蜂巢式多階無線網路：架構、路由、實作

Abstract

本篇論文提出了一個蜂巢式多階(MCN)的無線網路架構，它保留了傳統蜂巢式單階網路架構(SCN)的好處，其中SCN需建置許多固定基地台以提供服務；另外，MCN也結合了任意(ad-hoc)網路架構的靈活性，其中ad-hoc 網路可允許資料封包經由其它行動台轉送以達到多階路由。MCN可以減少所需的固定基地台數目並提昇網路效能，另外它也儘量避免了在ad-hoc網路所遇到的路徑易斷的弱點。本論文包含了三個部份：(1)MCN和SCN的效能分析與比較，(2)為MCN設計的路由協定，和(3) MCN原型的實作。 首先是分析與比較MCN與SCN在不同封包流量與不同訊號傳輸距離時的效能表現，分析結果顯示MCN表現的比SCN好，並且效能表現隨著訊號傳輸距離減小而增加，這主要是因為平均階數和平均同時可傳送的封包數隨著訊號傳輸距離減小而分別以線性和平方次的方式增加。接著，鑑於原有的路由協定並不能完全適用於MCN，本論文亦設計了一個中央具計算能力的混合式路由協定，其中基地台利用表格驅動(table-driven)的方法追蹤網路拓撲圖，因而可進一步為行動台計算所需的路徑以展現中央計算能力；當行動台需要路徑時會先以單一傳送(unicast)方式送詢問信息給基地台，若行動台沒有收到基地台的回答就會用泛流方式去廣播詢問信息給所有的行動台，而此泛流方式則源於需求驅動(demand-driven)路由協定，如AODV；本論文經由系統模擬的結果驗證效能分析的結果，並且得知當MCN的訊號傳輸距離是SCN的1到1/4倍時其效能表現是SCN的2至3倍；另外由於具中央計算能力，此混和式路由協定的總體表現比AODV好，因為大部份的詢問信息是利用unicast方式送給基地台從而大幅降低詢問信息的數量。最後，本論文亦在無線網路平台上實作出一個具備多階繞路及漫遊兩大重要功能的網路模型，從而證明MCN架構的可行性。

This study presents a novel architecture, multihop cellular network (MCN), for wireless data communications. MCN preserves the benefit of conventional single-hop cellular networks (SCN) where the service infrastructure is constructed by fixed bases, and it also incorporates the flexibility of ad-hoc networks where wireless transmission through mobile stations (MSs) in multiple hops is allowed. MCN can reduce the number of required bases or improve the throughput performance, while limiting path vulnerability encountered in ad-hoc networks. This thesis consists of three parts: (I) the modeling of MCN and SCN, (II) the routing protocol designed for MCN, and (III) the implemented prototype of MCN. First of all, this thesis analyzed the performance of MCN and SCN in terms of mean hop count, mean number of channels (i.e. simultaneous transmissions), hop-by-hop throughput, and end-to-end throughput under different traffic localities and radio distance. Analytical results show that the throughput of MCN exceeds that of SCN; the former also increases as the radio distance decreases. The above results can be accounted for by the different orders, linear and square, at which mean hop count and mean number of channels increase, respectively. Then, because the existing routing protocols designed for ad-hoc networks are not suitable for MCN, herein, a hybrid of table-driven and demand-driven protocols with base-centric computing is designed. The base tracks network topology by the table-driven method and can thus compute paths for MSs, constituting base-centric computing. When MSs need paths, the path query messages are unicast to the base. If MSs do not obtain paths from the base, then path query messages will be flooded as in demand-driven AODV. The simulation confirms the analytical results and shows that the throughput of MCN is about 2 to 3 times that of SCN when the radio distance is 1 to 1/4 of that in SCN. Besides, with the base-centric computing, the hybrid protocol overall outperforms AODV because most path query messages are unicast to the base and the overhead is greatly reduced. At last a prototype of MCN, capable of multihop routing and roaming, is implemented over a wireless LAN platform. Demonstration shows that MCN is a feasible architecture for wireless LANs.