Novel waveform designs for future wireless systems:non-coherent orthogonal frequency division multiplexing with subcarrier power modulation (NC-OFDM-SPM)&multi-user auxiliary signal superposition transmission (MU-AS-ST)

Future wireless systems are expected to serve very challenging requirements such as enhancing the spectral efficiency and transmission reliability, securing the transmission and guaranteeing low-complexity and low latency communications. In this scope, we investigate and propose in this work some promising research directions for ensuring an effective design for future wireless systems: 1) we study the combination of multi-dimensional OFDM modulations and non-coherent detection for enhancing the spectral efficiency and reducing the complexity in the design of future wireless systems. Particularly, in this regard, we propose and study a new technique termed as 'Non-Coherent Orthogonal Frequency Division Multiplexing with Subcarrier Power Modulation (NC-OFDM-SPM)' for doubling the spectral efficiency per receiving user/device through the exploration of the power of the subcarriers inside an OFDM block as an additional dimension for conveying extra information. The use of non-coherent detection ensures low-design complexity in this idea. 2) We propose a novel physical layer security design for effective and secure future multiple access communications. The proposed design is called 'Multi-User Auxiliary Signal Superposition Transmission (MU-AS-ST)' which is presented as an alternative design for the current conventional Power Domain NOMA which was studied by the 3GGP (3rd Generation Partnership Project) from release 13 till 16 under the name 'Multi- User Superposition Transmission (MUST)' before being eliminated from the study items in release 17. The proposed design superimposes auxiliary signals with the users data for can- celling the inter-user interference fully while achieving perfect secrecy against both internal (presence of an untrusted legitimate user) and external eavesdroppers. MU-AS-ST achieves better reliability than conventional NOMA and does not use Successive Interference Cancellation. Moreover, this design works for the combination of any two users regardless of their distance from the base station unlike conventional NOMA which works only for the cases where there exists a significant path-loss channel difference between paired (or super-imposed) users. Furthermore, carrying all the processing at the base station makes this design an appealing choice for processing-restricted communication devices such as IoT devices. 3) We study the integration of multi-dimensional OFDM modulation formats in multiple access setups for enhancing the spectral efficiency per area and per device for a more optimal usage of the spectrum allocated for wireless communications. As an example of this integration, we study the combination of OFDM-SPM with MU-AS-ST where we show that this leads to doubling the spectral efficiency per area and per device. The proposed designs were studied thoroughly and their performance was evaluated in terms of different performance metrics such as bit error rate, spectral efficiency, design complexity and peak to average power ratio (PAPR). Keywords: auxiliary signals, eavesdropping, IoT, low-complexity, multi-dimensional OFDM, multiple access, non-coherent detection, physical layer security, power domain NOMA, reliability, spectral efficiency, subcarrier power modulation, wireless communications.