Koninklijke Philips Corporation N.V.

Delphine Legrand

Antoine Chouly

Americo Brajal

Am&eacute;rico Brajal

According to one example embodiment, a communication system includes a transmitter and a receiver for receiving symbols from a phase-shift shift keying modulation. The system also includes estimation means for estimating a frequency error relating to a symbol based on a sequence of symbol phases. The receiver includes calculation means for calculating a phase sequence, called an initial sequence, based on decisions made on symbols. The receiver also includes means for detecting and correcting phase jumps in this initial sequence in order to supply a phase sequence, called a final sequence, to the frequency error estimation means.

Detection and correction of phase jumps in a phase sequence

A system and method is disclosed for transmitting TDMA packets between interactive terminals and a head station using a transmission medium. The system includes an iterative method for determining an optimal sampling instant by computing the average amplitudes only for a predetermined number of the input samples, determining a maximum of the average amplitudes of these samples, deriving an approximation of the optimal sample using the maximum, repeating the average amplitude computation for input samples between the approximation and a neighboring sample whose previously computed average amplitude is the largest, and comparing of the result of each average amplitude computation with a previously computed maximum corresponding to the previous approximation for deriving a new approximation of the optimal sample.

Searching the optimal sampling instant in a TDMA packet transmission system

The invention relates to a system for transmitting TDMA packets between interactive terminals and a head station via a transmission medium, in which the receiver effects a oversampling of the received signal so as to retrieve the optimal sample corresponding to the transmitted symbol. The invention proposes a method of recovering this optimal sampling instant very rapidly by performing a polynomial interpolation computation between the generated oversamples so as to derive the optimal sampling instant and by filtering the received signal by means of a low-pass filter centered at the optimal sampling instant.

Estimating the optimal sampling instant in a TDMA packet transmission system

A method of estimating the frequency at the receiving end for a packet transmission system, for estimating a carrier frequency error between received symbols (r ) and transmitted symbols (c ). An error function (H(&Dgr;{circumflex over (f)})) defined for minimizing a magnitude which is representative of an average distance between the received symbols compensated in phase (r&prime; ) and estimations of the received symbols affected by a frequency error estimation (&ccirc; e ) is computed. The estimations of the received symbols affected by the frequency error estimation are obtained by varying the frequency error (&Dgr;{circumflex over (f)}) in an acquisition interval (&lsqb;&minus;f , &plus;f &rsqb;) for estimations of the transmitted symbol (&ccirc; ). The estimations of the transmitted, symbols (&ccirc; ) are obtained based on a threshold relating to the phase of the received symbol which is compensated in phase (r&prime; ), in the case of a modulation of the PSK type. For a modulation of the QPSK (Quadrature PSK), the threshold decision is based on the sign of the real and imaginary parts of the received, phase-compensated symbol (r&prime; ).

Semi-NDA frequency correction at the receiving end in a packet transmission system

The invention relates to a system for transmitting packets from interactive terminals to a head station. The terminals intended for consumers are provided with local oscillators which are not very accurate and use carriers having frequency errors which are relatively large with respect to the theoretical reference value (Fp). The invention provides an improvement of the reception of signals having such a frequency shift at the receiver end. To this end, the invention provides a method of estimating the frequency error &Dgr;{circumflex over (f)}, which consists of rapidly obtaining the maximum value of a discrete error function denoted Z(&Dgr;{circumflex over (f)}) for a given accuracy (Acc) by computing the function Z(&Dgr;{circumflex over (f)}) for a minimal number of points.

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Paris, France

Delphine Legrand