What is GP (guard period)?

A guard period is a time interval that is a part of a burst period where no radio transmission can happen. GP is utilized to control the switching between the UL and DL transmission. The guard period for changing from DL to UL is necessary because all UL transmissions from multiple UEs should show up simultaneously at the eNB receiver. However, guard period from UL to DL switching is not needed due to the eNB being the only entity transmitting.