There are mainly two types of cyclic prefix used.

1. Normal cyclic prefix

2. Extended cyclic prefix

For both the types, minimum values are defined as follows:

Normal Cyclic Prefix : There will be total 7 symbols per time slot . First symbol is 5.2 microseconds long while remaining 6 symbols would be 4.69 microseconds long

Extended cyclic prefix : There will be total 6 symbols per time slot and each symbol will be 16.67 microseconds long.

**Reference:**

https://home.zhaw.ch/kunr/NTM1/literatur/LTE%20in%20a%20Nutshell%20-%20Physical%20Layer.pdf