Hi,
On 05/21/2017 11:45 PM, Qurat-Ul-Ann Akbar wrote:
Hi,
I want to look at the number of symbols copied for *each frame received
*in wifi_rx flow graph. I have been trying to understand how the start
of each frame is calculated and by looking at the code it seems like its
being done in the wifi sync_short block where the auto correlation
coefficient is being checked against a threshold and then the d_plateau
is being updated until it reaches MIN_PLATEAU.
However, for the number of symbols per frame, there is a MAX_SAMPLES
which is set to 540*80 where 80 is the number of samples per symbol but
I don't understand why is the total number of symbols per frame set to 540?
IIRC, that corresponds to a 1500 byte BPSK 1/2 frame. It just pipes in
the maximum number of samples, since this block doesn't know the actual
size of the frame.
Whats the role of MIN_GAP? Why is it being used to detect a shorter frame?
The autcorrelation has a plateau at the beginning of the frame. To avoid
triggering multiple times, the receiver waits at least MIN_GAP samples.
But even if the receiver still copies samples, it can already
resynchronize after MIN_GAP samples, i.e., if it's not one large frame,
but short ones with low interarrival time.
Moreover, does it mean that the number of symbols per frame can be
either MAX_SAMPLES or MIN_GAP because in both cases it starts searching
for new frames. What if one frame has less number of symbols than
MIN_GAP and MAX_SAMPLES?
It will receive frames with __up to__ MAX_SAMPLES and short frames
back-to-back, if they are spaced __at least__ MIN_GAP samples.
Best,
Bastian
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