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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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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42 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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25 views
Can anyone tell me about active cancellation techniques?
Can anyone tell me more about active cancellation techniques in detail ? Because i saw this paper : ( https://www.researchgate.net/publication/263352526_All-Digital_Self-...
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1answer
39 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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10 views
Is the network coding similar to decode and forward or coded and cooperative?
There are three methods that relay can transmit the information:
Amplify and forward
decode and forward
coded and cooperative
I want to ask which method is similar to the method i said
Device $...
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1answer
17 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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45 views
Is there a better estimator with lower variance?
The output of a 2-input 2-output communication channel is given by:
$x^{(1)}(t) = \sum_n {a^{(1)}_n}h_{11}(t-nT-\tau^{(1)})+\sum_n {a^{(2)}_n}h_{12}(t-nT-\tau^{(2)})$, and
$x^{(2)}(t) = \sum_n {a^{(1)...
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52 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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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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1answer
34 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
28 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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24 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
59 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)\}$$
How this can be represented in matlab.
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16 views
What is the function of RF chain in this system model?
Here is the system model from this paper :
https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7008332
What is the function of RF chain in this system model ? Because i can't understand that what ...
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1answer
22 views
What are the definitions of symbols and samples related to PCM?
What are the definitions of symbols and samples related to PCM? For example in binary encoding $\{0,1\}$ with 8 levels of quantization, is one symbol either of $ \ 0 \ or \ 1\ $? or is it the ...
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15 views
How to design the weighting coefficient of null space?
How to design the weighting coefficient of null space ? I mean if the received signal is
$$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
45 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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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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12 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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17 views
performance analysis of channel
I am studying channel precoding, and as HW lab it was given a task to implement a system with different precoding algorithms and to apply an algorithm that was given in lab description. So I have ...
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1answer
45 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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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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23 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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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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16 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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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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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
40 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
29 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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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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29 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
48 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
55 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
63 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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17 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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17 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
31 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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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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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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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
35 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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Convolutional coding that payload length does not change
This is the question about Sigfox radio specification.
The stack:
Specifically, in Section 3.10 of the specification, we have a convolutional coding (after CRC) with three possible polynominals.
I ...
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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
46 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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17 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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29 views
Why when the SINR of transmitting signal is very large ,the device cannot decode the received signal at the same time? [closed]
$A$ transmit $x$ and receive the $y$ at the same time.If the SINR for transmitting $x$ is very large,$A$ cannot decode the $y$ signal.Why?
In my opinion,If the SINR for transmitting $x$ is very ...
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1answer
43 views
How can i know the full duplex does work from the Shannon's theorem?
There is a full duplex system below,two user are $A$ and $B$,according the definition of full duplex ,$A$ and $B$ have to transmit and receive the signal at the same time.that is, transmitted signal ...
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1answer
82 views
Digital FM Demodulation
I have created a Common Lisp Library to receive samples of an FM signal from BladeRF1 SDR. I want to write a subroutine to implement FM demodulation. The input should be in the format of IQ data.
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