WiFi Access Point Front End Module Trends and Challenges
As 802.11ac WiFi becomes mainstream the next generation of 802.11ax requirements have become mature over the last year. Chip sets will roll out in 2018 for 11ax and front end module (FEM) specifications are getting much more challenging. 11ax is driving transmit FEM EVM levels down to
-47dB with 1024 QAM signals and 160MHz wide channels. The duty cycle variability is putting difficult challenges on designing for dynamic EVM in the -47dB range. Access point equipment providers are finding thermal management as a key driver with up to 8x8 MIMO. 802.11ac power amplifier efficiency in the 15% range is breaking the power budgets. Fine line CMOS transceivers and closed loop memory based digital pre-distortion (DPD) appear to be the solution which ushers nonlinear high efficiency power amp design techniques back to the forefront. Riding the coat tails of cellular handsets, envelope tracking advances are encroaching upon being usable for advanced WiFi signals to enable better overall power efficiency. 802.11ax brings a standardized approach to power back off and network management. No longer do access points simply boom out max power, but only transmit what is necessary for an individual client. This opens up new modes of power amp operation and power detector design challenges. On the receive side it is about integration, low noise figure, ruggedness and getting the cost out with trends to advanced silicon approaches thru 6GHz. The request placed before the FCC by the 802.11 standards working group to extend WiFi bands up to 7.125GHz has dramatic implications on FEM design and the technologies to select. The data rates and overall performance demands continue to increase in WiFi and the next generation 11ax standard will deliver.