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Chapter 3 -- Power Line Communication Technologies. Why not use electrical lines?. PLC -- Power Line Communication. 60%+ U.S. homes have Internet access 10% broadband Inaccessible and costly PLC = No new wires: Emerging Technology Use of Power grid for communication

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Chapter 3 -- Power Line Communication Technologies


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    1. Chapter 3 -- Power Line Communication Technologies Why not use electrical lines?

    2. PLC -- Power Line Communication • 60%+ U.S. homes have Internet access • 10% broadband • Inaccessible and costly • PLC = No new wires: • Emerging Technology • Use of Power grid for communication • Extensive infrastructure • "Every" building

    3. PLC • Features • Home-Plug 1.0 PLC networking protocol • Other services (in the house) • In-home entertainment • Internet home appliances • BPL -- Broadband Power Line (outside house) • A "last-mile" technology • Wireless Internet

    4. PLC -- Problems • Need high frequencies: current lines designed @ 50-60 Hz to 400 Hz • Contaminated -- noise, unreliable • Legal restrictions on frequency bands limit data rates • Power Loss • Directly proportional to square of current • Proportional to distance • High, medium, & low voltage lines & customer premise lines • See Figure 3.1 (pg. 49)

    5. PLC -- Previous Use • Due to past low data rate communication needs, utility companies used PLC to maintain power grid • New technologies allow high data-rate communication over low-tension lines

    6. Regulatory Constraints • Regulatory agencies • Federal Communications Commission (FCC) • European Committees for Electrotechnical Standardization (CENELEC) • North America • 0 to 500 kHz and part of 2 to 30 MHz unlicensed spectrum are used for PLC • General -- Regulate • Band allocation • Radiation emission • Power transmission on band

    7. European Regulations (p. 50) Frequencies / Use • 3-9 kHz: energy providers; customers premises • 9-95 kHz (A-band): energy providers & concession holders • 95-125 kHz (B-band): energy provider's customers • 125-140 kHz (C-band): energy provider's customers • 140-148.5 kHz (D-band): energy provider's customers • B & D-band no access protocol defined

    8. European Regulations 6. 2-30 MHz • Home plug 1.0 uses • Unlicensed by FCC • Europe: efforts to develop a standard for electromagnetic compatibility with PLC General: Regulate • Band allocation

    9. Power Line Characteristics • Not designed for high frequencies • Power line "hostile" to signal propagation

    10. Attenuation in PLC • *The decrease in the value of something • Decrease in amplitude of an electrical signal • Opposite of amplification • Dependant upon Impedance

    11. Impedance in PLC • *The opposition a circuit presents to an electrical circuit (in ohms) • Maximum signal received only when impedance of all components (transmitter, power line, receiver) match • Power line systems vary significantly • Also varies with signal frequencies, time, load pattern • Mismatches are destructive (Figure 3.2 -- Pg. 51) • Ethernet & other dedicated lines have known impedance

    12. Noise in PLC • Major source: Electrical Appliance • e.g. run vacuum cleaner when TV on • those @ 60 Hz (N.A.) & 50 Hz (Eur.) • Also radio signals from broadcast, commercial, military, CB, amateur stations • 3 categories of appliance noise • Impulsive: on/off switches • Periodic impulsive: dimmers • Continuous impulsive: AC motors (vacuum, shavers) -- most severe)

    13. PLC Electromagnetic Compatibility • Power lines are leaky: radiate high-frequency electromagnetic signals • Interferes with nearby wireless devices • Need filters to prevent leakage • 802.11b wireless network protocol (WiFi)

    14. Modulation • Process of varying a carrier signal to use the signal to convey information • Analog vs. digital • Amplitude, phase, frequency • Why? To allow different components compatible • Modem: modulate -- demodulate

    15. PLC Modulation SchemeNecessary Properties • Ability to overcome nonlinear channel characteristics • PLC is very nonlinear • Requires expensive, complex equalization to obtain more than 10 Mbps • Should overcome without highly involved channel equalization • Ability to cope with multipath spread • Impedance mismatch causes echo signal, delaying signal by ~1ms • Must handle delays

    16. Modulation Properties 3. Ability to adjust dynamically • PLC changes with load • Must track without large overhead or complexity 4. Ability to mask certain frequencies • PLC uses unlicensed frequency band but regulations limit radiation in some sub & adjacent bands • Masking would help marketability of PLC

    17. Orthogonal Frequency DivisionModulation Scheme - OFDM • OFDM -- Collection of transmission techniques • OFDM meets all desirable properties • Used in European digital audio broadcast (DAB) • Also in some variants of 802.11x -- wireless protocols • Used in Home Plug 1.0 • See list of advantages on pg. 54

    18. PLC Protocols • Several for low-bandwidth digital services • Products for home automation & home network are based on these • Differ in modulation, frequency, channel access

    19. X-10 Protocol • Oldest, uses ASK modulation • Originally unidirectional -- controller to devices • Some bidirectional products • Typically, signals over PL to receivers controlling lights & appliances • Poor bandwidth utilization • 60 bps on 60 Hz line • Poor reliability in noisy environments • Limited application

    20. CE Bus Protocol • Peer-to-peer communication • Avoids collisions via CSMA/CRCD protocol (carrier sense multiple access/collision resolution & collision detection) • Physical layer: spread spectrum technology patented by Intellon Corp. • Sweeps thru frequencies rather than hopping • From 100 to 400 kHz • Sweep called chirp -- used for synchronization, collision resolution, data transmission • Data rate ~10kb/s • Frequency used limits use in North America

    21. Lon Works Protocol • Peer-to-peer communication • Developed by Echelon Corp. • Uses CSMA • Narrow band spread spectrum modulation • 125 to 140 kHz • Patented noise cancellation technique • Preserves data in presence of noise • Can be used in N. America and Europe • Due to narrow band

    22. Home Plug 1.0 Protocol • Achieves Ethernet class network on-site using existing electrical wiring • Has been introduced in American market • Mitigates unpredictable noise • Splits bandwidth into many small sub channels • Masks noisy ones & others • Maintain 76 for use in U.S. market • Data rate: 1 to 14 Mbps • Nodes estimate each 5 sec. & adapt to optimal data rate

    23. Home Plug 1.0(cont) • But, still use DSL or cable for Internet into home • CSMA/CA -- collision avoidance • MAC -- medium access control • Avoidance • PHY layer detects preamble of frame • MAC layer maintains virtual timer • Each frame is preceded by contention period, if none transmits during, it can

    24. Home Plug 1.0 (cont) • 4 Priorities (for QoS) • Use back off schedules if detect transmission • (8-16-32-64) & (8-16-16-32) • Also use decremented counter for ties

    25. Home Plug AVUnder Research/Development • By Home Plug Alliance • Goal 100 Mb/s for in home PL network • Necessary for multimedia (e.g. HDTV) • Rivals wired nw protocols (Ethernet) • Accommodates new hybrid power lines & wireless network – • Simple, reliable, cost-effective • Plug-and-play

    26. PL & Last Mile Broadband Internet • Home Plug 1.0 -- still depends on DSL or cable to bring Internet into home • 18 million miles of power lines in U.S. • Developing countries have PL but not DSL/cable • Techniques/devices being developed for this (pg. 59)

    27. PLC Security • PLC is shared channel (like WiFi) • Robust security is serious issue • Encryption necessary: security vs. complexity • Rivest: 128 bit key • Home Plug: DES - 56 bit key • Intrusion & interference from adjacent subnets • e.g. Apartments - contention, degradation • Decoupling filters - isolate circuits at meter • Can also "separate" power line with router

    28. PLC -- Summary • Tremendous potential • Existing infrastructure • Much research -- many companies • Relatively low cost • Obstacles • Compatibility, security, reliability • Bandwidth • Regulatory issues • Two related "problems" • Inside house vs. Outside the house