如何设计低成本的亚GHz无线接入控制的物联网

　　如何设计低成本的亚GHz无线接入控制的物联网

　　安全和访问控制是物联网系统设计者关注的两个关键领域，但在实施成本上存在着很大的挑战。本文着眼于设计的选项使用亚GHz ISM频段如Z-Wave保持低成本无线安全接入控制系统

　　不受管制的ISM（工业，科学，医疗）无线频段在各种应用中非常流行。亚GHz频段在868兆赫在欧洲和美国的915兆赫特别受欢迎，主要是相对较低的成本实现。

　　在这些频段操作有许多优点，从范围开始。这些RF频带的渗透是显着长于在2.5 GHz和5 GHz的高ISM频段，这给设计师更多的选择在访问控制系统的发展。

　　更长的范围内可以交易更长的电池寿命，使用较少的权力，使一个链接。试图建立一个链接，在最远的范围内达到或通过门或墙壁可能需要更多的权力。限制的范围，然后给出了更长的电池寿命或允许较小的电池使用与较短的范围内，降低了整体系统的尺寸和成本。最新的射频设计技术和制造技术也很好地建立在这些频率。这意味着低成本CMOS技术可用于收发器，增加了组件的集成在一个单一的设备，并进一步降低成本。因为许多这些收发器也可以用在简单的无线传感器的设计，工作在同一ISM频段，也有规模效益，进一步降低成本。

　　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.