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Broadband Access Alternatives
Broadband access and services are delivered using a variety of technologies, network architectures and transmission methods. The most significant broadband technologies include:
Â¢ Digital Subscriber Line (DSL)
Â¢ Fiber Technologies
Â¢ Coaxial Cable
Â¢ BPL (Broadband Over Power Lines)
The following is a brief description of each of the above referenced access technology.
1.1 Digital Subscriber Line (DSL) - Broadband over faster copper
DSL is a very high-speed connection to Internet that uses the same wires as a regular telephone line. A standard telephone installation in the United States consists of a pair of copper wires. This pair of copper wires has sufficient bandwidth for carrying both data and voice. Voice signals use only a fraction of the available capacity on the wires. DSL exploits this remaining capacity to carry information on the wire without affecting the lineâ„¢s ability to carry voice conversations. Standard phone service limits the frequencies that the switches, telephones and other equipment can carry. Human voices, speaking in normal conversational tones, can be carried in a frequency range of 400 to 3,400 Hertz (cycles per second). In most cases, the wires themselves have the potential to handle frequencies of up to several-million Hertz. Modern equipment that sends digital (rather than analog) data can safely use much more of the telephone lineâ„¢s capacity, and DSL does just that.
1.1.1 Advantages of DSL
Â¢ Simultaneous Use - Phone line can be used for voice calls and the Internet connection
at the same time.
Â¢ A much higher speed when compared to regular modem (1.5 Mbps vs. 56 Kbps).
Â¢ Does not necessarily require new wiring, the existing phone line can be used.
Â¢ Providers generally include modem as part of the installation.
1.1.2 Limitations of DSL
Â¢ The quality of connection depends upon the proximity to the providerâ„¢s central
office, closer the better
Â¢ Receiving data is faster than sending data over the internet
Â¢ DSL is not available everywhere
1.2 Fiber Technologies
In recent years, carriers have begun constructing entirely fiber optic cable transmission facilities that run from a distribution frame (or its equiva lent) in an incumbent local exchange carrierâ„¢s (ILECâ„¢s) central office to the loop demarcation point at an end-user customer premise. These loops are referred to as fiber-to-the-home (FTTH) loops. FTTH technology offers substantially more capacity than any copper-based technology. For example, Wav7 Optics provides a FTTH system today using commercially available equipment that delivers transmission speeds up to 500 Mbps shared over a maximum of 16 subscribers. This system can also provide up to 500 Mbps symmetrically to one subscriber if desired. The speed an actual user will experience depends upon the time of day and the number of users online. A typical FTTH system can deliver up to 870 MHz of cable television video services (for high definition television) or IP video services along with multiple telephone lines and current and next-generation data services at speeds in excess of 100 Mbps.
There are three basic types of architectures being used to provide FTTH. The most common architecture used is Passive Optical Network (PON) technology. This technology allows multiple homes to share a passive fiber network. In this type of network, the plant between the customer premises and the head-end at the central office consists entirely of passive components â€œ no electronics are needed in the field. The other architectures being used are Home Run Fiber or Point-to-Point Fiber, in which subscribers have a dedicated fiber strand, and active or powered nodes are used to manage signal distribution, and hybrid PONs, which are a combination of home run and PON architecture.
Although FTTH technology is still in its infancy, the deployment of FTTH is growing significantly. Also, the equipment costs for FTTH have decreased significantly. As of May 2004, carriers have deployed FTTH technology to 128 communities in 32 states. Companies plan to deploy FTTH further in the future. Competitive carriers are also building FTTH facilities. In addition to FTTH technologies, some carriers are constructing fiber-to-the-curb (FTTC) facilities that do not run all the way to the home, but run to a pedestal located within 500 feet of the subscriber premises. Copper lines are then used for the connection between the pedestal and the network interface device at the customerâ„¢s premises. Because of the limited use of copper, FTTC technologies permit carriers to provide high-speed data in addition to high definition video services.
1.3 Coaxial Cable
For millions of people, television brings news, entertainment and educational programs into their homes. Many people get their TV signal from cable television (CATV) because cable TV provides better reception and more channels. Many people who have cable TV can now get a high-speed connection to the Internet from their cable provider. Cable modems allow subscribers to access high-speed data services over cable systems that are generally designed with hybrid fiber-coaxial (HFC) architecture. Cable modem service is primarily residential, but may also include some small business service. Cable modems compete with technologies like Asymmetrical Digital Subscriber Lines (ADSL). Following is a look at how a cable modem works and how 100 cable television channels and web sites can flow over a single coaxial cable. In a cable TV system, signals from the various channels are each given a 6-MHz slice of the cableâ„¢s available bandwidth and then sent down the cable to your house. The coaxial cable used to carry cable television can carry hundreds of megahertz of signals and therefore, a large number of channels. In some systems, coaxial cable is the only medium used for distributing signals. In other systems, fiber-optic cable goes from the cable company to different neighborhoods or areas. Then the fiber is terminated and the signals move onto coaxial cable for distribution to individual houses.
When a cable company offers Internet access over the cable, Internet information can use the same cables because the cable modem system puts downstream dataâ€data sent from the Internet to an individual computerâ€into a 6-MHz channel. On the cable, the data looks just like a TV channel. So Internet downstream data takes up the same amount of cable space as any single channel of programming. Upstream dataâ€information sent from an individual back to the
Internetâ€requires even less of the cableâ„¢s bandwidth, just 2 MHz, since the assumption is that most people download far more information than they upload. Putting both upstream and downstream data on the cable television system requires two types of equipment: a Cable Modem on the customer end and a Cable Modem Termination System (CMTS) at the cable providerâ„¢s end. Between these two types of equipment, all the computer networking, security and management of Internet access over cable television is put into place.
1.3.1 Advantages and Disadvantages of Coaxial cable
If you are one of the first users to connect to the Internet through a particular cable channel, then you may have nearly the entire bandwidth of the channel available for your use. The disadvantage of coaxial cable however, is as new users, especially heavy-access users, are connected to the channel, you will have to share that bandwidth, and may see your performance degrade as a result. It is possible that, in times of heavy usage with many connected users, performance will be far below the theoretical maximums. The cable company can resolve this particular performance issue by adding a new channel and splitting the base of users.
Another benefit of the cable modem for Internet access is that, unlike ADSL, its performance does not depend on distance from the central cable office. A digital CATV system is designed to provide digital signals at a particular quality to customer households. On the upstream side, the burst modulator in cable modems is programmed with the distance from the head-end, and provides the proper signal strength for accurate transmission. Cable industry has extended the broadband services offering to at least 90 percent of homes passed by cable systems. The cable industry expects that industry-wide facilities upgrades enabling the provision of broadband Internet access to residential customers will be completed in the near future.
1.4.1 Unlicensed Wireless
Since the Commission first allocated spectrum in the 902-928 MHz band for use on an unlicensed basis under Part 15 of the rules, there has been an increasingly rapid expansion of products and markets in bands designated for unlicensed use. This Industrial, Scientific, and Medical (ISM) band was the first to experience the large-scale introduction of devices such as cordless phones, security alarms, wireless bar code readers, and data collection systems. A number of original equipment manufacturers continue to provide equipment for point-to-point and point-to multipoint systems for such applications as Supervisory Control and Data Acquisition. In addition, there are several providers of wireless local area network equipment in this band.
Wi-Fi, short for Wireless Fidelity, is a term that is used generically to refer to any product or service using the 802.11 series standards developed by the Institute of Electrical and Electronics Engineers (IEEE) for wireless local area network connections. Wi-Fi networks operate on an unlicensed basis in the 2.4 and 5 GHz radio bands and provide multiple data rates up to a maximum of 54 Mbps. The bandwidth is shared among multiple users. Wi-Fi enabled wireless devices, such as laptop computers or personal digital assistants (PDAs), can send and receive data from any location within signal reach of a Wi-Fi equipped base station or access point (AP).
Typically, mobile devices must be within approximately 300 feet of a base station. The Wi-Fi technology features a creation of a wireless cloud that covers a hot-spot area. The specific dimensions of the coverage area vary based on environmental and power specifications of the equipment in use. Typically, coverage radius is in the range of 300-500 feet. Environmental conditions, like weather and line of site, can affect the ability to reach target customers. With the expansion of Wi-Fi access to the Internet there has been a rapid growth of hot-spots. Networks of hot-spots consisting of many access points have been constructed to cover larger areas such as airports.
Of all the different Wireless LAN interfaces, 802.11b has the most popular appeal due to the low number of technical problems and lower hardware costs. It is the only standard with widespread popularity and focused on residential users.
Wireless Local Area Networks (LANs) based on the IEEE 802.11 or Wi-Fi standards have been quite successful, and therefore the focus in wireless is moving towards the wide area. While Wi- Fi dominates in the local area, the wide area market is still very much open. The cellular carriers got into this market first with their 2.5G/3G data services, but they were positioned to offer essentially add-on to voice service. The real competition to cellular data services may come from emerging data-oriented technology, WiMax.
WiMax, short for Worldwide Interoperability for Microwave Access, refers to any broadband wireless access network based on the IEEE 802.16 standards. Internationally, a European Telecommunications Standards Institute (ETSI) initiative called HIPERMAN addresses the same area as WiMax/802.16 and shares some of the same technology.
WiMax includes fixed systems employing a point-to-multipoint architecture operating between 2 GHz and 66 GHz. WiMax based broadband wireless access (BWA) or, also known as wireless DSL, will offer data rates between 512 Kbps and 1 Mbps. The key will be to deliver low-cost, indoor, user installable premises devices that will not have to be aligned with the base station i.e., the antenna in the premises equipment would be integrated with the radio modem. WiMax is designed to deliver a metro area broadband wireless access (BWA) service. The idea behind BWA is to provide a fixed location wireless Internet access service to compete with cable modems and DSL. WiMax systems could support users at ranges up to 30 miles and is intended as the basis of a carrier service.
The WiMax standards include a much wider range of potential implementation to address the requirements of carriers around the world. The original version of the 802.16 standard, when released addressed systems operating in the 10 GHz to 66 GHz frequency band. Such high frequency systems require line-of-sight (LOS) to the base station, which increases cost and limits the customer base. Also, in LOS systems, customer antennas must be realigned when a new cell is added to the network. Since the initial release, 802.16a standard released in 2003 has changed the playing field. The standard 802.16a describes systems operating between 2 GHz and 11 GHz. These lower frequency bands support non-line-of-sight (NLOS), thereby eliminating the need to align the customer unit with the base station.
1.4.2 Fixed Wireless Technologies
Point-to-point microwave connections have a long history in the backhaul networks of phone companies, cable TV companies, utilities and government agencies. In recent years, technology has advanced to enable higher frequencies and smaller antennas. This has resulted in lower cost systems that could be sold by carriers for the last mile of communications.
Multi-channel multipoint distribution service (MMDS)
This band, located at 2.5GHz, was initially used to distribute cable television service.
Now MMDS is being developed for residential Internet service. MMDS wireless technology can be deployed to offer two-way service at throughputs ranging from 64 kbps to 10Mbps. However, MMDS systems require line of sight between transmitter and receiver. The lower MMDS frequencies (2 GHz) do not attenuate very quickly and services can be provided at up to 30 miles from the hub, equivalent to coverage of approximately 2,800 square miles. This is one of the largest coverage areas of any point-to-multipoint communications system available today.
Local multipoint distribution service (LMDS)
This band (27.5GHz to 28.35 GHz, 29.1GHz to 29.25 GHz and 31GHz to 31.3 GHz) is
being used for point-to-multipoint applications similar to the 39GHz band â€œ Internet access and telephony. LMDS, though, only has a 3-mile coverage radius and uses TDMA (Time-Division Multiple Access) so that multiple customers can share the same radio channel.
The technology uses a cellular like network architecture of microwave radios placed at the clientâ„¢s location and at the companyâ„¢s base station to deliver fixed services, mainly telephony, video and Internet access. The use of time-division multiple access (TDMA) and frequencydivision multiple access (FDMA) technologies allows multiple customers within a 3-5 mile coverage radius to share the same radio channel. Customers can receive data rates between
64kbps to 155Mbps.
Satellite Internet access is ideal for rural Internet users who want broadband access. Satellite Internet does not use telephone lines or cable systems, but instead uses a satellite dish for two way (upload and download) data communications. Upload speed is about one-tenth of the 500 kbps download speed. Cable and DSL have higher download speeds, but satellite systems are about 10 times faster than a normal modem.Two-way satellite Internet consists of approximately a two-foot by three-foot dish, two modems (uplink and downlink), and coaxial cables between dish and modem. The key installation planning requirement is a clear view to the south, since the orbiting satellites are over the equator area. And, like satellite TV, trees and heavy rains can affect reception of the Internet signals.
Two-way satellite Internet uses Internet Protocol (IP) multicasting technology, which means that a maximum of 5,000 channels of communication can simultaneously be served by a single satellite. IP multicasting sends data from one point to many points (at the same time) in a compressed format. Compression reduces the size of the data and the bandwidth. Usual dial-up land-based terrestrial systems have bandwidth limitations that prevent multicasting of this magnitude.
1.5 Comparative Analysis of Access Alternatives
Table 1.1 Comparison of Access Technologies
Access Technology Speed Typical Prices per
Month Reach Remarks
BPL Commercial â€œ
up to 3 Mbps
Residences - 5 Mbps $28 to $39
depending on speed and features Ubiquitous electric distribution
network Speeds same for upload and download; Number of Users affects the speed
Cable 1 Mbps to 3 Mbps $39 to $60 Available where cable has
been installed so some rural
and suburban locations may
not have access speed of the signal varies by the number of users on neighborhood network loop;
it degrades with high numbers of users.
DSL 1.5 Mbps $27 to $49 In general, a residence must
be within about 18,000 ft. of
the DSL central equipment Not capable of transmitting TV signals
Fiber 30 Mbps to 1 Gbps $28 to $65
features, and speed Deployment has
limited by high
costs Cost reductions enabled by passive optical
networks and advances in component
Technologies are expected to bring costs down.
Satellite 500 Kbps $50 to $100 Requires a clear
view to the
south Trees and even heavy
rain may affect
reception on Internet data
Introduction to Broadband Over Powerlines
Broadband over Power Line (BPL) is a technology that allows voice and Internet data to be transmitted over utility power lines. BPL is also sometimes called Power-line Communications or PLC. Many people use the terms PLC and BPL interchangeably. The FCC chose to use the term broadband over power line for consumer applications. In order to make use of BPL, subscribers use neither a phone, cable nor a satellite connection. Instead, a subscriber installs a modem that plugs into an ordinary wall outlet and pays a subscription fee similar to those paid for other types of Internet service.
2.2 Basic principle
If you know something about broadband Internet already, you're probably aware that it works by splitting your ordinary telephone line into a number of separate channels. Some of them carry your phone calls, as usual, some carry downloads (information coming from the Internet to your home), and some handle uploads (information going the opposite way). Broadband uses low-frequency electric signals to carry ordinary phone calls and higher-frequency signals to carry Internet data. Electronic filters separate the two kinds of signal, with the low frequencies going to your telephone and the higher frequencies to your Internet modem. A single piece of telephone cable carries both phone calls and Internet data. Your telephone listens just to the calls; your modem lists only to the data.
Standard AC electricity is transmitted at a frequency of 50 Hz or 60 Hz. Researchers noted that this left almost the entire frequency range of the line free, which suggested that perhaps, like the local loop, the line could be used for additional purposes. Consequently, it was proposed to transmit data over the unused frequencies of the power lines, using methods similar to those used for DSL. This is the foundation idea upon which BPL technology is constructed.
Fig 2.1 High and low frequency waves
2.3 Big Idea
Despite the proliferation of broadband technology in the last few years, there are still huge parts of the world that don't have access to high-speed Internet. When weighed against the relatively small number of customers Internet providers would gain, the cost of laying cable and building the necessary infrastructure to provide DSL or cable in rural areas is too great. But if broadband could be served through power lines, there would be no need to build a new infrastructure. Anywhere there is electricity there could be broadband.
By slightly modifying the current power grids with specialized equipment, the BPL developers could partner with power companies and Internet service providers to bring broadband to everyone with access to electricity.
At this point, the proposal is for two types of BPL service:
Â¢ In-House BPL will network machines within a building.
Â¢ Access BPL will carry broadband Internet using power lines and allow power companies to electronically monitor power systems.
2.4 Access BPL: bringing broadband to your home
If you can send computer data down a phone line, there's no reason why you can't channel it down a power line as well. Some Internet service providers (ISPs) are already using overhead and underground power lines to carry broadband data long distances to and from their customers in what's called access BPL. It's exactly the same principle as sending broadband over a phone line: a high-frequency signal carrying the broadband data is superimposed on the lower-frequency, alternating current that carries your ordinary electric power. In your home, you need to have slightly modified power outlets with an extra computer socket. Plug in a special BPL modem, plug that into your computer, and your broadband is up and running in no time.
2.5 In-house BPL: carrying broadband within your home
You can also use BPL with traditional telephone or cable broadband to bring Internet access to all the different rooms in your home. You simply plug the Ethernet lead from your normal modem into a special adapter that fits into one of the power outlets. Your home electricity circuit then takes the broadband to and from every room in your house as a high-frequency signal superimposed on top of the power supply. If you want to use broadband in a bedroom, you simply plug another Ethernet adapter into one of the ordinary power outlets in that room and plug your computer into it. In-house BPL, as this system is known, is a great way of getting broadband in any part of your home. It's particularly useful if you have a big house with thick walls that make wireless Internet impossible.
BPL opens up an even more exciting possibility for the future. If we can connect computers using the ordinary power lines in our home, there's nothing to stop us connecting up domestic appliances both to one another and to the Internet. "Smart homes" (in which appliances are switched on and off automatically by electronic controllers or computers) have used this basic idea for yearsâ€but BPL could take it much further and make it far more widespread. Imagine a future where you can use a Web browser on your computer at work to switch on the electric cooker in the kitchen at home, ready for when you arrive. Or how about using a Web browser to turn your home lights on and off when you're staying in a hotel, to give added protection against intruders? Just imagine the possibilities: BPL could take remote control to an amazing new level!
2.6 Technical Details
Since extremely few BPL systems are commercially available, there has been no attempt to standardize the underlying protocols. Instead, trials have typically tested a multitude of technologies, in an attempt to find the most appropriate one for the harsh data transmission medium of a power line . It should be noted that solutions designed for BPL are often based upon those used in mobile communications, since both technologies could potentially suffer from high error rates and, consequently, from low data rates.
2.6.1 CDMA and OFDM
The two main choices of technology used to implement BPLâ„¢s physical layer are CDMA (Code Division Multiple Access), which is used in some mobile telephone systems, and OFDM (Orthogonal Frequency Division Multiplexing), which is used in IEEE 802.11a. Both exhibit favorable characteristics, although performance studies indicate that CDMA performs substantially better than OFDM in terms of the data rate achieved . However, if the line were very noisy, OFDM would perform much better. Consequently, OFDM is more fault-tolerant. It is, perhaps, for these reasons that OFDM has been more widely researched than CDMA. Further, the ESBâ„¢s trials were conducted using OFDM . Additionally, CDMA is not currently viable due to difficulties in creating enough CDMA chips. Work is already in progress to overcome these limits, however.
Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne and CDMA2000 (which are often referred to as simply "CDMA"), which use CDMA as an underlying channel access method.
One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of different frequencies. This concept is called multiplexing. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.
Orthogonal frequency-division multiplexing (OFDM), essentially identical to coded OFDM (COFDM) and discrete multi-tone modulation (DMT), is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, wireless networking and broadband internet access.
The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of high frequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without complex equalization filters. Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to handle time-spreading and eliminate intersymbol interference (ISI). This mechanism also facilitates the design of single frequency networks (SFNs), where several adjacent transmitters send the same signal simultaneously at the same frequency, as the signals from multiple distant transmitters may be combined constructively, rather than interfering as would typically occur in a traditional single-carrier system.
2.6.2 MAC sub layer
Two conditions must be considered when designing the MAC (Medium Access Control) sub layer of BPLâ„¢s data link layer: there is no limit to the distance between nodes and multiple nodes may transmit simultaneously. The first condition eliminates the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol used with Ethernet. However, the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol used with IEEE 802.11 is suitable and is a widely researched solution. The Bluetooth protocol is also suitable. However, as could be expected, CSMA/CA performs better, as its design goals are a closer match to BPLâ„¢s .
3.1 Power Distribution Systems
The power distribution system begins at the power generation facility and ends at the business or
residential end user location. The lines extending from the power generation facility spread and
branch out at successively lower voltages.
Fig 3.1 - Simplified Power Distribution System
Power distribution systems consist of the following segments:
Transmission (also known as high voltage or HV) lines, typically 69 kilovolts (kV) and
above, run from the power generation facility to a set of distributed substations. Transformers
at the substations lower the high voltage to medium voltage for the next stage of distribution.
Primary distribution (also known as medium voltage or MV) lines, typically between 2.4kV and 35kV, extend from the substations. Pole-mounted, pad-mounted, or underground transformers distributed throughout the service area again lower the medium voltage to the final delivery voltage that is provided to homes and businesses (typically 6 to 10 homes per transformer in the US).
Secondary distribution (also known as low voltage or LV) lines, typically up to 600 Volts,
connect the pole, pad, or underground transformers to the home or business end users.
3.2 Network components
The Last Mile is the portion of the network that connects end users, such as homes and business, to high-speed services and the Internet. For residential broadband service customers who get cable modem service, for example, the drop wire connecting the interface on a house to cable companyâ„¢s network and the wire from the interface connecting to the wall plates in the home would all be part of the last mile.
BPL modems use silicon chips designed to send signals over electric power lines, much like cable and DSL modems use silicon chips designed to send signals over cable and telephone lines. Advances in processing power have enabled new BPL modem chips to overcome difficulties in sending communications signals over the electric power lines.
Fig 3.2 BPL modem
Inductive couplers are used to connect BPL modems to the medium voltage power lines. An inductive coupler transfers the communications signal onto the power line by wrapping around the line, without directly connecting to the line. A major challenge is how to deliver the signal from the medium voltage line to the low voltage line that enters your house, because the transformer that lowers the electric power from several thousand volts down to 220/110 is a potential barrier to the broadband signal.
Fig. 3.3 Coupler and injector
Router is a device that acts as an interface between two networks and provides network
Repeater is a physical-layer hardware device used on a network to extend the length, topology, or interconnectivity of the physical medium beyond that imposed by a single segment.
Concentrator/Injector is a device that aggregates the end-user CPE data onto the MV (medium voltage) grid. Injectors are tied to the Internet backbone via fiber of T1 lines and interface to the MV power lines feeding the BPL service area.
Extractors provide the interface between the MV power lines carrying BPL signals and he households within the service area. BPL extractors are usually located at each LV distribution transformer feeding a group of homes.
3.3 Network architecture
At a high-level, a Powerline Telecom network consists of three key segments, the backbone, the middle mile, and the last mile as shown below in Figure 4.2.1. The BPL vendors are primarily seeking to address the last mile segment all the way into the home market.
From the end userâ„¢s perspective, BPL technology works by sending high-speed data along
medium or low voltage power lines into the customerâ„¢s home. The signal traverses the network
over medium and low voltage lines either through the transformers or by-passes the transformer
using bridges or couplers. The technology transports data, voice and video at broadband speeds to the end-userâ„¢s connection. The user only needs to plug an electrical cord from the BPL modem into any electrical outlet then plug an Ethernet or USB cable into the Ethernet card or USB interface on their PC. Any Internet Service Provider (ISP) can interface with the BPL network and provide high speed Internet access. The data signal can also interconnect with wireless, fiber or other media for backhaul and last mile completion. The actual hardware used for the deployment varies by manufacturer but typically feature some common characteristics.
Fig 3.4 Network architecture
By combining the technological principles of radio, wireless networking, and modems,
developers have created a way to send data over power lines and into homes at speeds equivalent
to those of DSL and cable. By modifying the current power grids with specia lized equipment, the BPL developers could partner with power companies and Internet service providers (ISPs) to
bring broadband to everyone with access to electricity. The Internet is a huge network of networks that are connected through cables, computers, and wired and wireless devices worldwide. Typically, large ISPs lease fiber-optic lines from the phone company to carry the data around the Internet and eventually to another medium (phone, DSL or cable line) and into the homes. Trillions of bytes of data a day are transferred on fiberoptic lines because they are a stable way to transmit data without interfering with other types of transmissions.
The idea of using AC (alternating current) power to transfer data is not new. By bundling radio frequency (RF) energy on the same line with an electric current, data can be transmitted without the need for a separate data line. Because the electric current and RF vibrate at different
frequencies, the two donâ„¢t interfere with each other. Electric companies have used this technology for years to monitor the performance of power grids. There are even networking solutions available today that transfer data using the electrical wiring in a home or business. But this data is fairly simple and the transmission speed is relatively slow.
There are several different approaches to overcoming the hurdles presented when transmitting data through power lines. The power lines are just one component of electric companies' power grids. In addition to lines, power grids use generators, substations, transformers and other distributors that carry electricity from the power plant all the way to a plug in the wall. When power leaves the power plant, it hits a transmission substation and is then distributed to highvoltage transmission lines. When transmitting broadband, these high-voltage lines represent the first hurdle.
The power flowing down high-voltage lines is between 155,000 to 765,000 volts. That amount of power is unsuitable for data transmission. It's too "noisy." Both electricity and the RF used to transmit data vibrate at certain frequencies. In order for data to transmit cleanly from point to point, it must have a dedicated band of the radio spectrum at which to vibrate without interference from other sources. Hundreds of thousands of volts of electricity don't vibrate at a consistent frequency. That amount of power jumps all over the spectrum. As it spikes and hums along, it creates all kinds of interference. If it spikes at a frequency that is the same as the RF used to transmit data, then it will cancel out that signal and the data transmission will be dropped or damaged en route. BPL bypasses this problem by avoiding high-voltage power lines all together. The system drops the data off of traditional fiber-optic lines downstream, onto the much more manageable 7,200 volts of medium-voltage power lines. Once dropped onto the medium-voltage lines, the data can only travel so far before it degrades. To counter this, special devices are installed on the lines to act as repeaters. The repeaters take in the data and repeat it in a new transmission, amplifying it for the next leg of the journey.
In one model of BPL, two other devices ride power poles to distribute Internet traffic. The Coupler allows the data on the line to bypass transformers, and the Bridge , a device that
facilitates carrying the signal into the homes.The transformer's job is to reduce the 7,200 volts down to the 240-volt standard that makes up normal household electrical service. There is no way for low-power data signals to pass through a transformer, so you need a coupler to provide a data path around the transformer. With the coupler, data can move easily from the 7,200-volt line to the 240-volt line and into the house without any degradation. The last mile is the final step that carries Internet into the subscriber's home or office. In the various approaches to last-mile solutions for BPL, some companies carry the signal in with the electricity on the power line, while others put wireless links on the poles and send the data wirelessly into homes. The Bridge facilitates both. The signal is received by a power line modem that plugs into the wall. The modem sends the signal to your computer.
BPL modems use silicon chipsets specially designed to handle the work load of pulling data out of an electric current. Using specially developed modulation techniques and adaptive algorithms, BPL modems are capable of handling powerline noise on a wide spectrum. A BPL modem is plug_and_play and is roughly the size of a common power adapter. It plugs into a common wall socket, and an Ethernet cable running to your computer finishes the connection. Wireless versions are also available.
Electric utilities may not necessarily want to enter the communications business. In fact, they may want to leave that part of BPL to a partner, perhaps an ISP, a Competitive Local Exchange Carrier (CLEC), or a long distance company looking for an alternative last mile path to their customers. Current focus of most electric utilities is using BPL for an intelligent electric
distribution grid. Power companies have often employed low-speed power line communication
for their own internal useâ€to monitor and control equipment in the power grid. This could result
in lower electric power costs, less pollution and greater reliability and security, essentially, a
more intelligent electric power grid.The Broadband services enabling partners may be in one or more of the delivery segments.
4.1 The last mile
This is the portion of the network that connects end users, such as homes and business, to high-speed services and the Internet. For residential broadband service customers who get cable modem service, for example, the drop wire connecting the interface on a house to cable companyâ„¢s network and the wire from the interface connecting to the wall plates in the home would all be part of the last mile.
4.2 The middle mile
This portion of the network consists of high-speed fiber backbones and other middle-mile pipes that connect computers to networks, connect those networks into the complex that constitutes the Internet, and deliver traffic among ISPs, content providers, online service companies, and other customers.
4.3 Internet service providers (ISPs)
These are companies that receive and translate internet bound data and help customers obtain online information from the Internet.
4.4 Content providers
This part of broadband consists of companies that provide information, goods, and services available to consumers through the Internet. These characteristics and distinctions are based on network functionality and the fact that each of these categories has its own economic properties with distinct regulatory issues. Currently there is a dearth of competition in the provision of middle -mile services, which means existing providers can discriminate against their customers. Content providers, on the other hand, raise competitive issues in terms of their ability or willingness to engage in exclusive contracts for the carrying of their content, as well as posing challenges in the area of consumer protection and free speech.
Fig 4.1 Key players interested in BPL
A partnership between a utility and an external third party service provider offers strategic value as each player can focus on what it does best. Utilities have operated as monopolies and, while good at building infrastructure they lack experience in competitive environment. On the other hand, ISPs operate in a very competitive environment. The key success factors include effectively marketing to customers, cost effective customer acquisition and a high quality customer service. Current broadband environment is expected to become very competitive with both cable modem providers and DSL providers aggressively marketing their services and other alternate providers looking at entering the market. Customer service appears to be a key differentiator with most of the consumers. A partnership with an ISP (or a local CLEC) might leverage key strengths: The utility could focus on network management while the ISP could focus on marketing. The opportunity to work together could also involve shared investment.
Problems & Solutions
5.1 Error sources
There are many ways in which the communication signal may have error introduced into it. Interference, cross chatter, some active devices, and some passive devices all introduce noise or attenuation into the signal. When error becomes significant the devices controlled by the unreliable signal may fail, become inoperative, or operate in an undesirable fashion.
1. Interference: Interference from nearby systems can cause signal degradation as the modem may not be able to determine a specific frequency among many signals in the same bandwidth.
2. Signal Attenuation by Active Devices: Devices such as relays, transistors, and rectifiers create noise in their respective systems, increasing the likelihood of signal degradation.
3. Signal Attenuation by Passive Devices: Transformers and DC-DC converters attenuate the input frequency signal almost completely. "Bypass" devices become necessary for the signal to be passed on to the receiving node. A bypass device may consist of three stages, a filter in series with a protection stage and coupler, placed in parallel with the passive device.
5.2 Need for repeaters
Because of the above attenuation losses the signal gets weak after travelling some considerable amount of distance, which if further prolonged will lead to loss of data. Thus equipment to boost the signal is needed along the power lines. The power lines would need repeaters to maintain signal integrity.
5.3 Bypassing across the transformers
Since the data signal cannot pass through transformers (in which case it would be lost), they must be bypassed. Routing data around transformers can be costly. Since power supply networks vary from country to country, the cost of transformer bypassing can vary. To generalize, houses take in a low voltage (LV), so the medium voltage (MV) used for transmission must pass through a MV/LV transformer before it can enter a house. In the US, 1-10 houses are served by a MV/LV transformer, in Japan the figure can be up to thirty, while in Europe several hundred houses can be serviced by a single transformer. This may account for the fact that BPL has been made commercially available in some European countries, while in the US utility companies are still engaging in trials. On the other hand, a report by the National Exchange Carrier Association estimated that it would cost $10.9 billion to lay the wiring needed to provide rural areas in the US with (conventional) broadband. Just because BPL would be a cheaper alternative does not mean it is economically viable.
The cost of transformer bypassing is not the sole economic headache for potential providers. Since power lines were never intended to be used for piggybacking data, a number of problems arose when trying to do so. These include high attenuation at high frequencies and noise (internal and external). As has been mentioned earlier, this leads to the necessity for a lot of error correction/prevention in any protocols using power lines as a physical layer.
5.5 Aerial effects
One thing that cannot be resolved, however is a failing in the electrical properties of the power lines themselves. They act as aerials because they are not shielded. This means that they can pick up noise and transmit it on as well as emit interference. Unfortunately, BPL operates at the same frequencies as short wave radio and low-band VHF. This can render various radio systems including those of governments unusable. Amateur radio enthusiasts the world over seem to be united in their distaste for what BPL does to the airwaves. This interference has historically scuppered BPL trials. A good example of this is the Nor.Web trial that began in 1998 in Manchester. Despite complaints about the interference and warnings from the Radiocommunications Agency, the company consistently rubbished criticism and insisted that the roll out would take place. By the end of 1999, the company had been closed down. In Japan, the technology will not be adopted because of the interference problem.
Fig 5.1: BPL acts as an aerial
Current trials seem to be suffering from the same problem. Power company Scottish Hydro Electric is currently offering BPL in three towns for Ã‚Â£35.99 and Ã‚Â£29.99 per month for 1 Mbps and 512 kbps connections respectively. While the price is in the region of DSL, the interference problem has not gone away: BBC engineers have confirmed this. Even in Germany where there are many companies offering commercially available BPL, the University of Duisburg-Essen has had similar findings when testing interference levels.
In the US, the FCC has approved guidelines for the implementation of BPL. This means that there is a set limit for acceptable radio emissions from the technology. Many US trials have found BPL financially unviable. Others currently taking place cannot meet the FCC requirements restricting radio emissions. In other countries, there are no guidelines for what is acceptable. Electricity companies have a steady core business. Why invest heavily in an unproven, unregulated technology that could be shut down as soon as a government realises that it is time to regulate or even ban the technology? The shareholders would not be very impressed.
Another problem with BPL is security. Since it transmits on a shared medium, like cable broadband, this makes it easier to snoop the line. Even though European operators have to spend less on transformer bypasses as has been already explained, the fact that the LV signal can potentially go to several hundred homes is not very secure. The same line going into many homes means the same traffic going down that line. This provides an opportunity for hackers to acquire sensitive data.
5.7 Solution to the radio interference
The only proposed solution to the radio interference BPL causes is one proposed by Corridor Systems. They propose to use microwaves instead of the lower frequency bands to transmit the data, meaning that radio equipment should not be interfered with. Supposedly, this could lead to data rates of up to 216 Mbps. In the US, the National Association for Amateur Radio (or ARRL, which has been one of BPLâ„¢s most vehement critics) has acknowledged that such a technology would not interfere with radio signals used by amateur radio enthusiasts. The electromagnetic spectrum is quite congested, however, and using the 2-20 GHz bands may just spawn more opponents to BPL. Radio astronomers, who make use of several protected frequency bands from 13 MHz all the way up to 275 GHz may be BPLâ„¢s next opponents. Given that the 1-10 GHz bands are especially important in this field of study, and that Corridor Systemsâ„¢ 2-20 GHz BPL has not yet undergone extensive trials (or even been implemented?), we can only speculate at this time.
5.8 Medium voltage lines
Access BPL equipment consists of injectors (also known as concentrators), repeaters, and
extractors. BPL injectors are tied to the Internet backbone via fiber of T1 lines and interface to the Medium Voltage (MV) power lines feeding the BPL service area. MV lines, typically carrying 1,000 to 40,000 volts, bring power from an electrical substation to a residential neighborhood. Low Voltage distribution transformers step down the line voltage to 220/110 volts for residential use.
MV power lines may be overhead on utility poles that are typically 10 meters above the ground. Three-phase wiring generally comprises an MV distribution circuit running from a substation, and these wires may be physically oriented on the utility pole in a number of configurations (e.g.horizontal, vertical, or triangular). This physical orientation may change from one pole to the next. One or more phase lines may branch out from the three phase lines to serve a number of customers. A grounded neutral conductor is generally located below the phase conductors and runs between distribution transformers that provide Low Voltage (LV) electric power for customer use. In theory, BPL signals may be injected onto MV power lines between two-phase conductors, between a phase conductor and the neutral conductor, or onto a single phase or neutral conductor.
Extractors provide the interface between the MV power lines carrying BPL signals and the households within the service area. BPL extractors are usually located at each LV distribution transformer feeding a group of homes. Some extractors boost BPL signal strength sufficiently to allow transmission through LV transformers and others relay the BPL signal around the transformers via couplers on the proximate MV and LV power lines. Other kinds of extractors interface with non-BPL devices (e.g. WiFi, WiMax) that extend the BPL network to the customersâ„¢ premises.
For long runs of MV power lines, signal attenuation or distortion through the power line may lead BPL service providers to employ repeaters to maintain the required BPL signal strength and fidelity.
6.1 Consumer products and services
Data and telephony are the primary consumer broadband products.
6.1.1 Broadband Internet Access
Broadband Internet access is the most common consumer application for a BPL network. BPL networks can provide data speeds in the range of 1.5 Mbps up to 12 Mbps, more than competitive with other broadband technologies. As electric power utilities already own and operate a network that reached right into almost all homes and businesses, a BPL network can make broadband service universally available to any residential or business consumer with electricity.
6.1.2 Voice over Internet Protocol (VoIP)
Voice over Internet Protocol (VoIP) is another common application on broadband data networks.The "always on" nature of the BPL connection combined with number portability allow a seamless replacement of consumers' current land line phone service. Continuing growth in domestic voice service demand is predicted, even in areas where service is available from traditional telephone service providers.Additionally, in some emerging economic areas of the world, the traditional telephone infrastructure is not well developed and typically lags behind the deployment of electric service. Telephone service delivered via BPL is an economic solution for these areas.
6.1.3 Multiple Dwelling Unit Deployments
BPL networks are ideally suited for the delivery of internet services in multiple-dwelling unit (MDU) buildings common in the residential, hospitality, and commercial markets. While similar to area-wide installations, MDU BPL networks typically connect to a new or existing high-speed data link in the basement where electricity enters the building, or with a roof-top wireless access point, and utilize the medium-voltage and/or the low-voltage power lines in the building.In buildings such as the one shown, a node located in the basement connects to the backhaul network and intelligently manages the interface to several in-building BPL network segments on the vertical risers.
In the meter rooms, the BPL communications signal is transferred to and from the vertical risers, amplified and managed by a node, and transferred to and from the apartment electrical feeds. This leverages the existing electrical infrastructure to avoid having to core drill through concrete, run conduit or pull cables to distribute the signal to every end unit. End-users plug a BPL modem into any of their power outlets to connect to the network. An in-building BPL network such as this is successfully currently supplying a 16 floor, 213 unit condominium building on Manhattan's West Side with high-speed internet access including VoIP service.
6.1.4 Utility Communications
These are possible at any point on the power distribution network by connecting a Voice over Internet Protocol (VoIP) gateway to an Ambient node. VoIP service is transmitted via the BPL connection, providing the reliability of a wired telephone
with the low infrastructure cost of a BPL solution. The system shown here is currently operating in a Consolidated Edison steam tunnel in New York City. In the inset, the VoIP phone is shown next to the node.
6.1.5 Real Time Pricing
This is where a variable price is charged based on current system demand, is facilitated by having a constant data path to each customer. Whereas traditional peak load pricing was dependent upon published time of day pricing, the BPL network allows the current price and usage data to be continually transmitted.
6.1.6 Intelligent Demand Side Management (IDSM)
This is enabled by Real Time Pricing. When customers have access to the actual current power cost, they can then choose to reduce their load or transfer that load to a more economical time.
6.1.7 Direct Load Control
These systems, in which the utility compensates the customer for the right to curtail certain loads (air conditioners, hot water heaters, dryers) for limited periods at peak load times. Once the BPL network is in place it can be used to monitor and disable loads,and allows for verification of compliance.
6.2 Public and industrial services
The same BPL network that serves the consumer and fulfills the utilityâ„¢s operating needs is also available to government and industry. The ability to access an economical high-speed always-on data network at any point on the electrical grid again enhances existing applications and enables new ones. Public and industrial applications are expected to grow rapidly as BPL networks are deployed and currently include:
6.2.1 Traditional remote monitoring applications
Alarms, door or window status, temperature, fire, or flood are enabled and enhanced by the continuous transmission afforded by the BPL network. The two way data path will surely lead to new enhancements in this area.
6.2.2 Video Security Surveillance (VSS)
This is also enhanced by integration into a BPL network. The high bandwidth and constant availability obsolete the need for recording equipment in each location - audio and video data can now be monitored in real-time from one central location.
6.2.3 Industrial process monitoring
This now requires dedicated internet or hardwired connections, can be easily implemented at any location on the BPL network, enabling applications ranging from simple monitoring of process conditions and equipment status to remote equipment operation.
6.2.4 Real-time traffic monitoring
Real-time traffic monitoring of high volume traffic areas via traffic cams can be greatly
expanded since once the BPL network is deployed every possible location is accessible through a high speed link.
6.3 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 intereference with other radio frequency devices in the vehicle or other places.
6.4 Overview Of Different Applications That Can Be Offered With BPL
Advances in BPL technology now allow for high-speed, broadband communications over medium and low voltage lines yielding potential market opportunities. Using BPL technology the utilities can now offer new facilities-based competition for broadband services and provide high speed access to qualified urban, suburban, and rural areas of the country.
BPL can help utilities maximize the value of their existing assets by leveraging the transmission and distribution network infrastructures. The business development managers in utilities, at present, are focused on more traditional transition into the market via energy related applications such as Automatic Meter Reading (AMR), demand side management, outage notification, distribution transformer overload analysis, phase loss monitoring, fault characterization, and several others.
Table 6.1. Different applications of BPL
Retail Applications Utility Applications
Â¢ Applications Management
Â¢ Community Websites
Â¢ Data Storage
Â¢ Distance Learning
Â¢ Electronic Markets
Â¢ File Transfer
Â¢ High Speed data
Â¢ Home Energy Management
Â¢ Home Networking
Â¢ Home Security
Â¢ Smart Appliance Monitoring
Â¢ Video Conferencing
Â¢ Voice-Over-IP (VOIP)
Â¢ Web-based government services Â¢ Automatic Meter Reading (AMR)
Â¢ Capacitor Control
Â¢ Copper Wire System Replacement
Â¢ Demand Prediction
Â¢ Detection and diagnosis of events at
capacitors and regulators
Â¢ Distribution transformer overload
Â¢ Line testing
Â¢ Microwave system replacement
Â¢ Outage localization and fault
Â¢ Phase loss detection
Â¢ Power quality monitoring
Â¢ Safety Check for isolated circuits
Â¢ SCADA delivery
Â¢ Substation monitoring
Â¢ URD outage diagnosis
Broadband over powerlines is definitely a beneficial technology when speed of access and cost of establishment are considered. It stands as best method of broadband access for those living in isolated areas, who have no other viable means of broadband access. In spite of providing high speed internet at low costs it suffers from interference problems and transformer bypassing problems. These problems seem to be severe when implemented in practical conditions. Many researches are going on this topic to explore all the benefits of this technology by nullifying the limitations to full extent. This technology is being tested in northern parts of America and Europe. Siliconindia News Buereau states that Broadband over power lines is set to overtake cable and digital subscriber lines (DSL) across United States. Sooner or later, transferring voice and data through power lines will be a reality in India as well.
Thus, I conclude that methods to nullify the limitations if explored, then BPL would be most successful technology in the competitive world of internet service.
Books referred :
1.Understanding broadband over power line by Gilbert Held ,
2. Broadband over powerlines by Ranveig Jordet
Websites referred :
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BROADBAND OVER POWERLINES
Gyana Ranjan Sethi
bpl is :-
An emerging technology in the competitive world of broadband Internet service offering high-speed access to your home through the most unlikely path: a common electrical outlet.
Combines technological principles of radio, wireless networking, and modems.
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