Hybrid Precoding Algorithm for Millimeter-Wave Massive MIMO Systems with Subconnection Structures

In mmWave massive MIMO systems, traditional digital precoding is difficult to be implemented because of the high cost and energy consumption of RF chains. Fortunately, the hybrid precoding which combines digital precoding and analog precoding not only solves this problem successfully, but also improves the performance of the system effectively. However, due to the constant mode constraint introduced by the phase shifter in the analog domain, it is difficult to solve the hybrid precoding directly. There is a solution which divides the total optimization problem into two stages to solve, that is, first fix the digital precoding matrix, solve the analog precoding matrix, and then optimize the digital precoding matrix according to the obtained analog precoding matrix. In this paper, a high energy-efficient hybrid precoding scheme is proposed for the subconnection structure. In the first stage, the optimization problem can be decomposed into a series of subproblems by means of the independent submatrix structure of the analog precoding matrix. When the optimized analog precoding matrix is obtained, the digital precoding matrix can be solved by the minimum mean error (MMSE). Finally, the digital precoding matrix is normalized to satisfy the constraint conditions. The simulation results demonstrate that the performance of the proposed algorithm is close to that of fully digital precoding based on subconnection structure and better than that of the existing algorithms. In addition, this paper presents the simulation analysis of the algorithm performance under imperfect channel state information. Simulation results show that when the estimation accuracy of channel state information is 0.8, the spectral efficiency of the proposed algorithm can already be maintained at a good level.

HP-SFC Algorithm for MmWave Massive MIMO Hybrid Precoding Systems

This paper presents an alternating iteration hybrid precoding algorithm for the switch network-based dynamic fully-connected (SFC) structure, namely HP-SFC algorithm. Firstly, based on the sparsity of switch network, the optimization problem of the analog switch precoding matrix is transformed into a binary dictionary updating problem, which avoids to deal with the binary constraint straightly. Then, the optimization problem of the analog phase shifter (PS) precoding matrix is modeled as a quadratic unimodular programming problem by the vectorization of the analog PS precoding matrix. So that the analog PS precoding matrix can be readily optimized. Finally, the analog switch precoding matrix, the analog PS precoding matrix and the digital precoding matrix are alternately optimized via the block coordinate descent, the generalized power method and the least square, respectively. Theoretical analysis and simulation results show that the proposed algorithm can provide brilliantly hybrid precoding performence campared with the previous works, for example: 1) it reduces the hybrid precoding matrix residual, so that its spectral efficiency is close to the full digital optimal precoding; 2) it provids at least 15\% energy efficiency improvement comparing with related algorithms.

Artificial-Noise-Aided Energy-Efficient Secure Multibeam Wireless Communication Schemes Based on Frequency Diverse Array

In this paper, we research synthesis scheme for secure wireless communication in multibeam directional modulation (MBDM) system, which consists of multiple legitimate users (LUs) receiving their own individual confidential messages, respectively, and multiple eavesdroppers (Eves) intercepting confidential messages. We propose a new type of array antennas, termed frequency diverse arrays (FDA), to enhance security of confidential messages. Leveraging FDA technology and artificial noise (AN) technology, we aim to address the PHY security problem for MBDM by jointly optimizing the frequency offsets, the precoding matrix and the AN projection matrix. In the first stage, with known locations of Eves, precoding matrix is designed to minimize Eve’s receiving power of confidential message (Min-ERP), while satisfying power requirement of LUs. And then artificial-noise projection matrix (ANPM) is calculated to enhance AN impact on Eves without influencing LUs. Furthermore, we research a more practical scenario, where locations of Eves are unknown. Unlike the scenario of the known locations of Eves, precoding matrix is designed to maximize AN transmit power (Max-ATP), while satisfying each LU’s requirement received power of confidential message. In the second stage, we analyze and further optimize secrecy capacity. The problem is solved by optimizing frequency offsets through modified artificial bee colony (M-ABC) algorithm. Numerical results show that the proposed scheme can achieve a secure transmission in MBDM system.