Lucent Technologies DSP1611, Information Manual, Page: 333 / 443

Information Manual DSP1611/17/18/27/28/29 DIGITAL SIGNAL PROCESSOR
April 1998 Error Correction Coprocessor (DSP1618/28 Only)
Lucent Technologies Inc.
DRAFT COPY
14-7
14.4 Operation of the ECCP
To operate the ECCP, the user first programs its mode of operation by setting the control register (ECON), setting
the traceback length register (TBLR), and appropriately initializing the present state accumulated costs. The com-
plete Viterbi decoding operation is achieved by the following steps: recursively loading the received symbols into
the ECCP; executing the ECCP with an UpdateMLSE, an UpdateConv, or a TraceBack instruction; and, finally,
unloading the decoded symbol from the ECCP. The operation of the ECCP is captured in the signal flow diagram in
Figure 14-3 .
5-4502
Figure 14-3. ECCP Operation Sequence
DSP PROGRAMS ECCP
DSP LOADS CHANNEL/GENERATING
POLYNOMIALS INTO THE ECCP
DSP LOADS RECEIVED
SYMBOLS INTO THE ECCP
DSP EXECUTES
UPDATE INSTRUCTION
NEW
ADAPTED
CHANNEL
TL = TBLR
FETCH MINIMUM COST INDEX
CALCULATE
REVERSED PATH
TL = TL – 1
IS
TL = 0?
IS
TRACEBACK
INSTR.
?
?
DECREMENT
TBLR BY ONE
OUTPUT
DECODED SYMBOL
VITERBI
DECODING
COMPLETE
ALL
SYMBOLS
DECODED
?
NO
YES
YES
NO
NO
NO
YES
SET K = 0
CALCULATE BRANCH METRIC
CALCULATE ACCUMULATED COST
FOR STATE TRANSITIONS TO K
FOR BOTH STATE TRANSITIONS TO K
SELECT MINIMUM ACCUMULATED
COST AS SURVIVOR PATH
UPDATE MINIMUM COST INDEX
STORE SURVIVOR PATH
INCREMENT
K BY ONE
IS
K < 2
(C – 1)
– 1
?
YES NO
YES