信號雜訊比與信號干擾比之量測及其應用

Abstract

在無線通訊系統中信號、雜訊、干擾之間的功率比與系統性能如錯誤機率等息息相關，其他許多相關的系統機制如功率控制、交接(handoff)、通道指定(channel assignment)或允入控制(admission control)等也都與這些比率有直接的關係。另外在Ka頻帶的衛星通訊中雨衰補償或在軍事通訊中的低攔截率測試，都需要信號雜訊功率比的測量。諸如上述的應用，大部分均需要準確的信號雜訊功率比或信號干擾功率比的估測，但鮮有人提及詳細的測量方法。 在本論文中我們提出數種信號雜訊功率比與信號干擾功率比的估測法。首先我們使用全功率輻射計(total power radiometer)與迪克式輻射計(Dicke radiometer)來做為信號接收機，利用動差法(method of moments)及最大可能性(maximum likelihood)原理提出了數種信號雜訊功率比的估測器。隨後在相位調變的數位系統與分碼多工系統下，我們提出數種根據動差法及柱狀統計特性匹配(histogram matching)而得到之信號干擾功率比的估測法。針對這些估測法，我們詳細的分析並模擬其性能表現，並證明這些估測皆為近似地有效 (asymptotic efficient)。

Carrier-to-noise power ratio (CNR), signal-to-interference ratio (SIR) and other similar signal quality indicators have been used in algorithms for wireless applications such as power control, inter-cell handoff, dynamic channel assignment and admission/access control, to name a few. We also find rain fade compensation methods based on CNR for satellite communications in $K$ and $Ka$ bands. Although all these algorithms require accurate SIR or CNR measurement but there is very few mentioning of the measurement method. This dissertation presents several new efficient CNR and SIR estimation algorithms,analyzes their performance, discusses their properties and describe their applications.The CNR algorithms use output samples from various radiometers and are based on the method of moments or the maximum likelihood principle. We also presents viable solutions for real-time SIR estimations under various channel conditions for phase modulated TDMA or WCDMA signals. These solutions are based on either the method of moments or the histogram matching concept. Numerical results are provided to demonstrate the efficacy of the proposed methods and to study their behaviors predicted either by analysis or by simulations.