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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42 views

Can someone explain me how to generatee a doppler spectrum? [duplicate]

I have a signal generated in matlab, with Rayleigh Fading, how can I add a given type of Doppler spectrum ( Gaussian for instance) to that signal ? Any help will be really appreciated
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35 views

timing recovery resampler filter

I will explain the system: i am trying to transfer data from tx node to rx at UHF band on 400 MHz. I am trying first only wired transfer then i will try wireless.i am assuming only gaussian noise. My ...
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39 views

MMSE- Channel estimated based - DFE Equalization

For HF ionospheric channels ( frequency range 3 up to 30 MHz), I Want to make channel equalization in time domain, using MMSE criterion. I have to do it using the channel estimation. I have some ...
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33 views

Why we have to multiply the images with $(-1)^{x+y}$ to center the transform in frequency domain filtering?

To perform the filtering infrequency domain we perform multiplication of $(-1)^{x+y}$ why??
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207 views

why does DFE feedback filter matters?

I recently came across an article on the inventor of adaptative equalizer Robert Lucky, In this article : An Oral History by Robert Lucky (http://www.ieeeghn.org/wiki/index.php/Oral-History:...
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21 views

to choose the right preamble in the rx

What is the criteria to choose the preamble in the receiver. Is it good to have many transitions in both I and Q so that i can get faster timing lock? if there are less transitions probably my timing ...
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23 views

Two-GSMK channels demodulation: 3dB difference in BER

I am trying to demodulate individually two GSMK channels separeted by 50kHz (one channel = 25kHz). I am working on a limited ressources hardware so I decided to make some optimization on the signal ...
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134 views

Early-Late Symbol Synchronizer on Non-Triangular Pulses

I've been studying the basics of digital communications using the free book at desktopsdr.com. One of the examples is a 4-QAM demodulator which where symbol timing recovery is done with some Early-...
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60 views

RRC filter order

I have a question on rrc filter. Hope somebody can answer it. Tx path: My symbol rate is 1 mbps. I am using rrc 8x which becomes 8mpbs. For four symbols the order of the filter becomes 32. Next ...
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61 views

farrow resampler in timing recovery

My receiver contains: AGC,timing recovery,carrier recovey blocks. I am using gardner timing recovery with loop filter and farrow parabolic filter. The input to the farrow filter is the fractional ...
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Designing a PI filter for a Costas Loop

I am currently trying to implement a Costas Loop in order to demodulate a BPSK signal. Here is the reference block diagram I have been using to design the loop:Costas Loop Block Diagram I originally ...
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1answer
30 views

Channel impulse response in freqency domain

I have a doubt about DFT matrix and channel impulse response. Let $h$ is a channel impulse response , $F$ is a DFT matrix. IF I take a product. I got: $$ F* h=\tilde{h}$$ $\tilde{h}$ is a frequency ...
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54 views

processing gain in the receiver

I am always confused about the processing gain in the receiver. assume my receiver had LNA-> mixer->filter->ADC. does the filter in the analog section has any role to play with the processing gain? ...
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MIMO multipath delay [duplicate]

How is multi-path delay dealt with in MIMO systems? Most of the theory I have read on MIMO doesn't address multipath delay and assumes the multipath interference is limited to secondary antenna ...
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23 views

Rayleigh multipath fading channel in Matlab

I have to calculate eigen values of covariance matrix of Rayleigh multipath fading channel. The exact value should depends on delay spread and subcarrier spacing. I am able to find eigen values but ...
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1answer
148 views

Getting hilbert transform of IQ signal

Im new to communications so this may be a stupid question, but I am somewhat confused. I am trying to train an automatic modulation classification (AMC) algorithm on IQ data from the RadioML dataset. ...
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65 views

What exactly is transmit power in wireless communication?

My background is computer science. Recently, I had to come across some concepts in wireless communication/cellular mobile communication. Despite having gone through many materials, I am still having a ...
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38 views

phase response of an analog filter

I am trying to understand the relation between phase response of an analog filter and its influence on the quality of a signal with PSK modulation. For example I want to design a BPF for HF ...
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33 views

interpolation control in timing recovery

I was able to implement qpsk on my board. I could check data transfer between two seperate boards and it working fine. but what i observed was sometimes when mu goes to maximum it starts toggling ...
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Covariance matrix and eigen values

In my reference paper related to wireless communication the covariance matrix is made from vector comprising of channel coefficients. And non zero eigen values of the covariance matrix are calculated. ...
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35 views

std::cosf fluctuation: Results are off in low frequencies [closed]

I attempted to generate a continuous wave signal by using the C++ cos/sin functions. It's partly successful, meaning high frequencies seems ok, but very low frequencies give unexpected results. The ...
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29 views

correlator for cdma

I use a CDMA protocol for a multiuser communication. Let $c_i(t)$ the signature for the $i$-th user and $d_{i,k}$ the $k$-th modulated symbol for the $i$-th user. At the reception, we have $$r(t)=\...
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27 views

Modulation classification via demodulation confidence?

I'm not sure if this is the right place to post this question, but will try anyway :-) I recently started reading up on the field of automated modulation classification (AMC) where an algorithm ...
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25 views

expression sinr and gain processing

In a DSSS communication (spread communication with $1$ user). We have: $\DeclareMathOperator{\SINR}{SINR}\DeclareMathOperator{\SNR}{SNR}\DeclareMathOperator{\SF}{SF}\SINR=\SNR+10\log_{10}(\SF)$ with $\...
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RF signal identification algorithms

There exist many, many analog and digital data transmission protocols. It is often difficult to tell which mode one listens to and tedious to do for many signals. In Ham Radio, a Reed-Solomon ...
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60 views

How can I manipulate the time signal to insert zeros in between frequency domain bins?

I generate Multi tones in the frequency domain with constant amplitude and phase, for a fixed distance between tones. As the figure below, where r is the change in frequency spacing between different ...
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52 views

Hilbert transform Use as a Single Sideband Frequency Translator in Analog communication

How Hilbert transform helps us in communication? What is the practical significance of it? Specifically how is the Hilbert Transform used to create single side-band frequency translators?
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Update rule in Soft Output Viterbi Algorithm (SOVA) -Hagenauer rule

Soft output of SOVA, suggested by Hagenauer http://www.cse.lehigh.edu/~jingli/teach/S2003turbo/notes/SOVA.pdf , says in 2.2.2 "The Soft-Output Viterbi Algorithm" that $L_{j}^{\verb|^|}:= f(L_{j}^{\...
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32 views

interpretation of simulation results : capacity with precoder

I am studying the concept of computation the capacity. I have early asked about the difference between CSI unknown/ known to transmitter here. In the book about Matlab implementation OFDM system, the ...
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27 views

Relation between PDP (Power Delay Profile) and channel impulse response

I am traying to perform a simulation in Matlab and I faced up with some practical/theorical problems. The channel I want to simulate is frequency selective fading. The packets are short compared with ...
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25 views

What is the flow of data from a wifi receiver to the application layer?

I am not sure if I should ask this here but I am researching to build a receiver similar to a wifi one. I don't know here to look to find the flow that the data goes through. For example, what I ...
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21 views

Can we use ICA (Independent component analysis) on a noisy signal

If a receiver received a noisy signal can we use ICA to separate the noise from the signal ?
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48 views

Meaning: channel unknown and known at the transmiiter

What does "channel unknown" and "known at the transmitter" mean? In books about signal processing, it has always mentioned it if capacity or transmission (estimation) is discussed. I can't understand ...
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Power of ICI in OFDM System

I am studying the effect of time offset in OFDM system, I am interested in calculating the power of the ICI on each subcarrier, I am a bit confused about how to do it in Matlab, so how can I measure ...
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77 views

What's the difference between spreading and scrambling

I have a question regarding the scrambling code, What's the difference between spreading and scrambling? As I know, following the below figure, the scrambling doesn't affect the signal bandwidth: As ...
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220 views

What are the advantages and disadvantages of PN sequence over Walsh code

I would like to ask what are the disadvantages and advantages of PN sequence over Walsh code? and also Gold code over Walsh code. I have checked online, but I didn't get clear explanation for that. ...
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96 views

SNR Signal to noise ratio of Pseudo random bit sequence (PRBS)

How should I estimate the Signal to noise ratio of a 20 Gbps NRZ PRBS pattern from power spectral density--where should I take the noise floor if I can assume well the noise is AWGN? I know roughly ...
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62 views

What does it mean to plot a PAM signal over a number of symbols?

Our course has been using the book Introduction to Communication Systems by Upamanyu Madhow for our communications course. There is a question in the book on page 87 Software lab 2.1 which is ...
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synchronization with 2 users

I have $2$ users with different distance from the receiver and each user's message is spread with a different waveform. The $2$ waveforms are orthogonals. With a perfect synchronization, I don't have ...
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53 views

Digital Tanlock carrier recovery loop

I’m currently trying to understand a digital tanlock carrier recovery loop for QPSK (for example) I cannot understand how it works. For example we an ideal QPSK constellation. phi = atan2(Q/I) = pi/...
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29 views

FSK carrier frequency estimation in non equiprobable data

We know that in equiprobable data,change in phase over a time interval, this result will be directly proportional to frequency: f∝Im(s(n)s(n−1)∗) Where s(n) is the normalized complex FSK time domain ...
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receiver for a multi-user communication

I have an asynchronous multi-user communication with $10$ users. With a matched filter, I see the average BER by user is small ($<0.08$). Do you know any methods that can reduce the BER by user on ...
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42 views

decorrelating detector

In this paper decorrelating detector we have the decorrelating detector. With $K$ users, the correlation matrix of the signature waveform is $R=S^TS$ with $S=[s_1,...,s_K]$. Moreover $size(R)=K \times ...
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should implementing the MMSE equalizer in time domain and frequency domain give same results?

Assume we have a received signal $r$ explained as below: $r = h * x + n$ where $h, x ,*, n$ denote to the multi-path channel, transmitted signal, convolution operation and AWGN, respectively. ...
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IID noise assumption at Matched Filter sample time

I read that at the correct sample times of a matched filter output the noise is independent assuming a Nyquist pulse. Can someone provide a proof of this or explain it more? Assuming your matched ...
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Calculating average power of a discrete random signal with complex values

I have a Rayleigh channel that transmits discrete values according to the following: $$y(n) = h(n) * s_n + \omega_n$$ Where $y$ is the received message, $s_n$ is the symbol sent (constellation 2-PSM), ...
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What is the difference between SFO (sampling frequency offset) and SCO (Sampling clock offset)?

What is the difference between SFO (sampling frequency offset) and SCO (Sampling clock offset)? I think they are essentially the same phenomenon?
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Smooth factor in matlab

I use smooth function in matlab, in this function there is the smf (smooth factor) parameter that get different values. In different applications, this parameter ...
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How to generate rayleigh fading coefficients in matlab

I want to calculate received SNR for each cellular user CUs, so i want the corresponding transmission power P of base station BS to each user, the noise, and the channel gain coefficient of the ...
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37 views

Deep Learning based NDA Channel Estimation

I was wondering if it is possible to use Deep Learning to estimate the Channel Impulse Response for NDA synchronization? I understand Deep Learning is not normally used for regression problems but I ...

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