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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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46 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 ...
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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 ...
3
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0answers
149 views

GNU Radio | Transceiver loopback adapted | Transmission stops unexpectedly

(This is a follow up question to a previous question: link) I have implemented a flowgraph of a transceiver loopback inspired by the examples found at ...
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0answers
326 views

Symbol timing recovery design

I am trying to design the Symbol timing recovery(#STR) block of #DVBS Receiver. These are the specifications Symbol rate ($f_s$) = $2\textrm{ MHz}$ Acquisition range = $10\%$ of Symbol rate ...
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516 views

Phase noise estimation and compensation schemes

Brief background There is a known problem that high order modulation schemes suffers from phase noise of reference generator. It's very important issue for e.g. line-of-sight (LOS) modems exploiting ...
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0answers
3k views

Why does my simulation of the binary symmetric channel disagree with theory?

Could someone please answer me why the simulated performance (using matlab) of a Hamming code over a binary symmetric channel does not fit exacly with the theoretical? Here is my code: ...
2
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0answers
52 views

Problem with 1st order PLL update equation

The output of a communication channel is given by: $x(t) = \sum_n{a_n}h(t-nT)$, where $\{a_n\}$ are BPSK symbols, $h(t)$ is the channel response, and $T$ is the symbol period. If there is an ...
2
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1answer
126 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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185 views

Dynamic loop bandwidth for a Costas loop

I'm using a Costas loop for carrier recovery. The BER vs SNR (from GNU Radio Simulation) curve for different loop bandwidths (0.03,0.05 and 0.07) is shown in the graph below. It can be seen that the ...
2
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0answers
111 views

Why is channel estimation done after synchronization and why does it work?

I am interested in Software Defined Radio communications where almost all processing is pushed to the digital domain. I'm wondering why is channel estimation done after frequency and phase ...
2
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0answers
143 views

How can I oversample the received signal by double of sampling time and have two signals

I have a question, how can I make the sampling in Matlab for the received the signal by half of time duration of symbol (Ts), and have two copies of signal (that's the process of fractional sampling ...
2
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0answers
88 views

Blind coarse OFDM frequency estimation

Is it possible to blindly estimate a coarse carrier frequency offset of an OFDM signal where $\lvert f_{\rm off}\rvert > \frac{\Delta f}2$, where $\Delta f$ = subcarrier spacing? Blind is defined ...
2
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1answer
201 views

Why does signaling overhead for time synchronization scale up with the number of transmitter nodes in a multiple access system?

I was recently reading about random multiple access methods without time synchronisation (of the pure Aloha type). In this paper it is stated that, The need for transmitter synchronization is a ...
2
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0answers
107 views

What is actually transmitted following LPC of a speech frame?

For each frame, what's sent over to the receiver for decoding? The coefficients , pitch in some bits, voiced/unvoiced classification in another bit? Another broad question to develop intuition about ...
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0answers
138 views

Sub-carriers spacing in DVB-T2

Looking at DVB-T2 technical specifications I see that sub-carriers spacing has, in the worst case, a value of few hundred hertz, (something like 279 Hz). 32K sub-carriers are used to reach such a low ...
2
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0answers
293 views

DC offset removal from tetra signal

Hey I want to remove DC offset from tetra signal captured as inphase and quadrature phase samples(I and Q samples). I and and Q samples are 16 bit signed values. I tried averaging 2000 I and Q samples ...
2
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0answers
129 views

TDE, OFDE and FDE equalizer simplest exmple in matlab

I want to implement the equalizer in matlab. I am just learning this. I want a good kick start code that can help me to learn it further. I searched a lot on Google but do not find a good reference ...
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0answers
36 views

GNU Radio - Bandwidth and Band Reject Filter

I am currently trying to generate a psk modulated carrier with gnu radio. Attach is an image of my flow graph. As can be seen I am generating a bit stream using the Random Source module and ...
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0answers
50 views

Does this system of equations have a solution?

My heuristic approaches to find a solution for the following system of equations have failed so far. Does a solution exist? $$ \left[ {\begin{array}{cc} a_k & 0 \\ a_{k-1} & a_k \\ ...
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1answer
54 views

What does the physical meaning of $\mathbf{U} \Sigma \ \mathbf{V}^{*} $ in the MIMO system?

SVD is a method to cancel the interference in MIMO system,we often do the SVD of channel as below \begin{align} \mathbf{H} &= \mathbf{U} \ \Sigma \ \mathbf{V}^{T} \\ % \end{align} So $ \...
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16 views

Why is the $G_{rx}=\sqrt{\frac{N_{rx}}{\hat{N}_{rx}}}S^T_{rx}\tilde{U}^H$ ? How does author calculate it?

I search for some information about Null Space Projection,and saw some information from this pdf: http://taneli.riihonen.fi/presentations/C027slides.pdf ,in the page 16,the author begin explaining ...
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13 views

Convolutional coding that payload length does not change

This is the question about Sigfox radio specification. The stack: Specifically, in Section 3.10 of the specification, we have a convolutional coding (after CRC) with three possible polynominals. I ...
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1answer
88 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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2answers
113 views

About understanding a Matched Filter

I have some basic doubt in understanding a matched filter (MF). Please note that I have already seen very informative post in this context Understanding the Matched Filter In what follows, I list ...
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1answer
63 views

upsampling in the frequency domain

I have the Fourier transform $S(\nu)$. If I oversample by a factor $R$ in the frequency domain. Does the duration of the signal $s(t)=IFFT(S(\nu))$ change?
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0answers
48 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 ...
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1answer
89 views

Symbol Timing recovery for modulation producing ISI

I am interested in understanding why the common timing recovery algorithms function for modulation schemes which produce ISI. For example, suppose you are receiving at the output of a matched filter ...
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0answers
200 views

Blind equalization with constant modulus algorithm in GNU Radio

I'm currently simulating the effect of multitap channel on BPSK as well as its remedy i.e. equalization. The modem is expected to work with satellite TT&C transponder. The communication channel ...
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0answers
28 views

Question about direct spread spectrum in 802.15.4 at 2.4 GHz

I read the 802.15.4 standard and something is really confusing me: How is spreading achieved in 802.15.4? is it by multiplying, encoding or modulating each data symbol (4 bits) with a certain code ...
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0answers
337 views

DPCM Encoder and Decoder Simulation in MATLAB

I am trying to simulate DPCM in order to understand how it works. I am trying to implement the simplest version of DPCM which has a system scheme like in figure 1. Sorry for the quality of the ...
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1answer
190 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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0answers
41 views

Required number of measrments for signal recovery in a compressed sensing MMV problem?

For multiple measurement vector (MMV) problem $Y=AX$ where $A$ is $m \times n$ sensing matrix and $X$ is $n \times L$ matrix haveing K non zero rows. What are the necessary conditions on the ...
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0answers
66 views

Beamforming with NDP frames

During beamforming, the Tx first sends NDP Announcement (which is a broadcast frame) thereby reaching all Rx in its area. And then it follows by sending NDP. Is the 2nd frame (NDP) is also a ...
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0answers
51 views

Doppler Shift and Wireless Access Points

I am trying to design and implement a system that would calculate the velocity of a hand motion in smartwatch. The general idea is to calculate the Doppler Shift of each access point and find ...
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0answers
51 views

Random multipath power and delay generation

I'm trying to simulate an indoor environment that exhibits multipath propagation. However, I don't know how to generate random multipath variables like path power and path delay (power-delay profile)....
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0answers
57 views

Is an extra symbol at the origin of a QAM constellation ok?

This question is specifically directed at Maximilian Matthé (as you work with 5G systems), and to anyone who can shed some light. I am trying to implement a GFDM system with a total of N = K*M ...
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0answers
66 views

Sufficient conditions for exact signal recovery using OMP?

For a compressive sensing model : $$y_{_{MXN}}=A_{_{MXN}}x_{_{NX1}}$$ where $x$ is $K$ sparse, what is the sufficient condition for Orthogonal matching Pursuit (OMP) to exactly recover the data for ...
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0answers
186 views

AWGN Build vs Randn noise do not match

I am generating noise in two different cases with the same SNR once using AWGN command which is a built in command and second time using randn function with the correct scaling however I am getting ...
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0answers
58 views

What type of coding has been used in this communication?

I am trying to decode this signal coming from a control board for car ultrasound sensors. The first part of the signal seems to be a kind of sync frame. In the second part, instead, I should find the ...
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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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0answers
291 views

How to calculate the doppler shift?

I am writing a QPSK receiver in MATLAB. In the transmitter part, I have generated random data using randi, QPSK modulated and pulse shaped using a RRC filter. The ...
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0answers
130 views

OFDM in multipath channel simulation in it++

I am trying to simulate OFDM for an multi-path channel. I am using it++ for simulation. ...
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0answers
90 views

Received signal envelope PDF to power PDF [Wireless Communications]

I am deriving the probability density function (pdf) of the received wireless signal envelope in multi-path fading channels. I wish to transform this envelop PDF to the power PDF of that signal. I ...
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0answers
206 views

How to find frequency and phase shift in the recorded wave( .wav file )

I am working on BPSK at frequecies near 20 kHz with a sample rate of 44100 Hz. We can't afford sample rates above than this due to computational complexities. Have found that the frequency of ...
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1answer
198 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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0answers
92 views

Proving DFT equation

How can I prove the equation $(3)$? I can't understand why there is a $2/N$ in $(3)$. Why he just get the second term in DFT? Consider a sinusoidal input signal of frequency $\omega$ given by ...
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0answers
227 views

Loop Filter Coefficients in Timing Recovery loop in Baseband Receiver

I am trying to design the Symbol timing recovery(#STR) block of #DVBS Receiver. For reference, I am using the following matlab simulink design (NDA timing recovery part within Digital Baseband ...
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0answers
615 views

Generating LDPC codes of arbitrary sizes in MATLAB

I am having problems generating LDPC codes of arbitrary sizes in MATLAB primarily because MATLAB insists on the parity check matrix that is input into its ldpcenc ...
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0answers
139 views

How often do a LTE eNodeB scheduler schedule?

Scheduler schedules the resource for each UE. How often do a LTE eNodeB scheduler schedule? Is the time between each scheduling fixed? any idea/reference will be great help on this regard. Thanks.
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0answers
2k views

Minimum bandwidth condition in FSK

I know that FSK occupies a larger bandwidth compared other keying schemes, $$ BW= f_1 -f_2 +2R_b $$ where $f_1$ and $f_2$ are carrier frequencies and $R_b$ is the bit rate. For achieving a ...