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Traffic Flow Estimation based Channel Assignment for Wireless Mesh Networks
( Wooguil Pak ),( Saewoong Bahk ) 한국인터넷정보학회 2011 KSII Transactions on Internet and Information Syst Vol.5 No.1
Wireless mesh networks (WMNs) provide high-speed backbone networks without any wired cable. Many researchers have tried to increase network throughput by using multi-channel and multi-radio interfaces. A multi-radio multi-channel WMN requires channel assignment algorithm to decide the number of channels needed for each link. Since the channel assignment affects routing and interference directly, it is a critical component for enhancing network performance. However, the optimal channel assignment is known as a NP complete problem. For high performance, most of previous works assign channels in a centralized manner but they are limited in being applied for dynamic network environments. In this paper, we propose a simple flow estimation algorithm and a hybrid channel assignment algorithm. Our flow estimation algorithm obtains aggregated flow rate information between routers by packet sampling, thereby achieving high scalability. Our hybrid channel assignment algorithm initially assigns channels in a centralized manner first, and runs in a distributed manner to adjust channel assignment when notable traffic changes are detected. This approach provides high scalability and high performance compared with existing algorithms, and they are confirmed through extensive performance evaluations.
FRFC: Fast Table Building Algorithm for Recursive Flow Classification
Wooguil Pak,Saewoong Bahk IEEE 2010 IEEE communications letters Vol.14 No.12
<P>Policy lookup is a very essential function in packet forwarding and network security. As it is becoming a main cause of bottleneck in many network systems, this letter introduces a new policy lookup algorithm called FRFC (Fast table building for Recursive Flow Classification). Although it is based on RFC which shows the best policy lookup speed but the worst policy table update speed, it achieves high performance in table update as well as policy lookup. FRFC divides the whole rule set into smaller sub-rule sets and by doing so, it speeds up the table building time by 50 times compared to RFC when the considered rule set size is 10,000. With the rule set size increasing, the performance gap becomes larger.</P>
R-SplitC: Collision Minimization for Cellular Communication in Unlicensed Spectrum
김지훈,이재홍,Saewoong Bahk 한국통신학회 2021 Journal of communications and networks Vol.23 No.4
The 3rd generation partnership project (3GPP) has stan dardized 5G new radio in unlicensed spectrum (NR-U) that usesa wide unlicensed spectrum as an alternative solution to the insuf ficient bandwidth problem of the existing NR. NR-U has a listen before-talk (LBT) operation similar to the carrier sense multipleaccess with collision avoidance (CSMA/CA) operation of Wi-Fi. It allows nodes to transmit only after LBT success. NR-U suf fers from the collision issue because its channel access mecha nism is similar to that of Wi-Fi. Wi-Fi solves the collision prob lem through the request-to-send/clear-to-send (RTS/CTS) mecha nism. However, NR-U has no way of solving the collision problem. As a result, NR-U suffers severe performance degradation due tocollisions as the number of contending nodes increases. In thispaper, we propose to use an extended and split reservation signal(RS) for reservation in NR-U that consists of front RS and rear RSand design a new collision minimization scheme, termed R-SplitC,that contains two components: new RS structure and contentionwindow size (CWS) control. The new RS structure helps to min imize collisions in NR-U transmissions, and CWS control worksto protect the performance of other communication technologiessuch as Wi-Fi. We mathematically analyze and evaluate the perfor mance of our scheme and confirm that R-SplitC improves networkthroughput by up to 99.3% compared to the baseline RS schemewithout degrading Wi-Fi performance.
Energy efficient scheduling for downlink elastic traffic in wireless networks
Lee, Jongwook,Bahk, Saewoong John Wiley Sons, Ltd. 2010 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.10 No.7
<P>In wireless networks, maximizing throughput and minimizing energy consumption are two conflicting objectives. For elastic traffic, it is the total completion time, not the delay constraint of a single packet or the short-term throughput requirement, that directly affects the quality-of-service (QoS). At the same time, the energy consumption should be minimized in order to prolong the battery lifetime of the mobile station (MS). In this paper, we propose energy efficient schedulers that consider throughput and energy saving simultaneously. Through extensive simulations, we compare the proposed schemes with the conventional scheme where a mobile terminal stays awake until all the pending packets are completely serviced. The simulation results show that our schemes outperform the conventional one in terms of utility, i.e., user satisfaction, which is defined as inversely proportional to the multiplication of weighted service completion time and energy consumption. Copyright © 2009 John Wiley & Sons, Ltd.</P> <B>Graphic Abstract</B> <P>For a mobile station which is downloading elastic traffic in a wireless network, it is shown that Best-pick sleep (BPS) scheme which is proposed in this paper is effective in performance by balancing between the throughput and energy saving. <img src='wiley_img_2010/15308669-2010-10-7-WCM803-gra001.gif' alt='wiley_img_2010/15308669-2010-10-7-WCM803-gra001'> </P>
Seowoo Jang,Saewoong Bahk IEEE 2015 IEEE transactions on mobile computing Vol.14 No.3
<P>The major goal of IEEE 802.11ac is to provide very high throughput (VHT) performance while at the same time guaranteeing backward compatibility. To achieve this goal, 802.11ac adopts the channel bonding technique that makes use of multiple 20 MHz channels in 5 GHz band. Due to the heterogeneity of bandwidth that each device exploits, and the fixed total transmission power in the standards, a problem called `Hidden Channel' arises. In this paper, we first analyze the problem and show how the contention parameters and transmission time affect collision probability and fairness in some deployment scenarios. Then, we propose a heuristic channel allocation algorithm that aims to avoid such problematic situations effectively. Through simulations, we demonstrate that our proposed channel allocation algorithm lowers the packet error rate (PER) compared to uncoordinated and received signal strength indicator(RSSI) based allocation schemes and increases the network-wide throughput as well as the throughput of a station that experiences poor performance. This implies improved fairness performance among transmission pairs with various channel bandwidths.</P>