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Project中主要的程式碼在這幾個檔案中，控制聲波傳送的程式碼主要在MainActivity.java和SoundPlayer.java中。

SoundPlayer.java

void genTone(){
        // fill out the array
        for (int i = 0; i < numSamples; ++i) {

            sample[i]=0;
              for(int j=0;j<numfreq;j++) {
                sample[i] =sample[i]+ Math.cos(2 * Math.PI * i / (sampleRate / (freqOfTone[j])));//第i個取樣點，t為i/sampleRate
            }
            sample[i]=sample[i]/numfreq;
        }

        // convert to 16 bit pcm sound array
        // assumes the sample buffer is normalised.
        int idx = 0;
        for (final double dVal : sample) {
            // scale to maximum amplitude
            final short val = (short) ((dVal * 30000));//加振幅，加音量
            // in 16 bit wav PCM, first byte is the low order byte
            generatedSound[idx++] = (byte) (val & 0x00ff);//低8位元
            generatedSound[idx++] = (byte) ((val & 0xff00) >>> 8);//高8位元

        }
    }

該函數是生成聲波的函數，先填入sample陣列每個取樣點的值。這裡的聲波是多個頻率的cos函數相加除以頻率數，論文中表示使用多個頻率是為了減輕多徑效應的影響。接著，該函數將聲波的振幅調到最大，並且將聲波訊號轉換成PCM編碼，存入generatedSound陣列中。sample[0]的低8位元放在generatedSound[0]中，高8位元放在generatedSound[1]中；然後sample[1]的低8位元放在generatedSound[2]中，且將高8位元放在generatedSound[3]中，以此類推。

public void PrepareSound() {
        genTone();

        Log.d("llap", "" +audioTrack.write(generatedSound, 0, generatedSound.length));//write函數向audioTrack寫入聲波資料
        audioTrack.setLoopPoints(0, generatedSound.length / 2, -1);//迴圈
    }

該函數先呼叫genTone()函數，genTone()函數執行完後要傳送的聲波訊號就轉換為PCM編碼儲存在generatedSound陣列中了。Log函數是把資訊寫到紀錄檔裡，audioTrack.write函數將聲波訊號的PCM編碼generatedSound寫入audioTrack中，audioTrack.setLoopPoints函數用於設定迴圈數，把loopcount設定成了-1，表示無限迴圈。

SoundPlayer(int setsamplerate, int setnumfreq, double setfreqs[]) {


        sampleRate=setsamplerate;
        numfreq=setnumfreq;
        for (int i=0;i<numfreq;i++)
        {
            freqOfTone[i]=setfreqs[i];
        }
        //STREAM_MUSIC  STREAM_VOICE_CALL
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, sampleRate, AudioFormat.CHANNEL_OUT_MONO,
                AudioFormat.ENCODING_PCM_16BIT, generatedSound.length, AudioTrack.MODE_STATIC);//初始化

        PrepareSound();
    }

該函數是SoundPlayer類別建構函式，給freqOfTone陣列賦值，new一個audioTrack，呼叫PrepareSound函數生成聲波並將聲波的PCM編碼傳給AudioTrack。

MainActivicty.java

//初始化wavefreqs陣列和wavelength陣列
        for(int i=0;i<numfreq;i++)
        {
            wavefreqs[i]=startfreq+i*freqinter;//直線，初始化，startfreq = 15050，freqinter = 350
            wavelength[i]=soundspeed/wavefreqs[i]*1000;
        }

此段程式碼在用於初始化wavefreqs陣列和wavelength陣列。

btnPlayRecord.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                btnPlayRecord.setEnabled(false);
                btnStopRecord.setEnabled(true);

                recBufSize = AudioRecord.getMinBufferSize(sampleRateInHz,
                        channelConfig, encodingBitrate);

                mylog( "recbuffersize:" + recBufSize);

                playBufSize = AudioTrack.getMinBufferSize(sampleRateInHz,
                        channelConfig, encodingBitrate);

                audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC,
                        sampleRateInHz, channelConfig, encodingBitrate, recBufSize);


                mylog("channels:" + audioRecord.getChannelConfiguration());

                new ThreadInstantPlay().start();
                new ThreadInstantRecord().start();
                new ThreadSocket().start();
            }
        });

該事件監聽器負責設定audioRecord並且啟動傳送聲波訊號的執行緒。

    class ThreadInstantPlay extends Thread
    {
        @Override
        public void run()
        {
            SoundPlayer Player= new SoundPlayer(sampleRateInHz,numfreq,wavefreqs);
            blnPlayRecord=true;
            Player.play();
            while (blnPlayRecord==true){}
            Player.stop();
        }
    }

該執行緒是傳送聲波訊號的執行緒，new一個SoundPlayer並且呼叫play()方法傳送聲波。