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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1answer
36 views

Error probability for orthogonal signaling with unequal symbol probabilities

I'm trying to derive the equation of error probability in orthogonal signaling. Here what I've tried: Let $\vec{s_1} = (\sqrt{E_b} , 0)$ and $\vec{s_2} = (0, \sqrt{E_b} )$ be vector representation of $...
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1answer
39 views

Can Oversampling help to mitigate the effect of additive white gaussian noise?

Oversampling the signal at the receiver's ADC is a common technique to improve the ADC's resolution, dynamic range and to improve the signal to noise ratio (SNR) due to ADC quantizaiton noise, thermal ...
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1answer
31 views

How to perform a phase recovery for higher order modulation schemes

My objective is to demodulate the signals with different modulation orders and schemes. In particular, I want to recover the phase first. Let us say, my signal looks like in the constellation below . ...
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2answers
50 views

Application of MAP criteria

This question has been asked in GATE 2019. I am unable to understand how MAP criteria is "applied" here. I've read about MAP but I'm unable to get how they're solving it by graphical method. ...
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0answers
17 views

How to solve this question on communication lines?

The Question asked is as follows: A communication link operates at a bitrate of 20 Mbps. The receiver is expected to perform at a $BER$ of $10^{-6}$ or better using $QPSK$ modulation scheme. [Note: $...
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1answer
34 views

Why does my zoom audio, when there are nearby microphones, seem to usually take an open loop format?

The signal from the speaker on device A gets into the microphone from device B, then the amplifier and then the speaker from device B, back into device A. The result is a sort of runaway signal that ...
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1answer
86 views

QPSK demodulation

My objective is to demodulate QPSK signal. At this moment, my constellation in the best case looks like in the picture below: and the corresponding eye-pattern: Eyes are completely closed, which ...
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0answers
20 views

In OFDM, does the parameter time offset is important if there is only one mobile in the cell?

I am learning about OFDM, and in my reading, I have noticed that (mentioned everywhere) synchronization is a very critical aspect of OFDM. Here, I am writing in the context of time synchronization (...
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1answer
30 views

The order of processing the prerecorded samples (DC removal, Hilbert transform, frequency shifting)

I have a samples prerecorded by a radio device. Samples are not in baseband, contain large DC component and include only one channel (written in int32 format). My goal is to move it to the baseband, ...
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1answer
32 views

For Direct-Sequence Spread Spectrum, can we reduce the transmit power of the signal to maintain a fixed BER?

How to reduce the transmit power of the signal to maintain a fixed BER in CDMA ? I am thinking noise power spectral density, signal energy , and signal rate.
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2answers
276 views

Geometric representation of a signal using basis functions

I'm trying to solve the following problem where I need to express $x(t)$ in terms of the given $φ_i(t)$ functions. (It is proven that the $φ_i(t)$ functions are orthonormal).: Here's what I tried: In ...
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4answers
107 views

Why is phase range between $-\pi$ and $+\pi$ (instead of $0$ and $2\pi$)?

I wonder why the phase range in DSP applications is between $-\pi$ and $+\pi$. For example, why is that not between $0$ and $2\pi$? This question popped when I was reading about synchronization in ...
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1answer
41 views

Decision directed TED (timing error detector). What does it mean?

I am reading about symbol rate recovery and there is a term that I didn't grasp - 'decision directed' TED. Can somebody explain what does it mean or provide me with accurate reading? Thanks
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1answer
43 views

DC removal from IQ samples

I am wondering what is the proper way to remove DC component from PSK modulated signals. Should I calculate mean value for I and Q channel separately and correct then samples in each of the channel or ...
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1answer
37 views

guidance for designing a pilot signal

Introduction I wish to design a pilot signal which will be used to estimate the channel, and will be sent prior to data, on a wireless acoustic link (underwater acoustic communication). I've been ...
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1answer
47 views

Digital demodulator (SDR) for receiving legacy analog modulated wave

I understand that in SDR, after the ADC the signal processing is fundamentally based on I/Q modulated waves where any discrete value that can be transmitted corresponds to a symbol which is ...
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0answers
93 views

Soft-output decoder

I am trying to implement the soft-output for my soft-decoder, however, the resulting log-likelihood ratios are not corresponding to the corrected hard bits. The soft-output regards the LLR-values for ...
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0answers
18 views

Unstable Phase in Channel Impulse Response

I'm using DW1000 UWB radio transceiver and extract its channel impulse response (CIR). The CIR output by the transceiver is the complex baseband CIR. In a static environment, the CIR is a LTI filter ...
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2answers
79 views

FFT- based frequency offset estimation algorithm

I am trying to understand and implement FFT based recovery algorithm suggested me in the post and it was also discussed here Let assume rx_signal -signal at the ...
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0answers
26 views

Intersymbol Interference calculation

$p(t) = \frac{1}{\pi\sqrt{2B}(1-64B^2\rho^2t^2)} \ \Big\{ 8B\rho\cos\left(2{\pi}B\left(1+\rho\right)t\right )+ \frac{\sin\left(2{\pi}B\left(1-\rho\right)t\right)}{t} \Big\} $ Given a Square Root ...
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1answer
85 views

PLL: cycle slipping correction

i am working on a receiver in the space communication. Under low SNR, big frequency offset, phase offset. I started with phase/frequency correction. I used digital PLL and it doesn't work for it. I ...
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1answer
37 views

Difference ;Phase and frequency offset

can someone explain what a difference is between phase and frequency shift/offset in estimation algorithm? Honestly I dont understand this difference. If i estimate , i will do it for phase estimation....
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3answers
61 views

Using large DFT for OFDM to avoid the guard interval

In OFDM, we usually insert the guard interval to avoid the inter-symbol interference at the expense of achieved data rate. that guard interval can be either zeros or CP guard interval, which it must ...
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1answer
22 views

Find symbol duration from symbol rate

How can one find symbol duration if bit rate is 100 kbs (as BPSK is used, symbol rate = bit rate)?
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1answer
32 views

Question on PCM Sampling and Quantization order

I had a doubt in my mind regarding the orders of sampling and quantization in PCM. What is the impact if the order is reversed, that is, the continuous time signal is first quantized and then sampled? ...
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1answer
74 views

What is the advantage of using a Stepped Frequency waveform over FMCW?

What is the advantage of using a Stepped Frequency Waveform instead of a traditional linear FMCW ?
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2answers
79 views

clock + phase recovery

I am working on the implementation phase and time recovery algorithm and have doubts. Could you please explain to me some question? PLL for time and phase recovery I have found I can use PLL not ...
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1answer
42 views

Finding optimal decision threshold for binary comm system

I'm trying to solve the following exercise: Given a system that transmits bit $b$ with probability $p_b$ and $-b$ with $p_{-b}$ and the transmission is degraded by AWGN $N(0,\sigma^2)$. What is the ...
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1answer
103 views

Phase correction algorithm: minimisation phase error

Thank you for your participation in my discussion in advance. I am working on the implementation of a phase correction. Currently, I have finished the algorithm. I think it is a standard algorithm ...
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1answer
36 views

How to simulate a continuous signal passing through a capacitor (simple coupling capacitor)

the differential equation for the current flowing through a serial capacitor (see for example https://www.allaboutcircuits.com/textbook/direct-current/chpt-13/capacitors-and-calculus/) indicates that ...
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3answers
56 views

Role of windowing in implementing FIR filters using Fast Convolution

In Fast Convolution the filtering is performed by taking FFT of both the signal and impulse response and multiplication in frequency domain using Overlap add/Overlap save method for processing ...
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1answer
20 views

Analysis Received Signal at receiver side

I'm trying to understand something which is really confusing me and I made my best to understand it but still confused. If I have transmitted and receiver. Assume I want to transmit S(t) data and ...
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1answer
43 views

Using DFT Rotation for Frequency Down-Mixing

Is it possible to perform Frequency Down-Mixing (sometimes referred to as Down-Conversion) by simply rotating the DFT sequence? If so what are the Advantages and Disadvantages of this method?
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How is CFi related to Code Rate and link Quality of the lte network?

Im trying to understand the relation between CFi and Code Rate and Quality of the network? like if I have bad quality then we need to decrease CFi? what about Code Rate we need to increase? About ...
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1answer
63 views

Maximum NCO frequency and filter design for down-conversion of complex input signal

I am trying to perform digital down conversion by using the DDC from Matlab dsp toolbox. My question is that the bandwidth property is limited to Fs/2 and the filters created are real filters. If the ...
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0answers
58 views

What are considered key EM signal measurements to help identify unique emissions?

I plan to conduct an EM study which hopes to identify unique signals emitted from a device. While in acoustic signals, features which can be extracted include the likes of spectral centroids, etc. ...
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1answer
60 views

Design a timing recovery algorithm with predefined samples with max amplitude

I need your help in understanding how to simulate a timing recovery algorithm. I have already read a lot of literature and posted here the question but I have still doubts how it works. Let me briefly ...
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0answers
21 views

Beamforming and AoA with a small number of elements

So I have an antennae array with only three elements. I want to know what kind of beamforming and AoA estimation I can do with such a small number of elements. I understand that there are lots of ...
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1answer
65 views

Implementation of Overlap Save Filtering with Decimation

I am trying to implement Matlab code which performs FIR filtering with complex bandpass filter using Overlap Save method and perform decimation as well by using different length forward and inverse ...
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1answer
42 views

Time domain representation of a modulated signal when symbol rate >> carrier frequency?

I need to understand the relationship between carrier vs. bits with PSK modulation, and what the signal in the time domain would look like if my symbol rate is far greater than my carrier frequency. ...
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1answer
46 views

Discussion of simulation results of a signal sequence: amplitude

I need your help in understanding if the simulation result is correct. I have simulated a random BPSK sequence that was upsampled and filtered with a raised cosine filter. The length of the filter is ...
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2answers
135 views

CORDIC, What is it?

I am reading about CORDIC (Coordinate Rotation Digital Computer) and I have t implement it. Honestly, I am reading and don't understand the difference between phase detection algorithm ( PLL, Costas ...
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1answer
28 views

Can the DFT can be performed without normalization?

If we have OFDM system with $N$ sub-carriers, the DFT matrix can be expressed as follows: $F = dfmtx(N)/sqrt(N)$ My question, is it possible and practical to use the matrix without Normalization, it ...
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0answers
20 views

understanding the result of the simulation of In-phase and quadrature part BPSK signal

I am a student and working on a hardware implementation of a transceiver and going to check an algorithm of time recovery that includes symbol synchronization and sampling clock synchronization. The ...
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1answer
56 views

Why Does ASK Modulation Create Fourier Sidebands?

I know why analog amplitude modulation has side bands, it is related to (fc+fd) and (fc-fd). But what about DAM? ASK(DAM) is a type of digital modulation, and there are only two state: carrier signal ...
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0answers
25 views

Interference Diversity for management of inter-cell interference in cellular communications

What is interference diversity? and how is it different in CDMA and OFDM? I have a problem understanding the concept Reference book: Fundamentals of Wireless Communications, chapter3/4 Author: David ...
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2answers
55 views

Generate binary signal and convert to integer in Matlab

I am going to test an algorithm and need a test signals. My first test signal is a binary signal of 1 or -1. I was thinking about how to implement such a sequence in matlab and wrote this: ...
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1answer
36 views

CDMA and Pulse Shapping

I am a little confused on CDMA and its interaction with the typical pulse shaping filter ex, raised root cosine. Is the RRC filter bandwidth selected to be consistent with the CDMA spreading/update ...
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0answers
28 views

OFDM symbols terminology explanation

I've already read and understand what does OFDM mean and what does it stand for and why we use it in our wireless technology today. My question that I didn't understand is what does it mean number of &...
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1answer
36 views

Does same data inserted to all antenna at beamforming?

I wonder do I understand beamforming right. Question 1 Does same data inserted to all antenna at beamforming? Like figure below? The only different is through different phase shift? If it is right how ...

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