On Enhancing the Pilot-Aided Sampling Clock Offset Estimation of Mobile OFDM Systems

Abstract

Sampling Clock Offset (SCO) estimation is an important issue in Orthogonal Frequency-Division Multiplexing (OFDM) systems because sampling frequency mismatch between the transmitter and the receiver may severely degrade the system performance due to the loss of orthogonality between the subcarriers. SCO estimation in mobile environment is quite challenging since channel variation leads to an additional phase rotation that masks the SCO effects. However, most of the existing techniques rely on the assumption of a time-invariant channel and become considerably inaccurate in a mobile environment. In this paper, we propose an improvement to an existing pilot-aided SCO estimator aiming to provide robustness against channel variations. Performance was evaluated through simulations in an ISDB-T (Integrated Services Digital Broadcasting Terrestrial) compliant system and the results have shown a considerable improvement for all ranges of signal-to-noise ratios, specially for higher Doppler spread.

Robust Blind Detection of Integer Carrier Frequency Offset for Terrestrial Broadcasting Systems Using Band Segmented Transmission

“…After frequency synchronization, there are residual CFO and SFO errors that continuously rotate the phase of the OFDM symbol. During the tracking phase, the residual CFO and SFO are typically estimated based on a set of dedicated pilots, which are estimated and compensated periodically because of its time-accumulative nature [19][20][21]. Since data demodulation can be correctly performed only after successful compensation of the IFO, the IFO represents an important task in the overall synchronization procedure.…”

“…Some kinds of pilot and control symbols, such as SP, CP, AC, and TMCC, are specified to enable reliable synchronization between the transmitter and receiver, whose configuration varies according to the ISDB-T segment format. The CP is mainly utilized to perform time and frequency synchronization [20,21], whereas the SP is provided only in coherent modulated segments for the purposes of channel estimation [22,23]. The AC2 is present only in differential modulated segments.…”

Successive Interference Cancellation-Based Weighted Least-Squares Estimation of Carrier and Sampling Frequency Offsets for WLANs

“…A number of CFO and SFO estimation algorithms have been studied throughout the years. These studied algorithms can be classified into two types: blind algorithms that do not use pilot symbols [7][8][9] and data-aided (DA) [10][11][12][13][14][15][16][17][18][19][20] algorithms using pilot symbols. Because of their simple form and computational convenience, DA methods have received more attention and are considered in this paper.…”

“…ML estimation requires at least a onedimensional exhaustive search and is not suitable for hardware implementation. Therefore, many DA suboptimal linear algorithms have been suggested [14][15][16][17][18]. A simple joint CFO and SFO estimation was presented in [14], where the value of the CFO was estimated for every symbol, but the SFO was derived from the early estimation of the CFO, resulting in a residual SFO and performance decrease.…”

Effective Blind Frequency Offset Estimation Scheme for BST-OFDM Based HDTV Broadcast Systems

“…One of the major weakness of OFDM is its sensitivity to carrier frequency offset (CFO) and sampling frequency offset (SFO) which are caused by the mismatch between transmitter and receiver oscillators [7,8]. If not accurately estimated and compensated, the CFO and SFO can destroy the orthogonality among the subcarriers, leading to performance loss at the OFDM receiver [9,10]. In the literature, several types of pilot-aided algorithms have been proposed to perform the joint estimation of CFO and SFO, including maximum likelihood (ML) and linear least-squares (LS) strategies [11][12][13][14][15][16][17][18][19][20][21][22][23].…”