Protecting The Robustness Of ADSL And VDSL DMT Modems When Applying DSM

When transmitting data over an ADSL or VDSL link, performance is very important. In order to improve the bit rate that can be achieved over the copper link, a lot of techniques like power backoff (PBO) and dynamic spectrum management (DSM) focus on the crosstalk and try to operate with lower noise margin. Today's ADSL and VDSL modems are very robust. Both in ADSL and VDSL there exist reconfiguration protocols that take care of changing noise environments. The intent of the paper is to know what the impact is of DSM on the robustness of these systems. If the noise increases, the modem may lose showtime, unless the modem can adapt its PSD to compensate for the increase of noise. In this paper, we investigate for DSM the speed and robustness of various online reconfiguration protocols that exist today. We will consider a worst case noise : a noise that also impacts the communication channel that is needed to reconfigure the modem. Since reconfiguration is essential to recover from a degraded environment, the speed and the robustness of this reconfiguration protocol is very important

Simulation of DSL systems

-This report contains simulations of performance for different versions of ADSL, VDSL and SHDSL in 0.4 mm twisted pair cables. An important part of the work has been to investigate the compatibility between different DSL systems. The range of SHDSL system compliant with ITU G.991.2 Annex G has been analysed. These systems allow for bitrates up to 3.848 Mbit/s and 5.696 Mbit/ for 16-PAM and 32-PAM systems respectively. The overall conclusion is that downstream ADSL and ADSL2+ is compatible with both SHDSL Annex G and HDSL systems. The degradation in bitrate of downstream ADSL due to these systems is moderate, less than 13% compared to a cable containing only ADSL systems. ADSL subloop means that an ADSL DSLAM is installed between the local exchange and the subscriber. The purpose is to reduce the loop length between the DSLAM and the subscriber in order to increase the bitrate. This subloop signal will represent a strong interference in the downstream direction of the ADSL systems from the local exchange. As is shown in Section 7 in this report there is a severe degradation in the downstream direction of the ADSL system from the local exchange. The remedy to reduce this degradation is to use power backoff in the subloop systems. Use of power backoff regimes is not analysed in this report. The potential bitrates for VDSL2 systems have been analysed for bandplans 997 and 998. The simulations show that bandplan 997 will give almost symmetrical up- and downstream bitrates for the cables less than 800 meters, whereas for bandplan 998 the downstream/upstream ratio is close to 2:1. Three different bandwidths have been analysed, 12 MHz, 17 MHz and 30 MHz. The frequency bands above 12 MHz are used only for loop lengths less than 800 meters. The frequency bands above 17 MHz are used only for loop lengths less than 650 meters. Bandplans that makes use of the lowest upstream band U0 can still provide adequate upstream capacity (1 Mbit/s) even for loop lengths in excess of 2 km. The downstream bitrate is significant (17-18 Mbit/s) for both 997 and 998 at these lengths. A discussion of the use of ADSL in equalisation cables is given in Section 9. Alternative ways to install ADSL in pairs that contain 1+1 systems are presented in Section 10. Oppdragsgiver: Post- og teletilsyne

ICT and exporting: the effects of broadband on the extensive margin of business service exports.

Over recent decades the global economy has witnessed rapid growth of international trade in services. This has been particularly true of service-intensive countries such as the UK. Developments in information and communication technologies are an obvious explanation for this. We provide empirical evidence for the effects of broadband use on the firm-extensive margin of UK service exports. To deal with the issue of causality we build a novel instrument that exploits exogenous variation in access to broadband technologies due to the historic telephone network. We find evidence for a causal effect from the internet on trade in business services, but no evidence for an effect on trade in services more generally

Orthogonal transmultiplexers : extensions to digital subscriber line (DSL) communications

An orthogonal transmultiplexer which unifies multirate filter bank theory and communications theory is investigated in this dissertation. Various extensions of the orthogonal transmultiplexer techniques have been made for digital subscriber line communication applications. It is shown that the theoretical performance bounds of single carrier modulation based transceivers and multicarrier modulation based transceivers are the same under the same operational conditions. Single carrier based transceiver systems such as Quadrature Amplitude Modulation (QAM) and Carrierless Amplitude and Phase (CAP) modulation scheme, multicarrier based transceiver systems such as Orthogonal Frequency Division Multiplexing (OFDM) or Discrete Multi Tone (DMT) and Discrete Subband (Wavelet) Multicarrier based transceiver (DSBMT) techniques are considered in this investigation. The performance of DMT and DSBMT based transceiver systems for a narrow band interference and their robustness are also investigated. It is shown that the performance of a DMT based transceiver system is quite sensitive to the location and strength of a single tone (narrow band) interference. The performance sensitivity is highlighted in this work. It is shown that an adaptive interference exciser can alleviate the sensitivity problem of a DMT based system. The improved spectral properties of DSBMT technique reduces the performance sensitivity for variations of a narrow band interference. It is shown that DSBMT technique outperforms DMT and has a more robust performance than the latter. The superior performance robustness is shown in this work. Optimal orthogonal basis design using cosine modulated multirate filter bank is discussed. An adaptive linear combiner at the output of analysis filter bank is implemented to eliminate the intersymbol and interchannel interferences. It is shown that DSBMT is the most suitable technique for a narrow band interference environment. A blind channel identification and optimal MMSE based equalizer employing a nonmaximally decimated filter bank precoder / postequalizer structure is proposed. The performance of blind channel identification scheme is shown not to be sensitive to the characteristics of unknown channel. The performance of the proposed optimal MMSE based equalizer is shown to be superior to the zero-forcing equalizer

DSM in Practice: Iterative Waterfilling Implemented on ADSL Modems

New techniques emerge in the DSL world to increase the bit rate and deployment range of particular services. These techniques are better known as Dynamic Spectrum Management (DSM) applied at different levels. The increasing DSM levels can be seen as an evolution towards increasing coordination between multiple DSL lines: from level 1 and 2 (multi-user power allocation resulting in crosstalk avoidance) to level 3 (multi-user detection resulting in crosstalk mitigation). In this paper we focus on DSM at level 1 and in particular on a specific algorithm called iterative water-filling which has been implemented on ADSL modems. Measured performance results are given showing a big performance increase

Exploring the hot-carrier effect on the wireless transceivers

Phase noise can be regarded as the most severe cause of performance degradation in the wireless communication systems. The hot-carriers (HCs), found in the CMOS synchronization circuits, are the high-energy charge carriers that degrade the MOSFET devices’ performance by increasing the threshold voltage required to operate the MOSFETs. The HC effect manifests itself as the phase noise whose level increases with the continued MOSFET operation and such increases result in the performance degradation of the voltage-controlled oscillator (VCO) built on the MOSFETs. The HC effect is particularly evident in the short-channel MOSFET devices. In this dissertation, we analyze the wireless transceiver performances in the presence of the synchronization errors induced by the HC effect, for both single-carrier and multi-carrier communication systems. We derive the relationship between the corresponding system performances and the HC effect in terms of a crucial parameter, the MOSFET threshold voltage. We employ a new phase noise model for the wireless systems influenced by the HC effect, which is based on a new precise phase noise mask function. In addition, we analyze the impact of the phase noise arising from the HC effect on the single-carrier wireless systems in terms of the BER and the signal-to-interference-plus-noise ratio (SINR). We derive the exact BER expression and show the SINR degradation for the QPSK systems that suffer from the phase noise. We apply Monte Carlo simulations to verify our analysis. To study the HC effect thoroughly, we simplify the BER expression as a new asymptotical analysis as the signal-to-noise ratio approaches to infinity and obtain the lower bound of the achievable BER for the single-carrier wireless systems. For multi-carrier systems, we focus our discussions on the orthogonal frequency division multiplexing (OFDM) systems. According to our simulations, we show that the bit-error-rate (BER) evaluation for OFDM using our new phase noise model in the presence of the HCs can be very different up to three orders-of-magnitude from the existing models disregarding the HCs. We have also found that the ICI self-cancellation coding is very effective for combating the phase noise in the OFDM systems

QoE in Pull Based P2P-TV Systems: Overlay Topology Design Tradeoff

Abstract—This paper presents a systematic performance anal-ysis of pull P2P video streaming systems for live applications, providing guidelines for the design of the overlay topology and the chunk scheduling algorithm. The contribution of the paper is threefold: 1) we propose a realistic simulative model of the system that represents the effects of access bandwidth heterogeneity, latencies, peculiar characteristics of the video, while still guaranteeing good scalability properties; 2) we propose a new latency/bandwidth-aware overlay topology design strategy that improves application layer performance while reducing the underlying transport network stress; 3) we investigate the impact of chunk scheduling algorithms that explicitly exploit properties of encoded video. Results show that our proposal jointly improves the actual Quality of Experience of users and reduces the cost the transport network has to support. I

Cost effective DSL solutions for the developing countries.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Westville, 2004.Developing countries in Africa present a graphic picture of the digital divide. High costs associated with serving rural customers are the major cause of uneven distribution of services. Rural areas are characterised by a high rate of unemployment and a poor level of education. This results in a scenario where most of the residents are unable to utilize IT resources. Some people in these areas are not informed about the availability and importance of these technologies in the market. Those who are academically fit for accessing these technologies often cannot afford them. Some of the areas still have no existing telecommunications infrastructure. High deployment costs associated with broadband services makes it even more challenging to deploy such services in this environment. In Africa approximately 80% of the population is living in rural areas, which alone creates a demand for the coverage of rural regions. Leaving such a large number of residents not connected, means poor medical care, students cannot participate in distance learning programs which means poor quality of education, poor performance in businesses, poor farming and crippling delivery of government services. DSL technologies were originally designed to suit suburban to urban conditions. In this research it is shown that broadband services can be delivered to rural people by applying DSL technologies, using the existing telecommunications infrastructure. This will mean significant savings, as it does not need core network investments. DSL increases network capacity to a network, which is no longer limited to voice. With this technology a number different high bandwidth applications are delivered to the homes, schools, hospitals, telecentres and small businesses. The cost effectiveness of these technologies for several reach and rural traffic environment is investigated. This is done by investigating several promising DSL solutions in terms of diverse geography, demographics and other cost dictating parameters

Loading Algorithms for Adaptive SS-MC-MA Systems over Wireline Channels: Comparison with DMT

In this paper, we propose to combine adaptive loading principles with the spread-spectrum multicarrier multiple access (SS-MC-MA) scheme. Such an approach has particular interests in the context of powerline communications (PLC), where the transmitter has not only to exploit robust transmission techniques, but has also to adapt the waveform to the channel response. We introduce finite-granularity loading algorithms that dynamically handle the configuration of the system under power spectral density constraints. The presented algorithms assign subcarriers, spreading codes, bits and energy to each user in order to maximize either the data rate or the noise margin at a given target symbol error rate. These algorithms can actually be viewed as a widening of the classical waterfilling approach in the case of an hybrid spread-spectrum multicarrier system. Simulation results of the new scheme are presented for different measured PLC channels and are compared with those of the classical discrete multitone modulation (DMT) approach. It is shown that the adaptive SS-MC-MA scheme performs significantly better than DMT, due to its natural energy gathering capability. Adaptive SS-MC-MA then leads to a more efficient bits and energies distribution and constitutes a simple solution to reduce the quantification loss induced by the use of finite order modulation