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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EIRP for JWST HGA
I am attempting to compute the EIRP for transmissions from the James Webb Space Telescope using the high-gain antenna. I found the following reference...
https://www.ioag.org/Public%20Documents/2019-...
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Help me understand the concept of IQ signals
I am a computer science student working on a school project involving RTL-SDR receivers, and I have a hard time grasping the concept of IQ data. Basically what I think I have learned from all of the ...
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What is the relationship between Symbol Duration and Sampling Frequency in a 256 MPSK radio link
I'm struggling to work out the relationship between Symbol Duration and Sampling Frequency in an MPSK link.
For instance, if the Sampling Frequency is 10MHz this means that a sample is taken every ...
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How is the normalized power required for unipolar NRZ twice that of polar NRZ?
So, the normalized power for unipolar NRZ scheme is $\frac{1}{2}V^2$. According to my book, the normalized power required for polar NRZ is half that of unipolar NRZ. So, the power should be $\frac{V^2}...
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The MSE after each synchronization block doesn't go consistently down at the output of each block
I have a synchronization chain that consists of
Coarse frequency synchronization block
Frame synchronization block
Symbol time synchronization block
Fine frequency synchronization block
PLL phase ...
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Why symbol rate equal to bit rate despite the fact that the transmission scheme use 5 bit per symbol?
I am practicing Digital communication (Baseband demodulation/Detection) when I encounter this question.
An analog signal is PCM formatted and transmitted using binary waveforms over a
channel that is ...
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What are different encoding schemes used in gigabit ethernet?
I was reading about digital transmission, there are many steps namely
Analog to Digital conversion
Source coding
Channel coding
Line coding
Pulse shaping
Modulation
Multiple access techniques
Out of ...
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spread spectrum communication and timing recovery
I use a DBPSK modulation. Each modulation symbol is spread by a signal $c_i(t)$ which is different for each DBPSK symbol. The transmitted signal is given by: $s(t)=\sum_{i=1}^{N_s}d_ic_i(t-iT_s)$ ...
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DSSS and DQPSK receiver
I use a spread spectrum communication with a DQPSK modulation. Each modulation symbol is spread with a different spreading sequence. At reception, I use a sliding window for despreading with the ...
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Synchronization blocks and the domain in which they operate
I'm studying the full synchronization chain, and it's not clear to me at which domain each block works on in terms of sample vs. symbol domain. I'm particularly confused between frame synchronization ...
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How does PAM-4 encoding of a digital signal relate to theoretical *pulse* amplitude modulation?
Pulse amplitude modulation in general is often explained using plots like this one from wikipedia:
There is a sinusoid analog signal (red) to be "imprinted" on a train of pulses. The result ...
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Phase locked-loop and DSSS
Suppose we use a DSSS system such that each modulation symbol is spread by a different code. On reception, the signal has a frequency drift and a phase-locked loop (PLL) must be used to correct it. ...
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Probability of miss detection and probability of false alarm in frame synchronization
I'm working on frame synchronization, and I don't fully understand the probability of miss detection and probability of false alarm in evaluating the performance of the synchronization block. As far ...
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Why do we ever use low-order modulation schemes?
Many communication standards implement adaptive modulation and coding with modulation and coding scheme (MCS) tables. In these tables, we typically use low order modulation for low spectral ...
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How to implement maximum likelihood (ML) detector in MATLAB?
Consider the MIMO system which has $N_t$ antennas at transmitter and $N_r$ antennas at receiver and uses Generalized space shift keying (GSSK) modulation. The received signal is given by:
$$Y = H X + ...
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Approximating variable-length coding by "aggregating" fixed-length coding
Consider the problem where I want to quantize a univariate standard Gaussian with two bits, and the objective is to minimize MSE reconstruction loss. According to these slides, the Lloyd algorithm and ...
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Multipath Propagation Correction for LTE signals
How can I correct multipath propagation for LTE signals generated from different eNodeBs?
My end goal is to implement localization of my USRP using LTE or FM signals. Currently I am carrying out a few ...
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How to express random signal in MATLAB which is transmitted from transmitter to receiver
I am trying to model a random transmitted signal between transmitter (source) to receiver.
Specifically, the transmitter has $N_s = 1$ antenna and receiver has $N_r = 2$ antennas.
My query is that I ...
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What is self-interference channel matrix in full-duplex system?
I am learning about full-duplexing systems, and I saw that we have self-interference (SI) in the systems.
I read some papers that model the SI channel of the base station ${H_{SI}} \in \mathbb{C}^{L \...
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Delayed waves existing MIMO eigenmode transmission
Assume that the numbers of transmitting antennas, receiving antennas, and delayed waves are $N_t$, $N_r$, and $N_p$, respectively. The channel matrix is three-dimensional ($N_r$, $N_t$, $N_p$).
In ...
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simulation models unique to each researcher? Or use a specific common model?
Are the simulation models used by researchers at each university unique to each university? Or use a specific common model?
I started working on OFDM research at university, but I'm at a loss as to ...
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How to calculate capacity using Shannon and path-loss?
I am working on tasks offloading on edge computing. I need to find the transmission delay, through calculating Shannon capacity-theoretical maximum data rate- when sending results from the server back ...
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Is there any specific order for the synchronization blocks at the receiver?
I am working on frequency, time and phase synchronization at the receiver, and although there is a consensus that coarse frequency synchronization is the first block in the chain, I am confused about ...
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PLL in noise-free and noisy channels
I'm trying to evaluate the performance of PLL in compensating the phase noise in the absence and presence of AWGN noise, and the counterintuitive result I consistently get is that PLL performs better ...
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optimal RX beamforming
I was asked this question in an interview couple of weeks ago. I think I answered it correctly, but I think I might missing some points. Here is the problem, following by my answer.
Part 1)
In Figure ...
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Why for bandpass signals complex envelope and pre-envelope signal representations are used in digital communications/analog communications (FM)?
When we need to analyse band pass signals we use complex envelope and preenvelope representations, wherein a signal is given an equivalent low pass representation.
My issue is why it is done, though I ...
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Analyzing the OFDM out-of-band effect when using different guard interval
I am trying to understand the concept of out-of-band (OOB) which occur with OFDM, I have tried to read about it, but I couldn’t understand how I can illustrate that effect with MATLB.
This is the ...
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MUSIC algorithm on CSI data
I am trying to write a simulation code to estimate AOA's from channel state informations(CSI) using MUSIC algorithm. I am using OFDM with 64 subcarriers. Is there any material on how to estimate AOAs ...
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Detection problem with extra noise observation. Does the extra observations help with detection?
Assuming all “real” number, consider the detection problem of $x$ given $y_1$ and $y_2$ below
$y_1= x + n_1$
$y_2= n_1 + n_2$
where $x$ is either $+A$ or $-A$ with equal probability, and $n_1$ and $...
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Programming a delay in Matlab
Let $x(t)$ a signal of duration $T$, the sampling frequency is $f_s$.
I know the signal $x(t+\tau)$ orresponds to a signal delayed by a delay $\tau$. In Matlab, the signal $x(t+\tau)$ is given by: $[...
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Symbols to samples at the transmitter and samples to symbols at the receiver
Suppose I have the $N\times 1$ vector $\mathbf{x}$ that contains binary phase shift keying (BPSK) symbols each with power $P_s$ Watts.
At the transmitter: I want to convert these symbols into samples ...
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DS-CDMA Spreading Code Length Selection
I'm trying to wrap my head around the process of selecting DS-CDMA spreading codes, and I'm having trouble understanding the tradeoffs of longer codes. For all scenarios described below, I'm using a ...
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MC-CDMA Spread Signal
In the MC-CDMA (to simplify with $1$ user), the spreading sequence is a sequence of -1 and 1. I would like to know if it is possible to replace this sequence with a signal $s(t)$ of bandwidth $B$ to ...
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OFDM combined with chirp signal
I want to achieve OFDM modulation combined with a chirp signal (for example a LFM signal). Is it correct to do as below (this is a global scheme):
Mapping
Spreading with chirp signal
OFDM Modulation
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OFDM design considerations for choosing the number of subarriers $N$
I was trying to think of all possible constraints or factors that needs to be taken into consideration while designing an OFDM-based wireless communication system (For example, LTE, 5G technologies ...
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cyclostationary signal and spreading sequence
I am using DSSS (Direct Sequence Spread Spectrum) communication. The mathematical expression for the spreading sequence is given by: $g(t)=\sum_{i=0}^{L-1} c_i g(t-lT_c)$ where $c=[c_0,...,c_L]$ is ...
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How can I simulate the process of transmitting BPSK signal from start to end?
I would like to simulate the process of transmitting a binary phase shift keying (BPSK) signal from start to finish, going through each step over additive white Gaussian noise (AWGN) channel. I know ...
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direct spread spectrum
I am studying the DSSS method and I have a question. For example, the emitter and the receiver use a $c_1$ sequence for spreading of length $L$. An eavesdropper uses a $c_2 $sequence of length $L$. We ...
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spectral bandwidth of QPSK signal
When running the MATLAB QPSK transmitter and receiver example (found here: QPSK Tx and Rx Example) you can see on the plot of the spectrum that the bandwidth is ~80kHz.
If we double click on ...
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How to choose a decoding algorithm with AWGN performance
Decoding algorithms for convolutional code, turbo code, ldpc code and so on, are usually evaluated in AWGN channel. They are finally used with other receiver modules in fading channels. The ...
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Optical Communication APD problem
A germanium APD (with $x= 1.0$) operates at a wavelength of $1.35μm$ where its responsivity is $0.45AW^{-1} $. The dark current is $200nA$ at the operating temperature of $250K$ and the device ...
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Is it better to do fixed-length Lempel Ziv Encoding or variable length?
I performed variable-length LZW encoding in Matlab on a large set of text where my dictionary looks like this (size = 28):
...
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QPSK demodulation carrier frequency offset compensation on python
I am new to signal processing and I am trying to demodulate the IQ data, and I am stuck on the carrier frequency offset compensation.
I has 1000 samples and it is 1MHz data.
For the general idea, I ...
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Recognizing different pulse shaping forms (16-QAM modulation)
I have three versions of a 16-QAM modulated signal, each showing the time curve of the real and imaginary parts, the spectrum and the symbol constellation. These three versions differ by the ...
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Hilbert transform with non-modulated signals
Is it correct to compute the Hilbert Transform and then the complex envelope, expressed as $v = z~ e^{-j 2\pi f_c t}$, where $z$ represents the analytic signal and $f_c$ represents the carrier ...
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Dsss in digital communication, acquisition, tracking
I have some questions of direct sequence spread spectrum.
Does dsss need a pulse shaped filter before it is transmitted?
And is there any reference how to realize a dsss system in digital ...
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fractionally spaced channel equalizer code [closed]
I want to write a program in matlab for an adaptive fractionally spaced equalizer with lms algorithm.consider each packet with 150 bits that 25 first bits are pilot and used to train weights of the ...
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Rayleigh flat fading channel and pulse shaping
I'm trying to implement the Rayleigh flat fading channel in MATLAB using SRRC (Square-root raised cosine) pulse shape. The modulation scheme is BPSK. Here is my code:
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Is this an appropriate Huffman code?
The problem is question 6.25 from Proakis, Communication Systems Engineering (2001)
Design a ternary Huffman code, using 0, 1, 2 as letters, for a source with output
alphabet probabilities given by {...
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How can I simulate a random delay offset between two data streams?
Suppose I'm transmitting two streams at the same time in blocks each of length $N$ samples each sample of duration $T_s$ seconds. Block $t$ of stream $i$ is $\mathbf{x}_i[t]=\left[x_{i,0}[t],\,\,\,x_{...
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