Infostations: A New Design for Wireless Computing

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Infostations A New Designfor Wireless Computing

• Christopher Crammond
• Charuhas Pandit
• Yaling Yang

2
Computing Trends
1980s
Desktop
Laptop
1990s
Network
200?
Wireless
3
The Downfall of 3G

• 3G clearly addresses the issue of increased data
  rate.
• What about ...
• System Asymmetry
• Cost per Bit

4
3G System Asymmetry

• Voice - equal amounts of traffic on both uplink
  and downlink
• Data - produces more traffic for downlink

• 3G wastes bandwidth

5
3G Cost Analysis

• Voice requires 10 Kbit/s at v cents/min
• Implying a data rate of 1 MByte/s corresponds to
  13v cents/MByte
• if v 10, require 1.30 per Mbyte

• 3G is expensive

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Exit 3G, Enter Infostations

• Infostation an isolated pocket of high bit-rate
  coverage
• Smaller areas of coverage

• Lower Transmit Power

• Lower cost per bit

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Infostation The Premise

• Designed to account for system asymmetries
• Acknowledges data is bursty.
• Tolerate longer delays.
• Disjoint pockets of coverage allow for reducing
  the reuse factor N 1.
• Use unlicensed frequency band.

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Achievable Data Rates

• Optimistically 500 Mbit/s in 100 MHz Band
• Preliminary analysis under ideal conditions
• Realistically 4 Mbit/s in 1 MHz Band
• Infostations at 100 meter intervals
• Using current technology
• Iacono August 1998

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Mathematical Justification

• Optimization Problem
• With finite energy, when to transmit?
• Solution
• For optimum throughput, transmit the most power
  to the user with the best channel
• Implies use of smaller coverage i.e., (r/R)lt1

Water-filling Principle
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Calculations Infostations

• No need for ubiquitous coverage
• Better SIR conditions
• Smaller cluster size
• More bandwidth available gives higher data rate

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SIR in 2D Infostation system
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Which system is better?
2M bps
6M bps
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Answer Depends!

• User Density
• Importance of throughput vs. delay
• Type of application offered

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Queuing Analysis

• Modeled as M/M/1 queue with reneging
• If coverage (r/R) increases,
• Worst case SIR decreases, so data rate available
  decreases, so m decreases.
• Dwell time in area increases, so reneging rate
  (n) decreases
• Arrival rate (l) increases

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Relating l, n, m to r/R

• Arrival rate l pruEv u mobile user
  density v mobile speed
• Reneging rate n 2Ev/pr
• Service rate m related to data rate, c, related
  to modulation scheme
• Performance of modulation scheme related to r/R.

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Mailbox accumulation performance parameter

• Between infostations, mailbox accumulates
  messages
• X accumulated mailbox size between successive
  infostation visits (random variable)
• EX lu tc (m/c), where lu is the messages per
  user per second and tc is the average time
  between visits to Infostations.
• tc (pR2)/(2r EV)

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2D Numerical Example
u(0...0.0004), R500, EV2.5, m2e6, lu0.01
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What Does it all Mean?

• Lowest EX for r/R .25 (reduced coverage) and
  64 QAM (high modulation)
• Thus justifying the use of infostations
• For 1D, delay is also better (WPMC 99)

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Infostation Protocol Layering

• Intelligent transmission protocol for
  Infostations.

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WINMAC

• Support both fairness and preemptive service
• Multiple access channel resource allocation
• Transmission rate switching
• Retransmission scheme

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Multiple Access Protocol

• Slot Allocation Algorithm When a mobile with
  higher priority arrive, assign it most of the
  channel resources. Otherwise provide fair
  service.
• TDMA/TDD configuration A frame consist of a
  number of time slot and each slot can carry one
  packet
• Reservation and Transmission
• Look for beacons
• Choose a rate based on the highest rate and the
  the largest of available slots
• Send reservation and registration request
• Transmit data

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Transmission Rate

• Rate Switching algorithm (suppose 3 rates)
• Listen to beacons of 3 data rates
• Monitor Packet Error Rate of current channel
  condition
• Suppose transmission in rate 2 and find out that
  2 out of 3 recent beacons of rate 3 is heard and
  PERlt0.1 then switch to rate 3. Otherwise, if less
  or equal to one beacon out of 3 is heard of rate
  2 and PERgt0.5, then switch to rate 1.

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Retransmission Scheme

• Combine SR (selective repeat) GBN (Go back N)
  ARQ.
• SR Only require sender to retransmit the lost
  packet.
• GBN Require the sender to retransmit all the
  packet after the error or lost packet.
• Using SR within the processing ability of
  hardware or software and use GBN beyond the
  ability.

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Architecture
UMTS SS7 signaling Network
Infostation Controller
Radio Port
Proxy Cache
Radio Port
Internet
ATM or Frame Relay
Radio Port
Radio Port
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Infostation and Mobile IP

• Current Proposals for Mobile IP fit well into the
  Infostation concept.

Correspondent Host
Mobile Host
Foreign Agent
Home Agent
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Infostations and Mobile IP I

• When the mobile recognizes that it is no longer
  connected to its home network, it is assigned a
  care-of-address from the network it is visiting.
  In an infostation system, the IC will assign the
  care-of-address to the mobile .
• The mobile then informs the home agent about its
  current location to allow packets to be forwarded
  to it.

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Infostations and Mobile IP II

• The mobile can also inform the other party of its
  current care-of address, which the other party
  can use to directly communicate with the mobile.
• When a mobile enters the RP of another
  Infostation it would register there, obtain a new
  care-of-address, and continue the session using
  the new Infostation.

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TCP Solution

• Split Connection A TCP connection between a
  fixed host and mobile host is split into two
  connections at the BS.
• End-to-End approach-TCP smart The snoop agent in
  the Infostation Controller (IC) monitors all of
  its TCP connections. The IC will cache all
  segments received from the fixed Host and not yet
  acknowledged by the MH.

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Application Design for a Network of Infostations

• Example A map service for vehicles on a highway.

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Open Infostation Research

• Transmitting in unlicensed bands
• Randomized movement of mobile.
• Data transfers over multiple sessions.
• All the hassles of increased bit-rate.

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Infostation Downside

• Difficult to track down explicit numbers.
• Exclusively at WINLAB.
• Lack of commercial interest.
• Dependent of failure of 3G.

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Bibliography

• Borras, Joan and Roy D. Yates. "Infostation
  Overlays in Cellular Systems." IEEE WCNC (1999)
  495-9
• Elaoud, Moncef and Parameswaran Ramanathan.
  "TCP-SMART A Technique for Improving TCP
  Performance in a Spotty Wide Band Environment."
  IEEE (2000) 17-83-7
• Goodman, David. "The Wireless Internet Promises
  and Challenges." computer.org 2/01
• Frenkiel, Richard, B.R. Badrinath, Joan Borras,
  and Roy D. Yates. "The Infostations Challenge
  Balancing Cost and Ubiquity in Delivering
  Wireless Data." IEEE Personal Communications
  (2000) 66-71.
• Iacono, Ana Lucia and Christopher Rose.
  "Minimizing File Delivery Delay in an Infostation
  System." WINLAB, 1998.
• Irvine, J., D. Pesch, D. Robertson, and D. Girma.
  "Efficient UMTS Data Service Provision using
  Infostations." IEEE (1998) 2119-23.
• Yates, Roy D., Narayan B. Mandayam. "Challenges
  in Low-Cost Wireless Data Transmission." IEEE
  Signal Processing (2000) 93-102.
• Wu, Gang, Churng-Wen Chu, Kevin Wine, James
  Evans, and Richard Frenkiel. "WINMAC A Novel
  Transmission Protocol for Infostations." IEEE
  VTC'99. 1999.
• Ye, Tao, H. Arno Jacobsen, and Randy Katz.
  "Mobile Awareness in a Wide Area Wireless Network
  of Info-stations." Berkeley.