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know how to simulate communication link?

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kibrun

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transformer coupled nrz matlab

hi all,
i do need help on my project. i've been building an simple RF system but i need some method:

1) to proof that manchester coding is better than NRZ. some mathematical model/ simulation might help and clarify more.

2) probability test upon the codes that were used. right now i'm pumping a 17 bits code into the system. i do need to know the risk of failure to decode for each series of bits in a 2kHZ code signal with a carrier frequency at 315MHz.

3) to proof that FM system is more effective to avoid collision compared to AM system.

4) code correction can be implemented in one way communication (but i don't know how :? )

if anybody knows.. please help :)

thanks.
 

flatulent

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Some suggestions

Simulators are very expensive. If your school does not have one you will probably have to use theory and math.

There are many good books on communication theory. Your school library should have them. They will provide the information you need to prove your points.

There are several methods of forward error correcting codes. They are generally classified as block codes or convolution codes. Both methods add extra bits to the data stream. Look up "error control codes" in the index at your library and several good books will probably show up.
 

eYe

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Using MATLAB/Simulink with Communication Toolbox may help...
 

zorro

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Hi kibrun,

Remarks or suggestions:

1) Manchester is not better than NRZ in BER theoretical performance (BER vs. Eb/No with perfect synchronization), but the fact of having at less one transition per bit improves the bit synchronization at the receiver, and this improves performance especially with nonrandom data. Spectral properties are also important: Manchester needs more bandwidth than NRZ (twice) but because its power spectral density is zero at DC, it is more robust than NRZ in channels with poor response at low frequencies (e.g. transformer-coupled).

2) Sorry, I don't understand the point.

3) I think that the advantage of FM for avoiding collision that tyou mention can be related to the capture effect of FM.

4) Agree with flatulent.

I think that topics as 1) and 3) have to be explained by theory and analysis rather than just proved by simulation. Simulation would be useful for verifying your analysis and show its agreement with results. Analysis explains "how" and "why".

Z
 

zorro

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sorry, it went twice and this was the second... :oops:
 

toonafishy

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For item #4 look at SITOR (maritime communications) or AMTOR (amateur radio communications). They both support error correction in one way communications.
 

kibrun

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reed solomon for small data?

thanks zorro and flautulent for your guys feedback.
i came across a topic saying that reed-solomon is one of the way to avoid collision in one way communication. what i knew was reed-solomon is used for data storage esp. on CD. anyway, if you guys have tried to apply them in one way communication link.. please inform me of the outcome. i'm new at this and have to read/ understand about this scheme first. is it suitable for small data packets let say.. in 5k?

i have a link that can help me:

http://www.stanford.edu/class/ee387/

if you guys have an easier approach than what i'm trying to do please advice :)
 

zorro

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Hi kibrun,

Yes, Reed-Solomon coding is very efficient for protecting the one-way communications link against errors, but I don't see how it could avoid collisions although it can detect them.
RS codes are used not only for storage, but also in terrestrial and spatial radio links. One can choose the word size, block size and number of redundant words. Typical block sizes are 255 8-bit words, of which 80-90% are information (and the rest redundant). You can find their properties in several books.
Regards

Z
 

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