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A new analytical model for optimized cognitive radio networks based on stochastic geometry
Hwang, Ganguk,Lee, Seunghee American Institute of Mathematical Sciences 2017 Journal of industrial and management optimization Vol.13 No.2
<P>In this paper, we consider an underlay type cognitive radio network with multiple secondary users who contend to access multiple heterogeneous licensed channels. With the help of stochastic geometry we develop a new analytical model to analyze a random channel access protocol where each secondary user determines whether to access a licensed channel based on a given access probability. In our analysis we introduce the so-called interference-free region to derive the coverage probability for an arbitrary secondary user. With the help of the interference-free region we approximate the interferences at an arbitrary secondary user from primary users as well as from secondary users in a simple way. Based on our analytical model we obtain the optimal access probabilities that maximize the throughput. Numerical examples are provided to validate our analysis.</P>
Yoon, Jonghun,Hwang, Ganguk IEEE 2018 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.17 No.6
<P>We propose a distance-based inter-cell interference coordination (ICIC) scheme in small cell networks (SCNs). While most of the previous works focus on a randomly selected user called a typical user, we focus on an edge user because the main purpose of ICIC is to improve the performance of an edge user. Since there are many inactive small cell base stations (SBSs) in SCNs, a simple criterion for an edge user such as being located near a cell boundary is not appropriate for SCNs. To accurately detect edge users experiencing severe performance degradation, we newly define an edge user in SCNs based on the nearest active neighbor SBS. We then apply our scheme only to edge users where SBSs within so-called the cooperation radius from each edge user cooperate. With the help of the stochastic geometry we obtain a semi-closed expression for the coverage probability of an edge user with our scheme. We investigate two tradeoffs on the resource efficiency of a network and the coverage probability of an interior user. We then determine the optimal cooperation radius that maximizes the coverage probability of an edge user considering the two tradeoffs. Our analytical results are validated through simulations.</P>
Design and Analysis of Medium Access Protocol: Throughput and Short-Term Fairness Perspective
Yunbae Kim,Ganguk Hwang IEEE 2015 IEEE/ACM transactions on networking Vol.23 No.3
<P>We consider a simple MAC protocol, called the renewal access protocol (RAP), that adopts all of the legacy 802.11 standard but the backoff stage feature. To meet two objectives in the design of the RAP-optimal throughput and high short-term fairness-we develop a mathematical model of the RAP and rigorously analyze the performance of the RAP. First, we show that the throughput performance of the RAP depends only on the expectation of the selection distribution where the backoff counter is selected, provided that the number of terminals is fixed, which is in accordance with a well-known result. Second, with the help of renewal and reliability theories, we analyze the short-term fairness of the RAP. We also show that if the RAP has a selection distribution of the New Better than Used in Expectation (NBUE) type, the RAP can guarantee high short-term fairness. Third, we construct a special binomial distribution that is obviously of the NBUE type that can achieve high short-term fairness as well as optimal throughput when used as the selection distribution of the RAP. Furthermore, by the Poisson approximation for binomial distributions, we propose to use in practice a Poisson distribution corresponding to the special binomial distribution. Numerical and simulation results are provided to validate our analysis.</P>
Short-Term Fairness Analysis for the Renewal Access MAC Protocol
Yunbae Kim,Ganguk Hwang 한국산업응용수학회 2012 한국산업응용수학회 학술대회 논문집 Vol.7 No.2
As the demands for better quality of service (QoS) increases, requirements for high fairness performance for a short periods of time are also arisen in the Wireless Local Area Network (WLAN). Although the IEEE 802.11 Distributed Coordination Function (DCF) is the most widely used in WLAN, relatively little attention have been paid to improve the short-term fairness of the IEEE 802.11 DCF. In this study, we propose a simple random access protocol as an alternative of the IEEE 802.11 DCF, called the renewal access protocol, where each terminal selects a back off counter value from a priori probability distribution, called the selection distribution. We mathematically model the successful packet transmission behavior by delayed renewal process. And then we use this modeling and the Jain’s fairness index to measure the extent of short-term fairness. We conjecture that the short-term fairness is considerably affected by the variance value of selection distribution. This behavior is verified through numerical and simulation studies.
Yunbae Kim,Ganguk Hwang,Jungsun Um,Sungjin Yoo,Hoiyoon Jung,Seungkeun Park IEEE 2016 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.15 No.5
<P>As a promising solution for handling super dense wireless networks, wireless local area networks (WLANs) have been intensively considered due to their wide availability. However, the contention-based MAC protocol in WLANs should be modified because of its inefficiency. To this end, we consider a recently proposed novel MAC protocol called the renewal access protocol (RAP). With the RAP, we analyze two strategies for resolving collisions efficiently and achieving optimal throughput performance in super dense WLANs: strategies without and with grouping. First, we analyze the asymptotic behavior of the RAP itself (i.e., without grouping) as the number of terminals goes to infinity. We show that the RAP can achieve optimal throughput even in super dense WLANs and the relevant optimal access probability can be derived in a closed form. Second, we propose a grouping strategy in the RAP called the grouped RAP (G-RAP). While a grouping strategy in the IEEE 802.11ah standard is based on time division, our G-RAP is based on transmission attempts. So the G-RAP does not waste channel resources. We show that the G-RAP achieves the optimal network throughput for any group structure if terminals use the optimal access probability that we derive. Our analytical results are validated by simulation.</P>
Tail asymptotics of fluid queues in a distributed server system fed by a heavy-tailed ON-OFF flow
Lee, Byeongchan,Yoon, Jonghun,Shin, Yang Woo,Hwang, Ganguk AMERICAN INSTITUTE OF MATHEMATICAL SCIENCES 2016 JOURNAL OF INDUSTRIAL AND MANAGEMENT OPTIMIZATION Vol.12 No.2
<P>The appearance of heavy-tailedness in users' traffic significantly degrades the performance of communication systems, and a distributed server system is considered as a good solution to this problem because of its distributed service characteristic by multiple servers. So we tackle the question in this paper that a distributed server system can alleviate heavy-tailedness, so that users experience good QoS as if there were no heavy-tailedness. To this end, we first mathematically model a distributed server system and obtain a heavy-tailed random sum with the help of the theory of perturbed random walk. We then analyze the tail asymptotic of the heavy-tailed random sum to find a condition with which the distributed server system can alleviate heavy-tailedness.</P>