Sangho Ahn

A Novel Scheme for Frequency Offset Estimation in OFDM Systems

In this paper, a novel integer frequency offset estimation scheme which is not affected by the timing offset is proposed for orthogonal frequency division multiplexing (OFDM) systems. Most of the schemes proposed for the integer frequency offset estimation assume the absence of the timing offset; however, such an assumption is not appropriate in practical systems. In this paper, using differential combining between two successive subcarriers, we propose a novel frequency offset estimation scheme. The simulation results show that the proposed scheme is robust to the timing offset variation, and thus, performs better than the conventional scheme when the timing offset range is not known.

A Novel Frequency Offset Estimation Algorithm Using Differential Combining for OFDM-Based WLAN Systems

The timing offset is one of the main error sources in estimating the frequency offset in orthogonal frequency division multiplexing (OFDM)-based wireless local area network (WLAN) systems. Although some works have been done to mitigate the effect of the timing offset on the frequency offset estimation, most of the investigations require the knowledge of the timing offset range, which is not generally available in practical systems. In this paper, we propose a new frequency offset estimation algorithm using differential combining between two successive correlation samples, which does not require the knowledge of the timing offset range, and thus, is robust to the timing offset variation. The simulation results show that the proposed algorithm is not only robust to the timing offset variation, but also generally performs better than the conventional algorithm, in the case of the timing offset range being not known exactly.

New synchronization schemes for UWB systems

This paper addresses the decision rules for synchronization in ultra-wideband (UWB) systems. The conventional decision rule cannot guarantee a good performance in receiver operations such as detection and decoding after the synchronization. To solve this problem, in this paper, we propose new decision rules for synchronization in UWB systems. We first derive an optimal decision rule based on the maximum likelihood (ML) criterion and then a simpler suboptimal decision rule. Simulation results show that the proposed decision rules have better synchronization performance than the conventional decision rule.

Integer frequency offset detection methods for OFDM-based WLAN systems

Recently, a frequency offset estimation method for orthogonal frequency division multiplexing (OFDM) has been proposed by Ren et al. (REA) [9]. The method can estimate an frequency offset for any training symbol structure. In the REA method, however, the integer frequency offset detection probability is rapidly varying according to the fractional frequency offset. In this paper, we first analyze the REA frequency offset estimation method, and define new detection criteria suitable for integer frequency offset detection. Then, we propose two efficient integer frequency offset estimation methods based on maximum likelihood method. The proposed methods overcome the drawback of the REA method, maintaining its advantage. The numerical results demonstrate that the proposed methods outperform the REA method in terms of the integer frequency offset detection probability.

Code Tracking Bias Compensation Scheme for the Galileo E1 OS signal

Galileo system uses direct sequence/spread spectrum (DS/SS) as its modulation method. Single delta delay lock loop (Delta-DLL), where Delta is sample duration between early and late correlation values, has been widely used for code tracking in DS/SS systems. When the Delta-DLL is used for code tracking in ideal environments, code tracking bias does not arise because the symmetry of the correlation function is not destroyed. However, in multipath (MP) environments, a large code tracking bias arises owing to the asymmetrical correlation function. An MP signal always has a propagation delay time after that of the line of sight signal. Thus, correlation values in the advanced offset region are less distorted than those in the delay offset region. From this observation, we propose an effective tracking bias compensation scheme for the Galileo E1 open service signal.

A Robust Frequency Offset Estimation Scheme to Fractional Frequency Offset Variation for OFDM Systems

A frequency offset estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) systems. In the conventional scheme, there is a disadvantage that the performance is sensitive to the fractional frequency offset variation. Thus, a novel scheme is employed to estimate the frequency offset. The proposed scheme is robust to the fractional frequency offset variation and the performance is better than the conventional scheme.