Multi-carrier transmission techniques toward flexible and efficient wireless communication systems

制度:新 ; 文部省報告番号:甲2562号 ; 学位の種類:博士(国際情報通信学) ; 授与年月日:2008/3/15 ; 早大学位記番号:新470

Application of integer quadratic programming in detection of high-dimensional wireless systems

High-dimensional wireless systems have recently generated a great deal of interest due to their ability to accommodate increasing demands for high transmission data rates with high communication reliability. Examples of such large-scale systems include single-input, single-output symbol spread OFDM system, large-scale single-user multi-input multi-output (MIMO) OFDM systems, and large-scale multiuser MIMO systems. In these systems, the number of symbols required to be jointly detected at the receiver is relatively large. The challenge with the practical realization of these systems is to design a detection scheme that provides high communication reliability with reasonable computational complexity, even as the number of simultaneously transmitted independent communication signals becomes very large.^ Most of the optimal or near-optimal detection techniques that have been proposed in the literature of relatively low-dimensional wireless systems, such as MIMO systems in which number of antennas is less than 10, become problematic for high-dimensional detection problems. That is, their performance degrades or the computational complexity becomes prohibitive, especially when higher-order QAM constellations are employed.^ In the first part of this thesis, we propose a near-optimal detection technique which offers a flexible trade-off between complexity and performance. The proposed technique formulates the detection problem in terms of Integer Quadratic Programming (IQP), which is then solved through a controlled Branch and Bound (BB) search tree algorithm. In addition to providing good performance, an important feature of this approach is that its computational complexity remains roughly the same even as we increase the constellation order from 4-QAM to 256-QAM. The performance of the proposed algorithm is investigated for both symbol spread OFDM systems and large-scale MIMO systems with both frequency selective and at fading channels.^ The second part of this work focuses on a reduced complexity version of IQP referred to as relaxed quadratic programming (QP). In particular, QP is used to reformulate two widely used detection schemes for MIMO OFDM: (1) Successive Interference Cancellation (SIC) and (2) Iterative Detecting and Decoding (IDD). First, SIC-based algorithms are derived via a QP formulation in contrast to using a linear MMSE detector at each stage. The resulting QP-SIC algorithms offer lower computational complexity than the SIC schemes that employ linear MMSE at each stage, especially when the dimension of the received signal vector is high. Three versions of QP-SIC are proposed based on various trade-offs between complexity and receiver performance; each of the three QP-SIC algorithms outperforms existing SIC techniques. Second, IDD-based algorithms are developed using a QP detector. We show how the soft information, in terms of the Log Likelihood Ratio (LLR), can be extracted from the QP detector. Further, the procedure for incorporating the a-priori information that is passed from the channel decoder to the QP detector is developed. Simulation results are presented demonstrating that the use of QP in IDD offers improved performance at the cost of a reasonable increase in complexity compared to linear detectors

Low-Rank Channel Estimation for Millimeter Wave and Terahertz Hybrid MIMO Systems

Massive multiple-input multiple-output (MIMO) is one of the fundamental technologies for 5G and beyond. The increased number of antenna elements at both the transmitter and the receiver translates into a large-dimension channel matrix. In addition, the power requirements for the massive MIMO systems are high, especially when fully digital transceivers are deployed. To address this challenge, hybrid analog-digital transceivers are considered a viable alternative. However, for hybrid systems, the number of observations during each channel use is reduced. The high dimensions of the channel matrix and the reduced number of observations make the channel estimation task challenging. Thus, channel estimation may require increased training overhead and higher computational complexity. The need for high data rates is increasing rapidly, forcing a shift of wireless communication towards higher frequency bands such as millimeter Wave (mmWave) and terahertz (THz). The wireless channel at these bands is comprised of only a few dominant paths. This makes the channel sparse in the angular domain and the resulting channel matrix has a low rank. This thesis aims to provide channel estimation solutions benefiting from the low rankness and sparse nature of the channel. The motivation behind this thesis is to offer a desirable trade-off between training overhead and computational complexity while providing a desirable estimate of the channel

Advanced receivers and waveforms for UAV/Aircraft aeronautical communications

Nowadays, several studies are launched for the design of reliable and safe communications systems that introduce Unmanned Aerial Vehicle (UAV), this paves the way for UAV communication systems to play an important role in a lot of applications for non-segregated military and civil airspaces. Until today, rules for integrating commercial UAVs in airspace still need to be defined, the design of secure, highly reliable and cost effective communications systems still a challenging task. This thesis is part of this communication context. Motivated by the rapid growth of UAV quantities and by the new generations of UAVs controlled by satellite, the thesis aims to study the various possible UAV links which connect UAV/aircraft to other communication system components (satellite, terrestrial networks, etc.). Three main links are considered: the Forward link, the Return link and the Mission link. Due to spectrum scarcity and higher concentration in aircraft density, spectral efficiency becomes a crucial parameter for largescale deployment of UAVs. In order to set up a spectrally efficient UAV communication system, a good understanding of transmission channel for each link is indispensable, as well as a judicious choice of the waveform. This thesis begins to study propagation channels for each link: a mutipath channels through radio Line-of-Sight (LOS) links, in a context of using Meduim Altitude Long drones Endurance (MALE) UAVs. The objective of this thesis is to maximize the solutions and the algorithms used for signal reception such as channel estimation and channel equalization. These algorithms will be used to estimate and to equalize the existing muti-path propagation channels. Furthermore, the proposed methods depend on the choosen waveform. Because of the presence of satellite link, in this thesis, we consider two low-papr linear waveforms: classical Single-Carrier (SC) waveform and Extented Weighted Single-Carrier Orthogonal Frequency-Division Multiplexing (EW-SC-OFDM) waveform. channel estimation and channel equalization are performed in the time-domain (SC) or in the frequency-domain (EW-SC-OFDM). UAV architecture envisages the implantation of two antennas placed at wings. These two antennas can be used to increase diversity gain (channel matrix gain). In order to reduce channel equalization complexity, the EWSC- OFDM waveform is proposed and studied in a muti-antennas context, also for the purpose of enhancing UAV endurance and also increasing spectral efficiency, a new modulation technique is considered: Spatial Modulation (SM). In SM, transmit antennas are activated in an alternating manner. The use of EW-SC-OFDM waveform combined to SM technique allows us to propose new modified structures which exploit exces bandwidth to improve antenna bit protection and thus enhancing system performances

Interleaved frequency Division Multiple Access with Multiple Antennas and Block spreading for Mobile Broadband Communications

Ph.DDOCTOR OF PHILOSOPH

The deep space network

A report is given of the Deep Space Networks progress in (1) flight project support, (2) tracking and data acquisition research and technology, (3) network engineering, (4) hardware and software implementation, and (5) operations

Cooperative Partial Detection for MIMO Relay Networks

This paper was submitted by the author prior to final official version. For official version please see http://hdl.handle.net/1911/64372Cooperative communication has recently re-emerged as a possible paradigm shift to realize the promises of the ever increasing wireless communication market; how- ever, there have been few, if any, studies to translate theoretical results into feasi- ble schemes with their particular practical challenges. The multiple-input multiple- output (MIMO) technique is another method that has been recently employed in different standards and protocols, often as an optional scenario, to further improve the reliability and data rate of different wireless communication applications. In this work, we look into possible methods and algorithms for combining these two tech- niques to take advantage of the benefits of both. In this thesis, we will consider methods that consider the limitations of practical solutions, which, to the best of our knowledge, are the first time to be considered in this context. We will present complexity reduction techniques for MIMO systems in cooperative systems. Furthermore, we will present architectures for flexible and configurable MIMO detectors. These architectures could support a range of data rates, modulation orders and numbers of antennas, and therefore, are crucial in the different nodes of cooperative systems. The breadth-first search employed in our realization presents a large opportunity to exploit the parallelism of the FPGA in order to achieve high data rates. Algorithmic modifications to address potential sequential bottlenecks in the traditional bread-first search-based SD are highlighted in the thesis. We will present a novel Cooperative Partial Detection (CPD) approach in MIMO relay channels, where instead of applying the conventional full detection in the relay, the relay performs a partial detection and forwards the detected parts of the message to the destination. We will demonstrate how this approach leads to controlling the complexity in the relay and helping it choose how much it is willing to cooperate based on its available resources. We will discuss the complexity implications of this method, and more importantly, present hardware verification and over-the-air experimentation of CPD using the Wireless Open-access Research Platform (WARP).NSF grants EIA-0321266, CCF-0541363, CNS-0551692, CNS-0619767, EECS-0925942, and CNS-0923479, Nokia, Xilinx, Nokia Siemens Networks, Texas Instruments, and Azimuth Systems

Standardisation of preclinical PET/CT protocols across multiple research centres

Preclinical Positron Emission Tomography/Computed Tomography (PET/CT) is a well-established non-invasive imaging tool for studying disease development/progression, the development of novel radiotracers and pharmaceuticals for clinical applications. Over the last five years more than 8,200 preclinical studies using PET/CT were conducted. Despite this pivotal role, standardisation of preclinical PET/CT protocols, including CT absorbed dose guidelines, is essentially non-existent. Therefore, the first and second aims of this project were: (1) to quantitatively assess the variability of current preclinical PET and CT acquisition and reconstruction protocols in routine use across multiple centres and scanners; and (2) to propose optimized standardised acquisition and reconstruction PET/CT protocols for routine scanning procedures across all sites in a preclinical PET/CT laboratory. By assessing quantitative accuracy (known versus measured) and precision (reduced variability) of currently used routine protocols between five different sites/scanners (Bruker Albira, Mediso nanoPET/CT, Sedecal Super Argus, Siemens Inveon and Trifoil LabPET/CT), standard protocols were determined. Thereby, irrespective of scanner characteristics the least biased empirical quantitative and qualitative protocol results defined the standard protocol. In essence, neutralizing the manufacturers' difference, replacing scanner variability for scanner similarity to establish global standard protocols. The analysis of sites’ routine protocol results revealed significant quantitative differences between all five sites/scanners. Whereas the standard protocols put forth improved accuracy and precision across all sites. Additionally, the large disparity and measured amounts of CT absorbed ionising radiation amongst sites brought to light the lack of preclinical radiation guidelines and dose regulations. Unregulated CT radiation dose is of great concern. CT ionising radiation is known to have biological adverse effects. Thus, overexposure of radiation will potentially cause unnecessary animal suffering and confound research outcomes. Overall, the proposed standard CT protocol reduced radiation doses. The implementation of preclinical PET/CT standardised protocols, developed and tested in this project, will provide more robust, reliable and reproducible translational data sets for clinical applications. In accordance with the National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs) objectives, the refinement of PET/CT protocols and reduction of CT absorbed dose impacts animal welfare positively and potentially reduces the number of animals used. Reducing study variability in site and across sites through standardisation of protocols improves statistically significant results using less animals. For study specific imaging parameters in preclinical PET/CT rodents are commonly used to design the protocol. The third aim of this project strives to develop a tissue equivalent material (TEM) anthropomorphic rodent phantom for the replacement of animals when designing and optimizing varying in vivo rodent imaging protocols. Using a TEM phantom reduces potential biological experimental variability caused by the animals and increases reproducibility of findings. To address this aim, twenty-four commercially available 3D printing materials were X-rayed for the evaluation Hounsfield units (HU). A comparison of calculated 3D material attenuation coefficients and accepted tissue attenuation coefficient was also done. CT images were acquired using four CT protocols and the developed standard CT protocol. Based on measured material HUs compared to accepted tissue/organ HU values, four materials were chosen for testing and further evaluation in a 3D printed phantom prototype was undertaken. In order to obtain the anatomical features of the rodent a CT acquisition of a scheduled 1 rodent was acquired. The CT images were used for the 3D printing design. A 3D printed (TEM) anthropomorphic rodent phantoms was printed and tested. Measured HU analysis of the phantom TEM materials shows promise as a replacement strategy. This imaging protocol optimisation approach is also in line with the NC3Rs objective of replacing and/or avoiding the use animals