Why we use different access schemes/technologies for up link anddownlink

Hi Every One,

I am confused regarding these different access schemes for up link and
downlink or more precisely different access schemes in forward and
reverse channel of UMTS / LTE(you can generalise my question).

As far as I am getting, say we use OFDMA for downlink (Base Station to
Mobile Terminal) and SC-FDMA (Mobile Terminal to Base Station), the
main reason is that if a user (MT) is sending any request say he send
www.google.com then he what actually he is doing is sending just few
kbs of data but in return he will get data more then he send that is
why the download data rate should be high, thats why we use different
access schemes.

But still many things are unclear like, okay we are using OFDMA for
higher data rate but what about a video call the user will make? there
also he will need high data rate because of real time constraints then
why Sc - FDMA and not OFDMA for that????



Thanks and Regards
Ashwini