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Hi all,
I found a question on Wi-Figurus website and I think it may be useful to discuss in this forum.

Given the following scenario, is there likely adequate signal coverage for client in each situations? Yes or Not please explain your answer.

1-
Access point received signal strength = -70 dBm
Client received signal strength= -65 dBm
Average noise= -95 dBM

2-
Access point received signal strength = -85 dBm
Client received signal strength= -70 dBm
Average noise= -90 dBM

Regards,

Client will work better in scenario-1 as the SNR is better
Noise is just too much in scenario-2 where AP receive strength is -85 while noise floor is -90

Hope that answer the question

Dear Kashif,

You consider average noise and access point received signal strength for your answer what about
client received signal strength?
Is it important for calculating adequate signal coverage for client or not?

it is of course important to consider the client side however think of it this way.

The AP RSSI means the signal that the AP receives from the client while the client RSSI is the signal that the client receives from the AP. In normal situation, AP transmits signal at higher level than the client (or AP might have higher gain antenna) as such the AP RSSI is usually lower than the client RSSI (not always)

We need to take ito consideration the client RSSI because the receive sensitivity of the client might differ from the AP

You are right cgo. Access points usually use higher power levels for transmits than clients. For example PCMICIA clients commonly use power levels of 15 to 30mW and APs generally use between 30 to 100mW of power and some APs use higher. So regarding this fact, what is the answer of the question? Please explain your answer.

Which is why there is no point really in having the AP transmit power to be greater than the client's

In regards to the answer.

Situation 1 should work since the SNR at the AP AND Client exceeds 25dB

Situation 2 will likely have the AP's SNR too low for it to be able to decipher client's transmission from the background noise and therefore might not work

I don't think there is enough information to answer this question properly.

Are these signal levels a design level or an actual level? Is there any unstated margin for client orientation, position, different radio clients, and what sort of service is required from the clients? VoIP, streaming video, low data rate like Telenet, but sessions that can't be interrupted without loss of data?

For actual, worst case signals, both 1 and 2 should work ok.

For design goals, neither 1 nor 2 will work well in some situations and for some uses of a wireless network. Both 1 and 2 specify average noise, which is very likely to be higher in some locations and at some times (close to break room microwave oven). If some clients, like PDAs, or those with a single, small antenna like some tablet PCs, have lower EIRP than other clients, the AP RSSI will probably drop below a reliable point even sooner.

I performed some throughput experiments in a building, and found that once signal levels dropped below -68 dBm, reliability started going down. By reliability I'm talking about sessions that dropped to very low throughput or dropped connections. As RSSI at the client got below about -73 dBm, reliability dropped faster. In some locations, there was good throughput at -78 dBm or lower, but the probability was much lower.

Thank you.
Charles Preston
http://www.comsec-wireless.net