Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

1
vote
1answer
16 views

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 ...
1
vote
3answers
38 views

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 ...
0
votes
0answers
17 views

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 ...
0
votes
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 ...
0
votes
0answers
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)...
1
vote
1answer
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 ...
0
votes
0answers
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 ...
0
votes
1answer
20 views

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 ...
0
votes
1answer
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) ...
1
vote
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 ...
-1
votes
0answers
16 views

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?
2
votes
1answer
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/...
0
votes
2answers
28 views

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{...
0
votes
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 ...
2
votes
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 ...
0
votes
0answers
19 views

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, ...
1
vote
1answer
44 views

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 ...
0
votes
0answers
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 ...
0
votes
0answers
13 views

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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
0answers
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, ...
0
votes
0answers
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 ...
0
votes
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....
0
votes
0answers
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 ...
2
votes
1answer
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 ...
0
votes
0answers
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 ...
0
votes
0answers
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 $3B'=B$? ...
1
vote
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
1answer
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 ...
0
votes
0answers
12 views

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 ...
0
votes
0answers
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}\...
0
votes
0answers
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 ...
1
vote
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 ...
0
votes
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 ...
0
votes
0answers
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 ...
2
votes
1answer
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"??
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
0answers
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 ...
0
votes
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. ...
1
vote
1answer
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 ...
5
votes
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 (...
0
votes
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 ...
0
votes
0answers
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, ...
2
votes
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 ...