Online Packet Dispatching for Delay Optimal Concurrent Transmissions in Heterogeneous Multi-RAT Networks

In this paper, we consider the problem of concurrent transmissions in a wireless network consisting of multiple radio access technologies (multi-RATs). That is, a single flow of packets is dispatched over multiple RATs so that the complementary advantages of different RATs can be exploited. One of the challenging issues arising in concurrent transmissions is the packet out-of-order problem due to diverse wireless channel states and scheduling policies of different RATs, leading to substantial performance degradation to delay sensitive applications. To address this problem, we first propose a state-independent packet dispatching (SIPD) policy, which attempts to find the traffic dispatching ratios over multiple RATs to minimize the maximum average delay across different RATs in the long run. We further propose a state-dependent packet dispatching (SDPD) policy, which achieves fine-grained packet dispatching in the short-term. We use the value function as a measure of the admittance cost for packet dispatching given the current queueing states, and formulate the SDPD problem as a convex optimization problem. We derive the closed-form solutions for both problems for the special case of two RATs, and adopt the dual decomposition technique as the solution for the general cases. Simulation results are presented to compare the performance of the proposed schemes with existing solutions.