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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24 views

SNR in analog and digital domain

In the digital domain a higher sampling will have a better SNR. Similarly does a narrow filter give a better SNR in analog domain? Once analog signal is converted into digital signal can SNR be ...
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About length of the signal

In my research work i have the equation y(n) = hx(n)+w(n). My understanding about this equation from MATLAB point of view are: h has to be a single number. (for e.g., rayleigh generated). x(n) , w(n) ...
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Correlated fading channel: transmit and receive antenna correlation matrices

I am trying to create a non-i.i.d channel: correlated Rayleigh fading channel. $$ H= R_H \cdot H_o,$$ where $H_o$ is i.i.d. channel ( uncorrelated) and $ R_H$ is a channel correlation matrix, is ...
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87 views

How to compute (in non adaptative way based on MMSE FIR) the feedback and feedword filter for DFE equalization?

System Model Consider the single-input single-output (SISO) communication system in the figure below: where the information bit stream is encoded and mapped such that the output of the encoder is a ...
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2answers
32 views

From symbol rate to sample rate fractional ratio

My design has symbol rate and sample rate to DAC fixed but the ratio is not an integer. For example assume my symbol rate is 3 Mbps but the sample rate to DAC is 20 Mbps. So i am having 3 MHZ and ...
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36 views

Simulation of wireless communication system

In monte carlo simulation of the wireless communications system why we multiply noise by SNRlin( Signal to Noise Ratio in linear). What is the logic behind doing this. Any help in this basic doubt is ...
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33 views

How to write the matlab code for the below question? [closed]

i am dealing with a research in which for a single bit (0 or 1) there are 40 consecutive complex gaussian signals at receiver . How to get these 40 consecutive complex gaussian signals.
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19 views

My preamble bits not enough for locking the timing recovery for a gaussian channel

I have chosen the preamble to be 48 bits (16 bits for carrier recovery+16 bits for timing recovery+ 16 bits for AGC of 30dB + 16 bits for phase ambiguity) As channel is gaussian and there is no much ...
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39 views

Can two modulations be used in the same frame

Can two modulations be used in the same frame? For qam/qpsk/psk/ modulation scheme for the data bits can i have a fixed preamble with psk modulation? does this help in achieving faster carrier freq ...
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26 views

Complex gaussian random variable

In my work i need to generate circularly symmetric complex gaussian random variables with non zero mean and certain variance in matlab. I know the command for generating in case of zero mean , but ...
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30 views

Degrees of freedom in coding (for a communication channel)

I was reading on my lecture slides about how to achieve diversity (i.e. transmit more copies of the same message in order to avoid its corruption; this technique may be realized by repeating the ...
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212 views

QPSK Phase Recovery : Maximum-likelihood Vs Costa's Loop

I have implemented a QPSK Costa's loop in GNU Radio and run some BER benchmarking. All is going well. Out of curiosity, I'm trying to implement the Maximum Likelihood phase recovery shown below. For ...
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Power allocation for frequency selective channel [waterfilling ]

I am studying channel capacity with channel state information at a transmitter, where the water-filling algorithm is discussed. The algorithm should allocate more power to some subcarriers with larger ...
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1answer
45 views

Offset in Carrier and Timing

Is my understanding about carrier and timing offset right? Suppose my transmit frequency is 100 MHz and if my reference is 1ppm; then the transmit frequency has +/-100Hz offset. Similarly, if my ...
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23 views

error performance of ASK Demodulation [closed]

Why do we use the error performance of ASK Demodulation?
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29 views

Cross-Correlation in digital communication system

I've RF data that I can see my packets inside by Matlab, the file of RF data is a raw data(IQ SAMPLES DATA) .... I have did demodulation to those data which the output is also a demodulated raw data ...
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Combiner vs mixer vs coupler?

All these three terms are often used in communication texts and apparently they are some how similar But what is exact difference between each of them?
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40 views

How $\Delta f=\frac{1}{2T}$ satifies the orthogonality condition?

Let $$s_{ml}(t)=\sqrt{\frac{2E}{T}}\exp(j2\pi\Delta fmt)$$ where $T$ is the time-period of signal $\Delta f$ is the frequency spacing The text says that two signals $s_{ml}(t)$ and $s_{nl}(t)$ are ...
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57 views

Preamble length in the communication system

how many bits my preamble should be typically?? course carrier bits+ carrier recovery bits + timing recovery bits+ phase ambiguity ?? i have see typically carrier recovery bits + timing recovery ...
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Implementing time varying channel in matlab

i want to implement time varying channel in matlab. From the literature i understood that it can be done using First order Auto regressive process (AR-1). But in AR-1 process we need to estimate the ...
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1answer
127 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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30 views

symbol synchronization

PLL is typically used in carrier synchronization and its diagram is well known, consisting of a multiplier, a low pass filter, and a VCO. In "Phase-locked Loop" at wiki (https://en.wikipedia.org/wiki/...
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87 views

The relation of sub-carrier and FDMA

In Mengyu Liu, Yuan Liu, "Charge-then-Forward: Wireless Powered Communication for Multiuser Relay Networks", it is said that while information signals are conveyed by using FDMA over $N$ sub-...
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1answer
27 views

how to determine a length of a channel? ( given path, delay)

Given a channel matrices for each subcarrier of a frequency selective channel (OFDM): i.i.d.. channel =(randn(ntx,nrx, N)+1i*randn(ntx,nrx, N))/sqrt(2); simulated ...
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31 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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how to use robot framework to launch unit tests on matlab?

I Know the syntax of rfw and and I want to make some unit test, for some kernels and functions in matlab and I need some help to begin with
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What channel model to choose while simulating a system in passband with frequencies over GHz range?

I was wondering as to what kind of channel model do we use to test for BER vs SNR in a passband RF system. The system that I designed is basically a wideband frequency hopped OFDM system where I use ...
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1answer
21 views

bandwidth vs. bandwidth range

As known, Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. OK, what means when saying that bandwidth range is 15 ~ 20 KHz ? Does that mean that ...
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41 views

Instantaneous SNR

A relay system with 3 nodes: S (power node), R (relay node), and D (destination node). S transmit the signal x to R, received signal at R: $$y_R=\sqrt{P_sd_1^{-\beta}} h_{SR}\,x + n_r$$ with: $...
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2answers
452 views

Why do we express complex noise as Gaussian distributed while the channel is Rayleigh distributed?

I have a confusion regarding the distribution of noise and channel fading. As we know channel fading is usually modeled with Rayleigh fading since it has Gaussian distributed real and imaginary ...
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1answer
23 views

How to reduce PAPR with constellations choice?

How to tune constellations mapping M ary-psk or x-qam to reduce PAPR ?
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37 views

What's the computational complexity of MMSE equalizer in OFDM system

As I know that in case of one tap OFDM equalizer, (ZF equalizer), we should have $N$ division complexity since we divide every subcarriers by its correspondent channel tap in frequency domain. But I ...
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1answer
73 views

noise floor estimation

I want to estimate noise floor in the spectrum. I tested many methods using journals, but I couldn't find a stable method. Suggest that we have a spectrum consist of many signal and we want to ...
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34 views

What is difference between Phase shift keying (PSK) and Quadrature Amplitude Modulation (QAM) mathematical equation

I went through a literature and found the following expression for PSK signal. On this basis, what will be the equation for **QAM signal **. Also from where i would be able to read about this equation ...
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27 views

Matched filter (Non-Sychronous Detection)

I have IQ samples data file, RF data, that I sampled it by dongle SDR RTL which this file has packets that I transmitted them and the dongle has sampled them, so the IQ samples data file which is the ...
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48 views

How does subcarrier correlation affect the BER of OFDM?

I am studying the OFDM system and would like to examine it under different subcarrier correlation scenarios. I have calculated BER for the uncorrelated scenario and now I have rewritten it for the ...
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1answer
71 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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How does the length of matched filter affects the fft of my signal

I have one matched filter that Im applying it on FM signal (with noise) in order to detect specific signal from my FM signal(with noise), Im trying to find out what's the relation between the length ...
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1answer
25 views

BFSK modulation coding on MATLAB

Like for BPSK we generate random bits and then data= round(rand(1,num_bit)); %Generate binary data bpskModulated = 2*data-1 % mapping to -1 and +1 Can we do ...
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22 views

I am looking for a book where I can find the implementation on matlab of a non adaptative DFE

I've already implemented RLS/LMS DFE and I need a MMSE implementation
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1answer
50 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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29 views

Non coherent detection BFSK demodulation?

I am simulating BER performance of BFSK under AWGN and Rayleigh fading, BFSK has two symbols one entirely on the real plane while other on the complex plane for representing let's say zero and one, ...
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1answer
83 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
60 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
56 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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31 views

Carrier frequency offset estimation for QPSK and asymmetrical spectrum

I am working on estimation of carrier frequency offset for QPSK data from a satellite. From my understanding, there are two main approaches: either remove data from the carrier (by taking the fourth ...
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3answers
93 views

Why should the number of subcarriers of OFDM system be a power of 2?

I notice that almost all papers use the number of subcarriers of 64, 128,256.. so on, which is a number of $2^k$ and $k$ is an integer. Why is the number of subcarriers always like that? Can we use ...
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1answer
18 views

channel impulse and frequency response: H?

The received signal of MIMO system is given as: $$ y= H \cdot x +n, (*)$$ where $H$ is a channel matrix. $h(\tau_l)$ is a channel impulse response. It is determined as a matrix $\in \mathbb{C}^{Nr \...
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7 views

What is role of BW and frequency in internet speeds?

First the bandwidth (BW): It is the amount of data that can be transferred simultaneously.just like more no. of highway lanes so that many cars can travel side by side simultaneously. Frequency It ...
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55 views

matched filter position

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

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