OFDM, DSSS and Modulation

[robbyde0100]

Hello,

I'm training for my 200-355 wireless exam but I'm struggling with how two comcepts fit together.

I've just covered modulation i.e. BPSK, QPSK and QAM and I'm happy I understand that the way you modulate a signal allows for different data rates.

Then I read about spread spectrum and OFDM and DSSS.  I.e. OFDM is a frequency division multiplexing, it sends the signal using multiple frequencies to the destination. where as DSSS uses the entire frequency (single frequency) to be sent to the destination.

But how does DSSS and OFDM fit together with modulation. 

Does OFDM for example send its signal over multiple frequencies using QAM??

[patoberli]

Try this: https://www.gaussianwaves.com/2011/05/introduction-to-ofdm-orthogonal-frequency-division-multiplexing-2/

[Rasika Nayanajith · Accepted solution]

In OFDM, 20MHz is divided into 64 small sub-carriers. Each of them transmitting 90 degree angle to one another (hence called orthogonal)

Given sub-carrier will use BPSK/QPSK or QAM for modulation that wave.

Below taken from CCNA Wireless CiscoLive 2017 session, that you should watch

HTH

Rasika

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