Uplink Scheduling In Multi-Cell OFDMA Networks With and Without Coordination

In cellular networks, a local uplink scheduler cannot compute good estimates of the inter-cell interference even with exact channel state information (CSI). Losses (due to decoding errors) will hence frequently occur. The maximum achievable performance (MAP) can only be achieved when all the cells are scheduled simultaneously centrally so as to manage interference and power optimally. In this paper, we focus on the performance of a practical system with local schedulers (i.e., each cell is scheduled independently) and compare it to MAP. We also study how to improve the performance of practical systems when a Cloud Radio Access Network (C-RAN) is present, with simple coordination schemes. To this end, to compute MAP, we first formulate an offline system-wide scheduling problem and transform it into a more tractable signomial problem that we solve quasi-optimally using an iterative algorithm. Since this problem requires all the channel information in the system and it has a high computational complexity, it is not suitable for a real-time system. Then, we show that a practical system using an efficient local scheduler (in each cell) yields a much lower performance than MAP. To decrease this performance gap, in a system with a C-RAN, we propose a very simple and fast scheme to coordinate the scheduling in all cells and show that it improves the performance significantly (in terms of throughput and losses) even when only partial CSI is available.