An impulsive noise analyser using amplitude probability distribution (APD) for broadband-wired communication

Electromagnetic interference or noise which is of impulsive nature is known to affect data communication performance. It is useful to correlate the characteristics of the noise with the bit error probability (BEP). The amplitude probability distribution (APD) has been proposed within CISPR for characterisation of the impulsive noise. However, there is no analyser available to perform direct measurement of the noise within the bandwidth of asymmetric digital subscriber line (ADSL2+) communication. This research presents a novel development of APD analyser for measurements of impulsive noise emission and its impact on ADSL2+ communication. A unique noise APD pattern is obtained from each measurement of noise emission from different electrical and electronic appliances. It is vital to have correct measurement set-up, signal power level, sampling rate, sample points and filter characterisation in order to acquire accurate data representation of the noise patterns. The APD graph is generated by the analyser using the APD algorithm method which employs the envelope sampling technique from actual probability. The noises are characterised using α-stable distribution which exhibits its own distinct APD parameters. The APD curve can be related with the single modulation scheme communication channel performance for estimation of bit error probability. The analyser has been developed successfully with dynamic range of 70 dB higher than the 60 dB CISPR 16 requirement, 0.02 dB amplitude resolution compared to 0.25 dB CISPR 16 requirement and 0.59 dB amplitude accuracy compared with the CISPR 16 standard of +/- 2.7 dB. In addition, the limits for noise in copper cable have been proposed for estimating the severity of the interference towards digital communication performance in ADSL2+ system. An advantage of the analyser is its ability to not only record the noise but the ability to regenerate back the noise which can be used for further analysis. In conclusion, the analyser can provide a comprehensive platform for impulsive noise interference verification towards ADSL2+ communication performance

Multimode precoding for crosstalk mitigation in ultra-broadband DSL systems

The achievable downstream bit‐rate performance of digital subscriber line (DSL) channels using low‐complexity linear precoders is suboptimal when the row‐wise diagonally dominant property of the channel matrix does not hold at high frequencies anticipated to be exploited in future‐generation DSL systems, while the optimal nonlinear precoder is computationally demanding. In this paper, we propose two multimode precoders, which are operable in four modes on each tone. Specifically, the proposed precoding strategies exploit the insertion loss and crosstalk information inferred from the channel matrix to execute mode selection for all the transmission tones. The computational complexity of the proposed multimode precoders is derived and compared with existing precoders. Simulation results show that the proposed precoders can achieve near‐optimal performance at a lower computational complexity

Copper line pre-qualification assessment for high-speed broadband in Malaysia

The copper access-network operators face the challenge of developing andmaintaining the cost-effective digital subscriber line (DSL) services that arecompetitive toother broadband access technologies. The copper line qualityassessment process is crucial to ensure the customers enjoy their speedsubscription. Through this process, service providers can evaluate the capabilityof copper lines before deploying the broadband service. Furthermore, for theunstable condition of copper lines, the root cause of the problems can be identifyingearlier, which helps the operators to do preventive action and avoid offering theservice to customers using that copper lines. This paper discusses the proposed prequalification assessment method and the impact of every proposed stage. Thisproposed assessment showed that the speed performance would be dropped morethan 50% if the impairments exit in the copper line. Thus, any service providerscan avoid serving high-speed broadband to subscribers using the unstable cablecondition. Through this preventive process, it will benefit the service providers

Virtual signal-integrity verification tool for copper twisted-pairs using TDR

Time-domain reflectometry (TDR) is an important technique for verifying the impedance and quality of signal paths in components, interconnects, and transmission lines. However, the success of channel condition assessment through on-site interpretation of TDR echoes hinges on the skill and experience of the operator. This study presents a TDR simulator to assist loop diagnostics on copper twisted pairs widely used in current digital subscriber line (DSL) access networks. The simulator is developed based on established frequency-dependent cable models to synthesise realistic TDR echoes arising from various cable discontinuities. Modelling of arbitrary loop configurations and faults is accomplished by cascading multiple sub-lines with different characteristics through ABCD parameters modelling. The usability of the simulator is enhanced using a graphical user interface and its accuracy has been verified experimentally using TDR echoes obtained from commercial TDR testers. Since lengthy twisted pairs are deployed in real DSL access networks, the TDR simulator can be used to perform on-site simulation and verification during DSL network maintenance and troubleshooting, as well as to gain mastery of TDR handling while circumventing the need for bulky and costly cabling test beds. The simulator can also be useful to supplement the teaching of electromagnetics and high-frequency measurement

Performance of linear and non-linear precoders in G. fast ultra-broadband DSL networks

The new International Telecommunication Union Telecommunication G.fast standard for next-generation ultra-broadband digital subscriber line systems has stipulated mandatory use of vectoring for crosstalk mitigation. In this paper, we study the performance of downstream precoders in G.fast networks utilising the extended bandwidth up to 212 MHz. In particular, the issue of strong crosstalk encountered in practical copper cable bundles at high frequencies giving rise to channel matrices which are not row-wise diagonally dominant (RWDD) as predicted theoretically, as well as the ramification of deploying precoders designed based on the RWDD assumption in practical G.fast channels are studied. To serve these purposes, an enhanced stochastic far-end crosstalk (FEXT) model which provides distinct FEXT transfer functions with the dispersion range characterised experimentally whilst encompassing the dual-slope FEXT encountered in non-RWDD cables is used for evaluating the performance of precoders in diverse G.fast deployment scenarios. Furthermore, the performance sensitivity of precoders under realistic amount of channel estimation errors is investigated on a common framework, allowing a direct and fair comparison between linear and non-linear precoders. Results show that the nonlinear optimal precoder outperforms linear precoders in all channel conditions; however, the former is found to be slightly more sensitive to channel estimation errors on shorter loops. Copyright © 2016 John Wiley & Sons, Ltd

Adaptive multimode precoding for ultra-broadband vectored DSL systems

In the downstream of a digital subscriber line (DSL) system transmitting over a large bandwidth, the row-wise diagonally dominant (RWDD) characteristic of the copper channel matrix, which holds at low frequencies, may not be valid at high frequencies because of the presence of strong crosstalk. Consequently, linear precoders result in sub-optimal bit-rate performance whilst the optimal non-linear precoders incur high computational complexity. In this work, we investigate a quad-mode precoder (QMP) which selectively operates on one of four modes on each frequency tone. A block-based adaptation strategy is introduced for complexity reduction whereby mode selection is invoked adaptively over blocks of tones. The computational complexity associated with the proposed precoder is analyzed and quantified against existing precoders. Results demonstrate that by suitably adapting the operating mode and block length of the proposed QMP according to the channel conditions, moderate computational saving could be attained without compromising the bit-rate performance. More importantly, the QMP facilitates green DSL as energy savings are feasible when some tones are de-activated to conserve energy