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Enhancing Vehicular Internet Connectivity using Whitespaces , Heterogeneity and A Scouting Radio. Tan Zhang ★ , Sayandeep Sen † , Suman Banerjee ★ ★ University of Wisconsin Madison, † IBM Research India. Motivation. Infotainment. Entertainment. Road Safety.

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enhancing vehicular internet connectivity using whitespaces heterogeneity and a scouting radio

Enhancing Vehicular Internet Connectivity using Whitespaces, Heterogeneity and A Scouting Radio

Tan Zhang★,SayandeepSen†, Suman Banerjee★

★University of Wisconsin Madison, †IBM Research India

motivation
Motivation

Infotainment

Entertainment

Road Safety

Growing trend of vehicular Internet access

motivation1
Motivation

300 million vehicles connected to Internet by 2020 [Cisco report]

motivation2
Motivation

WiFi

Small (0.2km)

Cellular

Congested

Large (10km)

Present-day approaches

motivation3
Motivation

Whitespace

Up to 180MHz spectrum

“This new unlicensed spectrum will be

a powerful platform for innovation…” - FCC Chairman

TV

Vacant

Long propagation range

(2km)

Large

  • New opportunity in TV whitespaces
    • FCC released vacant TV channels for unlicensed use
slide6
Goal

Design robust communication protocols to use TV whitespaces for vehicular Internet access

outline
Outline
  • Scout – TV whitespace network for vehicles
    • Heterogeneous architecture
    • Scouting radio based channel estimation
    • Scouting based communication stack
  • Implementation
  • Evaluation
  • Conclusion
outline1
Outline
  • Scout – TV whitespace network for vehicles
    • Heterogeneous architecture
    • Scouting radio based channel estimation
    • Scouting based communication stack
  • Implementation
  • Evaluation
  • Conclusion
a metro hotspot1

Super

A Metro Hotspot

Whitespaces

Gateway

Whitespaces

Base Station

problem of power asymmetry
Problem of Power Asymmetry

AsymmetricPower Limits (FCC 10-174)

Whitespaces

Gateway

0.5 km

Whitespaces

Base Station

Primary

Incumbents

2 km

scout a heterogeneous network
Scout – A Heterogeneous Network

40 Kbps downlink TCP throughput

Cellular BS

Whitespaces BS

Additional advantages:

  • Offloading the majority of traffic
  • Zero interference to primary incumbents
challenges in heterogeneous networks
Challenges in Heterogeneous Networks

Delayed Feedback

Poor Protocol Decisions

Fast Changing Environment

Cellular path has highlatency

problem of delayed feedback
Problem of Delayed Feedback

Whitespaces BS

6Mbps

Cellular BS

6Mbps

Can the client foresee channel at a future location?

ACK

6Mbps

outline2
Outline
  • Scout: TV whitespace network for vehicles
    • Heterogeneous architecture
    • Scouting radio based channel estimation
    • Scouting based communication stack
  • Implementation
  • Evaluation
  • Conclusion
intuition behind scouting radio
Intuition behind Scouting Radio

Whitespaces BS

Cellular BS

Scout

Receiver

Front

Rear

scouting based rate adaptation
Scouting Based Rate Adaptation

Whitespaces BS

1Mbps

Cellular BS

6Mbps

6Mbps

1Mbps

How does base station identify relevant feedback?

NACK

Front

6Mbps

Front(scouting)

Rear(receiving)

Current Reception Location

Future Reception Location

time based feedback alignment
Time based Feedback Alignment

Calculate loss rates in a small window around aligned time

Base station stores scouted feedback according to its received time

Delay for rear radio to reach front location:

Loss = 0.5

Now

outline3
Outline
  • Scout: TV whitespace network for vehicles
    • Heterogeneous architecture
    • Scouting radio based channel estimation
    • Scouting based communication stack
  • Implementation
  • Evaluation
  • Conclusion
scouting based communication stack
Scouting based Communication Stack

Packet Buffer

Client

Base Station

Packet

Loss

Over the Air

scouting based communication stack1
Scouting based Communication Stack

Packet Buffer

3

4

5

2

1

3

2

1

Packet Batch

Client

Base Station

Assign PHY rate

6

6

6

k redundant packets to

tolerate <= k lost packets

6

6

Over the Air

scouting based communication stack2
Scouting based Communication Stack

Packet Buffer

3

4

5

2

1

Client

Base Station

6

6

6

6

6

TV Whitespaces

Over the Air

Cellular

If Loss >= 0.75

successful error correction
Successful Error Correction

Packet Buffer

3

3

4

5

2

2

1

1

3

2

1

Client

Base Station

3

1

Loss <= k Packets

TV Whitespaces

Cellular

error correction failure
Error Correction Failure

Feedback

Link-layer Retransmission

Packet Buffer

3

3

4

5

2

1

Missing Packets

3

Client

Base Station

3

Loss > k Packets

TV Whitespaces

Cellular

system implementation
System Implementation

RF chain 1

RF chain 2

  • Downlink: translate WiFi to TV whitespaces
    • Wide Band Digital Radio (WDR)
  • Uplink: use a 3G link
outline4
Outline
  • Scout: TV whitespace network for vehicles
    • Heterogeneous architecture
    • Scouting radio based channel estimation
    • Scouting based communication stack
  • Implementation
  • Evaluation
  • Conclusion
evaluation
Evaluation
  • Experiment setup
    • Mount a base station on top of a 8-floor building
    • Drive about 500 miles along multiple routes
advantage of scouting r adio
Advantage of Scouting Radio

Single Static

Scout 25mph

Single 10mph and 25mph

29

  • Approach: measure how accurate a previousobservation to the current channel condition
  • Metric: packet loss rates
  • Traffic: 200 byte UDP packets at 12Mbps
advantage of scouting r adio1
Advantage of Scouting Radio

Singlehas 27% - 34% estimation error

Single has high variation under mobility

Typical 3G Delay

Scouthas 5xlower estimation error

Lag (ms)

Low variation in static scenarios

overall performance
Overall Performance

8x and 3x gain over A-3 and A-4

2.5x

Approach: measure downlink performance during 5 drives for each system

Metric: TCP throughput averaged over 1 second bins

conclusion
Conclusion
  • Explored the opportunity in using TV whitespaces to provide vehicular network connectivity.
  • Designed a heterogeneous network to extend network coverage under asymmetric power limits.
  • Designed a scouting radio to improve channel estimation under feedback delay.
  • Designed a scouting based communication stack to enhance link robustness.
slide33

Thanks a lot!

Contact: tzhang@cs.wisc.edu

Video demo: http://youtu.be/_rnzH7owtBw