Feedback reduction methods for distributed cooperative antenna systems with temporally-correlated channels

We investigate distributed cooperative antenna (COOPA) systems with limited feedback. A feedback link is required to provide channel state information, and in many cases it is based on the codebook which consists of maximally spaced codes. The feedback overhead can be reduced by organizing the codebook structure in a smart way to exploit the temporal correlation of the channel. We have proposed the combined feedback scheme in our previous work. In this paper we suggest a method which works as a useful guideline to determine the best feedback periods. We also propose a recursive codebook design which has a subspace tracking capability. The simulation results show that the tracking capability of the feedback allows the feedback overhead to be reduced by more than 30 % compared with the combined codebook.