%%-----------Chapters start-------------------------------------
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\chapter{Introduction}

In the area of multiple-input-multiple-output (MIMO) antenna arrays, it is often difficult to define mathematically or model all factors in a real-world environment. Thus, the reliability of simulations are limited by the accuracy of the models used~\cite{ZhBrFi05}. This thesis is part of a larger project called Communication Networks and Services Research (CNSR). The goal of this thesis is to develop a centrally controlled, reconfigurable, four-channel radio testbed which takes advantage of space-time techniques as well as new antenna spacing theories. This testbed will be used for experimental research in the areas of antenna system, algorithms, and radio channel estimation, to name a few. Furthermore, it will enable researchers to take advantage of the rapid prototyping capabilities of field programmable gate array (FPGA) technology, in order to better investigate their hypotheses.

\section{Background and Literature Review}

Currently, there is a great deal of academic and industrial interest in the area of MIMO radio systems. This movement stems from the throughput gains achieved through the use of multiple transmit and receive antennas, first demonstrated by Telatar~\cite{Te95}. Since that time, there have been many testbeds, and commercial systems alike, which make use of MIMO technology to increase throughput and reliability~\cite{ZhBrFi05,WaJeJe02,YoZh01}. Three testbeds in particular highlight the different types of testbeds currently in existence. The first is a four transmitter, four receiver testbed from the University of California, Los Angeles (2005) which is designed for indoor use, has a \legoReg robotic rail system to move the antennas along a fixed track, and is remotely controllable via the internet~\cite{ZhBrFi05}. The second system was built at Virginia Polytechnic in 2005. It consists of one transmitter and one receiver, and is designed for ultra wideband communication algorithm testing with sampling rates up to 8 giga-samples per second (GSPS)~\cite{AgAnAt05}. The third system, developed at McGill University in 2003, supports up to twelve transmitters and tweleve receivers and is built from COTS components which reside in a rack mount system.

Recent findings by Zhu et al.~\cite{ZhPeCo05} and Yanikomeroglu et al.~\cite{YaSo02} suggest that receive antennas should be separated by at least one signalling wavelength rather than some multiple of the carrier wavelength, in near line-of-sight (LOS) environments. According to Zhu, this leads to signalling wavelength antenna placement (SWAP) gain; Yanikomeroglu and Sousa called this the chiplength~\cite{YaSo02}.

\section{Thesis Contribution}

The goal of this thesis is to develop a centrally controlled, highly reconfigurable, four-channel radio testbed which takes advantage of space-time techniques as well as new antenna spacing theories. This testbed will be used to receive signals from commercial radio systems, to make radio channel measurements, and to enable researchers to take advantage of the rapid prototyping capabilities of FPGA technology, in order to better investigate their hypotheses.

The system is comprised of four transmitters and four receivers. A space-time (ST) receiver has been designed in order to distinguish amongst users and provide diversity gain. The receive antennas are separated by one signalling wavelength, in order to take advantage of SWAP gain. We used the 2.4~GHz industrial, scientific, and medical (ISM) band for this thesis with a 10~Mbps data rate, and a symbol rate of 5~Mega-Symbols Per Second (MSym/s). Based on signalling-wavelength-spaced antennas, this corresponds to receiver inter-antenna spacing of 60~meters (with 100\% excess bandwidth),

\begin{equation}
\begin{split}
\lambda_{g} &= \frac{c}{f_{g}}\\
&= \frac{3\times10^{8}}{5\times10^{6}}\\
&= 60~\mathrm{m}.
\end{split}
\end{equation}

In order to allow for more flexibility and to avoid having to create our own radio frequency (RF) front end, we have chosen suitable high-end radio receivers with 10.7~MHz intermediate frequency (IF) outputs, automatic gain control (AGC), and phase locking capabilities to interface to the system.

The MIMO testbed, developed in this thesis, will provide researchers with a rapid prototyping platform for algorithm analysis and radio channel measurements. The use of signalling-wavelength-spaced antennas affords the capability to explore the real-world effects of SWAP gain. However, this is merely one potential application of the testbed. The functionality of the testbed allows most, if not all, parameters to be modified. The antennas are physically repositionable, while many other parameters such as the carrier frequency, baseband processing, and RF front-end configuration are under centralized software control. Furthermore, the current hardware platform supports up to eight receive channels which could be useful for future work with Aliant's base station in the 1900 MHz range.

\autoref{tbl:testbedFeatureComparison} compares some of the main features of the testbed developed in this thesis to those of the existing testbeds outlined above.

\begin{table}
\begin{center}
\caption{Testbed Features Comparison} \label{tbl:testbedFeatureComparison}
\begin{tabular}{|c|c|c|c|c|c|}%[t]
%{@{\extracolsep{\fill}}|p{2.5cm}|p{1cm}|p{1cm}|p{1cm}|p{1cm}|p{1cm}|}
\hline
Feature & UCLA & VAP & McGill & UNB\\
\hline
\hline
Repositionable antennas & \checkmark & & & \checkmark\\
\hline
SWAP Gain & & & & \checkmark\\
\hline
Central Control & \checkmark & \checkmark & \checkmark & \checkmark\\
\hline
FPGA Based & \checkmark & \checkmark & \checkmark & \checkmark\\
\hline
Portable & & & & \checkmark\\
\hline
Num. of Channels & 4 & 1 & 12 & 4*\\
\hline
\end{tabular}
\end{center}
\end{table}

\noindent *Note: The system has been designed for seamless expansion with the addition of more FPGA boards and ADC boards.

\section{Thesis Structure}

The remainder of this document is broken down into four chapters. \autoref{chap:Design} describes the system requirements analysis, high-level design decisions, and the subsequent architecture design and hardware selection process. \autoref{chap:Implementation} outlines the details of the system implementation, and \autoref{chap:Testing} describes the development process along with the testing procedures used during the implementation of the system. \autoref{chap:Summary} summarizes the work completed in the thesis and outlines potential future work for the project.
