MZig: Enabling Multi-Packet Reception in ZigBee Linghe Kong, Xue Liu McGill University 2015-09-08 MobiCom 2015

mZig: Enabling Multi-Packet Reception in ZigBee

Linghe Kong, Xue LiuMcGill University

2015-09-08

MobiCom 2015MobiCom 2015

MotivationMotivationMotivationMotivation11

PreliminaryPreliminaryPreliminaryPreliminary22

DesignDesignDesignDesign33

ImplementationImplementationImplementationImplementation44

Performance EvaluationPerformance EvaluationPerformance EvaluationPerformance Evaluation55

Table of ContentsTable of Contents

MotivationMotivation MotivationMotivation11

22

33

44

55


ZigBee CommunicationZigBee Communication

• Standard: IEEE 802.15.4• Applications: Sensor networks; Smart homes;

Internet of things; Industrial control; ......

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Convergcast in ZigBeeConvergcast in ZigBee

Tree topology Cluster topology

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Collision ProblemCollision Problem

Collision

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Related WorkRelated Work

Collision AvoidanceCollision Avoidance

CSMA/CA[JSAC'04,ToN'08] RTS-CTS[AHNet'03]

backoff, hidden terminal latency

Collision ResolutionCollision ResolutionAnalog NC[SigComm'07], XORs[SigComm'06], Full Duplex[MobiCom'11]

Constructive Interference [IPSN'11, NDS

I'13, TPDS'15]

ZigZag[SigComm'08]

partial known info same content retransmission required

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PreliminaryPreliminary PreliminaryPreliminary22

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ZigBee SpecificationZigBee Specification

FrequencyFrequency CoverageCoverage Data RateData Rate # of Chan# of Channelsnels

Rx SensitiRx Sensitibitybity ModulationModulation

2.4GHz World 250kbps 16 -85dBm O-QPSK

868MHz Europe 20kbps 1 -92dBm BPSK

915MHz USA 40kbps 10 -92dBm BPSK

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Baseband Signal in ZigBeeBaseband Signal in ZigBee

Half chip offset 0.5μs

Chip = 1Chip = 0

Duration of one chip 1μs

1 0 1 1

111

0 0

0 00

I Phase

Q Phase

Amplitude

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Features of ZigBee ChipsFeatures of ZigBee Chips• Oversampling: sampling rate of recent ADCs

(at RX side) is much higher than 2MHz.

• Known shaping: half-sine.

• Uniform amplitude: O-QPSK, no ASK or QAM.

How to leverage these features to design mZig?

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Chip = 1

Am

plit

ude

Time

0

Chip = 0

0 2μs1μs

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DesignDesign DesignDesign33

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A Novel Technique: mZigA Novel Technique: mZig

Alice

Bob

RX

1 chip

Sign

alSi

gnal

Time

Time

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• mZig leverages the physical layer features and decomposes a multi-packet collision directly.

• Example: a two-packet collision.

Two Categories of CollisionsTwo Categories of Collisions

• with chip-level time offset (w/ CTO)

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Chip-level time offset

Alice

Bob

Packet-level time offset Packet-level time offset

No chip-level time offset

1 chip

• without chip-level time offset (w/o CTO)

CrossICCrossIC

• Cross Interference Cancellation (CrossIC) for collision w/ CTO.

Packet from Bob

Chip-level time offset

Packet from Alice

RX

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CrossICCrossIC

Alice

Bob

RX


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CrossICCrossIC

RX


Alice

Bob

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Collision-free samples

Step I: Extract collision-free samples

CrossICCrossIC

RX


Alice

Bob

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Estimated samples

Step II: Estimate samples to form a whole chip

CrossICCrossIC

RX


Alice

Bob

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5New collision-free samples

Substract the estimated chip from the collision

CrossICCrossIC

RX


Alice

Bob

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Repeat the extraction and estimation steps

CrossICCrossIC

RX


Alice

Bob

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CrossICCrossIC

RX


Alice

Bob

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CrossICCrossIC

RX


Alice

Bob

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CrossICCrossIC

RX


Alice

Bob

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CrossICCrossIC

RX


Alice

Bob

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AmpCoDAmpCoD

• Amplitude Combination based Decomposition (AmpCoD) for collision w/o CTO.

Packet from Bob

No chip-level time offset

Packet from AliceAssume Assume α>βα>β

L1 α+β

L2 α-β

L3 -α+β

L4 -α-βLevel L1 L2 L3 L4AliceBob

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1 0 010 0

L400

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Core DesignCore Design

CrossICCrossIC AmpCoDAmpCoD

Design EnhancementDesign Enhancement

Time Offset DetectionTime Offset Detection Anti-NoiseAnti-Noise

Multipath FilterMultipath Filter Frequency Offset ComFrequency Offset Compensationpensation

ScopeScope

mm-Packet Collision-Packet Collision Bluetooth & WiFiBluetooth & WiFi

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ImplementationImplementation ImplementationImplementation44

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RX PHY: ZigBee v.s. mZigRX PHY: ZigBee v.s. mZig

Demodulation

Down-sampling

ADC

RX

Despread

Radio Front-endDmZig

………

M p

aral

lel l

ines

DemodulationDown-

sampling ADC

RX

DespreadRadio

Front-end

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DmZig ModuleDmZig ModuleStart

End

Collision?

CrossIC

CTO?

AmpCoD

Separated?

CrossIC

AmpCoD

Output: Collided original

sequence of samples

Output: Collision-free

original sequence of samples

Output: Collision-free m

sequences of samples

Yes

No

Yes

No

Yes

No

Hybrid

Input: Baseband samples

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TestbedTestbed

• RX: USRP X310 + PC

• TX: USRP B210*6 + Laptop*6 + iRobots*6

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Performance EvaluationPerformance Evaluation Performance EvaluationPerformance Evaluation55


Experiment SettingExperiment Setting

ConfigurationConfiguration

Sampling rate: 32Msps

TX power: 0dB (1mW)

Channel selection: 26

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FieldField

7.5m×6.8m office

MetricsMetrics

Bit Error Rate (BER)

Throughput

Compared withCompared with

ZigBee

ZigZag

BER: Different Sampling RatesBER: Different Sampling Rates 1

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Reference

BER: Different TechniquesBER: Different Techniques 1

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Reference

Throughput: Different TechniquesThroughput: Different Techniques 1

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Throughput: Different TechniquesThroughput: Different Techniques 1

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4.5X

1X

Throughput: Static v.s. MobileThroughput: Static v.s. Mobile 1

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ConclusionConclusion

• We design mZig, a novel RX design to enable multi-packet reception in ZigBee. Theoritcally, the maximal concurrent transmissions is m=S/2C.

• We implement mZig on USRPs. In our testbed, the throughput of mZig achieves 4.5x of ZigBee with four or more TXs.

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Q & [email protected]

Backup

PHY in ZigBee

bits

Modulation DAC

chips

1001Demodulation

Down-sampling ADC

TX

RX

chips

1001Spread

PulseShaping

bits

DespreadRadio

Front-end

Radio Front-end

Time Offset Detection

Anti-Noise Design

• For CrossIC

• For AmpCoD

Multipath Filter

• Channel estimation is required to estimate the impulse responses of multipath.

• Multipath effect is filtered chip-by-chip.

Impulse response of multipath

*=

Estimated chip

Frequency Offset Compensation

• Channel estimation is also required to estimate the frequency offset.

• Compensate the frequency offset chip-by-chip.

I

Q

I

Q

Alice Bob

Scope

mm-Packet Collision in Zi-Packet Collision in ZigBeegBee

BluetoothBluetooth

WiFiWiFi

MAC for mZig

• The conventional MAC for ZigBee cannot be applied directly:– CSMA/CA– ACK

RX m TXs

m concurrent packets

mACK

mZig start

CSMA disable

Simulation

Impact of CTO Impact of SNR

Simulation (cont)

Multipath Filter Freq. Compensation

Documents

MZig: Enabling Multi-Packet Reception in ZigBee Linghe Kong, Xue Liu McGill University 2015-09-08 MobiCom 2015