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.

Filter by
Sorted by
Tagged with
1
vote
1answer
53 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
76 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
103 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
66 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
103 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
22 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
36 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
43 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
79 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
30 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
35 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
113 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
28 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
35 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
24 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
167 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
189 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
37 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
593 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
130 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
18 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
31 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 ...
3
votes
0answers
176 views

GNU Radio | Transceiver loopback adapted | Transmission stops unexpectedly

(This is a follow up question to a previous question: link) I have implemented a flowgraph of a transceiver loopback inspired by the examples found at ...
0
votes
1answer
56 views

Time frequency analysis for a spreading signal

I am a beginner in digital communications: I am studying the spread spectrum communication and I have a question on the spreading signals. For example I have 2 spreading signals and I do a time ...
0
votes
1answer
43 views

Why can the :$\mathbf W^*_{MMSE} $ be written as $E[\mathbf s \mathbf y^*]E[\mathbf y \mathbf y^*]^{-1}$

I read this paper: https://arxiv.org/pdf/1305.2460.pdf And there is a formula about MMSE:$\mathbf W^*_{MMSE}= E[\mathbf s \mathbf y^*]E[\mathbf y \mathbf y^*]^{-1}$ $\mathbf W _{BB}$:Baseband ...
1
vote
1answer
78 views

Carrier frequency of chirp signal

I am computing the link budget for a communication-radar (CoRadar) system. The formula for maximum distance, in communication, is: $d_{max} = \sqrt{\frac{P_t}{\tau}\frac{G_t G_{r, comm} \lambda^2}{(4\...
0
votes
0answers
26 views

phase shift for a spreading signal

For a chirp spread spectrum with $2$ users, I can use an up-chirp and down-chirp for the spreading signals. This is my questions: 1) These $2$ signals have a phase shift. If my $2$ users are at ...
0
votes
0answers
11 views

Why can the C5 formula also means that $\sum\limits_{k=1}^{K}tr(\mathbf F_{K4E})>P_T$?

In this paper:https://arxiv.org/pdf/1805.08898.pdf I can understand why C4 means $P_E > P^*$,I just need to times $1-\rho_k$ in both two side,the C4 will become $(1-\rho_k)[\sum\limits_{k=1}^{K}\...
0
votes
0answers
21 views

Can the j be equal to k in the first formula ?In MISO system

In this system model,the received signal available for RF EH at each RX_k is given by However,its SINR formula is given by We can find that author said the j can't be equal to k,but their range are ...
0
votes
1answer
80 views

What are the limitations of using Magnetic induction rather than acoustic communication in underwater communication

In underwater environment, Why acoustic underwater communications are still famous more than magnetic induction communication however in magnetic induction underwater communication, higher data rate ...
0
votes
1answer
65 views

DSSS direct sequence spread spectrum - encoding each raw data bit (question)

For implementing DSSS, it is understood that each raw data bit needs to be encoded as a new recognizeable/identifiable bit pattern. In many literature involving DSSS, there is mention of using PN ...
0
votes
0answers
12 views

What is the unit of a complex AWGN variance? mW or W?

In this paper https://arxiv.org/pdf/1805.08898.pdf ,there is a variance be written as $\sigma^2_{h,k}=\theta d_k^{- \alpha}$, $\sigma^2_{h,k}$ is the variance of th channel,$d_k$ is the distance ...
0
votes
2answers
209 views

From IQ to pi/4 DQPSK

I need to decode $\frac\pi4$-DQPSK packets from an SDR, preferably in C#. I have the SDR receiver part done. Now I'm trying to learn how to take the IQ stream and get the packet info from it. I've ...
0
votes
0answers
58 views

5G NR base matrix

The 5G NR specs for channel code are found here: https://www.etsi.org/deliver/etsi_ts/138200_138299/138212/15.02.00_60/ts_138212v150200p.pdf Starting on page 21 there is base matrix for the LDPC code ...
-1
votes
1answer
38 views

Spatial diversity: symbol error probability, upper bound

I am trying to understand the calculation upper bound that is given in book. Edit 1: I added 3,44 Can someone explain to me how to come from (5.5) to (5.7) ?
0
votes
0answers
130 views

Working principal of MIMO(2 by 2)-OFDM (802.11n)

I have gained basic knowledge on MIMO-OFDM from online sources and in process of building 802.11n standard in GnuRadio+USRP B210. My goal is to analyze the channel state information and play with it ...
0
votes
1answer
39 views

Using Spreading spectral with Maximal likelihood

As asked here, HERE if we have the signal x = [0.7 + 0.7i; 0.7 - 0.7i; -0.7 + 0.7i; -0.7 -0.7i]; Which was spread over code ...
0
votes
1answer
164 views

Channel model: LOS Component and Rician K-factor

I am asking about Rician K- Factor in this model: I know that if $K=0$ then it is a pure Rayleigh fading, if $K= \infty$, then non fading Channel. What is it, if $0<K<\infty$ ? If i represet ...
0
votes
0answers
31 views

Training Fractionally Spaced Channel Estimator and Equalizer

If you are attempting least squares channel estimation with a fractionally spaced channel estimator, do you want the training sequence to also be fractionally spaced or symbol spaced? It looks like ...
0
votes
1answer
48 views

Channel estimation

In single-carrier systems, at the receiver, when we need to do channel estimation and equalization? Do we need to do before timing synchronization and CFO correction or before it? And, please let me ...
0
votes
0answers
60 views

Determining signal using Optimal receiver(Matched filter)

I'm given a signal that has been passed through a noisy channel using binary polar signaling with a pulse value of p(t) = 1. The receiver is coherent and the length of each pulse (in samples) is 10 ...
0
votes
1answer
50 views

chirp spread spectrum with 2 users

I am a beginner in digatal communications. I have 2 users and I want use a chirp spread spectrum. Can we take an up-chirp and a down-chirp as spreading signals for the 2 users? and if yes, why? The ...
0
votes
1answer
17 views

operations valid for predicting new codewords for a Linear block code having linear encoder mapping

I want to know which operations are valid for predicting/finding a new codeword from a set of known codewords for a linear block code having linear encoder mapping, for eg.: Consider a linear ...
0
votes
1answer
78 views

Using MIMO with DS-CDMA and spread spectrum

I have a question about using MIMO with DS-CDMA. suppose we are using 4 TX antennas, and 4 RX antennas, then the Reyleigh ...
0
votes
2answers
297 views

Understanding FFT size in OFDM modulation

I know that the FFT size is the the number of subcarriers OFDM system have. But I also know that the FFT has to be $ 2^N $ big (in order to process N samples from time domain to frequency domain). ...
0
votes
0answers
32 views

bandwidth for a chirp

Let $s(t)$ an up-chirp with bandwidth $B$ and $y(t)$ an down-chirp with the same bandwidth. For a multi user chirp spread spectrum (2 users), I use the up-chirp and down-chirp as spreading signal. The ...
0
votes
0answers
62 views

OFDM system with cyclic prefix

I have: Bit rate $ R_b = 25.6 [Mbit/s]$ Sampling frequency at the input of the receiver: $ f_p = 8 [MHz]$ Protective spacing between successive OFDM symbols: $ τ = 16 [µs] $ The combined length of ...
4
votes
0answers
47 views

orthogonal family and pulse shaping filter

I am a beginner in digital communications and I have a question on the pulse shaping filter. For example, I have an orthogonal family $ \{s_1,...,s_N \}$. Can we preserve the orthogonality with a ...
0
votes
1answer
66 views

QAM constellation coder - transmitting a file

The file with size 6 MB is transmitted in 100 seconds using a constellation coder QAM with a constellation of 6 bit/symbol $ { M = 10^6, B = 8} $ Tasks: 1. What is the signal bandwidth if the band ...
2
votes
2answers
141 views

upsampling in the frequency domain

I have the Fourier transform $S(\nu)$. If I oversample by a factor $R$ in the frequency domain. Does the duration of the signal $s(t)=IFFT(S(\nu))$ change?