Wireless Personal Area Networks
A significant number of development projects have a wireless component. There are many different wireless technologies available, including Wi-Fi, GSM, RFID, Bluetooth, 2.4G custom protocols and Personal Area Networks. Personal Area Networks use a high level communication protocols to create area networks built from small, low-power digital radio-enabled devices.
Personal Area Networks in particular have been growing in popularity; this is due to a number of factors:
◦ Small form factor
◦ Low power solutions available
◦ Low complexity improves reliability
An expansion port with a supply rail and SPI communication can easily provide the option for wireless connectivity in the future.
Personal Area Network Solutions
Among the many providers of Personal Area Network (Wikipedia) solutions are Microchip, Atmel and Texas Instruments; each of which supports a variety of protocols. Some of the protocols available and some we have worked with include:
◦ Microchip: ZigBee and custom MiWi protocol
◦ Atmel: ZigBee and custom ZigBit modules
◦ Texas Instruments: ZigBee, SimpleLink and custom SimpliciTI protocol
Figure 1 – A small, low-power circuit using a Microchip module and MiWi module
These protocols and modules encompass a wide range of capabilities and features. When choosing a protocol and module, the key requirements include:
Solutions exist which support everything from two to many thousands of networked devices.
The way in which the devices are linked together affects the complexity, latency and reliability of the network. The simplest topology is a peered network, where each device only communicates directly to its neighbours.
Figure 2: Peered Topology
For a larger network, a cluster-tree topology introduces routing, allowing messages to be sent to non-neighbouring devices through established “branches”.
Figure 3: Cluster-Tree topology
While the cluster-tree topology allows for routing, it does not do so in the most efficient way – some messages will be routed all the way down to the base of the tree before being routed back out to the destination. For a more adaptable, reliable and faster network a mesh topology is more suitable. Mesh networking allows each device to freely route along the most direct path.
Figure 4: Mesh topology
The range of a module can vary from a few metres to hundreds of meters.
Many modules and protocols allow low power devices which can easily achieve a battery life of two or more years.
Modules come in small form factors, 10mm to 20mm.
Many of the vendors have solutions that will meet many needs, and have evaluation boards for quickly getting a network working, speeding up development time. Experience with a particular module or protocol is invaluable for assessing and selecting technologies. Many performance limitations are unknown and only discovered once the development process has started. A selecting newly released technology, or the first generation, is always a flag for being cautious.
There are tight Regulations around wireless systems and the process for getting approval is time consuming and expensive process. Many of the above solution providers have pre-approval, which results in faster and cheaper product development with less risk.
Interconnectivity between electronics devices is a growing requirement. Personal Area Network technology provides a platform for creating a small to large, short distance wireless network, with the ability to improve efficiency, security and convenience.