• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7B
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• pp.827-833
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• 2011

Directional MAC protocols have drawn great attentions recently in super high speed wireless local/personal area networks due to their higher antenna gain, better spatial reuse, longer transmission range, and lower interference. Despite of these merits, directional MAC protocols suffer from deafness problem. The deafness problem occurs if a node does not answer an RTS frame addressed to it. To overcome this problem, directional MAC protocols have aimed at avoiding the deafness problem using multiple control frames or advance notice techniques or distinguishing deafness from collision. In this paper, we analyze the performance of these schemes in deafness environments with some scenarios. Through performance analysis, we compare the performance of these schemes through evaluating actual network throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.278-286
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• 2011

Directional antennas have been used in Ad Hoc networks, significantly improving the spatial reuse of the networks. However, the extended transmission range causes collisions at the receivers of neighbors, which prevents full exploitation of the potential of the directional antenna. In this paper, we propose a new power control MAC protocol for a directional antenna. For this protocol, we propose a method to detect a set of interference nodes in the neighbors of a receiver. We then use a power control algorithm to calculate the minimum transmission power and send data. Simulation results demonstrate that this protocol increases the network performance and reduces energy consumption.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1B
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• pp.15-20
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• 2012

In this paper, an algorithm that enhances the conventional directional CSMA/CA protocol in IEEE 802.15.3c is proposed under saturation environments. For the algorithm, a Markov chain model is presented and analyzed in no-ACK mode. The effects of directional antennas and the features of IEEE 802.15.3c MAC are considered in the model. The optimal sizes of contention window are derived from the numerical results. The numerical results show that the proposed directional CSMA/CA algorithm outperforms conventional one. The overall analysis is verified by simulation. The obtained results provide the criterion for selecting the optimal parameters and developing a MAC protocol that enhances the performance of mmWave WPANs.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.4
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• pp.627-635
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• 2008

Using directional antenna in wireless network can offer many advantages including significant decrease of interference, increase of spatial reuse and possibility of improving network capacity. However, existing 802.11 MAC is designed for use of omni-directional antenna then those advantages can not be shown in that MAC protocol when it uses directional antenna. In this paper, we present a MAC protocol specifically designed for directional antenna to achieve spatial reuse and improve capacity of MAC protocol. Simulation result shows the advantages of our proposal in comparison with existing MAC in terms of end-to-end delay and network throughput.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.917-920
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• 2007

무선 Ad-hoc 네트워크에서는 주로 IEEE 802.11 MAC 프로토콜을 이용한다. IEEE 802.11 MAC 프로토콜은 제어 메시지인 RTS-CTS를 통해서 채널 예약을 하고 데이터를 전송하는 방식으로 모든 통신에 Omni-directional 안테나를 이용하여 전송한다. 본 논문에서는 기존 IEEE 802.11 MAC 프로토콜보다 성능을 향상시키기 위해서 directional 안테나를 이용한 MAC 프로토콜을 사용한다. Directional 안테나를 사용한 MAC 프로토콜은 IEEE 802.11 MAC 프로토콜에 비해서 Spatial Reuse를 증가함으로서 채널 자원을 더욱 효율적으로 사용하는 것이 가능하다. 또한 Directional 안테나의 사용은 안테나의 지향성에 따른 안테나 이득 및 전송 범위의 증가 그리고 전송 범위를 Omni-directional 안테나와 동일하게 적용할 경우에는 저 전력 통신이 가능하다는 장점을 가지고 있다. 그러나 Directional 안테나의 사용은 IEEE 802.11 MAC보다 좋은 성능을 갖기는 하지만 새로운 문제들이 발생한다. 이러한 문제들로는 New Hidden Terminal, Deafness, Capture, 그리고 위치 인식에 관련된 문제들이 발생한다. 본 논문에서서 위에서 언급한 Directional 안테나의 이점과 그리고 문제점에 대해서 설명하고, 이러한 문제들 중에 Deafness 문제를 완화시킬 수 있는 방법을 제안한다. 그리고 QualNet 4.0을 이용한 시뮬레이션을 통해서 제안된 프로토콜의 성능을 평가한다.

• Journal of KIISE:Information Networking
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• v.33 no.1
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• pp.16-27
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• 2006

The wireless transmission medium inherently broadcasts a signal to all neighbor nodes in the transmission range. Existing asynchronous MAC protocols do not provide a concrete solution for reliable broadcast in link layer. This mainly comes from that an omni-directional broadcasting causes to reduce the network performance due to the explosive collisions and contentions. This paper proposes a reliable broadcast protocol in link taller based on directional antennas, named MDB(MAC protocol for Directional Broadcasting). This protocol makes use of DAST(Directional Antennas Statement Table) information and D-MACA(Directional Multiple Access and Collision Avoidance) scheme through 4-way handshake to resolve the many collision problem wit]1 omni-directional antenna. To analyze its performance, MDB protocol is compared with IEEE 802.11 DCF protocol [9] and the protocol 2 of reference [3], in terms of the success rate of broadcast and the collision rate. As a result of performance analysis through simulation, it was confirmed that the collision rate of the MDB protocol is lower than those of IEEE 802.11 and the protocol 2 of reference [3], and that the completion rate of broadcast of MDB protocol is higher than those of IEEE 802.11 and the protocol 2 of reference [3].

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.11
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• pp.2447-2458
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• 2009

Ad hoc wireless networks operate without any infrastructure where a node can be a source and a router at the same time. This indispensably requires high throughput and low delay performance throughout the wireless network coverage span, particularly under heavy traffic conditions. Recent research on using multiple antennas in beam-forming or multiplexing modes over a wireless channel has shown promising results in terms of high throughput and low delay. Directional antennas have shown to increase spatial reuse by allowing multiple transmitters and receivers to communicate using. directional beams as long as they do not significantly interfere with each other. However directional antenna performance asymptotically approaches the omni-directional performance in a high density ad hoc network. Simulation results in QualNet validate that average throughput and packet corruption ratio of directional antenna approach omni-directional performance. Moreover, we further highlight some important issues pertaining to the directional antenna performance in wireless networks.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.118-127
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• 2006

The wireless transmission medium inherently broadcasts a signal to all neighbor nodes in the transmission range. Existing asynchronous MAC protocols do not provide a concrete solution for reliable broadcast in link layer. This mainly comes from that an omnidirectional broadcasting causes to reduce the network performance due to the explosive collisions and contentions. This paper proposes a directional broadcast protocol by using neighborhood information in the link layer based o,1 directional antennas, named MNDB (MAC protocol with Neighborhood for reliable Directional Broadcast). This protocol makes use of neighborhood information and DMACA (Directional Multiple Access and Collision Avoidance) scheme through 4-way handshake to support a reliable directional broadcast. To analyze its performance, MNDB protocol si compared with $RMDB^{[1]}$, the protocol 2 of reference [3], and IEEE 802.11 $protocol^{[9]}$, in terms of the number of collisions, the number of dropped packets, the number of redundant packets, and broadcast delay.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.113-114
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• 2007

무선 Ad Hoc 네트워크 환경에서 기존 IEEE 802.11 MAC 프로토콜에서 Omni-Directional 안테나를 이용하여 방식으로부터 자원의 활용을 늘이기 위해서 Directional 안테나를 이용한다. Directional 안테나의 사용으로 기존 802.11 MAC 프로토콜에 비해 Spatial reuse가 증가하고, 안테나의 높은 이득과 간섭의 감소, 그리고 전송범위의 증가의 장점을 갖는다. 그러나, Directional 안테나를 이용함으로서 New Hidden Problem, Deafness, 그리고 Capture 등과 같은 문제점이 발생하였다. 본 논문에서는 이러한 문제점들을 파악하고, 이를 해결하는 방안들을 분석하고 각 해결방안들에 대한 성능을 비교평가한다.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.4
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• pp.9-16
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• 2015

Quick and safe message transmission is an important research topic of vehicular ad hoc networks (VANET). Most studies assume that the periodic broadcast of beacon-frames between vehicles increases the safety of the driver. In this paper, we propose a medium access control (MAC) protocol and location-based clustering for the VANET to support reliable data transfer. In our proposal, the cluster heade (CH) manage the access and allocate the resources of the node. Our proposal uses simulation to confirm the reduction of the transmission delay and the collision rate of the signal.