Communication Range, defined as the maximum distance allowing a reliable radio link to exchange information between a transmitter and a receiver.
Purpose:
Communication range calculation could be for:
- Wireless network deployement study
- Communication systems benchmrak (comparaison)
- Communication system troubleshooting
- Communication system choice according to application constraites
- ....
Key Definitions:
In order to estimate communication range, tow key factors must be evaluated, Path loss and Link budget.
Path loss: it refers to the natural reduction in signal strength that occurs as a radio wave propagates through the air. This is due to the fact that initial power is diluted on a bigger and bigger sphere surface as the energy propagtes from the source point. In addition to that, path loss is impacted by the environment and obstacles between the transmitter and the receiver. It depends mainly on frequency and distance.
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Lower frequency signals tend to propagate over longer distance, while higher frequency signals allow higher data rates but are more susceptible to attenuation due to obstacles and atmospheric conditions. On the other hand, lower frequencies require biggest antennas than higher frequencies for the same performances. |
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As distance between transmitter and receiver increase, power loss increase. |
First of all, lets calculate the path loss according to FRIIS formula:
Path Loss (dB) = n x [ 90 + 10 . LOG10 ( 4 . π / C ) + 10 . LOG10 ( F ) + 10 . LOG10( D ) ]
Where:
- C : The speed of light (about 300 000 Km/sec)
- F : Signal frequency expressed in MHz
- D: Expected distance to be covered, expressed in Km
- n: FRIIS exponent, caracterizing the propagation environnement (see table bellow for some typical values)
| Environnement | Exponent (n) |
| Free space | 2 |
| Grocery store | 1.8 |
| Retail store | 2.2 |
| Office (hard walls) | 3 |
| Office (soft walls) | 2.6 |
| Dense office | 4 |
Notes:
- For a specific environnement, exponent "n" can be determined empirically by measuring signal strenght (RSSI) received versus distance to used transmitter. Environement exponent will be the "n" value of the theoritical FRIIS curve, that best models the experimental behavior.
Link Budget: It is simply an equation describing the performance of a communication link accounting for all gains and losses in the RF-path elements of the link. A typical Link Budget equation looks like this:
LB (dB) = Transmit power (dBm) + Transmit antenna gain (dB) + Receiver antenna gain (dB) - Receiver sensitivity (dBm)
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By analogy to sound, think of receiver sensitivity as the quietest sound you can hear and understand, so, better is the sensitivity, better will be the range. Take a look on "Measureing receiver sensitivity with attenuator" for more details. |
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Transmit power level is a tradeoff between range and power consumption. More over, even we suppose having acces to an unlimited source of electrical power ! RF power can not be increased indefinitely because of applied standards and regulations. Take a look on "RF transmitter power measurement" for more details. |
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Antenna location, package size, and design can greatly impact how effective the signal is transmitted and received. The effective antenna gain is relevant for both the transmitting and receiving antenna. The higher the antenna gain, the greater the range will be. |
So, What's the range of my system ?
After calculating your system Link Budget, it is easy to find the distance giving the path loss, consuming that link budget. However, it is a good practice to have some margin on link budget to answer a reliable radio link in most conditions. The fact is that environnement is not constant !