Overview: 802.15.4 Wireless Network Architectures for Controls Systems
Wireless technology in use with Building Automation, SCADA, Demand Response, DCIM and Energy Conservation applications is becoming more commonplace every year.
Many System Integrators have ventured into this space, some with better end results than others. The following informational subjects may help shed some light on how best to approach and select products and architectures for your intended application.
It is important to know what type of architecture the wireless products you may be considering using are. There are several that cover the field of commercially available products. The most common are:
- Point to Point
- Point to Multi-Point
- Star Mesh
Some basic definitions are in order here. There are basically 3 types of devices that you will deal with. Those are Reduced Function Devices (RFD), Full Function Devices (FFD) and Personal Area Network (PAN) Coordinators. Some manufacturers use alternative names relative to their product architecture.
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|The simple definition of a Reduced Function Device is that it is not a Router Repeater. These Devices are dependent upon being able to communicate directly to the PAN Coordinator or one or more Full Function Devices.||Full Function Devices, in addition to whatever form factor they are supplied as are Router Repeaters.||PAN Coordinators are the Network Management hub, and are termed as PAN Coordinators, Beacons, Gateways, Aggregators, Receivers and other reference names. They are the primary Network Management agent and the configuration mechanism for your Network.|
Point to Point Wireless Network Topology
|Point to Point architecture is usually found in definite purpose applications. Pulse Counters are a good example. At the meter an RFD is placed and wired to the Output of a Pulse generating meter. At the Receiver the pulse is replicated in the form of a dry contact closure which would be wired in to an Input of your BAS/SCADA system.|
Point to Multi-Point Wireless Network Topology
|Point to Multi-Point is a magnification of Point to Point where the particular manufacturer’s products may take many forms in terms of the RFD’s. This architecture depending upon the manufacturer may or may not in fact include the ability to have FFD’s acting as Repeaters so as to extend the range to overcome distance and barrier limitations your site presents.|
Mesh Wireless Network Topology
|Mesh architecture is where every device is an FFD and communicates as peers. The PAN Coordinator need not be able to directly communicate with all of the FFD’s. This type of architecture is very robust if in fact you have a high density of devices in a given physical geography. It is essential that the physical placement of the PAN Coordinator would allow it to communicate directly with several of the FFD’s. If it was only directly communicating with 2 FFD’s out of a Network of 64 FFD’s that would likely result in comm errors, buffer overloads on the devices and related issues.|
Star-Mesh Wireless Network Topology
|Star-Mesh Architecture combines FFD’s and RFD’s in a flexible and scalable Network. With some manufacturers you may be able to construct networks of several thousand devices reporting through a single PAN Coordinator. It strictly depends upon the physical environment where the various devices are located. As with any Wireless Network application where large numbers of devices are in play, data latency must be taken into account. Most manufacturers allow each device to have an independently set report interval. Others regulate latency by the physical numbers of devices allowed to exist on a single Network. In this architecture the RFD’s are dependent upon the FFD’s for communication to and from the PAN Coordinator.|
Now that you have the basics on the various topologies that the 802.15.4 technology can take we can now look at how to gauge, estimate and test your specific implementation. By doing this, you will help minimize your expense and exposure.
This technology is valid and it isn’t going away. The primary reason for that is cost reduction. We all know that cost is a big driver.
What types of situations have you come across that used 802.15.4 wireless sensors and devices? Was cost a factor versus using a wired solution?