Experimental link channel characteristics in wireless body sensor systems

In the resource-constrained environment such as wireless body sensor networks (WBSNs), all sensor nodes operating with limited battery need the very-low-power wireless technologies. The representative approach to reduce energy consumption in WBSNs is transmission power control (TPC). The TPC technique is used to maintain acceptable packet delivery performance with the low power consumption. So, it has been widely researched as the important subject in WSNs. However, the TPC algorithms which have been researched in WSNs are not directly applicable in WBSNs which deploy sensor nodes in, on, or around a human body. This is because instantaneous channel condition is frequently changed due to sensor mobility resulting from human movements in WBSNs. Therefore, we need a sophisticated TPC technology to achieve reliable communication in WBSNs. To do this, in this paper, we investigate link layer channel characteristics in WBSNs. For understanding link characteristics in terms of power and placement, we conducted diverse experiments with real sensor devices. Through the analysis of experimental results, we knew that RSSI values are deeply depended on the transmission power and sensor placement in WBSNs.