• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.1075-1082
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• 2004

Wireless LAN is a rather mature communication technology connecting mobile terminals. IEEE 802.11 is a representative protocol among Wireless LAN technologies. The basic medium access control (MAC) mechanism of IEEE 802.11 is called distnbuted coordination function (DCF). DCF shows poor throughput and high drop rate as the number of stations and offered traffic load increase. In this paper we propose an effective mechanism using dynamic mimmum contention window(CWmin) in wireless LAN~ and show that performance improves via simulations. Proposed dynamic CWmin scheme exhibits superior performance as the number of stations and offered load grow. As, our proposed scheme is expected to be more effective in highly densed wireless LAN environment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.1
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• pp.334-349
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• 2022

The effectiveness of Wi-Fi networks is greatly influenced by the optimization of contention window (CW) parameters. Unfortunately, the conventional approach employed by IEEE 802.11 wireless networks is not scalable enough to sustain consistent performance for the increasing number of stations. Yet, it is still the default when accessing channels for single-users of 802.11 transmissions. Recently, there has been a spike in attempts to enhance network performance using a machine learning (ML) technique known as reinforcement learning (RL). Its advantage is interacting with the surrounding environment and making decisions based on its own experience. Deep RL (DRL) uses deep neural networks (DNN) to deal with more complex environments (such as continuous state spaces or actions spaces) and to get optimum rewards. As a result, we present a new approach of CW control mechanism, which is termed as contention window threshold (CW_Threshold). It uses the DRL principle to define the threshold value and learn optimal settings under various network scenarios. We demonstrate our proposed method, known as a smart exponential-threshold-linear backoff algorithm with a deep Q-learning network (SETL-DQN). The simulation results show that our proposed SETL-DQN algorithm can effectively improve the throughput and reduce the collision rates.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8A
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• pp.600-609
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• 2009

The traditional carrier sense multiple access (CSMA) protocol like IEEE 802.11 Distributed Coordination Function (DCF) does not handle the constraints adequately, leading to degraded delay latency and throughput as the network scales are enlarged. We present more efficient method of a medium access for real-time wireless sensor networks. Proposed MAC protocol is like the randomized CSMA protocol, but unlike previous legacy protocols, it does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports, we carefully decide to select a fixed-size contention window with non-uniform probability distribution of transmitting in each slot. We show that the proposed method can offer up to severaansimes latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using widely using network simulation package,caS-2. We finally show that proposed MAC scheme comes close to meet bounds on the best latency being achieved by a decentralized CSMA-based MAC protocol for real-time wireless sensor networks which is sensitive to delay latency.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.2
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• pp.93-100
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• 2014

IEEE 802.11 Wireless LAN Medium Access Control(MAC) supports two transmission methods, a DCF basic and a RTS/CTS in contention-based access. Even though the RTS/CTS method has been optionally introduced to solve the hidden terminal problem, it is able to produce better performance in some network environments than the basic transmission method. In this paper, the collision probability of wireless channel is mathematically analyzed and applied to measure network throughput using real transmission parameters so that a reference value between throughputs of two methods is obtained. We also confirmed that control signal rates affect overall network throughput and evaluated network throughputs considering collision probability, number of stations, and contention window size of Backoff between two methods respectively.

• Journal of Communications and Networks
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• v.15 no.6
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• pp.606-613
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• 2013

This paper proposes a complete solution of a contention-based medium access control in wireless local networks to provide station level quality of service guarantees in both downstream and upstream directions. The solution, based on the mature distributed coordination function protocol, includes a new fixed contention window backoff scheme, a tuning procedure to derive the optimal parameters, a super mode to mitigate the downstream bottleneck at the access point, and a simple admission control algorithm. The proposed system guarantees that the probability of the delay bound violation is below a predefined threshold. In addition, high channel utilization can be achieved at the same time. The numerical results show that the system has advantages over the traditional binary exponential backoff scheme, including efficiency and easy configuration.

• Journal of Communications and Networks
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• v.6 no.4
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• pp.376-386
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• 2004

In ad hoc networks, loss-based congestion window progression by the traditional means of duplicate ACKs and timeouts causes high network buffer utilization due to large bursts of data, thereby degrading network bandwidth utilization. Moreover, network-oriented feedbacks to handle route disconnection events may impair packet forwarding capability by adding to MAC layer congestion and also dissipate considerable network resources at reluctant intermediate nodes. Here, we propose a new TCP scheme that does not require the participation of intermediate nodes. It is a purely end-to-end scheme using TCP timestamps to deduce link conditions. It also eliminates spurious reductions of the transmission window in cases of timeouts and fast retransmits. The scheme incorporates a receiver-oriented rate controller (rater), and a congestion window delimiter for the 802.11 MAC protocol. In addition, the transient nature of medium availability due to medium contention during the connection time is addressed by a freezing timer (freezer) at the receiver, which freezes the sender whenever heavy contention is perceived. Finally, the sender-end is modified to comply with the receiver-end enhancements, as an optional deployment. Simulation studies show that our modification of TCP for ad hoc networks offers outstanding performance in terms of goodput, as well as throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.7
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• pp.543-552
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• 2013

For the safety messages in IEEE 802.11p/WAVE vehicles network environment, strict periodic beacon broadcasting requires status advertisement to assist the driver for safety. In crowded networks where beacon message are broadcasted at a high number of frequencies by many vehicles, which used for beacon sending, will be congested by the wireless medium due to the contention-window based IEEE 802.11p MAC. To resolve the congestion, we consider a MAC scheme based on slotted p-persistent CSMA as a simple non-cooperative Bayesian game which involves payoffs reflecting the attempt probability. Then, we derive Bayesian Nash Equilibrium (BNE) in a closed form. Using the BNE, we propose new congestion control algorithm to improve the performance of the beacon rate under saturation condition in IEEE 802.11p/WAVE vehicular networks. This algorithm explicitly computes packet delivery probability as a function of contention window (CW) size and number of vehicles. The proposed algorithm is validated against numerical simulation results to demonstrate its stability.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.681-685
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• 2004

Design of efficient Medium Access Control (MAC) protocols with both high throughput performances is a major focus in distributed contention-based MAC protocol research. In this paper, we propose an efficient contention-based MAC protocol for wireless Local Area Networks, namely, the Developed Collision Resolution (DCR) algorithm. This algorithm is developed based on the following innovative ideas: to speed up the collision resolution, we actively redistribute the backoff timers for all active nodes; to reduce the average number of idle slots, we use smaller contention window sizes for nodes with successful packet transmissions and reduce the backoff timers exponentially fast when a fixed number of consecutive idle slots are detected. We show that the proposed DCR algorithm provides high throughput performance and low latency in wireless LANs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1811-1813
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• 2016

DCF (Distributed Coordination Function) resolves the channel contention problem in a distributed manner by forcing nodes to randomly choose a waiting time in a contention window. However, since the size of a contention is limited, the collision probability increases with the number of sending nodes. To resolve the problem, in this paper, we propose a transmission control method based on the minority game (MG). Each node can determine autonomously whether to send or not without message exchanges with other nodes to maximize its profit. Through simulation studies, we verify that the proposed method can improves the performance of DCF in terms of collision probability in a congestion situation.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.793-805
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• 2001

In the recent priority system, high-priority packet will be served first and low-priority packet will be served when there isn\`t any high-priority packet in the system. By the way, even high-priority packet can be blocked by HOL (Head of Line) contention in the input queueing System. Therefore, the whole switching performance can be improved by serving low-priority packet even though high-priority packet is blocked. In this paper, we study the performance of preemptive priority in an input queueing switch for high speed switch system. The analysis of this switching system is taken into account of the influence of priority scheduling and the window scheme for head-of-line contention. We derive queue length distribution, delay and maximum throughput for the switching system based on these control schemes. Because of the service dependencies between inputs, an exact analysis of this switching system is intractable. Consequently, we provide an approximate analysis based on some independence assumption and the flow conservation rule. We use an equivalent queueing system to estimate the service capability seen by each input. In case of the preemptive priority policy without considering a window scheme, we extend the approximation technique used by Chen and Guerin [1] to obtain more accurate results. Moreover, we also propose newly a window scheme that is appropriate for the preemptive priority switching system in view of implementation and operation. It can improve the total system throughput and delay performance of low priority packets. We also analyze this window scheme using an equivalent queueing system and compare the performance results with that without the window scheme. Numerical results are compared with simulations.