# Energy and Spectrally Efficient Modulation Scheme for IoT Applications
## 1 Introduction
This channel estimator provides a superior enhancement when it is compared to the state whereupon the channel estimation and the data detection processes are performed independently. The use of the one-bit ADC with massive spatial MIMO (SM-MIMO) was first tackled in [17], in which an LS channel estimator was employed for multiuser detection over frequency-selective fading channels. The implications of using low-resolution ADCs on the performance of the massive MIMO when deploying orthogonal frequency division multiplexing (OFDM) was debated in [18]. Moreover, the spectral efficiency of the one-bit ADC massive MIMO systems deploying single-carrier or OFDM transmissions was analyzed in [19]. [PERSON] et al. [20] extended this analysis to the performance over Rician fading channels under the effect of both perfect and imperfect channel state information. All of the aforementioned studies tried to handle the problems of the massive MIMO with a one-bit ADC at the RX side, without concerning the problems at the transmitter (TX) side. These problemsincluded but were not limited to the high power consumption and the high hardware complexity of the massive MIMO TXs. The multiple-input multiple-output constant envelope modulation (MIMO-CEM) with the one-bit ADC [21; 22; 23; 24; 25] was recently introduced as a low-power and low-complexity wireless communication system. In such a system, constant envelope modulation techniques such as minimum shift keying (MSK) or Gaussian minimum shift keying (GMSK) are utilized to minimize the peak to average power ratio (PAPR) of its transmitted signal. Therefore, efficient nonlinear power amplifiers (PAs) (class C or class D) are used in the MIMO-CEM at the TX side. In addition to that, due to the constant envelope feature of the transmitted signal of the MIMO-CEM, a low-resolution one-bit ADC is used at the RX side to digitalize the MIMO-CEM received signal. Consequently, the MIMO-CEM fulfills a tremendous reduction in terms of cost, power consumption, and hardware complexity. However, the MIMO-CEM with the one-bit ADC suffers from harsh quantization errors, which in turn add more challenges to the channel estimation process [21]. The channel estimation problem of the MIMO-CEM was firstly touched upon in [22], where the channel is adaptively estimated by using the preamble transmission of code division multiplexing (CDM). This CDM adaptive estimator was extended to a decision-directed channel estimator (DDCE) in order to track the fluctuation of the channel [23]. Moreover, in [24], adaptive filtering and correlation estimation were applied to estimate the MIMO-CEM channel. The problem of the low spectral efficiency of the MIMO-CEM with the one-bit ADC was implicitly introduced in [25]. This problem without a doubt impedes the MIMO-CEM from fulfilling the high achievable data rates of the massive MIMO systems. Therefore, innovative ways should be sought to boost up the spectral efficiency of the MIMO-CEM while retaining all of its inherent advantages. To the best of the authors' knowledge, heretofore, there have been no systematic studies in the literature concerning the spectral efficiency problem of the MIMO-CEM with the one-bit ADC until the authors proposed the MIMO orthogonal shaping pulses minimum shift keying (OSP-MSK) modulation/demodulation scheme [26]. The OSP-MSK is a low-power and low-complexity MIMO scheme that introduces a higher spectral efficiency than the MIMO-CEM by increasing the number of bits per symbol (bps) without additional bandwidth. Ensuing the above concepts, the major contributions of this paper can be summarized as follows:  
* The OSP-MSK Modulation/Demodulation Scheme: The OSP-MSK is proposed as a low-power and low-cost modulation scheme. The OSP-MSK relaxes both the power budget and the hardware complexity by using nonlinear PAs at the TX side and by deploying a low-resolution one-bit ADC at the RX side.