Method of detecting reference symbols for a digital data receiver

DETAILED DESCRIPTION A particular object of the present invention is to mitigate that drawback.
More precisely, an object of the invention is to provide a method of detecting reference signals that are uniformly inserted in a digital stream, whereby the ratio between the number I of items of useful data and the number R of reference symbols is large, i.
e.
whereby insertion losses are low.
This object and others that appear below are achieved by providing a method in which a cross-correlation is calculated every T.
sub.
e on successive frames, each calculated cross-correlation supplying a magnitude I.
sub.
n equal to: ##EQU3## where x.
sub.
n+dNe represents the sample received at instant n+dNe, S*.
sub.
d,k represents the complex conjugate of the reference symbol of index d, k .
epsilon.
{0, .
.
.
, R-1) and represents the frame index, r=R/q, where q is an integer not less than 1, said cross-correlations being summed over M frames so as to form energy levels J.
sub.
M,d equal to: ##EQU4## where m is the frame index, M is the number of sums performed, and where d .
epsilon.
(0, .
.
.
, N.
sub.
e (R+I)-1}, the method further including a step of detecting the largest of the quantities J.
sub.
M,D =MAX.
sub.
d J.
sub.
M,d, the position D of the maximum corresponding to the positions of the reference symbols in the received frames.
The invention also provides apparatus for implementing the method, it being possible for the apparatus to co-operate with synchronization tracking apparatus so as to form rate recovery apparatus.