無線網絡的拓撲結構

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

　　無線局域網

　　Wi-Fi在過去的十年里已經很好地建立起來了，在個人電腦和移動電話上實現了接入點和客戶終端的低成本基礎設施。它使用具有沖突檢測和TCP/IP包的共享體系結構，非常適合互聯網連接，但不太適合嵌入式應用程序。一個低速率的網絡鏈接，如10 Mbit / s的802.11b，當一個節點要鏈接到一個繁忙的網絡碰撞檢測迫使它倒經常和數據鏈路的速度很慢。這就限制了Wi-Fi在過去工業網絡中的應用。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技術更為廣泛的網絡應用越來越普及。802.11n的MIMO功能，提供更高的靈敏度，從而轉化為更長的距離（和更少的接入點，因此，較低的成本對于一個大型網絡）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.