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UHD C/C++ 程式設計執行個體 USRP發送、接收資料

UHD C/C++ 程式設計執行個體 USRP發送、接收資料

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1. UHD庫函數簡介

1.1 發送函數

建立一個usrp裝置

std::string args = " "; args指定USRP位址，配置USRP參數等

uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(args);

設定時鐘源和時鐘頻率

std::string ref = "internal"; // internal, external, MIMO.

usrp->set_clock_source(ref);

double rate = 40e6;

usrp->set_master_clock_rate(rate);

usrp->get_clock_source() //擷取目前的時鐘源

usrp->get_clock_sources() //擷取所有可用的時鐘源

usrp->get_master_clock_rate(); //擷取時鐘頻率

設定采樣率

double samp_rate = 20e6;

usrp->set_tx_rate(samp_rate);

usrp->get_tx_rate() //擷取目前的采樣率

usrp->get_tx_rates() //擷取采樣率的采樣範圍

設定發射中心頻點

double freq = 2.412e9;

usrp->set_tx_freq(freq);

usrp->get_fe_tx_freq_range();

usrp->get_tx_freq();

usrp->get_tx__freq_range();

設定發射增益

double tx_gain = 60;

usrp->set_tx_gain(tx_gain);

設定發射天線

預設情況下無需設定發射天線，如需指定特定發射天線時設定。

usrp->set_tx_antenna(0);

usrp->get_tx_antenna();

usrp->get_tx_antennas();

建立發送流

建立發送流參數

std::string cpu_format = "fc32";

目前cpu_format支援的類型有：fc64 - complex fc32 - complex sc16 - complex sc8 - complex

std::string wire_format = "sc16";

目前wire_format支援的類型有：sc16 - Q16 I16 sc8 - Q8_1 I8_1 Q8_0 I8_0

uhd::stream_args_t stream_args(cpu_format, wire_format);

uhd::tx_streamer::sptr tx_stream = usrp->get_tx_stream(stream_args);

中頻資料管理

uhd::tx_metada_t md; //結構體描述接收到的中頻信号

md.start_of_burst = false; // 設定為真的時候發送第一個資料包

md.end_of_burst = false; // 設定為真的時候發送最後一個資料包

md.has_time_spec = false; // 設定為false時立即發送，設定為真的時候在特定時間發送

1.2 接收函數

建立一個usrp

std::string args = " ";

uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(args);

設定時鐘源和時鐘頻率

std::string ref = "internal"; //internal, external and MIMO

usrp->set_clock_source(ref);

double clock_rate = 40e6;

usrp->set_master_clock_rate(clock_rate);

設定采樣率

double rate = 20e6;

usrp->set_rx_rate(rate);

設定中心頻率

double freq = 2.412e9;

usrp->set_rx_freq(freq);

設定增益

double rx_gain = 50;

usrp->set_rx_gain(rx_gain);

建立接收流

std::string cpu_format = "fc32";

std::string wire_format = "sc16";

uhd::stream_args_t stream_args(cpu_format, wire_format);

uhd::rx_streamer::sptr rx_stream = usrp->get_rx_stream(stream_args);

設定接收模式

uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS);

//UHD_STREAM_MODE_START_CONTINUOUS=97,

//UHD_STREAM_MODE_STOP_CONTINUOUS=111,

//UHD_STREAM_MODE_NUM_SAMPS_AND_DONE=100,

//UHD_STREAM_MODE_NUM_SAMPS_AND_MORE=109

stream_cmd.num_samps = 1000; // 接收采樣點數

stream_cmd.stream_now = true; //現在開始接收

rx_stream->issue_stream_cmd(stream_cmd); //配置rx_stream參數

2. USRP發送資料

　　代碼實作USRP發送二進制檔案802.11a_BUPT41.seg内的資料。裡面的資料為float complex類型，複數的實部和虛部交替存儲。即如下圖所示。使用者可以把要發送的資料生成對應的二進制檔案，也可以直接寫成數組放在代碼中。注意：float類型資料的機關1就是 “1”。

UHD C/C++ 程式設計執行個體 USRP發送、接收資料

源碼

#include <uhd/usrp/multi_usrp.hpp>
#include <signal.h>

#define SAMPLE_PER_BUFF 2000

int stop_signal_called = ;
void sig_int_handle(int)
{
    stop_signal_called = ;
    printf("stop tx.........\n");
    exit();
}

int main()
{
    std::string addr_args = " ";
    uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(addr_args);
    printf("Create a usrp......\n");

    // set the ref and clock rate
    std::string ref = "internal";
    usrp->set_clock_source(ref);

    float clock_rate = ;
    usrp->set_master_clock_rate(clock_rate);
    printf("set the  clock rate %0.2f \n", usrp->get_master_clock_rate() );

    // set the sample rate
    float samp_rate = ;
    usrp->set_tx_rate(samp_rate);
    printf("set the tx sample rate to %0.2f \n", usrp->get_tx_rate());

    // set the center frequency
    float center_freq = ;
    usrp->set_tx_freq(center_freq);
    printf("set the tx center freq to %0.2f \n", usrp->get_tx_freq());

    // set the rf gain
    float tx_gain = ;
    usrp->set_tx_gain(tx_gain);
    printf("set the tx gain to %0.2f \n", usrp->get_tx_gain());


    // create a tx stream
    std::string cpu_format = "fc32";
    std::string wire_format = "sc16";
    uhd::stream_args_t stream_args(cpu_format, wire_format);
    uhd::tx_streamer::sptr tx_stream = usrp->get_tx_stream(stream_args);

    uhd::tx_metadata_t md;

    // catch the INT signal
    signal(SIGINT, sig_int_handle);
    float read_buff[SAMPLE_PER_BUFF * ] = {};

    while(!stop_signal_called)
    {
        FILE *fp = fopen("802.11a_BUPT41.seg", "rb");
        md.start_of_burst = false;
        md.end_of_burst = false;


        while( (!md.end_of_burst) && (!stop_signal_called) )
        {
            int read_length = ;
            if( (read_length = fread(read_buff, sizeof(uint32_t), SAMPLE_PER_BUFF * , fp) ) == (SAMPLE_PER_BUFF * ) )
            {
                //int index;
                //for(index = 0; index < SAMPLE_PER_BUFF * 2; index++)
                //    printf("%0.2f ", read_buff[index]);
                //puts("");

                //md.start_of_burst = true;
                tx_stream->send(read_buff, SAMPLE_PER_BUFF, md);
                //md.start_of_burst = false;
                //sleep(1);
            }
            else if(read_length >= )
            {
                md.end_of_burst = true;
            }
        }

        fclose(fp);
    }


    return ;
}

編譯

g++ 編譯時需要連結uhd庫，系統需提前安裝UHD驅動。具體過程參見之前部落格。Ubuntu14.04 源碼安裝 UHD3.8.0

g++ tx.cpp -o tx -luhd

3. USRP接收資料

　　啟動USRP，并使USRP一直接收資料。

源碼

#include <uhd/usrp/multi_usrp.hpp>
#include <csignal>

#define SAMPLE_PER_BUFF 2000

int stop_signal_called = false;
void sig_int_handle()
{
    stop_signal_called = true;
}

int main()
{
    std::string addr_args = " ";
    uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(addr_args);

    // set the clock source and clock rate
    std::string ref = "internal";
    usrp->set_clock_source(ref);

    float clock_rate = ;
    usrp->set_master_clock_rate(clock_rate);
    printf("set the  clock rate %0.2f \n", usrp->get_master_clock_rate() );

    // set the sample rate
    float samp_rate = ;
    usrp->set_rx_rate(samp_rate);
    printf("set the tx sample rate to %0.2f \n", usrp->get_rx_rate());

    // set the center frequency
    float center_freq = ;
    usrp->set_rx_freq(center_freq);
    printf("set the tx center freq to %0.2f \n", usrp->get_rx_freq());

    // set the rf gain
    float rx_gain = ;
    usrp->set_rx_gain(rx_gain);
    printf("set the tx gain to %0.2f \n", usrp->get_rx_gain());

    std::string cpu_format = "fc32";
    std::string wire_format = "sc16";
    uhd::stream_args_t stream_args(cpu_format, wire_format);
    uhd::rx_streamer::sptr rx_stream = usrp->get_rx_stream(stream_args);

    uhd::rx_metadata_t md;

    //uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_NUM_SAMPS_AND_DONE);
    uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS);
    stream_cmd.num_samps = SAMPLE_PER_BUFF;
    stream_cmd.stream_now = true;
    //stream_cmd.time_spec = uhd::time_spec_t();
    stream_cmd.time_spec = usrp->get_time_now();
    rx_stream->issue_stream_cmd(stream_cmd);

    uint32_t buff[SAMPLE_PER_BUFF*] = {};
    unsigned long long num_total_samps = ;

    while(!stop_signal_called)
    {
        //int num_rx_samps = rx_stream->recv(buff, SAMPLE_PER_BUFF, md);
        memset(buff, , SAMPLE_PER_BUFF * sizeof(uint32_t));
        int num_rx_samps = rx_stream->recv(buff, SAMPLE_PER_BUFF, md, , false);
        if(md.error_code == uhd::rx_metadata_t::ERROR_CODE_TIMEOUT)
        {
            printf("Timeout while streaming......\n");
            break;
        }
        if(md.error_code == uhd::rx_metadata_t::ERROR_CODE_OVERFLOW)
        {
            printf("Overflowing while stream......\n");
            continue;
        }
        if(md.error_code != uhd::rx_metadata_t::ERROR_CODE_NONE)
        {
            //printf("Receive error: %s \n", md.strerror());
            continue;
        }

    //printf("num_rx_samps = %d \n",num_rx_samps);
        num_total_samps += num_rx_samps;

    }
    printf("num_total_samps = %d \n", num_total_samps);

    stream_cmd.stream_mode = uhd::stream_cmd_t::STREAM_MODE_STOP_CONTINUOUS;
    rx_stream->issue_stream_cmd(stream_cmd);

    return ;
}

編譯

g++ 編譯時需要連結uhd庫，系統需提前安裝UHD驅動。具體過程參見之前部落格。Ubuntu14.04 源碼安裝 UHD3.8.0

g++ rx.cpp -o rx -luhd

４. 結論

　　以上代碼在Ubuntu上采用USRP B200測試通過。

　　掌握UHD庫函數的使用、g++ 連結 UHD庫等是基于USRP開發軟體無線電項目的基礎。之後，我們可以進一步設計發送程式和接收程式，用USRP搭建一套SDR 收發系統。

軟體無線電 USRP執行個體 UHD程式設計 軟線無線電 g++連結UHD
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