Optimisation des réseaux cellulaires pour les communications professionnelles critiques

Abstract : Business- and mission-critical communications are communications between professional users either from the public safety sector or operating critical infrastructures. Owing to special coverage, priority access, reliability and resilience requirements, as well as additional services for professional users, these communications are conveyed by Professional Mobile Radio (PMR) networks. Driven by the demand growth, significant changes are taking place in the PMR industry. The existing PMR technologies are indeed not well suited to provide high data rates mobile services like video and photo transfers; hence, the adoption of commercial technologies for mission-critical communications is gaining strong momentum. On the other hand, the next generation cellular networks are envisioned to support a large variety of applications and services with heterogeneous performance requirements, i.e., enhanced Mobile BroadBand (eMBB), massive Machine-Type Communications (mMTC) and Ultra-Reliable Low Latency Communications (URLLC). Recently, mission-critical communications have been classified in a URLLC use case family, characterized by the need to a higher priority over other communications in the networks.In this context, we focus on enhancing the coverage of wireless networks providing group communications, the main service allowed by PMR networks, taking advantage of the current technologies (e.g. Multimedia Broadcast/Multicast Service), to meet the mission-critical communications needs. First, we evaluate the performance of unicast and multicast transmission techniques, i.e., the Multicast/Broadcast Single Frequency Network (MBSFN) and Single-Cell Point-To-Multipoint (SC-PTM), in terms of radio quality, system spectral efficiency and cell coverage, assuming static MBSFN configurations. Then, we introduce an analytical model to derive an approximate closed-form formula of the Signal to Interference plus Noise Ratio (SINR) in a MBSFN network.Furthermore, we propose a simple repetition scheme without request, as an alternative to Hybrid Automatic Repeat re-Quest (HARQ), in the aim of improving the network coverage in presence of group communications. By considering the wireless channel characteristics, as well as the service delay constraints, we show that our proposed scheme provides significant gains over traditional repetition schemes.Finally, we assess the trade-off in the cluster’s size of serving cells which arises between network coverage and capacity in multi-point transmissions. We formulate an optimization problem to maintain an acceptable system blocking probability, while maximizing the average SINR of the multicast group users. For group calls, a dynamic cluster of cells is selected based on the minimization of a submodular function that takes into account the traffic in every cell through some weights and the average SINR achieved by the group users. Traffic weights are then optimized using a Nelder-Mead simplex method with the objective of tracking a blocking probability threshold. Results show the importance of dynamic clustering in improving system capacity and coverage.
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Alaa Daher. Optimisation des réseaux cellulaires pour les communications professionnelles critiques. Réseaux et télécommunications [cs.NI]. Université Paris-Saclay, 2019. Français. ⟨NNT : 2019SACLT009⟩. ⟨tel-02196785⟩

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