Affine linear transformation based sphere decoder for 1-bit ADC MIMO-constant envelope modulation

Multi-input multi-output constant envelope modulation (MIMO-CEM) is considered as a promising low power PHY layer design for emerging Internet of Things (IoT) smart devices. MIMO-CEM efficiently overwhelms the high power consumption in MIMO-OFDM transmit signal comes from its high peak-to-average power ratio (PAPR). Despite its high efficiency in reducing the power consumption in the radio frequency (RF) band, MIMO-CEM suffers from high computational complexity in the digital signal processing performed by the receiver, e.g., MIMO decoding and channel estimation. This comes from the 1-bit analog to digital converter (ADC) operating in the intermediate frequency (IF) band used at the receiver side. In this paper, a low complexity sphere decoder (SD) is proposed for MIMO-CEM. A low complexity baseband modeling of MIMO-CEM based on an affine linear transformation is used to specify the sphere radius in addition to enumerating the lattice candidates within the sphere. Then, the more accurate (the more complex) IF based maximum likelihood decoder (MLD) is used to pick up the candidate that most likely to be transmitted. Decreasing the number of candidates examined by the high complex IF based MLD leads to a great complexity reduction in the proposed decoder. We test the proposed MIMO-CEM decoder under different scenarios and compare its performance with the recent decoders proposed for MIMO-CEM detection.