Hyungkeuk Lee

Visual Entropy Gain for Wavelet Image Coding

Wavelet image coding exhibits a robust error resilience performance by utilizing a naturally layered bitstream construction over a band-limited channel. In this letter, a new measure that appears to provide a better assessment of visual entropy for comparing and evaluating progressive image coders is defined based on a visual weight over the wavelet domain. This visual weight is characterized by the human visual system (HVS) over the frequency and spatial domains and is then utilized as a criterion for determining the coding order of wavelet coefficients, resulting in improved visual quality. A transmission gain, which is expressed by visual entropy, of up to about 23% can be obtained at a normalized channel throughput of about 0.3. In accordance with the subjective visual quality, a relatively high gain can be obtained at a low channel capacity

Optimal Channel Adaptation of Scalable Video Over a Multicarrier-Based Multicell Environment

To achieve seamless multimedia streaming services over wireless networks, it is important to overcome inter-cell interference (ICI), particularly in cell border regions. In this regard scalable video coding (SVC) has been actively studied due to its advantage of channel adaptation. We explore an optimal solution for maximizing the expected visual entropy over an orthogonal frequency division multiplexing (OFDM)-based broadband network from the perspective of cross-layer optimization. An optimization problem is parameterized by a set of source and channel parameters that are acquired along the user location over a multicell environment. A suboptimal solution is suggested using a greedy algorithm that allocates the radio resources to the scalable bitstreams as a function of their visual importance. The simulation results show that the greedy algorithm effectively resists ICI in the cell border region, while conventional nonscalable coding suffers severely because of ICI.

Optimal Carrier Loading Control for the Enhancement of Visual Quality over OFDMA Cellular Networks

A recent dynamic increase in demand for wireless multimedia services has greatly accelerated the research on dynamic channel adaptation of high quality video applications. In this paper, we explore a theoretical approach to cross-layer optimization between multimedia and wireless networks by means of a quality criterion termed ldquovisual throughputrdquo for downlink video transmission using a layered coding algorithm. We obtain the optimal loading ratio of orthogonal frequency division multiple access (OFDMA) subcarriers through an optimization problem balancing the tradeoff relationship between inter-cell interference (ICI) and channel throughput. Through numerical link capacity analysis, we show that the upper bounds of the visual throughput gain at the cell boundary is obtained at about 27%.

Semisoft Handover Gain Analysis Over OFDM-Based Broadband Systems

Various approaches to analyze handover have been developed to guarantee the quality of service of multimedia services over mobile communication networks. However, no framework for multicarrier-based broadband systems, e.g., multicarrier code-division multiple access and orthogonal frequency-division multiple access, is available based on the perspective of link capacity. This paper presents a handover technique referred to as semisoft-handover-utilizing macroscopic diversity, which permits both hard and soft handover advantages for services over multicarrier-based broadband networks to be retained. Theoretical analysis is then performed to measure the handover gain over the forward link in terms of an outage probability. Simulation data verify that semisoft handover outperforms other traditional handover techniques, in particular for high-data-rate services.

Dynamic Bandwidth and Carrier Allocation for Video Broadcast/Multicast Over Multi-Cell Environments

Recently, broadcast/multicast over cellular networks has been actively discussed over commercial wireless mobile terminals. Compared to conventional terrestrial or satellite broadcasting systems, the quality-of-service (QoS) for edge users is an important issue due to inter-cell interference over multi-cell environments. In this paper, we introduce a dynamic bandwidth and carrier allocation (DBCA) technique by fully utilizing different visual importance of each layer in multi-layer video for broadcast/multicast services when the number of users is limited over macro/micro/femto cell environments. To ensure an acceptable video quality for edge users, the bandwidth and the loading ratio are dynamically controlled to enhance the utility through the radio resource control in accordance with the visual importance. The simulation results show that DBCA exhibits much better QoS by sending visually more important data with high priority in the cell border region.

A cross-layer optimization for energy-efficient MAC protocol with delay and rate constraints

We propose the energy efficient MAC algorithm in this paper. In the proposed algorithm, each node sets the contention window size with respect to the residual energy, the harvesting energy and the transmit power. This algorithm makes the sensor nodes consume their energy efficiently. To achieve this goal, we use the game theory and the cross-layer optimization. Introducing the non-cooperative game, we can formulate the utility function easily. In this paper, we can allocate the optimal power by the cross-layer optimization on the PHY and the MAC.

Visually Weighted Compressive Sensing: Measurement and Reconstruction

Compressive sensing (CS) makes it possible to more naturally create compact representations of data with respect to a desired data rate. Through wavelet decomposition, smooth and piecewise smooth signals can be represented as sparse and compressible coefficients. These coefficients can then be effectively compressed via the CS. Since a wavelet transform divides image information into layered blockwise wavelet coefficients over spatial and frequency domains, visual improvement can be attained by an appropriate perceptually weighted CS scheme. We introduce such a method in this paper and compare it with the conventional CS. The resulting visual CS model is shown to deliver improved visual reconstructions.

Cross-Layer Optimization for Downlink Wavelet Video Transmission

Cross-layer optimization for efficient multimedia communications is an important emerging issue towards providing better quality-of-service (QoS) over capacity-limited wireless channels. This paper presents a cross-layer optimization approach that operates between the application and physical layers to achieve high fidelity downlink video transmission by optimizing with respect to a quality criterion termed “visual entropy” using Lagrangian relaxation. By utilizing the natural layered structure of wavelet coding, an optimal level of power allocation is determined, which permits the throughput of visual entropy to be maximized over a multi-cell environment. A theoretical approach to optimization using the Shannon capacity and the Karush-Kuhn-Tucker (KKT) conditions is explored when coupling the application with the physical layers. Simulations show that the throughput gain for cross-layer optimization by visual entropy is increased by nearly 80% at the cell boundary as compared with peak signal-to-noise ratio (PSNR).

OFDM-Based Semi-Soft Handover for High Data Rate Services

Various approaches for analyzing handover have been developed to guarantee the QoS (Quality of Service) of multimedia services over mobile communication networks. However, no framework for multicarrier-based broadband systems, such as MC-CDMA (Multi-Carrier Code Division Multiple Access) or OFDMA (Orthogonal Frequency Division Multiple Access) is available, from the perspective of link capacity. This paper presents a handover technique, referred to as semi-soft handover utilizing macro diversity, which permits both hard and soft handover advantages for services over multicarrier-based broadband networks to be retained. A theoretical analysis is then performed to measure the handover gain over the forward link in terms of an outage probability. The simulation data verifies that the semi-soft handover outperforms other traditional handover techniques, in particular, for high data rate services.

Compression Gain Measurements Using ROI-Based Data Reduction

For mobile visual communications, the development of more robust and efficient video traffic control and transmission techniques remains one of the most important issues. Foveated video originates from visual entropy reduction by removing undetectable high visual frequencies that occur at a distance from the fixation point. In this paper, compression gain is defined and measured to quantify the enhanced performance when the visual throughput of the regions of interest (ROI) is increased over a capacity-limited channel.