different kind of relaying in communication

can anyone tell me what is the difference between demodulate and forward relaying and decode and forward relaying? and also i searched alot in internet but couldnt undrestand the what particular process is done in decode and forward relaying? i just know it should be something about decoding the signal , removing noise and retransmiting it to UE. is that all?
thanks in advance

Those are different things.
I am assuming you are talking about digital communications.

- Modulate: to change the characteristics of a carrier wave (usually high frequency sinewave) to send data. Some common types of simple digital modulation: OOK/ASK, FSK, PSK, etc... A modulator takes the carrier, the baseband signal, and outputs the modulated signal;

- Demodulate: the reverse. A demodulator receives the input modulated wave and outputs the baseband signal.

The baseband signal may be encoded, such as Manchester encoded, biphase encoded, and so on.

Relaying is just receiving a signal and forward it to other place. Depending on the technologies involved, your signal may be just relayed, have to be demodulated or not, or have to be demodulated and deencoded or not.

thanks for your attention
but i have another question , so what is the benefit of demodulation and forward relaying or decode and forward ? the former just makes the baseband original signal again and retransmit it to UE what is the point in it?

y.ettefagh said:

thanks for your attention
but i have another question , so what is the benefit of demodulation and forward relaying or decode and forward ? the former just makes the baseband original signal again and retransmit it to UE what is the point in it?

Click to expand...

You may be doing it in different technologies. Say, suppose you are receiving an input signal from an optical fiber and you want to relay it through a microwave link.

I was :roll: too, but last night I got an idea about it. I've noticed that Decode-And-Forward strategy means that the system uses a kind of coding (detecting/correcting codes) in order to deal with channel errors. The point is that, it is a very time consuming strategy and to implement it you will need a more complex hardware as well. On the other hand, Amplify-And-Forwrad completely suffers from error propagations due to source-relay channel errors, but it is epic simple :-D (even if you want to simulate it not to implement it). So, there must be a strategy that holds a position between these two. Here it comes, Demodulate-And-Forward.
It just makes the base-band signal as you said, but it removes the effects of channel Noise and Fading (and ...) by detection algorithms like ML.
Also in Decode-And-Forward if relay receives an incorrect data it will do nothing => no diversity gain,
but in Demodulate-And-Forward there is a chance to migitate errors through demodulation techniques plus it doesn't take into account the correctness of the demodulated data => Error Propagation decreased, diversity gain increased.

Demodulate and forward relaying is simpler but requires spacial and time diversity with adequate BER margin

While decode and forward relaying is more complex but assumes protocol for error detection and repeat or correct improves performance before relaying. It is a tradeoff between complexity,cost and BER for a given path loss and network design.
If no correction is done relaying errors from fading then as stated before diversity gain is increased only.

I didn't understand why there's no diversity gain in Decode & Forward relaying and why there is in Demodulate & Forward relaying...

diversity gain is the increase in signal-to-interference ratio due to some diversity method.
With training and knowledge of each path's signal quality and cooperation from sources, some gains may be possible.
**broken link removed**