• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.6B
• /
• pp.406-415
• /
• 2005

The standards which use shared medium like IEEE 802.11 wireless LAN have transmission opportunity by contention in contention period. If there are collisions in contention period, medium access control protocol may solve problem by using backoff algorithm. Backoff algorithm is important part in medium access control, but legacy backoff method which is used under IEEE 802.11 standards is not adjusted when load is heavy because of increasing collisions. In this paper, we propose a new load-based dynamic backoff algorithm in contention-based wireless shared medium to improve throughput of medium and to reduce the number of collisions. Proposed backoff algorithm can increase the network utilization about $20\%$ higher than that of binary exponential backoff algorithm.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.3
• /
• pp.541-546
• /
• 2004

Space-Time Coding(STC) is a technique that utilizes joint correlation of transmitted signals in both time and space domains. Through this approach, diversity and coding gains can be simultaneously obtained. In this paper, we use SPW simulation tool to implement the IEEE 802.11a system. Based on this system, OFDM system with STC and convolutional coder concatenated is implemented. The system performance is analyzed and compared with the performance of the IEEE 802.11a system. The simulation results show that the performance with concatenated codes at a data rate of 6Mbps shows approximately a 5dB gain over the system with the convolutional code only. At a data rate of 12Mbps, the performance with concatenated codes is further improved by approximately 6dB.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.18 no.4
• /
• pp.155-159
• /
• 2004

This paper describes the design and the simulation of a single pole double throw(SPDT) FET switch for wireless LAN(IEEE802.11a ＆ IEEE802.11b) applications using drain impedance transformation network with Microstrip transmission line. At the receiving path insertion losses were from 0.8(㏈) to 1.462(㏈) between 2(㎓) and 4(㎓), from l.26(㏈) to 2.3(㏈) between 4.7(㎓) and 6.7(㎓) and the isolations were under 30(㏈) between 2(㎓) and 6.7(㎓). At the transmitting path insertion loss were from 1.18(㏈) to 2.87(㏈) between 2(㎓) and 4(㎓) from 0.625(㏈) to 1.2(㏈) between 4.7(㎓) and 6.7(㎓) and the isolations were under 30(㏈) between 2(㎓) and 6.7(㎓).

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.9 no.4
• /
• pp.798-803
• /
• 2005

This paper describes a design of AES(Advanced Encryption Standard)-based CCMP core for IEEE 802.1li wireless LAN security. To maximize its performance, two AES cores ate used, one is for counter mode for data confidentiality and the other is for CBC(Cipher Block Chaining) mode for authentication and data integrity. The S-box that requires the largest hardware in AES core is implemented using composite field arithmetic, and the gate count is reduced by about $20\%$ compared with conventional LUT(Lookup Table)-based design. The CCMP core designed in Verilog-HDL has 13,360 gates, and the estimated throughput is about 168 Mbps at 54-MHz clock frequency. The functionality of the CCMP core is verified by Excalibur SoC implementation.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.49 no.12
• /
• pp.64-72
• /
• 2012

Synchronization including timing recovery, frequency offset compensation, and frame synchronization is most important signal processing block in all wireless/wired communication systems. In most communication systems, synchronization schemes based on training sequences or preambles are used. WLAN standards of 802.11a/g/n released by IEEE are based on OFDM systems. OFDM systems are known to be much more sensitive to frequency and timing synchronization errors than single carrier systems. A loss of orthogonality between the multiplexed subcarriers can result in severe performance degradations. The starting position of the frame and the beginning of the symbol and training symbol can be estimated using correlation methods. Correlation processing functionality is usually complex because of large number of multipliers in implementation especially when the reference signal is non-binary. In this paper, a simple correlation based synchronization scheme is proposed for IEEE 802.11a/g/n systems. Existing property of a periodicity in the training symbols are exploited. Simulation and implementation results show that the proposed method has much smaller complexity without any performance degradation than the existing schemes.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.20 no.5
• /
• pp.89-98
• /
• 2010

Wireless LAN (WLAN) is type of wireless service that has higher data transmission than current cellular networks. The usage is continually increasing. There are a lot of vulnerabilities in wireless network, due to the properties of the wireless environment, regardless of its popularity. IEEE announced the 802.11i security standard to solve these problems. The vulnerable point of messages used in the process of key distribution for 802.11i makes the target node attacked lose memory through continuous messages and blocks the legitimate WLAN service. In this paper, we proposed new schemes to solve this problem and compared our proposals with the current process. The proposed protocol eliminates the memory exhaustion problem on the client side by using methods for reduction of memory usage.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2005.05a
• /
• pp.1781-1784
• /
• 2005

2.4GHz ISM 밴드의 무선 통신 기술이 상업적으로 활발히 활용됨에 따라, 이 대역을 이용하는 무선 전송 기술 중 IEEE 802.11 표준을 이용한 다양한 활용이 시도되고 있다. 본 논문은 GDM5302 임베디드 프로세서를 이용하여 차량에 적용할 수 있는 다기능 Set-Top Box를 구현하였다. 논문에서 제시한 Set-Top Box는 무선 네트워크 연결 기능을 이용하여 음악의 재생, 차량 상태 정보 관리, 개인 정보 관리 등 다양한 기능을 유비쿼터스 컴퓨팅 환경으로 구현하였다.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.12
• /
• pp.2262-2269
• /
• 2016

In IEEE 802.11 wireless LANs, when a source node with low data rate occupies the channel resource for a long time, network performance degrades. In order to improve performance, the cooperative communication has been proposed. In the previous cooperative communication protocols, relay nodes deliver data packets only for a source node. In this paper, we propose an additional transmission scheme in which relay nodes select an additional source node based on several information and deliver data packets for the original source node and the selected additional source node. The proposed scheme improves performance and provides fairness among source nodes. Performance of the proposed scheme is investigated by simulation. Our results show that the proposed scheme outperforms the previous protocol in terms of fairness index and throughput.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.2A
• /
• pp.188-194
• /
• 2007

In order to become ubiquitous world, the compatibility of wireless machines has become the significant characteristic of a communication terminal. Thus, SDR is the most necessary technology and standard. However, among the environment which has different communication protocol, it's difficult to make a terminal with only hardware using ASIC or SoC. This paper suggests the processor that can accelerate several communication protocol. It can be connected with main-processor, and it is specialized PHY layer of network The C-program that is modeled with the wireless protocol IEEE802.11a and IEEE802.11b which are based on widely used modulation way; OFDM and CDM is compiled with ARM cross compiler and done simulation and profiling with Simplescalar-Arm version. The result of profiling, most operations were Viterbi operations and complex floating point operations. According to this result we suggested a co-processor which can accelerate Viterbi operations and complex floating point operations and added instructions. These instructions are simulated with Simplescalar-Arm version. The result of this simulation, comparing with computing only one ARM core, the operations of Viterbi improved as fast as 4.5 times. And the operations of complex floating point improved as fast as twice. The operations of IEEE802.11a are 3 times faster, and the operations of IEEE802.11b are 1.5 times faster.

• Proceedings of the Korean Information Science Society Conference
• /
• 2004.04a
• /
• pp.682-684
• /
• 2004

최근 유비쿼터스 혁명으로 인해 장소 및 통신기기에 제약 없이 정보를 주고받는 환경으로의 요구가 증대되고 있다. 이러한 요구를 충족하고자 IP 계층에서 투명한 이동성을 제공하는 차세대 무선 프로토콜인 Mobile IPv6 기술이 필수적이다. 그러나 기존 Mobile IPv6는 제한된 컴퓨팅 능력을 가진 소형 이동 단말에는 탑재할 수 없다는 문제점이 있다. 이를 해결하기 위해서는 Mobile IPv6를 하드웨어 모듈로 구현하는 것이 필요하고, 이와 더불어 무선 환경을 지원하기 위해서 무선랜 MAC 기술의 하드웨어 구현이 요구된다. 이에 본 논문에서는 Mobile IPv6 모듈이 무선랜을 지원할 수 있도록 IEEE 802.11 MAC 모듈을 하드웨어로 설계 및 구현하였다.