A power-saving standby method to extend battery life in dual-mode cellular phones

Dual-mode cellular phones, including smartphones, are recently attracting much attention from both users and telecom operators throughout many countries. To avoid traffic concentration generated by these devices on 3G networks, it is important to lead users to connect with fixed networks via WLAN. However, keeping both 3G and WLAN interfaces on consumes a great deal of power, which considerably shortens the standby time. To achieve longer battery life, we propose a power-saving standby method (PSSM) whose features are: (1) constant deactivation of the WLAN interface except for when required; (2) no additional functions in a mobile operator´s network; and (3) avoidance of a WLAN AP search distant from a cellular phone. We implemented PSSM as a BREW application and measured the electrical current in a cellular phone as well as the delay in email retrieval transaction. Experimental results using the prototype system show that PSSM achieves about 73%-134% longer battery life than a conventional dual-mode cellular phone, while PSSM keeps the application transaction delay short by reducing unproductive WLAN AP searches.