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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44 views

bandwidth for a chirp spread spectrum

For a PSK communication with a symbole time $T$, the bandwidth of the system is $B=\frac{1} {T}$. But for a chirp spread spectrum with the same symbol time $T$ and the bandwidth of the chirp is $...
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1answer
137 views

What is the mixed numerology in OFDM

In order to meet the user requirements in the next generation radio access technology, the ongoing standardization within 3rd Generation Partnership Project (3GPP) offers flexibility in terms of ...
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1answer
205 views

White noise and entropy confusion about concepts

The spectral entropy (SE) of a signal is a measure of its spectral power distribution. The concept is based on the Shannon entropy, or information entropy, in information theory. The SE treats the ...
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1answer
40 views

What is an intuitive understanding of the difference between the minimum required bandwidth and actual bandwidth?

When using for example, polar signaling of full width rectangular pulses, the bandwidth is equal to the pulse rate $Rb$, which is also the bit rate. $B=R_b$ for full width rectangular pulses. But ...
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1answer
37 views

Using IFFT for the purpose of “Multiple Orthogonal Frequency Shift Keying”

Is it possible to create a set of complex orthogonal sinusoids using FFT or IFFT In other words a kind of "Multiple Frequency Shift Keying" using multiple sinusoids that are created with a fourier ...
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1answer
232 views

ADC quantization +thermal noise

ADC noise can affect the overall noise performance of a receiver. The noise is partially quantization noise and partially thermal noise and as a general rule it extends up to the Nyquist frequency = ...
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1answer
132 views

Doppler Shift of Phase Coded Pulse Compression Waveform

Suppose I want to transmit the signal: $$ x(t) = g\Big(\frac{t-t_{0}}{T}\Big) \cdot \cos(2 \pi f_{0} t + \theta_{0}) + g\Big(\frac{t-t_{1}}{T}\Big) \cdot \cos(2 \pi f_{1}t + \theta_{1}) $$ Where $g(...
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2answers
108 views

Why Convolution between Signal and a Channel Is Not Done Directly in SIMO Channel

In OFDM system, I need to transmit a signal $x$ in SIMO channel $H$ with one $Tx$ antenna and 4 $Rx$ receiver's antennas. The initial equation for that convolution is $r=Hx+n$ where $n$ is the noise. $...
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195 views

Use of Long Training Field (LTF) of 802.11 standard

In 802.11a/n the preamble part has L-LTF(Legacy-Long Training Field) and HT-LTF(High Throughput-Long Training Field). I want to clarify my understanding of these two fields: Are the only difference ...
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1answer
39 views

Generation of a stream of data bits 0s and 1s at a certain bit or data rate [closed]

This is a very basic question ,but basics important, : How is a stream of data bits (zeros and ones that express a certain information) and at a certain rate being generated? what is involved in terms ...
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1answer
152 views

OFDM Short Training Field clarification

I want to clarify my understanding of OFDM training fields. Please correct me if I am wrong as I am getting 2 different information from online resources. For 802.11a standard the preamble contains ...
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2answers
129 views

Why would we simulate baseband rather than passband

My question is, Why do we usually use baseband in simulation rather than passband? however, if we want to test our simulated idea in real environment, it must be sometimes in passband !! So, should ...
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1answer
70 views

Complex filters used in analog domain [closed]

Complex filters can be used in low IF architecture especially in DSP in order to phase out (reject) the image signal. How are complex filters implemented in the analog domain?
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1answer
48 views

Time for a preamble (underwater acoustic communication)

What is the maximum duration of a preamble for underwater acoustic communications? For example, can we have a preamble $>10 \textrm{ sec}$?
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1answer
118 views

Why must the Region Of Convergence (ROC) contain infinity and the system function be a right-sided sequence for it to be causal?

I need the simple logic on the condition a system becomes causal. We know that causal contains only past values. I can't relate this with the Region Of Convergence (ROC) concept.
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51 views

How general are adaptive-filtering techniques? [closed]

How often do problems arise that let you use adaptive filters? Unless I am understanding something incorrectly it seems the requirement that the input signal be stationary(or even WSS) is too strong ...
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1answer
89 views

Is sparse signal in time domain is sparse in Frequency domain

In OFDM system, if we have a multi-path environment, we supposed to have a sparse received signal in time domain, then $FFT$ is performed to convert it into frequency domain. My question, does the ...
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2answers
78 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 ...
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1answer
43 views

Inter-Symbol Interference (ISI) channels

Is there any open and free data-set for digital ISI channels? I want to have a variety of ISI channels' taps, such as $h[k]$ here. Especially looking for BPSK channels.
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3answers
108 views

Quality of experience engineer

I have noticed certain overlap between digital signal processing and quality assurance for jobs that require expertise in evaluating the quality of the transmitted signals on telecommunication systems ...
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1answer
59 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
65 views

Phase synchronization between 2 PLLs

If 2 PLLs as the one shown are driven from the same reference/crystal and the ratio between divider N and R is an integer (note that divider R is outside the loop), does one need a sync pulse for ...
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1answer
43 views

how to set Equalizer's coefficient using generalized eigenvector.

In that paper https://jwcn-eurasipjournals.springeropen.com/articles/10.1186/1687-1499-2012-72 .. Equation 3, $J(w) = w^HBw/w^HCw$ .. $B$ and $C$ are matrices, $w$ the filter coefficients vector ...
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2answers
94 views

Averaging out noise and SNR improvement

Suppose I have a sequence of identical symbols carrying the same information at a sample rate equal to the symbol rate, why do we always talk about averaging them to average out noise, why not just ...
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1answer
79 views

Calculating the energy of trapezoid wave

Here is the trapezoid wave,although i know we can use $\int^{4}_0 |x(t)|^2dt$ to calculate its power,but i want to divide this trapezoid to right triangle$(t=0$~$2)$,and a square ($(t=2$~$4)$). I ...
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1answer
351 views

Noisy and Noiseless Channels

I am trying to understated the the achievable bit rate in noiseless and noisy channels. Particularly, I would like to solve the following problem: Let a real symbol $0\leq x_i < 1$ be ...
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1answer
51 views

External frequency divider in a PLL

Does a frequency divider external to the loop BW of a PLL cause any phase ambiguity ? and why? and is the result of dividing by an odd number different than dividing by an even number?
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3answers
163 views

“Complex Matched Filter”

What does a complex matched filter mean? . A complex bandpass filter can be formed by multiplying a low pass filter by exp(jwt) getting an analytic filter (one sided in the frequency domain) which is ...
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1answer
36 views

How does a telephone change your voice? [closed]

Is it due to vocal length normalization during MFCC? Please be kind enough to explain.
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1answer
368 views

Symbol timing synchronization using a high sampling rate

Symbol timing synchronization usually relies on a digital PLL procedure, an iterative process that relies on detecting a timing error signal that is used to control an interpolation filter that in its ...
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1answer
52 views

What does it mean that the normalized power of a received equals one?

I have read in that lecture, page 2, here that, the symbols are independent, and normalized to have power 1, which means $E(x x^H) = I$ .. what does that mean? could you please explain that for me?
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0answers
125 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 ...
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2answers
192 views

Carrier Frequency Offset, Rotating Constellation and Correlator

I have been further reading up on carrier recovery methods and something is not clear to me: It's written that a carrier frequency offset results in a rotating constellation diagram but if you are ...
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1answer
17 views

What does SDMA's space actually mean?

What does SDMA's space mean? I mean,T for TDMA is time,and unity of time is second. F for FDMA is frequency,and unity of frequency is Hz.Now i know the S for SDMA is space or spatial,but i don't ...
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1answer
63 views

Phase versus time graph of QPSK

In wikipedia, there was an example on QPSK modulation where the main signal was 11000110 and I contained 1001 and Q contained <...
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1answer
1k views

What is the difference between Antenna port and Physical Antenna in LTE?

I have just started working on the 5G NR physical layer and I have difficulty understanding the concept of Antenna Port at the downlink. In release 10 there supposedly 15-22 antenna ports for CSIRS (...
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1answer
56 views

Frame acquisition vs symbol timing synchronization

For a known length of frames and using a known sequence in a preamble that is also of known length can auto correlation at the receiver be enough to acquire timing or is timing synchronization at ...
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1answer
809 views

Generate Complex White Gaussian Noise in MATLAB

n_3=sqrt(0.1)*randn(1,K); n_4=sqrt(0.1)*randn(1,K); beta_NLoS=(n_3+1i*n_4); % CN(0,0.1) I want to create a $CN(0,0.1)$,does my code have any problem?
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2answers
141 views

Timing error detector used for symbol timing synchronization

The Gardner timing error detector is independent of carrier phase and frequency error, and is also quite immune to self noise (to my understanding, I may wrong about that). Can one assume that it is a ...
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2answers
71 views

BPSK signal that has not been pulse shaped by any filter

Can one consider that a BPSK signal that has not gone through any pulse shaping filter to be equivalent to a signal that has gone through a rectangular filter of which the pass BW is equal to the ...
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2answers
325 views

Intersymbol interference due to limited channel bandwidth

What is the difference between limited-bandwidth induced intersymbol interference (ISI) and ISI due to multipath propagation. I noticed that the delay spread in indoor environment is in the range of ...
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1answer
1k views

Maximum Likelihood Detection of Signal Vectors in Gaussian Noise

Consider a binary-input additive white Gaussian noise channel. Let $\mathbf{x}_0 = (\sqrt{Es},\sqrt{E_s},⋯,\sqrt{E_s})$ and $\mathbf{x}_1 = (-\sqrt{E_s},-\sqrt{E_s},⋯,-\sqrt{E_s})$, be two codewords ...
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2answers
104 views

Signal bandwidth of an 802.15.4 signal at 2.4 GHz

This signal uses Offset QPSK with a half sine pulse shaping filter for the purpose of getting a constant signal envelop. Does anyone know the exact bandwidth of this signal after being pulse shaped, ...
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4answers
69 views

Bandlimiting and OFDM spectrum - what is considered “bandlimited”?

I have been reading about OFDM modulation, it's not clear to me how you can have band-limited OFDM but given its prevalence in wireless communication there must be some designation of approximately ...
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2answers
874 views

What is a constant envelope modulation?

The Book "Digital Modulation Techniques" by Fuqin Xiong groups digital modulation schemes into two classes: "constant envelope" and "nonconstant envelope." However, I was surprised by the inclusion ...
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0answers
53 views

Implementing Fractionally Spaced Equalizer

I have been searching for robust algorithm that can be implemented for avoiding the ISI (Inter-Symbol interference), I came across two types of channel equalizations are there. One is data Aided (...
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1answer
159 views

Recursive Least Square Adaptive Linear Equalizer

For the adaptive filter to work properly, a desired signal d(n) needs to be provided. The output from the equalizer y(n) is subtracted from d(n) to produce an error signal, which is used to adjust the ...
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2answers
190 views

Software PLL tracking of carrier frequency in bandlimited transmission

My understanding is that a PLL(either in hardware or software) can recover the carrier frequency(or be used to correct the frequency offset) of a system. My question is how does this work when the ...
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1answer
29 views

Is there just a carrier in each frequency band in FDMA?

The figure is the FDMA,and i know that FDMA is that dividing the bandwidth into many blocks(frequency band),i want to ask Is there just a carrier in each frequency band in FDMA?i mean one carrier for ...
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2answers
193 views

Inter Symbol Interference (ISI) / Equalization in Digital Signal Processing

I am studying the OFDM system and before to start I have decided to study the main concepts of modulation. And I have spent yet a lot of time to understand the concept of an equalization to reduce ISI....