Considerations of spectral efficiency in future communications

The scarcity of radio spectrum and increasing consumer demand have brought many of today´s analogue 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 utilised more effectively. The impetus for this research is the hypothesis that certain digital cellular systems utilise 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. This paper describes a study of the relative performance of different digital communication systems from the view point of spectrum utilisation. The number of users per MHz per unit coverage area best defines the spectrum efficiency. This definition is used to develop a novel intelligent mathematical model to analyse the spectrum performance. The model is based on coherent QPSK modulation, ultra narrow band access technology and 2-bit error correction self-orthogonal convolutional code. The study has been carried out for the cases of diversity (MRC) and non-diversity. The study suggests 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