Asymmetric Digital Subscriber Loop Research Articles

Prediction of short-lived TCP transfer latency on bandwidth asymmetric links

TCP over bandwidth asymmetric networks such as Cable TV and Asymmetric Digital Subscriber Loop (ADSL) exhibits different characteristics from TCP on symmetric links. A number of techniques have been proposed to address this problem. However, previous research has been largely focused on bulk transfers. This paper investigates the effects of bandwidth asymmetry on Web-like short-lived transfers. Two prediction models, one given in a closed form and the other in a recursive form, are presented for TCP transfers without and with ACK Filtering (AF), a representative optimizing technique for TCP transfers over bandwidth asymmetric links. Ns-2 based experiments show that these models can predict TCP transfer latency with a high degree of accuracy.

Low-power variable-length fast Fourier transform processor

Fast Fourier transform (FFT) processing is one of the key procedures in the popular orthogonal frequency division multiplexing (OFDM) communication systems. Structured pipeline architectures and low power consumption are the main concerns for its VLSI implementation. In the paper, the authors report a variable-length FFT processor design that is based on a radix-2/4/8 algorithm and a single-path delay feedback architecture. The processor can be used in various OFDM-based communication systems, such as digital audio broadcasting (DAB), digital video broadcasting-terrestrial (DVB-T), asymmetric digital subscriber loop (ADSL) and very-high-speed digital subscriber loop (VDSL). To reduce power consumption and chip area, special current-mode SRAMs are adopted to replace shift registers in the delay lines. In addition, techniques including complex multipliers containing three real multiplications, and reduced sine/cosine tables are adopted. The chip is fabricated using a 0.35 /spl mu/m CMOS process and it measures 3900 /spl mu/m /spl times/ 5500 /spl mu/m. According to the measured results, the 2048-point FFT operation can function correctly up to 45 MHz with a 3.3 V supply voltage and power consumption of 640 mW. In low-power operation, when the supply voltage is scaled down to 2.3 V, the processor consumes 176 mW when it runs at 17.8 MHz.

Asymmetric DSL Technology of Signal Transmission

Asymmetric flow of information is the key feature of theADSL (Asymmetric Digital Subscriber Loop) technology, i.e.higher data transmission rate towards the user than from theuser towards the network. Characteristic is the short messagesending by the user with a certain request to the se!Ver. These!Ver responds to the request by a significantly longer messageof various electronic forms (data, digitized speech, pictures orvideo). Therefore, this technology is most often used by smalland medium users. ADSL is currently the only commerciallyavailable DSL technology which is still experiencing the breakthroughon the seiVice market. It enables faster access to theInternet, LAN (Local Area Network), videoconferencing, VoD(Video on Demand) and interactive multimedia. In order tostandardize such se/Vices, the !TU (International TelecommunicationsUnion) G. 992.1 (standardized DMT-discrete multi-tone line coding technology) and ANSJ (American NationalStandards Institution) Tl.413-95!98 are used for ADSL. DMT(Discrete Multi Tone), as the more popular one, uses the linecoding technique, which splits a certain frequency range intoseveral sub-channels. Most of these sub-channels are used forupstream and downstream transmission of speech and data,whereas some are used as pilot signals or kept in rese/Ve. Suchmodulation technique expands the frequency spectrum, allowingthe usage ofbroadband se/Vices per one pair of wires. In thisway the sharing of speech and data se/Vice transmission is realized.

Blind, adaptive channel shortening by sum-squared auto-correlation minimization (sam)

We propose a new blind, adaptive channel shortening algorithm for updating the coefficients of a time-domain equalizer in a system employing multicarrier modulation. The technique attempts to minimize the auto-correlation terms of the effective channel impulse response outside a window of desired length. The proposed algorithm, known as sum-squared auto-correlation minimization (SAM), requires the source sequence to be zero-mean, white, and wide-sense stationary, and it is implemented as a stochastic gradient descent algorithm. Simulation results are provided, demonstrating the success of the SAM algorithm in an asymmetric digital subscriber loop (ADSL) system.

Novel efficient bit-loading algorithms for peak-energy-limited ADSL-type multicarrier systems

We develop solutions for the loading of digital subscriber loop (DSL) multicarrier (MC) systems that present constraints both on overall available energy and maximum energy per carrier. In the emerging G.DMT-based systems planned for high-throughput multimedia applications, the constraint on the peak-energy arises from spectral compatibility issues. However, until today, optimal solutions for loading peak-energy constrained MC systems do not seem explicitly developed in the literature. Hence, starting from suitable applications of the Kuhn-Tucker conditions, we present the analytical relationships characterizing the optimal solution of the peak-energy-limited loading for the general case of concave rate-functions, and then, we apply them in the context of the so-called gap analysis. Thus, a low-complexity iterative algorithm implementing this solution is also developed, and its performance is numerically tested on several ANSI-standard asymmetric DSL (ADSL)-type loops impaired by crosstalk. Furthermore, a version of the presented loading algorithm that guarantees integer bit rates with low computational effort is also presented, and its performance is tested. The carried-out performance comparisons allow us to evaluate the throughput loss induced by peak-energy constraints in emerging ADSL-like services.

TCP performance analysis and optimization over DMT based ADSL system

This paper studies the transmission control protocol (TCP) performance over a discrete multi-tone (DMT) based asymmetric digital subscriber loop (ADSL) network. The impact of DMT subchannel bit loading on the TCP throughput performance is studied. The simulation results show that there is a threshold for the signal-to-noise ratio (SNR) gap or bit error rate (BER) above which TCP throughput drops quickly. This threshold takes its value in a wide range depending on the TCP round-trip time as well as channel noises. This suggests that it would be insufficient to set a fixed target BER at, e.g. 10 −7, when calculating the number of bits to be loaded in each subchannels. Instead, the bit loading should take TCP performance into account. Finally a dynamic bit loading scheme is proposed, which jointly optimizes the channel bit rate and TCP throughput performance.

Multidimensional carrierless AM/PM systems for digital subscriber loops

Carrierless amplitude/phase modulation (CAP) is a viable alternative for digital subscriber loop (DSL) systems such as high-speed DSL, asymmetric DSL, and very high-speed DSL. In this paper, two novel orthogonal-based modulation schemes are introduced for the DSL environment. In the first technique, the conventional two-dimensional (2-D) CAP-16 line code is extended to a three-dimensional (3-D) scheme. The 3-D system is designed so that the new overall transfer matrix maintains perfect reconstruction (PR) of the transmitted information. The system is designed by solving a minimax optimization problem by using the sequential quadratic programming algorithm; this searches the whole space of signals under the PR condition and the DSL constraints. The 3-D CAP system leads to a 50% increase in throughput at the expense of the output signal-to-noise ratio (SNR) degradation by 3-4 dB. It should be noted that this increase in throughput can also be achieved by a CAP-64 system. Nevertheless, the dynamic range of the proposed 3-D CAP approach is 7.4 dB less than CAP-64, which leads to faster equalization. Furthermore, the equalizer performance in the 3-D case is 1-3 dB better, depending on channel and noise considerations. Another application of the multidimensional CAP approach, referred to as orthogonality division multiple access (ODMA) is presented. In this approach, the CAP system is extended to more than three dimensions by maintaining the same overall symbol rate as in the 2-D case. The ODMA system allows multiple-access operation of the DSL communication link with minimal hardware penalty. The performance of the ODMA system for the multiple-access environment is found to match the conventional 2-D CAP, allowing suitable multiple-access topology with minimal complexity overhead. The ODMA system complexity is compared with discrete multitone and is found to have 25% less complexity for the same bit rate. Theoretical analysis of the ODMA system using zero-forcing equalization shows that the equalization process yields better SNR as the number of dimensions increases, asymptotically approaching the intersymbol interference-free matched filter bound.

Service provisioning in an ATM-over-ADSL access network

Asymmetric digital subscriber loop technology is a new platform for delivering broadband services to homes and small businesses, thus bringing the information highway to the mass market. Successful deployment of an ADSL-based access network is not only a matter of delivering faster rates, but also offering solutions that are cost-effective and easy to use and manage. As deregulation and competition spread globally, an ADSL-based access network should also enable end users to choose their service providers dynamically, and to switch from one provider to another easily and rapidly, even on a real-time basis. In light of these requirements, this article addresses the issue of service provisioning in an ATM-over-ADSL access network. It concentrates on the provisioning of services using the PPP protocol. PPP is the common protocol for service provisioning in circuit-switched telephone networks. However, it is also considered a good choice for the delivery of broadband services since it has built-in mechanisms for IP address assignment, layer-2 security, and AAA (authentication, authorization and accounting). This article presents the problem of initiating a PPP connection at an Ethernet-based host. It presents several solutions for this problem and discusses the advantages and disadvantages of each solution.

Green design of telecom products: the ADSL high speed modem as a case study

This paper discusses the principles of life cycle assessment (LCP) and design for environment (DFE) and their application in the design and development of the asymmetric digital subscriber loop (ADSL) high speed modem, This application was used as a case study to evaluate the feasibility of incorporating "green" issues into the design cycle, Section II focuses on the green design methodology. It describes some fundamentals and the state-of-the-art of LCA/DFE. It also raises some critical issues that show up in the definition of LCA/DFE methodology. Section III describes the actual case study. It shows how the green design methodology, described in Section Il, is adopted to the project under study. More specifically, it is described how the LCA is introduced into the physical design stage of the product, which assumptions are taken into account for the LCA analysis, and how the analysis affects the usual product design flow. It discusses how the study started by performing an LCA of the ADSL high speed modem R1 (Release 1), with a large emphasis on the analysis of manufacturing processes. Secondly, these LCA results were used as input for the DFE methodology, in order to design a perceived greener product, the ADSI high speed modem R2 (Release 2). The "greenness" of this new product is validated by comparing the two environmental profiles. This case study resulted in a coherent and extensive environmental assessment of some fundamental design options (and the associated manufacturing processes) involved in complex electronic devices. By implementing the results of this LCA into a specific DFE methodology, green design issues have been introduced in the design cycle as just another design constraint to be dealt with.

Broadband multimedia delivery over copper

Asymmetric digital subscriber loop (ADSL) technology has proved itself in various video-on-demand (VoD) trials as a technically viable means of delivering VHS-quality moving video over the existing twisted copper pairs of the access network. A very high-speed version of this technology (VDSL) is now emerging which has the potential to deliver more channels of higher quality broadband multimedia services over a hybrid fibre-copper access network. This paper provides an overview of the enabling copper transmission technologies (both ADSL and VDSL) and the metallic access environment.