Two Time-Scale Cross-Layer Scheduling for Cellular/WLAN Interworking

In this paper, we investigate uplink resource allocation for wireless local area network and cellular network interworking to provide multi-homing voice and data services. The problem is formulated based on the physical layer and medium access control layer technologies of the two networks to ensure that the resource allocation decisions are feasible and can be executed at the lower layers. Furthermore, to efficiently utilize users' equipment (UEs) battery power, the power distribution among multiple network interfaces of the UEs is included in the problem formulation. The optimal resource allocation problem is a multiple time-scale Markov decision process (MMDP) as the two networks operate at different time-scales and due to voice and data service requirements. We derive decision policies for the upper and the lower levels of the MMDP by decomposing each resource allocation problem over multiple time slots to a set of resource allocation problems for individual time slots and solving the resource allocation problems corresponding to individual time slots using convex optimization techniques. To reduce the time complexity, we further propose a heuristic resource allocation algorithm by deriving the decision policies based on a single system state. The system state consists of average square channel gains for dual variable calculation and instantaneous channel gains for resource allocation based on the calculated dual variables. Simulation results demonstrate the achievable throughput and service quality improvements by employing these two algorithms.