• Journal of information and communication convergence engineering
• /
• v.15 no.1
• /
• pp.28-36
• /
• 2017

The medium access control (MAC) protocol based on dynamic time division multiple access/time division duplex (TDMA/TDD) is responsible for random access control and radio resource allocation in dynamic traffic environments. These functions of random access and resource allocation are very important to prevent wastage of resources and improve MAC performance according to various network conditions. In this paper, we propose new random access and resource allocation schemes to guarantee quality of service (QoS) and provide priority services in a dynamic TDMA/TDD system. First, for the QoS guarantee, we propose an adaptive random access and resource allocation scheme by introducing an access probability. Second, for providing priority service, we propose a priority-based random access and resource allocation scheme by extending the first adaptive scheme in both a centralized and a distributed manner. The analysis and simulation results show that the proposed MAC protocol outperforms the legacy MAC protocol using a simple binary exponential backoff algorithm, and provides good differential performance according to priorities with respect to the throughput and delay.

• Proceedings of the KIEE Conference
• /
• 2000.07b
• /
• pp.1387-1389
• /
• 2000

Railway signalling system is required to be high safety against collision, derailment and collision at level crossing and to be high availability. The signalling system is usually divided into automatic train control, interlocking and centralized traffic control systems and each system must be high fail safe and availability. This study focused on reliability calculation of vital systems in train control system.

• The KIPS Transactions:PartC
• /
• v.14C no.6
• /
• pp.525-536
• /
• 2007

Network Control Platform(NCP) and Qualify of Service Switch(QSS) are being developed to realize centralized control and management technology, which is essential for guaranteeing traffic engineering and service quality in a next generation network. This paper adopts a parallel mechanism, and a thread and object pool to achieve high-speed connection management in the existing SNMP interface between NCP and QSS. We built up a connection management test-bed in laboratory environment to validate the functionality of high-speed connection management. We also measured and analyzed a performance of connection setup delay and a completion ratio using the test-bed. We ascertain that the parallel mechanism and the object pool are the most important performance parameters to achieve high-speed connection management in the SNMP interface between NCP and QSS.

• The Journal of Korean Institute of Next Generation Computing
• /
• v.15 no.4
• /
• pp.80-88
• /
• 2019

Software Defined Networking (SDN) is the future network paradigm of decoupling control and data functions. In SDN structure, it is hard to address scalability in case of large-scale networks because single controller managed thousands of switches in a centralized fashion. Most of previous studies have focused on horizontal scalability, where distributed controllers are assigned to network devices. However, they have abstracted the control plane and the application plane into a single controller. The layer of the common SDN architecture is divided into data plane, control plane, and application plane, but the control plane and application plane have been modeled as a single controller although they are logically separated. In this paper, we propose a analytical traffic model considering the both application plane and control plane based on queuing theory. This model can be used to address scalability issues such as controller placement problem without complicated simulations.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.9
• /
• pp.1819-1827
• /
• 2015

ICT-based on-board oriented train control system has been proposed to improve operation efficiency in low-density railway line. It is also needed to develop a new ICT-based local control center which relates to existing centralized traffic control lines. In order to meet the qualitative target of these developing system, RAMS activities are required. In this paper, through preliminary hazard analysis, hazards and their contributing factors are addressed, then countermeasures are established to control the risk to an acceptable level.

• Journal of Communications and Networks
• /
• v.13 no.4
• /
• pp.319-326
• /
• 2011

Beamforming techniques have been successfully utilized for traffic channels in order to solve the interference problem. However, their use for control channels has not been sufficiently investigated. In this paper, a (semi-) centralized beamforming strategy that adaptively changes beam patterns and controls the total transmit power of cells is proposed for the performance enhancement of the common channel in hierarchical cell structure (HCS) networks. In addition, some examples of its practical implementation with low complexity are presented for two-tier HCS networks consisting of macro and pico cells. The performance of the proposed scheme has been evaluated through multi-cell system-level simulations under optimistic and pessimistic interference scenarios. The cumulative distribution function of user geometry or channel quality has been used as a performance metric since in the case of common control channel the number of outage users is more important than the sum rate. Simulation results confirm that the proposed scheme provides a significant gain compared to the random beamforming scheme as well as conventional systems that do not use the proposed algorithm. Finally, the proposed scheme can be applied simultaneously to several adjacent macro and pico cells even if it is designed primarily for the pico cell within macro cells.

• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.35S no.6
• /
• pp.36-45
• /
• 1998

This paper discusses multiple access control aspects for a wireless extension of high-speed asynchronous transfer mode(ATM) networks. One challenging requirement is that mobile systems convey of diverse types of information including voice, computer data, facsimile, and video data that have different quality of service constraints. Basically, a centralized control scheme for a coordinated multiple access is required in order to efficiently accommodate multimedia traffic on wireless links. The proposed scheme dynamically scheduling the mobile terminal, which has data to transfer according to the service, types at base station. In this scheme, the scheduling algorithm is performed on the basis of traffic descriptors and QoS parameters, which required in the connection set up phase. As a consequence, the transmission scheduling is very flexible and can account for the different traffic rate and delay constraints that emerge from voice and data integration. The simulation result shows that the proposed scheme has better performance over other scheduling algorithms.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.9 no.3
• /
• pp.9-17
• /
• 2009

A Mobile Ad hoc network(MANET) is a network consisting of a set of wireless mobile nodes, which communicate with each other without centralized control or established infrastructure. In this paper, to obtain a better understanding of AODV(Ad hoc On-Demand Distance Vector Routing Protocol)and OLSR(Optimized Link State Routing Protocol) routing protocols, different performances are simulated and analyzed using OPNET modeler 14.5 with the various performance metrics, such as packet delivery ratio, end-to-end delay and routing overhead. As a conclusion, in static analysis, the routing overhead of OLSR is affected by the number of nodes, but not data traffic. In AODV case, it is affected by both data traffic and number of nodes. In mobility analysis, routing overhead is not greatly affected by mobility speed in AODV and OLSR, and the PDR(Packet Delivery Ration) of OLSR is decreased as the node speed increased, while AODV is not changed. AS to delay, AODV is always higher than OLSR in both static and nobility cases.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.8B
• /
• pp.757-763
• /
• 2006

In this paper, a novel multiple access scheme using SMA(Split and Merge Algorithm) is proposed to reduce the accessdelay of wireless MAC protocols. The key idea of the SMA is to dynamically split and merge the contending terminals depending on their traffic loads for effective control of access to the channels. The SMA divides the collided terminals into several sub-groups if a collision occurs and merges the idle terminals of the split sub-groups into their original group. The merge algorithm can be used to resolve collision and split operation can be used to dynamic group management. The simulation results indicate that our algorithm may provide a higher throughput and a lower collision rate than the existing algorithms, especially under heavy traffic loads.

• Smart Structures and Systems
• /
• v.5 no.1
• /
• pp.43-54
• /
• 2009

This study introduces a novel approach for locating damage in a structure using wireless sensor system with local level computational capability to alleviate data traffic load on the centralized computation. Smart wireless sensor systems, capable of iterative damage-searching, mimic an optimization process in a decentralized way. The proposed algorithm tries to detect damage in a structure by monitoring abnormal increases in strain measurements from a group of wireless sensors. Initially, this clustering technique provides a reasonably effective sensor placement within a structure. Sensor clustering also assigns a certain number of master sensors in each cluster so that they can constantly monitor the structural health of a structure. By adopting a voting system, a group of wireless sensors iteratively forages for a damage location as they can be activated as needed. Since all of the damage searching process occurs within a small group of wireless sensors, no global control or data traffic to a central system is required. Numerical simulation demonstrates that the newly developed searching algorithm implemented on wireless sensors successfully localizes stiffness damage in a plate through the local level reconfigurable function of smart sensors.