HFA3863IN96 Intersil Corporation, HFA3863IN96 Datasheet - Page 20

• Manufacturer Part Number: HFA3863IN96
• Description: Processor, Direct Sequence Spread Spectrum Base band Processor with Rake Receiver and Equalizer, Tape And Reel
• Manufacturer: Intersil Corporation

performance of the CCK modes. The losses in both figures
include RF and IF radio losses; they do not reflect the
HFA3863 losses alone. The HFA3863 baseband
processing losses from theoretical are, by themselves, a
small percentage of the overall loss.
The PRISM demodulator performs with an implementation
loss of less than 4dB from theoretical in a AWGN
environment with low phase noise local oscillators. For the
1 and 2Mbps modes, the observed errors occurred in
groups of four and six errors. This is because of the error
extension properties of differential decoding and
descrambling. For the 5.5 and 11Mbps modes, the errors
occur in symbols of four or eight bits each and are further
extended by the descrambling. Therefore the error patterns
are less well defined.
FIGURE 14. BER vs Eb/N0 PERFORMANCE FOR PSK MODES
FIGURE 15. BER vs Eb/N0 PERFORMANCE FOR CCK MODES
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
1.E-09
7
THY 1, 2
5
THY 11
8
THY 5.5
6
9
7
Eb/N0
8
BER 2.0
20
10
BER 11
9
Eb/N0
10
11
11
BER 1.0
12
12
BER 5.5
13
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
14
HFA3863
Clock Offset Tracking Performance
The PRISM baseband processor is designed to accept data
clock offsets of up to ±25ppm for each end of the link (TX
and RX). This effects both the acquisition and the tracking
performance of the demodulator. The budget for clock offset
error is 0.75dB at ±50ppm. No appreciable degradation was
seen for operation in AWGN at ±50ppm. Symbol tracking is
accomplished by one of two methods. If both ends of the link
employ locked oscillators for their bit timing and carrier
frequency generation, symbol tracking is done by dividing
down the carrier frequency offset. If either one of the ends of
the link do not have locked oscillators, then symbol tracking
is done by a conventional early-late chip tracking method.
Carrier Offset Frequency Performance
The correlators used for acquisition for all modes and for
demodulation in the 1 and 2Mbps modes are time invariant
matched filter correlators otherwise known as parallel
correlators. They use two samples per chip and are tapped
at every other shift register stage. Their performance with
carrier frequency offsets is determined by the phase roll rate
due to the offset. For an offset of +50ppm (combined for both
TX and RX) will cause the carrier to phase roll 22.5 degrees
over the length of the correlator. This causes a loss of
0.22dB in correlation magnitude which translates directly to
Eb/N0 performance loss. In the PRISM chip design, the
carrier phase locked loop is inactive during acquisition.
During tracking, the carrier tracking loop corrects for offset,
so that no degradation is noted. In the presence of high
multipath and high SNR, however, some degradation is
expected.
RSSI Performance
The RSSI value is reported on CR62 in hex and is linear with
signal level in dB. Figure 16 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.
120
100
80
60
40
20
-100
0
FIGURE 16. RSSI vs SIGNAL LEVEL
-80
SIGNAL LEVEL IN dBm
-60
-40
-20
RSSI
0