On Wed, Jan 23, 2013 at 4:11 PM, Zhiwen He <[email protected]> wrote:
> you mean that i need to add an access code for the system, or just leave > 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 > > > On Wed, Jan 23, 2013 at 3:56 PM, Tom Rondeau <[email protected]> wrote: > >> On Tue, Jan 22, 2013 at 11:07 AM, Zhiwen He <[email protected]> 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 >> >> >
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