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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30 views

where we use estimation and detection in communication system?

I read from the book that we use estimation when we are dealing with analog signal or continuous random variable and the term detection when the transmitted signal is a discrete value even if a ...
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What is impulse response in simple AWGN channel?

Assume a sender and receiver communicate through an AWGN channel. Let $x(t)$ be a transmitted signal and $y(t)$ be a received signal and $z(t)$ be the Gaussian noise. It is known that $y(t) = kx(t-\...
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QPSK constellation Zero Crossings

What causes zero crossings in a QPSK constellation to be a a problem for linearity or PAPR ( Peak to Average Power Ratio)?
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107 views

Find power of a sum of sinusoids

We got this question to solve: Calculate the power of the signal: $$s(t) = 8\cos\left(20\pi t-\frac \pi4\right) + 4\sin(15\pi t)$$ Now, I thought of two approaches : Use Parseval theorem, so first ...
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Matched Filter Impulse Response

At the receiver end of a digital communication system, the matched filter is designed with impulse response matched to the effective signal that is given as : $$x_{(z,1)}^{*}(T_p-t)-x_{(z,0)}^{*}(T_p-...
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Baseband Signals have zero imaginary component

I was revising a few basics on communication systems and I stumbled upon this line that I thought was incorrectly articulated. I thought that baseband signals were complex and passband signals were ...
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Variance of AWGN in BFSK system

I am trying to compute the variance of AWGN in the system for finding the BER with $Q$ function. The PSD of the AWGN is $N_0/2$, my answer was $N_0T$ but it was incorrect. This is my calculation (...
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16 views

Which modulation technique is better for long distance transmission, if I'm using the CC1101?

I'm using the Texas Instrument transceiver cc1101 at 430-440 [MHz] and I'm wondering what the best modulation technique is for long distance transmission. This transceiver offers several modulation ...
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31 views

BER and distance relation

I have a system using 16-QAM, with 2.4 GHz, working up to 2 km at different bit rates, e.g. 1Mbit/s. My task is to provide graph, which will show relation between BER and distance for different bit ...
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Is there an optimal way to quantize log-likelihood ratios of an AWGN channel?

My understanding is that given an AWGN channel and BPSK modulation, an LDPC decoder that uses message passing takes as input log-likelihood ratios $L$ of the following form by Bayes' rule: $$ L=\frac{...
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70 views

Verifying LDPC matrices in CCSDS blue book

My understanding is that LDPC is a linear block code such that its generator matrix $\mathbf{G}$ and parity check matrix $\mathbf{H}$ satisfy $\mathbf{GH}^T=0$. I am using the CCSDS blue book here as ...
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In pulse code modulation what is pulse word represent?

we study lot of things in PCM we do sampling quantization encoding etc but we never come across pulse so what is pulse word represent in PCM
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Spatial receive diversity: a different view

It is well known that spatial diversity can combat multipath small scale Rayleigh fading in a SIMO system by offering the receiver multiple options of independent receptions using more than one ...
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Coefficients of a Zero Forcing linear equalizer for infinite length input

Given a discrete-time white noise model: $$y_k = \sum_{i=0}^{\infty} \alpha^{-i}a_{k-i} + \eta_k$$ where $E(|a_k|^2)=2$, $|\alpha|>1$, $\eta_k$ are uncorrelated zero mean random variables with $E(|\...
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Degradation of BPSK system using matched filter with a timing error

Given a BPSK system with: \begin{align*} s_1(t) &= Au_T(t) \\ s_2(t) &= -Au_T(t) \\ \end{align*} where $u_T(t)=1$ for $0<t<T$, and zero otherwise. Given $A > 0$, and Gaussian white ...
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Received Signal Strength Calculation for Probabilistic Line of Sight Channel

Scenario: Given a UAV which emits a beacon and the beacon is received by a node on the ground. The node calculates the received signal strength. Considering the channel is Probabilistic LoS, the ...
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SNR measurement

I am using QPSK modulation for a BER of $10^{-6}$ at $\text{SNR}=E_b/N_0=10 \ \rm dB$. If my data rate is $5 \ \rm kbps$ then $$S/N_0 = 10\log_{10}(5000)+10 = 47\ \rm dB$$ And if my RF section has a ...
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How to detect the burst data?

At high SNR i am able to detect the burst by taking the magnitude of the data and setting the threshold. for low SNR it it difficult to set the threshold?
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Why do we need DFT when we already have DTFT?

We already have DTFT so why do we need DFT? Please don't write DTFT is used for discrete, aperiodic signal which transfers in the frequency domain to periodic and continuous, but in DFT is discrete ...
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1answer
52 views

16-APSK NDA Carrier Synchronization Problem

I'm working on a DVB-S2 Symbol Timing + Carrier Synchronizer with a focus on 16-APSK | 32-APSK modulation Scheme. I understand that the first section could be achieved using a Polyphase Clock Sync ...
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65 views

Blind STBC question

I am working on blind identification of the physical layer parameters of a particular protocol. Everything was going well until I got to the MIMO part. The system contains two transmitter antennas and ...
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43 views

inversion of the sum

In the article Analysis of the Performance of a Non-Coherent Large Scale SIMO System Based on M-DPSK Under Rician Fading Fig.1: I would like to know if we could invert the block of the sum with the ...
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how to do initialization of random vectors in matlab

I have to generate random vectors for $\mathbf{p}^{(0)}$, $\mathbf{u}_l^{(0)}$, and $\mathbf{v}_l^{(0)}$ for $l=1\ldots L$. Now I am confused about how to generate these vectors as $l=1\ldots L$ is ...
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116 views

Difference between Analog IQ sampling and creating IQ digitally

In the context of wideband receiver design, what are the advantages and disadvantages of Analog IQ sampling vs creating IQ digitally (with Hilbert transform)? Why do we use different ADCs to create ...
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How to figure out the polynom of Convolutional encoder

I have Convolutional encoder with K=7, r=1/2 that steam of bits get enter to it from right to left (7 registers and steam of input is entering the convolutional encoder from left to right .. ) the ...
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64 views

Difference in information between IQ Sampling vs. Real Sampling at $2F_s$

As per my current understanding we use IQ sampling as way to increase the useful bandwidth to Fs rather than $F_s/2$ when viewing the FFT because the IQ sampling removes the negative frequencies and ...
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22 views

pulse shaping filter and BER

For example, in a PSK modulation. I saw that to plot the BER curves as a function of the noise, we never took into account the pulse shaping filter. More precisely, the signal is not filtered by the ...
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1answer
24 views

compute a difference( dB) between two BER curves

For example, given these 4 curves and I would like to compute a loss/difference between BER of BPSK and BER 8PSk in dB. How to do that? let say for BER 10^-2
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38 views

How to remove frequency offset with RRC as pulse shaping filter

I am working on a project with QPSK modulation format and a RRC filtering at the transmitter (TX) side. The channel introduces a constant dropper shift ($f_d$) to the received signal. To make the ...
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Why does carrier frequency offset (CFO) cause carrier phase error (CPE)?

I've already asked 2 questions on this but there is one discrepancy I cannot reconcile and is the crux of the problem: \begin{align} \newcommand{\prefix}{\frac1N\sum\limits_{n=0}^{N-1}} R_l &= \...
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23 views

Output of encoder RS-code: analyze the results

I found some simulation results of RS-encoder. In the description are written the following: “When the program implementation is run, the clock is set to high i.e. ‘1 ’ and reset is set to low i.e. ‘ ...
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How to calculate the upsampling rate (sample per symbol) for a recorded raw IQ .wav file?

I am not familiar with raw IQ wave files. For tetra-1 signal, the bit rate is $36$ k bps (or $18$ k as the symbol rate). If the Fs saved in the .wav file is $48000$ Hz, what should be the SPS (sample ...
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How composite signal in CDMA is normalise in general?

I had CDMA composite signal with 3 users. I assume that the signals are linearly sum together so for my maximum and minimum amplitude of composite signal are +3 and -3 respectively. How can i ...
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How to add a frequency offset to a buffer of MPSK signal for simulation purposes?

I need to simulate some channel effect to a buffer of MPSK signal. How to add a frequency offset to a buffer of baseband MPSK signal?
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Viterbi decoder R=1/2 , K=3 transition table / matrix Implementation

Im trying to understand the transition table / matrix of Viterbi decoder K=3 r=1/2 from communication digital book called bernand sklar first or second edition . Im confused about the transition ...
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Viterbi decoder K=3 using ADD-COMPARE-SELECT Operation

I am in trouble with Viterbi decoder for a while. I have some questions. I need to decode messages from a continuous stream which is encoded. I'm reading from book : digital communications bernard ...
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49 views

Convolution of two bipolar rectangular pulses

I'm having a lot of trouble wrapping my head around what the convolution of two identical rectangular pulses that go from amplitude +A to -A with period T looks like. Please see my drawing below. I ...
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1answer
45 views

Transition table / matrix for convolutional encoder K=3 understandings

Im trying to understand convolutional encoder $K=3$ , and I almost understand it but still confused about what's called transition matrix which in other words it means what input value ($0$ or $1$) ...
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141 views

What will be the distribution of a given signal

Suppose I have a signal $$ \mathbf{s} \sim C \mathcal{N}\left(\mathbf{0}, \sigma^{2} \mathbf{I}_{N_{}}\right) $$ The signal going through a channel : $$ {\mathbf{r}}_{}=\mathbf{s}+{\delta \mathbf{n}} ...
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Finding preferred pair of $m$-sequence for Gold code

I would like to find a preferred pair of $m$-sequence of degree 34 (not a multiple of 4) for Gold code. However, I am lost when I am checking William Wesley Peterson's table in his Error-correcting ...
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Channel coder: Does encoder help? Input signal distortion:

I am studying the channel coding theory. The channel coder adds redundant information to the input signal, that helps a decoder to reconstruct the signal. BUT: Can encoder help to eliminate effects ...
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QPSK transmission simulation

I am trying to simulate a QPSK transmission using GNU Radio following mpsk_stage6.grc example in Gnuradio tutorials. Currently I have no idea where is the problem and everytime I execute the flow ...
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Pulse shaping filter for FSK

After a BPSK modulation we have the upsampling and the pulse shaping filter. But for a FSK, do we have upsampling and pulse shaping filter, or just the pulse shaping filter?
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FSK modulation in baseband

In a $4$-FSK we have $$s_i(t)=\cos(2 \pi f_i t)=\cos(2 \pi (f_c+\alpha_i \Delta f)t)$$ with $\alpha_i=2i-5$, and $\Delta_f=\frac 1T$, where $T$ is the time symbol and $i \in [1,4]$. But with the ...
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Packet Encoder GNU QPSK Transmission

Hello everyone!. This is a template to QPSK transmission but Packet Encoder block is no longer available in new GNURadio versions, what do I need to replace this block in order to do a QPSK ...
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Optimal receiver for a binary system employing waveform $s=A\cos^{2}(\pi f_c t \pm \alpha)$

I want to design an optimal (minimizing error probability) receiver for system of two waveforms (with $0<\alpha<\frac{\pi}{2}$): \begin{align} s_1 &=A\cos^{2}(\pi f_c t + \alpha)\\ s_2 &=...
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Digital Phase Modulation baseband or passband?

Say I want to transmit messages using PSK: I send the message $$s_m(t) = \text{Re} \left [g(t) e^{\frac{j 2 \pi (m-1)}{M}}e^{j 2 \pi f_c t} \right]$$ where $f_c$ is the carrier frequency. Now my ...
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164 views

Difference between double-sided and single-sided AWGN noise after bandpass filtering?

Consider a bandpass signal $s(t)$ with bandwidth $W$. After bandpass filtering, let the output signal be $r(t)=s(t)+n(t)$ I have read a paper that denotes $n(t)$ as Gaussian noise with one-sided power ...
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73 views

two dimensional integration of a trigonometric function

I am working on a detection problem which finally, I have to solve the following 2-D integral: $$\int\limits_{a}^{b} \int\limits_{c}^{d}e^{A\sin(x)\cos(y-B)}\, \mathrm{d}x \, \mathrm{d}y \ ,$$ where $...
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Understanding the Eye Patterns: analysis [duplicate]

I got the following Eye Patterns: how to understand them? what kind of information can I get?

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