Daniel Cederholm

Estimating Video Quality over ADSL2+ under Impulsive Line Disturbance

QoS Provisioning for 3P over xDSL remains a challenging task due to the effects of line impairments on such services. Differently from simple data, video and voice services have strict requirements for loss and delay tolerance. The accurate assessment of final service quality is part of this provisioning process, but its direct measurement is yet not practical. In this paper we explore the possibility of estimating service quality, with focus on video delivery, by investigating its relationship with performance data available to xDSL operators and deriving models for estimating quality from this data. Experiments using a real xDSL platform and different noise types were conducted. The derived models showed to be accurate enough to estimate video quality for the scenarios evaluated.

Backscattering in Twisted-Pair Nonhomogeneous Transmission Lines

The development of the communication networks tends gradually toward exploiting higher frequencies, sometimes even reaching the lowest microwave band (P-band). As the signal bandwidth used for transmission over twisted-pairs increases, as recommended by G.fast and other broadband systems, new phenomenon was observed, namely, backscattering. Motivated by the measurements of copper cables in frequency band up to 400 MHz, we propose a novel backscattering model. It may be productively applied to the problem of loop diagnostics. The methods to accurately and reliable determine the relevant transmission-line parameters are sine qua non condition to appropriately exploit the potential of short-to-medium range access lines. In this paper, a recursive formulation of the frequency-domain response of the backscattering is used for a space–time characterization. To confirm the practical use of the finding, we evaluate the properties of a loop using wideband, high-frequency

Analytic model for cross-layer dependencies in VDSL2 access networks

S_{11}

Determination of the Propagation Constant From Single-Ended Line Test Data

measurements of the real cables. These laboratory results confirm the effectiveness and accuracy of the proposed method.

Method for transmission line analysis

Recent changes in user employment of Internet based services, new deployment technologies for mobile networks as well as an ongoing realisation of fixed and mobile converged networks e.g. the EU FP7 project COMBO, are significant examples of enablers for increasing demands on DSL links. Investigating cross-layer dependencies between all layers in the OSI reference model becomes increasingly important. In this paper we present an analytical model and experimental results for the relation between impulse noise on a VDSL2 link and the effect this have on the network layer packet loss. We show how the packet loss rate is dependent not only on the disturbance signal level and periodicity but also on the link utilisation.

SINGLE ENDED ESTIMATION OF FAR-END CROSSTALK IN A DIGITAL SUBSCRIBER LINE

This paper presents a numerical method, here, called recursive obliquely moving approximation (ROMA), for determining the propagation constant from single-ended line test measurements. The method is based on deriving an equation binding the input impedance of the open-ended transmission line and the characteristic impedance with the line propagation constant. The algorithm solving this equation relies on a recursive Newton-Raphson-type procedure. Initial guesses are generated using oblique least squares on the complex plane for the extrapolation of previous data while moving toward higher frequencies. For residential access, the loops often consist of multiple sections. In those scenarios, the ROMA algorithm gives a less accurate and more difficult-to-interpret estimate of the propagation constant than for single-segment loops. Nevertheless, it still enables a quick and credible estimation of the loop capacity. ROMA provides these estimates without à priori information; it is insensitive to local solutions, and it has low numerical complexity. Moreover, for single-segment loops, common in, e.g., mobile backhaul applications, the algorithm gives a highly accurate estimation of the propagation constant.