Title: Accurate bus occupancy estimation for WLAN probing utilising probabilistic models

Authors: Lars Mikkelsen; Tatiana Madsen; Hans-Peter Schwefel

Addresses: Wireless Communication Networks, Aalborg University, Aalborg, 9220, Denmark ' Wireless Communication Networks, Aalborg University, Aalborg, 9220, Denmark ' Wireless Communication Networks, Aalborg University, Aalborg, 9220, Denmark

Abstract: This paper obtains an enhanced estimator of the number of people on buses using probabilistic models and wireless local area network (WLAN)-based device counts. The improved estimator exploits probabilistic models of false positives and false negatives of a previously presented baseline estimator. False positives of the baseline estimator result from devices on the roadside outside the bus that fail to be filtered out by the used threshold approaches. False negatives may be caused by low probe emission frequency, message losses due to collisions of the WLAN transmissions, medium access control (MAC) address randomisation, WLAN channel selection, and occur in particular when passengers stay on the bus only for short duration of time. The extensions of the baseline model by probabilistic models for false positives and false negatives enables to apply maximum likelihood estimation. Distribution parameters for false positives and false negatives are found from measurements. Field tests on buses in a Danish town are used to validate and quantify the gain of the enhanced estimator.

Keywords: WLAN probes; bus occupancy; device count; stochastic models; public transport; devices per person; MLE; maximum likelihood estimator; MAC randomisation; probe frequency; probe signal strength.

DOI: 10.1504/IJSNET.2019.101240

International Journal of Sensor Networks, 2019 Vol.30 No.4, pp.231 - 241

Received: 17 Jan 2018
Accepted: 14 Feb 2019
Published online: 29 Jul 2019 *

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