Studies on Fundamental Properties of MMFSK Systems

To compare the transmission system suitability for power-line communications the spectral efficiency and the required transmission power are two important fundamental factors. In this paper these two factors are studied for our proposed MMFSK (M-ary multilevel FSK) system. Spectral efficiency eta of MMFSK system is a function of number of frequency levels n, number of time chips L, number of hopping patterns h. An equation connecting eta and n, L, h is derived and quantitative relationships between these parameters are studied. As a comparison spectral efficiency of existing systems such as OFDM, MFSK, multilevel FSK are also shown. Results show that compared to ordinary OFDM systems one tenth of spectral efficiency can be achieved by the proposed system which may not be attained by the other systems. The required transmission power for a fixed error rate directly relates to the radiation power. To obtain the required transmission power, relation between error rates and signal to noise ratio should be clarified. Transmission feature between the output of the transmitter and the input of the receiver for MMFSK is same as that for MFSK and the symbol error probability at the receiver input is same. Difference in bit error rate comes from difference of symbol to bit transformation process. A consideration on the relation between bit error probability and symbol error probability in MMFSK is given and a formula representing worst case probability of bit error is derived. A comparison between the worst case bit error probability and the bit error probability obtained by a simulation is shown. Using these results it is cleared that the radiation power of MMFSK is 20~50 times smaller than that of OFDM.