# 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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### Why is CDMA so complicated, wouldn't this simpler solution work?

I am now reading about Code Division Multiple Access method (CDMA), which is used for multiple hosts to send data at the same time. The main idea behind it is to use orthogonal vector basis to ...
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### Two signals with the same frequency in the same area can interfere?

If one signal is transmitting form transmitter $TX_1$ with some frequency $X$ and some other transmitter $TX_2$ is sending some other signal with same frequency $X$ will there be any clash or ...
267 views

### FWGN model implementation vs explaination (textbook pages attached)

I came across the FWGN model for multipath channel simulation in the book: "MIMO-OFDM Wireless Comuunications with MATLAB" Here is an explanation about Clarke/Gans model: Some code to generate a ...
52 views

### DSSS/CDMA: Number of distinguishable users with gold codes [duplicate]

From wikipedia, I know that Gold codes have length $2^n-1$, where $n$ is number of LFSR elements and that there are $2^n-1$ different Gold sequences for this case. E.g. assuming that $n=6$, I have a ...
130 views

### How to do base-band simulation of coherent detection of M-ary orthogonal signals?

I currently have a complex base-band simulator for non-coherent detection of M-ary orthogonal waveforms (such as M-FSK). I run the noisy signal through M correlators at lag=0, compute the magnitude ...
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### What are the fundamental reasons that suggest us to minimise transmission power for energy-efficient radio link design?

My question in short: Under which scenarios minimising transmission power is beneficial in terms of transmitter energy-efficiency? is there any fundamental reason to keep a low-power oriented design ...
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### Minimum bandwidth condition in FSK

I know that FSK occupies a larger bandwidth compared other keying schemes, $$BW= f_1 -f_2 +2R_b$$ where $f_1$ and $f_2$ are carrier frequencies and $R_b$ is the bit rate. For achieving a ...
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### Bandwidth of M-ary modulation schemes

I am confused with regard to how bandwidth increases with increase in number of bits transmitted for given duration. 1) Usually say in PCM system, when we increase the number of bits (n) for a given ...
221 views

### OFDM channel estimation

As we know, if we want to get the time domain response of the channel $h[n]$, we can first get the frequency domain response of the channel $H[k]=Y[k]/X[k]$. And then we do IFFT. But now one OFDM ...
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### Exact definition of soft bits in digital receiver

At which stage of digital receiver, the bits are considered as soft bits? I am unable to find the exact definition. I have rough idea how soft bits are different from hard bits but in terms of signal ...
265 views

### Mutual information of $\infty$-PAM

I'm trying to compute using matlab the mutual information for an $\infty$-PAM input (the limit of a very dense PAM constellation) for a range of snr and I got stuck. I'm working with a real-valued ...
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### How do we find the capacity of MIMO wideband point to point system?

This question is in the context of digital communication . In many text books (wireless communication), when people derive the capacity of point to point communication system (one transmit one ...
288 views

### Friis law and the power delay profile

Assume we have communication system between transmit and receive over wireless channel. The Friis path loss model is given by the following equation $$P_r = P_t G_t G_r (\frac{\lambda}{4\pi D})^2$$ ...
51 views

### Optimized resource allocation problem

I am from ECE background and trying to solve channel allocation problem. Let's assume I have three users and three available channels. I would like to allocate channel among them in such a way that ...
785 views