Digital PSK-type demodulator having clock recovery before carrier recovery

Claim 3

A method according to claim 1, wherein said function is of the form F[z(t).z*(t-T s )] where z=x+jy represents a value of the signal resulting from values x and y on I and Q paths, and T s is a period of occurence of successive symbols of the signal.

Claim 4

A method according to claim 2, wherein the minimum of said function F is searched by determining where the function H(t)=G(t+T s /4)-G(t-T s /4) is zero, G representing a mean value of F[z(t).z*(t-T s )].

Claim 7

Apparatus for demodulating a received signal consisting of a carrier with M-state phase modulation, the apparatus comprising: means for transposing the received signal to an intermediate frequency: means for conversion of the transposed signal into two baseband signals on two paths (I, Q) in quadrature, including a local oscillator at a frequency; means for sampling and digitally converting the two signals on the two paths, comprising an adjustable phase clock at a bit frequency of the received signal; and means for recovering the carrier and demodulating the input signal, the demodulation using the recovered carrier and the two signals on the two paths, further comprising: means for adjusting the phase of the adjustable phase clock to a value which corresponds to a minimum of intersymbol interference, without reference to the carrier, having: means for calculating a non-linear function F[z(t).z*(t-T s )] where z=x+jy represents the value of components x and y of the digitized signal on the I and Q paths, and T s is the symbol period, and means for controlling the phase of the adjustable phase clock in a direction to cause said function to become equal to zero.

Claim 8

Apparatus for demodulating a received signal consisting of a carrier with M-state phase modulation, the apparatus comprising: means for transposing the received signal to an intermediate frequency: means for conversion of the transposed signal into two baseband signals on two paths (I, Q) in quadrature, including a local oscillator at a frequency; means for sampling and digitally converting the two signals on the two paths, comprising an adjustable phase clock at a bit frequency of the received signal; and means for recovering the carrier and demodulating the input signal, the demodulation using the recovered carrier and the two signals on the two paths, further comprising: means for adjusting the phase of the adjustable phase clock to a value which corresponds to a minimum of intersymbol interference, without reference to the carrier, having: means for calculating a non-linear function F[z(t).z*(t-T s )] where z=x+jy represents the value of components x and y of the digitized signal on the I and Q paths, and T s is the symbol period, and means for controlling the phase of the adjustable phase clock in a direction to cause said function to become equal to zero.

Claim 9

Apparatus for demodulating a received signal consisting of a carrier with M-state phase modulation, the apparatus comprising: means including at least one first local oscillator for transposing the received signal to an intermediate frequency; means for conversion of the transposed signal into two baseband signals on two paths (I, Q) in quadrature, including a second local oscillator; means for sampling and digitally converting the two signals on the two paths, comprising an adjustable phase clock at the bit frequency of a clock of the received signal; and means for recovering the carrier and for coherent demodulation using the two signals on the two paths, further comprising: means for adjusting the phase of the adjustable phase clock to a value which corresponds to a minimum of intersymbol interference by analyzing the sampled and digitized signals prior to recovering the carrier, arranged to calculate energy distribution as a function of the phase of the adjustable clock phase and to control the clock phase so as to obtain a maximum of said energy distribution.

Claim 10

Apparatus for demodulating a received signal consisting of a carrier with M-state phase modulation, the apparatus comprising: means including at least one first local oscillator for transposing the received signal to an intermediate frequency; means for conversion of the transposed signal into two baseband signals on two paths (I, Q) in quadrature, including a second local oscillator; means for sampling and digitally converting the two signals on the two paths, comprising an adjustable phase clock at the bit frequency of a clock of the received signal; and means for recovering the carrier and for coherent demodulation using the two signals on the two paths, further comprising: means for adjusting the phase of the adjustable phase clock to a value which corresponds to a minimum of intersymbol interference by analyzing the sampled and digitized signals prior to recovering the carrier, arranged to calculate energy distribution as a function of the phase of the adjustable clock phase and to control the clock phase so as to obtain a maximum of said energy distribution.

Claim 11

Apparatus according to claim 6, wherein said means for adjusting the phase are arranged to seek a maximum of an energy distribution function P by estimating two average powers, one over a plurality of successive even samples at a symbol frequency 1/T s , and the other over the same plurality of odd samples, by taking the difference of the two estimated powers, and by controlling the adjustable clock based on the difference.

Claim 12

Apparatus according to claim 6, for a 4PSK signal, wherein said means for controlling the phase of the clock are connected to receive digital sample sequences (I s , Q s ) at twice the symbol frequency 1/T s , and comprise: a first branch for calculating the average power for even samples and a second branch for calculating the average power for odd samples, each branch having two elements for raising to the square associated with the paths I and Q and accumulating a plurality of successive samples, plus an adder; a subtracter forming an output signal that is continuously representative of the difference of outputs of the adders; and means performing digital-to-analog conversion and lowpass filtering of said output signal.

Claim 13

Apparatus according to claim 8, further including an input amplifier located between said means for transposing the received signal and said means for conversion, means for automatically controlling the gain of said input amplifier, comprising a supplemental adder for adding the outputs from the adders, and a digital-to-analog converter feeding a gain control input of the amplifier.