BEST Paper Award @ MobiCom 2017 Zhijun Li and Tian He Computer Science and Engineering University of Minnesota
Wireless is Everywhere <wigle.net> 2 Tian He @ UMN
… and Increases Rapidly ~4B 1.8B 130M Source: ABI Research Source: Navigant Research Gartner predicts 20 billion IOT devices by year 2020 3 Tian He @ UMN
… also Diversifies Quickly 4 Tian He @ UMN
Coexist and Collaborate LAN Network of “Things” Thermostat PAN Smoke detector Humidity detector Many more WAN Smart Hospital Tian He @ UMN
Objective: Ubiquitous Connectivity Q: How to Interconnect/bridge them ? WAN LAN PAN PAN 6 Tian He @ UMN
Bridging Wireless Tech: Gateway MutiRadio Gateway Extra HW/deployment cost Traffic overhead into/out of the gateway Pre-deployment, unsuitable for ad hoc/mobile 7 Tian He @ UMN
The New Paradigm: CTC Cross-Technology Communication (CTC) enabling heterogeneous devices talks directly! 8 Tian He @ UMN
What CTC can Achieve: Low Cost A WiFi AP controls all smart home ZigBee- enabled devices in one hop without gateway 9 Tian He @ UMN
What CTC can Achieve: Mobility VANET Battle Field Inventory Wearables Tracking Direct Communication among mobile IOT devices without pre-deployed gateways 10 Tian He @ UMN
What CTC can Achieve: Coordination Support Explicit channel coordination No traffic I need next next 20ms 200ms Time Wifi ZigBee Wifi Extends local mechanisms globally across wireless tech. Global RTS/CTS Reservation. Global Time Division Multiple Access (TDMA) 11 Tian He @ UMN
WEBee Physical-Layer Cross-Technology Communication WEBee: WiFi Emulated ZigBee 12 Tian He @ UMN
Outline The State of the Art The Design Implementation & Evaluation Extensions 13 Tian He @ UMN
The State of the Art 14 14 Tian He @ UMN
A Brief History of CTC Research 16,000X Faster!!! Packet-level CTC WE ARE HERE Using packet length, gap, or offset A packet can only express a few bits PHY (RSSI) Energy CTC 0 1 1 time 100s Kbps HoWiES FreeBee ESENSE GSense Comb. Packet Beacon Interval Packet Length Gap Length Length S. Kim K. Chebrolu X. Zhang Y. Zhang bps bps bps Mobicom MobiCom INFOCOM MobiCom 2009 2015 2013 2017 15 Tian He @ UMN
A Brief History of CTC Research 16,000X Faster!!! Physical-Level CTC WE ARE HERE By emulating receiver’s RF waveform, A packet achieves Rx’s maximum rate PHY CTC 1 1 1 0 In-phase 100s Quadrature I/Q RSSI Kbps …… time bps bps bps Mobicom MobiCom INFOCOM MobiCom 2009 2015 2013 2017 16 Tian He @ UMN
The Design 17 17 Tian He @ UMN
The Key Idea of WEBee WiFi Frame with selected Payload WiFi Sender Emulated ZigBee Signals ZigBee Frame ZigBee Receiver Ignore Ignore ZigBee Compatible Signal 18 Tian He @ UMN
Challenges of Physical-Layer CTC Key Innovation Signal Modulation : QAM, OFDM Emulation Rate : ~54Mbps (802.11g) @ Distance ：300m Wi-Fi Sender Tx ：26dBm Sensitivity ：-80dBm Modulation : OQPSK, DSSS Rate : ~250Kbps Distance ：100m Tx ：0dBm Without translator Sensitivity ：-97dBm 19 Tian He @ UMN
How Wi-Fi Transmits Channel Coding Wi-Fi Convolutional Scrambler Interleaver Encoder Frame payload Coded Bits Modulation (QAM) Pilot Cyclic IFFT Insertion Prefixing Wi-Fi Signal Post-QAM Processing 20 Tian He @ UMN
Emulation via a Reverse Path Channel Coding Emulation Wi-Fi Convolutional Scrambler Interleaver Encoder Frame payload Coded Bits Transmission QAM Modulation (QAM) Emulation Emulation Pilot Cyclic IFFT Insertion Prefixing ZigBee Signals Post-QAM Emulation To be Emulated 21 Tian He @ UMN
QAM Emulation RF Signal Spectrogram in the Air Mimic QAM/OFDM signals OQPSK signals 22 Tian He @ UMN
Minimizing Emulation Distortion Minimizing emulation distortion in the time-domain is equivalent to minimizing the total deviation of frequency components (based on Parseval’s theorem) QAM FFT Emulation Desired Corresponding The Closest Wi- Time-domain Frequency-domain Fi QAM Points ZigBee Signals Components 23 Tian He @ UMN
Other Technical Challenges Reverse channel coding Parallel CTC For details, refer to the paper Pilot/Null avoidance Link-level reliability 24 Tian He @ UMN
Innovative Features of WEBee 25 25 Tian He @ UMN
Dual-Standard Compliance A part of WiFi frame is a Zigbee frame 26 26 Tian He @ UMN
No change in Sender’s Hardware/Firmware Send a normal WiFi Frame 27 27 Tian He @ UMN
No change in receiver’s Hardware/firmware Receive a normal ZigBee Frame 28 28 Tian He @ UMN
Combine the advantages of two technologies. Tx：26dbm Rx：0dbm Sensitivity：-65dbm Sensitivity：-97dbm Big Mouth Good Ear WEBee has a longer range than Wi-Fi! 29 29 Tian He @ UMN
Support parallel CTC in one WIFI Packet 2MHZ 2MHZ 20MHZ Simultaneous Unicast 30 30 Tian He @ UMN
Support high mobility and duty cycled operations Low Power Listening Longer Range, better mobility 31 31 Tian He @ UMN
An 16,000x faster CTC with 99.9% reliability For details referring to our mobicom 2017 paper 32 32 Tian He @ UMN
Implementation & Evaluation 33 Tian He @ UMN
System Implementation Sender Receiver WEBee@Laptop WiFi(Commodity) AR2425 AR9485 RX Wi-Fi Frame WEBee@ Smartphone ZigBee(Commodity) LG RX CC2420 Nexus 5 ZigBee Frame WEBee @ USRP ZigBee(USRP) RX N210 N210 ZigBee Frame 34 Tian He @ UMN
Experimental Setting Lab Hallway Outdoor Experiment setting 10,000 runs each trial • Varying distances • Varying Tx Power • Varying packet length • Varying content • Varying duty-cycle • Varying Mobility 35 Tian He @ UMN
Symbol Error Ratio vs Data Rate FreeBee [Mobicom ’ 15] 7.5bps @ 99% WEBee [Mobicom ’ 17] 63,000bps @ 99% ~8,000x Speed up *250kbps theoretically 36 Tian He @ UMN
Frame Reception Ratio A frame fails with one symbol error WEBee(Commodity) 100 Recept. Ratio (%) AR2425 80 ~50% ZigBee 60 CC2420 WEBee(USRP) 40 N210 20 0 WEBee(USRP) WEBee(WiFi) è ZigBee è ZigBee 37 Tian He @ UMN
Reliability after Retransmission 99% after 6 retransmissions Less re-TX with Repeated preamble and coding 38 Tian He @ UMN
Parallel CTC With two channels, WEBee vs. FreeBee = ~16,000x Channel I Channel II 39 Tian He @ UMN
WEBee in Action 40 40 Tian He @ UMN
WEBee Demo 41 Tian He @ UMN
Application: Smart Light Control You can control ZigBee Smart Bulb with WEBee Vs. GE Gateway Solution WeBee Solution 42 Tian He @ UMN
Release: WEBee Payload Generator V1.o You can conduct cross-technology research using WEBee Generator! Available at: http://tianhe.cs.umn.edu/CTC Possible New Topics: • Channel Access Control • Coordination • Neighbor Discovery • Multi-Technology Routing • CTC Time Synch. • CTC Localization • ….. 43 Tian He @ UMN
Extension 44 44 Tian He @ UMN
Question: Whether Signal Emulation is a generic technology? 45 Tian He @ UMN
BlueBee: BlueTooth to ZigBee [SenSys ’17] 46 Tian He @ UMN
LTEBee: LTE (band 7) to ZigBee LTE smartphone controls a CC2530 ZigBee Blub directly after 7-layers channel coding and 6-step modulation. 47 Tian He @ UMN
Conclusion WEBee is the first physical-layer CTC design, a paradigm shift with a significantly higher throughput, while requiring no change of HW. Our work indicates Signal Emulation is a generic technology to build light-weight SDR, striking a delicate balance between flexibility and cost. Our work brings a surge of opportunities to expand many local wireless mechanisms globally (e.g., coordination, discovery, etc.) across technologies. 48 Tian He @ UMN
CTC Technical Support is available at http://tianhe.cs.umn.edu/CTC 49 Tian He @ UMN
Can support two-way Long Range Wake Slave Master nodes Node Duty-Cycle Mode Always On Mode 50 50 Tian He @ UMN
Opportunity for Cross-Tech.-Comm. Wireless technologies share unlicensed ISM bands, offering opportunity for cross-tech. communication <ni.com> Channel Center Frequency (MHz) <digikey.com> 51 Tian He @ UMN
Channel Mapping OFDM Has 64 subcarrier, 48 data, 12 null and 4 pilot 52 Tian He @ UMN
Four-to-one emulation Four Wi-Fi symbols are used to emulate one ZigBee symbol 53 Tian He @ UMN
Link Layer Reliability Repeated preamble and hamming coding 54 Tian He @ UMN
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