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Authors
Advisor(s)
Abstract(s)
Cooperating mobile robots are real-time systems
that often require mutual synchronisation, either to carry out
cooperative sensing and actuation, or to improve the quality of
wireless communications. Concerning this last aspect, a common
technique to improve the communication channel is to eliminate
access collisions by allocating predefined disjoint time slots to
robots, in a circular list, which is known as Time Division
Multiple Access (TDMA). This technique typically requires a
global clock to identify each slot. However, this method is not
robust with respect to asynchronous transmissions generated by
external or joining nodes. Consequently, this work proposes a
global TDMA protocol that allows for real-time and guaranteed
delivery of messages within deadlines, given its predictable
schedule, and that: i) applies to dynamic mesh networks of
cooperating mobile robots; ii) synchronises slots in a relative
fashion using locally perceived delays of message exchanges that
are globalised throughout the network, thus not relying on a
global clock; and iii) tolerates external traffic and asynchronous
joining robots using underneath standard ad-hoc wireless RF
technologies that provide CSMA-type arbitration. We describe
our protocol and prove that under common operating conditions
all robots eventually reach synchronisation. We also propose a
heuristic for the few cases that were not covered by the previous
proof, which always led to consensus under extensive simulation
testing. To the best of our knowledge, this is the first guaranteed
clockless synchronisation approach for ad-hoc networks of mobile
robots that works over commodity wireless protocols.
Description
RTAS 2018 was held as part of the CPS Week 2018, 10-13 Abril, Porto, Portugal.
Keywords
Wireless Robotics TDMA Synchronisation Clockless
Citation
Publisher
Institute of Electrical and Electronics Engineers