Dual-Mode Low-Complexity Codebook Searching Algorithm and VLSI Architecture for LTE/LTE-Advanced Systems

Codebook is a useful precoding technique for bandwidth limited systems because only few bits are required to feedback channel information. Many researchers propose several codebook selection criteria for linear receivers. However, these selection criteria are very computationally intensive, and most of them are not feasible for aperiodic feedback reporting in both LTE and LTE-Advanced (LTE-A) systems. Under the limited processing hardware and feedback delay constraints, low-complexity receivers with efficient codebook selection scheme are desirable. In this work, a low-complexity codebook searching engine is proposed to support both LTE and LTE-A operations. Also, it can be operated for both aperiodic and periodic feedback reporting. The properties and mutual correlations of the LTE and LTE-A codebooks are firstly analyzed. Then, a low-complexity grouping FFT-based codebook searching algorithm is proposed, which can be shared by LTE and LTE-A systems. Since the proposed algorithm is an algorithmic transformation, there is no performance loss. The proposed schemes have significant effect of reducing the number of multiplications by 56% compared with referenced works. Finally, a dual-mode low-complexity codebook searching engine with TSMC 90 nm is implemented. The IP size is 2.2 mm$^{2}$ and the equivalent gate count is 547.6 K. The operating frequency is 125 MHz.