# 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-PM Modulation

As you know, in the Binary shift keying modulation(BPSK) with the change of phase, we can modulate signal, but recently in many resource(Residual carrier tracking with PLL) I see that after BPSK ...
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### BW of a modulated signal

I come across different types of bandwidth. In digital modulation should it be null to null always? when do we use 3 db bandwidth?
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### transmitting the real/imaginary parts of pass-band signal

As I know, the transmitted pass-band signal whose carrier frequency is $f_c$ can be written as follow: $s_1(t) = \text{Re}(a(t)e^{j2πf_ct})$ , where $a(t)$ is the complex modulated base-band signal. ...
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### Relation between ICI and EVM in OFDM System

in an OFDM system with ICI, how can I calculate the ICI power using the error vector magnitude (EVM) constellation? thanks
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### A communication system

I am solving the following problem as an exercise. I have a signal $$z(t) = x(t)\cos(wt) + y(t)\cos(ut)$$ and we assume $x,y$ to be band-limited continuous time signals. In the frequency domain we ...
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### Sampling of bandpass signal with bandpass filter

Trying to solve the following problem about bandpass signal sampling. I have a signal whose Fourier transform is such that $X(w)= 0$ if $w>w_h$ or $w<w_l$. The reconstruction is done using a ...
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### the best pre emphasis for MMSE equalizer

The system consists of multiple low-pass filter and noise, $h_1$, $h_2$, $h_3$, ..., $n_1$, $n_2$, $n_3$, ... At the transmitter, the power of signal is fixed; and at the receiver, MMSE equalizer is ...
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### Matched filter for recieved RF digital packet by LPF

Im transmitting by cc1350 launchpad microprocessor digital RF Packets, transmitted modulation FSK. bit rate of transmitting is 50Kbouad, frequency of transmitting is 868MHZ . Im sampling the signal(...
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### ZP-OFDM vs. CP-OFDM channel equalization

Now, I am working on OFDM equalization, according to what I understood, Adding CP into the OFDM block change the convolution from linear to circular. That circular convolution enables using point-wise ...
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### Does the channel impulse response change over time?

Let's suppose we have an emitter and a receiver in fixed positions the emitter sends a signal $s_1(t)$ and after a period $T$ it sends $s_2(t)$, the receiver receives $r_1(t)$ and $r_2(t)$. My ...
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### filtering my received Signal by LPF

I've received my transmitted signal that I sampled it on 20480000 frequency , transmitted frequency 868MHZ , bitrate 100KHZ , I see the "bits" that Im transmitting in my plot in matlab it ...
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### why don't we use Broadband technology to transmit digital signals ,and use Baseband technology to transmit analog signals? [closed]

I learn the Broadband technology and baseband technology in this website: https://www.computernetworkingnotes.com/networking-tutorials/differences-between-baseband-and-broadband-explained.html ...
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### autocorrelation peak

Let $s(t)$ a signal of duration $T_s$ on a bandwidth $B$. The matched filtering of this signal gives: $R=max|s(t) \ast s^{\ast}(-t)|$ and here theoretically I saw that $R=BT_s$. But does anyone know ...
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### continuous chain of ones or zeros for transmit

If my data has long chain of 1's or 0's. Can the data be modulated and transmitted as it is. Will this have any effect of the receiver adc as this may increase dc value of the signal or any other ...
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### Use of I/Q representation for unmodulated Rx Signal

it may be a stupid question but while learning about DSP and Modulation I was wondering, if the I/Q representation of an RF Signal is of any use, when the received signal does not contain any ...
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### Converting Received RF packets to binary file that RF packets sampled by dongle rtl-sdr

Im using #SDR software that I transmit packets from cc1350 launchpad to the air and I want to validate that if those packets are valid or not by checking its CRC. my problem is actually the step to ...
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### Capacity and channel estimation algorithms: explanation of results

I study a spectral efficiency of a system with a precoding scheme with different channel schemes. Algorithm A for channel estimation gives a smaller estimation error instead of Algorithm B. I have ...