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

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.

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

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.

That was really a very clear explanation

Thank you so much.

Now i got the difference between the terms and also concept behind it

Thanks

sandhya