An important indicator commonly used to evaluate the quality of a communication link is signal-to-interference ratio (SIR). However, studies in the literature dealing with SIR for orthogonal frequency division multiplexing (OFDM) systems are relatively few. This paper analytically investigates OFDM system performance by including major channel impairments such as excess delay spread, synchronization error, sample timing error, frequency offset, and time-varying fading. We derive a closed-form expression for SIR, accounting for both variations of inter-carrier interference (ICI) and inter-symbol interference (ISI) with the number of subcarriers, and the susceptibility to channel impairments. A condition relating peak ISI to peak ICI is derived. An expression quantifying the impact of synchronization error in ISI is obtained. SIR behavior with respect to the tradeoff among numbers of subcarriers and other system parameters are investigated. A numerical method, as well as a polynomial equation for an analytical solution, is formulated to find the optimal number of subcarriers for a given set of constraints. We demonstrate the variations of SIR with various parameters and analyze the leakage of power (unwanted power distribution across subcarriers).

中文翻译：

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带有设计缺陷和信道障碍的OFDM系统性能，可变性和最优性

通常用于评估通信链路质量的重要指标是信号干扰比（SIR）。但是，有关正交频分复用（OFDM）系统的SIR的文献研究相对较少。本文通过分析主要的信道损伤，如过量延迟扩展，同步误差，采样定时误差，频率偏移和时变衰落，来分析性地研究OFDM系统的性能。我们导出了SIR的闭式表达式，考虑了子载波数量对载波间干扰（ICI）和符号间干扰（ISI）的变化以及对信道损伤的敏感性。得出将峰值ISI与峰值ICI相关的条件。获得一个量化ISI中同步误差影响的表达式。针对子载波数量与其他系统参数之间的折衷，研究了SIR行为。提出了一种数值方法以及用于解析解的多项式方程式，以找到给定约束条件下子载波的最佳数量。我们演示了具有各种参数的SIR的变化，并分析了功率泄漏（子载波之间不必要的功率分布）。