Adaptive Crosstalk Cancellation Research Articles

A 5 Gbps 1.6 mW/G bps/CH Adaptive Crosstalk Cancellation Scheme With Reference-less Digital Calibration and Switched Termination Resistors for Single-Ended Parallel Interface

A low power adaptive crosstalk cancellation for single-ended parallel interface is presented. A fast digital calibration which accurately detects the amount of crosstalk without a reference clock (reference-less) is proposed. To transfer calibration information from a receiver to a transmitter without additional channels, switched termination resistors (STR) are implemented. The reference-less adaptation and STR schemes achieve low power consumption and small area. A crosstalk compensator with simple structure is placed at transmitter-side, and it requires less design effort and low power. The proposed adaptive crosstalk cancellation scheme rapidly determines the optimum calibration point only during 4-cycle calibration time, and eliminates from 50% to 87.1% of the crosstalk-induced jitter (CIJ). It operates up to 5 Gbps consuming 1.6 mW/Gbps/CH in a 130 nm CMOS.

A blind detection-guided approach for normalised multi-modulus crosstalk estimator in sparse multi-user DSL channels

In high-speed digital subscriber lines (DSL), far-end crosstalk is the main limiting factor on data rates. However, most of the crosstalk is due to the neighbouring twisted pairs in the binder. Therefore, the crosstalk channel matrix is sparse. Using Level 3 of Dynamic Spectrum Management, users are co-ordinated at the central office to cancel the crosstalk. Means for estimating the crosstalk canceller matrix are of critical importance for the cancellation to prove effective. Preferably, the estimation procedure should have low overhead both in computation and bandwidth. Normalised least mean squares (NLMS) based adaptive crosstalk cancellers (Gujrathi et al. (2009) [1]) have a low computational overhead but use a training sequence to ensure they converge adequately. However, using a training sequence consumes some amount of bandwidth which can be avoided if an unsupervised or blind algorithm like a normalised multi-modulus algorithm (NMMA) is used instead. A limitation of NMMA is that its convergence time is often longer than that of the NLMS algorithm. Furthermore, this is made worse as the number of canceller coefficients is made larger. In application to adaptive crosstalk cancellation within the multi-user DSL binder-channel, we argue that the convergence time can be significantly decreased by using an activity detector to exclude canceller coefficients below an appropriate minimum. In this paper, we present an activity detector design using a thresholding criterion based on the least squares technique, Akaike's information criterion (Homer et al. (1998) [2]) and Donoho's universal thresholding principle (Donoho (1995) [3]). This enables us to identify the significant crosstalkers within a DSL binder for each user. We further incorporate this strategy within the blind estimation NMMA and propose an enhanced crosstalk canceller. Our simulations indicate this multi-modulus detection-guided crosstalk canceller demonstrates improved convergence speed and has a steady state error close to that of the standard (non-detection-guided) canceller.

A Detection Guided Normalized Least-Mean-Squares Adaptive Partial Crosstalk Canceller for Multi-User DSL Environments

Block crosstalk cancellation techniques in practical multi-user digital subscriber line (DSL) environments may involve a high computational complexity as the channel and noise statistics can vary over time. We follow an adaptive approach by designing a structurally consistent significance-test feature within the normalized least-mean-square (NLMS) adaptive crosstalk canceller, aimed to detect significant crosstalkers within a DSL binder. The proposed detection-guided NLMS adaptive partial crosstalk canceller for DSL targets the dominant crosstalkers across user lines and tones, has low run-time complexity, demonstrates significantly faster convergence, and requires smaller training sequences when compared via simulation to the equivalent standard NLMS adaptive crosstalk canceller.

Adaptive crosstalk cancellation and laser frequency drift compensation in dense WDM networks

Two variations of the LMS algorithm are proposed to cancel received linear crosstalk in dense WDM networks. Analysis and simulations show that with the addition of a few photodetectors, channel spacing requirements can be reduced by over 50 percent. Simulations using a demultiplexer with Gaussian bandpass characteristics show that a 2.5 dB signal-to-crosstalk-plus-noise ratio can be increased to over 35 dB. The decision-directed algorithm will work with OOK data or any intensity modulation scheme which uses the absence of light as one symbol. The decision-directed algorithm makes assumptions on the desired laser frequency so it can accommodate only limited laser drift. A second cancellation algorithm uses pilot tones added to each laser signal in order to cancel the crosstalk. It will work with analog or digital intensity-modulated data and will automatically configure itself to account for laser drift. Both algorithms are blind in that they do not require training sequences for initialization. Analysis shows that weights derived from pilot tones are nearly optimum for canceling crosstalk for the data. Simulations of both algorithms are presented. Finally both algorithms are shown to be capable of canceling nonlinear beating terms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive crosstalk cancellation in dense wavelength division multiplexing networks

The LMS algorithm is proposed to cancel received linear crosstalk in dense wavelength division multiplexing (WDM) networks. Analysis and simulations show that with the addition of a few photodetectors, channel spacing requirements are reduced by over 50%. Simulations using a demodulator with Gaussian bandpass characteristics show that a 2.5 dB signal-to-crosstalk ratio is increased to over 35 dB.

Adaptive crosstalk cancellation for crosspolarised digital transmissions

Cancellation of crosspolarisation for modulated orthogonally polarised signals is feasible. Some networks are presented. The most interesting lie in baseband processing.