Fujitsu Corporation

Leland Stanford Junior University

Kazutomo Hasegawa

Seiji Miyoshi

Nobukazu Koizumi

Yutaka Awata

Takashi Sasaki

Hidetake Asahina

John Matthew Cioffi

Georgios Ginis

Carlos Aldana

A digital subscriber line transmission (xDSL), system includes a transmitting side which transmits training symbols by adding some data that is contained in a training symbol sequence onto at least one of the beginning and the end of this symbol sequence and then transmits the training symbol sequence. A receiving side removes the data that has been added onto the training symbol sequence and executes training processing. The length of the training symbol sequence and of a transmit symbol sequence at time of normal communication is set in such a manner that the symbol sequence will not fall within an interval in which effects of near-end crosstalk from a neighboring line are received. The data added to the training symbol sequence specifies an interval in which effects of the crosstalk are received.

Digital subscriber line transmission method, apparatus and system

Methods, apparatus, techniques and computer program products for joint reduction of crosstalk in a synchronized, time division duplexed DSL systems use sequential removal of NEXT interference followed by removal of FEXT interference from a received DSL signal. Crosstalk is removed from a primary signal in a synchronized TDD DSL system having a primary channel that carries the primary signal, at least one NEXT generating channel that generates NEXT interference in the primary signal and at least one FEXT generating channel that generates FEXT interference in the primary signal. Signal data is acquired, where the signal data includes received signal data for the primary channel and at least one FEXT generating channel, transmitted signal data for at least one NEXT generating channel, and channel data comprising channel transfer function data and crosstalk coupling coefficient data for the primary channel, each NEXT generating channel and each FEXT generating channel. After the signal data is acquired, NEXT interference in the primary signal is then removed using the transmitted signal data and the channel data, followed by removal of FEXT interference in the primary signal using vectored DMT FEXT removal, the received signal data and the channel data. In another system in which FEXT generating received signals are not necessarily available, FEXT removal can be achieved using expectation cancellation, the primary signal and the channel data in connection with possible transmitted signal values.

Joint reduction of NEXT and FEXT in xDSL systems

A digital subscriber line transmission (xDSL) system includes a transmitting side which transmits training symbols by adding some data that is contained in a training symbol sequence onto at least one of the beginning and the end of this symbol sequence and then transmits the training symbol sequence. A receiving side removes the data that has been added onto the training symbol sequence and executes training processing. The length of the training symbol sequence and of a transmit symbol sequence at time of normal communication is set in such a manner that the symbol sequence will not fall within an interval in which effects of near-end crosstalk from a neighboring line are received. The data added to the training symbol sequence specifies an interval in which effects of the crosstalk are received.

A digital subscriber line transmission (xDSL)-, system includes a transmitting side which transmits training symbols by adding some data that is contained in a training symbol sequence onto at least one of the beginning and the end of this symbol sequence and then transmits the training symbol sequence. A receiving side removes the data that has been added onto the training symbol sequence and executes training processing. The length of the training symbol sequence and of a transmit symbol sequence at time of normal communication is set in such a manner that the symbol sequence will not fall within an interval in which effects of near-end crosstalk from a neighboring line are received. The data added to the training symbol sequence specifies an interval in which effects of the crosstalk are received.

A digital subscriber line communicating system for communicating between a transmitting side and a receiving side tough a communication line, the system including a hyperframe counter for periodically counting a predetermined number of continuous transmitting data symbols constituting a hyperframe synchronized with a timing signal, and a decoder for discriminating, based on the count value of the hyperframe counter, whether a transmitting data symbol belongs to a FEXT, or a NEXT. A sequencer is provided for initializing the status during an initialization period before starting usual communication. The initialization period includes an activation and acknowledgement sequence, a transceiver training sequence, a channel analysis sequence, and an exchange sequence. According to a single bitmap mode, the initialization is carried out by transmitting modulated symbols through only inside of the sliding window. According to a dual bitmap mode, the initialization except for an S/N measuring sequence in the channel analysis sequence is carried out by transmitting modulated symbols through only inside of the sliding window, and the S/N measuring sequence is carried out by transmitting modulated symbols through both inside and outside of the sliding window.

Digital subscriber line communicating system and a transceiver in the system

A digital subscriber line communicating system for communicating between a transmitting side and a receiving side through a communication line, comprising a hyperframe counter for periodically counting a predetermined number of continuous transmitting data symbols constituting a hyperframe synchronized with a timing signal, and a decoder for discriminating, based on the count value of the hyperframe counter, whether a transmitting data symbol belongs to a FEXTor a NEXT. A sequencer is provided for initializing the status during an initialization period before starting usual communication. The initialization period includes an activation and acknowledgement sequence, a transceiver training sequence, a channel analysis sequence, and an exchange sequence. According to a single bitmap mode, the initialization is carried out by transmitting modulated symbols through only inside of said sliding window. According to a dual bitmap mode, the initialization except for an S/N measuring sequence in the channel analysis sequence is carried out by transmitting modulated symbols through only inside of said sliding window, and the S/N measuring sequence is carried out by transmitting modulated symbols through both inside and outside of said sliding window.

A subscriber communication machine is provided with an off-synchronous detector detecting off-synchronization of communication with an office communication machine, a correlation processor, when the off-synchronization is detected, correlatively processing received data received over a communication line and held data having been transmitted from the office communication machine, and a resynchronization controller specifying a synchronous timing by the correlation process in the correlation processor to establish resynchronization in the communication with the office communication machine. When the subscriber communication machine cannot keep synchronization with a transmission cycle in a predetermined transmission system such as TCM in steady communication, it is possible to promptly resume the communication without the necessity for initializing all over again.

Resynchronous control apparatus of subscriber communication machine, and resynchronizing method

A data transmission system which trains its internal equalizers both in an initialization phase and in a normal communication session. In a transmitter unit, a modulation unit modulates a data signal to be transmitted. This signal is sent out to a telephone subscriber line by a transmitter after being added a cyclic prefix by a prefixing unit. A receiver unit accepts the data signal at its receiver portion. The received signal, however, has been impaired because of non-ideal transmission characteristics of the subscriber line. The receiver unit employs a processor which serves as an equalizer to confine the signal impairment within a period of cyclic prefix of each symbol. The receiver unit further comprises a target channel which provides reference characteristics for use in adapting the processor to the current line characteristics. At an initialization stage, a first training unit performs training by tuning both the target channel and processor. When a normal communication session begins, a second training unit performs training by mainly tuning the processor.

Data transmission system and receiver unit thereof

A digital subscriber line communicating system and a transceiver therein are disclosed. The system or the transceiver comprises: a unit for calculating a bitmap which defines the number of transmissible bits for each carrier signal in each of periodical noise durations and a rate converter for converting a constant rate of an input transmitting data into a rate determined by the bitmap, and for adding, in a predetermined number of the periodical noise durations, dummy bits to the data having the converted rate. The bitmap calculating unit includes: a line quality measuring unit for measuring the quality of the communication line in each of the periodical noise durations, a transmission bit number converter for calculating the number of transmissible bits to be allocated to each carrier to form the bitmap, and a bitmap optimizing unit for minimizing the dummy bits by decreasing the number of the transmissible bits allocated to each carrier signal of the symbols. The decreasing is performed in the order from the number of bits allocated to a carrier with a smaller S/N margin to the number of bits allocated to a carrier with a larger S/N margin.

In a training method in a time domain equalizer provided in a digital data transmission system for updating tap coefficients in the time domain equalizer so that an error between the tap coefficients and channel target characteristic becomes zero, the training method includes steps of: obtaining a first sum of the tap coefficients of the channel target characteristic before a rectangular window is provided to the tap coefficients, and storing the first sum in a memory; obtaining a second sum of the tap coefficients of the channel target characteristic after the rectangular window was provided to the tap coefficients; subtracting the second sum from the first sum, and dividing a resultant value of subtraction by the numbers of the tap coefficients existing within the rectangular window; and obtaining each of tap coefficients of the channel target characteristic by adding a divided value to each tap coefficient existing within the rectangular window.

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Kawasaki, Japan

Kazutomo Hasegawa