OFDM with subcarrier number modulation (OFDM-SNM):
Orthogonal Frequency Division Multiplexing (OFDM) is a form of digital modulation that makes use of a large number of closely-spaced orthogonal subcarriers to transmit data. It divides the available frequency spectrum into multiple subcarriers, each of which carries a portion of the signal data. In OFDM with subcarrier number modulation, the number of subcarriers used for a particular transmission is varied depending on the amount of data that needs to be transmitted. This is done by increasing or decreasing the number of subcarriers in the signal, allowing for more efficient use of the available spectrum, while still providing reliable communication. The number of subcarriers used can be changed on the fly, allowing the modulation scheme to adapt to changing traffic conditions. This makes OFDM with subcarrier number modulation an attractive choice for wireless networks, as it can provide both flexibility and robustness.
MIMO with Antenna number modulation (MIMO-ANM):
Multiple input multiple output system with antenna number modulation (MIMO-ANM) is proposed in this paper as a novel transmission method that can be used instead of conventional MIMO with spatial modulation (MIMO-SM) for providing more advantageous and reliable data transmission in future wireless systems. In this scheme, the additional data bits are conveyed by changing the number of active transmit antennas instead of their indices while the number of receive antennas is kept singular. As such, MIMO-ANM is different from MIMO-SM as it can make the selection of the antennas in MIMO to be both channel and data dependent at the same time, resulting in what is called MIMO-ANM with adaptive antenna selection (MIMO-ANM-AAS), while MIMO-SM is unable to make the selection of the antennas channel-dependent because the indices of the selected antenna are purely data-dependent. By using such a transmission scheme, the overall reliability of the transmitted data stream can significantly be improved, which characterizes MIMO-ANM-AAS with much lower bit errors compared to MIMO-SM. In this paper, the concepts of MIMO-ANM and MIMO-ANM-AAS are established on the basis of conventional MIMO using binary phase shift keying (BPSK) symbol modulation over a Rayleigh fading channel. The validity of the system is investigated, where analytical and simulation results showing the bit error rate (BER) performance of the system are given. The numerical computer simulations furthermore compare the performances of MIMO-ANM-AAS with MIMO-SM to show its superiority, and the advantages of the concept are discussed. The acquired results show that MIMO-ANM-AAS offers highly reliable and resilient system thanks to its simultaneous bit transmission by different number of active antennas that can be made adaptive to the channel gains.