Keywords: voice over IP (VoIP), VoIP over WLAN (VoWLAN), radio resource management, load balancing, WLAN
Received February 2, 2007; accepted July 13, 2007.
Communicated by K. Robert Lai, Yu-Chee Tseng and Shu-Yuan Chen.
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Shiao-Li Tsao and Chih-Chien Hsu
Department of Computer Science
National Chiao Tung University
Hsinchu, 300 Taiwan
Coverage areas of WLAN access points (APs) are usually overlapped so a WLAN
station (STA) might be able to find several APs to attach in a WLAN hotspot. Experimental
results indicate that a WLAN STA normally associates with an AP with the
maximal signal strength and requests the bandwidth of the AP for establishing network
connections. However, this kind of STA-centric association and bandwidth request policy
may introduce unbalance loads of APs, and the bandwidths of APs in a WLAN hotspot
cannot be fully utilized. This unbalance load problem is a critical issue for the commercial
deployment of voice over IP (VoIP) over WLAN (VoWLAN) service which has
to maximize the number of concurrent VoWLAN sessions with Quality of Service (QoS)
guarantees. In this paper, a novel dynamic load balancing scheme is proposed for a
VoWLAN system. The network-assisted association policy first advices an STA to request
a VoWLAN session through an AP with the minimal load. In case of the APs
which the STA can attach are all overloaded, the proposed load balancing scheme further
rearranges the serving VoWLAN STAs between APs in order to spare enough resources
for accommodating that new request. Simulation results demonstrate that the reject rate
of service requests for a VoWLAN system can be considerably reduced by employing
the proposed scheme.
Received February 2, 2007; accepted July 13, 2007.
Communicated by K. Robert Lai, Yu-Chee Tseng and Shu-Yuan Chen.