Efficient Framing and ARQ for High-Speed PLC Systems Srinivas Katar Larry Yonge (Intellon)...
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Transcript of Efficient Framing and ARQ for High-Speed PLC Systems Srinivas Katar Larry Yonge (Intellon)...
![Page 1: Efficient Framing and ARQ for High-Speed PLC Systems Srinivas Katar Larry Yonge (Intellon) srinivas.katar@intellon.com Richard Newman Haniph Latchman (Univ.](https://reader030.fdocuments.net/reader030/viewer/2022032805/56649ee95503460f94bfabed/html5/thumbnails/1.jpg)
Efficient Framing and ARQ for High-Speed PLC Systems
Srinivas Katar
Larry Yonge
(Intellon)[email protected]
Richard Newman
Haniph Latchman
(Univ. of Florida)[email protected]
![Page 2: Efficient Framing and ARQ for High-Speed PLC Systems Srinivas Katar Larry Yonge (Intellon) srinivas.katar@intellon.com Richard Newman Haniph Latchman (Univ.](https://reader030.fdocuments.net/reader030/viewer/2022032805/56649ee95503460f94bfabed/html5/thumbnails/2.jpg)
PLC Evolution in a Nutshell
• > 5 yrs ago: Low speed control applications• 1-5 yrs ago: Medium speed data transfer• Now + future: High speed AV, BPL
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QoS Goals for AV PLC
• Data speeds - must sustain application rates of – 6 Mbps per SDTV connection– 24 Mbps per HDTV connection
• Must be QEF (quasi-error-free) for video• Must meet latency requirements (10 ms for
voice, 300 ms for video)
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PLC MAC
• High attenuation => CS but no CD• Per-channel adaptation => Virtual Carrier
Sense• VCS => Broadcast delimiters• Broadcast => high fixed OH per MPDU• High PHY rates => concatenation• Impulse noise….
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Framing Processes
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Powerline Characteristics
• High attenuation• Periodic noise floor variations• Isolated impulse noise• Periodic impulse noise• Continuous impulse noise
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Powerline Attenuation Example
Typical Frequency Response
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Powerline Noise Examples
Dimmer switch
Hair dryer
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Channel Adaptation and MAC Framing
• Impulse noise power is high• Adapting channel to eliminate impulse
noise effects may be impossible• Even when possible, it may reduce data
rate excessively• Hence, need robust ARQ mechanism
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MAC Framing Requirements
• High efficiency absent errors• Ability to cope with errors from impulse
noise• Efficient retransmission• Privacy
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MAC Framing Strategies• 1 MSDU per MPDU - low efficiency
– 25% efficiency sans errors for 1518 B enet pkt
• Require concatenation of MSDUs
• Even with concatenation, single acknowledgement per MPDU too inefficient– <8% for 24 FEC blocks at 10% FER– <30% for 24 FEC blocks at 5% FER
• Require partial delivery to handle inevitable impulse errors
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Viable MAC Framing Strategies
• Viable = concatenation and partial delivery
• Simple Concatenation• Concatenation with demarcation• 2-level framing
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Simple Concatenation
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Simple Concatenation
• Framing– MSDU sequence number (SN)– MSDU Length (Len)– MSDU Frame Check Sequence (FCS)
• Advantages– Low, low overhead– Simplicity
• Disadvantages– MPDU padding to fit PPDU– Loss of all data following FEC block error
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Concatenation with Demarcation
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Concatenation with Demarcation• Framing
– add Header Check Sequence (HCS) to resynchronize after FEC block error
– ID within MPDU (for bitmap Selective ACK)
• Advantages– Can recover data after FEC block error– Selective retransmission of MSDUs
• Disadvantages– More complex– still pad– single FEC block error can corrupt two MSDUs
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2-Level Framing2-LevelFraming
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2-Level Framing• Framing per MSDU - Length• Framing per FEC block
– FCS per FEC block– FEC block SN– MSDU boundary flag and offset
• Advantages– Selective retransmission of FEC blocks– Padding may be avoided– simplifies memory management
• Disadvantages– Complexity
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Framing Efficiency Metrics
• Ratio of total bits of data successfully delivered to total bits sent
• Bits sent includes framing overhead bits and retransmissions
• Ignore MPDU overheads (same for all and system dependent)
• Assume fixed size FEC blocks• Assume FEC block errors independent
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Simple Concatenation Efficiency
fec
msdu
mf
feck
mf
fecN
k
kSC LN
L
L
Lkp
L
Lkpp
111
1
• p = FEC Block error rate• k = location of first error
• Lfec = Length of FEC Block
• Lmf = Length of MAC Frame
• Lmsdu = Length of MSDU
• N = number of FEC Blocks
![Page 21: Efficient Framing and ARQ for High-Speed PLC Systems Srinivas Katar Larry Yonge (Intellon) srinivas.katar@intellon.com Richard Newman Haniph Latchman (Univ.](https://reader030.fdocuments.net/reader030/viewer/2022032805/56649ee95503460f94bfabed/html5/thumbnails/21.jpg)
2-Level Framing Efficiency
• p = FEC Block error rate
• Lfec = Length of FEC Block
• LOH,sb,2L = per FEC Block overhead
• Lmsdu = Length of MSDU
• N = number of FEC Blocks
fec
msdu
fec
LsbOHfecL LN
L
L
LLp 2,,
2 1
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MSDU length = 1518 bytes (Ethernet)
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Conclusions• Fixed overheads in PLC and wireless
communications require concatenation when PHY rates are high
• Simple concatenation methods suffer from poor retransmission options
• 2-Level framing method solves these problems, is highly efficient; efficiency independent of MPDU length