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 InfotainmentEntertainment Road Safety Growing trend of vehicular Internet access

Motivation 300 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 Hotspot

Whitespaces Base Station A Metro Hotspot Whitespaces Gateway

Problem of Power Asymmetry Primary Incumbents Whitespaces Base Station Asymmetric Power Limits (FCC ) 2 km 0.5 km Whitespaces Gateway

A Simple Symmetric Network Solution 16x base stations

Scout – A Heterogeneous Network Cellular BS Whitespaces BS 40 Kbps downlink TCP throughput Additional advantages: Offloading the majority of traffic Zero interference to primary incumbents Additional advantages: Offloading the majority of traffic Zero interference to primary incumbents

Challenges in Heterogeneous Networks Cellular path has high latency Delayed Feedback Poor Protocol Decisions Fast Changing Environment

Problem of Delayed Feedback ACK Whitespaces BS Cellular BS 6Mbps 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 Scout Receiver

Whitespaces BS Scouting Based Rate Adaptation NACK Rear(receiving) Cellular BS Future Reception Location Front(scouting) 1Mbps 6Mbps 1Mbps Front 6Mbps 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 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 Packet Loss Over the Air

Scouting based Communication Stack Base Station Packet Buffer Client Assign PHY rate 6 6 Packet Batch Over the Air k redundant packets to tolerate <= k lost packets k redundant packets to tolerate <= k lost packets

Scouting based Communication Stack Base Station Packet Buffer Client TV Whitespaces Cellular Over the Air If Loss >= 0.75

Successful Error Correction Base Station Packet Buffer Client TV Whitespaces Cellular Loss <= k Packets

Error Correction Failure Base Station Packet Buffer Client TV Whitespaces Cellular 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 29 Single Static Single 10mph and 25mph Scout 25mph

Advantage of Scouting Radio Low variation in static scenarios Single has 27% - 34% estimation error Typical 3G Delay Scout has 5x lower estimation error Single has high variation under mobility Lag (ms)

Overall Performance 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.

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