SungKyunKwan Univ.

1VADA Lab.

L40: Lower Power Equalizer

J. W. Kim and J.D.Cho성균관대학교

http://vada.skku.ac.kr

SungKyunKwan Univ.

2VADA Lab.

Low Power Equalizer • Jin Woo Kim, J.D.Cho, 1999, SKKU• Introduction• Equalizer• Low-Power Methodology in Equalizers• Simulation• Future Work• Reference

SungKyunKwan Univ.

3VADA Lab.

Introduction – xDSL(Digital Subscriber Line)

• Provide high bandwidth over copper twisted pair local loop cable, without amplifiers or repeaters

• Utilize full potential of a copper telephone subscriber loop up to a few hundred times that of a voiceband modem

• Support industry – standard transmission formats and bit rate such as T1 and E1

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4VADA Lab.

Introduction – xDSL Channel Configuration

CentralOffice

RemoteLocation

CentralOffice

CentralOffice

CentralOffice

ONU

CentralOffice

RemoteLocation

RemoteLocation

RemoteLocation

RemoteLocation

ADSL

HDSL

SDSL

VDSL

FTTH

6Mbps(1Mbps)

1.5Mbps

784Kbps

52Mbps

2.4Gbps

3Mbps

64Kbps(384Kbps)

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5VADA Lab.

DMT for ADSL( Discrete MultiTone Modulation)

• Built-in subchannel optimization• Ongoing active monitoring• Maximum loop variation coverage• Highest level of rate flexibility• Superior noise immunity for greater throughput• Broad industry chipset support• Interoperability through standards• Virtually future proof

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6VADA Lab.

DMT SubChannel Allocation for ADSL

• #1 ~ #6 : Analog Voice• #7 ~ #38 : Upstream Channels• #7 ~ #256 : Downstream Channels

10 32 7 8 38 256

4.3125 30.1875 163.875 1104 [KHz]

[Subchannelnumber]

AnalogVoice

Upstream

Downstream

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7VADA Lab.

ADSL Block Diagram ( DMT )

ErrorControlCoding

BitMapping

Pre-coding IFFT

CyclicPrefix

Insertion

DigitalFilter DAC

AnalogFilter

HybridCircuit

AnalogFilter

AGC

ADC

POTSSplitter

TEQCyclicPrefix

RemovalFFT

EchoCanceller

FEQSymbolRecovery

ErrorDe-

coding

Twisted PairTelephone Loop

POTS Telephone Setor Voice Band Modem

TransmitBit

ReceiveBit

TEQ : Time Domain EqualizerFEQ : Frequency Domain EqualizerAGC : Auto Gain Control

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8VADA Lab.

Equalizer – TEQ ( Time Domain Equalizer )

• TEQ with a small number of taps can reduce the cyclic prefix(CP)

• Power Consumption Critical Part

• Adaptive FIR filters (LMS algorithm)– The Filter Output

– The Filter Coefficient

– The Error Signal

1

,0

N

k k n k nn

y w x

1, , 0 1kk n k n k nw w e x for n N

k k ke I y

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9VADA Lab.

Equalizer – Example of TEQx (n)

w0 w1 w 2 w 3 w 4

x (n)

y (n)

e (n )

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10VADA Lab.

Equalizer – FEQ ( Frequency Domain Equalizer )

• Compensate for the remaining frequency dependent attenuation and phase rotation of each subchannel

• Complex One-Tap FIR filter per one subchannel (ADSL ; 256-7)

SungKyunKwan Univ.

11VADA Lab.

Equalizer – Example of FEQ• LMS(Least Mean Square) Adaptive Filter

x y

x̂

Conjugate

x *

c

- +

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12VADA Lab.

Low Power Methodology in Equalizers – Circuit

• FIR Filter– Carry-save adder– Grouped Multipliers(Wallace Tree Multiplier)– Booth Recoding technique

• Updating Circuits– Power-of-two LMS updating– The use of register file– Coefficient freezing– Make step size constant() to power-of-2

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13VADA Lab.

Low Power Methodology in Equalizers – Run-time

• The Error Monitor

• Adaptive Bit Precision

• Burst-Mode Update

• Adaptive Filter Length

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14VADA Lab.

Low Power Methodology in Equalizers – Example

FIR filter Programmablegain Slicer

Update Errormonitor

Control

x

w A

z y

e

FreezeLocal_update

Error_statusCheck_Err

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15VADA Lab.

Simulation – Environment (1)

Input SequencePRD(Pseudo Random Sequence)[T1E1.4]

4 9

1 for n=1to9for n=10 to 512

n

n n n

dd d d

Make 4-QAM symbols as Training Sequence

SungKyunKwan Univ.

16VADA Lab.

Simulation – Environment (2)• Test Channel

– CSA#6• 26AWG(0.4mm)• 9000ft(about 2.7Km)

– AWGN noise environment– SNR 40dB

ATU-C ATU-R9000ft

26 AWG

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17VADA Lab.

Simulation – Channel ( Impulse Response )

Impulse Response

- 0.001

0

0.001

0.002

0.003

0.004

0.005

1 51 101 151 201 251

Time

Magn

itude

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18VADA Lab.

Simulation – Before Training( Received constellation )

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19VADA Lab.

Simulation – Before Training( Coefficient constellation )

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20VADA Lab.

Simulation – Before Training( Output constellation )

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21VADA Lab.

Simulation – After Training( Output constellation )

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22VADA Lab.

Simulation – Output SNR

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23VADA Lab.

Simulation – Result Analysis• Step Constants() are power-of-2

– 0.5 -> ½ (2-1)– 0.125 -> 1/8 (2-3)– 0.03125 -> 1/32 (2-5)– 0.007125 -> 1/128 (2-7)

• The smaller Constant, the longer convergence time• Replace Complex Multiplier to Just Exponent

Adder• Low Power Consumption is acquired

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24VADA Lab.

Simulation – Using HP ADSSchematic - Transceiver

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25VADA Lab.

Simulation – Using HP ADSSchematic - Channel

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26VADA Lab.

Simulation – Using HP ADSSchematic - Receiver

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27VADA Lab.

Future Work (1)• Simulation

– TEQ simulation– NEXT, FEXT Channel Modeling– Attach Cyclic Prefix– Echo Canceller Simulation– Apply more Low-power Method– Apply Auto Bit Loading– Transmission Test to 215-QAM

SungKyunKwan Univ.

28VADA Lab.

• Hardware Synthesis– Implement FEQ in VHDL (Synopsys)– Implement TEQ in VHDL (Synopsys)– Apply Low-Power algorithm to EQ– Verify the function between Classical EQ and L

ow-Power EQ– Compare the power between Classical EQ and

Low-Power EQ

Future Work (2)

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29VADA Lab.

Future Work (3)

• Current Simulation and Implementation

model is for ADSL, but after improve the

Speed and Power, I will apply all the

algorithms to VDSL.

SungKyunKwan Univ.

30VADA Lab.

Reference (1)• W. Y. Chen, “DSL”, Macmillan Technical publishing, 199

8• W. Goralski, “ADSL and DSL Technologies”, McGraw-Hi

ll, 1998• K. Azadet et al, “Low-Power Equalizer Architectures for

High-Speed modems”, IEEE Comm. Magazine, Oct. 1998• C. Nicol et al, “A Low-Power 128-Tap Digital Adaptive E

qualizer for Broadband Modems”, IEEE jour. Of Solid-state Circuits, Nov. 1997

SungKyunKwan Univ.

31VADA Lab.

Reference (2)• H. Lee et al, “A New Hardware-Efficient Architecture for

Programmable FIR Filters”, IEEE Trans. On Circuits and Systems, Sep. 1996

• J. Rinne et al, “Equalization of Orthogonal Frequency Division Multiplexing Signals”, Proc. Of GLOBECOM’94, pp. 415-419, Nov 27, 1994

• “DSP Solutions for Voiceband and ADSL Modems”, Texas Instrument, June, 1998