I tried 4 QAM and 16 QAM. I used a FFT Sink to see the Amplitude in dB after the kanal, which include the signal and the noise, I think : SNR = Amplitude of Singal - Amp. of Noise, is this right?
On Wed, Jan 23, 2013 at 4:23 PM, Tom Rondeau <t...@trondeau.com> wrote: > On Wed, Jan 23, 2013 at 10:20 AM, Zhiwen He <hey...@gmail.com> wrote: > >> >> >> On Wed, Jan 23, 2013 at 4:11 PM, Zhiwen He <hey...@gmail.com> wrote: >> >>> you mean that i need to add an access code for the system, or just leave >>> blank? >> >> > There is a default 64-bit access code that is used when you leave this > field blank. > > >> how to make the system better? I mean that, for example, when the SNR< >>> 20, there are too many errors for the packet decoder, it doesn't work >>> anymore, but for practise, i think it should keep working, although there >>> are much more errors. for the simulation, how can I get the data for >>> SNR<20, so that i can compare with the source data to calculate the BER? >>> >>> Thanks, >>> >>> Zhiwen >>> >> > It's possible that you are calculating your SNR incorrectly.I know that > under standard channel conditions (that is, AWGN) the modulators work > pretty close to their theoretical performance. So when you say SNR < 20, > which modulation are you trying to use? GMSK, DBPSK, and DQPSK should work > under these conditions. > > Tom > > > >> On Wed, Jan 23, 2013 at 3:56 PM, Tom Rondeau <t...@trondeau.com> wrote: >>> >>>> 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
