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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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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15 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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26 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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18 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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20 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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21 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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21 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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26 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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16 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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39 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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22 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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32 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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31 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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49 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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45 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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26 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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86 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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58 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 ...
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28 views

What is SIC? And why should we decode some signal first when we know that we will decode it again in the future?

I read the paper :http://jultika.oulu.fi/files/nbnfi-fe2019040110636.pdf The author said : First ,$x_s=x_1+x_2$,and the transmitter transmit the $x_s$ to $U_1$,and the received signal in the $U_1$ ...
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16 views

What is the advantage of this system (DA port in the DAS is usually equipped with its own power amplifier at the analog front-end)

I saw a paper,https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8283591 ,and it said Each DA (distributed antenna) port in the DAS (distributed antenna system) is usually equipped with ...
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27 views

preamble for doppler shift estimation

To estimate the doppler shift in a multiuser communication, I use preambles (PN codes). When I send the preambles with the datas (BPSK symbol), the estimation for the doppler shift are not correct. ...
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43 views

How to calculate Eb/N0 for a digital BPSK modulated multicarrier waveform

Suppose that I have a BPSK modulated multicarrier carrier waveform $L$ samples long at a sampling rate of $f_{s}$: $$ x_{tx}[l] = \sum\limits_{n=0}^{N-1} A \cdot \cos\left(2 \pi \frac{f_{n}}{f_{s}} ...
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26 views

Discrete Frequency Equation and Relation

I think I am looking at conflicting equations from a few sources, or maybe I just dont understand it. $ \Omega $ is Discrete frequency $ N $ is Discrete Period in number of samples $ \omega $ is ...
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35 views

How to measure a signal's initial phase given a buffer of received samples of the signal?

For CPM and FSK, how to measure a received signal's INITIAL phase based on its I and Q components given a buffer of received samples of the signal?
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39 views

frequency/phase offset estimation in satellite DOA beamforming applications

In satellite QPSK demodulation, we first estimate and remove the phase offset introduced by the channel. Then, we demodulate the baseband information bits (I & Q channels). In satellite DOA ...
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31 views

IT++ and Alternatives DSP Libraries

I want to implement some signal processing blocks in C++ so I did a bit of search on the available libraries for signal processing in C++ and I found that IT++ provides comprehensive set of functions, ...
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43 views

Binary vs 4-PAM PSD

I'm struggling to understand how you would form an expression for the PSD of a 4-PAM signal which is using rectangular pulse shaping. I understand for binary the likelihood of +/1 is equal so the ...
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22 views

data rate cdma chirp

I combined a chirp with a CDMA and I would like to know how to find the data rate. To begin, I spread the datas with the chirp and after I spread the previous signal with the PN code. My bandwidth is ...
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1answer
30 views

Cellular communication uplink

I can see, from my apartment, a cell tower. From what I have learned, in a time division duplex system the uplink and downlink communication are kept separate in time. Uplink from some time, then ...
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17 views

Average number of time slots until successful transmission in adaptive tree walking protocol

i was searching everywhere and couldn't find in any paper or book the average number of time slots until a successful transmission. for simplicity sake, in a simple network as given in the picture, ...
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175 views

How is DJI OcuSync wireless link physical layer implemented?

I'm looking for documentation on the wireless command link of the DJI OcuSync. I found this website (in Chinese). It seems like an OFDM link that uses Alamouti codes? I'm specifically interested in ...
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17 views

The theoretical formula of error probability and the data rate in MIMO,and the relation between $G^T$ and $G^R$ and $M$

I want to use Matlab to plot these two figures,fig(a) is the error probability,and as we can see,the higher M is,the lower error probability it has in the same SNR . The fig(b) is data rate,the higher ...
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17 views

waveform and multiuser communication

Sorry for my very simple question but I am a beginner in digital communication. Why in a multiuser communication, we have to have the same waveforms for each user? Is this an important rule for ...
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25 views

bandwidth and multiuser communication

I assume $3$ users. In the CDMA, the signals after the spreading for the $3$ users have the same bandwidth $B$. Is it possible to have $3$ spreading signals of the same band $B'$ such that $3B'=B$? ...
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25 views

Parity Check matrix from degree and check nodes polynoms, LDPC codes

I'm trying to simulate LDPC codes which were optimized for the BEC channel. I generated the degree and check nodes polynomials according to chapter 3.15 in "Modern Coding Theory" by Richardson and ...
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36 views

Symmetric Capacity of a Binary Discrete Memoryless Channel

While reading this paper https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5075875, I found that the the symmetric capacity of BDMC $W$ is given by $$I(W) = \sum_{y\in Y}\sum_{x\in X}\...
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44 views

PLL carrier recovery: intermediate versus baseband

When looking at carrier recovery, a PLL is often applied to correct the frequency offset between the local oscillator and the transmitter after down conversion. I'm wondering what happens to the PLL ...
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34 views

Synchronization Accuracy Required For Communications

One of the biggest problems in phase modulated communication is discovering when your signal has arrived. High accuracy in this area is important, as even a quarter wavelength error can cause the ...