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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Do we need a transmit and a receive filter in a OFDM transceiver system?
can anyone specify in brief what are the filters that can be used as a transmit and receive filter in OFDM. Any material to start with will be very much appreciated. Thank you!
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How do you determine the power required for a phase shift keying modulation scheme?
This wiki article has a diagram :
which shows how the message "11000110" is conveyed as a waveform.
I'm trying to understand how the power to transmit this message can be determined.
Do I need ...
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Canceling interference (such as harmonics from out of band source )
I have a vague-ish question, if it makes sense:
The desired received signal (from source S1) was carried at 3 GHz passband carrier frequency, with bandwidth 20 MHz. It was interfered with by the 3rd ...
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1answer
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how can the channel fading model (Rayleigh, or Rice, or Log normal distribution) infer the way channel estimation is done?
For a dense urban environment with rich scattering and no Line of sight (LoS)
path, the Rayleigh distribution can be used to model the fading.
Rician fading is a stochastic model for radio propagation ...
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Comparing the performance of a digital communication sim against a reference
I have a complex baseband simulation of binary FSK modulation and demodulation. The modulated signal $s[k]$ is computed as
$$
s[k] = e^{-j2\pi f_ik/f_s} , i \in [0,1]
$$
where the sampling rate is $...
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1answer
29 views
Is there a term called “Fourier Beamforming”?
I understand delay and sum beamforming, where we want to add the signals obtained from different sensors. But adding different time samples from different element of the array depending on the angle ...
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17 views
Channel Capacity of OFDM with Index Modulation
I am trying to figure out the channel capacity of OFDM with index modulation (OFDM-IM). One of the article reports that the conditional channel capacity of OFDM-IM is $\mathcal{C}_{\mathrm{OFDM-IM}}(\...
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How to add LLR? [closed]
I am working on soft decision codes like turbo, LDPC and Polar codes. I need some help understanding how to add two LLR.
Thanks a lot
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2answers
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Orthogonal Codes for Band Limited Channel
In this question orthogonal family and pulse shaping filter the user asked about possible loss of orthogonality of orthogonal codes due to the use of raised cosine pulse shaping and I showed as an ...
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Looking for WiFi Phase and RSSI data
I'm not sure if this is right platform to post . I am researching on WiFi Localization algorithms using Machine learning and was wondering if anyone knows any dataset which is publicly available. ...
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How to compute the LMS DFE based equalizer FF and FB coefficients in a adaptative way?
I am still struggling to understand the filter updating process, the computation of the demodulated result and the computation of the error.
Attached you can find the simulation I've done so far, the ...
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1answer
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Serial to Parallel Converter
in many texts about modulators I have seen there is a component called "Serial to Parallel Converter". For instance, let's consider this scheme and let's focus on the second block (reference):
The ...
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1answer
44 views
Confusion about collection of bits and symbols
I'm taking an intro communications module and I'm quite confused on what the term "symbol" really means?
Consider this setup:
My understanding is as folllows
After the information source, we have ...
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1answer
25 views
start of packet detection
With the current lockdown, I'm spending some time in understanding L1 PHY development and have some questions on the start of packet detection in an IQ capture
Let's say I have a WiFi IQ capture ...
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1answer
42 views
What does filtering do to a signal in time domain? Does the signal gets distorted?
When considering a transceiver system, if we do a certain filtering operation on the signal, will the BER of the system be affected? My point is, since filtering in frequency domain filters a portion ...
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1answer
34 views
Effect of Adding the cyclic prefix on the toeplitz matrix in OFDM
Assuming we have $N$ symbols to transmit encoded in block $k$,
Performing $N$−iFFT at the transmitter, we now have
The resulted signal $x(k)$ has length of $N$. inserting a cyclic prefix $CP$ ...
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MSK receiver blocks [closed]
I am trying to implement MSK mod and demod. Literature shows different way of implementing. Can anybody tell the actual blocks required in MSK I Q demodulation ?? Is carrier recovery and timing ...
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2answers
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Eye pattern construction and interpretation
I have read some text about the eye pattern (or eye diagram), but I do not understand how should I read it.
The wikipedia definition of it is this one:
In telecommunication, an eye pattern, also ...
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1answer
23 views
Help in designing filter for DUC (Digital Up-Converter) and DDC (Digital Down-Converter) using the built-in DUC and DDC blocks in MATLAB Simulink
Can anyone please help me in simulating a simple BPSK transceiver system that correctly receives a signal through a DUC and DDC? I have attached the screenshot of my Simulink system along with ...
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2answers
28 views
bandwidth between the signal and the channel
I have a signal with a bandwidth $B=4$ kHz and the bandwitdh is between $6$ kHz and $10$ kHz. I want to transmit this signal in a channel with bandwidth $B'=4$ kHz but for the channel the bandwidth is ...
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3answers
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I can't wrap my mind around the concept of filtering and the unit circle ? any help?
Can someone elaborate this theory where there is a link between the stability of a filter and the zeros or nulls being on the unit circle?
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How to compute the DFE based MMSE equalizer FF and FB coefficients in a non adaptative way?
I seek your assistance,
I am reading the Proakis 5th edition and I came across a paragraph explaining the tuning of DFE filters, i.e, how to compute the FF(FeedForward) and FB (Feedback Filter) ...
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1answer
36 views
WiFi Channelization for 40, 80 and 160 MHz
I have some questions on WiFi channelization in 802.11n and 802.11ac. Here is the snip of List of WiFi channels (source: WiKi):
I am working on the L1 layer for 802.11n and 802.11ac model where I am ...
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1answer
71 views
Timing recovery lock in receiver
I have done my receiver design with QPSK modulation. I am trying to communication between two systems at L band. My data rate is 1 Mbps. As my data rate is high I have allocated 64 bit for timing ...
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3answers
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Blind Carrier Synchronization
From my reading, I see that there are two ways people usually do carrier synchronization:
Decision directed, where the transmitted symbols are unknown are the receiver, decisions are made, and then ...
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1answer
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Interference Distribution Assumption in NOMA IoT Scenario
I am assuming a NOMA IoT Uplink scenario, which is interference marred. I have to ascertain the SINR at the Access Point (AP) for the NOMA users. A sub-channel is allocated to various users and ...
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Can anyone tell what is the general BER obtained when using a DUC and a DDC in the system?
I am trying to build a wideband frequency hopping OFDM system on Simulink and later on hardware. My OFDM system, along with subcarrier interleaving works fine otherwise. The problem arises when I ...
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Code implementation of Channel estimation based DFE Equalizer in matlab (or octave) without the the signal processing tool box
I want to implement a DFE in matlab without the signal processing toolbox:
I have two filters ( FeedForward and FeedBack) with taps length equal to 15.
I know the update equation of the LMS ...
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16 views
Relation between Gaussian and bi-Gaussian distribution
A Gaussian Doppler Spectrum can be seen as a bi-Gaussian Doppler spectrum in wich only one Gaussian function is present ( the second having a zero power gain) ?
any help will be really appreciated
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HF ionospheric Channel Model Example in matlab : Watterson model
In the example file in matlab HFIonosphericChannelModelExample.m, the watterson model is simulated. In this model the channel is represented as one tap (for the sake of simplification) delay channel.
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1answer
22 views
Can someone explain me what is the doppler spectrum?
I have a signal generated in matlab, with Rayleigh Fading, how can I add a given type of Doppler spectrum ( Gaussian for instance) to that signal ?
Any help will be really appreciated
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timing recovery resampler filter
I will explain the system:
i am trying to transfer data from tx node to rx at UHF band on 400 MHz. I am trying first only wired
transfer then i will try wireless.i am assuming only gaussian noise. My ...
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1answer
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MMSE- Channel estimated based - DFE Equalization
For HF ionospheric channels ( frequency range 3 up to 30 MHz), I Want to make channel equalization in time domain, using MMSE criterion. I have to do it using the channel estimation.
I have some ...
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Reinforcement Learning based signal processing
Has anyone tried using RL for classic signal processing tasks like beamforming etc? Or even things like frequency synchronization, etc?
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Why we have to multiply the images with $(-1)^{x+y}$ to center the transform in frequency domain filtering?
To perform the filtering infrequency domain we perform multiplication of $(-1)^{x+y}$ why??
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1answer
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why does DFE feedback filter matters?
I recently came across an article on the inventor of adaptative equalizer Robert Lucky, In this article : An Oral History by Robert Lucky (http://www.ieeeghn.org/wiki/index.php/Oral-History:...
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How to determine a number of taps in channel
I need to determine the number of taps of a channel. I have the channel simulated via channel simulator. My task is to try to estimate the channel by using pilots position. How the channel was ...
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to choose the right preamble in the rx
What is the criteria to choose the preamble in the receiver. Is it good to have many transitions in both I and Q so that i can get faster timing lock? if there are less transitions probably my timing ...
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1answer
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Two-GSMK channels demodulation: 3dB difference in BER
I am trying to demodulate individually two GSMK channels separeted by 50kHz (one channel = 25kHz).
I am working on a limited ressources hardware so I decided to make some optimization on the signal ...
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125 views
Early-Late Symbol Synchronizer on Non-Triangular Pulses
I've been studying the basics of digital communications using the free book at desktopsdr.com.
One of the examples is a 4-QAM demodulator which where symbol timing recovery is done with some Early-...
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1answer
38 views
RRC filter order
I have a question on rrc filter. Hope somebody can answer it.
Tx path:
My symbol rate is 1 mbps. I am using rrc 8x which becomes 8mpbs. For four symbols the order of the filter becomes 32. Next ...
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1answer
50 views
farrow resampler in timing recovery
My receiver contains: AGC,timing recovery,carrier recovey blocks.
I am using gardner timing recovery with loop filter and farrow parabolic filter.
The input to the farrow filter is the fractional ...
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Designing a PI filter for a Costas Loop
I am currently trying to implement a Costas Loop in order to demodulate a BPSK signal. Here is the reference block diagram I have been using to design the loop:Costas Loop Block Diagram
I originally ...
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1answer
27 views
Channel impulse response in freqency domain
I have a doubt about DFT matrix and channel impulse response.
Let $h$ is a channel impulse response , $F$ is a DFT matrix. IF I take a product. I got:
$$ F* h=\tilde{h}$$
$\tilde{h}$ is a frequency ...
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1answer
48 views
processing gain in the receiver
I am always confused about the processing gain in the receiver.
assume my receiver had LNA-> mixer->filter->ADC.
does the filter in the analog section has any role to play with the processing gain?
...
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47 views
MIMO multipath delay [duplicate]
How is multi-path delay dealt with in MIMO systems? Most of the theory I have read on MIMO doesn't address multipath delay and assumes the multipath interference is limited to secondary antenna ...
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Rayleigh multipath fading channel in Matlab
I have to calculate eigen values of covariance matrix of Rayleigh multipath fading channel. The exact value should depends on delay spread and subcarrier spacing.
I am able to find eigen values but ...
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1answer
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Getting hilbert transform of IQ signal
Im new to communications so this may be a stupid question, but I am somewhat confused. I am trying to train an automatic modulation classification (AMC) algorithm on IQ data from the RadioML dataset. ...
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1answer
58 views
What exactly is transmit power in wireless communication?
My background is computer science. Recently, I had to come across some concepts in wireless communication/cellular mobile communication. Despite having gone through many materials, I am still having a ...
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1answer
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phase response of an analog filter
I am trying to understand the relation between phase response of an analog filter and its influence on the quality of a signal with PSK modulation.
For example I want to design a BPF for HF ...
