Won-Jae Shin

A Robust Estimation of Residual Carrier Frequency Offset With I/Q Imbalance in OFDM Systems

In this paper, we focus on improving the accuracy of frequency offset estimation for an orthogonal frequency-division multiplexing (OFDM) system under the conditions of the joint impairments in both carrier frequency offset (CFO) and in-phase/quadrature (I/Q) imbalance. To propose a robust CFO estimation scheme and to benchmark its performance, the performance of the conventional frequency estimation algorithm in the presence of I/Q imbalance is analyzed, and some modifications to the conventional estimation scheme are highlighted. We show via simulations that such a design achieves a remarkable robustness against I/Q imbalance; thereby, the proposed scheme can efficiently estimate the CFO, irrespective of the I/Q mismatch.

Performance of carrier frequency synchronization for OFDM-based mobile cellular systems over time selective fading channels

Abstract This paper evaluates the performance of a cell-specific reference signal (RS)-assisted residual carrier-frequency offset (CFO) detection scheme for a long-term evolution (LTE) downlink in a time-varying channel. Channel variations severely degrade the performance of OFDM by introducing both a complicated multiplicative distortion and an additive inter-carrier interference. Taking into consideration the effect of time-variant fading channels, an analytical closed-form expression of the mean square error (MSE) of the post-FFT CFO detection scheme is derived. The analytical expression is verified through simulations using the parameters of the LTE standard.

A Robust Joint Frequency Offset Estimation for the OFDM System Using Cyclic Delay Diversity

Cyclic delay diversity (CDD) is a low-complexity transmit diversity technique for orthogonal frequency division multiplexing (OFDM), which transforms a multiple-input channel into an equivalent single-input channel with a large delay spread. Consequently, high frequency selectivity makes channel and frequency estimation a challenging task. This paper proposes an improved joint estimation of carrier frequency offset and sampling frequency offset for the OFDM system using CDD technique. By finding the amount of a transmit-antenna specific delay which reduces the variance of the frequency estimation scheme, these parameters improve the robustness of the joint frequency estimation scheme against the frequency selectivity of the channel. Computer simulation shows that the joint frequency-offset estimation scheme with properly designed cyclic delay parameters performs robustly, with the performance better than the conventional scheme.

A scattered pilot synchronization scheme by partial correlation for DVB-H systems

This paper presents an improved, scattered pilot synchronization (SPS) scheme in digital video broadcasting-handheld (DVB-H) systems, which detect the pilot pattern of the currently received orthogonal frequency division multiplexing (OFDM) symbol. To reduce the SPS time, and to mitigate the influence of the sampling frequency offset (SFO), the proposed SPS method is based on the conventional correlation-based SPS, and adopts a partial correlation. By using computer simulations, the synchronization performances of the traditional SPS and the new proposed SPS algorithms are evaluated in terms of their probabilities of synchronization failure.

Computationally effective sampling frequency-offset estimation for OFDM-based LTE downlink systems

In this paper, we present a low-complexity sampling frequency-offset (SFO) estimation scheme suitable for the 3GPP long-term evolution (LTE) downlink system. First, a novel SFO estimation method for a pilot-aided orthogonal frequency division multiplexing system is proposed providing a good performance with reduced complexity. To achieve low complexity, the proposed estimation scheme uses a central conjugate-symmetric primary synchronisation signal specified in the LTE standard, which eases the SFO estimation at the receiver. For performance evaluation, we derive the mean square error expression of the proposed frequency estimation scheme. Simulations show that the proposed frequency estimation scheme can detect the SFO with higher accuracy and much lower complexity, compared with the conventional estimation schemes. Copyright

A Reduced Complexity Joint Cell Index and Carrier Frequency Offset Detection for OFDM-based LTE Systems

Abstract In cellular systems, user equipment must perform the cell search procedure in order to acquire symbol timing, frame timing, carrier frequency offset (CFO), sector cell index (CID) and group CID. This paper proposes a low-complexity sector CID and CFO detection scheme in a long term evolution downlink system. To achieve low complexity, a primary synchronization signal used for parameter estimation is grouped into a number of subsets so that the phase of pilots in each subset is unique. The performance and complexity of the proposed joint detection scheme are compared with those of the conventional joint detection schemes. We show via simulations that such a design achieves exactly the same detection accuracy as that of the conventional joint detection schemes with one half of complexity being saved.

Complexity Effective Integer Frequency Offset and Sector Cell Detection Scheme for LTE Downlink System

This paper proposes a low-complexity integer frequency offset (IFO) and sector cell index (CID) detection scheme in a long term evolution downlink system. In the proposed detection scheme, the IFO and CID are estimated in a decoupled manner. In doing so, the detection scheme is designed to first estimate IFO without a priori knowledge of cell-specific reference signals and then detect the CID consecutively. We show via simulations that such a design achieves not only a low computational load but also comparable performance, when compared to the conventional detection scheme.

An Improved Scattered Pilot Detection Scheme for OFDM-Based DVB-H

In this paper, we present an improved scattered pilot synchronization (SPS) scheme in the digital video broadcasting-handheld (DVB-H) system, which detects the pilot pattern of currently received orthogonal frequency division multiplexing (OFDM) symbol. To reduce the SPS time and mitigate the influence of sampling frequency offset (SFO), the proposed SPS method is based on the conventional correlation-based SPS and adopts a partial correlation. By using computer simulation, the synchronization performance of the traditional SPS and the proposed SPS algorithms is evaluated in terms of probability of synchronization failure.