24-07-2012, 12:59 PM
BROADBAND OVER POWER LINES
[attachment=28663]
Introduction
Despite the spread of broadband technology in the last few years, there are significant areas of the world that don't have access to high-speed Internet. When the number of customers is usually smaller, e.g. in rural areas, the Internet providers would face incremental expenditures of laying cable and building the necessary infrastructure to provide DSL or cable in many areas. 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.
Technology to deliver high-speed data over the existing electric power delivery network is now a reality. Broadband Over Powerline, is positioned to offer an alternative means of providing high-speed internet access, Voice over Internet Protocol (VoIP), and other broadband services, using medium – voltage and low – voltage lines to reach customers’ homes and businesses. 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 between 500 kilobits and 3 megabits per second (equivalent to DSL and cable). By 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.
1.1 Evolution of BPL
BPL is based on PLC technology developed in 1928 by AT&T Bell Telephone Laboratories, and which has been used for internal and low-speed data communication applications since that time by the electric power utilities. Based on PLC technology, some customer premises equipment (CPE) such as intercom systems, have used the embedded electrical wire to avoid the cost of special wiring. In Europe and most of the rest of the world, PLC standards allow for communications over the 220-240 volt power grid at frequencies of 30 KHz to 150 KHz. In the United States, the standards for the 120 volt power grid allow the use of frequencies above 150 KHz as well. Power utilities use the frequencies below 490 KHz for internal applications such as telemetry and monitoring and control of equipment at remote sub-stations. In the 1990s, development began on broadband over power line (BPL), which has since then been regionally standardized.
1.2 Possible media for broadband networking
Broadband access and services are delivered using a variety of technologies, network architectures and transmission methods. The most significant broadband technologies include:
• Digital Subscriber Line (DSL)
• Coaxial Cable
• Satellite
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 line’s ability to carry voice conversations.
Many people who have cable TV can now get a high-speed connection to the Internet from their cable provider. Cable modems allow users to access high-speed data services over the systems that are generally designed with hybrid fiber-coaxial (HFC) architecture.
Satellite Internet access is ideal for rural Internet users who want broadband access. Satellite Internet does not use telephone lines or cable systems, instead, it 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 disadvantages of the above systems are,
• In DSL systems, the quality of connection depends upon the proximity to the provider’s central office, closer the better. Also, receiving data is faster than sending data over the internet, i.e. it is asynchronous. And DSL is not available everywhere, hence for new connections, we have to trunk cables.
• The disadvantage of coaxial cable is that when there are heavy-access users, are connected to the channel, you will have to share the entire 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.
• 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 of sky, since the orbiting satellites are over the equator area. And, like satellite TV, trees and heavy rains can affect reception of the Internet signals.
1.3 Architecture of BPL
Broadband over Power Lines network is overlaid on the medium-voltage and low-voltage segments of the power distribution system. High-speed backhaul connections can be brought to the BPL network at substations or elsewhere along the medium voltage circuit. An Ambient node provides connectivity between the backhaul connection and the medium voltage segment of the BPL network. High speed data travels over this medium-voltage segment to remote locations where is it transferred to the low-voltage segment or to a wireless interface for the final leg to the end user or network element being managed. A simplified view is shown is Figure 1.1.
The diagram below (Inductive Coupling Injection Technique) shows how the BPL injector converts the IP data traffic into an RF signal in a signal cable. The signal is then injected into the MV or LV cable by induction using ferrite cores. This is known as “inductive coupling” and can be done without switching off power. An alternative injection technique, known as “conductive coupling” connects the signal cable directly to the electricity cables but requires the power to be switched off during connection for safety reasons.
The end-user simply connects a BPL modem to any power socket in the building for access to the BPL RF signal. The BPL modem converts the RF signal back into IP data. The end-user user then connects the BPL modem into a computer, server, switch, or wireless access point.
1.4Components of BPL Network
The entire BPL network can be built from a few basic types of components:
• Couplers
• Nodes
• Modems
• Coupleris a device that transfer the communications signal to and from power lines.
• Node is one whichreceives and transmits the signal from the medium and low voltage power lines. Nodes can be either a terminal equipment, repeaters or combination of both.
• Modemsare the devices that transfer the communications signal to and from end users. The modem is typically connected to either a router or the user's personal computer. In addition to an Ethernet interface, some modems may contain a standard telephone jack for internet telephony applications.
NICs convert the digital data to communication signals appropriate for the power lines and convert the broadband over power lines signals back into digital data. NICs also provide error correction and security functions. Each node can contain up to three NICs, depending upon the node's function. Each NIC is connected to either a primary (medium voltage) or secondary (low voltage) power line through a coupler.
1.5 Working of BPL
In order to provide data communication, the initial BPL systems coupled radio frequency (RF) data signals into the existing electric power lines. The high frequency data signals are transmitted through the same power lines that carry low frequency electricity to the household or business. This enables both signals to coexist on the same wire.
From the specific technological perspective, the basic idea of BPL technology is to modulate a radio signal with data and send it through power lines in a band of frequencies which are not used for supplying electricity. The frequencies used and the encoding scheme have a significant influence on the efficiency and the speed of BPL service. The encoding scheme which is used by most of the BPL providers is Orthogonal Frequency Division Multiplexing. OFDM is a technique used for transmitting large amounts of digital data over a radio wave. OFDM splits the radio signals into multiple smaller sub-signals that are then transmitted at different frequencies to the receiver. The transmission of data by OFDM along several of the carrier frequencies simultaneously increases speed and reliability. OFDM uses small packets to deliver data within the home, losing only small amounts of data rather than the whole signal.
Another encoding scheme which is used in BPL is Direct Sequence Spread Spectrum (DSSS). DSSS is one of two types of “spread spectrum techniques” wherein a data signal at the transmitter is combined with a higher data rate bit sequence, or chipping code, that divides the user data according to a spreading ratio. The chipping code is a redundant bit pattern for each bit that is transmitted, which increases the signal’s resistance to interference. Redundancy helps in recovering bits that are corrupted during transmission.
From the system’s perspective, BPL provides effective data communication through a combination of the electric network within the home or office, the power distribution grid, and the backbone network which transfers the data signal from the Internet Service Provider (ISP) to the power lines. BPL systems take advantage of one of the largest and the most pervasive networks, the power distribution grid.
The power distribution grid is made up of a number of components aimed at delivering electricity to customers, and includes overhead and underground Medium Voltage (MV) and Low Voltage (LV) power lines and associated transformers. First, power is generated at power stations and distributed around a medium to large geographical area via High Voltage (HV) lines. Second, in areas where power needs to be distributed to consumers, transformers will be used to convert this high voltage into a lower voltage to transport over MV power lines. These transformers are generally located at electrical sub-stations operated by the utility or power supplier. Such MV power lines will be used to transport electricity around smaller geographical areas such as small towns. Finally, for the purposes of using electricity in the home or business a transformer is used to reduce the voltage down to safer and more manageable voltages at the customer’s house or business premises. This power is usually transported over LV power lines. These LV power lines include the lines that traverse a customer’s home or business.
Figure 1.3 shows the simplified Medium Voltage (MV) BPL access network. The BPL signal in this network is transmitted over the MV system from a head-end in the local network, and for the purpose of final distribution of BPL service to the end user, either a local repeater to counter the signal-blocking effect of the local transformer, or alternatively a Wi-Fi wireless LAN access point can be used. In such countries as the United States where the local electricity supply is 120V, medium voltage (MV) systems deliver power very close to many premises with a much localised transformer providing the final 120V supply to relatively few premises, which can be as low as between one and six homes in rural areas.
Figure 1.4 shows the Low Voltage (LV) BPL access network, common in Europe and parts of Asia- Pacific. In this case, the system head-end is the local step-down transformer, and the LV wire is used for the broadband data distribution. In countries where the local electricity supply is 220-240V, the local step down transformer is usually located further from the final customer, and can distribute power to typically tens of hundreds of customers.
[attachment=28663]
Introduction
Despite the spread of broadband technology in the last few years, there are significant areas of the world that don't have access to high-speed Internet. When the number of customers is usually smaller, e.g. in rural areas, the Internet providers would face incremental expenditures of laying cable and building the necessary infrastructure to provide DSL or cable in many areas. 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.
Technology to deliver high-speed data over the existing electric power delivery network is now a reality. Broadband Over Powerline, is positioned to offer an alternative means of providing high-speed internet access, Voice over Internet Protocol (VoIP), and other broadband services, using medium – voltage and low – voltage lines to reach customers’ homes and businesses. 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 between 500 kilobits and 3 megabits per second (equivalent to DSL and cable). By 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.
1.1 Evolution of BPL
BPL is based on PLC technology developed in 1928 by AT&T Bell Telephone Laboratories, and which has been used for internal and low-speed data communication applications since that time by the electric power utilities. Based on PLC technology, some customer premises equipment (CPE) such as intercom systems, have used the embedded electrical wire to avoid the cost of special wiring. In Europe and most of the rest of the world, PLC standards allow for communications over the 220-240 volt power grid at frequencies of 30 KHz to 150 KHz. In the United States, the standards for the 120 volt power grid allow the use of frequencies above 150 KHz as well. Power utilities use the frequencies below 490 KHz for internal applications such as telemetry and monitoring and control of equipment at remote sub-stations. In the 1990s, development began on broadband over power line (BPL), which has since then been regionally standardized.
1.2 Possible media for broadband networking
Broadband access and services are delivered using a variety of technologies, network architectures and transmission methods. The most significant broadband technologies include:
• Digital Subscriber Line (DSL)
• Coaxial Cable
• Satellite
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 line’s ability to carry voice conversations.
Many people who have cable TV can now get a high-speed connection to the Internet from their cable provider. Cable modems allow users to access high-speed data services over the systems that are generally designed with hybrid fiber-coaxial (HFC) architecture.
Satellite Internet access is ideal for rural Internet users who want broadband access. Satellite Internet does not use telephone lines or cable systems, instead, it 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 disadvantages of the above systems are,
• In DSL systems, the quality of connection depends upon the proximity to the provider’s central office, closer the better. Also, receiving data is faster than sending data over the internet, i.e. it is asynchronous. And DSL is not available everywhere, hence for new connections, we have to trunk cables.
• The disadvantage of coaxial cable is that when there are heavy-access users, are connected to the channel, you will have to share the entire 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.
• 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 of sky, since the orbiting satellites are over the equator area. And, like satellite TV, trees and heavy rains can affect reception of the Internet signals.
1.3 Architecture of BPL
Broadband over Power Lines network is overlaid on the medium-voltage and low-voltage segments of the power distribution system. High-speed backhaul connections can be brought to the BPL network at substations or elsewhere along the medium voltage circuit. An Ambient node provides connectivity between the backhaul connection and the medium voltage segment of the BPL network. High speed data travels over this medium-voltage segment to remote locations where is it transferred to the low-voltage segment or to a wireless interface for the final leg to the end user or network element being managed. A simplified view is shown is Figure 1.1.
The diagram below (Inductive Coupling Injection Technique) shows how the BPL injector converts the IP data traffic into an RF signal in a signal cable. The signal is then injected into the MV or LV cable by induction using ferrite cores. This is known as “inductive coupling” and can be done without switching off power. An alternative injection technique, known as “conductive coupling” connects the signal cable directly to the electricity cables but requires the power to be switched off during connection for safety reasons.
The end-user simply connects a BPL modem to any power socket in the building for access to the BPL RF signal. The BPL modem converts the RF signal back into IP data. The end-user user then connects the BPL modem into a computer, server, switch, or wireless access point.
1.4Components of BPL Network
The entire BPL network can be built from a few basic types of components:
• Couplers
• Nodes
• Modems
• Coupleris a device that transfer the communications signal to and from power lines.
• Node is one whichreceives and transmits the signal from the medium and low voltage power lines. Nodes can be either a terminal equipment, repeaters or combination of both.
• Modemsare the devices that transfer the communications signal to and from end users. The modem is typically connected to either a router or the user's personal computer. In addition to an Ethernet interface, some modems may contain a standard telephone jack for internet telephony applications.
NICs convert the digital data to communication signals appropriate for the power lines and convert the broadband over power lines signals back into digital data. NICs also provide error correction and security functions. Each node can contain up to three NICs, depending upon the node's function. Each NIC is connected to either a primary (medium voltage) or secondary (low voltage) power line through a coupler.
1.5 Working of BPL
In order to provide data communication, the initial BPL systems coupled radio frequency (RF) data signals into the existing electric power lines. The high frequency data signals are transmitted through the same power lines that carry low frequency electricity to the household or business. This enables both signals to coexist on the same wire.
From the specific technological perspective, the basic idea of BPL technology is to modulate a radio signal with data and send it through power lines in a band of frequencies which are not used for supplying electricity. The frequencies used and the encoding scheme have a significant influence on the efficiency and the speed of BPL service. The encoding scheme which is used by most of the BPL providers is Orthogonal Frequency Division Multiplexing. OFDM is a technique used for transmitting large amounts of digital data over a radio wave. OFDM splits the radio signals into multiple smaller sub-signals that are then transmitted at different frequencies to the receiver. The transmission of data by OFDM along several of the carrier frequencies simultaneously increases speed and reliability. OFDM uses small packets to deliver data within the home, losing only small amounts of data rather than the whole signal.
Another encoding scheme which is used in BPL is Direct Sequence Spread Spectrum (DSSS). DSSS is one of two types of “spread spectrum techniques” wherein a data signal at the transmitter is combined with a higher data rate bit sequence, or chipping code, that divides the user data according to a spreading ratio. The chipping code is a redundant bit pattern for each bit that is transmitted, which increases the signal’s resistance to interference. Redundancy helps in recovering bits that are corrupted during transmission.
From the system’s perspective, BPL provides effective data communication through a combination of the electric network within the home or office, the power distribution grid, and the backbone network which transfers the data signal from the Internet Service Provider (ISP) to the power lines. BPL systems take advantage of one of the largest and the most pervasive networks, the power distribution grid.
The power distribution grid is made up of a number of components aimed at delivering electricity to customers, and includes overhead and underground Medium Voltage (MV) and Low Voltage (LV) power lines and associated transformers. First, power is generated at power stations and distributed around a medium to large geographical area via High Voltage (HV) lines. Second, in areas where power needs to be distributed to consumers, transformers will be used to convert this high voltage into a lower voltage to transport over MV power lines. These transformers are generally located at electrical sub-stations operated by the utility or power supplier. Such MV power lines will be used to transport electricity around smaller geographical areas such as small towns. Finally, for the purposes of using electricity in the home or business a transformer is used to reduce the voltage down to safer and more manageable voltages at the customer’s house or business premises. This power is usually transported over LV power lines. These LV power lines include the lines that traverse a customer’s home or business.
Figure 1.3 shows the simplified Medium Voltage (MV) BPL access network. The BPL signal in this network is transmitted over the MV system from a head-end in the local network, and for the purpose of final distribution of BPL service to the end user, either a local repeater to counter the signal-blocking effect of the local transformer, or alternatively a Wi-Fi wireless LAN access point can be used. In such countries as the United States where the local electricity supply is 120V, medium voltage (MV) systems deliver power very close to many premises with a much localised transformer providing the final 120V supply to relatively few premises, which can be as low as between one and six homes in rural areas.
Figure 1.4 shows the Low Voltage (LV) BPL access network, common in Europe and parts of Asia- Pacific. In this case, the system head-end is the local step-down transformer, and the LV wire is used for the broadband data distribution. In countries where the local electricity supply is 220-240V, the local step down transformer is usually located further from the final customer, and can distribute power to typically tens of hundreds of customers.