What is the best simulation for 5G Wireless Networks?

From Manish Nair point of view the best simulation for 5G Wireless Networks for PHY Layer is Matlab and Simulink.

Matlab 2017 under academic license from MathWorks has the latest and greatest 5G toolbox, and is a great resource.

MAC-PHY Split and Protocol Stack

Open Air Interface (OAI) software libraries.[1]

The MAC-PHY split is implemented as an amendment to OAI5G source code. The OAI source code itself is split into two projects: OAI Radio Access Network (OAI-RAN) and OAI Core Network (OAI-CN).

OAI-RAN code is available on GitLab, and is distributed under OAI 5G public license.[2]

OAI-CN project implements 4G LTE Evolved Packet Core (EPC) and 5G Core Network. The code repository is on GitHub, and licensed by Apache.[3] [4]

Traffic, Scheduling and Queueing

IEEE 802.1 Qbv.[5]

This is the standard for Local and Metropolitan Area Networks, MAC Bridges and Virtual Bridged Local Area Network (VB-LAN) Enhancement for scheduled traffic.

Codes and specs can be found on the links in the reference.