EP0449327A2 — Noise-immune space diversity receiver

Claim 1

Independent Claim 176 words

A diversity receiver having a plurality of diversity antennas for simultaneously receiving sequentially coded symbol sequences over distinct communications channels from a point of transmission to said antennas, comprising: a plurality of channel estimators respectively coupled to said diversity antennas for deriving estimates of impulse responses of said communication channels respectively from said received sequences; a plurality of matched filters associated respectively with said channel estimators and said diversity antennas, each of said matched filters having a tapped delay line coupled to the associated antenna and a plurality of multipliers coupled respectively to successive taps of said tapped delay line for controlling tap weight coefficients of said multipliers in response to an output signal from the associated channel estimator and integrating weighted signals generated by said multipliers to produce a matched filter output; a branch metric calculator for receiving the outputs of said matched filters and said estimates from said channel estimators for calculating a branch metric of the signals received by the antennas; and a maximum likelihood sequence estimator coupled to said branch metric calculator.

Claim 2

Dependent Claim 176 words

A diversity receiver having a plurality of diversity antennas for simultaneously receiving sequentially coded symbol sequences over distinct communications channels from a point of transmission to said antennas, comprising: a plurality of channel estimators respectively coupled to said diversity antennas for deriving estimates of impulse responses of said communication channels respectively from said received sequences; a plurality of matched filters associated respectively with said channel estimators and said diversity antennas, each of said matched filters having a tapped delay line coupled to the associated antenna and a plurality of multipliers coupled respectively to successive taps of said tapped delay line for controlling tap weight coefficients of said multipliers in response to an output signal from the associated channel estimator and integrating weighted signals generated by said multipliers to produce a matched filter output; a branch metric calculator for receiving the outputs of said matched filters and said estimates from said channel estimators for calculating a branch metric of the signals received by the antennas; and a maximum likelihood sequence estimator coupled to said branch metric calculator.

Claim 3

Dependent Claim 75 words

A diversity receiver as claimed in claim 1, wherein said branch metric calculating circuit comprises: a plurality of branch metric coefficient calculators for receiving output signals from said channel estimators for calculating branch metric coefficients; and a plurality of first adders for summing output signals from said branch metric coefficient calculators with output signals from said matched filters; and a second adder for adding the outputs of said first adders to produce a branch metric.

Claim 4

Dependent Claim 74 words

A diversity receiver as claimed in claim 1, wherein said branch metric calculator comprises: a vector adder for providing vector summation of impulse response vectors from said channel estimators to produce an output impulse response vector; a branch metric coefficient calculator for deriving a branch metric coefficient from said output impulse response vector; and an adder for summing output signals from said matched filters and said branch metric coefficient to produce a branch metric.

Claim 5

Dependent Claim 187 words

An adaptive diversity receiver having a plurality of diversity antennas for simultaneously receiving signals over distinct communications channels from a point of transmission to said antennas, comprising: a plurality of adaptive channel estimators respectively coupled to said diversity antennas for deriving estimates of impulse responses of said communication channels respectively from said received sequences and a previously received signal; a plurality of branch metric calculators coupled respectively to said diversity antennas for deriving first branch metrics respectively from said received sequences; a branch metric quality estimator coupled to said adaptive channel estimators for deriving from output signals of said channel estimators a plurality of branch metric quality estimates of said communications channels, respectively; a branch metric evaluation circuit coupled to said branch metric calculators and said branch metric quality estimator for evaluating said first branch metrics in accordance with said branch metric quality estimates and producing a second branch metric; and a maximum likelihood sequence estimator for deriving a maximum likelihood estimate of said received sequences from said second metric branch and applying said maximum likelihood estimate to said adaptive channel estimators as said previously received signal.

Claim 6

Dependent Claim 187 words

An adaptive diversity receiver having a plurality of diversity antennas for simultaneously receiving signals over distinct communications channels from a point of transmission to said antennas, comprising: a plurality of adaptive channel estimators respectively coupled to said diversity antennas for deriving estimates of impulse responses of said communication channels respectively from said received sequences and a previously received signal; a plurality of branch metric calculators coupled respectively to said diversity antennas for deriving first branch metrics respectively from said received sequences; a branch metric quality estimator coupled to said adaptive channel estimators for deriving from output signals of said channel estimators a plurality of branch metric quality estimates of said communications channels, respectively; a branch metric evaluation circuit coupled to said branch metric calculators and said branch metric quality estimator for evaluating said first branch metrics in accordance with said branch metric quality estimates and producing a second branch metric; and a maximum likelihood sequence estimator for deriving a maximum likelihood estimate of said received sequences from said second metric branch and applying said maximum likelihood estimate to said adaptive channel estimators as said previously received signal.

Claim 7

Dependent Claim 37 words

An adaptive diversity receiver as claimed in claim 4, wherein said second branch metric produced by said evaluation circuit is representative of a weighted mean value of said branch metrics, weighted with said branch metric quality estimates.

Claim 8

Dependent Claim 73 words

An adaptive diversity receiver as claimed in claim 4 or 5, wherein each of said adaptive channel estimators includes means for generating an error signal representative of a difference between an output signal from said maximum likelihood estimator and a corresponding one of said received sequences at said diversity antennas and supplying said error signal as one of said output signals supplied from said adaptive channel estimators to said branch metric quality estimator.

Claim 9

Dependent Claim 92 words

An adaptive diversity receiver as claimed in any of claims 4 to 6, wherein said branch metric quality estimator comprises: a plurality of power detector circuits for deriving signals representative of the power levels of said received sequences from the error signals from said adaptive channel estimators; and a plurality of comparator means coupled respectively to said power detector means for comparing said power representative signals with a threshold value and generating a plurality of signals each indicating whether the respective power representative signal is higher or lower than said threshold value.

Claim 10

Dependent Claim 170 words

An adaptive diversity receiver as claimed in any of claims 4 to 7, wherein each of said adaptive channel estimators comprises: a tapped delay having for receiving said output signal from said maximum likelihood sequence estimator; a plurality of multipliers respectively coupled to successive taps of said delay line; an adder for integrating output signals of said multipliers to produce an adder output; means for introducing a delay time to a corresponding one of said received sequences by an amount corresponding to the amount of processing time from a corresponding one of said diversity antennas and the output of said maximum likelihood estimator; error detector means for detecting a difference between said adder output and the output signal of said said maximum likelihood estimator to generate said error signal; and processor means for deriving tap weight coefficients from signals at said successive taps and said error signal and supplying said coefficients to said multipliers, respectively, and to a respective one of said branch metric calculators as said impulse response estimates.

Claim 11

Dependent Claim 172 words

An adaptive diversity receiver as claimed in any of claims 4 to 7, wherein each of said adaptive channel estimators comprises: a tapped delay having for receiving said output signal from said maximum likelihood sequence estimator; a plurality of multipliers respectively coupled to successive taps of said delay line; an adder for integrating output signals of said multipliers to produce an adder output; means for introducing a delay time to a corresponding one of said received sequences by an amount corresponding to the time taken for each of said signals received at said diversity antennas to appear at the output of said maximum likelihood estimator; error detector means for detecting a difference between said adder output and the output signal of said said maximum likelihood estimator to generate an error signal; and processor means for deriving tap weight coefficients from signals at said successive taps and said error signal and supplying said coefficients to said multipliers, respectively, and to a respective one of said branch metric calculators as said impulse response estimates.

Claim 12

Dependent Claim 84 words

An adaptive diversity receiver as claimed in any of claims 4 to 9, wherein said branch metric quality calculator comprises: a plurality of variation detector means coupled respectively to said adaptive channel estimators for detecting time-varying components from the channel estimates; and a plurality of comparator means coupled respectively to said variation detector means for comparing said time-varying components with a threshold value and generating a plurality of signals each indicating whether the respective time-varying components is higher or lower than said threshold value.

Claim 13

Dependent Claim 88 words

An adaptive diversity receiver as claimed in any of claims 4 to 10 wherein said evaluation circuit comprises: a first adder for deriving a first value representative of a sum of output signals from said comparators; a plurality of weighting means for respectively weighting said branch metrics with the output signals from said comparators; a second adder for summing the weighted branch metrics to produce a second value; and a division circuit for arithmetically dividing said second value with said first value to produce said second branch metric.

Claim 14

Dependent Claim 35 words

An adaptive diversity receiver as claimed in any of claims 4 to 11, wherein each of said comparator means has a hysteresis characteristic for maintaining the output signal thereof when said threshold value is exceeded.

Noise-immune space diversity receiver

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