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Free Bits The Challenge of the Wireless Internet

Free Bits The Challenge of the Wireless Internet. Roy Yates Rutgers University. Wireless Data over 2G Cellular. Cellular Voice: Anytime Anywhere Slow : 10K bps High cost/bit v cents/min voice = 13 v cents/MB Data over Cellular: Slow and Expensive: 20 cents/min voice = $2.60/MB.

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Free Bits The Challenge of the Wireless Internet

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  1. Free BitsThe Challenge of the Wireless Internet Roy Yates Rutgers University

  2. Wireless Data over 2G Cellular • Cellular Voice: • Anytime Anywhere • Slow: 10K bps • High cost/bitv cents/min voice = 13v cents/MB • Data over Cellular: • Slow and Expensive:20 cents/min voice = $2.60/MB

  3. Wireless Data over 3G Cellular • Higher speed: 144K or 384K bps • 2X or 3X increase in BW efficiency • Reverse link pilots • Wideband signal processing • Better multiplexing, adaptive modulation • 2X or 3X reduced cost/bit But voice is still 10K bps v cents/min = 13v cents/MB

  4. Cellular = Expensive Bits • v=1 cent/min = 13cents/MB • Fill an MP3 player: 30 MB = $3.90 • Upload digital camera photos • 32 MB = $4.16 • Sync laptop disk with desktop • 50 MB = $6.50 • 144 kbps Internet access on Amtrak • 75K bps average for 3 hours = $13.16

  5. Internet Access = Free Bits • Internet: Applications and attitudes are based on “free” bits • Conventional radio access is a toll booth • Radio bits need to be “free” How do we deliver free bits over radio?

  6. ANYTIME ANYWHERE costs $…but DATA can tolerate delay! • Information services: e-mail, voice mail, fax, maps, non-interactive web pages, ... • We don’t need ubiquitous coverage • Reduced coverage  Higher data rates • A little wait might be worthwhile!

  7. Infostations • Network of wireless ports • Discontinuous coverage • Asymmetric link • High data rate transmission • Data services

  8. Isolated Infostation • Optimization Problem: • With finite energy, how many bits can be delivered? • Solution: Wait for the very good channel, blast away!

  9. Highway Infostations • Distance attenuation time varying channel • Transmit power profile Time Average Capacity[Goldsmith]

  10. Coverage, Capacity, Delay • Cellular Infostations • Infostationsat BS cellsites • Do infostations really offer more capacity? • At what delay?

  11. Traditional Cellular • Modulation and BER  SIR threshold • SIR  Cluster size N (frequency reuse) • For worst-case location!

  12. Cell area Coverage area • No need for ubiquitous coverage • Better Radio Channel • Higher received power • Less interference • Smaller cluster size • More bandwidth available HIGHER DATA RATE!

  13. SIR in 2D Infostation system

  14. Possible operating points SIR with respect to r/R and N

  15. Which system is better? 6M bps (64 QAM) 2M bps (QPSK)

  16.   Approximate Queueing Model • Every Infostation is modeled as an M/M/1 queue with reneging Reneging: Customersleave before sending all bits

  17. User density, u Cell radius, R Mobile speed, v, fV(v) Coverage radius, r Data rate, c Messages per user per second, u Message size, m = (2p r)(u/2) E[V] 1/ m = E[X] = = u tc (m/c) n = 2E[V]/p r Queue Parameters f q R r

  18. 2D Cycle Time See [Borras & Yates, WCNC 99]

  19. Throughput N=1Reuse (r/R)2 64QAM 6.25% 16QAM 13.7% QPSK 31.4% BPSK 43.6%

  20. Delay Light LoadSimple ModulationWide Coverage Heavy LoadComplex ModulationLimited Coverage

  21. Infostations beyond Cellular • Cellsites aren’t ideal for Infostations • Cellsites are chosen for widest coverage • On hills, high towers • Infostations exploit being really close • Clever (convenient) locations can really help!

  22. Optimized Locations Download a map Low bit-rate cellular E-mail voice mail fax Internetaccess

  23. Cheap Bits, High Rates! • No coverage requirements • Lots of interference  range reduced. • Range may be zero in places • Need a sufficiency of good locations • No need for licensed spectrum • Use 100 MHz U-NII bands • Short range wideband communications • VERY High Rates!

  24. Infostation Applications • Upload digital camera photos • Walking by photo kiosk • 32 MB in 3 sec = 80 Mb/s • Internet access on Amtrak • Infostation every 500 feet • 25 ft coverage radius at 400 Mb/s • 40 Mb/s average capacity

  25. Infostation Applications • Sync laptop disk with desktop • At the airport in the X-ray machine • 50 MB in 1 sec = 400 Mb/s • Fill an MP3 player • While passing thru doorway • 30 MB in 2 sec = 240 Mb/s Very high data rates!!

  26. High Rates = New Applications • Data Sprinklers (or hoses) [Badrinath] • Download a local information database • Images of everything local • Where can I find …… ? • What’s that building? • Where am I? • If bits are fast and free, lots of content can go unused

  27. Research Problems • Network problems • Protocols for pre-fetching • Coordinated Data Delivery • Radio Problems • 500 Mb/s in a handset! • Channel estimation • Finding the coverage sweet spot • Coverage/channel shaping

  28. Systems Research New problems everywhere in the stack! Freebits LimitedCoverage High Bit Rates NewApplications • Propagation • Transceiver • Link Layer • Networks • Applications

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