Trellis decoding with multiple symbol noncoherent detection and diversity combining

US 6,339,624 B1
Filed: 08/14/1998
Issued: 01/15/2002
Est. Priority Date: 08/19/1997
Status: Expired due to Term

First Claim

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1. 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 r_o⁽¹⁾. . . r_n−

1⁽¹⁾,r_n⁽¹⁾1, said second received symbol sequence being denoted by r_o⁽²⁾. . . r_n−

1⁽²⁾, r_n⁽²⁾2, said first channel having a signal-to-noise ratio Â

⁽¹⁾/({circumflex over (σ

)}⁽¹⁾)², said second channel having a signal-to-noise ratio Â

⁽²⁾/({circumflex over (σ

)}⁽²⁾)², a surviving path into a state u being denoted by s_u,0,s_u,1, . . . s_u,n−

1, a surviving path into a state v being denoted by s_v,0,s_v,1, . . . s_v,n−

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 $W_{u, n - 1}^{(1)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(1)} s_{u, k,}^{*}$ $and$ $W_{u, n - 1}^{(2)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(2)} s_{u, k,}^{*};$ said path history evaluator maintains said path history variables for said surviving path into said state v for said first and second channels as $W_{v, n - 1}^{(1)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(1)} s_{v, k,}^{*}$ $and$ $W_{v, n - 1}^{(2)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(2)} s_{v, k,}^{*},$

wherein 0<

α

21 1, said branch metric evaluator determines a first branch metric for a transition from state u to a successor state w to be $\frac{{\hat{A}}^{(1)}}{{({\hat{σ}}^{(1)})}^{2}} Re [r_{n}^{(1)} {S_{u, n}^{*} (W_{u, n - 1}^{(1)})}^{*}] + \frac{{\hat{A}}^{(2)}}{{({\hat{σ}}^{(2)})}^{2}} Re [r_{n}^{(2)} {S_{u, n}^{*} (W_{u, n - 1}^{(2)})}^{*}],$

S_u,nbeing 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 $\frac{{\hat{A}}^{(1)}}{{({\hat{σ}}^{(1)})}^{2}} Re [r_{n}^{(1)} {S_{v, n}^{*} (W_{v, n - 1}^{(1)})}^{*}] + \frac{{\hat{A}}^{(2)}}{{({\hat{σ}}^{(2)})}^{2}} Re [r_{n}^{(2)} {S_{v, n}^{*} (W_{v, n - 1}^{(2)})}^{*}],$

S_v,nbeing a transmitted symbol associated with said transition from state v to state w.

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Abstract

A method and apparatus for taking advantage of diverse signals. Trellis decoding takes advantage of multiple symbol noncoherent detection and diversity combining. Accordingly, combination of diverse signals effectively occurs pre-detection. Tracking loops are not necessary to set weights for each channel. In a QPSK embodiment employing a rate 1/2 convolutional code, an improvement in effective SNR of 1-3 dB may be achieved as compared with non-diverse reception.

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4 Claims

1. 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 r_o⁽¹⁾. . . r_n−
  
  1⁽¹⁾,r_n⁽¹⁾1, said second received symbol sequence being denoted by r_o⁽²⁾. . . r_n−
  
  1⁽²⁾, r_n⁽²⁾2, said first channel having a signal-to-noise ratio Â
  
  ⁽¹⁾/({circumflex over (σ
  
  )}⁽¹⁾)², said second channel having a signal-to-noise ratio Â
  
  ⁽²⁾/({circumflex over (σ
  
  )}⁽²⁾)², a surviving path into a state u being denoted by s_u,0,s_u,1, . . . s_u,n−
  
  1, a surviving path into a state v being denoted by s_v,0,s_v,1, . . . s_v,n−
  
  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 $W_{u, n - 1}^{(1)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(1)} s_{u, k,}^{*}$ $and$ $W_{u, n - 1}^{(2)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(2)} s_{u, k,}^{*};$ said path history evaluator maintains said path history variables for said surviving path into said state v for said first and second channels as $W_{v, n - 1}^{(1)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(1)} s_{v, k,}^{*}$ $and$ $W_{v, n - 1}^{(2)} = \sum_{k = 0}^{n - 1} α^{n - 1 - k} r_{k}^{(2)} s_{v, k,}^{*},$
  
  wherein 0<
  
  α
  
  21 1, said branch metric evaluator determines a first branch metric for a transition from state u to a successor state w to be $\frac{{\hat{A}}^{(1)}}{{({\hat{σ}}^{(1)})}^{2}} Re [r_{n}^{(1)} {S_{u, n}^{*} (W_{u, n - 1}^{(1)})}^{*}] + \frac{{\hat{A}}^{(2)}}{{({\hat{σ}}^{(2)})}^{2}} Re [r_{n}^{(2)} {S_{u, n}^{*} (W_{u, n - 1}^{(2)})}^{*}],$
  
  S_u,nbeing 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 $\frac{{\hat{A}}^{(1)}}{{({\hat{σ}}^{(1)})}^{2}} Re [r_{n}^{(1)} {S_{v, n}^{*} (W_{v, n - 1}^{(1)})}^{*}] + \frac{{\hat{A}}^{(2)}}{{({\hat{σ}}^{(2)})}^{2}} Re [r_{n}^{(2)} {S_{v, n}^{*} (W_{v, n - 1}^{(2)})}^{*}],$
  
  S_v,nbeing a transmitted symbol associated with said transition from state v to state w.
- View Dependent Claims (2, 3, 4)
- - 2. The enhanced Viterbi decoder of claim 1 further comprising a path history evaluator that maintains a path history variable representing a phase reference for each surviving path for each of said first and second channels and wherein said likelihood measure for a selected transition from a selected state depends on the path history variables for both said first and second channels of a surviving path to said selected state.
  - 3. The enhanced Viterbi decoder of claim 1 wherein:
4. The enhanced Viterbi decoder of claim 3 wherein:
- said path history evaluator evaluates a path history variable for said surviving path into state w for said first channel to be W_w,n⁽¹⁾=r_n⁽¹⁾S_u,n*+α
  
  W_u,n−
  
  1⁽¹⁾; and
  
  said path history evaluator evaluates a path history variable for said surviving path into state w for said second channel to be W_w,n⁽²⁾=r_n⁽²⁾S_u,n*+α
  
  W_u,n−
  
  1⁽²⁾.

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Current Assignee
WSOU Investments, LLC (WSOU Holdings, LLC)
Original Assignee
Stanford Telecommunications, Inc. (Nokia Corporation)
Inventors
Ohlson, John
Primary Examiner(s)
Chin, Stephen
Assistant Examiner(s)
Liu, Shuwang

Application Number

US09/134,469
Time in Patent Office

1,250 Days
Field of Search

375/341, 375/347, 375/262, 375/232, 375/267, 375/265, 714/794, 714/791, 714/789
US Class Current

375/341
CPC Class Codes

H04L 1/0054   Maximum-likelihood or seque...

H04L 1/06   using space diversity

H04L 27/186   in which the information is...

H04L 27/233   using non-coherent demodula...

Trellis decoding with multiple symbol noncoherent detection and diversity combining

First Claim

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Trellis decoding with multiple symbol noncoherent detection and diversity combining

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