• 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.

• 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 Internet Computing and Services
• /
• v.15 no.2
• /
• pp.19-31
• /
• 2014

In this paper, a parallel backoff delay procedure on multiple IEEE 802.15.4 channels and a channel searching method considering the frequency spectrum of WiFi traffic are studied for IEEE 802.15.4 nodes to avoid the interference from WiFi traffic. In order to search the channels being occupied by WiFi traffic, we analyzed the methods measuring the powers of adjacent channels simultaneously, checking the duration of measured power levels greater than a threshold, and finding the same periodicity of sampled RSSI data as the beacon frame by signal processing. In an wireless channel overlapped with IEEE 802.11 network, the operation of CSMA-CA algorithm for IEEE 802.15.4 nodes is explained. A method to execute a parallel backoff procedure on multiples IEEE 802.15.4 channels by an IEEE 802.15.4 device is proposed with the description of its algorithm. When we analyze the data measured by the experimental system implemented with the proposed method, it is observed that medium access delay times increase at the same time in the associated IEEE 802.15.4 channels that are adjacent each other during the generation of WiFi traffic. A channel evaluation function to decide the interference from other traffic on an IEEE 802.15.4 channel is defined. A channel searching method considering the channel evaluations on the adjacent channels together is proposed in order to search the IEEE 802.15.4 channels interfered by WiFi, and the experimental results show that it correctly finds the channels interfered by WiFi traffic.

• Journal of information and communication convergence engineering
• /
• v.15 no.1
• /
• pp.28-36
• /
• 2017

The medium access control (MAC) protocol based on dynamic time division multiple access/time division duplex (TDMA/TDD) is responsible for random access control and radio resource allocation in dynamic traffic environments. These functions of random access and resource allocation are very important to prevent wastage of resources and improve MAC performance according to various network conditions. In this paper, we propose new random access and resource allocation schemes to guarantee quality of service (QoS) and provide priority services in a dynamic TDMA/TDD system. First, for the QoS guarantee, we propose an adaptive random access and resource allocation scheme by introducing an access probability. Second, for providing priority service, we propose a priority-based random access and resource allocation scheme by extending the first adaptive scheme in both a centralized and a distributed manner. The analysis and simulation results show that the proposed MAC protocol outperforms the legacy MAC protocol using a simple binary exponential backoff algorithm, and provides good differential performance according to priorities with respect to the throughput and delay.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.3A
• /
• pp.267-277
• /
• 2011

Like other wireless network protocols, IEEE 802.15.4 adopts CA (Collision Avoidance)algorithm to avoid the early collision of a new packet by randomizing its first transmission time rather than its immediate delivery. The traditional CA scheme of IEEE 802.15.4, however, selects the random access time from the predetermined range without considering the degree of current congestion. It probably causes either a long delay to settle in the suitable range for the current network load or frequent clashes especially during the long lasting heavy traffic period. This paper proposes an ACA(Adaptive Collision Avoidance) algorithm adapting the initial backoff range to the undergoing collision variations. It also introduces a mathematical model to predict the performance of ACA algorithm added to IEEE 802.15.4. With only small deviations from corresponding simulations, our analytical model shows that ACA technique can improve the throughput of IEEE 802.15.4 by up-to 41% maximally in addition to shortening the packet delays.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.46 no.4
• /
• pp.46-55
• /
• 2009

In RFID field, when the neighboring readers try to occupy the same or adjacent channel simultaneously, there exists reader-to-reader interference; it calls reader collision. From the reader collision, the tags cannot response correctly query from the reader. Reader anti-collision schemes have been developed, and particularly, the Listen-Before-Talk(LBT) scheme is proposed to avoid reader collision in ETSI in multi channel environment. However, in ETSI, there is a drawback that the reader collision does not decreases effectively because the reader selects randomly a channel without considering the channel environment and readers try to occupy the channel concurrently. In this paper, we propose a algorithm based on LBT scheme considering multi channel environment as well as made up for the drawbacks of LBT The proposed algorithm applies random backoff, the collision avoidance mechanism. And it can reduce delay because of our proposed estimation mechanism Simulation using OPNET shows that the proposed algorithm achieves higher superiority than that of the simple algorithms in sparse and dense reader mode.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.9 no.2
• /
• pp.388-394
• /
• 2008

In this paper, MAC(Medium Access Control) algorithm for the IEEE 802.11 DCF(Distributed Coordination Function) improving the performance is proposed and analyzed by simulation. The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF(Point Coordination function). The DCF controls the transmission based on CSMA/CA(Carrier Sense Multiple Access With Collision Avoidance). The DCF shows excellent performance relatively in situation that competition station is less but has a problem that performance is fallen from throughput and delay viewpoint in situation that competition station is increased. This paper proposes an enhanced DCF algorithm that increases the CW to maximal CW after collision and decreases the CW smoothly after successful transmission in order to reduce the collision probability by utilizing the current status information of WLAN. To prove efficiency of proposed algorithm, a lots of simulations are conducted and analyzed.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.10 no.11
• /
• pp.1225-1230
• /
• 2015

MAC protocol for WBAN performs CSMA/CA(:Carrier Sense Multiple Access with Collision Avoidance)algorithm that handles traffic which occurs in emergency with top priority in order to deal with variable data of sensor node for medicine. Emergency message that node sends undergoes collision and delay of transmission by retransmission of emergency message and waste of energy by retransmission. This paper suggests algorithm that minimizes loss of frame caused by collision and applies different backoff parameters by setting order of priority between MAC instruction frame and data frame in CSMA/CA algorithm case which applies order of priority queuing to improve aforementioned problem. According to performance evaluation, it has been found that using suggested MAC protocol showed lower collision probability, higher packet transmission processing ratio and lower packet loss compared with using IEEE 802.15.6.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.9 no.1
• /
• pp.91-100
• /
• 2010

According to the recent increase in air traffic a more efficient air traffic flow control is required. This paper proposes the algorithm for efficient air traffic flow control. Aeronautical communication environment is different from the common communication environment since it needs a direct communication between stations (or airplanes) and requires a strict priority for safety message. Moreover, the wide area for basic service causes high propagation delay. In this paper, by using existing CSMA/CA Media Access Control (MAC) protocol, we set the message priorities according to air traffic condition (congestion airport area, approach control area, En route area, and ocean area). This prioritization scheme enables the data transmission with higher access probability. Simulation results confirm that our protocol shows better performance in terms of channel efficiency and success probability compared to exisiting CSMA/CA protocol.

• Journal of KIISE:Information Networking
• /
• v.29 no.4
• /
• pp.447-458
• /
• 2002

In this paper, we design and implement Wireless Transaction Protocol(WTP) and evaluate it for wireless transaction processing in mobile computing environments. The design and implementation of WTP are based on the coroutine model that might be suitable for light-weight portable devices. We test the compatibility between our product and the other products such as Nokia, Kannel and WinWAP For the evaluation of WTP, we use an Internet simulator that can arbitrary generate random wireless errors based on the Gilbert model. In our experiment, the performance of WTP is measured and compared to those of Transmission Control Protocol(TCP) and TCP for Transactions. The experiment shows that WTP outperforms the other two protocols for wireless transaction processing in terms of throughput and delay. Especially, WTP shows much higher performance In ease of high error rate and high probability of burst errors. This comes from the fact that WTP uses a small number of packets to process a transaction compared to the other two protocols and introduces a fixed time interval for retransmission instead of the exponential backoff algorithm. The experiment also shows that the WTP performance is optimized when the retransmission counter is set to 5 or 6 in case of high burst error rate.