RF System and Circuit Challenges for WiMAX
This chapter focuses on the various RF challenges that exist on a radio frequency (RF) system level and shows how such challenges can translate into circuit designs. It describes the plethora of trade-offs and challenges for RF architectures in Microwave Access (WiMAX)-related radios and discusses frequency division duplex (FDD) and its cousin half FDD (HFDD) as well as time division duplex (TDD). RF is made more complicated by the fact that WiMAX addresses wireless markets across the world in both the licensed and unlicensed bands. The RF filter in a TDD system is not required to attenuate its transmitter (TX) noise as severely as in FDD systems. A high-performance RF front end is required in FDD systems. Collocation issues from a TX noise perspective are solved since the worst-case scenario of self-jamming is not possible. Various duplex schemes, including RF architectures, have been outlined and some methods to improve link margin considered. WiMAX poses significant challenges to the RF subsystem.