Synthesiser review for pan-European digital cellular radio

A pan-European cellular radio system is being devised by the Groupe Special Mobile (GSM), a committee originally set up by the CEPT and now transferred into ETSI. The system will employ a digital radio link with GMSK at a data rate of ~270 kb/s. Modulation requirements and frequency hopping pose many problems in the design of the synthesiser/modulator for handheld terminal equipment. The paper reviews solutions to implement the synthesiser/modulator functions, considering both fundamental problems and circuit cost, size and power requirements. The direct synthesis of GMSK by DSP and digital to analog conversion can meet modulation accuracy requirements, but is limited by speed and cost. However, direct modulation for the GSM radio system is not possible with many standard forms of synthesiser. These problems are discussed, and the use of two point modulation which overcomes the fundamental limitations is introduced