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Precise synchronisation of transmitters and receivers is particularly challenging in diffusive molecular communication environments. To this end, a point-to-point molecular communication system is examined wherein the design of the transceiver offers resilience to synchronisation errors. In particular, the development of a sequential probability ratio test-based detector, which allows for additional observations in the presence of uncertainty due to mis-synchronisation at the receiver, and a modulation design which is optimised for this receiver strategy, is considered. The structure of the probability of molecules hitting a receiver within a particular time slot is exploited. An approximate maximum log-likelihood estimator for the synchronisation error is derived and the Cramér-Rao bound (CRB) computed, to show that the performance of the proposed estimator is close to the CRB at low transmission rates. The proposed receiver and modulation designs achieve strongly improved asynchronous detection performance for the same data rate as a decision feedback based receiver by a factor of 3 to 5 on average.
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Emergence of the London Millennium Bridge instability without synchronisation
Abstract The pedestrian-induced instability of the London Millennium Bridge is a widely used example of Kuramoto synchronisation. Yet, reviewing observational, experimental, and modelling evidence, we argue that increased coherence of pedestrians’ foot placement is a consequence of, not a cause of the instability. Instead, uncorrelated pedestrians produce positive feedback, through negative damping on average, that can initiate significant lateral bridge vibration over a wide range of natural frequencies. We present a simple general formula that quantifies this effect, and illustrate it through simulation of three mathematical models, including one with strong propensity for synchronisation. Despite subtle effects of gait strategies in determining precise instability thresholds, our results show that average negative damping is always the trigger. More broadly, we describe an alternative to Kuramoto theory for emergence of coherent oscillations in nature; collective contributions from incoherent agents need not cancel, but can provide positive feedback on average, leading to global limit-cycle motion.
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- Award ID(s):
- 1909924
- PAR ID:
- 10360911
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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