# Tag Info

Accepted

### Confusion in Channel Encoding and Convolutional Encoding

Like other comments, I don't really understand your question. What I am trying to do is to list basic things so that other ones can suggest edit because I find it is much easier to write in answer ...
• 6,605
Accepted

### Interleaving or randomisation?

So, the technical difference between a scrambler and an interleaver: The interleaver is just a permutation of input symbols; a resorting. The scrambler is an operation designed to modify the ...
• 31.2k
Accepted

### Shannon capacity limit & FEC comparisons

I start with BPSK achieving 1 bits/sec/Hz over passband AWGN. Factoring in 1/3 rate coding this becomes 0.333 bits/sec/Hz. This is not correct. The Shannon noisy channel coding theorem states that ...
• 6,605
Accepted

### What is the forward error correction in 802.11a?

From the official standard, IEEE Std 802.11a-1999, Part 11, section 17.3.5.5 Convolutional encoder, see the rate 1/2 code: The resulting two streams A and B are interleaved bit-alternatingly. The ...
• 31.2k
Accepted

### Design of Reed-Solomon Code where $n < q-1$

You have the right idea but are missing some of the fine details. A cyclic Reed-Solomon code of length $n$, where $n$ is a proper divisor of $q-1$, is a BCH code and the key property is that if a ...
• 20.5k
Accepted

### Does Reed Solomon successful decoding guarantee valid payload?

No, you're missing nothing. Quite obviously, any valid code word (sequence) should decode correctly. And since noise can lead to any potential code word (sequence) at the receiver, these "false ...
• 31.2k

### What are trellis?

Might help to know that this is a trellis:
• 13.5k
Accepted

### What are trellis?

For computer scientists, I recommend Chapter 24 (Trellis Structure of Codes by Alexander Vardy) in The Handbook of Coding Theory, V. Pless and W. C. Huffman (eds) published by Elsevier. It is ...
• 20.5k

### Forward error correction with limited possible errors

Reed-Solomon codes are perfectly matched to a symmetric channel for which the probability that a given symbol $X$ is changed to a symbol $Y \neq X$ is the same for all choices of $Y \neq X$. That is, ...
• 20.5k

### Interleaving or randomisation?

Scrambler is generally used on the message bits itself (before coding happens on the message bits) to prevent long run of 0s or 1s in the message bit pattern. Originally it came from ethernet ...
• 2,263

### What's the shortest possible code that correct all the single bit errors?

In order to correct 1-bit errors, we need to have a Hamming distance (the number of bits that must be flipped) of 3 between all the symbols: when we flip one bit at random, then flipping another bit ...
• 156

### False positive rate with CRC

The CRC code is linear, so if you $w_0, w_1 \in \mathcal{C}$, then $w_0 \oplus w_1 \in \mathcal{C}$. The event you described, the false pass, means that you transmitted $w_0$ and received $w_1$, and ...
• 2,383

### Reed-Solomon error correction in GNU Radio

I know very little about GnuRadio (and your ETSI EN 300 744 link is broken) but typically $16$-error-correcting RS$(255,223)$ codes are what are called NASA Standard or JTIDS (Joint Tactical ...
• 20.5k
Accepted

### Eb/N0 on a VLC simulation using OOK modulation

$E_b$ refers to the energy spent per information bit. That's the whole point! You're technically right that you've got a visible light carrier, but you're using this as a baseband system, to be honest ...
• 31.2k
Accepted

### RS FEC correct more than t/2 errors sometimes... why is this happening?

Beware: what you're seeing could be the result of a bug in your code. Having said that: in general, algebraic codes such as BCH and RS are very hard to decode using algebraic algorithms. Practical ...
• 15.3k
1 vote

### Shannon capacity limit & FEC comparisons

You've computed the bound on the capacity of an AWGN channel. But with the additional constraint that the signal must use BPSK modulation the capacity will be lower (I don't know offhand what it is ...
• 11
1 vote
Accepted

### Error correction code with code rate 3/4

A point that doesn't seem to be stressed in the introductory literature on error correcting codes* is that in general, typical error correcting codes tend to run to hundreds or even thousands of bits. ...
• 12.9k
1 vote

### Optimal FEC option for extremely low SNR situation

Very shortly: as you approach the ultimate Shannon limit (-1.59 dB = Eb/N0) with a finite-length code, then you're better off not coding at all. Intuitively, you have very little energy to spend, and ...
• 31.2k
1 vote

### What are the most suitable methods for correcting sudden DC offsets or baseline offset? and Why? See the image for the use-case or example

I'd do this nonlinearily, in two steps: Detect the jump Correct the jump Detection sounds rather easy: a short (linear-phase) high-pass filtered version of your signal is compared to a threshold. ...
• 31.2k
1 vote

### Verifying LDPC matrices in CCSDS blue book

Found out where the issue was. The above code gives a matrix of 0s, 2s, and 4s, but I forgot to take the matrix multiplication $\mathbf G\mathbf H^T$ modulo 2, which would give the expected matrix of ...
• 65
1 vote
Accepted

### Channel encoding after digital modulation

The role of the modulator in your block diagram is to make an analog signal, while in classical communications, the data and the channel coder is discrete. So no, in the sense of your block diagram, ...
• 31.2k
1 vote
Accepted

### Column operations in LDPC generator matrix

Everything in me screams that's wrong, but it turns out if I just do the same thing on the decoding side it works out. Why? That just means you reorder some bits. On the other end, when you revert ...
• 31.2k
1 vote

### Why does the flat part of the BER curve appear after the Viterbi decoder (MatLab)?

I agree with Marcus Müller. In Monte Carlo simulations, due to the limited amount of trials, after a point, you come up with an error floor. To overcome this, the only way is to increase the number of ...
• 423
1 vote

### Why does the flat part of the BER curve appear after the Viterbi decoder (MatLab)?

while numErrsSoft < 100 && numBits < 1e7 Nope, you can't stop after 10⁷ bits if you're after error rates < 10⁻⁶. That means you expect to see ...
• 31.2k
1 vote

### I am trying to convert a signal into another unit, but the error keeps increasing during each iteration

If I understand your notation, you have $y[n] = \frac{1+x[n]}{1-x[n]}y[n-1]$, where $y[n]$ is the output signal. This can be rewritten as $y[n] = y[n-1] + \frac{2x[n]}{1-x[n]}y[n-1]$. This is an ...
• 5,026
1 vote
Accepted

### Does Forward Error Correction (FEC) affect upsampling factor?

Is the redundant data introduced during forward error correction (FEC) counted as upsampling? Yes. BUT, under certain conditions. The whole point of FEC is to be able to detect and correct an ...
• 10.7k
1 vote
Accepted

### Viterbi Decoder without traceback

A register exchange method implementation of Viterbi decoder avoids trace back and a nominal initial delay (one time delay or boot up delay) is unavoidable. But this method requires more memory ...
• 81
1 vote

### Confusion in Channel Encoding and Convolutional Encoding

Channel coding adds redundancy (making 1-bit to 10 bits what ever u mentioned; 9 redundant bits are added) Whereas GMSK is a form of modulation technique. Since it is a form of continuous phase ...
• 81

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