Comparison of the performance of multi-carrier IFSK and M-ary IFSK modulation techniques in indoor portable radio communications systems

The transmission rate in indoor portable radio communications (IPRC) environments is limited to ≈1.6 Mb/s in typical offices where rms delay spread is ≈50 ns. Attempts to increase the transmission rate are discussed. We study the effect of modulation index on the performance of wideband-incoherent-FSK (WIFSK), the best value of M for M-ary IFSK (MIFSK) and the multi-carrier-modulation (MCM)/IFSK techniques to increase the transmission rate of IPRC systems against ISI and inter-channel-interference (ICI). A new transmission medium simulator has been introduced based on millimetre wave propagation field measurements. As an alternative to the guard-time employed in the orthogonal frequency division multiplex (OFDM) system for ISI immunity and protection of orthogonality of sub-carriers, we introduced the carrier separation into the MCM/incoherent minimum shift keying (IMSK) system and evaluated the system performance by simulations as a function of the carrier separation. The large spectrum required is provided by the use of one-cell-per-room scenario at millimetre wave frequencies. We showed that, particularly for IPRC systems, the transmission rate can be increased indefinitely with the number of sub-carriers in MCM/IMSK systems. The WIFSK and MIFSK systems offer no advantage over IMSK. Pulse shaping is also shown not to increase bandwidth efficiency significantly