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 ...
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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 ...
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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 ...
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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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53 views

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 ...
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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 ...
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1answer
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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1answer
13 views

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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18 views

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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26 views

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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22 views

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 ...
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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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1answer
39 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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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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10 views

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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34 views

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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1answer
14 views

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 ...
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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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10 views

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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1answer
34 views

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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11 views

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 ...
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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 ...
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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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15 views

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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19 views

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 ...
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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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14 views

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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20 views

Still don't understand why the $\mathbf w$ can let all beamforming be orthogonal to one another

I saw orthogonal beamforming (OBFM) in this paper : https://ieeexplore.ieee.org/document/7959644 Let me just explain what does the paper said about OBFM First ,in the picture above,the channel is $\...
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13 views

If the beamforming of these signal,$x_B$ and $x_A$, are orthogonal to each other,can the SINR increase?

Here is my thinking ,two device transmit $x_A$ and $x_B$ at the same time and with same frequency,meanwhile,device $C$ transmits $x_C$ to the other devices,and as we know,because the device $C$ is a ...
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24 views

Is there any technology or method that let user $Z$ knowS which message is $x_B$ and which is $x_C$

There is a device $Z$ which transmits the signal $x_A$ and receives the informations $x_B $ and $x_C$ simultaneously. I think when this device receive the signal,it won't know which is $x_B$ and ...
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8 views

How to recover 2*Zc systematic bits punctured in LDPC?

In 5G NR LDPC encoder 2Zc systematic bits are punctured at the transmitter end. At the receiver end, it is able to recover all bits excluding the punctured bits at the transmitter end. As the ...
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15 views

Hardware that Mixes Two Digital Audio Source into One

Is there any off-the-shelf hardware that extracts two digital audio streaming source from two digital audio stream(like USB+SPDIF), mixes, and transmits in single digital stream real-time(if the ...
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30 views

How to detect missing bit position in a bit-stream?

I'm trying to establish a one-way communication and facing problem in the receiver end because of some missing bits. For example, if the sender sends 100 bits the receiver received 95/96 bit. Now the ...
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19 views

If i use some method to decrease the self interference,how should i rewrite the constraint?

In the MIMO full duplex energy harvest optimization,we can find the similar constraint like this: $SINR > \gamma $,this $ \gamma $ is some of SINR value,it means that my SINR want to be higher ...
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19 views

Convolutional Code: choosing a trellis and puncture pattern for code 2/3

I'm working on convolutional coding in which I'm using generator polynomials as {13, 15} with puncture pattern of {1 1 0 1} for code rate 2/3. I don't get expected BER trend. If I use puncture ...
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24 views

RRC filter or rectangular pulse shaping filter in LFM chirp signal

I am working with a LFM up chirp signal, and I wanted to embed some data on it using a BPSK constellation. My doubt was, ¿should I use a RRC filter, like in usual communications schemes, or should I ...
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10 views

Which channel is the suitable channel for the short distance?AWGN?rayleigh or rician channel?

What is the unsuitable channel for the short distance?The short distance i mentioned is 1m or 2m.Unsuitable channel I mean is that if i assume this channel in my system,it will be very strange. In my ...
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8 views

The dis-advantage that sensor use FDD (Frequency-Division Duplexing) to transmit the digital signal

We must need lots of sensors in IoT,sometimes these sensors have to transmit their information to other sensors at the same time.I want to say some disadvantages that sensor use FDD (Frequency-...
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30 views

Why will the FDMA usually be used in transmitting analog signal,not in digital signal?

I saw this in the WiKi:https://en.wikipedia.org/wiki/Frequency-division_multiple_access FDMA can be used with both analog and digital signal but it generally used with analog signal Why?Don't we ...
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1answer
37 views

What factors affect the propagation delay at wireless communication?

Generally, the signal propagation delay is d/c. d is a distance between a transmitting antenna and a receiving antenna. c is light speed. However in NS-3, there is Random Propagation Delay Model ...
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30 views

What is the threshold to prefer polyphase channelizer over FIR filtering?

A wideband signal need to be processed to extract several narrowband channels from it. There are two straightforward approaches to do so: For each narrowband channel shift frequency and filter it ...
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1answer
54 views

Translating Matlab scrambler function to C

I am trying to implement the following matlab function in c: Mathworks scrambler Function Documentation This is the code I've written: ...
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19 views

Why does this self-interference cancellation cancel other signal,not the self-interference?Do i misunderstand something?

In this paper, https://ieeexplore.ieee.org/document/8704259 ,i think transmitter with M antennas transmit $x_f[t]$ to Cell-center user ,and transmit $x_n[t]$ to the Cell-edge user,however,the distance ...
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37 views

How to remove sum and difference terms while computing frequency from fft?

I am currently operating in vhf band AND trying to detect frequencies using Fast Fourier transform thresholding method. While detection of multiple frequencies , i received spurs(May not appropriate ...
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29 views

law for a random variable

Let: $Y=|X_1+X_2|^2$ with $X_1 \sim N(\mu_1,\sigma_1^2)$ and $X_2 \sim N(\mu_2,\sigma_2^2)$. $X_1,X_2$ are independent complex random variables. Consequently, $Y=Re(X_1+X_2)^2+Im(X_1+X_2)^2$ My ...
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70 views

Implementing Costas loop for 4-PAM

EDIT 2: OK, regarding the code I’ve pasted below, and seeing the FFT plot, I suspect the LPFilters aren’t working since I’m getting $0.5*m(t)*[cos(2 \pi f_c t ( \theta_e)+cos(\theta_e)]$ instead of $0....
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22 views

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 ...
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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 ...
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14 views

Where will system,information and decoder are separated, be applied?why don't we consider maybe the splitter is too small to destroy the information?

In the research of energy harvest and SWIPT,some paper will design that information decoder and energy harvester will be in the same device,then use a power splitter to split the received power for ...
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47 views

Why is the received signal=information+RF signal+noise,not just information+noise?

In this paper: https://www.researchgate.net/publication/325008791_Beamforming_Design_for_Max-Min_Fair_SWIPT_in_Green_Cloud-RAN_with_Wireless_Fronthaul Here is its system model In this model,it said ...