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Broadband Access Networks

Chapter 2

Twisted-Pair based Access Networks

Byeong Gi Lee

Seoul National University

EE4541.759 Spring 2006

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BGL 2

2. TP-based Access Network

Limitation of POTS and ISDN

Digital Loop Carrier

DSL TechnologiesIDSL, HDSL, SDSL,

ADSL, G.Lite, VDSL, and Comparisons ADSL Access Network, Architecture,

Components, and Protocol Model

Spectrum Allocations Modulation Techniques

Applications, Challenges, and Penetration

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BGL 3

Structure of Access NetworkADSL: Asymmetric Digital Subscriber Line

DBS: Direct Broadcast SatelliteDMB: Digital Multimedia Broadcast

FTTC: Fiber To The Curb

HFC : Hybrid Fiber Coaxial

LMDS: Local Multipoint Distribution System

MMDS: Multi-channel Multipoint Distribution System

MSO: Multiple Service Operator

Digital DBS

DMB

HFC

FTTC/FTTO

ISDN Line (DSL)

VDSL Modem

ADSL Modem

Cable Modem

Analog

Modem

ISDN Adaptor

DBS STB/MMDS/LMDSSTB

Coax

MMDS/LMDS

56Kbps

6Mbp

s 640Kbps

FiberONU Coax or

CopperFiber

52Mbps

3Mbps

30Mbps

3Mbps

64Kbps

LMDS only

HomeTerminal

MSO

/CO

Hub

StationFiber or

Wireless

Twisted-pair

WMAX

WiBro

TP-based AN

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BGL 4

Access and Backbone Infrastructure

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BGL 5

Subscriber Line

Central

Office

(CO)

5.5 km

Twisted-pair

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BGL 6

Limitation in existing subscriber lines Restrictive for high-speed service

Limited data-carrying capacity of 56kbps using V.90

Analog mode and suppressing filters above 3,400Hz

Limitation of POTS Customer connected over thin-wire pairs (26guage, 24guage)

Local loops are bundled in binder groups (feeder part)

Limitation of ISDN services

Not possible to provision ISDN and POTS in same local loop

Problems in providing Internet services

POTS and ISDN carry data in circuit mode (voice switch)

Limitation of POTS and ISDN

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BGL 7

Advanced modulation technology basedbandwidth expansion (128kbps ~ 52Mbps)

xDSL easier to install than ISDN

needs inside wiring work and copper line cleaning

Variations depending on symmetry ofupward/downward data rates (ADSL vs HDSL)and the location of equipment (ADSL vs VDSL)

Supports POTS using splitter (split flter). ButG.Lite can eliminate splitter.

HDSL can replace T1/E1 without repeaters (DLC).

xDSL

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BGL 8

Digital Loop Carrier (DLC)

Central

Office

(CO)

Remote

Termina

l (RT)

Carrier Serving Area

(CSA)

Feeder Line

Multiple T1 Lines

Fiber

Distribution/

Drop Wire

Fiber LoopCarrier (FLC)

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BGL 9

Configuration of xDSL

Central

Office

(PSTN)

Central

Office

(PSTN)

EndUser

(POTS)

Headend

(Video)

End

User

(Video)

Headend

(Video)

End

User

(Video)

PSTN POTS

Optical

Network

Unit

POTS

ADSL

CO UnitADSL

RT Unit

HDSL

RT Unit

HDSL

CO Unit

VDSL

RT Unit

VDSL

CO Unit

Line

Repeater

Line

Repeater

CO

Repeater

End

User

(POTS)

PSTN

T1/E1

HDSL

ADSL

VDSL

TP (2 pairs)

TP (1 pair)

TP (2 pairs)

0.3~1km 1~1.8 km 0.3~1km

TP (1 pair)

SPF

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BGL 10

xDSL Genealogy

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BGL 11

ISDN Digital Subscriber Line is a cross pointbetween ISDN and xDSL

Made available with the introduction of ISDN

Circuit mode based integration of voice and dataNeeds ISDN terminals/adapters in the user side

2B + D basic rate access(BRA),144kbps+16kbps

B: 64kbps for voice or data

D: 16kbps for call control or packet data

Subscribers direct connection to CO

IDSL

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BGL 12

23B + Dprimary rate access(BRA),1.544Mbps

for the connections of PBXs, host computers, andLANs

Transmission

rate of 80 ksps

2B1Q modulated,

duplexing by TCM (time compressed multiplexing)ping pong

Travels over 5.4 km over 24 gauge (.5mm)

IDSL (contd)

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BGL 13

IDSL based Access System

PSTN/ISDN

Data Network

ISP

Voice Carrier

System

Switch

Router

ISDNNetwork

Termina

tion

(NT1)

Local Exchange Office Subscriber Premise

Twisted-pair

Subscriber Line

ISDNNetwork

Termina

tion

(NT1)AdapterAdapter

Adapter

PSTN/ISDN

Data Network

ISP

Voice Carrier

System

Switch

Router

ISDNNetwork

Termina

tion

(NT1)


Twisted-pair

Subscriber Line

ISDNNetwork

Termina

tion

(NT1)AdapterAdapterAdapterAdapter

AdapterAdapter

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BGL 14

Comparable with T1/E1 lines Carrier level subscriber lines

Beneficial to business users

PRA at 1.544Mbps (T1) or 2.048Mbps (E1) rate

Can replace T1/E1 lines without repeaters Can be used as feeder lines (for DLC systems)

Transmission with 2 twisted pairs For T1 rate (1.5Mbps), two TP wires necessary

For E1 rate (2Mbps), three TP wires necessary

2B1Q Modulated, CAP, DMT

2B1Q: 3.6km, CAP:5.5km over 24 gauge (.5mm)

Interference problem when bundled in large size

HDSL

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BGL 15

HDSL -- a simple means for loop transmission Transmits signals at normal power levels

Equalizer can compensate for the TP signal distortion,

Helps to restore the signal in the receiver regardless of

changes in environmental conditions.

Can maintain signal integrity even if TP wires are not perfect.

Does not require cable conditioning or bridged tap removal.

Becomes immune to crosstalk and polarity reversal.

Overall system reliability and transmission performance

improve.

HDSL (contd)

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BGL 16

Symmetric (or Single-line)HDSL(SHDSL,SDSL)

Single TP wire implementation of 2B1Q or CAP

Enabled by advanced electronics for echocancellation and adaptive equalization

Data rate of 192kbps~2.3Mbps (Sub-T1/E1 ratesobtainable)

HDSL2 (G.SHDSL) standards

Symmetric 2.3 Mbps over a single loop pair

Symmetric 4.6 Mbps over two loop pair

SDSL

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BGL 17

Up/down asymmetric bandwidth 1.5/2 ~6/8 Mbps down

16~820 kbps up

For use in Internet, VoD like applications

One TP - good for residential use Up to 5.4km without repeaters (0.5mm)

Uses advanced modulation techniques DMT (standardized)

CAP (market)

Enhancements Rate-Adaptive DSL (RADSL) - line condition

Universal ADSL (UADSL) - without split filter

ADSL

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BGL 18

TP diameter important to distance 1.5 or 2-Mbps channel

Reaches 5.4-km over 0.5-mm, 4.6-km over 0.4-mm TP

6-Mbps channel

Reaches 3.6-km over 0.5-mm, 2.7-km over 0.4-mm TP

POTS split through split filter (SF), or splitter

Analog telephone service and the high-speed data service are

FDM multiplexed

300-3,300Hz band for voice, 26-1,100kHz band for data

Splitter separates the two bands

Protocol stacks for ADSL (see the figure)

ADSL (contd)

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BGL 19

ADSL based Access System

Receiving filterHybridcouplerHybridcoupler

Demod/equalization/detection

Ethernet

Modulator

Coder/decoder

Pulseshaper

Voice filter

Subscriber line

26 138 KHz

.138 1.1 MHz

Splitter

0.3 3.3 KHz

Transmitting filter

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BGL 20

Example Protocol Stack for ADSL

TCP/UDP

Computer(or appliance)ADSL terminal

DSLAMDatanetworkterminal

IP

PPPEthernet

Ethernet

ADSL

ATM(optional)

ADSL

ATM(optional)

SONET

ATM(optional)

IP IP

ISP

SONET

ATM(optional)

IP

PPP

TCP/UDP Protocol servicessuch as DHCP

Central Office Subscriber Premise

Twisted pair

subscriber line

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BGL 21

ITU G.992.2 standard

Splitter set up is a hurdle in wide-spreading ADSL.

Requires technicians labor for installation

G.Lite is designed not to require splitter set up.

Designed not to use splitter Uses customer-installable ADSL modems.

G.Lite modem senses voice activity and controls power

G.Lite modem cuts back its power on detecting phone going

off-hook. Data transmission gets interrupted when phone or other POTS

device is used

ADSL G.Lite

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BGL 22

Offers the services of ADSL at a lower speed 1.5-Mbps downstream and 512-kbps upstream is achievable

at 5.4-km.

Fast retrain procedure needed to adjust the data

transmission rate To operate at a lower bit rate while off-hook.

1~2 s cessation of service

Prompted by off-hook to on-hook

Longer reach and much less power than full-rate ADSL

ADSL G.Lite (contd)

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BGL 23

ADSL G.Lite System

PSTN/ISDN

Data Network

ISP

Voice Carrier

System

Switch

Router

xDSLAccessMultiplexer


Twisted-pair

Subscriber Line

xDSL-liteModem

VoicebandFilter

PSTN/ISDN

Data Network

ISP

Voice Carrier

System

Switch

Router

xDSLAccessMultiplexer


Twisted-pair

Subscriber Line

xDSL-liteModem

VoicebandFilter

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BGL 24

ITU G.992.3 and 992.4 standards

Adds new features and functionality

To improve the rate and the reach

To improve performance and interoperability

For new applications, services, and deployment scenarios. Achieves higher transmission rates

12Mbps downstream, 1Mbps upstream

By taking advanced communication signal processing

improving modulation efficiency, reducing framing overhead,achieving higher coding gain, improving the initialization statemachine, and providing enhanced signal processing algorithms.

ADSL 2

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BGL 25

ITU G.992.5 standard

Achieves even higher transmission rates at shorter distance

Doubles the downstream bandwidth of ADSL2,

achieving the data rate of 24 Mbps on phone line as long as 1.5-km.

If loop is longer, the rate converges to that of ADSL2

Frequency band shift* ADSL2 specifies a downstream frequency band up to 1.1 MHz,

ADSL2plus specifies a downstream frequency from 1.1 MHz to 2.2 MHzby masking the downstream frequencies below 1.1 MHz

It helps to reduce the crosstalk from CO or RT.

The increase in frequency and the elimination of crosstalk results insignificant data rate increases on shorter phone lines

* Reference: DSL Forum, Marketing Report MR-001, DSL Anywhere issue 2,p.63, Sept 2004.

ADSL 2plus

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BGL 26

Spectrum Allocation for ADSL

4 10 80 100 200 1000 kHs

Power

Spectra

POTS ISDN ADSL

(Up)

ADSL (Down)

(Numbers for example)

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BGL 27

ITU 993.1 Standard Short distance, very high data rate, asymmetric

(or symmetric) DSL

Drop line for FTTC application (in CSA)

13~52 (~155) Mbps down depending on distance

300 m to 1.5 km distance (from curb to home)

CAP, DMT,QAM modulation

POTS split through split filter (SF)

Variation - VDSL2

VDSL

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BGL 28

Asymmetric mode

52 to 56-Mbps, up to the distance of 300-m;

26 to 28-Mbps, up to 1-km;

13 to 14-Mbps, up to 1.5-km downstream; and

1.6 to 2.3-Mbps, up to 300-m upstream

Symmetric mode 26-Mbps up to 300-m; and

13-Mbps up to 1.5-km for downstream and upstream

Spectrum arrangement

lowest 80-kHz band for ISDN signal, including

lowest 4-kHz band for the POTS signal,

300 to 700-kHz for the upstream data

beyond 1-MHz band for downstream data

VDSL (contd)

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BGL 29

Bit Rates vs. Distances

Table 2.1

Comparison of Digital Subscriber Line Technologies.

Technology Bit Rates Distances*

DSLHDSL

ADSL (DS)

ADSL (US)

VDSL+(DS)

160 kbps1.5 - 2 Mbps

1.5 - 8 Mbps

128-640 kbps

13 - 14 Mbps

26 - 28 Mbps52 - 56 Mbps

5.4 km4 km

2-5.4 km

1.5 km

1 km0.3 km

* Distance for 0.5-mm(24-gauge) TP wires.+Estimated values

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BGL 30

ITU and ANSI T1E1.4 Intended to deliver 100 Mbps at short distance

To enable broadband services like HDTV

DMT modulation based

Several features of ADSL2 included

Loop diagnostics modes, low power modes, commonmanagement interface with ADSL2

Multimodal functionality Upgrade customers service from ADSL to VDSL

without disturbing CPE.

VDSL2

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BGL 31

Spectrum Allocations for VDSL

FTT Exchange, FTT Cabinet

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BGL 32

ADSL vs. G.LiteFull-Rate ADSL G.Lite

ITU SpecificationITU G.992.1ANSI T1.413

ITU G.992.2No ANSI specification

Also known as G.dmt Splitterless ADSL

POTSYes, using a single splitterin home

Yes, using microfilters at eachanalog handset

Modulation scheme DMT DMT

Phones only after splitterfreely connected anywhere

Subbands 256 128

Downstream speed6 Mbps, maybe more forshorter distances Up to T1 (1.5 Mbps)

Upstream speed Up to T1 Up to 512 kbps

Professional installation Intended noYes, for splitter and insidewiring

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BGL 33

ADSL vs. VDSL

POTS/ISDN, therefore

requiring splitters Full-Rate ADSL

Modulation techniques

Yes

DMT, using 256 bands with4 kHz spacing

VDSL

Yes

DMT, CAP, or QAMDMT modulation would use256band with 40 kHz spacing, or2048 bands with 4 kHz spacing

Spectrum Allocation Up to 1 MHz Up to 30 MHz

Downstream bit rate

2 to 3 Mbps

Various up to 51.84 Mbps

Upstream bit rate Various up to T1

Various up to 6 Mbps

Standardization ASNI T1.E1ADSL ForumITU G.992.1

ASNI T1.E1ADSL ForumITU SG 15, G.vdsl, G.993

Distance to ONU Up to 5000 meters 300 to 1500 meters

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BGL 34

Comparison of xDSL (1)

ModulationScheme

ISDN 2B1Q 64 Kbps,

128 Kbps

64 Kbps,

128 Kbps

NoANSI T1.601

Uses 4B3Q coding in

some

European countries

IDSL

HDSL

HDSL-2

SDSL(ETSI)

2B1Q

2B1Q

128 Kbps

Up to 2 Mbps

2 Mbps

2 Mbps

128 Kbps

Up to 2 Mbps

No

Downstream

Bit Rate

UpstreamBit Rate

POTSSupport

Comments

Uses ISDN TA

NoUses four wires; current

T1

service

PAM-16 2 Mbps No Uses two wires; not rate-

adaptable

2B1Q 2 Mbps YesUses two wires; rate

adaptable

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BGL 35

Comparison of xDSL (2)

G.Lite

ADSL

ADSL

VDSL

2 Mbps

1.5 Mbps to

6Mbps

DMT 512 Kbps Yes ITU G.992.2

CAP 64 Kbps to

800 KbpsYes Mostly Paradyne

DMT1.5 Mbps to

6Mbps64 Kbps to

800 Kbps

Yes ANSI T1.413

QAM/CAP

DMT

12.96 Mbps to 51.84

Mbps

1.5 Mbps to

3 MbpsYes Range of 300 meters for top

speeds; ANSI T1.E1.4, ETSI

and ITU Study Group 15

ADSL2 DMT Up to 12 Mbps Up to 1 Mbps Yes ITU G.992.3, G.992.4

ADSL2+ DMT Yes ITU G.992.5Up to 24 Mbps Up to 2 Mbps

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BGL 36

Services vs. Bandwidth Requirement

ApplicationFile Type File Size

Modem28.8 kb/s

ISDN128 kb/s

ADSL1.5 Mb/s

ADSL6.1 Mb/s

All User Email 30 kB 8.3 sec 1.9 sec 0.16 sec 0.04 secConsumerDigitized Photo 125 kB 34.7 sec 7.8 sec 0.6 sec 0.2 secBusiness UserWord Files 250 kB 69.4 sec 15.6 sec 1.3 sec 0.3 secTelecommuterVideoconferencing 384kb/s No No YES YESTelemedicineX ray 5 MB 23.1 min 5.2 min 25.9 sec 6.5 secRemote LANAccess Bulk File 20 MB 1.5 hr 20.0 min 1.7 min 26.0 sec

* Acceptable response time < 3.0 sec

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BGL 37

A generic ADSL access network architecture

Service Architecture over ADSL (1)

Accessnode*

Service-specificinterfaces

*Access node can be co-located with the COswitch, or be remoted in the distribution plant.

Internetbackbone

ATM

network

Privateleased-line

network

Othernetworks(e.g., FR)

ATU-C

ATU-C

ATU-C ATU-R

PremisesLAN

Premisescablewiring

PC

Set-top

PSTN

Passivesplit

To phones

Networkinterface

Copper loop

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BGL 38

ATU-R

Splitter0~4 kHz

ADSL : Down 138 ~ 1,100 kHz,

Up 26 ~ 138 kHz

Splitter

Switch

DSLAM

Data

Comm.

Network

PSTN

Subscriber line

ADSL-R

* Splitter-less in ADSL.Lite

Subscriber line

ATU-C

* DSLAM: Digital Subscriber Lines Access Multiplexer

* ATU-C : ADSL Transceiver Unit, Central

* ATU-R : ADSL Transceiver Unit, Remote


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BGL 39

ADSL Transceiver Units

Physical layer device for frequency allocation, echo

cancellation, FDM, rate adaptation, etc.

POTS splitter

Lowpass/highpass filter that separates analog voice

from ADSL frequencies

DSL Access Multiplexer (DISLAM) Houses a set of ATU-C interfaces, mux/demuxes traffic

from multiple ATU-Cs onto a single high-speed trunk


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BGL 40

A plausible protocol stack for data over ADSL


IP

Any data

link layer or

ATM

with TC *

PPP

HDLC AAL5

MAC ATM

PMDTC

PMD

IP

PPP

HDLCAAL5

MACATM

TC

PMD

802.2 LLC

803.3 MAC

802.3

10BaseX

802.2 LLC

803.3 MAC

802.3

10BaseX

IP

Switch #

and/or

router

Internet/

WAN

ADSL-C modem ADSL-R modem Home terminalCopper wire

*Optionally, a standards-based ATM

UNI interface can be provided to

connect directly to an ATM backbone

#Switch can be a LAN, a frame relay

switch, or an ATM switch

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BGL 41

Basically a p2p switched transmission technology IP over PPP over HDLC over ADSL or

IP over ATM over ADSL

ADSL intended to be used as access technology forInternet or LAN access in conjunction with analog

telephony service

Various architectural models possible to meet the

specific service offerings, interconnection to thebackbone networks, and strategic direction of a

network provider


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BGL 42

ATU-C: encoding and modulating the DS data andcombining the analog POTS signal; in US,

demodulating the signal received from the customer

and outputting a data stream and POTS signal

Three main architecture options PDH (Plesiochronous Digital Hierarchy) mode

ATM (Asynchronous Transfer Mode) mode

Packet mode

Type of mode is independent of underlying line

encoding method used


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BGL 43

PDH Mode Traditional circuit-switched network digital hierarchy

Interface with either a backbone voice or data network via

existing CBR circuit-switched services

PDH supported in ADSL DS1 (1.544 Mbps); E1 (2.048 Mbps); DS2 (6.312 Mbps); E2 (8.448

Mbps)

An application will typically use the appropriate bandwidth

from the digital hierarchy meeting the bandwidth demand Data applications such as Internet and LAN interconnect

supported in this mode


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BGL 44

ATM Mode

ATU-R provides a native ATM interface to the user device ora legacy LAN interface with segmentation and reassembly(SAR) functionality

Edge switch ATM multiplexer in access node

Concentration and ATM layer routing function Alternatively, SAR and network layer routing can be provided

in CO such as DSLAM

On access side: multiplicity of service protocols (TCP/IP, PPP,FR, ATM cell relay, ATM circuit emulation) over a variety of

physical layer protocols (HDSL, ADSL, DS1) On backbone side: standard ATM user-network interface for

transport to ATM switch, which can connect to ATMbackbone


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BGL 45

Packet Mode MUX in the access node adapts the protocol carried over

ADSL to one of the commonly used packet transport

services

Switching and/or routing of variable-length layer 2 framesand/or layer 3 packets over an ADSL link

PPP and FR are the most popular L2 protocols (HDLC-like)

supporting any of L3 protocols (IP, IPS,..)

PPP encapsulation: allows many different protocols to be transportedover p2p links

FUNI encapsulation: variable-size frame to be transmitted is

encapsulated in FUNI frame


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BGL 46

Two services of ADSL/VDSL:

transparent access to legacy voice service

high-speed digital service

Voice Service (Analog)

Provision of voice service relatively simple In-home configuration

Frequencies below 3400Hz shunt by POTS splitters to POTS wiring athome and to voice switch at CO

NID (or NT) by telco powering, ATU-R by local powering

Voice service not to be subject to home wiring impairments Protection of NID from lightening required to protect home electronics.

Professional assistance needed for splitter installation (separate fromATU-R)

xDSL Operation (1)

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BGL 47

Digital (video and data) Service (1)

1. Determine latency: Video traffic subject to burst error, so interleaving and FEC

used.

ANSI provided 500 us burst protection against impulse noise,creating 20ms latency.

But data service has no such requirement as higher-layerprotocols can perform error correction,

delay of only 4ms

So ADSL provides two logical data channels

slow (20ms) and fast (4ms) Video on slow channel due to FEC and interleaving

Data on fast channel only with (de)modulation delay

ATU-R determines which latency type to take at start-up

xDSL Operation (2)

i ( )

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BGL 48

Digital Service (2)

2. Determine bit rate:

RADSL adapts to the line condition via negotiation process

When powered on, ATU-R probes the line to determine

signal carrying capacity.

Signal-carrying capacity is a function of distance, noise, and

allowable margins

Negotiation goes between ATU-C and ATU-R for

maximum sustainable bit rate (out of four start-up rates,

ANSI)

Entire negotiation within 20s.

xDSL Operation (3)

S O i ( )

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BGL 49

Digital Service (3)

3. Perform auto-configuration:

Configuring IP addresses and software filters for ATU-R

Relatively straightforward since each user has a dedicated ATU-C

Manually configured by DSLAM or some form of software

tunnel between ATU-R and a device

Method differs depending whether ATU-R or the end system

is IP-aware

If ATU-R and PC is IP-aware DHCP client is one

autoconfiguration technique

xDSL Operation (4)

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BGL 50

Digital Service (4)4. Digital Data Transfer

After startup complete, data transferring

ATU-R accepts data from home networking over an

Ethernet, ATM25, or other digital protocols, encapsulates,and then sends out.

MAC protocol is not required unlike HFC

Dynamic rate adaptation:

ATU-R and ATU-C renegotiation during data transmission byperiodic testing of line conditioning -- retraining time will be

required in support of this.

xDSL Operation (5)

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BGL 51

2B1Q (2 binary, 1 quaternary)

DMT (discrete multi-tone modulation)

CAP (carrier-less amplitude and phase

modulation)

QAM (quadrature amplitude modulation)

QPSK (quadrature phase shift keying)

Modulation Techniques for xDSL

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BGL 52

2B1Q

Bits 01 10 11 00 00 11 10 00 01 01 11 01 00 10

Quads -1 +3 +1 -3 -3 +1 +3 -3 -1 -1 +1 -1 -3 +3

Upstream

1stbit(sign)

2ndbit(magn)

Symbol(quat)

1 0 +3

1 1 +1

0 1 -1

0 0 -3-3

-1

+1

+3

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BGL 53

DMT (1)

Frequency

AttenBits/chan

Frequency

Bits/chan

Frequency

FrequencyFrequency

Atten

TWISTED-PAIR with TAP, AM/RF, and XTALK

AMBits/chan

Frequency

Bits/chan

TWISTED-PAIR

TAP

xtalk

DMT: Sub-channel based data rate allocation

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BGL 54

DMT (2)

Features

frequency efficiency

symbol length per sub-channel longer

frequency selective noise avoided

Issues

complexity, power consumption

timing and synchronization critical

ANSI standard

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BGL 55

DMT (3)

DMT Transceiver Block Diagram

Transmitted

signalEncoder

and

buffer

b=RT

2N Point

IDFT

Parallel to

serial

converterDAC LPF

R b/s

N QAM

Symbols

T

Decoder

and

buffer

b=RT

2N Point

DFT

Serial to

Parallel

converterADCLPF

R b/s

N QAM

Symbols

T

Channel

Noise

Received

signal

Generalization of DMT -- OFDM

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BGL 56

Generalization of DMT OFDM Basic Concept

Orthogonal Frequency Division Multiplexing : Advanced FDM

Divide into N orthogonal subcarriersTransmit N symbols in N subcarriers respectively

Reconstruct N symbols using orthogonality

FDM: Use separated subcarriers (A, C, E)

OFDM : Use overlapped orthogonal subcarriers(A,B,C,D,E)

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BGL 57

OFDMA System -Advantages

One Big Stream

Divided into multiple smallstreams

Long Symbol Period

Robust to multipath fading

( Small guard time overhead)

Large number of small channels +Orthogonality

Robust to narrowband

interferenceEfficient use of radio spectrum

Single Carrier:

1Mbps Stream

(symbol : 1us)

Multi-Carrier:

10 X 100 Kbps

(symbol : 10us)

1us delayed

path signal

Narrowband

interference

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BGL 58

OFDMA System -Disadvantages

Sensitive to synchronizationerrors

Susceptible to frequency offset

High PAPR (Peak to Average PowerRatio)

Freq.

The amplitude of the three

subcarrier are all max.

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BGL 59

QAM (1)

In

Qn

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BGL 60

QAM (2)

16QAM

b1 b2b0 b3 b0 b1 b2 b3 b0 b1 b2b3

increasing time

quadrantpoint within quadrant

symbol n (0..3) symbol n+1 (0..3)

lsb msbbyte alignment

TC layer

b2

+1

+1 +3-1-3

+3

-1

-3

00 01

10 1101

01

01

00

00 00

11

11 11

10

10

10

b2 b3

0001

11 10

currentstate

In

Qn

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BGL 61

CAP (1)

Input

Figure 2.10CAP tranceiver structure: (a) transmitter, (b) receiver.

Encoder

In-phase

filter

D/A LPFModulated

signalsignal

Modulated

signalA/D

Output

signal

(a)

(b)

Quad-phase

filter

In-phase

filter

Quad-phasefilter

DecoderDecision

device

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BGL 62

CAP (2) 16CAP

... b2 b3 b0 b1 b2 b3 b0 b1 b2 b3 b0 b1...

t

quadrant

point within quadrant

symbol

Qn

In

1011

01 00

1111

1111

0000

0000

10

10

10

10 01

01

01

01

+1

+1

-1

-1-3

-3

+3

+3

current state

b2 b3

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BGL 63

QPSK QPSK: Upstream DAVIC VDSL

Encoder

Symbol

TransmitFilter

Transmit

Filter

+

_

Data

Input

Signal

Output

BandPass

Filter

Qn

In

Oscillator

cos

sin

+1-1

+1

-1

0001

11 10

b0 b1

In

Qn

b1 b0b0 b1 b0 b1 b0 b1 b0 b1 b0b1

increasing time

lsb msb

byte alignment

TC layer

b0

symbol

nsymbol

n+1

symbol

n+2symbol

n+3

CAP DMT

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BGL 64

CAP vs. DMT

CAP DMTPower consumption Lower, fewer gates Higher peak/average, but will

likely narrow gapForward carriers 1 256Return carriers 1 32Increment 320 Kb 32 KbAdaptive equalizers Needed NoneLicensing Globespan Many sourcesStandardization In process ITU and ANSI

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BGL 65

High-speed Internet Access residential and business area

Intranet access to link

Remote Office and Branch Office (ROBO)

low cost, high throughput LAN-to-LAN connectivity Telecommuting

Small Office / Home Office (SOHO)

On-demand type applications

VOD, home shopping, tele-education, Interactive TV Leased line provisioning (HDSL/SDSL)

replacing conventional T1/E1 leased line

xDSL Applications

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BGL 66

End-to-end loop qualification impacted by Loop length, loading coils, quality of E2E splicing of wiring

segments, multiple changes of wire gauge, home wiring, age,

corrosion, hostile binder groups, crosstalk, and bridged taps

CrosstalkNear-end crosstalk (NEXT)

Far-end crosstalk (FEXT)

Bridged Taps

Y form branch => source of echo

Technical Challenges of xDSL (1)

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BGL 67

Powering remote terminals

Local power used to power DSL equipment; battery backup

Spectral masking

Long-term narrowband interference such as, AM radio andamateur radio ingress

Notching out specific frequencies

Impulse noise

Short-term interference with duration of 100ms with peakpower of 10mv

ART-R maintenance

Software upgrading such as, algorithms

Technical Challenges of xDSL (2)

DSL P i W ld id (1)

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BGL 68

xDSL Penetration Worldwide (1)

DSL P i W ld id (2)

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BGL 69


DSL P i W ld id (3)

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BGL 70


DSL P i i K (1)

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BGL 71

xDSL Penetration in Korea (1)

12 million broadband access subscribers (Jun. 2005)

Source:

1999 2000 2001 2002 2003 2004 2005. 6

() 37 395 781 1,041 1,118 1,192 1,226

() 1,806 1,904 2,438 2,627 2,922 3,158 3,257

PC () 1,153 1,862 2,249 2,350 2,425 2,620 -

() 123 409 1,131 1,771 2,275 2,427 2,290

() - 58 119 178 235 314 *81.7

() - 52 192 577 871 1,055 1,134

*20053

DSL P i i K (2)

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BGL 72


Source:2004

DSL P t ti i K (3)

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BGL 73


Subscribers for Service Providers

Source:

DSL P t ti i K (4)

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Service Providers and Base Technologies

bans ch2-tp 2006

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