A Differential Codebook Using 8-PSK Alphabets for Slowly Fading Channels

In this paper, a novel differential precoding scheme which employs a differential codebook to update the precoding matrices, is proposed for LTE systems. Due to the temporal correlation of the adjacent channel matrices, the consecutive precoding matrices are likely to be similar. This approach quantizes only the differential information of the channel instead of the whole channel subspace, which virtually increases the codebook size to realize more accurate quantization of the channel. Moreover, the proposed precoding utilizes only 8-PSK constellations for codebook design so that it is perfectly compatible with LTE codebooks. The capacity of the proposed codebook performs almost 1.5dB better than those of any other non-differential codebooks with the same amount of feedback information.