使用 STM32 通过 LoRaWAN 发送消息

Question

如何通过 LoRaWAN 发送消息？

static void PrepareTxFrame( uint8_t port )
{
switch( port ) {
    case 10: {
        int pos = 0;

        pc.printf("Prepare message\n");
#if 0
        uint32_t tempValue = ( uint32_t )( LightValue * 1000000.0 );
        AppData[0] = LightMode;
        AppData[1] = ( ( tempValue & 0xFF000000 ) >> 24 ) & 0xFF;
        AppData[2] = ( ( tempValue & 0x00FF0000 ) >> 16 ) & 0xFF;
        AppData[3] = ( ( tempValue & 0x0000FF00 ) >> 8 ) & 0xFF;
        AppData[4] = ( tempValue & 0x000000FF );
#else
        AppData[pos] = count;

        pc.printf("\n\r");
        pc.printf("The value of the counter is : %d", count);
        count++;
        pc.printf("\n\r");

        time_t seconds = time(NULL);
        printf("The time is %s", ctime(&seconds));
        AppData[++pos] = seconds;


        pc.printf("%d \n %d", AppData[0], AppData[1]);
        pc.printf("\n\r");
#endif
        pc.printf("Message Ready\n");
    }
    break;
    case 15: {
        int pos = 0;
        AppData[pos++] = AppLedStateOn;
#if 0

        if( IsTxConfirmed == true )
        {
            AppData[pos++] = LoRaMacDownlinkStatus.DownlinkCounter >> 8;
            AppData[pos++] = LoRaMacDownlinkStatus.DownlinkCounter;
            AppData[pos++] = LoRaMacDownlinkStatus.Rssi >> 8;
            AppData[pos++] = LoRaMacDownlinkStatus.Rssi;
            AppData[pos++] = LoRaMacDownlinkStatus.Snr;
        }
#endif
        AppDataSize = pos;
    }
    break;
    case 224:
        if( ComplianceTest.LinkCheck == true ) {
            ComplianceTest.LinkCheck = false;
            AppDataSize = 3;
            AppData[0] = 5;
            AppData[1] = ComplianceTest.DemodMargin;
            AppData[2] = ComplianceTest.NbGateways;
            ComplianceTest.State = 1;
        } else {
            switch( ComplianceTest.State ) {
                case 4:
                    ComplianceTest.State = 1;
                    break;
                case 1:
                    AppDataSize = 2;
                    AppData[0] = ComplianceTest.DownLinkCounter >> 8;
                    AppData[1] = ComplianceTest.DownLinkCounter;
                    break;
            }
        }
        break;
    default:
        break;
  }
 }

/*!
 * \brief
 *
  * Prepares the pay-load of the frame
  *
 * \retval  [0: frame could be send, 1: error]
 */
static bool SendFrame( void )
{
 McpsReq_t mcpsReq;
 LoRaMacTxInfo_t txInfo;

if( LoRaMacQueryTxPossible( AppDataSize, &txInfo ) != LORAMAC_STATUS_OK ) 
      {
    // Send empty frame in order to flush MAC commands
    mcpsReq.Type = MCPS_UNCONFIRMED;
    mcpsReq.Req.Unconfirmed.fBuffer = NULL;
    mcpsReq.Req.Unconfirmed.fBufferSize = 0;
    mcpsReq.Req.Unconfirmed.Datarate = LORAWAN_DEFAULT_DATARATE;

    LoRaMacUplinkStatus.Acked = false;
    LoRaMacUplinkStatus.Port = 0;
    LoRaMacUplinkStatus.Buffer = NULL;
    LoRaMacUplinkStatus.BufferSize = 0;
    SerialDisplayUpdateFrameType( false );
} else {
    LoRaMacUplinkStatus.Acked = false;
    LoRaMacUplinkStatus.Port = AppPort;
    LoRaMacUplinkStatus.Buffer = AppData;
    LoRaMacUplinkStatus.BufferSize = AppDataSize;
    SerialDisplayUpdateFrameType( IsTxConfirmed );

    if( IsTxConfirmed == false ) {
        mcpsReq.Type = MCPS_UNCONFIRMED;
        mcpsReq.Req.Unconfirmed.fPort = AppPort;
        mcpsReq.Req.Unconfirmed.fBuffer = AppData;
        mcpsReq.Req.Unconfirmed.fBufferSize = AppDataSize;
        mcpsReq.Req.Unconfirmed.Datarate = LORAWAN_DEFAULT_DATARATE;
    } else {
        mcpsReq.Type = MCPS_CONFIRMED;
        mcpsReq.Req.Confirmed.fPort = AppPort;
        mcpsReq.Req.Confirmed.fBuffer = AppData;
        mcpsReq.Req.Confirmed.fBufferSize = AppDataSize;
        mcpsReq.Req.Confirmed.NbTrials = 8;
        mcpsReq.Req.Confirmed.Datarate = LORAWAN_DEFAULT_DATARATE;
    }
}

if( LoRaMacMcpsRequest( &mcpsReq ) == LORAMAC_STATUS_OK ) {
    return false;
}
return true;
}

会发送计数器数据和时间吗？ AppData中的数据也是要传输的数据吗？我希望每次 LoRa 设备传输时都发送计数和时间戳。

Answer 1

要发送的有效负载（AppData）通过 MCPS（MAC 公共部分子层）请求提供给 LoRaMAC 层，例如对于未确认的帧：

mcpsReq.Req.Unconfirmed.fBuffer = AppData;

因此物理上（即通过RF），AppData被发送但之前被加密和封装。

PrepareFrame() 函数根据 PHYPayload 方案构建要发送的帧（请参阅 LoRaWAN™ 规范 1.0.2 文档中的 "MAC Message Formats" 部分），遵循以下字段：

MHDR（1 字节）Macheader
DevAddr（4 字节）end-device
FCtrl（1字节）帧控制
FCnt（2 字节）帧计数器
FOpts（0 - 15 字节）帧选项
FPort（0 - 1 字节）端口字段
FRMPayload（0 - N 字节）MAC 帧负载加密，您的 AppData 已加密
MIC（4 字节）消息完整性代码

FRMPayload按照FPort加密。加密算法基于AES 128.
如果 FPort = [1..255]，AppSKey 密钥将用于加密您的负载。
否则 (FPort = 0)，使用 NwkSKey 密钥加密。
有关详细信息，请参阅 LoRaMacPayloadEncrypt() 函数。

PHYPayload会被Radio PHY Layer封装并通过RF发送。

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