Abstract: A variety of bi-directional data transmission systems that facilitate communications between a plurality of remote units (15) and a central unit (10) using a frame based discrete multi-carrier transmission scheme are disclosed. In each of the systems, frames transmitted from the plurality of remote units (15) are synchronized at the central unit (10). A variety of novel modem arrangements and methods for coordinating communications between a plurality of remote units (15) and a central unit (10) to facilitate multi-point-to-point transmission are disclosed. The invention has application in a wide variety of data transmission schemes including Asymmetric Digital Subscriber Line systems that include the transmission of signals over twisted pair, fiber and/or hybrid telephone lines, cable systems that includes the transmission of signals over a coaxial cable, and digital cellular television systems that include the transmission of radio signals.

Abstract: A variety of bi-directional data transmission systems that facilitate communications between a plurality of remote units (15) and a central unit (10) using a frame based discrete multi-carrier transmission scheme are disclosed. In each of the systems, frames transmitted from the plurality of remote units (15) are synchronized at the central unit (10). A variety of novel modem arrangements and methods for coordinating communications between a plurality of remote units (15) and a central unit (10) to facilitate multi-point-to-point transmission are disclosed. The invention has application in a wide variety of data transmission schemes including Asymmetric Digital Subscriber Line systems that includes the transmission of signals over twisted pair, fiber and/or hybrid telephone lines, cable systems that includes the transmission of signals over a coaxial cable, and digital cellular television systems that include the transmission of radio signals.

Abstract: A data communication system that provides different types of service (e.g., telephone services and high-speed data transmission services) to a remote site even when the remote site lacks a splitter is disclosed. A central site (e.g., central office) is able to communicate with at least two different types of remote sites. One type of remote site includes a full splitter (i.e., both low-pass and high-pass filters), and the other type of remote site has only a partial splitter (i.e., includes high-pass filter but lacks a low-pass filter). Although conventionally the transceivers (e.g., ADSL transceivers) at these remote sites would be of the same design and use the same modulation technique for upstream as for downstream transmissions, here the remote site that lacks a low-pass filter (i.e., partial splitter type remote site) uses a different modulation technique for upstream transmissions.

Abstract: Disclosed are radio frequency (RF) interference cancellation techniques that effectively estimate RF interference to the data signals being received using a frequency domain model, and then remove the estimated RF interference from the received data signals. Improved techniques for digitally filtering multicarrier modulation samples to reduce sidelobe interference due to the RF interference are also disclosed.

Abstract: Disclosed are radio frequency (RF) interference cancellation techniques that effectively estimate RF interference to the data signals being received using a frequency domain model, and then remove the estimated RF interference from the received data signals. Improved techniques for digitally filtering multicarrier modulation samples to reduce sidelobe interference due to the RF interference are also disclosed.

Abstract: A method and apparatus for supporting multiple bit allocations in a multicarrier modulation system arc disclosed. Hence, symbols being transmitted or received can make use of different bit allocations. By supporting the multiple bit allocations, the multicarrier modulation system is able to support bit allocation on a superframe basis. Also disclosed are techniques for selection and alignment of superframe formats to improve system performance. In the case of data transmission systems involving different transmission schemes, different bit allocations can be used to reduce undesired crosstalk interference.

Abstract: Disclosed are radio frequency (RF) interference cancellation techniques that effectively estimate RF interference to the data signals being received using a frequency domain model, and then remove the estimated RF interference from the received data signals. Improved techniques for digitally filtering multicarrier modulation samples to reduce sidelobe interference due to the RF interference are also disclosed.

Abstract: Disclosed are radio frequency (RF) interference cancellation techniques that effectively estimate RF interference to the data signals being received using a frequency domain model, and then remove the estimated RF interference from the received data signals. Improved techniques for digitally filtering multicarrier modulation samples to reduce sidelobe interference due to the RF interference are also disclosed.

Abstract: Disclosed are radio frequency (RF) interference cancellation techniques that effectively estimate RF interference to the data signals being received using a frequency domain model, and then remove the estimated RF interference from the received data signals. Improved techniques for digitally filtering multicarrier modulation samples to reduce sidelobe interference due to the RF interference are also disclosed.

Abstract: An improved techniques for synchronizing transmissions and receptions of a data transmission system utilizing time division duplexing is disclosed. The improved synchronization techniques utilize the time-varying nature of the energy of the received data to obtain synchronization. In one embodiment, the improved synchronization technique uses the output signals from a multicarrier modulation unit (FFT unit) and thus provides the ability to avoid frequency tones that are susceptible to RF interference. The improved synchronization techniques can also utilize crosstalk interference levels to obtain synchronization. Remote receivers in the data transmission system are able to synchronize to central transmitters, central receivers in the data transmission system are able to synchronize to remote transmitters, and central transmitters are able to synchronize with one another.

Abstract: Methods and mechanisms for reducing the impact of radio frequency interference in multi-carrier data transmission systems are disclosed. In one aspect of the invention, dummy tones are used to suppress emissions within restricted frequency bands. In another aspect of the invention, signals received on designated quiet tones are detected and used to facilitate canceling of RF interference on adjacent active tones.

Abstract: Disclosed are radio frequency (RF) interference cancellation techniques that effectively estimate RF interference to the data signals being received using a frequency domain model, and then remove the estimated RF interference from the received data signals. Improved techniques for digitally filtering multicarrier modulation samples to reduce sidelobe interference due to the RF interference are also disclosed.

Abstract: A receiver or receiver system for high speed data communications having a radio frequency noise canceller is disclosed. The radio frequency noise canceller removes radio-frequency noise from received signals over a transmission medium by adaptively estimating the radio-frequency noise during data transmission. In one embodiment, the radio frequency noise canceller includes: an adaptive filter for producing a noise cancellation signal by filtering a reference noise signal based on filter parameters, a subtractor for subtracting the noise cancellation signal from the first signal to produce the second signal; and an update circuit for enabling, at predetermined times, modification of the parameters of the adaptive filter based on the then existing second signal. A method for removing radio frequency noise is also disclosed.

Abstract: A method and apparatus for transmitting digital sound is disclosed. The method contemplates transmitting a digital radio signal (such as an FM band signal) over a plurality of sub-channels subject to some constraints on the digital signal power. A control sub-channel, sometimes referred to as an auxiliary overhead channel is used to transmit control information which is interpreted by the receiver to identify the location and potentially the mode of the digital signals.

Abstract: A method of coordinating very high speed bi-directional data transmissions between a central unit and a plurality of remote units over distinct twisted pair transmission lines that share a binder is described. Specifically, periodic synchronized upstream and downstream communication periods are provided that do not overlap with one another. The upstream and downstream communication periods for all of the wires that share a binder are synchronized. With this arrangement, all of the very high speed transmissions within the same binder are synchronized and time division duplexed such that downstream communications are not transmitted at times that overlap with the transmission of upstream communications. In some embodiments, quiet periods are provided to separate the upstream and downstream communication periods. The described invention may be used in conjunction with a wide variety of modulation schemes, including both multi-carrier and single carrier transmission schemes.

Abstract: A transmission system includes transmit and receive paths coupled via a hybrid circuit to a bidirectional transmission path. The transmit path includes a digital-to-analog converter (DAC) having a given range and precision. The transmit path signal is limited and truncated to this range and precision before the DAC. In one arrangement including an echo canceller coupled between the transmit and receive paths, a difference of the transmit path signal before and after limiting and truncation is used to produce an estimated echo response which is subtracted from the receive path signal. In another arrangement, all of the inputs to the echo canceller are derived from the transmit path after the limiting and truncation. Instead, or in addition, the amplitudes of transmit path signal samples can be shaped in conjunction with the limiting. The system can in particular be an ADSL transmission system using multicarrier modulation.

Abstract: An oversampling technique that improves signal-to-quantization noise ratio without requiring substantial amounts of processing power is disclosed. The oversampling technique determines the oversample values by successively scaling the previous value using a scaling factor. The effect of the invention is the randomize the quantization error for each of the oversample values so that the quantization error becomes uncorrelated from one oversample value to the next. When such decorrelation occurs, the quantization noise is spread over the enlarged frequency band associated with the oversampling. The invention is applicable to any transmission scheme which utilizes oversampling and digital-to-analog conversion.

Abstract: A method of coordinating very high speed bi-directional data transmissions between a central unit and a plurality of remote units over distinct twisted pair transmission lines that share a binder is described. Specifically, periodic synchronized upstream and downstream communication periods are provided that do not overlap with one another. The upstream and downstream communication periods for all of the wires that share a binder are synchronized. With this arrangement, all of the very high speed transmissions within the same binder are synchronized and time division duplexed such that downstream communications are not transmitted at times that overlap with the transmission of upstream communications. In some embodiments, quiet periods are provided to separate the upstream and downstream communication periods. The described invention may be used in conjunction with a wide variety of modulation schemes, including both multi-carrier and single carrier transmission schemes.

Abstract: A variety of methods of coordinating communications between a plurality of remote units and a central unit to facilitate communications using a frame based discrete multi-tone (DMT) transmission scheme am disclosed. In one aspect of the invention, synchronized quiet times are periodically provided in the upstream communication stream. The synchronized quiet times are used to handle a variety of control type functions such as synchronization of new remote units, transmission channel quality checking and handling data transfer requests. The information received is used to facilitate the dynamic allocation of bandwidth during use. In another aspect, a data request signal may be used to indicate either a desire to transmit at a particular data rate or a desire to transmit a particular amount of information. In the former case, the central unit allocates sufficient sub-channels to the remote unit to facilitate transmission at a requested data rate that is specified in the data request information.

Abstract: A transmission system includes transmit and receive paths coupled via a hybrid circuit to a bidirectional transmission path. The transmit path includes a digital-to-analog converter (DAC) having a given range and precision. The transmit path signal is limited and truncated to this range and precision before the DAC. In one arrangement including an echo canceller coupled between the transmit and receive paths, a difference of the transmit path signal before and after limiting and truncation is used to produce an estimated echo response which is subtracted from the receive path signal. In another arrangement, all of the inputs to the echo canceller are derived from the transmit path after the limiting and truncation. Instead, or in addition, the amplitudes of transmit path signal samples can be shaped in conjunction with the limiting. The system can in particular be an ADSL transmission system using multicarrier modulation.