BEST Paper Award @ MobiCom 2017 Zhijun Li and Tian He Computer - - PowerPoint PPT Presentation

Zhijun Li and Tian He

Computer Science and Engineering University of Minnesota

BEST Paper Award @ MobiCom 2017

Tian He @ UMN

Wireless is Everywhere

<wigle.net>

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1.8B

… and Increases Rapidly

Source: ABI Research

~4B

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Gartner predicts 20 billion IOT devices by year 2020

Source: Navigant Research

130M

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… also Diversifies Quickly

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Coexist and Collaborate

LAN

Network of “Things”

Thermostat Smoke detector Humidity detector Many more

PAN WAN

Smart Hospital

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Objective: Ubiquitous Connectivity

Q: How to Interconnect/bridge them?

PAN

LAN PAN WAN

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MutiRadio Gateway

Bridging Wireless Tech: Gateway

—Extra HW/deployment cost —Traffic overhead into/out of the gateway —Pre-deployment, unsuitable for ad hoc/mobile

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The New Paradigm: CTC

Cross-Technology Communication (CTC) enabling heterogeneous devices talks directly!

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What CTC can Achieve: Low Cost

A WiFi AP controls all smart home ZigBee- enabled devices in one hop without gateway

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What CTC can Achieve: Mobility

Direct Communication among mobile IOT devices without pre-deployed gateways

Battle Field VANET Inventory Tracking Wearables

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Support Explicit channel coordination

— Extends local mechanisms globally across wireless tech.

— Global RTS/CTS Reservation. — Global Time Division Multiple Access (TDMA)

What CTC can Achieve: Coordination

Time

Wifi

No traffic next 20ms

ZigBee Wifi I need next 200ms

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WEBee

Physical-Layer Cross-Technology Communication

WEBee: WiFi Emulated ZigBee

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Outline

— The State of the Art — The Design — Implementation & Evaluation — Extensions

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The State of the Art

Tian He @ UMN

Packet-level CTC

Using packet length, gap, or offset A packet can only express a few bits

A Brief History of CTC Research

Mobicom 2009 INFOCOM 2013 MobiCom 2015 MobiCom 2017 ESENSE Packet Length

• K. Chebrolu

GSense Gap Length

• X. Zhang

HoWiES

• Comb. Packet

Length

• Y. Zhang

FreeBee Beacon Interval

• S. Kim

bps

PHY CTC 100s Kbps

bps bps

16,000X Faster!!!

WE ARE HERE 15

time Energy (RSSI)

1 1

Tian He @ UMN

Physical-Level CTC

By emulating receiver’s RF waveform, A packet achieves Rx’s maximum rate

A Brief History of CTC Research

Mobicom 2009 INFOCOM 2013 MobiCom 2015 MobiCom 2017

bps

PHY CTC 100s Kbps

bps bps

16,000X Faster!!!

WE ARE HERE 16

I/Q RSSI

time Quadrature In-phase 1 1 1 ……

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The Design

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The Key Idea of WEBee

WiFi Sender

Emulated ZigBee Signals

ZigBee Receiver WiFi Frame with selected Payload

ZigBee Frame

Ignore Ignore

ZigBee Compatible Signal 18

Tian He @ UMN

Challenges of Physical-Layer CTC

Modulation: QAM, OFDM Rate: ~54Mbps (802.11g) Distance：300m Tx：26dBm Sensitivity：-80dBm Modulation : OQPSK, DSSS Rate: ~250Kbps Distance：100m Tx：0dBm Sensitivity：-97dBm

Without translator

Key Innovation

Signal Emulation

@ Wi-Fi Sender

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How Wi-Fi Transmits

Wi-Fi Frame

Modulation (QAM) Scrambler Convolutional Encoder Interleaver

Channel Coding

Pilot Insertion IFFT Cyclic Prefixing

Post-QAM Processing Wi-Fi Signal

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Coded Bits payload

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Emulation via a Reverse Path

Wi-Fi Frame

Scrambler Convolutional Encoder Interleaver Pilot Insertion IFFT Cyclic Prefixing Modulation (QAM)

Transmission Emulation Channel Coding Emulation Post-QAM Emulation QAM Emulation ZigBee Signals To be Emulated Coded Bits payload

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QAM Emulation

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Mimic

RF Signal Spectrogram in the Air

QAM/OFDM signals OQPSK signals

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— Minimizing emulation distortion in the time-domain is

equivalent to minimizing the total deviation of frequency components (based on Parseval’s theorem)

The Closest Wi- Fi QAM Points

Minimizing Emulation Distortion

Desired Time-domain ZigBee Signals

FFT QAM Emulation

Corresponding Frequency-domain Components 23

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Parallel CTC Link-level reliability

Other Technical Challenges

Reverse channel coding Pilot/Null avoidance

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For details, refer to the paper

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Innovative Features of WEBee

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Dual-Standard Compliance

A part of WiFi frame is a Zigbee frame

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No change in Sender’s Hardware/Firmware

Send a normal WiFi Frame

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No change in receiver’s Hardware/firmware

Receive a normal ZigBee Frame

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Combine the advantages of two technologies.

Tx：26dbm Sensitivity：-65dbm Rx：0dbm Sensitivity：-97dbm

Big Mouth Good Ear

WEBee has a longer range than Wi-Fi!

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Support parallel CTC in one WIFI Packet

Simultaneous Unicast 20MHZ 2MHZ 2MHZ

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Support high mobility and duty cycled operations

Longer Range, better mobility Low Power Listening

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An 16,000x faster CTC with 99.9% reliability

For details referring to our mobicom 2017 paper

Tian He @ UMN

Implementation & Evaluation

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System Implementation

WiFi(Commodity)

AR9485

ZigBee(USRP)

N210

ZigBee(Commodity)

CC2420 WEBee @ USRP N210 WEBee@ Smartphone LG Nexus 5 WEBee@Laptop AR2425 Receiver Sender

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RX Wi-Fi Frame RX ZigBee Frame RX ZigBee Frame

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

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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

~50%

WEBee(USRP) è ZigBee WEBee(WiFi) è ZigBee

• Recept. Ratio (%)

20 40 60 80 100

A frame fails with one symbol error

WEBee(Commodity)

AR2425

WEBee(USRP)

N210

ZigBee

CC2420

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Reliability after Retransmission

99% after 6 retransmissions

Less re-TX with Repeated preamble and coding

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Parallel CTC

With two channels, WEBee vs. FreeBee = ~16,000x

Channel I Channel II

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WEBee in Action

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WEBee Demo

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Application: Smart Light Control

GE Gateway Solution WeBee Solution Vs.

— You can control ZigBee Smart Bulb with WEBee

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Release: WEBee Payload Generator V1.o

You can conduct cross-technology research using WEBee Generator!

Available at: http://tianhe.cs.umn.edu/CTC

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Possible New Topics:

• Channel Access Control
• Coordination
• Neighbor Discovery
• Multi-Technology Routing
• CTC Time Synch.
• CTC Localization
• …..

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Extension

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Question: Whether Signal Emulation is a generic technology?

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BlueBee: BlueTooth to ZigBee [SenSys ’17]

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LTEBee: LTE (band 7) to ZigBee

— LTE smartphone controls a CC2530 ZigBee Blub directly

after 7-layers channel coding and 6-step modulation.

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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.

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Tian He @ UMN

CTC Technical Support is available at http://tianhe.cs.umn.edu/CTC

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Can support two-way

Master Node Slave nodes

Duty-Cycle Mode Always On Mode

Wake Long Range

Tian He @ UMN

— Wireless technologies share unlicensed ISM bands,

• ffering opportunity for cross-tech. communication

Opportunity for Cross-Tech.-Comm.

<ni.com> <digikey.com>

Channel

Center Frequency (MHz)

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Channel Mapping

— OFDM Has 64 subcarrier, 48 data, 12 null and 4 pilot

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Four-to-one emulation

— Four Wi-Fi symbols are used to emulate one ZigBee symbol

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Link Layer Reliability

— Repeated preamble and hamming coding

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