This article investigates the optimum threshold bounds for the signal travelling through a body surface to external nodes of a body area network. An ultra-wideband system ranging from 3.1-10.6 GHz is used for the observations of the signal transmitting through different body directions using NICT's statistical model. Through simulative investigation, the link performance is evaluated by calculating outage probability using sub-optimum Rake receivers, which are based on either partial combining (P-Rake) or selective combining (S-Rake). The optimum numbers of Rake taps are also identified. The obtained results give an assessment to better understand the effect of body direction and Rake structure on the selection of optimum threshold bounds for a channel model CM4 of body area communication.