HFA3863IN96 Intersil Corporation, HFA3863IN96 Datasheet - Page 12

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

ϕ1 is added to all code chips, ϕ2 is added to all odd code
chips, ϕ3 is added to all odd pairs of code chips and ϕ4 is
added to all odd quads of code chips.
The phase ϕ1 modifies the phase of all code chips of the
sequence and is DQPSK encoded for 5.5 and 11Mbps. This
will take the form of rotating the whole symbol by the
appropriate amount relative to the phase of the preceding
symbol. Note that the last chip of the symbol defined above
is the chip that indicates the symbol’s reference phase.
For the 5.5Mbps CCK mode, the output of the scrambler is
partitioned into nibbles. The first two bits are encoded as
differential symbol phase modulation in accordance with
Table 6. All odd numbered symbols of the MPDU are given
an extra 180 degree (π) rotation in addition to the standard
DQPSK modulation as shown in the table. The symbols of
the MPDU shall be numbered starting with “0” for the first
symbol for the purposes of determining odd and even
symbols. That is, the MPDU starts on an even numbered
symbol. The last data dibits d2, and d3 CCK encode the
basic symbol as specified in Table 7. This table is derived
from the CCK formula above by setting ϕ2 = (d2*pi)+ pi/2, ϕ3
= 0, and ϕ4 = d3*pi. In the table d2 and d3 are in the order
shown and the complex chips are shown LSB to MSB (left to
right) with LSB transmitted first.
At 11Mbps, eight bits (d0–d7; d0 first in time) are transmitted
per symbol.
The first dibit (d0, d1) encodes the phase ϕ1 based on
DQPSK. The DQPSK encoder is specified in Table 6 above.
The phase change for ϕ1 is relative to the phase ϕ1 of the
preceding symbol. In the case of rate change, the phase
change for ϕ1 is relative to the phase ϕ1 of the preceding
CCK symbol. All odd numbered symbols of the MPDU are
given an extra 180 degree (π) rotation in accordance with the
DIBIT PATTERN (d(0), d(1))
d2, d3
d(0) IS FIRST IN TIME
00
01
10
11
TABLE 7. 5.5Mbps CCK ENCODING TABLE
-1j
-1j
1j
1j
00
01
11
10
TABLE 6. DQPSK ENCODING TABLE
-1
-1
1
1
-1j
-1j
1j
1j
EVEN SYMBOLS
PHASE CHANGE
12
3
π
-1
-1
1
1
CHIPS
(+j
/2 (-
π
π
0
ω)
/2
π
-1j
-1j
/2)
1j
1j
1
1
1
1
PHASE CHANGE
ODD SYMBOLS
3
π
/2 (-
(+j
-1j
-1j
1j
1j
π
π
0
/2
ω
π
)
/2)
1
1
1
1
HFA3863
DQPSK modulation as shown in Table 8. Symbol numbering
starts with “0” for the first symbol of the MPDU.
The data dibits: (d2, d3), (d4, d5), (d6, d7) encode ϕ2, ϕ3,
and ϕ4 respectively based on QPSK as specified in Table 8.
Note that this table is binary, not Grey, coded.
TX Power Control
The transmitter power can be controlled by the MAC via two
registers. The first register, CR58, contains the results of
power measurements digitized by the HFA3863. By
comparing this measurement to what the MAC needs for
transmit power, the MAC can determine whether to raise or
lower the transmit power. It does this by writing the power
level desired to register CR31.
Clear Channel Assessment (CCA) and
Energy Detect (ED) Description
The clear channel assessment (CCA) circuit implements the
carrier sense portion of a carrier sense multiple access (CSMA)
networking scheme. The CCA monitors the environment to
determine when it is clear to transmit. The CCA circuit in the
HFA3863 can be programmed to be a function of RSSI (energy
detected on the channel), CS1, SQ1, or various combinations.
The CCA output goes to the MAC. The MAC decides on
transmission based on traffic to send and the CCA indication.
The CCA indication can be ignored, allowing transmissions
independent of any channel conditions. The CCA in
combination with the visibility of the various internal parameters
(i.e., Energy Detection measurement results), can assist
the MAC in executing algorithms that can adapt to the
environment. These algorithms can increase network
throughput by minimizing collisions and reducing
transmissions liable to errors.
There are three measures that can be used in the CCA
assessment. The receive signal strength indication (RSSI)
which indicates the energy at the antenna, CS1 and carrier
sense (SQ1). CS1 becomes active anytime the AGC portion
of the circuit becomes unlocked, which is likely at the onset
of a signal that is strong enough to support 11Mbps, but may
not occur with the onset of a signal that is only strong
enough to support 1 or 2MBps. CS1 stays active until the
AGC locks and a SQ1 assessment is done, if SQ1 is false,
then CS1 is cleared, which deasserts CCA. If SQ1 is true,
then tracking is begun, and CCA continues to show the
channel busy. CS1 may occur at any time during acquisition
DIBIT PATTERN (d(i), d(i+1))
d(i) IS FIRST IN TIME
TABLE 8. QPSK ENCODING TABLE
00
01
10
11
3
π
PHASE
/2 (-
π
π
0
/2
π
/2)