多通道複頻鍵移信號之偵測

Abstract

本論文針對多通道複頻鍵移信號(multichannel MFSK signals)在有 干擾環境下探討最佳化信號偵測法則。前人依據經驗法則提出種種通訊接 收機架構，並針對這些架構做性能分析比較。我們首先假設信號強度與雜 訊指數已知，利用最大可能性法則，提出最佳化接收機架構，依此架構利 用小信號近似法(small signal approximation)獲得三種次佳化接收機架 構，並提出分析方法比較系統性能的優劣。這些接收機架構建於信號強度 與雜訊指數皆已知的前題，之後，我們利用鄰近通道的能量偵測器( energy detector)做為雜訊指數的估算器，由此估算器的估計值代入原先 獲得的四種接收機架構，我們發現最佳化接收機在非理想假 設( imperfect side information)下不再具有最佳的系統性能。 為探討 具有干擾環境多通道複頻鍵移信號的信號偵測法則，進一步假設信號與雜 訊強度皆為未知數，首先利用所有能量偵測器的信號使用廣義最大可能性 法則(generalized maximum likelihood)推導出新接收機架構，縱然架構 與方法均屬創新，然而結果尚不能滿意；再利用廣義最大可能性法則擴大 接收頻寬，成功推導出新接收機架構，再依照信號近似法獲得數種新架構 ，性能及抗干擾能力均優於前人依據經驗法則提出的通訊接收機架構。 除了考慮具有蓄意干擾的信號偵測之外，尚有同頻干擾(非蓄意干擾)環境 的多人使用信號偵測(multiuser detection)的探討，其通道雜音除了白 色高斯雜訊之外還有通道衰褪(channel fading)，其偵測方法依然使用廣 義最大可能性法則。 Incoherent detection of Multichannel M-ary frequency-shift keyed (MFSK) signals in ststionary Gaussian noise jammingis studied. The communication environment under consideration is one in whicheach channel has a different AWGN power level. We give a brief derivation of the optimalmaximum likelihood (ML) receiver with the assumption that both the signal andnoise levels are known and suggest three suboptimal receivers. We then turn ourattention to case of unknown signal and noise levels. Both optimal and suboptimalsolutions are investigated and relationships between these solutions and some exsitingproposals are discussed.The approach of the case of the perfect side information is not new but their analyzedmethods are. When the signal and noise levels are unknown, genaralized maximum likelihoodpriciple is applied for detection of signal. For multiuser detection the transmitted signalis not corrupted by white Gaussian noise only, but also by the fading and interferencedsignals from other users. A new diversity combiner with optimal nonlinearity is reported.The soft-like nonlinearity is not easy to implement and analyze and a multi-level quantizeris then followed. We discuss and compare three suboptimal receivers with nonuniform quantizer.