Transmit-Diversity-Assisted Space-Shift Keying for Colocated and Distributed/Cooperative MIMO Elements

Space-shift keying (SSK) modulation is a recently proposed multiple-input-multiple-output (MIMO) technique, which activates only a single transmit antenna during each time slot and uses the specific index of the activated transmit antenna to implicitly convey information. Activating a single antenna is beneficial in terms of eliminating the interchannel interference and mitigates the peak-to-mean power ratio while avoiding the need for synchronization among transmit antennas. However, this benefit is achieved at a sacrifice, because the transmit diversity gain potential of the multiple transmit antennas is not fully exploited in existing SSK-assisted systems. Furthermore, a high-SSK throughput requires the transmitter to employ a high number of transmit antennas, which is not always practical. Hence, we propose four algorithms-open-loop space-time space-shift keying (ST-SSK), closed-loop feedback-aided phase rotation, feedback-aided power allocation, and cooperative ST-SSK-to achieve a diversity gain. The performance improvements of the proposed schemes are demonstrated by Monte Carlo simulations for spatially independent Rayleigh fading channels. Their robustness to channel estimation errors is also considered. We advocate the proposed ST-SSK techniques, which can achieve a transmit diversity gain of about 10 dB at a bit error rate (BER) of 10^-5, at the cost of imposing a moderate throughput loss that is dedicated to a modest feedback overhead. Furthermore, our proposed ST-SSK scheme lends itself to efficient communication, because the deleterious effects of deep shadow fading no longer impose spatial correlation on the signals that are received by the antennas, which cannot readily be avoided by colocated antenna elements.