mZig: Multi-Packet Reception in ZigBee
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What is mZig? mZig is a novel physical layer design that enables a receiver to simultaneously decode multiple packets from different transmitters in ZigBee. As a low-power and low-cost wireless protocol, the promising ZigBee has been widely used in sensor networks, cyber-physical systems, and smart buildings. Since ZigBee based networks usually adopt tree or cluster topology, the convergecast scenarios are common in which multiple transmitters need to send packets to one receiver. For example, in a smart home, all appliances report data to one control plane via ZigBee. However, concurrent transmissions lead to the severe collision problem. The conventional ZigBee avoids collisions using backoff time, which introduces additional time overhead. Advanced methods resolve collisions instead of avoidance, in which the state-of-the-art ZigZag resolves one m-packet collision requiring m retransmissions. mZig resolves one m-packet collision by this collision itself, so the theoretical throughput is improved m-fold. Leveraging the unique features in ZigBee's physical layer including its chip rate, half-sine pulse shaping and O-QPSK modulation, mZig subtly decomposes multiple packets from one collision in baseband signal processing. The practical factors of noise, multipath, and frequency offset are taken into account in mZig design. Experiment results demonstrate that mZig can receive up to four concurrent packets in our testbed. The throughput of mZig is 4.5x of the conventional ZigBee and 3.2x of ZigZag in the convergecast with four or more transmitters.
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People Postdoctoral: Linghe Kong Faculty: Xue Liu Contact: linghe.kong@mail.mcgill.ca |
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Publications mZig: Enabling Multi-Packet Reception in ZigBee [paper]
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Frequently Asked Questions
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Does mZig require any modification on ZigBee devices? mZig requires no change on the physical layer (PHY) of transmitters, but some lightweight changes on the PHY of receivers. |
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Why mZig can decode multi-packet collisions? mZig leverages the PHY features of ZigBee including oversampling, known shaping and uniform amplitude to decompose collision chip-by-chip. |
How many concurrent transmissions can be decomposed by mZig? It depends on the sampling rate and the SNR. Generally, higher sampling rate and lower noise result in more concurrent transmissions. |
Can we apply mZig in other wireless protocols for collision resolution? mZig can be applied in the wireless protocols, whose PHY features are close to ZigBee. Hence, mZig can be applied in Bluetooth but not in WiFi. |
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© CPS Lab, School of Computer Science, McGill University.