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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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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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(\...
1 vote
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36 views

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 ...
1 vote
1 answer
70 views

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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1 answer
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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 ...
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37 views

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 ...
5 votes
1 answer
100 views

The Amplitude of the Correlation Function Peaks After Matched Filtering

I have 2 signals: $s_1(t)$ and $s_2(t)$. The autocorrelation functions are given by $R_{s_1}(\tau)$ and $R_{s_2}(\tau)$ with $|R_{s_2}(\tau)|<|R_{s_1}(\tau)|$. I would like to know if the previous ...
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1 answer
70 views

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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1 answer
75 views

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 ...
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1 answer
22 views

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 ...
1 vote
1 answer
36 views

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 ...
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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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1 answer
36 views

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 ...
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1 answer
35 views

encryption key exchange algorithm

We have RSA algorithm for encryption key exchange for example for e-commerce. If we consider the case of wireless telecommunications. Is it possible to implement an encryption key exchange algorithm (...
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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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2 answers
66 views

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 $1250 \, \textrm{MHz}$...
5 votes
3 answers
4k views

Do BPSK vs QPSK have the same performance?

I'm trying to re-learn digital communication theory again and am creating a bit error probability simulation for various modulations. So far I've added BPSK, QPSK, and 8PSK and below is a plot that ...
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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 ...
1 vote
3 answers
143 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 ...
1 vote
1 answer
31 views

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 ...
2 votes
1 answer
104 views

Generating signal in a different frequency band than another signal but transmitted at the same time

I have a signal $x(t)$ of bandwidth $W_1$ transmitted over carrier frequency $f_1$, and another signal $i(t)$ of bandwidth $W_2$ transmitted over carrier frequency $f_2$. The main lobe of both signals'...
0 votes
1 answer
71 views

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 ...
1 vote
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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 ...
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27 views

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?
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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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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 ...
0 votes
1 answer
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How to understand the relationship between complex baseband equivalent model and block-fading channel model?

Considering a bandpass communication system, where $y(t)=x(t)*h(t)+n(t)$ ($x(t)$ is the transmitted bandpass symbol, $h(t)$ is the channel impulse response, $n(t)$ is the AWGN, and "$*$" ...
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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 ...
1 vote
3 answers
437 views

Why only odd harmonics after non-linear amplification?

Why do I get only odd harmonics appearing? This not only happens at saturation of the transfer curve, but also in the linear portion of the curve. I make a input signal that has too high power that ...
3 votes
1 answer
140 views

dsss and correlation

Generally, a DSSS (Direct Sequence Spread Spectrum) communication is used to secure a communication. However, because of the repetition of the spreading sequence, a cyclostationary analysis makes it ...
1 vote
1 answer
89 views

Is code rate included in $E_{b}/N_{0}$ calculations when it increases message time?

I am seeking to calculate the individual sample SNR from a given $E_{b}/N_{0}$. I am calculating this as follows: $E_{s}/N_{0} = E_{b}/N_{0} + 10\log_{10}(M)$ $SNR = E_{s}/N_{0} - 10\log_{10}(n)$ ...
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44 views

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 ...
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2 answers
64 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 ...
1 vote
1 answer
133 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 ...
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 ...
1 vote
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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 ...
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1 answer
78 views

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 $\...
4 votes
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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 ...
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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 $\...
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1 answer
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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 ...
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1 answer
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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 ...
1 vote
1 answer
205 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 ...
3 votes
1 answer
417 views

Use of the harris-Moerder Nyquist Pulse Shaping Filter

I became aware today through fred harris' excellent presentation at the DSP Online Conference (https://www.dsponlineconference.com/) of the harris-Moerder pulse shaping filter which was published 15 ...
1 vote
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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 $...
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1 answer
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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 ...
0 votes
1 answer
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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}...
3 votes
1 answer
522 views

Symbol timing recovery design

I am trying to design the Symbol timing recovery(#STR) block of #DVBS Receiver. These are the specifications Symbol rate ($f_s$) = $2\textrm{ MHz}$ Acquisition range = $10\%$ of Symbol rate ...
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1 answer
310 views

How to estimate the average distance between peaks (maxima) of the magnitude of an OFDM signal?

Given an arbitrary configuration of carriers having bandwidths that belong to the 3GPP standard (5, 10, 15, 20, 25, 30, 35, 40, 50, ..., 100 MHz), is there a method/rule-of-thumb to estimate the ...
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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 ...
1 vote
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 ...

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