Ki-Won Kwon

Peak-to-average power control for multiple-antenna HIPERLAN/2 and IEEE802.11a systems

A combination of multi-input multi-output (MIMO) signal processing with orthogonal frequency division multiplexing (OFDM) is regarded as a promising solution for enhancing the performance of next generation wireless local area network (WLAN) systems. This paper evaluates the peak-to-average power ratio (PAR) performance in a MIMO OFDM-based WLAN system using a space-time block code (STBC). The investigated PAR control schemes, which are originally based on the selective mapping (SLM) and partial transmit sequence (PTS) approaches, select the transmitted sequence with the lowest average PAR over all transmit antennas and retrieve the side information (SI) very accurately at the expense of a slight degradation of the PAR performance. The low probability of false SI can improve the overall detection performance of the MIMO-WLAN system encountered with erroneous SI compared to the ordinary SLM and PTS approaches, respectively.

Low-complexity coarse frequency-offset synchronization for OFDM applications

We present a coarse frequency-offset synchronization technique for an OFDM-based transmission system with an emphasis on the Eureka-147 DAB receiver. The proposed frequency-offset synchronization algorithm using two defined correlation functions is shown to have high robustness against a large range of symbol timing offset with a moderate implementational complexity.

Low-complexity channel estimator for high-rate personal area networks employing CCK modulation

This paper considers a channel estimation technique in a wireless personal area network (WPAN) system with complementary code keying (CCK) signaling over multipath fading channels. The performance of the proposed coherent detector is compared with that of a noncoherent detector, and a significant improvement of performance is observed in terms of the bit error probability.

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.

Multiplication-Free Estimation of Integer Frequency Offset for OFDM-Based DRM Systems

This letter proposes a low complexity integer frequency offset (IFO) estimation scheme in an orthogonal frequency division multiplexing (OFDM) based digital radio mondiale plus (DRM+) system with nonuniform phased pilot symbols. To reduce the computational complexity, the pilot symbols used for frequency estimation in the DRM+ system are partitioned into a number of pilot subsets, and pilots in each subset are phase-rotated to have a unique phase so that the estimator is made computationally efficient.

Timing synchronization for IEEE 802.15.3 WPAN applications

This letter derives and computes the detection probability of timing synchronization in a wireless personal area network (WPAN) system encountered with a multipath Rayleigh fading channel. The timing synchronization scheme using CAZAC training symbols and correlation techniques is adopted. For measuring system performance, the sync detection probability derived in the considered system is evaluated in a multipath Rayleigh fading channel.

Pilot and Data Aided Channel Estimation for OFDM systems in Rapidly Time-Varying Channels

In this paper, we propose an efficient estimation technique for time-varying multipath channels by exploiting two dimensional delay-time nature in pilot inserted orthogonal frequency division multiplexing (OFDM) systems. The proposed technique consists of multipath snapshot estimation at periodic channel observation instances over an OFDM block and the linear interpolation of two consecutive multipath snapshots. Two decision-directed data utilizing schemes, data removed and data added correlation schemes, are proposed to enhance the performance of the multipath snapshot estimation.

Cooperative diversity scheme using virtual MIMO antenna array in a LTE-A uplink system

This paper proposes an effective cooperative communication scheme to obtain high reliability in a long-term evolution-advanced (LTE-A) uplink system. The proposed scheme constitutes the virtual multiple input multiple output antenna array by the cooperative communication scheme and suggests the transmission signal configuration applying spatial phase coding (SPC) with the modified hierarchical modulation. In the proposed transmission signal configuration, high diversity gain is provided by the SPC scheme and the data rate is improved by modified hierarchical modulation. The modified hierarchical modulation transforms the constellation of the conventional hierarchical-modulated signal in order to minimize the influence by noise in the proposed scheme. In the LTE-A uplink system, the proposed scheme is effective to a user equipment (UE) based on single carrier-frequency division multiple access because UE using only single antenna can obtain high reliability without additional antennas.

Residual symbol timing offset estimation for DRM+ system with cyclic delay diversity

In this study, we propose an enhanced residual symbol timing offset(STO) estimation scheme in an orthogonal frequency division multiplexing (OFDM) based digital radio mondiale plus (DRM+) system with cyclic delay diversity (CDD). By proper selection of the amount of cyclic delay and pilot subset partitioning, a robust and low-cost residual STO estimator is derived. By computer simulation, the proposed estimator is shown to benefit from properly designed delay parameter and pilot subsets.

FREQUENCY ESTIMATION BY PILOT SET PARTITIONING FOR OFDM SYSTEMS WITH MULTIPLE TRANSMIT ANTENNAS

Cyclic delay diversity (CDD) is a simple approach to increase the frequency selectivity of the channel in an orthogonal frequency division multiplexing (OFDM) based transmission scheme. However, CDD can cause serious degradation in the performance of channel and frequency estimation in the frequency domain. This paper suggests a post-FFT frequency estimation scheme suitable for arbitrary cyclic delays in the CDD-OFDM system. By partitioning uncorrelated pilot subcarriers into subsets to be flat, and performing frequency estimation for each pilot subset, a robust integer frequency offset estimation scheme is derived.