• Journal of the Korea Society for Simulation
• /
• v.23 no.4
• /
• pp.65-74
• /
• 2014

IEEE 802.11n standard has introduced the new schemes in MAC and PHY layers to improve network throughput. Frame aggregation and Block ACK are mainly defined to increase the efficiency of the MAC layer. There exists still problem in IEEE 802.11n. When block ACK request and/or response frames are missing or received in error, the sender does not know the status (success/failure) of each frame in the aggregated large frame and retransmits all the frames. This can cause a lower network performance. To solve this problem, we propose a new effective scheme, called reduced retransmission of MPDUs (RRM) scheme. In the proposed scheme, when a sender does not receive a block ACK response frame, it just transmits a next data frame and requests a block ACK. Therefore, it can retransmits the erroneous frames. Performance of the proposed scheme is investigated by simulation. Our results show that the proposed scheme is very effective and improves the performance under a wide range of channel error conditions.

• Journal of the Korea Society for Simulation
• /
• v.15 no.4
• /
• pp.79-86
• /
• 2006

Data transmission in poor environment like underwater has considerably serious delay rate and ewer rate. Like this environment usually has heavy fluctuation of error rate and limited wireless communication state. Therefore, mechanism using in such environment has to be efficient and simple. This paper suggests a new block ack mechanism, called the Pervasive Block ACK (PBA), which transmits aggregated ACKs. This mechanism takes effect on reducing number of traffic, decreasing overhead and delay rate in poor environment networks like underwater. Additionally, we can expect energy consumption. We verify propriety and efficiency of PBA through describing numerical result based analytical formula in this paper.

• Proceedings of the Korean Information Science Society Conference
• /
• 2006.06d
• /
• pp.319-321
• /
• 2006

본 논문에서는 블록 FEC(Forward Error Correction) 알고리즘을 적용한 IEEE 802.11e MAC(Medium Access Control)의 블록전송모드(Block Transfer Mode)의 성능을 분석한다. 성능 향상을 위해서 IEEE 802.11e MAC은 TXOP(Transmission Opportunity)시간 동안 특정 스테이션(station)에게 독점적인 전송 기회를 부여하며, 이 기간동안 하나의 블록 즉 연속적으로 여러 개의 데이터 프레임(frame)을 전송한다. 수신자는 블록내의 각 프레임에 수신 여부를 블록 ack (block Acknowledgment)방식, 즉 하나의 ack 패킷이 모든 수신 프레임의 일련번호를 모아 알려 준다. 그러나 오류가 빈번한 무선 채널 환경에서는 블록 ack 방식을 사용하더라도 빈번한 재전송으로 인해 채널의 성능이 현저히 감소한다. 이러한 문제를 해결하기 위해 심볼 단위로 오류를 복원하는 블록 FEC 알고리즘을 적용할 수 있는데, 본 논문에서는 802.11e에서 FEC 알고리즘을 적응하는 두 가지 방식의 성능을 해석적으로 분석한다. 즉 두 가지 방식은 프레임 당 블록 FEC를 적용하는 방법과 전체 블록 내의 프레임을 하나의 데이터로 간주하여 FEC를 적용하는 방식이다. 본 논문에서는 이 들 두 가지 방식의 채널 성능 향상 정도와 블록 ack만을 사용한 경우의 성능을 수식적으로 계산한다. 실험에 의하면 BER이 $10^{-4}$인 채널 환경에서 블록 FEC를 적용한 방식이 블록 ack를 사용한 방식에 비해 약 1.5%의 성능향상을 보인다.

• Proceedings of the Korean Institute of Communication Sciences Conference
• /
• 2004.07a
• /
• pp.63-63
• /
• 2004

• Journal of Korea Multimedia Society
• /
• v.12 no.12
• /
• pp.1769-1777
• /
• 2009

With the advent of the ubiquitous technology age, the progress of network technology has enabled a robust sensor communication, not just in cities, but also in poor surroundings such as deserts, polar regions, or underwater environments. In this paper, we propose a Multiple Acknowledgement (MA) technique to replace the conventional Automatic Repeat request (ARQ) technique. The MA mechanism is to send an Ack to many receivers simultaneously. The CH (master, coordinator) of the unit cluster broadcasts a Beacon frame where Ack information of the previously transmitted data is included. This technique can reduce the number of transmissions and overhead significantly. The proposed technique is a scheme improving the efficiency of an underwater sensor network where the uplink data transmission is the mainstream. The Performance of the ARQ, Block Ack, Pervasive Block Ack and the proposed method were compared with one another and analyzed. The proposed method showed significant performance improvement as compared with the ARQ, BA, and PBA in its channel efficiency.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2009.04a
• /
• pp.1267-1270
• /
• 2009

IEEE 802.15.4 프로토콜은 구현이 용이하여 다양한 응용 네트워크에서 사용되고 있다. 하지만 대용량 데이터 전송시 백오프(back-off), CCA(Clear Channel Assesment), IFS(Inter Frame Space), ACK 시간 등이 MAC 계층에서 오버헤드로 작용하여 네트워크 성능 저하의 요인이 된다. 본 논문에서는 IEEE 802.11e 프로토콜에서 사용되고 있는 블록(block) ACK 기법을 분석하고 이를 802.15.4 네트워크에 적용할 것을 제안하였다. 시뮬레이션을 통한 성능 분석을 실시하고 제안한 기법이 802.15.4에서도 네트워크 처리량을 크게 향상 시킬 수 있음을 확인하였다.

• Proceedings of the IEEK Conference
• /
• 2003.11c
• /
• pp.157-163
• /
• 2003

IEEE 802.11a Distributed Coordination Function(DCF) Protocol을 사용하여 Real-Time MultiMedia Data의 전송을 수행할 경우, DCF Protocol의 적합하지 못한 Mechanism에 의하여, Data 전송의 극대화를 이루지 못한다. Retransmission이 반복되는 경우, Binary Slotted Exponential Backoff Mechanism은 거대한 Packet Delay와 Jitter의 원인이 되며 Automatic Repeat Request(ARQ) 방식의 Ack Mechanism은 MultiMedia Data를 전송하기에 적합하지 못하다. 본 논문은 위와 같은 문제점을 해결하기 위하여 Real-Time MultiMedia Data을 주로 전송하는 STA에 따른 Real-Time/Non-Real-Time(RT/NRT) Station(STA)의 구분과 보내고자 하는 Real-Time MultiMedia Data의 Network Traffic Load(The Required Bandwidth)를 고려하여, Modified DCF(mDCF) Protocol의 Modified Backoff(mBackOff), Modified BlockAck(mBlockAck) Mechanism을 제시함으로서, Data 전송의 극대화를 제공하며, 또한 IEEE 802.11a와의 호환성을 제공한다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.7A
• /
• pp.666-673
• /
• 2006

In this paper, we evaluated the performance of 4 types of ARQ algorithms that have been adopted to offer reliable transmission between MAC layers. First of all, we implemented IEEE 802.16 ARQ algorithms with NS-2 network simulator and then evaluated the performances in various channel states. We used two performance measures to evaluate those performances. First, we used the total number of ARQ block in bytes that have been received without error. Second, we used ACK_Efficiency that is newly defined in this paper. From the results of simulation, we could be aware that each ARQ algorithm has different performance in a various channel states. For improving the transmission data rate in a specific channel state, we have to choose the right ACK interval as well as a suitable ARQ algorithm.

• Proceedings of the KIEE Conference
• /
• 2006.10c
• /
• pp.467-469
• /
• 2006

In wireless network environments, as users' demands on high-speed data communications due to increase of multi-media services, the necessity of new high-speed WLAN technologies has appeared. Nowaday, IEEE is standardizing a new WLAN protocol caned as IEEE 802.11n. To effectively use wireless resources, IEEE 802.11n introduces MAC aggregation function which is similar to that in IEEE 802.11e. In case of transmitting several frames without MAC aggregation, the frames include individual frame header and trailer, and their corresponding acknowledgement frames can appear on wireless link. However, if they are aggregated into single MAC frame, we can reduce the number of used bits due to frame headers/trailers and also remove redundant acknowledgement frames. In this paper, we explain two different MAC frame aggregation methods for IEEE 802.11e and IEEE 802.11n and evaluate their throughput by simulations.

• Journal of Broadcast Engineering
• /
• v.19 no.4
• /
• pp.510-520
• /
• 2014

By adopting the MAC(Media Access Control) protocol which enables to pack multiple MPDUs(MAC-level Protocol Data Units) into a single PPDU(Physical Layer Protocol Data Unit), IEEE 802.11n WLAN supports high throughput. Up to now, there have been a lot of existing channel information-based A-MPDU schemes dynamically determining the number of MSDUs according to the wireless channel condition information which is sent from the receiver to sender. However, the channel information-based scheme has a serious drawback having a high system overhead due to the frequent channel feedback information. To reduce the system overhead, the proposed BA-base dynamic A-MPDU scheme simply chooses the number of MSDUs to be retransmitted by not the frequent channel feedback information but the BA signal representing whether MPSUs belonging to the A-MPDU are received or not. Through NS-2(Network Simulator-2), we found that the proposed scheme had higher throughput and lower packet error rate than the existing fixed A-MPDU scheme.