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.

Filter by
Sorted by
Tagged with
0
votes
0answers
2 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 ...
0
votes
1answer
17 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 ...
0
votes
0answers
36 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 ...
0
votes
1answer
23 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 ...
0
votes
0answers
25 views

up chirp and down chirp

The expression for a HFM up-chirp is $$x_1(t)=e^{-j2\pi K\log(1-\frac{t}{t_0})}$$ with $\frac{-T}{2} \leq t \leq \frac{-T}{2}$ and $K=\frac{Tf_lf_h}{2(f_h-f_l)}$, $t_0=\frac{T(f_h+f_l)}{2(f_h-f_l)}$....
1
vote
0answers
23 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, ...,...
0
votes
0answers
23 views

Precoding algorithm for OFDM

I working on an implementation of a linear precoding algorithm for MIMO OFDM system and I have an issue with symbol estimation part. Let me briefly explain what I am doing: H- channel matrix ...
1
vote
0answers
28 views

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 ...
0
votes
0answers
15 views

How to find similar channels in freq-selective channel?

Early I have asked about precoding in frequency selective channel "Frequency-selective channel: Basic in theory" and got the following answer: In practice you might not want to do this as the ...
0
votes
2answers
35 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? ...
0
votes
2answers
39 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 ...
0
votes
0answers
9 views

Precoder selection in LTE

I am reading papers about LTE and "resource block (RB)" was mentioned in each of them and also "precoder selection" What kind of parameter is used to select precoder for each of RB? What is ...
0
votes
0answers
17 views

Create QPSK data In Matlab

How to form QPSK data in Matlab? I have written it as: Mod=4; s = randi([0 Mod-1], N*MT, 1 data=pskmod(s,Mod); Will be it enough to form QPSK data?
0
votes
0answers
10 views

How to use rayleighchan(ts,fd,tau,pdb) to form a channel matrix?

I am starting a transmission system simulation. To create a channel matrix I have used rand function in Matlab. But Matlab has a ...
2
votes
0answers
33 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: ...
-1
votes
0answers
31 views

Should we use propagation losses channel when we are simulation the system which is for the sensor communication?

Should we use propagation losses channel when we are simulation the system which is for the sensor communication?The sensor communication i said means that sensor will exchange their information to ...
-1
votes
0answers
27 views

Why does almost all paper usually add the RF wave power directly?it seems like feed the RF-DC converter,then sum the DC power

In the energy harvest, we need to decoding and harvest the energy,but i am confused with something,i find that if the receive antenna are not just one, when we calculate the harvest power,we just sum ...
0
votes
1answer
17 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 ...
0
votes
1answer
36 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 ...
1
vote
1answer
49 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 ...
0
votes
1answer
50 views

How to use “Filter” matlab function to apply channel to signal?

I need to use filter Matlab function to describe the following : H: MR x MT ...
0
votes
1answer
29 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) $\sum e^{-j\theta_k}(\sqrt{P}|h_k| e^{j\theta_k}x[n]+w[n])$ ...
0
votes
0answers
23 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 ...
0
votes
0answers
34 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 ...
1
vote
1answer
59 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 ...
2
votes
4answers
107 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(...
0
votes
0answers
20 views

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 ...
0
votes
1answer
21 views

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 ...
0
votes
0answers
33 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
2
votes
1answer
27 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 ...
0
votes
1answer
30 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 ...
0
votes
1answer
15 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 ...
0
votes
0answers
22 views

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 ...
0
votes
0answers
36 views

To determine the Baud rate (in symbols/s) and throughput (in bits/s) of the system

You need to design a data transmission system where the data symbols come from an alphabet A with cardinality 32; all symbols are equiprobable. The bandwidth constraint is Fmin=250 MHz, Fmax=500 MHz. ...
0
votes
1answer
25 views

Assumption of SINR measurement

I am assuming there is an Access Point (AP) and IoT Nodes in NOMA uplink scenario. Following is assumed: the AP does not know the channel gain of IoT Nodes the transmission power of nodes is also ...
0
votes
1answer
32 views

Relation between frequency and phase in PLL?

Apparently both frequency and phase are independent properties but what is the relation between frequency and phase in PLL?so that when one is locked ,other is also locked
1
vote
1answer
46 views

Output of Zero-forcing equalizer doesn't match theoretical calculations

Let's say I have a sequence $x[n]$ (signal) and perform convolution with another sequence $h[n]$ (channel), so: $$ y[n] = h[n]*x[n] = \sum_{k}{h[k]x[n-k]} \leftrightarrow Y(z) = H(z)X(z) $$ I'm ...
0
votes
1answer
22 views

Why can we know the best precoding direction after we do the SVD to the channel?

Why can we know the best precoding direction after we do the SVD to the channel?for example $\mathbf y=\mathbf H\mathbf s+\mathbf n$,now we do the SVD to the $\mathbf H$ If the $\sigma _1$ is the ...
0
votes
2answers
52 views

Does zero-forcing equalizer need known channel impulse response?

I'm studying some of the basic equalizing structres and I understand how Zero-forcing works, but it seems to me that a known channel impulse response is needed. Am I right? If so, what's the point? I ...
0
votes
0answers
34 views

Types of equalizers

I can't get my mind around the different types of equalizers and the difference between some of them. I've been looking at different books unsuccessfully. So far, I have Wikipedia's list and this ...
0
votes
1answer
45 views

Real Fast Fourier Transformation (FFT) in 2D changes with changing the axes order

I am using Python to calculate the real FFT for a 2D array. I found that the real FFT function does not return an array with the same size as the input array, rather, it returns an array with the same ...
1
vote
1answer
53 views

sum of 2 signals

I have $2$ signals: $x(t)$ and $y(t)$. They have the same bandwidth $B_x=B_y$. But the bounds for the bandwidth are not the same. For example, $B_x=f_{max}-f_{min}$ and $B_y=g_{max}-g_{min}$ with $f_{...
0
votes
1answer
32 views

Good Starting Material for a SEMI Beginner

I come from a hardware background and I am wanting to get myself more involved with the digital signal processing side of things. I understand a lot of concepts, but only through application meaning ...
0
votes
0answers
18 views

Temporally synchronize two different or more real time digital audio signals

Are there any DSP techniques to temporally synchronize two different or more real-time digital audio signals without timestamp information?
0
votes
0answers
10 views

Why will the power of signal become larger in the receiver ,but not smaller? the channel is a rayleigh fading channel

$\mathbf H_{AB}$ is a rayleigh fading ,$7$ is the antenna number for transmitting in the transmitter A, and $2$ is the antenna number for receiving in the receiver B H_{AB}=sqrt(1/2)*(randn(2,7), ...
0
votes
1answer
20 views

Why there is no paper optimize the consumption power of the circuit in energy harvest?

In the optimization of energy harvest ,some paper want to maximize the harvested power ,rate or minimize the transmitted power,so when they write the formula of optimization,they may assume the ...
0
votes
0answers
40 views

What is the difference between circularly symmetric complex gaussian channel and rayleigh fading?

What is different between circularly symmetric complex gaussian channel and rayleigh fading? or are they the same? I Saw the method of creating circularly symmetric complex gaussian in this website, ...
1
vote
0answers
71 views

Implementation OFDM system in Matlab

I am working on the OFDM transmission system. A channel is given, MR x MT; input data MT x S, and length of a cyclic prefix (CP)....
1
vote
2answers
66 views

How to generate random data with a specific bandwidth

I generate some random data (bits, actually, using MATLAB's randi) and then I convert such bits to BPSK (1 and -1). After that, I use a RRC pulse (roll-off factor ...
0
votes
1answer
22 views

replace input signal with δ will have the impulse response of the function?

Is my impulse response right? By definition,the impulse response is the output when the input is a impulse signal,so $y[n]=\sum\limits ^{n}_{k=-\infty}\frac{1}{2^{n-k}}\ x[k]$,the impulse response ...