A 64 kbps digital land mobile radio system employing M-16QAM

The authors describe a 64 kbps digital mobile radio system which has been tailored for trunked radio system applications. Using a combination of digital speech coding, time division multiple access (TDMA), and spectrally efficient linear modulation technologies, up to 6 voice links are supported per 25 kHz RF channel. A key feature of the system is a new modulation method, M-16QAM, which makes possible high speed signaling in land mobile radio channels without the use of an equalizer. After a brief description of the overall system, including the TDMA frame/slot structure and speech coder, focus is shifted to the modulation technique. The motivation behind M-16QAM, as well as its design and simulated performance, are discussed in more detail. Results of field trials of an experimental modem are also discussed