Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks

Soaring capacity and coverage demands dictate that future cellular networks need to soon migrate towards ultra-dense networks. However, network densification comes with a host of challenges that include compromised energy efficiency, complex interference management, cumbersome mobility management, burdensome signaling overheads and higher backhaul costs. Interestingly, most of the problems, that beleaguer network densification, stem from legacy networks' one common feature i.e., tight coupling between the control and data planes regardless of their degree of heterogeneity and cell density. Consequently, in wake of 5G, control and data planes separation architecture (SARC) has recently been conceived as a promising paradigm that has potential to address most of aforementioned challenges. In this article, we review various proposals that have been presented in literature so far to enable SARC. More specifically, we analyze how and to what degree various SARC proposals address the four main challenges in network densification namely: energy efficiency, system level capacity maximization, interference management and mobility management. We then focus on two salient features of future cellular networks that have not yet been adapted in legacy networks at wide scale and thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and device-to-device (D2D) communications. After providing necessary background on CoMP and D2D, we analyze how SARC can particularly act as a major enabler for CoMP and D2D in context of 5G. This article thus serves as both a tutorial as well as an up to date survey on SARC, CoMP and D2D. Most importantly, the article provides an extensive outlook of challenges and opportunities that lie at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201

An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks

With the expected introduction of fully autonomous vehicles, the long-term evolution (LTE)-based vehicle-to-everything (V2X) networking approach is gaining a lot of industry attention, to develop new strategies to enhance safety and telematics features. The vehicular and wireless industries are currently considering the development of an LTE-based system, which may co-exist, with the IEEE 802.11p-based systems for some time. In light of the above fact, our objective is to investigate the development of LTE Proximity Service (ProSe)-based V2X architecture for time-critical vehicular safety applications in an efficient and cost-effective manner. In this chapter, we present a new cluster-based LTE sidelink-based vehicle-to-vehicle (V2V) multicast/broadcast architecture to satisfy the latency and reliability requirements of V2V safety applications. Our proposed architecture combines a new ProSe discovery mechanism for sidelink peer discovery and a cluster-based round-robin scheduling technique to distribute the sidelink radio resources among the cluster members. Utilizing an OMNET++ based simulation model, the performance of the proposed network architecture is examined. Results of the simulation show that the proposed algorithms diminish the end-to-end delay and overhead signaling as well as improve the data packet delivery ratio (DPDR) compared with the existing 3GPP ProSe vehicle safety application technique

Spatial spectrum reuse in heterogeneous wireless networks: interference management and access control

Διαχρονικά, η κυρίαρχη σχεδιαστική επιλογή για την βελτίωση της φασματικής απόδοσης των ασύρματων δικτύων κινητών επικοινωνιών είναι η χωρική επαναχρησιμοποίηση φάσματος, η δυνατότητα δηλαδή να επαναχρησιμοποιείται το ίδιο κομμάτι φάσματος πολλές φορές στο χώρο με την προϋπόθεση ότι διατηρούνται χαμηλά τα επίπεδα των παρεμβολών. Στα σύγχρονα δίκτυα κινητών επικοινωνιών μελετώνται δύο νέοι τρόποι χωρικής επαναχρησιμοποίησης φάσματος: α) η ανάπτυξη φεμτοκυψελών (femtocells), η ανάπτυξη δηλαδή μικρών κυψελών για εξυπηρέτηση κυρίως εσωτερικών χώρων στην ευρύτερη περιοχή κάλυψης μία κύριας κυψέλης, και β) η ενεργοποίηση επικοινωνιών συσκευής-σε-συσκευή (Device-to-Device – D2D), απευθείας δηλαδή επικοινωνιών χωρίς την διαμεσολάβηση του σταθμού βάσης της κυψέλης. Σκοπός της παρούσας διατριβής είναι να μελετηθούν και να αντιμετωπιστούν οι προκλήσεις που προκύπτουν από την εισαγωγή φεμτοκυψελών και την υιοθέτηση επικοινωνιών συσκευής-σε-συσκευή σε κυψελωτά δίκτυα προτυποποιημένα από την 3GPP (3rd Generation Partnership Project). Πιο συγκεκριμένα, μελετώνται τα προβλήματα της διαχείρισης του φάσματος και των παρεμβολών, καθώς και θέματα πρόσβασης στο φάσμα για Long Term Evolution (LTE) και LTE-Advanced (LTE-A) δίκτυα με φεμτοκυψέλες και με επικοινωνίες συσκευής-σε- συσκευή. Για το σκοπό αυτό, αρχικά μελετήθηκαν τα LTE/LTE-A κυψελωτά δίκτυα ως προς το φυσικό επίπεδο, την αρχιτεκτονική και τις παρεμβολές, αποτυπώνοντας και την τρέχουσα κατάσταση στο τομέα της προτυποποίησης των φεμτοκυψελών και των επικοινωνιών συσκευής-σε-συσκευή. Ακολούθησε μια συγκριτική μελέτη μηχανισμών διαχείρισης παρεμβολών σε κανάλια ελέγχου ενός LTE/LTE-A δικτύου με φεμτοκυψέλες και ένας καινοτόμος μηχανισμός ελέγχου ισχύος για μεταδόσεις φεμτοκυψελών, βασισμένος στην ποιότητα εμπειρίας στο τελικό χρήστη. Η δουλειά αυτή άνοιξε νέους ερευνητικούς ορίζοντες, όπου το επίπεδο ικανοποίησης του τελικού χρήστη παίζει ενεργό ρόλο στη διαχείριση του δικτύου και την παροχή των υπηρεσιών. Παρόλα αυτά, η περεταίρω μελέτη προς την κατεύθυνση αυτή είναι εκτός του σκοπού της παρούσας διατριβής. Στην συνέχεια, το κύριο βάρος της μελέτης μεταφέρθηκε στο πρόβλημα της διαχείρισης του φάσματος και των παρεμβολών στο πολύ πιο δυναμικό περιβάλλον ενός κυψελωτού δικτύου όπου επιτρέπονται οι επικοινωνίες συσκευής-σε-συσκευή. Σε πρώτη φάση, θεωρήθηκε ένα σύνολο από ζεύγη συσκευών που επικοινωνούν μεταξύ τους με επικοινωνίες συσκευής-σε-συσκευή και προτάθηκε ένας μηχανισμός συλλογής πληροφορίας παρεμβολών και ένα σχήμα ανάθεσης πόρων βασισμένο στη θεωρία γράφων. Το κύριο αποτέλεσμα της μελέτης αυτής ήταν πως αν και υψηλά επίπεδα χωρικής επαναχρησιμοποίησης μπορούν να επιτευχθούν, η συλλογή και η επεξεργασία πληροφορίας παρεμβολών είναι ένα πολύπλοκο πρόβλημα το οποίο απαιτεί και επιπλέον πόρους σηματοδοσίας. Έτσι, προτάθηκε και αναλύθηκε μίας λύση βασισμένη στον ανταγωνισμό. Πρακτικά οι χρήστες των επικοινωνιών συσκευής-σε-συσκευή εφαρμόζουν ένα σχήμα ανταγωνισμού όμοιο με αυτό που χρησιμοποιείται στα δίκτυα WiFi (Wireless Fidelity), προσαρμοσμένο όμως στο φυσικό επίπεδο των LTE/LTE-A δικτύων. Μαθηματική ανάλυση του σχήματος έδειξε ισχυρή εξάρτηση των επιδόσεων από το πλήθος των χρηστών που ανταγωνίζονται για το φάσμα. Σε μια προσπάθεια περιορισμού του πλήθους των ανταγωνιζόμενων χρηστών μόνο σε αυτούς που βρίσκονται σε γειτνίαση, και άρα μονό σε αυτούς που η άμεση επικοινωνία τους είναι εφικτή, μελετήθηκε το πρόβλημα της ανίχνευσης γειτονικής συσκευής. Με βάση τις τρέχουσες προδιαγραφές της 3GPP, για την επίλυση του προβλήματος ανίχνευσης γειτονικής συσκευής, μία συσκευή είτε ανακοινώνει με μετάδοση περιοδικών μηνυμάτων την παρουσία της σε μια συγκεκριμένη περιοχή, είτε αιτείται από κάποια συγκεκριμένη συσκευή πληροφορία ανίχνευσης. Υιοθετώντας τη δεύτερη περίπτωση, προτάθηκαν βελτιώσεις στο LTE/LTE-A δίκτυο πρόσβασης ώστε να επιτρέπεται η ανάθεση φάσματος για μεταδόσεις ανίχνευσης γειτονικών συσκευών. Παράλληλα, δεδομένου ότι και για τις μεταδόσεις αυτές απαιτείται η κατανάλωση φάσματος, σχεδιάστηκε και αξιολογήθηκε μία λύση βασισμένη στη χωρική επαναχρησιμοποίηση φάσματος. Το βασικό συμπέρασμα ήταν ότι λόγω των χαμηλών απαιτήσεων ποιότητας των μηνυμάτων ανίχνευσης, κάτω από ορισμένες συνθήκες πυκνότητας του δικτύου, μπορεί να επιτραπεί η χωρική επαναχρησιμοποίηση του κυψελωτού φάσματος για μεταδόσεις ανίχνευσης συσκευής.Historically, the spatial spectrum reuse has been the most efficient approach for improving cellular system capacity. Based on this observation, the 3rd Generation Partnership Project (3GPP) has proposed new spatial spectrum reuse schemes, towards fulfilling the International Mobile Telecommunications-Advanced (IMT-Advanced) requirements for the 4G networks. In this direction, a major shift is realized from wide-range cells with high transmit power (macrocells) to low-power small-sized cells (femtocells), while a lot of effort is allocated to the spatial spectrum reuse by enabling Device-to-Device (D2D) communications, i.e., direct communications in a cellular network, without the intervention of the base station. The scope of this thesis is to deal with challenges arising from the introduction of femtocells and D2D communications in cellular networks standardized by 3GPP Release 8 and beyond, i.e., Long Term Evolution (LTE) and LTE-Advanced (LTE-A). More specifically, for the case of femtocells, the interference management problem is studied, while for the D2D communications the radio resource management and the spectrum access challenges are addressed. First, a comprehensive description of the physical layer and architecture of the LTE/LTE-A networks is provided, and the current standardization efforts for the introduction of femtocells and D2D communications are described. Subsequently, different control channel interference management schemes for femtocell-overlaid LTE/LTE-A networks are studied, while an innovative power control scheme for the femtocell downlink transmissions is proposed, utilizing the end user’s quality of experience. This work brings to the surface new research challenges, where the end user’s satisfaction level plays an active role in network management and service provisioning. However, the further investigation of these challenges is out of this thesis’ scope. Considering the much more dynamic environment defined by the D2D communications in a cellular network, the major research effort is then shifted to the resource and interference management problem for D2D communications. Assuming a predefined set of D2D pairs in a cellular network, an interference information collection mechanism and a D2D resource allocation scheme, based on the graph-coloring theory, are proposed. Evaluation results showed that even high spatial spectrum reuse levels can be achieved, the interference collection and processing problem is quite complex, while additional signaling is needed. Taking this into account, a contention-based approach is proposed. Under this approach, the D2D devices compete for accessing the spectrum following a procedure similar with that used in WiFi (Wireless Fidelity) networks. Performance analysis shows that the efficiency of the proposed scheme depends on the number of competing devices. Towards restricting the number of competing devices, only to those that are in proximity and, thus, in valid positions for D2D communication, the device discovery problem is studied. According to the 3GPP standardization efforts, the solution of the device discovery problem requires frequent transmission of discovery signals from each device, either announcing its presence in a specific area, or requesting discovery information from a target device. Adopting the second option, enhancements in the 3GPP standardized access network are proposed, enabling a resource request / allocation procedure for device discovery transmissions. In parallel, a spatial spectrum reuse scheme is designed and evaluated, as an effort to reduce the consumption of radio resources for discovery transmissions. Analytical and simulation results show that, under certain conditions for the network density, a number of discovery transmissions can be enabled in a multi-cellular network even if no interference information is available

Thirty Years of Machine Learning: The Road to Pareto-Optimal Wireless Networks

Future wireless networks have a substantial potential in terms of supporting a broad range of complex compelling applications both in military and civilian fields, where the users are able to enjoy high-rate, low-latency, low-cost and reliable information services. Achieving this ambitious goal requires new radio techniques for adaptive learning and intelligent decision making because of the complex heterogeneous nature of the network structures and wireless services. Machine learning (ML) algorithms have great success in supporting big data analytics, efficient parameter estimation and interactive decision making. Hence, in this article, we review the thirty-year history of ML by elaborating on supervised learning, unsupervised learning, reinforcement learning and deep learning. Furthermore, we investigate their employment in the compelling applications of wireless networks, including heterogeneous networks (HetNets), cognitive radios (CR), Internet of things (IoT), machine to machine networks (M2M), and so on. This article aims for assisting the readers in clarifying the motivation and methodology of the various ML algorithms, so as to invoke them for hitherto unexplored services as well as scenarios of future wireless networks.Comment: 46 pages, 22 fig

Enable Reliable and Secure Data Transmission in Resource-Constrained Emerging Networks

The increasing deployment of wireless devices has connected humans and objects all around the world, benefiting our daily life and the entire society in many aspects. Achieving those connectivity motivates the emergence of different types of paradigms, such as cellular networks, large-scale Internet of Things (IoT), cognitive networks, etc. Among these networks, enabling reliable and secure data transmission requires various resources including spectrum, energy, and computational capability. However, these resources are usually limited in many scenarios, especially when the number of devices is considerably large, bringing catastrophic consequences to data transmission. For example, given the fact that most of IoT devices have limited computational abilities and inadequate security protocols, data transmission is vulnerable to various attacks such as eavesdropping and replay attacks, for which traditional security approaches are unable to address. On the other hand, in the cellular network, the ever-increasing data traffic has exacerbated the depletion of spectrum along with the energy consumption. As a result, mobile users experience significant congestion and delays when they request data from the cellular service provider, especially in many crowded areas. In this dissertation, we target on reliable and secure data transmission in resource-constrained emerging networks. The first two works investigate new security challenges in the current heterogeneous IoT environment, and then provide certain countermeasures for reliable data communication. To be specific, we identify a new physical-layer attack, the signal emulation attack, in the heterogeneous environment, such as smart home IoT. To defend against the attack, we propose two defense strategies with the help of a commonly found wireless device. In addition, to enable secure data transmission in large-scale IoT network, e.g., the industrial IoT, we apply the amply-and-forward cooperative communication to increase the secrecy capacity by incentivizing relay IoT devices. Besides security concerns in IoT network, we seek data traffic alleviation approaches to achieve reliable and energy-efficient data transmission for a group of users in the cellular network. The concept of mobile participation is introduced to assist data offloading from the base station to users in the group by leveraging the mobility of users and the social features among a group of users. Following with that, we deploy device-to-device data offloading within the group to achieve the energy efficiency at the user side while adapting to their increasing traffic demands. In the end, we consider a perpendicular topic - dynamic spectrum access (DSA) - to alleviate the spectrum scarcity issue in cognitive radio network, where the spectrum resource is limited to users. Specifically, we focus on the security concerns and further propose two physical-layer schemes to prevent spectrum misuse in DSA in both additive white Gaussian noise and fading environments

Evolution Toward 5G Mobile Networks - A Survey on Enabling Technologies

In this paper, an extensive review has been carried out on the trends of existing as well as proposed potential enabling technologies that are expected to shape the fifth generation (5G) mobile wireless networks. Based on the classification of the trends, we develop a 5G network architectural evolution framework that comprises three evolutionary directions, namely, (1) radio access network node and performance enabler, (2) network control programming platform, and (3) backhaul network platform and synchronization. In (1), we discuss node classification including low power nodes in emerging machine-type communications, and network capacity enablers, e.g., millimeter wave communications and massive multiple-input multiple-output. In (2), both logically distributed cell/device-centric platforms, and logically centralized conventional/wireless software defined networking control programming approaches are discussed. In (3), backhaul networks and network synchronization are discussed. A comparative analysis for each direction as well as future evolutionary directions and challenges toward 5G networks are discussed. This survey will be helpful for further research exploitations and network operators for a smooth evolution of their existing networks toward 5G networks

Direct communication radio Iinterface for new radio multicasting and cooperative positioning

Cotutela: Universidad de defensa UNIVERSITA’ MEDITERRANEA DI REGGIO CALABRIARecently, the popularity of Millimeter Wave (mmWave) wireless networks has increased due to their capability to cope with the escalation of mobile data demands caused by the unprecedented proliferation of smart devices in the fifth-generation (5G). Extremely high frequency or mmWave band is a fundamental pillar in the provision of the expected gigabit data rates. Hence, according to both academic and industrial communities, mmWave technology, e.g., 5G New Radio (NR) and WiGig (60 GHz), is considered as one of the main components of 5G and beyond networks. Particularly, the 3rd Generation Partnership Project (3GPP) provides for the use of licensed mmWave sub-bands for the 5G mmWave cellular networks, whereas IEEE actively explores the unlicensed band at 60 GHz for the next-generation wireless local area networks. In this regard, mmWave has been envisaged as a new technology layout for real-time heavy-traffic and wearable applications. This very work is devoted to solving the problem of mmWave band communication system while enhancing its advantages through utilizing the direct communication radio interface for NR multicasting, cooperative positioning, and mission-critical applications. The main contributions presented in this work include: (i) a set of mathematical frameworks and simulation tools to characterize multicast traffic delivery in mmWave directional systems; (ii) sidelink relaying concept exploitation to deal with the channel condition deterioration of dynamic multicast systems and to ensure mission-critical and ultra-reliable low-latency communications; (iii) cooperative positioning techniques analysis for enhancing cellular positioning accuracy for 5G+ emerging applications that require not only improved communication characteristics but also precise localization. Our study indicates the need for additional mechanisms/research that can be utilized: (i) to further improve multicasting performance in 5G/6G systems; (ii) to investigate sideline aspects, including, but not limited to, standardization perspective and the next relay selection strategies; and (iii) to design cooperative positioning systems based on Device-to-Device (D2D) technology