power line communications: applications, trends and recent modeling results dr. stefano galli senior...

Power Line Communications:

Applications, Trends and Recent Modeling Results

Dr. Stefano GalliSenior ScientistTelcordia Technologies [email protected]://www.argreenhouse.com/bios/sgalli/

Copyright © 2006 Telcordia Technologies. All Rights Reserved.

Universita’ di Roma “La Sapienza”, Facolta’ di Ingegneria Elettrica, February 16, 2006Universita’ di Roma “La Sapienza”, Facolta’ di Ingegneria Elettrica, February 16, 2006

Telcordia Technologies Proprietary - Copyright 2006. 2

Outline

1) Applications: access, home network, in-vehicle, and beyond

2) PLC industry associations and IEEE standardization activities

3) Major research issues:

a) Coexistence

b) Channel modeling

4) Conclusions


• First applications date back to early 1920s, on HV lines.

• The first standard is the European CENELEC EN 50065, which mandates the use of the frequency range 3-148.5 kHz (1991).

• The first commercial attempt to use PLC for last mile access dates back to 1997, when Nortel announced the NorWeb partnership with United Utilities (a UK power utility company)

• Limited trials of broadband Internet access through power lines were conducted in Manchester and NorWeb prototypes were able to deliver data at rates around 1 Mbps.

• Cost and commercial viability became questionable and the pilot project was terminated few years later in 1999.

• In the past few years, interest in the technology has picked up again and possible applications have multiplied.

Power Line Communications


Power Line Communications – outdoor

(From ADVANCE, March 2005)



Power Line Communications – indoor


Power Line Communications – smart grid apps



Beyond Outdoor/Indoor…

• PLCs allows for easy in-vehicle networking:– In any vehicles (from automobiles to ships, from aircraft to space

vehicles), separate cabling is used to establish the PHY of a local command and control network which is becoming broadband

– The in-vehicle power distribution network may well perform double-dutydouble-duty, as an infrastructure supporting both power delivery and broadband digital connectivity.

– Weight, space and cost savings (aircraft, auto).– “Plug & Play”

• PLCs as the enabler for truly pervasive and ad-hoc networks: Just look around… power is everywhere

– Traffic lights, lamp posts, etc. can easily become network nodes

– Smart grid applications, better mains utilization and monitoring

– AMR, peak shaving, transformer monitoring, etc.


• PLC technology is still “young” and evolving

• Do we really need another access solution?

• Do the power utility companies really want to enter telecom?

• Is there a solid business case?

• Deregulation and liberalization are fairly recent

• Lack of standardization and interoperability of products

• Not everybody convinced of the technology:• PHY and MAC layers still a big issue

• Until recently, the available channel models could not predict accurately the channel transfer function a priori!!

• Electromagnetic compatibility issues

• Necessity of hybrid infrastructures, between PLC-based networks and existing wireless/fiber/copper-based ones.

Nevertheless, today PLCs are experiencing a renaissance !

Not Widespread Because …


From Brett Kilbourne, UPLC Conference, Sep. 2005


World Trends in PLCs



• 3Com, Cisco, Compaq, Conexant, Enikia, Intel, Intellon, Motorola, (Panasonic), AMD, RadioShack, Texas Instruments

• A non-profit organization

• Provides a forum for the creation of open specification for home power line networking products and services

• Traditionally focused on the indoor environment only.

• Two indoor specifications: 1.0 and A/V.

• Recently, the HomePlug Access BPL Working Group initiative was recently launched. HomePlug BoPL refers to the outdoor environment of power lines. Necessity of addressing outdoor:

• wires used in the home are the same of those coming from outside, and the utilized spectrum is the same• Home networks coming off a common transformer may interfere with each other.

HomePlug Powerline Alliance


Universal Powerline Association (UPA)

• Ambient Corporation, Ascom Powerline Communications, Corinex Communications, DS2, Electricite de France, Ilevo- Schneider Electric Powerline Communications, Itochu, Sumitomo Electric Industries, and TOYOCOM.

• A non-profit organization

• Trade association working to harmonize global standards and regulations, and to deliver UPA certified products which comply with agreed specifications. Covers both home and access.

• In May 2004, the UPA interest group was established and a Memorandum of Understanding was signed in September 2004.


Consumer Electronics Powerline Communication Alliance is a nonprofit corporation with the following members: Hitachi, Sony, Panasonic Toshiba, Mitsubishi, Yamaha, Pioneer.

Established to promote and continuously advance high speed PLC technology to utilize and implement a new generation of consumer electronics products through the rapid, broad and open industry adoption of CEPCA Specifications

The Purpose of Consumer Electronics Powerline Communication Alliance is to– Completely remove the mutual interference between PLC systems

that employ different technologies but use the same bands– Create and standardize technical specifications that enable

different PLC systems to coexist and achieve optimal performance

– Enable creation CEPCA implementations that become an essential function to the widespread usage of CE devices

Consumer Electronics Powerline Comms Alliance (CEPCA)


Open PLC European Research Alliance (OPERA)

• It is a European R&D Project with a budget of about 20 M Euros.

• Scientific and technological objectives of the project are:• Improve current PLC systems, both conditioning the power grid (using couplers and filters) and improving PLC equipment.

• Develop optimal solutions for connection of the PLC access networks to the backbone networks.

• Standardization of PLC systems.


United Power Line Council (UPLC)

• The United Power Line Council (UPLC) is an alliance of electric utilities and technology companies working together to drive the development of Broadband over Power Line (BPL) in a manner that helps utilities and their partners succeed.

• UPLC's efforts are focused in four strategic areas: Business Opportunities, Regulatory & Legislative Advocacy, Technical Operability and Utility Applications .


• The first society to promote standardization was PES, then came the others (EMS, AP, ComSoc)

• In October 2004, ComSoc created a Technical Sub-Committee on PLCs (sub-committee under Emerging Technology).

• In December 2005, The BoG of IEEE ComSoc upgraded the sub-committee to a Full Fledged IEEE Technical Committee:

• S. Galli, Telcordia Technologies, Chair • L. Lampe, University of BC, Vice-Chair and Events Liaison• R. Fantacci, University of Florence, Vice-Chair

• Haniph Latchman, University of Florida, Publications Liaison• Jim Mollenkopf, Current Technologies (VP), Standards Liaison• Peter Griffin, RadioShack Corporation, External Relations

• Broad consensus: 70+ members (industry, academia, retail)

The Role of IEEE


The Role of the IEEE ComSoc Technical Committee

• The interests of the committee span all the areas of PLCs, e.g., access, home networking, and in-vehicle applications.

• The committee will organize events in the PLC area, sponsor PLC conferences, contribute to the organization of technical events along ComSoc flagship conferences, and will promote the realization of special issues on leading ComSoc journals and magazines.

• The committee also promotes ComSoc involvement in the development of IEEE Standards in the area of PLCs

• Jim Mollenkopf nominated as Co-Chair BPL PHY-MAC Working Group

• Participates to the BoPL study group, to standardization efforts; will organize events, special issues, publications, etc.

• IEEE Communications Magazine special issue: “Power line local area networking,” April 2003• IEEE Communications Magazine special issue: “Broadband is Power: Internet Access Through the Power Line Network ,” May 2003• IEEE Journal on Selected Areas in Communications special issue on Power Line Communications, July 2006


IEEE Standardization Activities

P1901

• Focuses on MAC/PHY aspects and was officially approved by the IEEE Standards Board on 4 June 2005.

• The Working Group is co-chaired by Jim Mollenkopf (Current Technologies) and Jean-Philippe Faure (Snider Electric).

• P1901 operates as an entity standards development group, where all members are organizations instead of individuals.

• As of this date, 28 entities are members. The group has agreed use cases for in-home and access BPL, and will be developing detailed requirements in the coming months.

• Meetings are open to all (members and non-members), and the next meeting is in March 26-30 during ISPLC 2006 (Orlando Florida).

• More information can be found at the P1901 website at:http://grouper.ieee.org/groups/1901/index.html



P1775

• The P1775 effort focuses on specific measurement issues associated with BPL emissions.

• This group is chaired by Aron Viner.

• This group has formed three task groups focused on immunity measurements methods, emissions measurements methods, and overall network description.

• The next P1775 meeting will be during ISPLC 2006.

• Further information is available from the chair at [email protected]



P1675

• P1675 is focused on developing standards for equipment testing and installation.

• This effort is chaired by Terry Burns.

• An initial draft has been produced, and is currently being reviewed and revised by the Working Group.

• The next P1675 meeting is scheduled during ISPLC 2006.


Coexistence Issues

• There is no demarcation between access and in-home power line cables it is a bus running from sub-station transformer to every plug in the home

• Access signals and in-home signals must co-exist

From Mike Stelts (CEPCA), UPLC Conference, Sep. 2005


• Power line cables are a shared medium, like coax cable and unlike DSL

• Signals in your home become interference for your neighbor, and viceversa

• Not only complicated MAC problem, but also security issues

Coexistence Issues

From Mike Stelts (CEPCA), UPLC Conference, Sep. 2005


Coexistence Issues – a dilemma for standardization

• IEEE standardization for PLCs (P1901) has started few months ago, and Ballot Draft of standard is expected by mid 2006

• There are today two philosophies:• one technology for everything (all applications) and also for everywhere in the world• multiple technologies, but all constrained to coexist with each other anywhere and everywhere.

• Both positions seem extreme:• Difficult to envision only one technology for everything and everywhere given the wide variability of environments• Difficult to envision optimized solutions if so many constraints about coexistence are imposed.

• Probably, other approaches should be pursued:• Network segmentation, e.g. at the meter• Software Defined Radio approach

• Consumer pays premium of the DSP and the hardware of the SDR in the consumer electronic equipment, but has capability to change or upgrade its modem by downloading new software.


• InternationalInternational:

– wiring system uses a star (e.g., a single cable feeds all of the wall outlets in one room only) or tree arrangement

– ground bonding at the main panel

• Europe: Europe: – two wire (ungrounded) or three wire (grounded) outlets – If three phase supply is used, separate rooms in the same

apartment may be on different phases

• UK exceptions: UK exceptions: – special rings: a single cable runs all the way round part of a

house interconnecting all of the wall outlets; a typical house will have three or four rings.

– neutral not grounded in the home

– New buildsNew builds: three phase with four of five wires (neutral, ground)

– Problematic old wiringProblematic old wiring: two-wire 1 phase, neutral and ground share common wire

Channel Modeling Issues: Wide Variability of Environment


• Wiring and grounding come in many flavors, and this makes modem design much more challenging.

• However, international harmonization is happening:

– Typical outlets have three wires: hot, neutral and ground

– Classes of appliances (light, heavy duty appliances, outlets, etc.) fed by separate circuits

– Neutral and ground separate wires within the home, except for the main panel where they are bonded

Although complex topologies may exist, today’s

regulations can simplify analysis of signal transmission

International Harmonization


SERVICEPANELFEED

LIGHTING CIRCUITSNon-symmetric geometry

for B&W

RECEPTACLE CIRCUITS15-20 amps, branching, and

symmetric geometry for B&W

GROUNDBONDING

EMBEDDED APPLIANCES50 amps, non-branching, and symmetric

geometry for B&W

Wiring and Grounding Practices


NM-B

BX

Inside wiring environment


Inside wiring environment


RSB

BLK BLK

WHT WHT

GND GND

RTN HOT

RSB

L3 L2

CIRCUIT BREAKERS

SERVICE TRANSFORMER

SERVICE DROP

Wiring and Grounding Practices

Typical service panel, showing Typical service panel, showing bonding between the neutral and bonding between the neutral and

the ground cable through the ground cable through RRSBSB. .

Paradoxically, grounding and bonding has been completely

ignored in indoor PLC modeling


B

0.3 FREQUENCY ( MHz) 30.0

LOS

S

3dB

/DIV

Ground bonding introduces non negligible resonant modes due to pair-mode excitation.

Effects of Bonding on Signal Propagation

Same topology with bonding

Topology without bonding


Two-Conductor Transmission Line Model Hooijen - ISPLC’98

• Straightforward approach, follows TPC/coax modeling• Frequency domain model• Transfer function can be computed a priori

• Limitations:• Knowledge of whole topology is needed • Accuracy of results depend on accuracy of cable models• Incomplete model, presence of third wire not included so that wiring and grounding practices not explicitly accounted for

• Some aspects of signal propagations cannot be explained with this model

Channel Modeling Approaches


Multipath ModelPhillips, and Dostert & Zimmermann - ISPLC’99, T-COM’02

The multipath nature arises from the presence of several branches and impedance mismatches that cause reflections.


X A1(f)

A2(f)

LAB

LAY

A

B

Y

B(f)

LXA

Direct path XAY (i=0):

10

0

1 A

AYXA

g

LLd

Secondary paths XABA(BA)i-1Y(i>0):

Bi

ABAA

AYABXA

ig

LiLLid

1221 11

2


The multipath model is a good model, but has some limitations: • modeling is based on parameters that can be estimated only after the actual channel transfer function has been measured• wiring and grounding practices not explicitly accounted for, but “phenomenologically” included• computational cost in estimating the delay, amplitude and phase associated with each path (time-domain model) drawback for some indoor/in-vehicle channels.


gi: is a complex number that depends on the topology of the link;

(f) is the attenuation coefficient (skin effect and dielectric loss);

i is the delay associated with the ith path;

di is the path length;

N is the number of non-negligible paths.

N

i

dffji

ii eegfH1

)(2)(


B

0 5 10 15 20 25 30-25

-20

-15

-10

-5

0

5

Frequency in MHz

Mag

nitu

de o

f Tra

nsfe

r Fu

nctio

n (d

B)

LOS

S

4dB

/DIV


Effects of Bonding on Signal Propagation

Current Models(no bonding)

Measurements(when bonding present)


Multi-Conductor Transmission Line ModelGalli & Banwell - ISPLC’01, T-PD’05 Part I - II

• Based on Multi-conductor Transmission Line Theory and Modal Decomposition: can take into account multi-conductor nature of PL cables, as well as wiring and grounding practices.

• Transfer function can be computed a priori• Frequency domain model (limited computational complexity).• Allows to unveilunveil interesting and useful properties of the PLC, e.g.

superposition of resonant modes, isotropy of channel.

• Limitations:• Knowledge of whole topology is needed• Accuracy of results depend on accuracy of cable models

Recent Results on Channel Modeling: MTL



Three-conductor Analysis

• A three-conductor cable supports six propagating modes (TEM approximation): three spatial modes (differential, pair and common modes) each for two directions of propagation.

• The differential mode current, generally the desired signal.

• The pair-mode current (flowing between ground and the white/black wires “tied together”). This mode is excited due to certain wiring and grounding practices.

• The third common mode current Icm represents overall cable

current imbalance, which creates a current loop with earth ground. Lossy mode, can be neglected.

Pair-mode has been completely neglected in previous models



MTL modeling requires crossing several layers of abstraction:

• Derive the differential mode and pair mode circuit models of power line link • Tie the two modes through a transformer• Describe each circuit models as cascaded two-port networks• Obtain transfer function using transmission matrices

Treat with same formalism

both grounded and ungrounded links


0 5 10 15 20 25 30-25

-20

-15

-10

-5

0

5

Frequency in MHz

Mag

nitu

de o

f Tra

nsfe

r Fu

nctio

n (d

B)

MTL Approach: Better Accuracy

Current models (no bonding)MTL model

LOS

S

4dB

/DIV


B


Concluding Remarks

• We have today a better understanding of the PL channel

• PL channel more deterministic than originally thought– Determinism should be exploited for transceiver optimization

• Plethora of grounding and wiring practices, but harmonization of regulations can simplify analysis of signal transmission

– Wiring and grounding practices must be taken into account

• Lack of traditional research funding has kept PLC research out of academia, so that most work has been done within an industrial environment and has been directed towards winning skepticism

– Lack of a solid theoretical approach!

• System optimization is challenging– PLCs is one of the most inter-disciplinary fields we have

power line communications: applications, trends and recent modeling results dr. stefano galli senior...

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