An experimental study on the impact of human body shadowing in off-body communications channels at 2.45 GHz

Human body shadowing in off-body channels occurs when the body partially or completely obstructs the direct signal path between a bodyworn wireless device and nearby transceiver. In this paper a statistical approach is taken to analyse and model the impact of path loss, body shadowing and small scale fading caused by movements of a human at 2.45 GHz. A number of different scenarios including stationary, mobile and human body rotation were studied in an anechoic chamber to allow the isolation of environmental multipath ensuring that all changes in the received signal were caused by the human body. Under line of sight conditions and while the test subject was stationary, it is shown that signal variation is extremely low and is typically within 0.5 dB of that predicted by a log-distance path loss model. However, when the test subject's body obstructs the line of sight, two additional terms which account for body shadowing due to significant movements and fading due to small movements are necessary to allow the path loss model to be adapted for use in non-line of sight channels. It is also shown that when a person rotates in front of a nearby wireless transceiver, the received signal power may deteriorate by as much as 50 dB when using a bodyworn patch antenna.