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
  • Mesh
  • 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.

 

Reduced Function
Device

Full Function
Device

PAN
Coordinator

 reduced-function-wireless-device full-function-wireless-device Primary Network Management agent and the configuration mechanism for your Network.
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-pointPoint 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-pointPoint 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-wireless-networkMesh 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-wireless-networkStar-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?

 

7 Responses to Overview: 802.15.4 Wireless Network Architectures for Controls Systems

  1. Bill Simpkins September 11, 2013 at 15:57

    What I tell specifying Engineer is that it isn’t a matter “if” you will specify a wireless system but “When” will you specify a wireless system. Wireless is here to stay and it is faster and with less comm errors if it is designed and installed correctly.

    Reply
    • Abel B Ramirez II September 11, 2013 at 16:46

      I agree and the last two things you mentioned are the keys to it all… designed and installed correctly.

      in a phone conversation with Dave, I had said I screwed up big time buying to really cool 2 mile antennas to throw wireless Ethernet across the rooftops of two buildings a few 100 feet away from each other. EASY right?… Wrong.

      On the top edge of the roof was a 10 foot slanted metal awning that shaded the top floor windows. Now this only extended above the roof line a couple of feet and the antennas were mounting on top of the penthouse roof so they were atleast 12′ above that metal awning thing…

      Well it was enough to freak out the antenna signal and though we test them in a parking lot before hand, they didn’t work up on the roof after two days of sweating in 100° Texas sun. We ended up begging for a pair of fiber already run between buildings.

      Reply
  2. Jason Davd September 11, 2013 at 23:44

    When it comes to wireless comms, it is 80% of you design is at the mercy of the signal quality at the antenna, the quality of the radio and protocol is the other 20%. How many times have you seen a $1000+ radio equipment connected to a $10 antenna!

    Makes me chuckle.

    Reply
  3. Dave Craven September 12, 2013 at 06:45

    Antenna design and selection is important. That is why we have in board “F” antenna design on all but one of our products. Performance is predictable and uniform. The bigger issue that most first time users run into is basically exceeding device overall range when they lay out a project. Which is what this multi-part series will elaborate on.

    Reply
  4. Michael Lulchak September 13, 2013 at 15:48

    Does anyone have tools to assist in trouble-shooting wireless systems (mesh or otherwise)?

    When things stop working – where do you start?

    Can you isolate interference issues?

    What about equipment failures?

    Reply
  5. Dave Craven September 15, 2013 at 07:27

    Good questions. We actually go into those areas in subsequent sections of the series. There is a great free tool you can put on your Laptop called I N S S I D E R. Sorry the spell check overrides my typing the I , N , E and R are actually lower case. This application gives you a slick real-time view of the immediate geography in terms of existing RF services. This would normally be used prior to installation.
    After something gets installed and then stops functioning you have to rely on the toolset within the manufacturer’s product. Signal strength, actual network links are two essential tools that the product should have.
    Something you should ask before you buy is the 5 year product failure rate history, anything in excess of 2% should be avoided.

    Reply
  6. Abel B Ramirez II September 15, 2013 at 18:48

    inSSIDer is available from METAGeek.net. The Basic version is free and the Professional version has a free trial offer.

    Home/Basic Version – http://www.metageek.net/products/inssider/
    Office/Professional Version – http://www.metageek.net/products/inssider-for-office/

    Android – https://play.google.com/store/apps/details?id=net.metageek&hl=en
    MAC App Store – http://itunes.apple.com/us/app/inssider/id507308266?mt=12&ign-mpt=uo=4

    Reply

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