有線電視網路頻率多工交換系統實作之研究

Abstract

為廣播多頻道電視訊號, CATV系統採取頻率多工技術, 訊號載於各頻 帶, 頭端扮演著如同電話網路交換中心的角色. 基於頻率多工架構, 頻率 多工交換器可實現有線電視雙向傳輸. 本論文研究及實作頻率多工交換系 統. 我們將進入系統的訊號分成15-40MHz, 550-610MHz, 610-680MHz, 680-750MHz 四個頻帶, 且為解決鏡像頻率的問題, 分兩級下載至基頻交 換器做交換. 我們利用鎖相迴路原理做出相對四個頻帶的頻率合成器, 作 為穩定可調頻的本地振盪器, 此外也討論頻率合成器的理論與實作, 並進 一步分析本地振盪器的相位雜訊對傳送訊號的影響. 最後, 我們提一個新 的交換器架構, 相較於Omega 及Benes交換器, 它減少所經過的交換器數 目及阻塞機率. For broadcasting multichannel television signals, CATV system adoptsfrequency division multiplexing (FDM) to carry signals on different frequencies. Headends in the CATV networks behave as central offices in thetelephone network. Under the FDM based infrastructure, FDM switching could bea promising approach in the bidirectional CATV networks. In this thesis, westudy and implement an 16x16 FDM switching system prototype for CATV networks.Four incoming signals, locating respectively at 5-40MHz, 550-610MHz, 610-680MHz, and 680-750MHz bands, were converted to baseband in order to be switchedby the 16x16 switch. We adopted two stage conversion to resolve image problemand employed frequency synthesizers by phase-locked loop to achieve stablelocal oscillators. The theory and practice of PLL frequency synthesizers were discussed. We further analyze the affect of LO phase noise on the transmitted signal. Finally, we proposed a new switch architecture which can reduce thenumber of stages and blocking probability comparing with Omega and Benesswitches.