Splitting downlink multimedia traffic over WiMAX and WiFi heterogeneous links based on airtime-balance

We investigate the challenge of splitting a traffic flow over WiMAX and WiFi links. For traffic load distribution over heterogeneous RATs (Radio Access Technologies), heterogeneous link resources need to be commonly measured and fairly compared. To this end, an airtime cost model is considered as a common resource measure. The model can be used to estimate channel time consumed for a successful packet transmission. As a traffic split mechanism, an airtime-balance method is proposed. Using the airtime cost model, the offered traffic load (in Mbps) is converted into airtime cost required for its transmission, and IP packets are distributed to multiple RATs so that airtime is equally balanced between RATs. We have implemented a practical test-bed system, including both WiMAX and WiFi systems, and used it to conduct extensive experiments indoor and outdoor. Experimental results confirm that airtime-balance can achieve an improved flow split to reduce the waiting packets at the reorder buffer of the receiver. Moreover, it could realize a more rapid adaptation to link variations with local measurements, when compared to the RTT-based method, which also requires extra system overhead due to the use of probe packets.