ON SPECTRUM EFFICIENCY OF RADIO TRANSMISSION SCHEMES FOR CELLULAR MOBILE RADIO

摘要

It appears that there are contradictory opinions in considerations on cellular mobile radio. This paper is an attempt to clarify some of these issues.After a consideration on multiplexing, a simple transmission model for the cellular network is derived. With the aid of the model it is found that the optimum choice of the modulation method and its parameters, and the spectrum efficiency itself, are to a high degree determined by transmission quality requirements and the grade of service. The effect of fading is investigated and it is shown how the implementation of countermeasures against shadow effects and Rayleigh fading has an important impact on spectrum efficiency; there is a trade-off between performance and complexity. Consequently, comparison between systems in which the parameters mentioned are not explicitly taken into account must lead to conflicting conclusions. Spread spectrum schemes, if fully based on code division multiplex,cannot directly be treated with our model, which is based on frequency division multiplex. A relation can, however, be established by considering pseudo-noise spread spectrum coding as a bandwidth expanding modulation scheme. It can then be shown that the spectrum efficiency advantages often claimed for the spread spectrum schemes are largely based on unbalanced comparisons with frequency division schemes. Based on these considerations, it is believed that digital FDM transmission with adequate diversity measures is a promising technique for future mobile radio networks.