Byungjik Keum

Adaptive local tone mapping based on retinex for high dynamic range images

In this paper, we present a new tone mapping technique for high dynamic range images based on the retinex theory. Our algorithm consists of two steps, global adaptation and local adaptation of the human visual system. In the local adaptation process, the Gaussian filter of the retinex algorithms is substituted with a guided filter to reduce halo artifacts. To guarantee good rendition and dynamic range compression, we propose a contrast enhancement factor based on the luminance values of the scene. In addition, an adaptive nonlinearity offset is introduced to deal with the strength of the logarithm functions nonlinearity. Experiments show that our algorithm provides satisfactory results while preserving details and reducing halo artifacts.

A Radio Repeater Interference Cancellation Model for Mobile Communication Systems

When the gain of a radio repeater is larger than the isolation between the transmit and receive antennas of the repeater, the feedback signal that comes into the receive antenna from the transmit antenna of the repeater causes the repeater to go into feedback oscillation regardless of the input signal. To prevent feedback oscillation of the repeater by interference cancellation (ICAN), a feedback oscillation model of a radio repeater is first formulated. An ICAN model is then derived from that model. According to the ICAN model, iterative algorithms such as the least mean square (LMS) algorithm using the minimum mean square error criterion can be applied to perform the necessary ICAN. The validity of the ICAN model is confirmed by a computer simulation that shows the relationship among the level of ICAN, the repeaters gain, the estimated delay, and the filter length for the LMS algorithm.

A new low-complex interference cancellation scheme for WCDMA indoor repeaters

A new low-complex interference cancellation scheme for WCDMA indoor repeaters is presented in this paper. The real time interference cancellation performance of an indoor repeater depends on its computational complexity. In order to reduce the complexity of interference cancellation repeaters, computationally efficient interpolated filters are used as an input filter for frequency band selection and an output filter for spectrum mask control. Interpolation is applied to the implementation of an adaptive filter that performs interference cancellation under indoor channel environments. This allows the adaptive filter to calculate fewer filter taps and only uses them to estimate the feedback signal. For additional complexity reduction, a single common image rejection filter is designed to be shared among interpolated filters. The proposed scheme reduces the complexity of the conventional interference cancellation repeater by half without deterioration of the interference cancellation performance of the repeater.

An Efficient Hardware Simulator for the Design of a WCDMA Interference Cancellation Repeater

An efficient hardware simulator for the design of a WCDMA interference cancellation repeater (ICR) is presented. The ICR, which is composed of a digital interference canceller and analog parts, is a time-varying system that reacts to a time varying input signal. The design of the digital interference canceller is time-consuming due to the need for many iteration cycles of debugging, tuning, and performance verification. Furthermore, its performance, which is represented by the error vector magnitude (EVM) and the output power spectrum, can be verified only after it is implemented on a digital board, integrated into the repeater hardware with analog parts, and hooked up with expensive test equipment. Hence, a special computerized simulator is needed for fast and efficient verification of the interference cancellers design. The simulator consists of a signal generator, which emulates a base station, the ICR with an interference canceller, a feedback channel that models wireless fading channels, and a receiver that measures the EVM of the ICR. The accuracy of the simulator is verified by showing that the EVM and the output power spectrum of a reference interference canceller measured on this simulator match well within an error range of less than 8% with the corresponding values measured on the repeater hardware. The usefulness of the simulator is also confirmed by simulating the EVM performance of the ICR under various multipath fading channel conditions.

A frequency domain approach for complexity reduction in wideband radio interference cancellation repeaters

To cancel wideband feedback interference signals that enter the receive antenna via near-by reflectors from the transmit antenna of the radio repeater, the wideband input signal is first split into several narrowband signals by narrowband filters. Interference cancellation (ICAN) is then performed on each split narrowband signal separately. As a result, the major portion of the complexity of a feedback ICAN system in a wideband radio repeater is accounted for by input and output filtering for spectrum control instead of the complexity of the ICAN algorithm itself. In this work, to reduce the overall complexity of the feedback ICAN system, a frequency sampling filter that is efficiently designed in the frequency domain when the filterpsilas frequency response has a narrow bandwidth is applied to input and output filtering for spectrum control. The proposed filtering method reduces the complexity of the feedback ICAN system to less than a half that of the conventional system with no performance deterioration.

A scheme to compensate for the input multipath channel effect in an interference cancellation repeater for mobile communication systems

Conventional interference cancellation (ICAN) techniques are mainly used to prevent feedback oscillation of a radio repeater when the repeaterpsilas gain is larger than the isolation between the transmit and receive antennas of the repeater. Therefore, the output signal distortion of the radio repeater, which is caused by the multipath channel between the repeaterpsilas input antenna and a base station, is not properly compensated. In this paper, a scheme to compensate for the output signal distortion in conventional ICAN repeaters is proposed. The compensation is performed by estimating the input multipath channel, inverting the estimated channel, and compensating the input signal using the inverted channel prior to feedback signal cancellation. The validity of the proposed scheme is confirmed by showing that the output signal quality of a conventional ICAN repeater is considerably improved by this scheme.

A Selective HARQ Scheme Operating based on Channel Conditions for High Speed Packet Data Transmission Systems

A selective hybrid automatic repeat request (HARQ) scheme operating based on channel conditions for high speed packet data transmission systems is presented. This scheme exploits the channel condition identified by the channel quality indicator (CQI) to determine whether the retransmitted packet is directly decoded without soft combining or it is soft combined with the original packet and decoded. Since the channel condition is already measured and mapped to the CQI number by the receiver to report to the base-station for adaptive modulation and coding, additional increase of computational complexity at the receiver is not required for this scheme. The proposed selective HARQ scheme shows about two to three times performance improvement in terms of throughput because it takes the quality of retransmitted packets into account based on channel conditions before performing soft combining with the original packet with error.

Empirical non-local algorithm for image and video denoising

This paper presents a new denoising algorithm capable of effectively removing noise without too much loss of original data. Based on the non-local means (NL-means) algorithm proposed by Buades et al., This approach uses a concept of thresholding weight of neighborhood pixels which have low similarity and applies the three-step search (TSS) technique in order to save computations.

A complexity reduction scheme for interference cancellation radio repeaters

When applying the real time interference cancellation (ICAN) technique to a radio repeater, the most urgent task is to reduce the complexity of an ICAN system in the radio repeater. For complexity reduction, polyphase filters with a folded structure are used to perform downsampling and upsampling, and input and output filtering for spectrum control simultaneously. Frequency translation of the signal to avoid aliasing due to downsampling is efficiently executed by a Hilbert transform. The complexity of the proposed scheme is roughly one-fourth that of the conventional scheme with negligible deterioration of the signal quality and the power spectrum of the ICAN system.

A software-based receiver running on a single DSP for terrestrial digital multimedia broadcasting

This paper presents the design and implementation of a software (SW)-based receiver running on a single digital signal processor (DSP) for terrestrial digital multimedia broadcasting (TDMB). Implementing the functions of the physical layer such as synchronization and channel decoding as well as codec decoders for a TDMB receiver in software running a DPS raises numerous design and implementation issues. We present solutions to these issues including an efficient software receiver structure, efficient algorithms with low complexity, real-time scheduling, reduction of the execution cycle number, and data transfer and communication between function blocks in the receiver, with a focus on the physical layer. The SW-based TDMB receiver developed in the present work can change and upgrade its functions and adapt to new standards. The performance of the implemented receiver was verified through successful decoding of live audio and video signals.