Northern Telecom Limited

Ephraim Arnon

Michael W Chomik

Sami A Aly

Christopher J Barlow

Edward A Capkun

A plurality of ADSL (asymmetric digital subscriber line) terminals are coupled to the coaxial cable of a cable television distribution arrangement. Each ADSL terminal is coupled to a respective ADSL path and a respective customer premises telephone line for coupling of telephone signals. Each ADSL terminal comprises a transmitter for supplying asymmetric signals received via the respective ADSL path to the coaxial cable, and transmitters and receivers for communicating bidirectional data and control signals, communicated via the respective ADSL path, via the coaxial cable, in each case modulated at a frequency which is not used for television signals. Customer premises equipment includes corresponding receivers and transmitters. The arrangement permits the ADSL terminals to be used as a resource shared by a plurality of customer premises.

Customer premises ADSL signal distribution arrangement

In apparatus for receiving digital data signals in a digital communication system, especially an Integrated Services Digital Network, timing recovery problems associated with erratic zero crossing when multiple terminals transmit to a common receiver are mitigated by detecting the rate of change of the digital data signal between two predetermined positions and controlling sampling of the digital data signal in dependence upon the difference between such rate of change and a reference. The rate of change conveniently corresponds to the trailing 'corner' of a framing pulse, i.e. the point at which the signal commences the transition from one polarity to the other. The 'corner' is much more stable, i.e. less susceptible to variation due to multiple terminal effects, than the zero-crossing which follows it, since the zero crossing may vary relative to the 'corner'. The transition may be determined by sampling the digital data signal at two discrete positions and determining when the two resulting samples differ in amplitude by a predetermined amount. One of the two pulses, namely the one with the larger amplitude, may then be used for data recovery purposes.

Method and apparatus for timing recovery in digital data communications

In an adaptive digital filter for use in an echo canceller or a decision feedback equalizer in a digital data transmission system, reduced storage and lower arithmetic processing speed are attained by subsampling, in effect, the later parts of the waveform, i.e. the tail portion which changes relatively slowly. Such an adaptive digital filter comprises a storage device, such as a shift register, for storing a group of bits which represents symbols being transmitted in the digital data signal, a first stage for deriving an estimate for a first group of the stored bits, and at least one second stage for deriving an estimate for a second group of stored bits occurring earlier in time than the first group. The second stage has a summing device for summing the second group of bits to generate a quantity representing the cumulative sum of the symbols represented in the group, and a multiplier for multiplying the quantity by a single coefficient to obtain an echo estimate for the second stage. The estimates for the first and second echo canceller stages are summed, then subtracted from the received digital data signal. There will usually be a plurality of such second stages, each operative on a different group of bits of the digital data signal.

Coefficient storage reduction in adaptive filters in echo cancellers or

Apparatus for suppressing intersymbol interference and improving the signal-to-noise ratio in a digital line amplifier includes a filter with a fixed transfer function that couples equalized digital signals to a first differential input of a difference amplifier and substantially filters out high frequency random noise present in the signals to achieve signal-to-noise enhancement with consequent degradation of the signals by intersymbol interference. Subsequently, an output from the amplifier is sampled by a quantizer that produces a bit stream output of portions of the enhanced signals, excluding the intersymbol interference. Signals from the bit stream are then coupled to a fixed coefficient decision feedback equalizer having the same transfer function as the filter and are output therefrom as feedback signals to a second differential input of the amplifier such that the signals at both differential inputs are substantially equal in terms of intersymbol interference, thereby suppressing such interference in the amplifier output.

Apparatus and method for noise reduction in a digital line receiver

An adaptive hybrid arrangement for interfacing a bidirectional communications channel with two unidirectional channels, especially for connecting a two-wire telephone line to a four-wire telephone trunk or repeater, comprises a hybrid having four ports. One port is for the two-wire or bidirectional channel, the second and third are for the unidirectional channels. A multi-element balancing network is connected to the fourth port, i.e. opposite to the port connected to the bidirectional channel. Correlation detection means detects correlation between a signal in one of the unidirectional channels and an error signal in the other. If correlation exists, adjusting means adjusts the balancing network so as to reduce such correlation.

Adaptive hybrid

In an adaptive equalizer of the decision feedback type for reducing intersymbol interference in subscriber loops of a telephone system, the corrected digital signal is applied to means for detecting the occurrence in the signal of a zero state following a non-zero state. When that occurs, a correlator samples the signal during the 'zero' bit period and applies the sample to an integrator. The integrator output varies the coefficients of the feedback signal applied to the input means for addition to the incoming digital signal to provide the corrected signal. The equalizer may have several stages, each for detecting a 'zero' state in a different bit period following the original pulse. Also the circuitry may be duplicated for each polarity if the input signal is bipolar.

Decision feedback adaptive equalizer acting on zero states following a

A digital transmission system in which bursts of digital signals are transmitted in opposite directions over a two wire telephone loop at fixed frame intervals. Each signal burst is bounded by initial and final synchronization bits at its beginning and ending respectively. Once frame synchronization is established the signals are only gated to the receiver during a window interval which is coextensive with that of the received bursts.

Time compression multiplex digital transmission system

A digital transmission system in which bursts of digital signals are transmitted in opposite directions over a two wire telephone loop at fixed frame intervals. Each signal burst is bounded by initial and final synchronization bits at its beginning and ending respectively. Synchronization is established by determining coincidence of the final bit of one burst, the initial bit of the following burst, and two gating signals having an equivalent time interval therebetween.

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Ottawa, Canada

Ephraim Arnon