Crosstalk cancellation is a crucial issue for traditional digital subscriber line systems. For LTE-over-copper systems, however, the need for crosstalk cancellation varies depending on the analog fronthauling architecture and its parameters. A crosstalk handler that is decoupled as much as possible from the rest of the system architecture is thus preferred. Therefore, we propose a time-domain precoding scheme specifically in downstream direction to separate the precoding unit from the LTE signal flow, and perform crosstalk cancellation in an on-demand manner. Estimation of all direct and crosstalk paths is assisted by LTE cell-specific reference signals. The time-domain precoder transforms the interference channel into a crosstalk-free channel with identical direct paths, which allows for low-complexity inter-symbol interference mitigation. We evaluate the concept in terms of signal-to-noise ratio provided for LTE signals using measured wireline channel data.

With the introduction of smartphones and tablets and the dramatical increase of the data traffic on the cellular network, operators are seeking for new solutions to provide the users with continuous connectivity while preserving a good quality of service. Since most of current user terminals are equipped with multiple interfaces, one solution is to take advantage of the different access networks. However, with the current network architectures and user application, it is not possible to use both accesses at the same time or even to switch from one to another without loosing current sessions. In this paper, we present and analyse the main mechanisms of the literature that allow a user to use multiple access networks at the same time or to move between the different networks. We show how a converged network can permit the deployment of new solutions and present some of them accompanied by use cases.

Fixed-mobile convergence initially focused on optimizing fixed and mobile telephone infrastructure for voice services. The appearance of VoIP and smartphones, the growing popularity of social networks and video hosting services, the emerging of 5G, Internet of Things, machine-to-machine communication and ever newer over-the-top services motivated manufacturers, network operators and service providers to refocus and data delivery. The tutorial highlights the structural and functional aspects for efficiently instrumenting this convergence process, including infrastructure considerations, network function virtualization, software defined networking, unified functionality. The presentations are embedded into an overview of the past efforts, a summary of the state of the art, and a look-ahead for future communications networks. The authors are members of the Combo European consortium working on fixed-mobile convergence.

To increase indoor coverage for mobile services, we propose a residential small cell infrastructure making use of the existing copper plant. The system is cabinet-based, collocated with VDSL2 and uses small pieces of spectrum next to VDSL2. Inspired by the Ericsson Radio Dot System, it challenges the femtocell paradigm offering full macro functionality in the small cells. An interesting service potential is offered albeit the added mobile traffic capacity is moderate as it is limited by the copper fronthaul.

The densification of mobile networks in order to meet increased capacity demands is ongoing, needed and costly. A few papers have been published based on the insight that the fixed broadband networks offer a multitude of sites, for instance our homes, for potential small cell deployment providing backhaul capacity and power without site costs. However, in order to reach economical large-scale benefits, we explore the case when radio systems are deployed in coexistence with DSL. In this paper, we establish the feasibility of such a concept under constraints invoked by state-of-the-art and emerging systems (3GPP, VDSL2 and G.fast) and make statements about the required architecture. We also point out that the enthusiasm of previously published results should be lowered a notch.

The use of vectoring for crosstalk cancellation in the new ITU-T G.fast standard for next generation DSL systems becomes essential for efficient utilization of the extended bandwidth (up to 200 MHz). In VDSL2 (up to 30 MHz), a zero-forcing-based linear precoder is used in downstream which approaches single-line performance. However, at high frequencies, the linear precoder may amplify the signal power substantially since the crosstalk channel is much stronger than at lower frequencies. Performance could be significantly degraded by power normalization to keep the PSD below the mask. In this work, we extended a per-line power normalization scheme by linear programming (LP) optimization. By simulations using measured cable data it is shown how the LP-based scheme further improves the linear precoder and it is also capable of balancing the data rate between lines. Further, the simulations also show the non-linear Tomlinson-Harashima precoder performs better than the linear precoders.

G.fast is a new standard from the International Telecommunication Union, which targets 1 Gb/s over short copper loops using frequencies up to 212 MHz. This new technology requires accurate parametric cable models for simulation, design, and performance evaluation tests. Some existing copper cable models were designed for the very high speed digital subscriber line spectra, i.e., frequencies up to 30 MHz, and adopt assumptions that are violated when the frequency range is extended to G.fast frequencies. This paper introduces a simple and causal cable model that is able to accurately characterize copper loops composed by single or multiple segments, in both frequency and time domains. Results using G.fast topologies show that, apart from being accurate, the new model is attractive due to its low computational cost and closed-form expressions for fitting its parameters to measurement data.

The use of a hybrid copper and fiber architecture is attractive in both fixed access and mobile backhauling scenarios. This trend led the industry and academia to start developing the fourth generation broadband system, which aims at achieving bit-rates of 1 Gb/s over short copper loops. In this context, accurate models of short twisted-pair cables operating at relatively high frequencies are key elements. This work describes new parametric cable models that incorporate four important characteristics: support of frequencies up to 200 MHz, few parameters, causal impulse responses and require relatively easy fitting procedures. The results show that the models achieve good accuracy for single segments, which are the expected topology for G.fast deployments.

An iterative decoding scheme for woven convolutional codes is presented. It operates in a window sliding over the received sequence. This exploits the nature of convolutional codewords as infinite sequences and reflects the concept of considering convolutional encoding and decoding as a continuous process. The decoder is analyzed in terms of decoding delay and decoding complexity. Its basic building block is a symbol-by-symbol a posteriori probability (APP) decoder for convolutional codes, which is a windowed variant of the well-known Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm. Additional interleaving for the woven constructions is introduced by employing convolutional scramblers. It is shown that row-wise random interleaving preserves the lower bound on the free distance of the original woven constructions. Based on the properties of the interleavers, new lower bounds on the free distance of woven constructions with both outer warp and inner warp are derived. Simulation results for woven convolutional codes with and without additional interleaving are presented.

Encoders for convolutional codes with large free distances can be constructed by combining several less powerful convolutional encoders. This paper is devoted to constructions in which the constituent convolutional codes are woven together in a manner that resembles the structure of a fabric. The general construction is called twill and it is described together with two special cases, viz., woven convolutional encoders with outer warp and with inner warp. The woven convolutional encoders inherit many of their structural properties, such as minimality and catastrophicity, from their constituent encoders. For all three types of woven convolutional codes upper and lower bounds on their free distances as well as lower bounds on the active distances of their encoders are derived.

A family of active distance measures for general convolutional codes is defined. These distances are generalizations of the extended distances introduced by Thommesen and Justesen (1983) for unit memory convolutional codes. It is shown that the error correcting capability of a convolutional code is determined by the active distances. The ensemble of periodically time-varying convolutional codes is defined and lower bounds on the active distances are derived for this ensemble. The active distances are very useful in the analysis of concatenated convolutional encoders.

In this correspondence the error exponent and the decoding complexity of binary woven convolutional codes with outer warp and with binary convolutional codes as outer and inner codes are studied. It is shown that an error probability that is exponentially decreasing with the product of the outer and inner code memories can be achieved with a nonexponentially increasing decoding complexity.