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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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23 views

Simulation a received Signal in Matlab ( y=H*x)

I need your help in fixing an error in my simulation. Let me briefly explain what I simulate: OFDM, QPSK Channel H is represented as 3d dimensional array ...
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2answers
51 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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1answer
38 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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25 views

How to use “Filter” matlab function to apply channel to signal?

I need to use filter Matlab function to describe the following : H: MR x MT ...
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1answer
22 views

Understanding Matlab's Automatic Gain Control function

I am trying to understand the automatic gain control block provided by the communications toolbox. The documentation is here: Documentation My questions are in regards to two of the configurable ...
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10 views

Precoding technique for frequency selective channel

I am trying to understand the concept of precoding algorithm for frequency-selective channels. I have read the post "Basic in “Precoding and Equalization Schemes”, where it was explained for flat ...
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1answer
25 views

Is my concept of receive diversity right? EGC,MRC and SC

Is my concept of receive diversity right?There are three combining technology belong to receive diversity. 1.Equal gain combining(EGC) $\sum e^{-j\theta_k}(\sqrt{P}|h_k| e^{j\theta_k}x[n]+w[n])$ ...
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4answers
99 views

instantaneous frequency for a sum

In the literature, the instantaneous frequency for a signal $s(t)=e^{-j \phi(t)}$ is given by: $$f(t)=\tfrac{1}{2\pi}\frac{d\phi(t)}{dt}$$ This my problem: I have a signal $$u(t)=e^{-j \alpha_1 \phi(...
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2answers
96 views

upsampling in the frequency domain

I have the Fourier transform $S(\nu)$. If I oversample by a factor $R$ in the frequency domain. Does the duration of the signal $s(t)=IFFT(S(\nu))$ change?
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21 views

Can we use beamforming to make sure that the signal will not make interference together in Full duplex?if yes,why?

To avoid signals will make interference to each other in full duplex,there are two methods to solve this problem. Time-division duplexing and Frequency-division duplexing,they just use different ...
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32 views

Length of CDMA code and message length vs. number of participants

What is the minimum code size for CDMA codes for synchronuous CDMA (not asynchronous CDMA!) with N number of participants? Furthermore, suppose N parties want to uniquely transmit a message of length ...
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2answers
267 views

FSK: non-integer vs integer rmodulation index, peculiar peaks

I've been experimenting with frequency shift keying (FSK) and found a peculiar pattern I cannot explain. I noticed that there is a significant change to the shape of the power spectral density of the ...
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1answer
22 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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1answer
45 views

time for a signal after a sum

I have a signal $s(t)$ of duration $T$ with limited bandwidth. In matlab, I use a sampling frequency $fs$ and I have $L=T*fs$. After, I have $r=ones(size(s))+s$. To have a limited bandwidth, I filter ...
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1answer
51 views

Why do we need to increase sampling frequency at the transmitter?

I've thinking about this for some time now and I was wondering why do we need to increase smapling rate in the transmitter? I will explain a bit more. From the point of view of a software-defined ...
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20 views

How to prove that my combiner vector is $\mathbf H \vec f $?

When my received signal is $y=\mathbf H \vec f x+\vec n$,they we need a combiner vector in the receiver,how do i prove that combiner vector $\vec w$ is $\mathbf H \vec f $? After the received signal ...
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1answer
20 views

When i have already found beamforming,do i still need to use MRC?i have some problems for them

I have some problem when i learning MIMO,first thing is that i know designing beamforming and MRC can ensure better receive signals,but they are not the same,so i have some question about them. 1.I ...
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26 views

Optimal constellation in MAP

What are some strategies used to obtain Optimal constellation for MAP detection? I know we need to minimize symbol energy while trying to maximize the distance to reduce error.
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33 views

Matlab Plotting custom constellation along with decision regions

How do I create a custom constellation along with decision regions in Matlab, any help is greatly appreciated
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1answer
29 views

Will the received waves be the same if the transmitter use the beamforming to transmit the same signal?

If there is a transmitter with three transmitted antennas,and a receiver with five antennas,and these five antennas are very close to each others. Now transmitter use beamforming with these three ...
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1answer
26 views

Isn't Gardner's algorithm and Early-Late gate the same thing?

I'm reading about some symbol synchronization methods and I find these two (ELG and Gardner) very similar. Early-Late gate takes 2 samples, one at $t=T-\delta$ and the other at $t=T+\delta$, then ...
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2answers
166 views

About understanding a Matched Filter

I have some basic doubt in understanding a matched filter (MF). Please note that I have already seen very informative post in this context Understanding the Matched Filter In what follows, I list ...
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1answer
15 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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20 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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31 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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1answer
23 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
43 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
28 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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2answers
101 views

MU-MIMO Sensitivity to Line of Sight (LOS)

Why do researchers talk about MU-MIMO being "less sensitive to line of sight" / "LOS Okay"? For example in this video, time=[00:40,00:42] Similarly, "User separation based on spatial channel ...
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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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1answer
40 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
21 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
40 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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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
53 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
78 views

Does the Quality of the Pictures Taken by a USB 3.0 Camera Depend on Cable Length?

I've got a JAI GO-5000-USB camera and have tried several cable lengths, ranging from 40cm to 5m. So far, I haven't observed many differences in the quality of the pictures I've taken. Since I want ...
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0answers
63 views

Implementation OFDM system in Matlab

I am working on the OFDM transmission system. A channel is given, MR x MT; input data MT x S, and length of a cyclic prefix (CP)....
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1answer
32 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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0answers
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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1answer
186 views

What is the meaning of inverse signal bandwidth?

I have been studying the two ray model in communication systems. The text I'm studying has two signals, $u(t)$, which is Line of Sight and $u(t-t')$, which is the reflected signal. It quotes, ...
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44 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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1answer
19 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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0answers
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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36 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
54 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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2answers
64 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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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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0answers
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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3answers
2k views

Capacity of cascade binary symmetric channels

Let's imagine that we have interconnected in cascade $L$ binary symmetric channels each with the same transition probability $p(y|x) \in \{p, q=1-p\}$, where the output of each BSC is connected to the ...
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51 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 \\ ...