我打算执行 FSK 解调并遇到了 Androino 项目（https://code.google.com/p/androino/source/browse/wiki/AndroinoTerminal.wiki），它将 Adruino 中的数据读入手机的音频杰克，这真是太酷了。
我正在尝试浏览代码，但我无法理解一些 impt 值。:((
为什么位高 = 22 个峰值，位低 = 6 个峰值，私有静态 int HIGH_BIT_N_PEAKS = 12 和私有静态 int LOW_BIT_N_PEAKS = 7？为什么每个编码位有 136 个样本？
我是否也正确地说 Adruino 的 FSK 速率设置为 315Hz？
我也附上了硬件（softTerm）代码：https://code.google.com/p/androino/source/browse/trunk/arduino/SoftTerm/SoftModem/SoftModem.h并且 cpp 文件也在那里. 邓恩有足够的声望点来发布这两个链接。
/** Copyright (C) 2011 Androino authors
Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.androino.ttt;
import android.util.Log;
public class FSKModule {
// Experimental results
// Arduino sends "a" character (97) 1100001
// The generated message is 0110.0001
// 136 samples per encoded bit
// total message = 166 bits: 155(high)+1(low)+8bit+stop(high)+end(high)
private static int SAMPLING_FREQUENCY = 44100; //Hz
private static double SAMPLING_TIME = 1.0/SAMPLING_FREQUENCY; //ms
// reading zero+155(high)+1(low)+8bit+stop+end+zero
private static int FREQUENCY_HIGH = 3150;
private static int FREQUENCY_LOW = 1575;
//high: 7 samples/peak
//low : 14 samples/peak
// 1492 samples/message low+8bits+stop+end
// 136 samples/bit (=1492/11)
private static int SAMPLES_PER_BIT = 136;
private static int ENCODING_SAMPLES_PER_BIT = SAMPLES_PER_BIT/2; // 68
// bit-high = 22 peaks
// bit-low = 6 peaks
private static int HIGH_BIT_N_PEAKS = 12;
private static int LOW_BIT_N_PEAKS = 7;
private static int SLOTS_PER_BIT = 4; // 4 parts: determines the size of the part analyzed to count peaks
private static int N_POINTS = SAMPLES_PER_BIT/SLOTS_PER_BIT; // 34=136/4
private static double PEAK_AMPLITUDE_TRESHOLD = 60; // significant sample (not noise)
private static int NUMBER_SAMPLES_PEAK = 4; // minimum number of significant samples to be considered a peak
private static int MINUMUM_NPEAKS = 100; // if lower it means that there is no signal/message
private static final int BIT_HIGH_SYMBOL=2;
private static final int BIT_LOW_SYMBOL=1;
private static final int BIT_NONE_SYMBOL=0;
private static final int CARRIER_MIN_HIGH_BITS=12;
private static final int SOUND_AMPLITUDE = 31000;
private static final String TAG = "FSKModule";
private FSKModule(){
}
private static void debugInfo(String message){
//System.out.println(">>" + message);
Log.w(TAG, "FSKDEC:"+ message);
}
//-----------------------------------------
// DECODING FUNCTIONS
//-----------------------------------------
public static boolean signalAvailable(double[] sound){
FSKModule m = new FSKModule();
int nPoints = N_POINTS;
int nParts = sound.length / nPoints;
int nPeaks = 0;
int startIndex = 0;
int i = 0;
do {
int endIndex = startIndex + nPoints;
int n = m.countPeaks(sound, startIndex, endIndex);
nPeaks += n;
i++;
startIndex = endIndex;
if (nPeaks > MINUMUM_NPEAKS) return true;
} while (i<nParts);
if (nPeaks >3)
debugInfo("signalAvailable() nPeaks=" + nPeaks);
return false;
}
public static int decodeSound(double[] sound){
FSKModule m = new FSKModule();
// processing sound in parts and
//Log.w(TAG, "ENTRO EN processSound");
int[] nPeaks = m.processSound(sound);
if (nPeaks.length == 0) // exit: no signal detected
return -1;
//debugInfo("decodeSound nPeaks=" + nPeaks.length);
// transform number of peaks into bits
//Log.w(TAG, "ENTRO EN parseBits");
int[] bits = m.parseBits(nPeaks);//-------------------------> OK!!
//debugInfo("decodeSound nBits=" + bits.length);
// extract message from the bit array
int message = m.decodeUniqueMessage(bits, sound, nPeaks);
debugInfo("decodeSound(): message="+message + ":" + Integer.toBinaryString(message));
return message;
}
private int decodeUniqueMessageCorrected(int[] nPeaks, int startBit){
int message = 0;
// process nPeaks starting from the end
int index = (startBit+12)*SLOTS_PER_BIT;
// find zero -> non zero transition
for (int i = 0; i < index; i++) {
int i2 = nPeaks[index-i];
int i1 = nPeaks[index-i-1];
debugInfo("zero->nonzero index=" + (index-i) + ": i2=" + i2 + ":i1=" + i1);
if ( (i1-i2)>2) {
index = index-i-1;
break;
}
}
debugInfo("zero->nonzero index=" + index);
int[] bits = new int[2+8+1+2];
for (int i = 0; i < bits.length; i++) {
int peakCounter = 0;
for (int j = 0; j < 4; j++) {
peakCounter += nPeaks[index-j];
}
debugInfo("decode corrected: peakCounter="+i + ":" + peakCounter);
if (peakCounter > 7) { //LOW_BIT_N_PEAKS)
bits[i] = BIT_LOW_SYMBOL;
}
if (peakCounter > 12) { //LOW_BIT_N_PEAKS)
bits[i] = BIT_HIGH_SYMBOL;
message += Math.pow(2, i);
}
debugInfo("bit=" + bits[i] + ":" + message);
index = index -4;
}
debugInfo("decode corrected: message="+message + ":" + Integer.toBinaryString(message));
message = 0;
for (int i = 2; i < 10; i++) {
if ( bits[i] == BIT_HIGH_SYMBOL) {
message+= Math.pow(2, 7-(i-2));
}
}
return message;
}
private int decodeUniqueMessage(int[] bits, double[] sound, int[] nPeaks){
// start bit
int index = findStartBit(bits, 0);
debugInfo("decodeUniqueMessage():start bit=" + index);
if (index == -1) return -1; // no start-bit detected
if (index + 8 + 2 > bits.length)
throw new AndroinoException("Message cutted, start bit at " + index, AndroinoException.TYPE_FSK_DECODING_ERROR);
// debugging information
int number = 16; // n bits to debug
for (int i = index-5; i < index-5+number; i++) {
debugInfo("decodeUniqueMessage(): bits=" + i +":" + bits[i] );
}
for (int i = 0; i < number*SLOTS_PER_BIT; i++) {
int position = i + (index-5)*SLOTS_PER_BIT ;
debugInfo("decodeUniqueMessage(): npeaks=" + position+ ":" + nPeaks[position] );
}
// 8bits message
int value = 0;
for (int i = 0; i < 8; i++) {
int bit = bits[index+i];
if (bit==BIT_HIGH_SYMBOL) value+=Math.pow(2, i);
}
// stop bit: do nothing
// end bit: do nothing
debugInfo("MESSAGE =" + Integer.toBinaryString(value) + ":" + value);
*/
int correctedMessage = decodeUniqueMessageCorrected(nPeaks,index);
debugInfo("MESSAGE corrected=" + Integer.toBinaryString(correctedMessage) + ":" + correctedMessage);
return correctedMessage;
}
private int findStartBit(int[] bits, int startIndex){
// find carrier and start bit
int index = startIndex;
int highCounter = 0;
boolean startBitDetected = false;
do {
int bit = bits[index];
switch (bit) {
case BIT_HIGH_SYMBOL:
highCounter++; // carrier high bit
break;
case BIT_LOW_SYMBOL:
if (highCounter>CARRIER_MIN_HIGH_BITS) { // start-bit detected
startBitDetected = true;
}
else highCounter = 0; // reset carrier counter
break;
case BIT_NONE_SYMBOL:
highCounter = 0;// reset carrier counter
break;
}
index++;
if (index>=bits.length) return -1;
} while (!startBitDetected);
return index;
}
private int[] parseBits(int[] peaks){
// from the number of peaks array decode into an array of bits (2=bit-1, 1=bit-0, 0=no bit)
//
int i =0;
int lowCounter = 0;
int highCounter = 0;
int nBits = peaks.length /SLOTS_PER_BIT;
int[] bits = new int[nBits];
//i = findNextZero(peaks,i); // do not search for silence
i = findNextNonZero(peaks,i);
int nonZeroIndex = i;
if (i+ SLOTS_PER_BIT >= peaks.length) //non-zero not found
return bits;
do {
//int nPeaks = peaks[i]+peaks[i+1]+peaks[i+2]+peaks[i+3];
int nPeaks = 0;
for (int j = 0; j < SLOTS_PER_BIT; j++) {
nPeaks+= peaks[i+j];
}
int position = i/SLOTS_PER_BIT;
bits[position] = BIT_NONE_SYMBOL;
debugInfo("npeaks:i=" + i + ":pos=" + position+ ": nPeaks=" + nPeaks);
if (nPeaks>= LOW_BIT_N_PEAKS) {
//Log.w(TAG, "parseBits NPEAK=" + nPeaks);
bits[position] = BIT_LOW_SYMBOL;
lowCounter++;
}
if (nPeaks>=HIGH_BIT_N_PEAKS ) {
bits[position] = BIT_HIGH_SYMBOL;
highCounter++;
}
//if (nPeaks>5) bits[position] = 1;
//if (nPeaks>12) bits[position] = 2;
i=i+SLOTS_PER_BIT;
} while (SLOTS_PER_BIT+i<peaks.length);
lowCounter = lowCounter - highCounter;
debugInfo("parseBits nonZeroIndex=" + nonZeroIndex);
debugInfo("parseBits lows=" + lowCounter);
debugInfo("parseBits highs=" + highCounter);
return bits;
}
private int findNextNonZero(int[] peaks, int startIndex){
// returns the position of the next value != 0 starting form startIndex
int index = startIndex;
int value = 1;
do {
value = peaks[index];
index++;
} while (value==0 && index<peaks.length-1);
return index-1;
}
private int[] processSound(double[] sound){
// split the sound array into slots of N_POINTS and calculate the number of peaks
int nPoints = N_POINTS;
int nParts = sound.length / nPoints;
int[] nPeaks = new int[nParts];
int startIndex = 0;
int i = 0;
int peakCounter = 0;
do {
int endIndex = startIndex + nPoints;
int n = this.countPeaks(sound, startIndex, endIndex);
nPeaks[i] = n;
peakCounter += n;
i++;
startIndex = endIndex;
} while (i<nParts);
//} while (startIndex+nPoints<sound.length);
debugInfo("processSound() peaksCounter=" + peakCounter);
if (peakCounter < MINUMUM_NPEAKS) {
nPeaks = new int[0];
}
return nPeaks;
}
private int countPeaks(double[] sound, int startIndex, int endIndex){
// count the number of peaks in the selected interval
// peak identification criteria: sign changed and several significant samples (>PEAK_AMPLITUDE_TRESHOLD)
int index = startIndex;
int signChangeCounter = 0;
int numberSamplesGreaterThresdhold = 0;
int sign = 0; // initialized at the first significant value
do {
double value = sound[index];
if (Math.abs(value)>PEAK_AMPLITUDE_TRESHOLD)
numberSamplesGreaterThresdhold++; //significant value
// sign initialization: take the sign of the first significant value
if (sign==0 & numberSamplesGreaterThresdhold>0) sign = (int) (value / Math.abs(value));
boolean signChanged = false;
if (sign <0 & value >0) signChanged = true;
if (sign >0 & value <0) signChanged = true;
if (signChanged & numberSamplesGreaterThresdhold>NUMBER_SAMPLES_PEAK){
signChangeCounter++; // count peak
sign=-1*sign; //change sign
}
index++;
//debugInfo(">>>>>>>index=" + index + " sign=" + sign + " signChangeCounter=" + signChangeCounter + " value=" + value + " numberSamplesGreaterThresdhold=" + numberSamplesGreaterThresdhold);
} while (index<endIndex);
return signChangeCounter;
}
}