Communication Through Power Lines[Rahul Gupta]


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Communication Through Power Lines[Rahul Gupta]

  1. 1. 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 1
  2. 2. 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. 2
  3. 3. 1.1Basic 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 3
  4. 4. 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 4
  5. 5. 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, InHome 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 5
  6. 6. 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 6
  7. 7. 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 7
  8. 8. 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 userprogrammable 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. 8
  9. 9. 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. 9
  10. 10. 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 10
  11. 11. 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 11
  12. 12. 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 3KHz – 9KHz A-Band Usage This range is restricted to the Energy Providers. 9KHz-95KHz Restricted to the energy providers and their concession holders Restricted to the energy providers customers. B-Band 95KHz-125KHz There is no access rule defined for this frequency range. Restricted to energy providers customers. Simultaneous operations on multiple systems are C-Band 125KHz-140KHz 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. 12
  13. 13. 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 13
  14. 14. 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 14
  15. 15. 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 15
  16. 16. 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, 16
  17. 17. 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 17
  18. 18. 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. G3PLC 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. 18
  19. 19. 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. 19
  20. 20. 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. 20
  21. 21. 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. 21
  22. 22. 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 22
  23. 23. 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 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 preOPERA, 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, InHome 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 23
  24. 24. 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 24
  25. 25. 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. 25
  26. 26. 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 26
  27. 27. 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. 27
  28. 28. 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" [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" [6] "DC-LIN Over Power line" History Of File. 28