11 research outputs found

    Massive MIMO ģ‹œģŠ¤ķ…œģ„ ģœ„ķ•œ ģ±„ė„ ģ¶”ģ • ė° ķ”¼ė“œė°± źø°ė²•

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    ķ•™ģœ„ė…¼ė¬ø (ė°•ģ‚¬)-- ģ„œģšøėŒ€ķ•™źµ ėŒ€ķ•™ģ› : ģ „źø°Ā·ģ»“ķ“Øķ„°ź³µķ•™ė¶€, 2017. 2. ģ“ģ •ģš°.To meet the demand of high throughput in next generation wireless systems, various directions for physical layer evolution are being explored. Massive multiple-input multiple-output (MIMO) systems, characterized by a large number of antennas at the transmitter, are expected to become a key enabler for spectral efficiency improvement. In massive MIMO systems, thanks to the orthogonality between different users' channels, high spectral and energy efficiency can be achieved through simple signal processing techniques. However, to get such advantages, accurate channel state information (CSI) needs to be available, and acquiring CSI in massive MIMO systems is challenging due to the increased channel dimension. In frequency division duplexing (FDD) systems, where CSI at the transmitter is achieved through downlink training and uplink feedback, the overhead for the training and feedback increases proportionally to the number of antennas, and the resource for data transmission becomes scarce in massive MIMO systems. In time division duplexing (TDD) systems, where the channel reciprocity holds and the downlink CSI can be obtained through uplink training, pilot contamination due to correlated pilots becomes a performance bottleneck when the number of antennas increases. In this dissertation, I propose efficient CSI acquisition techniques for various massive MIMO systems. First, I develop a downlink training technique for FDD massive MIMO systems, which estimates the downlink channel with small overhead. To this end, compressed sensing tools are utilized, and the training overhead can be highly reduced by exploiting the previous channel information. Next, a limited feedback scheme is developed for FDD massive MIMO systems. The proposed scheme reduces the feedback overhead using a dimension reduction technique that exploits spatial and temporal correlation of the channel. Lastly, I analyze the effect of pilot contamination, which has been regarded as a performance bottleneck in multi-cell massive MIMO systems, and propose two uplink training strategies. An iterative pilot design scheme is developed for small networks, and a scalable training framework is also proposed for networks with many cells.1 Introduction 1 1.1 Massive MIMO 1 1.2 CSI Acquisition in Massive MIMO Systems 3 1.3 Contributions and Organization 6 1.4 Notations 7 2 Compressed Sensing-Aided Downlink Training 9 2.1 Introduction 10 2.2 System Model 13 2.2.1 Channel Model 13 2.2.2 Downlink Channel Estimation 16 2.3 CS-Aided Channel Training 19 2.3.1 Training Sequence Design 20 2.3.2 Channel Estimation 21 2.3.3 Estimation Error 23 2.4 Discussions 26 2.4.1 Design of Measurement Matrix 26 2.4.2 Extension to MIMO Systems 27 2.4.3 Comparison to CS with Partial Support Information 28 2.5 Simulation Results 29 2.6 Conclusion 37 3 Projection-Based Differential Feedback 39 3.1 Introduction 40 3.2 System Model 44 3.2.1 Multi-User Beamforming with Limited Feedback 45 3.2.2 Massive MIMO Channel 47 3.3 Projection-Based Differential Feedback 48 3.3.1 Projection-Based Differential Feedback Framework 48 3.3.2 Projection for PBDF Framework 51 3.3.3 Efficient Algorithm 57 3.4 Discussions 58 3.4.1 Projection with Imperfect CSIR 58 3.4.2 Acquisition of Channel Statistics 61 3.5 Simulation Results 62 3.6 Conclusion 69 4 Mitigating Pilot Contamination via Pilot Design 71 4.1 Introduction 72 4.2 System Model 73 4.2.1 Multi-cell Massive MIMO Systems 74 4.2.2 Uplink Channel Training 75 4.2.3 Data Transmission 77 4.3 Iterative Pilot Design Algorithm 78 4.3.1 Algorithm 79 4.3.2 Proof of Convergence 81 4.4 Generalized Pilot Reuse 81 4.4.1 Concept of Pilot Reuse Schemes 81 4.4.2 Pilot Design based on Grassmannian Subspace Packing 82 4.5 Simulation Results 85 4.5.1 Iterative Pilot Design 85 4.5.2 Generalized Pilot Reuse 87 4.6 Conclusion 89 5 Conclusion 91 5.1 Summary 91 5.2 Future Directions 93 Bibliography 96 Abstract (In Korean) 109Docto

    Cooperative Radio Communications for Green Smart Environments

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    The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: ā€¢ Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environmentsā€¢ Measurements, characterization, and modelling of radio channels beyond 4G networksā€¢ Key issues in Vehicle (V2X) communicationā€¢ Wireless Body Area Networks, including specific Radio Channel Models for WBANsā€¢ Energy efficiency and resource management enhancements in Radio Access Networksā€¢ Definitions and models for the virtualised and cloud RAN architecturesā€¢ Advances on feasible indoor localization and tracking techniquesā€¢ Recent findings and innovations in antenna systems for communicationsā€¢ Physical Layer Network Coding for next generation wireless systemsā€¢ Methods and techniques for MIMO Over the Air (OTA) testin

    Cooperative Radio Communications for Green Smart Environments

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    The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: ā€¢ Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environmentsā€¢ Measurements, characterization, and modelling of radio channels beyond 4G networksā€¢ Key issues in Vehicle (V2X) communicationā€¢ Wireless Body Area Networks, including specific Radio Channel Models for WBANsā€¢ Energy efficiency and resource management enhancements in Radio Access Networksā€¢ Definitions and models for the virtualised and cloud RAN architecturesā€¢ Advances on feasible indoor localization and tracking techniquesā€¢ Recent findings and innovations in antenna systems for communicationsā€¢ Physical Layer Network Coding for next generation wireless systemsā€¢ Methods and techniques for MIMO Over the Air (OTA) testin

    A survey on reconfigurable intelligent surfaces: wireless communication perspective

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    Using reconfigurable intelligent surfaces (RISs) to improve the coverage and the data rate of future wireless networks is a viable option. These surfaces are constituted of a significant number of passive and nearly passive components that interact with incident signals in a smart way, such as by reflecting them, to increase the wireless system's performance as a result of which the notion of a smart radio environment comes to fruition. In this survey, a study review of RIS-assisted wireless communication is supplied starting with the principles of RIS which include the hardware architecture, the control mechanisms, and the discussions of previously held views about the channel model and pathloss; then the performance analysis considering different performance parameters, analytical approaches and metrics are presented to describe the RIS-assisted wireless network performance improvements. Despite its enormous promise, RIS confronts new hurdles in integrating into wireless networks efficiently due to its passive nature. Consequently, the channel estimation for, both full and nearly passive RIS and the RIS deployments are compared under various wireless communication models and for single and multi-users. Lastly, the challenges and potential future study areas for the RIS aided wireless communication systems are proposed

    Investigating the data rate in reconfigurable intelligent surfaces assisted wireless communication

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    In the realm of wireless communications, reconfigurable intelligent surfaces (RIS) offer network providers the capability to manage the behaviour of electromagnetic signals, encompassing their scattering, reflection, and refraction properties. Numerous research findings have underscored RISā€™s effectiveness in controlling wireless wave attributes, such as amplitude and phase, without necessitating intricate equalization and decoding at the receiverā€™s end. However, itā€™s crucial to note that configuring the surface in practical scenarios with frequency-selective fading channels should be carefully addressed across the entire bandwidth. This entails considering a wideband orthogonal frequency division multiplexing (OFDM) communication system that is based on a practical RIS configuration, involving distinct phase shifts for each element on the surface. In this thesis, we propose a communication setup to investigate the user data rate enhancement with the aid of RIS surface using practical phase shift model for multi-bit RIS phase resolutions. It is observed that the achievable data rate enhances with higher bit resolutions but the cost of hardware complexity. The effects of mutual coupling (MC) due to the large RIS surface and the electromagnetic interference (EMI) due to the unavoidable signals from external sources are well investigated on the performance data rate. The MC and EMI degrade the achievable rate so, the RIS must be aware of such signal impairment parameters. Furthermore, we have extended the study of the performance of the achievable data rate for multi-users in single-input-single-output (SISO) wideband based-RIS system with single antenna at the access point (AP) and each user. The propagation environment was assumed to have both line-of-sight (LoS) and non-line-of-sight (NLoS) channels so, it is more realistic and practical. Different RIS algorithms are studied in both LoS and NLoS channels scenarios taking into considerations the computational complexity and run time. The semidefinite relaxation scheme shows higher performance than the other schems but at the cost of computational complexity and run time consequently, the thesis proposes low complex with comparable performance iterative power method that adopts codebook approach. The RIS demonstrated significant performance data rate not only in communication but also in localization. The RIS-enabled localization has been investigated in the near and far-field regimes using realistic RIS phase shift model that considers the phase and amplitude variations. We introduced an analysis of Fisher information using a straightforward expression for the Fisher information matrix (FIM), illustrating how the position error bound (PEB) is influenced by the phase profiles of RIS. We employed three types of RIS phase profilesā€”random, directional, and positional configurationsā€”to showcase the impact of RIS on localization and communication within the near-field range. These profiles were designed considering both the amplitude and phase responses of the RIS, utilizing a practical phase-dependent amplitude model. The random profile ensures a uniform signal-to-noise ratio (SNR) across the deployment area, while the directional and positional profiles enhance SNR towards the userā€™s location. Additionally, we devised a straightforward localization scheme to simplify the maximum likelihood (ML) estimatorā€™s complexity. In the near-field region, the achievable data rate diminishes with distance, mirroring the gradual increase in localization error as distance from the RIS grows. Both the achievable data rate and localization error exhibit subpar performance when employing the RIS phase-dependent amplitude model with amplitude values less than one. Consequently, the widespread assumption of unity amplitude in the RIS phase shift model, as commonly seen in literature, leads to overly optimistic and inaccurate results in localization and communication performance. Simulation results have shown the importance of utilizing RIS technology in both communication and localization. Finally, we have carried out RIS measurements field in the mast lab to configure the test bed hardware of 64Ɨ64 RIS elements in order to show the capability of such new technology in improving the signal strength and coverage

    Antenna Systems

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    This book offers an up-to-date and comprehensive review of modern antenna systems and their applications in the fields of contemporary wireless systems. It constitutes a useful resource of new material, including stochastic versus ray tracing wireless channel modeling for 5G and V2X applications and implantable devices. Chapters discuss modern metalens antennas in microwaves, terahertz, and optical domain. Moreover, the book presents new material on antenna arrays for 5G massive MIMO beamforming. Finally, it discusses new methods, devices, and technologies to enhance the performance of antenna systems

    Resource Allocation and Positioning of Power-Autonomous Portable Access Points

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