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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12 views

Can the DFT can be performed without normalization?

If we have OFDM system with $N$ sub-carriers, the DFT matrix can be expressed as follows: $F = dfmtx(N)/sqrt(N)$ My question, is it possible and practical to use the matrix without Normalization, it ...
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19 views

understanding the result of the simulation of In-phase and quadrature part BPSK signal

I am a student and working on a hardware implementation of a transceiver and going to check an algorithm of time recovery that includes symbol synchronization and sampling clock synchronization. The ...
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44 views

Why Does ASK Modulation Create Fourier Sidebands?

I know why analog amplitude modulation has side bands, it is related to (fc+fd) and (fc-fd). But what about DAM? ASK(DAM) is a type of digital modulation, and there are only two state: carrier signal ...
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25 views

Interference Diversity for management of inter-cell interference in cellular communications

What is interference diversity? and how is it different in CDMA and OFDM? I have a problem understanding the concept Reference book: Fundamentals of Wireless Communications, chapter3/4 Author: David ...
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QPSK, BPSK error probability [closed]

The Binary Phase-shift Keying (BPSK) and Quadrature Phase-shift Keying (QPSK) modulation schemes are shown in the figure. We consider that in both cases, the symbols (S) are sent over an additive ...
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Generate binary signal and convert to integer in Matlab

I am going to test an algorithm and need a test signals. My first test signal is a binary signal of 1 or -1. I was thinking about how to implement such a sequence in matlab and wrote this: ...
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33 views

CDMA and Pulse Shapping

I am a little confused on CDMA and its interaction with the typical pulse shaping filter ex, raised root cosine. Is the RRC filter bandwidth selected to be consistent with the CDMA spreading/update ...
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HOW TO DEAL WITH SQNR IN MATLAB

Given the digital speech signal in the file guitatune.wav, Write a MATLAB program to a) Read the audio file and find sampling frequency. b) Quantize (using 4-bit quantizers to obtain the quantized ...
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25 views

OFDM symbols terminology explanation

I've already read and understand what does OFDM mean and what does it stand for and why we use it in our wireless technology today. My question that I didn't understand is what does it mean number of &...
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1answer
33 views

Does same data inserted to all antenna at beamforming?

I wonder do I understand beamforming right. Question 1 Does same data inserted to all antenna at beamforming? Like figure below? The only different is through different phase shift? If it is right how ...
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1answer
63 views

QPSK demodulator on GNURadio continuously loses phase lock

I am designing a QPSK demodulator to be used for receiving Meteor M2 (LEO satellite) signals (QPSK at 72Kbaud). However, I am finding a lot of problems in my way. First of all, this is the flowchart I ...
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Detection of a Pulse pattern with Matched filter

I am working on a hobby transmitter-receiver project. Presence of 4 pulses in T seconds is regarded as 1(not any number of pulses, should match below): lack of pulses during that T seconds is ...
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Symbol time offset simulation

I ran a number of simulations for symbol timing synchronization in the past. I used GNU Radio mainly. Now, I'm trying to do the same thing in C++. To achieve that, I need a way to introduce symbol ...
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DFT-S-OFDM or SC FDMA in LTE or 5G uplink

Does DFT-S-OFDMA ( SCFDMA) in LTE uplink use windowing or pulse shaping (filter) in order to reduce the signal out of band spectrum?
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1answer
87 views

Bandwidth of PSK modulated signal

What does it mean that the bandwidth of PSK modulated signal without applying any filtering or shaping of the pulse, is equal to the sampling rate with "1st lobe" equal to two times of ...
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1answer
78 views

Sub-Band Extraction Techniques for Complex (I/Q) Signal

There is an application which processes Complex I/Q signal of 100 MHz bandwidth and it is required to extract independent sub-bands from this bandwidth at different center frequencies and bandwidths. ...
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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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z-transform ROC RIGHT SIDED INFINITY

MCQ The region of convergence (ROC) for a right-sided (infinite) sequence is 1 point Entire z-plane excluding zero and infinity Interior of a circle Entire z-plane including zero and infinity Exterior ...
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What does this mean? The elliptical constellation in the QPSK constellation diagram?

Can you explain what kind of signal is this or what can you characterize when you see QPSK constellation like this? to get a better signal it needs to be near 1 and be a round circular constellation. ...
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22 views

Prewhiting filter and matched filter

What is the formula of pre whiting filter and matched filter and their frequency response? How can I find the SNR? If two filters are combined, which formula I can use?
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1answer
102 views

Time recovery algorithm and a symbol with samples

I am working on my graduation thesis. The topic is a receiver implementation in FPGA. I am doing an implementation of symbol timing recovery. For this part I have decided to choose the Gardner ...
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2answers
95 views

Simulating a raised cosine filter

I am rewriting a simulation written in Matlab to C. I have a problem with a transmit data. The data is filtered by a raised cosine filter. In Matlab it was implemented by using the following function ...
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2answers
56 views

Filtering a QPSK signal

Envelope variation due to filtering of a QPSK signal becomes more pronounced at greater phase steps. Why is that? Why do greater phase steps (180 vs 90 degrees for example) lead to more pronounced ...
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1answer
33 views

How to recover data/information from real complex baseband signal?

I have recorded real complex baseband signal. I want to recover data from the same. The complex baseband signal is basically a composite CDMA signal. How can i recover that information ? Original Tx ...
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60 views

Demodulator: Time recovering algorithm

I am software engineer and working on a hardware implementation of a receaver. Actual, I am working on a Demodulator (phase offset with timing error detecting, filter, PLL). Gardner or Godard ...
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1answer
23 views

What is the correct block diagram of CDMA communication system?

I was reading someone's thesis and now i am more confused about CDMA system. From what i understood is CDMA is multiplexing which allows multiple signals to transmit over single channel. so general ...
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34 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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32 views

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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40 views

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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137 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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33 views

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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66 views

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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36 views

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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18 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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33 views

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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1answer
82 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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41 views

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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48 views

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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46 views

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
59 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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68 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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22 views

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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1answer
125 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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