On 03/06/2021 11:31 AM, Snehasish Kar via USRP-users wrote:
Hello everyone
I am trying to achieve frequency hopping in GSM using twinrx with usrp
x310. Here I am using timed command for tuning a single port across a
given frequency list. During hopping it stays in each frequency for
4msecs and till the time frequency hopping continues, I am able to
identify FCCH using phase difference. But as soon as the hopping is
over and it tunes back to the actual frequency containing the
broadcast channel, I am not getting phase difference greater than 0
and thus not able to demodulate the GSM burst. Can anyone please help
where I am going wrong below is the snippet of the code, responsible
for hopping.
Function handling hopping:
uhd::tune_request_t tune_request(rf_freq);
tune_request.rf_freq_policy = uhd::tune_request_t::POLICY_MANUAL;
tune_request.dsp_freq_policy = uhd::tune_request_t::POLICY_MANUAL;
tune_request.rf_freq = rf_freq;
tune_request.dsp_freq = dsp_freq;
uhd_src->set_rx_freq(tune_request, chan_num);
{
If(verbose_lvl==3){
char msg[100]={0x00};
sprintf(msg,"info: DSP freq: changed to channel %d: %fMHz offset
%fMHz", chan_num, uhd_src->get_rx_freq(chan_num)/1e6, dsp_freq);
vipl_printf(msg,error_lvl, __FILE__, __LINE__);
}
}
//uhd_src->clear_command_time();
usleep(110000); // allow LOs to lock
Module for setting back to original frequency with broadcast:
uhd_src->clear_command_time();
uhd::tune_request_t tune_request(rf_freq, 0x00); //considering
LO-Offset to be zero
tune_request.rf_freq_policy = uhd::tune_request_t::POLICY_AUTO;
tune_request.dsp_freq_policy = uhd::tune_request_t::POLICY_AUTO;
tune_request.rf_freq = rf_freq;
//tune_request.dsp_freq = -dsp_freq;
uhd_src->set_rx_freq(tune_request, channel);
{
char msg[100]={0x00};
sprintf(msg,"info: freq: set to channel %d: %fMHz requested freq
%fMHz", channel, uhd_src->get_rx_freq(channel)/1e6, rf_freq/1e6);
vipl_printf(msg,error_lvl, __FILE__, __LINE__);
}
usleep(110000);
My UHD version is 3.14.0.0
USRP: X310
Daughter board: 2 sets of Twinrx
OS: Debian 10
Interface: 10gig sfp+ ethernet
Thanks!!
Regards
Snehasish Kar
By "phase synchronization" you're describing the demodulator phase?
You're hoping that the LO phase would be the same as if you had not
hopped away from the original frequency? I don't think that's
even possible, but your description is not very precise, so perhaps
that's not what you meant?
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