BLE scan in sleep mode

Question

I'm developing a android app using ble. I want schedule a scan every 10 second. It work but when my device is in background, it doesn't work.

in Oncreate() i call StartHandler();

public class MyService extends Service{
......
....
public void StartHandler(){

    handlerScan = new Handler();
    handlerScan.postDelayed(new Runnable() {
        public void run() {
            if (!STOP) {

                scanLeDevice(true);

                handlerScan.postDelayed(this, 8000);

            }else{

                handlerScan.postDelayed(this, 3000);
            }
        }
    }, 500);
}

and scanLeDevice from Google

public void scanLeDevice(final boolean enable) {
    if(mLeScanCallback == null){
        mBluetoothManager = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE);
        mBluetoothAdapter = mBluetoothManager.getAdapter();
        try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); }
    }
    if (enable) {
        mHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mScanning = false;
                    mBluetoothAdapter.stopLeScan(mLeScanCallback);
                }
            }, 3000);

        mScanning = true;

        mBluetoothAdapter.startLeScan(mLeScanCallback);
    } else {
        mScanning = false;
        mBluetoothAdapter.stopLeScan(mLeScanCallback);
    }
}

• This is work when device is not in sleep. I have tried to use AlarmManager but the minimum time period for repeating alarm is 1 minute.
• TimerTask doesn't work in sleep mode.
• Handler doesn't work in sleep mode.

I Thought use WakeLock but if i acquire it here:

    public void StartHandler(){

    handlerScan = new Handler();
    handlerScan.postDelayed(new Runnable() {
        public void run() {
            if (!STOP) {
                wakelock.acquire();

                scanLeDevice(true);
                handlerScan.postDelayed(this, 8000);

            }else{

                handlerScan.postDelayed(this, 3000);
            }
        }
    }, 500);
}

and release my wakelock in scanLeDevice

public void run() {
       mScanning = false;
       wakelock.release();
       mBluetoothAdapter.stopLeScan(mLeScanCallback);
}

It work only first time. In various post i have read: "is not possibile acquire wakelock and release for for multiple times". Thank you.