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

Survey of Spectrum Sharing for Inter-Technology Coexistence

Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions

Interference modelling and management for cognitive radio networks

Radio spectrum is becoming increasingly scarce as more and more devices go wireless. Meanwhile, studies indicate that the assigned spectrum is not fully utilised. Cognitive radio (CR) technology is envisioned to be a promising solution to address the imbalance between spectrum scarcity and spectrum underutilisation. It improves the spectrum utilisation by reusing the unused or underutilised spectrum owned by incumbent systems (primary systems). With the introduction of CR networks, two types of interference originating from CR networks are introduced. They are the interference from CR to primary networks (CR-primary interference) and the interference among spectrum-sharing CR nodes (CR-CR interference). The interference should be well controlled and managed in order not to jeopardise the operation of the primary network and to improve the performance of CR systems. This thesis investigates the interference in CR networks by modelling and mitigating the CR-primary interference and analysing the CR-CR interference channels. Firstly, the CR-primary interference is modelled for multiple CR nodes sharing the spectrum with the primary system. The probability density functions of CR-primary interference are derived for CR networks adopting different interference management schemes. The relationship between CR operating parameters and the resulting CRprimary interference is investigated. It sheds light on the deployment of CR networks to better protect the primary system. Secondly, various interference mitigation techniques that are applicable to CR networks are reviewed. Two novel precoding schemes for CR multiple-input multipleoutput (MIMO) systems are proposed to mitigate the CR-primary interference and maximise the CR throughput. To further reduce the CR-primary interference, we also approach interference mitigation from a cross-layer perspective by jointly considering channel allocation in the media access control layer and precoding in the physical layer of CR MIMO systems. Finally, we analyse the underlying interference channels among spectrum-sharing CR users when they interfere with each other. The Pareto rate region for multi-user MIMO interference systems is characterised. Various rate region convexification schemes are examined to convexify the rate region. Then, game theory is applied to the interference system to coordinate the operation of each CR user. Nash bargaining over MIMO interference systems is characterised as well. The research presented in this thesis reveals the impact of CR operation on the resulting CR-primary network, how to mitigate the CR-primary interference and how to coordinate the spectrum-sharing CR users. It forms the fundamental basis for interference management in CR systems and consequently gives insights into the design and deployment of CR networks

INTERFERENCE MANAGEMENT IN LTE SYSTEM AND BEYOUND

The key challenges to high throughput in cellular wireless communication system are interference, mobility and bandwidth limitation. Mobility has never been a problem until recently, bandwidth has been constantly improved upon through the evolutions in cellular wireless communication system but interference has been a constant limitation to any improvement that may have resulted from such evolution. The fundamental challenge to a system designer or a researcher is how to achieve high data rate in motion (high speed) in a cellular system that is intrinsically interference-limited. Multi-antenna is the solution to data on the move and the capacity of multi-antenna system has been demonstrated to increase proportionally with increase in the number of antennas at both transmitter and receiver for point-to-point communications and multi-user environment. However, the capacity gain in both uplink and downlink is limited in a multi-user environment like cellular system by interference, the number of antennas at the base station, complexity and space constraint particularly for a mobile terminal. This challenge in the downlink provided the motivation to investigate successive interference cancellation (SIC) as an interference management tool LTE system and beyond. The Simulation revealed that ordered successive interference (OSIC) out performs non-ordered successive interference cancellation (NSIC) and the additional complexity is justified based on the associated gain in BER performance of OSIC. The major drawback of OSIC is that it is not efficient in network environment employing power control or power allocation. Additional interference management techniques will be required to fully manage the interference.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Full-duplex wireless communications: challenges, solutions and future research directions

The family of conventional half-duplex (HD) wireless systems relied on transmitting and receiving in different time-slots or frequency sub-bands. Hence the wireless research community aspires to conceive full-duplex (FD) operation for supporting concurrent transmission and reception in a single time/frequency channel, which would improve the attainable spectral efficiency by a factor of two. The main challenge encountered in implementing an FD wireless device is the large power difference between the self-interference (SI) imposed by the device’s own transmissions and the signal of interest received from a remote source. In this survey, we present a comprehensive list of the potential FD techniques and highlight their pros and cons. We classify the SI cancellation techniques into three categories, namely passive suppression, analog cancellation and digital cancellation, with the advantages and disadvantages of each technique compared. Specifically, we analyse the main impairments (e.g. phase noise, power amplifier nonlinearity as well as in-phase and quadrature-phase (I/Q) imbalance, etc.) that degrading the SI cancellation. We then discuss the FD based Media Access Control (MAC)-layer protocol design for the sake of addressing some of the critical issues, such as the problem of hidden terminals, the resultant end-to-end delay and the high packet loss ratio (PLR) due to network congestion. After elaborating on a variety of physical/MAC-layer techniques, we discuss potential solutions conceived for meeting the challenges imposed by the aforementioned techniques. Furthermore, we also discuss a range of critical issues related to the implementation, performance enhancement and optimization of FD systems, including important topics such as hybrid FD/HD scheme, optimal relay selection and optimal power allocation, etc. Finally, a variety of new directions and open problems associated with FD technology are pointed out. Our hope is that this treatise will stimulate future research efforts in the emerging field of FD communication

Cognitive code-division links with blind primary-system identification

Abstract—We consider the problem of cognitive code-division channelization (simultaneous power and code-channel allocation) for secondary transmission links co-existing with an unknown primary code-division multiple-access (CDMA) system. We first develop a blind primary-user identification scheme to detect the binary code sequences (signatures) utilized by primary users. To create a secondary link we propose two alternative procedures –one of moderate and one of low computational complexity – that optimize the secondary transmitting power and binary codechannel assignment in accordance with the detected primary code channels to avoid “harmful ” interference. At the same time, the optimization procedures guarantee that the signalto-interference-plus-noise ratio (SINR) at the output of the maximum SINR linear secondary receiver is no less than a certain threshold to meet secondary transmission quality of service (QoS) requirements. The extension of the channelization problem to multiple secondary links is also investigated. Simulation studies presented herein illustrate the theoretical developments. Index Terms—Blind user identification, code-channel allocation, code-division multiple-access, cognitive radio, dynamic spectrum access, power allocation, signal-to-interference-plusnoise ratio. I

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