Mobile relays for urban rail transportation systems
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Mobile relays for urban rail transportation systems Mauricio Iturralde1
· Tanguy Kerdoncuff1 · Thomas Galezowski2 · Xavier Lagrange1
Accepted: 19 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Assuring an uninterrupted high Quality of Service (QoS) of railway communications between on-board terminals and base stations creates challenges for the provider. This is partly explained by the inherent mobility and the high penetration loss of carriages. Deploying mobile relays in public transportation is possible with a 100%-compatible LTE/EPC architecture. This effectively ensures that the electromagnetic insulation is kept to a minimum as QoS on board can be dramatically affected and worsened within the railway vehicles. Yet all users’ traffic congregates via the radio backhaul link and needs to take into consideration the extra packet-overhead and signaling messages that as a general rule get transmitted via the fixed links. The paper’s aim is to analyze the performance of mobile relays in loaded conditions comparing this to the standard direct mode. We propose an analytical model to compute the signaling rate. We parametrize it with experiments done on a testbed with real radio transmissions and show that signaling has no major impact on performance. We then evaluate the QoS experienced by passengers by means of simulations for two representative services: Web browsing and voice communications. The packet loss ratio for voice communications is reduced at the expense of a slight end-to-end latency increase thanks to mobile relays. During the high load conditions there is a significant reduction in the load time of a Web page and the throughput is increased. Keywords LTE · EPC · 4G · Mobile relay · QoS · Signaling · Handover · Mobility management · Performance analysis · Railways
1 Introduction The use of wireless broadband services has risen significantly with the deployment of Long Term Evolution (LTE) networks and the generalization of smart phones, tablet computers and other new mobile devices. People make intensive use of these devices when they are on public transport vehicles such as buses, trams, or trains. According to Ericsson’s mobility report [14], the number of mobile broadband subscriptions grew 10% year-on-year, increasing by 120 million in Q3 2019. The number of smartphone subscriptions is forecast to reach 7.4 billion in 2025, or 83% of all mobile subscriptions. The quality of service in public transportation remains far from adequate. Vehicles are usually well shielded with coated windows, which leads to a rather high electromagnetic penetration loss between outdoor and in-vehicle. Commonly
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Mauricio Iturralde [email protected]
1
IRISA, UMR CNRS 6074, IMT Atlantique, 35700 Rennes, France
2
Société du Grand Paris, Paris, France
encountered, the User Equipments (UEs) moving within public transport vehicles are connected to Evolved Node B (eNB) via wireless links, in which the penetration loss critically attenuates the signal qualit
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