9

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 example, there are 18 m-sequences of period 127 but to have good cross-correlation properties, one must choose a set of no more than $\require{cancel}\cancel{\text{...


5

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 appriciated. Thanks. LoRa CSS modulation LoRa CSS uses linear chirp spread spectrum. To transmit $\log_2 M$ bits, LoRa CSS modulation divides bandwidth $[-\frac{B}{...


5

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, we use more bandwidth, say $M$ times, than what Nyquist advised. The used bandwidth is $BW=M\times BW_0=M/R_s$. In LoRa specifications, $BW=125, 250, 500 \...


4

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 System), you are usually limited with audio steganography comparing to image steganography. There are not many detalied publications with "Audio Steganography" tag....


4

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 tempted to do all the acquisition and tracking on the longer symbol and then simply despread the shorter symbols using the synchronization from the longer one— with ...


3

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 bandwidth? Capacity increases linearly with bandwidth, but only logarithmically with SNR. So, increasing SNR by decreasing bandwidth is a bad idea if your noise isn't ...


3

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) channel. Indeed, the spread signal uses only a small fraction of the capacity of the wideband channel, and the rest of the capacity is available for use by ...


3

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-accurate definition of frequency-selectivity I heard ;-) What you mean is channel is frequency-selective if the bandwidth of the signal is larger than the ...


3

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 duration of one data symbol. For example one such modulation using BPSK to send a “1” you send the entire sequence before it repeats and to send a “0” you send the ...


3

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 infer that it's narrowband (and, hence, riding on a real or suppressed sine-wave carrier), to infer its bandwidth, and from there to choose a suitable jamming ...


3

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 the first nulls spaced at $1/T$ away from the center of the Sinc, where $T$ refers to the duration of the pulse in time. (Just as that shown by the OP). If the ...


3

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 not introduce inter-symbol interference. For CDMA and specifically direct-sequence spread spectrum in many cases we have no concern for spectral containment (...


2

! 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 problem. Given a sequence $s_0, s_1, s_2, \ldots$ of elements of a field, find the shortest linear feedback shift register (LFSR) that generates ...


2

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 select between 63 different channels. Other methods are based on cubic and quadratic congruence codes. I don't know much about them myself, but look up the papers ...


2

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 one of bandwidth $B_1$! Assuming you're paying for your bandwidth, you'll save money. Note that Shannon's theorem also applies when you use $B_1$ instead of $B$....


2

Assuming one antenna transmits one symbol per time unit, then 16 symbols require 4 time units to be out. Then it is simply that r_1 = H_1 * x_1(1:4) r_2 = H_2 * x_1(5:8) r_3 = H_3 * x_1(9:12) r_4 = H_4 * x_1(13:16) If channel H is fixed during these 4 time units, [r_1 r_2 r_3 r_4] = H * [x_1(1:4) x_1(5:8) x_1(9:12) x_1(13:16)]; or r = reshape(H*reshape(...


2

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 accumulator. This is markedly different than changing the frequency with a classical PLL where we would typically break and reacquire lock to change frequency ...


2

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 difficult. Also, while the total energy in V21 is equals to the sum of the energies of V1 and V2, V21 uses 4 times the instantaneous power needed by either V1 or V2 and so the transmitter needs ...


2

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 is often done). So in this case you have a spreading sequence with a code of some particular length that is running at 6.138Mcps that is multiplied by your data ...


2

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 correlator (Early, Prompt and Late) would be complex; the complex Prompt correlator output is used for Carrier Recovery (measure rate of rotation or change in phase from ...


2

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 repeating DSSS signal that is buried well below the noise. Specifically this would occur when the sequence repeats such as done with the GPS C/A code signals (the PRN ...


2

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 reconstructed with pulses just because of the pulse shape but the underlying code as a stream of impulses has a more uniform distribution), and its auto-...


2

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 open source software receivers, the most comprehensive being gnss-sdr.


2

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 knowing more details in how jamming can take place and being more educated on it in general can help good actors in minimizing vulnerabilities in future designs. Yes ...


2

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 on only three distinct values. The $N+2$ Gold sequences are $$x,~~ y,~~ x\oplus y, ~~x\oplus Ty, ~~x\oplus T^2y,~~ \cdots, ~~x \oplus T^{N-1}y$$ (where operator ...


2

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 synchronized, as well as frequency offsets introduced through Doppler if the transmitter and receiver are in motion relative to each other. Further information on ...


1

OK, let me explain that for you. First, if you want to understand anything in engineering, it's recommended to write it in mathematical form, then try to solve it theoretically and build its code accordingly. Second, regarding your question, is it possible to use MRC for MIMO - CDMA, Yes, that's possible, why not? Now, The code you provided is not right. ...


1

Your query is mixing up ideas and formulas from very different systems to arrive at very questionable answers. The expression $\frac 12 \log_2(1+\text{SNR})$ is the capacity (measured in bits per use) of a discrete-time Gaussian channel. The model for this channel is that the $i$-th use of the channel consists of the transmission of a single real number ...


1

That's right, you can do spread using the kroon function, but be careful what you spread is not the data, it's the whole possibilities of data which is mod.The data is one of them, which is either, 0.7+0.7i or 0.7-0.7i ...etc. then you should know how you can do despread in the receiver side too. Good luck


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