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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35 views

Assumption of SINR measurement

I am assuming there is an Access Point (AP) and IoT Nodes in NOMA uplink scenario. Following is assumed: the AP does not know the channel gain of IoT Nodes the transmission power of nodes is also ...
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1answer
40 views

Relation between frequency and phase in PLL?

Apparently both frequency and phase are independent properties but what is the relation between frequency and phase in PLL?so that when one is locked ,other is also locked
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1answer
87 views

Output of Zero-forcing equalizer doesn't match theoretical calculations

Let's say I have a sequence $x[n]$ (signal) and perform convolution with another sequence $h[n]$ (channel), so: $$ y[n] = h[n]*x[n] = \sum_{k}{h[k]x[n-k]} \leftrightarrow Y(z) = H(z)X(z) $$ I'm ...
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1answer
26 views

Why can we know the best precoding direction after we do the SVD to the channel?

Why can we know the best precoding direction after we do the SVD to the channel?for example $\mathbf y=\mathbf H\mathbf s+\mathbf n$,now we do the SVD to the $\mathbf H$ If the $\sigma _1$ is the ...
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2answers
102 views

Does zero-forcing equalizer need known channel impulse response?

I'm studying some of the basic equalizing structres and I understand how Zero-forcing works, but it seems to me that a known channel impulse response is needed. Am I right? If so, what's the point? I ...
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2answers
63 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
91 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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1answer
83 views

sum of 2 signals

I have $2$ signals: $x(t)$ and $y(t)$. They have the same bandwidth $B_x=B_y$. But the bounds for the bandwidth are not the same. For example, $B_x=f_{max}-f_{min}$ and $B_y=g_{max}-g_{min}$ with $f_{...
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1answer
33 views

Good Starting Material for a SEMI Beginner

I come from a hardware background and I am wanting to get myself more involved with the digital signal processing side of things. I understand a lot of concepts, but only through application meaning ...
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25 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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1answer
20 views

Why there is no paper optimize the consumption power of the circuit in energy harvest?

In the optimization of energy harvest ,some paper want to maximize the harvested power ,rate or minimize the transmitted power,so when they write the formula of optimization,they may assume the ...
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63 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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2answers
91 views

How to generate random data with a specific bandwidth

I generate some random data (bits, actually, using MATLAB's randi) and then I convert such bits to BPSK (1 and -1). After that, I use a RRC pulse (roll-off factor ...
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1answer
26 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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29 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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15 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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0answers
119 views

GNU Radio - Bandwidth and Band Reject Filter

I am currently trying to generate a psk modulated carrier with gnu radio. Attach is an image of my flow graph. As can be seen I am generating a bit stream using the Random Source module and ...
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0answers
52 views

Does this system of equations have a solution?

My heuristic approaches to find a solution for the following system of equations have failed so far. Does a solution exist? $$ \left[ {\begin{array}{cc} a_k & 0 \\ a_{k-1} & a_k \\ ...
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2answers
98 views

Is it possible the difference between OFDM-CP and OFDM-ZP about 10dB

I'm building basic matlab code for ofdm, but when I change the CP OFDM into ZP-OFDM with sme parameters, I get the performance is worse by up to 10 dB!! Is that right ? or there is some thing wrong in ...
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0answers
58 views

Problem with 1st order PLL update equation

The output of a communication channel is given by: $x(t) = \sum_n{a_n}h(t-nT)$, where $\{a_n\}$ are BPSK symbols, $h(t)$ is the channel response, and $T$ is the symbol period. If there is an ...
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16 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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1answer
48 views

Mapping soft symbols in DQPSK

I'm trying to soft decode DQPSK. According to this paper the bits are: $b_1 = \mathrm{Re}\{s_n s^*_{n-1}\}, b_2 = \mathrm{Im}\{s_n s^*_{n-1}\}$ If I put 0.707 as a 100% probability of 0: $\begin{...
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1answer
51 views

How to calculate the channel gain if the channel is a $N$ by $M$ matrix,$N,M>1$ [closed]

How to calculate the channel gain if the channel is a $N$ by $M$ matrix,$N,M>1$ For example,i create a rayleight fading channel ...
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27 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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1answer
66 views

How we can represent a bandpass signal equation in matlab

The general form of bandpass signal is given by $$s(t) = \Re\{S_b(t)\exp(j2 \pi f_ct)\}$$ How this can be represented in matlab.
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24 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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1answer
31 views

What are the definitions of symbols and samples related to PCM?

What are the definitions of symbols and samples related to PCM? For example in binary encoding $\{0,1\}$ with 8 levels of quantization, is one symbol either of $ \ 0 \ or \ 1\ $? or is it the ...
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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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1answer
254 views

Frequency-selective channel: Basic in theory

In a lecture, it was covered a topic "frequency selective and flat fading channel models". For case, the frequency selective channel we have a channel impulse response ...
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0answers
21 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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2answers
52 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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1answer
74 views

What does the physical meaning of $\mathbf{U} \Sigma \ \mathbf{V}^{*} $ in the MIMO system?

SVD is a method to cancel the interference in MIMO system,we often do the SVD of channel as below \begin{align} \mathbf{H} &= \mathbf{U} \ \Sigma \ \mathbf{V}^{T} \\ % \end{align} So $ \...
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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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2answers
25 views

Does orthogonal beamforming mean $\mathbf f_a \cdot \mathbf f_b =0$?

If i said that these two beamformings $\mathbf f_a $ and $ \mathbf f_b $ are orthogonal to each other,does it mean $\mathbf f_a \cdot \mathbf f_b \approx 0$ ? Because i have see two paper about ...
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23 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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14 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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0answers
17 views

Why is the $G_{rx}=\sqrt{\frac{N_{rx}}{\hat{N}_{rx}}}S^T_{rx}\tilde{U}^H$ ? How does author calculate it?

I search for some information about Null Space Projection,and saw some information from this pdf: http://taneli.riihonen.fi/presentations/C027slides.pdf ,in the page 16,the author begin explaining ...
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25 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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0answers
37 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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1answer
330 views

DC Components and Frequency

I have started learning digital communication and was on line coding. I read there are certain characteristics that we need to keep in mind while choosing the right line coding method. One of these is ...
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1answer
64 views

What is the difference between the V-OFDM and OSDM

I am trying to understand the difference(s) between V-OFDM (Vector Orthogonal Frequency Division Multiplexing) and OSDM (Orthogonal Signal Division Multiplexing) which are used as a multicarrier ...
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0answers
19 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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0answers
41 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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1answer
890 views

Relationship between signal rate, data rate, minimum bandwidth

I need to understand the relationship between bit rate, signal rate and minimum bandwidth. I read in a textbook that We define three cases for relationship between bit rate and signal rate for ...
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2answers
110 views

How to get the inverse of Filter based on channel

Given a signal $X$, and a channel $h$, and the received signal $Y = Filter(h,1,X);$ What's the inverse of filter, it means if I know $h$, how can I get back $X$ ?
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1answer
82 views

Representation, Bandwidth and composition of Digital Signals

I have started learning data communication and I'm not able to grasp certain topics. First (i) I know that analog signals are continuous and digital signals are discrete. Analog signal are ...
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0answers
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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33 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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1answer
33 views

Assessing relative wireless channel quality using Capacity and Condition Number CDFs

I have Channel capacity analysis figures for two wireless channels show below: My question: While ergodic capacity in the first subplots are very clear in conveying the channel capacity, How to make ...

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