Hi Farah, is 5G faster than 4G due to h/w and mm-wave tech improvements or there is a s/w related improvements also?

Hi Sachin P.,
Of course there are SW improvements - that's why it take years and it's called 5G instead of 4.9G ;)
1. 5G uses OFDMA like 4G
2. Control information sent between phone and base station are different. For example - for tracking the phone and handle beam forming another control data have to be transmitted.
3. 5G has lots of new features that let, for example 2 phone sharing one slot or to increase number of phones connected or to handle many phones better way.
I can recommend you this document to know more about it:
https://www.keysight.com/upload/cmc_upload/All/Understanding_the_5G_NR_Physical_Layer.pdf