
OOK is on off keying

Power present means 1 , no power means 0

Each bit 0 or 1 is supported by modulation symbol

It’s simple
 But not suitable for high capacity Links
 The spectral efficiency is very low

OOK depends on amplitude to represent the information

Phase is zero

To increase the capacity of link we have to use more complex modulation types

In M ary modulation we use amplitude and phase

This type is more complex than OOK and higher sensitive to noise

But it’s spectral efficiency is higher

Spectral efficiency means higher capacity and higher bits can be transmitted per bandwidth of channel

If M is the number of symbols

Then we can tramsmit 3 bits per symbol

In 16 Qam modulation we have 16 symbol
 So we have 4 bits per symbol

In 74 Qam modulation we have 64 symbol
 6 bits / symbol

Ss capacity increasing, number of bits per symbol increase , number of symbols increasing

Then the distance between symbols in I  Q space is small, then the decision area is too small

So there’s not too much margin for errors
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