标题： 大规模 MIMO 下行链路中功率放大器失真的空间Σ-Δ抑制方法 显示英文标题

标题： A Spatial Sigma-Delta Approach to Mitigation of Power Amplifier Distortions in Massive MIMO Downlink

摘要： 在大规模多输入多输出（MIMO）下行系统中，基站（BSs）的物理实现需要使用廉价且节能的功率放大器（PA）以避免高昂的硬件成本和高功耗。然而，此类PA通常具有有限的线性放大范围。超出线性放大范围的操作产生的非线性失真会显著降低系统性能。现有处理非线性失真的方法，如数字预失真（DPD），通常需要准确了解或获取PA传输函数。本文提出了一种新的减少PA失真的概念。假设BS端有一个均匀线性阵列（ULA），想法是应用Sigma-Delta ($\Sigma \Delta$)调制器，将PA失真形状化到高角度区域。通过使系统在低角度区域运行，接收到的信号受到的PA失真影响较小。为了展示这种空间$\Sigma \Delta$方法的潜力，我们研究了该方法在多用户MIMO-正交频分复用（OFDM）下行场景中的应用。开发了一种符号级预编码（SLP）方案和一种迫零（ZF）预编码方案，并考虑了空间$\Sigma \Delta$方法的新设计要求。数值仿真被用来展示所开发的$\Sigma \Delta$预编码方案的有效性。 显示英文摘要

摘要： In massive multiple-input multiple-output (MIMO) downlink systems, the physical implementation of the base stations (BSs) requires the use of cheap and power-efficient power amplifiers (PAs) to avoid high hardware cost and high power consumption. However, such PAs usually have limited linear amplification ranges. Nonlinear distortions arising from operation beyond the linear amplification ranges can significantly degrade system performance. Existing approaches to handle the nonlinear distortions, such as digital predistortion (DPD), typically require accurate knowledge, or acquisition, of the PA transfer function. In this paper, we present a new concept for mitigation of the PA distortions. Assuming a uniform linear array (ULA) at the BS, the idea is to apply a Sigma-Delta ($\Sigma \Delta$) modulator to spatially shape the PA distortions to the high-angle region. By having the system operating in the low-angle region, the received signals are less affected by the PA distortions. To demonstrate the potential of this spatial $\Sigma \Delta$ approach, we study the application of our approach to the multi-user MIMO-orthogonal frequency division modulation (OFDM) downlink scenario. A symbol-level precoding (SLP) scheme and a zero-forcing (ZF) precoding scheme, with the new design requirement by the spatial $\Sigma \Delta$ approach being taken into account, are developed. Numerical simulations are performed to show the effectiveness of the developed $\Sigma \Delta$ precoding schemes.