Lucent Technologies Inc.

At&t Bell Laboratories

American Telephone and Telegraph, Co.

At&t Information Systems Inc.

Agere Systems Inc.

Alcatel-lucent USA Inc.

Agere Systems Guardian Corp.

Paradyne Corporation

Lgs Innovations LLC

Robert Louis Cupo

Mojtaba Shariat

Mohsen Sarraf

Mohammad Hossein Zarrabizadeh

Cecil William Farrow

Muhammad R Karim

Ahmad Khalid Aman

Nicholas A Zervos

Thomas W Goeddel

Tongtong Li

Masoud Sajadieh

Yong J Lee

Masood Yousefi

E Anthony Hinds

Mohammad Rez Karim

Mohammad Zarrabizadeh

A method and system for compensating for frequency dependent phase and amplitude imbalances is provided. A plurality of frequency sub-bands is extracted from a received wideband signal. Each of the plurality of frequency sub-bands is compensated to produce an associated plurality of compensated frequency sub-bands. The compensated sub-bands are summed in order to produce a compensated signal.

Frequency dependent I/Q imbalance compensation

Interleaving methods and apparatus are disclosed for an in-band on-channel digital audio broadcasting system. The guard periods that separate any two adjacent symbols in a conventional OFDM system can provide a mechanism for OFDM frame synchronization. The guard period of successive OFDM frames is utilized to establish one or more unique positive or negative patterns and thereby provide a mechanism for interleaver synchronization. By proper positioning of the guard period patterns, one or more particular portions of each interleaver block are identified, such as the beginning and midpoint of each interleaver block. The present invention identifies the beginning of each interleaver block, for example, by positioning the fourth negative cyclic prefix with OFDM frame zero (). The present invention can optionally identify the midpoint of each interleaver block, for example, by positioning the fourth negative cyclic prefix with OFDM frame. The beginning of an interleaver block can be distinguished from the midpoint using a unique cyclic prefix pattern. A receiver monitors the incoming data stream for a synchronization pattern to (i) establish interleaver synchronization, (ii) detect when synchronization is lost, and (iii) detect and correct a false synchronization.

Method and apparatus for establishing interleaver synchronization in an orthogonal frequency division multiplexing (OFDM) communication system

'Reliability-related' values are assigned to received signal samples containing noise and distortion. The samples are then sent to a Viterbi decoder in order to regenerate originally transmitted messages.

Methods and devices for decoding signals containing noise and distortion

An OFDM receiver recovers an rf signal as in-phase (I) and quadrature phase (Q) components of a baseband signal sampled in an A/D converter. The I and Q components of a received symbol are correlated at all sampling points. Correlation values are averaged over the latest L frames and saved in an L-deep FIFO. Symbol amplitude and phase are computed and passed to an offset estimator and an OFDM frame synchronization estimator. A phase-locked loop oscillator provides a sample number identifying the OFDM frame boundary to the offset estimator. An estimated offset value is selected as the negative of the phase angle of the auto correlation.

In-band-on-channel (IBOC) system and methods of operation using orthogonal frequency division multiplexing (OFDM) with timing and frequency offset correction

A frame formatting technique for filling a fixed length master frame with a number of variable length frames and adding additional data to synchronize the individual variable length frames and increase the randomness of the fixed length master frame. The technique fills unused portions of the fixed length master frame with random data to maximize the randomness of the fixed length master frame which can be used to produce a well behaved modulated signal for digital broadcasting, thereby increasing the efficiency of digital broadcasting system.

Frame formatting technique

An FM transmitter forms a Digital Audio Broadcasting (DAB) signal comprising a digital FM signal and an analog FM signal. The FM transmitter comprises an RF nonlinear amplifier coupled to a first antenna and an RF linear amplifier coupled to a second antenna. The RF non-linear amplifier and antenna transmit the analog FM signal. The RF linear amplifier and antenna transmit the digital FM signal. The FM transmitter controls the signal transmissions such that the transmitted analog FM signal and the transmitted digital FM signal are combined, or multiplexed, together in the channel itself (here, the atmosphere) to form the DAB signal.

Method and apparatus for combining signals

Interleaving methods and apparatus are disclosed for an in-band on-channel digital audio broadcasting system. The guard periods that separate any two adjacent symbols in a conventional OFDM system can provide a mechanism for OFDM frame synchronization. The guard period of successive OFDM frames is utilized to establish one or more unique positive or negative patterns and thereby provide a mechanism for interleaver synchronization. By proper positioning of the guard period patterns, one or more particular portions of each interleaver block are identified, such as the beginning and midpoint of each interleaver block. The present invention identifies the beginning of each interleaver block, for example, by positioning the fourth negative cyclic prefix with OFDM frame zero ( ). The present invention can optionally identify the midpoint of each interleaver block, for example, by positioning the fourth negative cyclic prefix with OFDM frame . The beginning of an interleaver block can be distinguished from the midpoint using a unique cyclic prefix pattern. A receiver monitors the incoming data stream for a synchronization pattern to (i) establish interleaver synchronization, (ii) detect when synchronization is lost, and (iii) detect and correct a false synchronization.

Method and apparatus for interleaver synchronization in an orthogonal frequency division multiplexing (OFDM) communication system

In accordance with the principles of the present invention, in addition to conventional use of frequency division multiplexed upper and lower side bands, the spectral area occupied by the analog host will be utilized by applying a one-dimensional modulation, e.g., pulse amplitude modulation (PAM) as opposed to the conventional use of a two-dimensional modulation, e.g., quadrature amplitude modulation (QAM). Furthermore, the analog and digital information within the analog host bandwidth may be combined in quadrature to keep the signals orthogonal. Thus, should one side band under the analog carrier be deteriorated or obliterated by adjacent channel interference, the other side band under the analog carrier can still provide useful data and hence better digital audio codec performance. By transmitting one or two digital data streams asymmetrically with respect to the center frequency, particular digital side bands can be rendered useless as environmental conditions warrant (e.g., as they become detrimentally affected by adjacent channel interference), reducing bandwidth capacity but not affecting the quality of the received digital data transmitted in any of the remaining digital side band regions.

Asymmetric pulse amplitude modulation transmission of multi-stream data embedded in a hybrid IBOC channel

A receiver of digital information typically performs a frame synchronization finction to locate the beginning of a frame of within received information. Frame and interleaver synchronization functions are complex tasks to accomplish, and are made more so when transmitted information is subjected to harsh interference by the environment of the transmission media, e.g., wireless media. Such interference may be sufficiently minimized by filtering the band signal at the receiver in a simple manner to allow receiver processes to perform successfully frame synchronization and interleaver functions on the filtered signal, in which such filtering may be achieved using a simple bandpass filter. Although such filtering renders the received signal sufficiently clean to recover frame synchronization and interleaver signals, it nevertheless corrupts the information carried in the signal, thereby making it extremely difficult to recover the information. This problem is overcome by shifting the unfiltered received signal in the way used to shift the filtered signal to locate the beginning of a frame and thus recover the underlying information.

Digital signal frame and interleaver synchronizer

A method and a receiver for reducing adjacent-channel interference to a digitally modulated receive signal evaluates error rates of the receive signal associated with different receive bandwidths of the receive signal. The receiver selects a preferential bandwidth among the different bandwidths based on a suitably low error rate associated with the preferential bandwidth. The selection of the different bandwidths is achieved by digital signal processing that weighs desired data bits representing a desired bandwidth differently than rejected data bits representing a rejected bandwidth.

Method and receiver for dynamically compensating for interference to a frequency division multiplex signal

A receiver for receiving synchronized digital transmissions organized in frames, each frame having a frame start, has a clock for generating pulses at time intervals with respect to a time reference and a counter for generating a count of the time intervals with respect to the time reference. A/D converters sample the digital transmission using the pulses from the clock. A cyclic prefix correlator detects the frame start during a count corresponding to an A/D sample. This count is indicative of the time interval during which the frame start was detected with respect to the reference. A memory is provided for storing a plurality (typically 36) counts indicative of the time interval during which the frame start was detected. A pointer is generated from the counts stored in memory. The pointer is indicative of a projected time interval during which a future frame start is expected to arrive. This projected time interval is computed by using a lead/lag digital filter and an oscillator responsive to the digital filter. One or more portions of the receiver are implemented using a programmable signal processor.

Fast frame synchronization

An OFDM subcarrier method and apparatus effectively reassigns subcarriers with respect to a data stream from a plurality of Digital Audio Broadcast (DAB) services or programs to reduce selective effects (e.g., selective channel fading) of the transmission channel (e.g., an FM station) on some of the DAB services or programs but not on others. In one embodiment, a symbol reassignment encoder at the transmitter shuffles the data or symbols in the data stream from the DAB services to effectively reassign the subcarriers used by each of the DAB services. The reassignment spreads the selective effects of the transmission channel, e.g., channel fading, over a larger group of DAB services, to improve the robustness and quality of the overall transmission channel.

OFDM subcarrier hopping in a multi service OFDM system

An orthogonal frequency division multiplexing (OFDM) technique which is time division multiplexed to reduce the overall effect on individual services from conditions such as selective fading. In accordance with the principles of the present invention, all available subcarriers in a channel are assigned to fewer than all of the requesting services, e.g., to just one particular service for a period of time. The period of time is preferably independent of the length of a conventional data frame. Thereafter, a second service is assigned access to the use of all available subcarriers for a period of time corresponding to its required bandwidth, and so on until all requesting services are allotted a portion of time for access to all available subcarriers. Any one service may utilize any number of the available subcarriers in a particular superframe containing one cycle of transmissions for all services.

Time division multiplexed transmission of OFDM symbols

A radio frequency (rf) receiver adapted to receive a number of different digitally modulated rf input signals such as quadrature amplitude modulated (QAM) and vestigial side band (VSB) rf input signals includes circuitry for down converting the rf input signals to an intermediate frequency (IF) range having a center frequency fc2 and a bandwidth of Bhz and converter circuitry for sampling the IF signals and then producing corresponding baseband signals. In a preferred embodiment, the intermediate frequency signals are applied to a sample and hold circuit which is sampled at a frequency fs and whose output is coupled via a low pass filter to an analog-to-digital converter whose output is then applied to a Hilbert filter for demodulating the sampled signals and producing baseband signals. In-phase (I) and quadrature (Q) signals are produced whose phase and amplitude are not a function of different components and their tolerance of different conduction paths, as in the prior art.

Sampling system for radio frequency receiver

Timing recovery circuitry for recovering digital data generates a timing signal which is a function of the delay provided by an equalizer to one or more predetermined frequency components of its input signal. Advantageously, this approach is applicable to systems which utilize one or more baseband or passband equalizers. The disclosed embodiments of the present invention pertain to a dual-duplex system. In such a system, the digital data to be transmitted is divided into two different digital signals and each signal is coupled through an associated transmission channel. At the receiver, the received version of each transmitted signal is processed by an associated equalizer and the outputs therefrom are combined to recover the digital data. In the disclosed embodiments of the present invention, the necessary timing signal for such recovery is a function of the delay introduced by each equalizer to at least one predetermined frequency component of that equalizer's input signal.

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Eatontown, NJ, United States of America

Robert Louis Cupo