Hokyom Kim

Providing seamless services with satellite and terrestrial network in mobile two way satellite environments

Satellite communication environment can be divided into LOS and NLOS environments. While, terminal can get satellite signal in LOS environment, NLOS needs additional function to get the signal such as cooperation between gap filler or terrestrial network (WLAN or WIMAX). In this paper, the two way satellite communication system is based on DVB-RCS specification and terrestrial networks are based on WLAN(IEEE 802.11) or WIMAX(IEEE 802.16). This paper adopt proper algorithms to handover among satellite and wireless network for providing seamless service when moving object enter NLOS environment in collaboration area and estimate the performance of the method by simulations.

Simulation and electrical design of the offset dual reflector antenna with conical beam scanning

In the paper, development of K/Ka-band linear-polarization tracking antenna for satellite communication is described. Antenna structures have a conical beam scanning for El/Az satellite tracking due to a sub-reflector nutation. This structure has polarization tracking based on minimizing signal of horizontal polarization. The tracking algorithm is based on equalizing of two output signals by rotation the feed assembly. Results of simulation and electrical design of the offset dual reflector antenna with conical beam scanning is for the required specifications as well as goniometric performances of the antenna are presented. Simulation and electrical design of dual-band Ka/K-band feed is a corrugated horn. It is shown that the feed in form of corrugated horn has better performances.

Optimal capacity assignment in interactive satellite return channels for mobile multimedia services

We develop an efficient method for optimal capacity assignment in an interactive satellite multimedia system using hybrid CDMA/TDMA channels. We mathematically formulate a throughput-maximizing capacity assignment problem as a binary integer programming (BIP) problem, and decompose this BIP problem into two subproblems. With this decomposition, we promote the computational efficiency in finding the optimal solution of the original BIP problem.

A hybrid matching algorithm based on contour and motion information for depth estimation

Depth estimation is an important part of free viewpoint television (FTV) because accuracy of depth information affects directly the synthesized video quality at virtual viewpoint. However, generating an accurate depth map is a computationally complex process, which makes real-time implementation challenging. In order to obtain accurate depth information with low complexity, a hybrid matching technique is proposed. It is composed of three types of matching mode: pixel matching, 3x3 and 5x5 block matching. By using contour and motion information in matching mode selection, the proposed technique is more complied with human visual system which is more sensitive moving regions than static one. Experimental results show that the proposed algorithm can not only enhance the synthesized visual quality, but also reduce the complexity in matching process.

Content-based cross-layer design for layered video multicasting

Receiver nodes can receive the layered video streams selectively using H.264/SVC, according to the display resolution of the terminal device or congestion status of the network. The characteristics of SVC can be expressed using rate-distortion point (RDP). SVC can also be used for layered multicast. Specifically, the encoded video layers can be mapped to the proper transmission layers for layered multicast, which can be more efficient than existing single layer multicast schemes. In this paper, we propose a mechanism to select an optimal operation point from the SVC server and maximize the PSNR-RDP path. Using this, actual layered multicast is performed at the point of attachment such as BS and eNodeB in the wireless network. We also show that QoS can be improved when optimal modulations and coding schemes are used for delivering the SVC video according to the user distribution and the network condition.

Performance analysis of MIMO system to improve data rate over wireless communication

This paper presents application to increase a data rate using Multi-Input Multi-Output (MIMO) system over wireless communications. Simplified MIMO radio channel is narrowband flat fading and richness scattering environment between the transmitter and receiver. Various environmental parameters such as the number of antenna elements of transmitter and receiver, a correlation of spatial property, spacing of antennas, effect of Rayleigh fading (LOS) are reflected in the simulation. The transceivers of MIMO system are implemented by spatial multiplexing (e.g. V-BLAST architecture) using the proposed channel models. The performance of the MIMO system and space diversity is analyzed and verified using the simulation. The MIMO system of 4 x 6 antenna configuration has similar SNR in BLER of 10 compared with 2 x 2 antenna configuration. It is found from the simulation results that the performance of MIMO system is improved by using space diversity and increasing the number of transmitter antennas.