Lucent Technologies Inc.

At&t Bell Laboratories

At+t Corp.

Globespan Technologies, Inc.

Other

American Telephone and Telegraph, Co.

Jin-Der Wang

Rajiv Laroia

Ehud Langberg

Jean-Jacques Werner

Lee-Fang Wei

Jalil Fadavi-Ardekani

Nuri Ruhi Dagdeviren

George John Kustka

Burton R Saltzberg

Daniel Amrany

Hanan Herzberg

Gi-Hong Im

Hong Y Chung

Richard Rogoszewicz

Jenn-Shing Lin

Tzy-Hong Chao

Shlomo Gadot

In an Asymmetric Digital Subscriber Loop (ADSL) Discrete Multi-Tone (DMT) system, ADSL DMT equipment includes a decoder that operates on a received DMT signal representing Nf symbols/second, where N>1, to recover f symbols per second. In particular, the decoder decides each symbol value of the recovered signal as a function of values of a respective 2N symbol values from the received DMT signal.

Decoding technique in discrete multi-tone (DMT) based communications systems

In an Asymmetric Digital Subscriber Loop (ADSL) Discrete Multi-Tone (DMT) system, ADSL DMT equipment includes an encoder that operates on a DMT input signal representing &fnof; symbols/sec. to generate, for transmission, a DMT output signal representing N&fnof; symbols/sec., where N>1, and where each symbol from the DMT input signal is generated in a redundant form in the DMT output signal. In one example of a redundant form, each symbol from the DMT input signal is repeated in N consecutive symbol intervals in the DMT output signal. In another example of a redundant form, every N DMT input symbol values are transmitted in 2N consecutive symbol intervals in the DMT output signal. These 2N consecutive symbols in the DMT output signal include 1) N symbols whose values equal the respective N DMT input symbol values and 2) N symbols whose values are a function of the respective N DMT input symbol values.

Coding technique in discrete multi-tone (DMT) based communications systems

An Asymmetric Digital Subscriber Loop (ADSL) Discrete Multi-Tone system has disjoint and adjacent upstream and downstream channels. During the training phase of an ADSL connection, an ADSL DMT transmitter first determines a round trip propagation delay by transmitting a ranging signal to a far-end ADSL endpoint. During the subsequent communications phase, the ADSL transmitter synchronizes transmission of DMT symbols to a reference clock. In addition, the cyclic extensions of each DMT symbol are increased as a function of the propagation delay.

Reduction of interference in discrete multi-tone (DMT) based communications systems

A known training sequence of binary, pseudo random signals, PN, is received over the channel and correlated with a modified pseudo random sequence PN,in which the zeros of the known sequence PN have been mapped to &minus;1. A transform of the correlator output will be observed to contain strong tones that indicate the degree of frequency offset. To facilitate synchronization in the presence of an unknown amount of frequency offset, the received signals may be rectified and the correlation step performed with the absolute value of the incoming signal to obtain new output samples. When the frequency offset is small its measurement is facilitated by modulating the incoming signals with a known, comparatively large frequency offset, before the correlation step to make sure that the overall frequency offset occurs around a frequency that is an integral multiple of the symbol rate divided by the number of symbols in the pseudo random sequence. After being compensated for the frequency offset, the received synchronization/sounding signal is used to sound the channel impulse response.

Channel synchronization and impulse sounding in the presence of frequency offset

The problem of error propagation is resolved by using the communications channel to adapt a pre-equalizer of a transmitter, in response to changes in the communications channel. In particular, the pre-equalizer adapts to changes in the communications channel by processing an error signal that is communicated over a reverse channel by a corresponding receiver.

Adaptive pre-equalizer for use in data communications equipment

A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver. The RF transmitter transmits an RF DAB signal that includes a pilot signal at 250 Khz. An RF section of the RF receiver includes a phase-lock-loop (PLL) to compensate for any carrier frequency differences in the received RF DAB signal. This PLL tracks the phase of the received RF DAB signal when an amplitude of a recovered IF signal is above a predetermined threshold and upon detection of the pilot signal.

Transmission system for digital audio broadcasting

A digital audio broadcasting (DAB) system includes a radio-frequency (RF) receiver that develops a characterization signal representative of a respective mobile communications channel as a precursor to estimating a channel impulse response. The latter is used to set coefficients of an equalizer of the receiver to compensate for distortion such as intersymbol interference. In generating the channel impulse response a Fast Fourier Transform (FFT) of the characterization signal is performed. The resulting FFT is then clipped such that frequency components above a predetermined upper threshold and less than a predetermined lower threshold are set to the respective threshold values. This allows coefficients for the equalizer to be generated such that the equalizer converges even in the presence of strong reflections in a mobile communications environment.

Developing a channel impulse response by using distortion

A digital audio broadcasting system includes an RF transmitter and a corresponding RF receiver. In the RF transmitter, a digitally compressed audio signal is encoded into a symbol stream that is first rotated using a frequency of 150,000 hertz (hz) before transmission to the RF receiver.

Transmission system for digital audio broadcasting that incorporates a

A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver that includes a frame detection circuit for providing a frame synchronization signal. The latter is used to inhibit a Reed-Solomon decoder from correcting data in any frame for which there was no synchronization.

A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver. The RF transmitter formats a DAB signal into a sequence of frames, each frame having a header comprising a predefined grouping of psuedo-random number sequences comprising 100 symbols. Of these 100 symbols, 86 symbols of the header are used for frame synchronization and channel sounding (for characterization of a communications channel), while the remaining 14 symbols are used for interleaver and data synchronization in an interleaved fashion.

In a digital audio broadcasting (DAB) system having a radio-frequency (RF) transmitter and a corresponding RF receiver, a system and method for providing improved frame synchronization is provided. In accordance with the preferred embodiment, the RF transmitter formats a DAB signal into a sequence of frames, each frame having a header with a predefined grouping of psuedo-random number sequences comprising 100 symbols. Of these 100 symbols, 86 symbols of the header preferable are used for frame synchronization and characterization of a communications channel, while the remaining 14 symbols are used for interleaver and data synchronization in an interleaved fashion. The formatted DAB signal, including the frame sequences, is transmitted to the receiver preferably using quadrature phase-shift keying modulation. At the receiver, a correlator, utilizing a synchronization detection algorithm, is generally designed to match a predetermined symbol pattern within the received signal. Once the frame synchronization is established, the channel is characterized and the data symbols are recovered.

System and method producing improved frame synchronization in a digital

A hybrid type of decision feedback equalizer (DFE) structure that approaches optimal DFE performance is described. The hybrid DFE includes both an intersymbol interference DFE (ISI-DFE) and a noise predictive DFE (NP-DFE). In particular, an adaptive feedforward filter section is followed by both an intersymbol interference (ISI) predictive filter and a noise predictive (NP) filter. The corresponding transmitter uses a precoder that utilizes optimal coefficient values, denoted as C(z), of the hybrid DFE structure. In particular, C(z) is equal to (1+I(z)) (1+N(z))-1, where, the notation I(z) and N(z), as known in the art, represent the resulting coefficient values after adaptation of the ISI-DFE and the NP-DFE, respectively.

Hybrid equalizer arrangement for use in data communications equipment

A hybrid type of decision feedback equalizer (DFE) structure that approaches optimal DFE performance is described. The hybrid DFE includes both an intersymbol interference DFE (ISI-DFE) and a noise predictive DFE (NP-DFE). The hybrid DFE structure is designed so that one form of tap values dominates over the other. This allows only the dominate tap values to be used by the transmitter during precoding and reduces the transmitter complexity. In particular, a hybrid DFE is designed so that the I(z) coefficient values dominate over the N(z) coefficient values, where the notation I(z) and N(z), as known in the art, represent the resulting coefficient values after adaptation of the ISI-DFE and the NP-DFE, respectively. A respective Tomlinson precoding scheme in the transmitter uses only the I(z) values. Since only the I(z) values are used in the precoder of the transmitter, the NP-DFE of the receiver is kept active during the communications phase. Conveniently, the continued use of the NP-DFE in the receiver allows the receiver to track small changes in the channel.

The present invention relates to correlation apparatus in which samples of a received signal are demultiplexed and coupled to a plurality of correlators in cyclic fashion so that successive samples are coupled to a different correlator in the plurality. Each correlator provides an output which is coupled to multiplexing apparatus. This apparatus is especially useful for determining signal dispersion characteristics and avoids the 'null taps' associated with conventional correlation apparatus.

Signal correlation technique

A signal dispersion cancellation structure receives incoming signal samples at an incoming rate, stores these samples in a first memory and then writes these samples at a submultiple of the incoming rate into a plurality of second memories. Each second memory is associated with a finite impulse response (FIR) filter and the second memory samples are coupled to the associated FIR filter at the incoming rate. Advantageously, apparatus is also provided which enables any sample in a second memory to be provided to the associated FIR filter and outputted therefrom at a time related to the position of any signal dispersion.

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Ocean, NJ, United States of America

Jin-Der Wang