Can FDM be Used to Multiplex OFDM Signals at Different Frequencies?

[thavamaran]

Hi guys, I'm currently generating OFDM signal and send it to DAC and then upconvert them to 1 GHz carrier signal.

I want to multiplex several of them, like say I upconvert them to 1 GHz, 800 MHz, 1.2 GHz, which represents 3 different signals, then multiplex them together using FDM, is it possible or is there any other better way to do this?

 

[f95toli]

I don't understand the question. If you have three signals that already have different and well separated carrier frequencies, why do you need to FDM them? As opposed to just combining them into one signal (using a power combiner)?

I suspect I've misunderstood what you are trying to do...

 

[thavamaran]

well, I want to combine them as in multiplexing them to combine bit rate and enhance my spectral efficiency and transmit them in optical. What do you meant by power combiner? Thanks for the reply.

 

[f95toli]

A power combiner is simply a device that just adds signals together; in the same way as a mixing board adds audio signal together.
The reason why you need a combiner (or maybe a coupler of some sort) is that it keeps the impedance constant, if you simply connect wires togther you'll an impedance mismatch which is bad if you are working at a few hundred MHz.
Note that a combiner can also work as a splitter.

As long as your signals are well separated in frequency there is no reason why you can't add and them an later split the result into components.

 

[thavamaran]

But mine works in 2.7 GHz. Is that still possible?

 

[f95toli]

2.7 GHz is not a very high frequency, as a rule of thumb you can assume that working up to 18 GHz is "easy" and reasonably cheap (although the price of the components go up with frequency).

That said, at 2.7 GHz you still need "proper" microwave engineering; but there is no need for any "exotic" solutions.