Institute of Radiocommunications, Poznan University of Technology, 61-131 Poznan, Poland.
Sensors (Basel). 2023 Jan 1;23(1):474. doi: 10.3390/s23010474.
While Orthogonal Frequency Division Multiplexing (OFDM) is a dominating spectrum access technology in modern, wideband access networks, it is important to maximize its transmission efficiency considering the underlying radio front-end characteristics. A practical front-end contains nonlinear components, e.g., a Power Amplifier (PA), resulting in nonlinear distortion being injected into OFDM band deteriorating symbols detection. A PA operating point, defined here by Input Back-Off (IBO), can be adjusted to balance the wanted signal power and nonlinear distortion power. While it is the most common to maximize the spectral efficiency (SE), recently, energy efficiency (EE) maximization gained momentum. However, EE maximization requires, in addition to PA nonlinearity modeling, modeling of the power consumption of the PA and all other transmitter components. While it is commonly overlooked, if a battery is used to power the transmitter, its model should be considered as well. This paper derives mathematical expressions for EE and SE of an OFDM transmitter considering Rapp and soft-limiter models of PA nonlinearity, class A, class B, and perfect PA power consumption models, and two battery models: perfect and worst-case. While closed-form expressions cannot be obtained for most of the derived integrals, numerical methods have been used to obtain the optimal IBO value in each case. The numerical results show, in addition to optimal IBO values, the expected Signal-to-Noise and Distortion Ratios (SNDRs). It is shown that the optimal IBO value changes significantly with the wireless channel properties, utilized hardware architecture, or the utilized optimization goal. As such, the proposed optimization is an important topic for 5G and beyond transmitters.
虽然正交频分复用（OFDM）是现代宽带接入网络中占主导地位的频谱接入技术，但考虑到底层无线电前端特性，最大限度地提高其传输效率非常重要。实际的前端包含非线性组件，例如功率放大器（PA），这会导致非线性失真注入到 OFDM 频段中，从而恶化符号检测。PA 的工作点（此处定义为输入回退（IBO））可以进行调整，以平衡所需信号功率和非线性失真功率。虽然最大化频谱效率（SE）是最常见的，但最近，能量效率（EE）最大化也得到了发展。然而，EE 最大化除了需要对 PA 非线性进行建模外，还需要对 PA 和所有其他发射机组件的功耗进行建模。虽然这通常被忽视，但如果使用电池为发射机供电，则还应考虑其模型。本文推导了考虑 PA 非线性的 Rapp 和软限幅模型、A 类、B 类和理想 PA 功耗模型以及两种电池模型（理想和最差情况）的 OFDM 发射机的 EE 和 SE 的数学表达式。虽然无法为大多数推导的积分获得封闭形式的表达式，但已使用数值方法获得了每种情况下的最佳 IBO 值。数值结果显示了除最佳 IBO 值外，还显示了预期的信噪比和失真比（SNDR）。结果表明，最优 IBO 值会随着无线信道特性、所使用的硬件架构或所使用的优化目标而发生显著变化。因此，所提出的优化是 5G 及以后的发射机的一个重要主题。
