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The increasing use of short-range radio links for applications such as ward or home based physiological monitoring creates the need for a better knowledge and understanding of the indoor propagation environment. The work presented concerns a body-worn, cross-band UHF transponder used for physiological signaling within single-room environments. A modified image-based ray-tracing algorithm is used to calculate the fading characteristics for a link under the worst case condition, when the direct path between the source and chest-mounted receiver is obstructed by the body itself. The approach adopted utilizes a FDTD-generated radiation pattern of a realistic adult-male body model, incorporating the directional gains into the three-dimensional indoor ray-tracing algorithm. A description of the biomedical transponder is followed by details of the computational technique; path loss and small area fading results are then presented for a 76 m/sup 2/ area representing a hospital ward. The cumulative distribution function (CDF) results were found to be characteristically bi-modal and this novel feature is investigated in more detail.