Channel equalization apparatus and method using the Fourier transform technique

Claim 5

Apparatus for determining the initial values of the coefficients of a transversal equalizer in a synchronous data transmission system having a transmitter, a receiver, and a communications channel connecting said transmitter and said receiver characterized in that said apparatus includes: means located at said transmitter of the system for transmitting a periodic sequence of data representing symbols over said communications channel; modulation means in said receiver for modulating the signal received from said channel by a time-domain window signal where the Fourier transform of said window signal exhibits a relatively flat central peak and has a comparatively low magnitude in the vicinity of those frequencies which are multiples of the inverse of the period of the transmitted sequence; means connected to the output of said modulation means for determining data representing the discrete Fourier transform, W k , of said modulated received signal; a first storage means for storing data representing the discrete Fourier transform, Z k , of the transmitted periodic sequence; means connected to said determining means and said first storage means for calculating the ratio F.sub.k =Z.sub.k /W.sub.k ; and means on the output of said calculating means to derive the factors representing the inverse Fourier transform of F k , to thereby determine the values of the coefficients c n of the equalizer.

Claim 6

Apparatus for determining the initial values of the coefficients of a transversal equalizer in a synchronous data transmission system having a transmitter, a receiver, and a communications channel connecting said transmitter and said receiver characterized in that said apparatus includes: means located at said transmitter of the system for transmitting a periodic sequence of data representing symbols over said communications channel; modulation means in said receiver for modulating the signal received from said channel by a time-domain window signal where the Fourier transform of said window signal exhibits a relatively flat central peak and has a comparatively low magnitude in the vicinity of those frequencies which are multiples of the inverse of the period of the transmitted sequence; means connected to the output of said modulation means for determining data representing the discrete Fourier transform, W k , of said modulated received signal; a first storage means for storing data representing the discrete Fourier transform, Z k , of the transmitted periodic sequence; means connected to said determining means and said first storage means for calculating the ratio F.sub.k =Z.sub.k /W.sub.k ; and means on the output of said calculating means to derive the factors representing the inverse Fourier transform of F k , to thereby determine the values of the coefficients c n of the equalizer.

Claim 7

An apparatus as set out in claim 3 and further characterized in that said modulation means includes: a second storage means for storing representations of the weighting factors that define the amplitude of said time-domain window signal at points separated from each other by an interval of T sec., where 1/T is the rate at which the data representing symbols of said periodic sequence are received; and a multiplication means for successively multiplying the successive amplitudes of the received signal by said weighting factors.

Claim 8

Apparatus for determining the initial value of the coefficients of a complex transversal equalizer in a data transmission system having a transmitter, a receiver and a communications channel connecting said transmitter and said receiver, said system using double sideband-quadrature carrier modulation and characterized in that it includes: means located at said transmitter of the system for transmitting over said channel, a periodic pseudo-random sequence of data symbols whose elements are representable as complex numbers, said sequence having a periodic autocorrelation function only the first coefficient of which is not zero, and in which all complex numbers in the sequence have a constant amplitude; modulation means in said receiver and connected to said transmission channel for modulating the received signal by a time-domain window signal where the Fourier transform of said window signal exhibits a relatively flat central peak and has comparatively low values in the vicinity of those frequencies which are multiples of the inverse of the period of the transmitted sequence; means on the output of said modulation means for determining the factors of the discrete Fourier transform, W k , of the modulated received signal; a storage means for storing factors representing the discrete Fourier transform, Z k , of one period of the transmitted sequence of data symbols; means connected to said discrete Fourier transform determining means and to said storage means for calculating the ratio F.sub.k =Z.sub.k /W.sub.k of said transforms; and means on the output of said calculating means for generating terms representing the inverse Fourier transform of F k , to thereby determine the values of the coefficients c n of the equalizer.

Claim 9

Apparatus for determining the initial value of the coefficients of a complex transversal equalizer in a data transmission system having a transmitter, a receiver and a communications channel connecting said transmitter and said receiver, said system using double sideband-quadrature carrier modulation and characterized in that it includes: means located at said transmitter of the system for transmitting over said channel, a periodic pseudo-random sequence of data symbols whose elements are representable as complex numbers, said sequence having a periodic autocorrelation function only the first coefficient of which is not zero, and in which all complex numbers in the sequence have a constant amplitude; modulation means in said receiver and connected to said transmission channel for modulating the received signal by a time-domain window signal where the Fourier transform of said window signal exhibits a relatively flat central peak and has comparatively low values in the vicinity of those frequencies which are multiples of the inverse of the period of the transmitted sequence; means on the output of said modulation means for determining the factors of the discrete Fourier transform, W k , of the modulated received signal; a storage means for storing factors representing the discrete Fourier transform, Z k , of one period of the transmitted sequence of data symbols; means connected to said discrete Fourier transform determining means and to said storage means for calculating the ratio F.sub.k =Z.sub.k /W.sub.k of said transforms; and means on the output of said calculating means for generating terms representing the inverse Fourier transform of F k , to thereby determine the values of the coefficients c n of the equalizer.

Claim 10

An apparatus as set out in claim 5 and further characterized in that said modulation means includes: a second storage means for storing representations of the weighting factors that define the amplitude of said time-domain window signal at points separated from each other by an interval of T sec., where 1/T is the rate at which the data representing symbols of said periodic sequence are received; and a multiplication means for successively multiplying the successive amplitudes of the received signal by said weighting factors.

Claim 11

A method as set out in claim 1, characterized in that said time-window signal is a triangular signal having a width equal to twice the period of said periodic sequence.

Claim 12

An apparatus as set out in claim 3 characterized in that said time-window signal is a triangular signal having a width equal to twice the period of said periodic sequence.

Claim 13

A method as set out in claim 2, characterized in that said time-window signal is a triangular signal having a width equal to twice the period of said periodic sequence.

Claim 14

An apparatus as set out in claim 4, characterized in that said time-window signal is a triangular signal having a width equal to twice the period of said periodic sequence.

Claim 15

An apparatus as set out in claim 5, characterized in that said time-window signal is a triangular signal having a width equal to twice the period of said periodic sequence.

Claim 16

An apparatus as set out in claim 6, characterized in that said time-window signal is a triangular signal having a width equal to twice the period of said periodic sequence.