Optimal Preamble Design for Short Packet Circularly Pulse-Shaped OFDM Transmissions

A preamble optimization design based on circularly pulse-shaped orthogonal frequency division multiplexing (CPSOFDM) modulation for subband-wise short packet transmissions in 5G mMTC and URLLC is proposed. To meet the four preamble signal requirements of periodically low autocorrelation (AC), low out-of-subband emission (OSBE), low peak-to-average power ratio (PAPR), and fixed energy simultaneously, a quartic minimization problem is formulated by taking the complex-valued pilot symbols fed into the CPS-OFDM transceiver as variables. This problem is then solved under the majorization-minimization (MM) convex-iteration (CI) algorithmic framework with semidefinite relaxation. As revealed in simulation results, the proposed CPS-OFDM preamble, resulting from the optimal pilot sequence solution, can achieve lower AC, OSBE, and PAPR, compared to the preambles produced by the existing Zadoff-Chu (ZC), pseudo-random (PN), and lowPAPR type 1 (LP1) sequences defined in the 3GPP specifications for 5G New Radio (NR). In addition, although there exists carrier frequency offset (CFO) and inter-block interference (IBI) in the CPS-OFDM system without guard interval, the proposed preamble also leads to better packet data detection reliability than the others, because of its excellent liming offset (TO) estimation performance.