使用凸優化的多用戶多輸入多輸出混合波束成型設計

Abstract

近年來，多輸入多輸出通信系統的研究一直引起關注。在毫米波多輸入多輸出通信系統中，大量的天線可以提供高速率。然而，常規的多用戶波束成型算法為每根天線配備了一個獨立的射頻鏈，由於每根天線都需要配置一個功率放大器而使其不實用，也具有相對較高的成本。因此，混合波束成型方法，其中波束形成器由低維度的數字波束成型器以及模擬波束成型器組成， 用於減少射頻鏈的數量， 同時提供可接受的性能。 本論文基於這一想法研究了多用戶大規模多輸入多輸出通信系統的混合波束成型設計。另外，考慮到在大規模天線下的可能的信道估計誤差，該問題被歸納為服務質量約束下的發射功率最小化， 同時也考慮對估量誤差的魯棒性。 我們採用最大允許均方誤差和最小容許信噪比作為約束， 并使用半定規劃來解決優化問題。 仿真結果表明，所提出的方法可以再系統中引入魯棒性的同時降低維護服務質量所需的功率。

The research of massive multiple-input multiple-output (MIMO) communication system has been of interest in recent years. In millimeter wave MIMO systems, a large number of antennas can provide high data rates. However conventional multiuser MIMO beamforming algorithms equip each antenna with one independent radio frequency (RF) chain, which has a relatively high cost because of the power amplifiers each antenna element and makes it not practical. Thus hybrid beamforming (HB) method in which the overall beamformer consists of a low-dimensional digital beamformer followed by an analog beamformer has been utilized to greatly reduce the number of RF chains, while providing an acceptable performance. Here, two practical problems are emphasized, the design of a beamforming structure with less RF chains than antennas and the demand for high power efficiency. This thesis studies hybrid beamforming design for multiuser massive MIMO systems based on this idea. In addition, considering possible channel estimation under large scale antennas, the problem is formulated as the transmit power minimization under quality of service (QoS) constraint with additional consideration of the robustness against estimation errors. We adopt maximum allowable mean square errors (MSEs) and minimum tolerated signal-to-interference-plus-noise-ratios (SINRs) as QoS constraints, and use semidefinite programming (SDP) for solving the optimization problem. The simulation results demonstrate the proposed method can reduce required power to maintain QoS while introducing robustness in the system.