Extensions to multi-antenna and multi-sector BTS

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Military and Naval uses cases

Military authorities are in charge of a very broad range of missions that require use of all possible communication media. Indeed, Military authorities rely on Command, Control, Communications, Computers, and Intelligence (C4I) to effectively address their missions. Communications for the military forces are very strategic for controlling and information sharing in real time among different forces to enable fast reaction to an event, as General Dempsey explains: “Information systems and networks provide the means to send, receive, share, and utilize information. The synthesis of advanced communications system capabilities and sound doctrine leads to information superiority, which is essential to success in all military operations” [1].
In most environments, deployed military forces have to rely heavily on wireless communications to answer their communication needs as there is either no fixed infrastructure available (i.e hostile territory) or their mobile behavior prevents them to use any. For instance, navies are operating at sea, from the sea side to high sea where there is no available infrastructure. Nevertheless, fleet marine forces have to communicate to several entities that can be close or very far away: civil surface ships; military surface ships and submarines; airplanes; UAVs and Unmanned Surface Vehicles (USVs); operational centers at land, etc. Figure 1 provides an overview of some communication needs of military and Naval Forces.

rat of autonomous network

Before designing a proper solution, we need to firstly select the underlying RATs to enable the solution. Baldiny et Al. survey from 2013 [9] compares the following communication systems for PS use: Analog Professional Mobile Radio (PMR); Digital Mobile Radio (DMR); P25; TETRA V.1; TETRA V.2; TETRAPOL; Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS)/ Universal Mobile Telecommunication System (UMTS) / 3G; LTE; Satellite Networks; WiFi /Worldwide Interoperability for Microwave Access (WiMAX); Ad-hoc Networks; Marine Communications; Avionics Communications. In their conclusion, the authors notice that « LTE has emerged as the technology of choice and future solution in PS ». Indeed, 4G LTE is designed with a number of interesting properties, namely high spectral efficiency, frequency flexibility, large coverage area through high power support and native support of variety of Internet Protocol (IP)-based services thanks to the flat IP architecture. Ferrus et Al. [21] come to the same conclusion, noting that LTE has reached the required maturity level and wide adoption to replace the previous PS communication systems. However, both articles observe that LTE faces several challenges to be adopted as the next PS wireless access technology as it is initially designed for commercial markets. However, some improvements have been achieved since 2013. 3GPP has started to address specific PS requirements from Release 11 due to growing demand for PS communications as we will show in the next subsection, and LTE has been officially selected as the next RAT for PS wireless access in the USA [22]. Moreover, LTE will serve as the technology basis for future 5G systems and should continue to evolve and to remain in use for commercial and private networks for a long period thanks to it wide deployment and co-existence features for use in unlicensed bands such as Licensed Assisted Access (LAA).

Backhaul link consideration

Several solutions can be envisioned for the wireless links that can realize the mesh to interconnect the mobile BTSs. Note that what we use the backhaul term hereinafter for the wireless links between the BTSs and not only to name the connection of a BTS to a CN. The most straightforward approach is to rely on a dedicated RATs for the inter-connection of the BTSs. In nominal cellular architecture with fixed deployments, wireless backhauling is often used relying on Point To Point (PTP) or Point To Multi-Point (PTMP) RAT using directional antennas. Taipale T. studies the feasibility of a wireless mesh for LTE small-cell backhauling [25] and details a new wireless mesh solution developed by Nokia Networks (NN) and VTT Technical Research Centre of Finland (VTT) as 802.11 (WiFi) and 802.16 (WiMAX) mesh features and other available mesh networks were found not to be suitable for this use case. However, the requirements of such a backhaul are quite different from the one of PS use cases where some communications can be handled locally, plus it relies on fixed BTS which is not adequate. The 911-NOW proposal from Bell Labs [26] details a PS architecture that relies on meshing of moving BTS and investigates several problems that arise independently of the meshing RAT. Thus, it does not really address the radio perspective and associated problems (limited frequency resources, scheduling, etc.). The Absolute FP7 project developed autonomous eNBs and new aerial LTE BTS and multi-mode UEs for emergency PS communications, supporting communications between eNBs through a satellite network or using dedicated WiFi links [27, 28]. While some of these solutions might cover the use cases we identified, none matches the external requirements we draw in section 3.1.
Indeed, using a dedicated RAT requires dedicated frequency bands and the associated hardware for the backhaul links while we target a solution that minimizes the hardware and frequency resource requirements and have already selected LTE as the access RAT. Even if some hardware resources can be shared (such as antennas), isolation between the access and backhaul bands at each BTS is required, which might not be possible due to regulatory constraints on getting frequency resources for each distinct band (PS use cases) or due to other systems (military use cases). For instance, dividing a 10MHz channel bandwidth into two 5MHz sub-bands to isolate access and backhaul will put high requirements on filters and amplifiers at each node to avoid self-interference or will require split in smaller subbands. Furthermore, the split of the bandwidth will not scale with the spatio-temporal traffic variability as access and backhaul resources are completely separated, which in turn may reduce the overall performance. Use of ISM bands to avoid regulatory constraints may limit the coverage due to the power limitations and interference, especially as the mobile behavior prevents the use of highly directional antennas. However, evolution of antenna tracking and beam forming techniques might solve this specific problem, at a higher cost due to more complex power and antenna systems.

Table of contents :

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Abstract
Résumé
Acknowledgments
Contents
List of Figures
List of Tables
1 introduction
1.1 Motivations
1.2 Contributions
2 state of the art and problem statement
2.1 Uses cases and current solutions
2.1.1 Military and Naval uses cases
2.1.2 Public Safety uses cases
2.2 Network topologies
2.2.1 Scenarios
2.2.2 Scenarios of reference
2.3 Problem Statement
2.3.1 High level requirements
3 design constraints and rat choice
3.1 External constraints
3.2 RAT of autonomous network
3.2.1 LTE state of the art
3.2.2 Backhaul link consideration
4 architecture of the autonomous bts
4.1 Challenges
4.1.1 Support of Legacy UEs
4.1.2 Autonomous operation
4.2 Architecture
4.3 e2NB states
4.4 e2NB network topologies
5 design elements and procedures of e2nb
5.1 Physical layer interfaces
5.1.1 Background LTE information
5.1.2 Uu interface
5.1.3 Un relay interface
5.2 Physical layer design issues
5.2.1 Synchronization
5.2.2 Range limitation
5.2.3 HARQ modifications for Un interface
5.3 e2NB procedures and parameters configuration
5.3.1 eNB parameters
5.3.2 vUE attach procedure
5.3.3 e2NB operation flow
5.4 Core Network logical connectivity
5.4.1 MME
5.4.2 HSS provisioning and cooperation
5.4.3 S/P-GW
5.4.4 Routing
5.4.5 Application and services
6 coe algorithms
6.1 Problem overview
6.2 COE role and proposed hierarchical approach
6.3 COE Controller Scheduling Algorithm
6.3.1 Superframe duration computation (LSuF )
6.3.2 SF allocation for inter-e2NB self-backhauling
6.3.3 Distributed link scheduling
6.4 Relaying direction selection
6.5 Extensions to TDD system
6.6 Extensions to multi-antenna and multi-sector BTS
6.6.1 Analysis of the approach complexity
6.7 Interference management
6.8 Discussion on security issues
7 experimentations
7.1 Physical channel performance evaluation
7.1.1 Computation time
7.1.2 Link-level performance
7.2 Evaluation of the proposed approach
7.2.1 Simulation environment
7.2.2 Considered Algorithms
7.2.3 Simulation Results
7.2.4 Summary
7.3 Performance comparison of in-band and out-band deployment
7.4 Summary
7.4.1 Limitations of the experiments
7.4.2 Potential improvements of the proposed approach
8 conclusion
8.1 Perspectives and future work
9 bibliography
Appendices
a additional figures
b résumé en français
b.1 Introduction
b.1.1 Motivation
b.1.2 Contributions
b.2 État de l’art et définition de la problématique
b.2.1 Cas d’utilisation militaires
b.2.2 Communications pour la sécurité publique
b.2.3 Topologies réseaux associées
b.2.4 Énoncé du problème
b.3 Contraintes de conception et choix de la technologie d’accès radio
b.3.1 Contraintes externes
b.3.2 Choix de la technologie d’accès radio
b.4 Architecture de station de base autonome
b.4.1 États de l’e2NB
b.4.2 Topologies réseaux possibles
b.5 Conception détaillée et procédures de l’e2NB
b.6 Algorithmes d’ordonnancement
b.6.1 Rôle du COE et approche hiérarchique proposée
b.7 Expérimentations
b.8 Conclusion
b.8.1 Perspectives et travaux futurs
c acronyms