| 1. |
- Almers, Peter, et al.
(författare)
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Exercises
- 2005
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Ingår i: Wireless Communications. - 9780470848883 - 047084888X - 0470848871 ; , s. 561-593
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Alayon Glazunov, Andres, et al.
(författare)
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On the Physical Limitations of the Interaction of a Spherical Aperture and a Random Field
- 2011
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Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 59:1, s. 119-128
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Tidskriftsartikel (refereegranskat)abstract
- This paper derives physical limitations on the interactions of antennas exciting TM or TE modes (but not both) and wireless propagation channels. The derivation is based on the spherical vector wave expansion of the electromagnetic field outside a sphere circumscribing the antennas. The result is an extension of the seminal work of Chu on the classical limitations on maximum antenna gain and radiation Q. Rather than maximizing antenna gain in a single direction we obtain physical limitations on the antenna gain pattern, which is directly translated to more condensed parameters, i.e., the instantaneous effective gain G(i) and the mean effective gain G(e) if instantaneous realizations or correlation statistics of the expansion coefficients of the electromagnetic field are known, spectively. The obtained limitations are on the maximum of G(i)/Q and G(e)/Q, which establish a trade-off between link gain and Q.
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| 3. |
- Khan, Muhammad Gufran, et al.
(författare)
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Measurements and Analysis of UWB Channels in Industrial Environments
- 2005
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Konferensbidrag (refereegranskat)abstract
- Communication in industrial environments is an important scenario for ultra wideband (UWB) systems. The characteristics of this environment differ considerably from office environments, where most of the channel measurements reported in the literature are performed. In this paper, we present the results and analysis of UWB channel measurements in an industrial environment. We investigate both peer-to-peer non-line-of-sight (P-P NLOS) and base station NLOS (BS NLOS) scenarios. The measurements are performed in the frequency range 3.1 to 8 GHz, at distances 2-16 m, using a vector network analyzer in conjunction with virtual antenna arrays. From these measurements, we extract channel model parameters such as power delay profiles, pathloss exponents, rms delay spread and the percentage of energy captured by RAKE receivers with a finite number of fingers. In addition, Saleh- Valenzuela parameters such as ray and cluster power decay constants and distribution of cluster interarrival times are extracted.
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| 4. |
- Miller, Chelsea L, et al.
(författare)
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Favorable Propagation with User Cluster Sharing
- 2020
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Ingår i: 2020 IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC). - 9781728144900
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Konferensbidrag (refereegranskat)abstract
- We examine the favorable propagation (FP) behavior of a massive multi-user multiple-input-multiple-output (MU-MIMO) system equipped with a uniform linear array (ULA), horizontal uniform rectangular array (HURA) or uniform circular array (UCA) using a ray-based channel model with user cluster sharing. We demonstrate FP for these systems and provide analytical expressions for the mean-squared distance (MSD) of the FP metric from its large-system limit for each of the aforementioned topologies. We use these results to examine the detrimental effects of user cluster sharing on FP behavior, and demonstrate the superior performance of the ULA as compared to the UCA and the HURA with equal inter-element spacing. Although cluster sharing has a negative impact on FP for finite arrays, we additionally examine the asymptotic rate of convergence to FP as a function of array size and show that this rate is unchanged with or without user cluster sharing.
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| 5. |
- Tataria, Harsh, et al.
(författare)
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6G Wireless Systems: Vision, Requirements, Challenges, Insights, and Opportunities
- 2021
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Ingår i: Proceedings of the IEEE. - 0018-9219. ; 109:7, s. 1166-1199
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Tidskriftsartikel (refereegranskat)abstract
- Mobile communications have been undergoing a generational change every ten years or so. However, the time difference between the so-called "G's" is also decreasing. While fifth-generation (5G) systems are becoming a commercial reality, there is already significant interest in systems beyond 5G, which we refer to as the sixth-generation (6G) of wireless systems. In contrast to the already published papers on the topic, we take a top-down approach to 6G. More precisely, we present a holistic discussion of 6G systems beginning with lifestyle and societal changes driving the need for next generation networks. This is followed by a discussion into the technical requirements needed to enable 6G applications, based on which we dissect key challenges, as well as possibilities for practically realizable system solutions across all layers of the Open Systems Interconnection stack (i.e., from applications to the physical layer). Since many of the 6G applications will need access to an order-of-magnitude more spectrum, utilization of frequencies between 100 GHz and 1 THz becomes of paramount importance. As such, the 6G eco-system will feature a diverse range of frequency bands, ranging from below 6 GHz up to 1 THz. We comprehensively characterize the limitations that must be overcome to realize working systems in these bands; and provide a unique perspective on the physical, as well as higher layer challenges relating to the design of next generation core networks, new modulation and coding methods, novel multiple access techniques, antenna arrays, wave propagation, radio-frequency transceiver design, as well as real-time signal processing. We rigorously discuss the fundamental changes required in the core networks of the future, such as the redesign or significant reduction of the transport architecture that serves as a major source of latency for time-sensitive applications. This is in sharp contrast to the present hierarchical network architectures, which are not suitable to realize many of the anticipated 6G services. While evaluating the strengths and weaknesses of key candidate 6G technologies, we differentiate what may be practically achievable over the next decade, relative to what is possible in theory. Keeping this in mind, we present concrete research challenges for each of the discussed system aspects, providing inspiration for what follows.
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| 6. |
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| 7. |
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| 8. |
- Huang, Chen, et al.
(författare)
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Artificial intelligence enabled radio propagation for communications – Part I: Channel characterization and antenna-channel optimization
- 2022
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 70:6, s. 3939-3954
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Forskningsöversikt (refereegranskat)abstract
- To provide higher data rates, as well as better coverage, cost efficiency, security, adaptability, and scalability, the 5G and beyond 5G networks are developed with various artificial intelligence techniques. In this two-part paper, we investigatethe application of artificial intelligence (AI) and in particular machine learning (ML) to the study of wireless propagation channels. It firstly provides a comprehensive overview of ML for channel characterization and ML-based antenna-channel optimization in this first part, and then it gives a state-of-the-art literature review of channel scenario identification and channel modeling in Part II. Fundamental results and key concepts of ML for communication networks are presented, and widely used ML methods for channel data processing, propagation channel estimation, and characterization are analyzed and compared. A discussion of challenges and future research directions for ML-enabled next generation networks of the topics covered in this part rounds off the paper.
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| 9. |
- Tataria, Harsh, et al.
(författare)
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Standardization of Propagation Models for Terrestrial Cellular Systems: A Historical Perspective
- 2020
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Ingår i: International Journal of Wireless Information Networks. - : Springer Science and Business Media LLC. - 1068-9605 .- 1572-8129.
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Tidskriftsartikel (refereegranskat)abstract
- Propagation models constitute a fundamental building block of wireless communications research. Before we build and operate real systems, we must understand the science of radio propagation, and develop channel models that both reflect the important propagation processes and allow a fair comparison of different systems. In the past five decades, wireless systems have gone through five generations, from supporting voice applications to enhanced mobile broadband. To meet the ever increasing data rate demands of wireless systems, frequency bands covering a wide range from 800 MHz to 100 GHz have been allocated for use. The standardization of these systems started in the early/mid 1980s in Europe by the European Telecommunications Standards Institute with the advent of Global System for Mobile Communications. This motivated the development of the first standardized propagation model by the European Cooperation in Science and Technology (COST) 207 working group. These standardization activities were continued and expanded for the third, fourth, and fifth generations of COST, as well as by the Third Generation Partnership Project, and the International Telecommnunication Union. This paper presents a historical overview of the standardized propagation models covering first to fifth-generation systems. In particular, we discuss the evolution and standardization of pathloss models, as well as large and small-scale fading parameters for single antenna and multiple antenna systems. Furthermore, we present insights into the progress of deterministic modelling across the five generations of systems, as well as discuss more advanced modelling components needed for the detailed simulations of millimeter-wave channels. A comprehensive bibliography at the end of the paper will aid the interested reader to dig deeper.
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| 10. |
- Osseiran, Afif, 1972-
(författare)
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Advanced Antennas in Wireless Communications : co-located & distributed
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a wireless radio network system, with an evolving standard, there is a need to increase system capacity due to the increase in the traffic demands, the higher data rate usage, and the need to further extend the coverage of the system. One possible solution is to use multiple antennas (co-located or distributed) for the radio links. The aim of this thesis is to estimate the capacity gain for these advanced antenna scenarios in comparison to the ones in current use (e.g. single antenna in a 3-sector site) with special emphasis on transmit diversity and beamforming techniques. The quantification of such gain is mainly performed, evaluated and analyzed in dynamic system simulators with an accurate interference modeling. A generalized Signal to Interference Noise Ratio (SINR) estimation for a MIMO DS-CDMA system is derived, and as a by-product a closed-form solution of the orthogonality factor is obtained. Moreover the effectiveness of an antenna system is evaluated in a MIMO-test bed. Transmit diversity (TXDiv) is evaluated in WCDMA systems for flat fading (i.e. Pedestrian A (PedA)) and frequency selective channels (i.e. Typical Urban (TU)). While in flat fading channels, TXDiv schemes such as Space Time Transmit Diversity (STTD) and Closed Loop Mode 1 (CL1) offer a substantial system capacity gain, the gain is negligible in frequency selective channels. In HSDPA systems, TXDiv offers negligible gain in flat fading channels and causes a significant loss in frequency selective channels. The loss is mainly due to random spatial interference patterns (the so called Flashlight Effect), that are present in the HSDPA system. A simple scheme that mitigates this phenomena is presented. The scheme yields a 70% gain for CL1 in a PedA channel, while 10% gain is observed in the TU channel. The introduction of beamforming in WCDMA systems leads to a substantial system capacity and coverage gain. Three different implementations are evaluated and analyzed: Higher Order Sectorization (HOS), Fixed Beams (FB) with S-CPICH as a phase reference and finally FB as P-CPICH as a phase reference. Further, the impact of angular spread, the interaction and impact of radio resource management as power tuning of the common channel, scrambling code allocation technique, admission control, handovers and various antenna configurations are analyzed. The 12-sector sites yield the best system capacity gain in comparison to 3-sector sites equipped with a single antenna, slightly more than a 3-sector sites equipped with 4 FB each. In HSDPA systems, FB offers an impressive capacity gain, up to 200% for a 4 FB system. Capacity estimations with a dynamic system simulator give a clear indication about the gain of the simulated system, but the robustness of any method have to be verified through test-beds. STTD with receive diversity is implemented and tested in a real-time DSP MIMO test-bed for a single carrier frequency domain equalization system. A new pilot structure for joint Carrier Frequency Offset (CFO) and channel estimation is proposed and evaluated to address the inter-symbol interference and the severe CFO due to hardware impairments. The new pilot scheme results in significant reduction of the required overhead signalling compared to previous schemes. Instead of having antennas co-located and connected to the same radio unit (i.e. BS or UE), antennas can be distributed but having the potential to cooperate together. Furthermore, the system provides a macro-diversity gain and also relaxes the hardware complexity at the BS and/or UE. Two novel methods that provide frequency and spatial diversity are proposed. The first one called Relay Cyclic Delay Diversity (RCDD), provides frequency and spatial diversity for a multihop system while requiring a lower overhead than the methods proposed in the literature. RCDD yields a high SINR gain which translates into a substantial cell throughput gain in comparison to a single hop system. The second method called two dimensional cyclic prefix (2D-CP), introduces artificial time diversity and requires only a single transmission phase for each direction in a cooperative relaying wireless communication system. Besides not requiring an antenna specific pilots, the 2D-CP provides a substantial data rate increase.
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