BPSK output abnormal

GNU Radio
1

Hi everyone,

I try to simulate file transfer using BPSK with block diagram

File Source --> PSK Mod --> PSK Demod --> File Sink

The block setting is
File Source :
-file type = .jpg (282,8 kB (282.765 bytes))
-repeat = no
-vec length = 1

PSK Mod :
-num of constellation = 2
-gray code = yes
-diff. encoding = yes
-sample/symbol = 2
-excess BW = 0.35
-verbose = off
=log = off

PSK Demod :
-num of constellation = 2
-diff. encoding = yes
-sample/symbol = 2
-excess BW = 0.35
-frequency BW = 6.28/100.0
-timing BW = 6.28/100.0
-phase BW = 6.28/100.0
-gray code = yes
-verbose = off
-log = off

File Sink
-vec length = 1
-unbuffered = on
-append file = overwrite

The size of input file = 282,8 kB (282.765 bytes)
but the size of output file = 2,3 MB (2.262.066 bytes)

What’s wrong with my fg?

Thank you,
Surya A.

2

On Sun, May 24, 2015 at 4:54 AM, Surya A. [email protected]
wrote:

-vec length = 1
PSK Demod :

Thank you,
Surya A.

The output is unpacked. So each sample only represents a single bit. You
have to repack them into 8 bits per byte, but you’ll also need to know
where to start through some kind of frame synchronization.

282765*8 = 2262120

The rest of the difference is due to delays in the filters. You can
zero-pad the input to “push” the samples through.

Tom

3

On Sun, May 24, 2015 at 4:25 PM, Surya A. [email protected]
wrote:

Oh thank you Tom, I can recover the file size. About frame synchronization,
am I need Polyphase Clock Sync Block? And also I have no idea about “You
can zero-pad the input to “push” the samples through.”?

(please keep emails on the mailing list)

The PFB clock sync handles symbol synchronization – it finds where the
bits are. You’ll need another level of synchronization to find the start
of
the frame, usually by looking for a known start pattern, preamble, etc.

And there are many ways to accomplish the zero-padding. I’ll leave that
up
to you to figure out :slight_smile:

Tom

4

Oh sorry I forgot to reply to all.

Now there’s a new problem. I use Packet Encoder to add preamble, the
setting is:
Encoder

  • sps = 2
  • bps = 1 (bpsk)
  • preamble = 1010010011110010
  • access code
    = 1010110011011101101001001110001011110010100011000010000011111100
  • pad for USRP = no
  • payload strength = 16
    Decoder
  • access code
    = 1010110011011101101001001110001011110010100011000010000011111100
  • threshold = -1

both access code and preamble are from
http://gnuradio.org/doc/sphinx-3.7.2/digital/pkt_utils.html

The output now become 0kB