Infostations: Infostations: A New DesignA New Designfor Wireless Computingfor Wireless Computing

Christopher Christopher CrammondCrammond

Charuhas PanditCharuhas Pandit

Yaling YangYaling Yang

Christopher Christopher CrammondCrammond

Charuhas PanditCharuhas Pandit

Yaling YangYaling Yang

Computing TrendsComputing Trends

LaptopLaptop NetworkNetwork

WirelessWireless

1980s1980s

1990s1990s

200?200?

DesktopDesktop

The Downfall of 3GThe Downfall of 3G

• 3G clearly addresses the issue of 3G clearly addresses the issue of increased data rate.increased data rate.

• What about ...What about ...– System AsymmetrySystem Asymmetry

– Cost per BitCost per Bit

3G: System Asymmetry3G: System Asymmetry

• Voice - equal amounts of traffic on both Voice - equal amounts of traffic on both uplink and downlinkuplink and downlink

• Data - produces more traffic for downlinkData - produces more traffic for downlink

• 3G wastes bandwidth3G wastes bandwidth

3G: Cost Analysis3G: Cost Analysis

• Voice requires 10 Kbit/s at v cents/minVoice requires 10 Kbit/s at v cents/min

• Implying a data rate of 1 MByte/s Implying a data rate of 1 MByte/s corresponds to 13v cents/MBytecorresponds to 13v cents/MByte

• if v = 10, require $1.30 per Mbyteif v = 10, require $1.30 per Mbyte

• 3G is expensive3G is expensive

Exit 3G, Enter InfostationsExit 3G, Enter Infostations

• Infostation: an isolated pocket of Infostation: an isolated pocket of high bit-rate coveragehigh bit-rate coverage

• Smaller areas of coverageSmaller areas of coverage

• Lower Transmit PowerLower Transmit Power• Lower cost per bitLower cost per bit

Infostation: The PremiseInfostation: The Premise

• Designed to account for system Designed to account for system asymmetriesasymmetries

• Acknowledges data is bursty.Acknowledges data is bursty.

• Tolerate longer delays.Tolerate longer delays.

• Disjoint pockets of coverage allow for Disjoint pockets of coverage allow for reducing the reuse factor N = 1.reducing the reuse factor N = 1.

• Use unlicensed frequency band.Use unlicensed frequency band.

Achievable Data RatesAchievable Data Rates

• OptimisticallyOptimistically: 500 Mbit/s in 100 MHz : 500 Mbit/s in 100 MHz BandBand– Preliminary analysis under ideal conditionsPreliminary analysis under ideal conditions

• RealisticallyRealistically: 4 Mbit/s in 1 MHz Band: 4 Mbit/s in 1 MHz Band– Infostations at 100 meter intervalsInfostations at 100 meter intervals

– Using current technologyUsing current technology

– Iacono August 1998Iacono August 1998

Mathematical JustificationMathematical Justification

Water-filling Principle

• Optimization ProblemOptimization Problem: : – With finite energy, when to transmit?With finite energy, when to transmit?

• SolutionSolution::– For optimum throughput, transmit the most power For optimum throughput, transmit the most power

to the user with the best channel to the user with the best channel

– Implies use of smaller coverage i.e., (r/R)<1Implies use of smaller coverage i.e., (r/R)<1

Calculations: InfostationsCalculations: Infostations

• No need for ubiquitous coverageNo need for ubiquitous coverage

• Better SIR conditionsBetter SIR conditions

• Smaller cluster sizeSmaller cluster size

• More bandwidth available gives More bandwidth available gives higher data ratehigher data rate

SIR in 2D Infostation SIR in 2D Infostation systemsystem

6

1

SIR

i

n

i

n

Dd

P

rd

P

n

r

RN

3

6

1SIR

Rr

D 1

D 3

D 6

D 4

D 2

D 5

Which system is better?Which system is better?

2M bps 6M bps

Answer: Depends!Answer: Depends!

• User DensityUser Density

• Importance of throughput vs. delayImportance of throughput vs. delay

• Type of application offered Type of application offered

Queuing AnalysisQueuing Analysis

• Modeled as M/M/1 queue with renegingModeled as M/M/1 queue with reneging

• If coverage (r/R) increases,If coverage (r/R) increases,– Worst case SIR decreases, so data rate Worst case SIR decreases, so data rate

available decreases, so available decreases, so decreases. decreases.

– Dwell time in area increases, so reneging Dwell time in area increases, so reneging rate (rate ()) decreases decreases

– Arrival rate (Arrival rate ()) increases increases

Relating Relating , , , , to r/Rto r/R• Arrival rate Arrival rate = = ruE[v]ruE[v]

u = mobile user densityu = mobile user densityv = mobile speedv = mobile speed

• Reneging rate Reneging rate = 2E[v]/ = 2E[v]/rr

• Service rate Service rate related to data rate, c, related to data rate, c, related to modulation schemerelated to modulation scheme

• Performance of modulation scheme related Performance of modulation scheme related to r/R.to r/R.

Mailbox accumulation – Mailbox accumulation – performance parameterperformance parameter

• Between infostations, mailbox accumulates Between infostations, mailbox accumulates messagesmessages

• X = accumulated mailbox size between X = accumulated mailbox size between successive infostation visits (random variable)successive infostation visits (random variable)

• E[X] = E[X] = uu ttcc (m/c), where (m/c), where uuis the messages is the messages per user per second and per user per second and ttcc is the average time is the average time between visits to Infostations.between visits to Infostations.

• ttcc= = ((RR22)/(2r E[V]))/(2r E[V])

2D Numerical Example2D Numerical ExampleModulation N c r/ R E[X]

BPSK 1 1 0.66 9.52 0.26

1 2 0.56 5.61 0.22QPSK 3 0.67 .97 9.72 0.38

1 4 0.37 4.25 0.15

3 1.33 0.64 7.36 0.25

4 1 0.74 8.49 0.2916 QAM

7 0.57 0.99 11.11 0.39

1 6 0.25 4.19 0.10

3 2 0.42 7.48 0.16

4 1.5 0.49 8.55 0.19

7 .86 0.65 11.28 0.2664 QAM

12 0.5 0.85 14.78 0.33

u=(0...0.0004), R=500, E[V]=2.5, m=2e6, u=0.01

What Does it all Mean?What Does it all Mean?

• Lowest E[X] for r/R = .25 (reduced Lowest E[X] for r/R = .25 (reduced coverage) and 64 QAM (high coverage) and 64 QAM (high modulation)modulation)

• Thus justifying the use of infostationsThus justifying the use of infostations

• For 1D, delay is also betterFor 1D, delay is also better (WPMC (WPMC ‘99)‘99)

Infostation Protocol Infostation Protocol LayeringLayering

• Intelligent transmission protocol for Intelligent transmission protocol for Infostations.Infostations.

Media Access Media Access ControlControl

PhysicalPhysical

Data Link ControlData Link Control

NetworkNetwork

TransportationTransportation

ApplicationApplication

PhysicalPhysical

WINMACWINMAC

Mobile IPMobile IP

Wireless TCP for Wireless TCP for InfostationsInfostations

ApplicationApplication

WINMACWINMAC

• Support both fairness and preemptive Support both fairness and preemptive serviceservice

• Multiple access & channel resource Multiple access & channel resource allocationallocation

• Transmission rate switchingTransmission rate switching

• Retransmission schemeRetransmission scheme

Multiple Access ProtocolMultiple Access Protocol

• Slot Allocation AlgorithmSlot Allocation Algorithm: When a mobile with higher : When a mobile with higher priority arrive, assign it most of the channel resources. priority arrive, assign it most of the channel resources. Otherwise provide fair service.Otherwise provide fair service.

• TDMA/TDD configurationTDMA/TDD configuration: A frame consist of a number of : A frame consist of a number of time slot and each slot can carry one packettime slot and each slot can carry one packet

• Reservation and TransmissionReservation and Transmission::• Look for beaconsLook for beacons

• Choose a rate based on the highest rate and the the largest # Choose a rate based on the highest rate and the the largest # of available slotsof available slots

• Send reservation and registration requestSend reservation and registration request

• Transmit dataTransmit data

Transmission RateTransmission Rate• Rate Switching algorithm (suppose 3 rates):Rate Switching algorithm (suppose 3 rates):

– Listen to beacons of 3 data ratesListen to beacons of 3 data rates

– Monitor Packet Error Rate of current channel Monitor Packet Error Rate of current channel conditioncondition

– Suppose transmission in rate 2 and find out that 2 Suppose transmission in rate 2 and find out that 2 out of 3 recent beacons of rate 3 is heard and out of 3 recent beacons of rate 3 is heard and PER<0.1 then switch to rate 3. Otherwise, if less PER<0.1 then switch to rate 3. Otherwise, if less or equal to one beacon out of 3 is heard of rate 2 or equal to one beacon out of 3 is heard of rate 2 and PER>0.5, then switch to rate 1.and PER>0.5, then switch to rate 1.

Retransmission SchemeRetransmission Scheme• Combine SR (selective repeat) & GBN (Go Combine SR (selective repeat) & GBN (Go

back N) ARQ.back N) ARQ.

• SRSR: Only require sender to retransmit the lost : Only require sender to retransmit the lost packet.packet.

• GBNGBN: Require the sender to retransmit all the : Require the sender to retransmit all the packet after the error or lost packet.packet after the error or lost packet.

• Using SR within the processing ability of Using SR within the processing ability of hardware or software and use GBN beyond the hardware or software and use GBN beyond the ability.ability.

ArchitectureArchitecture

Infostation Controller

Radio Port

Radio Port

Radio Port Radio Port

ATM or Frame Relay

UMTSSS7 signalingNetwork

Internet

Proxy Cache

Infostation and Mobile IPInfostation and Mobile IP

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

Home Agent Foreign Agent

Mobile HostCorrespondent Host

Infostations and Mobile IP Infostations and Mobile IP II• When the mobile recognizes that it is no When the mobile recognizes that it is no

longer connected to its home network, it longer connected to its home network, it is assigned a care-of-address from the is assigned a care-of-address from the network it is visiting. In an infostation network it is visiting. In an infostation system, the IC will assign the care-of-system, the IC will assign the care-of-address to the mobile . address to the mobile .

• The mobile then informs the home The mobile then informs the home agent about its current location to allow agent about its current location to allow packets to be forwarded to it. packets to be forwarded to it.

Infostations and Mobile IP Infostations and Mobile IP IIII• The mobile can also inform the other The mobile can also inform the other

party of its current care-of address, which party of its current care-of address, which the other party can use to directly the other party can use to directly communicate with the mobile.communicate with the mobile.

• When a mobile enters the RP of another When a mobile enters the RP of another Infostation it would register there, obtain Infostation it would register there, obtain a new care-of-address, and continue the a new care-of-address, and continue the session using the new Infostation. session using the new Infostation.

TCP SolutionTCP Solution

• Split ConnectionSplit Connection: A TCP connection between : A TCP connection between a fixed host and mobile host is split into two a fixed host and mobile host is split into two connections at the BS. connections at the BS.

• End-to-End approach-TCP smartEnd-to-End approach-TCP smart: The snoop : The snoop agent in the Infostation Controller (IC) agent in the Infostation Controller (IC) monitors all of its TCP connections. The IC monitors all of its TCP connections. The IC will cache all segments received from the will cache all segments received from the fixed Host and not yet acknowledged by the fixed Host and not yet acknowledged by the MH. MH.

High bandwidth High bandwidth info-station coverageinfo-station coverage

Application Design for a Application Design for a Network of InfostationsNetwork of Infostations

• ExampleExample: A map service for vehicles on a : A map service for vehicles on a highway.highway.

Open Infostation ResearchOpen Infostation Research

• Transmitting in unlicensed bandsTransmitting in unlicensed bands

• Randomized movement of mobile.Randomized movement of mobile.

• Data transfers over multiple Data transfers over multiple sessions.sessions.

• All the hassles of increased bit-rate.All the hassles of increased bit-rate.

Infostation DownsideInfostation Downside

• Difficult to track down explicit Difficult to track down explicit numbers.numbers.

• Exclusively at WINLAB.Exclusively at WINLAB.

• Lack of commercial interest.Lack of commercial interest.

• Dependent of failure of 3G.Dependent of failure of 3G.

BibliographyBibliography• 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.