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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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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4answers
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+100
What is the principle behind my voice echoing perpetually when 2 separate devices are used for playback and recording on video calls?
I had to use 2 separate devices for a video call, desktop for video/audio output and smartphone for recording, since the desktop microphone was not working properly. Unfortunately for me, when I ...
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1answer
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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0answers
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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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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1answer
23 views
To remove doppler for equalizer doppler does it need decision directed like carrier recovery?
Normally equalizer is used at the start of the receive chain .So do we need decision directed to estimate the doppler here and also later for carrier recovery for carrier phase recovery?
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2answers
44 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
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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36 views
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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1answer
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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0answers
21 views
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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1answer
43 views
how to determine a length of a channel? ( given path, delay)
Given a channel matrices for each subcarrier of a frequency selective channel (OFDM): i.i.d..
channel =(randn(ntx,nrx, N)+1i*randn(ntx,nrx, N))/sqrt(2); simulated ...
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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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2answers
266 views
SINR averaging in communication system
Under the simulation of a communication system suffering from noise (AWGN) and co-channel interference, what is the appropriate way of calculating SINR?
Could one calculate it at a packet level as:
$...
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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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1answer
30 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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1answer
33 views
How to reduce PAPR with constellations choice?
How to tune constellations mapping M ary-psk or x-qam to reduce PAPR ?
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1answer
333 views
Why must the Region Of Convergence (ROC) contain infinity and the system function be a right-sided sequence for it to be causal?
I need the simple logic on the condition a system becomes causal. We know that causal contains only past values. I can't relate this with the Region Of Convergence (ROC) concept.
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1answer
470 views
What is the meaning of inverse signal bandwidth?
I have been studying the two ray model in communication systems.
The text I'm studying has two signals, $u(t)$, which is Line of Sight and $u(t-t')$, which is the reflected signal.
It quotes,
...
3
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2answers
68 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
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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0answers
34 views
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
103 views
Carrier frequency offset estimation for QPSK and asymmetrical spectrum
I am working on estimation of carrier frequency offset for QPSK data from a satellite. From my understanding, there are two main approaches: either remove data from the carrier (by taking the fourth ...
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1answer
73 views
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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1answer
32 views
What is role of BW and frequency in internet speeds?
First the bandwidth (BW):
It is the amount of data that can be transferred simultaneously.just like more no. of highway lanes so that many cars can travel side by side simultaneously.
Frequency
It ...
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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 ...
2
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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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3answers
1k views
Capacity of AWGN channel
I am confused understanding basic concepts of communication over AWGN channels. I know the capacity of a discrete time AWGN channel is:
$$C=\frac{1}{2}\log_2\left(1+\frac{S}{N}\right)$$
and it is ...
2
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0answers
27 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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40 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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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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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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0answers
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
63 views
frequency/phase offset estimation in satellite DOA beamforming applications
In satellite QPSK demodulation, we first estimate and remove the phase offset introduced by the channel. Then, we demodulate the baseband information bits (I & Q channels).
In satellite DOA ...
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42 views
Any DVB-S2 sample streams, publicly available?
I'm working on a DVB-S2 receiver and I'd like to be able to test a part of the DSP chain with real-world signals, but getting good sample streams from a digitizer is not terribly easy.
Can anyone ...
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1answer
4k views
Differential BPSK vs BPSK what are the advantages and disadvantages?
Recently I have come across different variation of the sane modulation techniques. I am quite confused about the advantages of different constellations. In particular, what are the advantages of using ...
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1answer
44 views
Capacity and BER as performance of transmission system
We study the performance of the transmission system by channel capacity or BER/SER. If the system performance is studied as BER/SER, does it make sense to study a channel capacity?
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1answer
41 views
Do we need Channel estimation prior to (time domain DFE or linear) adaptative equalization in single tone transmission?
If we are to transmit a single tone signal over a channel impaired by inter symbol interference and awgn, and if the equalization is adaptative (LMS/RLS track) and is done in time domain by LE (linear ...
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1answer
166 views
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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1answer
2k views
difference between GMSK (Gaussian Minimum shift keying) and GFSK (Gaussain frequency shift keying) [closed]
I am unable to differentiate GMSK and GFSK.
How do the modulation techniques differ in Tx?
How do their receiving techniques differ..?
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3answers
776 views
What is the difference between (Sample Timing Offset), (Carrier Frequency offset), and (Sampling Frequency Offset)?
Briefly, can anyone explain to me what is the difference between (Sample Timing Offset), (Carrier Frequency offset), and (Sampling Frequency Offset)?
and is Sampling Frequency Offset (SFO) like STO ...
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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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0answers
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
138 views
Interleaving over OFDM symbols in same transmission
In this question I have asked what are the benefits from interleaving between two codewords over ONE OFDM symbol in packet based transmission made up of more than one OFDM symbol
Purpose of ...
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2answers
97 views
The relation of sub-carrier and FDMA
In Mengyu Liu, Yuan Liu, "Charge-then-Forward: Wireless Powered Communication for Multiuser Relay Networks", it is said that
while information signals are conveyed by using FDMA over $N$
sub-...
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2answers
47 views
Recover an OFDM signal affected by AWGN
I have an OFDM signal affected by AWGN, if I know the power of the gaussian noise, can I recover the OFDM signal? Can I perform deconvolution to recover the original signal?
thanks
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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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1answer
50 views
Decoder implementation
Im struggling to implement / build convolutional decoder .
I've done implementation of FEC encoder which it's as shown in the photo below:
So this is the encoder that I've implemented, and I want to ...
