A combined solution of the Feed-Forward Equalizer (FFE) and Near-End Crosstalk (NEXT) noise cancellation technique was suggested. The techniques increase data throughput and improve link quality in the 20-in FR4 legacy backplane application. Backplane channel loss and coupling noise were measured and characterized to develop the corresponding behavioral channel model. The receiver-side FFE with 4-tap Finite Impulse Response (FIR) filter structure was adopted as the optimum equalizer topology. The 4-tap FIR filter consists of tap delay line with tap-spacing 33 ps and linear tap-gain amplifiers. The tap coefficients were calculated with the Minimum-Mean-Squared-Error (MMSE) algorithm. A 0.18-um CMOS 4-tap FIR filter IC was designed and fabricated. The experiment results showed the 20-Gbit/sec 4-PAM and 10-Gbit/sec NRZ signal were successfully equalized for the 20-in FR4 legacy backplane channel. Moreover, the suggested NEXT noise cancellation technique consists of coarse- and fine-cancellation stages. The 0.18-um CMOS building block ICs such as 7-tap FIR filter, tunable active Pole-Zero (PZ) filter, and a temporal alignment delay line were fabricated. The experiment results showed that 6-dB Signal-to-Noise Ratio (SNR) improvement was achieved by the developed NEXT noise cancellation technique.

In xDSL technology, high-speed data are transferred between the central office and the customers, or between two or more central offices using unshielded telephone lines. A major impairment that hinders the increase in data-rate through the twisted-pair line is nearend crosstalk (NEXT) between the adjacent twisted pairs. DSL systems with overlapping transmit and receive spectra are susceptible to NEXT which significantly increases the interference noise in the received signal and also reduces the reliability and availablity of the system. One way to cancel the NEXT in the received signal is to deploy adaptive filters. However, if adaptive filters are deployed to cancel every possible NEXT signal from the other twisted pairs, the computational complexity increases in proportion to N2 where N is the number of twisted pairs in the bundle and, therefore, it becomes prohibitive even for small values of N. In this dissertation, four new methods for NEXT reduction are proposed. The methods aim at reducing computational complexity while maintaining speed and performance. In Chapter 3 an efficient NEXT cancellation system is proposed. The new system first detects the NEXT signals present in the received signal and then assigns adaptive filters to cancel the most significant NEXT signals detected. The detection process uses a fast and efficient algorithm that estimates the crosscorrelation between the transmitted and received signal. By subtracting the adaptive filter estimates of the NEXT signals that have been detected and assigned adaptive filters for cancellation, the magnitude of smaller NEXT signals can be estimated more accurately during the NEXT detection stage. The new system offers an overall computational complexity of order N. This represents a large reduction in the computational effort relative to that in previous NEXT cancellation system which offer computational complexities of order N2. In Chapter 4, the NEXT cancellation system proposed in Chapter 3 is implemented using frequency-domain least-mean-square (FDLMS) adaptive filters to cancel the NEXT signals. Several schemes for assigning the adaptive filter step sizes are explored. It has been found that by making the step sizes proportional to the magnitude of the NEXT signals during the initial phases of adaptation and then making them all equal during the later phases, the convergence rate can be significantly improved. And by returning after convergence to step sizes that are proportional to the magnitudes of the NEXT signals, a much better tracking performance is achieved. In Chapter 5, a new technique that reduces the computational complexity in adaptive filters for NEXT cancellation is proposed. In this technique, the filter length of each adaptive filter is adjusted according to the strength of the NEXT signal. Since the NEXT signals from the other twisted pairs are typically of different magnitudes, using such a technique leads to a significant reduction in the total number of filter taps when compared with fixedlength adaptive filters. The NEXT cancellation is started by using adaptive filters with minimum filter lengths. As the adaptation progresses, the filter length of each adaptive filter is adjusted according to the magnitude of the NEXT signal. Upon convergence, another algorithm is deployed which readjusts the filter lengths of those adaptive filters that are too long or too short. Chapter 6 deals with another new method to mitigate NEXT based on a wavelet denoising technique. In xDSL systems, the received signal typically has greater power in the lower end of the frequency spectrum whereas the NEXT signal has greater power in the higher end. The wavelet technique takes advantage of the difference between the power spectrum of the received signal and that of the NEXT to mitigate the crosstalk noise. In addition, the method has a low computational complexity which makes it fast, efficient, and well suited for high data-rate applications.

This work is focused on the subject of the interference modelling for xDSL technologies. First, the xDSL technologies are explained. Following is the presentation and description of the different kinds of the xDSL technologies. The next part deals with the basic parameters of metallic cable lines – especially the primary and secondary parameters. Nowadays wider bandwidths are used for the achievement of higher data transmission rates. During a higher frequency signal transmission a more intensive line attenuation appears. To identify the transfer characteristics of the lines while using an xDSL system, mathematic models of transmission lines are applied. That is why these mathematic models are dealt with in the next chapter. At the end of this section the mathematic models are compared using the modular and phase characteristics. The main aim of the work is to describe the different impacts which influence the efficiency of the xDSL systems. First, the causes interfering from the inside of the cable are deeply explained: Near End Crosstalk (NEXT), Far End Crosstalk (FEXT), Additive White Gaussian Noise (AWGN). Following is the explanation of the external interfering impacts: Radio Frequency Interference (RFI) and Impulse Noise. The next goal of this thesis is a design of a workstation for the tests of spectral features and the efficiency of the xDSL systems. The work also presents a designed GUI application and its description. The GUI application is an instrument for the choice or data entry of the final interference. The last chapter describes a realization of a measurement and shows the measured characteristics which were recorded on the ADSL tester and oscilloscope.

The thesis concerns the problem of interference modelling for xDSL technologies and Ethernet. The introduction describes the origin of crosstalk, that arise during the operation of the systems and the physical properties of the lines, therefore, the next section describes the properties of the primary and secondary parameters of the homogenous line and their modelling. In order to achieve higher data rates on the metallic line, systems with larger frequency spectrum are applied, resulting in a greater attenuation of the line. This issue and the characteristics determination of the transmission systems are subjects of the mathematical models, which are divided according to the modelling of primary or secondary parameters. The main goal of this work is to describe the effects which influence the performance of data transfer via xDSL and Ethernet technology focusing on internal and external disturbances acting on the cable lines. This is the crosstalk at the near and far end, adaptive white noise, radio frequency interference RFI and impulse noise. Following part of the thesis deals with the properties of xDSL technologies, specifically ADSL2+ and VDSL2 and Ethernet. Another aim is to design applications which enable to test the performance of xDSL and Ethernet transmission systems with its own award simulations interference. The conclusion describes the design and implementation of laboratory experiments for measuring of the efficiency and spectral properties of xDSL. The proposed laboratory protocols are annexed to this thesis, including the measured waveforms.