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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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Gausian Pulse shaping filter

I need expert advice on implementation of Gausian Pulse Shaping filter for generating GMSK signal in further steps. I have implemented as follows, Can anyone confirnm that the Pulse would be shaped as ...
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"Best" energy efficiency via capacity of uncoded BPSK AWGN

I have numerically approximated the capacity of an uncoded, binary uniform input, real AWGN BPSK channel versus the SNR using mutual information and entropy, via Gauss-hermite quadrature. My task is ...
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How can we estimate the channel in frequency and time domain jointly main

Given the received signal $ y \in \mathbb{C}^{N \times 1} $ defined by the equation $y = h \otimes x $, where $ h \in \mathbb{C}^{L \times 1} $ represents a channel of length $L $, $ x \in \mathbb{C}^{...
Sajjad's user avatar
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BERT (bit error rate test with ADC )

I'm trying to make a digital decoder. I sample a digitally modulated signal with the LTC2387, an 18-bit 15MHz SAR ADC. The carrier signal is at 2.1MHz, and is digitally mixed down to DC to obtain the ...
Abdel Djaferbey's user avatar
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Why is discrete-time spectral efficiency of 2-PAM stated as 2 bits per 2-dimensions?

In fact, 2-PAM uses one dimension and transmits one bit per symbol. So I see it as 1-bit per 1-dimension. But in communication theory, it is said to be 2-bits in 2-dimensions, and thus is equivalent ...
gschro's user avatar
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Rician Frequency Selective Channel Model

I have a question about Rician channel with $L$ taps. The frequency selective Rician fading channels with delay spread of $L = 6$ taps are considered for both direct link and reflecting link, where ...
Hossein's user avatar
1 vote
1 answer
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frequency selective channel $\ne$ multi-tap channel?

A frequency selective wireless channel is necessarily a multi-tap channel, in the tap-delay line model, as the delay spread is significantly larger than the symbol duration. And a single-tap channel ...
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Understanding about correlation between random variables in context of Wireless Communication

I am trying to understand about correlation between random variables in context of wireless communication. In research papers related to 6G, I came across the following statements: Suppose there is a ...
Tushar Muratkar's user avatar
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BER curve versus SNR for using matched filter receiver

I want to simulate matched filter receiver with rectangular pulse shape in an AWGN channel. My goal is to plot the BER curve versus SNR for BPSK modulation. I have written the code and my curve is as ...
Omid Abasi's user avatar
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Understanding the additive white Gaussian noise (AWGN) representation

In my research work in wireless communication, I came across an equation of received signal wherein the AWGN is denoted by $n\sim\mathcal{C}\mathcal{N}(\textbf{0},\textbf{I}_L)$. Note that dimension ...
Pranu's user avatar
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Related to dimension of wireless channel , transmitted signal and received signal

I am working on wireless research project and I had query in understanding dimensions. Consider a MIMO system, where a base station with $N$ antennas transmits signal $x$ to receiver with $M$ antennas....
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A question about CRC

The probability of the undetected errors for an n bit CRC is said to be $1/2^n$. But in practice, CRC also has bit errors in itself. Could I say that a 16 bit CRC reduces to a 13 bit CRC if the BER is ...
c1119's user avatar
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What's wrong with 180 degree phase shift in QPSK?

I red that 180 degree phase shift causes spurious high frequency components which As a result methods such as OQPSK are invented, but I can't understand how it can happens? In fact, I can't find any ...
Ang's user avatar
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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(\...
albusSimba's user avatar
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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 ...
syeh_106's user avatar
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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 ...
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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 ...
Pranu's user avatar
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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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-1 votes
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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
1 vote
1 answer
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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
1 vote
3 answers
149 views

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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47 views

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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2 answers
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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 $1250 \, \textrm{MHz}$...
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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 ...
RTS's user avatar
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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
104 views

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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1 answer
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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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2 answers
68 views

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
4 votes
0 answers
96 views

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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1 answer
31 views

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 ...
MaxFrost's user avatar
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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
1 vote
1 answer
207 views

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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1 answer
53 views

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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1 answer
65 views

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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1 answer
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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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1 answer
81 views

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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