Timing and Phase Offset Sensitivity of Autocorrelation Based Frequency Estimation in an FH-OFDM System

In this paper, a new aspect on the problem of carrier frequency offset (CFO) estimation is studied in a frequency-hopping (FH) orthogonal frequency division multiplexing (OFDM) system. Unlike in a traditional nonhopped OFDM system, in FH-OFDM system it is important to verify how accurately frequency-switching must be performed before the CFO estimation can take place with adequate performance. The accuracy of frequency-switching is evaluated through frequency-hopping timing offset (FHO) and frequency-hopping phase offset (PHO) between the received signal and the signal produced by the local frequency-hopping synthesizer of the receiver. The target system uses ultra-wideband (UWB) in order to achieve very high data rate of 1.6 Gbit/s. The performance of selected autocorrelation based algorithms is simulated in multipath fading channel under the FHO and PHO, and the results are compared to the performance of ideal frequency-switching and the corresponding analytical Cramer-Rao bound. It is found that the CFO estimators based on autocorrelation principle are quite robust to the FHO less than half the hopping period. Furthermore, simple methods are proposed to compensate the degradation caused by the FHO. The estimators are, however, sensitive to the PHO caused by the possible lack of phase memory in the frequency-hopping synthesizer resulting in a significant bias to the CFO estimate.