H-Infinity control based scheduler for the deployment of small cell networks

In this work, we address the joint problem of traffic scheduling and interference management related to the deployment of Small Cell Networks (SCNs). The base stations of the SCNs (which we will refer to as Micro Base Stations, MBSs) are low power devices with limited buffer size. They are connected to a Central Scheduler (CS) with limited capacity backhaul links. In this scenario, traffic flow has to be from the network to the MBS queues in such a way that the queue-length at MBS remains as close as possible to a given target queue-length. The challenge is to design a scheduler which is oblivious to the wireless link between the MBSs and the User Terminals (UTs). For the traffic arriving at the MBS, we need to efficiently transmit it over the wireless channel to the UTs in an interference limited environment. Additionally, real time centralized interference management techniques will not be feasible. In this paper, we decouple the joint scheduling and interference management into two separate parts. For the scheduling problem, we propose a H ∞ control based scheduler which regulates the arrival rates to the queues at the MBS. For the problem of interference management over the wireless channel, we propose a multi-cell beamforming technique and formulate a decentralized algorithm using tools from the field of random matrix theory. The beamforming vectors are designed to optimize two performance metrics of interest namely downlink power minimization and weighted sum rate maximization. Our simulation results show that the H ∞ based queue length control algorithm stabilizes the queue-lengths at the MBS and keeps the variation of the queue-length around the target to a minimum.