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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92 views

PLL: cycle slipping correction

i am working on a receiver in the space communication. Under low SNR, big frequency offset, phase offset. I started with phase/frequency correction. I used digital PLL and it doesn't work for it. I ...
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39 views

Difference ;Phase and frequency offset

can someone explain what a difference is between phase and frequency shift/offset in estimation algorithm? Honestly I dont understand this difference. If i estimate , i will do it for phase estimation....
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3answers
67 views

Using large DFT for OFDM to avoid the guard interval

In OFDM, we usually insert the guard interval to avoid the inter-symbol interference at the expense of achieved data rate. that guard interval can be either zeros or CP guard interval, which it must ...
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23 views

Find symbol duration from symbol rate

How can one find symbol duration if bit rate is 100 kbs (as BPSK is used, symbol rate = bit rate)?
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1answer
36 views

Question on PCM Sampling and Quantization order

I had a doubt in my mind regarding the orders of sampling and quantization in PCM. What is the impact if the order is reversed, that is, the continuous time signal is first quantized and then sampled? ...
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1answer
86 views

What is the advantage of using a Stepped Frequency waveform over FMCW?

What is the advantage of using a Stepped Frequency Waveform instead of a traditional linear FMCW ?
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82 views

clock + phase recovery

I am working on the implementation phase and time recovery algorithm and have doubts. Could you please explain to me some question? PLL for time and phase recovery I have found I can use PLL not ...
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1answer
47 views

Finding optimal decision threshold for binary comm system

I'm trying to solve the following exercise: Given a system that transmits bit $b$ with probability $p_b$ and $-b$ with $p_{-b}$ and the transmission is degraded by AWGN $N(0,\sigma^2)$. What is the ...
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1answer
112 views

Phase correction algorithm: minimisation phase error

Thank you for your participation in my discussion in advance. I am working on the implementation of a phase correction. Currently, I have finished the algorithm. I think it is a standard algorithm ...
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1answer
36 views

How to simulate a continuous signal passing through a capacitor (simple coupling capacitor)

the differential equation for the current flowing through a serial capacitor (see for example https://www.allaboutcircuits.com/textbook/direct-current/chpt-13/capacitors-and-calculus/) indicates that ...
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3answers
64 views

Role of windowing in implementing FIR filters using Fast Convolution

In Fast Convolution the filtering is performed by taking FFT of both the signal and impulse response and multiplication in frequency domain using Overlap add/Overlap save method for processing ...
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1answer
20 views

Analysis Received Signal at receiver side

I'm trying to understand something which is really confusing me and I made my best to understand it but still confused. If I have transmitted and receiver. Assume I want to transmit S(t) data and ...
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1answer
43 views

Using DFT Rotation for Frequency Down-Mixing

Is it possible to perform Frequency Down-Mixing (sometimes referred to as Down-Conversion) by simply rotating the DFT sequence? If so what are the Advantages and Disadvantages of this method?
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How is CFi related to Code Rate and link Quality of the lte network?

Im trying to understand the relation between CFi and Code Rate and Quality of the network? like if I have bad quality then we need to decrease CFi? what about Code Rate we need to increase? About ...
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1answer
70 views

Maximum NCO frequency and filter design for down-conversion of complex input signal

I am trying to perform digital down conversion by using the DDC from Matlab dsp toolbox. My question is that the bandwidth property is limited to Fs/2 and the filters created are real filters. If the ...
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58 views

What are considered key EM signal measurements to help identify unique emissions?

I plan to conduct an EM study which hopes to identify unique signals emitted from a device. While in acoustic signals, features which can be extracted include the likes of spectral centroids, etc. ...
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1answer
81 views

Design a timing recovery algorithm with predefined samples with max amplitude

I need your help in understanding how to simulate a timing recovery algorithm. I have already read a lot of literature and posted here the question but I have still doubts how it works. Let me briefly ...
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23 views

Beamforming and AoA with a small number of elements

So I have an antennae array with only three elements. I want to know what kind of beamforming and AoA estimation I can do with such a small number of elements. I understand that there are lots of ...
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66 views

Implementation of Overlap Save Filtering with Decimation

I am trying to implement Matlab code which performs FIR filtering with complex bandpass filter using Overlap Save method and perform decimation as well by using different length forward and inverse ...
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1answer
43 views

Time domain representation of a modulated signal when symbol rate >> carrier frequency?

I need to understand the relationship between carrier vs. bits with PSK modulation, and what the signal in the time domain would look like if my symbol rate is far greater than my carrier frequency. ...
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1answer
46 views

Discussion of simulation results of a signal sequence: amplitude

I need your help in understanding if the simulation result is correct. I have simulated a random BPSK sequence that was upsampled and filtered with a raised cosine filter. The length of the filter is ...
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2answers
155 views

CORDIC, What is it?

I am reading about CORDIC (Coordinate Rotation Digital Computer) and I have t implement it. Honestly, I am reading and don't understand the difference between phase detection algorithm ( PLL, Costas ...
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1answer
30 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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21 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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1answer
68 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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2answers
56 views

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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1answer
39 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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28 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
37 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
154 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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1answer
42 views

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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2answers
80 views

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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1answer
115 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
81 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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29 views

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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19 views

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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48 views

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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1answer
178 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
249 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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3answers
82 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
37 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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1answer
31 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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1answer
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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1answer
56 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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43 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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235 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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47 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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2answers
67 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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41 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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