BLE 5.0 Long Range - nRF52840

1. 概述

Long Range 是BLE 5.0中新增加的特性。Long Range特性对蓝牙的通信距离有很大提高，空旷地带，可达上千米。蓝牙通信距离的增加，也拓宽了其应用场景。

Nordic公司的nrf52840能够支持Long Range特性。下面就从芯片代码方面，介绍Long Range与普通蓝牙的区别。

2. 代码

下面以代码为例，来说明如何把普通蓝牙增加Long Range特性。
因为普通BLE 与 Long Range不兼容，所以测试时主从机代码都需要修改。测试例程选择为SDK\examples\ble_peripheral\ble_app_blinky 和 SDK\examples\ble_central\ble_app_multilink_central。

2.1 BLE Peripheral

1. 修改初始化定义参数
宏定义BLE_LONG_RANGE附近为修改点。

static uint8_t m_enc_advdata[BLE_GAP_ADV_SET_DATA_SIZE_MAX];            /**< Buffer for storing an encoded advertising set. */
#ifdef BLE_LONG_RANGE
#else
static uint8_t m_enc_scan_response_data[BLE_GAP_ADV_SET_DATA_SIZE_MAX];       /**< Buffer for storing an encoded scan data. */
#endif

/**@brief Struct that contains pointers to the encoded advertising data. */
static ble_gap_adv_data_t m_adv_data =
{
    .adv_data =
    {
        .p_data = m_enc_advdata,
        .len    = BLE_GAP_ADV_SET_DATA_SIZE_MAX
    },
#ifdef BLE_LONG_RANGE
#else
    .scan_rsp_data =
    {
        .p_data = m_enc_scan_response_data,
        .len    = BLE_GAP_ADV_SET_DATA_SIZE_MAX

    }
#endif
};

2. advertising_ini() 函数修改

#ifdef BLE_LONG_RANGE
    adv_params.interval        = APP_ADV_INTERVAL;
    adv_params.duration        = APP_ADV_DURATION;
    adv_params.p_peer_addr     = NULL;
    adv_params.filter_policy   = BLE_GAP_ADV_FP_ANY;
    adv_params.properties.type = BLE_GAP_ADV_TYPE_EXTENDED_CONNECTABLE_NONSCANNABLE_UNDIRECTED;     // extend bit set 1
    adv_params.primary_phy     = BLE_GAP_PHY_CODED;     // PHY_CODED
    adv_params.secondary_phy   = BLE_GAP_PHY_CODED;     // PHY_CODED
#else
    adv_params.primary_phy     = BLE_GAP_PHY_1MBPS;
    adv_params.duration        = APP_ADV_DURATION;
    adv_params.properties.type = BLE_GAP_ADV_TYPE_CONNECTABLE_SCANNABLE_UNDIRECTED;
    adv_params.p_peer_addr     = NULL;
    adv_params.filter_policy   = BLE_GAP_ADV_FP_ANY;
    adv_params.interval        = APP_ADV_INTERVAL;
#endif

3. 设置广播功率

#define RADIO_TX_POWER     8           /**< Radio TX power in dBm. Default to 8dBm, see product spec for valid range */

/**@brief Function for starting advertising.
 */
static void advertising_start(void)
{
    ret_code_t           err_code;

#ifdef BLE_LONG_RANGE
    err_code = sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_ADV, m_adv_handle, RADIO_TX_POWER);
    APP_ERROR_CHECK(err_code);
#endif

    err_code = sd_ble_gap_adv_start(m_adv_handle, APP_BLE_CONN_CFG_TAG);
    APP_ERROR_CHECK(err_code);
}

2.2 BLE Central

1. scan_init() 函数修改

    init_scan.connect_if_match = mode;
    init_scan.conn_cfg_tag     = APP_BLE_CONN_CFG_TAG;
#ifdef BLE_LONG_RANGE
    static ble_gap_scan_params_t m_scan_param =
    {
        .active        = 0x01,
        .extended      = 0x01,
        .interval      = 160,
        .window        = 160,
        .timeout       = 0x0000, // No timeout.
        .scan_phys     = BLE_GAP_PHY_CODED,
        .filter_policy = BLE_GAP_SCAN_FP_ACCEPT_ALL,
    };
    
    init_scan.p_scan_param = &m_scan_param;
#endif

    err_code = nrf_ble_scan_init(&m_scan, &init_scan, scan_evt_handler);
    APP_ERROR_CHECK(err_code);

2. sdk_config.h
NRF_BLE_SCAN_BUFFER宏定义的值由原来的31，修改为255.

#ifndef NRF_BLE_SCAN_BUFFER
#define NRF_BLE_SCAN_BUFFER 255
#endif

3. 设置扫描功率

#define RADIO_TX_POWER     8           /**< Radio TX power in dBm. Default to 8dBm, see product spec for valid range */

/**@brief Function for starting scanning. */
static void scan_start(void)
{
    ret_code_t ret;

    NRF_LOG_INFO("Start scanning for device name %s.", (uint32_t)m_target_periph_name);

#ifdef BLE_LONG_RANGE
    ret = sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_SCAN_INIT, BLE_CONN_HANDLE_INVALID, RADIO_TX_POWER);
    APP_ERROR_CHECK(ret);
#endif

    ret = nrf_ble_scan_start(&m_scan);
    APP_ERROR_CHECK(ret);

}

3. 测试记录

测试硬件使用两块官方 nRF52840-DK(PCA10056) 开发板。
可接收广播距离为900+m，通信距离为600+m。
接全向2dBm增益天线后，通信距离达到1km以上。

附录A 参考资料

• NordicPlayground/nRF52-ble-long-range-demo
• NordicPlayground/nrf52-ble-app-uart-long-range