• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.16 no.5
• /
• pp.906-912
• /
• 2012

A ship ad-hoc network (SANET) can provide ships with diverse multimedia services by replacing expensive satellite communications. While ITU-R M. 1842-1, standards for maritime VHF band digital communications, can be used as the specifications of physical layer for SANETs, no standards are specified for higher layers of SANETs. In this paper, we propose a ship ad-hoc communication (SAC) protocol for SANETs, based on medium access control (MAC) and routing protocols for terrestrial ad-hoc networks. SAC protocol is a cross-layer protocol which combines MAC and routing into one algorithm and considers maritime environments, including the existence of neighboring ships, the possibility of routing to a destination, and changing the communication mode in case of VHF channel failure.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2008.10a
• /
• pp.1491-1494
• /
• 2008

Typically internal mobile LCD display modules are connected to the mobile product baseband PCB with flexible printed circuit board equipped with board-to-board connector. This solution has a drawback of limiting the product concept work to certain solutions that are based on connector size, location, flexible PCB length, bending, etc. in the display module. Also flexible printed circuit board based solutions are not completely optimized from reliability point of view, causing flex circuit board breakings. For the external displays in the PC or Home entertainment market, the cable solution is too expensive and resource demanding. The wireless solution has obvious advantages over reliability, low cost and flexibility. This paper describes a wireless audio-visual interface solution.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.1
• /
• pp.183-195
• /
• 2014

Multicasting is an efficient way of group communications because one sender can transmit data to multiple receivers with only one transmission. Furthermore, multicasting is considered an appropriate transmission method for multimedia services. Multimedia applications are expected to become more prevalent over mobile ad-hoc networks in the near future. Therefore, achieving reliability in multimedia communications is an important task. In this paper, we propose a leader-based reliable multicast medium access control layer protocol for multimedia applications to enhance video quality. We present a Markov chain model and numerical formulation of our proposed system.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.11A
• /
• pp.1101-1112
• /
• 2006

With the recent growth in demand for high-data rate multimedia services in the wireless environments, the Mobile Broadband Wireless Access (MBWA) technologies, such as WiBro (Wireless Broadband internet) system, are gradually coming into the spotlight. Unlike the conventional mobile communication networks based on cellular system, the WiBro system basically consists of IP based backbone networks that will be ultimately deployed by Ipv6 (IP version six) based backbone networks according to the All-IP trend for the network evolution. In such wireless mobile environments, it is needed to support the mobility management protocol on network layer as well as physical layer and Medium Access Control (MAC) layer in WiBro system. Accordingly, in this paper, we propose a fast handover scheme for improving the handover performance in IPv6 based WiBro system and show that the proposed scheme achieves loss-free and low handover latency during inter-subnet movement of the mobile stations through the simulation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.6B
• /
• pp.595-604
• /
• 2009

The HCCA reserves the channel resources based on the mean data rate in IEEE 802.11e. It may cause either the waste of channel resource or the increase of transmission delay at MAC layer if the frame size is rapidly varied when a compressed mode video codec such as MPEG video is used. To solve these problems, it is developed that the packet scheduler allocates the wireless resource adaptation by according to the packet size. However, it is difficult to perform the admission control because of the difficulty with calculating the available resources. In this paper, we propose a CAC mechanism to solve the problem that may not satisfy the QoS by increasing traffic load in case of using EDCA. Especially, the proposed CAC mechanism calculates the EB of TSs using the traffic information transmitted by the application layer and the number of average transmission according to the wireless channel environment, and then determines the admission of the TS based on the EB. According to the simulation results of the proposed CAC mechanism, it admitted the TSs under the loads which are satisfied within the delay bound. Therefore, the proposed mechanism guarantees QoS of streaming services effectively.

• Journal of Communications and Networks
• /
• v.10 no.2
• /
• pp.213-220
• /
• 2008

This paper analyzes a broadcasting technique for wireless multi-hop sensor networks that uses a form of cooperative diversity called opportunistic large arrays (OLAs). We propose a method for autonomous scheduling of the nodes, which limits the nodes that relay and saves as much as 32% of the transmit energy compared to other broadcast approaches, without requiring global positioning system (GPS), individual node addressing, or inter-node interaction. This energy-saving is a result of cross-layer interaction, in the sense that the medium access control (MAC) and routing functions are partially executed in the physical (PHY) layer. Our proposed method is called OLA with a transmission threshold (OLA-T), where a node compares its received power to a threshold to decide if it should forward. We also investigate OLA with variable threshold (OLA-VT), which optimizes the thresholds as a function of level. OLA-T and OLA-VT are compared with OLA broadcasting without a transmission threshold, each in their minimum energy configuration, using an analytical method under the orthogonal and continuum assumptions. The trade-off between the number of OLA levels (or hops) required to achieve successful network broadcast and transmission energy saved is investigated. The results based on the analytical assumptions are confirmed with Monte Carlo simulations.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.14 no.2
• /
• pp.283-288
• /
• 2019

LPWA (Low Power Wide Area) networks have been considered as one of the technologies which can be implemented in IoT (Internet of Things) applications by providing less power and longer communication range compared with existing wireless technologies. In this paper, we investigate LoRa which is one of representative technologies for LPWA networks. First, we present general properties and several technologies of LPWA networks. Then, the technical specification, properties, and pros/cons of LoRa are studied. Finally, we discuss analysis of LoRa's performance and its ehancement technologies by focusing on physical layer and MAC (Medium Access Control) layer.

• Journal of Advanced Navigation Technology
• /
• v.15 no.5
• /
• pp.764-773
• /
• 2011

IEEE 802.15.4 is a standard for LWPAN based on TDMA. IEEE 802.15.4 has not been used widely because of restrictions on the QoS, scalability, and reliability. IEEE 802.15.4 utilizes GTS for one-hop QoS transmission. However GTS is not an effective method to satisfy QoS in multi-hop environments. Currently IEEE 802.15.4e, an extended version of IEEE 802.15.4 MAC sub-layer, is being developed to satisfy more diverse performance requirements than IEEE 802.15.4. IEEE 802.15.4e provides muti-hop QoS transmission functionality and uses multiple frequency channels. In this paper, a multi-channel TDMA scheduling scheme is proposed to satisfy end-to-end transmission delay in IEEE 802.15.4e. The performance of the proposed scheme is evaluated using simulation.

• Journal of KIISE:Information Networking
• /
• v.34 no.1
• /
• pp.48-61
• /
• 2007

WiBro (Wireless Broadband) service, developed in Korea, can provide the host mobility while its users hang around within the subnet. Next-generation Internet protocols, IPv6 and Mobile IPv6 (MIPv6), provide a plenty of addresses to the nodes and enable the handover between different subnets. However, MIPv6 is not enough to support a real time service such as VoIP (Voice over IP) due to the long latency, and it is necessary to develop an enhanced handover mechanism which is optimized to the WiBro networks. In this paper, we suggest an improved fast handover mechanism while the mobile node moves around WiBro networks. The proposal is based on Fast Mobile IPv6 (FMIPv6) which is the representative protocol for fast handover, and reduces the handover latency by the close interaction between the link layer (WiBro MAC) and IP layer (FMIPv6). Finally, we analyze the performance of proposed mechanism through the mathematical analysis.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.8
• /
• pp.1613-1621
• /
• 2015

This paper analyzes the rate adaptation scheme and suggests applicable strategy of the MCS(Modulation and Coding Scheme) for improving DCF throughput in the IEEE 802.11ad and 802.11ad wireless LAN. IEEE 802.11ac and 802.11ad wireless LAN provide MCS technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. But these standards did not provide rate adaptation algorithm, so this paper surveyes rate adaptation algorithm and suggests MCS scheme applied to IEEE 802.11ac and 802.11ad wireless LAN. Specially A MAC(Medium Access Control) layer throughput is evaluated over error-prone channel in the IEEE 802.11ac-based wireless LAN. In this evaluation, DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme are used. Using theoretical analysis method, the MAC saturation throughput is evaluated with the PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables.