# Questions tagged [digital-communications]

Digital Communication is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel.

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### Assumption of SINR measurement

I am assuming there is an Access Point (AP) and IoT Nodes in NOMA uplink scenario. Following is assumed: the AP does not know the channel gain of IoT Nodes the transmission power of nodes is also ...
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### Relation between frequency and phase in PLL?

Apparently both frequency and phase are independent properties but what is the relation between frequency and phase in PLL?so that when one is locked ,other is also locked
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### Output of Zero-forcing equalizer doesn't match theoretical calculations

Let's say I have a sequence $x[n]$ (signal) and perform convolution with another sequence $h[n]$ (channel), so: $$y[n] = h[n]*x[n] = \sum_{k}{h[k]x[n-k]} \leftrightarrow Y(z) = H(z)X(z)$$ I'm ...
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### Why can we know the best precoding direction after we do the SVD to the channel?

Why can we know the best precoding direction after we do the SVD to the channel?for example $\mathbf y=\mathbf H\mathbf s+\mathbf n$,now we do the SVD to the $\mathbf H$ If the $\sigma _1$ is the ...
102 views

### Does zero-forcing equalizer need known channel impulse response?

I'm studying some of the basic equalizing structres and I understand how Zero-forcing works, but it seems to me that a known channel impulse response is needed. Am I right? If so, what's the point? I ...
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### Types of equalizers

I can't get my mind around the different types of equalizers and the difference between some of them. I've been looking at different books unsuccessfully. So far, I have Wikipedia's list and this ...
91 views

### Real Fast Fourier Transformation (FFT) in 2D changes with changing the axes order

I am using Python to calculate the real FFT for a 2D array. I found that the real FFT function does not return an array with the same size as the input array, rather, it returns an array with the same ...
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### we have already know the number of null space,Why should we still do SVD when we want to use null space to cancel the interference?

What is the true meaning of using SVD when we use null space to cancel the interference signal ? I mean why when lots of paper mention that they use null space to cancel some interference signal ,...
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### Does orthogonal beamforming mean $\mathbf f_a \cdot \mathbf f_b =0$?

If i said that these two beamformings $\mathbf f_a$ and $\mathbf f_b$ are orthogonal to each other,does it mean $\mathbf f_a \cdot \mathbf f_b \approx 0$ ? Because i have see two paper about ...
23 views