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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The Amplitude of the Correlation Function Peaks After Matched Filtering

I have 2 signals: $s_1(t)$ and $s_2(t)$. The autocorrelation functions are given by $R_{s_1}(\tau)$ and $R_{s_2}(\tau)$ with $|R_{s_2}(\tau)|<|R_{s_1}(\tau)|$. I would like to know if the previous ...
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Capacity of channels with pilots?

Question is about "channel capacity". I guess it is pretty elementary for experts, however I have not seen it discussed in e.g. Proakis book or Tse "Fundamentals of Wireless Com". ...
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Distortion-Rate function for standard Gaussian signals quantized with a uniform alphabet

Let's say $X \sim N(0, 1)$ is a standard Gaussian input signal and $Y \sim U\{y_1, y_2, \cdots, y_{16}\}$ follows a discrete uniform distribution (in fact, $\{y_1, y_2, \cdots, y_{16}\}$ is a ...
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Block CMA algorithm

The Constant Modulus Algorithm is a common equalization method which adapts at every sample in an attempt to give a filter which produces a fixed power output. Divergence/convergence of the CMA ...
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OFDM channel estimation using the transmitted signal multiplied with a matrix

I have OFDM system, where the modulated signal $x$ with length $N$, and $N$ is the number of subcarriers in OFDM symbol. $x$ is multiplied with a well-known unitary matrix $G \in N \times N$ before ...
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How does matched filter output provide sufficient statistic when the channel has ISI + AWGN?

In Forney’s MLSE paper (link: https://ieeexplore.ieee.org/document/1054829), Forney mentioned that the matched filter output is still sufficient statistics even with ISI (second column on page 365). I ...
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GMSK Transmitter Implementation based on AMP representation ( laurent decomposition)

Implementation of a linear approximated GMSK block scheme based on Laurent decomposition. My goal is the Implementation of the following block scheme: I think $v_k$ is an NRZ element ( 1 or -1). <...
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dsss and correlation

Generally, a DSSS (Direct Sequence Spread Spectrum) communication is used to secure a communication. However, because of the repetition of the spreading sequence, a cyclostationary analysis makes it ...
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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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GNU Radio | Transceiver loopback adapted | Transmission stops unexpectedly

(This is a follow up question to a previous question: link) I have implemented a flowgraph of a transceiver loopback inspired by the examples found at ...
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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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Chip rate and sample rate

If a sequence of +1 and -1 with chip rate ($\frac{1}{0.57 ns}$) is being used for purpose of estimating channel impulse response with delay spread of 6ns. We decide to have a new rate change to rate ...
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Phase noise estimation and compensation schemes

Brief background There is a known problem that high order modulation schemes suffers from phase noise of reference generator. It's very important issue for e.g. line-of-sight (LOS) modems exploiting ...
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Why does my simulation of the binary symmetric channel disagree with theory?

Could someone please answer me why the simulated performance (using matlab) of a Hamming code over a binary symmetric channel does not fit exacly with the theoretical? Here is my code: ...
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IQ demodulation from specific rate

We have an acquisition hardware in our lab that acquires and digitizes data from a source generating band-limited signal in the MHz range. It samples the signal at a rate of 4 times the center ...
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How to prove the mutual infomation expression in paper "Optimized Degree Distributions for Binary and Non-Binary LDPC Codes in Flash Memory"

Recently I met a question when I read the paper Optimized Degree Distributions for Binary and Non-Binary LDPC Codes in Flash Memory and Soft Information for LDPC Decoding in Flash: Mutual-Information ...
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optimal RX beamforming

I was asked this question in an interview couple of weeks ago. I think I answered it correctly, but I think I might missing some points. Here is the problem, following by my answer. Part 1) In Figure ...
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multi h CPM implementation

I have understood the math behind CPM. but recently I came across multi h CPM. I haven't found any good document to explain about multi h CPM. Can anybody explain the math behind it. and how it ...
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Implementing digital controller in the time domain

I have simulated a digital control system in the Z domain using MATLAB and I have got satisfactory results. However, when I converted the plant and the digital controller to difference equations and ...
learn design's user avatar
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Generating signal in a different frequency band than another signal but transmitted at the same time

I have a signal $x(t)$ of bandwidth $W_1$ transmitted over carrier frequency $f_1$, and another signal $i(t)$ of bandwidth $W_2$ transmitted over carrier frequency $f_2$. The main lobe of both signals'...
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Understanding the In-band Emission limit in TS 38101-1 Table 6.4.2.3-1?

I am sharing the IBE table 6.4.2.3-1 on TS 38101-1 For General emission requirement, there are three parts.The third part is (-57 dBm+10*log10(scs/15kHz))-P_RB. Where, P_RB is the average transmitted ...
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localization based on TDOA

To locate a transmitter, I use a localization based on TDOA(Chan's method) with 3 receivers. The results obtained are not effective. What is a possible solution to improve the localization accuracy ...
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How to implement GMSK model by Thierry Turletti

I'm kind of new to signal processing and trying to implement a GMSK modulator using GMSK in a nutshell by Thierry Turletti to modulate a bunch of binary data and send them over RF antennas. I'm very ...
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Symbol timing recovery: Polyphase vs piecewise linear interpolation

A symbol timing recovery scheme shown below has been successfully implemented in C++. Different TEDs (Mueller & Mueller, Early-Late, Maximum Likelihood, Gardner, Zero-Crossing, etc) are included ...
Moses Browne Mwakyanjala's user avatar
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Software implementation of Gardner Loop

My objective is to create a Gardner loop to remove the timing offset present in my signal. To achieve best timing SNR, I downsample my signal to 2 samples per symbol. It is depicted below: where blue ...
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What does the sample entropy of a digital signal mean?

What sample entropy signifies about a signal and how it used to analyse a signal?
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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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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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Lagrange Vs Sinc interpolation

I was wondering what is the practical difference between Lagrange Interpolation using Farrow Structure and Sinc Interpolation? Both require pre-computation of time offset coefficients using a lookup ...
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Understanding and converting Matlab's coarse frequency compensation function

I am trying to understand and convert to C Matlab's coarse frequency compensator the documentation for which can be found here: Documentation Matlab's design itself is based on this IEEE paper: ...
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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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Dynamic loop bandwidth for a Costas loop

I'm using a Costas loop for carrier recovery. The BER vs SNR (from GNU Radio Simulation) curve for different loop bandwidths (0.03,0.05 and 0.07) is shown in the graph below. It can be seen that the ...
Moses Browne Mwakyanjala's user avatar
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Why is channel estimation done after synchronization and why does it work?

I am interested in Software Defined Radio communications where almost all processing is pushed to the digital domain. I'm wondering why is channel estimation done after frequency and phase ...
FourierFlux's user avatar
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How can I oversample the received signal by double of sampling time and have two signals

I have a question, how can I make the sampling in Matlab for the received the signal by half of time duration of symbol (Ts), and have two copies of signal (that's the process of fractional sampling ...
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AWGN Build vs Randn noise do not match

I am generating noise in two different cases with the same SNR once using AWGN command which is a built in command and second time using randn function with the correct scaling however I am getting ...
math's user avatar
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Blind coarse OFDM frequency estimation

Is it possible to blindly estimate a coarse carrier frequency offset of an OFDM signal where $\lvert f_{\rm off}\rvert > \frac{\Delta f}2$, where $\Delta f$ = subcarrier spacing? Blind is defined ...
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What is actually transmitted following LPC of a speech frame?

For each frame, what's sent over to the receiver for decoding? The coefficients , pitch in some bits, voiced/unvoiced classification in another bit? Another broad question to develop intuition about ...
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DC offset removal from tetra signal

Hey I want to remove DC offset from tetra signal captured as inphase and quadrature phase samples(I and Q samples). I and and Q samples are 16 bit signed values. I tried averaging 2000 I and Q samples ...
user46418's user avatar
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TDE, OFDE and FDE equalizer simplest exmple in matlab

I want to implement the equalizer in matlab. I am just learning this. I want a good kick start code that can help me to learn it further. I searched a lot on Google but do not find a good reference ...
Abdul Rehman's user avatar
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Zero Forcing Equalizer in ISI channel

I'm studying on designing 9-tap zero forcing equalizer to remove ISI in the channel. I assumed that the channel response is $h[n] = [0.41, 0.815, 0.41]$ and I tried to calculate bit error rate. When I ...
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BER of coherently detected DBPSK?

I understand that differential PSK is generally used when coherent detection is not possible, and so is usually detected non-coherently. However, for sake of theoretical analysis/understanding, what ...
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A question of channel capacity in precoding case

I’ve a general question about precoding. The channel capacity after precoding is $\log_2(\det(I+F’H’HF))$ where $\det$ is the determinant, $I$ the identity matrix, $F$ the precoding matrix, $H$ the ...
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Does Filtering changes the noise characteristics in a signal?

So, I tried out what i am learning in digital communication using GNU radio. The plan is to modulate two baseband signals(sine and cosine) 1kHz with no modulation protocol(don't know any(yet)) to a ...
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Is there something wrong with MATLAB's pwelch function?

The normalized factor for windowing, is it $(\sum w[n])^2$ or $\sum w^2[n]$? I try to reproduce the pwelch function, if I set the normalized factor to $(\sum w[n])^2$, I get the same result as MATLAB ...
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Understanding the (complex) GNU Radio implementation of Mueller & Muller

I have some questions about the M&M implementation of GNU Radio that uses complex samples. I started reading the implementation for real values: ...
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decision feedback equalizer building blocks (from Adaptive Filters: Theory and Applications” a book by Behrouz Farhang-Boroujeny)

Here you can see building blocks of DFE from "Adaptive Filters: Theory and Applications” a book by Behrouz Farhang-Boroujeny in chapter 17. Figure 17.9 shows the overall building blocks of DFE ...
Sadeq Ebrahimi's user avatar
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Channel equalization in uplink

I have a multiuser uplink signal $$ Y=h_1x_1+h_2x_2$$ where, $h_1$ and $h_2$ are channels for user 1 and user2 respectively. At the receiver how can I equalize the signal $Y$, assuming known $h_1$and $...
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Sending and receiving an image

After studying digital communication courses, I wanted to implement these theories and create an application for sending and receiving a gray image via WiFi between two Raspberry Pi devices. The ...
Mouh Kramo's user avatar
1 vote
1 answer
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spectral density of Modulated ofdm signal

I have formed my OFDM symbol his length is 88 (Nsubcarrier=72,Ncp=16) with Fs=1080000 Hz we call this symbol as Signal_from_baseband I want to modulate the OFDM symbol with Fc carrier=2.1 GHz and plot ...
ahmed bennani's user avatar
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Applying Blahut-Arimoto Algorithm for AWGN Channels Capacity Calculation with Cost

I am exploring the Blahut-Arimoto algorithm (or any numerical method) for channel capacity calculations, particularly for continuous channels. I understand its application in discrete scenarios, but I ...
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