Questions tagged [spread-spectrum]

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3answers
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What exactly happens with Spread Spectrum Modulation

With regard to DSSS and CDMA(DS), what does it mean to spread a signal over a spectrum of frequencies in terms of individual frequencies? Is it about sending the same signal redundantly on multiple ...
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3answers
298 views

How to reconcile “bandwidth” in the Shannon-Hartley Theorem with a spread-spectrum principle

I'm trying to understand something about channel "bandwidth" $B$ in the Shannon-Hartley Theorem: $$C = B \log_2 \left( 1 + \dfrac{S}{N} \right) $$ Suppose I have a bitstream encoded as a signal that ...
4
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1answer
2k views

Why are Gold codes and Kasami codes used instead of pure m-sequences?

I'm trying to understand why Gold codes and Kasami codes are used instead of pure m-sequences, in direct-sequence spread-spectrum (DSSS) communication systems, to prevent interference between multiple ...
4
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1answer
3k views

Conversion between Eb/N0 and SNR in spread-spectrum modulation like LoRa CSS?

This question is somewhat related to the one asked here: How is multiplexing achieved in spread-spectrum modulations like CSS? I am looking at the bit error rate (BER) performance of communication ...
3
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1answer
84 views

Is there any Spread Spectrum system that uses Rake with cyclic Prefix?

My question is that could the use of cyclic prefix can enhance the performance of Rake receiver ? I find this proposal here CP for DSSS Rake Receiver that seems correct. Without CP, ISI emerges and ...
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3answers
97 views

Is there an asymmetric crypto analog to direct sequence spread spectrum?

In section 12.1.1.2 of Digital Communications: Fundamentals and Applications, Bernard Sklar makes this claim about spread spectrum signals: Therefore, not only can the spread-spectrum signal be ...
2
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1answer
428 views

Minimum Output Samples needed to crack a “Gold Code” Generator (Dual LFSR)

Please preface your answer with spoiler notation by typing the following two characters first ">!" Below is an implementation of a "Gold Code" Generator formed by adding (in $GF(2)$) the outputs from ...
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2answers
551 views

How is multiplexing achieved in spread-spectrum modulations like CSS?

I understand why it doesn't interfere with narrowband communication systems but how do different clients communicate in a system like LoRa. Is it time orthogonality like TDM?
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1answer
417 views

Can i use frequency hopping spread spectrum technique for audio steganography?

I have been trying to use spread spectrum technique for audio steganography. I read a lot about it.But i didn't find any information about the steganography scheme using FHSS(frequency hopping spread ...
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2answers
88 views

Use of pseudo-random binary sequence (Gold, Kasami, etc.) in frequency hopped code-division multiple access (FH/CDMA)

I have a clear idea of how a PN-sequence is used in a Direct Sequence Code-Division Multiple Access(DS-CDMA) system with BPSK. In such a system, a different pn-sequence is assigned to each user and ...
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1answer
35 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 ...
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2answers
46 views

What is the duration of the spreading sequence

I have a question regarding the spreading sequence duration using Walsh matrix. I've read a paper related to that, they consider the signal $S = R(S) + I(S)$, where $R(S), I(S)$ are the real and ...
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1answer
124 views

Frequency Hopping Spread Spectrum Synchronization Methods

Frequency-hopping spread spectrum waveforms change the carrier frequency at some interval. I can see if the frequency is constant for the duration of an entire packet, the pilot symbols could be used ...
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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 ...
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0answers
142 views

What kind of signal modulation is more resistant to jamming?

I've understood that spread-spectrum type of modulations are more resistant to narrow band jamming, for obvious reasons. What is less obvious is why someone would try to jam for example a cellular ...
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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 ...
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2answers
71 views

About using Walsh matrix as spreading sequence

I'm asking about some details about using the Walsh matrix as spreading sequence code. For example, suppose I'm using a $4\times 4$ Walsh matrix given by $$H = \begin{pmatrix} 1 & 1 & 1 & ...
0
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1answer
491 views

Simulate capture effect in Matlab with LoRa modulation

I have a Matlab code to generate a LoRa signal modulation and demodulation. Now I would like to simulate a capture effect with 2 signals of slighly different powers. I need some help on how to proceed ...
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1answer
29 views

How can I spread a modulated signal over walsh code

I need to confirm if spreading signal by using walsh code in MATLAB is right or no, Suppose I'm using QAM modulation, so I need to spread the signal over walsh code, is the below step is right: <...
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2answers
36 views

Rate in CDMA setup

I am working on a CDMA system with only 4 chips/symbol. I want to use $R=\frac{1}{2}log_2(1+SNR)$ chips/channel use to calculate what $SNR$ I require to successfully receive a given transmission. In ...
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1answer
399 views

How does the PSK demodulator differentiates one carrier from the other in CDMA

I'm trying to understand the way in which CDMA works. Once the transmitter bit sequence is spread it is modulated for instance using a PSK modulator. Lets assume BPSK is used. I'm particularly ...
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1answer
321 views

Time and frequency domain spreading in CDMA and MC-CDMA?

For time domain CDMA transmitter, how the spreading sequences should look like? Is it necessary to be from $\{ -1,+1\}$ like PN sequences ? How will the codes be in frequency domain? I am confused in ...
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2answers
35 views

How are CDMA codes distributed?

I think this question is so trivial that it's nowhere explained (I would not find it) and the answer is probably trivial too. But I still wonder how codes in a typical CDMA system are distributed? ...
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0answers
29 views

Spread Spectrum (CDMA) signal phase noise measurement

A CDMA signal is considered for this application. I would like to have an information on the generated signal oscillator's quality using a phase noise measure. If the signal was a pure carrier, it ...
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0answers
343 views

How to Extract frequency bands from Short-time Fourier Transform?

I am reproducing the results reported by the author in a research paper. In which he takes the STFT of EEG signals. The input data has a shape of (1 X500) and I used Scipy library built-in function to ...
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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 ...
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1answer
55 views

Spreading sequence and equalization based on a paper

I am having difficulty in understanding how the Authors in this paper, An EM based method for semi blind identification of linear systems driven by Chaotic signals have used the expressions derived ...
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1answer
27 views

What's the effect of spread spectrum on frequency- selective channel

In brief, we consider the channel as frequency-selective channel if the frequency of the signal is larger than then frequency of channel. So, does using the spreading spectrum change the frequency-...
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1answer
46 views

How to solve signal MFSK or FHSS question (received signal+ noise+jamming)

I'm trying to solve the following: \begin{equation} A \cos(2\pi f t + \theta_1) + B \cos(2\pi f t + \theta_2) = D\cos(?f?\theta) \end{equation} I just need to know the correct value of D, the value ...
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1answer
250 views

Recovering DSSS signal from below noise Floor

I want to understand what actually happens in the direct sequence spread spectrum demodulator ? Why is it said that the signal is recovered from below the noise floor ? Can someone please explain the ...