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
4
votes
0answers
39 views

orthogonal family and pulse shaping filter

I am a beginner in digital communications and I have a question on the pulse shaping filter. For example, I have an orthogonal family $ \{s_1,...,s_N \}$. Can we preserve the orthogonality with a ...
0
votes
1answer
58 views

QAM constellation coder - transmitting a file

The file with size 6 MB is transmitted in 100 seconds using a constellation coder QAM with a constellation of 6 bit/symbol $ { M = 10^6, B = 8} $ Tasks: 1. What is the signal bandwidth if the band ...
0
votes
2answers
64 views

About using Walsh matrix as spreading sequence

I'm asking about some details about using the Walsh matrix as spreading sequence code. For example, suppose I'm using a $4\times 4$ Walsh matrix given by $$H = \begin{pmatrix} 1 & 1 & 1 & ...
1
vote
0answers
40 views

Band Edge Filters

I am interested in using Band Edge Filters to do carrier frequency recovery but this is kind of secondary to my question which is: How do you build an FIR filter which isn't symmetric about the ...
0
votes
0answers
79 views

Preamble detection using cross-correlation

I am generating a preamble with a sequence of [1 -1 1 -1 1 -1....] and spread with a barker-11 sequence. Now, the transmitted signal becomes [B(Barker), -B(Inverse of Barker), B, -B,....]. In channel, ...
1
vote
2answers
44 views

What is the duration of the spreading sequence

I have a question regarding the spreading sequence duration using Walsh matrix. I've read a paper related to that, they consider the signal $S = R(S) + I(S)$, where $R(S), I(S)$ are the real and ...
2
votes
2answers
97 views

How to solve equations for the MMSE receiver?

Given the following equations for the achievable rate of the Minimum Mean-Squared Error Receiver [1]: $$\mu = \frac{1}{K-1} \sum_{i=1, i \neq k}^{K}{\frac{1}{Mpd_{i}\left(1 - \frac{K-1}{M}+ \frac{K-1}...
0
votes
2answers
65 views

How to find the instantanous SNR over Fading channel

I would like to prove that the instantnous SNR of flat fading channel $$y=hx+n$$ is $$\gamma=\frac{|h|^2}{N_0}P$$ where $E\{z\}$ is the expectation of $z$ and $$ E\{x\}=P $$ $$ E\{n\}=0 $$ $$ E\{...
0
votes
1answer
37 views

Digital receivers for the reception of non pulse shaped signals [closed]

We are used to deal with pulse shaped signals, for example signals that go through root raised cosine filters at the transmit, and then matched with root raised cosine filters at the receive In ...
-1
votes
1answer
50 views

Beamforming question

I'm working on a beamforming network. Every node in the network is half-duplex and has a linear antenna array that is capable of digital beamforming. A receiving node can be capable of forming any ...
0
votes
1answer
54 views

Multiplication and Convolution in Wireless Communications

In Wireless Communication, sometimes the received signal is expressed (in time-domain) as follows: $$r=hx+n$$ where $h$ is called a fading coefficient and sometimes it is expressed as: $$r=h*x+n$$ ...
0
votes
2answers
113 views

Demodulation in Rayleigh Flat Fading Channels

A core part of demodulation in Flat-Fading channels is (assuming) the channel as a(random) constant complex number multiplied with your signal. This is done in order to de-rotate the symbol for ...
0
votes
0answers
13 views

Energy in the mcss

In an MCSS (Multiple Chirp Spread Spectrum) communication, for example with a gaussian channel. Why should spreading chirps have the same energy?
-3
votes
1answer
61 views

spectrum for a communication signal [closed]

I have a communication signal. Its bandwidth is limited. But does the $X(f)$ value is important? For example, I have $X(f)=6.10^3$ but for an other signal I have $X(f)=10^6$ (the channel is the same ...
2
votes
1answer
52 views

Is there a relationship between Average energy of transmission and power saving

As mentioned in many books, the average energy of transmitted symbol is given by: $E_s = (2/3)(M - 1) $ where $M$ indicated the modulation order. Suppose that we are using in the first scenario $...
0
votes
0answers
22 views

Noise power for decorrelating detector

I have the following setup: $\mathbf{y}=\mathbf{R}\mathbf{s}+\mathbf{w}$, where the details of each entity can be found at http://bard.ece.cornell.edu/downloads/sim_tools/spanc_me/report/node12.html. ...
0
votes
1answer
30 views

Modulation scheme for a noisy channel with a complicated transfer function

I want to build an audio modem with a speaker in a room and a smartphone. The channel is quite bad: Far field, so there is potentially significant reverb Typical residential background noise phone ...
0
votes
0answers
44 views

Multiple beam beamforming

For digital beamforming, we can form as many beams as we want. No matter where I read about this subject I cannot find any discussion of the interference that one would expect between beams (not ...
0
votes
0answers
28 views

Phase estimation in Beamforming

If I have a modulated signal $A\cos(2\pi f c t + \phi)$, I can demodulate it using IQ demodulator and estimate the phase using I and Q channel information. When it comes to MIMO case (specifically ...
0
votes
0answers
73 views

Phase demodulation vs frequency demodulation using a PLL

When demodulating a phase modulated signal using a PLL it is recommended to use a narrow loop BW, so that the VCO does not really follow the input phase modulated signal but outputs a reference ...
0
votes
1answer
45 views

AM-AM and AM-PM plots

I have complex baseband signal and its output when passed through power amplifier. How to plot the AM-AM and AM-PM plots?
0
votes
1answer
65 views

data rate in digital communications

I am a beginner in digital communications and I have question for the data rate with CDMA. Let, the length of the spreading sequence is $L_c$, The modulation is BPSK and the symbol time is $T_s$. To ...
0
votes
0answers
34 views

Fourier transform for a signal

If we want to sample a signal $s$ for digital transmission, the modulus of its Fourier transform, $|S|$, must be non-zero only in a frequency band $B$. But are the magnitudes of $|S|$ are important? ...
1
vote
1answer
137 views

Concatenated Deletion & Sticky Channel Capacity

Suppose you are sending information through a deletion channel with a deletion rate of .5 and then the output of this channel is sent through a sticky channel with a repeat rate of .5 also. No error ...
0
votes
2answers
32 views

Sampling vs repetition code

I'm working on a multiuser wireless system simulation and have run into something regarding sampling rates. From everything I've known for a matched filter receiver, the correlation step is performed ...
1
vote
2answers
660 views

Does a matched filter really improve SNR?

Does the matched filter actually improve SNR or does it maximize it (making sure that it is not less than what it should be) ? improving SNR would not make sense to me as suppose a receiver has a ...
-1
votes
1answer
21 views

multi-user communication

For a multi-user communication, I do many signals $s_i(t)$ with $i \in \{1,...,N \}$, $N$ the user number. The bandwith for each $s_i(t)$ is the same. But when I do the Fourier transform of $s_i(t)$, ...
0
votes
1answer
45 views

data rate with a FSK modulation

With a BPSK modulation the data rate is $D=\frac{1}{T_s}$ where $T_s$ is the symbol time. But for a BFSK modulation, how do we find the data rate?
2
votes
2answers
282 views

PSD of complex white gaussian noise

It may be a really simple question, but I'm not sure about this one: Given a complex white Gaussian noise process with iid real and imaginary parts and a double sided power spectral density of $N_0/2$...
0
votes
2answers
73 views

What is the advantage of MISO technology in communications?

What is the advantage if the MISO (Multiple Input Single Output) technology in communications? I have been searching it on the internet, but there are just about their model and full name. For ...
0
votes
1answer
19 views

Why do we need to minimize the TX power to require for meeting QoS?

Here is the part of the paper, Based on these architectures, a lot of recent developments have lately appeared intending at enhancing the rate-energy performance of multiuser Multiple Input ...
10
votes
4answers
14k views

How is symbol synchronization with OFDM done?

I'm trying to understand how symbol synchronization is done in OFDM using pilot tones, cyclic prefixes, or any other technique. I've read the following answers which provide some explanation, but I ...
-1
votes
1answer
33 views

power of the preamble

In a modulated communication signal, the power of the signal to be sent or received must be equal to 1 to after calculate the BER. But if I add a preamble at the beginning of the signal for example ...
1
vote
1answer
129 views

How to sketch a frequency spectrum for an AM signal?

So I have an AM signal, given by: $$v(t)=50\cos(\pi 10^{6} t )+ 20\sin(\pi 10^3t)\cos(\pi 10^6 t)$$ I was asked to sketch the spectrum of the signal obtained, so I found the fourier transform of it, ...
0
votes
1answer
54 views

Converting a non-stationary random process into a WSS process by adding a random phase

Here is an example where this method has been implemented. We were trying to calculate the spectrum of a transmitted signal(Random signal/weighted pulse) The auto correlation function of the pulse ...
1
vote
1answer
49 views

upsampling for a signal

We have a signal $s(t)$. If we do an upsampling, does the signal duration increase? What is the point of upsampling if the signal time increases? Can we do an upsampling if we don't use a shaping ...
1
vote
1answer
37 views

Questions about reproducing results of a paper on Communication Systems and Wireless Communication

I'm trying to reproduce the results of a paper on Device-to-Device Communication, channel assignment and mode selection (G. Yu, L. Xu, D. Feng, R. Yin, G. Y. Li and Y. Jiang, "Joint Mode Selection and ...
1
vote
1answer
28 views

differential phase tracking loop for the receiver

For a DBPSK modulation, how can we track the differential phase? I thought about using a phase tracking loop but I did not find articles for this.
1
vote
3answers
79 views

Representing data in combination of QAM and BPSK

I have a question regarding the data representation in different modulations. Assuming we are using MIMO system whith $4$ $T_x$ x $4$ $R_x$ which means four transmission antennas by four receiving ...
1
vote
1answer
48 views

Modulating ofdm in audio spectrum

Trying to modulate audio with OFDM data. My fs = 44.1khz, i'm using 64 sub-carriers, but i'm only using 5 sub-carriers for data, so my bandwidth is about 3.445khz. I'm not sure how to properly write ...
0
votes
1answer
43 views

phase tracking loop for dbpsk

I have a communication with a DBPSK modulation. The communication is disrupted by a Doppler shift (due to movement) and Doppler spread (due to channel). At the reception, after Doppler shift ...
2
votes
2answers
82 views

How to get sensor covariance matrix from CSI values?

I try to use musicdoa() function in Matlab to estimate the direction of arrival of the paths of signals received by the receiver in a wireless link. The function ...
0
votes
1answer
48 views

About combination between QAM and PAM

I have confused question regarding the possibility of combination between QAM modulation and PAM in order to improve the spectral efficiency. Is that possible? As you see in the below Figure, it's ...
0
votes
1answer
31 views

About Data spreading in CDMA

If we have data we need to transmit which is $i$, so we should multiply is using XOR function with spreading code $y$. How many bits (Maximum and Minimum) should $i$ and $y$ can have ?
0
votes
1answer
35 views

The notion of white and colored noise

The autocorrelation function of AWGN is an impulse response at t=0, and its fourier transform or its spectral power density has a flat infinite BW Now any receiver will have bandpass or low pass ...
0
votes
1answer
51 views

Is CMA equalization applicable for OFDM

I have a question regarding the constant modulus algorithm (CMA), as you know it's one of the known algorithms used for blind equalization. The cost function of the CMA is build blindly, it means ...
0
votes
2answers
36 views

How to calculate $p_c$ (binomial probability)

In the given image I don't understand how to calculate $p_c$, can anyone please explain?
0
votes
2answers
88 views

How to calculate $E_b/N_0$ for a 8-PSK?

How to calculate $E_b/N_0$ for a 8PSK? My BER is given. But I don't understand how to calculate $E_b/N_0$ as it is inside a Q function.
0
votes
1answer
493 views

Average Energy of modified QAM Constellation

How to compute the average energy for the modified 16-QAM constellation below? I know that for regular/rectangular 16-QAM we can utilize the 4-PAM along each axes but I'm not sure how can we find $E_{...
0
votes
1answer
238 views

How can I generate time-variant Rayleigh channel in MATLAB

One of known models for channel simulation is called Rayleigh Fading channel, it's usually used to simulate wireless channel in time variant/invariant. As I know, Rayleigh fading channel can be ...