DSL Modems Research Articles

Performance estimation and analysis of power line communication using single-ended loop testing

Using the electricity infrastructure for broadband data transmission is known as power line communication (PLC). The quality of broadband connectivity over a power line is a strong function of the line topology. Two-step hybrid single-ended loop testing (SELT) to estimate the open port loop topology of power lines is discussed in this paper. Correlation time domain reflectometry (CTDR) at different sockets is used to construct the initial topology. Optimization-based frequency domain reflectometry (FDR) is employed to ascertain more accurate power line topology. The discussed method has the advantage of reusing the existing DSL modem for the measurement and no prior knowledge is needed for the topology estimation. This method is validated for a wide range of line topologies with different numbers of bridge taps. The performance of the estimated topology is calculated using two-port network theory and the influence of the bridge taps on the performance of the line is analyzed.

Performance Evaluation of a Gigabit DSL Modem Using Super Orthogonal Complete Complementary Codes Under Practical Crosstalk Conditions

Performance Evaluation of a Gigabit DSL Modem Using Super Orthogonal Complete Complementary Codes Under Practical Crosstalk Conditions

Dissecting Last-mile Latency Characteristics

Recent research has shown that last-mile latency is a key network performance indicator that contributes heavily to DNS lookup and page load times. Using a month-long dataset collected from 696 residential RIPE Atlas probes and 1245 SamKnows probes, we measure last-mile latencies from 19 ISPs (RIPE Atlas) in the US and the EU, and 9 ISPs (SamKnows) in the UK. We show that DSL deployments not only tend to enable interleaving on the last-mile, but also employ multiple depth levels that change over time. We also witness that last-mile latency is considerably stable over time and not affected by diurnal load patterns. Unlike observations from prior studies, we show that cable providers in the US do not generally exhibit lower last-mile latencies when compared to that of DSL. We instead identify that last-mile latencies vary by subscriber location and show that last-mile latencies of cable providers in the US are considerably different across the US east and west coast. We further show that last-mile latencies vary depending on the access technology used by the DSL modem wherein VDSL deployments show last-mile latencies lower than ADSL1/ADSL2+ broadband speeds. The entire dataset and software used in this study is made available to the measurement community.

Design of a Gigabit DSL modem using super orthogonal complete complementary codes

AbstractThis paper describes the preliminary design and simulation towards a gigabit digital subscriber line modem that provides multi‐user interference‐free communication in a far‐end crosstalk dominated environment by incorporating super orthogonal complete complementary spreading into the existing xDSL modem architecture. This is in contrast to existing vectoring and dynamic spectral management techniques that use joint processing and pre‐processing of each user's signal to mitigate far‐end crosstalk. A novel code allocation algorithm is introduced to provide all users with equal data rate ratios, even with bad line profiles and high‐required data rates. Preliminary simulation results show that 1 Gbps aggregate throughput can be obtained for the system over a single pair of 0.5 mm copper wire over a distance from 180 to 150 m, depending on whether ADSL2+ or VDSL2 Profile 30a service bands are avoided, if present. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Sparse approximation based resource allocation in DSL/DMT transceivers with per-tone equalization

Per-tone equalization has been proposed as an alternative to time domain equalization for DMT receivers in DSL modems. It optimizes the bit rate performance of the receiver as each tone can be equalized independently. It has also been shown that using variable length equalizers can significantly reduce the total number of equalizer taps and hence the run-time complexity, without compromising performance. For a given transmit power loading, it has been shown that the equalizer taps can be allocated optimally using a dual decomposition based approach with per-tone exhaustive searches over all possible equalizer lengths. However, a more general approach is needed when optimal transmit power allocation is also considered to maximize the overall bit rate, where in addition the per-tone exhaustive searches are replaced by a more efficient procedure. In this paper, a sparse approximation based resource allocation algorithm is presented to allocate equalizer taps and transmit power over tones and maximize the overall bit rate. This algorithm is shown to provide efficient allocations at a relatively low computational cost.

Sustainable Broadband: A Monitoring Framework for Broadband Policy in Rural Areas in the Netherlands

As General Purpose Technologies (GPTs) (Bresnahan & Trajtenberg, 1995), information and communication technologies (ICT) have been applied in different ways across companies and regions. The differences in ICT adoption across regions have been approached from a variety of perspectives, e.g. from the business users (Forman, 2005) and residential users point of view (Goldfarb & Prince, 2008) showing that regional differences are key characteristics of ICT growth. But these spatial disparities have to be approached with caution as technological characteristics of broadband are important to define rural areas (Grubesic & Murray, 2002). Even if rural areas in the European Union are defined according to technological and geographical dimensions (CEU, 2012), there is ample of room for a variety of interpretations by market parties and local governments. In case of (local) government intervention in broadband markets, there is a need to evaluate broadband initiatives with respect to their economic benefits in rural areas. In order to evaluate the economic impact of broadband, numerous studies in particular in the United States have been conducted to examine the link between broadband availability and a number of economic characteristics of rural regions (Connected Nation, 2008; Gilllett, Lehr, Osorio, & Sirbu, 2006; Whitacre, Gallardo, & Strover, 2013). Just recently the literature has focused on elements which will put broadband on a sustainable path, i.e. taking environmental implications of ICT into account (Ropke, 2012). A number of evaluation exercises of broadband programs have been conducted showing that “encouraging broadband adoption is only part of a larger digital literacy effort, and programs work when they make non-users want to connect, make the Internet cheaper and easier to use, and adjust to users’ preferences” (Hauge & Prieger, 2010). However, there currently there is no generally accepted monitoring framework that can be used to evaluate and monitor the (social) costs and benefits of broadband programs in rural areas. The paper contributes to the discussion in providing a monitoring framework for sustainable broadband in rural areas. This framework is developed by using the (social) cost-benefit analysis (SCBA) methodology applied to (all) large infrastructure programs in the Netherlands since 2003 (Eijgenraam, Koopmans, Tang, & Verster, 2000). This methodology is applied to investigate the implementation of broadband technologies in rural areas. In this context, a DPSIR scheme (originally developed as a framework for environmental indicators) is applied to monitor and a SCBA to evaluate the choice between the different alternatives (Eijgenraam, et al., 2000). As proposed by Ramirez (2007), such alternative monitoring framework is needed to evaluate economic progress in rural areas (Ramirez, 2007). As part of NGA networks (CEU, 2009, 2012), fiber technologies are increasingly considered by provincial governments in the Netherlands as the most future-proof technology of broadband infrastructure in rural areas. Different provinces in the Netherlands have set up large infrastructural broadband funds aimed at stimulating local economic development and bridging the digital divide between rural and urban areas (Provincie Noord-Brabant/ Dialogic, 2012; Provincie Overijssel, 2010). It is expected that fiber technologies will provide higher value-added to society (compared to traditional broadband technologies such as DSL or cable modem technologies) over the long term. For rural areas, these benefits have, in particular, been related to the arrival of e-health services, teleworking and the renewal of rural areas. For residential users, benefits from e-health services are emerging due to smart homes solution supporting greater self-reliance of the elderly which allow people to stay longer at home. For business users, benefits from teleworking are related to the reduction of travel time (Van der Wee et al., 2012). New NGA technologies can also support the renewal of rural areas (McGranahan & Wojan, 2007; Stephens & Partridge, 2011). To complicate matters, provincial governments are facing a number of options with respect to evaluating different project proposals for rural broadband. For example, to what extent do these proposals reflect the goals of provincial plans for rural areas (e.g. do they support renewal of rural areas; do they improve or enhance self-reliance of inhabitants?); to what extent do these proposal opt for the “right” NGA network technology?; do they support a competitive supply structure and new trans-sectoral services? In this context, a monitoring framework for broadband policy in rural areas in the Netherlands will provide more certainty with respect to interventions by provincial government, a better evaluation of the emerging (social) benefits and their allocation with respect to the different stakeholders in provincial programs.

Sparse principal component analysis based sustainability assessment of EOL ICT service infrastructures

Sustainable Design and Manufacturing (SDM) is becoming a more effective approach to solve sustainable (environmental, social and economic) problems. Information and Communication Technology (ICT) positively made business more efficient and less polluting, while negatively contributes to environmental impacts by releasing of Greenhouse Gases (GHG) and producing e-wastes. This paper will develop a quantitative method of sustainability assessment in all three dimensions based on Sparse Principal Component Analysis (SPCA). A prototype model of Sustainability Performance Assessment Tool (SPAT) that can be integrated with existing systems and software to aid in product and process decision making is developed and discussed in detail in this paper. A DSL modem is taken as a case study to demonstrate the sustainability assessment and prototype model.

Open vs. Closed Access Femtocells in the Uplink

Femtocells are assuming an increasingly important role in the coverage and capacity of cellular networks. In contrast to existing cellular systems, femtocells are end-user deployed and controlled, randomly located, and rely on third party backhaul (e.g. DSL or cable modem). Femtocells can be configured to be either open access or closed access. Open access allows an arbitrary nearby cellular user to use the femtocell, whereas closed access restricts the use of the femtocell to users explicitly approved by the owner. Seemingly, the network operator would prefer an open access deployment since this provides an inexpensive way to expand their network capabilities, whereas the femtocell owner would prefer closed access, in order to keep the femtocell's capacity and backhaul to himself. We show mathematically and through simulations that the reality is more complicated for both parties, and that the best approach depends heavily on whether the multiple access scheme is orthogonal (TDMA or OFDMA, per subband) or non-orthogonal (CDMA). In a TDMA/OFDMA network, closed-access is typically preferable at high user densities, whereas in CDMA, open access can provide gains of more than 200% for the home user by reducing the near-far problem experienced by the femtocell. The results of this paper suggest that the interests of the femtocell owner and the network operator are more compatible than typically believed, and that CDMA femtocells should be configured for open access whereas OFDMA or TDMA femtocells should adapt to the cellular user density.

Development of 10 Gb/s EPON in IEEE 802.3av

The interest in the evolution of current PON systems toward high-data-rate systems capable of providing a future-proof platform for delivery of truly subscriber-oriented and personalized triple-play services resulted in the recent kickoff of the 10 Gb/s Ethernet PON system standardization effort in the IEEE . Ethernet PON has become a network of choice for low-cost subscriber-oriented digital service delivery, taking over the market previously dominated by DSL and cable modems. In this article we examine the current development process of 10 Gb/s EPON systems in more detail, standardized in the framework of the IEEE 802.3av task force, looking at the technical challenges, drivers, and possible evolution scenarios of the emerging high-data-rate access systems..

Embracing Wired Networks

Most people I know run wireless networks in their homes. Not me. I hardwired my home and leave the Wi-Fi turned off. My feeling is to do it once, do it right, and then forget about it. I want a low-cost network infrastructure with guaranteed availability, bandwidth, and security. If these attributes are important to you, Wi-Fi alone is probably not going to cut it. People see hardwiring as part of a home remodeling project and, consequently, a big headache. They want convenience. They purchase a wireless router, usually leave all the default settings in place, hook it up next to the DSL or cable modem, and off they go. Ease and convenience are the selling points, but there are certainly tradeoffs to consider. As the IT expert of last resort for family, friends, and sometimes their family and friends, here are some of my experiences with Wi-Fi in the home.

'Net Neutrality', Non-Discrimination and Digital Distribution of Content Through the Internet

The vast majority of US residential consumers face a monopoly or duopoly in broadband Internet access. Up to now, the Internet was characterized by a regime of “net neutrality” where there was no discrimination in the price of a transmitted information packet based on the identities of either the transmitter or the receiver or based on the application or type of content that it contained. The providers of DSL or cable modem access in the United States, taking advantage of a recent regulatory change that effectively abolished net neutrality and non-discrimination protections, and possessing significant market power, have recently discussed implementing a variety of discriminatory pricing schemes. This paper discusses and evaluates the implication of a number of these schemes on prices, profits of the network access providers and those of the complementary applications and content providers, as well as the impact on consumers. We also discuss an assortment of anti-competitive effects of such price discrimination, and evaluate the possibility of imposition of net neutrality by law.

A low complexity optimal spectrum balancing algorithm for digital subscriber lines

In modern DSL systems, multi-user crosstalk is a major source of performance degradation. Optimal spectrum balancing (OSB) is a centralized algorithm that mitigates the effect of crosstalk by allocating optimal transmit spectra to all interfering DSL modems. By the use of Lagrange multipliers the algorithm decouples the spectrum management problem into per-tone optimization problems. The remaining issues are then finding the Lagrange multipliers that enforce the constraints and solving the per-tone optimization problems. Finding the optimal Lagrange multipliers can become complex when more than two users are considered. Starting from the single-user case, this paper presents a number of properties, which are then extended to the multi-user case and lead to an efficient search algorithm for the Lagrange multipliers. Simulations show that the number of Lagrange multiplier evaluations is as small as 20–50, independent of the number of users. Secondly, the complexity of the per-tone optimization problems grows exponentially with the number of lines in the binder. For multiple-user scenarios this becomes computationally intractable. This paper presents an efficient branch-and-bound approach for the per-tone optimization problem. Simulations show enormous complexity reductions, especially for a large number of users.

The need for an essential acoustics curriculum and its delivery via distance education

Many individuals have identified a need to better educate engineers, industrial hygienists, and architects with an essential acoustical curriculum including noise control techniques. There are less than a dozen major programs training these individuals, and demand far exceeds the supply of education suppliers. One effective method of providing education to busy professionals who otherwise would not be exposed to an essential curriculum is distance education. Approximately 10 years ago Penn State developed a series of noise control engineering courses delivered through CD‐ROM. Now with DSL and cable modems more common, full motion video streaming is a preferred delivery method. Students currently take graduate level courses in acoustics at Penn State via resident education, continuing education, and distance education. There is no reason why an essential acoustical curriculum could not be delivered similarly. One benefit of video streaming is an opportunity for both live and archived lecture material. Students can attend live recitation sections while retaining the ability to see archived material on demand. Technology such as high‐bandwidth connections, inexpensive webcams, and microphones also allows two‐way audio and video for direct student‐instructor interaction.

Prospective reliability of the STRokE DOC Wireless/Site Independent Telemedicine System

The San Diego wireless telemedicine stroke evaluation arrangement described by Meyer et al.1 is unusual. Our similar REACH (Remote Evaluation of Acute isCHemic stroke) system at the Medical College of Georgia (MCG) uses secure Internet connections to evaluate acute stroke patients in rural hospitals of north central Georgia in the Nation's “stroke belt.” Like the San Diego system, REACH uses any broadband (DSL or cable modem) Internet accessible computer, nationwide. However, without a broadband wireless bubble over Augusta, Georgia, consulting …

Analysis and performance evaluation of the OFDM-based metropolitan area network IEEE 802.16

Wireless last mile technology is becoming a challenging competitor to conventional wired last mile access systems like DSL and cable modems or even fiber-optic cables. The Institute of Electrical a...

Analysis and performance evaluation of the OFDM-based metropolitan area network IEEE 802.16

Wireless last mile technology is becoming a challenging competitor to conventional wired last mile access systems like DSL and cable modems or even fiber-optic cables. The Institute of Electrical and Electronics Engineers has developed a standard for fixed broadband wireless access systems namely IEEE 802.16. Its OFDM mode targets frequency bands below 11 GHz. This paper gives an overview of the OFDM-based transmission mode of the IEEE 802.16 standard. The medium access control (MAC) and the physical layer are described in detail. Especially the MAC frame structure is elaborated. An analytical performance evaluation of an example scenario is performed which results in overall system performance measures. Especially the interaction of fragmentation and padding of OFDM symbols and its effect on the system capacity is evaluated. Furthermore, different MAC layer configurations with different levels of robustness are analyzed. Optional features to resist challenging channel conditions are outlined. Their trade off, i.e., a reduced MAC layer capacity is pointed out. It is shown that the system can be optimized while maintaining the necessary robustness against environmental challenges. A prototypical IEEE 802.16 protocol stack including a sophisticated channel model has been implemented. By means of this stochastic event-driven computer simulator, downlink and uplink delay as well as throughput evaluation is performed. Thus, performance results based on meaningful MAC configuration examples are provided. Simulative and analytical results are compared.

Of Processors and Processing

Digital signal processing is a stealth technology. It is the core enabling technology in everything from your cellphone to the Mars Rover. It goes much further than just enabling a one-time breakthrough product. It provides ever-increasing capability; compare the performance gains made by dial-up modems with the recent performance gains of DSL and cable modems. Remarkably, digital signal processing has become ubiquitous with little fanfare, and most of its users are not even aware of what it is. Therefore, it is worthwhile to look at the development history of DSP, an explanation of what the technology is, and a review of the many technologies that are used to implement modern digital signal processing systems.

Qos aware adaptive resource allocation techniques for fair scheduling in ofdma based broadband wireless access systems

A system based on orthogonal frequency division multiple access (OFDMA) has been developed to deliver mobile broadband data service at data rates comparable to those of wired services, such as DSL and cable modems. We consider the resource allocation problem of assigning a set of subcarriers and determining the number of bits to be transmitted for each subcarrier in OFDMA systems. We compare simplicity, fairness and efficiency of our algorithm with the optimal and proposed suboptimal algorithms for varying values of delay spread, number of users and total power constraint. The results show that the performance of our approach is appealing and can be close to optimal. We also consider another resource allocation scheme in which there is no fixed QoS requirements per symbol but capacity is maximized.

Advanced DSL management

Today's digital subscriber line deployments are often conservatively engineered to function in a statistically worst case environment. Crosstalk is treated as unknown and uncontrollable random noise, even though it is manmade. Other impairments are often treated by simply adding margin to crosstalk. While this simplistic practice currently suffices, it often provisions unnecessarily low bit rates. This article shows methods that can increase these bit rates and decrease DSL failure rates. Data can be collected about individual telephone lines and cables from loop databases, by automated test equipment, or from DSL modems. This data may then be fed into an advanced DSL management system with a database of DSL loop and noise characteristics, and an analysis engine that tailors DSL deployments to the actual individual line characteristics, to increase provisioned DSL bitrates while simultaneously increasing reliability and lowering maintenance costs. The maximum service can be provisioned with high accuracy, eliminating many service activation failures. Automated maintenance routines can even isolate faults before a customer experiences them. Dynamic spectrum management (DSM) treats crosstalk as the manmade noise it is, and jointly optimizes DSL transmit spectra and signals to minimize crosstalk and maximize received signals, allowing substantially higher DSL speeds than current practice. This opens the door for new services, including symmetric enterprise services and full video service, with minimal physical plant upgrade.