Tagged Questions

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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Phase synchronization in BPSK

In BPSK for demodulation at the receiver end we do phase recovery between received wave and carrier wave. We can find the phase difference between the carrier and received waves using : PLL And ...
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How to find frequency and phase shift in the recorded wave( .wav file )

I am working on BPSK at frequecies near 20 kHz with a sample rate of 44100 Hz. We can't afford sample rates above than this due to computational complexities. Have found that the frequency of ...
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Fast/efficient way to turn real passband samples to complex baseband

I have real-valued samples of a bpsk signal i am receiving (see frequency spectrum in figure A), that I want to turn into complex samples for further processing. However when I just use the received ...
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Why does signaling overhead for time synchronization scale up with the number of transmitter nodes in a multiple access system?

I was recently reading about random multiple access methods without time synchronisation (of the pure Aloha type). In this paper it is stated that, The need for transmitter synchronization is a ...
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Periodically-varying phase between transmitted sound and received sound

I have a function that can find the phase difference between two signals, this function uses Hilbert transform to do so. Here is the python code for it ...
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Both BPSK and 2-VSB transmit one bit of information per smybol and both modulate the real part of the signal. The difference is, as far as I understand, that BPSK does not modulate the imaginary part ...
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Bandwidth of ofdm symbol in a visible light communication system

What is the difference of the bandwidth of the LED and the optical channel? If ofdm symbols are transmitted over this system, is the bandwidth of ofdm symbol equal to BW of the LED or of the channel.
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Why are QAM Constellations regular and rectangular?

In most IQ graphs of QAM noise, it seems like the constellation ends up with more distortion the farther you get from the center: What causes this non-linear distortion, and why are QAM ...
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Generating two bursty signals that are unsynchronized with each other

I am testing adjacent (and non-adjacent) channel rejection for an OFDM signals. (Clause 18, IEEE 802.11-2012) In general the requirement is to generate test frames on what is referred to as the test ...
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Compute probability of error to each QPSK symbol

I'm trying to compute the probability error function of a QPSK modulation. I have a single user, who send a determined symbol $x = \frac{1}{\sqrt 2} \left(1+1j\right)$. Then I estimate at the ...
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Problem in understanding DDFS (Direct Digital Frequency Synthesizer.)

I need to generate sine and cosine signals using DDFS (Direct Digital Frequency Synthesizer.) I'm unable to get the idea of the phase increment applied as input which changes the frequency of the ...
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Location of Matched Filter

In a digital communication receiver, matched filter(SRRC filter) is used. In different literatures, the location of the matched filter is mentioned in two different places. One is just after the ADC ...
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Visible light communication and LED modulation

I work on a VLC system in which 16-PAM symbols with complex pilot symbols are as ifft input. I made the ifft output real and positive. Now how should i use these ofdm symbols to modulate LED? Their ...
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Estimation problem for M-ary PAM transmission over AWGN channel problem

Here is my AWGN channel model Input $\mathbf{x}$ is from a M-ary PAM alphabet $\mathcal{A}=[-3,-1,1,3]$ $\mathbf{n}\sim\mathcal{N}\left(0,\sigma^2\right)$ whose variance $\sigma^2$ is not known. ...
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Sampling signal after root raised cosine

I am generating series of 1 and 0. then pulse shaped them with root raised cosine and after than deciding to do match filtering and recovering the bits however it turns out that I am not getting the ...
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How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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The little problem with Kalman filter

I am trying to simulate the Kalman Filter. I have the covariance matrix P_{0|0}. Tell me please, how can I get the predicted (a priori) estimate covariance matrix ...
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How to find the time instant where my sent signal and received signal can synchronize?

I am having two .wav files, one is modulated wave that is made into a .wav file and another is a recieved .wav file which is recorded from microphone while playing first modulated .wav file. So now ...
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What is the coherence bandwidth of the channel?

I read the following sentence. "In wideband systems, the transmission bandwidth of a single channel is much larger than the coherence bandwidth of the channel." What is 'coherence bandwidth of the ...
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Why do we do oversampling in raised cosine?

I would like to do know why do we need to do oversampling in a raise cosine filter. There is already a question like this but the answer is very confusing and not sufficient. I need to know what ...
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Pull-in range or acquisition range of a phase-locked loop

I have a specification for my design(timing recovery) that acquisition range should be $10\%$ of symbol rate. On what factors does acquisition range depend that I should take care while designing?...
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why does the decision boundary change in BPSK? is it true?

I am working on modulation and demodulation of BPSK using python. i made a code for modulation and demodulation,while demodulate i tried to compare my actual data bit stream with demodulated bit ...
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Do convolution encoders exist with two separate (independent) inputs?

Do convolution encoders exist with two separate (independent) inputs? I got the question in my mind when I saw the question attached here.
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Why do the OFDM training (and payload) symbols have silent sub-carriers (aka virtual carriers)?

I am examining an OFDM signal. Training symbol: The first two OFDM symbols are training symbols, they are 2PSK modulated (within the subcarriers). In the first OFDM symbol the $(0+18N)^{\rm th}$ ...
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Symbol timing recovery design

I am trying to design the Symbol timing recovery(#STR) block of #DVBS Receiver. These are the specifications Symbol rate ($f_s$) = $2\textrm{ MHz}$ Acquisition range = $10\%$ of Symbol rate ...
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Loop bandwidth for symbol timing recovery

I am trying to design the Symbol timing recovery (STR) block of DVBS Receiver. How should I chose the loop bandwidth and damping ratio for determining the loop filter coefficients $k_1$ and $k_2$? ...
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How to derive the transmitted signal from a constellation diagram

Let us assume we have $16$ symbols to transmit. We can represent these $16$ symbols by $16$ unique signals and transmit. If at the receiver we can identify these $16$ signals correctly, we have ...
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Method of reconstructing a band-limited signal from discrete samples

I understand current cell phones use digital communications. Given that this industry brings in billions of dollars each year, there is much incentive to get the best performance possible. So what ...
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How does BER performance depend on gray or natural binary?

I read that BER performance would be improved if Gray code is used in 16 QAM rather than natural binary coding. I think that it should not depend on the coding used. 16 QAM simply assigns to each of ...
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Fractional spaced equalizer + timing (clock) recovery

I am trying to figure out how timing recovery is used after equalization (or, being more correct, when the equalizer is in the timing recovery loop), having a T/2 fractional spaced equalizer and using ...
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Proving DFT equation

How can I prove the equation $(3)$? I can't understand why there is a $2/N$ in $(3)$. Why he just get the second term in DFT? Consider a sinusoidal input signal of frequency $\omega$ given by ...
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Frequency autocorrelation function - Communication channel

If we have two discrete stochastic spectra and each spectra has $N$ points. We want to calculate the autocorrelation of these spectra, what should be the number of points in the resulting ...
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Loop Filter Coefficients in Timing Recovery loop in Baseband Receiver

I am trying to design the Symbol timing recovery(#STR) block of #DVBS Receiver. For reference, I am using the following matlab simulink design (NDA timing recovery part within Digital Baseband ...
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Digital Filters deal only with samples, right?

I'm new to digital filters. So I'm trying to get things right and I can't find an explicit answer to my question on the internet. Question: Digital filters only accept samples as input? I mean the ...
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What are the advantages of barker sequence over marker sequnce?

I read that barker sequence is used for synchronization among other uses. Barker sequences are rare and they have special properties - this part I understood. I am missing some thing when I think ...
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Generating LDPC codes of arbitrary sizes in MATLAB

I am having problems generating LDPC codes of arbitrary sizes in MATLAB primarily because MATLAB insists on the parity check matrix that is input into its ldpcenc ...
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Methods for calculating signal quality metric

i'm sure this is a fairly large topic area, but I'm not quite sure where to start. I have a signal in which I can change several parameters, such as the frequency, gain, etc. The modulation is a ...
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Entropy of a dynamical system and source code length

The entropy of a source $H(S)$, gives you the average codeword length to encode a given source alphabet. i.e. it is the average number of bits per symbol required to encode the information in the ...
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Cyclic prefix vs. guard interval. Why use one over the other?

I'm currently studying some OFDM techniques, and have found that in order to avoid Inter-Symbol Interference (ISI), there needs to be some space in between symbols. Lets assume this length to be $\mu$....
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Practical diversity combining at receivers (Maximal Ratio Combining & Equal Gain Combining)

I am trying to perform practical diversity combining implemented in GNU Radio by using Ettus N210 USRPs, one as a transmitter and two as receivers. To compare Equal Gain Combining (EGC) and Maximal ...
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What is the difference between multipath channel and fading channel? [duplicate]

what is the formula of channel reponse of multipath fading? is it h = 1/sqrt(2)[randn(1,N) + irandn(1,N)]; % with N: length of signal or 1/sqrt(2)1/sqrt(Ntap)[r andn(1,Ntap) + i*randn(1,Ntap)];%...
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How to calculate transmission capacity?

My textbook doesn't explain how they got the answer to this question: "If a transmission channel uses an analog carrier wave that is modulated by eight amplitudes and sixteen frequencies per bit ...
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M-Array DPSK decoding and encoding

So i'm trying to figure how how to do the encoding and decoding of an M-array Differential Phase Shift Keying (DPSK) signal. I understand how to do it for binary DPSK, but on higher ordered signals I'...
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Resources on Non-Gaussian Channels

I understand why most of the classic textbooks only consider Additive White Gaussian Noise channels in digital data transmission. Unfortunately in my case noise is not Gaussian and it might even be ...
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Reasoning Behind Additional Phase Shift in DPSK

In MATLAB's Comm System Toolbox there is an option for 'Phase Rotation', defined as the phase difference between previous and current modulated symbols when the input is zero. This is the first time I'...
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Is adding zeros part of the Hermitian Symmetry process?

I have been reading about DMT/OFDM and every source I find defines their system differently. I simply want to know if zero insertion is part of the Hermitian symmetry process that produces real OFDM ...
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Help using an example how to calculate the word length for words formed using sliding window

I have a binary sequence of length N as $10110110111...$ I want to segment the above series into equal blocks of a window of length $L$. One way of determining the block length is using the ...
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Maximum Likelihood for colored noise

I have the following question about the maximum likelihood (ML) in presence of inter-symbol interference and colored noise. Assume the communication system is as follows. Information source, ...