Jaume s i Riu

Semiblind Spectrum Balancing for DSL

Digital subscriber lines (DSLs) technology is vastly used for high-speed data transmission. Crosstalk is one of the main problems in DSL. The research community has done extensive work on how to optimize spectrum allocation across DSL frequencies and mitigate crosstalk, a subject that has been called dynamic spectrum management (DSM). This text presents a novel DSM solution, referred to as semiblind spectrum balancing (2SB). 2SB performs an optimization process with a virtual line, a fictitious line that represents to each user the damage it causes for all other users. With the aid of message exchanges between modems and a central agent, the method will adjust the virtual lines parameters so that it represents the real crosstalk scenario in the binder. In this paper, we provide the conditions for how such a situation can be achieved and show that it can do so with semicentralization, low complexity and limited crosstalk channel information-only the ratios between crosstalk channels are necessary. Performance is very close to optimal.

An energy resolved electron?ion coincidence study near the S 2p thresholds of the SF6 molecule

The fragmentation dynamics of the SF6 molecule following the excitations of S 2p electrons into unoccupied molecular orbitals has been studied using the energy-resolved electron–ion coincidence technique. Fragmentation patterns were found to depend on the particular excitation and on the electronic state of the molecular ion. The spectator resonant Auger decay at the 2p → 6a1g resonance induces changes in the ion distributions as compared to direct photoionization. Furthermore, coincidence spectra related to the same Auger structure display different ion abundances at the 2t2g and 4eg shape resonances. Differences were also found in the Auger decay spectra. These findings give further support for the previously suggested many-electron character of the 4eg shape resonance.

Semi-Blind Power Allocation for Digital Subscriber Lines

Digital subscriber lines (DSL) are today one of the most important means for delivering high-speed data transmission. An emerging technique for dealing with one of the technologys most harmful problems, crosstalk, is dynamic spectrum management (DSM). DSM literature already counts with some half a dozen important solutions. These solutions can be classified according to four different aspects: optimality, computational cost, distribution and required crosstalk channel information. In this work we present an algorithm, named semi- blind spectrum balancing, which achieves a compelling trade-off between these four aspects. The scheme is based on the idea of optimization against a virtual line, a fictitious line to represent the damage caused to other users in the network. This line is adjusted with the aid of limited message-passing between modems and a central agent and very simple crosstalk channel information. Crosstalk channel knowledge required should be much simpler to obtain than full channel estimation.

Measurement and modeling of short copper cables for ultra-wideband communication

High-speed communication using the copper network, originally installed for telephony, is one of the dominant Internet access techniques. Several variants of a technology referred to as digital subscriber line (DSL) have been developed, standardized and installed during the last two decades. Essentially, DSL achieves high rates by exploiting wide bands of the copper cable channel. The shorter the cable, the wider the band that can be used efficiently for communication. Current DSL standards foresee the use of bands up to 30MHz. Cable properties have been studied by means of measurements, characterization and modeling up to frequencies of 30MHz. Recent investigations have shown that it is feasible both from technical and from economical point of view to exploit very short cables (up to 200m) even further and use bands above 30MHz. A prerequisite for further evaluation and the design of such ultra-wideband copper (UWBC) systems is the extension of existing cable models to higher frequencies. This paper presents wideband measurement results of insertion loss and crosstalk coupling in a 10-pair cable of various length values for frequencies up to 200MHz. We compare the results with extrapolations of cable models that are established in the 30MHz-range.

Selective fragmentation of valence and core electron excited CD and SF molecules

Electron–ion coincidence measurements with energy-resolved electrons are a powerful tool in studies of molecular fragmentation processes, since fragmentation from a specific doorway state can be monitored while the remaining reactions are discriminated. Presently, we have applied this technique in measurements of coincidence spectra of the CD4 and SF6 molecules after valence and core electron excitation. The newly constructed energy-resolved electron–ion coincidence station developed for this project has been used. Our results on CD4 are the first demonstration of a correlation between vibrations and molecular dissociation observed in this molecule. The SF6 spectra reveal strong selectivity in dissociation following distinct electronic states of the molecule. This selectivity reflects the bonding properties of the potential surfaces involved in the studied processes. The obtained results exemplify the potential of the new multicoincidence station used in this work.

Impact of non-stationary noise on xDSL systems : an experimental analysis

Broadband services require data rates that can only be achieved by using relatively high spectrum frequencies. At such high frequencies, the DSL (Digital Subscriber Line) signal is more susceptible to external noise sources, such as radio frequency interference and impulsive noise. This paper aims to characterize how the impulsive noise impacts on services and applications for a broadband system using an ADSL2+ loop. The first approach was to use the impulsive noise defined in the standards G.996.1 (Test Procedures for DSL Transceivers) from ITU-T and TR-048 (ADSL Interoperability Test Plan) from DSL Forum. In this approach we have also used a HDSL (High Bit Rate DSL) and white noise disturbers on the line. The impulsive noises c1 and c2 (defined in G.996.1) are injected into the circuit at the CO (Central Office) end and CPE (Customer Premises Equipment) end of the loop simulator. Additionally, it was analyzed the spikes of noises impact on the ADSL2+ line. In this case, pre-defined models of NEXT (Near-end crosstalk) and white noise are injected on CO and CPE side, simultaneously. Metrics like packet rate, lost packet count, bandwidth, short-term average transfer delay, and errored seconds are used to characterize the DSL loop under the noise impairments.

The capacity of binders for MIMO digital subscriber lines

Crosstalk is one of the main limiting factors in the data rates achievable by digital subscriber line (DSL) systems, and several algorithms have been proposed to mitigate this impairment. In this paper, we compare the capacity of binders under different crosstalk-mitigating techniques. When computing capacity, we also compare two different power constraints: either on the total power in the binder or on the power in each pair. We will see that, for the scenarios considered in this paper, the fact that the signals are jointly processed in one or both ends of the DSL link leads to roughly the same performance, which is far superior to that of systems with no cooperation between the users. Both power constraints also lead to similar achievable rates.

Fixed-mobile convergence towards the 5G era: Convergence 2.0: The past, present and future of FMC standardization

Fixed-Mobile Convergence (FMC) has been a trending topic in telecommunications during the last decade. Standard Development Organizations (SDOs) have addressed FMC in the context of different access and core networks, with special focus in the 3rd generation Partnership Project (3GPP) and in the Broadband Forum (BBF). This paper describes the standardization work done in this area based on the work done in 3GPP, BBF and IETF. It also reflects on how the standardized FMC toolbox together with the new network deployment paradigms such as Network Function Virtualization (NFV), network programmability and automation, and network slicing impact the design and standardization of multi-access, 5G networks.

Sequence and Spread Spectrum Time Domain Reflectometry for Transmission Line Analysis

This paper describes Sequence Time Domain Reflectometry (STDR) and Spread Spectrum Time Domain Reflectometry (SSTDR), which utilizes concepts from direct sequence spread spectrum communications, as a technique for detecting impedance mismatches in telephone lines (twisted pair). The aim of this paper is to present methodologies for characterizing a subscriber loop, which is used for Digital Subscriber Line (DSL) technology, based on STDR and SSTDR tests. Those tests enable the TDR functionality to be incorporated into a DSL transceiver integrated circuit eliminating the need for costly test equipment. In addition to the cost savings, the characteristics of the STDR and SSTDR offer improved spectral compatibility, interference immunity and fault resolvability.

Characterization of Subscriber Local Loop by Measures and Analysis of Frequency and Impulse Responses

This paper presents methodologies that could be used for characterizing subscriber telephone loops that carry DSL services (ADSL and ADSL2+), by determination and analysis of frequency response, time domain reflectometry, and impulse response of the line. From this analysis, the subscriber loop length, identification and location of impairments such as bridged taps, gauge changes, and open ended termination across the line are carried out. To verify the methodologies presented, results obtained from measurements are drawn and compared to results obtained from computational simulations.