10
votes
Accepted
Why are Gold codes and Kasami codes used instead of pure m-sequences?
There are very few m-sequences of any given length with good cross-correlation properties. Their autocorrelation properties are excellent, but the cross-correlation properties are variable. For ...
- 20.9k
6
votes
How is multiplexing achieved in spread-spectrum modulations like CSS?
disclaimer
Because of the lack of document about LoRa CSS in Internet, the analysis below may be wrong with respect to LoRa system, not to the (linear) CSS principle. Any comment or update are ...
- 6,725
5
votes
Accepted
Conversion between Eb/N0 and SNR in spread-spectrum modulation like LoRa CSS?
Let's start by fixing a symbol rate $R_s$ symbols per second.
To modulate $R_s$ symbols per second without ISI, Nyquist says that we need a bandwidth at least $BW_0=1/R_s$ Hz.
With spread spectrum, ...
- 6,725
5
votes
Are there modulation schemes that use more bandwith than they need to, but don't require a spread-spectrum code to decode? (besides AM)
Yes, analog wideband FM is another example where the occupied bandwidth is wider than the bandwidth of the modulation signal, and provides a similar processing gain to digital spread spectrum ...
- 55k
4
votes
Accepted
Can I use frequency hopping spread spectrum technique for audio steganography?
Yes, it is possible to hide data inside audio files using FSSS technique. Have a look at this publication and this one.
Since HAS (Human Auditory System) is more sensitive than HVS (Human Visual ...
- 130
4
votes
How to reconcile "bandwidth" in the Shannon-Hartley Theorem with a spread-spectrum principle
If I'm only using bandwidth B1, doesn't that mean I can filter some of the noise out? And if so, would I be able to get S/N down? Wouldn't that be an alternative to occupying the full channel ...
- 32.5k
4
votes
Spread spectrum receiver
Just despread the same way with two different integrate and dump times for your two symbol types with appropriate blanking on each between longer and shorter code sequence periods.
I would be ...
- 55k
4
votes
Accepted
Is Bluetooth Low Energy jamming possible with an SDR like the HackRF on GNURadio?
I am not revealing any big secrets here on jamming and anti-jamming techniques, nor would I condone creating any such interference. What I am about to say is quite simplistic and well known, but ...
- 55k
4
votes
Accepted
Can an OFDM waveform be spread (DSSS)?
You can do a lot of things.
Some are sensible!
Remember why you're using OFDM (frequency-domain equalization) and remember that the temporal structure of the OFDM symbol (as the IDFT of the data ...
- 32.5k
3
votes
Accepted
How to reconcile "bandwidth" in the Shannon-Hartley Theorem with a spread-spectrum principle
You are mixing up two different notions that have little to do with each other.
The use of spread-spectrum signaling is not in an effort to achieve (or even approach) the capacity of the (wideband) ...
- 20.9k
3
votes
Accepted
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
No offense, but that ought to win the prize for the least-...
- 2,463
3
votes
DSSS spread method
There is no requirement that Direct Sequence Spread Spectrum (DSSS) have an integer number of chips per symbol, nor for the repetition rate of the code to be synchronous with the data (although this ...
- 55k
3
votes
Accepted
Detect low power DSSS-BPSK signal
Without disagreement to Dilip's valid comments, this is to show the corner case as to when you can detect the presence of DSSS. This is not demodulating the data but detecting the presence of a ...
- 55k
3
votes
Accepted
What's the difference between spreading and scrambling
Spreading refers to the process of multiplying your data sequence with a higher rate PRN sequence often but not necessary such that one complete duration of a repeating sequence occupies the time ...
- 55k
3
votes
Jamming resistance in spread spectrum systems
In order to work well, a jamming signal must be well-correlated with the signal it is trying to jam. In the case of sine-wave modulated signals, it's easy to detect the signal one wishes to jam, to ...
- 13.3k
3
votes
what are resources you recommend to learn GPS signal processing?
A good place to start is Van Diggelen and Enge's old course, now on YouTube.
There's a lot of GNSS related information on Wikipedia but I would look at Navipedia first.
Finally, you could try one of ...
- 186
3
votes
Spectral properties of QPSK modulation
The spectrum is that of the base pulse used in the modulation, so in this case a rectangular pulse. A single rectangular pulse in time, as given by the Fourier Transform, is a Sinc in Frequency with ...
- 55k
3
votes
How plausible is undetectable (covert) radio communication?
People in the SIGINT community spend their careers answering these sort of questions. Governments and their defense organizations are always working to be less detectable and their adversaries are ...
- 3,042
2
votes
Accepted
Minimum Output Samples needed to crack a "Gold Code" Generator (Dual LFSR)
! The answer by @cbos is correct in spirit but wrong in its details.
In an answer on crypto.SE, I wrote
"The Berlekamp-Massey algorithm is an iterative algorithm that solves the following ...
- 20.9k
2
votes
Use of pseudo-random binary sequence (Gold, Kasami, etc.) in frequency hopped code-division multiple access (FH/CDMA)
There are many ways to do this. A simple method is to take the current value of the register (not just its output) as the carrier frequency selector. For instance, a (6,1) LFSR with 63 states can ...
- 15.4k
2
votes
How to reconcile "bandwidth" in the Shannon-Hartley Theorem with a spread-spectrum principle
If your wireless channel has bandwidth $B$ but your signal has bandwidth $B_1 < B$, there are a few things you can do:
If your data rate is satisfactory, don't use a channel of bandwidth $B$, use ...
- 15.4k
2
votes
Accepted
Using MIMO with DS-CDMA and spread spectrum
Assuming one antenna transmits one symbol per time unit, then 16 symbols require 4 time units to be out. Then it is simply that
...
- 6,725
2
votes
Accepted
Frequency Hopping Spread Spectrum Synchronization Methods
This can be accomplished by changing the carrier frequency using a Numerically Controlled Oscillator (NCO) which maintains an accurate and continuous phase versus time trajectory via the phase ...
- 55k
2
votes
Is it possible to spread signal using sum of more than one orthogonal code
The disadvantage is that the signal V21 = V1 + V2 = [2, 0, 2, 0] disappears every other chip interval which makes maintaining carrier and phase synchronization more ...
- 20.9k
2
votes
Early - late gate spread spectrum
This is the common case for receiving spread spectrum signals since we do not know carrier frequency and phase offset but can determine that from the complex output of our correlators.
Each ...
- 55k
2
votes
Accepted
What are the advantages and disadvantages of PN sequence over Walsh code
A Pseudo-random noise (PRN) sequence ia a closer approximation to white random noise in that its energy is spread equally over the occupied frequency band (The energy is spread as a Sinc function if ...
- 55k
2
votes
Accepted
Multi-bit gold code
Yes, that is the whole point of Gold sequences. If $x$ and $y$ are a pair of preferred m-sequences of period $N$, then their periodic cross-correlation function is bounded. It also happens to be take ...
- 20.9k
2
votes
Accepted
How to recover data/information from real complex baseband signal?
In an actual received signal you will also have to address the frequency, phase and time offsets between the transmitter and receiver since they run off of independent clocks that aren’t otherwise ...
- 55k
2
votes
Accepted
CDMA and Pulse Shapping
Pulse shape filtering is used to constrain the signal bandwidth (with what would otherwise be a Sinc function in frequency given the rectangular pulse) and as a Nyquist filter done in such a way as to ...
- 55k
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