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In this paper, in order to improve the throughput of wireless communications, we investigate the variability in both the number of active transmit antennas (TAs) and the combination degree of multiple constellations in a multiple-input multiple-output (MIMO) system. By jointing the use of an arbitrary number of active TAs and the construction of one or two signal constellations, a new design, called as joint multiple constellations and variable active antennas selection for signal spaces design (SSD-MCVA), is proposed to exploit the spatial domain and then extend the signal spaces. Specifically, according to the dimensions of the spatial symbols that are constructed by three types of constellations (i.e., conventional QAM, the first secondary QAM (SQAM) and the second SQAM ( $\text{S}'$ QAM)) and the aid of the sign $j$ , four antenna index (AI) vector subsets are designed to extend the number of signal space vectors for enhancing the SE as well as the reliability of transmission. In addition, permutating signal spatial vectors with MCVA (PSSV-MCVA) is proposed to exploit the permutation index domain and then greatly improve the throughput for the app- lication of the large-scale MIMO systems. Furthermore, the spatial index bits, the detection complexity comparisons and the average bit error probability are provided. Simulation results show that the proposed systems achieve more spatial index bits and a lower bit error rate than existing index modulation systems.

Recently, utilizing the indexes of channel states, media-based modulation (MBM) has been viewed as a potential key technique for enhancing the reliability of communication systems. In addition, the available combinability of active transmit antennas (TAs) is a potential method for exploiting more additional information. In this letter, a new design, called as the variability of active antennas for the channel modulation (VA-CM), is proposed to further improve the communication quality. In the VA-CM, the in-phase and quadrature antenna index (AI) vector sets, which contain all possible vectors of active TA(s) (including the case of 0 active TA), are respectively designed. Then, with the I/Q AI bits, the in-phase/quadrature (I/Q) AI vector from the I/Q vector set is specified and its components are respectively multiplied by specified I/Q channel index (CI) vectors with ${n_{\mathrm {rf}}}$ I/Q CI bits, into one MBM signal vector. Meanwhile, in order to avoid the unrecoverable detection, with the control of the specified AI vector number with all zero I/Q AI bits, another CI vector set in one CI Vector Selector, which contains $2^{n_{\mathrm {rf}}}$ CI vectors of selecting two channel states, is selected for forming one non-zero MBM signal vector. Finally, the spectral efficiency and the average bit error probability (BEP) are analyzed. Simulation results show that the VA-CM outperforms other schemes in terms of the BEP performance.