india cewit br, iitm-cewit 1 towards a cellular broadband revolution in india bhaskar ramamurthi...
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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