HomePlug 1.0 PHY
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Transcript of HomePlug 1.0 PHY
HomePlug 1.0 PHY
(c) 2013 R. Newman
University of Florida
What is HomePlug 1.0?• Broadband PLC for home networking• Open industry standard
– 4 manufacturers (including Intellon)• Developed in 2000 by Homeplug Powerline
Alliance (HPA)– Consortium of chip designers, OEMs, PLC users– Products shipped in 2001
• First Ethernet class PLC, most widely available– 11 Mbps coded PHY data rate– 0ver 10 million units shipped ca. 2010
• Comprises– PHY – modulation, coupling, FEC, etc.– MAC – medium access, ARQ, etc.– Bridging – to other PLC networks or to 802.3/11/etc.
HP1.0 PHY• Orthogonal Frequency Division Modulation
• Cyclic prefix• Channel adaptation
• FEC• Turbo product code• RS/CC concatenated code
• Frames• Preamble• Delimiter• PHY body
• Physical Carrier Sense (PCS)
HP1.0 Transmitter
ProductEncoder
Frame Control
Interleaver
Frame Control FEC
ScramblerReed-
SolomonEncoder
Convo-lutionalEncoder
Puncturing
BitInterleaver
ROBOInterleaver
Data FEC
MappingInsert
PreambleIFFT
CyclicPrefix
RCShaping
Power Line
AFE
HP1.0 Receiver
ChannelEstimation
De-Interleaver
SynchronizationDetection
Convertto Polar
Demodulator
De-Puncture
ViterbiDecoder
Reed-SolomonDecoder
De-Scrambler
FFT
OFDM Demodulator
Data FEC Decoder
Frame Control De-
Interleaver
Product Decoder
Frame Control FEC Decoder
Power Line
AFE
HP1.0 OFDM
• 128 evenly spaced carriers 0-25 MHz• 5.12 us raw symbol time = 128 cycles 25MHz• 256 IFFT samples at 50 MHz clock
• Cyclic prefix set to typical delay spread• Reduces ISI• 172 IFFT samples, with 8 samples roll-off• 3.28 us guard interval• 8.4 us total symbol time
Cyclic Prefix
Ts
OFDM Symbol
Rolloff
Rolloff
Raw symbol
Transmit Spectrum Mask40
100
MASKy
300 y mhz0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
100
95
90
85
80
75
70
65
60
55
50
45
40
FREQUENCY MHZ
PO
WE
R D
BM
/ H
Z
FCC part 15 rules in North America restricts PSDDepends on frequency (other uses)
Band used by HomePlug 1.0
HP1.0 OFDM• Band used is 4.49-20.7 MHz
• 84 carriers fall in that band (23-106)• 8 carriers unused (FCC amateur bands)• 76 usable carriers
• FCC Part 15 rules limit power spectral density• -50dBm/Hz PSD– Much lower than WiFi
• OFDM (and high data rates) possible due to improved processing speeds/capabilities
• Good coupling across all power phases• Need only couple to one hot line + neutral
HP1.0 Carrier Modulation• 76 usable carriers
• All modulated with same method• Method depends on channel adaptation
• Modulation per carrier• Coherent BPSK (FC)• Differential BPSK (PHY payload)• Differential QPSK (PHY payload)
• Up to 14 Mbps raw PHY rate
• Physical Carrier Sense (PCS)
• based on sync detection
HP1.0 PHY Frame Format
PreambleFrameControl
FrameHeader
FrameBody
PAD FCS PreambleFrameControl
RIFS
PreambleFrameControl
25 bits 17 bytesVariable Byte
Count2 bytes 25 bits 25 bits
4 OFDMsymbol
4 OFDMsymbol
Start of frame delimeter(uses all tones)
Frameheader
Framebody
and pad
Checksequence
End of frame delimeter(uses all tones)
Responsedelimeter
(uses all tones)
4 OFDMsymbol
Variable symbol count20 - 160 OFDM symbols
HP1.0 FEC• Turbo product code/copy code
• Used in Frame Control (FC)
• RS/CC concatenated code
• Used in PHY Payload
• Rate 1/2 and 3/4 code – adapted to channel• Up to 10 Mbps after coding
• Robust Performance in presence of noise/jammers
• ROBO mode for broadcast/multicast
HP1.0 Frame Control FEC
Frame ControlInterleaver
ProductEncoder
25bits
100bits
336(max)
bits
• Rate ¼ Turbo Product code• (100,25,16) product code• Derived from (10,5,4) shortened extended
Hamming Code• Redundant Interleaver
• 4 symbols• 1 bit per carrier• Repeat codeword with offsets 0,25,50,75 over
the 4 symbols
HP1.0 Frame Control Interleaver
• Make table with S rows (one row per symbol)• S = 4 symbols in FC
• Fill each row with coded bits• Start row R with bit 25R for R=0,1,…,S• Step T = N/S, N = total coded bits
• Fill bits of symbol R with bits from row R• Since BPSK, use first K bits, K = # carriers
0 1 2 … … … … ... … … … … 74 75 … ... 98 9925 26 27… … … … … 74 75 … … 99 0 1 … … 2450 51 52… … … … … 99 0 … … 24 25 … … … 4975 76… … 99 0 … … 24 25 … … 49 50 … … … 74
Cutoff for coded bits for 76 carriers
HP1.0 Data FEC
• Reed-Solomon Code over GF(28)
• 23/39 – 238/254 for DBPSK, DQPSK
• 31/39 – 42/51 ROBO
• Derived from systematic (255,239,t=8) or (255,247,t=4) code
• Concatenated with Convolutional Code
• Constraint length 7
• Rate ½ or ¾
ScramblerReed-
SolomonEncoder
ConvolutionalEncoder Puncturing
Bit Interleaver
ROBO Interleaver
HP1.0 Convolutional Encoder
X output (G1 = 171 Octal)
rate-1/2, constraint length K=7
I input data
Y output (G2 = 133 Octal)
• Convolutional Code
• K=7
• Puncture rate ½ code to get ¾ rate code
HP1.0 ROBO Mode• Used for broadcast/multicast, or for unicast
when conditions are severe
• Coherent BPSK on all unmasked carriers
• 31/39 – 43/51 Reed-Solomon Code
• Rate depends on # unmasked carriers
• Derived from same codes as DPSK
• Convolutional Code
• Same as for DPSK
• Rate ½ only
• Redundant Interleaver makes 4x copy code
HP1.0 Channel Adaptation• Decide modulation and FEC rate
• Determine channel characteristics – Sounding
• DBPSK or DQPSK
• Convolutional Code Rate (½ or ¾) • Tone Map specifies these, plus• Which carriers to drop (SNR too low)
• RS rate adapted to # bits/PHY Tx block• Function of #carriers, bits/carrier, CC rate
• PHY transmission block 20 or 40 symbols
• 139 distinct rates achievable – nearly continuous• 1Mbps-14.1 Mbps
• Use ROBO if rate is better
HP1.0 Channel Adaptation
QPSK
QPSK- ¾ QPSK-½
BPSK-½
BPSK-¾
First determine highest rate R = CM each carrier’s SNR can supportFor each combination of coding C and modulation M rate, determine the
number N of carriers that can support itThen find combination that maximizes the product NR = bits/symbole.g., QPSK ¾ has NR = 5x¾x2=7.5 QPSK ½ has NR = 15x½x2=15 BPSK ¾ has NR = 22x¾x1=16.5 , BPSK, ½ has NR = 25x½x1=12.5
HP1.0 PHY PDU• Preamble
• Set pattern of symbols• Allows AGC, synch
• Frame Control (FC)• Heavily coded, BPSK (low rate)• Very robust• Very few information bits (25)
• FC holds info for PHY• Tone Map Index- for demodulation of body• Frame duration (how long to demodulate)
HP1.0 Preamble
• Preamble• Sync symbols lack cyclic prefix (repeated)
• + and – forms (– is inverted +) • 6 SYNC + symbols (give signal power, phase)• 1 ½ SYNC – symbols (give time reference)• Detection used for PCS
SYNCP GI FC1 GI FC2
FRAME CONTROLDATA
256 256 256 256 256 256 256 124420
SYNCPSYNCP SYNCPSYNCPSYNCP SYNCM
SY
NC
M
GI D1
....FC3GI FC4GI
PREAMBLE
HP1.0 PHY Frame Format
PreambleFrameControl
FrameHeader
FrameBody
PAD FCS PreambleFrameControl
RIFS
PreambleFrameControl
25 bits 17 bytesVariable Byte
Count2 bytes 25 bits 25 bits
4 OFDMsymbol
4 OFDMsymbol
Start of frame delimeter(uses all tones)
Frameheader
Framebody
and pad
Checksequence
End of frame delimeter(uses all tones)
Responsedelimeter
(uses all tones)
4 OFDMsymbol
Variable symbol count20 - 160 OFDM symbols
FC indicatesmodulationand length
• Detect delimiter from preamble, correct FC• SOF FC indicates symbol count, tone map• Pad Frame Body to PHY Tx block boundary• EOF FC delimits end of data frame
PreambleFrameControl
FrameHeader
FrameBody
PAD FCS PreambleFrameControl
RIFS
PreambleFrameControl
25 bits 17 bytesVariable Byte
Count2 bytes 25 bits 25 bits
4 OFDMsymbol
4 OFDMsymbol
Start of frame delimeter(uses all tones)
Frameheader
Framebody
and pad
Checksequence
End of frame delimeter(uses all tones)
Responsedelimeter
(uses all tones)
4 OFDMsymbol
Variable symbol count20 - 160 OFDM symbols
HP1.0 PHY Transmit Blocks• Basic unit of data transmission• 20-symbol and 40-symbol PHY Tx Blocks• Frame Length field in SOF FC gives length
• In multiples of 20 symbols• Start with as many 40 symbol PTBs as possible• End with zero or one 20 symbol PTB
• Note that PHY Transmit Blocks are not numbered or acknowledged individually• Whole MPDU is acknowledged
HP1.0 Priority Resolution Slots• Two Priority Resolution Slots (PRS0 and PRS1)• Follow end of a complete transmission (PPDU
plus response, if expected) and gap (CIFS)• Signal form is 6 SYNC– symbols
• These symbols have no CP, 30.72 usec. total• Same as preamble, but inverted and shorter
• Multiple senders will constructively interfere• Acts like “OR” of priority bits
• Priorities CA3=11, CA2=10,CA1=01,CA0=00• Start with MSB• If “1” assert bit, else listen if other STA asserts• If hear a “1” stop process, wait until next PRS0
• Slot duration 35.84 usec to allow processing time
HP1.0 PHY PerformanceIPT32 Throughput distribution - 472 houses - 6690 paths 5-11-01
0
200
400
600
800
1000
1200
1400
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5Mbps
Number
of paths
.00%10.00%20.00%30.00%40.00%50.00%60.00%70.00%80.00%90.00%100.00%
% of pa
ths with
through
put exce
eding X
axis valu
e
total paths in this 100 kbps band of thruput -includes missing pc2 filesno missing PC2 filesincluding missing PC2 files that could be noconnects
> 5 Mbps in 80% of paths> 1.5 Mbps in 98% of paths