Signal-to-Noise Ratio
If babble at the radio agenda is high, the radio agenda will accept adversity convalescent the signal, which
results in $.25 errors and retransmissions. An important arresting altitude is the signal-to-noise
ratio (SNR). The SNR (in dB) at a accurate point in the arrangement is artlessly the arresting power
(in dBm) bare the babble ability (in dBm). A arresting ability of –65 dBm and babble ability of
–90 dBm yields an SNR of 25 dB. The babble ability is annihilation added than signals corresponding
to the admission point or radio card.
RF Arresting Concepts 817
Table G-5 includes several SNR ethics and the consistent achievement of an 802.11b network
while application a Windows XP laptop browsing websites and downloading files. The after-effects in
Table G-5 characterize accepted end-user performance. The use of SNR to ascertain the ambit abuttals of
an admission point radio corpuscle is added able than either abstracts ante or arresting amplitudes. The higher
degrees of babble account added errors in frames and agnate retransmissions. Note that
Windows XP shows an adumbration of the arresting backbone in a alternation of confined on a graph, assuming no
bars as poor affection and bristles confined as the best quality.
Correlation of SNR Ethics to Wireless LAN Performance
KEY
POINT SNR Value Arresting Adumbration (Windows XP) Performance
> 40 dB Excellent arresting backbone (5 bars); always
connected with the admission point
Extremely fast web browsing and
file download
25–40 dB Very acceptable arresting backbone (3 to 4 bars);
always affiliated with the admission point
Very fast web browsing and file
download
15–25 dB Low arresting backbone (2 bars); always
connected with the admission point
Usually fast web browsing and file
download
10–15 dB Very low arresting backbone (1 bar); sometimes
disconnected from the admission point
Mostly apathetic web browsing and file
download
5–10 dB No arresting backbone (no bars); not connected
with the admission point
No arrangement services