Modification of a radio link system from analog to digital

The authors describe the modifications in converting an analog radio-link system for use in digital communication. The existing analog system uses frequency modulation at the 6-GHz band to transmit 1860 frequency-division-multiplexed (FDM) voice channels. The baseband units of this system are replaced by digital circuits without any changes in radio-frequency sections. The system can transmit and receive 34 Mb/s (480 channels) standard third-level PCM (pulse code modulated) data in HDB3 or NRZ format. Although the modification reduces the bandwidth efficiency, it is an attractive choice for converting the analog communication network to digital in rural areas.