Personal Area Networks (PAN) – A Simple Primer
The previous two articles in this series described the IEEE specifications for radios commonly used in Industrial and Building Automation (IA and BA) applications. We compared these radios to Ethernet. Instead of wire, the transceivers and media access software used in radios sends data over the air instead of through wire.
From that broad overview on radio technology discussed in the previous articles we are going to focus more closely on 802.15.4, also called Personal Area Networking but often confused with Mesh, Zigbee, Wireless Hart and other technologies. For the most part, those technologies are software built on the basic infrastructure known as 802.15.4.
So why is 802.15.4 the base technology for all these wireless systems when there is a plethora of technologies that could be used? The reason is that 802.15.4 has the right features for many applications we find in building, home and building automation.
It’s obvious that no technology can meet the requirements of every application. Remote data collection in the Sahara or the Arctic requires satellite. High data throughput or long range data applications are usually cellular. But for the majority of IA and BA applications 802.15.4 provides the best combination of features that makes it nearly ideal for these applications. These same features also make it close to ideal for Medical, Gaming, Home Automation and other applications. Here are some of the reasons why:
COST – Target applications for 15.4 devices are thermostats, level sensors, medical sensors and a host of low data rate devices. Most if not all of these devices are single point. Making a cost effective radio solution that is viable for single point analog or discrete signals was a major focus for the 15.4 technology definition team.
POWER – 802.15.4 are pretty low power systems making them excellent for low data rate applications. A 15.4 radio might use just 3 Milliwatts of power where your cell phone uses a whopping 3 Watts. And unlink your cell phone 15.4 radios aren’t on all the time. They’re on only when necessary making them almost ideal for battery powered applications that transmit data sporadically. An 802.15.4 node can spend most of its day snoozing. That’s perfect for your conference thermostat but not very good for I/O on your high speed conveyor line.
SHORT RANGE – 802.15.4 is designated as a PAN, a Personal Area Network. That means devices within 10-75 meters which is similar to your home WiFi (10-100m) but considerably more than your Bluetooth headset (10m).
LOW DATA RATES – 15.4 is designed for those applications that don’t send a lot of data therefore it doesn’t need a lot of speed. In fact, the highest data rate for 15.4 is for is only 250Kb (2.4Ghz operation). And the data rates are less for other frequencies; 20Kb for 868Mhz and 40Kb for 915Mhz. These data rates, though small, are entirely satisfactory for the majority of sensor devices in building and industrial automation.
In our next article we’ll explore the 802.15.4 Physical interface. How does data get on the air and what are the important electrical characteristics of an 802.15.4 radio?
John Rinaldi is the Technical Sales Manager for Real Time Automation in Brookfield, Wisconsin. RTA specializes in industrial and building automation software, hardware, systems and specialty controllers. He can be reached on 262-439-4999 or through the RTA website, http://www.rtaautomation.com/forms/contactus.html.