A Low-Complexity Grouping FFT-Based Codebook Searching Algorithm in LTE System

The codebook-based precoding is an effective technique to enhance the performance of LTE system over a limited-bandwidth feedback link. Among various precoder selection criteria, only mutual information selection criterion (MI-SC) and bit error rate selection criterion (BER-SC) are applicable to the codebook which is essential for the maximum number of transmitted data streams transmission, i.e. square codebook. However, MI-SC and BER-SC are computationally intensive when the number of transmit antennas and the number of sub streams are largest in LTE system. In this paper, we propose a low-complexity grouping FFT-based precoder selection criterion which is suitable for square codebook. We use the relation of precoding matrices to partition LTE codebook, and the FFT scheme is utilized to reduce the number of matrix inversions and matrix multiplications. The complexity analysis shows that the proposed scheme is able to reduce about 80% computational complexity without any performance loss compared with direct implementation and low-complexity cofactor scheme [10].