Patent ID: 7623598

Claim:
An apparatus for demodulation of an analog received signal which is frequency-modulated at the transmitter end with a data symbol sequence {d k }, said apparatus comprising: a detector for zero crossings of the received signal, a sequence generator for production of a sequence {z i }, with a sequence element z i being a function of the difference between the times t i and t i+1 associated with two successive zero crossings, and a calculation unit for reconstruction of the data symbol sequence {d k }, with that data symbol sequence being chosen from the possible data symbol sequences as the sought data symbol sequence {d k } for which the Euclidean distance between the sequence {z i } and a sequence which is calculated at the receiver end is a minimum, with each sequence element in the calculated sequence being formed from a convolution of the data symbol sequence {d k } with a coefficient sequence {h i,k } for the index k, wherein the coefficient sequences {h i,k } are obtained from the times t i and t i+1 , wherein the sequence elements h i,k in the coefficient sequences {h i,k } are defined in such a way that z i = ∑ k = - ∞ ∞ ⁢ ⁢ d k · h i , k wherein the sequence elements z i are given by the function z i = 1 - 2 ⁢ ω 0 π · ( t i + 1 - t i ) where ω 0 is the carrier frequency of the unmodulated signal, in that the coefficients h i,k are given by the function h i,k =2η·[q(t i+1 −k·T)−q(t i −k·T)] where η is the modulation index, T is the symbol time duration and q(t) is the integral over the elementary pulse shape g(t), and the modulation index ii is given by η = Δω · T π and the integral q(t) over the elementary pulse shape g(t) is given by q ⁡ ( t ) = 1 T ⁢ ∫ - ∞ t ⁢ g ⁡ ( τ ) ⁢ ⁢ ⅆ τ , where Δω is the modulation shift.