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
• Growing trend of vehicular Internet access
Infotainment
Entertainment
Road Safety
Motivation
300 million vehicles connected to Internet by 2020 [Cisco report]
Motivation
• Present-day approaches
WiFi
Cellular
Small (0.2km)
Congested
Large (10km)
Motivation
• New opportunity in TV whitespaces
– FCC released vacant TV channels for unlicensed use
Whitespace
Up to 180MHz spectrum
-50
TV
-60
-70
-80
Power (dBm)
“This new unlicensed
spectrum will be
a powerful platform for
innovation…”
- FCC Chairman
-90
-100
-110
-120
-130
-140
-150
Vacant
500
520
540
560
Long propagation range
Large (2km)
580
600
620
Frequency (MHz)
640
660
680
700
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 Hotspot
A
Metro Hotspot
Internet
Whitespaces
Gateway
Whitespaces
Base Station
Problem of Power Asymmetry
Asymmetric
Power Limits (FCC 10-174)
Internet
Whitespaces
Gateway
Whitespaces
Base Station
Primary
Incumbents
A Simple Symmetric Network Solution
16x base stations
Scout – A Heterogeneous Network
Internet
Cellular BS
Additional advantages:
40 Kbps downlink
BS
•Whitespaces
OffloadingTCP
thethroughput
majority of traffic
• Zero interference to primary incumbents
Challenges in Heterogeneous Networks
• Cellular path has high latency
Technology
One-way Latency
3G
100 – 150ms
4G
25 – 40ms
Whitespaces
< 5ms
Delayed Feedback
Fast Changing Environment
Poor Protocol
Decisions
Problem of Delayed Feedback
Whitespaces BS
Internet
Cellular BS
Can the client foresee channel at a future location?
ACK
6Mbps
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
Internet
Receiver Scout
Rear
Front
Cellular BS
Scouting Based Rate Adaptation
Candidate
Whitespaces
BS
Rates
Internet
Cellular BS
9Mbps
6Mbps
How does base station identify relevant feedback?
1Mbps
NACK
Rear(receiving)
Front
Front(scouting)
6Mbps
Current
ReceptionLocation
Location
Future Reception
Time based Feedback Alignment
loss rates
in a small
BaseCalculate
station stores
scouted
feedback
window around
aligned time
according
to its received
time
Time (s)
Delay for rear radio to reach
front location:
Feedback
1
2
3
4
5
Now
6
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
Packet Buffer
Base Station
Packet
Loss
Channel
Estimation
Client
Rate
Selection
FEC
Encoding
Traffic
Duplication
FEC
Decoding
Over the Air
Scouting based Communication Stack
Packet Buffer 1 2 3 4 5
1 2 3
Rate
1Mbps
Loss
Throughput Packet Batch
Base
0.1 Station
0.9Mbps
6Mbps
0.4
3.6Mbps
9Mbps
0.8
1.8Mbps
Channel
Estimation
Client
Rate
Selection
6 6 6
FEC
Encoding
Assign
PHY rate
k redundant packets to
tolerate <= k lost packets
6 6
Traffic
Duplication
Over the Air
FEC
Decoding
Scouting based Communication Stack
Packet Buffer 1 2 3 4 5
Rate
1Mbps
Loss
Throughput
Base
0.1 Station
0.9Mbps
6Mbps
0.4
3.6Mbps
9Mbps
0.8
1.8Mbps
Channel
Estimation
Client
Rate
Selection
FEC
Encoding
FEC
Decoding
6 6 6 6 6
Traffic
Duplication
TVOver
Whitespaces
the Air
Cellular
If Loss >= 0.75
Successful Error Correction
Packet Buffer 1 2 3 4 5
Base Station
1 2 3
Client
Rate
Selection
1 2 3
Channel
Estimation
FEC
Encoding
FEC
Decoding
Loss <= k
Packets
1 3
Traffic
Duplication
TV Whitespaces
Cellular
Error Correction Failure
Feedback
Packet Buffer 1 2 3 4 5
Link-layer
Retransmission
3
Missing Packets
Base Station
Client
Rate
Selection
3
Channel
Estimation
FEC
Encoding
FEC
Decoding
Loss > k
Packets
3
Traffic
Duplication
TV Whitespaces
Cellular
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
Single Static Single 10mph and 25mph
Scout 25mph
Advantage of Scouting Radio
Singlehas
hashigh
27%variation
- 34% estimation
error
Single
under mobility
Typical 3G Delay
Scout has 5x lower estimation error
Lag (ms) Low variation in static scenarios
Overall Performance
• Approach: measure downlink performance during 5 drives
for each system
• Metric: TCP throughput averaged over 1 second bins
Rate
Adaptation
Dual-radio
Combine
A-1
RRAA
No
A-2
Minstrel
No
A-3
RRAA
Yes
A-4
Minstrel
Yes
Throughput (Mbps)
System
68x
and 3x gain over A-3 and A-4
5
4
2.5x
3
2
1
0
A-1
A-2
A-3
A-4
Scout Cellular
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