[Discuss-gnuradio] Setting output buffer to contain one packet

[Muhammad Zulqarnain]

Dear All!

I am new to GNU-Radio. I have previously used MATLAB for packet transmission and detection. Here is the problem, I am facing:

I have inserted zeros between the packets and transmitting the same packet over and over again. In the packet formation, I have appended two preambles side-by-side and using auto-correlation approach to detect coarse estimate of frequency and start of the packet. This was already done in MATLAB, but in GNURadio I am stuck in buffer things. I want the output buffer to contain exactly one packet so I can do processing on each packet (i.e. doing synchronization, demodulating etc.) 

My approach of doing auto-correlation is similar to Schmidl & Cox synchronization but all I find in GNURadio is for OFDM. Where this is a case of simple packetized transmission.

As I am inserting zeros between the packets so detection of individual packets at the receiver won't be a problem. 

I have already set the max output buffer to packet length i.e.  set_max_noutput_items (495);

Here is what I am doing in work function. but somehow I am not getting any output.

      float curr_sample;

      int i =0;

      int y = 0;

      // Do <+signal processing+>

      while(i<=noutput_items){

        curr_sample = abs(in[y]);

          if (curr_sample >= 0.5 && packet_start == 0){ //0.5 is the threshold that signal is coming

                packet_start = 1;

                packet_length_count = 0;

          }

          if (packet_start == 1){

              out[i] = in[y];

              packet_length_count++;

              i++;

          }

          if (curr_sample <= 0.2 && packet_start == 1){  //0.2 is the threshold that zero is coming

              packet_start = 0;

              packet_length_count = 0;

            //  printf("curr_packet_length: %d \n",packet_length_count);

              return i;

          }

        y++;

      }

      consume_each (y);

Awaiting reply!

Regards,

Muhammad Zulqarnain