Abstract
The low power consumption merit of the multi-input multi-output constant envelope modulation (MIMO-CEM) system nominated it to be a favorable candidate to design the PHY layer of the low power smart devices that support the internet of things (IoT) technology. Thanks to the CEM, the MIMO-CEM system efficiently overcomes the high peak-to-average power ratio (PAPR) in the transmitter side (TX). Hence, an efficient class C or D power amplifier (PA) is used in the MIMO-CEM TX instead of the inefficient class A PA. Furthermore, depending on the constant envelope (CE) property of the MIMO-CEM received signal, a low resolution 1-bit analog to digital converter (1-bit ADC) is utilized in the receiver side (RX) to digitalize the MIMO-CEM received signal. The digitalization process relaxes the hardware complexity of the MIMO-CEM RX as it shifts the hardware complexity from the analog processing to the digital processing (DP). Although its high-power efficiency, spectrum efficiency (SE) of the MIMO-CEM is low compared to the MIMO-OFDM system. This owing to use of the low order modulation techniques such as minimum shift keying (MSK) or Gaussian minimum shift keying (GMSK) to keep the CE property of the MIMO-CEM signal. Accordingly, this paper addresses the MIMO-CEM SE problem. In this paper, an orthogonal shaping pulses minimum shift keying (OSP-MSK) modulation scheme is proposed as a higher order modulation for MIMO-CEM. The OSP-MSK increases the SE of the MIMO-CEM system and preserves the CE property of the transmitted signal as well. The bit error rate (BER) and the power spectrum density (PSD) performances of the proposed OSP-MSK are evaluated reference to the conventional MIMO-CEM system. The simulation results corroborated that the proposed system could capture the same BER performance of the conventional MIMO-CEM system with up to 100% improvement in the spectrum efficiency.