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- Pitarokoilis, Antonios
(författare)
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On the performance of Massive MIMO systems with single carrier transmission and phase noise
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the last decade we have experienced a rapid increase in the demand for high data rates over cellular networks. This increase has been partly satisfied by the introduction of multi-user multiple-input multiple-output (MU-MIMO). In such systems, the base station (BS) is equipped with multiple antennas and the users share the time-frequency resources. However, modern communication systems are highly power inefficient. Further, the increase in demand for higher data rates is expected to accelerate in the years to come due to the popularity of mobile devices like smartphones and tablets. Hence, next generation cellular systems arerequired to exhibit high energy efficiency as well as low power consumption. Recently, it has been shown that the deployment of a large excess of base station (BS) antennas in comparison to the served users can be a promising candidate to meet these contradictory requirements. These systems are termed as Massive MIMO. When the number of BS antennas grows large, the channels between different users become orthogonal and low complexity transceiver processing exhibits sum-rate performance that is close to optimal. In order to realize the promised gains of Massive MIMO systems, it is required that power efficient and inexpensive components are used. In contemporary cellular systems, multi-carrier transmission is used since it facilitates simple equalization at the receiver side. However, multi-carrier signals exhibit high peak-to-average-power-ratio (PAPR) and require expensive highly linear power amplifiers. Power amplifiers in this regime are also very power inefficient. On the other hand single carrier signals exhibit lower PAPR and are suitable for signal design that is more robust to non-linear power amplifiers. Further, single-carrier signals are less vulnerable to hardware impairments, such as phase noise. In this thesis we study the fundamental limits of Massive MIMO systems in terms of sum-rate performance with single-carrier transmission and phase noise and provide important insight on the design of Massive MIMO under these scenarios.
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| 2. |
- Sandgren, Niclas, 1977-
(författare)
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Advanced Spectral Analysis with Applications
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spectral analysis has advanced the last decades as a signal processing tool to extract significant information about certain properties of measured data. The practical use of spectral analysis techniques in time-series analysis has been emphasized in the immense amount of previous literature in the field and by a rapidly growing number of applications. In this thesis, a variety of spectral analysis techniques are presented which address some fundamental problems in signal processing. The proposed methods are accompanied by several experimental and simulated data examples showing the advantages of the suggested approaches. The concept of spectral analysis is briefly introduced along with a condensed presentation of the area of magnetic resonance spectroscopy (MRS), which is an application area treated in several parts of the thesis. The technical contributions include several methods for frequency-selective analysis of exponentially damped sinusoidal signals, invocation of prior knowledge about the signal parameter relations in MRS multiplets for improved parametric spectral estimation, theoretical expressions for the lower error bounds on estimated signal parameters for damped sinusoidal components in the frequency-selective analysis framework, multichannel spectral analysis of MRS data, area-selective spectral analysis of two-dimensional data, spectral smoothing via cepstrum thresholding in one and two dimensions, and spectral analysis of irregularly sampled data. The majority of the presented techniques for magnetic resonance spectroscopy data are parametric methods where a certain amount of prior knowledge about the signal of interest is required, but alternative semi-parametric and non-parametric approaches are also suggested for some of the considered problems. The suggested cepstrum thresholding-based methods are non-parametric, and the analysis on unevenly sampled data contains a set of both non-parametric and parametric approaches.
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