http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
A Reactive Cross Collision Exclusionary Backoff Algorithm in IEEE 802.11 Network
( Subodh Pudasaini ),( Yusun Chang ),( Seokjoo Shin ) 한국인터넷정보학회 2010 KSII Transactions on Internet and Information Syst Vol.4 No.6
An inseparable challenge associated with every random access network is the design of an efficient Collision Resolution Algorithm (CRA), since collisions cannot be completely avoided in such network. To maximize the collision resolution efficiency of a popular CRA, namely Binary Exponential Backoff (BEB), we propose a reactive backoff algorithm. The proposed backoff algorithm is reactive in the sense that it updates the contention window based on the previously selected backoff value in the failed contention stage to avoid a typical type of collision, referred as cross-collision. Cross-collision would occur if the contention slot pointed by the currently selected backoff value appeared to be present in the overlapped portion of the adjacent (the previous and the current) windows. The proposed reactive algorithm contributes to significant performance improvements in the network since it offers a supplementary feature of Cross Collision Exclusion (XCE) and also retains the legacy collision mitigation features. We formulate a Markovian model to emulate the characteristics of the proposed algorithm. Based on the solution of the model, we then estimate the throughput and delay performances of WLAN following the signaling mechanisms of the Distributed Coordination Function (DCF) considering IEEE 802.11b system parameters. We validate the accuracy of the analytical performance estimation framework by comparing the analytically obtained results with the results that we obtain from the simulation experiments performed in ns-2. Through the rigorous analysis, based on the validated model, we show that the proposed reactive cross collision exclusionary backoff algorithm significantly enhances the throughput and reduces the average packet delay in the network.
Pudasaini, Subodh,Kyung Sup Kwak,Seokjoo Shin IET 2015 IET COMMUNICATIONS Vol.9 No.5
<P>Maximising the tag reading rate of a reader is one of the most important design objectives in radio frequency identification (RFID) systems as it is inversely proportional to the time required to completely read all the tags within the reader's radio field. To this end, numerous techniques have been independently suggested so far and they can be broadly categorised into pure advancements in the link-layer tag anti-collision protocols and pure advancements in the physical-layer RF signal reception model. This study shows by rigorous mathematical analysis and Monte-Carlo simulations that how those two independent approaches can be coupled to maximise the tag reading efficiency in an RFID system, considering a slotted Aloha-based dynamic link-layer anti-collision protocol at tags and a multi-packet reception capable RF reception model at the reader.</P>
Subodh Pudasaini,신석주 한국차세대컴퓨팅학회 2013 한국차세대컴퓨팅학회 논문지 Vol.9 No.3
전통적인 회선교환 방식에서 패킷 교환 방식으로 네트워크가 진화함에 따라 분산된 클럭의 동기화를 위한 패킷 기반 동기화 방식은 큰 주목을 받고 있다. 특히 네트워크의 혼잡이 심각한 경우 패킷교환 네트워크의 특성에 기인하는 패킷 지연 변화 (PDV)는 IEEE1588 PTP (Precision Time Protocol)를 기반으로 하는 패킷 기반의 동기화 시스템에서 클럭 잡음의 주요 원인으로 작용한다. 본 논문에서는 IEEE1588 PTP의 동기화 성능을 개선하기 위해 이러한 클럭 잡음을 완화시킬 수 있는 비선형 SMoPF (Sample Mode Packet Filtering) 메커니즘을 제안하였다. 제안된 SMoPF 기법의 성능평가를 얻기 위하여 임의의 혼잡도를 갖는 패킷 교환 네트워크에서의 IEEE1588 PTP 동기화 프로토콜을 고려하였으며OMNET++ 툴 기반의 컴퓨터 시뮬레이션을 수행하였다. 또한, 제안된 기법의 성능은 기존의 샘플 최소 필터링, 평균 필터링, 최대 필터링 기법들과 비교 분석 되었다.
COMIC: Intelligent Contention Window Control for Distributed Medium Access
Pudasaini, Subodh,Moonsoo Kang,Seokjoo Shin,Copeland, John A IEEE 2010 IEEE communications letters Vol.14 No.7
<P>In this letter, a scheme for Collision Mitigation with Intelligent Contention Window Control (COMIC) is proposed for backoff based collision resolution algorithm. COMIC intelligently mitigates collisions by probabilistically maximizing the selection likelihood of relatively less collision-probable contention slots over the backoffed contention window. A unified Markovian model for the Distribution Coordination Function (DCF) that incorporates COMIC, DCF<SUB>comic</SUB>, is formulated for the performance analysis. The performance results show that DCF<SUB>comic</SUB> outperforms the conventional DCF in both throughput and average packet delay due to the significant reduction in packet collisions.</P>
A Novel Dynamic Contention Window Control in IEEE 802.11 DCF
Subodh Pudasaini,Anup Thapa,Seokjoo Shin 한국통신학회 2009 한국통신학회 학술대회논문집 Vol.2009 No.6
The primary Medium Access Control (MAC) technique of IEEE 802.11 is Distributed Coordination Function (DCF). DCF is a contention based access mechanism with Carrier Sense Multiple Access which incorporates Collision Avoidance (CSMA/CA) scheme with Binary Exponential Backoff (BEB) retransmission rules. Collision resolution using BEB is simple and effective when the network is lightly loaded, however, its performance starts worsening with increase in the network load. In this paper, we proposed a novel contention window control scheme on top of BEB with a minor modification. The proposed modification dynamically controls the randomness of deferring time by changing the distribution of the deferring time adaptively after each unsuccessful/colllided access attempt. The proposed protocol is expected to leverage the performance in terms of both average delay and average throughput in the whole range of offered load maintaining fairness among the competing stations meanwhile. More importantly, this protocol can be ported even to the already existing 802.11 network interface card (NIC) drivers only with a simple software upgrade.