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Widely distributed Mid-Neoproterozoic mafic rocks of the Qilian – Qaidam – East Kunlun region record the tectonic evolution of the northeastern Tibetan Plateau. This study presents whole-rock geochemistry, zircon U–Pb geochronology and Hf isotopes for the Xialanuoer gabbros of the central South Qilian Belt (SQB). Zircon laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb dating indicates that the gabbros were emplaced at ca. 738 Ma, indicating they are contemporaneous with mafic magmatism elsewhere in the northeastern Tibetan Plateau. The gabbros have low SiO2, Cr and Ni contents and Mg# values, are relatively enriched in light rare-earth elements (LREEs) and depleted in high-field-strength elements (HFSEs; e.g. Nb and Ta), have no positive Zr or Hf anomalies and have relatively high Nb/Ta but low Nb/La ratios. These data indicate that the Xialanuoer gabbros formed from calc-alkaline basaltic magmas that were originally generated by the partial melting of an enriched mantle of type-I (EMI-type) enriched region of the lithospheric mantle, underwent little to no crustal contamination prior to their emplacement, and have within-plate basalt geochemical affinities. Combining these data with the presence of widespread contemporaneous continental rift-related magmatism and sedimentation in the North Qilian, Central Qilian, South Qilian, Quanji, North Qaidam and East Kunlun regions suggests that the northeastern Tibetan Plateau underwent Mid-Neoproterozoic continental rifting, which also affected other Rodinian blocks (e.g. Tarim, South China, Australia, North America and Southern Africa).
This detailed, up-to-date introduction to heterogeneous cellular networking introduces its characteristic features, the technology underpinning it and the issues surrounding its use. Comprehensive and in-depth coverage of core topics catalogue the most advanced, innovative technologies used in designing and deploying heterogeneous cellular networks, including system-level simulation and evaluation, self-organisation, range expansion, cooperative relaying, network MIMO, network coding and cognitive radio. Practical design considerations and engineering tradeoffs are also discussed in detail, including handover management, energy efficiency and interference management techniques. A range of real-world case studies, provided by industrial partners, illustrate the latest trends in heterogeneous cellular networks development. Written by leading figures from industry and academia, this is an invaluable resource for all researchers and practitioners working in the field of mobile communications.
My name is Gordon Mansfield, and I currently serve as the elected chairman of the Small Cell Forum. The Forum is an industry body that promotes and drives the wide-scale adoption of small cell technologies to improve coverage, capacity and services delivered by mobile networks. I have many years of experience in the space, having previously served on the Femto Forum board from 2008-2010 and having led a tier one operators small cell effort since 2007. I consider it a great honor to be asked to write the foreword for this very informative book on small cells and heterogeneous networks. The authors are all highly respected researchers in academia and in industry, who have spent years working on the topics covered.
In recent years, small cells have become a very big topic when discussing mobile Internet and the tremendous data growth experienced over the past five years by operators around the globe. When we look at the recent history of data growth, some operators have experienced a 20,000 percent growth in data from 2007-2011. Combine that with the incredible forecast coming from all parts of the industry suggesting 10X and higher growth over the next four to five years, and it becomes clear that new ways to serve this data growth are necessary. We cannot continue to rely on new spectrum and advances in the air interface alone to sustain these types of data growth.
Compared with current cellular networks, next generation mobile networks are expected to encompass more sophisticated features, including the support of higher data transmission rates and user equipment (UE) mobility, location management, diversified service levels, etc. In order to accommodate these requirements, the 3rd Generation Partnership Project (3GPP) is devoted to the standardization of Long Term Evolution (LTE) and LTE-Advanced systems, which have been recognized as major candidates for the fourth-generation (4G) mobile networks. In LTE/LTE-Advanced systems, the network structure will be heterogeneous. How to maintain and improve mobility, handover (HO), and location management, while avoiding user experience deterioration, is a challenging task. In this chapter, we will study the mobility management challenge and illustrate advanced mobility management schemes.
In LTE/LTE-Advanced systems, the factors that make mobility, HO, and location management a challenging task are as follows
The rapid evolution of cellular networks results in the coexistence of multiple radio access technologies (RATs), e.g., Global System for Mobile Communications (GSM), Universal Mobile Telecommunication System (UMTS) and LTE/System Architecture Evolution (SAE). This demands optimized cooperation among multiple RATs to enable UEs to roam from one RAT to another.
The introduction of low-power nodes (LPNs) largely increases the total number of base stations (BSs), making the network structure and interference conditions more intricate. Thus, traditional mobility load balancing (MLB) and mobility management schemes need to be revisited to suit the new heterogeneous cellular network (HCN) architecture.
The complexity of LTE/LTE-Advanced systems leads to a large number of network parameters. Therefore, efforts need to be made in defining proper key performance indicators and developing optimization techniques for mobility management in various scenarios.
Nowadays, 50% of phone calls and 70% of data services are carried out indoors . For this reason, one may expect that operators' networks are optimized to provide good indoor coverage and capacity for voice, video, and high-speed data services. However, surveys have shown that 45% of households and 30% of businesses experience poor indoor coverage . This poor indoor coverage may lead to reduced subscriber loyalty and increased subscriber churn, which may significantly affect operators' revenues. As a consequence, vendors and operators are developing new solutions to address the indoor coverage problem.
A straightforward solution to enhance indoor coverage would be to increase the number of outdoor macrocell base stations (MBSs). Deploying a larger number of MBSs with a reduced cell radius may provide improved network coverage and capacity, but this approach is too expensive due to the high cost associated with MBSs. Moreover, this approach presents challenges in terms of site acquisition due to municipality and people's concerns about MBS towers . It is also very difficult to achieve high indoor signal quality when providing coverage from outdoors due to wall attenuation losses. Therefore, providing indoor coverage from outdoors is not the best solution.
As a result, indoor solutions such as distributed antenna systems (DASs) and picocells have become attractive alternatives to provide services in indoor hotspots, e.g., shopping malls and office buildings. These operator-deployed solutions improve in-building coverage, enhance signal quality, offload traffic from outdoor MBSs, and allow high-data-rate services due to the fact that transmitters are closer to receivers.
Driven by a new generation of wireless user equipments and the proliferation of bandwidth-intensive applications, mobile data traffic and network load are increasing in unexpected ways, and are straining current cellular networks to a breaking point. In this context, heterogeneous cellular networks, which are characterized by a large number of network nodes with different transmit power levels and radio frequency coverage areas, including macrocells, remote radio heads, microcells, picocells, femtocells and relay nodes, have attracted much momentum in the wireless industry and research community, and have also gained the attention of standardization bodies such as the 3rd Generation Partnership Project (3GPP) LTE/LTE-Advanced and the Institute of Electrical and Electronics Engineers (IEEE) Mobile Worldwide Interoperability for Microwave Access (WiMAX).
The impending worldwide deployments of heterogeneous cellular networks bring about not only opportunities but also challenges. Major technical challenges include the co-existence of various neighboring and/or overlapping cells, intercell interference and mobility management, backhaul provisioning, and self-organization that is crucial for efficient roll-outs of user-deployed low-power nodes. These challenges need to be addressed urgently to make the best out of heterogeneous cellular networks. This asks for a thorough revisit of contemporary wireless network technologies, such as network architecture and protocol designs, spectrum allocation strategies, call management mechanisms, etc. There is also an urgent need in the wireless industry, academia and even end-users to better understand the technical details and performance gains that heterogeneous cellular networks would make possible.
Mobile broadband demands are increasing rapidly, driven by the popularity of various connected mobile devices with data services, such as smartphones, tablets, vehicles, machines and sensors. The notion of connected devices actually expands to encompass basically everything that can take benefits from a wireless connection. A true mobile broadband experience of high quality everywhere can be expected by consumers in the near future.
Mobile applications have become an indispensable part of people's everyday life, with requirements on seamless access to social media, video contents and cloud-based contents anytime, anywhere. To provide services that meet these requirements is of top priority for operators with ambitions to be a key wireless communications provider in the networked society. These requirements can only bemet by mobile networks with sufficient capacity and coverage. Mobile broadband today is mainly provided via networks based on UMTS Terrestrial Radio Access (UTRA) or Evolved UTRA (E-UTRA), and solutions differ in the details. Mobile networks need to evolve through improving the existing mobile broadband networks and adding more cells in an optimal way to migrate to a heterogeneous cellular network (HCN). The migration path could be different for different operators. A thorough understanding of the various components involved is vital for a cost-efficient, spectrum-efficient and energy-efficient network evolution.
This chapter provides an introduction to the whole book. First, the need for more capacity and mobile broadband forecasts are discussed in Section 1.1.