TechVista January 06 IIT Madras Wireless Broadband for India ashok Jhunjhunwala

TechVista January 06 IIT Madras Motivation Indian Requirements: Urban and Rural Wireless Fundamentals: going beyond hypes Current and Emerging Technologies

TechVista January 06 IIT Madras Motivation

TechVista January 06 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

TechVista January 06 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

TechVista January 06 IIT Madras India’s Requirements: Urban and Rural

TechVista January 06 IIT Madras Dense Urban India 200 sq meter dwelling area, 2 homes per dwelling area, 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 ChennaiMaduraiErode Dense urban area10km x10km3km x 3km1km x 1km Dense urban homes1 Million90,00010,000 Dense urban population 75% 35%12%

TechVista January 06 IIT Madras To compete with low 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 month or 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

TechVista January 06 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: customers from a tower (in a cell) –260 Mbps required in a cell: impossible (11200/11) x 256 kbps or 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

TechVista January 06 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) 15-20km km ~5 km Fiber PoP village Cellular coverage villages per PoP

TechVista January 06 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

TechVista January 06 IIT Madras Wireless Transmission Fundamentals going beyond the hype with apologies to experts for over-simplifications

TechVista January 06 IIT Madras Single Channel Transmission What 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 Watts Signal needs to be five times larger than noise (signal to noise ratio of 5) for digital wireless –Required rec signal = 2 x Watts Maximum propagation loss allowed (system Gain)= 5 x or 137 db –Higher loss allowed if Bandwith less than 1MHz 1.38x x 300 x 10 6 or 4 x W Noise = W 1W

Propagation Loss in Rural Areas Rural Planes: 40 m tower can cover 15 – 20 km radius – m pole at village for LOS Losses are only around 130 dB or –6 m pole for Non-LOS (foliage) Losses around 160 dB or m 40m 10-12m 1W W Noise = W W

TechVista January 06 IIT Madras Urban Propagation Loss Urban Range of Kms, Built-up Area –Has around 160 dB or 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 W

TechVista January 06 IIT Madras How 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

TechVista January 06 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?

TechVista January 06 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

TechVista January 06 IIT Madras OFDM for higher data rates Divide the transmission band into multiple frequency bands & place bits on each carrier –Different frequency components fade differently 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, , Flash-OFDMA, others frequency

TechVista January 06 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?

TechVista January 06 IIT Madras Multi-Channel Communications

Divide area into cells to enable 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

TechVista January 06 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

TechVista January 06 IIT Madras New 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

TechVista January 06 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

TechVista January 06 IIT Madras Wireless Systems today and tomorrow

TechVista January 06 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:

Will 3.5G (HSDPA/HDR) do much better? Sector throughput at best 1.1 bits/sector/Hz The Evolution of UMTS:3GPP Rel.5 and Beyond, June 2004, 3G Americas HDR

TechVista January 06 IIT Madras New Wireless Internet Access Technologies 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?

TechVista January 06 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 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

TechVista January 06 IIT Madras Decreasing costs from Progressive Volume growth economics Comparison of Alternatives Broadband Narrowband Fixed Local Area Wide Area Typical User Data Rate g family Constant or high costs From Niche applicability Or 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 b family

TechVista January 06 IIT Madras Internet Modem Cable Headend TVCable And to compete with high end DSL Cable Wireless Down Stream on Cable Upstream on Wireless 2 Mbps DL and 256/512 kbps UL for each sub Video on demand possible

TechVista January 06 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

TechVista January 06 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