CC2420-RTR1 datasheet(24/92 Pages) TI

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CC2420

SWRS041B

Page 24 of 89

10 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 6 [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,

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 3. The chip sequence is

then transmitted at 2 MChips/s, with the

least significant chip (C0) transmitted first

for each symbol.

Bit-to-

Symbol

Symbol-

to-Chip

O-QPSK

Modulator

Transmitted

bit-stream

(LSB first)

Modulated

Signal

Figure 6. Modulation and spreading functions [1]

Symbol

Chip sequence (C0, C1, C2, … , C31)

1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0

1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0

0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0

0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1

0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1

0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0

1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1

1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1

1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1

1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1

0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1

0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0

0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0

0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1

1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0

1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0

Table 3. IEEE 802.15.4 symbol-to-chip mapping [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 7.

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