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RF Front-End Structure for Dual Mode GSM/UMTS-Handsets Disclosure Number: IPCOM000020536D
Original Publication Date: 2003-Dec-25
Included in the Prior Art Database: 2003-Dec-25

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In the UMTS (Universal Mobile Telecommunications System) project the status of the development can be summarized as successful operation in single mode configuration (within Global System for Mobile Communications GSM and UMTS, respectively). One challenge among the next steps is the integration of both the GSM and UMTS air interface into a common hardware solution. Key aspect of the endeavors is the implementation of simultaneous downlink operation in GSM and UMTS not only for GSM900 but also for DSC1800 (Digital Cellular Systems) frequencies. Simultaneous serving of two receiving frequency bands through one air interface requires that the signals can be split up by physical components instead of a time multiplex approach. Latter one can be addressed in downlink compressed mode, which is clearly a limitation on system performance and therefore not preferred. This splitting is done relatively easy between GSM900 and UMTS Band I frequencies as they are sufficiently separated in the frequency domain. Typically multilayer ceramic is the preferred technology to provide the duplexing function in small components (standard components). The splitting between DCS1800 and UMTS Band I frequencies puts heavy requirements on the filter response (steep band edges) and drastically increases the components both in size and cost. To achieve the necessary selectivity either a high number of poles have to be realized in multilayer or discrete blocks (resulting in high space and cost requirements) or resonator technologies have to be used like SAW (Surface Acoustic Wave) or ceramic resonators (that come along with other technical constraints like insertion loss due to high relative bandwidths etc.). Switching modules for dual mode GSM/UMTS terminals are not commercially available in the configuration which allows simultaneous downlink operation for DCS1800 and UMTS frequencies.