Wi-Fi Goes to Town: Rapid Picocell Switching for Wireless Transit Networks. Speaker: Zhenyu Song. Zhenyu Song, Longfei Shangguan, Kyle Jamieson

Transcription

1 Wi-Fi Goes to Town: Rapid Picocell Switching for Wireless Transit Networks Speaker: Zhenyu Song Zhenyu Song, Longfei Shangguan, Kyle Jamieson {zhenyus, longfeis, This work is supported by the NSF grant No and Google Research Award.

2 Motivation Billions of commuters on trains, light rails and in cars surf the internet Conference How can we increase the wireless network 1000X in bits/(second*dollar)? Online Video VR gaming 2

3 Motivation The majority of capacity gains over the past 45 years is due to the decreased size of each cell. Cooper increasing capacity gain

4 Two recent observations Very low-cost (<= $5) The ESP8266 Wi-Fi and system-on-chip module,available ca.2016 for $5. Commodity s can extract fine-grained channel state information [Halperin et al.] 4

5 Wi-Fi Goes to Town: Picocell network for transit 5

6 Problem: picocells + vehicular speed How to support switching between s? We need to switch fast! 6

7 Problem: rapid multi-path fading Rapid (ms-scale) channel fading due to the multi-path Channel Capacity Time (ms) Best We need sequence to switch is at not a millisecond left-to-right level! order 7

8 Design Who maintains states and makes switching decision When to switch (to which ) How to switch 8

9 Design Wi-Fi Goes to Town: system architecture 9

10 Design::who A controller maintains states and makes decisions 10

11 Design::when (and which) selection algorithm Controller maintains an Effective SNR value window (10 ms), and selects with largest median value window window window Time

12 Design::how Association Uplink (from client to ) Downlink (from to client) 12

13 Design::how Wi-Fi Goes to Town: -client association All s associate with client propagate info 1 extract hostapd client info hostapd 2 send to hostapd 3 13

14 Design::how Wi-Fi Goes to Town: Uplink flow Stripe and de-duplicate same bssid 1 tunneling

15 Design::how Wi-Fi Goes to Town: Downlink flow ack start

16 Design::how Wi-Fi Goes to Town: Downlink packet synchronization set as seq tunneling

17 Introduction of aggregation in n aggregate frame 1,2,3 MPDU sender sender window window partial ack frame 1 aggregate frame 2,3,4 block ack MPDU Sender Receiver 17

18 Problem: block ack lost causes mac layer inefficiency needlessly retransmits whole aggregate 18

19 Solution: block ack forwarding 1 (associated) kernel block ack (adjacent) kernel 19

20 Implementation Wi-Fi Goes to Town: Two Deployment Schemes 20

21 Implementation: hardware : TP-Link N750, Larid directional antenna, Atheros CSI Tool [Xie et al.] Controller: Lenovo Thinkpad T430 21

22 Evaluation: questions How much does Wi-Fi goes to town improve uplink reception rate? Does Wi-Fi goes to town increase jitter? Does Wi-Fi goes to town achieve higher end-to-end throughput? 22

23 Short demo Uplink packet 23 Downlink packet retrans packet

24 Strawman: r (enhanced) (Original r) Fast handover: Fast BSS transition. Client maintains time-averaged RSSI, and switch when below threshold (Enhanced) Fast nearby discovery: Each tells client nearby information Client overhears beacons 24

25 Wi-Fi goes to town achieve lower uplink loss rate by over-hearing Uplink loss rate 25

26 TCP Download Wi-Fi goes to town achieves seamless switching at speed RSSI, switch! (Too late) 26

27 TCP Download Wi-Fi goes to town achieves seamless switching at speed 27

28 TCP Download Wi-Fi goes to town achieves seamless switching at speed ms-scale switching 28

29 Wi-Fi goes to town achieves higher end-to-end throughput Single-client, download r s performance degrades with speed while Wi-Fi goes to town not 29

30 Multi-client Wi-Fi goes to town achieves higher end-to-end throughput Average Throughput (Mbit/s) Wi-Fi goes to town always achieves higher performance 30

31 Conclusion First roadside hotspot network at vehicular speeds with meter-sized picocells. Execute switch decisions at millisecond-level granularities. First step in a line of work that will scale out the wireless capacity of roadside hotspot networks using small cells. 31

32 Questions? 32