Energy efficient network mobility under scatternet/WLAN coexistence

Nowadays, it is common that people carry several kinds of portable devices such as cellular phone, MP3 player, and PDA etc. If we assume that these devices build a WPAN (Wireless Personal Area Network) via Bluetooth Piconet, the master node of the Piconet plays a role of MR (Mobile Router) with maintaining connection to Internet via WLAN (Wireless LAN). Thus WPAN with Bluetooth is quite suitable for realizing NEMO (Network Mobility). Furthermore, if it is assumed that two or more Piconets are connected with one another through Scatternet, the nested mobility is achieved easily. In this situation, each slave device will connect to Internet via the mobile router. Then the mobile router can use the path via WLAN or make a new path through Scatternet, i.e., via a master node in other Piconet, in order to forward the connection of each slave device. In this paper, we show that the path through Scatternet is more energy efficient, especially in terms of the lifetime of mobile routers. For this purpose, we present an energy consumption model of WLAN and Bluetooth, which is based on payload size and transmission/receiving duration. In addition, we show that making a new path through Scatternet built on two or more Piconets is more beneficial to prolonging the lifetime. We prove the energy efficiency of our proposal through ns-2 simulations.