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Method and apparatus for generating soft bit values in reduced-state equalizers

A soft-bit value and state technology, which is applied to the shaping network, transmission system, electrical components and other directions in the transmitter/receiver, and can solve the problems of reduced soft-bit value accuracy, poor soft-bit value accuracy, and unreliability.

Inactive Publication Date: 2012-05-02
TELEFON AB LM ERICSSON (PUBL)
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

Soft bit values ​​are less accurate when evaluating less than all possible paths
In some cases, for example, when the entire set of paths is not evaluated, the accuracy of soft bit values ​​can degrade so badly that they become unreliable

Method used

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  • Method and apparatus for generating soft bit values in reduced-state equalizers
  • Method and apparatus for generating soft bit values in reduced-state equalizers
  • Method and apparatus for generating soft bit values in reduced-state equalizers

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Embodiment Construction

[0014] figure 1 An embodiment of a demodulator component 100 included in a receiver 110 for detecting transmitted symbols is shown. The demodulator 100 performs coherent demodulation based on knowledge of the channel over which the symbols are transmitted. The channel consists of the net effect of the transmitter filter, propagation channel and receiver matched filter response. The demodulator 100 includes a channel estimator 120 for estimating a channel and a symbol detector 130 for detecting transmitted symbols. Channel estimator 120 estimates a channel using known transmitted symbols, such as training sequences or pilot symbols. The demodulator 100 also whitens the received signal r(n) to remove at least some interference that mixed with the desired signal during transmission. Whitening the received signal r(n) enables optimal detection of the transmitted symbols. A symbol detector 130 uses the whitened signal r(n) and the estimate of one or more channel taps h(k) gener...

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Abstract

A demodulator is provided that functions as a reduced-state equalizer and produces reliable soft bit values. According to an embodiment, soft bit values are generated for a sequence of transmitted symbols using a demodulator by updating an M-state trellis managed by the demodulator response e to a transition from symbol time n-1 to symbol time n, where M is a function of the number of bits per symbol in the sequence of transmitted symbols. Survivor metrics associated with the M states of the trellis are saved each symbol time so that the demodulator can calculate soft bit values with regard to transitions from symbol time n + D-1 to symbol time n+ D. The survivor metrics indicate the probability that each respective state represents the transmitted symbol associated with symbol time n+D-1. The trellis is traced back through to calculate soft bit values for a symbol detected at symbol time n-D based on survivor metrics saved for the M states at symbol time n-D.

Description

technical field [0001] The present invention relates generally to reduced-state equalizers, and more particularly to the use of reduced-state equalizers to generate reliable soft bit values. Background technique [0002] A reduced-state equalizer typically operates on a trellis using a Viterbi or BCJR algorithm to estimate the sequence of transmitted symbols. The lattice has multiple states per symbol time, the number of states being a function of the modulation. For example, assuming the channel has a memory of one symbol period, the lattice has 64 different states for 64-QAM (Quadrature Amplitude Modulation), and 32 possible states for 32-QAM. A reduced-state equalizer prunes lattices when determining the most probable path associated with a sequence of transmitted symbols. By pruning the lattice, the metrics of many paths in the lattice are not evaluated when determining the most probable path, thereby reducing computational complexity. However, soft bit value generati...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H03M13/37H04L25/03
CPCH04L25/03203H03M13/4146
Inventor D·陈
Owner TELEFON AB LM ERICSSON (PUBL)
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