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android蓝牙4.0(BLE)开发之ibeacon初步

此文使用的ibeacon模块是april beacon，至于什么是ibeacon。本文不做解释，具体请自查。

一个april beacon里携带的信息如下

1	`0201061AFF4C0002159069BDB88C11416BAC3F33468C2788A3044B0378C60C09417072696C426561636F6E051250002003020A0000000000000000000000`

具体是什么意思呢

02  Number of bytes that follow in first AD structure
01  Flags AD type
06
    Flags value 0x1A = 000011010
       bit 0 (OFF) LE Limited Discoverable Mode
       bit 1 (ON) LE General Discoverable Mode
       bit 2 (OFF) BR/EDR Not Supported
       bit 3 (ON) Simultaneous LE and BR/EDR to Same Device Capable (controller)
       bit 4 (ON) Simultaneous LE and BR/EDR to Same Device Capable (Host)
1a Number of bytes that follow in second (and last) AD structure
前面是常规智能硬件广播包部分
 
ff （FF代表后面是Manufacture Data）
 
 
4c 00   (组织标识，0x4c00苹果公司标识,https://www.bluetooth.org/en-us/specification/assigned-numbers/company-identifiers)
02 （0x02 ibeacon标识位）
15 （0x15,22个字节标识长度，uuid，major，minor总和的长度）
90 69 bd b8-8c 11-41 6b-ac 3f-33 46 8c 27 88 a3 (Proximity UUID)
04 4b(1099，major)
03 78(888，minor)
c6  （切记这里是补码，转化为原码就是-58，iBeacon的信号发出强度值，用来作为和RSSI一起测距的基准 ，txPower）
        计算
            C6
            1100 0110 补码
            1100 0101 反码
            1011 1010 原码
            -（32+16+8+2）
            -58
0c09    （未知）
417072696c426561636f6e（AprilBeacon字符串对应的十六进制）
051250002003020a0000000000000000000000（未知）

Proximity UUID ：这是将你所有的beacon与其他人的beacon设备区别开的id！例如，目前在商店里某个区域分布着多个beacon形成一条“链带”，用于为顾客提供特定的服务，那么归属于同一条“链带”的beacon将分配到相同的proximity UUID。为这条“链带”设计的专用应用程序将会在后台使用这个UUID扫描到这条“链带”中的beacon设备。

major 编号：用于将相关的beacon标识为一组。例如，一个商店中的所有beacon将会分配到相同的major编号。通过这种方式，应用程序就能够知道顾客位于哪一家商店。

minor 标号：用于标识特定的beacon设备。例如一个商店中的每一个beacon设备都拥有唯一的minor编号，这样你才能够知道顾客位于商店中的哪个位置。

Measuring distance（测量距离）
最后一个值， TX power ，用于确定你和beacon之间距离有多近。根据这个值不但可以获得粗略的信息（比如靠近/远离/不在范围内等），也可以获取精确到米的距离（当然你也可以转换为以步为单位的距离）。那么如何实现？

TX power （上面例子中为0xC6=198，根据2的补码测得256-198=-58dBm）是距离设备1米测得的信号强度值（RSSI- Received Signal Strength Indication，接收到的信号强弱指标）。假如接收到的信号强度减弱了，那么我们可能在远离。只要知道1米距离的RSSI，以及当前的RSSI（我们可以从接收到的信号中一块获取到这些信息），那么计算出当前的距离是可能的。IOS已经实现了个这个功能，对于其它平台需要自己手动编码计算。

一个简单的测距函数

protected static double calculateAccuracy(int txPower, double rssi) {
        if (rssi == 0) {
            return -1.0; // if we cannot determine accuracy, return -1.
        }
 
        double ratio = rssi * 1.0 / txPower;
        if (ratio < 1.0) {
            return Math.pow(ratio, 10);
        } else {
            double accuracy = (0.89976) * Math.pow(ratio, 7.7095) + 0.111;
            return accuracy;
        }
    }

在使用蓝牙时需要加权限

关键代码如下

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package cn.edu.zafu.ble;
 
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothManager;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
 
public class MainActivity extends Activity {
    private BluetoothAdapter mBluetoothAdapter;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        BluetoothManager bluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
        mBluetoothAdapter = bluetoothManager.getAdapter();
        if (mBluetoothAdapter == null || !mBluetoothAdapter.isEnabled()) {
            Intent enableBluetooth = new Intent(
                    BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBluetooth, 1);
        }
        mBluetoothAdapter.startLeScan(mLeScanCallback);
 
    }
 
    private BluetoothAdapter.LeScanCallback mLeScanCallback = new BluetoothAdapter.LeScanCallback() {
        @Override
        public void onLeScan(final BluetoothDevice device, final int rssi,
                final byte[] scanRecord) {
            int startByte = 2;
            boolean patternFound = false;
            // 寻找ibeacon
            while (startByte <= 5) {
                if (((int) scanRecord[startByte + 2] & 0xff) == 0x02 && // Identifies
                                                                        // an
                                                                        // iBeacon
                        ((int) scanRecord[startByte + 3] & 0xff) == 0x15) { // Identifies
                                                                            // correct
                                                                            // data
                                                                            // length
                    patternFound = true;
                    break;
                }
                startByte++;
            }
            // 如果找到了的话
            if (patternFound) {
                // 转换为16进制
                byte[] uuidBytes = new byte[16];
                System.arraycopy(scanRecord, startByte + 4, uuidBytes, 0, 16);
                String hexString = bytesToHex(uuidBytes);
 
                // ibeacon的UUID值
                String uuid = hexString.substring(0, 8) + "-"
                        + hexString.substring(8, 12) + "-"
                        + hexString.substring(12, 16) + "-"
                        + hexString.substring(16, 20) + "-"
                        + hexString.substring(20, 32);
 
                // ibeacon的Major值
                int major = (scanRecord[startByte + 20] & 0xff) * 0x100
                        + (scanRecord[startByte + 21] & 0xff);
 
                // ibeacon的Minor值
                int minor = (scanRecord[startByte + 22] & 0xff) * 0x100
                        + (scanRecord[startByte + 23] & 0xff);
 
                String ibeaconName = device.getName();
                String mac = device.getAddress();
                int txPower = (scanRecord[startByte + 24]);
                Log.d("BLE",bytesToHex(scanRecord));
                Log.d("BLE", "Name：" + ibeaconName + "\nMac：" + mac
                        + " \nUUID：" + uuid + "\nMajor：" + major + "\nMinor："
                        + minor + "\nTxPower：" + txPower + "\nrssi：" + rssi);
 
                Log.d("BLE","distance："+calculateAccuracy(txPower,rssi));
            }
        }
    };
    static final char[] hexArray = "0123456789ABCDEF".toCharArray();
 
    private static String bytesToHex(byte[] bytes) {
        char[] hexChars = new char[bytes.length * 2];
        for (int j = 0; j < bytes.length; j++) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = hexArray[v >>> 4];
            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
        }
        return new String(hexChars);
    }
 
    protected static double calculateAccuracy(int txPower, double rssi) {
        if (rssi == 0) {
            return -1.0; // if we cannot determine accuracy, return -1.
        }
 
        double ratio = rssi * 1.0 / txPower;
        if (ratio < 1.0) {
            return Math.pow(ratio, 10);
        } else {
            double accuracy = (0.89976) * Math.pow(ratio, 7.7095) + 0.111;
            return accuracy;
        }
    }
}