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Despite the arrival of cellular radio, private mobile radio (PMR) will continue to be the main provider of mobile communications to a number of important users, particularly in areas outside the main urban centres. The release of Band III for mobile radio services constitutes a significant factor in alleviating the spectrum shortage and should act as a spur for the development of new systems of spectrum utilisation. The paper discusses an integrated system for voice and data transmission using a number of novel modulation strategies suitable for multiplexing speech and data on a single 12.5 kHz mobile radio channel. Evaluations of these strategies and their implications for system design are conducted using a novel CAE simulation tool. The simulation shows that one of these modulation schemes is highly suitable for simultaneous voice and data transmissions. This is confirmed by experimental measurements on a prototype system.