Link budget is one of those magical terms that to most people means pretty much nothing, but if understood, quickly tells us so much.
Link budget isn’t how much you pay for online ads and it isn’t the budget you have per bratwurst link either. As you may have guessed, link budget is an engineering term. Link budget is actually the single most revealing metric for any wireless technology. It measures the signal power available for transmitting messages and is measured in dB (decibels). The higher the link budget the better signals propagate, or fly through the air with reckless abandon.
Link budget can be spent on a combination of coverage area, reliability of coverage, or penetration depth. If you were to take two wireless technologies and know nothing about them except their link budget you would easily know which one can provide more coverage, coverage reliability, and coverage penetration. And all three of those things are great for your M2M and IoT connected devices.
RPMA’s link budget, at 172 dB (FCC) in actual commercial deployments, is the highest among all IoT wireless options (Cellular: 164-167 dB; LPWA: 149-157 dB). RPMA also has the leading link budget in Europe with 168 dB (Cellular: 155-158 dB; LPWA: ~161 dB). Some may wonder why there is a difference between the FCC and Europe, and it’s not because Europe has syrupy air getting in the way of wireless signals. It all comes down to government regulations (darn those politicians!). Different radio frequency bands have different regulations governing how much power can be used to send and receive signals, among other things. The less power you are allowed to use means the less link budget you’ll get.
Link budget is magical in another way: a unit increase in link budget (say 1 dB) leads to an exponential increase in coverage. So to have one more dB than cellular means we get many multiples increase in coverage, not just a single unit increase in coverage. Link budget is the end result of combining receiver sensitivity, transmission power, antenna gain, legal restrictions in various regions, the natural propagation of the band chosen and ways to enhance each. RPMA’s link budget gets its largest boost from its industry leading receiver sensitivity at -142 dBm. Receiver sensitivity indicates how weak an incoming signal can be and still be obtained by the receiver. It’s like RPMA has super sensitive ears that are able to hear even a panting snail trying to cross a busy sidewalk.
For a quick and revealing way to compare wireless technologies look at link budget as it exists in actual real world commercial deployments (because it’s easy to say you have a much higher link budget before you actually deploy in real world conditions). So, that’s your primer on link budget, spend it well.