IQConverter.java

package de.tu.darmstadt.seemoo.ansian.tools;

import de.tu.darmstadt.seemoo.ansian.model.SamplePacket;

/**
 * <h1>AnSiAn - IQ Converter</h1>
 *
 * Module: IQConverter.java Description: This class implements methods to
 * convert the raw input data of IQ sources (bytes) to SamplePackets. It has
 * also methods to do converting and down-mixing at the same time.
 *
 * @author Dennis Mantz
 *
 *         Copyright (C) 2014 Dennis Mantz License:
 *         http://www.gnu.org/licenses/gpl.html GPL version 2 or higher
 *
 *         This library is free software; you can redistribute it and/or modify
 *         it under the terms of the GNU General Public License as published by
 *         the Free Software Foundation; either version 2 of the License, or (at
 *         your option) any later version.
 *
 *         This library is distributed in the hope that it will be useful, but
 *         WITHOUT ANY WARRANTY; without even the implied warranty of
 *         MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *         General Public License for more details.
 *
 *         You should have received a copy of the GNU General Public License
 *         along with this library; if not, write to the Free Software
 *         Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 *         02110-1301 USA
 */
public abstract class IQConverter {
	protected long frequency = 0; // Baseband frequency of the converted samples
									// (is put into the SamplePacket)
	protected int sampleRate = 0; // Sample rate of the converted samples (is
									// put into the SamplePacket)
	protected float[] lookupTable = null; // Lookup table to transform IQ bytes
											// into doubles
	protected float[][] cosineRealLookupTable = null; // Lookup table to
														// transform IQ bytes
														// into frequency
														// shifted doubles
	protected float[][] cosineImagLookupTable = null; // Lookup table to
														// transform IQ bytes
														// into frequency
														// shifted doubles
	protected int cosineFrequency; // Frequency of the cosine that is mixed to
									// the signal
	protected int cosineIndex; // current index within the cosine
	protected static final int MAX_COSINE_LENGTH = 500; // Max length of the
														// cosine lookup table

	public IQConverter() {
		generateLookupTable();
	}

	public long getFrequency() {
		return frequency;
	}

	public void setFrequency(long frequency) {
		this.frequency = frequency;
	}

	public int getSampleRate() {
		return sampleRate;
	}

	public void setSampleRate(int sampleRate) {
		if (this.sampleRate != sampleRate) {
			this.sampleRate = sampleRate;
			generateMixerLookupTable(cosineFrequency);
		}
	}

	protected int calcOptimalCosineLength() {
		// look for the best fitting array size to hold one or more full cosine
		// cycles:
		double cycleLength = sampleRate / Math.abs((double) cosineFrequency);
		int bestLength = (int) cycleLength;
		double bestLengthError = Math.abs(bestLength - cycleLength);
		for (int i = 1; i * cycleLength < MAX_COSINE_LENGTH; i++) {
			if (Math.abs(i * cycleLength - (int) (i * cycleLength)) < bestLengthError) {
				bestLength = (int) (i * cycleLength);
				bestLengthError = Math.abs(bestLength - (i * cycleLength));
			}
		}
		return bestLength;
	}

	public abstract int fillPacketIntoSamplePacket(byte[] packet, SamplePacket samplePacket);

	public abstract int mixPacketIntoSamplePacket(byte[] packet, SamplePacket samplePacket, long channelFrequency);

	protected abstract void generateLookupTable();

	protected abstract void generateMixerLookupTable(int mixFrequency);

}