Greedy and progressive user scheduling for CoMP wireless networks

In this work, we propose progressive user scheduling (PUS) and distributed successive zero-forcing (SZF) precoding for clustered coordinated multi-point transmission/reception (CoMP) systems. With joint transmission (JT) across a cluster of cells, centralized processing of precoding and user scheduling requires significant bandwidth resources for information exchange among coordinated base stations (BTSs) and the central controller, and channel state information (CSI) feedback from all users in the cluster to the central controller. In this work, we propose a greedy progressive user scheduling (PUS) and distributed SZF precoding to reduce CSI feedback and information exchange. With PUS, each BTS schedules and precodes its users in the coverage area of its cell separately from other BTSs in a cluster, but takes limited amount of feedback information available from other BTSs into account for user scheduling. Once the users are scheduled in that cell, BTS passes precoder information of the scheduled users to the next BTS. The second BTS schedules users in its cell taking the information from the first BTS into account. This process continues until the last BTS in the cluster schedules its users. With PUS, users in a cell do not completely estimate CSI from other cells in the cluster, which may significantly reduce the CSI feedback. Also, central controller is not necessarily required, but it may be utilized for limited amount of control signalling, e.g. an order in which the BTSs should schedule their users. Due to its distributed implementation, the proposed technique enables the use of various existing single-cell multiuser MIMO techniques that have been already standardized or proposed in the literature. In this work, we investigate the performance of greedy PUS and compare it with the greedy user selection for JT. It is shown that PUS can achieve sum rate close to the JT technique.