Cooperative feedback to improve capacity and error rate in multiuser diversity systems An OFDM case study

Allocating channel resources according to the users' channel states can significantly improve the performance of multiuser communication. With multiple users, different channel states are likely and a central scheduler can exploit their difference for resource allocation. This results in Multiuser Diversity (MUD) gains, which improve downlink capacity but require the scheduler to accurately know the users' Channel State Information (CSI) prior to transmission [1]. A well-known example of such a system is multiuser Orthogonal Frequency Division Multiplexing (OFDM), which we study in this article. Here, a Base Station (BS) increases the OFDM downlink capacity by subcarrier, power, and rate allocation [2, 3]. As uplink and downlink channels differ, the BS needs to obtain the downlink CSI from the users. If this CSI feedback is erroneous or outdated, the BS can only inaccurately allocate resources and the downlink performance decreases [4, 5]. Correspondence