無線網(wǎng)絡(luò)的拓撲結(jié)構(gòu)

　　有許多不同的拓撲可以用于無線網(wǎng)絡(luò)，每個網(wǎng)絡(luò)具有廣泛的不同功能集。有密切聯(lián)系的特定頻段，包括共享網(wǎng)絡(luò)，如Wi-Fi、ZigBee網(wǎng)狀網(wǎng)絡(luò)等，都在2.4 GHz頻段，而其他如Z-Wave可以用在許多不同的樂隊。未經(jīng)許可的ISM頻段有幾種不同的拓撲和協(xié)議，以及點對點無線網(wǎng)絡(luò)。

　　無線局域網(wǎng)

　　Wi-Fi在過去的十年里已經(jīng)很好地建立起來了，在個人電腦和移動電話上實現(xiàn)了接入點和客戶終端的低成本基礎(chǔ)設(shè)施。它使用具有沖突檢測和TCP/IP包的共享體系結(jié)構(gòu)，非常適合互聯(lián)網(wǎng)連接，但不太適合嵌入式應(yīng)用程序。一個低速率的網(wǎng)絡(luò)鏈接，如10 Mbit / s的802.11b，當一個節(jié)點要鏈接到一個繁忙的網(wǎng)絡(luò)碰撞檢測迫使它倒經(jīng)常和數(shù)據(jù)鏈路的速度很慢。這就限制了Wi-Fi在過去工業(yè)網(wǎng)絡(luò)中的應(yīng)用。然而，與802.11g標準的快和多，多出（MIMO）802.11n，提供顯著更高的利率，秋天的效果降低，這些2.4 GHz技術(shù)更為廣泛的網(wǎng)絡(luò)應(yīng)用越來越普及。802.11n的MIMO功能，提供更高的靈敏度，從而轉(zhuǎn)化為更長的距離（和更少的接入點，因此，較低的成本對于一個大型網(wǎng)絡(luò)）或更多的能力更強大的鏈接。

　　However， this popularity has come at a price. As more equipment becomes network enabled – from printers to phones – so the 2.4 GHz band is becoming increasingly congested. Even with the higher data rates， this is starting to slow many 2.4 GHz Wi-Fi networks， and means the network nodes have to consume significantly more power. This means the units have to be designed for more heat， making them more costly， or run the risk of early failure and costly replacement cycles.

　　All this is creating more interest in the 5 GHz band defined in the IEEE802.11a standard and the emerging 802.11ac standard. This is starting to drive up volumes and drive down costs. 802.11ac is the fifth generation of Wi-Fi and uses the 5 GHz band and beam forming to provide faster throughput， higher capacity， broader coverage and longer battery life.