Hi all,
I have a question on the synchronization of ofdm example,namely the
sch&cox source code.
The plateau_detector_fb_impl.cc can find the plateau,and then
header_payload_demux_impl can find the head data.
STEP 1: plateau_detector_fb_impl find the plateau.
flank_start = i;
while(i < noutput_items && in[i] >= d_threshold)
i++;
if((i - flank_start) > 1) { // 1 Sample is not a plateau
out[flank_start + (i-flank_start)/2] = 1;
i = std::min(i+d_max_len, noutput_items-1);
}
STEP 2:header_payload_demux_impl can find the head data
case STATE_HEADER:
if (check_items_available(d_header_len, ninput_items,
noutput_items, nread)) {
copy_n_symbols(in, out_header, PORT_HEADER, d_header_len);
STEP 3:
memcpy((void *) out, (void *) (in + d_gi * d_itemsize),
d_items_per_symbol * d_itemsize);
I think may be the code have some errors.For example,the data is
cdef+abcdef,the cyclic prefix is cdef,and the data is abcdef.
According step1,the output will ouput 0010000000.Because the sch&cox will
output a plateau in the cyclic prefix,namely the index corresponding to the
cdefa will be the plateau.The source code output 1 in the middle.Namely the
index corresponding to the middle "e" output 1.
According to the step 2 and step3, we copy the d_items_per_symbol *
d_itemsize bytes after (in + d_gi * d_itemsize) to the output.In the example,
cdef+abcdef,the d_gi is 4. (in + d_gi * d_itemsize) will correspond to the
c.Then output d_items_per_symbol is 6,then output cdef..But the true head data
is abcdef,so I think maybe the source code have some problems.Is my
understanding right?
Thank you.
Best regards,
zswx
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