IIT Madras Wireless Broadband for India ashok Jhunjhunwala
IIT Madras Wireless Broadband for India ashok Jhunjhunwala ashok@tenet. res. in Tech. Vista January 06
IIT Madras • • Motivation Indian Requirements: Urban and Rural Wireless Fundamentals: going beyond hypes Current and Emerging Technologies Tech. Vista January 06
IIT Madras Motivation Tech. Vista 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 Tech. Vista January 06
Indian Market boomed • IIT Madras 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 Tech. Vista January 06
IIT Madras India’s Requirements: Urban and Rural Tech. Vista January 06
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 Chennai Dense urban area 10 km x 10 km Dense urban homes 1 Million Dense urban population 75% • Madurai Erode 3 km x 3 km 90, 000 35% 1 km x 1 km 10, 000 12% 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 Tech. Vista January 06
To compete with low end DSL Service IIT Madras • 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 • To compete with this • Bit rate to be supported in each cell = 1152/11 = 100 Mbps • • 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 256 x 60 x 100 /8 Kbytes per month or 11. 52 Gbytes – does not include any business connections: only possible on fibre / DSL Tech. Vista 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: 11200 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 Tech. Vista January 06
IIT Madras 15 -20 km Rural India • • 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) Tech. Vista km – – ~5 • Rural population density = 250 people per Sq Km 25 Km radius implies = 2000 Sq Km 3 - 4 km Fiber Po. P village Cellular coverage • 250 -300 villages per Po. P January 06
Multi-operator Scenario IIT Madras • India has 4 to 5 operators competing: Also Desirable • Spectrum is scarce • 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 – No operator should expect more than 10 MHz spectrum • Spectrum requirement will double • Can be handled only by making cell size smaller • And what about high end DSL? – – Tech. Vista 1. 5 Mbps plus supporting Video broadcast / Vo. D Impossible on Wireless in years to come January 06
IIT Madras Wireless Transmission Fundamentals going beyond the hype with apologies to experts for over-simplifications Tech. Vista January 06
IIT Madras Single Channel Transmission What does it take to transmit 10 bps per Hz? Tech. Vista January 06
How far can one transmit? • Price increases dramatically beyond a certain Transmit power (Tx device / Battery) – • • Assuming Signal Bandwidth of 1 MHz, Noise at the receiver = k T Δf = 4 x 10 -15 Watts 1. 38 x 10 -23 x 300 x 106 Signal needs to be five times larger than noise -15 or 4 xof 105) (signal to noise ratio for digital wireless – • 1 W 1 Watt is optimum today 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 1 MHz 10 -14 W Noise =10 -15 W
1 W Propagation Loss in Rural Areas 10 -13 W Noise =10 -15 W 40 m 10 -12 m 10 -16 W 10 -20 m • Rural Planes: 40 m tower can cover 15 – 20 km radius – 10 -12 m pole at village for LOS • Losses are only around 130 d. B or 1013 – 6 m pole for Non-LOS (foliage) • Losses around 160 d. B or 1016
IIT Madras Urban Propagation Loss 1 W 10 -16 W • Urban Range of 2 - 3 Kms, Built-up Area • To Sum up: Propagation Losses • But System Gain with 1 W Transmitter is only 137 d. B – Has around 160 d. B or 1016 propagation losses for inside building coverage – 160 d. B for NLo. S (mobile) – and 130 d. B for Lo. S (Fixed) coverage – will enable up to 2 Mbps (using 4 level modulation) transmission in 1 MHz with no interference – Good enough for Lo. S, but requires more for NLo. S communications Tech. Vista 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 d. B – Subscriber Antenna • ~1 d. B for NLo. S • 10 to 15 d. B for Lo. S • Turbo Coding (Error Correction) and hybrid ARQ : 3 to 5 d. B • Signal Processing, multi-antenna diversity techniques can give another 3 to 5 d. B Tech. Vista 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) 11 10 10 00 – 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? Tech. Vista 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 multipath 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 Tech. Vista January 06
OFDM for higher data rates • IIT Madras Divide the transmission band into multiple frequency bands & place bits on each carrier – Different frequency components fade differently and has different amount of interference frequency – 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: IEEE 802. 11, 802. 16, Flash-OFDMA, others Tech. Vista 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? Tech. Vista January 06
IIT Madras Multi-Channel Communications Tech. Vista January 06
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
Will Sectorising a Cell help? • Divide a Cell in three 120 degree sector • Can same channel be reused in different sectors? IIT Madras – Use Directional Antenna to tx and rec in a sector – 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 • Reuse in every cell and each of three sector will imply a Reuse factor of 3: 1 – Improves Reuse factor – 30 MHz available in a cell with 10 MHz spectrum Tech. Vista 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 Tech. Vista 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 Tech. Vista January 06
IIT Madras Wireless Systems today and tomorrow Tech. Vista January 06
IIT Madras Beware of Marketing hypes – 2. 5 G Mobile: 3 G-1 x/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/ Tech. Vista January 06
Will 3. 5 G (HSDPA/HDR) do much better? • Sector throughput at best 1. 1 bits/sector/Hz HDR The Evolution of UMTS: 3 GPP Rel. 5 and Beyond, June 2004, 3 G Americas
New Wireless Internet Access Technologies IIT Madras • HDR/ HSDPA : today – 1. 8 bps per Hz per cell: mobile – Cost medium • Wi. Max : mid 2007 – 4 bps per Hz per cell: mobile – 802. 11 D is only 1. 8 bps per Hz per cell: not good – Cost: have to wait • Flash-OFDM & i. Burst: – 4 bps per Hz per cell: mobile – Cost: medium to high • So do we give up? Tech. Vista January 06
IIT Madras Lo. S Systems: Inherent Strengths • Disadvantage: Lo. S 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 Tech. Vista January 06
Lo. S 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 NLo. S – 5 -10 times higher spectrum efficiency Line-of Sight LOS Low interference from surrounding cells
Broadband cor. DECT • Designed for Indian situation to compete with DSL – 256/512 kbps dedicated: today • 10 bps per Hz per cell: fixed Lo. S • Cost very low – Optimised as a Lo. S 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
Comparison of Alternatives LMDS Broadband Typical User Data Rate 802. 11 g family 802. 11 b family India User Requirements Cable/DSL/ cable-wireless Wi. MAX BB cor. DECT 3 G+ IIT Madras Decreasing costs from Progressive Volume growth economics Constant or high costs From Niche applicability Or saturation growth Emerging Technologies cor. DECT 3 G Narrowband Satellite 2. 5 G Dial-up 1 G Local Area Tech. Vista Wide Area Fixed Portability January 06
And to compete with high end DSL IIT Madras Cable Wireless Down Stream on Cable Upstream on Wireless Internet Modem TVCable Headend 2 Mbps DL and 256/512 kbps UL for each sub Video on demand possible Tech. Vista January 06
To Sum Up IIT Madras • 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 Lo. S Systems – Innovations required towards this – Requires the right price point • Broadband will also require a appropriate home device • The Right Services Tech. Vista January 06
IIT Madras Novatium Net. PC 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 Tech. Vista January 06
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