tan zhang ★ , sayandeep sen † , suman banerjee ★

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

• Growing trend of vehicular Internet access

Motivation300 million vehicles connected to Internet by 2020 [Cisco report]

Motivation• Present-day approaches

WiFi

Small (0.2km)Cellular

Congested

Large (10km)

Motivation• New opportunity in TV whitespaces

– FCC released vacant TV channels for unlicensed use

TV

(2km)

Whitespace

Large

Vacant

Long propagation range

“This new unlicensed spectrum will be a powerful platform for innovation…”

- FCC Chairman

Up to 180MHz spectrum

Goal

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

Outline

• Scout – TV whitespace network for vehicles– Heterogeneous architecture– Scouting radio based channel estimation– Scouting based communication stack

• Implementation• Evaluation• Conclusion

Outline

• Scout – TV whitespace network for vehicles– Heterogeneous architecture– Scouting radio based channel estimation– Scouting based communication stack

• Implementation• Evaluation• Conclusion

A Metro HotspotSuper

Whitespaces Base Station

A Metro Hotspot

Whitespaces Gateway

Super

Problem of Power Asymmetry

Primary Incumbents

Whitespaces Base Station

Asymmetric Power Limits (FCC 10-174)

2 km

0.5 km

Whitespaces Gateway

A Simple Symmetric Network Solution

16x base stations

Scout – A Heterogeneous Network

Cellular BS

Whitespaces BS40 Kbps downlink TCP throughput

Additional advantages:• Offloading the majority of traffic• Zero interference to primary incumbents

Challenges in Heterogeneous Networks• Cellular path has high latency

Technology One-way Latency3G 100 – 150ms4G 25 – 40ms

Whitespaces < 5ms

Delayed Feedback Poor Protocol

DecisionsFast Changing Environment

Problem of Delayed Feedback

ACK

Whitespaces BSCellular BS

6Mbp

s

6Mbps

6Mbp

s

Can the client foresee channel at a future location?

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

Whitespaces BS Cellular BS

Rear Front

ScoutReceiver

Whitespaces BSCandidate

Rates

9Mbps

6Mbps

1Mbps

Scouting Based Rate Adaptation

NACK

Rear(receiving)

Cellular BS

Future Reception Location

Front(scouting)

1Mbp

s6M

bps

6Mbp

s1M

bps

Front 6Mbps

Current Reception Location

How does base station identify relevant feedback?

Calculate loss rates in a small window around aligned time

Time based Feedback Alignment

Time (s) Feedback

123456

Base station stores scouted feedback according to its received time

Now

Delay for rear radio to reach front location:

Loss = 0.5

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

Base Station

Packet Buffer

Client

Packet Loss

Over the Air

Scouting based Communication Stack

Base Station

Packet Buffer

ClientRate Loss Throughput

1Mbps 0.1 0.9Mbps

6Mbps 0.4 3.6Mbps

9Mbps 0.8 1.8Mbps

1 2 3 4 5

1 2 3

6 6 6

Assign PHY rate

6 6

Packet Batch

Over the Air

k redundant packets totolerate <= k lost packets

Scouting based Communication Stack

Base Station

Packet Buffer

Client

TV Whitespaces

Cellular

Rate Loss Throughput

1Mbps 0.1 0.9Mbps

6Mbps 0.4 3.6Mbps

9Mbps 0.8 1.8Mbps

1 2 3 4 5

6 6 6

6 6

Over the Air

If Loss >= 0.75

Successful Error Correction

Base Station

Packet Buffer

Client

TV Whitespaces

Cellular

1 2 3 4 5

Loss <= k Packets

1 3

1 2 3

1 2 3

Error Correction Failure

Base Station

Packet Buffer

Client

TV Whitespaces

Cellular

1 2 3 4 5

3

3

3

Link-layer Retransmission

Feedback

Missing Packets

Loss > k Packets

System Implementation• Downlink: translate WiFi to TV whitespaces

– Wide Band Digital Radio (WDR)• Uplink: use a 3G link

RF chain 1

RF chain 2

Outline

• Scout: TV whitespace network for vehicles– Heterogeneous architecture– Scouting radio based channel estimation– Scouting based communication stack

• Implementation• Evaluation• Conclusion

Evaluation• Experiment setup

– Mount a base station on top of a 8-floor building– Drive about 500 miles along multiple routes

Advantage of Scouting Radio• Approach: measure how accurate a previous

observation to the current channel condition• Metric: packet loss rates• Traffic: 200 byte UDP packets at 12Mbps

29Single Static Single 10mph and 25mph Scout 25mph

Advantage of Scouting Radio

Low variation in static scenarios

Single has 27% - 34% estimation errorTypical 3G Delay

Scout has 5x lower estimation error

Single has high variation under mobility

Lag (ms)

Overall Performance

System Rate Adaptation

Dual-radioCombine

A-1 RRAA No

A-2 Minstrel No

A-3 RRAA Yes

A-4 Minstrel Yes

• Approach: measure downlink performance during 5 drives for each system

• Metric: TCP throughput averaged over 1 second bins

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

2.5x

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.

Thanks a lot! Contact: tzhang@cs.wisc.edu

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