Stefano Galli

Recent Developments in the Standardization of Power Line Communications within the IEEE

Broadband connectivity to and within the home has been available to consumers for some time through various technologies. Among those technologies, power line communications is an excellent candidate for providing broadband connectivity as it exploits an already existing infrastructure. This infrastructure is much more pervasive than any other wired alternative (both to and within the home), and it allows virtually every line-powered device to become the target of value- added services. Therefore, PLC may be considered as the technological enabler of a multitude of future applications that probably would not be available otherwise. The most fundamental barrier to the widespread adoption of broadband PLC is the current lack of an international technical standard issued by a credible and globally recognized standards-setting body. Hopefully, this barrier will be eliminated soon through the work of the IEEE P1901 Corporate Standards Working Group. This group, which was created in June 2005, is entering a crucial phase. This article stresses the importance of standardization in the PLC context, gives an overview of the current activities of the IEEE P1901 working group, and also describes some of the technical challenges that the future 1901 standard must address to ensure the success of PLC in the marketplace.

A novel approach to the modeling of the indoor power line channel-Part II: transfer function and its properties

In Part I of this work, we introduced multiconductor-transmission-line (MTL) theory to model the indoor power-line (PL) channel. We have also shown that the proposed MTL approach can also be used to take into consideration both the topology of the link and particular wiring practices such as bonding. In this contribution, we continue our bottom-up approach to indoor PL channel modeling and we show that the circuit model found in Part I can be represented in terms of cascaded two-port networks (2PNs) coupled through a single modal transformer. Once the equivalent 2PN representation is obtained, it is possible to represent the whole PL link by means of transmission (ABCD) matrices only. The results presented here allow us to reveal that the PL channel is a more deterministic media than commonly believed and also allows us to unveil interesting properties of the PL channel, such as symmetry, that were previously unknown.

Power Line Communications and the Smart Grid

The design of the Smart Grid requires solving a complex problem of combined sensing, communications and control and, thus, the problem of choosing a networking technology cannot be addressed without also taking into consideration requirements related to sensor networking and distributed control. These requirements are today still somewhat undefined so that it is not possible yet to give quantitative guidelines on how to choose one communication technology over the other. In this paper, we make a first qualitative attempt to better understand the role that Power Line Communications (PLCs) can have in the Smart Grid. Furthermore, we here report recent results on the electrical and topological properties of the power distribution network. The topological characterization of the power grid is not only important because it allows us to model the grid as an information source, but also because the grid becomes the actual physical information delivery infrastructure when PLCs are used.

A novel approach to the modeling of the indoor power line channel part I: circuit analysis and companion model

Multiconductor Transmission Line (MTL) theory is utilized here for modeling the transfer function of power cables in the indoor environment. This approach allows us to determine a circuit model that well characterizes the underlying physics of signal propagation over power-line (PL) cables and that also allows us to account for particular wiring practices common in residential and business environments. In Part II of this work, we will show how the proposed approach allows one to compute a priori and in a deterministic fashion the transfer function of any PL link by using two-port transmission matrices, as commonly done for telephone channel modeling. In this two-part work we will cross several layers of abstraction following a bottom-up approach: starting from the definition of circuit models in this paper, we will arrive at a method for the computation of the transfer function of an indoor PL link in Part II of this work. Moreover, as discussed in Part II, the approach followed here allows us to unveil some special properties of the PL channel that were never reported earlier, such as the symmetry of the transfer function.

G.hn: The new ITU-T home networking standard

Several wired in-home networking technologies are currently available to consumers, although most of them were designed to cope with only one type of home wiring and are not interoperable with each other. In 2006 ITU-T started a standardization project called G.hn for a unified next generation networking technology, operating over all types of in-home wiring (phone line, power line, coaxial cable, and Cat-5 cable). ITU-T Recommendation G.9960, consented in December 2008, is the G.hn foundation: it specifies network architecture, most of the PHY, and some aspects of the MAC. The complete Recommendation is expected within 2009. Besides residential premises, G.hn is intended for small/home offices and public places such as multiple dwelling units, hotels, and conference rooms. This article gives an overview of G.hn technology focusing on the main principles used to build a single transmission scheme for multiple types of wires.

A deterministic frequency-domain model for the indoor power line transfer function

The characterization of the transfer function of the power line (PL) channel is a nontrivial task that requires a truly interdisciplinary approach. Until recently, a common attribute and limitation of existing models for the PL channel transfer function lay in the phenomenological or statistical approach usually followed. This approach allows one to describe the channel only partially, e.g., as dominated by multipath-like effects, and prevents one from unveiling special properties of it. Multiconductor transmission line (MTL) theory was recently found by the authors to be a useful and accurate tool in modeling the PL transfer function while, at the same time, taking into account the wiring and grounding practices mandated by several regulatory bodies for commercial and residential premises. Crossing several layers of abstraction and following a bottom-up approach, complex circuit-level models originating from MTL theory can be manipulated and represented in terms of cascaded two-port networks (2PNs), thus allowing one to compute a priori and in a deterministic fashion the transfer function of any PL link. In the present contribution, we present additional analysis and data that validate the accuracy of the MTL approach and further justify its use in the PL channel context. Moreover, we also describe in detail the methodology to follow for modeling both grounded and ungrounded PL links in a unified framework. A consequence of the validity of the proposed modeling is that it can facilitate the process of standardization of the PL transfer function, an important step toward the availability of a commonly agreed upon (set of) channel transfer functions.

Spectrally efficient optical CDMA using coherent phase-frequency coding

We demonstrate feasibility of a spectrally efficient wavelength-division-multiplexing-compatible optical code-division multiple-access system using 16 phase-locked laser lines within an 80-GHz tunable window as frequency bins and an ultrahigh frequency resolution spectral phase encoder-decoder. Coding and decoding using binary [0, /spl pi/] phase chips were demonstrated for four users at 2.5 Gb/s, and a single coded signal was separated from four copropagating signals, with bit-error rate <10/sup -9/.

Advanced signal processing for PLCs: Wavelet-OFDM

There are today broadband power line modems available in retail stores that are based on either conventional OFDM or on Wavelet-OFDM. However, the comparison of these two multicarrier modulation techniques in the specific context of power line communications has been seldom addressed in the literature. In this paper, OFDM and Wavelet OFDM are compared by focusing on two important aspects: transmission efficiency and spectral leakage. It will be shown that, for the case of the power line channel, Wavelet OFDM offers substantial advantages over conventional or windowed OFDM.

A simplified model for the indoor power line channel

We report for the first time some statistical properties of the indoor power line (PL) channel that exhibit some interesting similarities to the wireless channel, although some fundamental differences are also pointed out. In particular, we argue here that, while multipath propagation in wireless channels gives rise to Rayleigh distributed fading, multipath in PL channels gives rise to lognormally distributed fading similarly to shadow fading. We also report for the first time that both channel gain and Root-Mean-Square Delay Spread (RMS-DS) of indoor channels are lognormally distributed, leptokurtic and negatively correlated, thus suggesting that channels that introduce severe multipath are also characterized by large attenuation. These results are used to define a simplified PL channel model useful for comparative analysis of communication schemes and, at the same time, to draw some general conclusions on the design of multicarrier schemes.

Loop makeup identification via single ended testing: beyond mere loop qualification

Digital subscriber lines (DSLs) offer carriers the possibility of exploiting the existing loop plant to deliver high-speed data and voice services. However, before deploying DSL, local loops must be tested in order to see whether they can support service, and at what level. In fact, there are many impairments that could disqualify a loop for supporting DSL services: load coils, excessive loop length, bridged taps, and wideband noise. Single-ended automatic qualification is essential for achieving low-cost deployment of DSL, since it allows loops to be qualified in bulk and does not involve any human intervention at the customers location. An even more ambitious challenge is to fully characterize a loop, i.e., to identify its loop makeup. If it is feasible to perform loop makeup identification via single-ended measurements with sufficient accuracy, then operators will benefit substantially because, besides qualifying a loop for DSL service, this capability will allow the updating of telephone company loop-records. These records can in turn be accessed to support engineering, provisioning and maintenance operations. Despite its potential importance, the possibility of achieving loop makeup identification via single-ended measurements is not widely addressed in the current literature. In the present contribution the feasibility of loop makeup identification via single-ended measurements is presented.