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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6 views
How to compute the channel gain from the path loss model of a wireless channel
I did my research but I did not get a satisfying answer.
We have a transmitter and a receiver over a wireless communication channel. The channel's path loss is modeled as
$ 128 + 37 \log_{10} (d)$, ...
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1answer
23 views
Confussion on roll-off factor, sampling time and Raised Cosine pulses.
I am reviewing some bandlimited communications theory and something is bothering me -
My book says increasing the roll-off factor makes the received sequence more tolerant to timing recovery errors ...
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1answer
40 views
Where in the signal chain is Channel Equalization applied?
I am reading about channel equalization and I am somewhat confused on where in the signal chain channel equalization is normally applied and if it's before or after a correlator detector or matched ...
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0answers
13 views
Time difference between the outputs of the matched filters of 2 identical receivers that are not supposed to have synchronized ADC sampling clocks
I have 2 identical receivers both are supposed to be running with an ADC sampling clock of 4 MHz but the clocks are not synchronized and there may be a frequency difference between them , symbol rate ...
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0answers
19 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 ...
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0answers
18 views
Processing gain calculation in Zigbee 2.4 GHz
In Zigbee 2.4 GHz , data at a rate of 250KHz are spread as follows: every set of 4 bits is replaced by a code of 32 chips at a rate of 2 MHz. Afterwards an OQPSK signal is formed by alternating every ...
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0answers
22 views
Zigbee 2.4 GHz modulation, demodulation and processing gain
At 2.4 GHZ it seems that every 4 data bits are mapped into one of the 16 available 32 chip codes, by mapped I mean "replaced" , i.e. no multiplication nor modulation.Now at the receiver and by means ...
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0answers
13 views
Confusion on CDMA IS-95 uplink
In IS-95 on the uplink data is detected non-coherently at the receiver because
no pilot tone is used. The way this is done is that at the transmitter every set of 6 bits is replaced by one of 64 ...
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27 views
compensate doppler spread due to multipath
I want to transmit a chirp signal in a channel with multipath and doppler spread.
How can we compensate for the effect of doppler spread?
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1answer
31 views
The benefits of a fractionally spaced equalizer
I often read that one of the benefits of FSE vs a symbol rate equalizer, besides avoiding any aliasing in the roll off region, is that it is less sensitive to the timing phase. What does that really ...
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1answer
53 views
OFDM Simulation process
I'm trying to understand OFDM by making a simulation. Are these steps correct?
generate M random complex QAM symbols. example: (1+j,1-j,-1-j,1-j....)
Split my M samples into a N 2048 sized arrays
...
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1answer
27 views
Narrow band Interference affecting timing acquisition in spread spectrum communication systems
It is often said that a narrow band "in band" interferer will collapse and its BW will spread when it is correlated with a spreading code at the receiver of say a CDMA system while the signal of ...
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1answer
15 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
53 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
66 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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0answers
22 views
Soft Question: How many base-stations/cells are there?
I need white papers or reports having statistics on the number of base-stations/cells worldwide currently and the expected number in the future.
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0answers
26 views
what are the hot area of searching in FMBC and Massive MIMO
I'd like to ask about Massive MIMO, and FBMC. What are the hot areas of searching in these two topics?
I mean for example in OFDM, it's needed to check the ISI, ICI and channel estimation and so on.
...
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0answers
23 views
Frequency hopping signal bandwidth
I am confused about how to calculate the signal BW in a frequency hopping system, is the signal BW a function of the frequency separation and the number of frequencies used or is the hopping rate ...
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1answer
19 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
28 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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0answers
12 views
Multiple PLL phase alignment when using fractional N PLL in a hop away hop back format
In a fractional N PLL the output can settle to any of the MOD (fractional modulus) instantaneous phase offsets with respect to the input reference, so phase coherence may not be achieved between 2 PLL'...
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1answer
50 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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0answers
21 views
Measuring Frame Error Rate to a given Confidence Level
I'm currently simulating BER and FER for a gnuradio BPSK modem. To make sure that the simulation have enough samples, I used the formula
$ NBits =- \frac{\text{ln}(1 - CL)}{BER}$ from this link where ...
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0answers
20 views
Common Cyclic prefix for a set of cascaded OFDM symbols
I've seen research papers / baseband systems that deal with synchronization using a common CP(Cyclic Prefix).
The transmission structure comprises , a family of complex orthogonal sequences, with ...
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1answer
30 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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0answers
29 views
Spatial diversity at different frequencies in WiFi indoors channel propagation
There are two main conditions for antenna spatial diversity to be suitable:
A rich scattering environment that allows a wide power angular spread
Depending on the first condition a certain distance ...
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0answers
15 views
How multiple HT-LTF in 802.11n (MIMO-OFDM) standard is used to estimate the CSI
In the 802.11n preamble, the number of HT-LTF (High Throughput- Long Training Field) is equal to the number of spatial streams. Therefore, for a 2 by 2 MIMO system, there will be 2 HT-LTFs. These HT-...
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1answer
49 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
39 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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0answers
23 views
Using Walsh codes associated with CRC ( Cyclic Redundancy Check)
I have a system where I am sending different orthogonal walsh codes that need to be identified at the receiver.These walsh codes are not modulated with any data.In order to make sure especially at low ...
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2answers
87 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
50 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
31 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
35 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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0answers
41 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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0answers
13 views
Creating an aliasing effect in Matlab when a signal goes through a matched pulse shaping filter at Rx
What are the conditions necessary for the signal and for the filter in terms of sampling rates of each, roll off factor of the filter, to avoid aliasing when that signal is being pulse shaped on Tx ...
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0answers
23 views
blind channel estimation using EM implementation
I would like to implement EM for blind channel estimation.
The algorithm is briefly described in this paper, under the section "EM for blind channel identification".
I'd like to derive the algorithm ...
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1answer
51 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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1answer
23 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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0answers
25 views
Timing synchronization again
Text books and papers talk about different approaches and algorithms for symbol timing synchronization: maximum likelihood, zero crossing, etc.. but it seems that these are all for the purpose of ...
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1answer
30 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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0answers
39 views
OQPSK constellation question
The following block diagram shows an OQPSK modulator/demodulator.What I fail to understand is that the peaks at the output of the Rx matched filter give a nice QPSK constellation after compensating ...
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3answers
97 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
35 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
36 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
41 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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0answers
12 views
Shaping filter for a multi-user communication
In a CDMA system, should we multiply by the PN code before the shaping filter or after?Is the order of the steps important?
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2answers
48 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
25 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 ...
