• IE interfaces
• /
• v.17 no.spc
• /
• pp.111-121
• /
• 2004

In this paper, we propose an urgency and efficiency based wireless packet scheduling (UEPS) algorithm that is able to schedule real time (RT) and non-real time (NRT) traffics at the same time. The proposed UEPS algorithm is designed to support wireless downlink packet scheduling in the OFDMA system which is a strong candidate wireless system for the next generation mobile communications. The UEPS algorithm uses the time-utility function as a scheduling urgency factor and the relative status of the current channel to the average one as an efficiency indicator of radio resource usage. The design goal of the UEPS algorithm is to maximize throughput of NRT traffics with satisfying QoS requirements of RT traffics. The simulation study shows that the proposed UEPS algorithm is able to give better throughput performance than existing wireless packet scheduling algorithms such as proportional fair (PF) and modified-largest weighted delay first (M-LWDF) while satisfying QoS requirements of RT traffics such as the average delay and the packet loss rate under various traffic loads.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.12A
• /
• pp.1291-1297
• /
• 2004

In this paper, the new scheduling algorithm that supports the maximization of system throughput and the proportional fairness among non-real time traffic users is proposed in OFDMA wireless mobile communication systems. The concept of the proposed algorithm is based on the proportional fairness algorithm, which is deployed in 3GPP2, and sorting method. The proportional fairness algorithm is adapted to allocate the number of subcarrier per user. A sorting method is contributed to the maximization of system throughput in the practical allocation of subcarrier per user. Simulation results show that new algorithm had better performance than the max rate rule in case of fairness, higher throughput than the scheduling algorithm without sorting method. Even though the system throughput of the proposed algorithm is almost same with the iteration scheme using subcarrier swapping method between users, the computational time of the former is reduced up to 3 times than the latter.

• Proceedings of the Korean Information Science Society Conference
• /
• 2005.11a
• /
• pp.382-384
• /
• 2005

비례 공평성 스케줄러는 시간에 따라 변하는 무선 채널의 특성을 이용하는 기회주의적 패킷 스케줄링 방식으로서 시스템 수율을 크게 증가시키는 장점이 있으나 1) 로그 형태의 효용 함수만을 지원하고 2) 사용자 QoS를 고려하지 않으며 3) 단일 채널 시스템에만 적용 가능한 한계를 갖는다. 본 논문에서는 WiBro에서 채택하고 있는 다중 접속 방식인 OFDMA/TDD 환경에서 이러한 한계를 극복한 스케줄러를 제안하고 모의 실험에 의해 그 성능을 평가한다.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2006.05a
• /
• pp.1057-1060
• /
• 2006

본 논문에서는 OFDMA-TDD 환경에서 서비스 사용자들에게 QoS 를 보장해줄 수 있도록 예측 알고리즘을 이용하여 한정된 무선 자원을 효율적이고 공정하게 스케줄링 해주는 알고리즘을 연구하였다. 예측 알고리즘은 각 사용자의 이동 정보와 단말들의 변화해온 채널상태의 history data 를 이용하여 앞으로의 채널상태를 예측하고, 예측된 결과는 사용자의 이동 정보와 함께 무선 자원 스케줄링에 적용한다. 또한 이동단말과 고정단말이 공존하는 환경에서는 QoS 보장에 있어 공정하지 않음을 밝히고, 이와 같은 문제를 해결하는 방안을 제안하였으며, 실험결과를 PF 알고리즘과 비교하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2013.06a
• /
• pp.219-220
• /
• 2013

무선통신에서 다중안테나를 사용하지 않고 다이버시티 이득을 얻기 위한 대안으로 협력 통신 기법이 개발되어 왔다. 하지만 대부분의 협력기법들은 릴레이에 신호를 전송하는 과정에서 delay 가 발생하게 되어 전송률이 감소하는 단점이 있다. 본 논문에서는 OFDMA 시스템에서 feedback 정보를 이용하는 기법을 사용하여 전송 손실이 발생하지 않으면서 기존의 MISO(multi input multi output)시스템과 비슷한 성능을 갖는 새로운 협력모델을 제안한다. 제안된 기법은 bit error rate(BER) 관점에서 평가되고 협력하는 사용자와의 채널이 보장되면 기존의 MISO 기법과 비슷한 성능을 보이는 것을 보여준다.

• Proceedings of the IEEK Conference
• /
• 2008.06a
• /
• pp.239-240
• /
• 2008

A new frequency offset estimator using low cross-property of PN sequences is proposed in the orthogonal frequency division multiple access (OFDMA) uplink systems. Simulation results show that the proposed estimator improves the mean square error (MSE) performance compared to conventional estimator [2] where each user have both different timing offset and different frequency offset. In addition, the MSE performance is improved as the length of PN sequence increases.

• Journal of Advanced Navigation Technology
• /
• v.9 no.2
• /
• pp.192-199
• /
• 2005

Adaptive Modulation & Coding (AMC) is the method of varying the modulation and coding scheme for the changeable wireless channel environment. WiBro use AMC method because it has a very large variation caused by mobility interference and other cell interference. In this paper, we will compare and analysis the method of selecting the optimum MCS level for the efficiently use of mobile power consumption.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37 no.7A
• /
• pp.522-527
• /
• 2012

In this paper, union upper bound on convolutional coded bit error rates (BER) is derived for downlink orthogonal frequency division multiple access (OFDMA) networks. According to the numerical results, for the small network loads, the BER performance with Laplacian decoding metric outperforms the BER performance with Gaussian decoding metric under downlink OFDMA networks with Viterbi decoder.

• Journal of Communications and Networks
• /
• v.12 no.1
• /
• pp.30-42
• /
• 2010

In this work we consider the problem of downlink resource allocation for proportional fairness of long term received rates of data users and quality of service for real time sessions in an OFDMA-based wireless system. The base station allocates available power and subchannels to individual users based on long term average received rates, quality of service (QoS) based rate constraints and channel conditions. We formulate and solve a joint bandwidth and power optimization problem, solving which provides a performance improvement with respect to existing resource allocation algorithms. We propose schemes for flat as well as frequency selective fading cases. Numerical evaluation results show that the proposed method provides better QoS to voice and video sessions while providing more and fair rates to data users in comparison with existing schemes.

• Proceedings of the Korean Institute of Communication Sciences Conference
• /
• 2006.07a
• /
• pp.533-533
• /
• 2006