Method and apparatus for csi feedback in comp (coordinated multi-point) system

Abstract

This invention is a technique for coordinate multi-point wireless transmission between a plurality of geographically separated transmission points (TP) and at least one user equipment (UE). For coordinated multi-point communication (CoMP), UE measures the downlink wireless propagation channel corresponding to multiple geographically separated transmission points. The network configures multiple channel state indicator-reference signal (CSI-RS) resources, each of which is associated with a TP. UE measures the downlink channel using the multiple configured CSI-RS resources, and reports multiple CSIs in the uplink feedback channel. Each CSI report is defined as a “CSI-process”, where a CSI-process with a lower CSI-process-index has a higher priority. Multiple CSI-processes can be reported periodically. Each periodic CSI feedback comprises a single CSI-process. Different CSI-processes are time-domain-multiplexed on different uplink feedback time instances, and are not multiplexed in the same feedback time instance. If two CSI-processes collide in the time domain, the CSI-process of a higher priority is reported, and the CSI-process of a lower priority is dropped. The UE can also feedback multiple CSI-processes in an aperiodic manner, where multiple CSI-processes are reported simultaneously. Aperiodic feedback by the UE is triggered by an n-bit CSI-triggering field in an uplink grant transmitted by the network. Each codepoint of the n-bit triggering field triggers feedback of a subset of CSI-processes configured by the higher-layer. If a UE is configured with CoMP and without carrier aggregation (CA), CSI-processes are ordered by decreasing CSI-process priority. If a UE is configured with CoMP and carrier aggregation simultaneously, CSI-processes are ordered firstly by decreasing carrier index, and secondly by decreasing CSI-process priority.