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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7 answers
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Understanding the Matched Filter

I have a question about matched filtering. Does the matched filter maximise the SNR at the moment of decision only? As far as I understand, if you put, say, NRZ through a matched filter, the SNR ...
user968243's user avatar
7 votes
1 answer
4k views

Location of Matched Filter

In a digital communication receiver, matched filter(SRRC filter) is used. In different literatures, the location of the matched filter is mentioned in two different places. One is just after the ADC ...
avi1987's user avatar
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5 votes
1 answer
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Phase synchronization in BPSK

In BPSK for demodulation at the receiver end we do phase recovery between received wave and carrier wave. We can find the phase difference between the carrier and received waves using : PLL And ...
Sate's user avatar
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3 votes
1 answer
2k views

Loop bandwidth for symbol timing recovery

I am trying to design the Symbol timing recovery (STR) block of DVBS Receiver. How should I chose the loop bandwidth and damping ratio for determining the loop filter coefficients $k_1$ and $k_2$? ...
avi1987's user avatar
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4 votes
1 answer
26k views

Deriving SER & BER for 4QAM, 16QAM and 32QAM

Required to find symbol error rate vs $E_b/N_0$ for 4QAM, 16QAM & 32QAM. Thought that SER & BER are the same but did my research to find that BER is $1/\log_2(M)$ of SER. Could you please ...
John Smith's user avatar
2 votes
2 answers
3k views

Isn't Gardner's algorithm and Early-Late gate the same thing?

I'm reading about some symbol synchronization methods and I find these two (ELG and Gardner) very similar. Early-Late gate takes 2 samples, one at $t=T-\delta$ and the other at $t=T+\delta$, then ...
researcher9's user avatar
2 votes
1 answer
2k views

Symbol timing synchronization using a high sampling rate

Symbol timing synchronization usually relies on a digital PLL procedure, an iterative process that relies on detecting a timing error signal that is used to control an interpolation filter that in its ...
Hatem Tawfik's user avatar
12 votes
4 answers
19k views

How is symbol synchronization with OFDM done?

I'm trying to understand how symbol synchronization is done in OFDM using pilot tones, cyclic prefixes, or any other technique. I've read the following answers which provide some explanation, but I ...
Dan Sandberg's user avatar
6 votes
2 answers
6k views

How to Simulate AWGN (Additive White Gaussian Noise) in Communication Systems for Specific Bandwidth

I am trying to generate a AWGN waveform to add it to the signal of my simulated communication system. The operating bandwidth of the communication system is about ...
user113478's user avatar
13 votes
1 answer
12k views

How to perform carrier phase recovery in software?

What are the options for recovering the phase of a BPSK signal in software? The only resources I can find online contain circuit diagrams – there seems to be no one willing to explain this to people ...
Keith's user avatar
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9 votes
3 answers
4k views

PSD of complex white gaussian noise

It may be a really simple question, but I'm not sure about this one: Given a complex white Gaussian noise process with iid real and imaginary parts and a double sided power spectral density of $N_0/2$...
Phobos's user avatar
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4 votes
3 answers
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cyclic prefix in ofdm

In ofdm systems after applying IDFT we take the last N/x samples and place them before these N samples. This is called cyclic prefix(CP).So why to use a cyclic prefix? Why is the CP known to combat ...
phanitej's user avatar
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3 votes
2 answers
5k views

Bit Error Probability for 8PSK

I'm trying to understand how to derive the BEP for 8PSK by geometrically looking at the decision regions. Say I have this 8PSK signal set and the corresponding decision boundaries. I assume that '...
Rayne's user avatar
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3 votes
1 answer
420 views

Use of the harris-Moerder Nyquist Pulse Shaping Filter

I became aware today through fred harris' excellent presentation at the DSP Online Conference (https://www.dsponlineconference.com/) of the harris-Moerder pulse shaping filter which was published 15 ...
Dan Boschen's user avatar
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2 votes
2 answers
613 views

Fractional spaced equalizer + timing (clock) recovery

I am trying to figure out how timing recovery is used after equalization (or, being more correct, when the equalizer is in the timing recovery loop), having a T/2 fractional spaced equalizer and using ...
user1113242's user avatar
1 vote
1 answer
361 views

subquestion: original Q "Difference between MSK and GMSK?"

I am studying GMSK modulation for an understanding its realisation in practice. I have the question posted in 2021: "Difference between MSK and GMSK?" And Mr Boschen explained how the ...
FrimHart64's user avatar
1 vote
2 answers
2k views

Eye pattern construction and interpretation

I have read some text about the eye pattern (or eye diagram), but I do not understand how should I read it. The wikipedia definition of it is this one: In telecommunication, an eye pattern, also ...
Kinka-Byo's user avatar
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0 votes
3 answers
1k views

Processing OBPSK as OQPSK

I'm trying to create and process an OBPSK signal, which, as I understand it, transmits even bits on one axis and the odd bits on the opposite axis, resulting in a constellation with 4 unique points. ...
bruno617's user avatar
5 votes
2 answers
886 views

Why is CDMA not enough for wireless communication?

I have a question about CDMA, FDMA and TDMA. I don't understand why we suffer from limited capacity when we have CDMA. I can understand the limitation in FDMA and TDMA, as time and frequency are ...
Mio's user avatar
  • 59
5 votes
2 answers
591 views

Quadrature modulation

I have a question: What is the difference between $ I \cos(t) - Q \sin(t) $ and $ I \cos(t) + Q \sin(t) $ except that they are phase shifted 90 degrees ? On the internet I can find both ...
Przemek Lewandowski's user avatar
4 votes
1 answer
3k views

MATLAB : Proper estimation of weights and how to calculate MSE for QPSK signal for Constant Modulus Algorithm

I had asked conceptual Question about Constant Modulus Algorithm. I am implementing the simple steps of the algorithm, as I do not have the cma() built in module. ...
SKM's user avatar
  • 611
3 votes
1 answer
446 views

Laurent decomposition understanding: What is L?

I work on a GMSK modulation and trying to understand the concept of the Laurent decompositon of GMSK signal. My main reference is Pierre Laurent, "Exact and Approximate Construction of Digital ...
FrimHart64's user avatar
2 votes
3 answers
5k 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 ...
Amro Goneim's user avatar
2 votes
2 answers
2k views

How to Compensate for Frequency Offset in single carrier transmission Using Coarse and Fine Compensation?

How to compensate for the frequency offset of a PAM, PSK, or QAM signal when we are using single carrier transmission, I am looking for algorithms, explanations to be able to carry out the ...
user avatar
1 vote
1 answer
812 views

PLL for Phase Demodulation and Carrier Tracking

I've been playing around with using a PLL for phase demodulation and it's working pretty well. The PLL locks to the carrier and the error term is the demodulated message signal. However, depending on ...
user67081's user avatar
  • 723
0 votes
3 answers
1k views

OFDM SubCarrier and its relationship with IFFT in context of Real and Complex

In the process of OFDM Signal generation. We take symbols (constellation symbols) and map it to a sub-carrier (real analog time domain) harmonics of 15khz, add different sub-carriers separated by ...
Reddi Suresh's user avatar
-1 votes
1 answer
654 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 ...
schnajc's user avatar
24 votes
2 answers
9k views

Extracting Binary Magnetic-Strip Card Data from raw WAV

I am faced with a tricky challenge: To extract binary data from an iPhone magnetic strip card reader. This is what the magnetisation on the card looks like: Source Here is the .WAV the iPhone ...
P i's user avatar
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17 votes
1 answer
7k views

How to estimate and compensate for doppler shift in wireless signals?

I was wondering what good method(s) exist for the estimation (and subsequent compensation) of doppler shift for transmitted signals, be they acoustic or RF, in the context of comms. The question: ...
Spacey's user avatar
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8 votes
1 answer
3k views

Whitened Matched Filter

I am seeking for an advice on whitened matched filtering technique. I have looked into the literature and I do understand its the purpose and how to select the filter in order to achieve the desired ...
Milos Milosavljevic's user avatar
7 votes
3 answers
911 views

Maximum Likelihood for Colored Noise

I have the following question about the maximum likelihood (ML) in presence of inter-symbol interference and colored noise. Assume the communication system is as follows. Information source, ...
Noor's user avatar
  • 337
4 votes
1 answer
3k views

Sample rates, Samples per Symbol, and Digital Pulse Shaping

Having some confusion about digital pulse shaping for complex baseband (passband) signals. The complex baseband linear modulation equation is $$s(t)=\sum_{m=-\infty}^{\infty}\text{Re}\{a_m\}h(t-mT)+j\...
user67081's user avatar
  • 723
4 votes
2 answers
1k views

Alamouti code after or before IFFT block in OFDM

We are trying to implement Alamouti STBC on underlying ofdm signal. We were thinking as to where to write alamouti coder block. I thought we could write it after the cyclic prefixer block as we get a ...
Karan Talasila's user avatar
4 votes
6 answers
569 views

instantaneous frequency for a sum

In the literature, the instantaneous frequency for a signal $s(t)=e^{-j \phi(t)}$ is given by: $$f(t)=\tfrac{1}{2\pi}\frac{d\phi(t)}{dt}$$ This my problem: I have a signal $$u(t)=e^{-j \alpha_1 \phi(...
user46213's user avatar
4 votes
3 answers
1k views

The normalization of the autocorrelation function and how it changes the definitions you've learned about signal analysis in communication systems

Since this question is book-oriented, I will kindly ask you to accompany it with a book that is considered by many researchers the bible of Digital Communication: Proakis - Digital Communications, one ...
Rubem Pacelli's user avatar
3 votes
2 answers
1k views

Why do we express complex noise as Gaussian distributed while the channel is Rayleigh distributed?

I have a confusion regarding the distribution of noise and channel fading. As we know channel fading is usually modeled with Rayleigh fading since it has Gaussian distributed real and imaginary ...
abdVef's user avatar
  • 41
3 votes
2 answers
17k views

Relation between Bandwidth and Baud-Rate for 8-PSK

I have a query on relationship between Baud Rate and Bandwidth for 8-PSK. In 8-PSK as 3 bits together form a symbol, so Bandwidth = 2R/3 , R is Bit Rate As bit ...
Chandrahas Balleda's user avatar
3 votes
2 answers
2k views

Relationship between $E_b/N_0$ and $\rm SNR$ with channel coding

I would like to know what would be the relationship between $E_b/N_0$ and $\rm SNR$ when there is a coding rate of $R_c=K/N$. Normally when there is no channel coding according to this link. $$\...
user59419's user avatar
  • 353
2 votes
2 answers
170 views

Method of reconstructing a band-limited signal from discrete samples

I understand current cell phones use digital communications. Given that this industry brings in billions of dollars each year, there is much incentive to get the best performance possible. So what ...
Ted Ersek's user avatar
  • 509
2 votes
1 answer
2k views

Sampling signal after root raised cosine

I am generating series of 1 and 0. then pulse shaped them with root raised cosine and after than deciding to do match filtering and recovering the bits however it turns out that I am not getting the ...
user59419's user avatar
  • 353
2 votes
3 answers
3k views

Cyclic prefix vs. guard interval. Why use one over the other?

I'm currently studying some OFDM techniques, and have found that in order to avoid Inter-Symbol Interference (ISI), there needs to be some space in between symbols. Lets assume this length to be $\mu$....
gerrgheiser's user avatar
2 votes
1 answer
2k views

FFT-based coarse carrier recovery for QPSK

An FFT-based coarse frequency acquisition block is being tested in GNU Radio. The algorithm used can be found on the GOES satellite user manual and is summarized in the figure below. The algorithm ...
Moses Browne Mwakyanjala's user avatar
2 votes
2 answers
201 views

How can I shape my time channel response, in order to have Gaussian shaped Doppler Spread?

I know how to generate a Rayleigh fading channel but I have no clue how I can shape the Doppler spectrum to be Gaussian. Any help will be really appreciated. ps: I am coding on matlab
Abby_DSP's user avatar
  • 315
1 vote
2 answers
3k views

baseband and passband modulation

I have a simulink model over 2.4GHz. In the transmitter part, the modulation is O-QPSK modulated baseband instead of passband modulation. In Matlab Help this is the reason of using baseband ...
kate's user avatar
  • 13
1 vote
3 answers
3k views

Pulse Shaping in Digital communication

I am new here. I hope I can get help. I want to ask a question regarding digital communication. Does anyone know what are pulse shaping used for? Are they used for ISI mitigation or for something ...
Henry's user avatar
  • 227
1 vote
0 answers
181 views

Basic “filtering” in digital communications

I am completely stuck on solving some problems for my digital communications class. Junior level undergrad class, so fairly basic. I have been searching around all day for related articles etc but can'...
Kevin Dahm's user avatar
1 vote
1 answer
217 views

how to design the $\text{sinc}(\cdot)$ filter for OFDM oversampled system

We usually zero-padding into the moulated data of OFDM before performing IFFT operation to make the design of anti aliasing filters easier ( the cut off can be less sharp) hence save cost. That ...
Fatima_Ali's user avatar
1 vote
1 answer
288 views

External frequency divider in a PLL

Does a frequency divider external to the loop BW of a PLL cause any phase ambiguity ? and why? and is the result of dividing by an odd number different than dividing by an even number?
Hatem Tawfik's user avatar
1 vote
1 answer
531 views

Downsampling( decimation) theory: additional frequency

I work on a simulation decimation filter: downsampling + filter. My test environment: low data rate receiver, BPSK, square root raised cosine filter with cutoff frequency =0.5, transition bandwidth = ...
LeeLeeYa's user avatar
1 vote
1 answer
967 views

The benefits of a fractionally spaced equalizer

I often read that one of the benefits of FSE vs a symbol rate equalizer, besides avoiding any aliasing in the roll off region, is that it is less sensitive to the timing phase. What does that really ...
Hatem Tawfik's user avatar