Digital treinsmission of information is finding an ever-increasing number of applications in the leind-mobile radio service. There is a possibility that in the long term, due to the increasing demand for mobile radio channels, their bandwidths will be reduced to 5kHz. A digital minimum shift keying (MSK) modulation scheme is proposed in this work for narrow band digital mobile radio transmission. The design and implementation of an MSK modulator and coherent and noncoherent demodulators are given. Their structure is highly flexible and can accommodate a wide range of medium digital transmission rates. The demodulators were tested for the transmission of 2.4kbit/sec in simulated typical land-mobile radio transmission conditions. The results of these tests favoured the use of the noncoherent demodulator for this type of application. Achieving spectrum efficiency in this proposed scheme relies on postmodulation filtering of the MSK signal. A polar loop VHF transmitter was tested for high efficiency linear power amplification of the MSK signal. It proved its validity for this type of application. A digital clock recovery circuit suitable for use in mobile radio conditions has also been built and tested. The principles of the circuit operation and its implementation are discussed.
|Date of Award||1984|