In recent years, Digital subscriber line (DSL) technology has been gaining popularity as a high speedudnetwork access technology, capable of the delivery of multimedia services. A major impairment forudDSL is impulse noise in the telephone line. However, evaluating the data errors caused by this noise isudnot trivial due to its complex statistical nature, which until recently had not been well understood, andudthe complicated error mitigation and framing techniques used in DSL systems. This thesis presents audnovel analysis of the impact of impulse noise and the DSL framing parameters on transmission errors,udbuilding on a recently proposed impulse noise model. It focuses on errors at higher protocol layers, suchudas asynchronous transfer mode (ATM), in the most widely used DSL version, namely Asymmetric DSLud(ADSL).udThe impulse noise is characterised statistically through its amplitudes, duration, inter-arrival times,udand frequency spectrum, using the British Telecom / University of Edinburgh / Deutsche Telekomud(BT/UE/DT) model. This model is broadband, considers both the time and the frequency domains,udand accounts for the impulse clustering. It is based on recent measurements in two different telephoneudnetworks (the UK and Germany) and therefore is the most complete model available to date and suitedudfor DSL analysis. A new statistical analysis of impulse noise spectra from DT measurements showsudthat impulse spectra can be modelled with three spectral components with similar bandwidth statisticaluddistributions. Also, a novel distribution of the impulse powers is derived from the impulse amplitudeudstatistics.udThe performance of a generic ADSL modem is investigated in an impulse noise and crosstalk environmentudfor different bit rates and framing parameters. ATM cell and ADSL frame error rates, andudsubjective MPEG2 video quality are used as performance metrics. A new modification of a bit loadingudalgorithm is developed to enable stable convergence of the algorithm with trellis coding and restrictedudsubtone constellation size. It is shown that while interleaving brings improvement if set at its maximumuddepth, at intermediate depths it actually worsens the performance of all considered metrics in comparisonudwith no interleaving. No such performance degradation is caused by combining several symbols in audforward error correction (FEC) codeword, but this burst error mitigation technique is only viable at lowudbit rates. Performance improvement can also be achieved by increasing the strength of FEC, especiallyudif combined with interleaving. In contrast, trellis coding is ineffective against the long impulse noiseuderror bursts. Alien as opposed to kindred crosstalk degrades the error rates and this is an important issueudin an unbundled network environment. It is also argued that error free data units is a better performanceudmeasure from a user perspective than the commonly used error free seconds.udThe impact of impulse noise on the errors in DSL systems has also been considered analytically. Audnew Bernoulli-Weibull impulse noise model at symbol level is proposed and it is shown that other modelsudwhich assume Gaussian distributed impulse amplitudes or Rayleigh distributed impulse powers giveudoverly optimistic error estimates in DSL systems. A novel bivariate extension of the Weibull impulseudamplitudes is introduced to enable the analysis of orthogonal signals. Since an exact closed-form expressionudfor the symbol error probability of multi-carrierQAM assuming Bernoulli-Weibull noise modeluddoes not exist, this problem has been solved numerically. Multi-carrier QAM is shown to perform betterudat high signal-to-noise ratio (SNR), but worse at low SNR than single carrier QAM, in both cases becauseudof the spreading of noise power between subcarriers. Analytical expressions for errors up to frameudlevel in the specific case of ADSL are then derived from the impulse noise model, with good agreementudwith simulation results. The Bernoulli-Weibull model is applied to study the errors in single-pair highspeedudDSL (SHDSL). The performance of ADSL is found to be better when the burst error mitigationudtechniques are used, but SHDSL has advantages if low bit error rate and low latency are required.
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