STA002 datasheet(26/43 Pages) STMICROELECTRONICS

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6. REED SOLOMON DECODER

The STA 002 performs a real time block decoding

operation both on the Time Slot Control Channel

(TSCC) field and on the Broadcast Channel (BC)

stream by means of a programmable Reed-Solo-

mon (RS) decoder.

This decoder works on blocks of 255 words of 8

bit symbols where the first 223 words represent

the information and the last 32 the code redun-

dancy.

The synchrobyte is the first byte of the block.

All the correction capability of the code is used so

it is possible the correction of blocks containing

up to 16 errors while blocks with greater number

of errors are flagged as corrupted.

The RS decoder is programmable to support two

different Galois field generator polynomials as re-

quired by WorldSpace specifications and includes

an integrated BER estimator.

Monitoring the number of wrong words in each

block and correlating this number with the block

length, it is possible, provided that no corrupted

blocks are present, to get an estimation of the

signal quality at the Viterbi decoder output.

6.1 TSCC REED SOLOMON DECODER

The code generator polynomial is:

g(X) =

∏

= 112

143

(x − α11J) over the Galois Field

generated by X

8+X7+X2+X+1.

6.2 BROADCAST CHANNEL RS DECODER

AND DESCRAMBLER.

The code generator polynomial is:

g(x) = (x-

ω°) (x-ω1) (...) (x-ω31)

over the Galois Field generated by:

8+X4+X3+X2+1=0

6.3 ENERGY DISPERSAL DESCRAMBLER

The descrambler generator polynomial is:

9+X5+1

Reg name: RS_ERROR_CONTROL

Internal address: 212H

Type: R/W

Reset Value: 00H

MSB

LSB

b3b2b1b0

Description: Reed Solomon input errors measure-

ment windows length and error mode presettings

Monitor windows length (blocks)

b1b0 =

256

1024

Error Measurement Mode

Single acquisition mode

Continuous acquisition mode

End measurement (single /continuous

acquisition

Single acquisition start

Reg name: RS_BYTE_ERROR1,

RS_BYTE_ERROR2

Internal address: 215 H , 216H

Type: R/W

RS_BYTE_ERR0R1 (ERROR COUNTER LOW)

MSB

LSB

RS_BYTE_ERROR

(ERROR

COUNTER

HIGH)

MSB

LSB

b13

b12

b11

b10

Description: RS byte error counter register

Reg name: RS_BLOCK_ERROR

Internal address: 217H

Type: R/W

MSB

LSB

Description: RS block error counter register

STA002

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