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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1answer
42 views

What does it mean to plot a PAM signal over a number of symbols?

Our course has been using the book Introduction to Communication Systems by Upamanyu Madhow for our communications course. There is a question in the book on page 87 Software lab 2.1 which is ...
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1answer
21 views

LTE system. How to compute precoder for resourse block

guys! I am studying a massive Mimo system and 3gpp LTE system and have questions about precoding in the LTE system. In LTE RB (resource block) is used to group consecutive subcarriers. To compute ...
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1answer
19 views

The binary input frequency, should be equal, greater, or minor than the carrier's frequency? [closed]

The binary input frequency, should be equal, greater, or minor than the carrier's frequency? And about the length and amplitude of the binary input, any similar observations? Edit: In context of ...
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15 views

synchronization with 2 users

I have $2$ users with different distance from the receiver and each user's message is spread with a different waveform. The $2$ waveforms are orthogonals. With a perfect synchronization, I don't have ...
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17 views

Capacity frequency selective channel: basic in computation

I am trying to compute the capacity of the frequency selective channel and plot it. For visulisation I am using Maltab. for compuation the following math expression ( $N$ is # subcarriers): $$\text{...
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1answer
35 views

Digital Tanlock carrier recovery loop

I’m currently trying to understand a digital tanlock carrier recovery loop for QPSK (for example) I cannot understand how it works. For example we an ideal QPSK constellation. phi = atan2(Q/I) = pi/...
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Doppler effect on Baud Rate

I'm having a hard time wrapping my head around doppler and how it affects a digital communications signal's baud rate. The examples that I've seen explain that the center frequency of a signal is ...
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28 views

FSK carrier frequency estimation in non equiprobable data

We know that in equiprobable data,change in phase over a time interval, this result will be directly proportional to frequency: f∝Im(s(n)s(n−1)∗) Where s(n) is the normalized complex FSK time domain ...
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1answer
67 views

Error detection and correction algorithms for Wireless Body Area Networks

I am working on transmitting ECG signals over wireless body area network based on IEEE 802.15.4 standard. To reduce the BER and increase the signal reconstruction quality, I think that I need to ...
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1answer
33 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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1answer
62 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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1answer
49 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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1answer
47 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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44 views

matched filter position

I have seen that matched filter should be used in TED (gardner loop) after resampler ...
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2answers
93 views

Correlating a sequence or a code with itself at QPSK symbol rate

I am sending a QPSK signal that represents a certain sequence or code and that needs to be correlated with itself on the receiver (there are other sequences/codes in the system, and they are all ...
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1answer
50 views

Training Fractionally Spaced Channel Estimator and Equalizer

If you are attempting least squares channel estimation with a fractionally spaced channel estimator, do you want the training sequence to also be fractionally spaced or symbol spaced? It looks like ...
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1answer
49 views

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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1answer
34 views

Synchronization Accuracy Required For Communications

One of the biggest problems in phase modulated communication is discovering when your signal has arrived. High accuracy in this area is important, as even a quarter wavelength error can cause the ...
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19 views

receiver for a multi-user communication

I have an asynchronous multi-user communication with $10$ users. With a matched filter, I see the average BER by user is small ($<0.08$). Do you know any methods that can reduce the BER by user on ...
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1answer
19 views

decorrelating detector

In this paper decorrelating detector we have the decorrelating detector. With $K$ users, the correlation matrix of the signature waveform is $R=S^TS$ with $S=[s_1,...,s_K]$. Moreover $size(R)=K \times ...
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33 views

should implementing the MMSE equalizer in time domain and frequency domain give same results?

Assume we have a received signal $r$ explained as below: $r = h * x + n$ where $h, x ,*, n$ denote to the multi-path channel, transmitted signal, convolution operation and AWGN, respectively. ...
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1answer
35 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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2answers
2k views

highpass filter design in Matlab

I hope to design 1st order highpass filter from transfer function. In the example of 1st order lowpass filter, I first get the coefficients of numerator and denominator in the variable 'b' and 'a'. In ...
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2answers
238 views

Fractional spaced equalizer + timing (clock) recovery

I am trying to figure out how timing recovery is used after equalization (or, being more correct, when the equalizer is in the timing recovery loop), having a T/2 fractional spaced equalizer and using ...
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2answers
112 views

Alamouti Scheme. MISO. STBC for real constellation

I have a real orthogonal design for codeword... $$ \begin{bmatrix} s1 & s2 \\ -s2 & s1 \end{bmatrix} $$ $$ s=\begin{bmatrix} s1\\ s2 \end{bmatrix} $$ $$ Y^T=\sqrt{\frac{P}{Mt}} h^T ...
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22 views

IID noise assumption at Matched Filter sample time

I read that at the correct sample times of a matched filter output the noise is independent assuming a Nyquist pulse. Can someone provide a proof of this or explain it more? Assuming your matched ...
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14 views

Calculating average power of a discrete random signal with complex values

I have a Rayleigh channel that transmits discrete values according to the following: $$y(n) = h(n) * s_n + \omega_n$$ Where $y$ is the received message, $s_n$ is the symbol sent (constellation 2-PSM), ...
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What is the difference between SFO (sampling frequency offset) and SCO (Sampling clock offset)?

What is the difference between SFO (sampling frequency offset) and SCO (Sampling clock offset)? I think they are essentially the same phenomenon?
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1answer
157 views

Time delay estimation between two complex signals(IQ)

I need to time align two complex signals. The two signals obtained were at different RF frequency before digitisation. So,I have two complex signals(IQ) and I need to do delay estimation and apply ...
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1answer
102 views

Modulation and Noise

I am fairly new to studying communication systems. When it comes to different digital modulation techniques, does the effect of an additive complex noise (a) introduced by the system, and (b) by the ...
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1answer
27 views

Smooth factor in matlab

I use smooth function in matlab, in this function there is the smf (smooth factor) parameter that get different values. In different applications, this parameter ...
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1answer
452 views

Flat vs frequency selective fading in MC-CDMA?

I am trying to simulate an MC-CDMA system. I have NXK matrix $S$ which consists of subcarriers ($s_n,_k$ represents subcarrier $n$ of user $k$) and KX1 vector $X$ consists of user symbols. So my ...
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49 views

Basic in “Precoding and Equalization Schemes”

I have found the interesting following paper for me: SVD-based MIMO Precoding and Equalization Schemesfor Realistic Channel Knowledge: Design Criteria and Performance Evaluation The paper is old, ...
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1answer
97 views

IQ generation separation

To generate I & Q samples from data samples S I = S(1:2:length(S)-1) * cos(2*pi*f*t) ; Q = S(2:2:length(S) ) * sin(2*pi*f*t) ; I & Q to integer ...
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1answer
123 views

Interleaving over OFDM symbols in same transmission

In this question I have asked what are the benefits from interleaving between two codewords over ONE OFDM symbol in packet based transmission made up of more than one OFDM symbol Purpose of ...
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2answers
2k views

Golay complementary sequences for channel estimation - MATLAB

There are set of complementary sequences known as Golay sequences that are used for channel estimation because of the nice property they have which is that the sum of the autocorrelation function of ...
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1answer
452 views

How to convert the mean and variance of a processed received signal into a SNR or BER?

So I'm trying to eventually get some sort of signal quality metric, and to do that, I'm trying to take the mean and variance of my bit determination signal and use that to come up with a Signal to ...
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1answer
231 views

How can I make a mmWave frequency selective channel in matlab?

$$H_d=\sum_{\mathcal{\ell}}^{N_p}\alpha_\ell p(dT_s-\tau_\ell)\mathbb{a}_R(\phi_\ell)\mathbb{a}^*_T(\theta_\ell) $$ I'm trying for simulation of a frequency selective channel in matlab. my problem is ...
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1answer
171 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. ...
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30 views

How to generate rayleigh fading coefficients in matlab

I want to calculate received SNR for each cellular user CUs, so i want the corresponding transmission power P of base station BS to each user, the noise, and the channel gain coefficient of the ...
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1answer
305 views

Why are the mark and space tones of these FSK signals reversed?

I'm working on a project involving FSK-modulated signals. I'm trying to reverse-engineer these signals to determine the preamble pattern used, because the protocol is proprietary. Shown below is a ...
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30 views

Deep Learning based NDA Channel Estimation

I was wondering if it is possible to use Deep Learning to estimate the Channel Impulse Response for NDA synchronization? I understand Deep Learning is not normally used for regression problems but I ...
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1answer
251 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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2answers
379 views

What is the relation between noise (AWGN) variance and number of antennas?

I'm working in two Matlab scripts trying to simulate a MIMO system using OFDM (downlink) and SC-FDE (uplink). My question is: for different numbers of transmit and receive antennas, what is the ...
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2answers
44 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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1answer
41 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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1answer
26 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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1answer
182 views

Nyquist criterion for zero ISI in the frequency domain

Can someone explain in simple words /graphs the necessary and sufficient Nyquist criterion for zero ISI in frequency domain, namely: The constant folded Fourier Transform.
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49 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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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 ...