CC112X/CC1175
SWRU295C
Page 45 of 108
7.1.6
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 data often contain long sequences of zeros and ones making it difficult to track the data bits. In
these cases, performance can be improved by whitening the data before transmitting, and de-
whitening the data in the receiver.
With
CC112X
, this can be done automatically. By setting
, all data,
except the preamble and the sync word will be XORed with a 9-bit pseudo-random (PN9) sequence
before being transmitted. This is shown in Figure 18. At the receiver end, the data are XORed with the
same pseudo-random sequence. In this way, the whitening is reversed, and the original data appear
in the receiver. The PN9 sequence is initialized to all 1‟s.
If
CC112X
is set up to transmit random data, the PN9 whitening sequence will be transmitted
(see Table 24).
Figure 18: Data Whitening in TX Mode
Assume the following bytes should be transmitted: 0xAB, 0x80, 0xFF, 0x00
The first byte is XORed with 0xFF (initial value)
0xAB
⊕
0xFF = 0x54
shows how the bit shifting and XORing of bit 5 and bit 0 gives the bytes that the remaining
bytes in the packet should be XORed with.
TX_OUT[7:0]
TX_DATA
8
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
The first TX_DATA byte is shifted in before doing the XOR-operation providing the first TX_OUT[7:0] byte. The
second TX_DATA byte is then shifted in before doing the XOR-operation providing the second TX_OUT[7:0] byte.