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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How to calculate the data rate of OFDM system

I have OFDM system with following parameters, Bandwidth $B = 5$ KHz, Number of sub-carriers $N = 64$, guard interval $N_g = 8$; Sampling frequency $F_s = 10000$ and Modulation order $M$ is QPSK. Is it ...
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Which is more powerful Laplace transform or Fourier transform? [closed]

In undergraduate, in some books, we study the first Laplace after Fourier and vice versa. there is the type of signal for which we found the first Laplace and we put jw in place of s and find Fourier ...
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PAPR used in PAM constellations

Can anybody explain me how to derive analytically the PAPR (Peak-to-Average Power Ratio ) for PAM constellations. E.g. 2-ASK (unipolar/bipolar), 8-ASK (unipolar/bipolar), 16-QAM, and 8-PSK? Thank you ...
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How to calculate received signal power for a Multi-User MIMO OFDM system?

I have a Multi-User MIMO system where there are 2 users served by a base station. The base station consists of 64 transmit elements and the users are equipped with linear antenna array consisting of 3 ...
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Do the effects of OFDM pilot tones spacing appear in time or in frequency domain?

As known, the pilot tones are transmitted via subcarriers predefined and known in the transmitter and the receiver. The pilot spacing is repeated with a certain rate that depends on how fast the ...
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How does higher received signal power enable higher data rates?

On page 30, of the book Fundamentals of LTE by Arunabha Ghosh et al. it is written: This allows broadcast signals from different cells to combine over the air to significantly enhance the received ...
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51 views

In practice, why is there any overlap in frequency-division multiplexing?

Okay, so I am aware of the math behind perfect reconstruction in filterbank and wavelet theory when there is half-band symmetry. But I don't understand, when we have the computational power to do ...
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157 views

Setting the duration of subcarriers in OFDM system

If have an ofdm system with $N$ subcarriers, and sampling frequency $F_s$, that means that duration of each subcarrier is $T_s = \ {1/F_s}$ and the duration of whole symbol (which includes $N$ ...
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41 views

Phase offset analysis in real trsnsmitted signal

Assume we are transmitting a real signal $x(t)$ through a channel $h$ in passband as : $y(t) = x(t)cos(2πf_c t + ∅) * h(t)$ = $Re(x(t)e^{j2πf_c t})*h(t)$ where $f_c$ is the carrier frequency and $t$...
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34 views

What is the meaning of the channel gain is normalized

Transmitting the signal $x$ over the channel $h$ and affected by noise $n$ can be expressed: $y = hx + n$ $h$ is the channel gain, that is known for me. I sometimes see phrases saying "when the ...
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37 views

CDMA generating the sequence for gold codes

Is this the correct way to generate a set of Gold codes: Take a preferred pair of M sequence polynomials and load each one of them into a separate LFSR. The serial bit streams that are generated from ...
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Difference in methods: coarse and fine frequency correction algorithm [closed]

I am currently studying frequency and phase correction methods. Most probably my question very basic but i am having difficulties to understand it. Could you please explain what is a difference ...
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Convolution between a channel with real signal vs. channel with complex signal

The real transmitted signal $x(t)$ is convolved with channel $h$ in passband as : $y(t) = x(t)cos(j2πf_c t) * h(t)$ = $Re(x(t)e^{j2πf_c t})*h(t)$ where $f_c$ is the carrier frequency and $t$ is the ...
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Generating a 2D delay-Doppler channel matrix

I was wondering if anyone here has any idea on 2D delay-Doppler channel and how to generate the channel matrix? Even a hint or a resource would be helpful. I just want to understand and visualize the ...
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Modulation order in real signal and complex signal modulation

In real signal modulation, e.g. ofdm based on DCT transform, the modulation order $m$ should be $\sqrt{M}$ where $M$ is the modulation order of the complex signal. for example, if we are using QPSK ...
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How to choose frequency of local oscillator for heterodyne principal

I am trying to implement the heterodyne principle in order to make an AM signal demodulator that can demodulate signals on a set bandwidth(550 - 1720kHz). Is there a formula or some other method of ...
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Difference between single tone and dual tone signals?

Editted Single tone signal has 1 frequency: $$ y = \sin(2\cdot \pi \cdot f_1 \cdot t)$$ Dual tone was created by using 2 frequencies: $$\sin(2\cdot \pi \cdot f_1 \cdot t) + \sin(2\cdot \pi \cdot f_2 ...
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Can we use Gardner timing error detector for multi level QAM or OFDM systems? [duplicate]

Sampling frequency offset (SFO) between the transmitter and the receiver in any system causes a gradually increasing timing error which is seen as an increasing phase rotation (function of time). In ...
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How to find the bandwidth of the transmitted M-FSK signal?

I'm tried to find the solution, but I failed. my question in the figure below, and the correct answer it's shown at the end of Figure. I'm using this formula but the answer is not correct! Is there ...
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44 views

Optimal Combination of received signals from two antenna

I really appreciate an answer or any hint how to approach this problem: Problem: A receiver has two antennas. The first antenna receives $Y_1=hx+n_1$, where $x\in\{-A,+A\}$, $h$ estimated channel, and ...
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1answer
64 views

Downsampling( decimation) theory: additional frequency

I work on a simulation decimation filter: downsampling + filter. My test environment: low data rate receiver, BPSK, square root raised cosine filter with cutoff frequency =0.5, transition bandwidth = ...
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35 views

Why Bluetooth 2 use pi/4-DQPSK instead of OQPSK?

From the peak to average power ratio point of view OQPSK is better than pi/4-DQPSK. What is the advantage of pi/4-DQPSK compare to OQPSK? Why Bluetooth 2 use pi/4-DQPSK instead of OQPSK?
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Working out EIRP

There is a debate about the proper way of how to calculate the EIRP, so I need your help on which method is wrong and why please! Let's suppose we have the following: Output power: 165 W Reflected ...
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1answer
38 views

Does Maximum Likelihood detector (QAM symbol detection) enhance BER?

Assuming QAM symbols (or OFDM system) with AGWN, I found that the use of ML detector does not enhance the BER but only enhances (reduces) error vector magnitude (EVM) because of symbol decision and ...
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41 views

Fine frequency correction : grouping and finding max amplitude inside a group

I work on phase and frequency estimation algorithm. Currently I am working on a derivation and determination of the Doppler shift( dF – frequency step). For each dF, The following algorithm was ...
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28 views

How to Combine white gaussian random noises from different Seeds?

I have generated two different white gaussian random noises in MATLAB using two different seeds. For example: ...
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39 views

Wrong number of samples per symbol for BPSK in MATLAB?

Goal is to achieve 8 samples per symbol for BPSK signal. After analyzing the plot of below code, IMHO its not 8 sps, I am right? If yes what I do wrong? ...
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1answer
100 views

1ppm Sampling clock offset in Matlab

How to emulate a sampling clock offset (between the transmitter and the receiver) of 1 part per million (SCO=1ppm) in Matlab? Theoretically, I can upsample the signal by a factor of 1,000,001 (one ...
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31 views

Phase Error Growth in Digital Mixer Signal

I am working on a code where digital mixing is to be performed for down-conversion of incoming signal. The mixer signal is created using the phase accumulation approach. However it was observed that ...
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25 views

Alamouti scheme and MIMO OFDM model, theoretical or practical concept?

I am not an expert in signal processing but last week I attended a class of signal processing. We discussed MIMO, OFDM and Alamouti scheme. On this lecture it was represented a lot of math equations, ...
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Comparing self-made O-QPSK signal with Zigbee burst (Q-QPSK acc. to IEEE 802.15.4)

What might be the cause of the worse baseband demodulation result of the bottom VSA screenshot compared to the demodulation result shown in the top screenshot ? Randomized Q-QPSK signal generated by ...
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Decoding OOK MFM… where to start?

I'm attempting to create a software-based RF modem for a new ham radio digimode that uses on-off keying and relatively slow MFM coding (10ms per bit... shortest/longest-possible pulse/silence = 10ms/...
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3answers
79 views

What is Self-noise in TED algorithm

I am working on a research project. The main task is timing error correction algorithm. I start with studying algorithms which are exist. Currently I have read about Gardner TED algorithm for PSK ...
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30 views

DFT and baseband wave forms in OFDM

In most of the textbooks, the motivation for the usage of DFT in OFDM goes as follows. Let $X[0],\cdots,X[N-1]$ be complex symbols, and $$s(t)=\sum_{k=0}^{N-1}X[k]e^{j2\pi\frac{k}Tt}\qquad (0\leq t\...
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Timing Jitter in PLLs

Regarding white (uncorrelated) and coloured (correlated) timing jitter. I know that for free-running oscillators (such as VCOs), various kinds of noise causes the jitter, for example (1/f) coloured ...
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50 views

2FSK implementation with VCO GNURadio

I am fairly new to GNURadio. I am trying to generate a 2FSK with minimum frequency shift. Instead of multiplying with a 8MHz complex carrier, I directly use VCO to generate two frequencies. One at 7....
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3answers
66 views

Can we generate signals in reality that have non symmetric magnitude spectrum in the Fourier domain?

I am reading communication systems, and have a doubt: Is it possible to generate signals in reality that have a non-symmetric magnitude spectrum in the Fourier domain? For example, if I have a signal $...
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46 views

80-tap Decimation Filter: divide into stages? / Cost of having a number of taps

I did a FIR filter hardware implementation with 80 taps (FPGA/VHDL). I will use it later as the decimation filter. My questions: Does the number of taps affect a cost of implementation of FIR? FIR ...
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1answer
57 views

can $e^{j\phi_0}$ be incorporated into the sine and cosine terms?

This is from "communication system" by Carlson fifth edition page 109: If transfer function of a channel be like this: $H(f)= Ae^{j\phi_0}e^{-j2\pi ft_g} $ and input to this system be: $x(t)=...
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38 views

Extraction of the phase lag form cross-correlation function

I would like to find out the phase offset that my signal contains at the receiver side. For this, I use the cross-correlation function, where I cross-correlate signal before and after matched filter. ...
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Symbol timing recovery: Polyphase vs piecewise linear interpolation

A symbol timing recovery scheme shown below has been successfully implemented in C++. Different TEDs (Mueller & Mueller, Early-Late, Maximum Likelihood, Gardner, Zero-Crossing, etc) are included ...
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47 views

Software implementation of Gardner Loop

My objective is to create a Gardner loop to remove the timing offset present in my signal. To achieve best timing SNR, I downsample my signal to 2 samples per symbol. It is depicted below: where blue ...
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1answer
44 views

pi/4 QPSK modulation/demodulation in GNU Radio

Is there any quick mechanism to create pi/4 QPSK or pi/2 BPSK modulation scheme in GNU Radio using Constellation Modulator object or Constellation Object? Or I need to write it by myself? Thanks in ...
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RRC filter in receiver side well applied?

I would like to ask question bout the rrc filter that I applied as an matched filter for receiver side in communication. My aim after RRC filter is to draw the eye diagram, and so far the eye opening ...
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67 views

How to reconstruct original signal from sampled signal?

My original signal as f1=2; f2=5; fs=100; Ts=1/fs; t=0:Ts:1; xt=cos(2*pi*f1*t)+cos(2*pi*f2*t); figure plot(t,xt) as shown below figure. and my sampled signal ...
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The timing offset remains after Gardner loop

I would like to use Gardner loop to remove the timing offset in order to demodulate the signal. My signal contains the frequency offset, however I know that the Gardner loop can handle substantial ...
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1answer
108 views

Symbol timing recovery in Python

My objective is to demodulate QPSK signal. At the receiver I apply RRC filter and interpolate the signal to get the values of the signal (approximately) at the sampling instances. Then I am concerned ...
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Matlab: Could anyone suggest why Iam getting a different geometry for QPSK constellation diagram

I'm developing a Multi-user MIMO communication model in MATLAB where a base station communicates with 2 users. The model uses OFDM (QPSK) modulation. Channel model, precoding and covolutional encoder ...
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1answer
85 views

Error probability for orthogonal signaling with unequal symbol probabilities

I'm trying to derive the equation of error probability in orthogonal signaling. Here what I've tried: Let $\vec{s_1} = (\sqrt{E_b} , 0)$ and $\vec{s_2} = (0, \sqrt{E_b} )$ be vector representation of $...
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1answer
54 views

Can Oversampling help to mitigate the effect of additive white gaussian noise?

Oversampling the signal at the receiver's ADC is a common technique to improve the ADC's resolution, dynamic range and to improve the signal to noise ratio (SNR) due to ADC quantizaiton noise, thermal ...

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