Estimate the theoretical line-of-sight radius of a wireless VoIP link from a simple radio link budget. The calculation combines transmit power, antenna gains, receiver sensitivity, operating frequency, and a fade or obstruction margin. It is useful for early handset or access-point planning, but indoor walls, interference, body loss, roaming thresholds, and local radio rules still require a site survey.
The radius is the distance at which free-space path loss uses the available link budget. It is not a guaranteed indoor service radius.
This estimate assumes free-space propagation. Regulatory power limits, walls, people, multipath, interference, and roaming design can materially shorten coverage.
At 20 dBm transmit power, 2 dBi transmit gain, 0 dBi receive gain, 2,400 MHz, −75 dBm sensitivity, and a 20 dB margin, allowable loss is 77 dB and radius is about 70 meters.
No. It is a free-space link-budget estimate; indoor materials, people, interference, and multipath can reduce the radius substantially.
Use the sensitivity for the modulation or voice-performance threshold you intend to support, not merely the radio's minimum connectable level.
For the same link budget, free-space path loss increases with frequency, leaving less distance before the sensitivity threshold is reached.
Include normal fading, wall loss, body attenuation, antenna orientation, and other uncertainty not explicitly modeled.
Only for a rough upper bound. Real floor plans need overlap, capacity, channel reuse, wall attenuation, and a site survey.
| Input | Unit and effect |
|---|---|
| Transmit power | dBm added to the link budget |
| Antenna gain | dBi added at each endpoint |
| Sensitivity | Minimum target receive level in dBm |
| Margin | dB reserved for fading and obstructions |