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CIS 6930 Powerline Communications Special Issues

(c) 2013 Richard Newman. CIS 6930 Powerline Communications Special Issues. Special Issues in PLC. Noise PCS/VCS Hidden nodes High speed issues Cross-layer design Coexistence. Noise. Low transmit power Statutory limits on emissions in varous bands

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CIS 6930 Powerline Communications Special Issues

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  1. (c) 2013 Richard Newman CIS 6930Powerline CommunicationsSpecial Issues

  2. Special Issues in PLC • Noise • PCS/VCS • Hidden nodes • High speed issues • Cross-layer design • Coexistence

  3. Noise • Low transmit power • Statutory limits on emissions in varous bands • Vary by country – FCC part 15 rules in US • Lower in Europe, Japan, Korea • High interference • Dynamic and frequency-specific noise • Impulse noise

  4. Carrier Sense • Desirable to avoid collisions • Carrier sense (determine if medium is busy) • Physical Carrier Sense (PCS) • Possible in media with good SNR, strong carrier • Not feasible in PLC, wireless • Virtual Carrier Sense (VCS) • Needed when PCS not possible • Detect synch/delimiters • Increases logic, complexity, time

  5. Virtual Carrier Sense • Needed when PCS not possible • Carrier(s) difficult to detect directly (SNR) • Detect synch/delimiters • Circuit matches synch pattern when searching • Looks for delimiter following synch • Have to verify delimiter (false synch problem) • Must listen for sufficient time to detect busy state • Delimiters indicate busy duration • Include type and length field if not fixed length • Delimiter must be very robust, else collisions

  6. Hidden Nodes • Each node pair has channel characteristics • Local noise • Multipath effects • Interference • Attenuation • Hidden nodes • A may hear B but not C, B may hear A and C, etc. • May be multiple layers • Capture effect • If A and C both send, B may receive one and not other • Other sender acts as noise source, affects reliability

  7. Hidden Node “Solutions” • Request to send/Clear to sent (RTS/CTS) • Source issues RTS • Destination issues CTS if OK • Handles one layer of hidden nodes • Scheduling • Coordinator issues TDM periods for node sets • Reuse possible (disjoint node set neighborhoods) • Challenging • Multiple layers • Tree topology helps (two-coloring problem)

  8. High Speed Issues • Many fixed overheads • Synch, robust delimiters (SOF, ACK) • Required idle time gaps (spaces) on wire • RTS/CTS if hidden nodes • Diminishing returns on PHY speed • Time T = Tfixed + Tpayload • Efficiency E = Tpayload/(Tfixed + Tpayload) • Must increase Tpayload to improve E • Tpayload = Length/Data Rate = Lpayload /Rpayload • Must increase payload length….

  9. Cross-layer Design • Noise at PHY level affects what MAC must do • VCS requires robust delimiters • Impulse noise affects error handling in MAC • Speed of PHY affects MAC design • Robust delimiters take long time • Diminishing returns on PHY speed due to OH • MAC results affect PHY • Delimiter verification • VCS derived from MAC processing

  10. Coexistence • In-home and access broadband PLC operate in same band • Disaster if PLC technologies sabotage each other • Standardization efforts • CENELEC • IEEE p1901 • OPERA

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