ManKyu Park

Clock Synchronization for One-Way Delay Measurement: A Survey

In this paper we present the comprehensive survey on the clock synchronization algorithms, which should be considered for the measurements of the network delay. We categorize the clock synchronization algorithms into two basic types according to how they acquire synchronization between clocks, which are external source based schemes and end-to-end measurement based schemes. While external source based schemes are the synchronization methods using centralized time source such as NTP, GPS and IEEE 1588 to have global synchronization for all end hosts, end-to-end schemes obtain synchronization information through network measurements between end hosts. We briefly introduces some algorithms in both categories. However, we have focused more on the end-to-end schemes which can be classified again into online and offline shemes according to whether they can be applied for real time operation. We survey the recent progresses on these end-to-end algorithms and special concerns are on the estimation of true the one-way delay without the effect of clock skew. The problems in depolying each end-to-end scheme are also described. The potential further research issues in online one-way delay estimation are discussed.

Practical vertical handover mechanisms between satellite and terrestrial networks

In this paper, we propose practical vertical handover mechanisms for interworking between satellite and terrestrial network, which include new handover procedures and TCP congestion control. To support seamless handover, it should be considered L2-L4 layer operation all together. The proposed mechanisms include a vertical handover procedure using IEEE 802.21 and a TCP performance enhancing mechanism by adopting efficient congestion control scheme. IEEE 802.21 standard provides unified event messages from link layer to upper layer for helping seamless handover regardless whatever the physical layer interfaces are. The proposed TCP congestion control uses TCP Explicit Handover Notification which informs TCP sender directly of new available link bandwidth. We used ns-2 network simulator to evaluate our proposed mechanisms. Simulation results show that our mechanism can support a seamless handover and provide a better Internet service for fast train when there are different types of access networks such as a satellite and terrestrial network.

Cross-layer design for improving TCP PEP performance in DVB-RCS2 networks

Adaptive Coding and Modulation (ACM) scheme is commonly used to extend link availability and improve bandwidth efficiency in satellite networks. In particular DVB-RCS2 including ACM and Return Link Encapsulation (RLE) had been adopted as the standard to support the robust packet transmission. However TCP PEPs in satellite communication systems does not recognize a change in PHY layer according to ACM operation. To overcome this problem, we propose cross-layer design between TCP PEP and MAC layer for improving TCP PEP performance in DVB-RCS2 networks.

MMT based hybrid delivery system for a highly reliable UHD broadcasting service

Recently a terminal having the multiple interfaces for communication may further support a high data throughput and more robust connectivity. MPEG Media Transport (MMT) was standardized as a digital container standard by Moving Picture Expert Group(MPEG) in March 2014 for next-generation broadcasting and communication services. MMT is to allow efficient transmission and processing of the video, audio and signaling information to support the new service such as Ultra High Definition TV (UHD TV), multi-screen service, and etc. In this paper, we design an MMT based Hybrid delivery system (MHD system) to provide seamless UHD TV service using satellite broadcasting link and broadband link. Our system uses two network interfaces, one is DVB-S2 for satellite broadcasting service and the other one is Ethernet for broadband IP data service, especially we use a broadband link for providing a high connection reliability when satellite link has a problem. And we design our system to support compatibility to the MPEG2-TS based legacy satellite broadcasting system for the MMT based new services.

Dynamic resource management scheme for DVB-RCS2 networks

DVB-RCS2 which was standardization for next generation very small aperture terminal (VSAT) system defined various new technologies such as high code modulation, return link encapsulation (RLE) and the adaptive coding and modulation (ACM) support. ACM scheme can be used for extending the link availability and improving the efficiency of resources utilization. In this paper, we address a dynamic resource management scheme based on ACM. The proposed scheme basically uses proportional resource allocation and we define the satisfactory of resource usage (SRU) used for improving long-term fairness for each terminal.

DVB-RCS2 emulation system: To verify system level functions for multiple terminals

This paper describes a emulation system design based on DVB-RCS2 standard and verification of several system level functions. The proposed system can provide the testing environments of real performance evaluation using hardware type Hub system and VSATs, and it supports a lot of virtual VSATs created by VSAT emulators to test the return link access control procedure. We used our emulation system to verify system level functions such as the access control, control burst assignment algorithm, RLE performance evaluation, and PEPSal performance verification. And we realized that this emulation system will be very useful to verify system level functions of satellite communication system until the system will be released to the market.

Performance analysis of degradation detection method on millimeter wave channel

The rapid proliferation of the high quality video service and the wide spread of the Internet of Things (IoT) are expected to create an unprecedented growth in mobile data traffic. To satisfy the requirements of these services, the communication system supporting very high data rate (Giga-bps) is required. The next evolution of the access technologies is currently being discussed as 5G to provide the innovative solution and to overcome the problem of frequency band shortage. Many companies and research institutes are carrying out preliminary studies of next-generation services and providing their outlook and requirements for the 5G service. These studies pointed out that the possibility of service disruption due to high propagation loss and block cause by an obstacle in the communication path is a challenging issue. This paper analyzes the performance of the current state detection algorithm to detect the signal blockage and examine the applicability of millimeter wave (mmWave) service.

Hierarchical packet scheduler for supporting fairness and QoS over DVB-S2 ACM systems

In this paper, we propose a hierarchical scheduler offering fairness and QoS for DVB-S2 ACM systems while minimizing the decrease of throughput. As a result of the simulation, we show that the proposed scheduler supports bandwidth fairness to the individual RCST and can provide some level of QoS differentiation for user traffics.