isl3874 Intersil Corporation, isl3874 Datasheet - Page 32

• Manufacturer Part Number: isl3874
• Description: Wireless Lan Integrated Medium Access Controller With Baseband Processor With Mini-pci
• Manufacturer: Intersil Corporation

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 22 shows the performance of the SQ measure versus
signal to noise level.
ED Threshold
The performance of the ED threshold is shown in Figure 23.
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
100
FIGURE 22. SIGNAL QUALITY MEASURE AND PER vs SNR
90
80
70
60
50
40
30
20
10
0
-10
-5
SNR IN THE SPREAD BANDWIDTH AT 1Mbps
0
5
32
10
15
PER
MEAN
STDDEV
20
25
ISL3874
over microwave oven interference but not count the results
in rate shifting algorithms.
A Default Register Configuration
The registers in the ISL3874 are addressed with 7-bit numbers
where the lower 1 bit of an 8-bit hexadecimal address is left as
unused. This results in the addresses being in increments of 2.
The data is transmitted as either DBPSK, DQPSK, or CCK
depending on the configuration chosen. It is recommended that
you start with the simplest configuration (DBPSK) for initial test
and verification of the device and/or the radio design. The user
can later modify the CR contents to reflect the system and the
required performance of each specific application. The
Firmware sets the registers in accordance with a *.pda file. Be
sure to consult the latest “pda” file for the device which is
maintained on the Intersil WEB site.
-10
FIGURE 23. ED THRESHOLD vs SNR IN dB AT 1Mbps
40
30
20
10
0
0
10
SNR IN SPREAD BANDWIDTH
20
STARTS MISSING
MISSING
30
40