• ETRI Journal
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• v.26 no.5
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• pp.391-396
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• 2004

In this paper, we propose a packet scheduling discipline called packet loss fair scheduling, in which the packet loss of each user from different real-time traffic is fairly distributed according to the quality of service requirements. We consider an orthogonal frequency division multiple access (OFDMA) system. The basic frame structure of the system is for the downlink in a cellular packet network, where the time axis is divided into a finite number of slots within a frame, and the frequency axis is segmented into subchannels that consist of multiple subcarriers. In addition, to compensate for fast and slow channel variation, we employ a link adaptation technique such as adaptive modulation and coding. From the simulation results, our proposed packet scheduling scheme can support QoS differentiations while guaranteeing short-term fairness as well as long-term fairness for various real-time traffic.

• Journal of information and communication convergence engineering
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• v.6 no.1
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• pp.1-5
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• 2008

In this paper, we propose and analyze the AMC (Adaptive Modulation and Coding) system with efficient turbo coded V-BLAST (Vertical-Bell-lab Layered Space-Time) technique. The proposed algorithm adopts extrinsic information from a MAP (Maximum A Posteriori) decoder with iterative decoding as a priori probability in two decoding procedures of V-BLAST scheme; the ordering and the slicing. Also, we consider the AMC system using the conventional turbo coded V-BLAST technique that simply combines the V-BLAST scheme with the turbo coding scheme. And we compare the proposed decoding algorithm to a conventional V-BLAST decoding algorithm and a ML (Maximum Likelihood) decoding algorithm. In addition, we apply a STD (Selection Transmit Diversity) scheme to the systems for better performance improvement. Results indicate that the proposed systems achieve better throughput performance than the conventional systems over the entire SNR range. In terms of transmission rate performance, the suggested system is close in proximity to the conventional system using the ML decoding algorithm.

• The Magazine of the IEIE
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• v.30 no.8
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• pp.64-64
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• 2003

국내외적으로, 2.3GHz 대역의 휴대 인터넷 서비스와 이동 고속 무선 패킷 데이터 MBWA(Mobile Broadband Wireless Access) 서비스를 위한 기술 개발 및 표준화 작업이 진행중이며, 이들 기술 표준에서는 데이터 속도의 고속화를 달성하기 위하여 AMC(Adaptive Modulation and Coding)를 요구하고 있다. AMC방식 무선 패킷 시스템은 서비스 지역 내에서 SNR(Signal to Noise Ratio)의 값에 연동하여 가변적인 데이터 서비스 속도를 제공하게 되고, 사용자가 서비스 지역을 이동하면서 제공받는 서비스 품질은 물리 채널의 서비스 속도 변화에 대응하여 변화되므로, 서비스 사업자는 서비스 사용자의 속도 품질을 일정하게 유지하고 관리 제어할 수 있도록 하는 서비스 품질 설계 기준이 필요하다. 따라서, 본 기고문에서는 이들 AMC 방식의 고속 무선 패킷 서비스 시스템 기술의 표준화에 병행하여 공중망 무선 패킷 서비스 시스템의 망 구축 설계시 고려되어야 할 가입자 수용용량과 서비스 품질 등을 산정하고 관리하기 위한 파라미터로서 기지국의 평균 데이터 공급 용량 MDT(Mean Data Throughput), 평균속도 공유 패킷 링크 MSPL (Mean Shared Packet Link) 그리고 서비스 Uniformity 지수 UI(Uniformity Index) 등을 제안하고자 한다.

• The Magazine of the IEIE
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• v.30 no.8
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• pp.844-852
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• 2003

국내외적으로, 2.3GHz 대역의 휴대 인터넷 서비스와 이동 고속 무선 패킷 데이터 MBWA(Mobile Broadband Wireless Access) 서비스를 위한 기술 개발 및 표준화 작업이 진행중이며, 이들 기술 표준에서는 데이터 속도의 고속화를 달성하기 위하여 AMC(Adaptive Modulation and Coding)를 요구하고 있다. AMC방식 무선 패킷 시스템은 서비스 지역 내에서 SNR(Signal to Noise Ratio)의 값에 연동하여 가변적인 데이터 서비스 속도를 제공하게 되고, 사용자가 서비스 지역을 이동하면서 제공받는 서비스 품질은 물리 채널의 서비스 속도 변화에 대응하여 변화되므로, 서비스 사업자는 서비스 사용자의 속도 품질을 일정하게 유지하고 관리 제어할 수 있도록 하는 서비스 품질 설계 기준이 필요하다. 따라서, 본 기고문에서는 이들 AMC 방식의 고속 무선 패킷 서비스 시스템 기술의 표준화에 병행하여 공중망 무선 패킷 서비스 시스템의 망 구축 설계시 고려되어야 할 가입자 수용용량과 서비스 품질 등을 산정하고 관리하기 위한 파라미터로서 기지국의 평균 데이터 공급 용량 MDT(Mean Data Throughput), 평균속도 공유 패킷 링크 MSPL (Mean Shared Packet Link) 그리고 서비스 Uniformity 지수 UI(Uniformity Index) 등을 제안하고자 한다.

• Journal of Advanced Navigation Technology
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• v.7 no.1
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• pp.59-71
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• 2003

The channel scheduler is suggested the radio resource management method in order to provide service with guaranteeing fairness and throughput to the users who use limited wireless channel. Proportional fairness scheduling algorithm is the channel scheduler used in the AMC(Adaptive Modulation and Coding)/TDM system, and this algorithm increases the throughput considering the user's time fairness. In this paper is suggested the channel scheduler combining CDM scheme available in AMC/TDM/CDM system. Unlike the system which only uses TDM which provide the only one user at the same slot, this scheduler can service a lot of users since this uses the CDM scheme with multi-cord channel. At every moment, allocation of transmission power to multi-channel users is problematic because of CDM scheme. In this paper, we propose a water-filling scheduling algorithm to solve the problem. Water-filling fairness(WF2) scheduling algorithm watches the average channel environment. So, this modified method guarantees fairness for each user in terms of power and service time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.385-391
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• 2007

In this paper, we propose and observe the Adaptive Modulation system with optimal Turbo Coded V-BLAST (Vertical-Bell-lab Layered Space-Time) technique that is applied the extrinsic information from MAP (Maximum A Posteriori) Decoder with Iterative Decoding to use as a priori probability in two decoding procedures of V-BLAST: ordering and slicing. Also, comparing with the Adaptive Modulation system using conventional Turbo Coded V-BLAST technique that is simply combined V-BLAST with Turbo Coding scheme, we observe how much throughput performance has been improved. As a result of simulation, in the Adaptive Modulation systems with several Turbo Coded V-BLAST techniques, the optimal Turbo Coded V-BLAST technique has higher throughput gain than the conventional Turbo Coded V-BLAST technique. Especially, the results show that the proposed scheme achieves the gain of 1.5 dB SNR compared to the conventional system at 2.5 Mbps throughput.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.1-8
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• 2004

A simple AMC (Adaptive Modulation and Coding) technique using ARQ (Automatic Repeat Request) for a MIMO (Multiple Input Multiple Output) system is proposed which does not require the additional feedback. In addition, the proposed AMC technique is different from the conventional technique in the aspect of considering the MCS (Modulation and Coding Scheme) level from the previous packet. The proposed technique can discard fewer amounts of unsuitable packets than the conventional technique. In the proposed system not only same rate control method for transmit antennas but also individual rate control method can be applied. The performance of the proposed technique is verified under a MIMO-OFDM (Orthogonal Frequency Division Multiplexing) system based on WLAN (Wireless Local Area Network), IEEE 802.11a. The results of the computer simulation show that a MIMO system with the proposed technique achieves higher throughput than one with a fixed transmission rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11C
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• pp.1100-1106
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• 2006

In downlink of mobile communication systems, the feedback delay between channel estimation and actual transmission causes inaccuracy in channel-state-information (CSI) and this results in performance degradation. In order to overcome this phenomenon, channel prediction is inevitable. In this paper, an adaptive transmission scheme based on channel prediction is proposed and its performance is evaluated. From simulation results, it is shown that the performance degradation due to the feedback delay is successfully mitigated by using the proposed scheme.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.7
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• pp.29-35
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• 2010

The cooperative transmission between sectors in next generation communications standards, e.g., 3GPP LTE-Advanced and IEEE 802.16m, has become an important research issue. Hence methods to decide the optimal antenna tilting angle in cooperative transmission between sectors are needed. This paper proposes methods to decide the optimal antenna tilting angle in cases of non-cooperative and cooperative transmissions between sectors. The proposed methods use an objective function that maximizes the cell average log rate or the cell average rate for users distributed uniformly within the radius of the sector. Also, the objective function which maximizes the cell average rate determined by adaptive modulation and coding (AMC) used in actual cellular systems is considered. When the cell average rate becomes the objective function, the system rate efficiency increases significantly for both cooperative and non-cooperative transmission. When the cell average log rate and the AMC rate become the objective functions, an optimal antenna tilting decision method which effectively increases the efficiency of cell boundary users is discussed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.140-146
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• 2004

In this paper we proposed the reducing method of feedback information for transmitting of adaptable data rate in multi-user OFDMA/FDD systems. In order to transmit downlink channel information to Base-Station(BS) through the limited uplink control channel, the proposed algorithm exploits the channel variation level which describes the similarity among the adjacent clusters and uses just one modulation and coding scheme(MCS) level representing channel information of all clusters'. We investigated the performance in single cell environment. It has a similar overhead for feedback information with conventional algorithm and has better performance in that bandwidth efficiency and outage probability than the conventional algorithms.