Eu-Suk Shim

OFDM Carrier Frequency Offset Estimation Methods With Improved Performance

Orthogonal frequency division multiplexing (OFDM) systems are highly sensitive to carrier frequency offset and symbol timing error. This paper deals with estimation method of integer frequency offset (IFO) without the aid of pilot symbols. The proposed IFO estimator exploits two consecutive identical OFDM data symbols with only change of phase. In order to improve the accuracy of the IFO estimator, receive diversity is adopted. To demonstrate the efficiency of the proposed IFO estimators, comparisons are made with other existing estimators in terms of error performance, estimation range, and complexity.

OFDM Integer Frequency Offset Estimator in Rapidly Time-Varying Channels

In this paper, we present a simple way of estimating the integer frequency offset of orthogonal frequency division multiplexing (OFDM) system over a rapidly time-varying channel. By utilizing the channel responses of neighboring subcarriers within one pilot symbol, the frequency offset estimator is derived. We show by simulation that the proposed estimator can accurately estimate the integer frequency offset with reduced computational burden

A Frame Detector for Zero-Padded OFDM Systems

This letter proposes an orthogonal frequency division multiplexing (OFDM) frame synchronization scheme when the guard interval (GI) consists of a zero-padded (ZP) sequence. The frame synchronization method uses the ZP symbol where nothing is transmitted for GI so that the drop in received power can be detected to find the beginning of the frame. Simulations reveal that this method significantly improves synchronization performance of the ZP-OFDM system in a multipath fading channel.

Synchronization Receiver for OFDM-Based FM Broadcasting Systems

The digital radio mondiale (DRM) consortium is now preparing to test and verify the design of DRM plus, prior to standardization, produce a revision to the existing DRM system specification. This paper presents an overview of the OFDM-based DRM system, planned to operate in FM bands, utilizing important receiver aspects, such as timing and frequency synchronization, which can provide benefits to the overall system performance. In particular, algorithms are devised or selected for the sequential estimation of symbol timing and carrier frequency offsets by exploiting the structure of the data and pilot. The performance of using the proposed algorithms is demonstrated via several examples in the channel models for FM bands.

Pilot Subset Partitioning Based Integer Frequency Offset Estimation for OFDM Systems With Cyclic Delay Diversity

Cyclic delay diversity (CDD) is a simple transmit diversity technique for coded OFDM systems with multiple transmit antennas. However, high frequency selectivity caused by CDD degrades the performance of post- FFT estimation, i.e., integer frequency offset (IFO). This paper suggests a simple way of improving the performance of the IFO estimator based on the pilot subset partitioning which is designed to reduce the effect of frequency selective fading by adopting the CDD. By partitioning uncorrelated pilot subcarriers into subsets to satisfy high correlation, and performing frequency estimation for each pilot subset, a robust IFO estimation scheme is derived. The simulation results show that the proposed method can provide benefit to the overall system performance .

PARAMETER ESTIMATION AND ERROR REDUCTION IN MULTICARRIER SYSTEMS BY TIME-DOMAIN SPREADING

This paper suggests parameter estimation and error reduction scheme in a multicarrier transmission system. A multicarrier orthogonal frequency division multiplexing (OFDM) signal by using a time-domain spreading (TDS) coupled with a cyclic time shift enables a pilot-less synchronization. Exploiting the modified OFDM signal endowed with the TDS, the proposed synchronization receiver can accurately estimate the carrier-frequency offset as well as the timing offset of OFDM signals without the use of training symbol.

OFDM Timing Estimation Method without Training Symbol

In this letter, we present timing synchronization method using two consecutive orthogonal frequency division multiplexing (OFDM) symbols which are designed to be cyclic-shifted against each other. Our approach can be viewed as an expansion of Minns correlation methods. Using the proposed OFDM signal, however, we can estimate the timing offset without any training symbol.

Low-cost integer frequency offset estimation for OFDM-based DRM receiver

In this paper, we propose an improved and low-cost integer frequency offset (IFO) estimation method by partitioning pilot symbols effectively in an orthogonal frequency division multiplexing based digital radio mondiale (DRM) system. To this end, the time reference cell (TRC) symbol for frequency estimation is grouped into a number of pilot clusters, so that the TRC subcarriers in each cluster are closely spaced to show approximately frequency-nonselective characteristics. The performance of the proposed IFO estimator is compared with that of the conventional estimator, and shows that the proposed technique can effectively achieve lower estimation errors in frequency offset estimation as well as can be implemented with reduced computational complexity.

Robust frequency synchronization scheme for digital FM broadcasting systems using cyclic delay diversity

Cyclic delay diversity (CDD) is a simple transmit diversity technique for coded orthogonal frequency division multiplexing (OFDM) systems. However, high frequency selectivity caused by CDD degrades the performance of post-FFT estimation. This paper suggests a simple way of improving the performance of the integer frequency offset estimator in OFDM-based digital radio mondiale (DRM) system for FM broadcasting services. If compared to the conventional estimator, our proposed scheme has the advantage of being more robust against the frequency selective fading.

An Improved Autocorrelation Based Single Frequency Estimator with Reduced Complexity

This paper proposes an improved single frequency estimator for flat fading channels. The proposed carrier frequency offset (CFO) estimator decreases the number of computations in the calculation of the autocorrelation function (AF) when compared to AF-based conventional estimators. The results shown that the proposed estimator achieves better performance than the existing estimators. Furthermore, the performance of proposed method has been observed to lie very close to the Cramer-Rao lower bound (CRLB).