welcome, may one of appropriate plat forms to develop and implement communication protocols is using specification and description language SDL. For the application of this environment to implement some MAC functions can be followed in the link: https://www.researchgate.net/publication/270895953_Design_and_Simulation_of_Random_Access_Procedure_in_LTE?_sg=4tLU6RPUutVmkGfXscHS3QgnJAc0oGF
I think following link will give you an idea to develop your own MAC design and implementation using NS-3. I hope surely this link will provide you an answer