Minsu Shin

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.

Gap Filler Architectures for Seamless DVB-S2/RCS Provision in the Railway Environment

In this paper, we study the provision of broadband interactive services to passengers of Korean high-speed train in the ISM 2.4 GHz band. We address in particular the design of tunnel gap-fillers (GFs) able to provide bi-directional connectivity to train-based terminals. The work has been developed in the broader context of interactive services provision for high-speed trains through satellite networks. First, a channel model for the in-tunnel propagation is derived. Taking into account the results of the propagation analysis, a comparison between commercial technologies (belonging to both the IEEE and the DVB standard families) is provided, showing the possible strengths and weaknesses of the proposed solutions with respect to architectural and performance point of views.

The gap filler technology for mobile satellite system

To provide seamless broadband Internet and broadcasting services to passengers of high speed train via satellite link, gap filling is key technology to extend the service coverage in NLOS environment, so to speak, tunnel. The XpeedSAT system is a Ka/Ku band broadband mobile multimedia access system based on DVB-S2/DVB-RCS+M standard for satellite TV, video multicasting, Internet through wireless LAN. In this paper we introduce the various gap filling technologies and compare pros and cons. Finally we propose the gap filling method for NLOS environment in XpeedSAT system.

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.

Adaptive Logarithmic Increase Congestion Control Algorithm for Satellite Networks

This paper presents a new algorithm called the adaptive logarithmic increase and adaptive decrease algorithm (A-LIAD), which mainly addresses the Round-Trip Time (RTT) fairness problem in satellite networks with a very high propagation delay as an alternative to the current TCP congestion control algorithm. We defined a new increasing function in the fashion of a logarithm depending on the increasing factor α, which is different from the other logarithmic increase algorithm adopting a fixed value of α = 2 leading to a binary increase. In A-LIAD, the α value is derived in the RTT function through the analysis. With the modification of the increasing function applied for the congestion avoidance phase, a hybrid scheme is also presented for the slow start phase. From this hybrid scheme, we can avoid an overshooting problem during a slow start phase even without a SACK option. To verify the feasibility of the algorithm for deployment in a high-speed and long-distance network, several aspects are evaluated through an NS-2 simulation. We performed simulations for intra- and inter-fairness as well as utilization in different conditions of varying RTT, bandwidth, and PER. From these simulations, we showed that although A-LIAD is not the best in all aspects, it provides a competitive performance in almost all aspects, especially in the start-up and packet loss impact, and thus can be an alternative TCP congestion control algorithm for high BDP networks including a satellite network.

The feasibility study on the 4K-UHD satellite broadcasting service in Ka-band

The goal of the paper is to present an efficient way for providing satellite UHD broadcasting services via Ka frequency band and, for the purpose, to develop a service adaptation and stabilization technology which is adaptive to the channel conditions including rain attenuation.

The design of satellite mesh protocol for the DVB-RCS TDMA networks

This paper presents satellite mesh connectivity architecture based on DVB-RCS and C2P protocol, especially in terms of connection control procedure. C2P protocol provides dynamic connectivities in the diverse network scenarios over DVB-RCS system. Satellite mesh connectivities are requested in many market sectors, such as enterprise networks and government/military segments. In these network types, voice and video communications and other data applications are the most probable services that require strongly reliable mesh connectivities. DVB created C2P protocol to be adequately able to operate with its DVB-RCS standard. However, C2P protocol is so complicated to understand that it needs to make simple architecture for specific network architecture. In this paper, satellite mesh connection control procedure is addressed for transparent satellite mesh network which is the only probable option in the country.

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.

Robust End-to-End Available Bandwidth Estimation for Interactive Satellite networks

This paper presents an efficient and accurate available bandwidth estimation algorithm for satellite links which generally have long propagation delay. Either the method using the rate of returning ACKs or the method using timestamp option is adopted for the bandwidth estimation algorithms to enhance TCP performance in the literature. The method using the rate of returning ACKs, which is the most popular for the available bandwidth estimation for a TCP connection, is known to have the influences from the reverse link (TCP receiver to TCP sender) traffic variation, especially in the asymmetric satellite links. The bandwidth estimation method using packet sending time information from the TCP timestamp option also has the drawback that the influence of the bottleneck link presented in the forward path is not properly considered. To overcome these limits, our algorithm performs in two steps. A forward path delay is calculated at the sender with the receiver sending time for an ACK packet in the first step. And in the second step, the forward path delay is updated more delicately through removing unrelated part from the forward path delay, and is applied for available bandwidth estimation. The simulation results show that our algorithm can avoid the influence of the traffic variation in the return path (e.g., ACK compression, DAMA delay), and estimate the available bandwidth over the forward path more accurately. Satellite networks are becoming the important candidate in information and communication infrastructures because they provide several advantages to the wireless Internet communications. They generally provide wider coverage, higher bandwidth, and relatively faster establishment than other terrestrial wireless networks. Nevertheless, satellite links pose some challenges to the congestion control operation of the TCP (Transmission Control Protocol) (10). Main challenges of the satellite networks to the TCP performance are the long RTT (round-trip time) which is generally around 600msec in the bi-directional networks over the geostationary satellite, and the presence of the high packet loss rate by wireless random error which causes congestion control of the TCP spuriously. To solve the problems while keeping end-to-end semantics of TCP, an accurate bandwidth estimation algorithm is

NEW OFDM SCHEMES ROBUST TO DOPPLER AND PAR EFFECTS FOR BROADBAND MOBILE INTERNET SERVICES VIA SATELLITE TRANSPONDER

A new and effective Doppler effects compensation method based on constellation estimation as well as an average power saving strategy by modified modulation scheme utilizing zero point constellation are presented with theoretical analysis and relevant simulations. The suggested schemes are proved to be very effective for satellite OFDM signals relayed by power limiting transponder for the mobile terminal on high speed vehicles.