Carrier frequency offset estimation for FM and symbiotic FM radio data system hybrid signal

Abstract

The symbiotic FM radio data system (SRDS) is a radio data system that a specially designed OFDM signal co-lives with FM signal, which enables a significantly higher data rate than existing radio data systems. The cyclic prefix of the OFDM symbol has the same length as the OFDM body, which enables the analytic separation of the co-channel OFDM and FM signal at receiver side, utilizing the fact that the OFDM body and prefix is equal. In this work, we show that the OFDM body and prefix cannot be viewed as equal when there is sufficient carrier frequency offset (CFO). Thus, we propose a two-step CFO estimation algorithm for FM and SRDS hybrid signal. The first step estimates the coarse CFO by exploring the characteristics of the FM signal. Once the coarse CFO is removed, the residual CFO is small enough for FM and OFDM separation. The second step fine estimates CFO from the OFDM-only signal using its repeated PN structure after the separation. Detailed mathematical equations are formulated and simulation results are given. The results show that the proposed algorithm works fine with the simulation setup and has a final residual CFO less than 3.9Hz.