Getting Wired to Wireless Sensor and Actuator Network Design

Wireless More and more, wireless sensor and actuator networks (WSAN) are being put to use to control even the most mundane of daily tasks. Whether turning on lights in the house, monitoring whether an elderly patient has taken their medication, or just keeping the office at a consistent 69 degrees, WSANs are playing a larger and larger role in our society.

For those looking to set up their own WSAN, and going through the process of selecting wireless modules, there are some basic facts that need to be kept in mind in order to create an efficient network. Step one is to consider the range you require.

Range Equations

In essence, the range of each module is based on the transmitted power (Pt), the wavelength (λ) and the antenna gain (Gt and Gr). The stronger your transmitter, wavelength and antenna, the greater the power (Pr) for a given distance (d) or range. Louis E. Frenzel, in his March 2010 article for Electronic Design puts forth the following formula:

Pr=PtGtGrλ2/16Π2λ2

The basic premise behind the formula is that range (or distance) is increased with longer wavelengths, through lower frequencies, or both.

Obstacles

Walls, floors and other obstacles can add anywhere from 3 to 18 dB in path loss depending on composition and frequency of operation. You'll find that the lower the frequency, the less path loss. Structural solidity, for instance brick or concrete as opposed to wood or sheetrock, will also have an effect on how much path is lost over a given distance.

Lower Frequencies Are Better

Because higher frequencies tend to lose path with obstacles, and most likely there will be a few, the data stacks up in favor of a lower frequency for your WSAN.

One thing to keep in mind, if going with a lower frequency, as opposed to the higher (2.4GHz and above):

You'll need an antenna with less efficiency.
Louis E. Frenzel, the author of "Cut the Links to Your Sensor/Actuator Networks."