Space-Time Shift Keying and Constant-Envelope OFDM: A New Solution for Future Mm-Wave MIMO Multicarrier Systems

Future 5G systems are envisioned to support wide range of applications, from narrowband to broadband, by occupying non contiguous spectrum bands from lower sub-6GHz bands to higher millimeter wave (mmWave) bands. In this regard, significant challenges in design and implementation of 5G radio have to be addressed both in uplink and downlink. One of the challenges is related to the consideration of enabling physical layer (PHY) in the deployment of robust transmission systems able at striking an efficient tradeoff between power and spectral resources through the use of advanced MIMO-multicarrier techniques. In this paper, we address such challenge by proposing a novel technique based on space-time shift keying (STSK)-aided constant envelope orthogonal frequency division multiplexing (CE-OFDM) over frequency-selective mmWave channels. The main idea is to blend the benefits of STSK and CE-OFDM in mmWave transmissions by keeping complexity of the system as lowest as possible. We show that the STSK-CE-OFDM outperforms the state-of-the-art STSK-OFDM comprehensively in the presence of nonideal power amplifier. In particular, STSK-CE-OFDM can achieve a very large performance gain over the STSK-OFDM counterpart in the presence of nonlinear amplification. For this reason, STSK-CE-OFDM can strike a favorable and flexible tradeoff between power and spectral efficiency in the framework of 5G mmWave wireless communications. The price to be paid is an overall bandwidth increase with respect to conventional STSK-OFDM, due to the need of modulation indexes higher than 1.0 radians.