Design of OFDM Navigation Signal and Receiver for Accurate Ranging Estimation in a Power-Limited CubeSat Transmitter

Orthogonal Frequency Division Multiplexing (OFDM), well-established in cellular fifth-generation (5G) communication, is emerging as a navigation signal for CubeSats. Yet, CubeSats' limited transmit power complicates OFDM synchronization, potentially skewing distance measurements. This article introduces a differentially coherent accumulation (DCA) algorithm for utilizing the Synchronization Signal (SS) within the SS and Physical Broadcast Channel (PBCH) block (SSB). This approach aims to improve the sensitivity and accuracy of OFDM acquisition, enabling precise time of arrival (TOA) estimation even under the low signal-to-noise ratio (SNR) conditions characteristic of long-distance CubeSat signal transmissions. Additionally, the article applies a near-optimal likelihood ratio test (NOLRT) detector to resolve integer ambiguity inherent induced from the DCA algorithm, which prevents additional bias in TOA estimation. Numerical simulations validate the effectiveness of the proposed weak OFDM acquisition algorithm with the pre-defined SSB structure, demonstrating a significant reduction in ranging error. Specifically, the simulations achieved a standard deviation of 2.75 meters in ranging error at a SNR of -20 dB, utilizing a SSB comprising 15 times repeated ZC sequences.