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.

Filter by
Sorted by
Tagged with
0
votes
1answer
11 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 ...
1
vote
4answers
99 views
+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 ...
1
vote
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 ...
0
votes
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 ...
0
votes
0answers
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 ...
0
votes
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?
0
votes
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: ...
3
votes
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 ...
0
votes
0answers
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 ...
0
votes
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 ...
-4
votes
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 ...
1
vote
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 ...
0
votes
0answers
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 &...
1
vote
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 ...
1
vote
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 ...
0
votes
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: $...
0
votes
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. ...
0
votes
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 ...
0
votes
1answer
33 views
0
votes
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.
0
votes
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
votes
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 ...
2
votes
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 ...
-1
votes
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?
0
votes
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 ...
2
votes
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 ...
1
vote
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 ...
1
vote
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
votes
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 ...
10
votes
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
votes
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?
0
votes
0answers
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. ...
0
votes
0answers
13 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 ...
0
votes
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 ...
0
votes
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?
0
votes
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 ...
1
vote
0answers
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 ...
1
vote
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 ...
0
votes
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?
0
votes
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 ...
2
votes
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 ...
1
vote
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..?
2
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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-...
0
votes
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
0
votes
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 ...
0
votes
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 ...

1
2 3 4 5
23