Re: [Discuss-gnuradio] samples _per_symbol parameter

[Karan Talasila]

Hi Sandhya,

                 You need atleast 2 samples/symbol for demodulation. Normally when there are sharp transitions in modulated carrier, it results in high frequency components in the frequency domain. This is a problem because there will be power across frequencies beyond the bandwidth of the signal. Hence pulse shaping is employed where the time domain waveform is smoothened so that all the power in the freq domain is concentrated only within the bandwidth of signal and that prevents ISI. Hence because the waveform transitions are smoothened, there will be a need for higher samples/symbol to demodulate the symbol.

On Tue, Dec 3, 2013 at 4:35 PM, Sandhya G <address@hidden> wrote:

Hi karan ,

       Thanks for reply .

well ya in gnuradio also if i set the value of samples/symbol below 2 it is throwing me an error . 

So is there any specific reason behind using the value greater than 2?

and is that higher the value of samples/second the smoother will be the waveform? please correct me if i'am wrong .

Thanks 

Sandhya

On Tue, Dec 3, 2013 at 4:28 PM, Karan Talasila <address@hidden> wrote:

Hi,

    Bits/symbol depends on modulation scheme that you use to transmit.  For BPSK, it is 1 bit/symbol, for QPSK it is 2 bit/symbol and for 64-QAM it is 6 bits/symbol. So you can set it according to modulation scheme you use.

Samples/symbol is normally default set to 2. I am not aware in gnuradio but in certain other implementations samples/symbol is kept greater than 2, say 4 or 8 to account for pulse shaping.

On Tue, Dec 3, 2013 at 2:33 PM, Sandhya G <address@hidden> wrote:

Hi everyone,

       i'am trying to do simply QAM modulation for that the source i used is vector source which gives 1byte of 1's and 0's which is fed to QAM modulator .

Can anyone tell me how do i calculate samples/symbol .I know the traditional formula

samples/symbol=(samples/second)/(symbols/second).

symbols/sec= (Bits/sec)/(Bits/symbol)

I having the problem to decide bits/symbol and bits/sec.Please help me

Thanks

Sandhya

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Regards
Karan Talasila

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Regards
Karan Talasila