46 research outputs found
Spatial diversity in MIMO communication systems with distributed or co-located antennas
The use of multiple antennas in wireless communication systems has gained much attention during the last decade. It was shown that such multiple-input multiple-output (MIMO) systems offer huge advantages over single-antenna systems. Typically, quite restrictive assumptions are made concerning the spacing of the individual antenna elements. On the one hand, it is typically assumed that the antenna elements at transmitter and receiver are co-located, i.e., they belong to some sort of antenna array. On the other hand, it is often assumed that the antenna spacings are sufficiently large, so as to justify the assumption of independent fading. In this thesis, the above assumptions are relaxed. In the first part, it is shown that MIMO systems with distributed antennas and MIMO systems with co-located antennas can be treated in a single, unifying framework. In the second part this fact is utilized, in order to develop appropriate transmit power allocation strategies for co-located and distributed MIMO systems. Finally, the third part focuses on specific synchronization problems that are of interest for distributed MIMO systems
RECEIVER DESIGN AND PERFORMANCE ANALYSIS FOR COMMUNICATION CHANNELS WITH CARRIER PHASE NOISE AND FADING
Ph.DDOCTOR OF PHILOSOPH
Spatial modulation: theory to practice
Spatial modulation (SM) is a transmission technique proposed for multiple–input multiple–
output (MIMO) systems, where only one transmit antenna is active at a time, offering an increase
in the spectral efficiency equal to the base–two logarithm of the number of transmit
antennas. The activation of only one antenna at each time instance enhances the average bit
error ratio (ABER) as inter–channel interference (ICI) is avoided, and reduces hardware complexity,
algorithmic complexity and power consumption. Thus, SM is an ideal candidate for
large scale MIMO (tens and hundreds of antennas). The analytical ABER performance of SM
is studied and different frameworks are proposed in other works. However, these frameworks
have various limitations. Therefore, a closed–form analytical bound for the ABER performance
of SM over correlated and uncorrelated, Rayleigh, Rician and Nakagami–m channels is proposed
in this work. Furthermore, in spite of the low–complexity implementation of SM, there
is still potential for further reductions, by limiting the number of possible combinations by exploiting
the sphere decoder (SD) principle. However, existing SD algorithms do not consider
the basic and fundamental principle of SM, that at any given time, only one antenna is active.
Therefore, two modified SD algorithms tailored to SM are proposed. It is shown that the proposed
sphere decoder algorithms offer an optimal performance, with a significant reduction of
the computational complexity. Finally, the logarithmic increase in spectral efficiency offered
by SM and the requirement that the number of antennas must be a power of two would require
a large number of antennas. To overcome this limitation, two new MIMO modulation systems
generalised spatial modulation (GNSM) and variable generalised spatial modulation (VGSM)
are proposed, where the same symbol is transmitted simultaneously from more than one transmit
antenna at a time. Transmitting the same data symbol from more than one antenna reduces
the number of transmit antennas needed and retains the key advantages of SM.
In initial development simple channel models can be used, however, as the system develops it
should be tested on more realistic channels, which include the interactions between the environment
and antennas. Therefore, a full analysis of the ABER performance of SM over urban
channel measurements is carried out. The results using the urban measured channels confirm
the theoretical work done in the field of SM. Finally, for the first time, the performance of SM
is tested in a practical testbed, whereby the SM principle is validated
Spatial Modulation for Generalized MIMO:Challenges, Opportunities, and Implementation
A key challenge of future mobile communication research is to strike an attractive compromise between wireless network's area spectral efficiency and energy efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge, especially on multiple-input-multiple-output (MIMO) technologies. This motivates the proposal of an emerging wireless communications concept conceived for single-radio-frequency (RF) large-scale MIMO communications, which is termed as SM. The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communications, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless, and power-efficient communications. Furthermore, it has received sufficient research attention to be implemented in testbeds, and it holds the promise of stimulating further vigorous interdisciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field
Advanced Trends in Wireless Communications
Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics