Digital technologies in cellular radio

The technology choices are examined toward increasing capacity of the present analog 800 MHz cellular system in North America. A possible dual mode concept based on digital cellular radio technology is described. The basic choices regarding speech coding, channel coding, digital modulation and multiple access are discussed. It is found that a promising technique is 30 kHz TDMA (time-division multiple access). This method simplifies the coexistence with the present analog cellular system. The existing frequency plan can be used and there is no need to allocate separate frequencies for the digital system. 30 kHz TDMA allows that the system be based on low risk, high-quality speech coding; and, at the same time, it can support lower rate speech codecs. The TDMA approach allows that the existing 30 kHz channels are divided into two or three TDMA-slots in a flexible way without affecting frequency planning