Flight: A Flexible Light Communications network architecture for indoor environments

Recent experimental works have demonstrated the feasibility of the visible light based vehicular communications (VVLC) in intelligent transportation systems (ITS). However, in many respects, this technology is in its infancy and requires further research efforts in several areas. This work presents a flexible network architecture named flexible light (Flight), which is designed for VLC to tackle existing mobility challenges in the network environment. Flight proposes a low-latency handover system that decreases the handover delays to a few tens and hundreds of milliseconds. By means of experiments, we emulate and evaluate indoor mobile network scenarios using only VLC technology

Impact-analysis for coexisting G.fast and vectored VDSL2

G.fast recently standardized by the ITU aims at providing gigabit access from the Distribution Point (DP). The deployment of this new technology will be progressive as previous technological migrations, so G.fast will share the access network with existing DSL systems, particularly with vectored VDSL2. However, G.fast and vectored VDSL2 as defined by the standards are spectral-incompatible due to their overlapping spectrum, different carrier spacing implementation and conflicting multiplexing schemes. This work analyzes the coexistence issues that arise when G.fast and vectored VDSL2 services are deployed from the DP. Potential gains that could be obtained by introducing a synchronized transmission scheme, as well as the effectiveness of spectral-compatible band plans are discussed in order to help determine if those measures should be developed further and/or considered for standardization. In order to achieve this goal, we establish far-end crosstalk (FEXT) and near-end crosstalk (NEXT) models for realistic simulations and analyze the system performance for different deployment scenarios that reproduce the progressive migration from VDSL2 to G.fast. Our results show that synchronization between vectored VDSL2 and G.fast barely improves their performance, whereas the deployment of spectral-compatible band plans is an effective means to improve vectored VDSL2 performance with tolerable impact on G.fast

Practical source-network decoding

When correlated sources are to be communicated over a network to more than one sink, joint source-network coding is, in general, required for information theoretically optimal transmission. Whereas on the encoder side simple randomized schemes based on linear codes suffice, the decoder is required to perform joint source-network decoding which is computationally expensive. Focusing on maximum a-posteriori decoders (or, in the case of continuous sources, conditional mean estimators), we show how to exploit (structural) knowledge about the network topology as well as the source correlations giving rise to an efficient decoder implementation (in some cases even with linear dependency on the number of nodes). In particular, we show how to statistically represent the overall system (including the packets) by a factor-graph on which the sum-product algorithm can be run. A proof-of-concept is provided in the form of a working decoder for the case of three sources and two sinks.Fundação para a Ciência e a Tecnologia (grant SFRH/BD/29918/2006)European Commission (grant FP7-INFSOICT- 215252 (N-Crave Project))United States. Air Force Office of Scientific Research (award number FA9550-09-1-0196

Towards a range-enhanced and spectrum-friendly G.fast

The first standardized version of G.fast has been conceived to provide gigabit internet access from the distribution point (DP). Low transmit levels along its operational frequency range and low maximum aggregate transmit power (MAXATP) have been specified to restrict its electromagnetic emissions and enable the use of power available at customer premises to feed its access systems. Power constraints and a maximum bit-constellation size (Bmax=12 bits) limit its coverage and data rates, which could discourage service providers to deploy G.fast. This work analyzes different strategies that could be potentially pursued to enhance its coverage and improve its spectral compatibility with VDSL2 systems. We carry out an extensive simulation study to evaluate a) capacity boundaries of current G.fast systems; b) benefits of increasing MAXATP, Bmax and power spectrum density (PSD) mask levels; and c) spectral shaping as means to improve G.fast compatibility. Our simulation results show that increasing MAXATP and Bmax boosts data rates and coverage in short loop scenarios, whereas improvements in long loops performance are only determined by MAXATP. Since such modifications generally increase the interference on legacy systems, we propose to perform power back-off (PBO) in order to improve G.fast spectrum-compatibility. As a proof of concept we adopt the PBO from VDSL2 with a fixed parameter set. Although clearly not optimized for the combination of TDD G.fast and FDD legacy systems and despite the simplicity of the adopted approach, our results indicate that spectral shaping can be an effective means to turn G.fast into a more spectrum-friendly system

Evaluation of binder management for partially controlled DSL vectoring systems

Crosstalk between physically co-located lines is apressing issue in VDSL2 access networks. In order to enhance the crosstalk mitigation capabilities of the latest extension to VDSL2, vectoring G.993.5, full control over all lines within the same cable binder is required. However, this is not always possible in practical deployments due to regulatory, structural, or late technology adoption constraints. In these cases a technique tominimize interference from non-controlled lines, known as binder management, aims at rearranging the line configuration within each binder. In this work, we quantify the advantages of binder management in a partially controlled setup. We initially establish a model of a commonly used 50-pair cable binder and provide its far-end crosstalk (FEXT) characterization. We then carry out an extensive simulation study for various degrees of control over the lines and realistic line length distributions to yield tangible metrics on vectoring performance fordownstream transmission. Our results show that binder management is of limited use in partially controlled systems. Consequently, we provide an additional comparison study to help DSL providers to evaluate the remaining gains of upgrading to VDSL2-vectoring in such scenarios for different levels of dominance in the cable binder

Towards a Range-Enhanced and Spectrum-Friendly G.fast

The first standardized version of G.fast has been conceived to provide gigabit internet access from the distribution point (DP). Low transmit levels along its operational frequency range and low maximum aggregate transmit power (MAXATP) have been specified to restrict its electromagnetic emissions and enable the use of power available at customer premises to feed its access systems. Power constraints and a maximum bit-constellation size (Bmax=12 bits) limit its coverage and data rates, which could discourage service providers to deploy G.fast. This work analyzes different strategies that could be potentially pursued to enhance its coverage and improve its spectral compatibility with VDSL2 systems. We carry out an extensive simulation study to evaluate a) capacity boundaries of current G.fast systems; b benefits of increasing MAXATP, Bmax and power spectrum density (PSD) mask levels; and c) spectral shaping as means to improve G.fast compatibility. Our simulation results show that increasing MAXATP and Bmax boosts data rates and coverage in short loop scenarios, whereas improvements in long loops performance are only determined by MAXATP. Since such modifications generally increase the interference on legacy systems, we propose to perform power back-off (PBO) in order to improve G.fast spectrum-compatibility. As a proof of concept we adopt the PBO from VDSL2 with a fixed parameter set. Although clearly not optimized for the combination of TDD G.fast and FDD legacy systems and despite the simplicity of the adopted approach, our results indicate that spectral shaping can be an effective means to turn G.fast into a more spectrum-friendly system