FX919AD2 datasheet(12/44 Pages) CMLMICRO

12 / 44 page

4-Level FSK Modem Data Pump

FX919A

D/919A/4

1.5.4

Frame Structure

Figure 7 below shows how an over-air message frame may be constructed from Frame and Symbol Sync

patterns, followed by one or more 'Header', 'Intermediate' or 'Last' blocks.

SYMBOL

SYNC

FRAME

SYNC

FRAME

sent first

last

Over-air

signal

(symbols)

'LAST'

BLOCK

'HEADER'

BLOCK

INTERMEDIATE BLOCKS

0 7

Byte 0

Byte 1

Byte 11

'000'

Byte 4

Byte 5

Byte 6

Byte 7

Byte 8

Byte 9

Byte 0

Byte 1

Byte 2

Byte 3

Byte 10

Byte 11

4 3

CRC1

(2 bytes)

Data Bytes

(12)

CRC2

(4 bytes)

Header Block

Last Block

Intermediate Blocks

tri-bits

4-level

symbols

FEC TRELLIS CODING / DECODING

( ERROR CORRECTION )

INTERLEAVING / DE-INTERLEAVING

FRAME

PREAMBLE

-1

-3

-1

-3

-1

-3

-1

-3

Frame Sync:

Symbol Sync : at least 24 symbols of '..+3 +3 -3 -3 ...' sequence

Data Bytes

(10)

Data Bytes

(8)

Figure 7 Over Air Signal Format

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