An Investigation Into Relaying of Creeping Waves for Reliable Low-Power Body Sensor Networking

We investigate the use of relaying of creeping waves in the industrial scientific medical frequency bands of 434 MHz, 915 MHz, and 2.4 GHz. The investigation includes generic analysis and experimental setups. For generic analysis, a link budget model is derived based solely on the creeping wave component of the transmitted signal while marginalizing for other effects, such as reflections from the surrounding environment. Closed-form expressions of the gains in network lifetime and energy per bit are derived for a system covering the entire body using relays compared to a reference system offering the same level of reliability without relaying. The experimental setups are used to gather measurements in the 2.4-GHz band with a body sensor network development platform in a nonreflective open-space environment and in a reflective residential environment. The measurements are used to validate the link budget model and evaluate performance of practical systems. Analysis and experimentation demonstrate that relaying of creeping waves offers considerable performance gains in all frequency bands. For example, using a single relay on either side of the body in 2.4 GHz can potentially increase network-lifetime times 40 and decrease energy per bit by 48 dB. Part of this potential is achieved in experimental setups where relaying was shown to increase network lifetime times 13, decrease energy per bit by 13 dB and provide the ability to compensate for a wider fading margin.