Abstract: A method of demodulation and equalization is used to process an amplitude modulated compatible digital broadcasting signal including an amplitude modulated radio frequency signal having a first carrier modulated by an analog program signal in a first frequency spectrum, a plurality of digitally modulated carrier signals positioned within a bandwidth which encompasses the first frequency spectrum, a first group of the digitally modulated carrier signals including complementary carrier signals and lying within the first frequency spectrum, and second and third groups of the digitally modulated carrier signals including non-complementary carrier signals and lying outside of the first frequency spectrum.

Abstract: A method is provided for equalizing an amplitude modulated compatible digital broadcasting signal which includes an amplitude modulated radio frequency signal having a first frequency spectrum, the amplitude modulated radio frequency signal having a first carrier modulated by an analog program signal, a plurality of digitally modulated carrier signals positioned within a bandwidth which encompasses the first frequency spectrum, a first group of the digitally modulated carrier signals including complementary signals and lying within the first frequency spectrum, and second and third groups of the digitally modulated carrier signals including non-complementary signals and lying outside of the first frequency spectrum.

Abstract: A method of broadcasting digitally encoded information includes the transmission of a plurality of orthogonal frequency division multiplexed sub-carriers. The sub-carriers are modulated by a digitally encoded signal representative of data to be transmitted, with the digitally encoded signal including a plurality of symbols having varying phase and amplitude components. The amplitude modulation can vary between two or more levels. Portions of the digitally encoded signal may be differentially imposed across the sub-carriers. The method also includes receiving the sub-carriers, demodulating the sub-carriers to recover the digitally encoded signal, and decoding the digitally encoded signal.

Abstract: The present invention provides for a receiver addressable AM compatible digital broadcast system and method. The digital broadcast signal includes a plurality of digitally modulated signals and an analog signal. A transmitter useable within the system includes a data combiner for generating an aggregate digital data signal, and a waveform generator for forming the digital broadcast signal. A receiver useable within the system comprises a waveform detector for separating the signals and a data parser for separating the digitally modulated signals. The present invention further provides for a method of selectively transmitting data via a digital broadcast signal. The method includes forming the digital broadcast signal from an analog signal and a plurality of digitally modulated signals, transmitting and receiving the digital broadcast signal.

Abstract: This invention provides a method for reducing peak to average power ratio in a radio frequency signal. The method comprises the steps of modulating a plurality of sub-carriers with a plurality of data symbol vectors to produce a first modulated signal; limiting the magnitude of the first modulated signal to produce a first limited modulated signal; demodulating the first limited modulated signal to recover the constellation points; predistorting the data symbol vectors to provide a minimum magnitude for in-phase and quadrature components thereof to produce predistorted data symbol vectors; modulating the plurality of carriers with the predistorted data symbol vectors to produce a second modulated signal; limiting the magnitude the second modulated signal to produce a second limited modulated signal; and reducing intermodulation products in the second limited modulated signal. Transmitters that perform the method are also included.

Abstract: A broadcasting method encodes program material using convolutional codes having non-puncturable bits and puncturable bits and modulates orthogonal frequency division multiplexed carrier signals with the convolutional codes. The non-puncturable bits are carried by a first group of the carriers and the puncturable bits are carried by a second group of the carriers, where the first group of carrier signals is less susceptible to interference than the second group of carrier signals. The carrier signals are then broadcast to receivers which determine if the carriers in the second group have been corrupted and erase puncturable bits carried by any of the carriers which have been determined to be corrupted. This produces punctured codes which are subsequently decoded to recover the program material.

Abstract: Apparatus and method for transmitting a digitized wideband signal robust to multipath degradation and intersymbol interference within a predetermined broadcast band. A basis set of wideband mutually orthogonal pseudorandom basis signal waveforms of substantially equal length and having predetermined autocorrelation values and a predetermined spectral shape are generated. The length of the waveforms in the set represents a baud. The wideband waveforms of the basis set are data modulated so as to define digital data. The basis set substantially maintains the predetermined spectral shape during the modulation.

Abstract: A digital modulation technique, broadcast system, and apparatus for the spectral superposition of an analog AM signal and a novel digitally modulated signal. Multiple mutually orthogonal, continuous-valued noise-like sequences are amplitude and phase modulated. Preferably, modulation coefficients are mapped from the formatted data to be transmitted and basis waveforms are generated which are then modulated by the modulation coefficients. These modulated waveforms may be ASK modulated lowpass waveforms and QAM or in-phase ASK modulated bandpass waveforms. Alternatively, the modulated waveforms may be double sideband QAM modulated lowpass waveforms and QAM modulated bandpass waveforms. In the broadcast system of the present invention, an amplitude modulated signal having a first frequency spectrum is broadcast simultaneously with a plurality of amplitude and/or phase modulated orthogonal noise-like signals having a bandwidth which encompasses the first frequency spectrum.

Abstract: A system and method for transmitting digital information through a medium such as atmospheric free-space includes a transmitter which generates a signal based on a basis set of mutually orthogonal, spectrally-shaped, sequences of substantially equal length and having predetermined autocorrelation values. The sequences may resemble noise in at least some of their characteristics. The orthogonality or cross-correlation characteristics, the autocorrelation characteristics and the resemblance to noise are due to features derived from sequences of pseudo-random numbers which themselves resemble noise in at least some of their characteristics. The waveform set based on the sequences is modulated digitally. The modulated set may be summed together along with a wideband reference signal of reduced amplitude and optionally an FM analog signal to form a composite signal which is broadcast typically through free space to at least one receiver.

Abstract: An apparatus and method for generating a broadcast waveform is provided which, for generating an in-phase component, includes an in-phase digital signal generator; a first filter for filtering the in-phase digital signal; a first digital-to-analog converter for converting the filtered digital signal into a first analog signal; an AM baseband signal generator producing an AM baseband signal; a first summer for summing the first analog and AM baseband signals to produce a composite analog signal; and a first modulator for modulating the composite analog signal with a first carrier signal at a transmission frequency, thus producing a first modulated signal.

Abstract: A system and method for transmitting digital information through a medium such as atmospheric free-space includes a transmitter which generates a signal based on a basis set of mutually orthogonal, spectrally-shaped, sequences of substantially equal length and having predetermined autocorrelation values. The sequences may resemble noise in at least some of their characteristics. The orthogonality or cross-correlation characteristics, the autocorrelation characteristics and the resemblance to noise are due to features derived from sequences of pseudo-random numbers which themselves resemble noise in at least some of their characteristics. The waveform set based on the sequences is modulated digitally. The modulated set may be summed together along with a wideband reference signal of reduced amplitude and optionally an FM analog signal to form a composite signal which is broadcast typically through free space to at least one receiver.

Abstract: A service channel is provided for concurrent communication with an amplitude modulated compatible digital broadcast signal. A transmitter receives input program information and input data service and combines the program information and data service to produce composite data. The transmitter generates an over-the-air signal waveform using the composite data. This signal is an amplitude modulated compatible digital broadcast signal. At least one receiver is used in the system to detect the over-the-air signal waveform produced by the transmitter. The receiver parses the composite data into program information and data service. The parsing of this composite data is achieved by using header information provided on each of the input program information and input data service.

Abstract: A coherent signal detector for extracting analog and digital information from a received AM-compatible digital broadcast waveform is provided. The waveform can have an in-phase component and a quadrature component. The detector can include a down converter for shifting the in-phase and quadrature components in phase, frequency, or both, in response to a phase word, thereby providing a recovered in-phase output and a recovered quadrature output. The signal detector also includes an integration circuit for integrating a portion of the recovered quadrature output over a first preselected time interval, which can be one digital time frame.

Abstract: A system for combining AM and FM transmissions. In-band, On-channel, FM Digital Audio Broadcast (IBOC FM-DAB) allows simultaneous transmission of DAB and FM over existing FM allocations without interfering with conventional analog FM signals. The utility of existing FM spectrum allocations is therefore enhanced.

Abstract: A system and method are provided for reducing perceived distortion in an output audio signal derived from an amplitude modulated compatible digital broadcast signal having an analog portion and a digital portion. The digital portion of this signal is demodulated to produce a demodulated digital signal and the analog portion of the signal is demodulated to produce a demodulated analog signal. The noise in the demodulated digital signal is measured and an estimate of the signal-to-noise ratio is derived. This estimated signal-to-noise ratio is compared with a threshold level which is set at the minimum acceptable signal quality for the digital signal. Based upon the estimated signal-to-noise ratio, a switch directs either the analog derived audio output or the digitally derived audio output as the system output signal.

Abstract: In a broadcast system having a complex waveform of digital and analog segments, frame timing is recovered and the frame synchronous power of the digital portion of the composite AM compatible Digital Audio Broadcast (DAB) waveform is measured by examining a portion of the signal. The frame timing necessary for proper demodulation is recovered from the received signal, and a signal power measurement for scaling is provided. The composite AM compatible DAB waveform is produced by a modulation method in which a digital representation of an audio signal is encoded together with an analog amplitude modulated (AM) signal and transmitted simultaneously in the same frequency channel.

Abstract: A system for combining AM and FM transmissions. In-band, On-channel, FM Digital Audio Broadcast (IBOC FM-DAB) allows simultaneous transmission of DAB and FM over existing FM allocations without interfering with conventional analog FM signals. The utility of existing FM spectrum allocations is therefore enhanced.

Abstract: A system and method for transmitting digital information through a medium such as atmospheric free-space includes a transmitter which generates a signal based on a basis set of mutually orthogonal, spectrally-shaped, sequences of substantially equal length and having predetermined autocorrelation values. The sequences may resemble noise in at least some of their characteristics. The orthogonality or cross-correlation characteristics, the autocorrelation characteristics and the resemblance to noise are due to features derived from sequences of pseudo-random numbers which themselves resemble noise in at least some of their characteristics. The waveform set based on the sequences is modulated digitally. The modulated set may be summed together along with a wideband reference signal of reduced amplitude and optionally an FM analog signal to form a composite signal which is broadcast typically through free space to at least one receiver.

Abstract: A system and method are provided for reducing perceived distortion in an output audio signal derived from an amplitude modulated compatible digital broadcast signal having a monophonic portion and a stereo portion. The stereo portion of this signal is demodulated to produce a demodulated stereo signal and the monophonic portion of the signal is demodulated to produce a demodulated monophonic signal. The noise in the demodulated stereo signal is measured and an estimate of the signal-to-noise ratio is derived. This estimated signal-to-noise ratio is compared with a threshold level which is set at the minimum acceptable signal quality for the stereo signal. Based upon the estimated signal-to-noise ratio, a switch directs either the monophonic derived audio output or the stereo derived audio output as the system output signal.

Abstract: The invention provides a method and apparatus for demodulating a composite AM DAB waveform which contains digitally modulated carriers and which employ (1) a mixer for converting a received signal into two signals (the first of these two signals represents an in-phase component and the second of these two signals represents a quadrature component); (2) two analog-to-digital converters for converting the two signals into digital signals; and (3) two fast Fourier transform elements for extracting data separately from the two digital signals. Complementary digital carrier signals are recovered from the quadrature component, and non-complementary digital carriers are derived from a sum of the complementary data and the output of the in-phase component FFT process. Leakage of the AM signal through a highpass filter is prevented from interfering with the demodulation of the complementary carrier signals' use of separated demodulation channels.