Spatial Permutation Modulation for Multiple-Input Multiple-Output (MIMO) Systems

Spatial modulation (SM) for the multiple-input-multiple-output (MIMO) system has attracted research interests due to its high energy and spectral efficiency. SM creates a new modulation dimension by activating a single transmit antenna according to the data bits. In this paper, we propose spatial permutation modulation (SPM) that modulates data bits to a permutation vector and activates the transmit antenna at successive time instants accordingly. The SPM achieves higher diversity and thus lower error rate since the permutation vector disperses data along the time coordinate. The theoretical model of diversity and error rate are derived in both the slow-fading channel and fast-fading channel, leading to systematic and the fast SPM design exploration. Additionally, to show that the SPM can be easily combined with other SM-based techniques, space-time block coded spatial permutation modulation (STBC-SPM) and quadrature spatial permutation modulation (QSPM) is exemplarily designed based on space-time block coded spatial modulation (STBC-SM) and quadrature spatial modulation (QSM), respectively. The numerical results demonstrate the accuracy of our theoretical analyses and the superior SPM/STBC-SPM/QSPM performances to SM/STBC-SM/QSM, respectively, especially under the severe environments like low receive diversity or spatially-correlated channel, where SM fails to provide satisfactory performance. Under the environments where systems are allowed to operate with high throughputs, SPM also achieves lower error rate performance than SM. Last but not least, inspired by SM, numerous index modulation (IM) have been invented by activating various transmission entities, e.g., subcarrier in the orthogonal frequency division multiplexing (OFDM) system. The generalization from the SM to SPM can be easily applied to another IM system for the design of index permutation modulation (IPM).