Multiple Objective Optimization of OSBE and ISI for Cyclic Prefix Free DFT-s-OFDM Systems

This paper studies the out-of-subband emission (OSBE) and inter-symbol interference (ISI) problems for the cyclic prefix (CP) free DFT-s-OFDM system. Solving the OSBE problem, the waveform techniques such as precoding, windowing and filtering have been studied. However, most waveforms using windowing and filtering suffer from ISI. The ISI results in degradation of detection error performance, especially in a CP free DFT-s-OFDM system. In this paper, we study a joint optimization algorithm to design the spectral precoder and tail precoder iteratively. The spectral precoder supresses the OSBE and the tail precoder deals with the ISI. However, the spectral precoder and the tail precoder are not independent to each other. This work considers iterative design of spectral and tail precoders to reducie the OSBE and to mitigate ISI jointly with constraints on energy, spectrum emission mask (SEM) defined in 5G NR, and guaranteed spectral efficiency. In the joint optimization process, the decomposition techniques are also used to reduce the computation complexity. The numerical simulations have been conducted which shows that the proposed approach achieves better error performance than the prior arts of works in CP free DFT-s-OFDM systems.