The vertical handoff between GSM and Zigbee networks for vehicular communication

Wireless communication becomes important part of everyday life, and in the future, there will be new wireless technologies. Vertical handoff between networks with different wireless network interface becomes so important especially in mobile devices that move at high speed such as vehicles. The vertical handoff is required for a vehicle to connect to different wireless networks for different purpose. For example, vehicles may connect to cellular network to send short messages such as news or email, and may connect to short range networks to acquire some localized information. In this paper, we investigate the possibility and the performance of using GSM/GPRS module as an interface to cellular networks and Zigbee module as an interface to short range networks. In our experiments, we set up both soft and hard handoff scenario to measure the packet round trip time and delay. From the results, it shows that the packet round trip time (RTT) in GPRS networks on the average is around 1 - 2.5 seconds and in Zigbee network is less than 100 msec. In case of a hard handoff, mobile device needs to prepare for a connection to attach to networks before transferring data. From the results, the network attach time in GPRS network on the average is around 4.5 - 5 seconds while in Zigbee network is less than 10 msec.