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DSL lines diagnostics

This paper explores the Diagnostic Parameters of the analog portion of xDSL transceivers, focusing on Discrete Multitone (DMT) signal analysis in the time domain. Key metrics such as Total Harmonic Distortion (THD), Inter-Modulation Distortion (IMD), and Signal-to-Noise Ratio (SNR) plus Distortion are discussed. By measuring nonlinear distortion and related parameters, we gain insights into the performance of xDSL systems like ADSL and VDSL. The assessment is integral for understanding the robustness and efficiency of these networks.

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DSL lines diagnostics

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  1. DSL lines diagnostics - Parameters of analog part of xDSL transceiver Access Networks 2010/11 Ľ. Maceková, KEMT- FEI – TU - Košice

  2. ... Describing of DMT in time domain (DMT is transport method in ADSL and VDSL systems): Uk ... amplitudeof k-thcarrier (it is modulated by QAM) φk ... phase of k-thcarrier ω0 = 2π. 4312,5 s-1 ... angle speed limiting areas Fig.Typical time domain DMT signal look with limiting areas (signal mustn’t exceed their boundaries)

  3. Actually, we evaluate nonlinear distortion, which is integrated in parameters : THD… Total Harmonic Distortion IMD… Inter-Modulation Distortion SINAD… SNR plus Distortion THD + N ... THD plus Noise SFDR… Spurious Free Dynamic Range In addition, in DMT signal area: MTPR ... Multi-Tone Power Ratio SNR ... Signal-to-Noise Ratio… we know this already - all parametersare in units [dB](logarithmicarea) or clear number (ratio)or in [%]

  4. THD … Total Harmonic Distortion P1; f P1, P2, P3, ... input output power of basic frequency signal power of higher harmonics; result of devices nonlinearities (because of nonlinear transfer characteristics of amplifiers) We measure all higher harmonics which can be distinguished from noise

  5. IMD … Inter-Modulation Distortion • it is product of nonlinearities of transfer characteristics when actuated by two frequencies signal • it is sum of intermodulation products of 2 input harmonics (sums, differencies and multiples) f1,f2,; f2>f1 f2±f1, f2 ±2f1,f2 ±3f1,... input output - the measurement: by modulation method or by differencial method[1]

  6. SINAD – SNR plus Distortion • parameter which contains the noise and nonlinear distortion Psig in Psig, P2, P3, ..., noise distortion total output signal power output signal after filtration of input signal

  7. SFDR – Spurious Free Dynamic Range • it is about nonlinear properties of devices again • they measure partial harmonic elements and another distortion elements; we are interested in distortion element with highest amplitude power of the distortion element with highest amplitude (hence SFDR < 0 dB) power of basic signal (1-st harmonic frequency) (measurement signal) [1]

  8. MTPR… Multi – Tone Power Ratio • this parameter is established for DMT average subchannel power (applied; transmitted) max. power of distortion signal in the position of unused subchannel (‘empty bin’) [1], [2]

  9. … and another measurements: • measurementof impulse noise robustness • measurement of ADSL splitters • measurement of influensis of ADSL in voice (telephone) band • etc.

  10. References: [1] J. Vodrážka, M. Havlan: Přístupové přenosové systémy, Cvičení – Měření na přípojkách xDSL, ČVUT Praha, 2003. [2] http://www.analog.com/static/imported-files/tutorials/MT-053.pdf

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