# Tagged Questions

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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### Repeater based pathing

I'm having trouble finding information on the topic i'm interested in, and maybe my problem is just how i'm wording things. So, let's so i have a repeater-based communication system, where one Node ...
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### What benefits can we get from the use of GFDM?

Existing literatures say that the generalized frequency division multiplexing (GFDM) has lower out-of-band emission (OOBE) levels compared to orthogonal frequency division multiplexing (OFDM). ...
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### Level crossing rate, Rayleigh

So I'm solving an exercise and I'm wondering if I'm being tricked or not. The problem is to calculate the level crossing rate for a Rayleigh fading channel with threshold $15$ dB below the average ...
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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 ...
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### 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 ...
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### Wireless Resource Allocation Problem: How to acquire channel state information for different frequencies?

I am trying to understand frequency allocation in Dual Hop Relaying S-->R-->D. I have questions about Channel State Information. I am assuming the whole transmission occurs in two time slots and ...
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### How can I Map demodulated symbols using GRAY code [closed]

Could anyone help me by giving example how to do mapping of bits/ symbols using Gray code. your help will be much appreciated :)
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### 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 ...
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### 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= f1 -f2 +2Rb where f1 and f2 are carrier frequencies and Rb is the bit rate. For achieving a particular bit rate say 8 ...
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### 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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### What is the capacity or spectral efficiency of MIMO frequency selective wideband system?

Assume we have a frequency selective channel with Multiple Input Multiple Output (MIMO) antenna system with $M$ antennas at transmitter and $N$ antennas at receiver. Lets assume we have $K$ ...
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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 ...
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### How is each user's channel estimated in FH-CDMA under high Doppler?

Consider a CDMA system operating at high frequency band where the relative velocity between the transmitters and the receiver is high, which means that there is a non-negligible Doppler effect (e.g. a ...
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### 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 ...
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### 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 $$P_r = P_t G_t G_r (\frac{\lambda}{4\pi D})^2$$ ...
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### iterative decoding of serially concatenated convolutional code

Can SOVA (soft output Viterbi algorithm) be used for iterative decoding of serially concatenated convolutional code. i.e for decoding both inner and outer codes?
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### 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 ...
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### Understanding SNR in fading channels and MIMO systems

Signal to Noise ratio plays an important role in understanding the performance of any communication system. I understand the basic concepts of SNR but I am having trouble when trying to bring in a ...