進階性無線網路媒介存取控制與路由協定技術

Abstract

由於近年無線區域網路技術的興起，使得提高單位時間內有效的資料傳輸量成為很重要的議題。IEEE 802.11n中，訊框堆合為改善整體傳輸效率技術之一。為了使訊框堆合能有效使用於非理想傳輸通道中，錯誤重傳機制提供了可靠傳輸的解決辦法。在此篇論文中，針對選擇性訊框重傳以及混合式選擇性訊框重傳配合訊框堆合技術進行效能分析。混合式選擇性訊框重傳技術，利用直接錯誤更正技術，將發生錯誤之訊框直接更正，進而降低重傳訊框時所耗費的時間並提高了有效傳輸資料量。結果我們可以發現，當處於雜訊環境中，混合式選擇性訊框重傳機制配合訊框堆合技術，可以達到大幅提高有效資料傳輸量的目的。 論文的第二部份，針對無線網路中的群播協定進行研究與設計。當處於無線環境中，由於群播協定中常需要轉傳點以傳送資料至特定群組成員。而相同的資料封包，常存在有多餘的轉傳點傳送。若以省能點觀點角度思考，如何節省轉傳點的數量為實際面臨的問題，此篇論文對此問題提出試誤性的解決辦法，並實際利用嵌入式平臺作為演算法設計之系統。

The next generation wireless local networks (WLANs) with enhanced throughput performance have attracted significant amounts of attention in recent years. Based on the IEEE 802.11n standard, frame aggregation is considered one of the major factors to improve the system performance of WLANs from the medium access control (MAC) perspective. In order to fulfill the requirements of the highthroughput performance, feasible design of automatic retransmission request (ARQ) mechanisms is considered important for providing reliable data transmission. However, none of the existing retransmission schemes is specifically designed under high throughput requirements. In this paper, two ARQ schemes are proposed to consider the effect from frame aggregation for the enhancement of network throughput. An aggregated selective repeat ARQ (ASR-ARQ) algorithm is proposed, which incorporate the selective repeat ARQ scheme with the consideration of frame aggregation. On the other hand, the aggregated hybrid ARQ (AH-ARQ) mechanism is proposed to further enhance the throughput performance by adapting the forward error correction (FEC) scheme. The proposed AH-ARQ algorithm is considered as a MAC-defined retransmission scheme by exploiting the Reed-Solomon block code. The analytical models for both the ASR-ARQ and the AH-ARQ algorithms are established in this paper, where the scenarios with and without interfering stations are analyzed. Simulations are also conducted to validated and compare the proposed ARQ mechanisms with other existing schemes based on the service time distribution. It will be shown in the numerical evaluation that the proposed AH-ARQ algorithm outperforms the other retransmission schemes owing to its effective utilization of the FEC mechanism. In the second part of this paper, we focus the topic on the implementation and design of a multicast routing protocol. It is known that how to provide low energy consumption and high packet delivery ratio are considered the major issues in the protocol design for the wireless multihop networks. The main focus of this part is to reduce the number of data transmissions such that the energy consumption can be decreased. In the wired networks, the Steiner-Tree is regarded as an optimal approach to construct the multicast structure for specific senders and receivers. However, it is considered an NP-Hard problem for achieving the minimum cost multicast tree under the wireless broadcast environment. In this paper, an Energy-Conserving Multicast Routing (ECMR) protocol is proposed as a heuristic scheme to reduce the number of relaying nodes for the construction of the multicast mesh. Moreover, the proposed algorithm is implemented on an ARM-based embedded platform for performance evaluation. Comparing with the existing multicast routing protocol, the experimental results show that the proposed ECMR scheme can provide better energy conservation while the packet delivery ratio is still preserved.