Measures of spectrum utilization in digital radio systems

The security of radio spectrum and increasing consumer demand have brought many of today's analog mobile communication systems to the brink of saturation. A number of international committees are addressing this problem by proposing new digital transmission systems, claiming that in the long term spectrum will be utilized more effectively. The impetus for this research is the hypothesis that certain digital cellular systems utilize the allocated spectrum more efficiently than others. An extensive literature survey, conducted in order to shed some light on this particular subject, has yielded a sparsity of work addressing this issue, indicating a need for further research. The authors describe a study of the relative performance of different digital communication sytems (civilian or military) from the viewpoint of spectrum utilization. They also propose new techniques for the simulation of Rayleigh fading and for the accurate measurement of Doppler frequency shifts. It is confirmed that optimum spectrum efficiency is achieved by adopting digital narrowband access technology and diversity technique to mitigate the effects of multipath fading. Maximum efficiency performance is achieved at an optimum coding rate K = 80% for the diversity case; that is, a 13% improvement over the nondiversity case. It is also suggested that the European GSM system capacity is 6.5 times lower than the Japanese JDC system, and 5.5 times lower than the North American ADC system.<
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