SLNR Based Hybrid Precoding for HAP Massive MIMO Systems with Limited RF Chains

In this letter, a radio frequency (RF) precoding method is put forward for massive multiple-input multiple-output (MIMO) systems with limited RF chains on high altitude platform (HAP). In the proposed method, we formulate the RF precoder design as an average signal-to-leakage-plus-noise ratio (SLNR) maximization problem, where the RF precoder is composed of some columns of a specific discrete fourier transform (DFT) matrix. First, we obtain the lower bound of the average SLNR and transform it into a trace problem. Then, for ease of handling, signal-to-leakage ratio (SLR) is adopted to achieve the initial RF precoder. Finally, a greedy algorithm for RF precoding is proposed to update the initial RF precoder for better performance. Numerical simulations demonstrate that the design proposed in this letter has better performance than other RF precoding schemes.