The Stack Overflow podcast is back! Listen to an interview with our new CEO.

# 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.

793 questions
Filter by
Sorted by
Tagged with
13 views

### Convolutional coding that payload length does not change

This is the question about Sigfox radio specification. The stack: Specifically, in Section 3.10 of the specification, we have a convolutional coding (after CRC) with three possible polynominals. I ...
30 views

### What is the threshold to prefer polyphase channelizer over FIR filtering?

A wideband signal need to be processed to extract several narrowband channels from it. There are two straightforward approaches to do so: For each narrowband channel shift frequency and filter it ...
47 views

### Translating Matlab scrambler function to C

I am trying to implement the following matlab function in c: Mathworks scrambler Function Documentation This is the code I've written: ...
17 views

### Why does this self-interference cancellation cancel other signal,not the self-interference?Do i misunderstand something?

In this paper, https://ieeexplore.ieee.org/document/8704259 ,i think transmitter with M antennas transmit $x_f[t]$ to Cell-center user ,and transmit $x_n[t]$ to the Cell-edge user,however,the distance ...
29 views

### Why when the SINR of transmitting signal is very large ,the device cannot decode the received signal at the same time? [closed]

$A$ transmit $x$ and receive the $y$ at the same time.If the SINR for transmitting $x$ is very large,$A$ cannot decode the $y$ signal.Why? In my opinion,If the SINR for transmitting $x$ is very ...
43 views

### How can i know the full duplex does work from the Shannon's theorem?

There is a full duplex system below,two user are $A$ and $B$,according the definition of full duplex ,$A$ and $B$ have to transmit and receive the signal at the same time.that is, transmitted signal ...
87 views

### Digital FM Demodulation

I have created a Common Lisp Library to receive samples of an FM signal from BladeRF1 SDR. I want to write a subroutine to implement FM demodulation. The input should be in the format of IQ data. ...
29 views

### Is there any advantage on using a low span value in a RRC filter?

I know that in a RRC filter a high value of the span gives a better response, in the sense that the RRC filter response is more near to the ideal RRC filter response. However, would there be any ...
37 views

### How to remove sum and difference terms while computing frequency from fft?

I am currently operating in vhf band AND trying to detect frequencies using Fast Fourier transform thresholding method. While detection of multiple frequencies , i received spurs(May not appropriate ...
27 views

22 views

### Channel information from power spectra

Linked below is a previous post regarding a multipath channel. Equalisation of FFT spectra I am reusing the images here: The first image is that of the power spectra when there is no multipath and ...
43 views

### Is there any relation between QAM and streaming?

I am trying to determine whether there is any relation between QAM and streaming (e.g., video streaming). I know that QAM can be used for broadcast TV. I'm not sure if QAM is used for WiFi bit ...
14 views

### Do we need to distinguish which rate is it when the system is point to point?or we just say “rate”,not downlink rate or uplink rate

If i have four transmitter,(t1,t2,t3,and t4), and one receiver(R),and each of them just have one antenna. When t1 is transmit signal to R,the other transmitters (t2,t3 and t4)harvest the RF ,when t2 ...
24 views

### What is the definition of half duplex?Is this system,$A$ give $x$ to $B$,then $B$ give $x$ to $C$,called half duplex?

I saw the definition of half duplex in wiki,and it said half-duplex (HDX) system provides communication in both directions, but only one direction at a time (not simultaneously). Typically, once a ...
25 views

### Find the ber for the cdma protocol

Do you know a reference (book, article) which gives (with a proof) the theoretical BER in the CDMA protocol for a differential modulation?
37 views

### Confused about the definition of point to point ,this point means single antenna or single device?

What is the definition of point to point ? does the "point" mean single device or single antenna? I mean,can one transmitter with multiple antennas and one receiver with multiple antennas be called ...
14 views

### Where will system,information and decoder are separated, be applied?why don't we consider maybe the splitter is too small to destroy the information?

In the research of energy harvest and SWIPT,some paper will design that information decoder and energy harvester will be in the same device,then use a power splitter to split the received power for ...
47 views

### Why is the received signal=information+RF signal+noise,not just information+noise?

In this paper: https://www.researchgate.net/publication/325008791_Beamforming_Design_for_Max-Min_Fair_SWIPT_in_Green_Cloud-RAN_with_Wireless_Fronthaul Here is its system model In this model,it said ...
22 views

### What is SIC? And why should we decode some signal first when we know that we will decode it again in the future?

I read the paper :http://jultika.oulu.fi/files/nbnfi-fe2019040110636.pdf The author said : First ,$x_s=x_1+x_2$,and the transmitter transmit the $x_s$ to $U_1$,and the received signal in the $U_1$ ...
15 views

### What is the advantage of this system (DA port in the DAS is usually equipped with its own power ampliﬁer at the analog front-end)

I saw a paper,https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8283591 ,and it said Each DA (distributed antenna) port in the DAS (distributed antenna system) is usually equipped with ...
39 views

### Can we band pass filter QPSK signal?

Consider we have QPSK signal with carrier frequency 10kHz. Generally, we demodulate or use matched filter on the the QPSK signal and recover the transmitted bit or the symbols. If the QPSk signal is ...
22 views

### preamble for doppler shift estimation

To estimate the doppler shift in a multiuser communication, I use preambles (PN codes). When I send the preambles with the datas (BPSK symbol), the estimation for the doppler shift are not correct. ...
36 views

### How to calculate Eb/N0 for a digital BPSK modulated multicarrier waveform

Suppose that I have a BPSK modulated multicarrier carrier waveform $L$ samples long at a sampling rate of $f_{s}$:  x_{tx}[l] = \sum\limits_{n=0}^{N-1} A \cdot \cos\left(2 \pi \frac{f_{n}}{f_{s}} ...
66 views

### What is the minimum sampling rate for QPSK or what is the bandwidth of QPSK signal?

Consider we have created a QPSK signal with a carrier frequency 100kHz. Before applying matched filter or demodulation we need to take samples from the received signal. So what is the minimum ...
24 views

### What's the effect of spread spectrum on frequency- selective channel

In brief, we consider the channel as frequency-selective channel if the frequency of the signal is larger than then frequency of channel. So, does using the spreading spectrum change the frequency-...
38 views

### Is the zero part of a RRC filter generated signal sent?

When you use a RRC filter you add extra symbols at the end of your generated data because of the delay of the filter. When the data passes through the filter it gets up-sampled and the delay is ...
22 views

### Discrete Frequency Equation and Relation

I think I am looking at conflicting equations from a few sources, or maybe I just dont understand it. $\Omega$ is Discrete frequency $N$ is Discrete Period in number of samples $\omega$ is ...
107 views

### About understanding a Matched Filter

I have some basic doubt in understanding a matched filter (MF). Please note that I have already seen very informative post in this context Understanding the Matched Filter In what follows, I list ...
34 views

### spectrum for a baseband communication signal

I have a question for the spectrum: In baseband before passing through channel, should the spectrum of a communication signal be symmetrical?
46 views

### Rate vs throughput vs capacity

What is the difference between Rate , throughput and capacity ? Their unit are all bps/s,but it seems that there are something different between them,can anyone tell me? My research is optimizing ...
33 views

### How to measure a signal's initial phase given a buffer of received samples of the signal?

For CPM and FSK, how to measure a received signal's INITIAL phase based on its I and Q components given a buffer of received samples of the signal?
27 views

### Why does it seem most of people will optimize the downlink rate,not the uplink rate?

I search for some papers about energy harvest,SWIPT and optimization.And i found that there is just one paper to optimize the uplink rate,the others are for optimizing the harvested power,power budget ...
24 views

### duration for a signal after filtering [duplicate]

I have a signal $s(t)$ of duration $T$. This signal doesn't have a limited bandwidth. To solve this problem, I filter it with a pulse shaping filter (raised cosine filter). My question: Does ...
47 views

### What will it happen when the outage occur?

I saw this explanation about outage probability,it said: it is the probability that an outage will occur within a specified time period. So what will it happen when the outage occur? stop ...
34 views

### Is it possible to spread signal using sum of more than one orthogonal code

I was wondering if we can spread the signal using more than one spreading code. Assume we have the Walsh code used to spread the transmitted signal, the Walsh code is, for example, gotten based on ...
51 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 ...
139 views

### Calculating Data Rate using Bandwidth, Transmission Power, Noise Power Spectrum Density and Channel Gain

I'm a Software Engineering student researching on Load Balancing in IoT and I need to calculate data rate. However, I don't know how to use these values to attain data rate despite searching on the ...
33 views

### frequency/phase offset estimation in satellite DOA beamforming applications

In satellite QPSK demodulation, we first estimate and remove the phase offset introduced by the channel. Then, we demodulate the baseband information bits (I & Q channels). In satellite DOA ...
29 views

### Log Distance-Normal Shadow Model and Friis

Since I'm founding several but different results about this model, I would ask you if all it is OK with this formulas: 1) Friis Model --> $Pr_0 = Pt + Gt + Gr + 20\log_{10}\frac{\lambda}{4\pi d}$ 2) ...
38 views

### Dimension of Matrix in MIMO with multi-path

In a MIMO system, the received signal is supposed to be $y = Hx + n$, where $H$ is the channel of dimension $N_t \times N_r$, $x$ is the transmitted signal with dimension of $N_t\times 1$ , and $n$ is ...
100 views

### When Two Sampled Sinusoidal Are Orthogonal?

If two analog sinusoidal are orthogonal with duration T, their minimum frequency difference should be 1/2T in case of no phase offset between them. And if there is phase offset, the difference is 1/...
67 views

### Frequency Domain Correction of Frequency Offset or Doppler Frequency in LTE

We are working on LTE Uplink CFO Correction for 3 MHz band. The time domain CFO correction is easy, which depends on the processing of 3840 samples step by step multiply by \$\exp(-j 2\pi f_\text{...
82 views

### Does gray coding bring improvement to SER of QPSK, compared with natural coding?

I understand gray coding contributes to BER of QPSK, yet really don't understand why it brings improvement to SER. According to the relationship of SER and BER, it should be improved. Actually, when ...
126 views

### QPSK Phase Recovery : Maximum-likelihood Vs Costa's Loop

I have implemented a QPSK Costa's loop in GNU Radio and run some BER benchmarking. All is going well. Out of curiosity, I'm trying to implement the Maximum Likelihood phase recovery shown below. For ...