Access, Fronthaul and Backhaul Networks for 5G & Beyond
2: School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK
3: School of Engineering and Computing, University of the West of Scotland, UK
The widespread use of mobile internet and smart applications has led to an explosive growth in mobile data traffic, which will continue due to the emerging need of connecting people, machines, and applications in an ubiquitous manner through the mobile frastructure. The efficient and satisfactory operation of all these densely-deployed networks hinges on a suitable backhaul and fronthaul provisioning. The research community is working to provide innovative technologies with extensive performance evaluation metrics along with the required standardisation milestones, hardware and components for a fully deployed network by 2020 and beyond. Access, Fronthaul and Backhaul Networks for 5G & Beyond provides an overview from both academic and industrial stakeholders of innovative backhaul/fronthaul solutions. Covering a wide spectrum of underlying themes ranging from the recent thrust in edge caching for backhaul relaxation to mmWave-based fronthauling for radio access networks, this book is essential reading for engineers, researchers, designers, architects, technicians, students and service providers in the field of networking, mobile and wireless and computing technologies working towards the deployment of 5G networks.
Inspec keywords: 5G mobile communication; MIMO communication; virtualisation; cellular radio; Long Term Evolution; software defined networking; Internet; multi-access systems
Other keywords: Internet; GSM-LTE Advanced; software defined networking; backhaul networks; 5G access networks; fronthaul networks; network function virtualization; MIMO communication
Subjects: Multiple access communication; Other computer networks; General electrical engineering topics; Computer communications; Mobile radio systems; General and management topics
- Book DOI: 10.1049/PBTE074E
- Chapter DOI: 10.1049/PBTE074E
- ISBN: 9781785612138
- e-ISBN: 9781785612145
- Page count: 566
- Format: PDF
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Front Matter
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Part I: Access Network
1 Network densification
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Network densification is a promising cellular deployment technique that leverages spatial reuse to enhance coverage and throughput. Recent work has identified that at some point ultra-densification will no longer be able to deliver significant throughput gains. Throughout this chapter, we provide a unified treatment of the performance limits and from which shed light on how to leverage the potential of network densification. We firstly show that there are three scaling regimes for the downlink signal-to-interference-plus-noise ratio (SINR), coverage probability, and average rate. Specifically, depending on the near-field pathloss and the fading distribution, the user performance of ultra dense networks would either monotonically increase, saturate, or decay with increasing network density. Secondly, we show that network performance in terms of coverage density and area spectral efficiency can benefit from increased network infrastructure better than the user performance does. Furthermore, we analytically prove that enhancing the tail distribution of channel power is a fundamental way to leverage the benefit of network densification.
2 Massive and network MIMO
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This chapter, the techniques of massive multiple-input-multiple-output (MIMO) and network MIMO are studied. First, massive MIMO is compared with the conventional point-to-point MIMO used in current cellular systems in terms of capacity and energy efficiency. The comparison shows that massive MIMO has huge gains even under the modest conditions using simple linear processing. Then, the implementation of massive MIMO is discussed by focusing on the channel estimation method, the signal detection method and the precoding method. Following this, several main issues in massive MIMO are examined and relevant measures are discussed. Finally, network MIMO is studied by introducing cooperation between base stations to completely remove the inter-cell interference, at the cost of even higher complexity that places limits on the backhaul and fronthaul links.
3 The role of massive MIMO in 5G access networks: potentials, challenges, and solutions
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The massive multiple-input/multiple-output (MIMO) technique has been gaining momentum lately as a potential key enabler of the network spectral efficiency (and hence throughput) increase expected from the fifth generation (5G) ofcellularnetwork technology. This technique consists in equipping the base stations (BSs) with arrays having a large number, typically from tens to few hundreds, of antenna elements. This, in theory, guarantees the possibility of serving larger numbers of concurrent transmissions to or from the BSs than the multiplexing techniques used in previous generations of cellular technology, without compromising the throughput of each transmission. By exploiting the high spatial multiplexing gain that can be realized through massive MIMO systems, 5G networks could provide the expected boost to the overall throughput with respect to previous generations. On the one hand, having more antenna elements in the BS array increases the spatial resolution of both outgoing and incoming signals. On the other hand, it diminishes the effect of the additive white gaussian noise (AWGN) at the receiver. These features lead to several advantages both in terms of access mechanisms and associated signal processing: little intra-cell and multicell interference leakage, optimality of simple linear precoding/detection schemes, capability of simultaneously serving a multitude of competing wireless connections in each cell area without compromising their individual throughput, just to name a few. However, this comes at the cost of the acquisition of accurate uplink/downlink channel state information (CSI) at the BS. This operation is challenging in many respects, and has a non-negligible impact in terms of both algorithms implemented at the physical/access/network layer and practical hardware design. It is worth noting that the extent of this impact strongly depends on the frequency bands over which the transmissions are performed. In this regard, it is a common belief that signals transmitted in future 5G networks will likely span a wide spectrum of frequencies.In other words, their radio carrier wavelengths will range from decimeters, as in legacy cellular networks, to millimeters, as in millimeter wave (mmWave) communications. Evident peculiarities will characterize such signals, and future massive MIMO systems will have to leverage them in effective ways in order to achieve the promised network throughput increase. This chapter starts from these observations to present a discussion on the potential and the challenges associated to the deployment of massive MIMO systems for 5G networks.
4 Towards a service-oriented dynamic TDD for 5G networks
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The emerging 5G networks should accommodate a plethora of heterogeneous services with diverse Service Level Agreements, such as Internet of Things, location and social applications and multimedia. Dynamic Time Division Duplex (TDD) networks have the potential to support asymmetric services providing resource flexibility especially for small data applications and for social applications with interchanging uplink (UL) and downlink (DL) demands. TDD networks can leverage the benefits of network programmability via the means of the Software-Defined Network (SDN) paradigm that enables a logically centralized control plane capable of delivering efficient, optimized and flexible network resource management matching specific application UL and DL traffic requirements. This chapter describes the main mechanisms and components for evolving TDD networks toward 5G. In particular, it provides an overview of various dynamic TDD proposals, before elaborating the concept of TDD virtual cells, which allows users residing at the cell edge to utilize resources from multiple base stations forming a customized TDD frame. The adoption of SDN for programming the network resources and frame (re)configuration of TDD virtual cells follows, elaborating the SDN architecture, the resource programmability logic and the resource sharing in heterogeneous environments considering Frequency Division Duplex macros and TDD small cells. The adoption of SDN for enabling a TDD-specific network slice framework is described next, allowing a different TDD frame configuration to be employed within a certain amount of isolated resources, enhancing in this way the network utilization while optimizing the application perceived performance. Finally, some further considerations and challenges are analyzed considering the adoption of TDD in future 5G networks.
5 Traffic aware scheduling for interference mitigation in cognitive femtocells
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Femtocells are designed to co-exist alongside macrocells, providing spatial frequency re-use, higher spectrum efficiency and data rates. However, interference between two networks is imminent; therefore, ways to manage it must be employed to efficiently avoid problems such as coverage holes. In this chapter, we employ cognitive radio enabled femtocells (CFs) and propose a novel scheduling algorithm to address the problem of cross and co-tier interference in a two-tier network system. Macrocell user equipments (MUEs) usually transmit with varying traffic loads and at times it is highly likely for their assigned resource blocks (RBs) being empty. Based on the interweave concept of spectrum assignment, CFs in our proposed scheme assign the RBs of MUEs with a low-data traffic load and low-interference temperature to its FUEs, thereby mitigating cross-tier interference, whereas co-tier interference is mitigated by resolving the contention for the same RBs by employment of matching policy among the coordinating CFs. System-level simulations are performed to investigate the performance of proposed scheme and results obtained are compared with best channel quality indicator and proportional fair schemes both in no fading and fading conditions. It is found that our proposed scheduling scheme outperforms compared schemes in no fading conditions; however, it provides competitive results when fading conditions are considered. The concept of matching policy successfully mitigates the effect of co-tier interference in collocated femtocells by providing improved signal-to-interference-plus-noise ratio, throughput and spectral efficiency results, thereby proving the effectiveness of scheme.
6 5G radio access for the Tactile Internet
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In this chapter, the key features of the emerging fifth generation (5G) wireless networks are highlighted briefly together with 5G architecture and the 5G radio access network (RAN), as specified by the standardisation bodies. The flexible nature of 5G networks and the anticipated 5G RAN design are introduced to be the enabling wireless edge for the Tactile Internet by providing ultra-reliable, ultra-responsive, and intelligent network connectivity. After discussing the architectural aspects and technical requirements of the Tactile Internet, the core design challenges are identified and some directions for addressing these design challenges are also provided. Ajoint coding method to the simultaneous transmission of data over multiple independent wireless links is presented in this context. Moreover, radio resource slicing and application-specific customisation techniques are introduced to enable the co-existence of different vertical applications along with Tactile Internet applications. Finally, edge-intelligence techniques are investigated to enable the perception of real time and to overcome the physical limitation due to the finite speed of light.
7 Fronthauling for 5G and beyond
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This chapter focused on the practical aspects of fronthauling the next generation radio access networks. One of the important characteristics of 5G RAN is likely to be an increased degree of coordination between RAN nodes in networks that are becoming more dense. In this context CRAN becomes an interesting concept with overlaps with other emerging concepts such as NFV and MEC, however realisation of CRAN and associated requirements on fronthaul are dependent on the distribution of the RAN functions between central unit and the remote unit. This chapter provided an overview of the interdependence between RAN functions through the scheduling functions within a base station. One of the main observations highlighted in this chapter is that many backhaul technologies can support 5G fronthaul requirements, however there is a significant opportunity for optimisation. In particular, while the use of CPRI can be viable for point-to-point links, associated transport overheads may be prohibitive for a dense network, especially where base stations utilise some of the proposed 5G air interface techniques such as higher order MIMO over large channel bandwidths. Provided examples of real-world split RAN operation illustrate the viability of alternative split RAN architectures that can be more efficient from deployment perspective, and invite further research in the area.
8 Interference management and resource allocation in backhaul/access networks
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The interface management and resource allocation in backhaul (BH)/access networks for the cloud/centralized radio access networks (C-RAN) are two of the largest challenges to enable the C-RAN architecture deployment successfully in cellular wireless systems. From the PHY perspectives, one major advantage of C-RAN is the ease of implementation of multicell coordination mechanisms to manage the interference and improve the system spectral efficiency (SE). Theoretically, a large number of cooperative cells leads to a higher SE; however, it may also cause significant delay due to extra channel state information feedback and joint processing computational needs at the cloud data center, which is likely to result in performance degradation. In order to investigate the delay impact on the throughput gains, we divide the network into multiple clusters of cooperative small cells and formulate a throughput optimization problem. We model various delay factors and the sum-rate of the network as a function of cluster size, treating it as the main optimization variable. For our analysis, we consider both base stations' as well as users' geometric locations as random variables for both linear and planar network deployments. The output signal-to-interference-plus-noise ratio and ergodic sum-rate are derived based on the homogenous Poisson-point-processing model. The sum-rate optimization problem in terms of the cluster size is formulated and solved. From the radio resource management (RRM) perspective, we consider the problem of joint BH and access links optimization in dense small-cell networks with special focus on time division duplexing mode of operation in BH and access links transmission. Here, we propose a framework for joint RRM where we systematically decompose the problem in BH and access links. To simplify the analysis, the procedure is tackled in two stages. At the first stage, the joint optimization problem is formulated for a point-to-point scenario where each small cell is simply associated to a single user. In the second stage, the problem is generalized for multiaccess small cells. In addition, the chapter addressed thejoint routing and BH scheduling in a dense small-cell networks using 60 GHz multihop BH, coordinated by a local C-RAN central unit. The problem is formulated as a generalized vehicle routing problem and decoupled into two subproblems, channel-aware path selection and queue-aware link scheduling.
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Part II: Fronthaul Networks
9 Self-organised fronthauling for 5G and beyond
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The connecting link between the baseband unit (BBU) and the remote radio unit (RRU), in a centralised radio access network (C-RAN), is the fronthaul, which is the topic of this chapter. The fronthaul is presented as a key disruptive technology, vital to the realisation of 5G networks, but one with stringent requirements in terms of capacity, latency, jitter, and synchronisation. This chapter explains the fronthaul paradigm and presents an overview of legacy and new solutions in backhauling/fronthauling with critical analysis of respective advantages and limitations. In view of the debilitating expectations of 5G fronthaul performance, hybrid RAN architectures are also explored and analysed from their respective RAN gain and fronthaul requirements, leading to promising alternative RAN functional splits and innovations in X-hauling. The chapter delves into the (centralised) C-RAN/fronthaul versus (distributed) D-RAN/backhaul dilemma, offering a joint backhaul/RAN perspective and tangible trade-off analysis of the available options. The study advocates the need for a fronthaul architecture that is dynamic, adaptable, flexible, and expandable. To this end, a key catalyst to the realisation of the 5G fronthaul is equipping the network with self-optimisation and organisation (SON) capabilities that would timely adapt the network following the dynamically changing conditions. In this context, SON operation in the fronthaul becomes essential for optimisation objectives such as energy efficiency, latency reduction, or load balancing. Moreover, the SON-enabled joint RAN/fronthaul optimisation has a pivotal role in adjusting the level of centralisation according to the fronthaul capabilities and vice-versa.
10 NFV and SDN for fronthaul-based systems
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The trend to employ softwarisation in order to introduce virtualisation of network functions in the mobile core is driven by the increasing need for flexible configuration and operation of the network. Such needs are stipulated by the wide and dynamic requirements of new services that next-to-come fifth generation (5G) of mobile networks will be supporting. Traditional hardware-based network deployments would incur high capital and operation expenditures (CAPEX and OPEX, respectively) as a result of network expansion or modification requiring hardware addition or replacement. Flexibility is thus one of the key drivers in the design of 5G networks in order to support the heterogeneous requirements of all 5G applications, and to enable multiple network embodiments within one single network deployment.
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Part III: Backhaul Network
11 Mobile backhaul evolution: from GSMto LTE-Advanced
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Mobile backhaul describes the connectivity between cellular radio base stations and the associated mobile network operator's (MNO's) core network. Previously, this was known as `transmission' but during the 1990s, the term backhaul was adopted. This chapter will review the development of mobile backhaul for the global system for mobile communications (GSM), universal mobile telecommunications system (UMTS) and long-term evolution (LTE), including LTE-Advanced radio access technologies. Original GSM terrestrial transmission interfaces were defined as time division multiplexing (TDM), within Europe and elsewhere these were based on 2.048 Mbps E1 circuits. These circuits could be multiplexed via the plesiochronous digital hierarchy (PDH) and synchronous digital hierarchy (SDH) standards to realise higher order transmission systems. The introduction of UMTS brought a new requirement to support asynchronous transfer mode (ATM) technology within the mobile backhaul domain. ATM is a fixed length cell switching technology which is carried over TDM transmission systems such as PDH and SDH. The evolution of mobile networks from predominately voice-centric to increasingly data-centric operation resulted in the development of High Speed Downlink Packet Access technologies which, together with advanced uplink technologies, resulted in the need to significantly scale the capacity of mobile backhaul networks. To address the need for scalability mobile backhaul evolved from n × E1 and TDM systems to Carrier Ethernet, there was however a few challenges to address to support this migration, firstly, the end points on base stations and network controllers were all TDM based and secondly, the E1 circuits provided a deterministic synchronisation signal via the native line code which ensured the base station operated within its allocated radio frequency channels. To address the first requirements, there was widespread adoption of pseudo-wire technology, whereas the second challenge was addressed by the introduction of Synchronous Ethernet or alternatively by the deployment of a local or packet-based synchronisation reference. Overtime, the base station and network controllers migrated to native Ethernet interfaces and therefore supported end-to-end Carrier Ethernet transmission with an Internet Protocol (IP) transport network layer. LTE was introduced with native Ethernet and IP support, the LTE radio interface offers significantly higher peak and average data rates than previous generations of cellular radio access networks. To support the deployment of LTE technology, the need for combined GSM, UMTS and LTE backhaul and the growing trend towards network sharing between MNOs, resulted in 1 Gbps Carrier Ethernet backhaul solution being deployed. This increase in backhaul capacity requirements effectively ruled out copper twisted-pair-based technologies in favour of ever more optical fibre and high-capacity microwave and millimetre wave radio backhaul technologies. The ongoing development of LTE-Advanced features, such as carrier aggregation, continues to drive the capacity of backhaul networks, whereas new products and services ensure constant evolution of performance with lower latency and reduced packet error loss rates becoming the norm.
12 Wired vs wireless backhaul
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Wireless networks are becoming even more pervasive and an indispensable part of our daily life. In order to cope with a large increase in traffic volume, as well as in the number of connected devices, new technologies, practices and spectrum rearrangements are required. In this context, a key question arises: how to provide extensive backhaul (and including fronthaul and midhaul) connectivity and capacity in a cost-effective and sustainable way for such pervasive networks? The answer, if exists, is rather complex and not the goal of this chapter. However, this chapter aims at providing the reader with an overview of some of the most prominent solutions and shed some light into the technical challenges ahead. This chapter is organized as follows. The vision of a backhaul solution for future wireless networks is first introduced, then wired, and radio-frequency (RF) wireless candidate solutions are covered. Special attention is given to the advantages and disadvantages of each technology. Overall, this chapter provides extensive qualitative comparison and discussion of the key components of each available solution. The tone of this chapter is to emphasize that, due to the pervasiveness of wireless networks, an one-size-fits-all approach is not attainable and hybrid wired-wireless solutions will take place.
13 Spectral coexistence for next generation wireless backhaul networks
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In this chapter, starting with the recent trend in terrestrial and satellite backhaul technologies, we provide possible use cases for HSTB networks and their potential benefits and challenges. Subsequently, we focus on the spectrum sharing aspects of wireless backhaul networks considering the following two categories of enabling techniques: (i) spectral awareness techniques and (ii) spectral exploitation techniques. The first category mainly comprises radio environment awareness techniques such as spectrum sensing and databases while the second category includes interference mitigation and resource allocation techniques. Furthermore, we present three case studies along with the numerical results considering the coexistence of satellite and terrestrial systems in the Ka-band. Finally, this chapter provides some interesting recommendations for future research directions.
14 Control data separation and its implications on backhaul networks
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As soon as 2020, network densification will be the dominant theme to support enormous capacity and massive connectivity. However, such deployment scenarios raise several challenges and they impose new constraints. In particular, signalling load, mobility management and energy efficiency will become critical considerations in the fifth generation (5G) era. These aspects suggest a paradigm shift towards a signalling and energy conscious radio access network (RAN) architecture with intelligent mobility management. In this direction, the conventional RAN design imposes several constraints due to the tight coupling between the control plane (CP) and the data plane (DP). Recently, a futuristic RAN architecture with CP/DP separation has been proposed to overcome these constraints. In this chapter, we discuss limitations of the conventional RAN architecture and present the control/data separation architecture (CDSA) as a promising solution. In addition, we identify the impact of the CDSA on the backhaul network. An analytical framework is developed to model the backhaul latency of the CDSA, and a densification limit under latency constraints is derived. Furthermore, the impact of the backhaul technology on the CDSA energy saving gains is discussed and an advanced non-direct backhaul mechanism is presented.
15 Backhaul relaxation through caching
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In this chapter the idea of content centric mobile wireless networks introduced as a solution to the traffic expansion problem faced by MNOs. We denoted the essential role that in-network caching plays in the transition from our current host centric to the content centric networking paradigm and we presented the metrics required to define the performance of such caching mechanisms. A comprehensive study on the content placement problem in the heterogeneous cellular networks has been presented while some of the most promising methods has been described in detail. The content placement problem is investigated from different objectives. QoS, backhaul relaxation through caching and energy consumption were the main aspects that we aimed to address in this chapter. These principles has been mainly investigated for the case of video content delivery due to its prominent role in the future mobile wireless traffic.
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Part IV: System Integration and Case Studies
16 SDN and edge computing: key enablers toward the 5G evolution
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“2020 and Beyond” is announced by the International Telecommunication Union to be the era of the next mobile network generation. After Long-Term Evolution (LTE)/fourth generation, fifth generation (5G) is promising to be a major evolution in the communication domain, not simply due to the acceleration of the data rate, but rather due to the new applications. The challenging objectives such as minimum user-plane latency, uninterruptable connectivity, high quality of service, high data rate communications, and network capacity, while dealing with ubiquitous and heterogeneous network access, call for a major overhaul of the whole mobile network architecture. The limitations of today's mobile systems, derived from their dependency on hardware-based designs, led to inflexible and limited architectures. It is essential to have dynamic and flexible management systems at several levels, starting from the radio access network (RAN), passing by the Evolved Packet Core (EPC), up to the application interfaces. These future demands and the requirement for a self-adaptive system can be realized by adopting the software-defined-networking (SDN) paradigm, which leads to the integration of SDN in the network components of the upcoming 5G technology. Benefiting from software flexibility on one hand and control and management centralization on the other hand, SDN has its positive impact in the communication world from several aspects. SDN will provide 5G with a smooth transition and unified management among various wireless standards and among different RANs and wired core networks. Furthermore, SDN can optimally orchestrate the interference between cells, handovers, roaming process, routing, and signaling between access and core networks, management of the gateways, and even the management of user data. Furthermore, the new bandwidth and latency requirements, and the ability to support the innovative 5G applications, cannot be satisfied by centralizing the data in the cloud. Pushing the data to the user's proximity will be vital for some time-critical applications, which is a requirement supported by edge computing. Therefore, the geo-distribution of data requires an optimal networking design for these edges. On top of this distributed data layer, the network function virtualization coupled with SDN promises easier management of such an infrastructure. In this chapter, we investigate how SDN can be integrated into the 5G network architecture at different levels (RAN, EPC, security, etc.) and highlight the solutions, challenges, and benefits resulting from such integration. Also, we present the mobile edge computing concept, its integration with SDN, and its implications on 5G. We review the designs and architectures that have been proposed in this area and others that are under development, including the innovative applications and use cases that will be enabled by the SDN-5G combination. Our work will be concluded by proposing an architecture for SDN-5G for telecom operators.
17 Low latency optical back-and front-hauling for 5G
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Looking forward to the not-so-far future, wireless networks will comprise centralised processing, mixed macro and small cells deployments as well as new radio technologies in order to support very high data rates and traffic types that are characterised by connectionless and sporadic transmission of short packets such as those employed by machine to machine communication devices. In current radio access networks, there is a very clear difference between the fronthaul and backhaul. In comparison with the advent of centralised radio access networks, the difference between the fronthaul and backhaul networks has been shifted further away from the user. Subsequently, in the latest propositions for 5G architectures, they are being merged into an `xhaul' (crosshaul) network where the fronthaul and backhaul concepts no longer exist. In particular instead of using a dedicated centralised processing pool for a set of cellular access points, the idea of using centralised processing within the core network has emerged. With the use of network function virtualisation and centralised processing in data centres, cloud-RANs can be used to provide access to the distribution antenna, removing the need for backhauling and fronthauling. The cloud-RAN can perform the duties of the Mobility Management Entity and Serving Gateway and at the same time can also process each cellular access point's analogue processing using a flexible virtualised software environment. Assuming this is used along with split processing, what needs also to be addressed is the means of communication between the cloudRAN and the distribution antenna. Traditional solutions such as the common public radio interface might not be sufficient to meet all requirements. Largely, Ethernet is being proposed. When Ethernet is used, software-defined networking (SDN) can also be used to dynamically control data flows to and from the cloud-RAN, as well as providing additional benefits, such as network slicing, allowing multiple cellular operators to use the same xhaul infrastructure. This chapter, therefore, largely elaborates on xhaul networks by investigating the potential of SDN to provide an effective user experience for the services provided. The control of specific services such as billing, roaming and registration could then be sent via alternative links such as satellite links, as latency for these packets are not critical, resulting in reduced packet delay on the data plane. It is apparent that for Gbps wireless connectivity, targeted by 5G, the data rate requirements on the centralised cloud xhaul link will be in the range of several Gbps with a latency requirement close to 1 ms.
18 Fronthaul and backhaul integration (Crosshaul) for 5G mobile transport networks
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In this context, the distinction between fronthaul and backhaul transport networks blurs as varying portions of functionality of 5G points of attachment (5GPoAs) might be moved towards the network as required for cost efficiency reasons. The traditional capacity overprovisioning approach on the transport infrastructure will no longer be possible with 5G. Hence, a new generation of integrated fronthaul and backhaul technologies will be needed to bring capital expenditure (CAPEX) and operational expenditure (OPEX) to a reasonable return on investment (ROI) range. Also, for cost reasons, the heterogeneity of transport network equipment must be tackled by unifying data, control and management planes across all technologies as much as possible. A redesign of the fronthaul/backhaul network segment is a key point for 5G networks as current transport networks cannot cope with the amount of bandwidth required for 5G. Next-generation radio interfaces, using 100 MHz channels and squeezing the bit-per-megahertz ratio through massive multiple-input and multiple-output (MIMO) or even full-duplex radios, require a ten-fold increase in capacity, which cannot be achieved just through the evolution of current technologies.
19 Device-to-device communication for 5G
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Fourth generation (4G) communication technology was introduced to accommodate the rising demands of mobile user equipments (UEs) in terms of data rates and network reliability. However, a sharp rise in the number of mobile users has resulted in recent years and is expected to grow exponentially in the years to come, which prompted the need for a futuristic standard which could support a rather complex infrastructure of communication. Fifth generation (5G) communication technology is labelled as a platform for providing higher data rates with efficient utilisation of resources. The techniques which would undergo development under 5G communication standard include heterogeneous networks (HetNets), machine-to-machine (M2M) communications, device-to-device (D2D) networks and Internet of things (IoT) among others. Spectrum constraints have given impetus to the concept of offloading traffic from cellular network. D2D networks are viewed as an apt technology for providing direct peer-to-peer (P2P) links for data transfer, thus minimising their dependence on the base station (BS). Direct communication between devices will open up a window of opportunity for realising proximity services such as public safety networks, health monitoring, disaster area networks and numerous multimedia services. However, there are several challenges associated with D2D communication that include interference and resource management, network discovery, context aware services and network security. Viewing the resource constraints such as limited battery of the hand-held devices, it is important that a D2D network is able to cope up with the energy requirements to ensure network sustainability. In this chapter, we provide an overview of the techniques reported in the literature regarding the aforementioned challenges. Moreover, we also discuss some emerging trends and new aspects related to D2D networks such as energy harvesting and simultaneous wireless information and power transfer (SWIPT), pricing and incentive mechanisms and millimetre wave (mmWaves) spectrum. We conclude by providing emerging aspects with regards to D2D communication and delineate issues which require further research and analysis.
20 Coordinated multi-point for future networks: field trial results
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Wireless networks face big capacity challenges, struggling to meet ever increasing user data demands. Global mobile data traffic grew by 74% in 2015 and it is expected to grow 8-fold by 2020. Future wireless network will need to deploy massive number of small cells and improve spectral efficiency to cope with this increasing demand. Dense deployment of small cells will require advanced interference mitigation techniques to improve spectral efficiency and enhance much needed capacity. Coordinated multipoint (CoMP) is a key feature for mitigating inter-cell interference and to improve throughput and cell edge performance. In this chapter, we first provide the motivation for CoMP deployment from an operator perspective. Then, we discuss different types of CoMP schemes, their associated challenges and the third generation partnership project (3GPP) standardisation roadmap. Next, we provide insights into operational requirements for CoMP implementation and discuss potential solutions to enable cost-effective CoMP deployment. We then provide results for an intra-site uplink (UL) joint reception (JR) CoMP trial in a large Long-Term Evolution-Advanced (LTE-A) operator in the United Kingdom (UK) for three different deployment scenarios namely, dense, medium density and sparse deployment at macro layer. CoMP sets consist of co-located cells only with joint baseband processing units, and hence no backhaul is required for data exchange. On the other hand, interference between cells from different locations are not mitigated. Only two cells are allowed for coordination and interference rejection combining (IRC) is employed for joint processing. Trial performance is measured based on average network counters. Results show an average increase in signal-to-interference-plus-noise ratio (SINR) on physical uplink shared channel (PUSCH) by 5.56% which is then reflected in improved usage of higher modulation schemes and better UL user throughput. An average increase of 11.32% is observed on UL user throughput. Additionally, we discuss the limitations of the trialled CoMP scheme and suggest improvements for better CoMP gains. Furthermore, we review the evolution of CoMP into 5G and potential improvements CoMP can provide for some of the key 5G network objectives such as spectral efficiency, energy efficiency, load balancing and backhaul optimisation.
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Back Matter
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