ZigFi: Harnessing Channel State Information for Cross-Technology - PowerPoint PPT Presentation

ZigFi: Harnessing Channel State Information for Cross-Technology Communication Xiuzhen Guo 1 , Yuan He 1 , Xiaolong Zheng 1 , Liangcheng Yu 2 , Omprakash Gnawali 3 1 Tsinghua University 2 KTH Royal Institute of Technology 3 University of Houston 1

Wireless is everywhere 1. Smart Hospital Smart Home Smart Factory 2

CTC among different technologies 1. FreeBee GapSense FreeBee Esense HoWiEs B 2 W 2 FreeBee WiZig WEBee BlueBee 3

The state of the art 1.  Packet Energy: WiZig [Infocom ’ 17] CTC symbol window CTC symbol window WiFi Time T WiFi Time T 1 0 1 1 0 ZigBee 0 1 0 0 1 1 1 0 0 0 0 1 ZigBee Time Time 1 CTC symbol 1 0 CTC symbol 0 WiFi packet  Packet Size: Esense [MobiCom ’ 09], HoWiEs [Infocom ’ 13] WiFi Packet RSSI value CTC messsage 100 Bytes 200 Bytes 100 Bytes WiFi Time E Time 010 ZigBee 4 Time

The state of the art 1.  Packet Transmission Timing: FreeBee [MobiCom ’ 15], Gap Sense [Infocom ’ 13]    t   t   t   t    ( / 2 ) 2 2 t T / 2 t T ... ... Time Modulation via shifting t (reference position)  Physical Signal Emulation: WEBee [MobiCom ’ 17], WiFi Packet BlueBee [SenSys ’ 17] WiFi Emulated ZigBee Signals Ignore Ignore ZigBee Packet ZigBee 5 Demodulation

Challenges 1. Using RSSI is inefficient Bandwidth: 2M Rate: 250Kbps Modulation: OQPSK , DSSS T x ： 0dBm Directly decoding is difficult Bandwidth: 20M Rate: 54Mbps Modulation: QAM, OFDM T x ： 20dBm Physical emulation is infeasible 6

Feasibility of using CSI 1. WiFi channel ZigBee channel DC Subcarrier (1) Pilot Subcarrier (4) Data Subcarrier (48) Null Subcarrier (11) #11 ... ... ... ... ... ... ... ... WiFi 2462 f (MHz) #21 #22 #23 #24 ZigBee 2465 f (MHz) (Without ZigBee) (With ZigBee) The transmission of ZigBee packets affects the CSI significantly 7

Challenges of using CSI 1. #Subchannel  Frequency domain: Select a proper subchannel #Packet Length  Time domain: ZigBee length satisfies a threshold # Transmission Power  CSI sequence: Choose an appropriate ZigBee power 8

ZigFi: Harnessing CSI for CTC 1.  ZigBee packets piggy-backed to the existing WiFi link  WiFi receiver collects two sets of information  SVM classification WiFi ZigBee ZigFi Message Message PHY Layer PHY Layer Encoding SVM Decoding WiFi Packets Modulation Demodulation Decoding Packets CSI Sequence Existing WiFi Link 9

Encoding and decoding 1.  Encoding: Presence or absence of ZigBee packets  Decoding: SVM identifies the interfered CSI sequence ZigBee packet WiFi packet Preamble CSI sample not interfered by ZigBee CSI sample interfered by ZigBee 0 1 1 1 ZigBee TX T DZ T IZ WiFi TX WiFi RX 1 0 1 1 10 0

SINR in ZigFi 1. 𝑇 𝑎 𝑇𝐽𝑂𝑆 = 10𝑚𝑕 𝐽 𝑋 + 𝑂 SINR in range [-0.25,1.25], decoding accuracy > 0.9 11 1

The Receiver-initiated mechanism 1.  Establish a WiFi link  Obtain an appropriate SINR 12 2

Evaluation 1.  WiFi: Commercial WiFi device + CSITool, channel 11  ZigBee: TelosB mote, channel 23  Noise: USRP generator  Metrics: Throughput and SER WiFi Sender Noise d 5 d 4 d 1 WiFi ZigBee Receiver Sender d 2 d 3 WiFi RX WiFi TX ZigBee TX 13 USRP 3

ZigFi vs. FreeBee 1. ZigFi shows significant enhancement over FreeBee in terms of throughput and SER. 14 4

Distance 1.  The ZigBee Tx and the WiFi Rx Adaptive is better than default. ZigFi performs well under the adaptive mode. 15 5

Distance 1.  WiFi Tx and the WiFi Rx Adaptive is better than default. ZigFi in the adaptive mode performs well. 16 6

Noise 1. Throughput of ZigFi degrades with noise intensity increases. ZigFi in the adaptive mode is more resilient to noise. 17 7

NLoS Scenario 1. ZigFi in the adaptive mode is robust under NLoS scenario 18 8

The impact on the WiFi communication 1. (With ZigFi) (Without ZigFi) ZigFi has limited impact on the WiFi communication 19 9

Summary 1.  We harness CSI as a side channel to achieve CTC from ZigBee to WiFi and translate the decoding problem into a CSI classification problem.  We design a receiver-initiated protocol for practical application of ZigFi.  Proper subchannel  Appropriate packet length  Suitable transmission power  Experimental results show that ZigFi achieves efficient and robust CTC . 20

Q&A Thanks guoxz16@mails.Tsinghua.edu.cn 21