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


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


FrameHeader

FrameBody


RIFS




4 OFDMsymbol

4 OFDMsymbol


Frameheader

Framebody

and pad

Checksequence


Responsedelimeter

(uses all tones)

4 OFDMsymbol


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


FrameHeader

FrameBody


RIFS




4 OFDMsymbol

4 OFDMsymbol


Frameheader

Framebody

and pad

Checksequence


Responsedelimeter

(uses all tones)

4 OFDMsymbol


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

Documents

HomePlug 1.0 PHY