• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.2A
• /
• pp.168-175
• /
• 2006

To cope with channel variation, wireless networks such as IEEE 802.11 WLAN provide multiple transmission rates by employing different channel modulation and coding schemes. However, the coexistence of different transmission rates degrades the total system performance of the network. In order to eliminate this performance abnormality and improve protocol capacity, we propose a new Packet transmission algorithm, the RAT(Rate-Adapted Transmission) scheme. The RAT scheme distributes the wireless channel fairly based on the channel occupancy time. Moreover, it efficiently transmits packets even in a single station using rate-based queue management. Therefore, the RAT scheme obtains not only the inter-rate contention gain among stations but also the intra-rate contention gain among connections in a single station.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.42 no.11
• /
• pp.1-12
• /
• 2005

In wireless personal area networks(PANs), the successful design of channel time allocation algorithm is a key factor in guaranteeing the various quality of service(QoS) requirements for the stringent real-time constraints of multimedia services. In this paper we propose a dynamic channel time allocation algerian for providing delay guarantees to multimedia traffics such as MPEG streams in the IEEE 802.15.3 high-rate WPANs. The dynamic algorithm exploits the characteristics of MPEG stream, wherein the devices (DEVs) send their channel time requests only at the end of superframe boundaries. The algerian uses mini packets for feedback control in order to deliver dynamic parameters for channel time requests from the DEVs to the piconet coordinator (PNC). In this scheme, the duration of channel time allocated to a DEV during a superframe is changed dynamically depending on the MPEG frame type, traffic load and delay bound of the frame, etc. Performance of the proposed scheme is investigated by simulation. Our results show that compared to traditional scheme, the proposed scheme is very effective and has high performance while guaranteeing the delay bound.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.48 no.11
• /
• pp.60-66
• /
• 2011

LTE (Long Term Evolution) supports QoS (Quality of Service) with several service classes. For each class of traffic, a big difference exists on BER (Bit Error Rate) requirement. This leads to a considerable difference in transmission power for various classes of traffic. In this paper, a novel scheduler is designed and proposed for LTE which supports CoS (Class of Service) with the consideration of priority as well as target BER. By the CQI (Channel Quality Indicator) and QCI (QoS Class Identifier), a minimum transmission power is assigned from the target BER for each class of traffic per each user. Hence, with the other information such as user's used rate in the past and the priority of traffic, the probability of occupying channels is determined. The simulation results of Service Class scheduling are compared with that of Maximum Rate and Proportional Fair. The results show that the service class-aided scheduling can improve the throughput of whole system significantly.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.18 no.2
• /
• pp.289-294
• /
• 2014

In this paper, we investigate the user scheduling, transmit beamforming, and receive beamforming of uplink space division multiple access (SDMA) systems where multiple users are allowed to transmit their signal to a base station (BS) using the same frequency band simultaneously. The BS performs a receive beamforming using the predetermined pseudo-random pattern and select users with a specific criterion. Especially, in this paper, we propose the threshold-based transmit power control, in which a user decrease its transmit power according if its generating interference to other users's signal is larger than a predetermined threshold. Assuming that the TDD system is used, the channel state information (CSI) can be obtained at each user from pilot signals from the BS. Simulation results show that the proposed technique significantly outperforms the existing user scheduling algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.10A
• /
• pp.896-905
• /
• 2005

In this paper, we propose a SPD(Selective Packet Delay) scheme to improve the performance of High-Speed Downlink Shared Channel(HS-DSCH) employing N-Channel Stop and Wait retransmission scheme in High Speed Downlink Packet Access(HSDPA) system. The proposed SPD coordinates packet transmissions according to the channel condition. When the channel condition is bad, packet transmission is forcedly delayed, and the designated time slot is set over to other users in good channel condition. Hence, the SPD is able to reduce the average transmission delay for packet transmission under the burst error environments. In addition, we propose two packet scheduling schemes called SPD-LDPF(Long Delayed Packet First) and SPD-DCRR(Deficit Compensated Round Robin) that are effectively combined with the SPD scheme. Simulation results show that the proposed scheme has better performance in terms of delay, throughput and fairness.

• ETRI Journal
• /
• v.32 no.5
• /
• pp.819-822
• /
• 2010

Supporting QoS over multihop wireless mesh networks is difficult because end-to-end delay increases quickly with the increasing number of hops. This paper introduces a novel multichannel time-division multiple-access media access control (McTMAC) protocol that can help to efficiently reduce delay over multihop networks. Performance evaluation results demonstrate that McTMAC outperforms existing alternative protocols. The max-delay can be reduced by as much as 60% by using McTMAC.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.55 no.5
• /
• pp.236-239
• /
• 2006

A wireless MAC scheduler that provides a high level of quality-of-service (QoS) for video-on-demand (VOD) applications while achieving a reasonable level of system throughput is proposed. The proposed scheduler considers both channel qualities of mobiles and the urgency of real-time packets coming from VOD applications in a cross-layer approach between application and MAC layers.

• 제어로봇시스템학회:학술대회논문집
• /
• 2002.10a
• /
• pp.41.6-41
• /
• 2002

In this paper, we present a remote control strategy for vehicles moving in an intelligent Vehicle Highway System(IVHS). We study a method for optimal off-line scheduling of a limited communication channel that is used for lead vehicle control in a platoon. The deviated distance from the desired trajectory is used for defining a cost functional that measures the performance of the system with communication constraints in relation to the desired system without communication constraints. The optimal communication sequence is obtained by simulations.

• Proceedings of the Korean Information Science Society Conference
• /
• 2002.10e
• /
• pp.88-90
• /
• 2002

본 논문에서는 ATM 망의 트래픽 제어 기능 중의 하나인 UPC(Usage Parameter Control) 알고리즘을 제안하고 VHDL을 이용하여 칩(chip)을 구현하였다. 제안한 알고리즘은 우선순위가 높은 셀의 손실을 최소로 하고, 트래픽의 다중화 및 역다중화 과정에서 발생되는 트래픽의 군집성을 해소할 수 있다는 장점을 갖고 있다. 구현한 칩은 입력 모듈과 UPC 모듈, 출력 모듈의 3부분으로 이루어지며, 편의상, UPC 모듈에서는 커넥션 테이블의 index를 VCI(Virtual channel Identifier)와 동일하게 할당하였다. 또한 UPC 모듈의VSA(Virtual Scheduling Algorithm)블럭에서 셀의 도착시간을 계수하는 카운터가 랩-어라운드(wrap-around)할 때 생기는 VSA의 오류를 보정하여 구현하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2016.05a
• /
• pp.635-637
• /
• 2016

센서 네트워크에서 각 센서 노드의 에너지 소모를 최소화하여 에너지 소모를 줄임으로써 망의 지속시간을 늘이는 것이 중요하다. 기존의 MAC(Medium Access Control) 프로토콜은 채널 폴링 기법을 이용하여 효율적인 에너지 관리에 대한 해결책을 제시 하였으나, 그러한 방식에 따른 각 노드의 Duty Cycle이 길어짐으로써 발생하는 에너지 소모에 대한 해결책은 제시하지 못하였다. 본 논문에서는 기존의 채널 폴링과 함께 스케쥴링 알고리즘을 적용하여 Duty Cycle의 주기를 줄임으로써 에너지 소모를 줄인다. 특히 이 방식을 이용하여 멀티홉과 과다한 트래픽에 대한 성능의 평가를 위해 실험을 통해 제안하는 프로토콜의 우수한 성능을 보인다.