CC2430 Datasheet, PDF (154/212 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
Radio : IEEE 802.15.4 Modulation Format
14.1 IEEE 802.15.4 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. For a complete description, please
refer to [1].
The modulation and spreading functions are
illustrated at block level in Figure 33 [1]. 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.
Each symbol is mapped to one out of 16
pseudo-random sequences, 32 chips each.
The symbol to chip mapping is shown in Table
44. The chip sequence is then transmitted at 2
MChips/s, with the least significant chip (C₀)
transmitted first for each symbol.
Transmitted
bit-stream
(LSB first)
Bit-to-
Symbol
Symbol-
to-Chip
O-QPSK
Modulator
Modulated
Signal
Figure 33: Modulation and spreading functions [1]
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 34.
Table 44: IEEE 802.15.4 symbol-to-chip mapping [1]
Symbol Chip sequence (C₀, C₁, C₂, … , C₃₁)
0
11011001110000110101001000101110
1
11101101100111000011010100100010
2
00101110110110011100001101010010
3
00100010111011011001110000110101
4
01010010001011101101100111000011
5
00110101001000101110110110011100
6
11000011010100100010111011011001
7
10011100001101010010001011101101
8
10001100100101100000011101111011
9
10111000110010010110000001110111
10
01111011100011001001011000000111
11
01110111101110001100100101100000
12
00000111011110111000110010010110
13
01100000011101111011100011001001
14
10010110000001110111101110001100
15
11001001011000000111011110111000
CC2430 Data Sheet (rev. 2.1) SWRS036F
Page 154 of 211