Method and device for acquiring the initial phase of the clock in a synchronous data receiver

In a synchronous data transmission system wherein the data are transmitted by modulating a carrier wave f.sub.c at a signaling rate 1/T, a method of determining the initial phase value by which the phase of the receiver clock must be varied during an initial synchronization operation during which a synchronization signal whose spectrum includes two distinct lines at frequencies f.sub.1 =f.sub.c -1/2T and f.sub.2 =f.sub.c +1/2T is transmitted, said method being characterized in that it includes the steps of:

• (a) sampling the synchronization signal received at the input of the receiver at a rate 1/.tau. which is a multiple of the signaling rate, to obtain a signal x(k.tau.) there k=0, 1, . . . ,
• (b) multiplying signal x(k.tau.) by itself to obtain a signal s(k.tau.),
• (c) computing the real, Re C.sub.o, and imaginary, Im C.sub.o, parts of complex coefficient C.sub.o, which corresponds to frequency 1/T, of the discrete Fourier transform of signal s(k.tau.) from N samples thereof, in accordance with the following relations:
• ##EQU7## said number N being given by
• N=1/R.tau.
• where R is the resolution expressed in H.sub.z and is equal to the difference between 2f.sub.1 and 1/T, and
• (d) computing from the real and imaginary parts of complex coefficient C.sub.o the phase thereof that represents the initial phase value by which the phase of the receiver clock is to be varied.

In a synchronous data transmission system wherein the data are transmitted by modulating a carrier wave of frequency f.sub.c at a signaling rate 1/T, a device for determining the initial phase value by which the phase of the receiver clock must be varied during an initial synchronization operation during which a synchronization signal whose spectrum includes two distinct lines at frequencies f.sub.1 =f.sub.c -1/2T and f.sub.2 =f.sub.c +1/2T is transmitted, said device being characterized in that it includes:

• sampling means for sampling the signal received at the input of the receiver at a rate 1/.tau. which is a multiple of the signaling rate, thereby providing a signal x(k.tau.) where k=0, 1, . . . ,
• first multiplier means for multiplying signal x(k.tau.) by itself, thereby providing a signal s(k.tau.),
• first computing means for computing from said signal s(k.tau.) the complex coefficient C.sub.o, which corresponds to frequency 1/T, of the discrete Fourier transform of signal s(k.tau.) from a number N of samples of said signal, in accordance with the following relation:
• ##EQU8## said number N being given by
• N=1/R.tau.
• where R is the resolution expressed in H.sub.z and is equal to the difference between 2f.sub.1 and 1/T and,
• second computing means for computing the phase of complex coefficient C.sub.o which represents the initial phase value by which the phase of the receiver clock must be varied.

In a synchronous data transmission system wherein the data are transmitted by modulating a carrier wave of frequency f.sub.c at a signaling rate 1/T, a device for determining the initial phase value by which the phase of the receiver clock must be varied during an initial synchronization operation during which a synchronization signal whose spectrum includes two distinct lines at frequencies f.sub.1 =f.sub.c -1/2T and f.sub.2 =f.sub.c +1/2T is transmitted, said device being characterized in that it includes:

• sampling means for sampling the received signal at a rate 1/.tau. which is a multiple of the signaling rate, thereby providing a signal x(k.tau.),
• first multiplier means for multiplying said signal x(k.tau.) by itself, thereby providing a signal s(k.tau.),
• first storage means in which the precomputed values of cos (2.pi./T) k.tau. for k=0, 1, . . . , (N-1) are stored, where N is given by
• N=1/R.tau.
• where R is the resolution expressed in H.sub.z and is equal to the difference between 2f.sub.1 and 1/T,
• second multiplier means for multiplying said signal s(k.tau.) by said precomputed values stored in said first storage means, thereby providing the products s(k.tau.) cos (2.pi./T) k.tau. for k=0, 1, . . . , (N-1),
• first accumulator means having its input connected to the output of said second multiplier means for accumulating the products successively provided by said second multiplier means, said accumulator containing the value of the real part of complex coefficient C.sub.o after all of the products have been accumulated,
• second storage means in which the precomputed values of -sin (2.pi./T) k.tau. for k-0, 1, . . . , (N-1) are stored,
• third multiplier means for multiplying said signal s(k.tau.) by said precomputed values stored in said second storage means, thereby providing the products -s(k.tau.) sin (2.pi./T) k.tau. for k=0, 1, . . . , (N-1),
• second accumulator means having its input connected to the output of said third multiplier means for accumulating the products successively provided by said third multiplier means, said accumulator containing the value of the imaginary part of complex coefficient C.sub.o after all of the products have been accumulated, and
• a resolver for deriving the value of the phase of coefficient C.sub.o from the real and imaginary parts thereof, the value of said phase representing the initial phase value by which the phase of the receiver clock must be varied.