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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Is it possible to spread signal using sum of more than one orthogonal code
I was wondering if we can spread the signal using more than one spreading code. Assume we have the Walsh code used to spread the transmitted signal, the Walsh code is, for example, gotten based on ...
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3answers
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Why only odd harmonics after non-linear amplification?
Why do I get only odd harmonics appearing? This not only happens at saturation of the transfer curve, but also in the linear portion of the curve.
I make a input signal that has too high power that ...
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What does the offloading and local computing do?
It only mention that the advantage of giving the bit to offloading and local computing at the same time in this paper: Joint Offloading and Computing Optimization in Wireless Powered Mobile-Edge ...
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2answers
45 views
Decoding .wav file to bit level data
I have been given the following waveform and asked to read the data and write to a buffer using Java. The .wav file has a sampling rate of 44100 Hz, 2 channel and 16-bit depth. From the waveform, I ...
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31 views
duration for a signal
I am a beginner in the signal processing and I have questions for the duration of a signal.
My system has a bandwidth $B$. I have a signal $s(t)$, the duration for this signal is $T$. The signal $s(t)...
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69 views
Calculating Data Rate using Bandwidth, Transmission Power, Noise Power Spectrum Density and Channel Gain
I'm a Software Engineering student researching on Load Balancing in IoT and I need to calculate data rate. However, I don't know how to use these values to attain data rate despite searching on the ...
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24 views
um between a random vector and a signal
I have a signal $f(t)$ with its duration is $T_f$. To have the discrete signal $f(n)$, I use a sampling frequency $f_s$. Consequently $L_f=T_f*f_s$. I have a random vector $v$ that has the same length ...
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frequency/phase offset estimation in satellite DOA beamforming applications
In satellite QPSK demodulation, we first estimate and remove the phase offset introduced by the channel. Then, we demodulate the baseband information bits (I & Q channels).
In satellite DOA ...
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17 views
Log Distance-Normal Shadow Model and Friis
Since I'm founding several but different results about this model, I would ask you if all it is OK with this formulas:
1) Friis Model --> $Pr_0 = Pt + Gt + Gr + 20\log_{10}\frac{\lambda}{4\pi d}$
2) ...
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2answers
35 views
Dimension of Matrix in MIMO with multi-path
In a MIMO system, the received signal is supposed to be $y = Hx + n$, where $H$ is the channel of dimension $N_t \times N_r$, $x$ is the transmitted signal with dimension of $N_t\times 1$ , and $n$ is ...
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what is considered as low data rate and high data rate in wireless communication?
With the current advanced wireless communication. Is data rate around 10 Mbps considered high data rate nowadays?
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80 views
When Two Sampled Sinusoidal Are Orthogonal?
If two analog sinusoidal are orthogonal with duration T, their minimum frequency difference should be 1/2T in case of no phase offset between them.
And if there is phase offset, the difference is 1/...
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Frequency Domain Correction of Frequency Offset or Doppler Frequency in LTE
We are working on LTE Uplink CFO Correction for 3 MHz band. The time domain CFO correction is easy, which depends on the processing of 3840 samples step by step multiply by $\exp(-j 2\pi f_\text{...
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2answers
35 views
Does gray coding bring improvement to SER of QPSK, compared with natural coding?
I understand gray coding contributes to BER of QPSK, yet really don't understand why it brings improvement to SER. According to the relationship of SER and BER, it should be improved. Actually, when ...
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1answer
54 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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IT++ and Alternatives DSP Libraries
I want to implement some signal processing blocks in C++ so I did a bit of search on the available libraries for signal processing in C++ and I found that IT++ provides comprehensive set of functions, ...
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Offset QPSK detection in GNU Radio - Sample delay
An OQPSK detector is being tested in GNU Radio. The architecture was obtained from Michael Rice's Digital Communications - A discrete-time approach. The flowgraph is shown below.
The modulator ...
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21 views
Binary vs 4-PAM PSD
I'm struggling to understand how you would form an expression for the PSD of a 4-PAM signal which is using rectangular pulse shaping. I understand for binary the likelihood of +/1 is equal so the ...
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data rate cdma chirp
I combined a chirp with a CDMA and I would like to know how to find the data rate. To begin, I spread the datas with the chirp and after I spread the previous signal with the PN code.
My bandwidth is ...
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2answers
49 views
Why is bit error rate = symbol error rate / number of bits per symbol in QPSK
I saw a code computing the error probability of QPSK, and I found that in this code the bit error rate is computed as symbol error rate divided by $2$.
I think that $2$ is because the QPSK symbol ...
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1answer
10 views
Cellular communication uplink
I can see, from my apartment, a cell tower.
From what I have learned, in a time division duplex system the uplink and downlink communication are kept separate in time. Uplink from some time, then ...
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12 views
Average number of time slots until successful transmission in adaptive tree walking protocol
i was searching everywhere and couldn't find in any paper or book the average number of time slots until a successful transmission.
for simplicity sake, in a simple network as given in the picture, ...
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28 views
How is DJI OcuSync wireless link physical layer implemented?
I'm looking for documentation on the wireless command link of the DJI OcuSync. I found this website (in Chinese). It seems like an OFDM link that uses Alamouti codes?
I'm specifically interested in ...
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2answers
41 views
What is the difference between frame error rate (FER) and symbol error rate (SER)?
What is the difference between frame error rate (FER) and symbol error rate (SER)?
I know the difference between frame error rate (FER) and bit error rate (BER) from the website below
https://www....
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12 views
The theoretical formula of error probability and the data rate in MIMO,and the relation between $G^T$ and $G^R$ and $M$
I want to use Matlab to plot these two figures,fig(a) is the error probability,and as we can see,the higher M is,the lower error probability it has in the same SNR . The fig(b) is data rate,the higher ...
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65 views
FFT-based coarse carrier recovery for QPSK
An FFT-based coarse frequency acquisition block is being tested in GNU Radio. The algorithm used can be found on the GOES satellite user manual and is summarized in the figure below.
The algorithm ...
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16 views
waveform and multiuser communication
Sorry for my very simple question but I am a beginner in digital communication.
Why in a multiuser communication, we have to have the same waveforms for each user? Is this an important rule for ...
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25 views
bandwidth and multiuser communication
I assume $3$ users. In the CDMA, the signals after the spreading for the $3$ users have the same bandwidth $B$.
Is it possible to have $3$ spreading signals of the same band $B'$ such that $3B'=B$? ...
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1answer
45 views
Is it possible to use MRC with DS-CDMA-MIMO [closed]
I'm wondering how to use the Maximum Ratio Combining with MIMO-DS-CDMA, I have used the MIMO with DS-CDMA using Walsh code, then at receiver I couldn't recover the transmit signal using the MRC. here ...
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1answer
34 views
Continuous Phase Modulation
The wikipedia article on continuous-phase modulation states the following:
For instance, with QPSK the carrier instantaneously jumps from a sine to a cosine (i.e. a 90 degree phase shift) whenever ...
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1answer
51 views
ADC and Matched Filtering
A basic theorem in communications is the matched filter maximizes the SNR at sampling. I'm a little confused on how this relates to discrete time systems and sampling rate.
Normally if you sample at ...
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1answer
26 views
Are the error probability of orthogonal signal and on/off signal the same?
I have to write the error probability of orthogonal signal and on/off signal,and now i have finished the error probability of on/off signal,but i don't know how to write the code about error ...
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59 views
Why do we need to write the noise as randn(2,1)./sqrt(2*SNR) instead of randn(1,1)/sqrt(2)?
I saw this code, about the error probability of on/off signal ,on the internet
...
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Parity Check matrix from degree and check nodes polynoms, LDPC codes
I'm trying to simulate LDPC codes which were optimized for the BEC channel.
I generated the degree and check nodes polynomials according to chapter 3.15 in "Modern Coding Theory" by Richardson and ...
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12 views
Symmetric Capacity of a Binary Discrete Memoryless Channel
While reading this paper https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5075875, I found that the the symmetric capacity of BDMC $W$ is given by
$$I(W) = \sum_{y\in Y}\sum_{x\in X}\...
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29 views
PLL carrier recovery: intermediate versus baseband
When looking at carrier recovery, a PLL is often applied to correct the frequency offset between the local oscillator and the transmitter after down conversion.
I'm wondering what happens to the PLL ...
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1answer
65 views
Maximum likelihood estimation complexity computation
I have a basic question about maximum likelihood (ML) estimator and its implementation.
I am trying to simulate a communication system, while using ML at the receiver side to find the transmit ...
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1answer
20 views
Synchronization Accuracy Required For Communications
One of the biggest problems in phase modulated communication is discovering when your signal has arrived. High accuracy in this area is important, as even a quarter wavelength error can cause the ...
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29 views
data rate and PN code
I have a question about the spreading sequence for CDMA. Normally, we use a PN code but imagine that we use a cosine wave combined with a PN code where the PN code has for length $T * fs$. With $T$ is ...
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49 views
OQPSK vs QPSK envelope query
We use OQPSK because of envelope of signal but my question is
"In Phase Shift Keying(or QPSK) the amplitude of the transmitted signal is constant then how the envelope will change in OQPSK"??
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1answer
23 views
Identifying the correct source of packets
I have a basic question regarding digital communication , especially pertaining to wireless internet .
A packet is basically a stream of bits . And a bit is detected as zero or 1 depending on ...
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1answer
32 views
Possibility of using Power allocation with Maximum likelihood estimation
I have a basic question about maximum likelihood (ML) estimator and its implementation with power allocation.
Suppose we are using $MIMO$ system with $4$x$4$ transmit and receive antennas, so the ...
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1answer
22 views
What is Assymptotic Equipartition Property?
I am currently studying about Polar Codes in 5G standard and while reading my paper I found something called AEP which is required for channel coding. I surfed the web but didn't found a satisfying ...
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55 views
Why does power spectral density of OFDM signal changes with number of zero subcarriers
I am trying to plot the power spectral density (PSD) of an OFDM signal with $N_{dsc}$ subcarriers and $N_{zeros} = N_{fft}-N_{dsc}$ zero subcarriers.
I am using the matlab function pwelch() to plot ...
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1answer
36 views
BER vs Eb/N0 (db) Curve
So, I was trying to plot BER (Bit Error Rate) vs. Eb/No (in dB) curve using Python. Here is what I get,
Eb/N0 is in dB on the x-axis
But I know that this is not the correct graph.
Here is my code.
...
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28 views
confused in practical example of shift invariance?
I am reading book of w smith ,"The scientist and engineer guide to digital signal processing" 2 edition
I am trying to understand topic of shift invariance from theory given on pg 92
I have attached ...
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3answers
567 views
Compress a signal by storing signal diff instead of actual samples - is there such a thing?
I am working with EMG signals sampled at 2kHz and 16 bits, and noticed that they "look smooth", that is, the signals are differentiable, and if I apply a "diff" function (...
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1answer
61 views
Time delay estimation between two complex signals(IQ)
I need to time align two complex signals. The two signals obtained were at different RF frequency before digitisation. So,I have two complex signals(IQ) and I need to do delay estimation and apply ...
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9 views
guard interval calculation for multi-cell massive MIMO
I am interested in a multi-call massive-MIMO system modeled as in the works of T. Marzetta, for example:
"Inter-Cell Interference in Noncooperative TDD Large Scale Antenna Systems".
In these works, ...
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1answer
19 views
Beamforming back lobes question
When performing a conventional digital beamforming I see in some textbooks they show beam patterns as
where the arrival angle ranges between -90 to 90 degrees. But then other places show the full ...
