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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How to remove sidelobes 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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How to decode a Barker code
Let's suppose that I send the following sequence of bits:
$x = [1, 0]$
I use a 7 length Barker code ($b = [−1,−1,−1,1,1,−1,1]$) in a BPSK modulation scheme, resulting in the following sequence:
$...
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1answer
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Definition of MIMO (Multi-input Multi-output ),does this output mean antenna or transmitter?
I want to ask the definition of MIMO(Multi-input Multi-output )
If there are one transmitter and one receiver,each of them has $N$ antennas,$N >1$.
So i can say it is a MIMO system.
But if now i ...
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1answer
36 views
What is matched filter in QPSK signal?
Consider we have received a QPSK signal. We than make I (In phase) and Q (quadrature component) which I understand is nothing but multiplying the received signal by the cos(2*pi*f) and -sin(2*pi*f) ...
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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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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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Is there any relation between QAM and streaming?
I am trying to determine whether there is any relation between QAM and streaming (e.g., video streaming).
I know that QAM can be used for broadcast TV. I'm not sure if QAM is used for WiFi bit ...
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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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Why must the MRC SINR become smaller?
In this paper: https://www.researchgate.net/publication/328012548_Analysis_and_Optimization_for_Weighted_Sum_Rate_in_Energy_Harvesting_Cooperative_NOMA_Systems
Its system model is that a transmitter (...
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1answer
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What is the definition of half duplex?Is this system,$A$ give $x$ to $B$,then $B$ give $x$ to $C$,called half duplex?
I saw the definition of half duplex in wiki,and it said
half-duplex (HDX) system provides communication in both directions, but only one direction at a time (not simultaneously). Typically, once a ...
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1answer
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Find the ber for the cdma protocol
Do you know a reference (book, article) which gives (with a proof) the theoretical BER in the CDMA protocol for a differential modulation?
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How do i know this system is the NOMA system if the paper does't mention which system he use?
How do i know this system is the NOMA system if the paper does't mention which system he use?
Take the explanation of this paper for example:
From this figure explanation,i can determine which ...
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2answers
37 views
Confused about the definition of point to point ,this point means single antenna or single device?
What is the definition of point to point ? does the "point" mean single device or single antenna? I mean,can one transmitter with multiple antennas and one receiver with multiple antennas be called ...
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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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37 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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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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15 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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1answer
36 views
Can we band pass filter QPSK signal?
Consider we have QPSK signal with carrier frequency 10kHz. Generally, we demodulate or use matched filter on the the QPSK signal and recover the transmitted bit or the symbols. If the QPSk signal is ...
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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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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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1answer
56 views
What is the minimum sampling rate for QPSK or what is the bandwidth of QPSK signal?
Consider we have created a QPSK signal with a carrier frequency 100kHz. Before applying matched filter or demodulation we need to take samples from the received signal. So what is the minimum ...
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What's the effect of spread spectrum on frequency- selective channel
In brief, we consider the channel as frequency-selective channel if the frequency of the signal is larger than then frequency of channel.
So, does using the spreading spectrum change the frequency-...
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Is the zero part of a RRC filter generated signal sent?
When you use a RRC filter you add extra symbols at the end of your generated data because of the delay of the filter. When the data passes through the filter it gets up-sampled and the delay is ...
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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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2answers
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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
30 views
spectrum for a baseband communication signal
I have a question for the spectrum:
In baseband before passing through channel, should the spectrum of a communication signal be symmetrical?
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1answer
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Rate vs throughput vs capacity
What is the difference between Rate , throughput and capacity ? Their unit are all bps/s,but it seems that there are something different between them,can anyone tell me?
My research is optimizing ...
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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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Why does it seem most of people will optimize the downlink rate,not the uplink rate?
I search for some papers about energy harvest,SWIPT and optimization.And i found that there is just one paper to optimize the uplink rate,the others are for optimizing the harvested power,power budget ...
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duration for a signal after filtering [duplicate]
I have a signal $s(t)$ of duration $T$. This signal doesn't have a limited bandwidth. To solve this problem, I filter it with a pulse shaping filter (raised cosine filter).
My question:
Does ...
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2answers
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What will it happen when the outage occur?
I saw this explanation about outage probability,it said: it is the probability that an outage will occur within a specified time period.
So what will it happen when the outage occur?
stop ...
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1answer
32 views
Is it possible to spread signal using sum of more than one orthogonal code
I was wondering if we can spread the signal using more than one spreading code. Assume we have the Walsh code used to spread the transmitted signal, the Walsh code is, for example, gotten based on ...
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3answers
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Why only odd harmonics after non-linear amplification?
Why do I get only odd harmonics appearing? This not only happens at saturation of the transfer curve, but also in the linear portion of the curve.
I make a input signal that has too high power that ...
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1answer
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Calculating Data Rate using Bandwidth, Transmission Power, Noise Power Spectrum Density and Channel Gain
I'm a Software Engineering student researching on Load Balancing in IoT and I need to calculate data rate. However, I don't know how to use these values to attain data rate despite searching on the ...
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1answer
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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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1answer
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Log Distance-Normal Shadow Model and Friis
Since I'm founding several but different results about this model, I would ask you if all it is OK with this formulas:
1) Friis Model --> $Pr_0 = Pt + Gt + Gr + 20\log_{10}\frac{\lambda}{4\pi d}$
2) ...
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2answers
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Dimension of Matrix in MIMO with multi-path
In a MIMO system, the received signal is supposed to be $y = Hx + n$, where $H$ is the channel of dimension $N_t \times N_r$, $x$ is the transmitted signal with dimension of $N_t\times 1$ , and $n$ is ...
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1answer
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When Two Sampled Sinusoidal Are Orthogonal?
If two analog sinusoidal are orthogonal with duration T, their minimum frequency difference should be 1/2T in case of no phase offset between them.
And if there is phase offset, the difference is 1/...
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2answers
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Frequency Domain Correction of Frequency Offset or Doppler Frequency in LTE
We are working on LTE Uplink CFO Correction for 3 MHz band. The time domain CFO correction is easy, which depends on the processing of 3840 samples step by step multiply by $\exp(-j 2\pi f_\text{...
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Does gray coding bring improvement to SER of QPSK, compared with natural coding?
I understand gray coding contributes to BER of QPSK, yet really don't understand why it brings improvement to SER. According to the relationship of SER and BER, it should be improved. Actually, when ...
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1answer
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QPSK Phase Recovery : Maximum-likelihood Vs Costa's Loop
I have implemented a QPSK Costa's loop in GNU Radio and run some BER benchmarking. All is going well. Out of curiosity, I'm trying to implement the Maximum Likelihood phase recovery shown below.
For ...
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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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Offset QPSK detection in GNU Radio - Sample delay
An OQPSK detector is being tested in GNU Radio. The architecture was obtained from Michael Rice's Digital Communications - A discrete-time approach. The flowgraph is shown below.
The modulator ...
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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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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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2answers
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Why is bit error rate = symbol error rate / number of bits per symbol in QPSK
I saw a code computing the error probability of QPSK, and I found that in this code the bit error rate is computed as symbol error rate divided by $2$.
I think that $2$ is because the QPSK symbol ...
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1answer
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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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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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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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What is the difference between frame error rate (FER) and symbol error rate (SER)?
What is the difference between frame error rate (FER) and symbol error rate (SER)?
I know the difference between frame error rate (FER) and bit error rate (BER) from the website below
https://www....
