應用於IEEE 802.11智慧型天線系統信標訊號效能增強之設計

Design of Enhancing Beacon Performance in IEEE 802.11 Smart Antenna System

李雯菁(Wen-Ching Lee)

指導教授 ： 許獻聰

國立中央大學/資訊電機學院/通訊工程研究所碩士在職專班/碩士(2014年)

摘要

隨著無線通訊科技的迅速發展，內建無線區域網路 (Wireless LAN, WLAN) 功能的終端裝置以及無線接取點 (Access Point, AP) 裝置架設的普及化，WLAN的技術已廣泛的應用在商務區、學校、機場及其它公共區域，使得無線網路的使用需求也越趨高速、穩定、省電、涵蓋率高等技術上發展，然而智慧型天線技術的開發，提供了較高的涵蓋率與相對聰明的服務。
智慧型天線技術可以視為充分利用空間資源進行訊號傳輸品質的提昇，干擾的抑制及適應性波束調整的機制。信標訊號 (Beacon) 主要是用來宣告網路的存在，定期傳送的信標訊號，可以讓行動工作站 (Mobile Station, MS) 知道網路的存在，從而調整加入該網路所需的參數，而Beacon 所涵蓋的範圍即為網路基本服務區域，一般陣列式智慧型天線系統，會因為所選擇的陣列天線方向的不同，使得新加入的MS接收AP的信標訊號封包遺失，然而此類系統應用於室內環境，會受限於天線陣列的方向與環境的遮蔽，造成電磁波訊號的多重反射與折射現象，而產生Beacon封包遺失的結果。所以，為了提升MS對於網路基本服務區域的整體感受，設計適當且有效率的Beacon 接收顯得相對有其必要性。
本論文提出智慧天線系統利用全向性天線 (Omni Antenna) 發送Beacon的概念，藉由一個擁有涵蓋方向全面的天線來發送Beacon封包，不僅可以達使用一個AP，擁有高的訊號傳輸品質與好的抗干擾性，且MS感受上可以達到較好的網路涵蓋率。實驗結果顯示出，藉由全向性天線發送Beacon封包，能使來自各方向的MS接收到的Beacon數量維持在高接受率的表現。此實驗不僅可以實現原系統的高品質傳輸，並且提升了AP的高涵蓋率的感知。結果說明，本論文提出的智慧天線系統信標訊號效能增強的設計能讓Beacon接收率提升。

關鍵字

無線區域網路 ； 無線接取點 ； 行動工作站 ； 信標訊號 ； 智慧型天線系統 ； 全向性天線

並列摘要

With rapid growth of Wireless LAN (WLAN), mobile devices and access point (AP) have become more popular. For example, WLAN technology has been widely used in business districts, schools, airports and public areas. Development of smart antenna technology is important to provide a full coverage for smart services.
The smart antenna in modern wireless networks has enhanced the quality of wireless data links under the situations of limited spectrum and severe wireless channel fading. Array antenna for wireless system often uses unique technique of beam forming. By properly applying adaptive algorithms, the smart array antenna can be effective with the use of interference cancellation technique. Normally, beacon frames contain all the information about the operating WLANs. That is, beacon frames are transmitted at an AP periodically for announcing the presence of a WLAN. In a WLAN with smart antenna solution, beacon loss ratio could be increased due to the directional of signals. Therefore, in order to enhance the coverage for whole basic service area, it is necessary to consider the coverage of beacon frames.
This paper compares the performance of smart antenna and traditional Omni-directional antenna in terms of beacon loss ratio and coverage area. Experimental results shows that the WLAN with smart antenna still requires an Omni-directional antenna for the beacon transmission.

並列關鍵字

Wireless LAN ； Access point ； Beacon ； Smart antenna system ； Omni-directional antenna

參考文獻

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