On Tue, Jan 22, 2013 at 11:07 AM, Zhiwen He <hey...@gmail.com> wrote:
> Hello all, > > i'm working on the digital modultaion, and i build a system like this: > > random source -> packet encoder -> qam mod -> (adder and noise source) -> > qam demod -> packet decoder ->file sink > > I found that, when the amplitude of the noise is low, there will be some > data in file sink, but when the amplitude of noise is high, the packet > decoder doesn't output any more. Who can tell me why? does the noise > destroy the structure of the packet so that i can not be decoded any more? > > I also tried psk mod/demod and gmsk mod/demod, it comes the same problem. > > > thanks, > > Zhiwen > Yes, you are correct. The packet decoder looks for an access code. If the access code is valid to some number of bits, it will pull out a frame. If there are too many garbles in the access code, the packet decoder will never see it as a valid frame. By default, the access code is 64 bits and, I think, there can be up to 12 bit errors in it (this is the threshold value). Tom
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
