• Journal of the Institute of Convergence Signal Processing
• /
• v.8 no.4
• /
• pp.266-271
• /
• 2007

In mobile channel environments, the effect of the multi-path fading reduces the performance of the mobile communication severely. Previous studies on the effect of the multi-path fading show that, only the channel between fixed base stations and mobile terminals are considered. However, the future mobile communication service such as telematics may use the communication between moving mobile terminals, so called mobile ad-hoc communication, the studies on the channel is required for such situations. In this paper we have measured the mobile channel and analyzed the fading characteristics when using the linear array antennas. In the data measurements, we sent the QPSK modulated signal with carrier frequency of 2GHz band and received the signal using the array antennas equipped on moving vehicles. We have analyzed the fading characteristics and the effects of the fading reduction using the CDF of fading depth using data collected from two moving vehicles. The simulation results show that the beamforming technique adds 6 or 7dB to the fading margin than that of the selection diversity depending on channel environments.

• ETRI Journal
• /
• v.34 no.1
• /
• pp.98-101
• /
• 2012

The directional medium access control (MAC) protocol improves the throughput of mobile ad hoc networks but has a deafness problem and requires location information for neighboring nodes. In the dual-channel directional MAC protocol [12], the use of omnidirectional packets does not require the exact location of destination node. In this letter, we propose a tone dual-channel MAC protocol with directional antennas to improve the throughput of mobile ad hoc networks. In the proposed MAC protocol, we use a directional CTS and an out-of-band directional DATA tone with a new blocking algorithm to improve the spatial reuse. We confirm the throughput performance of the proposed MAC protocol by computer simulations using the Qualnet simulator.

• Journal of Korea Society of Industrial Information Systems
• /
• v.17 no.6
• /
• pp.11-17
• /
• 2012

The HC-128 stram cipher which selected for the final eSTREAM portfolio is suitable for mobile Ad-Hoc network environments because of the ability of high-speed encryption in restricted memory space. In this paper, we analyzed the vulnerability of side channel analysis attack on HC-128 stream cipher. At the first, we explain a flaw of previous theoretical analysis result which defined the complexity of side-channel attack of HC-128 stream cipher as 'low' and then re-evaluate the security against side-channel attack by estimating the concrete complexity for recovering the secret key. As a result, HC-128 stream cipher is relatively secure against side-channel attack since recovering the secret key have $2^{65}$ computation complexity which is higher than other stream cipher's one.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.10 no.9
• /
• pp.1654-1662
• /
• 2006

An ad hoc network is multi-hop network composed of radio links. and the transmission quality of a radio link is more unstable than that of a wired circuit. Packet loss thus occurs frequently in an ad hoc network, and the consequent connection failure results in a severe deterioration of TCP performance. TCP performance also deteriorates because of the collision of data packets and ACK packets in the radio channel. In this paper we study to improve the performance of the Mobile Ad-hoc network by using Delayed ACK algorithm with our proposed ODA(Ordering-Delayed ACK) method. The proposed ODA algorithm increases the number of the data packets orderly at the receiver side which is going to be applied for the Mobile Ad-hoc network. We accomplished a computer simulation using NS-2. From the simulation results, we find the proposed ODA algorithm obviously enlarge the channel capacity and improve the network performance at the situation of multi-hop of ad-hoc network than the existing Delayed ACK algorithm.

• International Journal of Contents
• /
• v.7 no.2
• /
• pp.6-10
• /
• 2011

The directional MAC (DMAC) protocol improves the spatial reuse, but directional packets on the control channel cause the deafness problem. In this paper, we propose a tone dual-channel DMAC protocol for mobile ad-hoc networks. In the proposed MAC protocol, the use of omnidirectional transmissions using an omnidirectional out-of-band tone solves the deafness problem and decrease packet collisions on the control channel. The use of an omnidirectional out-of-band tone also mitigates the hidden terminal problem. We use the negative CTS (NCTS) mechanism to solve the exposed terminal problem. The throughput performance of the proposed MAC protocol is confirmed by simulations using the Qualnet simulator.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.3
• /
• pp.482-488
• /
• 2009

Mobile Ad-hoc Networks provide communication without a centralized infrastructure, which makes them suitable for communication in disaster areas or when quick deployment is needed. On the other hand, they are susceptible to malicious exploitation and have to face different challenges at different layers due to its open Ad-hoc network structure which lacks previous security measures. Denial of service (DoS) attack is one that interferes with the radio transmission channel causing a jamming attack. In this kind of attack, an attacker emits a signal that interrupts the energy of the packets causing many errors in the packet currently being transmitted. In harsh environments where there is constant traffic, a jamming attack causes serious problems; therefore measures to prevent these types of attacks are required. The objective of this paper is to carry out the simulation of the jamming attack on the nodes and determine the DoS attacks in OPNET so as to obtain better results. We have used effective anomaly detection system to detect the malicious behaviour of the jammer node and analyzed the results that deny channel access by jamming in the mobile Ad-hoc networks.

• Journal of Communications and Networks
• /
• v.6 no.4
• /
• pp.317-330
• /
• 2004

In this paper, we explore the utility of recently discovered multiple-antenna techniques (namely MIMO techniques) for medium access control (MAC) design and routing in mobile ad hoc networks. Specifically, we focus on ad hoc networks where the spatial diversity technique is used to combat fading and achieve robustness in the presence of user mobility. We first examine the impact of spatial diversity on the MAC design, and devise a MIMO MAC protocol accordingly. We then develop analytical methods to characterize the corresponding saturation throughput for MIMO multi-hop networks. Building on the throughout analysis, we study the impact of MIMO MAC on routing. We characterize the optimal hop distance that minimizes the end-to-end delay in a large network. For completeness, we also study MAC design using directional antennas for the case where the channel has a strong line of sight (LOS) component. Our results show that the spatial diversity technique and the directional antenna technique can enhance the performance of mobile ad hoc networks significantly.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 2005.11a
• /
• pp.161-164
• /
• 2005

Mobile device users are sensitive to pay telecommunication charge for downloading Internet data, because the cost is proportional to the amount of data received. If there are device users who want to download the same content, they may cooperate each other to form an ad hoc network and share the partially downloaded content in order to reduce the amount of data downloaded. Each mobile device, called a peer, downloads a specific portion of the whole content using fee-based telecommunication channel, and exchanges the portion with other peers with free ad hoc channel in order that all participating peers are able to reconstruct the whole content in this situation, al1 participating peers become senders and receivers at the same time. In order to distribute the partial content to other peers, the ad hoc network requires a control led distribution mechanism. This paper introduces the per-peer-based distribution method in which one designated peer can transmit partial data to its neighbors at a time. Simulation results show that 90$\%$ of the telecommunication cost is saved with as few as 10 peers .

• Journal of the Korea Society for Simulation
• /
• v.12 no.4
• /
• pp.73-81
• /
• 2003

An Ad Hoc network is a dynamic multi-hop wireless network that is established by a group of mobile hosts on a shared wireless channel by virtue of their proximity to each other. Since wireless transmissions are locally broadcast in the region of the transmitting host, hosts that are in close proximity can hear each other and are said to be neighbors. The transitive closure of the neighborhood of all the hosts in the set of mobile hosts under consideration forms an Ad Hoc network. Thus, each host is potentially a router and it is possible to dynamically establish routes by chaining together a sequence of neighboring hosts from a source to a destination in the Ad Hoc network. In a network, various real-time services require the network to guarantee the Quality of Services provided to the receiver. End-to-end QoS can be provided most efficiently when each layer of the protocol stack translates the requirements of the application into layer classified requirements and satisfies them. In this study, a mechanism to guarantee the QoS in Ad Hoc networks with buffer nodes is proposed. They effectively prevent traffic congestion and yield better transmission rate. In this way QoS is enhanced.

• Journal of Satellite, Information and Communications
• /
• v.6 no.1
• /
• pp.75-79
• /
• 2011

Wireless devices can communicate between each other without existing infrastructure in mobile Ad-hod network. Ad hoc networks can be used under difficult conditions, where it is difficult to construct infrastructures, such as shadowing areas, disaster areas, war area, and so on. In order to support to considerable and various wireless services, more spectrum resources are needed. However, efficient utilization of the frequency resource is difficult because of spectrum scarcity and the conventional frequency regulation. Ad-hoc networks employing cognitive radio (CR) system that guarantee high spectrum utilization provide effective way to increase the network capacity. In this paper, we simulate and compare the performance of conventional single and cooperative spectrum sensing with CR system using ad-hoc networks in additive white Gaussian noise (AWGN) and Rayleigh channel model. And we demonstrate performance improvement by analyzing the system performance.