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Towards a Cellular Broadband Revolution in India

Bhaskar Ramamurthi

Professor, TeNeT Group, IITM

and

Hon. Director, Centre of Excellence in Wireless Technology

www.tenet.res.in

www.cewit.org.in

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Cellular Telephony Revolution

5M+ subscribers being added per month Urban/suburban potential will be realized soon : ~200M ARPU : Rs 250 p.m.

Handset from Rs 1500 Infrastructure @ Rs 2000 – 3000 per subscriber Tower spacing 300m in urban areas!

Rural revolution is poised to begin First 30-50M subscribers only needs coverage to be

extended Next 100M will require ARPU of Rs 100 p.m to be

interesting to operators Innovative business models needed

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Whither Broadband?

Connectivity

Content Terminal

Handset+

Docking station

MultimediaThin Client

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B3G/4G Expectations in a Nutshell

Subscriber expectations Mobile voice and data connectivity 0.5-1 Mbps (sustained) per user downstream

can be somewhat lower when mobile ~ 64-256 kbps per user upstream

64 kbps needed to support 1 Mbps DL speed would like more for uploads, can’t get it with low-power hand-

held terminals Terminal with hand-held form factor (no mounted antennas,

etc) feature-rich, multi-function under Rs 4500, going down every year

85% of users in portable / pedestrian / nomadic mode from indoors

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B3G/4G Expectations in a Nutshell (contd.)

Operator expectations Min 40 Mbps per cell downstream with 10 MHz overall and

reuse 1 Typical DL/UL ratio: 2:1 6 bps / Hz / cell DL efficiency

Roadmap for 9 bps / Hz / cell going up to 15 bps / Hz cell in 4G 40 Mbps will support ~ 500 – 1000 subscribers per cell

33% active in busy hours 33% bursting data simultaneously

ARPU of DSL ~ Rs 250 p.m. (as with mobile phone service) international link BW is a significant cost, unlike in telephony

Low cost BTSs and all-IP network Infrastructure cost << Rs 2500 per subscriber unlike mobile

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Broadband Technologies in the Near-Term

HSPA, EVDO Natural upgrade for existing GSM/EDGE and 3G1x networks Competition for spectrum between data and voice (for

400M subs!) services DL Spectrum efficiency ~ 3 – 4 bps / Hz / cell

Wimax New network – fibre and infra can be shared with existing

networks Will be positioned primarily as competition for DSL services New spectrum Work on Wimax-2 (802.16m) set to begin

LTE, EVDOrevC Essentially a new network, though dual-mode operation

with GSM/WCDMA or 3g1x likely

OFDMAbased

(CDMA based)

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Innovations in Broadband Wireless Technology

How can we move towards 10-15 bps/Hz/cell in DL ? lower cost infrastructure with high scalability ?

Innovate at PHY and MAC layers Exploit the fact that 85% users are nomadic

Wireless channel to these users changes relatively slowly Build interference mitigation into all aspects of PHY

Exploit spectrum reuse 1 to the hilt Build new architectures for BTS

Tower-top RF electronics and tower-base / centralized SDR components

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Base Station Evolution Base station typically conceived as being less sensitive to

cost, power consumption, size, … Not true anymore ! BTS spacing ~ 300m in India Connected by optical fiber : high capacity, low cost

In broadband systems, each BTS serves fewer users than in telephony systems

Very cost sensitive Low profile, low power, tower/pole-top

Interest in moving horse-power to remote location, and RF electronics to tower-top GigE and upcoming 10GigE are low-cost communication links

100 m on copper 10 – 20 km on fiber even for backplane, or inter-connect of sub-systems !

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Innovation -- Downlink Rx

SyncChannel

ProcessingST

DecoderHARQ

CombineCTC

Decoder

-- Pilot-less channel tracking (CT) – for OFDM-- Orthogonal pilots + DDCT – for OFDMA-- CCI Aware CIR estimation/tracking

-- Low Complexity SMUX decoder-- SINR maximizingST coding schemes

-- ModifiedCTC Decoding(insensitive tosymbol-variant CCI)

Innovations in LDPC decoderdesign & implementation

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Innovation -- Downlink Tx

Upper MAC(QoS, SINR based Scheduling)

Lower MAC(Link Adaptation, Burst

Mapping, HARQ

Permutation,FFT, add CP, etc.

MIMO Precoding

Virtual Antenna Mode

…..-- De-centralised schedulingacross cells/sectors for Band AMC

FEQ (TCC, CTC)

PA

PR

R

educt

ion

-- Partial Feedback STC -- Interference Mitigation in STC-- Closed Loop Spatial Muxing

New Preamble Designs-- CCI Aware, MIMO Aware

Pilot-less/Less of Pilots

-- DL power control is important(in addition to rate control)

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Some recent research results

Work done by several people in CEWiT, and TeNeT Group

faculty and research scholars

Focus is on interference mitigation The crucial problem in improving performance in reuse-1

systems

Patents and papers Individual credits not mentioned here

The process of taking the work to standards meetings has begun

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CCI Aware Channel Estimation –

New Preamble Design

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Estimation

(Pilot-based estimation on Downlink)

Enhanced CEin presence of High CCI

FFT based CE

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Nulling vs MRC(with 2 Rx antennas)

1 x 2 OFDMA system

No. of subcarriers=512

Length of CP=32

Channel taps=4

No. of interferers=1

Performance comparison of Subspace based CE method with “Nulling” and “MRC” combining

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OFDMA downlink CE-- Impact on Nulling Performance

Performance comparison of different CE methods with “nulling”

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Enhanced Channel Estimation-- Application to Uplink FDOSS & GMC

2 4 6 8 10 12 14 16 18 2010

-4

10-3

10-2

10-1

100

Normalized Fade rate > 0.01, 5 dB SNR

Symbols

BER Channel known

Enhanced estimation with tracking

Delay locations known

Enhanced estimation w/o tracking

MLS

2 4 6 8 10 12 14 16 18 20-30

-20

-10

0

10

20

30Normalized Fade Rate > 0.01, 5 dB SNR

Symbols

NMSE

(dB)

Enhanced with tracking

Delay locations known

Enhanced w/o tracking

MLS

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Pilotless Channel Tracking

Modified DDCT here outperforms 12.5%pilot-aided tracking

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Modified turbo decoder (for 10% NBI)

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Improved two-(Tx)antenna diversity-4 SFC with modest feedback

Diversity 4Diversity 4

Diversity 3Diversity 3

With a nominal feedback rate, fourth order diversity can be achieved with 2 Tx antennas

Doppler - 5 Hz

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Interference mitigation in multi-user MIMO-OFDM

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New Closed-loop Precoding Scheme2x2, corr.=0.9

New PrecodedSpatial Muxing

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How will the innovations reach the market?

India-specific system requirements need to be articulated

India-focused research to fulfil requirements needs to be incorporated in standards

Early technology demonstration of new systems in Indian network

Low-cost highly scalable infra to be deployed, exploiting the existing towers and backhaul

Indian technology developers must be the first in international markets

ANSWER : Broadband Wireless Consortium of India (BWCI)

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BWCI Concept

Bring all stake holders together Operators Tech. services industry Vendors Semiconductor companies Research Groups Government (DoT, MIT, Regulators)

Play the roles commensurate with being the world’s second largest telecom market, and the largest source of information and communications

technology services

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Operators

Most have cell sites every 500m-1000m in the towns and cities Fiber backhaul to all the sites Most are both mobile and Internet service providers Want to provide DSL-like 256/512 kpbs service to subscribers

Revenue model is very tight Operators want high-capacity system that is

Highly scalable Low cost Delivers best performance for fixed/nomadic subs Handles mobile subs quite well

Operators benefit from strong local vendors whom they can drive to meet their needs Innovations that improve performance and drive down cost

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Tech Services Industry

Typically develop stacks, ASICs, and IP for clients even as standards are drafted

Want to reduce time to market Want to establish proveness asap

Keen to participate in standards meetings Tech demonstrator

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Manufacturers

Want operator inputs on requirements / specs want to develop equipment to suit operator needs and

jointly conduct trials and evaluation Want operator inputs on modifications / inputs early Will work with tech. services industry and research

groups to incorporate IP and new ideas into their equipment

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Semi-conductor Companies

Most large semi-con companies have big development centers in India

Keen to develop products for local market Achieve new cost-efficiencies and mass-market setpoints

Several small ASIC companies with strong wireless domain knowledge

Can develop products for OEMs

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Research Groups

A few strong wireless research groups active Some are beginning to develop IPR with immediate

potential Keen to partner with industry to realize the potential of

their ideas Keen to build up critical mass in research at national

level CEWiT set up to provide a platform for this

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Consortium Structure

Steering Committee Subgroups for focus technologies (e.g., WiMAX, LTE, RevC)

Number of groups depending on critical mass in each subgroup (operator, vendor, tech service company)

Committee of operators to specify technical requirements Focus of Research Groups : influencing emerging standards

e.g., 3GPP LTE WiMAX 2 when it starts

Tech demonstrator For each major subgroup Multiple BTS and UE platforms Each platform with different combination of vendor, tech

service company, semicon company, and operator (for field trial)

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BWCI Mission

Demonstrate new broadband technologies Based on standards, with increasing Indian influence in

the standards over time That push the envelope of system capacity

With focus on reuse-1 and Interference management With new architectures for scalability and adaptation

Using SDR ideas Using new partitions of hardware between tower-top, tower

base and central location Leveraging Moore’s-law based cost-reductions in IP transport

that specifically meet requirements of Indian operators

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Scope for Foreign Collaboration

Partnering between research groups Validate each other’s ideas through simulations Explore new ideas jointly wherever there are common

research goals

Partnership between industry in India and abroad for systems that go into the tech demonstrator

Establish performance of specific technologies

CEWiT has already one MOU with REMON Consortium of Israel

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Time Frame

2007 – 2009 Tech demonstrators in IInd half 2007 and 2008 Leverage prior work in partner organizations

CEWiT Simulator PHY Research at CEWiT, IITs, IISc, others Platform development in vendor companies Software stacks in tech service companies Semicon development in semicon companies

Prof. David Koilpillai, on sabbatical from IITM as Chief Scientist in CEWiT is heading BWCI