Hi Nikita,
I'll jump into the general_work method here, directly:
switch(d_state) {
case SEARCH: {
int i;
for(i = 0; i < ninput; i++) {
if(in_cor[i] > d_threshold) {
if(d_plateau < MIN_PLATEAU) {
d_plateau++;
} else {
d_state = COPY;
… break;
}
… }
consume_each(i);
return 0;
}
case COPY: {
int o = 0;
while( o < ninput && o < noutput && d_copied < MAX_SAMPLES) {
if(in_cor[o] > d_threshold) {
if(d_plateau < MIN_PLATEAU) {
d_plateau++;
// there's another frame
} else if(d_copied > MIN_GAP) {
d_copied = 0;
d_plateau = 0;
… break;
}
…
out[o] = in[o] * exp(gr_complex(0, -d_freq_offset *
d_copied));
o++;
d_copied++;
}
if(d_copied == MAX_SAMPLES) {
d_state = SEARCH;
}
…
consume_each(o);
return o;
}
}
So, this is a pretty classical state machine approach: at every call of
general_work, the block is in either the COPY or the SEARCH state. We
only care about whether COPY also does a search operation, and, lo:
if(d_plateau < MIN_PLATEAU) {
d_plateau++;
// there's another frame
} else if(d_copied > MIN_GAP) {
d_copied = 0;
d_plateau = 0;
is exactly that.
Best regards,
Marcus
On 12.04.2017 12:12, Nikita Airee wrote:
> Hello everyone,
>
> I was trying to understand how the synchronization in gr-ieee802-11
> actually works and went through:
>
> Bastian Bloessl, Michele Segata, Christoph Sommer and Falko Dressler,
> "An IEEE 802.11a/g/p OFDM Receiver for GNU Radio"
>
> However, it seems that the Short Sync and many other blocks have
> developed further since then.
>
> From what I understand, the current sync_short.cc does the following:
>
> 1) searches for the peak normalized correlator o/p and compares with
> the set threshold
> 2) as enough number of simultaneous peaks are detected in correlator
> o/p, it moves onto the copy stage
>
> Here is where my doubt lies. Does the block keep looking for new
> frames while the old one is being copied? Also, what is MIN_GAP's
> function in the code and how is its value decided upon?
>
> Could you please clear up these doubts a little?
>
> Bests,
> Nikita Airee
>
>
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
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