Path-oriented decoder for signal-dependent noise
AssigneeLucent Technologies Inc.
InventorLee-Fang Wei
Life of this patent
Estimating the term…
Abstract
A path-oriented approach is provided to determine surviving paths in a decoder. The paths that are retained as the surviving paths are some number, M, of the paths which have the smallest path metrics, even if two or more of those paths come into a given state. This approach provides significantly improved performance in at least those applications in which branch metrics are a function of the surviving path from which the branch emanates.
Claims24
A method for use in a decoder for decoding a sequence of signal points corrupted by intersymbol interference, said signal points having been generated using a particular trellis code defined by a trellis diagram, the method comprising the steps of
- a) generating in response to each received signal point a plurality of equalized signal points, each equalized signal point being generated as a function of a respective estimate of the intersymbol interference component of said each received signal point, each estimate being a function of a respective present surviving path of said decoder,
- b) generating a path metric for each of a plurality of candidate paths, each candidate path comprising a respective one of the present surviving paths extended from its respective terminating state of the trellis code along a branch of said trellis diagram, said generated path metrics being a function of said generated equalized signal points,
- c) selecting ones of the candidate paths to be updated surviving paths, said selected ones of the candidate paths having the smallest overall path metrics relative to all candidate paths,
- d) forming a decision as to a particular one of the signal points of said sequence as a function of at least one of the candidate paths.
In a method for use in a decoder wherein surviving paths are determined as a function of path metrics associated with respective candidate paths, the improvement comprising:
- retaining as surviving paths a number of said candidate paths having the smallest overall path metrics relative to all of said candidate paths.
A method for decoding a stream of signal points, said signal points having been generated using a predetermined trellis code defined by a state transition diagram, said method comprising the steps of
- a) maintaining a path metric associated with each of a plurality of surviving paths through the code trellis, each of said surviving paths terminating on a particular state of the code,
- b) responsive to a received one of said signal points, generating an updated path metric for each of a plurality of candidate paths, each candidate path comprising a respective one of the surviving paths extended from that surviving path's terminating state along a branch of said trellis,
- c) identifying those M candidate paths having the smallest overall updated path metrics relative to all candidate paths as new surviving paths, M being an integer, and
- d) forming a decision as to the value of a previously received one of said signal points as a function of at least one of said candidate paths.
Apparatus comprising
- means for receiving signal points having been generated using a code characterized by a trellis, said trellis having a plurality of states and paths, and
- means for determining a path metric associated with every path entering a state and for retaining a number of surviving paths, said surviving paths being ones of said paths associated with the smallest overall path metrics relative to all of said paths.
A method for use in a decoder for each of a plurality of received signals which was encoded with a trellis code, said decoder maintaining a plurality of surviving paths through the trellis of said trellis code, each of said surviving paths having an associated path metric, comprising the steps of
- utilizing a value of each said received signal to generate at least one extended version of said surviving paths through said trellis and to update the path metric for each said extended version, and
- retaining as new surviving paths ones of said extended versions, said new surviving paths being those ones of said extended versions with the smallest overall path metrics relative to all of said extended versions.
A method for use in a decoder comprising
- a) receiving a stream of signal points, said signal points having been generated using a trellis code,
- b) responsive to each received signal point, computing a branch metric for at least ones of the branches associated with a transition from a current state to a next state of said code,
- c) computing a path metric at said next state for each of a plurality of paths through said trellis, each said path including a respective one of said branches, said path metric being a function of said branch metric for said respective included branch, said branch metric being a function of said received signal point and of a portion of said path which includes said respective branch, said portion of said path terminating at said current state,
- d) retaining ones of said paths which include said branches as surviving paths, said surviving paths having the smallest overall path metrics relative to all of said paths, and
- e) forming a decision as to an individual one of said signal points as a function of at least a particular one of said paths which include said branches.
Dependencies are inferred from the claim text.