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The search for the right wireless technology

Posted: 28 Mar 2016 ?? ?Print Version ?Bookmark and Share

Keywords:cloud? Wi-Fi? Internet of Things? IoT? ZigBee?

If your gateway has a complete application level overview of the devices on the network and their functions and encrypts and decrypts all messages, 6LoWPAN does not provide much value. This is generally the case if you're building a network that needs to continue to provide functionality when the Internet connection is not available. This is the case for lighting or home automation networks where you expect light switches and alarm functions to work even during a loss of Internet connection. The gateway would then expose the entirety of the network functionality to a cloud server with an application specific interface.

If, on the other hand, the service that your network provides is of little value without the Internet connection, you can use 6LoWPAN with a much simpler application on your gateway and have it simply pass messages between your end nodes and the Internet much like your Wi-Fi router does. The advantage is that authentication and encryption can be end-to-end so data does not have to be decrypted and re-encrypted in the gateway. It means that the gateway does not have to be a trusted party in your application, and one can imagine a single gateway serving many different applications from different vendors in the future. The burden of establishing an https connection or similar is moved to the end node. Do you need interoperability at the application level?

Figure 2: Application intelligence in the gateway.

Do you need interoperability at the application level?
Back to the example of the wireless light, simply by choosing Wi-Fi for example, the standard does not dictate how the light should connect to the server or what a "turn on" message should look like. This means that two Wi-Fi lights are not likely to be interoperable at a local level. You cannot expect that if you buy a Wi-Fi light switch from one vendor, it will be able to successfully control a light from another vendor without passing through translation at an application-aware server. ZigBee is one of the few infrastructure protocols that have endeavored to make certified interoperable products at an application level. It's a brave undertaking and has not been without its challenges, but some of the profiles have reached a considerable rate of adoption.

To mesh or not to mesh?
One of the challenges with mesh networks is that the network topology is complex and requires route discovery with healing, addressing, mesh over or mesh under routing algorithms and handover mechanisms to deal with mobile nodes that physically and topologically move through the network. This adds significant memory requirements to routing nodes in the network and complicates testing and debugging significantly.

A good alternative in networks with a central node/gateway is to go with a simple star network topology with range to cover the whole house/building. To get the required range and penetration of walls and floors with a low-power network, the Sub-1GHz frequencies are ideal. The 868MHz band in Europe and 915MHz band in the North America offer a good compromise between penetration, data rate, and required antenna size for indoor applications. This is how most alarm and security networks are built for example.

The new thing is that there are devices that support standards based PHY's for Sub-1GHz operation based on IEEE 802.15.4g. The FSK (Frequency Shift Keying) PHY itself is nothing new, in fact it is probably among the most shipped low-power radio PHYs, but it has not been standardised for use in IoT solutions before now. The advantage of choosing a standards based solution is that several vendors offer compatible solutions that gives flexibility in vendor choice and even offers the prospect of buying hardware components to your network from a third party (the Internet gateway for example).

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