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15.1
Data Whitening
From a radio perspective, the ideal over the air
data are random and DC free. This results in
the smoothest power distribution over the
occupied bandwidth. This also gives the
regulation loops in the receiver uniform
operation conditions (no data dependencies).
Real world data often contain long sequences
of zeros and ones. Performance can then be
improved by whitening
transmitting, and de-whitening the data in the
receiver. With CC2500 , this can be done
15.2
Packet Format
The format of the data packet can be
configured and consists of the following items
(see Figure 11):
Preamble
Synchronization word
Preamble bits
(1010...1010)
8 x n bits
16/32 bits
the data
before
Figure 10: Data Whitening in TX Mode
Optional data whitening
Optionally FEC encoded/decoded
Optional CRC-16 calculation
Data field
8
8
8 x n bits
bits
bits
Figure 11: Packet Format
SWRS040C
automatically
PKTCTRL0.WHITE_DATA=1. All data, except
the preamble and the sync word, are then
XOR-ed with a 9-bit pseudo-random (PN9)
sequence before being transmitted as shown
in Figure 10. At the receiver end, the data are
XOR-ed
with
the
sequence. This way, the whitening is reversed,
and the original data appear in the receiver.
The PN9 sequence is reset to all 1's.
Data whitening can only be used when
PKTCTRL0.CC2400_EN=0 (default).
Length byte or constant programmable
packet length
Optional address byte
Payload
Optional 2 byte CRC
Legend:
Inserted automatically in TX,
processed and removed in RX.
Optional user-provided fields processed in TX,
processed but not removed in RX.
Unprocessed user data (apart from FEC
and/or whitening)
16 bits
CC2500
by
setting
same
pseudo-random
Page 29 of 89
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