isl3873 Intersil Corporation, isl3873 Datasheet - Page 30

• Manufacturer Part Number: isl3873
• Description: Wireless Lan Integrated Medium Access Controller With Baseband Processor
• Manufacturer: Intersil Corporation

RSSI Performance
The RSSI value is reported on CR62 in hex and is linear with
signal level in dB. Figure 22 shows the RSSI curve
measured on a whole evaluation radio. This takes into
account the full gain adjust range of all radio parts. To get
signal level in dBm on a radio, simply subtract the RSSI
value in decimal from 100.
Signal Quality Estimate
A signal quality measure is available on CR51 for use by the
MAC. This measure is the SNR in the carrier tracking loop
and can be used to determine when the demodulator is
working near to the noise floor and likely to make errors.
Figure 23 shows the performance of the SQ measure versus
signal to noise level.
120
100
80
60
40
20
-100
0
FIGURE 22. RSSI vs SIGNAL LEVEL
-80
SIGNAL LEVEL IN dBm
-60
30
-40
-20
RSSI
0
ISL3873
ED Threshold
The performance of the ED threshold is shown in Figure 24.
Setting this threshold will effect CCA only. Using ED as part
of the CCA measure will allow deferral to large signals even
if they are not correlated to the desired spread signals.
ED can be read from CR61 bit 4. Using ED and RSSI can
assist the MAC in determining the presence of non
correlating signals such as frequency hoppers or microwave
ovens. For example, the MAC can elect to try to transmit
over microwave oven interference but not count the results in
rate shifting algorithms.
100
FIGURE 23. SIGNAL QUALITY MEASURE AND PER vs SNR
90
80
70
60
50
40
30
20
10
0
-10
-10
40
30
20
10
FIGURE 24. ED THRESHOLD vs SNR IN dB AT 1Mbps
0
0
-5
SNR IN THE SPREAD BANDWIDTH AT 1Mbps
10
0
SNR IN SPREAD BANDWIDTH
5
20
10
STARTS MISSING
MISSING
15
30
PER
MEAN
STDDEV
20
25
40