# 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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### QAM Amplitude Levels

I'm working on a project to stream video between 2fpgas by using QAM. While mapping symbols with different amplitude pulses(PAM) a question popped up in my mind. In real life how does communicating ...
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### FSK technique to superpose the digital communication on top of 4–20 mA signals

I start a working with HART devices and I really try to understand how digital data is transferred trough 4-20ma current loop. I start read this article: https://instrumentationtools.com/hart-...
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### How to encode binary sequence if the number of bits are odd to e.g. 4-PAM? (Beginner)

I'm new to signal constellation and trying to understand how M-PAM works. If there is a binary sequence that has on odd number of bits and I want to send a 4-PAM signal, there will be one bit left ...
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### Quantization types

Suppose i have input sequence {-1.3,1.2,-0.2,-0.5,0.4,0.89,1.3} Which are uniformly quantized through a quantizer having range (-1.5,1.5) with 4 levels My calculted answers for- First method:mid rise ...
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### SNR of μ-law companding

I know the snr after μ-law compression is $\text{SNR}\approx\frac{3L^2}{[\ln(1+ \mu)]^2}$ when $\mu \gg \frac{\max_t m(t)}{\text{rms}(m(t))}$, where $m(t)$ is the message signal, and $L$ the number ...
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### How do I prove Energy and Power Signals

How do I prove that if energy of a signal is non-zero and finite and the power of the signal is zero. Also draw conclusions for signals where power is non zero and finite.
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### μ-law compression technique

In μ-law compression formula i have always seen that the value of Xmax and Ymax is always same but can they be different?
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### Quantization processs

In a quantization process what happens when the signal range is more than the quantizer range? Suppose i have a sinusoidal signal which ranges from -5 to +5 but the quantizer which has four levels ...
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I am trying to understand how to calculate the power of a received signal under Raleigh fading. What I gather is that the Rayleigh fading is a complex Gaussian random variable and that the multipath ...
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### Self-correlation vs Digital frequency: figure from paper

In the paper, is discussed a MIMO-OFDM system over the frequency self-correlation of i.i.d. Rayleigh channels and subcarrier grouping. in this paper is shown the following figure. it shows the self-...
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### How to infer mathematically if the transmission error is correctable after applying Longitudinal and Vertical Redundancy Check LRC,VRC?

I have the following message in binary: Transmitted Message: 1 | 0 | 1 | 1 | 0 | 1 1 | 1 | 0 | 1 | 1 | 0 1 | 1 | 0 | 0 | 1 | 1 1 | 0 | 1 | 0 | 0 | 0 Received Message: 1 | 1 | 1 | 0 | 0 | 1 1 | 0 | 1 | ...
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### BPSK and QPSK demodulation computational complexity

I wanted to ask about the real operations of BPSK and QPSK demodulation. How can we calculate it? I mean for example if I have a received symbol +0.6, then I need to demodulate it to be 0 or 1. what's ...
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### Series Sum Operator Properties and Identities

As I was reading my book, I came across the following expression: \begin{equation} \sum _{n=-N}^N\sum _{m=-N}^N \phi \left(n-m\right) \end{equation} Then the book said, if we let $k = n-m$, then: \...
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### Isn't the rect pulse filter implicit at the transmitter?

I've heard about shaping the symbol with a rect filter at the transmitter, but why? Isn't this just implicit from the fact that it's going to be transmitted as a symbol truncated to the symbol period ...
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### CFO estimation and compensation

I am reading about CFO estimation in OFDM system, assume for example that we estimate it based on CP as mentioned HERE and the estimated CFO for the received signal $r(t)$ is $β$. My question, how now ...
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### Recover an OFDM signal affected by AWGN

I have an OFDM signal affected by AWGN, if I know the power of the gaussian noise, can I recover the OFDM signal? Can I perform deconvolution to recover the original signal? thanks
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### Decoder implementation

Im struggling to implement / build convolutional decoder . I've done implementation of FEC encoder which it's as shown in the photo below: So this is the encoder that I've implemented, and I want to ...
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### Non Coherent BPSK with no Channel State Information at the receiver

Where or what is the proof for the failure of BPSK in fading channel when we have no knowledge of the fading coefficient $h$ at the receiver in the equation $y=hx+w$, where $x$ is BPSK symbol equally ...
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### In a communications system does the order of channels is in a cascaded channel affect the overall capacity?

I'm currently looking at capacity for cascaded channels as part of my Communications Systems module and we're looking at a question in which we have four identical channels represented by the ...
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### FEC decoder processing delays

I am trying to implement a burst demodulator. I have catered bits in premable for carrier and timing recovery and for fec also in the recieve side if i am using viterbi decoder/TPC coder will the ...
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### Design RRC filter [closed]

I have designed a RRC filter, as below : ...
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### OFDM time-domain equalization

I am working on OFDM, and recently I have read a new type of OFDM called TDS-OFDM, where they guard interval is not neither zeros nor CP. It's a pseudo-noise inserted between symbols. The structure ...
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### What can be a limit to the maximum possible power of a pilot signal

In practice, what can be a limit to the maximum power of a pilot signal in wireless communication?
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### Doopler spread and delay spread in an equation of channel freq response

Assumed the transmission system with channel impulse response is determined by the matrices $H(\tau_l) \in C^{N_R \times N_T}$ ( $N_R$ and $N_T$ are numbers of received and transmit antennas) By ...
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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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### Estimation algorithms for Multi-User MIMO

I am interested in a question how to estimate a channel/symbol in a multi-user system. In the case of a single-user, it can used ZF/ pilot estimation/ MS/ LS algorithms. Do we have a difference in ...
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### The similitude of interference cancellation and the use of earplugs

I am trying to model a network for performance evaluation on a wireless system with interference cancellation. Then I stumbled upon a question that I needed to answer before I can proceed. Can ...
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### How can i identify number of return of the ping in the sonar?

I am writing a fake function which is actually doing active pinging (basically SONAR). I am little confuse here about how to identify the number of sonar return i got ? Let's say i am continuously ...
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### How to check my CRC of my RF packet? [duplicate]

The "problem" is that I want to validate if my received RF packet is valid or not valid, in other words I want to validate if my RF packet corrupted or not corrupted . the transmitter that ...
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### Implementation of modulation/demodulation models

I am trying to implement mod demod for data rate of few kbps . I would like to know is it better/ easier to implement in DSP/FPGA. I am aware of both C and VHDL programming. I think the code flow and ...