Novel CQI update methods in CoMP transmission

Abstract

This paper proposes two novel channel quality indicator (CQI) update methods that provide conservative CQIs to improve the cell edge user throughput in coordinated scheduling/beamforming (CS/CB) schemes. In CS/CB, a user usually needs to feed back channel state information (CSI) to its serving cell as the first step. However, due to the lack of knowledge regarding neighboring coordinated cells, e.g., the precoding matrix, the reported CQI is not accurate and must be updated before it can be applied. In the proposed methods, we assume that for each data stream the user receiver is tuned to match each incoming source of interference from the coordinated cell, or the precoder of the coordinated cell matches the row space of the channel from the coordinated cell to the user as much as possible. Two lower-bounds of the real CQI in actual transmission are derived and adopted. Both theoretical analysis and simulation results show the effectiveness of the proposed methods.