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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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plc power line communication
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
slide3
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
plc problems
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)
plc previous use
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
regulatory constraints
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
european regulations p 50
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
european regulations
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
power line characteristics
Power Line Characteristics
  • Not designed for high frequencies
  • Power line "hostile" to signal propagation
attenuation in plc
Attenuation in PLC
  • *The decrease in the value of something
  • Decrease in amplitude of an electrical signal
  • Opposite of amplification
  • Dependant upon Impedance
impedance in plc
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
noise in plc
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)
plc electromagnetic compatibility
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)
modulation
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
plc modulation scheme necessary properties
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
modulation properties
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
orthogonal frequency division modulation scheme ofdm
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
plc protocols
PLC Protocols
  • Several for low-bandwidth digital services
  • Products for home automation & home network are based on these
  • Differ in modulation, frequency, channel access
x 10 protocol
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
ce bus protocol
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
lon works protocol
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
home plug 1 0 protocol
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
home plug 1 0 cont
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
home plug 1 0 cont1
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
home plug av under research development
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
pl last mile broadband internet
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)
plc security
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
plc summary
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