New answers tagged

1

The diagram from the textbook in the opening post appears to have some mistakes. For this IFFT method, the box that says 'QAM modulator' should just be a complex number generator (such as a digital QAM generator that produces a complex number from 'x' binary bits at a time - that is meant to represent a vector on a QAM grid). And there should be two D/A ...


1

yes, you are right. But there is misconception that figure of merit is the ratio of output to input SNR. It is actually the ratio of output SNR of a receiver to the output SNR of a baseband system (without modulation). Here, the output SNR of a baseband system is taken as a benchmark for judging noise performance of receiver. Hence, FoM = (...


0

Robert's explanation is nice. Although, for finite difference, 𝑥[𝑛]−𝑥[𝑛−1] translates to 𝑥[𝑛+1]−𝑥[𝑛], which translates to X(z).z^(-1) - X(z) = X(z).{(1-z)/z}. And for the case of actual differentiation, the finite difference will generally be divided by sampling period T. Those other expressions from text books eg. z/(z-1) tend to get lost in ...


1

The zero padding (or the cyclic prefix) takes care of inter-symbol interference that occurs due to delay spread. It is hence something you append to your signal in time domain. Hence the order is this: Assemble all the data symbols along the subcarriers (can contain data for multiple users, as you said). Compute DFT (via FFT, typically) Add cyclic prefix (...


0

Thinking in terms of convolution with shifted impulses help. Multiplication in the time domain corresponds to convolution in the frequency domain. Your example is a classic showcase of frequency/band shifting using a "carrier" such as a cosine (or sine) or a complex exponential. Now, note, that the Fourier transform of these carriers are actually shifted ...


Top 50 recent answers are included