Impact of Coordination Delay on Distributed Scheduling in LTE-A Femtocell Networks

We consider wireless femtocell networks where scheduling of transmissions is coordinated across multiple cells to mitigate interference and deliver fairness and quality of service (QoS). Coordination across multiple cells entails (i) exchange of (serving and interfering) channel information and traffic priority (which is a function of packet delays, average rate, queue length), and (ii) signalling of transmission powers over pilots so that neighboring cells can determine the expected SINR to pick the right modulation and coding scheme. Such an exchange entails delay in coordination, resulting in scheduling decisions being made on the basis of stale information received from other cells. In this paper, we study aspects of practical signalling and algorithm design to account for such coordination delay and study its impact. When the coordination across cells is done over a high latency backhaul, we design a hybrid signalling mechanism where minimal amount of additional over-the-air (OTA) signalling enhancement can lead to tremendous performance improvement. We numerically demonstrate the benefits of our approach via comparison to a centralized scheduler and reuse one scheme using system simulations based on 3GPP evaluation methodology.