CC2520_11 Datasheet, PDF (63/133 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
17 IEEE 802.15.4-2006 Modulation Format
This section is meant as an introduction to the 2.4 GHz direct sequence spread spectrum (DSSS) RF
modulation format defined in IEEE 802.15.4-2006. For a complete description, please refer to the standard
document [2].
The modulation and spreading functions are illustrated at block level in Figure 12. Each byte is divided into
two symbols, 4 bits each. The least significant symbol is transmitted first. For multi-byte fields, the least
significant byte is transmitted first, except for security related fields where the most significant byte it
transmitted first.
Each symbol is mapped to one out of 16 pseudo-random sequences, 32 chips each. The symbol to chip
mapping is shown in Table 16. The chip sequence is then transmitted at 2 Mchips/s, with the least
significant chip (C₀) transmitted first for each symbol. The transmitted bit stream and the chip sequences are
observable on GPIO pins. See Table 9 for details on how to configure the GPIO to do this.
Figure 12: Modulation
Table 16: IEEE 802.15.4-2006 symbol to chip mapping
Symbol
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Chip sequence (C₀, C₁, C₂, … , C₃₁)
11011001110000110101001000101110
11101101100111000011010100100010
00101110110110011100001101010010
00100010111011011001110000110101
01010010001011101101100111000011
00110101001000101110110110011100
11000011010100100010111011011001
10011100001101010010001011101101
10001100100101100000011101111011
10111000110010010110000001110111
01111011100011001001011000000111
01110111101110001100100101100000
00000111011110111000110010010110
01100000011101111011100011001001
10010110000001110111101110001100
11001001011000000111011110111000
The modulation format is Offset – Quadrature Phase Shift Keying (O-QPSK) with half-sine chip shaping.
This is equivalent to MSK modulation. Each chip is shaped as a half-sine, transmitted alternately in the I and
Q channels with one half chip period offset. This is illustrated for the zero-symbol in Figure 13.
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