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PLC Transmission PLC Transmission Prototype using TDS-O d Ch lOFDM and MV Channel ModelingModeling

Jian SongDept Of Electronic EngineeringDept. Of Electronic Engineering

Tsinghua University2012-03-29

OutlineOutline

Introduction

TDS-OFDM based PLC Prototype

Medium-Voltage Channel Modeling

Summary and Future Plan

DTV Technology R&D Center

ObjectiveObjective

Major system parameters j y pBandwidth: 20MHz (with scalability)Length of frame body: 4096 data symbolsLength of frame head: 350 and 700 symbolsModulation: QPSK/16QAM/64QAM/256QAMFEC rate: 0 4/0 6FEC rate: 0.4/0.6

Performance specificationsMax. throughput: 160 Mbps (W/O PN)Max. payload: >100MbpsMax multi path delay: 25usMax. multi-path delay: 25usMax. frequency offset: 300Hz


OutlineOutline

Introduction





System block diagramSystem block diagramFrame Head

FECMappingInterleaver

Scrambler

MUX

FrameBodyPro-

i

BasebandProcessing

Datainput

CombinePowerLine

SystemInformation

X cessing

SynchronizerDigital Signal

Processor

ADC SRRC filterChannel Estimator

and EqualizerPower Line

De-interleaverDe-mappingLDPC decoder

De-scramblerOutput data


Characteristic of TDS-OFDMCharacteristic of TDS OFDM

PN sequence is used as the guard interval, PN sequence is used as the guard interval, as well as the training sequence for the channel acquisition, time synchronization, and channel estimationMain featureFast channel acquisition since this can be done directly

in the time domain, robust for timing variable channel

High spectrum efficiency as it avoids both continuousHigh spectrum efficiency as it avoids both continuous and scattered pilot insertion into the frame body by CP-OFDM approach

More accurate channel estimation due mainly to the good correlation of PN sequence (spreading gain)


TDS-OFDM vs C-OFDMC-OFDM

Copy

CP IDFT D t Pil t CP IDFT D t Pil t

Copy

C-OFDM

CP IDFT Data+Pilots CP IDFT Data+Pilots

IDFT DataGI ZP could be another possible padding

C-OFDM：Process in Frequency domainIDFT=Inverse Discrete Fourier Transform

ZP could be another possible padding

TDS-OFDM Symbol

PN IDFT Data IDFT DataPNTDS-OFDM

PN IDFT Data IDFT DataPN

TDS-OFDM：Process in Time/Frequency domain


Interference Cancellation is NEEDED

Channel estimation is challengingChannel estimation is challenging- Mutual interference between Data and PN sequence

Transmitted Signal

DATA DATAPN PN

g

ConvolutionReceived Signal

DATA PN DATA PN

?PN signal without

PN

?g

interference from dataDouble PN to avoid

mutual interference?


PN

Hardware Platform

The highest payload data e g est pay oad datathroughput is 104 Mbps within 20MHz by using 256-QAM and LDPC rate of 0.6


Prototype SetupPrototype Setup


Frame Structure DesignFrame Structure Design

, 1 ,Lt

Lu

m i m i

p p

p p1, ,m i m i p p


Multiple AccessMultiple Access

Scalable TDMA + TDS-OFDMA


Scalable TDMA + TDS-OFDMA

Adaptive Bit LoadingAdaptive Bit Loading

Bit-loading algorithms for multi-rate Bit-loading algorithms for multi-rate LDPC coded OFDM system Optimization overOptimization overQPSK/16QAM/64QAM/256QAM

LDPC 0 4/0 6LDPC 0.4/0.6

Adapt the Constellation & coding mode according to the SNR estimation on each according to the SNR estimation on each sub-carrier and SNR threshold for each code rate and constellationcode rate and constellation


OutlineOutline

Introduction





Channel modelingChannel modeling

N

Approximation by the echo model:

0 1

1

2 /( ) i i pN

a a f

ii

k d j f d vH f g e e

attenuation delayh

1i attenuation delayweighting portion portion factor

E d fi itiError definition:

1 M

1

1 M

i ii

ERR H yM


1iM

Channel measurementChannel measurement


MV-Measurements

DTV Technology R&D Center 18Frequency (MHz)

MV-Measurements (cont’d)( )

DTV Technology R&D Center 19Frequency (MHz)

Average Attenuationg

10

-20

-10

Attenuation in three siteSite A--Site BSite B--Site ASite B--Site CSite C--Site B

-40

-30

B

-60

-50

Atte

nuat

ion:

dB

-80

-70

0 5 10 15 20 25 30 35 40-100

-90

Frequency:MHz

DTV Technology R&D CenterFrequency (MHz)

Frequency:MHz

Measurement (site B-> site A)

-20Station B --> Station A

meas

-30

meas.model

-40

dB

-60

-50

|H(f)

| in

-70

0 5 10 15 20 25 30-80

Frequency in MHz, ERR=0.697dB


Measurement (site A-> site B)Measurement (site A > site B)

-20Station A --> Station B

-30

20meas.model

-40

B

-50

|H(f)

| in

dB

-70

-60

0 5 10 15 20 25 30-80


Frequency in MHz, ERR=1.27dB

OutlineOutline

Introduction

TDS-OFDM based PLC prototype

Medium-voltage Channel Modeling



SummarySummary

TDS OFDM h l i f ibl b TDS-OFDM technology is feasible to be adopted by the powerline communication systems with potentially high spectrum efficiency

better capability to track the channel variation

Medium voltage channel is different from the low-voltage with the clear large scale effect

Research on power allocation algorithm can Research on power allocation algorithm can be conducted based on good channel modeling


Future WorkTraining sequence in frequency domain helping

remove the noise enhancement effect for the remove the noise enhancement effect for the channel estimation

BICM-ID for better error correction performance

0.15

0.2

0.25

0.3

-2-1

01

23

-2

-1

0

1

2

30

0.05

0.1

-3-3

Only Gaussian inputs achieve the AWGNOnly Gaussian inputs achieve the AWGN channel capacity. circular APSK rather than square QAM constellations seem closer to


Gaussian inputs.

Future work

X

p | ,λy x p | ,λy x

Λ

2.5QAM w/o SSD or Rotation

2.0

64-aryut (d

B)

QAM w/o SSD or Rotation QAM with SSD and 45o Rotation APSK w/o SSD APSK with SSD

Gaps between the DCMC

1.0

1.5

y

Gau

ssia

n in

pu 16-ary capacity and the channelcapacity. APSK plus SignalSpace Diversity (SSD) overi i d R l i h f di h l

0.5

Gap

to th

e G i.i.d. Rayleigh fading channels.

DTV Technology R&D Center1 2 3 4 5

0.0

AMI (bits/channel use)

ReferencesReferences

1. H. Liu, et al., “Channel Study for Medium-voltage Power Network”, IEEE International Symposium on PowerLine Communications and its Applications 2006, P.245-250, Florida, USA.

2. J. Song, et al., “Field Trial of Digital Video Transmission over Medium-Voltage Powerline with Time Domain Synchronous Orthogonal Frequency Division Multiplexing Technology”, IEEE International Symposium on PowerLine Communications and its Applications 2007, pp.559-564, Pisa, Italy

3. Z. Yang, et al., “Labeling optimization for BICM-ID systems,” IEEE Commun. Letters, vol. 14, no. 11, pp. 1047–1049, Nov. 2010.

4. H. Zhang, et al., “A Hughes-hartogs algorithm based bit loading algorithm for OFDM systems”, ICC 2010, Cape Town, South Africa.

5. Dai LingLong, et al., “A Novel Time Domain Synchronous 5. Dai LingLong, et al., A Novel Time Domain Synchronous Orthogonal Frequency Division Multiple Access Scheme”, IEEE Globecom 2009.


Thanks to all the diligent work of Jian Fu, Jintao Wang, Fang Y H i Y Li l D i H i i Zh Qi W dYang, Hui Yang, Linglong Dai, Huimin Zhang, Qing Wu, and etc.

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