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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. - PowerPoint PPT Presentation
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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
• 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.
