# 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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18 views

### Amplitude of a signal

I want to transmit a communication signal. The signal consists of a preamble and data. However, the amplitude of the preamble is different from that of the data. Here are my questions: Is it ...
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### Why the average signal power should be 1

When I read some books or papers related into signal modulation, for example, frequency-domain OFDM signal, it's always mentioned that the average power of signal is assumed to be 1. Why does that ...
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### MAP Estimation Problem for Frequency Band Occupancy Calculation

Consider designing a wireless communication system. Your communication link is not iso- lated in the environment, there are other similar devices trying to communicate in the same general frequency ...
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### How is signal to noise ratio actually measured by receiver equipment?

This sounds like quite a basic question but it surprised me, how is SNR actually measured? You have the incoming signal: It seems like the SNR is just the visual comparison of the peak signal '...
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### What is the benefit of adding zeros subcarriers in frequency-domain OFDM signal?

I have noticed in some OFDM systems, some null subcarriers are added in frequency domain. What's the benefit of those zero subcarriers, and is that mandatory ? An example I have read about that adding ...
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### Optimal Receiver Using Complex Baseband

Given the below signals and a square pulse shape, I want to design the optimal receiver using complex baseband: $s_0 = p(t)sin(300\pi t)$ $s_1 = p(t)sin(301\pi t)$ I know that I will be using a ...
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### linear convolution toeplitz matrix vs circular convolution toeplitz matrix

I have an issue in understanding the difference between building the Toeplitz matrix when the convolution is linear and when it's circular. As I know that Toeplitz matrix $H$ can be built as following ...
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### Should the correlation check should happen at the start of the receive chain?

Should the correlation check should happen at the start of the receive chain. does it act like a start of burst data? But does phase and freq offset has any effect on this? or should it happen at bit ...
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### disrupts frequencies detection

Let's say I flew a Drone in the air and someone disrupts frequencies of the Drone, Changing the frequency of the drone to the signal of the jamming frequency can it prevent its falling?
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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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### 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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### differential modulation and reception

I use a differential modulation with a SIMO system. At the reception, I have $2$ antennas.To find my symbol, I use the relation $r^{\ast}_i(n-1)r_i(n)$ to have the phase of the symbol with \$r_i(n)=\...
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### Capacity and BER as performance of transmission system

We study the performance of the transmission system by channel capacity or BER/SER. If the system performance is studied as BER/SER, does it make sense to study a channel capacity?