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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

Free BitsThe Challenge of the Wireless Internet

Roy Yates

Rutgers University


Wireless data over 2g cellular
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


Wireless data over 3g cellular
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


Cellular expensive bits
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


Internet access free bits
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?


Anytime anywhere costs but data can tolerate delay
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!


Infostations
Infostations

  • Network of wireless ports

  • Discontinuous coverage

  • Asymmetric link

  • High data rate transmission

  • Data services


Isolated infostation
Isolated Infostation

  • Optimization Problem:

    • With finite energy, how many bits can be delivered?

  • Solution: Wait for the very good channel, blast away!


Highway infostations
Highway Infostations

  • Distance attenuation time varying channel

  • Transmit power profile Time Average Capacity[Goldsmith]


Coverage capacity delay
Coverage, Capacity, Delay

  • Cellular Infostations

    • Infostationsat BS cellsites

  • Do infostations really offer more capacity?

  • At what delay?


Traditional cellular
Traditional Cellular

  • Modulation and BER  SIR threshold

  • SIR  Cluster size N (frequency reuse)

  • For worst-case location!


Cell area coverage area
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!



Sir with respect to r r and n

Possible operating points

SIR with respect to r/R and N


Which system is better
Which system is better?

6M bps (64 QAM)

2M bps (QPSK)


Approximate queueing model

Approximate Queueing Model

  • Every Infostation is modeled as an M/M/1 queue with reneging

Reneging: Customersleave before sending all bits


Queue parameters

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


2d cycle time
2D Cycle Time

See [Borras & Yates, WCNC 99]


Throughput
Throughput

N=1Reuse

(r/R)2

64QAM 6.25%

16QAM 13.7%

QPSK 31.4%

BPSK 43.6%


Delay
Delay

Light LoadSimple ModulationWide Coverage

Heavy LoadComplex ModulationLimited Coverage


Infostations beyond cellular
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!


Optimized locations
Optimized Locations

Download

a map

Low bit-rate

cellular

E-mail voice mail

fax

Internetaccess


Cheap bits high rates
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!


Infostation applications
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


Infostation applications1
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!!


High rates new applications
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


Research problems
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


Systems research
Systems Research

New problems everywhere in the stack!

Freebits

LimitedCoverage

High Bit Rates

NewApplications

  • Propagation

  • Transceiver

  • Link Layer

  • Networks

  • Applications


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