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1. INTRODUCTION

Different communication technologies are being used for the transmission of information

from one end to another depending on the feasibility and needs. Some include Ethernet cables,

fiber optics, wireless transmission, satellite transmission, etc. A vast amount of information

travels through the entire earth every day and it creates an essential need for a transmission

medium that is not only fast but economically reasonable as well. One of the technologies that fit

in the above stated criteria is Power Line Communication.

Power line communication or power line carrier (PLC), also known as power line digital

subscriber line (PDSL), mains communication, power line telecom (PLT), power line

networking(PLN), or broadband over power lines (BPL) are systems for carrying data on a

conductor also used for electric power transmission. The communication flow of today is very

high. Many applications are operating at high speed and a fixed connection is often preferred. If

the power utilities could supply communication over the power-line to the costumers it could

make a tremendous breakthrough in communications. Every household would be connected at

any time and services being provided at real-time. Using the power-line as a communication

medium could also be a cost-effective way compared to other systems because it uses an existing

infrastructure, wires exists to every household connected to the power-line network. The

deregulated market has forced the power utilities to explore new markets to find new business

opportunities, which have increased the research in power-line communications the last decade.

The research has initially been focused on providing services related to power distribution such

as load control, meter reading, tariff control, remote control and smart homes. These value-added

services would open up new markets for the power utilities and hence increase the profit. The

moderate demands of these applications make it easier to obtain reliable communication. Firstly,

the information bit rate is low; secondly, they do not require real-time performance.

During the last years the use of Internet has increased. If it would be possible to supply

this kind of network communication over the power-line, the utilities could also become

communication providers, a rapidly growing market. On the contrary to power related

applications, network communications require very high bit rates and in some cases real-time

responses are needed (such as video and TV). This complicates the design of a communication

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system but has been the focus of many researchers during the last years. Systems under trial exist

today that claim a bit rate of 1 Mb/s, but most commercially available systems use low bit rates,

about 10-100 kb/s, and provides low-demanding services such as meter reading. The power-line

was initially designed to distribute power in an efficient way, hence it is not adapted for

communication and advanced communication methods are needed. Today’s research is mainly

focused on increasing the bit rate to support high-speed network applications.

While the idea of sending communication signals on the same pair of wires as are used

for power distribution is as old as the telegraph itself, the number of communication devices

installed on dedicated wiring far exceeds the number installed on AC mains wiring. The reason

for this is not, as one might think, the result of having overlooked the possibility of AC mains

communication until recent decades. In the 1920’s at least two patents were issued to the

American Telephone and Telegraph Company in the field of ―Carrier Transmission Over Power

Circuits‖. United States Patents numbers 1,607,668 and 1,672,940, filed in 1924 show systems

for transmitting and receiving communication signals over three phase AC power wiring. Others

have suggested that what was required for power line communication to move into the main

stream was a commercialized version of military spread spectrum technology. It has been

suggested that this is what was needed in order to overcome the harsh and unpredictable

characteristics of the power line environment. Commercial spread spectrum power line

communication has been the focus of research and product development at a number of

companies since the early 1980’s. After nearly two decades of development, spread spectrum

technology has still not delivered on its promise to provide the products required for the

proliferation of power line communication.

A wide range of power line communication technologies are needed for different applications,

ranging from home automation to Internet access. Electrical power is transmitted over long

distances using high voltage transmission lines, distributed over medium voltages, and used

inside buildings at lower voltages. Most PLC technologies limit themselves to one set of wires

(such as premises wiring within a single building), but some can cross between two levels (for

example, both the distribution network and premises wiring). Typically transformers prevent

propagating the signal, which requires multiple technologies to form very large networks.

Various data rates and frequencies are used in different situations.

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1.1 Basic

Power line communications systems operate by impressing a modulated carrier signal on

the wiring system. Different types of power line communications use different frequency bands,

depending on the signal transmission characteristics of the power wiring used. Since the power

distribution system was originally intended for transmission of AC power at typical frequencies

of 50 or 60Hz, power wire circuits have only a limited ability to carry higher frequencies. The

propagation problem is a limiting factor for each type of power line communications.

Data rates and distance limits vary widely over many power line communication

standards. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission

lines may carry one or two analog voice circuits, or telemetry and control circuits with an

equivalent data rate of a few hundred bits per second; however, these circuits may be many miles

long. Higher data rates generally imply shorter ranges; a local area network operating at millions

of bits per second may only cover one floor of an office building, but eliminates the need for

installation of dedicated network cabling.

Fig 1.1 : A Typical Power Line

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2. LITRATURE SURWEY

In the past few years, the availability of much faster digital signal-processing capabilities

and the development of sophisticated modulation, encoding, and error correction schemes have

allowed the introduction of new, low-power designs for carrier current devices. These new

designs can overcome earlier technical bandwidth limitations caused by the inherent noise and

impedance mismatches that are common on commercial power lines. The new designs include

the use of spread spectrum or multiple carrier techniques that employ highly adaptive algorithms

to effectively counter the noise on the line. They also include the use of ―turbo code‖ (TC)

techniques such as concatenated Reed-Solomon Forward Error Correction (FEC) and

convolutional coding employing the Viterbi algorithm, which can provide decibel (dB) gains that

approach Shannon’s famous channel capacity law1. PLC Access and In-home technologies

currently suffer from the absence of recognized international and, in most cases, national

standards. Consequently, there is relatively little detailed public technical information available

on PLC systems, reflecting their proprietary state. BPL manufacturers today maintain a secretive

posture with respect to the technical details of their equipment. Although the US does follow the

electrical power standards set by the International Electro technical Committee (IEC), each

power company has wide flexibility in how their own transmission facilities are implemented.

Thus it is difficult to render accurate generalizations about even the underlying power structure

that facilitates PLC. This will improve over the next few years after a number of current

standardization efforts, discussed later, are concluded.

The Power Lines available today were built for the purpose of power transmission from one

place to another. The attempt to transmit data over these power lines leads to the reception of a

lot of noise. This noise is due to the numerous devices connected to the power lines. An analysis

of this noise and their characteristics helps us better understand how to tackle the problem of

noise elimination in the power lines. The characteristics of the modulation techniques and their

subsequent analysis give us an idea of the advantages and disadvantages of each technique. The

receiver contains a phase locked loop. We studied the modulation techniques and compared their

performance in the present of noise. Finally Spread Spectrum technology is reviewed for the use

of communications on power lines. Spread Spectrum is a method of signal modulation where the

transmitted signal occupies a bandwidth considerably higher than the minimum necessary to

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send the information and some function other than the information being sent is used to increase

this Bandwidth. Spread Spectrum was found to be unsuitable and rather detrimental for the

PLCC system.

Over the past few years advances in signal processing technology have enabled the

advent of modem chips that are able to overcome the transmission difficulties associated with

sending communications signals over electrical power lines. In the United States, this capability

has been termed ―Broadband over Power Lines‖ or BPL. There are two predominant types of

BPL communications configurations: Access BPL and In-Home BPL. Access BPL is comprised

of injectors (used to inject High Frequency (HF) signals onto medium or low voltage power

lines), extractors (used to retrieve these signals) and repeaters (used to regenerate signals to

prevent attenuation losses). In addition to taking advantage of the power line infrastructure, In-

Home BPL modems utilize the existing house wiring to provision a Local Area Network (LAN)

that can be used throughout the home. One of the largest commercial markets for BPL is the

ability to provide Internet Services by means of the Transmission Control Protocol/Internet

Protocol (TCP/IP) protocols, which can support voice, data, and video services. Another

significant benefit of BPL is the ability to employ ―intelligent‖ power line networks that make

use of Supervisory Control and Data Acquisition (SCADA)i devices, dynamic provisioning, and

other forms of modernized electrical power networks. A SCADA system can save time and

money by reducing the need for service personnel to physically visit each site for inspection, data

collection, and routine logging or even to make adjustments. The benefits also include the ability

for real-time monitoring, system modifications, troubleshooting, increased equipment life, and

automatic report generating.

The Federal Communications Commission (FCC) monitors approximately 59,000

frequencies for military, National Security & Emergency Preparedness (NS/EP), and other

purposes. A key concern associated with BPL is that coupling of HF signals onto unshielded

wiring, such as that used for outdoor power lines, may generate interference signals that could

impact licensed services such as amateur radio, or ―hams‖. Public safety agencies including fire,

police, the Red Cross and other agencies also depend on the use of the special propagation

properties found only in the HF radio spectrum. This Technical Information Bulletin (TIB)

examines the architecture and considers possible benefits and concerns of BPL technology with

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respect to the National Communications System (NCS) and the communication requirements for

NS/EP.

According to the Institute for Electronic and Electrical Engineers (IEEE)iv and the International

Telecommunications Union (ITU) the United States is lagging behind other countries in the

deployment of broadband telecommunications networks. In December 2005 the ITU documented

(see Figure 1) that among the top 20 worldwide economies, US broadband deployment ranks in

the bottom 20%. In the US, broadband services to the home are largely provided by cable

modems and digital subscriber loop (DSL) services.

Fig 2.1: Broadband Penetration

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3. WORKING OF POWER LINE COMMUNICATON

3.1 Operating Principle

PLC is like any other communication technology whereby a sender modulates the data to

be sent, injects it onto medium, and the receiver de-modulates the data to read it. The major

difference is that PLC does not need extra cabling, it re-uses existing wiring. Considering the

pervasiveness of power lines, this means with PLC, virtually all line- powered devices can be

controlled or monitored. The communication device used for the communication over the power

lines is a MODEM, commonly known as Power Line MODEM (PLM). It works as both

transmitter and receiver, i.e., it transmits and receives data over the power lines. A power line

modem not only modulates the data to transmit it over the power lines and but also demodulates

the data it receives from the power lines. By using modulation techniques, binary data stream is

keyed on to a carrier signal and then coupled on to the power lines by PLM. At the receiver end

another PLM detects the signal and extracts the corresponding bit stream.

Fig 3.1: Signal, Data and Information Flow

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The above image shows the working of a PLCC system. Data is processed before

transmission on power lines according to the above figure. First data is modulated & filtered and

then by using couplers, it is sent over the power lines.

Power-line communication is based on electrical signals, carrying information,

propagating over the power-line. A communication channel is defined as the physical path

between two communication nodes on which the communication signal is propagated. The

quality is estimated from how good the communication is on a channel. The quality is mostly a

parameter of the noise level at the receiver and the attenuation of the electrical signal at different

frequencies. The higher the noise level the harder it is to detect the received signal. If the signal

gets attenuated on its way to the receiver it could also make the decision harder because the

signal gets more hidden by the noise.

3.1.1 PLC Technology

When discussing communication technology, it is often useful to refer to the 7-layer OSI

model. Some PLC chips can implement only the Physical Layer of the OSI model, while others

integrate all seven layers. One could use a Digital Signal Processor (DSP) with a pure software

realization of the MAC and an external PHY circuit, or an optimized System-on-Chip (SoC)

solution, which includes the complete PLC – MAC and PHY. The Cypress CY8CPLCXX series

is an example of the latter, with a ready-to-use Physical and Network layer, and a user-

programmable application layer. Before moving on to the applications of PLC, let’s first

understand the various aspects of the Physical layer by viewing it as three segments on the basis

of data rate.

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Fig 3.2: PLC Technology Classification

3.1.2 Power Line Characteristics

The use of power line cables for HF data transmission presents a number of technically

difficult challenges. In addition to large attenuation, the power line cable network is one of the

most electrically contaminated environments. Power line networks have been assembled with a

variety of materials and cross sections are joined almost at random. This means that the inductive

reactance along the wire itself will render a wide range of characteristic impedances at different

points in the network.

Further, the power line network terminal impedance varies both at different

communication signal frequencies and with the time of day as the network’s electrical load

pattern varies. Atmospheric conditions, such as temperature, humidity, barometric pressure,

lightning, sunspots, and the distance above ground all have an effect. Power-transmission-line

engineering is a highly specialized field.

Despite the aforementioned transmission impediments, MV power lines are excellent

carriers of RF energy as they are comprised of open wire equipment. The number of MV line

crossovers is much less than is found on LV lines. Thus, a low power transmission of only 10

watts can be sufficient to overcome distances of 500 kilometers or more.

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3.1.3 PLC Modems/Transceivers

PLC Transceiver is the key component of a PLCC system. It is the device which

transmits & receives data to & from the power lines and acts as a hub between the power stations

and our Computers/Network utilization devices. They are wired with the electrical voltage lines

at home or business and work on two modes – transmit mode and receive mode. In transmit

mode, they simply receive data from receiver end installed on the same network and further

transmit them. In receive mode, they work the opposite way.

A number of companies provide PLC transceivers and other networking devices for

PLCC communication. A PLC transceiver is shown in the following image.

Fig 3.3: PLC Modem/ Transceivers

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3.2 Modulation Technique

Characteristics of the power line channel continuously vary with time and load. So

conventional modulation techniques like ASK, FSK or PSK cannot be employed with them.

PLCC needs a technique that can deal with the unpredictable attenuation and phase shifts.

Modulation techniques that opt lower frequency ranges of 35 KHz to 95 KHz can

perform better as compared to the ones using the whole available frequency band. OFDM

(Orthogonal Frequency Division Multiplexing) is the modulation technique that is used in Home

Plug specification network appliances. In OFDM, information is modulated on to multiple

carriers, where each carrier occupies its own frequency in the range of 4.3 to 20.9 MHz.

Incoming bit stream is de-multiplexed into N number of parallel bit streams each with 1/N of

original bit rate which are then modulated on N orthogonal carriers. By using multiple carriers at

a time, the modulation technique uses the available spectrum most efficiently. During the

transmission, each frequency is monitored and if any interference, noise or data loss occurs, the

responsible frequency is removed. However this technique does not perform well when a large

attenuation and jamming occurs in the communication channel, but still it can be very efficient

comparatively.

Fig 3.4: Comparison of Modulation Schemes

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3.2.1 PLCC Standards

Proper standardization makes a technology comprehensive and deployable. A few standards

pertaining to PLCC exist in different parts of the world.

1. European Committee for Electro technical Standardization (CENELEC)

Countries from the Western Europe formed a standard known as CENELEC standard to

standardize the issues and concerns related to power line communication. This standard defines

standards for allowed frequency ranges and output voltages for the communication over power

lines.

A frequency range of 3 to 148.5 KHz is allowed for the communication and this range is

further divided in 5 sub-bands. These are according to the following table:

Band

Frequency Range

Usage

3KHz – 9KHz This range is restricted to the Energy Providers.

A-Band 9KHz-95KHz Restricted to the energy providers and their

concession holders

B-Band 95KHz-125KHz

Restricted to the energy providers customers.

There is no access rule defined for this frequency

range.

C-Band 125KHz-140KHz

Restricted to energy providers customers.

Simultaneous operations on multiple systems are

possible for this frequency band, A protocol

named Carrier Sense Multiple Access Protocol is

defined for this using a frequency of 132.5KHz.

D-Band 140KHz-148.5KHz Restricted to customers. No access protocol is

defined for this band.

2. Federal Communications Commission (FCC)

FCC standardizes the frequency ranges and transmitted power ranges for the power line

communications in North America. The allowed base frequencies range from 0 to 530 KHz.

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3. HomePlug Power line Alliance

HomePlug Power line Alliance is a group of companies dedicated to improve the

technology for the networking and communication over power lines. In June 2001, first

specification named HomePlug 1.0 was launched. The standard uses a physical layer protocol

(PHY) based on 128 equally divided carrier OFDMs (Orthogonal Frequency Division

Multiplexing) from a frequency range of 0 to 25MHz. It uses concatenated Viterbi and Reed

Solomon coding for payload data, Turbo product codes for control data and BPSK, DBPSK,

DQPSK or ROBO modulation with a cyclic prefix for modulation of the data.

4. IEEE 1901

Institute of Electrical and Electronics Engineers (IEEE) stated a standard named IEEE 1901 for

high speed power line communications. This group was formed in 2005 and gave its first

standard in 2010 which includes two different physical layers, first one based on OFDM

modulation and the other one based on wavelet modulation. Network devices that employ only

OFDM physical layer will not be interoperable with the device that employ Wavelet physical

layer.

3.2.2 How signals are superimposed on Power Lines?

There are two different ways by which we can connect a PLC unit with the power lines –

capacitive coupling and inductive coupling. In capacitive coupling, a capacitor is used to

superimpose the modulated signal on to the network’s voltage waveform. Another way is

inductive coupling which employs an inductor to couple the signal with the network’s waveform.

No physical connection is required to establish inductive coupling. This makes it safer as

compared to capacitive coupling. However this method has higher tendency to lose the signal

during coupling.

3.3 Long haul, low frequency

Utility companies use special coupling capacitors to connect radio transmitters to the

power-frequency AC conductors. Frequencies used are in the range of 24 to 500 kHz, with

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transmitter power levels up to hundreds of watts. These signals may be impressed on one

conductor, on two conductors or on all three conductors of a high-voltage AC transmission line.

Several PLC channels may be coupled onto one HV line. Filtering devices are applied at

substations to prevent the carrier frequency current from being bypassed through the station

apparatus and to ensure that distant faults do not affect the isolated segments of the PLC system.

These circuits are used for control of switchgear, and for protection of transmission lines. For

example, a protective relay can use a PLC channel to trip a line if a fault is detected between its

two terminals, but to leave the line in operation if the fault is elsewhere on the system.

On some power lines in the former Soviet Union, PLC-signals are not fed into the high

voltage line, but in the ground conductors, which are mounted on insulators at the pylons.While

utility companies use microwave and now, increasingly, fiber optic cables for their primary

system communication needs, the power-line carrier apparatus may still be useful as a backup

channel or for very simple low-cost installations that do not warrant installing fiber optic lines.

Power line carrier communication (PLCC) is mainly used for telecommunication, tele-protection

and tele-monitoring between electrical substations through power lines at high voltages, such as

110 kV, 220 kV, 400 kV. The major benefit is the union of two applications in a single system,

which is particularly useful for monitoring electric equipment and advanced energy management

techniques (such as OpenADR and OpenHAN).

The modulation generally used in these system is amplitude modulation. The carrier

frequency range is used for audio signals, protection and a pilot frequency. The pilot frequency is

a signal in the audio range that is transmitted continuously for failure detection. The voice signal

is compressed and filtered into the 300 Hz to 4000 Hz range, and this audio frequency is mixed

with the carrier frequency. The carrier frequency is again filtered, amplified and transmitted. The

transmission power of these HF carrier frequencies will be in the range of 0 to +32 db W. This

range is set according to the distance between substations. PLCC can be used for interconnecting

private branch exchanges (PBXs).

To sectionalize the transmission network and protect against failures, a "wave trap" is

connected in series with the power (transmission) line. They consist of one or more sections of

resonant circuits, which block the high frequency carrier waves (24 kHz to 500 kHz) and let

power frequency current (50 Hz - 60 Hz) pass through. Wave traps are used in switchyard of

most power stations to prevent carrier from entering the station equipment. Each wave trap has a

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lightning arrester to protect it from surge voltages. A coupling capacitor is used to connect the

transmitters and receivers to the high voltage line. This provides low impedance path for carrier

energy to HV line but blocks the power frequency circuit by being a high impedance path. The

coupling capacitor may be part of a capacitor voltage transformer used for voltage measurement.

Power line carriers may change its transmission system from analog to digital to enable

Internet Protocol devices. Digital power line carrier (DPLC) was developed for digital

transmission via power lines. DPLC has the required quality of bit error rate characteristics and

transmission ability such as transmitting information from monitored electric-supply stations and

images. Power line carrier systems have long been a favorite at many utilities because it allows

them to reliably move data over an infrastructure that they control. Many technologies have

multiple applications. For example, a communication system bought initially for automatic meter

reading can sometimes also be used for load control or for demand response applications.

A PLC carrier repeating station is a facility, at which a power line communication (PLC)

signal on a power line is refreshed. Therefore the signal is filtered out from the power line,

demodulated and modulated on a new carrier frequency, and then re-injected onto the power line

again. As PLC signals can carry long distances (several 100 kilometers), such facilities only exist

on very long power lines using PLC equipment. PLC is one of the technologies used for

automatic meter reading. Both one-way and two-way systems have been successfully used for

decades. Interest in this application has grown substantially in recent history—not so much

because there is an interest in automating a manual process, but because there is an interest in

obtaining fresh data from all metered points in order to better control and operate the system.

PLC is one of the technologies being used in Advanced Metering Infrastructure (AMI) systems.

In a one-way (inbound only) system, readings "bubble up" from end devices (such as

meters), through the communication infrastructure, to a "master station" which publishes the

readings. A one-way system might be lower-cost than a two-way system, but also is difficult to

reconfigure should the operating environment change. In a two-way system (supporting both

outbound and inbound), commands can be broadcast out from the master station to end devices

(meters) -- allowing for reconfiguration of the network, or to obtain readings, or to convey

messages, etc. The device at the end of the network may then respond (inbound) with a message

that carries the desired value. Outbound messages injected at a utility substation will propagate

to all points downstream. This type of broadcast allows the communication system to

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simultaneously reach many thousands of devices—all of which are known to have power, and

have been previously identified as candidates for load shed. PLC also may be a component of a

Smart Grid.

3.4 Medium frequency (100 kHz)

3.4.1 Home control (narrowband)

Power line communications technology can use the electrical power wiring within a

home for home automation: for example, remote control of lighting and appliances without

installation of additional control wiring.

Typically home-control power line communication devices operate by modulating in a

carrier wave of between 20 and 200 kHz into the household wiring at the transmitter. The carrier

is modulated by digital signals. Each receiver in the system has an address and can be

individually commanded by the signals transmitted over the household wiring and decoded at the

receiver. These devices may be either plugged into regular power outlets, or permanently wired

in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same

distribution system, these control schemes have a "house address" that designates the owner. A

popular technology known as X10 has been used since the 1970s.

The "universal power line bus", introduced in 1999, uses pulse-position modulation

(PPM). The physical layer method is a very different scheme than the X10. Lon Talk, part of the

Lon Works home automation product line, was accepted as part of some automation standards.

3.4.2 Low-speed narrow-band

Narrowband power line communications began soon after electrical power supply

became widespread. Around the year 1922 the first carrier frequency systems began to operate

over high-tension lines with frequLencies of 15 to 500 kHz for telemetry purposes, and this

continues. Consumer products such as baby alarms have been available at least since 1940.In the

1930s, ripple carrier signaling was introduced on the medium (10-20 kV) and low voltage

(240/415 V) distribution systems. For many years the search continued for a cheap bi-directional

technology suitable for applications such as remote meter reading. EDF (French power)

prototyped and standardized a system called "spread frequency shift keying" or S-FSK. It is now

a simple low cost system with a long history, however it has a very slow transmission rate,

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between 200 and 800 bits per second. In the 1970s, the Tokyo Electric Power Co ran

experiments which reported successful bi-directional operation with several hundred units.

Since the mid-1980s, there has been a surge of interest in using the potential of digital

communications techniques and digital signal processing. The drive is to produce a reliable

system which is cheap enough to be widely installed and able to compete cost effectively with

wireless solutions. But the narrowband power line communications channel presents many

technical challenges, a mathematical channel model and a survey of work is available.

Applications of mains communications vary enormously, as would be expected of such a widely

available medium. One natural application of narrow band power line communication is the

control and telemetry of electrical equipment such as meters, switches, heaters and domestic

appliances. A number of active developments are considering such applications from a systems

point of view, such as demand side management. In this, domestic appliances would intelligently

co-ordinate their use of resources, for example limiting peak loads.

Control and telemetry applications include both 'utility side' applications, which involves

equipment belonging to the utility company up to the domestic meter, and 'consumer-side'

applications which involves equipment in the consumer's premises. Possible utility-side

applications include automatic meter reading (AMR), dynamic tariff control, load management,

load profile recording, credit control, pre-payment, remote connection, fraud detection and

network management, and could be extended to include gas and water. A project of EDF, France

includes demand management, street lighting control, remote metering and billing, customer

specific tariff optimization, contract management, expense estimation and gas applications

safety. There are also many specialized niche applications which use the mains supply within the

home as a convenient data link for telemetry. For example, in the UK and Europe a TV audience

monitoring system uses power line communications as a convenient data path between devices

that monitor TV viewing activity in different rooms in a home and a data concentrator which is

connected to a telephone modem.

3.4.3 Medium-speed narrow-band

The Distribution Line Carrier (DLC) System technology used a frequency range of 9 to

500 kHz with data rate up to 576 k bit/s. A project called Real-time Energy Management via

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Power lines and Internet (REMPLI) was funded from 2003 to 2006 by the European

Commission. In 2009, a group of vendors formed the Power line Intelligent Metering Evolution

(PRIME) alliance. As delivered, the physical layer is OFDM, sampled at 250 kHz, with 512

differential phase shift keying channels from 42–89 kHz. Its fastest transmission rate is 128.6

kilobits/second, while its most robust is 21.4 kbit/s. It uses a convolutional code for error

detection and correction. The upper layer is usually IPv4.

In 2011, several companies including distribution network operators (ERDF, Enexis),

meter vendors (Sagemcom, Landis&Gyr) and chip vendors (Maxim Integrated, Texas

Instruments, STMicroelectronics) founded the G3-PLC Alliance to promote G3-PLC technology.

G3-PLC is the low layer protocol to enable large scale infrastructure on the electrical grid. G3-

PLC may operate on CENELEC A band (35 kHz to 91 kHz) or CENELEC B band (98 kHz to

122 kHz) in Europe, on ARIB band (155 kHz to 403 kHz) in Japan and on FCC (155 kHz to 487

kHz) for the US and the rest of the world. The technology used is OFDM sampled at 400 kHz

with adaptive modulation and tone mapping. Error detection and correction is made by both a

convolutional code and Reed-Solomon error correction. The required media access control is

taken from IEEE 802.15.4, a radio standard. In the protocol, 6loWPAN has been chosen to adapt

IPv6 an internet network layer to constrained environments which is Power line

communications. 6loWPAN integrates routing, based on the mesh network Loading, header

compression, fragmentation and security. G3-PLC has been designed for extremely robust

communication based on reliable and highly secured connections between devices, including

crossing Medium Voltage to Low Voltage transformers. With the use of IPv6, G3-PLC enables

communication between meters, grid actuators as well as smart objects. In December 2011, G3

PLC technology was recognized as an international standard at ITU in Geneva where it is

referenced as G.9903, Narrowband orthogonal frequency division multiplexing power line

communication transceivers for G3-PLC networks.

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3.5 Technical Parameters in PLC Communication

Noise on Residential Power Circuit (RPC):

A variety of noises may occur during the communication caused by the home appliances.

Following are some of the types:

Noise synchronous to the power system frequency (50Hz or 60 Hz) – This type of noise

is generated because of different kind of switching devices.

Noise with a smooth spectrum – The sources of such type of noise is the appliances that

are not operating synchronously with the power line frequency. For example the small

motors with several windings can generate such type of noise.

Single Event Impulse Noise – Switching of devices, that contain a capacitor, generates

such type of noise. The reason is sudden discharge of the capacitor in the RPC.

Periodic Noise – The type of noise is generated by fluorescent lights, television receivers

etc.

These are some ways to reduce the noise in between the communication over power lines:

Implementation of Forward Error Correction (FEC) codes with interleaving can reduce

the noise in category 1, 2 and 3.

Frequency Hopping with the FEC coding can be implemented to deal with the unknown

frequencies.

While modulating the signal on to the power lines, television line frequencies should be

avoided.

Signal to Noise Ratio:

Signal to Noise Ratio (SNR) is a measurement of quality of the signal. It indicates the amount of

the noise in a signal. SNR can be formulated in the following way:

SNR = Received Power / Noise Power

Increasing SNR means increasing the performance of the communication system. By

applying noise filters on household appliances, the noise entering into the power system can be

reduced. However it will increase the cost of the appliances but is a better solution to improve

overall performance.

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Signal Attenuation:

Signal attenuation is basically the reduction in strength of the signal. A signal attenuation

of about 100dB/Km occurs for low voltage power lines and 10dB/km for high voltage lines. It

creates a need of continuous repeaters over a fixed distance. A number of factors that are

responsible for signal attenuation include distance, time, frequency of the signal, etc.

3.6 Application of Power Line Communication

Power Line Communication Is used in various applications, which is listed below.

3.6.1 Meter Reading

Automatic Meter Reading using PLCC technology is quite useful as it saves a lot of

human efforts and also makes the whole system more efficient. The automatic meter reading

system consists of three components, namely, Multifunction Node (MFN), Concentrator &

Communication Node (CCN) and Operation & Management System (OMS). Different

components and their inter-connections are shown in the figure.

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Fig 3.5: A Typical Automatic Meter Reading

MFN is a unit installed in household meters, either incorporated in the meter itself or

externally connected to it. Its function is to take reading of the meter on an hourly basis and store

it in a memory chip. CNN is another part which manages all MFNs within a particular area and

collects meter readings from all MFNs. It is generally installed on substations and needs a

computer. The computer is installed with Operation and Management System (OMS) which

further manages all the data and meter readings from CNNs.

3.6.2 Home Automation

In modern homes, there is a huge requirement of sending digital information, audio, and video all

over the home. Running new wires to support this will increase the burden and cost of

maintenance. To overcome this, PLCC is the right choice to implement home automation

concept. Home automation or also known as Smart Home technology is a collection of systems

and devices in a home that have an ability to interact with each other or function individually in

order to be optimized in best way. Using PLCC technology, existing power wirings of the house

is used to connect home appliances with each other as well as with internet.

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Fig 3.6: A Typical Home Automation Using PLC

Architecture of a PLCC based home automation system is shown in the above image.

Various home appliances are connected within a loop through the existing power cables. This

technology can connect each device with the network which is connected to an AC outlet. All

appliances are also connected with a centralized control panel which controls them.

3.6.3 Home networking (LAN)

Power line communications can also be used in a home to interconnect home computers

and peripherals, and home entertainment devices that have an Ethernet port. Power line adapter

sets plug into power outlets and establish an Ethernet connection using the existing electrical

wiring in the home. (Power strips with filtering may absorb the power line signal.) This allows

devices to share data without the inconvenience of running dedicated network cables.

The most widely deployed power line networking standard is from the Home Plug Power

line Alliance. Home Plug AV is the most current of the Home Plug specifications and was

adopted by the IEEE 1901 group as a baseline technology for their standard, published 30

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December 2010. Home Plug estimates that over 45 million Home Plug devices have been

deployed worldwide. Other companies and organizations back different specifications for power

line home networking and these include the Universal Powerline Association, SiConnect, the

HD-PLC Alliance, Xsilon and the ITU-T’s G.hn specification.

3.6.4 Broadband over power line

Broadband over power line (BPL) is a system to transmit two-way data over existing AC

MV (medium voltage) electrical distribution wiring, between transformers, and AC LV (low

voltage) wiring between transformer and customer outlets (typically 110 to 240V). This avoids

the expense of a dedicated network of wires for data communication, and the expense of

maintaining a dedicated network of antennas, radios and routers in wireless network. BPL uses

some of the same radio frequencies used for over-the-air radio systems. Modern BPL employs

frequency-hopping spread spectrum to avoid using those frequencies actually in use, though

early pre-2010 BPL standards did not. The criticisms of BPL from this perspective are of pre-

OPERA, pre-1905 standards.

The BPL OPERA standard is used primarily in Europe by ISPs. In North America it is

used in some places (Washington Island, WI, for instance) but is more generally used by electric

distribution utilities for smart meters and load management. Since the ratification of the IEEE

1901 LAN standard and its widespread implementation in mainstream router chipsets, the older

BPL standards are not competitive for communication between AC outlets within a building, nor

between the building and the transformer where MV meets LV lines.

Over the past few years advances in signal processing technology have enabled the

advent of modem chips that are able to overcome the transmission difficulties associated with

sending communications signals over electrical power lines. In the United States, this capability

has been termed ―Broadband over Power Lines‖ or BPL. There are two predominant types of

BPL communications configurations: Access BPL and In-Home BPL. Access BPL is comprised

of injectors (used to inject High Frequency (HF) signals onto medium or low voltage power

lines), extractors (used to retrieve these signals) and repeaters (used to regenerate signals to

prevent attenuation losses). In addition to taking advantage of the power line infrastructure, In-

Home BPL modems utilize the existing house wiring to provision a Local Area Network (LAN)

that can be used throughout the home. One of the largest commercial markets for BPL is the

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ability to provide Internet Services by means of the Transmission Control Protocol/Internet

Protocol (TCP/IP) protocols, which can support voice, data, and video services. Another

significant benefit of BPL is the ability to employ ―intelligent‖ power line networks that make

use of Supervisory Control and Data Acquisition (SCADA) devices, dynamic provisioning, and

other forms of modernized electrical power networks. A SCADA system can save time and

money by reducing the need for service personnel to physically visit each site for inspection, data

collection, and routine logging or even to make adjustments. The benefits also include the ability

for real-time monitoring, system modifications.

3.6.5 Automotive Uses

Power-line technology enables in-vehicle network communication of data, voice, music

and video signals by digital means over direct current (DC) battery power-line. Advanced digital

communication techniques tailored to overcome hostile and noisy environment are implemented

in a small size silicon device. One power line can be used for multiple independent networks.

The benefits would be lower cost and weight (compared to separate power and control wiring),

flexible modification, and ease of installation. Potential problems in vehicle applications would

include the higher cost of end devices, which must be equipped with active controls and

communication, and the possibility of interference with other radio frequency devices in the

vehicle or other places. Prototypes are successfully operational in vehicles, using automotive

compatible protocols such as CAN-bus, LIN-bus over power line (DC-LIN) and [DC-bus]. Lon

Works power line based control has been used for an HVAC system in a production model bus.

The SAE J1772 committee developing standard connectors for plug-in electric vehicles

proposes to use power line communication between the vehicle, off-board charging station, and

the smart grid, without requiring an additional pin; SAE and the IEEE Standards Association are

sharing their draft standards related to the smart grid and vehicle electrification.

3.7 Advantage and Disadvantage

In order to completely analyze the advantages and disadvantages of PLCC technology, we look

into its basic application that is access to telecommunication networks. From the economic

standpoint, it is very reasonable to use a pre-installed wired network instead of running new

wires. It certainly reduces a lot of time & money and so is the biggest advantage of the

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technology. In many countries, PLCC is becoming a reliable high speed source to get Internet.

And in some places, especially in remote areas, PLCC technology thankfully made it possible to

avail internet connections.

Power line communication is quite different in characteristics than the conventional

dedicated wirings. Comparatively, it is a harsh medium and data transfer through it can create a

lot of problems. Household appliances like halogen tubes, washing machines, televisions, etc.

can become prone to an unpredictable noise and interference in the transmission. Continuous

plugging and unplugging of electronic devices makes power line characteristics vary constantly.

Having a negative impact on the output hence should be avoided. FSK is found to be most

immune to noise and hence chosen for our project.

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4. Conclusion

With the FCC regulatory position of PLC clarified by the revision of Part 15, the

technology is poised for expansion in both access and in-home configurations over the next

decade. PLC has been considered as a potential 3rd wire that can compete with cable and DSL

Internet services. Ultimately, many factors will influence the degree of market penetration that

PLC achieves, including cost, standards progress, competition, regulations, and technical

acceptance. Electrical power lines offer a clear benefit with regard to the large coverage area

from which broadband service could be obtained, but it is important to remember that PLC

provisioning does not come without the additional infrastructure costs for injectors, repeaters,

extractors, management systems, and operations and maintenance. For initial PLC deployments,

lower customer costs appear to be the dominant customer consideration since Access PLC

speeds are not competitive with cable Internet. Second generation PLC may offer better

performance with speeds of up to 200 Mb/s but to leverage this as a competitive advantage

beyond a 3rd wire status, PLC will need to deliver the higher speeds sooner than cable or DSL.

The Power Corridor tm product literature from Corridor Systems already promises to deliver

PLC performance speeds that exceed 1 Gb/s. At speeds above 1 Gb/s, PLC could serve a role in

bridging the transition from Internet to Internet2.

Around the globe, various PLC studies, prototypes, and deployments have been

conducted with mixed results. In a noteworthy number of locations, including the United States,

PLC prototypes have been terminated in association with interference complaints. However, the

FCC accurately recognized PLC as an infancy-stage technology and appropriately assigned it to

a regulatory climate that is intended to foster innovation. It is clear that ongoing studies such as

that documented in ITU-R P.372-8 Radio Noise provide an excellent baseline to insure that

manmade factors contributing to interference are managed appropriately. The FCC support for

PLC is already resulting in the emergence of designs that significantly reduce interference

concerns, and this trend is expected to continue. US power companies, to date, have not

demonstrated a firm stand with respect to PLC investment and deployment in favor of insuring

stability for their electrical-power- business customer base. However, as PLC technology

advances, this business climate is also subject to change. Initially, power companies’ interest in

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PLC has been focused on its ability to improve control over elements of the electrical power

grid.

Altering the mix of communications assets deployed to support NS/EP is presently an

expensive proposition that requires long project schedules. Consequently, it is not currently

possible to adjust the NCS infrastructure to compensate for rapid technology or regulatory

changes. Regulatory agencies such as the FCC need to partner with both industry and the NCS

community members to insure that the interests of the private sector and national security are

properly balanced. However, these interests are not mutually exclusive, and the NCS can

ultimately benefit from technologies like PLC, which offer new means for asset diversification.

The PLC studies that have been conducted by the BBC and others around the world have

raised serious concerns about detrimental interference effects on HF radio spectrum. These

concerns are resulting in further PLC scientific studies and in additional work within standards

bodies around the world. HF radio spectrum is a highly valued natural resource that should be

allocated in a manner that serves the greatest good. As required, further technical refinements

will be made to PLC technologies to enable them to reduce harmful emissions.

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5. References

[1] Stanley H. Horowitz; Arun G. Phadke (2008). Power system relaying third

edition. John Wiley and Sons. pp. 64–65.

[2] Edward B.Driscoll, Jr. "The history of X10"

http://home.planet.nl/~lhendrix/x10_history.htm

[3] Hosono, M (26–28 October 1982). "Improved Automatic meter reading and load

control system and its operational achievement". 4th International Conference on

Metering, Apparatus and Tariffs for Electricity Supply. IEE. pp. 90–94.

[4] Duval, G. "Applications of power line carrier at Electricite de France". Proc 1997

Internat. Symp. on Power Line Comms and its Applications: 76–80.

[5] "Daewoo Bus Case Study"

http://www.echelon.com/solutions/transportation/appstories/DaewooBus.

[6] "DC-LIN Over Power line" http://www.yamar.com/DC-LIN.htmlThe History Of

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