Forum

The range of a radio link is a combination of several factors, including:

- Transmit power
- TX Amplification gain, if any
- TX Antenna gain
- Loss during propagation through the air
- RX Antenna gain
- RX amplification gain, if any
- Receive sensitivity

To put it simply, output power (including amplification and antenna gain) minus propagation losses plus RX gain must be greater than or equal to receive sensitivity. Therefore, higher output power means that you can tolerate more loss before a signal is too weak to receive. So does more receive sensitivity.

Increasing the output power of a single transmitter doesn't necessarily increase the range of the link. Because 802.11 communication is basically always bi-directional, having one communicator be MUCH stronger than the other doesn't always increase range. If the AP has a very high output power, it may be able to get packets to a station that is 1/2 mile away, but if the station doesn't have similarly high output, it can't get a response back, and the link is essentially non-viable. This is referred to as the Unbalanced Power Effect, or UPE.

One additional factor is the data rate that is use. Because higher data rates have lower receive sensitivities--i.e. they require stronger signals--the UPE is not necessarily a matter of link vs. no link. If the AP has 100 mW output power, it may be able to reach a station with 54 Mbps data rates. The station's lower output power might mean that it has to drop to lower data rates to get packets back. In this case, a link exists, but it has asymmetric data rates.

I don't understand questions 2 and 3. Can you post your math?

I have written extensively on these topics in my company's newsletter, and I suggest that you refer to these articles for more detailed information on this topic:

http://www.connect802.com/wcu/2005/newsletter_051101.htm#tech_eng

http://www.connect802.com/wcu/2005/newsletter_050501.htm#essential_wifi

http://www.connect802.com/wcu/2005/newsletter_050601.htm#essential_wifi