对于rssi，Android蓝牙LE扫描始终返回-2.147483648E9

Question

我正在尝试测量执行BLE扫描的Galaxy Tab 4（蓝牙4.0）上的iBeacon距离。我收到的rssi数据似乎是错误的。它总是在-2.147483648E9。

这是我的代码：

public class MainActivity extends AppCompatActivity {

    private ScanFilter mScanFilter;
    private ScanSettings mScanSettings;
    private BluetoothLeScanner mBluetoothLeScanner;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findBeaconClickListener();

        BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        mBluetoothLeScanner = mBluetoothAdapter.getBluetoothLeScanner();


    }

    public void findBeaconClickListener() {
        setScanFilter();
        setScanSettings();
        Button findBeacon = (Button) findViewById(R.id.findBeacon);
        findBeacon.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mBluetoothLeScanner.startScan(Arrays.asList(mScanFilter), mScanSettings, mScanCallback);
            }
        });
    }

    private void setScanFilter() {
        ScanFilter.Builder mBuilder = new ScanFilter.Builder();
        ParcelUuid pUUID = ParcelUuid.fromString("0000fff0-0000-1000-8000-00805f9b34fb");
        mBuilder.setServiceUuid(pUUID);
        mScanFilter = mBuilder.build();
    }

    private void setScanSettings() {
        ScanSettings.Builder mBuilder = new ScanSettings.Builder();
        mBuilder.setReportDelay(0);
        mBuilder.setScanMode(ScanSettings.SCAN_MODE_LOW_POWER);
        mScanSettings = mBuilder.build();
    }

    protected ScanCallback mScanCallback = new ScanCallback() {
        @Override
        public void onScanResult(int callbackType, ScanResult result) {
            ScanRecord mScanRecord = result.getScanRecord();
            int txPower = mScanRecord.getTxPowerLevel();

            String deviceName = mScanRecord.getDeviceName();

            int mRssi = result.getRssi();
        }
    };

所以当我从结果中读取这个rssi值时，它显然是错误的。 devicename和txPower似乎没问题。