# 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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### 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 ...
330 views

### Chip rate and sample rate

If a sequence of +1 and -1 with chip rate ($\frac{1}{0.57 ns}$) is being used for purpose of estimating channel impulse response with delay spread of 6ns. We decide to have a new rate change to rate ...
2k views

### spectral mask and power spectral density

I have been reading a paper that specifies the spectral mask for certain communication devices attempting transmit over a channel Can someone explain 1) importance if this spectral mask, is it a ...
137 views

### Basic “filtering” in digital communications

I am completely stuck on solving some problems for my digital communications class. Junior level undergrad class, so fairly basic. I have been searching around all day for related articles etc but can'...
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### spread spectrum communication in airport

Does anyone know , how the spread spectrum sequences are used in airports. I've attended a presentation this morning regarding spread spectrum in my college, the author mentioned that the sequences ...
195 views

### PPM Variant - Analytic symbol error probability

I'm trying to calculate symbol error probability of variant of pulse position modulation considering only AWGN channel. The decoder is maximum likelihood so the implementation of the detector is by ...
63 views

### Modulating ofdm in audio spectrum

Trying to modulate audio with OFDM data. My fs = 44.1khz, i'm using 64 sub-carriers, but i'm only using 5 sub-carriers for data, so my bandwidth is about 3.445khz. I'm not sure how to properly write ...
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### What is the advantage of multiple antenna in receiver in energy harvesting ?harvested more power?

What is the advantage of multiple antenna in receiver in energy harvesting ? Assume there are $3$ transmitted antennas in the A device,and $1$ received antenna in the B device,now assume A device use ...
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### Doubts about Huffman and Shannon - Fano Coding

I was reading these slides about Source Coding and I have the following questions: 1) Let's consider this part: Can you explain me step by step the reasons of a, b, c? Which is the general rule to ...
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### To determine the Baud rate (in symbols/s) and throughput (in bits/s) of the system

You need to design a data transmission system where the data symbols come from an alphabet A with cardinality 32; all symbols are equiprobable. The bandwidth constraint is Fmin=250 MHz, Fmax=500 MHz. ...
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### Best way to represent the result of the simplification algorithm

I need to represent a result of my algorithm and show that with this algorithm a calculation is simplified. I am going to plot a figure with 3 variables: The first one, on Y-axis I will show an ...
33 views

### 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 ...
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### 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 ...
18 views

### Temporally synchronize two different or more real time digital audio signals

Are there any DSP techniques to temporally synchronize two different or more real-time digital audio signals without timestamp information?
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### Why will the power of signal become larger in the receiver ,but not smaller? the channel is a rayleigh fading channel

$\mathbf H_{AB}$ is a rayleigh fading ,$7$ is the antenna number for transmitting in the transmitter A, and $2$ is the antenna number for receiving in the receiver B H_{AB}=sqrt(1/2)*(randn(2,7), ...
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### What is the difference between circularly symmetric complex gaussian channel and rayleigh fading?

What is different between circularly symmetric complex gaussian channel and rayleigh fading? or are they the same? I Saw the method of creating circularly symmetric complex gaussian in this website, ...
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### replace input signal with δ will have the impulse response of the function?

Is my impulse response right? By definition,the impulse response is the output when the input is a impulse signal,so $y[n]=\sum\limits ^{n}_{k=-\infty}\frac{1}{2^{n-k}}\ x[k]$,the impulse response ...
28 views

### Why using a secondary observation increases the estimation variance?

The output of a 2-input 2-output communication channel is given by: $x^{(i)}(t) = \sum_{j=1}^{2}\sum_n {a^{(j)}_n}h_{ij}(t-nT-\tau^{(j)})$, where $x^{(i)}(t)$ is the i-th output, $\{a^{(j)}_n\}$ are ...
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### Theoretical maximum throughput of an adsl channel

Using a QAM transmission system, an N channel ADSL with FS sampling frequency, how could we derive the maximum throughput of a specific channel? I have access to SNR-Probability of error ratios and ...
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### Basic in “Precoding and Equalization Schemes”

I have found the interesting following paper for me: SVD-based MIMO Precoding and Equalization Schemesfor Realistic Channel Knowledge: Design Criteria and Performance Evaluation The paper is old, ...
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### What ICA should be applied?

I am using ICA from EEGLAB toolbox (not sure if I can use MATLAB's RICA() function as well). I am trying to use Infomax or JADER ICA to seperate two sources which transmitting at a carrier froquency ...
25 views

### How to add multiple sub bands of frequency into on wide band

Context: I am doing a project where I have to sample a video signal from a monitor with an SDR. The data is coming in for each pixel left to right top to bottom. Since my receiver doesn't have a very ...
16 views

### What is the function of RF chain in this system model?

Here is the system model from this paper :　 https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7008332 What is the function of RF chain in this system model ? Because i can't understand that what ...
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### How to design the weighting coefficient of null space?

How to design the weighting coefficient of null space ? I mean if the received signal is y_A=B+C+A=\sqrt{P_B} \mathbf H_{BA} \vec f_B x_B[m]+\sqrt{P_C} \mathbf H_{CA} \vec f_C x_C[m]+\sqrt{P_A} \...
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### How to form the data matrix for channel estimation?

I want to estimate a channel (its length is $L_c$) with a preamble (its length is $L$) and a least square estimator. Let $p_r$ the preamble received. I have a problem to build the data matrix $X$ for ...
16 views

### sc-fdma vs single carrier signal PAPR

Why is the PAPR of a single user sc-fdma signal different than the PAPR of a conventional single carrier signal if they both use the same modulation? aren't they both single carrier signals?
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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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### Channel information from power spectra

Linked below is a previous post regarding a multipath channel. Equalisation of FFT spectra I am reusing the images here: The first image is that of the power spectra when there is no multipath and ...
14 views

### Do we need to distinguish which rate is it when the system is point to point?or we just say “rate”,not downlink rate or uplink rate

If i have four transmitter,(t1,t2,t3,and t4), and one receiver(R),and each of them just have one antenna. When t1 is transmit signal to R,the other transmitters (t2,t3 and t4)harvest the RF ,when t2 ...