Improving Channel Scanning Procedures for WLAN Handoffs

WLAN has been widely deployed over public and private areas and has become one of popular access technologies for mobile Internet services in recent several years. Handoff between WLAN access points (APs) that introduce packet loss and delay is one of the critical issues for mobile Internet applications, especially for real-time communications. Previous studies indicated that channel scanning time contributes a significant portion of handoff latency and introduces packet loss and delay. Therefore, solutions based on active scan were proposed to reduce total scanning time of channels so that the service disruption of a communication can be minimized. The other solutions based on passive scan scattering scans between packets did not optimize the total scanning time but avoid packet loss and delay. However, solutions for channel scanning procedures which combine active and passive scan strategies and take total scan latency, packet loss, and delay together into consideration have not yet been investigated. In this paper, a generic channel scanning model is proposed and solutions to improve scanning procedures for WLAN handoff are presented. Simulation results demonstrate that the proposed approaches achieve faster scan time than the existing solutions without violating packet delay and loss requirements specified by the applications during WLAN handoff. Moreover, the implementation of the proposed mechanisms on a WLAN SoC (System-on-Chip) is also discussed in this paper.