標題: 軌道通訊系統設計與分析:車對地、車廂間與車站內通訊
Design and Analysis of Railway Communication System: Train-to-Ground, In-Train and In-Station Communications
作者: 王鴻翔
Wang, Hung-Hsiang
吳文榕
陳志成
Wu, Wen-Rong
Chen, Jyh-Cheng
電信工程研究所
關鍵字: 軌道通訊;光載無線電;分散式天線系統;迴聲通道;換手;符碼間干擾;分時長期演進技術;時序飄移;裝置間直接通訊;比例式公平;Railway Communications;Radio over Fiber; RoF;Distributed Antenna System; DAS;Echo channel;Handover;Inter-Symbol Interference; ISI;Time Division Long Term Evolution; TD-LTE;timing drift;Device-to-Device Communication; D2D;Proportional Fair; PF
公開日期: 2015
摘要: 近年來對於如何在軌道運輸系統中提供寬頻服務的技術研究獲得大量關注。本論文主要對軌道通訊;包含了車對地通訊,車廂間與車站內通訊系統;進行整體性的系統設計考量與分析。 在車對地的通訊研究方面,主要為分析並解決當系統布建採用分時雙工之分散式天線系統架構(Time Division Duplex - Distributed Antenna System;TDD-DAS)的問題:包含了遠端天線單元(Remote Antenna Unit;RAU)訊號涵蓋的範圍(coverage)以及迴聲通道(echo channel)效應。在軌道車對地通訊中採用分散式天線系統架構的目的,主要為擴大單一基地臺所能服務的訊號涵蓋範圍:透過複數個遠端天線單元將訊號延伸至如隧道等等的覆蓋盲區(coverage hole)來提升服務訊號品質,或藉由擴大訊號涵蓋範圍來減少換手(hand over)的發生頻率。然而由於這些遠端天線單元所傳送的訊號都來自同一個訊號源,因而造成了迴聲通道效應-即接收端會受到同時來自不同方向的相同訊號所造成的符碼間干擾(Inter-Symbol Inter-ference;ISI)效應,造成解調的錯誤而使系統效能降低。雖然使用移動天線(moving antenna)技術可解決在TDD-DAS的迴聲問題,但我們發現若採用此設計方法將造成資料上行(Uplink;UL)方向的時序漂移(timing drift),進而損害系統效能。為了克服這個問題,我們提出了天線選擇及時間補償的控制技術:藉由控制訊號傳輸天線的啟用與關閉來解決迴聲問題,並進一步配合時間的補償來解決上行方向的時序漂移問題,以維持傳輸訊號的穩定性。在研究中以分時長期演進技術(Time Division Long Term Evolution;TD-LTE)系統為例,針對TD-LTE的系統參數來制定天線控制所造成的通道變化程度之決定準則(criteria)分析與擬訂。模擬結果顯示,所提出的時間補償天線的控制技術能有效地解決迴聲通道與改善上行時序飄移問題。 在車廂間或車站內通訊研究方面,主要為考慮在這些服務地點進行裝置間直接通訊(Device-to-Device communication; D2D)的應用情境,利用資源空間重複增益(resource spatial reuse)的特性,來提升頻譜使用效率。考慮在裝置間直接通訊的架構下,由一個中央控制單元對直接通訊裝置進行無線通訊資源排程(scheduling),以同時達到最大化系統效能(system throughput)及資源公平性(fairness)分配的目標。提出的資源排程演算法為將直接通訊資源劃分為兩個區間:資源專用區間和資源競爭區間,並考慮空間重複增益和滿足比例式公平性(Proportional Fair;PF),提出基於PF metric值來做為決定準則,進行動態調整資源分配區域和資源競爭區域之間的比例。透過模擬結果顯示,所提出的演算法可有效利用空間重複增益來提高系統整體效能,並且維持所有裝置間直接通訊使用者擁有資源比例式公平性。
It has attracted much attention to provide broadband wireless services in railway transport systems in recent years. In this dissertation, we aim to analyze and overcome some issues in railway communication systems, including train-to-ground communications, in-train communications and in-station communications. For the train-to-ground communications, we discuss echo channel effect and define the corresponding criteria in a Time Division Duplexing (TDD) DAS railway com-munications system. Furthermore, timing drift problem while applying moving an-tenna selection technique to solve the echo channel effect is illustrated. Compensation algorithms then are proposed. Simulation results show that the proposed techniques can solve not only the interference problem in TDD-DAS, but also provide better scalability in system deployment. In the in-train and in-station communications, we consider a central-controlled D2D architecture, in which a cellular operator can decide whether mobile devices can connect to each other directly. We aim to maximize system throughput while also achieve fairness in resource allocation. An algorithm that separates resource frame into resource-dedicate area and resource-contention area for fairness and throughput improvement is proposed. The algorithm dynamically adjusts the boundary of the resource-dedicate area and resource-contention area. Criteria based on Proportional Fair (PF) metric are formulated. Simulation results show that the proposed algorithm can maintain good fairness level and increase system throughput by exploring radio resource spatial reuse gain among D2D communication pairs.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079413812
http://hdl.handle.net/11536/125964
Appears in Collections:Thesis