The tag has no usage guidance.

learn more… | top users | synonyms

2
votes
0answers
28 views

Code rate in IEEE 802.11b (DSSS)

I would like to know what code rates for forward error correction the physical layer of IEEE 802.11b uses for the different supported data rates. So far I didn't find any source for that. Actually in ...
1
vote
1answer
85 views

Why does FEC seem to make BER worse at low Eb/N0?

I've been plotting BER curves and am wondering why FEC seems to make a BER curve worse at low Eb/N0 than the un-coded theoretical BER curve? My example plot below is for Differential BPSK using a ...
1
vote
2answers
473 views

Why is a precoder necessary for DQPSK and what does it accomplish?

I've implemented a soft-decoder for DQPSK using the wonderful answers I received here: How to soft decode DQPSK? To get the soft-decoder working properly I needed to precode the data I was sending ...
1
vote
2answers
218 views

Viterbi Decoder - Symbol Alignment

With a 1/2-rate convolutional encoder, $n$ bits are encoded into $2n$ symbols. Assume we have a long encoded stream such as $[... s_0, s_1, s_2, s_3, s_4, s_5, s_6, s_7, s_8, s_9, ..., s_{100}, ...]$...
1
vote
1answer
250 views

Viterbi Decoder - How does inverting the input bits affect the result?

Does converting zeros into ones and ones into zeros in the input stream affect the decoding result? Empirically I have seen that it does not affect, decoding $[0 1 0 1 \ldots]$ and $[1 0 1 0 \ldots]$ ...
5
votes
2answers
2k views

How to soft decode DQPSK?

I'm successfully soft-decoding D-BPSK by taking the dot-product of the constellation-position of the symbol and of the previous symbol. If the result is >= 1, then the symbol phase hasn't changed and ...
3
votes
3answers
1k views

Why is an interleaver often placed between an outer block code and an inner convolution code?

It seems that when doing FEC with a concatenated-code, an interleaver is often placed between the outer block code and the inner convolution code. The explanations I've seen say that this is because ...
0
votes
1answer
190 views

Viterbi Decoder - Decoding Continuously Encoded Stream Partially

I am in trouble with Viterbi decoder for a while. I have some questions. I need to decode messages from a continuous stream which is encoded without resetting the state metrics. Each message starts ...
3
votes
1answer
187 views

Viterbi decoder on a bit stream where the preamble is also coded

I hope this is not off-topic for this site. In my problem, Viterbi decoder is used for decoding convolutional-coded (rate = 1/2, constraint length = 7) messages. A message is 250 bits where the ...
1
vote
1answer
404 views

determining FEC or parity bits from percent error

I am very new to signal processing and my background is in physics. I would like to know if it is possible to determine the number of parity bits needs to theoretically get 100% transmission from a ...
3
votes
3answers
16k views

Calculate symbol rate for QAM modulation

Not sure if this is the right place to ask, feel free to move it if any other site suits this better. Anyway I am referring to QAM modulation used in US Cable TV. I know it comes under Annex B which ...
4
votes
1answer
268 views

Why is privacy scrambling a standalone block in a communications transmitter?

In some telecommunication systems, scrambling of transmitted data is applied to provide some level of security. For example, the communication system might look like: Data -> Scrambling -> ...