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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5 views

The plot in MATLAB gets changed

in my research work on wireless communication, every time i run the program my PLOT in MATLAB gets changed to some extent (some times to larger extent too). I understood that the channel is random and ...
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2answers
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Understanding of wireless communication system from MATLAB point of view

I am dealing with a communication model described as $$\overrightarrow{y(n)}=\pmb{H(n)}\overrightarrow{x(n)}+\overrightarrow{w(n)}$$ where $\pmb{H(n)}$ is the $M\times M$ fading coefficient matrix ...
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27 views

SNR in analog and digital domain

In the digital domain a higher sampling will have a better SNR. Similarly does a narrow filter give a better SNR in analog domain? Once analog signal is converted into digital signal can SNR be ...
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7 views

Correlated fading channel: transmit and receive antenna correlation matrices

I am trying to create a non-i.i.d channel: correlated Rayleigh fading channel. $$ H= R_H \cdot H_o,$$ where $H_o$ is i.i.d. channel ( uncorrelated) and $ R_H$ is a channel correlation matrix, is ...
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2answers
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About length of the signal

In my research work i have the equation y(n) = hx(n)+w(n). My understanding about this equation from MATLAB point of view are: h has to be a single number. (for e.g., rayleigh generated). x(n) , w(n) ...
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1answer
33 views

How to write the matlab code for the below question? [closed]

i am dealing with a research in which for a single bit (0 or 1) there are 40 consecutive complex gaussian signals at receiver . How to get these 40 consecutive complex gaussian signals.
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2answers
32 views

From symbol rate to sample rate fractional ratio

My design has symbol rate and sample rate to DAC fixed but the ratio is not an integer. For example assume my symbol rate is 3 Mbps but the sample rate to DAC is 20 Mbps. So i am having 3 MHZ and ...
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1answer
37 views

Simulation of wireless communication system

In monte carlo simulation of the wireless communications system why we multiply noise by SNRlin( Signal to Noise Ratio in linear). What is the logic behind doing this. Any help in this basic doubt is ...
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1answer
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My preamble bits not enough for locking the timing recovery for a gaussian channel

I have chosen the preamble to be 48 bits (16 bits for carrier recovery+16 bits for timing recovery+ 16 bits for AGC of 30dB + 16 bits for phase ambiguity) As channel is gaussian and there is no much ...
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1answer
27 views

Complex gaussian random variable

In my work i need to generate circularly symmetric complex gaussian random variables with non zero mean and certain variance in matlab. I know the command for generating in case of zero mean , but ...
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30 views

Degrees of freedom in coding (for a communication channel)

I was reading on my lecture slides about how to achieve diversity (i.e. transmit more copies of the same message in order to avoid its corruption; this technique may be realized by repeating the ...
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2answers
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Can two modulations be used in the same frame

Can two modulations be used in the same frame? For qam/qpsk/psk/ modulation scheme for the data bits can i have a fixed preamble with psk modulation? does this help in achieving faster carrier freq ...
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1answer
45 views

Offset in Carrier and Timing

Is my understanding about carrier and timing offset right? Suppose my transmit frequency is 100 MHz and if my reference is 1ppm; then the transmit frequency has +/-100Hz offset. Similarly, if my ...
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23 views

error performance of ASK Demodulation [closed]

Why do we use the error performance of ASK Demodulation?
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29 views

Cross-Correlation in digital communication system

I've RF data that I can see my packets inside by Matlab, the file of RF data is a raw data(IQ SAMPLES DATA) .... I have did demodulation to those data which the output is also a demodulated raw data ...
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18 views

Power allocation for frequency selective channel [waterfilling ]

I am studying channel capacity with channel state information at a transmitter, where the water-filling algorithm is discussed. The algorithm should allocate more power to some subcarriers with larger ...
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Implementing time varying channel in matlab

i want to implement time varying channel in matlab. From the literature i understood that it can be done using First order Auto regressive process (AR-1). But in AR-1 process we need to estimate the ...
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1answer
40 views

How $\Delta f=\frac{1}{2T}$ satifies the orthogonality condition?

Let $$s_{ml}(t)=\sqrt{\frac{2E}{T}}\exp(j2\pi\Delta fmt)$$ where $T$ is the time-period of signal $\Delta f$ is the frequency spacing The text says that two signals $s_{ml}(t)$ and $s_{nl}(t)$ are ...
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1answer
21 views

Combiner vs mixer vs coupler?

All these three terms are often used in communication texts and apparently they are some how similar But what is exact difference between each of them?
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57 views

Preamble length in the communication system

how many bits my preamble should be typically?? course carrier bits+ carrier recovery bits + timing recovery bits+ phase ambiguity ?? i have see typically carrier recovery bits + timing recovery ...
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30 views

symbol synchronization

PLL is typically used in carrier synchronization and its diagram is well known, consisting of a multiplier, a low pass filter, and a VCO. In "Phase-locked Loop" at wiki (https://en.wikipedia.org/wiki/...
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1answer
27 views

how to determine a length of a channel? ( given path, delay)

Given a channel matrices for each subcarrier of a frequency selective channel (OFDM): i.i.d.. channel =(randn(ntx,nrx, N)+1i*randn(ntx,nrx, N))/sqrt(2); simulated ...
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how to use robot framework to launch unit tests on matlab?

I Know the syntax of rfw and and I want to make some unit test, for some kernels and functions in matlab and I need some help to begin with
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1answer
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What channel model to choose while simulating a system in passband with frequencies over GHz range?

I was wondering as to what kind of channel model do we use to test for BER vs SNR in a passband RF system. The system that I designed is basically a wideband frequency hopped OFDM system where I use ...
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1answer
21 views

bandwidth vs. bandwidth range

As known, Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. OK, what means when saying that bandwidth range is 15 ~ 20 KHz ? Does that mean that ...
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41 views

Instantaneous SNR

A relay system with 3 nodes: S (power node), R (relay node), and D (destination node). S transmit the signal x to R, received signal at R: $$y_R=\sqrt{P_sd_1^{-\beta}} h_{SR}\,x + n_r$$ with: $...
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37 views

What's the computational complexity of MMSE equalizer in OFDM system

As I know that in case of one tap OFDM equalizer, (ZF equalizer), we should have $N$ division complexity since we divide every subcarriers by its correspondent channel tap in frequency domain. But I ...
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35 views

What is difference between Phase shift keying (PSK) and Quadrature Amplitude Modulation (QAM) mathematical equation

I went through a literature and found the following expression for PSK signal. On this basis, what will be the equation for **QAM signal **. Also from where i would be able to read about this equation ...
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1answer
23 views

How to reduce PAPR with constellations choice?

How to tune constellations mapping M ary-psk or x-qam to reduce PAPR ?
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27 views

Matched filter (Non-Sychronous Detection)

I have IQ samples data file, RF data, that I sampled it by dongle SDR RTL which this file has packets that I transmitted them and the dongle has sampled them, so the IQ samples data file which is the ...
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How does the length of matched filter affects the fft of my signal

I have one matched filter that Im applying it on FM signal (with noise) in order to detect specific signal from my FM signal(with noise), Im trying to find out what's the relation between the length ...
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2answers
48 views

How does subcarrier correlation affect the BER of OFDM?

I am studying the OFDM system and would like to examine it under different subcarrier correlation scenarios. I have calculated BER for the uncorrelated scenario and now I have rewritten it for the ...
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1answer
25 views

BFSK modulation coding on MATLAB

Like for BPSK we generate random bits and then data= round(rand(1,num_bit)); %Generate binary data bpskModulated = 2*data-1 % mapping to -1 and +1 Can we do ...
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1answer
74 views

noise floor estimation

I want to estimate noise floor in the spectrum. I tested many methods using journals, but I couldn't find a stable method. Suggest that we have a spectrum consist of many signal and we want to ...
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22 views

I am looking for a book where I can find the implementation on matlab of a non adaptative DFE

I've already implemented RLS/LMS DFE and I need a MMSE implementation
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29 views

Non coherent detection BFSK demodulation?

I am simulating BER performance of BFSK under AWGN and Rayleigh fading, BFSK has two symbols one entirely on the real plane while other on the complex plane for representing let's say zero and one, ...
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1answer
31 views

Carrier frequency offset estimation for QPSK and asymmetrical spectrum

I am working on estimation of carrier frequency offset for QPSK data from a satellite. From my understanding, there are two main approaches: either remove data from the carrier (by taking the fourth ...
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1answer
18 views

channel impulse and frequency response: H?

The received signal of MIMO system is given as: $$ y= H \cdot x +n, (*)$$ where $H$ is a channel matrix. $h(\tau_l)$ is a channel impulse response. It is determined as a matrix $\in \mathbb{C}^{Nr \...
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1answer
7 views

What is role of BW and frequency in internet speeds?

First the bandwidth (BW): It is the amount of data that can be transferred simultaneously.just like more no. of highway lanes so that many cars can travel side by side simultaneously. Frequency It ...
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23 views

Calculation of channel autocorrelation for LMMSE

I am currently trying to implement an LMMSE estimator/equalizer for a python based ofdm receiver. The actual reception is done with a SDR and iq-samples are stored in a file for the "ofdm-receiver" ...
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1answer
32 views

what happens if you take the absolute value of a complex modulated signal? [closed]

I was going through some methods of eliminating carrier frequency offset (CFO). and one way is to take the absolute value of a received signal (somewhat like looking at the power of the signal) and ...
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24 views

Designing Matched filter based on frequency for outputting back base band of digital signal [closed]

Im having complex signal (I mean the output of the signal is in complex plain) , Im trying to do a demodulation for it , how can I use do a demodulation in order to back to my previous signal? my ...
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4answers
78 views

Negative frequency in the Fourier Transform [duplicate]

Why use this instead of a positive frequency? I asked on the math forum but it just wasn't helpful. I understand the idea of a negative frequency is important in general since many real signals like ...
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1answer
35 views

Channel encoding after digital modulation

Generally, when using channel encoding followed by interleaving, that process should be performed before the modulator and the system structure should be like that : For me, I only use the ...
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1answer
48 views

A Practical Method for Correcting Phase Errors in a Transceiver System Comprising of OFDM + DUC and DDC

I am back with a question related to my OFDM Transceiver System that I am designing where I use DUC and DDC. I could get rid of the high BER problem. I realized that the problem was due to the phase ...
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91 views

How to compute (in non adaptative way based on MMSE FIR) the feedback and feedword filter for DFE equalization?

System Model Consider the single-input single-output (SISO) communication system in the figure below: where the information bit stream is encoded and mapped such that the output of the encoder is a ...
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1answer
11 views

Receiver figure of merit

So I am solving receiver figure of merit. I have gain in dB and noise temperature in K. I know [G/T] = [G] - [T] dB/K Here should I need to take T in dB or just as K?
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what is the best technique to detect a given signal : energy detection, autocorrelation, and matched filter based sensing, CRC?

In order to detect the presence of a signal impaired by noise, what is the best technique (best metrics) one can use ? energy detection, autocorrelation, matched filter based sensing, CRC data ...
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2answers
44 views

How to Compensate for Frequency Offset in single carrier transmission Using Coarse and Fine Compensation?

How to compensate for the frequency offset of a PAM, PSK, or QAM signal when we are using single carrier transmission, I am looking for algorithms, explanations to be able to carry out the ...
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1answer
32 views

How to implement Signal transmitted by RF source

I am implementing a research paper, in which i have to implement signal transmitted by RF source in matlab. The equation given in this paper is : $s(n)e^{j \cdot 2 \cdot \pi \cdot f \cdot n}$. Any ...

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