PowerPoint Presentation

Song Min Kim and Tian HeComputer Science and EngineeringUniversity of Minnesota

FreeBee Cross-technology Communication via Free Side-channel

# Song Min Kim @MobiCom 2015#1OutlineBackground and Motivation

FreeBee Design

System Implementation & Evaluation

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Song Min Kim @MobiCom 2015#OutlineBackground and Motivation

FreeBee Design

System Implementation & Evaluation

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Song Min Kim @MobiCom 2015#Wireless is everywhere

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Song Min Kim @MobiCom 2015#4 and is only becoming denser 5

Source: Navigant Research

Source: ABI Research

~3B~70M1.5B Song Min Kim @MobiCom 2015#5Issue & opportunityDark sideCross-interference due to incompatible PHY/MAC6Bright sideNew application via information sharing

collision

Internet

Location

Personal Health Information

Environmental Monitoring Information

Address issue &Explore opportunityvia comm. between tech. Song Min Kim @MobiCom 2015#Is there an existing solution?Traditionally, technologies communicate via multi-radio gateways

FreeBee allows coexisting wireless technologies to directly talk to each other

FreeBee- Extra HW cost (> $150)- Control traffic overhead- Deployment complexity Song Min Kim @MobiCom 2015#7A building block for explicit channel access coordination, reducing cross-technology interference

Extends local mechanisms globally across wireless tech.Global NetworkAllocation Vector (NAV) Global RTS/CTS ReservationGlobal Time Division Multiple Access (TDMA)

For spectrum efficiency Time8WiFi

No traffic next 20ms

ZigBee

WiFiI need next 200ms Song Min Kim @MobiCom 2015#8For cost efficiencySupport for Smart Home

Eliminates the need for the Gateway HW bridging WiFi and ZigBee technologies (>$150)

Smartphone not associated9

Away ModeHome Mode

Smartphone associatedZigBee smart home devices

WiFi AP Song Min Kim @MobiCom 2015#9

State-of-the-art Wake-on-WLAN (MobiCom `10)

Wake-on selective WLANKeep WiFi interface OFF for private WiFi AP Wake WiFi interface ON only when OPEN AP nearby

For energy efficiencyZigBee module in SD card(Spectec Computer Co., Ltd)

OFF

ONServes as the secondary radioWiFi interface is turned offWakes up WiFi interface when it detects any WiFi AP in proximity

However, urban areas are usually overfilled with WiFi APs, where they are MOSTLY PRIVATE (Secured)It is waste of energy to wake up for inaccessible private WiFi APs. Can we improve this?

OFF

ONPrivate WiFi AP

Free (open) WiFi AP

Song Min Kim @MobiCom 2015#OutlineBackground and Motivation

FreeBee Design

System Implementation & Evaluation

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Song Min Kim @MobiCom 2015#FreeBee in a nutshell12Operational RequirementSender: Support beacon operations

Receiver: A wireless RF chip for RSS sampling

Frequency (partial) overlap

SupportedSupportedSupported

?Provisional patent filed Song Min Kim @MobiCom 2015#12Key features of FreeBeeTechnology Independent: WiFi, ZigBee, Bluetooth, etc

Free & Transparent: establishes side-channel with mandatory beacons. No impact to the legacy traffic.

Easy to Deploy: no HW/PHY modification.

For Control : mainly for delivering control information. Up to 1.4Kbps throughput (more on this later)Broadcast via beacon for receivers to listen on-demand, supporting mobile and/or duty-cycled receivers

13 Song Min Kim @MobiCom 2015#13FreeBee architectureFreeBee Multiple AccessFreeBee ModulatorIEEE Standard MAC/PHYFreeBee Multiple AccessIEEE Standard RSS SamplerTxRx14FreeBee DemodulatorFreeBee design(All software)ZZZZZCommodity HW

Song Min Kim @MobiCom 2015#14FreeBee architecture: PHYFreeBee Multiple AccessFreeBee ModulatorIEEE Standard MAC/PHYFreeBee Multiple AccessIEEE Standard RSS SamplerTxRx15FreeBee Demodulator

Song Min Kim @MobiCom 2015#15S-FreeBee: modulation16Initially beacons are transmitted at the reference positionLet receiver learn the position

Shift beacons between (-T/2, T/2] from the reference position to embed S-FreeBee symbol.T is beacon intervalLet is the unit of shift, then

One S-FreeBee symbol is worth log2(T/) bits timet(reference position)t+2t+T/2t-t-2t-T/2t+

Requires time sync to keep track of the reference positionNot suitable for mobile environment? Song Min Kim @MobiCom 2015#16A-FreeBee: modulation17timett+2Tt+4Tt+(T- )t+(3T- )t+(5T- )Beacons shifted by -Shift every other beacons, between (-T/2, T/2]

Use the distance between two consecutive beacons to convey a symbol (instead of shift offset in S-Freebee)

Lower symbol rate, but no learning needed.

Song Min Kim @MobiCom 2015#17FreeBee Architecture: PHYFreeBee Multiple AccessFreeBee ModulatorIEEE Standard MAC/PHYFreeBee Multiple AccessIEEE Standard RSS SamplerTxRx18FreeBee Demodulator

Song Min Kim @MobiCom 2015#18FreeBee demodulation Challenge: receiver can only sense RSS, no decoding possible (due to incompatible PHY)

Idea: We utilize the periodicity of beacons, as others are most likely not periodicReceiver demodulate statistically.19

RSS Samples under Cross Technology InterferenceHidden Beacons Song Min Kim @MobiCom 2015#19Beacon detection solutionReceiver samples RSS continuously(This is by default in standards; e.g. ZigBee (802.15.4))Samples are quantized (0 or 1) according to threshold.Digital signal processing of Folding* is utilized to statistically determine the position of beacons

100011001101Fold sum: 2 3 0 1Column with the peak valueindicate beacon positionNon-periodic signals spread outBeacons with interval of 4Non-periodic data packets/noise-70-87-9592-56-68-90-91-59-69-87-55Threshold = -75 dBmFold by the interval (=4)*David H. Staelin, Fast folding algorithm for detection of periodic pulse trains, Proceedings of The IEEE -PIEEE, 1969

Song Min Kim @MobiCom 2015#

Detection in practiceS-FreeBee (Fold by T) with Time syncA-FreeBee (Fold by 2T)Without Time Sync

Distance=symbolOffset=symbolReference PositionA-FreeBee is more practical,(time sync not required)but is slower than S-FreeBee Song Min Kim @MobiCom 2015#Analytics on symbol error rateFactors affecting Symbol Error Rate (SER)

: The number of beacons captured in RSS samplesT: beacon interval Sampling duration: time to obtain one symbol (=T)B: Channel busy ratio (=ratio of 1s in RSS samples)22100011001101100011001101Beacons with interval of 4Non-periodic data packets (noise)1101 =3 =4Fold sum: 2 3 0 1Fold sum: 2 4 1 1B =9/16T =4Sampling duration= T=16

SER derivation in paperControls tradeoff: bit rate Vs. reliability Song Min Kim @MobiCom 2015#22FreeBee architecture: MACFreeBee Multiple AccessFreeBee ModulatorIEEE Standard MAC/PHYFreeBee Multiple AccessIEEE Standard RSS SamplerTxRx23FreeBee Demodulator

Song Min Kim @MobiCom 2015#23FreeBee MAC: interval multiplexingWe term this new scheme as interval multiplexingAs it is achieved by selecting appropriate beacon intervals (T) to ensure orthogonal channels

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Many to many

Many to one Song Min Kim @MobiCom 2015#Interval multiplexing: example100100100

001000010

TX1TX2

101100110+RXMerged signal1011001101011001101Fold by 3Fold by 5Detected!T1=3T2=525RSS noise from APs of non-interest are evenly distributed throughout the columns, which prevent RSS noise from forming a high fold sum.Holds for arbitrary number of signals when they are pairwise co-primes(Details in paper) Song Min Kim @MobiCom 2015#

FreeBee ensures communication when frequency overlaps

Cross-technology broadcast

Cross-tech/channel broadcast26Cross-channel broadcast

Ch. 14Ch. 15

Song Min Kim @MobiCom 2015#26OutlineBackground and Motivation

FreeBee Design

System Implementation & Evaluation

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Song Min Kim @MobiCom 2015#FreeBee prototype implementations28

MICAz

USB dongle (IOGEAR)WARP v3Laptop (ASUS K200MA)

Song Min Kim @MobiCom 2015#28Symbol error ratePerforms better outside due to less noiseReaches below 1% error at 360 ms under both scenariosOr equivalently, when = 4

Song Min Kim @MobiCom 2015#Interval multiplexing

30F1 ONF1-F2 ONF1-F3 ONF1-F4 ONF1-F5 ON Aggregated F1

Legacy APLegacy APLegacy APLegacy APLegacy AP

F1F2F3F4F5FreeBee ONFreeBee ONFreeBee ONFreeBee ONFreeBee ONNegligible noise between FreeBee signalsTo test noise between FreeBees Five APs, turn on FreeBee 1 by 1 every 10 minutes Effect of interval multiplexing Song Min Kim @MobiCom 2015#30Max. aggregated throughput31

S-FreeBeeA-FreeBeeEsense (MobiCom `09)S-FreeBee folds with TA-FreeBee folds with 2T

4.3 x> 4 x< 1/4 xThroughput difference due to:Sampling freq., unit shift duration (), and so on(Please refer to paper for details) Song Min Kim @MobiCom 2015#31Mobile & duty-cyclingIn a residential areaSpeeds: Walk (4.3 mph), Run(6.8), Bicycle(10.8), Car(30)Tested on three A-FreeBee sendersRepeated 30 times for each speed

32 Song Min Kim @MobiCom 2015#

Mobile & duty-cyclingWalkReliable at: 1.5%

Run3%

Car10%

Bicycle4.5%33 Song Min Kim @MobiCom 2015#SummaryWireless coexistence brings challenges (e.g., interference) as well as opportunities (e.g., information sharing)

FreeBee enables coordination and sharing without the need for gateways

Free-side channel design in FreeBee does not impact legacy network traffic, while offering free-benefits.

34 Song Min Kim @MobiCom 2015#Thank you!!Questions?35 Song Min Kim @MobiCom 2015#