Delay optimal concurrent transmissions in multi-radio access 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 stream of packets are split to transmit over multiple RATs simultaneously so that the complementary advantages of different RATs can be exploited. One of the challenging issues is the packet out-of-order problem due to different wireless channel states and transmission scheduling policies over different RATs, leading to substantial performance degradation to delay sensitive applications. To address this problem, we adopt a M/G/1 queueing model to characterize the delay experienced by batch arrival packets in a RAT. A convex optimization problem is formulated. It attempts to find the optimal traffic splitting over multiple RATs such that maximum delay across different RATs is minimized. We derive the close-form solution for the problem under the special condition of two RATs, and the dual decomposition technique is adopted to solve the optimization problem for general cases. Numerical results are presented to show the performance of the proposed scheme and compare with existing solutions.