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

MotivationMotivation 1 PreliminaryPreliminary 2 DesignDesign 3 ImplementationImplementation 4 Performance Evaluation 5 Table of Contents

Motivation Motivation Table of Contents

ZigBee Communication Standard: IEEE Applications: Sensor networks; Smart homes; Internet of things; Industrial control;

Convergcast in ZigBee Tree topology Cluster topology

Collision Problem Collision

Related Work Collision Avoidance CSMA/CA [JSAC'04,ToN'08] RTS-CTS [AHNet'03] backoff, hidden terminallatency Collision Resolution Analog NC [SigComm'07], XORs [SigComm'06], Full Duplex [MobiCom'11] Constructive Interference [IPSN'11, NDSI'13, TPDS'15] ZigZag [SigComm'08] partial known infosame content retransmission required

1 Preliminary Preliminary Table of Contents

ZigBee Specification FrequencyCoverage Data Rate # of Channels Rx Sensitibity Modulation 2.4GHzWorld250kbps16-85dBmO-QPSK 868MHzEurope20kbps1-92dBmBPSK 915MHzUSA40kbps10-92dBmBPSK

Baseband Signal in ZigBee

Features 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?

1 2 Design Design Table of Contents

A Novel Technique: mZig mZig leverages the physical layer features and decomposes a multi-packet collision directly. Example: a two-packet collision.

Two Categories of Collisions with chip-level time offset (w/ CTO) without chip-level time offset (w/o CTO)

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

CrossIC

CrossIC Collision-free samples Step I: Extract collision-free samples

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO Estimated samples Step II: Estimate samples to form a whole chip

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO New collision-free samples Substract the estimated chip from the collision

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO Repeat the extraction and estimation steps

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO Repeat the extraction and estimation steps

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO Repeat the extraction and estimation steps

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO Repeat the extraction and estimation steps

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO Repeat the extraction and estimation steps

CrossIC Cross Interference Cancellation (CrossIC) for collision w/ CTO Repeat the extraction and estimation steps

AmpCoD Amplitude Combination based Decomposition (AmpCoD) for collision w/o CTO. Assume α>β L1L1 α+β L2L2 α-βα-β L3L3 -α+β L4L4 -α-β-α-β

Core Design CrossICAmpCoD Design Enhancement Time Offset Detection Anti-Noise Multipath Filter Frequency Offset Compensation Scope m-Packet Collision Bluetooth & WiFi

1 2 3 Implementation Implementation 4 5 Table of Contents

RX PHY: ZigBee v.s. mZig

DmZig Module

Testbed RX: USRP X310 + PC TX: USRP B210*6 + Laptop*6 + iRobots*

Performance Evaluation Performance Evaluation 5 Table of Contents

Experiment Setting Configuration Sampling rate: 32Msps TX power: 0dB (1mW) Channel selection: Field 7.5m×6.8m office Metrics Bit Error Rate (BER) Throughput Compared with ZigBee ZigZag

BER: Different Sampling Rates Reference

BER: Different Techniques Reference

Throughput: Different Techniques

X 1X

Throughput: Static v.s. Mobile

Conclusion 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

40 Q & A

Backup

PHY in ZigBee

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.

Frequency Offset Compensation Channel estimation is also required to estimate the frequency offset. Compensate the frequency offset chip-by-chip.

Scope m-Packet Collision in ZigBee Bluetooth WiFi

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

Simulation Impact of CTOImpact of SNR

Simulation (cont) Multipath FilterFreq. Compensation