Dynamic network slicing for multitenant heterogeneous cloud radio access networks

Multitenant cellular network slicing has been gaining huge interest recently. However, it is not well-explored under the heterogeneous cloud radio access network (H-CRAN) architecture. This paper proposes a dynamic network slicing scheme for multitenant H-CRANs, which takes into account tenants' priority, baseband resources, fronthaul and backhaul capacities, quality of service (QoS) and interference. The framework of the network slicing scheme consists of an upper-level, which manages admission control, user association and baseband resource allocation; and a lower-level, which performs radio resource allocation among users. Simulation results show that the proposed scheme can achieve a higher network throughput, fairness and QoS performance compared to several baseline schemes

Advanced Techniques for Future Multicarrier Systems

Future multicarrier systems face the tough challenge of supporting high data-rate and high-quality services. The main limitation is the frequency-selective nature of the propagation channel that affects the received signal, thus degrading the system performance. OFDM can be envisaged as one of the most promising modulation techniques for future communication systems. It exhibits robustness to ISI even in very dispersive environments and its main characteristic is to take advantage of channel diversity by performing dynamic resource allocation. In a multi-user OFDMA scenario, the challenge is to allocate, on the basis of the channel knowledge, different portions of the available frequency spectrum among the users in the systems. Literature on resource allocation for OFDMA systems mainly focused on single-cell systems, where the objective is to assign subcarriers, power and data-rate for each user according to a predetermined criterion. The problem can be formulated with the goal of either maximizing the system sum-rate subject to a constraint on transmitted power or minimizing the overall power consumption under some predetermined constraints on rate per user. Only recently, literature focuses on resource allocation in multi-cell networks, where the goal is not only to take advantage of frequency and multi-user diversity, but also to mitigate MAI, which represents one of the most limiting factor for such problems. We consider a multi-cell OFDMA system with frequency reuse distance equal to one. Allowing all cells to transmit on the whole bandwidth unveils large potential gains in terms of spectral efficiency in comparison with conventional cellular systems. Such a scenario, however, is often deemed unfeasible because of the strong MAI that negatively affects the system performance. In this dissertation we present a layered architecture that integrates a packet scheduler with an adaptive resource allocator, explicitly designed to take care of the multiple access interference. Each cell performs its resource management in a distributed way without any central controller. Iterative resource allocation assigns radio channels to the users so as to minimize the interference. Packet scheduling guarantees that all users get a fair share of resources regardless of their position in the cell. This scheduler-allocator architecture integrates both goals and is able to self adapt to any traffic and user configuration. An adaptive, distributed load control strategy can reduce the cell load so that the iterative procedure always converges to a stable allocation, regardless of the interference. Numerical results show that the proposed architecture guarantees both high spectral efficiency and throughput fairness among flows. In the second part of this dissertation we deal with FBMC communication systems. FBMC modulation is a valid alternative to conventional OFDM signaling as it presents a set of appealing characteristics, such as robustness to narrowband interferers, more flexibility to allocate groups of subchannels to different users/services, and frequency-domain equalization without any cyclic extension. However, like any other multicarrier modulations, FBMC is strongly affected by residual CFOs that have to be accurately estimated. Unlike previously proposed algorithms, whereby frequency is recovered either relying on known pilot symbols multiplexed with the data stream or exploiting specific properties of the multicarrier signal structure following a blind approach, we present and discuss an algorithm based on the ML principle, which takes advantage both of pilot symbols and also indirectly of data symbols through knowledge and exploitation of their specific modulation format. The algorithm requires the availability of the statistical properties of channel fading up to second-order moments. It is shown that the above approach allows to improve on both frequency acquisition range and estimation accuracy of previously published schemes

Admission control and resource allocation for LTE uplink systems

Long Term Evolution (LTE) radio technologies aim not only to increase the capacity of mobile telephone networks, but also to provide high throughput, low latency, an improved end-to-end Quality of Service (QoS) and a simple architecture. The Third Generation Partnership Project (3GPP) has defined Single Carrier FDMA (SC-FDMA) as the access technique for the uplink and Orthogonal Frequency Division Multiple Access (OFDMA) for the downlink. It is well known that scheduling and admission control play an important role for QoS provisioning, and that they are strongly related. Knowing that we can take full advantage of this property we can design an admission control mechanism that uses the design criterion of the scheduling scheme. In this thesis, we developed two new algorithms for handling single-class resource allocation and two algorithms for handling multi-class resource allocation, as well as a new admission control scheme for handling multi-class Grade of Service (GoS) and QoS in uplink LTE systems. We also present a combined solution that uses the resource allocation and the admission control properties to satisfy the GoS and QoS requirements. System performance is evaluated using simulations. Numerical results show that the proposed scheduling algorithms can handle multi-class QoS in LTE uplink systems with a little increase in complexity, and can be used in conjunction with admission control to meet the LTE requirements. In addition, the proposed admission control algorithm gain for the most sensitive traffic can be increased without sacrificing the overall system capacity. At the same time, guaranteeing GoS and maintaining the basic QoS requirements for all the admitted requests

Analytical characterization of inband and outband D2D Communications for network access

Mención Internacional en el título de doctorCooperative short-range communication schemes provide powerful tools to solve interference and resource shortage problems in wireless access networks. With such schemes, a mobile node with excellent cellular connectivity can momentarily accept to relay traffic for its neighbors experiencing poor radio conditions and use Device-to-Device (D2D) communications to accomplish the task. This thesis provides a novel and comprehensive analytical framework that allows evaluating the effects of D2D communications in access networks in terms of spectrum and energy efficiency. The analysis covers the cases in which D2D communications use the same bandwidth of legacy cellular users (in-band D2D) or a different one (out-band D2D) and leverages on the characterization of underlying queueing systems and protocols to capture the complex intertwining of short-range and legacy WiFi and cellular communications. The analysis also unveils how D2D affects the use and scope of other optimization techniques used for, e.g., interference coordination and fairness in resource distribution. Indeed, characterizing the performance of D2D-enabled wireless access networks plays an essential role in the optimization of system operation and, as a consequence, permits to assess the general applicability of D2D solutions. With such characterization, we were able to design several mechanisms that improve system capabilities. Specifically, we propose bandwidth resource management techniques for controlling interference when cellular users and D2D pairs share the same spectrum, we design advanced and energy-aware access selection mechanisms, we show how to adopt D2D communications in conjunction with interference coordination schemes to achieve high and fair throughputs, and we discuss on end-to-end fairness—beyond the use of access network resources—when D2D communications is adopted in C-RAN. The results reported in this thesis show that identifying performance bottlenecks is key to properly control network operation, and, interestingly, bottlenecks may not be represented just by wireless resources when end-to-end fairness is of concern.Programa Oficial de Doctorado en Ingeniería TelemáticaPresidente: Marco Ajmone Marsan.- Secretario: Miquel Payaró Llisterri.- Vocal: Omer Gurewit

A Scheduling and Resource Allocation Algorithm for LTE Networks Using Tree Structures

Το σύστημα LTE σχεδιάστηκε από τη 3GPP με στόχο την ικανοποίηση των ολοένααυξανόμενων αναγκών για ασύρματη ευρυζωνική πρόσβαση. Τεχνικές όπως το σχήμα πολλαπλής πρόσβασης OFDMA, το MIMOκαι η Προσαρμοστική Διαμόρφωση και Κωδικοποίηση υιοθετήθηκαν προκειμένου να αυξήσουν τους επιτεύξιμους ρυθμούςμετάδοσης και να βελτιώσουν τη φασματική απόδοση. Ωστόσο, απαιτείται η ανάπτυξη εξελιγμένων αλγορίθμωνχρονοπρογραμματισμού προκειμένου να αξιοποιηθεί η πλήρης δυναμική αυτών των τεχνικών. Παρά το γεγονός ότι η 3GPPέχειπροτυποποιήσει πλήρως τη σηματοδοσία ελέγχου που απαιτείται για την εκτέλεση του χρονοπρογραμματισμού, οι αλγόριθμοι πουχρειάζεται να εκτελεστούν προκειμένου να ληφθούν αποδοτικές αποφάσεις έχουν αφεθεί στους κατασκευαστές για υλοποίηση.Ωςεκ τούτου, σημαντική ερευνητική προσπάθεια έχει καταβληθεί προς αυτή την κατεύθυνση και έχουν προταθεί αρκετοίαλγόριθμοιχρονοπρογραμματισμού. Το κύριο συμπέρασμα που εξάγεται από τη μελέτη της βιβλιογραφίας είναι ότι οχρονοπρογραμματισμόςσε ένα σύστημα πολλών φερουσών με τους περιορισμούς του LTE αποτελεί ένα πολυδιάστατο πρόβλημα.Ανάμεσα στις πολλέςδιαστάσεις του, αυτές που κυρίως λαμβάνονται υπόψη στους προτεινόμενους αλγορίθμους είναι ηρυθμαπόδοση, η δικαιοσύνη και η εξασφάλιση εγγυημένης ποιότητας υπηρεσίας.Η κύρια συμβολή της παρούσας διατριβής είναι η πρόταση ενός νέου αλγόριθμου χρονοπρογραμματισμού και διαχείρισης πόρων ο οποίος αντιμετωπίζει τα περισσότερα από τα θέματα που καθορίζουν τησυνολική απόδοση μίας οντότητας χρονοπρογραμματισμού του LTE. Η πρόταση εστιάζει κυρίως στην πολυπλοκότητα πουεισάγεται κατά τη λήψη μίας απόφασης χρονοπρογραμματισμού. Επιχειρεί δε να επιλύσει αυτό το πρόβλημα με την εισαγωγή μίαςεξελιγμένης δενδρικής δομής η οποία επιτρέπει την αποδοτική αποθήκευση όλων των παραμέτρων που θεωρούνται ουσιώδεις στηδιαδικασία λήψης μίας απόφασης χρονοπρογραμματισμού. Με αυτό τον τρόπο η οντότητα χρονοπρογραμματισμού έχει άμεσηπρόσβαση σε αυτές τις πληροφορίες. Στην εργασία περιγράφεται ένας πλήρης αλγόριθμος προγραμματισμού στο πεδίο τουχρόνου που αξιοποιεί αυτή τη δενδρική δομή και επιπλέον προτείνονται δύο νέοι αλγόριθμοι κατανομής πόρων. Οι αλγόριθμοιαυτοί επίσης αξιοποιούν κάποιες επιπρόσθετες δενδρικές δομές οι οποίες παράγονται ύστερα από κατάλληλη προ-επεξεργασίαπου λαμβάνει χώρα πριν τη λήψη της απόφασης χρονοπρογραμματισμού. Ο πρώτος αλγόριθμος παρουσιάζει χαμηλήπολυπλοκότητα και ικανοποιητική απόδοση ενώ ο δεύτερος βελτιωμένη απόδοση με το κόστος κάποιας επιπρόσθετηςπολυπλοκότητας. Αποτελέσματα εκτεταμένων προσομοιώσεων επιβεβαιώνουν την ικανότητα του προτεινόμενου σχήματος στηνικανοποίηση των αυστηρών απαιτήσεων του LTE σε ότι αφορά την ποιότητα υπηρεσίας, ενώ ταυτόχρονα η απόδοση τωνπροτεινόμενων αλγορίθμων συγκρίνεται με γνωστές τεχνικές χρονοπρογραμματισμού. Οι προτεινόμενες λύσεις είναι εφαρμόσιμες μόνο στην περίπτωση της κατωφερούς ζεύξης, ωστόσο η ίδια ιδέα μπορεί να προσαρμοστεί κατάλληλα για να παρέχει μία αποδοτική λύση και στην περίπτωση της ανωφερούς ζεύξηςLong Term Evolution (LTE) has been designed by 3GPP with the target to meet the ever increasing demands in broadband wireless access. Techniques such as OFDMA multiple access scheme, MIMO and Adaptive Modulation and Coding (AMC) have been adopted in order to boost the achieved data rates and improve spectral efficiency. However, the development of sophisticated scheduling algorithms is required so that the full potential of those techniques is exploited. Even though 3GPP has fully standardized the control signaling required to perform scheduling, the algorithms that need to be executed to make efficient decisions are left to vendor implementation. Therefore significant research effort has been dedicated to this direction and several scheduling algorithms have been proposed. The main conclusion drawn from the study of the literature is that scheduling in a multicarrier system with the restrictions of LTE constitutes a multidimensional problem. Among the multiple dimensions, those that are mostly considered in the proposed algorithms are throughput, fairness and QoS guarantee. The main contribution of this thesis is to propose a new scheduling algorithm that addresses most of the issues that define the overall performance of an LTE scheduler. The proposal focuses mainly on the complexity involved in making a scheduling decision. It attempts to resolve this issue by the introduction of a sophisticated tree structure that enables the efficient storage of all the parameters that are considered essential in the scheduling decision process. Thus the scheduler can have immediate access to this information. A full time domain scheduling algorithm that utilizes this tree structure is described and two new resource allocation algorithms are proposed. These algorithms also utilize some additional tree structures derived from appropriate preprocessing actions that take place before the actual scheduling decision. The first algorithm has low complexity and satisfactory performance while the second has improved performance with the cost of some additional complexity. Extensive simulation results confirm the capability of the proposed scheme in satisfying the strict QoS requirements of LTE, while the performance of the newly proposed algorithms is compared with well-known scheduling techniques. The proposed solutions are applicable to the downlink case, while the same concept may be adapted properly to provide an efficient solution for the uplink case

Mobility and resource management for 5G heterogeneous networks

The conventional topology of current cellular networks is a star structure, where central control points usually serve as base stations (BSs). This provides the advantage of simplicity while still providing quality of service (QoS). For next-generation networks, however, this topology is disadvantageous and difficult to use due to the insufficient availability of network access. The hybrid topology radio network will thus naturally be the future mobile access network that can help to overcome current and future challenges efficiently. Therefore, relay technology can play an important role in a hybrid cellular network topology. Today, with the recent long-term evolution-advanced (LTE-A) standards, the 3rd Generation Partnership Project (3GPP) supports a single-hop relay technology in which the radio access link between the BS and users is relayed by only one relay station (RS). With the help of multi-hop relay, however, the radio link between the BS and users can be extended to more than two hops to improve the coverage and network capacity. Multiple hops to transmit data to and from the corresponding BS results in the reduction of path loss. However, using a multi-hop relay system requires more radio resources to transmit data through different hops. More interference is also created due to a greater number of simultaneous transmissions in the network. New mobility and resource management schemes are thus important for achieving a high QoS while increasing the whole network capacity. In the first part, the problem of relay selection and radio resource allocation is studied, and choosing how the bandwidth should be shared between direct, backhaul, and access links in multi-hop relay networks is discussed. In such a network, resource allocation plays a critical role because it manages channel access in both time and frequency domains and determines how resources are allocated for different links. The proposed solution includes a nonlinear programming technique and a heuristic method. First, the problem formulation of resource allocation and relay selection is presented to provide an integrated framework for multi-hop relay networks. Second, an analytical solution to the problem is presented using a nonlinear programming technique. Finally, an iterative two-stage algorithm is presented to address the joint resource allocation and relay selection problem in multi-hop relay networks Under backhaul and capacity limitation constraints. In particular, the first stage proposed a fast approximation analytical solution for a resource allocation algorithm that takes into account the trade-off between the optimality and the complexity of the multi-hop relay architecture; the second stage presented a heuristic relay selection strategy that considers the RS load and helps to keep the relay from being overloaded is proposed. In the second part, the mobility problem in downlink multi-hop relay networks is addressed. In addition to the resource allocation issue, the relay selection problem is studied from a network layer perspective. Therefore, this part includes the issue of radio path selection. As an alternative to the heuristic algorithm developed in the previous part, the presented work describes the development and evaluation of a relay-selection scheme based on a Markov decision process (MDP) that considers the RS load and the existing radio-link path to improve handoff performance. First, the problem formulation of resource allocation and relay selection is presented. Second, an MDP mathematical model is developed to solve the relay selection problem in a decentralized way and to make the selection process simple. This relay selection scheme has the objective of maintaining the throughput and ensuring seamless mobility and service continuity to all mobile terminals while reducing the handoff frequency and improving handoff performance. In the third part, the admission and power control problem of a general heterogeneous network (HetNet) consisting of several small cells (SCs) is solved. Compared to the first two parts of this work, the system is expanded from a multi-hop RS to a general SC context. This part therefore focuses only on the access link problem, assuming the capacity of the SC backhaul links are large enough not to be bottlenecks. This part mainly deals with the problem of how to maximize the number of admitted users in an overloaded system while minimizing the transmit power given a certain QoS level. First, the problem is formulated to address concerns about QoS requirements in a better way. Second, a Voronoi-based user association scheme for maximizing the number of admitted users in the system under QoS and capacity limitation constraints is proposed to find near-optimal solutions. Finally, a twostage algorithm is presented to address the joint admission and power control problem in a downlink heterogeneous SC network. In particular, the first stage proposes a dynamic call admission control policy that considers the SC load and call-level QoS while also helping to keep the system from being overloaded. The second stage presents an adaptive power allocation strategy that considers both user distribution and the density of SCs in HetNets. Finally, the proposed solutions are evaluated using extensive numerical simulations, and the numerical results are presented to provide a comparison with related works found in the literature

Opportunistic Spectrum Utilization by Cognitive Radio Networks: Challenges and Solutions

Cognitive Radio Network (CRN) is an emerging paradigm that makes use of Dynamic Spectrum Access (DSA) to communicate opportunistically, in the un-licensed Industrial, Scientific and Medical bands or frequency bands otherwise licensed to incumbent users such as TV broadcast. Interest in the development of CRNs is because of severe under-utilization of spectrum bands by the incumbent Primary Users (PUs) that have the license to use them coupled with an ever-increasing demand for unlicensed spectrum for a variety of new mobile and wireless applications. The essence of Cognitive Radio (CR) operation is the cooperative and opportunistic utilization of licensed spectrum bands by the Secondary Users (SUs) that collectively form the CRN without causing any interference to PUs\u27 communications. CRN operation is characterized by factors such as network-wide quiet periods for cooperative spectrum sensing, opportunistic/dynamic spectrum access and non-deterministic operation of PUs. These factors can have a devastating impact on the overall throughput and can significantly increase the control overheads. Therefore, to support the same level of QoS as traditional wireless access technologies, very closer interaction is required between layers of the protocol stack. Opportunistic spectrum utilization without causing interference to the PUs is only possible if the SUs periodically sense the spectrum for the presence of PUs\u27 signal. To minimize the effects of hardware capabilities, terrain features and PUs\u27 transmission ranges, DSA is undertaken in a collaborative manner where SUs periodically carry out spectrum sensing in their respective geographical locations. Collaborative spectrum sensing has numerous security loopholes and can be favorable to malicious nodes in the network that may exploit vulnerabilities associated with DSA such as launching a spectrum sensing data falsification (SSDF) attack. Some CRN standards such as the IEEE 802.22 wireless regional area network employ a two-stage quiet period mechanism based on a mandatory Fast Sensing and an optional Fine Sensing stage for DSA. This arrangement is meant to strike a balance between the conflicting goals of proper protection of incumbent PUs\u27 signals and optimum QoS for SUs so that only as much time is spent for spectrum sensing as needed. Malicious nodes in the CRN however, can take advantage of the two-stage spectrum sensing mechanism to launch smart denial of service (DoS) jamming attacks on CRNs during the fast sensing stage. Coexistence protocols enable collocated CRNs to contend for and share the available spectrum. However, most coexistence protocols do not take into consideration the fact that channels of the available spectrum can be heterogeneous in the sense that they can vary in their characteristics and quality such as SNR or bandwidth. Without any mechanism to enforce fairness in accessing varying quality channels, ensuring coexistence with minimal contention and efficient spectrum utilization for CRNs is likely to become a very difficult task. The cooperative and opportunistic nature of communication has many challenges associated with CRNs\u27 operation. In view of the challenges described above, this dissertation presents solutions including cross-layer approaches, reputation system, optimization and game theoretic approaches to handle (1) degradation in TCP\u27s throughput resulting from packet losses and disruptions in spectrum availability due non-deterministic use of spectrum by the PUs (2) presence of malicious SUs in the CRN that may launch various attacks on CRNs\u27 including SSDF and jamming and (3) sharing of heterogeneous spectrum resources among collocated CRNs without a centralized mechanism to enforce cooperation among otherwise non-cooperative CRN