ent of the new amendment. This would allow system design and selection criteria with widely agreed targets using unified simulation assumptions and methodology. The group further developed a system description document to unambiguously describe the RAN architecture and system operation of the IEEE 802. entities, which set a framework for the development of the IEEE 802.16m standard specification. To enable a smooth transition from Release 1.0 mobile WiMAX systems to the new generation of the mobile WiMAX radio access network, and to maximize reuse of legacy protocols, strict backward compatibility was required. The author's original view and under- standing of backward compatibility was similar to that already seen in other cellular systems such as the migration of 1 X EV-DO Revision 0 to 1 X EV-DO Revision A, to 1 X EV-DO Revision B on the cdma2000 path and evolution of UMTS Release 99 to HSDPA to HSPA, and to HSPA+ on the WCDMA path. In these examples, the core legacy protocols were reused and new protocols were added as complementary solutions, such that the evolved systems maintained strict backward compatibility with the legacy systems, allowing gradual upgrades of the base stations, mobile stations, and network elements. Had it been materialized, the author's vision would have resulted in a fully backward compatible system with improvement and extension of the legacy protocols and function- alities built on top of the existing protocols as opposed to from ground up. However, the enthusiasm for the IMT-Advanced systems and the ambitious baseline requirements set by the IEEE 802.16 group resulted in deviation from the original vision and the new amendment turned into describing a new system that was built more or less from scratch. A large number of legacy physical, lower and upper MAC protocols were replaced with new and non-backward compatible protocols and functions. The co-deployment of the legacy and the new systems on the same RF carrier is only possible via time- division or frequency-division multiple