# 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-...
573 views

### 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 ...
1 vote
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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 ...
116 views

1 vote
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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 ...
1 vote
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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 ...
1 vote
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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 ...
1 vote
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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 ...
61 views

### 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 ...
30 views

### 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 ...
1 vote
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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 ...
1 vote
106 views

### 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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### 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 ...
54 views

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 ...
1 vote
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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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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 ...
163 views

### 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 ...
29 views

### 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): ... 190 views

### 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 ...
97 views

### 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 ...
1 vote
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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 ...
172 views

### 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: ... 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_{...