring a Subject Sleeping

A dynamic characterization of the wireless body-area communication channel for monitoring a sleeping person is presented. The characterization uses measurements near the 2.4 GHz ISM band with measurements of eight adult subjects each over a period of at least 2 hours. Numerous transmit-receive pair (Tx-Rx) locations on and off the body for a typical body-area-network (BAN) are used. Three issues are addressed: 1) modeling of channel gain, 2) outage probability, and 3) outage duration. It is shown that over very large durations (far in excess of a delay requirement of 125 ms that is typical for many IEEE 802.15.6 medical BAN applications) there is not a reliable communications channel for star-topology BAN. The best case outage probability, with 0 dBm Tx power and - 100 dBm Rx sensitivity, is in excess of a packet-error-rate of 10%. Following from these issues the feasibility of using alternate on-body or off-body links as relays is demonstrated.