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This book organizes principles and methods of signal processing and machine learning into the framework of coherence. The book contains a wealth of classical and modern methods of inference, some reported here for the first time. General results are applied to problems in communications, cognitive radio, passive and active radar and sonar, multi-sensor array processing, spectrum analysis, hyperspectral imaging, subspace clustering, and related. The reader will find new results for model fitting; for dimension reduction in models and ambient spaces; for detection, estimation, and space-time series analysis; for subspace averaging; and for uncertainty quantification. Throughout, the transformation invariances of statistics are clarified, geometries are illuminated, and null distributions are given where tractable. Stochastic representations are emphasized, as these are central to Monte Carlo simulations. The appendices contain a comprehensive account of matrix theory, the SVD, the multivariate normal distribution, and many of the important distributions for coherence statistics. The book begins with a review of classical results in the physical and engineering sciences where coherence plays a fundamental role. Then least squares theory and the theory of minimum mean-squared error estimation are developed, with special attention paid to statistics that may be interpreted as coherence statistics. A chapter on classical hypothesis tests for covariance structure introduces the next three chapters on matched and adaptive subspace detectors. These detectors are derived from likelihood reasoning, but it is their geometries and invariances that qualify them as coherence statistics. A chapter on independence testing in space-time data sets leads to a definition of broadband coherence, and contains novel applications to cognitive radio and the analysis of cyclostationarity. The chapter on subspace averaging reviews basic results and derives an order-fitting rule for determining the dimension of an average subspace. These results are used to enumerate sources of acoustic and electromagnetic radiation and to cluster subspaces into similarity classes. The chapter on performance bounds and uncertainty quantification emphasizes the geometry of the Cramèr-Rao bound and its related information geometry.
This dissertation investigates multiuser networks where the fading links experience unequal coherence conditions as well as dissimilar link CSI availability. It is shown that the disparity in coherence conditions for multiple users leads to a novel gain in the transmission rates compared with techniques that do not explicitly take advantage of this disparity. This gain is denoted coherence diversity and is demonstrated by product superposition transmission. First, a frequency-selective broadcast channel is considered, where two users have a disparity in coherence time and coherence bandwidth. This channel is analyzed under three broad scenarios of the disparity between the link qualities: when the disparity is in coherence time, in coherence bandwidth, and in both coherence time and coherence bandwidth. For each scenario, an analysis is provided and coherence diversity gain is demonstrated. The results are obtained in the framework of OFDM transmission covering a variety of pilot transmission schemes and different channel estimation techniques. Numerical simulations are presented to show coherence diversity gains. Second, coherence diversity is investigated in broadcast and multiple access channels with an arbitrary number of users. The users experience unequal fading block lengths, and CSI is not available. In the broadcast channel, product superposition is employed to find the achievable degrees of freedom. The case of multiple users experiencing fading block lengths of arbitrary ratio or alignment is studied. Also, in the multiple-access channel with unequal coherence times, achievable and outer bounds on the degrees of freedom are obtained. Third, a MISO broadcast channel is considered where some receivers experience longer coherence intervals and have CSIR, while some other receivers experience shorter coherence intervals and do not enjoy free CSIR. A variety of CSIT availability models is considered, including no CSIT, delayed CSIT, or hybrid CSIT. For each model, coherence diversity gains are merged with interference alignment and beamforming to achieve degrees of freedom. For several cases, inner and outer bounds are established that either partially meet, or the gap diminishes with increasing coherence times.
This SpringerBrief presents channel estimation strategies for the physical later network coding (PLNC) systems. Along with a review of PLNC architectures, this brief examines new challenges brought by the special structure of bi-directional two-hop transmissions that are different from the traditional point-to-point systems and unidirectional relay systems. The authors discuss the channel estimation strategies over typical fading scenarios, including frequency flat fading, frequency selective fading and time selective fading, as well as future research directions. Chapters explore the performance of the channel estimation strategy and optimal structure of training sequences for each scenario. Besides the analysis of channel estimation strategies, the book also points out the necessity of revisiting other signal processing issues for the PLNC system. Channel Estimation of Physical Layer Network Coding Systems is a valuable resource for researchers and professionals working in wireless communications and networks. Advanced-level students studying computer science and electrical engineering will also find the content helpful.
Multi-Carrier Techniques for Broadband Wireless Communications provides an accessible introduction to OFDM-based systems from a signal processing perspective. The first part presents a concise treatment of some fundamental concepts related to wireless communications and multicarrier systems, while the second offers a comprehensive survey of recent developments on a variety of critical design issues. These include synchronization techniques, channel estimation methods, adaptive resource allocation and practical schemes for reducing the peak-to-average power ratio of the transmitted waveform.
The issue of channel estimation in wireless communication systems is very crucial for coherent detection of the transmitted signal at the receiver end of the systems.Different techniques have been proposed in many books in a bid to obtain near-optimum channel state information for wireless communication systems. In this book, these techniques are reviewed and efficient channel estimation techniques for employment in Single Input Single Output (SISO) wireless communication systems, Single Input Single Output - Orthogonal Frequency Division Multiplexing (SISO-OFDM) Systems and Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems are proposed. The review of various channel estimation techniques and the proposed techniques presented in this book should be of great interest to both undergraduate and postgraduate students in the general field of telecommunication engineering systems. The professional engineers in the field of telecommunication engineering will also find this book useful in designing new communication equipments for wireless communication systems.
With rapid growth of digital communication in recent years, the need for high speed data transmission is increased. Moreover, future wireless systems are expected to support a wide range of services which includes video, data and voice. OFDM is a promising candidate for achieving high data rates in mobile environment, due to its resistance to ISI, which is a common problem found in high speed data communication. In OFDM, modulation may be differential or coherent. When using differential modulation there is no need for a channel estimate but its performance is inferior to the coherent system. Coherent modulation requires the channel estimation which gives better performance but with relatively more complex receiver structure. Training Symbol Assisted Modulation is used to achieve reliable channel estimates by transmitting Training along with data symbols. In this thesis, Shazib Naveed has analyzed different channel estimation patterns in terms of BER and propose a new scheme for transmitting Training symbols in wireless OFDM systems. Author has also proposed an adaptive scheme of channel estimation in wireless OFDM systems, which track the multi-path fading channel.
The emerging wireless communication systems, such as cellular communications systems and wireless net-works, are changing the life style nowadays dramatically. The prospect of modern wireless communication systems is very attractive by declaring the ability of ubiquitous access to information with high-quality and high-speed service. The Orthogonal Frequency Division Multiplexing (OFDM) technique is one promising candidate for the $4^{th}$ generation wireless systems, due to its merits of high flexibility and low equalization complexity for wideband wireless communication applications. To further enhance the communication system capacity and reliability, multiple antenna techniques can be integrated into OFDM systems. As a preliminary step, the physical characteristics of wideband radio channels and the channel modeling issue are addressed. The channel capacity with multiple antennas is presented by considering both cases of ideal and practical estimated channel state information (CSI) in the system. The fundamentals of the OFDM transmission technique are introduced. With the OFDM transmission structu-re the frequency-selective wideband radio channel is decomposed into a set of parallel subcarriers, and each subcarrier can be treated as a flat-fading narrowband channel. Several Multiple-Input-Multiple-Output (MIMO) technologies are discussed, in the scope of subcarrier-based MIMO encoding and decoding within the MIMO-OFDM transceiver structure, i.\ e.\ integrate the MIMO signal processing algorithms into a wideband OFDM system, where each OFDM subcarrier is regarded individually as a narrowband flat-fading subsystem with the Discrete Fourier Transform (DFT) and Inverse Discrete Fou-rier Transform (IDFT). The simulation results and analysis are presented under various radio channel condi-tions with ideal CSI. For practical reasons, channel estimation is necessary for coherent-detection MIMO-OFDM systems. The Pilot-based Channel Estimation (PBCE) schemes are implemented to evaluate the system performance with the realistically estimated CSI. With estimated CSI for MIMO encoding/decoding and data symbol detection, the system performance is reasonably degraded. The system performance results with estimated CSI are presented, and the impact of channel estimation errors is analyzed. In order to ensure a reliable and flexible data transmission in MIMO-OFDM systems, the indicator-based link adaptation procedure is employed to optimize the system throughput by selecting a proper Transmission Mode (TM) according to the instantaneous channel conditions. The Transmission Mode Selection (TMS) procedure with two-dimensional (2D) indicators is developed. A set of indicator candidates and their appro-ximation functions are proposed. With the indicator simulation results and the proposed TMS procedure for MIMO-OFDM systems, the average system throughput results are illustrated for both the conventional link adaptation method and the proposed 2D indicator-based TMS approach. Finally, the general system performance results of MIMO-OFDM systems are summarized. Arguments and suggestions are further made on how to design a MIMO-OFDM system in various wideband wireless com-munication applications.