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# 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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67 views

### Frequency-selective channel: Basic in theory

In a lecture, it was covered a topic "frequency selective and flat fading channel models". For case, the frequency selective channel we have a channel impulse response ...
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### How to form the data matrix for channel estimation?

I want to estimate a channel (its length is $L_c$) with a preamble (its length is $L$) and a least square estimator. Let $p_r$ the preamble received. I have a problem to build the data matrix $X$ for ...
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### sc-fdma vs single carrier signal PAPR

Why is the PAPR of a single user sc-fdma signal different than the PAPR of a conventional single carrier signal if they both use the same modulation? aren't they both single carrier signals?
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### If the beamforming of these signal,$x_B$ and $x_A$, are orthogonal to each other,can the SINR increase?

Here is my thinking ,two device transmit $x_A$ and $x_B$ at the same time and with same frequency,meanwhile,device $C$ transmits $x_C$ to the other devices,and as we know,because the device $C$ is a ...
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### Why is the $G_{rx}=\sqrt{\frac{N_{rx}}{\hat{N}_{rx}}}S^T_{rx}\tilde{U}^H$ ? How does author calculate it?

I search for some information about Null Space Projection,and saw some information from this pdf: http://taneli.riihonen.fi/presentations/C027slides.pdf ,in the page 16,the author begin explaining ...
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### Is there any technology or method that let user $Z$ knowS which message is $x_B$ and which is $x_C$

There is a device $Z$ which transmits the signal $x_A$ and receives the informations $x_B$ and $x_C$ simultaneously. I think when this device receive the signal,it won't know which is $x_B$ and ...
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### How to recover 2*Zc systematic bits punctured in LDPC?

In 5G NR LDPC encoder 2Zc systematic bits are punctured at the transmitter end. At the receiver end, it is able to recover all bits excluding the punctured bits at the transmitter end. As the ...
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### DC Components and Frequency

I have started learning digital communication and was on line coding. I read there are certain characteristics that we need to keep in mind while choosing the right line coding method. One of these is ...
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### What is the difference between the V-OFDM and OSDM

I am trying to understand the difference(s) between V-OFDM (Vector Orthogonal Frequency Division Multiplexing) and OSDM (Orthogonal Signal Division Multiplexing) which are used as a multicarrier ...
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### Hardware that Mixes Two Digital Audio Source into One

Is there any off-the-shelf hardware that extracts two digital audio streaming source from two digital audio stream(like USB+SPDIF), mixes, and transmits in single digital stream real-time(if the ...
31 views

### How to detect missing bit position in a bit-stream?

I'm trying to establish a one-way communication and facing problem in the receiver end because of some missing bits. For example, if the sender sends 100 bits the receiver received 95/96 bit. Now the ...
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### Relationship between signal rate, data rate, minimum bandwidth

I need to understand the relationship between bit rate, signal rate and minimum bandwidth. I read in a textbook that We define three cases for relationship between bit rate and signal rate for ...
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### How to get the inverse of Filter based on channel

Given a signal $X$, and a channel $h$, and the received signal $Y = Filter(h,1,X);$ What's the inverse of filter, it means if I know $h$, how can I get back $X$ ?
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### Representation, Bandwidth and composition of Digital Signals

I have started learning data communication and I'm not able to grasp certain topics. First (i) I know that analog signals are continuous and digital signals are discrete. Analog signal are ...
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### If i use some method to decrease the self interference,how should i rewrite the constraint?

In the MIMO full duplex energy harvest optimization,we can find the similar constraint like this: $SINR > \gamma$,this $\gamma$ is some of SINR value,it means that my SINR want to be higher ...
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### Convolutional Code: choosing a trellis and puncture pattern for code 2/3

I'm working on convolutional coding in which I'm using generator polynomials as {13, 15} with puncture pattern of {1 1 0 1} for code rate 2/3. I don't get expected BER trend. If I use puncture ...
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### Assessing relative wireless channel quality using Capacity and Condition Number CDFs

I have Channel capacity analysis figures for two wireless channels show below: My question: While ergodic capacity in the first subplots are very clear in conveying the channel capacity, How to make ...
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### RRC filter or rectangular pulse shaping filter in LFM chirp signal

I am working with a LFM up chirp signal, and I wanted to embed some data on it using a BPSK constellation. My doubt was, ¿should I use a RRC filter, like in usual communications schemes, or should I ...
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### Which channel is the suitable channel for the short distance?AWGN?rayleigh or rician channel?

What is the unsuitable channel for the short distance?The short distance i mentioned is 1m or 2m.Unsuitable channel I mean is that if i assume this channel in my system,it will be very strange. In my ...
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### The dis-advantage that sensor use FDD (Frequency-Division Duplexing) to transmit the digital signal

We must need lots of sensors in IoT,sometimes these sensors have to transmit their information to other sensors at the same time.I want to say some disadvantages that sensor use FDD (Frequency-...
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### Why will the FDMA usually be used in transmitting analog signal,not in digital signal?

I saw this in the WiKi:https://en.wikipedia.org/wiki/Frequency-division_multiple_access FDMA can be used with both analog and digital signal but it generally used with analog signal Why?Don't we ...
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### What factors affect the propagation delay at wireless communication?

Generally, the signal propagation delay is d/c. d is a distance between a transmitting antenna and a receiving antenna. c is light speed. However in NS-3, there is Random Propagation Delay Model ...
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### 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 ...
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### 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 ...
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### 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: ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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. ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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?
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### 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 ...
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### 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 ...
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### 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 ...
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 $U_1$ ...