While at the Embedded Systems Conference in Minnesota I attended a session entitled “Introduction to RF for Embedded Designers” presented by Kyle Sporre, RF hardware manager, and Dustin Morris, antenna engineer, of Digi Wireless Design Services. The pair presented a look at RF technology for developers without much prior experience in dealing with RF now tasked with adding wireless connectivity to their embedded designs. Rather than focus on theory, however, they presented approaches to consider along with practical advice designers can apply immediately. Here are five of the tips that I considered among the most important.
Consider the tradeoffs — One of the first things developers should do is consider the system tradeoffs they must make when developing a wireless system. These include:
- Range vs data rate – All other factors held frozen, the achievable range of a wireless connection goes up as data rate decreases. You'll have to decide which of them is most important.
- Range vs antenna size – Antenna performance (gain) is directly proportional to its size up to half the wavelength for the operating frequency. Given that the antenna is the last stage of transmission and the first stage of reception, its performance has a major impact on the achievable range for the design.
- Power consumption vs data rate/throughput, range – If minimizing power consumption is your aim, you may have to compromise on data rate or range or both.
- Bill of material vs infrastructure cost – An inexpensive radio is unlikely to achieve top performance, so the infrastructure of gateways, receive towers, and mesh nodes will need to make up the difference. This typically requires more sophisticated (and expensive) antennas, closer tower spacing, or the like, increasing the system's infrastructure cost.
Start mechanical design with the antenna — Because the antenna is a critical component in radio performance, a wireless embedded system's mechanical design should cater to the antenna's needs, rather than have the antenna be constrained by the mechanical design. The antenna's size and the size of its ground plane affect antenna efficiency as well as achievable bandwidth, so ensure that adequate space is provided. Further, the antenna's placement is important. Avoid other conductors, absorbers, and dielectrics. Especially stay away from things like batteries, LCD panels, cables, and the like.