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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2answers
429 views

What is the main difference between the acoustic and electromagnetic waves?

For simulation purpose, what will be the difference between using acoustic and electromagnetic waves? Just the carrier frequency only??
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1answer
70 views

Temporal Orthogonality

I'm studying Digital Communication and I couldn't understand the relationship between temporal orthogonality and sampling theorem. Definition of the Temporal Orthogonality is as follows: $$\mathrm{...
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1answer
54 views

MATLAB produces too short output for frequency modulation

I have a voice data contained in a vector. Vector length is 118796 and sampling frequency is 8000 Hz. So it's around 15 seconds of voice data. When I doing frequency modulation with fmmod (Carrier ...
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1answer
498 views

Question on the definition of one-sided PSD in AWGN channel

I am currently simulating the following in a telecommunications exercise in Python: Consider a binary sequence $m[n]$ that is being modulated with QPSK (Gray-mapped) that is being transmitted via ...
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1answer
2k views

What is the theoretical bit error rate for QPSK Matlab simulation when constellation points are transmitted (no symbol duration)?

I'm simulating a QPSK system in Matlab and I'm trying to calculate the theoretical bit error rate to compare it with the simulated ber. The formula that I'm aware of involves the term Eb/N0, but how ...
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1answer
49 views

RF for Data Transmit and Receicve for Beginners

Is there any good matrial avialable for data specific DSP? I have gone through some great DSP intros for beginners in python but all of them revolve around the characteristics of audio signal
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1answer
45 views

Compensating effects of a system with a known transfer function

Suppose we have a system which we want to know the exact transient times. In ideal case, we can extract the transient times, but in practice it will be affected by another system with a known transfer ...
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1answer
572 views

Power Spectral Density of Digital Modulations

I want to simulate the power spectral densities of different modulations in MATLAB (without Simulink). Unfortunately I have only very basic understanding of signal processing, hence I struggle with ...
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1answer
1k views

The error probability of 16QAM

The signal constellation for a communication system with 16 equiprobable symbols is shown as below. The channel is AWGN with noise power spectral density of $N_ 0/2.$Using the union bound, find a bound ...
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1answer
64 views

Newbie looking for an interesting introductory book to telecommunication and signals/data processing

I am currently in my first year of Bsc Applied Physics. Over the past two years, I have realized I'm interested in majoring in telecommunication after I finish my bachelor. Also, for one of my classes ...
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1answer
54 views

Transmitting over Unknown Fading Channel

I have a system with no diversity and the channel's coefficients change every $T = 10\text{ bits}$ transmitted. The channel estimation system has a flaw and detects the channel's coefficients equal to ...
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3answers
45 views

Some problem with the expression of QAM basis and signal

The expression of QAM basis is \begin{align} \psi_1&= \sqrt{\frac{2}{E_g}}g(t)\cos(2\pi ft)\\ \psi_2&= -\sqrt{\frac{2}{E_g}}g(t)\sin(2\pi ft) \end{align} I want to ask why is $\psi_2= -\sqrt{\...
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2answers
73 views

Does Forward Error Correction (FEC) affect upsampling factor?

Is the redundant data introduced during forward error correction (FEC) counted as upsampling? I'm taking a binary data stream, doing convolutional encoding of rate 1/2 on it, then making it NRZ ...
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1answer
597 views

Typical number of samples per symbol

Assuming a pulse shaping of a source of symbols (like $s=\{3,-i,2+5i\}$), and a SRRC waveform (or any other waveform). I know that it depends on many factors like modulation scheme, but, in practice, ...
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1answer
239 views

File size adjustment using FFT

I have been given the task of doing audio compression using FFT. The assignment is below. Below is my MATLAB code: ...
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0answers
49 views

Doppler Shift and Wireless Access Points

I am trying to design and implement a system that would calculate the velocity of a hand motion in smartwatch. The general idea is to calculate the Doppler Shift of each access point and find ...
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1answer
173 views

Computing the decimation ratio between two m-sequences

Let's suppose I have an LFSR that generates an m-sequence $y_1[k]$ --- in other words, the LFSR has $N$ bits and $y_1[k]$ has period $m=2^N - 1$. Now suppose I know someone has decimated this and ...
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0answers
38 views

Random multipath power and delay generation

I'm trying to simulate an indoor environment that exhibits multipath propagation. However, I don't know how to generate random multipath variables like path power and path delay (power-delay profile)....
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1answer
886 views

Upsampling before performing pulse shaping

I know what an upsampler does. We insert L-1 zeros between the samples. As a result, it creates spectral repetitions. What if we have a symbol impulse stream and then we apply a Root Raised Cosine ...
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1answer
331 views

Deciding for the correct way to calculate coherence time

I have to calculate the coherence time of an indoor environment. The signal I am sending is modulated with GFSK, the carrier frequency is about 2.4 GHz and my symbol time is 1 microsecond. During my ...
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1answer
24 views

Computing overall bitrate of a transmitter with a two chunks package

I'm programming a digital communication system in MATLAB and I have a two chunk package, let's say a header and a body, and I'm using a different channel code for each chunk, i. e. BHC1 and BCH2. But ...
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2answers
721 views

Correct way to simulate Rayleigh fading for indoor environments

I am trying to simulate indoor communications with all components included. But something disturbs me when it comes to Rayleigh fading part. I am adding my rayleigh fading to the transmitted signal ...
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1answer
878 views

In-Phase and Quadrature components of low-pass equivalent of a band-pass signal?

I was wondering what is the physical meaning of IN-PHASE and QUADRATURE components? In the context of low-pass equivalent of band-pass signals. Any help is appreciated!
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2answers
299 views

Will the capacity of a channel becomes unbounded if i increase its signal-to-noise ratio $S/N$ without limit?

According to the Shannon-Hartley theorem the capacity $C$ of a channel which has a signal-to-noise ratio of $S/N$ and a bandwidth $B$ can be calculated to be $C = B \log_2 \left( 1 + \frac{S}{N}\right)...
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3answers
322 views

Will signal get distorted if channel bandwidth is lesser than the signal bandwidth?

This statement is given in the book "digital communicatinon by Taub schilling " Now one point I am unable to understand that if the channel bandwidth is lesser than the signal bandwidth,how it is ...
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2answers
2k views

Capacity of cascade binary symmetric channels

Let's imagine that we have interconnected in cascade $L$ binary symmetric channels each with the same transition probability $p(y|x) \in \{p, q=1-p\}$, where the output of each BSC is connected to the ...
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1answer
32 views

Why GCD(1+D, 1+D^2) = 1+D?

I'm reading Digital Communications, Proakis, and in order to classify an encoder as catastrophic or noncatastrophic I need the GCD of the elements in the generator G(D). I don't really know what kind ...
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4answers
707 views

How can the I and Q components of a quatrature signal be different from each other (apart from the 90º phase shift)

I've spent many hours reading and doing research about this. I don't attend any university classes or any type of classes that may approach such a topic. I am trying to learn this by my own without ...
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1answer
439 views

Why zeroes near the unit circle cause a dip in frequency response, while poles cause a peak?

I have an exam tomorrow and I really can't figure out the question in the title.
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2answers
3k views

How does transition width of a low-pass filter affect a message which is well within the pass-band?

I'm taking a communication systems course and we use GNURadio in the lab. In an exam, we had a simple question where we were asked to demodulate a Dual Side Band (with carrier) AM signal in GNURadio. ...
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1answer
223 views

Noise variance calculation for 16APSK Demodulator

I need to use approximate LLR algorithm for 16APSK demodulation. For that, I need to calculate noise variance which is given as $Noise\;variance = \frac {Signal\;power\;\times\;Symbol\;time}{Sample\;...
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1answer
109 views

Energy Detection Algorithm Uncertainty

I'm currently working on a project to perform energy detection of an IEEE 802.15.4 using the block diagram illustrated below. However, I do have a little uncertainty about the algorithm. I'm wondering ...
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1answer
649 views

Matlab : Adding noise with regard to signal-to-noise ratio or EbNo?

A signal x takes values from an alphabet set. My objective is to estimate the channel parameters hest using adaptive methods and ...
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1answer
406 views

Flat vs frequency selective fading in MC-CDMA?

I am trying to simulate an MC-CDMA system. I have NXK matrix $S$ which consists of subcarriers ($s_n,_k$ represents subcarrier $n$ of user $k$) and KX1 vector $X$ consists of user symbols. So my ...
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1answer
60 views

Study resource for Digital communication

I am in my 5th semester of computer science and we have a digital communication course. All the textbooks of digital comm. available in my library demand a prerequisite of Circuit analysis and Signals ...
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0answers
54 views

Is an extra symbol at the origin of a QAM constellation ok?

This question is specifically directed at Maximilian Matthé (as you work with 5G systems), and to anyone who can shed some light. I am trying to implement a GFDM system with a total of N = K*M ...
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2answers
280 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 ...
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0answers
63 views

Sufficient conditions for exact signal recovery using OMP?

For a compressive sensing model : $$y_{_{MXN}}=A_{_{MXN}}x_{_{NX1}}$$ where $x$ is $K$ sparse, what is the sufficient condition for Orthogonal matching Pursuit (OMP) to exactly recover the data for ...
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1answer
343 views

Aliasing in digital communication system

In a digital communication system, is it possible to counteract the aliasing problem by properly tuning the constellation order $M$ and/or the carrier frequency? Here is my train of thought, please ...
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3answers
1k views

Under what circumstances is a non-uniform quantizer preferable over a uniform quantizer? [closed]

I am studying btech ECE 3rd year. I want answer that question. Please tell me.
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1answer
59 views

Doubts and some confusion on variance for complex rv

This question is in continuation of the one asked here. Let's say that the measurement noise $w$ or any random variable is circularly Gaussian complex. If the imaginary and real components each has ...
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1answer
1k views

Why are Gold codes and Kasami codes used instead of pure m-sequences?

I'm trying to understand why Gold codes and Kasami codes are used instead of pure m-sequences, in direct-sequence spread-spectrum (DSSS) communication systems, to prevent interference between multiple ...
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1answer
95 views

Effect of nonlinear transformation on digital signal

Currently, I know that by passing a band-limited baseband digital signal through a nonlinear system results in the expansion of the original signal's bandwidth and creates harmonics. Therefore, I ...
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3answers
660 views

Sending complex signal over a single wire

The G.hn protocol uses OFDM to transmit data. And it sounds like they are doing it on a single wire. OFDM symbols are a complex number with I and Q components. How are they able to send two separate ...
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3answers
467 views

Lower digitisation rate for long distance communcation

Why is it that usually lower digitisation rates are used for long distance communications? e.g. sound is highly distorted in undersea communications, is this because of the lower digitisation rate ...
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1answer
55 views

Predistortion of signal constellation?

I am trying to learn aspects of space/satellite communications. So Amplitude-Phase Shift Keying is quite popular in this domain. APSK over Non Linear channels has worse performance than the earlier ...
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2answers
2k views

Relation between Normal Phase Shift of a wave and Phase Modulation

I am little confused with the Phase Modulation and the phase of a sine wave. I get the phase modulated wave from the google images as below: Phase modulation has the form: $$PM(t)=A_c \cos\big(2\pi ...
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1answer
405 views

How is the number of amplitude levels decided in modulation techniques?

For M-QAM modulation, where e.g. $M = 64$ there are 8 amplitude levels. Each level is represented by a symbol that is further represented by bits through the relation: $$b=\log_2(M)$$ This means ...
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1answer
187 views

coding gain and shaping gain in SCMA

It is said that sparse code multiple access (SCMA) has the advantage of higher shaping and coding gain over LDS-CDMA due to the multidimensional constellation. What exactly is the shaping gain and how ...
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1answer
391 views