Lu Wu

Codebook Design for LTE-A Downlink System

Multiple-input multiple-output (MIMO) has been adopted by long term evolution (LTE) and its updated version LTE-Advanced (LTE-A) to increase the spectrum efficiency. However, the benefits of multi-user (MU) MIMO highly rely on the accurate channel knowledge at the transmitter. So proper codebook design is a key problem for LTE-A FDD downlink system. In this paper, a codebook design with phase adjustment in the precoder targeting wideband channel properties is proposed. The average cell spectrum efficiency and cell-edge user spectrum efficiency of the proposed scheme are evaluated through system level simulation and compared to the discrete Fourier transform (DFT) based feedback scheme. The results show that the proposed codebooks significantly improve feedback efficiency and system performance for co-polarized linear antenna array.

Capacity Balancing for Multiuser MIMO Cognitive Radio Network

We propose a capacity balancing beamforming technique for a multiple inputs and multiple outputs (MIMO) based cognitive radio (CR) network. The proposed algorithm is based on mean square error (MSE) duality and it is aimed at maximizing the worst case user capacity of multiple secondary users (SUs) by jointly designing their transceiver beamformers while ensuring the interference leakage to multiple primary users (PUs) are below a specific set of thresholds. We use an iterative approach to determine the transceiver beamformers so that the capacities achieved by all SUs are balanced and maximized. The performance of the algorithm is demonstrated through Monte Carlo simulation results.

Codebook Design for Cross-Polarized Linear Antenna Array in LTE-A Downlink System

Multiple-input multiple output (MIMO) has been adopted by long term evolution (LTE) and its updated version LTE-Advanced (LTE-A) to increase system spectrum efficiency. However, the benefits of multi-user (MU) MIMO highly rely on an accurate channel knowledge at the transmitter. So proper codebook design is a key problem for LTE-A FDD downlink system. In this paper, the channel characteristic specific to cross-polarized linear antenna array is analyzed, then its codebook design based on amplitude and phase adjustment is proposed for LTE-A downlink system. The proposed codebooks are compared to the differential scheme [7] on the average cell spectral efficiency and cell-edge user spectral efficiency evaluated through system level simulations. Simulation results show that the proposed codebooks significantly improve channel feedback efficiency and system performance.

On Implementing Spatial-Correlation-Information Aided Feedback in Practical MIMO Systems

This work investigates implementing spatial-correlation-information aided feedback in practical multiple-input multiple-output (MIMO) systems. It is presented that the existing spatial-correlation-information aided feedback approach could be simplified in computational complexity with little performance loss. In comparison with Grassmannian codebooks, the feedback codebooks in the 3GPP LTE Release-8 specification is shown to be a near-optimal base codebook. An efficient quantization approach is proposed for quantizing transmit spatial covariances matrices for closely-spaced co-polarized uniform linear arrays (ULA). The good performance of the entire practical feedback solution is demonstrated via system-level simulation.

Hadamard Transform Based Codebook Design for Uniform Circular Arrays in Mobile Radio Communications

Multiple-input multiple-output (MIMO) has been adopted by long term evolution (LTE) and its updated version LTE-Advanced (LTE-A) to increase spectrum efficiency. However, the benefits of multi-user (MU) MIMO highly rely on the accurate channel knowledge at transmitter. So proper codebook design is a key problem for frequency division multiplexing (FDD) downlink systems. In this paper, an efficient codebook design based on Hadamard transform is proposed for uniform circular arrays. Then a two-stage feedback scheme is further proposed to reduce the feedback overhead. The average cell spectrum efficiency and cell-edge user spectrum efficiency of the proposed scheme are evaluated through system level simulation and compared with LTE Rel-10 feedback. The results show that the proposed codebook significantly improves feedback efficiency and system performance.