EM2420 ETC [List of Unclassifed Manufacturers], EM2420 Datasheet - Page 22

• Manufacturer Part Number: EM2420
• Description: 2.4 GHz IEEE 802.15.4 / ZigBee RF Transceiver
• Manufacturer: ETC [List of Unclassifed Manufacturers]

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 5 [1].
Each byte is divided into two symbols, 4
bits each. The least significant symbol is
transmitted first. For multi-byte fields, the
Figure 5. Modulation and spreading functions [1]
Table 3. IEEE 802.15.4 symbol-to-chip mapping [1]
The
Quadrature Phase Shift Keying (O-QPSK)
with half-sine chip shaping. This is
equivalent to MSK modulation. Each chip
Ember Part Number: 120-0049-000C
modulation
Symbol
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Transmitted
bit-stream
(LSB first)
format
Chip sequence (C
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
Symbol
Bit-to-
is
Offset
EM2420 Datasheet
0
, C
–
1
, C
Symbol-
to-Chip
2
, … , C
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
each. The chip to symbol mapping is
shown in Table 3. The chip sequence is
then transmitted at 2 MChips/s, with the
least significant chip (C
for each symbol.
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 6.
31
)
Modulator
O-QPSK
sequences,
Modulated
EM2420
Signal
0
) transmitted first
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chips