Patent ID: 6339624
Filing Date: 2002-01-15
Classification: H04L

Abstract:
In a digital communication system, an enhanced Viterbi decoder system that processes a first stream of received symbols and a second stream of received symbols by selecting a maximum likelihood path through states of a trellis, said path comprising successive transitions between states, said enhanced Viterbi decoder comprising:a branch metric evaluator that determines a likelihood measure for a particular transition between states, said likelihood measure being responsive to both said first stream and said second stream; and a path evaluator that selects and eliminates non-maximum likelihood paths based on a cumulative likelihood measure evaluated based on likelihood measures for successive transitions as evaluated by said branch metric evaluator, said first received symbol stream being denoted by ro(1) . . . rnâˆ’1(1),rn(1) 1, said second received symbol sequence being denoted by ro(2) . . . rnâˆ’1(2), rn(2) 2, said first channel having a signal-to-noise ratio Ã‚(1)/({circumflex over (&sgr;)}(1))2, said second channel having a signal-to-noise ratio Ã‚(2)/({circumflex over (&sgr;)}(2))2, a surviving path into a state u being denoted by su,0,su,1, . . . su,nâˆ’1, a surviving path into a state v being denoted by sv,0,sv,1, . . . sv,nâˆ’1, wherein said path history evaluator maintains said path history variables for said surviving path into said state u for said first and second channels as Wu,n-1(1)=&Sum;k=0n-1&it;Î±n-1-k&it;rk(1)&it;su,k,*andWu,n-1(2)=&Sum;k=0n-1&it;Î±n-1-k&it;rk(2)&it;su,k,*;said path history evaluator maintains said path history variables for said surviving path into said state v for said first and second channels as Wv,n-1(1)=&Sum;k=0n-1&it;Î±n-1-k&it;rk(1)&it;sv,k,*andWv,n-1(2)=&Sum;k=0n-1&it;Î±n-1-k&it;rk(2)&it;sv,k,*,â€ƒwherein 0said branch metric evaluator determines a first branch metric for a transition from state u to a successor state w to be A^(1)(Ïƒ^(1))2&it;Re[rn(1)&it;â€ƒ&it;Su,n*(Wu,n-1(1))*]+A^(2)(Ïƒ^(2))2&it;Re&af;[rn(2)&it;Su,n*&af;(Wu,n-1(2))*],â€ƒSu,n being a transmitted symbol associated with said transition from state u to state w; and said branch metric evaluator determines a second branch metric for a transition from state v to state w to be A^(1)(Ïƒ^(1))2&it;Re[rn(1)&it;â€ƒ&it;Sv,n*(Wv,n-1(1))*]+A^(2)(Ïƒ^(2))2&it;Re&af;[rn(2)&it;Sv,n*&af;(Wv,n-1(2))*],â€ƒSv,n being a transmitted symbol associated with said transition from state v to state w.