diff options
Diffstat (limited to '')
| -rw-r--r-- | doc/thesis/chapters/conclusions.tex | 32 | ||||
| -rw-r--r-- | doc/thesis/chapters/implementation.tex | 28 |
2 files changed, 39 insertions, 21 deletions
diff --git a/doc/thesis/chapters/conclusions.tex b/doc/thesis/chapters/conclusions.tex index d71d58d..d7b8e8c 100644 --- a/doc/thesis/chapters/conclusions.tex +++ b/doc/thesis/chapters/conclusions.tex @@ -1,18 +1,34 @@ -% vim: set ts=2 sw=2 noet: +% vim: set ts=2 sw=2 noet spell: \chapter{Conclusions} \label{chp:conclusions} -The goal to build a functional demonstrator could be realized, unfortunately not with all futures as originally planned. A functional receiver and transmitter chain, for QPSK were implemented, -but the 16-QAM dosent work as hoped. +\section{Results} + +The goal to build a functional demonstrator had been achieved, unfortunately not all of the originally planned features were implemented. A stable wireless link using QPSK modulation that computes the BER was developed. + Some different typ of multiple fading model were tested and illustrated. -Two different Models for the simulation options are build. One discrete time model whish is basicly a FIR filter in the channel, the other with a statistical model which is based on a GR block. -And another file to implement the hardware with. Unfortunately it wasent possible to measure those models in a meaningful way. For that a least square approximation could be used as described in the further steps. An other difficulty is to reproduce the same effect in a simulation compare with the hardware, because of al the side effect of an environment, which cant be predicted in a simulation. +Two different Models for the simulation options are build. One discrete time model whish is basicly a FIR filter in the channel, the other with a statistical model which is based on a GR block. + +One other file to implement the hardware with. Unfortunately it was not possible to measure those in a meaningful way. For that a least square approximation could be used as described in the further steps. An other difficulty is to reproduce the same effect in a simulation compare with the hardware, because of al the side effect of the environment, which cant be predicted in a simulation. + +% TODO Mention QAM16 + +\section{Future Work} + +\subsection{Improve BER measurements and simulations} + +An interesting continuation of the current work could be to automate the collection of the BER data, and to measure and observe the influence of each parameters in the fading channel model. In addition, new flow graphs for further modulation schemes could be easily added to the current framework. + +\subsection{Improvements of GUI frontend} + +The current GUI prototype built with DearPyGUI has some issues, the most critical begin a single-threaded application. The interprocess communication (with GR's flow graphs) should be on a separate thread from the graphics. The problem is not noticeable as long as the flow graphs in the background keep sending data, but as soon as the UDP/IP data stream stops the timeout of the socket interface causes the interface to run at less that 20 frames per second. +In addition to fixing the aforementioned issue, a very important missing feature that is currently missing is the ability to change the fading parameters in real time from within the GUI. Dear PyGUI offers many graphical elements that could be used to control the parameters, however a new GR block would need to be created to propagate the updated values into the flow graph. +\subsection{Channel parameters estimation with Pilot Symbols} -\section{Further Steps} -To improve this project a simulation environment could be implementer, which can be replicated for more accurate measurements. So then it is possible to compare the simulation with the measurements. +\section{Closing words} -An other developnet basde on this project could be to show the BER with the help of a least Square approximation.(like in the paper) +\section{Acknowledgements} diff --git a/doc/thesis/chapters/implementation.tex b/doc/thesis/chapters/implementation.tex index 0863cf9..934b3a8 100644 --- a/doc/thesis/chapters/implementation.tex +++ b/doc/thesis/chapters/implementation.tex @@ -399,9 +399,9 @@ For generating the byte error rate it is focus on byte-blocks of a specific leng \subsection{Non modulated access codes} -Currently as described in section \ref{sec:data-frame}, the access codes are put as bytes in front of the frame in the \(k\)-byte preamble. For this to work, the access code bytes must still have a good autocorrelation function after being modulated into symbols using the chosen modulation scheme. This works well with QPSK, because the constellation is quite simple and the length of the sequence is only halved after the modulation (since QPKS has 2 bits per symbol). Thus in the QPSK flow graph, the longest known 13 bit Barker sequence \texttt{0x1f35} padded with zeros after MSB is sufficient (\(\approx 7\) symbols). +Currently as described in section \ref{sec:data-frame}, the access codes are put as bytes in front of the frame in the \(k\)-byte preamble. For this to work, the access code bytes must still have a good autocorrelation function after being modulated into symbols using the chosen modulation scheme. This works well with QPSK, because the constellation is quite simple and the length of the sequence is only halved after the modulation (since QPKS has 2 bits per symbol). Thus, in the QPSK flow graph the longest known Barker sequence \texttt{0x1f35} (13 bits, left padded with zeros) is sufficient (\(\approx 7\) symbols). -With QAM however, the complexity of the constellation and the higher number of bits per symbol makes it increasingly difficult to find binary sequences that after being modulated still retain a good autocorrelation function. A better solution would be to use for example a \emph{constant amplitude zero autocorrelation waveform} (CAZAC) of length \(N\), which is computed with +With QAM however, the complexity of the constellation and the higher number of bits per symbol makes it increasingly difficult to find binary sequences retain a good autocorrelation function after being modulated. A better solution would be to use for example a \emph{constant amplitude zero autocorrelation waveform} (CAZAC) of length \(N\), which is computed with \begin{equation} u_k = \exp\left(j\frac{M\pi K}{N}\right) \text{ where } K = \begin{cases} @@ -409,31 +409,33 @@ With QAM however, the complexity of the constellation and the higher number of b k(k+1) & \text{when } N \text{ is odd} \end{cases}, \end{equation} -and \(M\) is relatively prime to \(N\). CAZAC waveforms are ideal because they have a Dirac delta as autocorrelation\cite{Chu1972}, i.e. \(R_{uu}(\tau) = \delta(\tau)\). Though unfortunately, since these complex values are not on any constellation point they break some assumptions of the polyphase clock sync and the LMD DD equalizer (but not CMA). Thus to use CAZAC waveforms the transmitter needs to put them in front of the modulated symbols (for example using a correctly parametrized stream mux block in GR), and the receiver would need to synchronize with the sequence before the clock recovery or equalization. The latter is especially problematic because then it is no longer possible to identify the peak by comparing the autocorrelation value to a fixed threshold as done in section \ref{sec:implement-phasecorr}. +and \(M\) is relatively prime to \(N\) \cite{Chu1972}. CAZAC waveforms are ideal because they have a Dirac delta as autocorrelation \cite{Chu1972}, i.e. \(R_{uu}(\tau) = \delta(\tau)\). Though unfortunately, since these complex values are not on any constellation point they break some assumptions of the polyphase clock sync and the LMD DD equalizer (but not CMA). Thus to use CAZAC waveforms the transmitter needs to put them in front of the modulated symbols (for example using a correctly parametrized stream mux block in GR), and the receiver would need to synchronize with the sequence before the clock recovery or equalization. The latter is especially problematic because then it is no longer possible to identify the peak by comparing the autocorrelation value to a fixed threshold as done in section \ref{sec:implement-phasecorr}. +\subsection{Single threaded GUI application} -\subsubsection{GUI Parameter change} -%TODO: Picture of the GUI -As in \ref{sec:GUI} described the GUI was implemented, but unfortunately the parts where the parameter could be changed, will showing the current simulation isn`t possibl - like the noise voltage of the channel or the bandwidth from the Polyphase Clock , the Gain of the Equalizer aren`t implemented yet. Actually everything which needs a responds from the interfaces to the GR. - -The second part which is missing is to be able to change the timing plot for the different scattering plots. - -% TODO : Piczure of the setup -%TODO: Plots from the Hardware \subsection{Incomplete parts} -\subsubsection{Hardware clock} +\subsection{Clock synchronization issues} + Unfortunately the SDR needs an external clock generator. For that a Rubidium Frequency STd. Model FS725 is used. Better said two of them, to make them more movable and independent, with the clock frequency \SI{10}{\mega\hertz}. Those Rubidiums where used, because the synchronization, dosn`t work as planed in \ref{sec:preforming-implementation}. %TODO: Right squenz? Without those only the amplitudes could be seen in the Plots, with all the noise from the inter-symbol differences. +\subsection{GUI Parameter change} + +As in \ref{sec:GUI} described the GUI was implemented, but unfortunately the parts where the parameter could be changed, will showing the current simulation isn't possibl like the noise voltage of the channel or the bandwidth from the Polyphase Clock , the Gain of the Equalizer aren't implemented yet. Actually everything which needs a responds from the interfaces to the GR. + +The second part which is missing is to be able to change the timing plot for the different scattering plots. + +% TODO : Picture of the setup +% TODO: Plots from the Hardware \newgeometry{ top = 25mm, bottom = 25mm, inner = 15mm, outer = 15mm, } +% \section{Constellation plots} \begin{figure} \centering \label{fig:qpsk-simulations-static} |