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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78 views

How to Emulate Sample Frequency Offset for OFDM in Matlab?

I am studying the effect of sampling frequency offset on OFDM, and in order to emulate SFO, I have to slightly change the sampling rate of the signal. In order to have a +5ppm offset, I have to change ...
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79 views

FSK carrier frequency estimation

In the MPSK Modulations, Cyclic Spectrum Density method can give a peaks, for example for the QPSK: But in the FSK signal, this peaks do'nt appear. How to solve it?
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307 views

What is the difference between (Sample Timing Offset), (Carrier Frequency offset), and (Sampling Frequency Offset)?

Briefly, can anyone explain to me what is the difference between (Sample Timing Offset), (Carrier Frequency offset), and (Sampling Frequency Offset)? and is Sampling Frequency Offset (SFO) like STO ...
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2answers
62 views

Early - late gate spread spectrum

For situation that received signal is complex, how Early and late are calculated in spread spectrum tracking? How I can consider both real and imaginary in error calculation?
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31 views

help with bandwidth diagrams for digital transmission

I am taking a undergrad network course that uses Data Communications and Networking 5th edition containing diagrams and legends which I cannot decipher. Specifically the diagram on the right, has y-...
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46 views

(Frequency Offset): Relationship between Normalized Carrier Frequency Offset (normalized CFO) & ppm in OFDM system

How can I change a normalized carrier frequency offset (CFO) to ppm? And If the DAC sampling rate is 30GS/s, and the clock frequency is 15GHz, then should I use 30G or 15G when I calculate ppm? ...
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77 views

Why can't we have IoT from 2005? but begin now,or future? [closed]

In 2005,ITU announce the "IoT",but why can't we have IoT at that time? Is it because the speed of internet is not fast enough?wireless communication is not good at that time?Does anyone have some ...
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3answers
261 views

Why are we always interested in mean-squared distortion?

When dealing with quantizers, and in many other communications problems, the interest is usually on the mean-squared distortion or mean-squared error, rather than mean absolute error or anything else. ...
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1answer
52 views

Receiver for low data rate

I am working on satellite receiver burst mode I am trying to build receiver. My data rate is typically 10kpbs. As the data rate is low and carrier frequency offset may also be around 10kbps so i have ...
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50 views

Damped spring mass system - parameter estimation

I've tried to calculate the parameters of a damped spring mass system of the form $m~ y''(t)+d~y'(t)+c~y(t)=F(t)$ but I have some problems determining the mass m of the system. The damped ...
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84 views

Carrier frequency offset

Can i track any frequency offset my increasing samples/symbol. For example if my symbol rate is 1Msps. If my sample rate is 10 Msps. Can my receiver correct upto 5 Msps carrier offset using FFT I can ...
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55 views

Carrier recovery samples

Should carrier recovery be done always 1 sample per symbol? This is ok if carrier recovery is before timing. But Nco inside carrier recovery may work at higher rate If my carrier recovery is first ...
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60 views

I/Q plane plot understanding?

I am experimenting with some signals. I ma generating a 2.47 Ghz signal from signal generator and receiving it by an SDR (LMS7002m Rf chip) with Rx frequency tuned to 2.47 GHz. Upon plotting the ...
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Resampler and PLL reference document

can anybody suggest good documents on resampler for TED and PLL by which i can understand basics because there is lot of confusion for resampler and PLL
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Pi/4 dqpsk carrier recovery

I think we don't have to do carrier phase recovery. Do i need to do carrier frequency recovery. My symbol rate is high around 2 MHz so i am thinking carrier freq offset is less compared the symbol ...
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1answer
26 views

Question about a diagram of PWM detection

I have this diagram in a book(taken from Slideshare for clarity) as described in the book PWM is put on the differential to obtain A(as starting of pulse) and B(as the end of pulse) The A is used to ...
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59 views

burst qpsk demodulator

i am working in burst qpsk demodulator i just want to double check if what i am doing is right large frequency feedforward recovery by fft carrier recovery costas with 4 samples/symbol timing ...
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62 views

Carrier and timing offset

Assume my reference is 1 ppm so if my transmit frequency is 400 MHz and symbolrate is 100 kHz. Then, my carrier will have +/- 400 Hz offset and then my symbol will have +/-0.001 Hz offset. Similarly,...
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57 views

matched filter position

I have seen that matched filter should be used in TED (gardner loop) after resampler ...
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1answer
46 views

SNR estimation prior to demodulation?

What are the standard ways to measure SNR, particularly before demodulation/synchronization?
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Is the SWIPT technology not the good method to increase the life of using battery?

Is the SWIPT( simultaneous wireless information and power transfer ) technology not the good method to increase the life of using battery? Because I design the Full duplex system with three device,...
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1answer
40 views

How many bps would be required to reproduce the words in speech recognizably?

In Robert Gallager's lecture notes for 6.450 Principles of Digital Communications I, Exercise 2.1 asks an interesting conceptual question: Voice waveforms could be converted to binary data by ...
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39 views

Block CMA algorithm

The Constant Modulus Algorithm is a common equalization method which adapts at every sample in an attempt to give a filter which produces a fixed power output. Divergence/convergence of the CMA ...
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1answer
32 views

Wireless communications outage

For communication systems, there is usually a target minimum rate $R$ bits per second. An outage occurs if the actual rate ever falls below $R$. Since $\frac{1}{2}\text{log}_2(1+\text{SNR})$, ...
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why if I want to create a rayleigh fading channel with $E[|H_{i,j}|^2]$,I should multiply $\sqrt{\frac{1}{N_R \times N_T}}$?

I want to create a rayleigh fading channel,and my classmate told me that I can create an $N_R \times N_T $ channel $\mathbf H$ with $E[|H_{i,j}|^2]$,that is,$\sqrt{\frac{1}{N_R \times N_T}}\times CN(0,...
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30 views

Example of Entropy and Channel Capacity Computation

Can you help me on verifying if this computation of entropy is correct and on understanding its meaning? I am not sure of the result especially because it is equal to 0: it means that we cannot ...
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1answer
70 views

NDA timing estimation for mutli-level QAM(RC pulse)

What non-data0aided techniques are used to estimate the timing for multi-level QAM? For single level QAM(so 4 QAM) you can use variance minimization or power maximization but I'm not sure these ...
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24 views

Can we really use equal gain combining in the receiver in the real world?

Can we really use equal gain combining(EGC) in the receiver in the real world? Because we have to know the phase of elements in the channel matrix first before we do the EGC,however,the channel should ...
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117 views

Lagrange Vs Sinc interpolation

I was wondering what is the practical difference between Lagrange Interpolation using Farrow Structure and Sinc Interpolation? Both require pre-computation of time offset coefficients using a lookup ...
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1answer
82 views

Zero Forcing Equalizer in ISI channel

I'm studying on designing 9-tap zero forcing equalizer to remove ISI in the channel. I assumed that the channel response is ht = [0.41 0.815 0.41] and I tried to calculate bit error rate. When I ...
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1answer
45 views

Understanding Asymptotic Equipartition Property

I have some problems in understanding the precise meaning of the Asymptotic Equipartition Property, related to a large number n of independent and identically distributed random variables (X1, X2, ...,...
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About the post “How to use “Filter” matlab function to apply channel to signal?”

I would like to add my question to the post How to use “Filter” matlab function to apply channel to signal?, but I don't have permission to do that. The user @Anna Koroleva discussed with @Enginner ...
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64 views

How are CDMA codes distributed?

I think this question is so trivial that it's nowhere explained (I would not find it) and the answer is probably trivial too. But I still wonder how codes in a typical CDMA system are distributed? ...
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47 views

Definition of Perfect Code (and example of Hamming Code)

Let's consider the following sentences about coding a message before transmitting it in a communication system (here you find the complete pdf) First question: can you explain me these two ...
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104 views

Understanding and converting Matlab's coarse frequency compensation function

I am trying to understand and convert to C Matlab's coarse frequency compensator the documentation for which can be found here: Documentation Matlab's design itself is based on this IEEE paper: ...
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1answer
21 views

Small Scale Fading time varying or position varying

I would like to ask how small scale fading can affect a transmission with time. The particular system is an antenna transmitting an ASK modulated signal at 915MHz and with bandwidth between 200KHz to ...
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44 views

Does any paper use energy harvest to in the baseband?

Most of RF energy harvest system just harvest $\rho$ of the RF signal for charging the battery,and the other part RF energy will be processed to baseband signal by RF Chain to do the information ...
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1answer
65 views

Understanding Matlab's Automatic Gain Control function

I am trying to understand the automatic gain control block provided by the communications toolbox. The documentation is here: Documentation My questions are in regards to two of the configurable ...
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1answer
37 views

Is my concept of receive diversity right? EGC,MRC and SC

Is my concept of receive diversity right?There are three combining technology belong to receive diversity. 1.Equal gain combining(EGC) $\sum e^{-j\theta_k}(\sqrt{P}|h_k| e^{j\theta_k}x[n]+w[n])$ ...
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25 views

Can we use beamforming to make sure that the signal will not make interference together in Full duplex?if yes,why?

To avoid signals will make interference to each other in full duplex,there are two methods to solve this problem. Time-division duplexing and Frequency-division duplexing,they just use different ...
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45 views

Length of CDMA code and message length vs. number of participants

What is the minimum code size for CDMA codes for synchronuous CDMA (not asynchronous CDMA!) with N number of participants? Furthermore, suppose N parties want to uniquely transmit a message of length ...
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142 views

Why do we need to increase sampling frequency at the transmitter?

I've thinking about this for some time now and I was wondering why do we need to increase smapling rate in the transmitter? I will explain a bit more. From the point of view of a software-defined ...
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4answers
132 views

instantaneous frequency for a sum

In the literature, the instantaneous frequency for a signal $s(t)=e^{-j \phi(t)}$ is given by: $$f(t)=\tfrac{1}{2\pi}\frac{d\phi(t)}{dt}$$ This my problem: I have a signal $$u(t)=e^{-j \alpha_1 \phi(...
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How to prove that my combiner vector is $\mathbf H \vec f $?

When my received signal is $y=\mathbf H \vec f x+\vec n$,they we need a combiner vector in the receiver,how do i prove that combiner vector $\vec w$ is $\mathbf H \vec f $? After the received signal ...
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When i have already found beamforming,do i still need to use MRC?i have some problems for them

I have some problem when i learning MIMO,first thing is that i know designing beamforming and MRC can ensure better receive signals,but they are not the same,so i have some question about them. 1.I ...
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45 views

Matlab Plotting custom constellation along with decision regions

How do I create a custom constellation along with decision regions in Matlab, any help is greatly appreciated
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166 views

Isn't Gardner's algorithm and Early-Late gate the same thing?

I'm reading about some symbol synchronization methods and I find these two (ELG and Gardner) very similar. Early-Late gate takes 2 samples, one at $t=T-\delta$ and the other at $t=T+\delta$, then ...
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33 views

Will the received waves be the same if the transmitter use the beamforming to transmit the same signal?

If there is a transmitter with three transmitted antennas,and a receiver with five antennas,and these five antennas are very close to each others. Now transmitter use beamforming with these three ...
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24 views

What is the advantage of multiple antenna in receiver in energy harvesting ?harvested more power?

What is the advantage of multiple antenna in receiver in energy harvesting ? Assume there are $3$ transmitted antennas in the A device,and $1$ received antenna in the B device,now assume A device use ...
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Doubts about Huffman and Shannon - Fano Coding

I was reading these slides about Source Coding and I have the following questions: 1) Let's consider this part: Can you explain me step by step the reasons of a, b, c? Which is the general rule to ...

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