Channel Estimation And Tracking For Mimo Ofdm Systems Using Em Algorithm

The desire to build lower cost analog front-ends has triggered interest in a new domain of research. Consequently the joint design of the analog front-end and of the digital baseband algorithms has become an important field of research. It enables the wireless systems and chip designers to more effectively trade the communication performance with the production cost. Digital Compensation for Analog Front-Ends provides a systematic approach to designing a digital communication system. It covers in detail the digital compensation of many non-idealities, for a wide class of emerging broadband standards and with a system approach in the design of the receiver algorithms. In particular, system strategies for joint estimation of synchronization and front-end non-ideality parameters are emphasized. The book is organized to allow the reader to gradually absorb the important information and vast quantity of material on this subject. The first chapter is a comprehensive introduction to the emerging wireless standards which is followed by a detailed description of the front-end non-idealities in chapter two. Chapter three then uses this information to explore what happens when the topics introduced in the first two chapters are merged. The book concludes with two chapters providing an in-depth coverage of the estimation and compensation algorithms. This book is a valuable reference for wireless system architects and chip designers as well as engineers or managers in system design and development. It will also be of interest to researchers in industry and academia, graduate students and wireless network operators. Presents a global, systematic approach to the joint design of the analog front-end compensation, channel estimation, synchronization and of the digital baseband algorithms Describes in depth the main front-end non-idealities such as phase noise, IQ imbalance, non-linearity, clipping, quantization, carrier frequency offset, sampling clock offset and their impact on the modulation Explains how the non-idealities introduced by the analog front-end elements can be compensated digitally Methodologies are applied to the emerging Wireless Local Area Network and outdoor Cellular communication systems, hence covering OFDM(A), SC-FDE and MIMO Written by authors with in-depth expertise developed in the wireless research group of IMEC and projects covering the main broadband wireless standards

Designing spectral efficient, high-speed wireless links that offer high quality- of-service and range capability has been a critical research and engineering challenge. In this thesis, we mainly address the complexity and performance issues of channel estimation and data detection in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems over time-varying channels. We derive the probability density function (pdf) expressions of the condition number (i.e., the maximum-to-minimum-singular-value ratio, MMSVR) of the channel state information matrix of MIMO OFDM systems. It is shown that this ratio is directly related to the noise enhancement in open-loop systems and provides a significant insight on the system capacity. A decision-directed (DD) maximum a posteriori probability (MAP) channel estimation scheme of MIMO systems is derived. Error performance of a zero- forcing receiver with the DD MAP and perfect channel estimates is provided and compared. This scheme has a low complexity and can be applied to time-varying Rayleigh fading channels with an arbitrary spaced-time correlation function. We propose an iterative channel estimation and data detection scheme for MIMO OFDM systems in the presence of inter-carrier-interference (ICI) due to the nature of time-varying channels. An ICI-based minimum-mean-square error (MMSE) detection scheme is derived. An expectation-maximization (EM) based least square (LS) channel estimator is proposed to minimize the mean-square error (MSE) of the channel estimates and to reduce the complexity of the implementation. With the estimate of the channel and initially detected symbols, ICI is estimated and removed from the received signal. Thus more accurate estimation of the channel and data detection can be obtained in the next iteration. An EM-based MAP channel estimator is derived by exploiting the frequency/time correlation of the pilot and data sub-carriers. Performance comparison is made between the proposed schemes and the ideal case - time-invariant channels and perfect channel estimation. We optimize the data transmission by exploiting the long term correlation characteristics. The transmitted data is successively detected without an error floor in spatially correlated channels. The algorithms proposed in this thesis allow low-complexity implementation of channel estimation and data detection for MIMO OFDM systems over time-varying fading channels, while providing good error performance.