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: 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: Improved Fourier transform processing systems for a data transmission system are disclosed. The improved Fourier transform processing systems efficiently performs Fourier transform signal processing. In addition, the improved Fourier transform processing can perform address transformations to better and more efficiently use a memory system for in-place processing. The address transformations are provided by a generalized address translation algorithm that works for any size Fourier transform, in any radix, and with various memory architectures. The processing system can also be pipelined. The invention is particularly well suited for performing in-place processing in a data transmission system.

Abstract: Improved initialization techniques for initializing data transfer between a pair of transceivers in a multicarrier modulation transmission system are disclosed. The multicarrier modulation transmission system normally includes a central office and a remote unit, with the central office having at least one transceiver and the remote unit having a transceiver. For each pair of transceivers, the transceiver at either the central office or the remote unit controls the determining of bit allocations for both upstream and downstream data transmissions without assistance from the other transceiver of the pair. The initialization processing for the pair of transceivers is thus performed efficiently and with better centralized control.

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: Improved Fourier transform processing systems for a data transmission system are disclosed. The improved Fourier transform processing systems efficiently performs Fourier transform signal processing. In addition, the improved Fourier transform processing can perform address transformations to better and more efficiently use a memory system for in-place processing. The address transformations are provided by a generalized address translation algorithm that works for any size Fourier transform, in any radix, and with various memory architectures. The processing system can also be pipelined. The invention is particularly well suited for performing in-place processing in a data transmission system.

Abstract: Improved initialization techniques for initializing data transfer between a pair of transceivers in a multicarrier modulation transmission system are disclosed. The multicarrier modulation transmission system normally includes a central office and a remote unit, with the central office having at least one transceiver and the remote unit having a transceiver. For each pair of transceivers, the transceiver at either the central office or the remote unit controls the determining of bit allocations for both upstream and downstream data transmissions without assistance from the other transceiver of the pair. The initialization processing for the pair of transceivers is thus performed efficiently and with better centralized control.

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 bi-directional data transmission system that facilitates communications between a central unit and a plurality of remote units using a frame based discrete multi-tone (DMT) transmission scheme is disclosed. The discrete multi-tone data transmission system has a multiplicity of discrete subchannels including an overhead bus. In a method aspect of the invention, frames transmitted from the plurality of remote units are synchronized at the central unit. When a selected remote desires to initiate communications, it loop times it own clock to the clock of the central unit and transmits a remote initiated synchronization signal to the central unit over a dedicated overhead subchannel in the overhead bus. The central unit responds with a centrally initiated synchronization signal that contains information indicative of a frame boundary phase shift required to synchronize the selected first remote unit with other remote units that are currently communicating with the central unit.

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: A convolutional interleaving process which utilizes an addressing scheme that enables the amount of memory to be used in the convolutional interleaving process to be reduced is disclosed. A stream of data is convolutionally interleaved at a designated interleaving depth and a designated interleaving block length such that a first symbol in a designated block has an associated predetermined delay and each subsequent symbol in the designated block has a delay equal to more than its predecessor symbol. A plurality of delay related arrays, as well as an initial value array, a lower limit array, and an upper limit array, are calculated in order to define interleaving orbits. The convolutional interleaving process is accomplished by a convolutional interleaver which is arranged to take an incoming stream of data and output an interleaved stream of bits which is conceptually partitioned into blocks. A convolutional deinterleaving process, which is similar to the convolutional interleaving process is also disclosed.

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: An improved discrete multi-tone transmission scheme is describe that contemplates encoding digital data and modulating the encoded data onto a discrete multi-tone signal having a total bandwidth of at least 1.6 MHz. In some embodiments bandwidths of 8 MHz or more are provided. The modulation system is capable of dynamically updating the subcarriers used and the amount of data transmitted on each subcarrier during transmission in order to accommodate real time changes in the line quality over particular subcarriers. In one preferred embodiment of the invention the multi-tone encoding and modulation is done in substantial compliance with the ATIS North American Asymmetric Digital Subscriber Lines standard. However, additional subchannels (such as a total of 512 subchannels) may be used and/or subchannel bandwidths of greater than 4.3125 kHz may be used.

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 discrete multitone modulation transmission system is described in which frame synchronization is monitored at the receiver by correlating frequency domain complex amplitudes of a synchronizing frame with a stored synchronizing pattern. If the correlation result falls below a threshold, indicating a loss of frame synchronization, a plurality of correlations are performed, in each case using the stored complex amplitudes of the synchronizing frame multiplied by a respective complex value representing a respective complex derotation corresponding to a respective possible time shift of the synchronizing frame. The best correlation result, if it exceeds another threshold, indicates a time shift for restoring frame synchronization, this being possible before the next synchronizing frame is received.

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.