Simulation of BD Precoding in Multi-User MIMO Systems with BER Performance Analysis

In multi-user MIMO systems, BD (Block Diagonalization) precoding serves as a crucial interference cancellation technique. This simulation focuses on a typical 4-transmit 2-receive antenna configuration scenario, with primary emphasis on analyzing the system's Bit Error Rate (BER) performance. The implementation involves creating channel matrices and computing null spaces for precoding matrix design.

The system model employs an architecture with 4 transmit antennas and 2 users (each equipped with 2 receive antennas), a configuration commonly found in cellular network downlink transmissions. The core concept of BD precoding involves constructing specialized precoding matrices to achieve interference alignment among multiple users, ensuring that each user receives only its intended signals without interference from other users. In code implementation, this requires calculating the null space of other users' channel matrices for each target user.

During the simulation process, the first step involves constructing channel matrices while considering independent channel state information for each user. By computing the null space of each user's channel matrix, we can design precoding matrices that satisfy BD conditions. This design approach ensures signal enhancement in the target user's channel while placing the signals in the null space of other users' channels. The algorithm implementation typically uses singular value decomposition (SVD) for null space computation and matrix multiplication for precoding application.

BER performance evaluation is typically conducted under different Signal-to-Noise Ratio (SNR) conditions. As SNR increases, the BER should ideally demonstrate a decreasing trend. However, practical systems are affected by factors such as channel estimation errors and antenna correlation, leading to performance gaps compared to theoretical values. The simulation allows observation of how these practical factors impact system performance, providing valuable references for actual system deployment. Code implementation includes SNR sweeping loops and BER calculation using Monte Carlo simulations with error counting mechanisms.

This BD precoding technology under multi-antenna configuration is particularly suitable for scenarios with significant differences in channel conditions among users. It effectively enhances spectrum utilization while ensuring communication quality for all users. The MATLAB implementation typically involves functions like 'null' for null space calculation, 'svd' for matrix decomposition, and custom functions for precoding matrix optimization and performance metric computation.