Cyclic prefix length for symbols in 5G frame structure

I was trying to understand the frame structure importance and its requirement along with the cyclic prefix attachment.

I have basic two questions here:

  1. Why is a frame structure requires in sending traffic and control signals in 5G/LTE?
    Can’t we send just series of symbols as it is? Why is a frame structure defined in first place?

  2. Why is cyclic prefix for 1st and 7th symbol more when compared to other symbols in the slots. The time/length of cyclic prefix for 1st and 7th symbol is more. Why can’t it be same for all the symbols? What is the purpose.

Thank you

The symbols 0 and 7 were selected in order to synchronise the start of these symbols with time at 0 ms, 0.5 ms, 1 ms, 1.5 ms, and so on (0 and 14 for 30 kHz, etc.).
The symbol in the middle won’t begin at a multiple of 0.5ms if you simply divide the available cyclic prefix by the number of symbols.
Because of this, the first and middle symbols have higher CP.
Some of these symbols ought to be given greater CP in order to be the ones chosen.

The frame structure is established to enable time synchronisation between the transmitter and receiver.
Knowing that a frame has 10 milliseconds, a subframe has 1 millisecond, and that some symbols begin at multiples of 0.5 milliseconds makes things easier.