In my experience to learn LTE protocol, openairinterface5g open source project from EURECOMM is nice to pick up LTE knowlege in reality for students. I had involved in openair-cn(Evolved Packet Core, which known as EPC) subproject in openairinterface5g and made its function work with commercial base stations and user equipments successfully. Openair-cn could be built and run in only one Ubuntu OS within virtualbox. For example, you can learn NAS