Philipp Zhang

Fast Depth Modeling Mode selection for 3D HEVC depth intra coding

This paper proposes a fast mode decision algorithm for 3D High Efficiency Video Coding (3D-HEVC) depth intra coding. In the current 3D-HEVC design, it is observed that for most the cases, Depth Modeling Modes (DMM) full-RD search could be skipped since the coding units (CUs) of depth map are usually very flat or smooth and DMMs are designed for CUs with edge or sharp transition. Using Most Probable Mode (MPM) as the indicator, we propose a fast DMM selection algorithm to speed up the encoding process. The test result for the proposed fast algorithm reports 27.8% encoding time saving with 0.31% bitrate increasing in coded and synthesized view for All-Intra test case.

A Fractional Soft Handover Scheme for 3GPP LTE-Advanced System

Mobility enhancement and carrier aggregation are important aspects to investigate as part of the LTE-Advanced study. Hard handover is the only handover scheme in LTE Rel-8. Generally, hard handover is fairly simple, but its outage probability is high and the handover procedure may be unreliable, especially for VoIP service. In this paper, we propose a fractional soft handover scheme based on the carrier aggregation. The main idea is to partially perform soft handover for VoIP, but non-VoIP service is only transmitted from source eNodeB or target eNodeB. The theoretical analysis and simulation results show that the proposed fractional soft handover scheme not only attains the lowest handover outage probability, but also improve the reliability of VoIP service.

Preamble Design for Non-Contiguous Spectrum Usage in Cognitive Radio Networks

Cognitive radios can significantly improve spectrum efficiency by using locally available spectrum. The efficiency, however, depends heavily on their transceiver design. In particular, being able to use non-contiguously aligned spectrum bands simultaneously is a critical requirement. Prior work in this area requires a control channel so that transmitter/receiver pairs can synchronize on their spectrum usage patterns. However, this approach can suffer from high cost and control congestion. In this paper, we propose an in-band solution for informing receivers the spectrum usage patterns. By judiciously designing packet preambles, we embed the spectrum usage patterns in each data packet. Using the legacy 802.11 preamble structure, we focus on choosing the appropriate preamble sequences to maintain reliable packet detection in the presence of noise and interference. We verify our design using simulation and show that it can lead to reliable packet transmissions comparable to those of contiguous spectrum usage. We also identify the impact of interference on our design and propose refinements to choose the preamble sequence using information on the interference.

Protection of Wireless Microphones in IEEE 802.22 Cognitive Radio Network

To improve the utilization of licensed spectrums, the IEEE 802.22 standard is designed to reuse the bandwidths allocated for TV and Wireless Microphones opportunistically for data communication. To avoid interference from equipments of 802.22 networks, beacon devices are designed to protect the Wireless Microphones. They generate beacons so that the devices in 802.22 networks can detect their existence. In this paper, we explore the details of beacon design in the IEEE 802.22 Task Group 1. As an active member of the group, we have made contributions on FEC design of the beacon. We also provide some simulation results of the designed beacon.

Fast bi-partition mode selection for 3D HEVC depth intra coding

This paper proposes a fast mode decision algorithm for 3D High Efficiency Video Coding (3D-HEVC) depth intra coding. In the current 3D-HEVC design, it is observed that for most of the cases, full Rate-Distortion (RD) cost search of Bi-partition mode could be skipped since most coding units (CUs) of depth map are very flat or smooth while Bi-partition modes are designed for CUs with edge or sharp transition. Using the rough RD cost value calculated by HEVC Rough Mode Decision as a selection threshold, we propose a fast Bi-partition modes selection algorithm to speed up the encoding process. The test result for the proposed fast algorithm reports 34.4% encoding time saving with 0.3% bitrate increasing on synthesized view for All-Intra test case. Moreover, by simply varying the selection threshold, we can make a tradeoff between encoding time saving and bitrate loss based on the requirement of different applications.

Inter-Cell Interference Management in LTE-A Small-Cell Networks

This paper is concerned with inter-cell interference in co-channel Long-Term Evolution-Advanced (LTE-A) small-cell networks (SCNs). A practical SCNs architecture with small-cell group muting (SCGM) is proposed to mitigate the interference between the hosting macro-cell and small-cells as well as interference between adjacent small-cells. Lower power consumption can also be achieved in the proposed architecture. Our system level simulation results show that the proposed solution outperforms todays default operational methods in terms of both macro-cell average and cell-edge throughput.

Joint Transmission for LTE-Advanced Systems with Non-Full Buffer Traffic

Joint Transmission (JT) as an example of downlink coordinated multi-point (CoMP) transmission can improve the overall system performance, particularly cell average and cell-edge throughput. Many studies are related to JT in homogeneous network and based on full buffer traffic which is not a practical scenario. We propose a JT method for LTE-Advanced systems with non-full buffer traffic in both homogeneous and heterogeneous networks. System-level simulations demonstrate that the proposed JT techniques clearly outperform single cell transmission scheme in terms of cell average and cell-edge performance.

Relay-aided interference alignment for MIMO cellular networks

Interference alignment scheme for multiple-in multiple-out (MIMO) cellular networks is discussed in this paper. An enhanced relay-aided interference alignment (eRIA) scheme is proposed. To align the interference, the scaling coefficients at relay is designed carefully and the design criterions of eRIA are given. The achievable degrees of freedom (DoF) of eRIA is derived. Both theoretical analysis and simulation results show that compared with Suhs scheme [8], eRIA can achieve higher DoF and require less time extensions.

Image retargeting quality assessment based on support vector regression

Image retargeting is to re-represent the image, usually with a different image size to cater for the display size of the end-user (e.g., computer, smartphone). In this paper, we propose an image retargeting quality assessment scheme based on four quality factors and support vector regression. The accounted quality factors are of two categorizes: 1) shape distortions, they are visual unpleasant artifacts introduced by retargeting, e.g., a straight line may be retargeted as a curve, a circle may be retargeted as an ellipse, etc.; 2) visual content changes, they mainly refer to the loss of visual information due to retargeting. Both spatial and frequency information are used toward a complete assessment. The spatial quality factors measure shape distortions and visual content changes separately and independently, and therefore it is possible to control their relative importance to the overall assessment. Since spatial quality factors need image matching which may cause measurement error, another quality factor in frequency domain is also used. The overall image retargeting quality is contributed by the four quality measures collectively and machine learning is used accounts for such a combination, corresponding discussions are also provided for each factor. The effectiveness of the proposed scheme is verified with the publicly-available subject-rated database (comprising of diverse images and retargeting methods) and better performance (in terms of both accuracy and complexity) is achieved in comparison with the state of the art schemes. Formulated major quality factors (in both spatial and frequency domains) into IRQA.Identified shape distortion and proposed a measure for it.Proposed frequency domain estimator to alleviate the measurement error in spatial domain.Used machine learning to integrate different quality factors.

On the Efficient Channel State Information Compression and Feedback for Downlink MIMO-OFDM Systems

This paper is concerned with the efficient compression and feedback of channel state information (CSI) in downlink multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. Inspired by video coding, we propose a novel CSI compression and feedback scheme, referred to as hybrid transform coding (HTC). HTC consists of two coding types, i.e, selective time-domain coding (STDC) and differential time-domain coding (DTDC), which are adopted to exploit the correlation of CSI in both the frequency and time domains. We first develop closed-form expressions for the overhead-distortion performance of these two coding types in HTC. The parameters involved in HTC are then optimized based on the analytical results. Finally, the system-level performance of HTC is evaluated in both maximum eigenmode beamforming (MEB)-based single-user MIMO (SU-MIMO) and zero-forcing beamforming (ZFBF)-based multiuser MIMO (MU-MIMO) under Long Term Evolution Advanced (LTE-A) Release 10-based cellular networks. Simulation results show that HTC can significantly outperform the available alternative.