On Tue, Mar 9, 2010 at 3:03 AM, Fisheep <[email protected]> wrote: > > Hi: > > I have some problem about dbpsk and bpsk using benchmark_tx/rx.py with some > modification. > > My experiment set up was that the transmitter waits for a time delay (0.5 s) > after sending a packet. > It means that we transmit data discontinuously. > > If we using dbpsk modulation, we can successfully receive every packet. > But if we removed the differential encoder/decoder (equals to bpsk > modulation), we uaually > lost some packet (almost half of the data lost). > > However, when we transmit data continuously,the bpsk modulation seems work > fine and we can successfully receive every packet. > > My problem is that what reason causing the bpsk modulation can not > successfully receive packet when > transmit data discontinuously. > > Could anyone have any idea about it, please let me know. > I am deeply appreciative. > > Fisheep :)
Fisheep, I'm wondering how you are compensating for the phase ambiguity of the BPSK signal in the receiver? In the current DBPSK, there is no method to properly rotate the constellation because the differential encoding doesn't care. If you are just transmitting BPSK, you'll have a 180 degree phase ambiguity in the receiver. If that's the case, then for every burst of a packet, when the receiver locks to the constellation, it will be in one of two phase rotations, one which works and one which inverts every symbol. They should be distributed with equal probability, so half of the time you'll have the correct rotation and the other half you won't. When you transmit continuously, I would expect that you'll also see the same behavior. If you've got the right rotation, you'll receive every packet. Otherwise, you'll see nothing. Does that happen sometimes? Tom _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
