Digital Subscriber Line Networks Research Articles

Minimal Delay Violation-Based Cross-Layer Scheduler and Resource Allocation for DSL Networks

The quality of service of many modern communication systems depends on the delay performance of the underlying network. In digital subscriber line (DSL) networks, for example, crosstalk introduces competition for data rate among users, which influences the delay distribution. In such a competitive environment, delay performance is largely determined by the manner in which resources are dynamically allocated to the different users. A common approach to this allocation problem is through a cross-layer scheduler. Such a scheduler violates the OSI model by allowing communication between different layers, in order to steer the physical layer towards operating points that maximize some upper layer performance metric. In this paper, we present a new cross-layer scheduler and resource allocation algorithm in the context of DSL networks, referred to as the minimal delay violation (MDV) scheduler, which aims to minimize the number of delay violations and achieve a high throughput. Rather than solving a linear network utility maximization problem, as most other schedulers from literature, we consider a problem that is reciprocal with the service rate, allowing the scheduler to allocate the data rates at a finer level, while still maintaining good performance. Through simulations, we show that the MDV scheduler performs better than cross-layer scheduling algorithms from literature with respect to packet loss ratio, delay and throughput performance for various scenarios, and often operates closely to an ideal scheduler.

Comparing simulation model for objective QoE video evaluation with real IPTV test scenario during appearance of packet losses

The aim of this article is to explain benefits of the simulation model for objective QoE (Quality of Experience) video evaluation in order to find similarities with real IPTV (Internet Protocol TeleVision) system distribution in a DSL (Digital Subscriber Line) network. In DSL networks, it is known that packet losses appear suddenly and might have a "burst" character, at any time during IPTV service delivery. In addition, these packet losses usually appear in groups and lead to huge degradation of the IPTV video service, which decreases a customer's QoE guaranteed level. Hence, estimation of this degradation in an access network is crucial and this paper explains a simulation model based on SSIM (Structural Similarity Index) analysis, which can be used as one perceptive video quality assessment by imitating a real environment with packet losses. To check this, we compared simulation model cases with the real ones in IPTV video distributed over DSL and exposed to different packet loss appearances.

Far-End Crosstalk Mitigation for Future Wireline Networks Beyond G.mgfast: A Survey and an Outlook

With the escalating demand for high speed, high reliability, low latency, low cost and ubiquitous connectivity, the telecommunications industry is entering a new era where the ultimate optimality of the current wireline-wireless access network has to be achieved. Regarding the current wireline network paradigm, dominated by the copper-based digital subscriber lines (DSL) technology, multi-Gigabit data rate is the ambitious design objective at the customer end for the forthcoming ITU-T G.mgfast standard. In order to prepare for the new challenges in the era of total network convergence, both the wireline and the wireless community must be able to think beyond their respective conventions and learn from each other if necessary. Overall, the current DSL-based wireline network architecture is prone to the mutual interference resulting in far-end crosstalk (FEXT). The newly expanded 424/848 MHz spectrum of the ambitious G.mgfast project introduces far higher FEXT than that over the current 212/30 MHz G.fast/VDSL2 band. Additionally, the coexistence of multiple standards will also cause `alien' FEXT. In these cases, using the plain zero forcing precoding (ZFP) will no longer attain a sufficiently high performance. However, as shown in the field of wireless communications, using lattice reduction as a signal space remapping technique significantly improves the performance of traditional multi-user detectors (MUD) and of the respective multi-user precoders (MUP). These promising techniques have largely remained unexploited in commercial wireless communications, due to their complexity in the face of the rapidly fluctuating wireless channels. In this survey, we present an overview of the state-of-the-art in wireline access network and an outlook for recent technological advances in the holistic `wireline + wireless' access network in the context of network convergence, focusing on the dominant challenge of FEXT mitigation in future DSL networks. Against this background, we investigate both the family of linear precoding and of the Tomlinson-Harashima precoding (THP) schemes conceived for classic DSL. Furthermore, we present a tutorial on the family of lattice reduction aided MUPs, as well as quantifying their expected performances in realistic DSL scenarios. As a by-product, we also demonstrate the duality between MUP and MUD, in the hope that the fifty years' history of MUD could be used to accelerate the development of efficient near-optimal MUPs for future DSL. Under the recommended operating conditions of the 212 MHz profile of G.fast, our benchmark comparisons indicate that the lattice reduction aided techniques are very powerful compared to conventional schemes. In particular, their good performances do not rely on optimized spectrum balancing, and they are also shown to be relatively robust against channel state information (CSI) estimation error, under the assumption of perfectly time-invariant DSL channels.

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.

Dynamic Spectrum Management in Digital Subscriber Line Networks With Unequal Error Protection Requirements

Digital subscriber line (DSL) technology remains the most popular broadband access technology. A variety of algorithms has been developed to improve performance in DSL networks, which are commonly referred to as dynamic spectrum management (DSM) algorithms. The main goal of these algorithms is to fight crosstalk between different lines in a cable bundle. Current DSM algorithms provide an equal level of error protection for each serviced application and each user. However, different applications may have unequal error protection (UEP) requirements. The equal level of error protection usually provided by DSM algorithms may then be excessive for some applications, which leads to a waste of valuable resources. This paper, therefore, considers DSM for DSL networks providing UEP. Four joint signal and spectrum coordination algorithms are presented, enabling a different level of error protection for different applications. These algorithms are modified versions of existing optimal spectrum balancing and distributed spectrum balancing algorithms for joint signal and spectrum coordination in upstream as well as downstream DSL. In addition, an algorithm is presented which, for each application, selects a suitable modulation and coding (MC) scheme from a set of admissible MC schemes. Through simulations, it is shown that DSM with UEP can indeed lead to moderate performance gains.

Mathematical Bottom-to-Up Approach in Video Quality Estimation Based on PHY and MAC Parameters

This paper presents an extension of research scope of the relationship between quality of service (QoS) and quality of experience (QoE), which is based on contribution of lower open system interconnection layers, such as physical and media access control, in overall QoS/QoE paradigm. Degradations that inevitably occur in transmission channel are an important reason for appearance of QoS distortion and therefore low values of video quality. Various channel quality indicators (CQIs) relating to domain of communication channel can be used for notification of different interferences in the channel. In order to extend the relationship between QoS and QoE to the transmission channel, the paper proposed the mathematical model that used CQI to estimate values of QoS indicators by using statistical analysis. The model was also expanded by objective video quality metrics in order to evaluate QoE. Verification of the model was checked by experimental method with consideration of Internet protocol television (IPTV) service delivery in Digital Subscriber Line network.

DSL and PLC Co-Existence: An Interference Cancellation Approach

It is often advocated that a solution to the problem of interference to digital subscriber line networks (DSL) from a power line communications (PLC) network is to prevent the PLC networks from utilizing the DSL spectrum. However, this solution will render PLC networks inoperable with the introduction of wide-band DSL technology like G.Fast. We propose utilizing an interference cancelling scheme to ensure the co-existence of DSL and PLC networks within the home environment. A measurement campaign is conducted where a set of 480 measurements are collected within a residential house to characterize the PLC-to-DSL interference environment for two DSL modem installation scenarios. The interference cancelling scheme is based on an adaptive frequency domain interference canceller (FDIC) that utilizes the common mode (CM) PLC interference to estimate the differential mode (DM) PLC interference. The effectiveness of the FDIC, which is insensitive to the non-stationarity of the PLC channel, is demonstrated using analysis that incorporates the measured PLC-to-DSL coupling channels.

General Framework and Algorithm for Data Rate Maximization in DSL Networks

In this paper, we treat the combined signal and spectrum coordination problem in digital subscriber line (DSL) networks with linear design for transmitters and receivers. The transmission is modeled as a multitone MIMO system where each user has a number of transceivers and there is coordination between sets of users on the transmitter and on the receiver sides. We consider the possibility of an asynchronous transmission, i.e. when the transmission of DMT blocks for different users is not aligned in time. This gives rise to inter-carrier interference. Our objective is the maximization of the weighted sum of users' data rates subject to power constraints. Although this problem is well known in the literature, previous works have always based their designs on strong assumptions about the network infrastructure. In this paper, we propose a general framework and algorithm that apply for any infrastructure, including any number of users, any number of transceivers, any number of tones, any kind of coordination on both the transmitter and on the receiver sides, and synchronous or asynchronous transmission. We also do not assume any special structure of the channel matrix. Our algorithm is seen to perform very well and is polynomial time solvable.

Low-complexity optimal discrete-rate spectrum balancing in digital subscriber lines

Discrete-rate spectrum balancing in interference-limited multi-user and multi-carrier digital subscriber lines (DSL) is a large-scale, non-convex and combinatorial problem. Previously proposed algorithms for its (dual) optimal solution are only applicable for networks with few users, while the suboptimality of less complex bit-loading algorithms has not been adequately studied so far. We deploy constrained optimization techniques as well as problem-specific branch-and-bound and search-space reduction methods, which for the first time give a low-complexity guarantee of optimality in certain multi-user DSL networks of practical size. Simulation results precisely quantify the suboptimality of multi-user bit-loading schemes in a thousand ADSL2 scenarios under measured channel data.

Autonomous dynamic optimization for digital subscriber line networks

Digital subscriber line (DSL) technology allows copper access network operators to offer high-speed links at a reasonable cost. The optimization of the DSL network is a cumbersome task due to the abundance of physical layer configuration parameters and significant differences between lines with respect to interference and attenuation. This paper discusses concepts for dynamic optimization techniques that trade off rate, latency, stability, and power usage in an automated and transparent fashion. The techniques use an initial configuration selection to swiftly obtain a near-optimal configuration and then proceed to acquire additional statistics on noise and interference in order to be able to fine-tune the configuration and gradually increase performance. Optimization results for a DSL network that is carrying video services are presented by aid of the Dynamic Line Management module in the Alcatel-Lucent 5530 Network Analyzer.

Impact of Crosstalk Channel Estimation on the DSM Performance for DSL Networks

The development and assessment of spectrum management methods for the copper access network are usually conducted under the assumption of accurate channel information. Acquiring such information implies, in practice, estimation of the crosstalk coupling functions between the twisted-pair lines in the access network. This type of estimation is not supported or required by current digital subscriber line (DSL) standards. In this work, we investigate the impact of the inaccuracies in crosstalk estimation on the performance of dynamic spectrum management (DSM) algorithms. A recently proposed crosstalk channel estimator is considered and a statistical sensitivity analysis is conducted to investigate the effects of the crosstalk estimation error on the bitloading and on the achievable data rate for a transmission line. The DSM performance is then evaluated based on the achievable data rates obtained through experiments with DSL setups and computer simulations. Since these experiments assume network scenarios consisting of real twisted-pair cables, both crosstalk channel estimates and measurements (for a reference comparison) are considered. The results indicate that the error introduced by the adopted estimation procedure does not compromise the performance of the DSM techniques, that is, the considered crosstalk channel estimator provides enough means for a practical implementation of DSM.

Greening the copper access network with dynamic spectrum management

This paper investigates the benefits of dynamic spectrum management (DSM) in terms of reducing the power consumption and improving the data rates and robustness in digital subscriber line (DSL) networks. Non-DSM solutions cause strong interference in a shared DSL binder and lead to instability in the network. However, DSM mitigates such interference, stabilises DSL service, and saves power consumed by the DSL networks. This paper compares the savings in power and the improvement in data rates and robustness of the DSL networks when the proposed DSM methods are used instead of other non-DSM techniques. The power savings, data rate increase and quality-of-service improvement by DSM make the operation of DSL networks greener and more efficient, which in turn reduces operational expenditure and brings higher customer satisfaction for DSL service providers.

SCALE: A Low-Complexity Distributed Protocol for Spectrum Balancing in Multiuser DSL Networks

Dynamic spectrum management of digital subscriber lines (DSLs) has the potential to dramatically increase the capacity of the aging last-mile copper access network. This paper takes an important step toward fulfilling this potential through power spectrum balancing. We derive a novel algorithm called SCALE, that provides a significant performance improvement over the existing iterative water-filling (IWF) algorithm in multiuser DSL networks, doing so with comparable low complexity. The algorithm is easily distributed through measurement and limited message passing with the use of a spectrum management center. We outline how overhead can be managed, and show that in the limit of zero message-passing, performance reduces to IWF.

Global Concave Minimization for Optimal Spectrum Balancing in Multi-User DSL Networks

Dynamic spectrum management (DSM) is an effective technique for mitigating detrimental effect of crosstalk in digital subscriber lines (DSL). Among various DSM techniques, centralized optimal spectrum balancing (OSB) achieves the maximum possible data rates by computing the optimal power spectral densities (PSDs) for all modems in DSL systems. Unfortunately, its computational complexity grows exponentially in the number of users and becomes intractable for large . To reduce the complexity of OSB, this paper exploits the fact that the non-convex optimization problem in OSB can be reformulated as an equivalent global concave minimization problem by representing its objective function explicitly as the difference of two convex functions (dc). This dc structure makes the non-convex optimization problem in OSB suitable for being solved by various dc algorithms developed over the decades. In particular, a modified prismatic branch-and-bound algorithm, which only requires solving a sequence of linear programming subproblems, is applied to find the global optimum with substantial reduction in complexity especially for large .

Advanced Signal Processing for Digital Subscriber Lines

The recent deployment of digital subscriber line (DSL) technology around the world is rapidly making broadband access for the mass consumer market a reality. The ever-growing customer demand for higher data rates has been fueled by the popularity of applications like peer-to-peer (P2P) filesharing networks and video-streaming and high-definition television (HDTV). DSL technology allows telephone operators to getmaximum leverage out of their existing infrastructure by delivering broadband access over existing twisted-pair telephone lines. At the heart of DSL lies a plethora of signal processing techniques which enable such high-speed transmission to be achieved over a medium originally designed with only voice-band transmission in mind. These advanced signal processing techniques address many challenges that exist in DSL networks today, such as the near-end and far-end crosstalk (NEXT/FEXT), impulse noise, peak-toaverage-power ratio (PAR), intersymbol and intercarrier interference (ISI/ICI), radio-frequency interference (RFI), and so forth. The goal of this special issue is to discuss the state-of-the-art and recent advances in signal processing techniques for DSL.

A novel approach to solve DSL network data rate problems

Digital subscriber line (DSL) is a service that offers much faster Internet connection than a standard dial up connection. Crosstalk is a major impairment in DSL telecommunication networks. It degrades the upstream and downstream data rates and risks the DSL service providers ability to meet their service level agreement requirements. A novel approach to solve the upstream and downstream data rate problems is presented in this paper. The approach considered is to control the power spectral density and aggregate power level of the DSL access multiplexer.