A low-complexity adaptive transmission scheme based on the dual-codebook of 3GPP LTE-advanced

In order to meet the peak spectral efficiency requirements of up to 30 bit/s/Hz, LTE-Advanced supports up to eight transmit antennas in its downlink, for which a dual codebook is agreed for precoding. In the dual-codebook approach, the precoding matrix to be used is obtained via the multiplication of two precoding matrices Wi and W₂ selected from each of the dual-codebook. For adaptive precoding under this configuration, user equipment (UE) is required to include in its feedback information the precoding matrix indicators (PMIs) corresponding to both Wi and W₂. In this paper, we propose a low-complexity precoding select method to select Wi and W₂ separately, considering the the dual-codebook functionality. In the proposed scheme, a Wi for every possible rank will be chosen firstly according to the principal directions of the long-term channel and thereafter an appropriate rank and W₂ are sought to maximize the sum minimum mean square error (MMSE) rate. Besides, UE will feed back a channel quality indicator (CQI) for each codeword to signal the supported adaptive modulation and coding scheme to achieve a target codeword error ratio (CWER). Simulation results show that the proposed scheme has a comparable performance with the general extensive joint select method but with a substantially reduced complexity due to the significantly reduced number of channel inversions.