A Study of the Viability of RF MEMS for the Implementation of a Single-Chip Programmable RF Front End for Software Defined Radio Femto Cells

Abstract

The RF front end circuitry makes up over 60% of the cost of a base transceiver station (BTS, also referred as Node B in 3G networks). Included in this cost is that of the Power Amplifier unit, RF filters, and the GPS unit for clock recovery and synchronization. Because of the evolving mobile wireless communications standards (2G/2.5G/3G/LTE/4G and their various implementation standards including CDMA2000, WCDMA, TD-SCDMA, WiMAX, etc), the BTS original equipment manufacturer (OEM) is faced with the monumental task of designing a BTS RF Front End for each mobile network standard that they wish to support. Moreover, the OEMs are forced to manufacture and maintain in the field all of these BTS variants.

One way to address the frequency re-use and power range limitations of today’s base stations is to have more base stations covering smaller geographical areas by implementing what is called a femtocell, which also implies a significant cost reduction of the RF front end. Thus the RF front end represents the single biggest opportunity for cost reduction and logistics simplification for the base station of the future: the software-defined radio based cellular femtocell. The problem is that today’s BTS RF front end implementations are not programmable but fixed to work with a specific RF frequency (e.g., 1,900 MHz) for a specific mobile network standard (e.g., CDM2000 or W-CDMA). To band-aid this problem, the OEMs typically implement multiple RF front ends to give the illusion of a “multi-band” programmable system at twice, triple or quadruple the cost of a single-band system.

RF MEMS (micro-electro-mechanical systems) is a technology that has the potential to not only help solve the BTS cost and logistic issues, but also to complement SDR architectures by providing a true low cost, high performance, programmable RF front end. Because of its potential in the implementation of low cost, high performance, programmable RF front end filters and antennas, the author is investigating the possibility of implementing a single-chip programmable RF MEMS front end for SDR-based cellular pico and femto base stations for commercialization by 2015 or earlier. This dissertation summarizes the author’s findings, conclusions, and future work recommendations.