TechVista January 06 IIT Madras Wireless Broadband for India ashok Jhunjhunwala [email protected].

TechVista January 06

IIT Madras

Wireless Broadband for India

ashok [email protected]


IIT Madras

• Motivation• Indian Requirements: Urban and Rural• Wireless Fundamentals: going beyond hypes• Current and Emerging Technologies


IIT Madras

Motivation


IIT Madras

Indian Telecom Market is booming

• Telephones:– 1994: 8 million

• Today: Over 110 million– 5 million lines added

last month– Fastest growing

telecom market in the world

• Broadband– Today : 1 million

• 2010 target: 50 million 0

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500

2003 2004 2005 2006 2007 2008 2009 2010

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Number of Telephones in India

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406080

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IIT Madras

Indian Market boomed• When Telecom became affordable

– Telecom Infrastructure Capex < $ 100 per line • with handset price of $30 onwards and tariff under 2 cents per minute• ARPU of about $ 8

• And easily Deployable: wireless• Competition drove the prices down

• Broadband will boom– At right price points– Competition and easy deployment

• Incumbents can use DSL on existing copper

• New Operators need Wireless Broadband


IIT Madras

India’s Requirements: Urban and Rural


IIT Madras

Dense Urban India• 200 sq meter dwelling area, 2 homes per dwelling area,

10000 homes per sq Km– All Cities and Towns have a highly dense part

• Market penetration by an operator: minimum 15% – 1500 homes per sq Km

• Broadband towers to serve at least 1 Km radius– Area Served: 3 sq Km– Number of Customers from each tower / cell: 4500

Chennai Madurai ErodeDense urban area 10km x10km 3km x 3km 1km x 1kmDense urban homes 1 Million 90,000 10,000Dense urban population 75% 35% 12%


IIT MadrasTo compete withlow end DSL Service

• Lowest end Service on DSL = 256 kbps Always ON

• 4500 homes x 256 kbps from each tower (cell-site) = 1152 Mbps– Impossible on Wireless– But Internet Bandwidth can be shared

• Low-end DSL Service offering in India: 1 G Byte download at $7 per month

256 x 60 x 60 x 100 /8 Kbytes per monthor 11.52 Gbytes

• To compete with this• Define Busy Hour: four hour 25 days in a month• Assume all 1 G byte downloaded by each customer spread over these Busy

Hours• At 256 kbps peak download, one can download 11.5 Gbytes in 100 hours• 11 customers can share a 256 kbps pipe

• Bit rate to be supported in each cell = 1152/11 = 100 Mbps– does not include any business connections: only possible on fibre / DSL


IIT Madras

Suburban Areas• Suburban Population Density: 2000 homes per Sq Km

• Let towers serve 5 Km radius or 75 Sq Km– 150,000 homes in a coverage area– 7.5% market penetration: 11200 customers from a tower (in a cell)– 260 Mbps required in a cell: impossible

(11200/11) x 256 kbpsor 260 Mbps

• Let Tower serve 3 Km radius or 27 Sq Km– 54000 homes in coverage area of a tower– 7.5 % market penetration : 4050 customers in a cell– 95 Mbps in a cell

• Suburban areas may need some business connections on wireless increasing the requirement


IIT Madras

Rural India

• Rural population density = 250 people per Sq Km

• 25 Km radius implies = 2000 Sq Km– 500,000 people– 1% penetration: 5000 connections– 116 Mbps from a tower (cell)– May be very difficult to provide such a

bit-rate at 25 Km range

• More doable– 15 – 20 Km radius– 1000 Sq Km: 2500 connections

• 8 to 10 connections per village including schools, business, Government

• Number of connections may be less, but higher usage as connections are shared

– 58 Mbps from a tower (cell)

15-2

0km

3 - 4 km

~5 km

Fiber PoP

village

Cellular coverage

• 250-300 villages per PoP


IIT Madras

Multi-operator Scenario• India has 4 to 5 operators competing: Also Desirable

• Spectrum is scarce– No operator should expect more than 10 MHz spectrum

• 100 Mbps in each cell site with total spectrum allocation of 10 MHz is a very tough task– Requires a Spectral Efficiency of 10 bps per Hz per Cell site

• And what happens if the DSL operator double the download to 2 Giga byte per month

• Spectrum requirement will double• Can be handled only by making cell size smaller

• And what about high end DSL?– 1.5 Mbps plus supporting Video broadcast / VoD– Impossible on Wireless in years to come


IIT Madras

Wireless Transmission Fundamentalsgoing beyond the hype

with apologies to experts for over-simplifications


IIT Madras

Single Channel TransmissionWhat does it take to transmit 10 bps per Hz?

How far can one transmit?

• Price increases dramatically beyond a certain Transmit power (Tx device / Battery)

– 1 Watt is optimum today

• Assuming Signal Bandwidth of 1 MHz, Noise at the receiver = k T Δf = 4 x 10-15 Watts

• Signal needs to be five times larger than noise (signal to noise ratio of 5) for digital wireless

– Required rec signal = 2 x 10-14 Watts

• Maximum propagation loss allowed (system Gain)= 5 x 1013 or 137 db

– Higher loss allowed if Bandwith less than 1MHz

0.001 0.01 0.1 1 10

Power Output (W)

Pric

e

1.38x10-23 x 300 x 106

or 4 x 10-15

10-14 W

Noise =10-15 W

1W

Propagation Loss in Rural Areas

• Rural Planes: 40 m tower can cover 15 – 20 km radius

– 10 -12 m pole at village for LOS• Losses are only around 130 dB or 1013

– 6 m pole for Non-LOS (foliage)• Losses around 160 dB or 1016

10-20m

40m10-12m

1W

10-13 W

Noise =10-15 W

10-16 W


IIT Madras

Urban Propagation Loss

• Urban Range of 2 - 3 Kms, Built-up Area– Has around 160 dB or 1016 propagation losses for inside building

coverage

• To Sum up: Propagation Losses – 160 dB for NLoS (mobile)– and 130 dB for LoS (Fixed) coverage – will enable up to 2 Mbps (using 4 level modulation) transmission in 1

MHz with no interference

• But System Gain with 1W Transmitter is only 137 dB– Good enough for LoS, but requires more for NLoS communications

1W

10-16 W


IIT MadrasHow can we Enhance System Gain?

• Base Station can transmit 3 to 5 W (4 to 7 db gain)– Base Station to Subscriber Communication can have higher bit-rate

• Antenna: can focus beams and enhance power in certain directions– Base Station Antenna gain: 12 to 16 dB– Subscriber Antenna

• ~1 dB for NLoS• 10 to 15 dB for LoS

• Turbo Coding (Error Correction) and hybrid ARQ : 3 to 5 dB

• Signal Processing, multi-antenna diversity techniques can give another 3 to 5 dB


IIT Madras

If we had higher system gain?

• Multi-level Modulation

– If Signal is 5 times larger than noise• Can have four distinct levels and

noise will not result in error (bit-error)• 2 bit can be transmitted per symbol (QPSK)

– in 1 MHz can transmit 1 M Symbols per sec or up to 2 Mbps

– If SNR is another 3 times (5 db) higher, one can transmit 3 bits per symbol (8-QAM) or 3 Mbps in 1 MHz

– For every additional 5 db SNR, bit ratel can be increased to 4 Mbps, 5 Mbps, 6 Mbps …

• 16-QAM, 32-QAM, 64-QAM … 256-QAM

• But where can this extra System Gain come from?– And are there penalties?

11

10

10

00


IIT Madras

Penalties due to multiple paths

• Time Dispersion– Can be corrected by equalization– If bit duration is too small,

correction not possible• TDMA fails beyond 1-2 Msps

• Frequency Dispersion– different frequency components of the signal fade differently due to

multi-path scattering– CDMA takes advantage of it

• But too many RAKE fingers in CDMA if bit-rate beyond 4 to 5 Msps

• Neither TDMA nor CDMA can have data rates > 5 M Symbols per sec


IIT Madras

OFDM for higher data rates

• Divide the transmission band into multiplefrequency bands & place bits on each carrier

– Different frequency components fadedifferently and has different amount of interference

– Signal to Noise (plus interference) ratio will vary from band to band• where SNR is low: Assign less number of bits per symbol (even zero)• where SNR is high: Assign more number of bits per symbol• Distribute the power available to maximise the bit rate

• Channel condition (fade / interference) will vary from instant to instant– Assign more or less number of bits per symbol on dynamic basis– Combats frequency dependent fading and interference

• Technology of future: IEEE802.11, 802.16, Flash-OFDMA, others

frequency


IIT Madras

• OFDM and Signal Processing techniques like coding, equalisation, diversity can enable us to have a single point to point link with– Close to 10 bit per second per Hz

– But can we do this for multiple users?


IIT Madras

Multi-Channel Communications

Divide area into cells toenable reuse

• Assume 10 MHz spectrum assigned– Say it is assigned to Central cell

• Can a neighboring cell use the same spectrum?• Spectrum reuse 1:1 in every cell

• Use of same spectrum in neighboring Cell can interfere with each other– Can not be reused unless Signal to Interference (SIR) is high– Same channel can be reused only in a far away cell– An Example Reuse 1:7: but then only 10/7 or 1.4 MHz can be

reused in every cell– Only 1:1 reuse will enable all 10 MHz to be reused in every cell


IIT Madras

Will Sectorising a Cell help?

• Divide a Cell in three 120 degree sector– Use Directional Antenna to tx and rec in a sector

• Can same channel be reused in different sectors?– Depends on SIR: can be reused if SIR > 10

• Reusable in first case, not in second case– Can not be reused in neighboring sectors unless

orthogonal code (CDMA) is used

• May be reusable in some sectors of neighboring cells– Improves Reuse factor

• Reuse in every cell and each of three sector will imply a Reuse factor of 3:1– 30 MHz available in a cell with 10 MHz spectrum


IIT MadrasNew techniques to enhance Reuse

• Opportunistic Scheduling– Schedule order of transmission based on

• who has the best channel conditions– can maximize data-rate to such users

• Optimizing over several sectors and multiple cells

• Multiple Input Multiple Output (Space Time diversity) – Essentially like beam-forming to improve re-use

• Like virtual sectors or pipes


IIT Madras

Wireless Fundamentals summary

• Not only important to transmit maximum bit rate in each Hz of available spectrum– Signal Processing, Error Correction, Multi-level

Modulation, OFDM

• Equally important to reuse spectrum as often as one can– Opportunistic Scheduling, MIMO

• Still in infancy, a lot of work needed over the next few years

• To get close to 10 Bits per second per Hz per Cell


IIT Madras

Wireless Systems today and tomorrow


IIT Madras

Beware of Marketing hypes

– 2.5 G Mobile: 3G-1x/GPRS/Edge• 2 bps/Hz downstream per sector in the middle of a sector• drops to about a tenth as one leaves the center of the sector

as interference from neighboring cells catch up• Effective 0.7 bps per Hz per cell

Computerworld: http://www.corante.com/unwired/

Will 3.5G(HSDPA/HDR) domuch better?

• Sector throughput at best1.1 bits/sector/Hz

The Evolution of UMTS:3GPP Rel.5 and Beyond, June 2004, 3G Americas

HDR


IIT MadrasNew Wireless Internet AccessTechnologies• HDR/ HSDPA : today

– 1.8 bps per Hz per cell: mobile– Cost medium

• WiMax : mid 2007– 4 bps per Hz per cell: mobile– 802.11D is only 1.8 bps per Hz per cell: not good– Cost: have to wait

• Flash-OFDM & iBurst: – 4 bps per Hz per cell: mobile– Cost: medium to high

• So do we give up?


IIT Madras

LoS Systems: Inherent Strengths

• Disadvantage: LoS enables only Fixed Connection – not mobile– Requires installation Effort for each subscriber

• subscriber patch antenna sees interference only from BTSs behind serving BTS spectrum re-use in every cell – 8 sectors or even 12

• Multi-level modulation

• H and V polarization for each carrier doubles capacity

LoS Systems

• Have much lower path Loss– Can use higher gain subscriber antenna, eight or even

twelve sectors and horizontal and Vertical Polarisation

• Result– But gives 10-20 times longer range as compared to NLoS– 5-10 times higher spectrum efficiency

Line-of Sight LOS

Low interference from surrounding cells

Broadband corDECT• Designed for Indian situation to compete with DSL

– 256/512 kbps dedicated: today• 10 bps per Hz per cell: fixed LoS• Cost very low

– Optimised as a LoS System• Can compete with low-end DSL today

US$ 200 per line deployed Exchange and tower in town Works at 55 C Power requirement: 1 KW


IIT Madras

Decreasing costs fromProgressive Volume growth economics

Comparison of AlternativesB

road

ban

dN

arro

wb

and

FixedLocal Area Wide Area

Typ

ical

Use

r D

ata

Rat

e

802.11g family

Constant or high costsFrom Niche applicabilityOr saturation growth

India User

Requirements

1G

2.5G

3G

3G+

WiMAX

Emerging Technologies

Portability

LMDS

Satellite

Dial-up

Cable/DSL/cable-wireless

BB corDECT

corDECT

802.11bfamily


IIT Madras

Internet

Modem

Cable Headend

TVCable

Radio tower

And to compete with high end DSL

Cable WirelessDown Stream on Cable Upstream on Wireless

2 Mbps DL and 256/512 kbps UL for each sub

Video on demand possible


IIT Madras

To Sum Up

• Broadband is waiting to boom in India

– Requires competition• Broadband Wireless technology competing with DSL can enable

this• Difficult in near future, except with Fixed LoS Systems

– Innovations required towards this

– Requires the right price point

• Broadband will also require a appropriate home device

• The Right Services


IIT Madras

Novatium NetPC enabling Broadband

• Connected to a Server on LAN or Broadband– No virus, no back-up required, no upgradadtion every four years,

negligible maintenance– Management at server

– Target price: US$ 80 plus monitor• Works with Windows, Solaris, Unix and Linux Servers

TechVista January 06 IIT Madras Wireless Broadband for India ashok Jhunjhunwala [email protected].

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Transcript of TechVista January 06 IIT Madras Wireless Broadband for India ashok Jhunjhunwala [email protected].