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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Matching closed form BER with integrals for QPSK modulation

I am trying numerically compute the $\bar{P}_b$ for QPSK in a Rayleigh fading channel according to the formula, $$ \bar{P}_b = \int_0^\infty P_b(\gamma)p_{\gamma_s}(\gamma)\ d\gamma $$ for QPSK $P_b(\...
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BER of coherently detected DBPSK?

I understand that differential PSK is generally used when coherent detection is not possible, and so is usually detected non-coherently. However, for sake of theoretical analysis/understanding, what ...
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BPSK decoding with a non-ideal transmission medium

I'm simulating tranmission via power line communications (PLC) using BPSK. Due to the coupling circuit and slightly inductive nature of the line, the BPSK signal received is far from ideal. In the ...
mr_js's user avatar
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Related to SNR in wireless communication

I am working on a research paper related to wireless communication, wherein I am facing some doubt while writing expression of SNR (which is a ratio of Signal variance in numerator to Noise variance ...
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Regarding SINR (Signal to Interference Plus Noise Ratio) in wireless communication

I am working on a research paper related to wireless communication, wherein I am facing some doubt while writing expression of SINR (which is a ratio of Signal variance in numerator to Interference ...
Pranu's user avatar
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instantaneous frequency for a complex signal

Let $s(t)$ be a complex signal. I would like to know how to find a signal from its instantaneous frequency. I programmed the following function which calculates the instantaneous frequency. ...
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Why is my Hard Decision Decoding of Convolutional codes not performing well?

I am encoding and decoding a randomly generated bitstream of data using a [5 7] convolutional code. For the decoding part I am using a Viterbi Decoder and trying both HDD and SDD. However, my results ...
Sherlock Rozman's user avatar
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Spreading sequence for dsss or cdma

In spread spectrum systems like DSSS or CDMA, we can take a pseudo-random sequence composed of 1 and -1. But can we use a complex number sequence between -1 and 1? Why is this type of sequence never ...
user71634's user avatar
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A question of channel capacity in precoding case

I’ve a general question about precoding. The channel capacity after precoding is $\log_2(\det(I+F’H’HF))$ where $\det$ is the determinant, $I$ the identity matrix, $F$ the precoding matrix, $H$ the ...
c1119's user avatar
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pulse shaping filter and passband

Most of the time, the baseband transmission chain is: modulation->oversampling->shaping filter (SRRC)->bandpass conversion on a carrier frequency $f_0$. But can we change the previous order ...
user71558's user avatar
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Does Filtering changes the noise characteristics in a signal?

So, I tried out what i am learning in digital communication using GNU radio. The plan is to modulate two baseband signals(sine and cosine) 1kHz with no modulation protocol(don't know any(yet)) to a ...
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Issue with small signal ML TED with low RRC excess bandwidth

I have a simple BPSK system using RRC TX & RX filters with 10% excess bandwidth with a receiver that uses a symbol synchronizer of the common type consisting of a polyphase filter bank (performing ...
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Unable to decode LDPC using Belief Propagation algorithm

I'm writing a MATLAB code to decode LDPC codes using the BP algorithm. I'm trying this with a (7,4) code. I tried the message-passing algorithm between variable and check nodes. L_r is the check to ...
Milli_Wizard369's user avatar
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Energy of Transmit Pulses in Digital Communication

Consider the problem of transmitting just two SRRC pulses through an noiseless Channel. The two transmit bits are {+/-1}. In plots below, the individual transmit pulses are shown in black, while the ...
lakshminarayanan raghavendran's user avatar
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Is there something wrong with MATLAB's pwelch function?

The normalized factor for windowing, is it $(\sum w[n])^2$ or $\sum w^2[n]$? I try to reproduce the pwelch function, if I set the normalized factor to $(\sum w[n])^2$, I get the same result as MATLAB ...
Devin's user avatar
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Free space path loss and ofdm

I want to apply the Friis equation of free space path loss on OFDM signal. Do I multiply signal by $\frac{c}{4\pi f_cd}$ before IFFT or after?
ahmed bennani's user avatar
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Understanding the (complex) GNU Radio implementation of Mueller & Muller

I have some questions about the M&M implementation of GNU Radio that uses complex samples. I started reading the implementation for real values: ...
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Mapping PAM-17 levels to PAM-5 levels

A $17$-level $\left\{ -4,-3.5,-3,\ldots,0, 0.5, 1,\ldots, 3.5, 4 \right\}$ digital signal coming at $125 \, \textrm{MHz}$ is passed through an FIR filter ($10$ taps) operating at $1250 \, \textrm{MHz}$...
Isha's user avatar
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real time streaming image encoding options

I'm interested in streaming video real time. There is an issue of deciding how to properly encoder the images and the format they should be. Since the data will be streamed over UDP, it needs to be ...
FourierFlux's user avatar
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outage capacity of K user fading channel

Suppose you have $K$ users, each seeing a point to point fading channel with $n$ receive diversity. So the rate of the kth user is at most $\log(1+ SNR|h_k|^2)$. Now suppose, each user transmits at ...
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Received signal from channel model

I'm struggling with this because I don't fully understand it. My goal is to estimate a received signal that is transmitted through a channel that follow a stochastic process. My doubt is, if the PDF ...
ThGeng32's user avatar
2 votes
2 answers
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What exactly is transmitted in the channel in lossy compression?

Consider the problem of lossily compressing a memoryless binary source $X \sim \operatorname{Bernoulli}\left(\frac{1}{2}\right)$ at target Hamming distortion $D < \frac{1}{2}$. According to the ...
nalzok's user avatar
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decision feedback equalizer building blocks (from Adaptive Filters: Theory and Applications” a book by Behrouz Farhang-Boroujeny)

Here you can see building blocks of DFE from "Adaptive Filters: Theory and Applications” a book by Behrouz Farhang-Boroujeny in chapter 17. Figure 17.9 shows the overall building blocks of DFE ...
Sadeq Ebrahimi's user avatar
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MMSE is approximately zero-forcing at high SNR

In https://stanford.edu/~dntse/Chapters_PDF/Fundamentals_Wireless_Communication_chapter8.pdf page 360, it is stated that for a flat fading MIMO channel with receiver CSI only: at high SNR, the $\...
RTS's user avatar
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Understanding Fresnel reflection coefficient formula

In textbook "Wireless Communications Principles and Practice" by Theodore S. Rappaport, the expression of Fresnel reflection coefficient ($\Gamma$) for parallel polarization is given as $\...
Heretolearn's user avatar
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How to detect when signals overlap in OFDM?

If you are in an environment with multiple transmitters of similar signal strengths, before band selection has taken place, how do receivers parse out overlapping OFDM signals from multiple ...
FourierFlux's user avatar
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Distortion-Rate function for standard Gaussian signals quantized with a uniform alphabet

Let's say $X \sim N(0, 1)$ is a standard Gaussian input signal and $Y \sim U\{y_1, y_2, \cdots, y_{16}\}$ follows a discrete uniform distribution (in fact, $\{y_1, y_2, \cdots, y_{16}\}$ is a ...
nalzok's user avatar
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Understanding frequency band specification in wireless networks

I am trying to clear my understanding of frequency bands. When a particular wireless network standard like WiFi 6 claims operation in the $2.4$ GHz or $5$ GHz band, what do these values refer to? I am ...
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How to derive the error probability for pulse position modulation in digital communication?

I am trying to build a simulation on MATLAB for PPM transmission through AWGN channel. I have a function wrapping the transmitter, channel and receiver that takes a SNR value as input. My simulation ...
Aloys Reant's user avatar
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MIMO reading clarification

On page 301 of https://stanford.edu/~dntse/Chapters_PDF/Fundamentals_Wireless_Communication_chapter7.pdf, equation (7.33) says that the magnitude of the dot product of two unit complex vectors is ...
Ray's user avatar
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Channel equalization in uplink

I have a multiuser uplink signal $$ Y=h_1x_1+h_2x_2$$ where, $h_1$ and $h_2$ are channels for user 1 and user2 respectively. At the receiver how can I equalize the signal $Y$, assuming known $h_1$and $...
Digi1's user avatar
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Can PLL for OQPSK be used for carrier frequency recovery?

This is the phase detector of PLL of OQPSK modulation. Apparently, it introduces a self-noise labeled in red which can’t be offset. I simulate this algorithm in Matlab, it doesn’t perform as well as ...
Xiang Li's user avatar
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Ergodicity clarification

On page 201 of https://stanford.edu/~dntse/Chapters_PDF/Fundamentals_Wireless_Communication_chapter5.pdf, it is mentioned that This observation suggests that the capacity result (5.89) holds for a ...
Ray's user avatar
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I/Q scatter plot of raised cosine filter in QPSK

I am using a raised cosine filter in my QPSK receiver and I see this IQ diagram of the signal, but it seems off to me. Can someone explain why this happens? This is the MATLAB code I used to generate ...
Jacob's user avatar
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Symbol Sync blocks in GNU Radio seem to use PID (well, PI) for their clock sync feedback loops. Why not IIR/FIR?

E.g. the Symbol Sync block has a Loop Bandwidth, which (if I read the source right) ends up as a PI loop. I know what PID does mathematically, and what FIR and IIR ...
Thomas's user avatar
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Where am I wrong in terms of 16-QAM with union bounds?

The following is my analysis. (The analysis is based on analysis from ESE 471: Example Union Bound M=8 Box QAM) Please correct me if I am wrong. Suppose each symbol has a distance of $d$ from its ...
kile's user avatar
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Sample Use vs Sampling Frequency

I need to acquire an analog signal via an ADC and send it via a digital communication line (CAN bus) with a given frequency $f_{send}=100Hz$. If I understand correctly this means that this constraint ...
Jhonathan Asimov's user avatar
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Sending and receiving an image

After studying digital communication courses, I wanted to implement these theories and create an application for sending and receiving a gray image via WiFi between two Raspberry Pi devices. The ...
Mouh Kramo's user avatar
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1 answer
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How do you model the channel between a satellite(LEO) and a ground station?

If the transmitter is on a satellite in a circular orbit at Low Earth Orbit with a QPSK modulated waveform at 1 megabaud centered at 12 GHz downlinking to the receiver, which is stationary on the ...
Jacob's user avatar
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How to prove the mutual infomation expression in paper "Optimized Degree Distributions for Binary and Non-Binary LDPC Codes in Flash Memory"

Recently I met a question when I read the paper Optimized Degree Distributions for Binary and Non-Binary LDPC Codes in Flash Memory and Soft Information for LDPC Decoding in Flash: Mutual-Information ...
Milin's user avatar
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Convolution with an impulse train in time, what happens in frequency domain

Following figure is drawn as the block diagram of the digital modulator: The output of the filter block (with the impulse response p(t)) is the convolution of the weighted impulse train with the ...
Ang's user avatar
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FOURIER TRANSFORM: How can i find the index of data points

I am a senior in high school and am currently trying to conduct an exploration of Fourier Analysis, specifically using the Discrete Fourier Transform to analyse a chord played on my piano. Basically, ...
Ralph Khouri's user avatar
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Adding Narrowband Interference to Spread Spectrum Signal in MATLAB (Baseband Model)

I am interested in adding a narrowband interfering signal to my spread spectrum signal. In the waveform model, it's straightforward to generate a narrowband signal within the frequency range of the ...
Digi1's user avatar
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Discrete Frequency representation for central frequency/ discretize up-converted signal in time and frequency

I want to analyze a signal after up-conversion in discrete time and frequency, for example: Let's assume a continuous up-converted signal is: $$e^{j2\pi ft} \cdot e^{j2\pi f_c t} = e^{j 2 \pi (f+fc) t}...
user70521's user avatar
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In wireless communication, is pulse shaping applied to each BPSK signal before OFDM is used, or not?

I have read a number of posts that seem to ask this question but have not been able to find a definitive answer. Here goes... I understand that BPSK with NO pulse shaping would produce a signal in ...
Drummy's user avatar
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1 answer
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spectral density of Modulated ofdm signal

I have formed my OFDM symbol his length is 88 (Nsubcarrier=72,Ncp=16) with Fs=1080000 Hz we call this symbol as Signal_from_baseband I want to modulate the OFDM symbol with Fc carrier=2.1 GHz and plot ...
ahmed bennani's user avatar
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2 answers
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What does the frequency domain of bipolar Alternate Mark Inversion (AMI) look like?

Someone said to me that Bipolar AMI is not low-pass; it does not include the 0Hz in its frequency domain. I doubt that that is the case. However, at present I am unable to do Fourier transformations. ...
tryingtobeastoic's user avatar
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Applying Blahut-Arimoto Algorithm for AWGN Channels Capacity Calculation with Cost

I am exploring the Blahut-Arimoto algorithm (or any numerical method) for channel capacity calculations, particularly for continuous channels. I understand its application in discrete scenarios, but I ...
Alireza Ghazavi's user avatar
1 vote
1 answer
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Typical values of Amplitude and Phase Imbalance (IQ Imbalance) in 802.11ax (Wifi 6)

I want to simulate the IEEE 802.11ax waveform and include the IQ impairment and its mitigation. What is a reasonable/expected value of the Amplitude and Phase Imbalance coefficients? Please specify ...
vidyesh's user avatar
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Coordinates of cluster in CDL channel model

I was reading the 3gpp specification to understand the CDL channel models. (See section 7.7.1 and tables within). It says that for a cluster $C$,it has angles of arrival/departure along the azimuth $(\...
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