PSK31 Demodulation (Kurt & Michael) - Revision history

Michael.vonpohle: /* PID Controller Problems */

2013-05-18T06:22:23Z

PID Controller Problems

← Older revision		Revision as of 23:22, 17 May 2013
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	In most cases, our guess frequency is within 0.2Hz of the actual frequency. As the guess frequency exceeds these bounds, the text decode becomes increasingly garbled.		In most cases, our guess frequency is within 0.2Hz of the actual frequency. As the guess frequency exceeds these bounds, the text decode becomes increasingly garbled.
	==== PID Controller Problems ====		==== PID Controller Problems ====
	The first iteration did not take into account the I component of the signal and was constantly trying to drive the signal to the positive I coordinates. A ~~smiple~~ if-else statement solved this problem. However there are some bugs. There might be a singularity at (0,0) which causes the controller to perform in a strange fashion. Also, the code has very bad noise rejection. It can produce baseband but not very well once noise is added. Finally, it doesn't decode signals that we generate ourselves. When we produce our signal in MATLAB, the code works fine. However, the signal from wikipedia.com and Dr. Frohne's signal don't work. One problem with the wikipedia.com signal is that it's native format is .ogg which is lossy. This could've presented problems when we convert the signal to a wave file as high frequencies get chopped in lossy formats.		The first iteration did not take into account the I component of the signal and was constantly trying to drive the signal to the positive I coordinates. A simple if-else statement solved this problem. However there are some bugs. There might be a singularity at (0,0) which causes the controller to perform in a strange fashion. Also, the code has very bad noise rejection. It can produce baseband but not very well once noise is added. Finally, it doesn't decode signals that we generate ourselves. When we produce our signal in MATLAB, the code works fine. However, the signal from wikipedia.com and Dr. Frohne's signal don't work. One problem with the wikipedia.com signal is that it's native format is .ogg which is lossy. This could've presented problems when we convert the signal to a wave file as high frequencies get chopped in lossy formats.

	==Authors==		==Authors==

Michael.vonpohle: /* Receiver */

2012-12-14T10:33:31Z

Receiver

← Older revision		Revision as of 03:33, 14 December 2012
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	<pre>		<pre>

	%% Mix and Filter		%% Mix and Filter

Michael.vonpohle: /* Receiver */

2012-12-14T10:32:42Z

Receiver

Show changes

Michael.vonpohle: /* Receiver */

2012-12-14T10:25:37Z

Receiver

← Older revision		Revision as of 03:25, 14 December 2012
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	<li>We run the signal through an FFT and take an average over the range of the FFT spike to obtain a carrier frequency guess.</li>		<li>We run the signal through an FFT and take an average over the range of the FFT spike to obtain a carrier frequency guess.</li>
			<pre>



			</pre>
	<li>A PID controller was implemented to help offset the fact that a carrier frequency derived from the FFT produces an inaccurate carrier frequency. An offset in the carrier frequency causes the constellation diagram to rotate in a circle. The PID tries to compensate for this by adding to or subtracting from the phase of the signal while trying to drive the Q-component of the signal to zero. The feedback loop is described by the code below.</li>		<li>A PID controller was implemented to help offset the fact that a carrier frequency derived from the FFT produces an inaccurate carrier frequency. An offset in the carrier frequency causes the constellation diagram to rotate in a circle. The PID tries to compensate for this by adding to or subtracting from the phase of the signal while trying to drive the Q-component of the signal to zero. The feedback loop is described by the code below.</li>
	<code>		<code>
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	<li>We multiply the signal with a cosine wave at our guess frequency. This splits the signal into two parts: a high frequency component (with frequency equal to the sum of the ''actual'' carrier frequency and our ''guess'' frequency) and a low frequency component (due to the difference of the two frequencies). </li>		<li>We multiply the signal with a cosine wave at our guess frequency. This splits the signal into two parts: a high frequency component (with frequency equal to the sum of the ''actual'' carrier frequency and our ''guess'' frequency) and a low frequency component (due to the difference of the two frequencies). </li>
	<li>We filter the multiplied signal through a butterworth filter with a 75Hz cutoff frequency to remove the high frequency component.<br/>[[File:K&M_Signal_Mixed_and_Filtered.png\|600px]]</li>		<li>We filter the multiplied signal through a butterworth filter with a 75Hz cutoff frequency to remove the high frequency component.<br/>[[File:K&M_Signal_Mixed_and_Filtered.png\|600px]]</li>
	<li>We mark the locations where the filtered signal changes sign. This identifies possible "sync" points where zeros in the signal may occur. [[File:K&M_Sync_Points.png\|600px]]</li>		<li>We mark the locations where the filtered signal changes sign. This identifies possible "sync" points where zeros in the signal may occur.<br/>[[File:K&M_Sync_Points.png\|600px]]</li>
	<li>We compare the length of time that occurs between each sync point with the baud rate to determine how many baud periods occur between each sync point. A single baud period indicates a zero. Each additional period over the first baud period indicates a one. (Ex. Three baud periods -> '110')</li>		<li>We compare the length of time that occurs between each sync point with the baud rate to determine how many baud periods occur between each sync point. A single baud period indicates a zero. Each additional period over the first baud period indicates a one. (Ex. Three baud periods -> '110')</li>
	<li>We send the resulting bit stream through a text decoder which translates the ones and zeros into a text message.</li>		<li>We send the resulting bit stream through a text decoder which translates the ones and zeros into a text message.</li>

Michael.vonpohle at 05:23, 14 December 2012

2012-12-14T05:23:04Z

← Older revision		Revision as of 22:23, 13 December 2012
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	<pre>		<pre>
	clear all		clear all

	close all		close all
	clc		clc
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	ylabel('Amplitude')		ylabel('Amplitude')
	movegui('northwest')		movegui('northwest')

	</pre>		</pre>

Michael.vonpohle: /* Transmitter */

2012-12-14T05:22:27Z

Transmitter

← Older revision		Revision as of 22:22, 13 December 2012
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	Our code creates a PSK31 signal given an input carrier frequency and message. For testing our receiver code, the transmitter is setup to generate a random carrier frequency and phase. It also adds random noise to the signal before writing it to a wav file.		Our code creates a PSK31 signal given an input carrier frequency and message. For testing our receiver code, the transmitter is setup to generate a random carrier frequency and phase. It also adds random noise to the signal before writing it to a wav file.
	<br/>		<br/>
	<pre>clear all		<pre>
			clear all

	close all		close all
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	xlabel('Time (s)')		xlabel('Time (s)')
	ylabel('Amplitude')		ylabel('Amplitude')
	movegui('northwest')</pre>		movegui('northwest')

			</pre>

	<br/>[[Image:K&M_PSK31Signal.png\|600px]]		<br/>[[Image:K&M_PSK31Signal.png\|600px]]

Michael.vonpohle: /* Receiver */

2012-12-14T05:21:55Z

Receiver

@@ Line 76: / Line 76: @@
 <ol>
 <li>We read in the signal from a wav file and generate utility variables and matrices.</li>
 <li>We run the signal through an FFT and take an average over the range of the FFT spike to obtain a carrier frequency guess.</li>
 <li>A PID controller was implemented to help offset the fact that a carrier frequency derived from the FFT produces an inaccurate carrier frequency. An offset in the carrier frequency causes the constellation diagram to rotate in a circle. The PID tries to compensate for this by adding to or subtracting from the phase of the signal while trying to drive the Q-component of the signal to zero. The feedback loop is described by the code below.</li>

Michael.vonpohle at 05:19, 14 December 2012

2012-12-14T05:19:10Z

@@ Line 15: / Line 15: @@
 Our code creates a PSK31 signal given an input carrier frequency and message. For testing our receiver code, the transmitter is setup to generate a random carrier frequency and phase. It also adds random noise to the signal before writing it to a wav file.
 <br/>
-<code>
+<pre>clear all
-Test Code
-</code>
+close all
 <br/>[[Image:K&M_PSK31Signal.png|600px]]

Michael.vonpohle at 05:05, 14 December 2012

2012-12-14T05:05:34Z

← Older revision		Revision as of 22:05, 13 December 2012
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	Our code creates a PSK31 signal given an input carrier frequency and message. For testing our receiver code, the transmitter is setup to generate a random carrier frequency and phase. It also adds random noise to the signal before writing it to a wav file.		Our code creates a PSK31 signal given an input carrier frequency and message. For testing our receiver code, the transmitter is setup to generate a random carrier frequency and phase. It also adds random noise to the signal before writing it to a wav file.
	<br/><code>		<br/>
			<code>
			Test Code

	</code>		</code>

Michael.vonpohle: /* Code Overview */

2012-12-14T05:02:35Z

Code Overview

← Older revision		Revision as of 22:02, 13 December 2012
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	== Our Approach ==		== Our Approach ==


	=== Code Overview ===		=== Code Overview ===

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	Our code creates a PSK31 signal given an input carrier frequency and message. For testing our receiver code, the transmitter is setup to generate a random carrier frequency and phase. It also adds random noise to the signal before writing it to a wav file.		Our code creates a PSK31 signal given an input carrier frequency and message. For testing our receiver code, the transmitter is setup to generate a random carrier frequency and phase. It also adds random noise to the signal before writing it to a wav file.
			<br/><code>



			</code>

	<br/>[[Image:K&M_PSK31Signal.png\|600px]]		<br/>[[Image:K&M_PSK31Signal.png\|600px]]