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

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

3. 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. 4 Cellular = Expensive Bits v=1 cent/min = 13 cents/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. 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. 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. 7 Infostations Network of wireless ports Discontinuous coverage Asymmetric link High data rate transmission Data services

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

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

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

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

12. 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. 13 SIR in 2D Infostation system

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

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

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

17. 17 Queue Parameters User density, u Cell radius, R Mobile speed, v, f V (v) Coverage radius, r Data rate, c Messages per user per second, u Message size, m = (2  r)(u/2) E[V] 1/  = E[X] = = u t c (m/c)  = 2E[V]/  r R r  

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

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

20. 20 Delay Light Load Simple Modulation Wide Coverage Heavy Load Complex Modulation Limited Coverage

21. 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. 22 Optimized Locations Download a map Internet access Low bit-rate cellular E-mail voice mail fax

23. 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. 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. 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. 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. 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. 28 Systems Research New problems everywhere in the stack! Free bits Limited Coverage High Bit Rates New Applications Propagation Transceiver Link Layer Networks Applications