When designing a wireless system for any purpose, probably the most important factor to understand is wireless communication range. At Link Labs, often the first question we get when talking to a new customer about Symphony Link is, “what is the range?” It is not a cut and dry answer. If we said “7 miles,” we risk misleading customers, but if we say “please list the following 10 assumptions,” we sound too much like an engineer-who-gets-in-the-way-of-progress.
Wireless communication range comparisons and resources:
Wireless communication range is really a simple concept at the highest level. A transmitter must put enough energy into a “symbol” for the receiver to be able to “hear” it. Simple, right?
A few definitions then:
Symbol- A radio signal that represents a information. Binary digital data is the easiest to understand. 1 or 0. And FSK (Frequency Shift Keying) is the easiest radio signal to understand. It goes like this- if the radio is transmitting at frequency X, it is communicating a 1, and if it is transmitting at frequency Y, it is communication a 0. Easy.
Now there are some important details about how the transmitter and receiver get synchronized, so the receiver knows how to interpret a these bits (1s and 0s). If there is a long period of transmission at frequency X, just how many 1s does that represent? It gets complicated quickly, so we’ll leave that for now.
Hear- The ability of a receiver to hear the transmission of the transmitter is a function of “energy per symbol” that makes it to the receiver. There are tons of places to lose power as the radio energy travels from the transmitter to the receiver. See our post on Link Budgets here. Antenna losses, structure attenuation, path loss, etc. all dissipate the energy of your signal on its way to the receiver.
One of the easiest ways to increase range is to slow down the data rate. What this does is effectively put more energy into each symbol. If your data rate slows by half, you are doubling the amount of energy per symbol (3 dB).
If you decrease data rate (increase energy per symbol) by a factor of 4 (6 dB), you will DOUBLE your range (assuming free space propagation). For ground propagation, you might need as much as a 12 dB (16x more energy per symbol) to double your range, OUCH!
Another factor that is often overlooked, is interference. Since the ability of a receiver to “hear” is really a function of signal-to-noise (SNR) ratio, if noise is elevated by 10 dB, the minimum detectable signal must be 10 dB stronger. Unlicensed frequency bands, like the 2.4 GHz or 915 MHz ISM bands, can have quite a bit of noise created by other users.
If you’re interested in figuring out new and creative ways to achieve very long RF communication links in your M2M or Internet of Things project, or are interested in our long range wireless communication technology - Symphony Link - please get in touch!