Automatic mode detection in digital audio receivers
AssigneeSGS-Thomson Microelectronics S.A.
InventorStefano Cervini
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Abstract
The broadcast mode of the different ones set by the international standards for digital audio broadcasting (DAB) according to a coded orthogonal frequency division multiplexing scheme (COEFDM) may be automatically detected in a receiver through a detection routine. Many of the calculation modules required by the automatic mode detection system of the invention are already present in a receiver and can be exploited for performing the digital signal processing that leads to an automatic recognition of the broadcast mode of the station on which the receiver is tuned.
Claims11
A method for automatic broadcasting mode detection (AMD) for a receiver of digital audio broadcasting (DAB) of coded orthogonal frequency division multiplexed (COFDM) signals, the method comprising the steps of:
- calculating a Fast Fourier Transform (FFT) and an Inverse Fast Fourier Transform (IFFT) of a received digital input signal according to a butterfly time decimation algorithm and parallely for different numbers of points or samples of the input signal, and executing a division among complex numbers in Cartesian form (I/Q), with a dividend being represented by a complex number in Cartesian form (I/Q) resulting from a respective calculation of the FFT and a divider being a preestablished complex number;
- calculating a square of a module of results of the IFFT calculation relative to numerical sequences corresponding to said different numbers of points or samples of the input signal;
- detecting peaks of different numerical sequences resulting from the preceding calculation of the square and accumulating relative peak values in an N number of registers relative to each of said numerical sequences;
- discriminating and storing in a dedicated register a maximum value among the peak values accumulated in said N registers for each of said numerical sequences;
- calculating a square of a difference between a sum of peak values of said N registers, normalized by dividing by a relative maximum peak value and storing the results in dedicated registers;
- and
- discriminating a minimum value among contents of said dedicated registers as an information that identifies the broadcasting mode according to a relative truth table.
An automatic mode detection (AMD) system for a receiver of digital audio broadcasting (DAB) coded orthogonal frequency division multiplexed signals (COFDM), comprising:
- first means for calculating a Fast Fourier Transform (FFT) parallely for different numbers of samples of an input signal;
- second means for carrying out a division among complex numbers in Cartesian form (I/Q), wherein dividends are represented by numerical sequences output by said first means, respectively, and wherein dividers are preestablished variable complex numbers pertaining to different modes of broadcasting, respectively;
- third means for calculating an Inverse Fast Fourier Transform (IFFT) of numerical sequences produced by said second means, according to a butterfly time decimation algorithm;
- fourth means for calculating a square of a module of results of said third means relative to numerical sequences pertaining to said different numbers of samples of the input signal.
- fifth means for detecting peak values of numerical sequences produced by said fourth means and for storing said peak values in a number N of output registers relative to each of the numerical sequences, and for discriminating and storing in a dedicated register a maximum value among said peak values stored in the N output registers for each of the numerical sequences;
- sixth means for calculating a square of a difference among the normalized sum values of values stored in said N output registers of said fifth means and for discriminating and storing in a dedicated register a maximum peak value;
- and
- seventh means for discriminating a minimum value among said maximum peak values stored in the dedicated registers of said sixth means.
A digital audio broadcasting (DAB) receiver for coded orthogonal frequency division multiplexed (COFDM) signals, said DAB receiver comprising:
- an automatic mode detection system comprising:
- first means for calculating a Fast Fourier Transform (FFT) parallely for different numbers of samples of an input signal;
- second means for carrying out a division among complex numbers in Cartesian form (I/Q), wherein dividends are represented by numerical sequences output by said first means, respectively, and wherein dividers are preestablished variable complex numbers pertaining to different modes of broadcasting, respectively;
- third means for calculating an Inverse Fast Fourier Transform (IFFT) of numerical sequences produced by said second means, according to a butterfly time decimation algorithm;
- fourth means for calculating a square of a module of results of said third means relative to numerical sequences pertaining to said different numbers of samples of the input signal;
- fifth means for detecting peak values of numerical sequences produced by said fourth means and for storing said peak values in a number N of output registers relative to each of the numerical sequences, and for discriminating and storing in a dedicated register a maximum value among said peak values stored in the N output registers for each of the numerical sequences;
- sixth means for calculating a square of a difference among the normalized sum values of values stored in said N output registers of said fifth means and for discriminating and storing in a dedicated register a maximum peak value;
- and
- seventh means for discriminating a minimum value among said maximum peak values stored in the dedicated registers of said sixth means.
Dependencies are inferred from the claim text.