Clustered pilot tones for carrier frequency offset estimation in OFDM systems

Abstract

A new pilot tone placing and pilot sequence design is proposed to compensate the carrier frequency offset (CFO) in OFDM systems. Unlike the conventional approach where isolated pilot tones are used, in this paper every two pilot tones are clustered as a group and these groups are equally spaced. The pilot sequence is carefully designed, of which the left hand sided pilot symbol in each cluster is antipodal with the right hand sided one. The performance in terms of the pilot channel interference ratio (CIR) can be significantly improved by the proposed pilot scheme. Theoretical analysis shows that the clustered pilot tones can give a substantially lower CFO variance than that of the isolated pilot tones. Simulation results are presented to verify our newly proposed theory.

Antipodal pilot tones in orthogonal frequency division multiplexing systems for carrier frequency offset estimation

“…The estimation is based on the phase shift of pilot symbols in two consecutive OFDM symbols. The estimation in [21] can be written aŝ…”

“…In addition, by subtracting the adjacent received pilot signals on each pilot group, it not only improves the signal energy of antipodal pilot signals but also reduces the ICI power on each group [21]. However, the performance of this technique is based on the specific assumption as mentioned earlier so the real performance in case of the severe frequency selective fading channel will provide more estimation errors.…”

“…By inserting pilot tone in every OFDM symbol, CFO can be continually estimated by measuring the phase shift of pilot symbols in two or more consecutive OFDM symbols [19]. However, the estimation performance in [19] is based on pilot-to-data interference ratio where this ratio has been described in [20,21]. The works in [20,21] can improve the ratio of pilot tones to their intercarrier interference (ICI) where the estimation range in [19][20][21] still is ±0.5 of subcarrier spacing.…”

“…However, the estimation performance in [19] is based on pilot-to-data interference ratio where this ratio has been described in [20,21]. The works in [20,21] can improve the ratio of pilot tones to their intercarrier interference (ICI) where the estimation range in [19][20][21] still is ±0.5 of subcarrier spacing. However, even if [20,21] can improve the estimation performance by increasing pilot-to-data interference ratio, ICI caused by data still is existent and it is severe if CFO goes high.…”

“…The works in [20,21] can improve the ratio of pilot tones to their intercarrier interference (ICI) where the estimation range in [19][20][21] still is ±0.5 of subcarrier spacing. However, even if [20,21] can improve the estimation performance by increasing pilot-to-data interference ratio, ICI caused by data still is existent and it is severe if CFO goes high. In addition, these techniques require a channel to be unchanged during the estimation period.…”