Why do we still have paired spectrum?
At least in 4G and 5G? (You still need it in 3G.)
TDD or FDD - I find it interesting people always talk about the 5G spectrum when the real issue is why do we keep spectrum split as in FDD?
Shouldn’t the carriers be allowed to convert it to TDD once they go 5G?
Hell, even in 4G they preferred TDD. It’s a more efficient use of spectrum in today’s world.
Think about the fact you have to be tied to a specific amount of spectrum for uplink and downlink when if you had TDD you could make it anything you want.
For the uplink, it is better to transmit 100% of the time in 10 MHz than 50% of the time in 20 MHz. With 20 MHz, the link budget reduces in 3 dB. However, if the system is highly limited by interferences, this may not be important at all and the guard band is not needed in TDD. Regarding “You can make anything you want”, we are constrained by what your neighbours are doing to some extent, otherwise UL to DL interference (and viceversa) will happen. Also, ultra low latency is easier to achieve in FDD than in TDD, where you might need to wait some slots until the uplink turn arrives.
I am just pointing some advantages of FDD, of course TDD has such good points that may well outweigth those advantages…