On Improving Data Rates of Users in LTE HetNets

The proliferation of smartphones and tablets has led to huge demand for data services over cellular networks. Cisco VNI mobile forecast (2014-2019) tells that although only 3.9% of mobile connections were Long Term Evolution (LTE) based they accounted for 40% of the mobile traffic and this will rise to 51% by 2019, by which the mobile data usage will grow 11 fold to over 15 Exabytes per month. Reports by Cisco and Huawei tell that 70% of the traffic is generated in indoor environments such as homes, enterprise buildings and hotspots. Hence, it is very important for mobile operators to improve coverage and capacity of indoor environments. Indoor data demand is partly met by intensifying the deployment of Macro Base Stations (MBSs/eNodeBs) in LTE cellular networks. Owing to many obstacles in the communication path between MBS and users inside the building, radio signals attenuate at a faster rate as the distance increases. Thus, Indoor User Equipments (IUEs) receive still low signal strength ( i.e., Signal-to-Noise Ratio, SNR) compared to Outdoor User Equipments (OUEs). To address this problem, one can deploy a large number of Low Power Nodes (LPNs) a.k.a. small cells (e.g., Picos and Femtos) under an umbrella MBS coverage and thereby form an LTE Heterogeneous Network (HetNet). Small cells are mainly being deployed in homes, enterprise buildings and hotspots like shopping malls and airports to improve indoor coverage and data rates. This is a win-win situation as telecom operators also benefit by reduction in their CAPEX and OPEX. Though the deployment of Femtocells improves indoor data rates, the resulting LTE HetNet may face a host of problems like co-tier and cross-tier interference (due to frequency reuse one in LTE) and frequent handovers (due to short coverage areas of Femtocells). Deployment of Femtos inside a building can lead to signal leakage at the edges/corners of the buildings. This causes cross-tier interference and degrades the performance of OUEs in High Interference Zone (HIZone) around the building area, which are connected to one of the MBSs in the LTE HetNet. Arbitrary placement of Femtos can lead to high co-channel cross-tier interference among Femtos and Macro BSs and coverage holes inside buildings. If Femtos are placed without power control, this leads to high power consumption and high inter-cell interference in large scale deployments. Our goal is to address these problems by developing efficient architecture, Femto placement and power control schemes in LTE HetNets. Random or unplanned placement of the Femtos leads to poor SNR and hence affects achievable data rates of IUEs. Hence, placement of Femtos is important for the cellular operators to perform planned deployment of minimum number of Femtos with no coverage holes and guarantee a good signal quality with no co-tier interference. Once the placement of Femtos is done optimally in enterprise environments, operators need to ensure that traffic load is evenly distributed among neighboring Femtos for improving Quality of Service (QoS) of IUEs by efficiently utilizing the network resources. In traditional cellular networks, the uplink access and downlink access of UEs are coupled to the same (Femto) cell. Suppose a Femto is fully loaded when compared to its neighboring Femtos, the traditional offloading or load balancing algorithms will try offloading some of the UEs for both their uplink and downlink access from the loaded cell to one of less loaded neighboring cells (i.e., target cell) provided that these UEs could get connected to the chosen target cell. This type of offloading is a forced handover to reduce traffic imbalance and trigger for handover is not based on better signal strength from the target cell. But, the offloaded UEs are connected for both their uplink and downlink access to the same target cell. Since UEs are most likely separated by walls and floors from their connected cells in enterprise environments, these offloaded UEs now have to transmit with higher transmit power in the uplink and thereby affects their battery lives. In order to reduce the battery drain for the offloaded UEs while maintaining their QoS, we employ the Decoupled Uplink and Downlink (DUD) access method in such a way that, the uplink of UE is connected to the closest Femto while the downlink is connected to a less loaded neighboring Femto. To maximize the utilization of the limited operating spectrum and provide higher data rate for IUEs, operators can configure Femtos in open access mode with frequency reuse one (i.e., all Femtos and MBSs operates on a same frequency) in LTE HetNets. However, this leads to high co-tier interference and cross-tier interference. Another problem in enterprise buildings having Femtos is frequent handovers, that happens when IUEs move from one room/floor to another room/floor inside the building. This leads to degradation of network performance in terms of increased signaling overhead and low throughputs. In order to reduce this kind of unnecessary handovers in enterprise buildings, Femtos should be placed optimally with handover constraints. Hence, we obtain the optimal coordinates from the OptHO model by adding handover constraints to the Minimize Number of Femtos (MinNF) model which guarantees threshold Signal-to-Interference plus Noise Ratio (SINR) of -2 dB for all IUEs inside the building. Such optimized deployment of Femtos reduces the number of handovers while guaranteeing good SINR to all IUEs. In LTE HetNets, even though planned deployment of Femtos in open access mode boosts the IUEs performance, the power leakage from indoor Femtos create interferix ence to the OUEs in the HIZone in the buildings surrounding areas. We propose an efficient placement and power control SON (Self organizing Network) algorithm which optimally places Femtos and dynamically adjusts the transmit power of Femtos based on the occupancy of Macro connected OUEs in the HIZone. To do this, we use the same MinNF model to place the Femtos optimally and solve Optimal Femto Power (OptFP) allocation problem (Mixed Integer Linear Programming (MILP)) which guarantees threshold SINR of -4 dB for IUEs with the Macro users SINR degradation as lesser than 2 dB. In the OptFP model, Femto’s transmit power is tuned dynamically according to the occupancy of OUEs in the HIZone. But the presence of even a single OUE in the HIZone decreases SINR of numerous IUEs, which is not fair to IUEs. In order to address this issue, we propose two solutions a) On improving SINR in LTE HetNets with D2D relays and b) A novel resource allocation and power control mechanism for Hybrid Access Femtos in LTE HetNets, which we describe in the following two paragraphs. To guarantee certain minimum SINR and fairness to both IUEs and OUEs in HIZone, we consider a system model by applying the concept of Device-to-Device (D2D) communication wherein free/idle IUEs connected to Femto act like UE-relays (i.e., UE-like BS, forwarding downlink data plane traffic for some of the HIZone users connected to MBS). We formulate a Mixed-Integer Linear Programming (MILP) optimization model which efficiently establishes D2D pairs between free/idle celledge IUEs and HIZone users by guaranteeing certain SINRT h for both IUEs and HIZone users. As D2D MILP model takes more computation time, it is not usable in real-world scenarios for establishing D2D pairs on the fly. Hence, we propose a two-step D2D heuristic algorithm for establishing D2D pairs. In above works, we assume that Femtos are configured in open access mode. But Hybrid Access Femtocells (HAFs) are favored by the operators because they ensure the paid Subscribed Group (SG) users certain QoS and then try to maximize the system capacity by serving near-by Non Subscribed Group (NSG) users in a best-effort manner. To reap in the benefits of HAFs, the operators need to employ effective resource sharing and scheduling mechanisms to contain co-tier and cross-tier interference arising out of reuse one in the HetNet system. Towards this, we address various challenges in terms of deployment and operation of HAFs in indoor environments. We propose an Optimal Placement of hybrid access Femtos (OPF) model which ensures a certain SINRT h inside the building and a certain SINRT h in the HIZone of the building. Unlike in previous optimization models, in this model, users in HIZone are connected to HAF s deployed inside the building. Also we propose a decentralized Dynamic Bandwidth Allocation (BWA) mechanism which divides the available HAF bandwidth between the two sets of user groups: SG and NSG. In order to mitigate co-tier and cross-tier interference, we then propose a dynamic Optimal Power Control (OPC) mechanism which adjusts the transmit powers of HAFs whenever the users in the HIZone cannot be served by the HAFs. In such a case, HIZone users connect to an MBS instead. Since the OPC problem is hard to solve in polynomial time, we also present a Sub-Optimal Power Control (SOPC) mechanism. To maintain fair resource allocation between SG and NSG users, we propose an Enhanced Priority (EP) scheduling mechanism which employs two schedulers which are based on the Proportional Fair (PF) and the Priority Set (PS) scheduling mechanisms. In above works, placement of Femtos is optimized to reduce co-channel co-tier interference among neighboring Femtos and transmit power of Femtos is optimized to reduce cross-tier interference between MBSs and Femtos. But, for arbitrary deployed Femtos, Inter Cell Interference Coordination (ICIC) techniques could be employed to address co-tier interference problem among Femtos which are connected with each other over X2 interface. Hence, in this work, we propose an ICIC technique, Variable Radius (VR) algorithm which dynamically increases or decreases the cell edge/non-cell edge regions of Femtos and efficiently allocates radio resources among cell edge/non-cell edge regions of Femtos so that the interference between neighboring Femtos can be avoided. We implement the proposed VR algorithm on top of PF scheduler in NS-3 simulator and find that it significantly improves average network throughput when compared to existing techniques in the literature

Measurement-based coverage function for green femtocell networks

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Efficient resource allocation algorithm for dense femtocell networks

La couverture d'intérieur pauvre et la basse capacité d'utilisateur représentent deux défis importants pour les opérateurs cellulaires. Plusieurs solutions (telles que les antennes distribuées) ont été proposées pour résoudre ces problèmes. Cependant, aucune de ces solutions ne fournit le niveau désiré de l'évolutivité et elles manquent l'aspect pratique. Pour ces raisons, une solution attrayante caractérisée par sa faible puissance et son prix faible connue sous le nom de femto-cellule a été introduite pour offrir une meilleure capacité et couverture d'utilisateur. Malgré tous les avantages provoqués par l'intégration de cette nouvelle technologie femto-cellule, plusieurs nouveaux défis ont émergé. Ces défis sont principalement présentés dans deux genres d'interférences ; connu comme interférence cross-tier et interférence co-tier. Tandis que l'impact d'interférence cross-tier (provoqué en partageant le spectre de fréquence) peut être réduit en mettant en application des algorithmes efficaces de réutilisation de fréquence, l'interférence co-tier continue à présenter un défi difficile pour les opérateurs et les chercheurs dans le domaine de réseaux cellulaires. Le déploiement non planifié et mal organisé des stations de base femto-cellule a comme conséquence une réduction radicale de la capacité d'utilisateur qui peut mener à une déconnexion des utilisateurs. L'impact de l'interférence co-tier devient plus provocant dans un déploiement dense des femto-cellule où les utilisateurs demandent des services en temps réel (par exemple, taux de données constant). Afin de réduire l'interférence co-tier, plusieurs solutions ont été proposées dans la littérature comprenant des algorithmes de contrôle de puissance, des techniques de détection avancées et des schémas d'allocation de ressources intelligentes. Dans ce projet, nous proposons une stratégie intelligente d'attribution des fréquences avec une stratégie avancée d'association de station de base femto-cellule pour les réseaux femto-cellule basés sur LTE. L'objectif des deux stratégies proposées est d'atténuer l'interférence co-tier et de réduire la probabilité de panne des utilisateurs en augmentant le nombre d'utilisateurs actifs par station de base femto-cellule. Nous montrons par simulations l'efficacité de notre solution proposée.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : femtocell base station, interference management, resource block assignment, base station assignment, outage probability

Project Final Report – FREEDOM ICT-248891

This document is the final publishable summary report of the objective and work carried out within the European Project FREEDOM, ICT-248891.This document is the final publishable summary report of the objective and work carried out within the European Project FREEDOM, ICT-248891.Preprin

Mobile Edge Cloud: Intelligent deployment and services for 5G Indoor Network

This thesis was submitted for the award of doctor of Philosophy and was awarded by Brunel University LondonFifth-Generation (5G) mobile networks are expected to perform according to the stringent performance targets assigned by standardization committees. Therefore, significant changes are proposed to the network infrastructure to achieve the expected performance levels. Network Function Virtualization, cloud computing and Software Defined Networks are some of the main technologies being utilised to ensure flexible network design, with optimum performance and efficient resource utilization. The aforementioned technologies are shifting the network architecture into service-based rather device-based architecture. In this regard, this thesis provides experimental investigation, design, implementation and evaluation of various multimedia services along with integration design and caching solution for 5G indoor network. The multimedia services are targeting the enhancement of UEs’ Quality of Experience, by exploiting the intelligence offered by the synergy between SDN and NFV technologies, to design and develop new multimedia solutions with improved QoE. The caching solution is designed to achieve a good trade-off between latency reduction and resource utilization that satisfies efficient network performance and resource utilization. The proposed network integration design targets deploying IoRL gNB with its innovative intelligent services. It have successfully achieved lower overhead signalling compared to the traditional network architectures. Whilst all of the proposed solutions have proven to provide enhancement to the system performance, the testing results for the multimedia services showed high QoS performance parameters in the form of zero packet loss due to route switching, very high throughput and 0.03 ms jitter. The caching solution test results provided up to 300% server utilization improvement (based on the deployed scenario) with negligible extra delay cost (0.5ms). As for the proposed integration design, the quantification of the performance enhancement is represented by the amount of the reduced overhead signalling. In the case of Intra-secondary gNB handover within the same Main eNB, the back-haul signalling for the AMF was reduced 100% while the overall overhead signalling is reduced by 50% compared to traditional deployment architecture.European Union’s Horizon 2020 research progra

Hybrid Access Control Mechanism in Two-Tier Femtocell Networks

The cellular industry is undergoing a major paradigm shift from voice-centric, structured homogeneous networks to a more data-driven, distributed and heterogeneous architecture. One of the more promising trends emerging from this cellular revolution is femtocells. Femtocells are primarily viewed as a cost-effective way to improve both capacity and indoor coverage, and they enable offloading data-traffic from macrocell network. However, efficient interference management in co-channel deployment of femtocells remains a challenge. Decentralized strategies such as femtocell access control have been identified as an effective means to mitigate cross-tier interference in two-tier networks. Femtocells can be configured to be either open access or closed access. Prior work on access control schemes show that, in the absence of any coordination between the two tiers in terms of power control and user scheduling, closed access is the preferred approach at high user densities. Present methods suggest that in the case of orthogonal multiple access schemes like TDMA/OFDMA, femtocell access control should be adaptive according to the estimated cellular user density. The approach we follow, in this work, is to adopt an open access policy at the femtocell access points with a cap on the maximum number of users allowed on a femtocell. This ensures the femto owner retains a significant portion of the femtocell resources. We design an iterative algorithm for hybrid access control for femtocells that integrates the problems of uplink power control and base station assignment. This algorithm implicitly adapts the femtocell access method to the current user density. The distributed power control algorithm, which is based on Yates' work on standard interference functions, enables users to overcome the interference in the system and satisfy their minimum QoS requirements. The optimal allocation of femtocell resources is incorporated into the access control algorithm through a constrained sum-rate maximization to protect the femto owner from starvation at high user densities. The performance of a two-tier OFDMA femtocell network is then evaluated under the proposed access scheme from a home owner viewpoint, and network operator perspective. System-level simulations show that the proposed access control method can provide a rate gain of nearly 52% for cellular users, compared to closed access, at high user densities and under moderate-to-dense deployment of femtocells. At the same time, the femto owner is prevented from going into outage and only experiences a negligible rate loss. The results obtained establish the quantitative performance advantage of using hybrid access at femtocells with power control at high user densities. The convergence properties of the proposed iterative hybrid access control algorithm are also investigated by varying the user density and the mean number of femto access points in the network. It is shown that for a given system model, the algorithm converges quickly within thirty iterations, provided a feasible solution exists

Self-Organizing Radio Resource Management and Backhaul Dimensioning for Cellular Networks

The huge appetite for mobile broadband has resulted to continuous and complementary improvement in both radio access technology and mobile backhaul of cellular networks, along with network densification. Femtocells are foreseen to complement traditional macro base stations (BSs) in Long Term Evolution (LTE) and future cellular networks.  Deployment of femtocells, introduce new requirements for distributing phase synchronization and interference management in heterogeneous network. Achieving phase synchronization for indoor femtocells will be beneficial for time division duplexing (TDD) operation and inter-cell interference cancellation and management techniques, but challenging to achieve as global positioning system does not work indoors. In this thesis, we propose coordinated transmission and reception algorithms to reduce interference across BSs, and thereby achieve better network-wide phase synchronization over the air. We also cover the problem of selecting component carriers for dense small cell network, by improving the throughput of cell-edge user equipment's (UEs). We propose three strategies: Selfish, Altruistic and Symmetric for primary carrier selection and remove the outage of the macro UEs near the closed subscriber group (CSG) femtocells. Further, we propose dynamic frequency selection algorithm for component carrier selection, where decisions to select or drop a carrier are based on gain/loss predictions made from UE handover measurements. Thereby, we maximize the sum utility of the dense femtocell network, which includes mean-rate, weighted fair-rate, proportional fair-rate and max-min utility.  Mobile backhaul dimensioning is studied to improve the handover and provide the cost-effective backhaul opportunity for femtocells deployed in emerging markets. In a packet-switched wireless system e.g. LTE, data packets are needed to be efficiently forwarded between BSs during handover over the backhaul. We improve the packet forwarding handover mechanism by reducing the amount of forwarded data between BSs. Another challenge lies in equipping the femtocells with backhaul, where copper cable, optical fiber or microwave radio links are expensive options for unplanned emerging market case. We consider leveraging macro LTE networks to backhaul High Speed Packet Access femtocells, thereby highlight the possibilities for cost-effective capacity upgrades of dense settlements

Context-based Resource Management and Slicing for SDN-enabled 5G Smart, Connected Environments

Τα συστήματα κινητής επικοινωνίας πέμπτης γενιάς (5G) τα οποία αναμένονται τα αμέσως επόμενα χρόνια, θα αντιμετωπίσουν πρωτοφανείς απαιτήσεις όσον αφορά τον όγκο και το ρυθμό μεταδόσης δεδομένων, τις καθυστερήσεις του δικτύου, καθώς και τον αριθμό των συνδεδεμένων συσκευών. Τα μελλοντικά δικτυακά οικοσυστήματα θα περιλαμβάνουν μια πληθώρα τεχνολογιών ασύρματης επικοινωνίας (είτε τεχνολογιών 3GPP, είτε μη-3GPP) όπως το Wi-Fi, το 3G, το 4G ή LTE, το Bluetooth, κτλ. Τα σενάρια ανάπτυξης του 5G προβλέπουν έναν πολυεπίπεδο συνδυασμό μακρο- και μικρο-κυψελών, όπου πολυλειτουργικές συσκευές –οι οποίες μπορούν να υποστηρίξουν ποικιλία διαφορετικών εφαρμογών και υπηρεσιών- εξυπηρετούνται από διαφορετικές τεχνολογίες. Οι περιορισμοί που υπήρξαν στα παλιότερα συστήματα κινητών επικοινωνιών πρέπει να εξαλειφθούν, ανοίγοντας το δρόμο για ένα νέο κύμα υπηρεσιών και συνολική εμπειρία χρήστη. Ως εκ τούτου, η διαχείριση των ασύρματων πόρων μέσω της χαρτογράφησης και διανομής τους στις κινητές συσκευές, μέσω της πλέον κατάλληλης τεχνολογίας πρόσβασης, η οποία εξυπηρετεί τις ανάγκες των συγκεκριμένων υπηρεσιών/εφαρμογών αποκτά πρωταρχική σημασία. Οι κύριοι μηχανισμοί διαχείρισης πόρων δικτύου πρόσβασης δηλαδή η επιλογή κυψέλης (cell selection/reselection), η παράδοση υπηρεσίας από τη μία κυψέλη στην άλλη (handover), καθώς και ο έλεγχος εισαγωγής κλήσεων/υπηρεσιών (call/service admission control), είναι αυτοί που τελικώς θα μπορέσουν να προσφέρουν στους χρήστες εξαιρετικά υψηλή ποιότητα υπηρεσιών (Quality of Service - QoS) και εμπειρίας (Quality of Experience - QoE) προς τις πολύ απαιτητικές περιπτώσεις χρήσης του 5G. Αυτό θα γίνει εφικτό μέσω της βελτιστοποίησης του συσχετισμού-χαρτογράφησης μεταξύ των διαφορετικών (τελικών) κινητών συσκευών και των συνυπαρχόντων ασύρματων δικτύων πρόσβασης. Επιπλέον της οπτικής του χρήστη, οι Πάροχοι Δικτύων Κινητής θα είναι σε θέση να εκμεταλλευτούν τη μέγιστη αποδοτικότητα και χρήση των –ήδη δυσεύρετων- ασύρματων πόρων. Ευφυείς βελτιστοποιήσεις και αποδοτικές λύσεις όσον αφορά το κόστος και την κατανάλωση ενέργειας πρέπει επίσης να εισαχθούν στα δίκτυα 5ης γενιάς με σκοπό να προάγουν ένα συνεκτικό, στοχευμένο στο χρήστη και πολυδιάστατο οικοσύστημα πληροφοριών. Η παρούσα διατριβή αυτή εστιάζει στη Διαχείριση Ασύρματων Δικτυακών Πόρων (ΔΑΔΠ - RRM) από την οπτική των κύριων διαδικασιών που σχετίζονται με την επιλογή ασύρματης τεχνολογίας πρόσβασης και στρώματος κυψέλης (μικρο-, μάκρο κυψέλη, κτλ.), δηλαδή η επιλογή κυψέλης, η παράδοση υπηρεσίας και ο έλεγχος εισαγωγής κλήσεων/υπηρεσιών. Έπειτα, η διατριβή προχωρά ένα βήμα παραπέρα, με σκοπό να συνδέσει τη ΔΑΔΠ με μία από τις πιο πρόσφατες προσεγγίσεις διαχείρισης δικτυακών πόρων, δηλαδή τον «τεμαχισμό δικτύου» (network slicing), όπως αυτή εισάγεται σε περιβάλλοντα που χρησιμοποιούν τη μέθοδος της Δικτύωσης Βασισμένης στο Λογισμικό (Software Defined Networking), η οποία δημιουργεί μικρότερα, εικονικά τμήματα του δικτύου, προσαρμοσμένα και βελτιστοποιημένα για συκεκριμένες υπηρεσίες και αντίστοιχες απαιτήσεις. Σαν πρώτο βήμα, πραγματοποιήθηκε μια ολοκληρωμένη ανάλυση για τις υπάρχουσες λύσεις – όπως αυτές προδιαγράφονται στα πρότυπα της 3GPP, στη βιβλιογραφία, καθώς και τις σχετικές πατέντες-. Η διατριβή αυτή αρχικά εντοπίζει τους δεσμούς μεταξύ των προσπαθειών της ερευνητικής κοινότητας, των υλοποιήσεων της βιομηχανίας, καθώς και των δράσεων προτυποποίησης, σε μια προσπάθεια να επισημανθούν ρεαλιστικές λύσεις εφαρμογής, να προσδιοριστούν οι κύριοι στόχοι, τα πλεονεκτήματα, αλλά και οι ελλείψεις αυτών των προσπαθειών. Όπως θα δειχθεί, οι υπάρχουσες λύσεις προσπαθούν να εξισορροπήσουν σε ένα σημείο μεταξύ της βέλτιστης λύσης και μιας απλής υλοποίησης. Έτσι, οι λύσεις που έχουν προταθεί είτε είναι απλοποιημένες σε τέτοιο βαθμό που απομακρύνονται από μια ρεαλιστική πρόταση, και επιτυγχάνουν υπο-βέλτιστες λύσεις ή από την άλλη παρέχουν πολύ σημαντικές βελτιώσεις, αλλά η πολυπλοκότητά τους και η επιβάρυνση που επιβάλλουν στο δίκτυο (όσον αφορά για παράδειγμα κόστος σηματοδοσίας, ή επεξεργαστικής ισχύος) τις καθιστούν ελκυστικές για μια πραγματική ανάπτυξη. Προς αυτή την κατεύθυνση, η παρούσα διατριβή εισαγωγή ένα σύνολο μηχανισμών επίγνωσης πλαισίου για τη διαχείριση δικτυακών πόρων, που αποτελείται από τρεις επιμέρους μηχανισμούς με διακριτό ρόλο: Δύο από τους μηχανισμούς χρησιμοποιούν πληροφορία πλαισίου με σκοπό τη βελτίωση τη διαχείριση πόρων και και τη χαρτογράφηση μεταξύ ροών δεδομένων κινητών συσκευών και κυψέλης/τεχνολογίας δικτύου. Ο τρίτος μηχανισμός δρα με έναν ενισχυτικό ρόλο στους δύο προηγούμενους, μέσω μιας προ-επεξεργασίας που πραγματοποιεί πάνω σε πληροφορία πλαισίου, με σκοπό τον περιορισμό του κόστους της επιπλέον σηματοδοσίας που απαιτείται για την μεταφορά της πληροφορίας πλαισίου μεταξύ των διαφόρων ενδιαφερόμενων δικτυακών οντοτήτων. Εκτός από τους τρεις μηχανισμούς αυτούς, πραγματοποιήθηκαν εκτενείς μελέτες σε σχέση με αρχιτεκτονικά ζητήματα και πτυχές, στο πλαίσιο της επικείμενης αρχιτεκτονικής δικτύου 5G και χαρτογράφηση των προτεινόμενων μηχανισμών στα συστατικά στοιχεία του δικτύου 5G -όπως αυτά εισήχθησαν στα τελευταίο κείμενα προτυποποίησης της 3GPP-. Η πρώτη κύρια συμβολή της παρούσας διατριβής είναι το COmpAsS, ένας μηχανισμός επιλογής Τεχνολογίας Ασύρματης Πρόσβασης πολλαπλών κριτηρίων, με γνώμονα το περιβάλλον, το κύριο μέρος του οποίου λειτουργεί στην πλευρά του Εξοπλισμού Χρήστη (UE), ελαχιστοποιώντας με αυτό τον τρόπο τις επιβαρύνσεις σηματοδότησης στη διεπαφή αέρα και το φορτίο υπολογισμού στους σταθμούς βάσης. Ο μηχανισμός COmpAsS εκτελεί παρακολούθηση σε πραγματικό χρόνο, υιοθετώντας την Ασαφή Λογική (Fuzzy Logic -FL) ως μία από τις βασικές προσεγγίσεις αντίληψης και ανάλυσης της κατάστασης του δικτύου. Σε συνδυασμό με ένα σύνολο προκαθορισμένων κανόνων, υπολογίζει μια λίστα με τις καταλληλότερες διαθέσιμες επιλογές πρόσβασης δικτύου, για κάθε μία από τις ροές δεδομένων/υπηρεσίας που είναι ενεργές εκείνη τη στιγμή. Τα πλεονεκτήματα του COmpAsS παρουσιάζονται μέσω μιας εκτεταμένης σειράς σεναρίων προσομοίωσης, ως μέρος των περιπτώσεων χρήσης εξαιρετικά πυκνών δικτύων (UDN) 5G. Τα αποτελέσματα αποδεικνύουν τον τρόπο με τον οποίο ο προτεινόμενος μηχανισμός βελτιστοποιεί τους βασικούς δείκτες επιδόσεων (Key Performance Indicators - KPIs), όταν αντιπαρατίθεται σε έναν από τους καθιερωμένους LTE αλγορίθμους. Η δεύτερη σημαντική συμβολή της παρούσας διατριβής είναι η Μηχανή Εξόρυξης Πλαισίου και Δημιουργίας Προφίλ (Context Extraction and Profiling Engine – CEPE), ένας μηχανισμός διαχείρισης πόρων, ο οποίος αναλύει συμπεριφορικά πρότυπα των χρηστών/κινητών συσκευών, εξάγει ουσιώδη γνώση και δημιουργεί αντίστοιχα προφίλ/πρότυπα συμπεριφοράς, με σκοπό να τα χρησιμοποιήσει για βέλτιστο προγραμματισμό πόρων, καθώς επίσης και για την μελλοντική πρόβλεψη απαιτήσεων πόρων. Το CEPE συλλέγει πληροφορίες σχετικά με τους χρήστες, τις υπηρεσίες, τις κινητές συσκευές, καθώς και τις συνθήκες δικτύου, και μέσω επεξεργασίας -χωρίς σύνδεση, ετεροχρονισμένα- αποκτά ένα μοντέλο γνώσης, το οποίο στη συνέχεια χρησιμοποιείται για τη βελτιστοποίηση των κύριων μηχανισμών ΔΑΔΠ (RRM). Το προαναφερθέν μοντέλο γνώσης μεταφράζεται έπειτα σε προφίλ χρηστών/κινητών συσκευών, τα οποία εφαρμόζονται ως είσοδος κατά τις διαδικασίες ΔΑΔΠ. Η βιωσιμότητα και η εγκυρότητα του CEPE επιδεικνύεται μέσω εκτεταμένων σεναρίων προσομοίωσης. Η τρίτη σημαντική συμβολή είναι το CIP (Context Information Preprocessor), ένας μηχανισμός προεπεξεργασίας πληροφοριών πλαισίου, με στόχο τον εντοπισμό και την απόρριψη περιττών δεδομένων κατά τη σηματοδοσία πριν από την εξαγωγή της γνώσης. Το CIP θα μπορούσε να θεωρηθεί ως αναπόσπαστο μέρος των προαναφερθέντων σχημάτων σχεδίασης, δηλαδή των COmpAsS και CEPE. Ο προτεινόμενος μηχανισμός περιλαμβάνει τη συγκέντρωση και συμπίεση πληροφοριών πλαισίου σχετικά με το δίκτυο ανά μοναδικό αναγνωριστικό κινητής συσκευής/χρήστη, -όπως η διεθνής ταυτότητα συνδρομητή κινητού (IMSI)-, καθώς και τεχνικές που σχετίζονται με την αναγνώριση και την απόρριψη δεδομένων πλαισίου που δε συμβάλλουν στην βελτίωση ή διόρθωση του πρόφιλ χρήστη, πριν από οποιαδήποτε μετάδοση προς το CEPE (ή άλλο μηχανισμό ΔΑΔΠ). Οι βελτιώσεις και τα κέρδη του CIP στη διαδικασία της σηματοδοσίας απεικονίζονται μέσω λεπτομερούς αναλυτικής προσέγγισης, η οποία καθορίζεται από τις καθιερωμένες απαιτήσεις περί χρήσης 5G. Ως τελική σημαντική συμβολή αυτής της διατριβής, διεξάγεται μια εκτεταμένη ανάλυση όσον αφορά τη διασύνδεση των CEPE-COmpAsS, στο πλαίσιο της επικείμενης αρχιτεκτονικής δικτύου 5G και της χαρτογράφησης αυτών με τα τελευταία συστατικά στοιχεία του δικτύου 5G –όπως αυτά παρουσιάστηκαν στις τελευταίες δημοσιεύσεις προτυποποίησης της 3GPP -. Το έργο σε αυτή την ενότητα δείχνει πώς μπορεί να παρουσιαστεί το προτεινόμενο πλαίσιο ως μέρος των συνιστωσών του δικτύου 5G και των λειτουργιών που εισάγονται σε περιβάλλοντα με δυνατότητα SDN, όπως η προσέγγιση του «Τεμαχισμού Δικτύου», ο Μηχανισμός Ανάλυσης Δικτυακών Δεδομένων (Network Data Analytics Function – NWDAF), η λειτουργία επιλογής βέλτιστου τεμαχίου δικτύου (Network Slice Selection Function) - προς περαιτέρω βελτιστοποίηση της διανομής και της διαχείρισης των διαθέσιμων πόρων δικτύου μεταξύ των συσκευών-, καθώς και το ATSSS – Access Traffic Steering, Switching and Splitting, μια οντότητα υπεύθυνη για τη διαχείριση των ροών δεδομένων των UE –με δυνατότητες επαναδρομολόγησης, διαχωρισμού και σύνδεσης της κάθε ροής με την αντίστοιχη βέλτιστη, διαθέσιμη τεχνολογία πρόσβασης. Δύο συμπληρωματικές μελέτες περιλαμβάνονται –τέλος- σε αυτή τη διατριβή: μια αρχική ανάλυση των πολιτικών μηχανικής κυκλοφορίας (Traffic Engineering) που βασίζονται σε προφίλ χρηστών που προκύπτουν από το CEPE, καθώς και μία περίπτωση χρήσης 5G που σχετίζεται με τον τομέα του Διαδικτύου των Πραγμάτων - και πιο συγκεκριμένα την «Καλλιέργεια Ακριβείας» (Precision Farming), με σκοπό να δοθεί έμφαση σε ρητές απαιτήσεις των περιπτώσεων χρήσης 5G, όπως η επικοινωνία τύπου μηχανής κρίσιμης σημασίας (Mission-Critical Machine Type Communication).The fifth-generation (5G) mobile communication systems, which are expected to emerge in the forthcoming years, will address unprecedented demands in terms of system capacity, service latency and number of connected devices. Future 5G network ecosystems will comprise a plethora of 3GPP and non-3GGP Radio Access Technologies (RATs), such as Wi-Fi, 3G, 4G or LTE, Bluetooth, etc. Deployment scenarios envision a multi-layer combination of macro, micro and femto cells where multi-mode end devices, supporting diverse applications, are served by different technologies. Limitations previously posed by legacy generation systems need to be eliminated, paving the way to a new wave of services and overall experience for the user. As a result, the management of radio resources via mapping the end devices to the most appropriate access network becomes of paramount importance; the primary Radio Resource Management (RRM) mechanisms, i.e. cell selection/reselection, handover and call admission control will be able to offer extremely high Quality of Service (QoS) and Experience (QoE) to the users, towards the very demanding 5G use case requirements; this will be realised via an optimal association between the diverse end devices and the coexisting available access networks. Besides the user’s perspective, the Mobile Network Operators (MNOs) will be able to take advantage of the maximum efficiency and utilization over the –already scarce- wireless resources. Intelligent optimizations, as well as cost and energy efficient solutions need to be introduced in 5G networks in order to promote a consistent, user-centred and all-dimensional information ecosystem. This thesis focuses on the radio resource management (RRM) from the perspective of the primary RAT and cell layer selection processes (i.e., cell (re)selection, handover, admission control); afterwards, it goes one step beyond, in order to link the RRM with one of the latest RRM optimization approaches, i.e. the Network Slicing, as introduced in Software Defined Networking (SDN)-enabled environments, which creates smaller, virtual “portions” of the network, adapted and optimized for specific services/requirements. As a first step, a comprehensive analysis for the existing solutions -as these are specified in 3GPP standards, research papers, and patents has taken place. This thesis initially identifies the links between the research community efforts, the industry implementations, as well as the standardization efforts, in an attempt to highlight realistic solution implementations, identify the main goals, advantages and shortcomings of these efforts. As will be shown, existing solutions attempt to balance between implementation simplicity and solution optimality. Thus, solutions are either simple to implement but achieve sub-optimal solutions or provide significant improvements but their complexity and the burden placed on the network components renders them unattractive for a real-life deployment. Towards this end, this thesis introduces a context-based radio resource management (RRM) framework, comprised of three distinct mechanisms: Two out of the three mechanisms exploit contextual information with the aim of optimising the resource management and UE-RAT mapping, while the third mechanism acts with an augmenting role to the former two, by pre-processing the contextual information required by such, context-based mechanisms and –thus- by limiting the signalling cost required for communicating this contextual information among network entities. In addition to the three mechanisms, comprehensive analysis has taken place in relation to architectural aspects, in the context of the forthcoming 5G network architecture and by mapping them with the latest 5G network components –as these were introduced in the latest 3GPP work-. The first major contribution of this thesis is COmpAsS, a context-aware, multi-criteria RAT selection mechanism, the main part of which operates on the User Equipment (UE) side, minimizing signalling overhead over the air interface and computation load on the base stations. COmpAsS mechanism performs real-time monitoring and adopts Fuzzy Logic (FL) as one the core logic modules, responsible for the perception of the network situation and, in combination with a set of pre-defined rules, calculates a list of the most suitable available access network options. The merits of COmpAsS are showcased via an extensive series of simulation scenarios, as part of 5G ultra dense networks (UDN) use cases. The results prove how the proposed mechanism optimises Key Performance Indicators (KPIs), when juxtaposed to a well-established LTE handover algorithm. The second major contribution of the current thesis the Context Extraction and Profiling Engine (CEPE), a resource management framework, which analyzes user behavioral patterns, extracts meaningful knowledge and performs user profiling in order to apply it for optimal resource planning, as well as prediction of resource requirements. CEPE collects information about users, services, terminals and network conditions and –based on offline processing– derives a knowledge model, which is subsequently used for the optimization of the primary RRM mechanisms. Then, the extracted context information is translated into user profiles and is finally applied as input for enhanced cell (re)selection, handover or admission control. The viability and validity of CEPE is demonstrated via an extensive set of simulation scenarios. The third major contribution is CIP, a Context Information Pre-processing scheme, aiming to identify and discard redundant or unnecessary data during network signalling and before knowledge extraction. CIP could be considered as an integral part of the afore described profiling schemes, i.e. COmpAsS and CEPE. The module comprises aggregating and compressing mobile network-related context information per unique identifier, such as the end device’s International Mobile Subscriber Identity (IMSI), as well as techniques related to identifying and discarding user profile-redundant or unnecessary context data, before any transmission to CEPE. CIP gains are illustrated via a detailed analytical approach, guided by well-established 5G use case requirements. As a final major contribution of this thesis, a comprehensive analysis takes place with regard to the CEPE-COmpAsS interworking, in the context of the forthcoming 5G network architecture and by mapping them with the latest 5G network components –as these were introduced in the latest 3GPP work-. The work in this section shows how the proposed framework can be instantiated as part of the 5G network components and functions introduced in SDN-enabled environments, such as the Network Slicing approach, the Network Data Analytics and the Network Slice Selection Functions, towards further optimising the distribution and management of the available infrastructure and network resources among the UEs, as well as the Access Traffic Steering, Switching and Splitting (ATSSS), responsible for managing the UE data flows and mapping each single UE flow with the optimal available access technology.. Two supplementary studies are finally included in this dissertation: a preliminary analysis on traffic engineering policies based on user profiling realised by CEPE, as well as a 5G use case related to the Internet of Things domain -and more specifically, Precision Farming-, aiming to highlight explicit requirements such as mission-critical machine type communication

A Planning and Optimization Framework for Hybrid Ultra-Dense Network Topologies

The deployment of small cells has been a critical upgrade in Fourth Generation (4G) mobile networks as they provide macrocell traffic offloading gains, improved spectrum reuse and reduce coverage holes. The need for small cells will be even more critical in Fifth Generation (5G) networks due to the introduction of higher spectrum bands, which necessitate denser network deployments to support larger traffic volumes per unit area. A network densification scenario envisioned for evolved fourth and fifth generation networks is the deployment of Ultra-Dense Networks (UDNs) with small cell site densities exceeding 90 sites/km2 (or inter-site distances of less than 112 m). The careful planning and optimization of ultra-dense networks topologies have been known to significantly improve the achievable performance compared to completely random (unplanned) ultra-dense network deployments by various third-part stakeholders (e.g. home owners). However, these well-planned and optimized ultra-dense network deployments are difficult to realize in practice due to various constraints, such as limited or no access to preferred optimum small cell site locations in a given service area. The hybrid ultra-dense network topologies provide an interesting trade-off, whereby, an ultra-dense network may constitute a combination of operator optimized small cell deployments that are complemented by random small cell deployments by third-parties. In this study, an ultra-dense network multiobjective optimization framework and post-deployment power optimization approach are developed for realization and performance comparison of random, optimized and hybrid ultra-dense network topologies in a realistic urban case study area. The results of the case study demonstrate how simple transmit power optimization enable hybrid ultra-dense network topologies to achieve performance almost comparable to optimized topologies whilst also providing the convenience benefits of random small cell deployments

Application of fractional frequency reuse technique for cancellation of interference in heterogeneous cellular network

The continuously growing number of mobile devices in terms of hardware and applications augments the necessity for higher data rates and a larger capacity in wireless communication networks. The Long Term Evolution (LTE) standard was designed to provide these mobile users with a better throughput, coverage and a lower latency. This thesis studies a specific area in Heterogeneous Networks; the subject of femtocells. The aim of femtocells is to provide better indoor coverage so as to allow users to benefit from higher data rates while reducing the load on the macro cell. Femtocells were proposed for Long Term Evolution (LTE) for indoor coverage. It is achieved using access points by home users. However, co-channel interference is a serious issue with femtocells that may dramatically reduce the performance of femto and macrocells. The system capacity and throughput decreases. As femtocells use the same spectrum as the macrocells, and the femtocells are deployed without proper planning, interference from femtocells to macrocells becomes a major issue. In this thesis, the interference from femtocells to macrocells is studied and a solution for the mitigation of this kind of interference is suggested using FFR mechanism. In our proposed scheme for interference avoidance, femtocells use those frequency sub bands which are currently not being used within the macrocell, the process of assigning the frequency bands is based on FFR. The simulation results suggest that the suggested technique enhances total/edge throughputs, and optimizes the SINR and CDF of femtocells users (FUEs) and reduces the outage probability of the network