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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296 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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1answer
40 views

Coefficients of a Zero Forcing linear equalizer for infinite length input

Given a discrete-time white noise model: $$y_k = \sum_{i=0}^{\infty} \alpha^{-i}a_{k-i} + \eta_k$$ where $E(|a_k|^2)=2$, $|\alpha|>1$, $\eta_k$ are uncorrelated zero mean random variables with $E(|\...
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452 views

What is the relation between noise (AWGN) variance and number of antennas?

I'm working in two Matlab scripts trying to simulate a MIMO system using OFDM (downlink) and SC-FDE (uplink). My question is: for different numbers of transmit and receive antennas, what is the ...
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45 views

Degradation of BPSK system using matched filter with a timing error

Given a BPSK system with: \begin{align*} s_1(t) &= Au_T(t) \\ s_2(t) &= -Au_T(t) \\ \end{align*} where $u_T(t)=1$ for $0<t<T$, and zero otherwise. Given $A > 0$, and Gaussian white ...
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262 views

Nyquist criterion for zero ISI in the frequency domain

Can someone explain in simple words /graphs the necessary and sufficient Nyquist criterion for zero ISI in frequency domain, namely: The constant folded Fourier Transform.
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54 views

Does any paper use energy harvest to in the baseband?

Most of RF energy harvest system just harvest $\rho$ of the RF signal for charging the battery,and the other part RF energy will be processed to baseband signal by RF Chain to do the information ...
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1answer
35 views

tx and rx model supporting all data rates

i am trying to build complete tx and rx path which can support varies data rates. for example if my data rate have to support from 10 kbps to 1000 kbps. Can i keep the baseband processing fixed for ...
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1answer
78 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 ...
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43 views

Received Signal Strength Calculation for Probabilistic Line of Sight Channel

Scenario: Given a UAV which emits a beacon and the beacon is received by a node on the ground. The node calculates the received signal strength. Considering the channel is Probabilistic LoS, the ...
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1answer
30 views

Viterbi decoder K=3 using ADD-COMPARE-SELECT Operation

I am in trouble with Viterbi decoder for a while. I have some questions. I need to decode messages from a continuous stream which is encoded. I'm reading from book : digital communications bernard ...
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Why do we need DFT when we already have DTFT?

We already have DTFT so why do we need DFT? Please don't write DTFT is used for discrete, aperiodic signal which transfers in the frequency domain to periodic and continuous, but in DFT is discrete ...
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SNR measurement

I am using QPSK modulation for a BER of $10^{-6}$ at $\text{SNR}=E_b/N_0=10 \ \rm dB$. If my data rate is $5 \ \rm kbps$ then $$S/N_0 = 10\log_{10}(5000)+10 = 47\ \rm dB$$ And if my RF section has a ...
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153 views

BER Analysis of Dual hop Decode and Forward Relay

I want to perform fair BER analysis between Two-hop Decode and Forward relay communication (S-->R-->D) and Direct Transmission from S-->D. The links have Rayleigh fading. Now for fair analysis 1) ...
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2answers
72 views

Minimum Number of Errors required for BER Curves in Matlab Simulation

what should be minimum Number of Errors required for getting BER Curves in Matlab Simulation for different number of transmitted bits ?
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1answer
389 views

Frequency domain vs time domain equalization

It is said that a frequency domain equalizer is equivalent to an infinite length time domain equalizer, why is that? And if this is the case, why hasn't frequency domain equalization been used ...
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1answer
120 views

Dimension of channel matrix elements in MIMO systems

In a MIMO system we have: $y= \mathbf{H} \star \mathbf{x} +n$ with $x \in \mathbb{C}^{N_t \times 1}$ ($N_t$ the number of transmission antennas) and $\star$ the convolution product. For the matrix, $\...
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How to detect the burst data?

At high SNR i am able to detect the burst by taking the magnitude of the data and setting the threshold. for low SNR it it difficult to set the threshold?
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1answer
2k views

MATLAB: Adding Noise with Regard to Signal to Noise Ratio (SNR) or EbNo?

A signal x takes values from an alphabet set. My objective is to estimate the channel parameters hest using adaptive methods and ...
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66 views

Blind STBC question

I am working on blind identification of the physical layer parameters of a particular protocol. Everything was going well until I got to the MIMO part. The system contains two transmitter antennas and ...
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1answer
52 views

16-APSK NDA Carrier Synchronization Problem

I'm working on a DVB-S2 Symbol Timing + Carrier Synchronizer with a focus on 16-APSK | 32-APSK modulation Scheme. I understand that the first section could be achieved using a Polyphase Clock Sync ...
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2answers
56 views

filtering my received Signal by LPF

I've received my transmitted signal that I sampled it on 20480000 frequency , transmitted frequency 868MHZ , bitrate 100KHZ , I see the "bits" that Im transmitting in my plot in matlab it ...
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1answer
40 views

Channel coder: Does encoder help? Input signal distortion:

I am studying the channel coding theory. The channel coder adds redundant information to the input signal, that helps a decoder to reconstruct the signal. BUT: Can encoder help to eliminate effects ...
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1answer
38 views

Matched filter for recieved RF digital packet by LPF

Im transmitting by cc1350 launchpad microprocessor digital RF Packets, transmitted modulation FSK. bit rate of transmitting is 50Kbouad, frequency of transmitting is 868MHZ . Im sampling the signal(...
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94 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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1answer
48 views

The meaning of correlating “Time Aligned” pseudo-random or walsh code sequences

Correlation is from a mathematical point of view a shift in time domain +multiplication + summation operation I thought that if 2 codes are "time aligned" then correlation reduces to a dot product ...
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1answer
98 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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234 views

Correlated phase noise and delay

2 identical signals generated by the same PLL/VCO should have the same phase noise profile and their respective phase noises should be correlated. Suppose one of them is delayed and I start sampling ...
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1answer
44 views

How many bps would be required to reproduce the words in speech recognizably?

In Robert Gallager's lecture notes for 6.450 Principles of Digital Communications I, Exercise 2.1 asks an interesting conceptual question: Voice waveforms could be converted to binary data by ...
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1answer
33 views

FSK modulation in baseband

In a $4$-FSK we have $$s_i(t)=\cos(2 \pi f_i t)=\cos(2 \pi (f_c+\alpha_i \Delta f)t)$$ with $\alpha_i=2i-5$, and $\Delta_f=\frac 1T$, where $T$ is the time symbol and $i \in [1,4]$. But with the ...
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1answer
42 views

continuous chain of ones or zeros for transmit

If my data has long chain of 1's or 0's. Can the data be modulated and transmitted as it is. Will this have any effect of the receiver adc as this may increase dc value of the signal or any other ...
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43 views

inversion of the sum

In the article Analysis of the Performance of a Non-Coherent Large Scale SIMO System Based on M-DPSK Under Rician Fading Fig.1: I would like to know if we could invert the block of the sum with the ...
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1answer
56 views

Bandwidth of a modulated signal in analog domain

If i am using QPSK modulation with data rate 4 Mbps with rolloff factor $0.5$, then the bandwidth will be symbol $\rm rate\times (1 + rolloff\ factor)$. So here it will be $\rm 2\ MHz\times 1.5 = 3\ ...
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172 views

Symbol Timing recovery for modulation producing ISI

I am interested in understanding why the common timing recovery algorithms function for modulation schemes which produce ISI. For example, suppose you are receiving at the output of a matched filter ...
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1answer
234 views

Why does signaling overhead for time synchronization scale up with the number of transmitter nodes in a multiple access system?

I was recently reading about random multiple access methods without time synchronisation (of the pure Aloha type). In this paper it is stated that, The need for transmitter synchronization is a ...
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22 views

how to do initialization of random vectors in matlab

I have to generate random vectors for $\mathbf{p}^{(0)}$, $\mathbf{u}_l^{(0)}$, and $\mathbf{v}_l^{(0)}$ for $l=1\ldots L$. Now I am confused about how to generate these vectors as $l=1\ldots L$ is ...
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1answer
66 views

Difference in information between IQ Sampling vs. Real Sampling at $2F_s$

As per my current understanding we use IQ sampling as way to increase the useful bandwidth to Fs rather than $F_s/2$ when viewing the FFT because the IQ sampling removes the negative frequencies and ...
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1answer
35 views

What is the advantage of multiple antenna in receiver in energy harvesting ?harvested more power?

What is the advantage of multiple antenna in receiver in energy harvesting ? Assume there are $3$ transmitted antennas in the A device,and $1$ received antenna in the B device,now assume A device use ...
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How to figure out the polynom of Convolutional encoder

I have Convolutional encoder with K=7, r=1/2 that steam of bits get enter to it from right to left (7 registers and steam of input is entering the convolutional encoder from left to right .. ) the ...
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1answer
29 views

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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1answer
23 views

pulse shaping filter and BER

For example, in a PSK modulation. I saw that to plot the BER curves as a function of the noise, we never took into account the pulse shaping filter. More precisely, the signal is not filtered by the ...
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1answer
131 views

Frequency synchronization in OFDM

Could you please help me understanding how the null sub-carriers can be used to estimate the carrier frequency offset and thus performing frequency Synchronization at the receiver?
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1answer
41 views

How to remove frequency offset with RRC as pulse shaping filter

I am working on a project with QPSK modulation format and a RRC filtering at the transmitter (TX) side. The channel introduces a constant dropper shift ($f_d$) to the received signal. To make the ...
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2answers
595 views

Inter Symbol Interference (ISI) / Equalization in Digital Signal Processing

I am studying the OFDM system and before to start I have decided to study the main concepts of modulation. And I have spent yet a lot of time to understand the concept of an equalization to reduce ISI....
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Why does carrier frequency offset (CFO) cause carrier phase error (CPE)?

I've already asked 2 questions on this but there is one discrepancy I cannot reconcile and is the crux of the problem: \begin{align} \newcommand{\prefix}{\frac1N\sum\limits_{n=0}^{N-1}} R_l &= \...
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1answer
23 views

How do we know the receiver delay in an OFDM transceiver system?

I was simulating a simple OFDM transceiver system without a channel (just the transmitter and the receiver directly connected). I saw that if I use the "Find Delay" block in Simulink between the ...
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96 views

Types of equalizers

I can't get my mind around the different types of equalizers and the difference between some of them. I've been looking at different books unsuccessfully. So far, I have Wikipedia's list and this ...
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23 views

Output of encoder RS-code: analyze the results

I found some simulation results of RS-encoder. In the description are written the following: “When the program implementation is run, the clock is set to high i.e. ‘1 ’ and reset is set to low i.e. ‘ ...
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1answer
31 views

channel impulse and frequency response: H?

The received signal of MIMO system is given as: $$ y= H \cdot x +n, (*)$$ where $H$ is a channel matrix. $h(\tau_l)$ is a channel impulse response. It is determined as a matrix $\in \mathbb{C}^{Nr \...
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1answer
118 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
83 views

Why is the received signal=information+RF signal+noise,not just information+noise?

In this paper: https://www.researchgate.net/publication/325008791_Beamforming_Design_for_Max-Min_Fair_SWIPT_in_Green_Cloud-RAN_with_Wireless_Fronthaul Here is its system model In this model,it said ...

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