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 layer, S1AP, attach and detach procedure in openair-cn source codes. Openairinterface5g also has eNB and UE subproject, and you could dig into their source codes. In my observations at September 2015, the develop team of EURECOMM has been put much efforts on eNB than openair-cn.  If you have some questions about how to build, run and debug these subprojects, it’s recommend to read wiki, gitlab bugs list and mailing list of openairinterface5g.  Especially, engaging in discussions of mailing list is a better way to receive some responses for bugs and supports. 

以我的經驗來說，學生可以從EURECOMM的openairinterface5g開放原始碼專案裡面學到真正的LTE背景知識。我曾經參與子專案openair-cn（LTE的電信網路核心），修改一些內容，搭配其他環境要求，成功使其能夠連通商用基地台與商用手機。你能夠在virtualbox內僅架一臺Ubuntu虛擬機，並在其中建立與順利執行EPC。例如可從openair-cn子專案學到NAS層, S1AP, UE attach和detach的流程。建議想要自己架環境與除錯的人，可從他們的wiki網頁, gitlab的bug list和訂閱openairinterface5g的郵件論壇找到更多資訊，以我的經驗，尤其能從郵件論壇得到很多除錯方法與資訊。

Although now I’m not working in mobile communication technology area, I recommand that you, who are interested in LTE technology, must read the guide for LTE field test engineer and sharing of studying 3GPP spec experiencewritten by Winnie Lee. These references ever help me a lot when I was a newbie to LTE protocol. Last but not least, I won’t give helps to anyone, who got stuck in openair-cn, due to the contract with former coporation.

另外，強烈建議在執行與除錯LTE協定時，參考Winnie Lee寫下的LTE field test engineer訓練指導，以及研讀3GPP文件規格的經驗分享，這會對你幫助很大。因為當我曾對LTE完全不了解與一竅不通時，她寫下的文件讓我成長許多，足以應付openair-cn的除錯，以及因工作上需要的背景知識提升。最後，因為與前公司的合約，我不會幫忙任何人因為openair-cn而困擾的相關問題。