Cross-correlation arrangement

Claim 1

A cross-correlation arrangement for determining the presence or absence of at least one tone signal x 2 (t), having a known frequency and having a given minimum time duration τ o , in an information signal x 1 (t) whose form and frequency are unknown, said arrangement comprising an input channel means for receiving the information signal x 1 (t), said input channel comprising: means comprising adder means and sampling and coding means coupled to said adder means for producing a first series {s(nT)} of sum signal samples, said sum signal samples s(nT) being produced with a sampling period T, the relationship between each of the sum signal samples s(nT) and information signal samples x 1 (nT) being given by s(nT) = sign [x 1 (nT) + a 1 (nT)], in which expression a 1 (nT) represents a sample of a predetermined auxiliary signal; a pulse generator means coupled to said sampling means for producing sampling pulses with a period T for controlling the sampling means; at least two correlating channels each comprising: multiplying means coupled to said sampling means for producing a series z 1 (nT) of signal samples z 1 (nT) occurring with a period T, the relation between the signal sample z 1 (nT) and the signal samples s(nT) and y(nT) being given by the expression z 1 (nT) = s(nT) ·y(nT), first integration means coupled to said multiplying means to which said signal samples z 1 (nT) are applied; and means coupled to said first integration means for converting the integration means output signals into a unipolar signal; adder means having inputs coupled to said converter means respectively and an output; second integration means coupled to said adder output; detection means having an input coupled to said second integration means for comparing the signals applied to the detection means with a predetermined reference level and for producing an output signal which characterizes the presence or absence of the tone signal x 2 (t) in the information signal x 1 (t); and a pair of generation means coupled to said multiplying means respectively for producing a periodical series {y(nT)} comprising a periodical repetition of a sub-series {y per (kT)} including of a plurality of N signal samples y per (kT) where k = 0,1, . . . N-1 which occur one after the other with the sampling period T, the relation between the signal samples y per (kT) and the tone signal x 2 (T) being given by the expression y per (kT) = sign {x 2 [(p+k)T] + a 2 [(p+k)T]} where p represents a fixed number; x 2 (p+k)T the instantaneous value of the tone signal x 2 (t) at an instant (p+k)T and a 2 (p+k)T, the instantaneous value of a second auxiliary signal a 2 (t) at the instant (p+ k)T and in which the time duration NT of the sub-series {y per (kT)} is smaller than or equal to the minimum time τ o during which the known tone signal x 2 (t) is at least present in the information signal x 1 (t).