Hello every one, I am using USRP1 with RFX2400 daughter card.
I have a system (any state of the art system, let say Atmel's narroband FSK which works in 2.4 GHz band) transmitting a fixed packet cyclically (let say cycle time = T ms). I want to use USRP system to sense the spectrum and calculate (or guess) the cycle time of this FSK system, and to do this I have following idea: I am using fftsink2.py to sense the spectrum with FFT = 512 at a fixed center frequency (which must be exactly same as FSK system). Then I set the decimation rate = 160 , hence getting B = 400 kHz (FSK's B = 800 kHz). USRP start scanning the spectrum and in each scan it come up with 512 bins and I compare the max(of 512 bins) with a predefined threshold energy level. When I find this max energy above my predefined threshold value, I suppose FSK is detected, I save this number and start counting the number of scans which do not detect the FSK system (lets call it empty scan). After 'n' empty scans there is again a scan with FSK detection. In this way between two FSK detected scans I calculate the value of 'n' empty scans. Now I already now that one 512 bin scan take 'K micrseconds', so I simply calculate the cycle time in the following way: cycle tile = K(time for one scan) * n (no. of empty scans between two detected scans) BUT IT IS NOT WORKING!!!!!!!!!!!!!!!!!!!! If 'p' stands for peak (the scan which detect the FSK system), and dots represent empty scans, then I was expecting an output as follows: >----n----< >-----n---< [all n's should be equal because cycle time is fixed] p . . . . . . p . . . . . .p . . . . . . p . . . . . . p mean that after running for long time I would get the value of n (n=6 in above example scenerio), the value of n would be almost same between any two peaks as shown in above scenerio. BUT I get following results: >----n---< > n < >---------n----------< [all n's are not equal????????????] p..p...........p..p..p...p..p....p.............................p.... Means that there is no consistency between the value of n between different peaks. *POSSIBLE REASONING: I guessed that one possible reason can be that there are multiple threads and the scan process is not really continues and because of this some times the FSK system is not detected (because when the FSK system transmits the scanning thread is not executing??? Is it possible)which makes some p's to disappear and hence leaving the length of intervals between different p's (value of n) unequal.???? Now I want your suggestions: 1- Is the thread sharing time so significant that above given reasoning (*POSSIBLE REASONING) has some worth. 2- What other possiblitities can be there 3- Can you suggest some different way to solve this problem, The problem is simply to calculate the cycle time of some system which is already working in the environment Thaks in advance and Best Regards -- View this message in context: http://www.nabble.com/Cycle-time-calculation-tp22556892p22556892.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
