建立無(wú)線運(yùn)動(dòng)檢測(cè)系統(tǒng)

　　無(wú)線技術(shù)是實(shí)現(xiàn)易于使用的運(yùn)動(dòng)檢測(cè)系統(tǒng)的關(guān)鍵。有一系列廣泛的無(wú)線技術(shù)用于將運(yùn)動(dòng)探測(cè)器連接到中心集線器，從ISM頻段到ZigBee，到Wi-Fi和其他因特網(wǎng)連接的協(xié)議，但無(wú)線鏈路的可靠性非常重要。從制造商如Atmel、Silicon Labs和恩智浦半導(dǎo)體器件，可以用不同的方式來(lái)提供無(wú)線連接到中央集線器作為一個(gè)強(qiáng)大的運(yùn)動(dòng)檢測(cè)和報(bào)警系統(tǒng)的一部分。

　　運(yùn)動(dòng)探測(cè)器變得越來(lái)越普遍，但結(jié)果是對(duì)各種惡意攻擊變得更加開放。這對(duì)運(yùn)動(dòng)傳感器系統(tǒng)的設(shè)計(jì)產(chǎn)生了影響，無(wú)線元素的關(guān)鍵是確保一個(gè)安全而靈活的實(shí)現(xiàn)，它適合于實(shí)際應(yīng)用——實(shí)際上在有入侵時(shí)能夠標(biāo)志。

　　在這種系統(tǒng)中，無(wú)線技術(shù)以多種不同的方式被使用。許多運(yùn)動(dòng)傳感器包括無(wú)線鏈路回到中央集線器，但這為開發(fā)人員提供了更多的技術(shù)和安全選擇。無(wú)線電波本身甚至被用作運(yùn)動(dòng)傳感器，比被動(dòng)紅外傳感器提供更多的能力。

　　The problem is highlighted by recent examples where thieves have drilled through walls to avoid motion sensors. One way around this problem has been developed by a US startup called Xandem. It is using the fact that the presence of a body reduces the penetration of radio waves， and so can be used to detect motion. Its tomographic motion detection （TMD） technology can sense through walls and obstructions， and senses over areas that are otherwise extremely difficult to cover. It can remain completely hidden from view， enhancing both the security and the aesthetics of the installation.

　　A Xandem TMD system is built with two kinds of devices： nodes and a processing unit. Multiple nodes surround the area where motion is to be detected， using mesh networking technology that senses when objects move within the area of the mesh， even through walls and obstructions. Each node is not a sensor; the mesh network connecting the nodes is the sensor. The processing unit is a gateway with normally-closed relays that connect to any standard panel to act as the hub.