如何設計低成本的亞GHz無線接入控制的物聯網

　　安全和訪問控制是物聯網系統設計者關注的兩個關鍵領域，但在實施成本上存在著很大的挑戰。本文著眼于設計的選項使用亞GHz ISM頻段如Z-Wave保持低成本無線安全接入控制系統

　　不受管制的ISM（工業，科學，醫療）無線頻段在各種應用中非常流行。亞GHz頻段在868兆赫在歐洲和美國的915兆赫特別受歡迎，主要是相對較低的成本實現。

　　在這些頻段操作有許多優點，從范圍開始。這些RF頻帶的滲透是顯著長于在2.5 GHz和5 GHz的高ISM頻段，這給設計師更多的選擇在訪問控制系統的發展。

　　更長的范圍內可以交易更長的電池壽命，使用較少的權力，使一個鏈接。試圖建立一個鏈接，在最遠的范圍內達到或通過門或墻壁可能需要更多的權力。限制的范圍，然后給出了更長的電池壽命或允許較小的電池使用與較短的范圍內，降低了整體系統的尺寸和成本。最新的射頻設計技術和制造技術也很好地建立在這些頻率。這意味著低成本CMOS技術可用于收發器，增加了組件的集成在一個單一的設備，并進一步降低成本。因為許多這些收發器也可以用在簡單的無線傳感器的設計，工作在同一ISM頻段，也有規模效益，進一步降低成本。

　　However， there are also disadvantages. These bands are very popular and so are particularly crowded. This means a lot more attention has to be paid to interference by other systems. This can mean having to have wider guard bands on a channel or having to implement frequency-hopping protocols， which have not been necessary in the past. This is also a challenge for developers of systems that have to be secure such as access control and building automation to protect against both inadvertent interference and deliberate tampering. The longer range gives tremendous benefits， but there is an increased risk of interception of the signals. These can be decoded to provide access codes， or copied and re-broadcast. This copy can either be used as a man-in-the-middle-attack to gain access to wider systems， or re-broadcast at a later time to let in an intruder.

　　This is leading to a need for further security techniques， such as encryption and one-time codes， to be added to relatively simple system designs.