2
$\begingroup$

My understanding of sampling frequency is when we have an analog signal x(t) we convert it to a digital signal. Assume the sampling frequency is denoted by $f_s$ then the sampling time $T_s$. In my understading this is denoted the number of samples per second.

In MATLAB programs, I have come across generation of base band signal. The authors have upsampled the base band signal and the sampling rate was stated to be 3 samples per symbol.

My question is what does samples per symbol mean.Assuming we have QAM symbols are we repeating it three times?

Thanks

Improve this question
$\endgroup$
2
$\begingroup$

A digital communications signal such as QAM can be generally written as $$s(t) = \sum_{n=0}^{N}a_n p(t-nT),$$ where $a_n$ are (possibly complex) amplitudes taken from a finite alphabet, and the symbol rate is $1/T$. The pulses $p(t-nT)$ are often called "symbols". Matlab commands that ask you to specify "samples per symbol" are asking how many samples you want to use to define $p(t)$.

Of course, since you know the pulse duration, specifying the samples per symbol is an indirect way of specifying the sampling rate.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Thank you very much. Is the pulse duration the inverse of symbol rate? i.e the symbol time? How is it related to the transmissiob bandwidth. Thanks again. $\endgroup$ – Henry Sep 16 '15 at 3:15
  • $\begingroup$ The pulse duration is not, in general, the inverse of the symbol rate, because the pulses may overlap. In the equation in my answer, one pulse is transmitted every $T$ seconds, so the symbol rate is $R_s=1/T$. The bandwidth is determined by the spectrum of $p(t)$, but it cannot be less than $1/(2T)$. The pulse with smallest bandwidth for a given symbol rate is the sinc pulse. $\endgroup$ – MBaz Sep 16 '15 at 13:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.