Decision feedback equalization for digital cellular radio

Claim 2

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; circuit means for initially adapting the adaptive filter means to the sequence of synchronizing symbols, said circuit means including means for switchably coupling an input of the (m) plurality of feedback taps to a time slot midamble of synchronizing symbols; and means for buffering all of the symbols of the time slot.

Claim 3

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; and means responsive to duration of a propagation delay shorter than a threshold value, for causing the received signal to bypass the adaptive filter means.

Claim 4

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; and means responsive to duration of a propagation delay shorter than a threshold value, for causing the received signal to bypass the adaptive filter means.

Claim 5

Apparatus as set forth in claim 2 wherein the threshold value is approximately one third of the duration of a symbol.

Claim 6

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; and means responsive to duration of a propagation delay shorter than a threshold value, for varying the number of taps of the adaptive filter means.

Claim 7

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; and means responsive to duration of a propagation delay shorter than a threshold value, for varying the number of taps of the adaptive filter means.

Claim 8

Apparatus as set forth in claim 4 wherein the threshold value is approximately one third of the duration of a symbol.

Claim 9

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; and means responsive to the receiver means for estimating symbol timing and compensating for a phase rotation of the received signal in accordance with an expression: ##EQU7## where, j=sampling instant, θ i =phase angle of the i th symbol of the preamble, Δθ=phase rotation given to received signal, and θ i e (j)=decoded phase angle corresponding to the i th symbol at the j th sampling instant.

Claim 10

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; and means responsive to the receiver means for estimating symbol timing and compensating for a phase rotation of the received signal in accordance with an expression: ##EQU7## where, j=sampling instant, θ i =phase angle of the i th symbol of the preamble, Δθ=phase rotation given to received signal, and θ i e (j)=decoded phase angle corresponding to the i th symbol at the j th sampling instant.

Claim 11

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; and coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; said coefficient generating means including means for adding a dither signal to arithmetic operations performed thereby, the dither signal being expressive of a Gaussian random variable.

Claim 12

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising: receiver means for receiving the signal over a channel; adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filter means having an input coupled to an output of the receiving means and comprising a decision feedback equalizer having a plurality (n) of feed-forward taps and a plurality (m) of feedback taps; a plurality of multiplying nodes, each of the taps, respectively, being coupled to one of said nodes, respectively, for modifying the output signal on each of the taps, respectively, in accordance with a value of an associated coefficient; and coefficient generating means coupled to an output of the adaptive filter means for recursively generating the coefficients for each of said nodes in accordance with a Complex Fast-Kalman Algorithm; said coefficient generating means including means for adding a dither signal to arithmetic operations performed thereby, the dither signal being expressive of a Gaussian random variable.