Design of MIMO-OFDM systems for indoor wireless transmissions

This thesis is concerned with the use STC and SM techniques in MIMO orthogonal frequency division multiplexing (OFDM) wireless system over indoor frequency selective radio channel

A Practical Scheme for Frequency Offset Estimation in MIMO-OFDM Systems

This paper deals with training-assisted carrier frequency offset (CFO) estimation in multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. The exact maximum likelihood (ML) solution to this problem is computationally demanding as it involves a line search over the CFO uncertainty range. To reduce the system complexity, we divide the CFO into an integer part plus a fractional part and select the pilot subcarriers such that the training sequences have a repetitive structure in the time domain. In this way, the fractional CFO is efficiently computed through a correlation-based approach, while ML methods are employed to estimate the integer CFO. Simulations indicate that the proposed scheme is superior to the existing alternatives in terms of both estimation accuracy and processing load

Advanced Techniques for Frequency Synchronization in Multicarrier Transmissions

We are now facing a new information age with high demand of wireless communication systems. New services such as data and video require reliable high-speed transmissions over frequency-selective channels. Moreover, the radio spectrum, which is scarce and very expensive resource, must be allocated to many different applications and systems. Multicarrier communications based on orthogonal frequency division multiplexing (OFDM) have grown in popularity due to their ability to fulfill most of the requirements of such systems. However, among other problems, accurate frequency synchronization is a crucial issue for multicarrier systems as it is essential for reliable signal reception. This problem has received much attention in the last few years and several methods which deal with the frequency synchronization problem are available in literature. The aim of this thesis is to present novel advanced techniques for the frequency synchronization in multicarrier systems. In general terms, the main contribution of this dissertation is threefold. First, we address the problem of carrier frequency estimation for orthogonal frequency-division multiplexing (OFDM) systems in the presence of narrowband interference (NBI) with unknown power. This scenario is encountered in emerging spectrum sharing systems, where coexistence of different wireless services over the same frequency band may result into a remarkable co-channel interference. A second contribution comes from addressing the frequency synchronization in multiple-input multiple-output (MIMO) OFDM systems. In such systems accurate frequency synchronization in necessary in order to obtain the improvement in terms of capacity promised by the deployment of multiple antennas. Finally, the frequency synchronization in a multiuser OFDM network with space division multiple access (SDMA) is investigated in the last part. In this scenario, the main obstacle is the large number of parameters involved in the estimation process, which makes the multiuser synchronization a rather challenging task