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Chapter 1
Introduction
The multiple-input multiple-output systems (MIMO) are systems, where both transmitter and receiver are provided with more than one antenna (see Figure 1.1). They provoke a lot of interest because, as we will see, they allow to improve performances of a wireless communication system in comparison with the traditional scenery, where both transmitter and receiver are provided of only one antenna (single-input single-output systems, SISO).
In particular, under the same available band and transmit power, the MIMO systems guarantee the possibility or to increase the information rate (spectral efficiency) or to improve the error probability (energetic efficiency) or to realize a combination of these two effects. It is straightforward as these properties are ever more important in a context in which the available band is subdivided among a lot of users who have constraints on the maximum tolerable error probability and available power.
In practice the performance gain can be achieved using two strategies, that are spatial multiplexing (SM) and space-time coding (STC).
The SM techniques exploit the degrees of freedom provided from the multiple transmit antennas in order to transmit more independent data streams and therefore increasing the spectral efficiency of the system.
The STC techniques exploit the degrees of freedom provided from the multiple antennas to transmit the same signal on the maximum possible number of independent parallel channels maximizing the spatial diversity and therefore increasing the energetic efficiency of the system.
2 Figure 1.1. Schematic representation of a MIMO wireless system.
1.1 Overview of the thesis
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.
In particular for the uplink (from mobile station to base station), we make use of spatial multiplexing techniques at the transmitter and investigate the performance of several single-user data detection strategies.
Otherwise for the downlink (from base station to mobile station), we investigate different transmit space-time diversity coding techniques.
The thesis is organized as follows.
Chapter 2: we give an overview of the SISO and MIMO channel models
Chapter 3: this Chapter concerns the diversity and the role of diversity in improving
the performances of a wireless system. We aim at demonstrating the improvement in terms of energetic efficiency of a system that uses multiple antennas in conjunction with diversity techniques over a SISO system.
Chapter 4: here we provide the channel capacity expression of multiple-input
MIMO systems, assuming channel knowledge only at the receiver. The objective of this Chapter is to demonstrate the improvement in terms of spectral efficiency of a MIMO system over a SISO system.
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Chapter 5: this Chapter provides an overview of the basic principles of OFDM.
Chapter 6: this Chapter concerns the performance of spatial multiplexing techniques
in a MIMO-OFDM system and provides the simulation results for several data detection strategies over an indoor frequency selective wireless channel model.
Chapter 7: here we investigate different transmit space-time coding techniques for a
MIMO-OFDM system. In particular, we provide the simulation results of space-time block coding (STBC) and delay diversity over an indoor frequency selective wireless channel model.
