| 摘要: | 最新技術的Wi-Fi傳輸標準802.11n，不僅有較大的無線網路傳輸頻寬，且有更大的覆蓋範圍及更佳的可靠性，達到802.11g與802.11a產品的六倍數據傳輸量。 802.11n選擇使用MIMO(Multiple Input，Multiple Output)多重發送卅接收技術為其核心，可利用多支天線發射及接送訊號，改善訊號延伸性及通道匯整功能，大幅增強訊號強度及穩定度。802.11n的PHY傳輸頻寬最高可提升到600MHz，並強化MAC效能與訊框匯集能力，也可同時支援2.4GHz及5GHz雙頻帶通訊與20MHz/40MHz通道，並能向下相容目前的802.11a/b/g規格。 在本論文中，我們選定四家市占率高的802.11n AP及Station在Infrastructure mode的架構下做最佳吞吐量的效能量測，並根據結果來做分析與比較，並找出目前市場上所使用的晶片組中最穩定及最佳表現的組合。另外我們依據IEEE草案提出的新技術的通訊協定來做效能測試，如綠燈區與混合模式的效能探討 、20MHz/40MHz通道的效能差距、及在相鄰或相同通道上有其他頻帶干擾所造成的影響，加以分析研究。在實際環境架設上，我們選定802.11n及802.11g模式在不同天線或相同頻帶上，在室內的地點來做效能測試，並針對這些有阻隔物或走道轉折不同距離的測試點，量測傳輸效能並做比較與分析。我們的實驗結果證實在多天線的整體表現上會有較快的傳輸頻寬及較佳的覆蓋範圍。 The latest standard of Wi-Fi technology, IEEE 802.11n, has greater wireless transmission bandwidth, broader transmission coverage and even more reliability than 802.11g and 802.11a. The data transmitting rate can reach six times which higher than the capacity of 802.11g and 802.11a. IEEE 802.11n utilizes MIMO (Multi-Input Multi-Output) as its core technology using multiple antennas to send and receive signals, which increases not only signal capability but overall network-capacity by using more channels. The experimental results show that significant improvement on both signal strength and signal stability. Therefore, the PHY (Physical layer) transmission bandwidth of 802.11n can reach up to 600MHz, which strengthens MAC (Media Access Control layer) enhancement and frame aggregation. Consequently, it is capable of supporting 2.4 and 5GHz dual-band network and 20/40 MHz bandwidth as well. Furthermore, it is compatible with the current specification of 802.11a/b/g. In this thesis, we choose the most four popular 802.11n APs (Access Point) and Stations from the market, and then evaluate their performance under infrastructure mode. According to out experimental results, we will identify the combinations of the most reliable and efficient chip which are available in the market. In addition, some experiments are performed based on the protocols of latest IEEE draft standard such as (1) working on the Greenfield and the Mixed mode, (2) the differences of 20 MHz/40MHz bandwidth, and (3) the effect of other band interference working on the same bandwidth. These experimental results are analyzed and discussed in depth. Otherwise, in order to set up the experimental environment, the modes of 802.11n and 802.11g are used at the same indoor environment with two different restrictions: the different antennas and the same types of bands. We also do some experiment that we set up some different access points in the environments of blockage, paths with multiple crossroads and various distances. According to our experimental results, we confirm that using multiple antennas the transmission can become faster and provide better coverage area. |
