Method and device for transmitting and identifying a modulation type in digital communication systems by way of a phase rotation factor applied to a training sequence
View Patent ↗Data symbols in the training sequence are rotated at the transmitter end through a phase rotation factor which is specific for a given modulation type that is used. For blind modulation detection at the receiver end, the data symbols are derotated through different phase rotation factors, and a correlation function is formed between the sequences obtained in this way and the original training sequence. The type of modulation which is used is obtained from the phase rotation factor which produces a maximum for the correlation function.
1. A transmission and reception method in a digital telecommunications system, which comprises:
at a transmitter end, rotating each data symbol in a predetermined initial sequence known to a receiver through a phase rotation factor specific for a type of modulation being used to thereby form rotated data symbols;
at a receiver end, derotating the rotated data symbols through different phase rotation factors to generate a derotated sequence; and
forming a correlation function between the derotated sequence and the initial sequence based on an assumed temporal position of the initial sequence contained in a signal received at the receiver end for each phase rotation factor, wherein a temporal position of the initial sequence is known up to a certain accuracy;
forming a summation of products between the derotated sequence and the initial sequence for individual moments in time from the correlation function, and squaring a magnitude of the summation to form squares; and
comparing the squares of the magnitudes and determining therefrom a modulation type used at the transmitter end.
2. The transmission and reception method according to claim 1 , wherein the initial sequence is a training sequence of a data burst.
3. The transmission and reception method according to claim 1 , which comprises forming the correlation function between the received sequences and the initial sequence in an original, unfiltered state.
4. A receiver for a digital telecommunications system, comprising:
means for receiving a data signal from a transmitter, the data signed containing an initial sequence known to said receiver and each data symbol being rotated through a phase rotation factor;
means connected to said receiving means for derotating the data symbols in the received initial sequence through different phase rotation factors;
means for forming a correlation function between the sequence obtained by said derotating means and the initial sequence on the basis of an assumed temporal position of the initial sequence contained in the received signal for each phase rotation factor, wherein a temporal position of the initial sequence is known up to a certain accuracy;
means for forming a summation of products between the sequence obtained by said derotating means and the initial sequence for individual moments in time;
means for squaring a magnitude of a summation for forming squares; and
means for determining a maximum of the squares formed in said squaring means and determining therefrom a modulation type used at the transmitter.
5. The transmission and reception method according to claim 1 , which comprises forming the correlation function several times successively, thereby forming one correlation function at an assumed temporal position of the initial sequence contained in the received signal, and forming further correlation functions by shifting the received sequence and the initial sequence incrementally in time with respect to one another.