Introduction to ADSL Modems Prof. Brian L. Evans Dept. of Electrical and Comp. Eng. The University of Texas at Austin Graduate students: Ming Ding, Milos Milosevic (Schlumberger), Zukang Shen

A D S L

Ex-graduate students: Güner Arslan (Cicada), Biao Lu (Schlumberger) Ex-undergraduate students: Wade Berglund, Jerel Canales, David Love, Ketan Mandke, Scott Margo, Esther Resendiz, Jeff Wu Other key collaborators: Lloyd Clark (Schlumberger), Sayfe Kiaei (ASU), Lucio Pessoa (Motorola), Arthur Redfern (Texas Instruments) http://www.ece.utexas.edu/~bevans/projects/adsl

Outline • Broadband Access – Applications – Digital Subscriber Line (DSL) Standards

• ADSL Modulation Methods – ADSL Transceiver Block Diagram – Quadrature Amplitude Modulation – Multicarrier Modulation

• ADSL Transceiver Design – Inter-symbol Interference – Time-Domain Equalization – Frequency-Domain Equalization

• Conclusion 25-2

Applications of Broadband Access Residential Application

Downstream Upstream Willing to pay rate (kb/s) rate (kb/s) 384 9 High Database Access 384 9 Low On-line directory; yellow pages 1,500 1,500 High Video Phone 1,500 64 Low Home Shopping 1,500 1,500 Medium Video Games 3,000 384 High Internet 6,000 0 Low Broadcast Video 24,000 0 High High definition TV

Demand Potential Medium High Medium Medium Medium Medium High Medium

Business Application

Demand Potential High Low Low High Low Medium Medium Low

Downstream Upstream Willing to pay rate (kb/s) rate (kb/s) 384 9 Medium On-line directory; yellow pages 1,500 9 Medium Financial news 1,500 1,500 High Video phone 3,000 384 High Internet 3,000 3,000 High Video conference 6,000 1,500 High Remote office 10,000 10,000 Medium LAN interconnection 45,000 45,000 High Supercomputing, CAD

25-3

DSL Broadband Access

Internet

DSLAM downstream

Central ADSL Office modem

ADSL modem upstream

Voice Switch

LPF

LPF

Customer Premises

PSTN 25-4

DSL Broadband Access Standards xDSL ISDN T1 HDSL

SHDSL Splitterless ADSL Full-Rate ADSL VDSL

Meaning Integrated Services Digital Network T-Carrier One (requires two pairs) High-Speed Digital Subscriber Line (requires two pairs) Single Line HDSL Splitterless Asymmetric DSL (G.Lite) Asymmetric DSL (G.DMT) Very High-Speed Digital Subscriber Line (proposed)

Data Rate Mode Applications 144 kbps Symmetric Internet Access, Voice, Pair Gain (2 channels) 1.544 Mbps Symmetric Business, Internet Service 1.544 Mbps Symmetric Pair Gain (12 channels), Internet Access, T1/E1 replacement 1.544 Mbps Symmetric Same as HDSL except pair gain is 24 channels Up to 1.5 Mbps Downstream Internet Access, Video Up to 512 kbps Upstream Phone Up to 10 Mbps Downstream Internet Access, Video Up to 1 Mbps Upstream Conferencing,ÿRemote LAN Access Up to 22 Mbps Downstream Internet Access, VideoUp to 3 Mbps Upstream on-demand, ATM, Up to 6 Mbps Symmetric Fiber to the Hood

Courtesy of Shawn McCaslin (Cicada Semiconductor, Austin, TX)

25-5

Spectral Compatibility of xDSL 1.1 MHz

POTS ISDN

ADSL - USA ADSL - Europe HDSL/SHDSL HomePNA VDSL - FDD

optional

10k

100k

1M

10M

Frequency (Hz)

Upstream

Downstream

100M 12 MHz Mixed 25-6

ADSL Modem N/2 subchannels N real samples Bits

00110

S/P

quadrature amplitude modulation (QAM) encoder

mirror data and N-IFFT

add cyclic prefix

P/S

D/A + transmit filter

TRANSMITTER channel

RECEIVER N/2 subchannels

P/S

QAM demod

invert channel =

decoder

frequency domain equalizer

N real samples N-FFT and remove mirrored data

remove S/P cyclic prefix

time domain equalizer (FIR filter)

receive filter + A/D 25-7

Bit Manipulations • Serial-to-parallel converter 110 00110

110

S/P

S/P

00 Bits

• Parallel-to-serial converter

Words

• Example of one input bit stream and two output words

00110

00 Words

Bits

• Example of two input words and one output bit stream 25-8

Amplitude Modulation by Cosine Function • Multiplication in time is convolution in Fourier domain y (t ) = f (t ) cos(ω 0t ) Y (ω ) =

1 F (ω ) ∗ π (δ (ω + ω 0 ) + δ (ω − ω 0 )) 2π

• Sifting property of the Dirac delta functional ∞ x(t ) ∗ δ (t ) = ÿ δ (τ )x(t − τ )dτ = x(t ) −∞ ∞

x(t ) ∗ δ (t − t0 ) = ÿ δ (τ − t0 )x(t − τ )dτ = x(t − t 0 ) −∞

• Fourier transform property for modulation by a cosine 1 1 Y (ω ) = F (ω + ω 0 ) + F (ω − ω 0 ) 2

2

25-9

Amplitude Modulation by Cosine Function F(ω)

• Example: y(t) = f(t) cos(ω0 t)

1

– f(t) is an ideal lowpass signal – Assume ω1