• Proceedings of the IEEK Conference
• /
• 2003.11c
• /
• pp.235-238
• /
• 2003

본 논문에선 Binomial확률을 이용한 재전송 슬롯 선택방식과 충돌해결과정의 수정을 통하여 CSMA/CA 프로토콜을 항공용 VHF통신에 적합하게 변형시켰다. 일반적으로 CSMA/CA 프로세스는 경쟁 서비스에서 충돌이 일어났을 때 재전송 지연시간만큼 기다리게 되고 경쟁윈도우의 크기가 두 배로 커진다. 이로 인해 부하가 증가하면 지연시간이 커지고 처리량이 감소하며 이를 해결하기 위해 본 논문에선 충돌 플래그를 이용하여 본래의 CW의 크기 변화 과정을 변형시켰으며, CSMA/CA 전체 상태 천이 과정에서 충돌 시의 과정을 좀더 적게 거치도록 하였다. 시뮬레이션을 수행한 결과 부하가 증가하여도 처리량 및 지연 시간에 좋은 특성을 나타내었으며 제안된 프로토콜은 항공용 VHF 통신에 적합함을 확인하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.40 no.11
• /
• pp.10-16
• /
• 2003

In this paper, a dynamic contention periods based on the collision group(DCCG) algorithm is proposed for collision resolution in the IEEE 802.16 broadband wireless access network. The DCCG algorithm determines the contention periods according to the a number of collided slot and collided requests to the base station(BS). The DCCG algorithm is useful to improve the performance of throughput and system delay characteristic than binary backoff algorithm.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.42 no.10 s.340
• /
• pp.39-50
• /
• 2005

In this paper, we propose a performance improving MAC algerian for the IEEE 802.11 DCF. WLAN based IEEE 802.11 uses two control methods called 'Distributed Coordination Function(UF)' and 'Point Coordination Function(PCF)'. The nF controls the Urnsmission based on carrier sense multiple access with collision detection(CSMA/CA), that decides a random backoff time with the range of contention window for each terminal. Normally, each terminal the CW double after collision, and reduces the CW to the minimum after successful transmission. This paper proposes an enhanced DCF algorithm that decreases the CW smoothly after successful transmission in order to reduce the collision Probability by utilizing the current status information of WLAN. We also analyze the throughput and delay performance for the unsaturated case mathematically. Simulation results show that our algorithm enhances the saturation throughput of WLAN. They also coincide well with the analytical results.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.46 no.7
• /
• pp.45-51
• /
• 2009

We have presented a routing mechanism that selects a route by considering channel statuses in order to fast transfer delay-sensitive data in WSNs (Wireless Sensor Networks). The existing methods for real-time data transfer select a path whose latency is the shortest or the number of hops is the smallest. An algorithm to select a real-time transfer path based on link error rates according to the characteristic of wireless medium was also suggested. However, the propagation delay and retransmission timeout affected by link error rates are shorter than channel assessment time and backoff time. Therefore, the mechanism proposed in this paper estimated the time spent in using a clear channel and sending out a packet, which is based on channel backoff rates. A source node comes to select a route with the shortest end-to-end delay as a fast transfer path for real-time traffic, and sends data along the path chosen. We found that this proposed mechanism improves the speed of event-to-sink data transfer by performing experiments under different link error and channel backoff rates.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2016.10a
• /
• pp.136-137
• /
• 2016

WSN의 활용 분야 중 하나로 표준화된 IEEE 802.15.4 WBAN(wireless body area networks)은 웨어러블 디바이스의 무선 통신환경을 고려한 기술이다. WBAN은 높은 밀집도를 가지는 특징을 가지며, 이로 인하여 데이터 충돌이 큰 이슈가 되고 있다. 본 논문에서는 WBAN의 표준에서 제시한 메시지 우선순위를 백오프 알고리즘에 적용하여 WBAN 환경에 더 효율적인 전송을 제공하는 것을 목표로한다.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2008.05a
• /
• pp.841-844
• /
• 2008

본 논문은 공개 네트워크 시뮬레이터 ns-2.31(Network Simulator 2.31)의 802.11 DCF 모듈에서 버그(bug)를 소개하고 이의 영향 결과를 분석한다. ns의 802.11 DCF 모듈은 다음과 같은 문제점을 가지고 있다. 첫째, 백오프(backoff) 알고리즘은 표준안에서 명시한 알고리즘대로 작성되지 않았다. 둘째, 특정조건에 해당되는 충돌에 대하여 트레이스 파일에 출력하지 않는다. 셋째, 전파 오류 모듈을 삽입하여도 전파 오류 결과를 트레이스 파일에 출력하지 않는다. 넷째, MAC(Medium Access Control) 알고리즘만을 평가할 수 있는 기법을 제공하지 않는다. 이러한 문제점을 수정한 ns-2와 수정전의 ns-2와 평균4.6%의 충돌률 차이를 보인다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2011.05a
• /
• pp.796-798
• /
• 2011

The IEEE 802.11 MAC uses DCF for media access among the participating network nodes. But DCF alone is neither capable nor suitable for fulfilling the QoS requirements of realtime applications. There are many ways in which QoS is provided by modifying DCF based MAC. This paper proposes (m,k)-collision scheme which is based on IEEE 802.11 and (m,k)-firm scheme tries to improve DCF functionality. The proposed scheme uses different Contention Window according to the number of collision in the node. The simulation result shows that the proposed scheme helps improve the throughput of the DCF.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.2B
• /
• pp.98-106
• /
• 2006

In order to provide a realtime transmission over a wireless LAM, we here present a new jamming based retransmission mechanism. In a legacy wireless LAN system, all stations use the binary exponential backoff algorithm to avoid collisions among frames. It is well known that the backoff algorithm causes more collisions as the numbers of active stations increases. This makes transmission of real time traffic hard. In the proposed scheme, when each station senses collisions, it promptly allows to send a jamming signal during a unique jamming window period which is determined by its own channel access count database(CACDB). This jamming windows is chosen not to be overlapped each other by using of CACDB, and thus channel access of another station is prevented. Hereafter the station gets the ownership of the medium when the wireless medium becomes idle after sending the jamming signal and sensing carrier, and then sends frame in medium. In our proposal, repeating collisions is never happened. We here assume that real time traffic use a frame of fixed length in order to make the time for receiving its ACK frame same. Comparing the proposed jamming-based retransmission scheme with the the 802.11 and 802.11e MAC by simulation. one can find that the proposed scheme have advantages in terms of delay, average backoff time, and average number of collisions per frame. One can find that the proposed scheme might be practically applicable to several applications of realtime traffic transmission in wireless LAN systems.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• v.9 no.1
• /
• pp.561-564
• /
• 2005

This paper proposes an access control algorithm for guaranteeing fair packet transmissions in CDMA-based slotted ALOHA systems. In the proposed algorithm, the base station calculates the packet transmission and retransmission probabilities based on the offered loads and then broadcasts these probabilities to all mobile stations. Mobile stations, which have a packet to transmit, attempt to transmit a packet with the received probabilities. Simulation results show that the proposed algorithm can offer better system throughput and average delay than the conventional algorithm. Results also show that the proposed algorithm can guarantee a good fairness among all mobile stations regardless of the offered loads.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.45 no.4
• /
• pp.53-63
• /
• 2008

Reader collision may occur when neighboring RFID readers use the same channel at the same time. Especially when the readers are operated in dense mode, even though many channels are available, because of frequent reader collisions we can not guarantee the performance of RFID readers. Conventional solutions such as FH(Frequency Hopping) or LBT(Listen Before Talk) are not effective in this situation because they can not schedule RFID readers effectively when RFID readers are operated in multi-channel, dense reader mode, In this paper, we propose a new RFID reader anti-collision algorithm which employs LBT, random backoff before channel access, and probabilistic channel hopping at the same time. While LBT and Random backoff before channel access reduces collisions between competing readers, probabilistic channel hopping increases channel utilization by adaptively changing the hopping probability by reflecting the reader density and utilization. Simulation results shows that our algorithm outperforms conventional methods.