Boris Dortschy

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.

Crosstalk channel estimation via standardized two-port measurements

The emerging multiuser transmission techniques for enabling higher data rates in the copper-access network relies upon accurate knowledge of the twisted-pair cables. In particular, the square-magnitude of the crosstalk channels between the transmission lines are of interest for crosstalk-mitigation techniques. Acquiring such information normally requires dedicated apparatus since crosstalk-channel measurement is not included in the current digital subscriber line (DSL) standards. We address this problem by presenting a standard-compliant estimator for the square-magnitude of the frequency-dependent crosstalk channels that uses only functionality existing in todays standards. The proposed estimator is evaluated by laboratory experiments with standard-compliant DSL modems and real copper access network cables. The estimation results are compared with both reference measurements and with a widely used crosstalk model. The results indicate that the proposed estimator obtains an estimate of the square-magnitude of the crosstalk channels with a mean deviation from the reference measurement less than 3 dB for most frequencies.

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.

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.

Impact of Crosstalk Estimation on the Dynamic Spectrum Management Performance

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. However, this estimation is not supported or required by current digital subscriber line (DSL) standards. In this work, we investigate the impact of non-ideal crosstalk estimation on the dynamic spectrum management (DSM) performance. Two different crosstalk estimators are considered: a conventional model-based estimator and a novel estimation procedure. The DSM performance is evaluated based on the obtained crosstalk estimates for two different network scenarios consisting of real twisted-pair cables. For a reference comparison, the crosstalk channels are measured with a network analyzer. The simulation results indicate that the novel estimation procedure achieves DSM performance results close to the ones obtained with the network analyzer and that the model-based estimator can lead to an inaccurate rate estimation.

Small cell strategy: meeting the indoor challenge

In this work we present an innovative solution to reach good quality of service while using mobile broadband indoors: the fiber radio-dot. This solution consists of a new architectural logical point-to-point optical link that brings the macro layer indoors. This solution provides higher bandwidth, no eavesdropping, frequency reuse, low latency, interference and network management, and cell selection. We tested the solution in the lab achieving an EVM of 0.75 %rms, SFDR of around 95 dBxHz2/3 and an LTE transmission of 75 Mbit/s.

Measurement and Modeling Techniques for the Fourth Generation Broadband Over Copper

Digital subscriber lines (DSL), the broadband data transmission technologies that use the copper cable as channel, are the most used Internet media around the world with more than 300 million users (Oksman et al., 2010), Much of the DSL success is related to the cost-benefit for both operators and served consumers. As the transmission channel is the common copper twisted-pair telephone cable, there is no need for large investments in infrastructure, because the telephone network is largely consolidated and active in almost all the world.

Achievable rates of DSL with crosstalk cancellation

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 achievable rates of binders under different crosstalk-mitigating techniques. When computing these rates, we also compare two different power constraints: either on the total power in the binder or on the power in each twisted wire 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 can be far superior to that of systems with no cooperation between the users. Both power constraints also lead to similar achievable rates. Copyright

An Algorithm for Improved Stability of DSL Networks Using Spectrum Balancing

The proper management of the signal to noise ratio margin is important for improving the stability of digital subscriber line (DSL) networks and increasing the customer satisfaction regarding services such as triple-play. This work presents a novel algorithm for multiuser margin optimization that benefits from the relationships between power and margin adaptation. The proposed multiuser margin maximization (MMM) is a meta algorithm that repeatedly invokes a spectrum balancing base algorithm. The base algorithm corresponds to a dynamic spectrum management (DSM) algorithm of level one or two, and is responsible for part of the overall spectra optimization procedure. Simulation results illustrate the performance of the proposed algorithm when using two base algorithms: iterative water-filling (IWF) and iterative spectrum balancing (ISB). The results show that the proposed MMM is able to design better noise margins and spectra, providing performance improvements when compared to a previous margin optimization algorithm that is restricted to using DSM level 1 coordination.

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.