SDR(Software Defined Radio)
OpenLTE is an Open Source Project on SourceForge that has been going on for a couple of years now. This project is mainly for LTE eNB and some additional higher layer. You can download full source code written in C and in Octave. If you are interested only in understanding the details of LTE Physical layer and do not have to implement it in real hardware. Just looking into and trying with Octave code would give you great help. Refer to the official OpenLTE page for the details.