• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.5
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• pp.37-43
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• 2009

Streaming video service over wireless and mobile communication networks has received significant interests from both academia and industry recently. Specifically, mobile WiMAX (IEEE 802.16e) is capable of providing high data rate and flexible Quality of Service (QoS) mechanisms, supporting mobile streaming very attractive. However, we need to note that streaming videos can be partially deteriorated in their macroblocks and/or slices owing to errors on OFDMA subcarriers, as we consider that compressed video sequence is generally sensitive to the error-prone channel status of the wireless and mobile network. In this paper, we introduce an OFDMA subcarrier-adaptive mobile streaming server based on cross-layer design. This streaming server system is substantially efficient to reduce the deterioration of streaming video transferred on the subcarriers of low power strength without any modifications of the existing schedulers, packet ordering/reassembly, and subcarrier allocation strategies in the base station.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2A
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• pp.34-42
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• 2005

In orthogonal frequency-division multiple access (OFDMA) uplink environments, asynchronously received signals can cause multiple access interference (MAI). This paper focuses on the performance degradation due to the MAI over frequency-selective fading channels. We first introduce the timing misalignment, which is defined as the relative timing difference between asynchronous timing error of uplink user and reference time of the base station, and analytically derive the MAI using the power delay profile of wide-sense stationary uncorrelated scattering (WSSUS) channel model. Then, the effective signal-to-noise ratio (SNR) and the average symbol error probability (SEP) are derived. The proposed analytical results are verified through simulations with respect to the region of the timing misalignment and the number of asynchronous users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.43-51
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• 2015

Upcoming cellular networks such as LTE-advanced and IEEE 802.16m are enhanced by relay stations to support high data rate multimedia services and minimize the shadow zone with low cost. Enhancing the relay stations, however, divides the multihop cellular network into smaller microcells and the distance between microcells is closer, which intends large intra-cell and inter-cell interference. Especially the access link on downlink in the OFDMA cellular network is the throughput bottleneck due to the severe interference caused by base stations and relay stations transmitting large data to mobile stations simultaneously. In this paper, we present interference aware channel allocation algorithm to avoid severe interference on multihop cellular networks with random topology. Proposed algorithm increases SINR(signal to interference plus noise ratio) and decreases number of required control messages for channel allocation, so that increases overall throughput on the networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.76-83
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• 2009

In this paper, we provide opportunistic scheduling schemes for elastic services in OFDMA systems with fairness constraints for each user. We adopt the network utility maximization framework in which a utility function is defined for each user to represent its level of satisfaction to the service. Since we consider elastic services whose degree of satisfaction depends on its average data rate, we define the utility function of each user as a function of its average data rate. In addition, for fair resource allocation among users, we define fairness requirements of each user by using utility functions. We first formulate an optimization problem for each fairness requirement that aim at maximizing network utility, which is defined as the sum of utilities of users. We then develop an opportunistic scheduling scheme for each fairness requirement by solving the problem using a dual approach and a stochastic sub-gradient algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9A
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• pp.888-897
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• 2007

In this paper, we propose an uplink dynamic resource allocation algorithm to increase sector throughput and fairness among users in 802.16e OFDMA TDD system. In uplink, we address the difference between uplink and downlink channel state information in 802.16e OFDMA TDD system. The simulation results show that not only an increment of 10% of sector throughput but higher level of fairness is achieved by round-robin using the FLR and the rate / margin adaptive inner closed-loop power control algorithm. The FLR algorithm determines the number of sub-channels to be allocated to the user according to the user's position. Also, we get 31.8% more sector throughput compared with the round-robin using FLR by FASA algorithm using uplink channel state information. User selection, sub-channel allocation, power allocation algorithms and simulation methodology are mentioned in Part I.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3A
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• pp.235-243
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• 2009

In this paper, we investigate the cognitive and cooperative communication scheme to improve the spectral efficiency in multiuser OFDMA systems using wireless relays. First, we propose the frame structure in which the efficient frequency reuse scheme with the cognitive technique is performed to increase the system throughput. And in the case where the THP (Tomlinson-Harashima preceding) is used for the elimination of interference from the relay, we derive the effective signal to noise ratio of the link largely affected by the channel quantization error. From the system level simulation results, it is shown that the proposed cognitive and cooperative communication scheme increases the overall system performance including the feedback overhead.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2A
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• pp.99-106
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• 2009

In this paper, we propose UCA algorithms that are applied to the unified inter-cell interference mitigation through frequency plannings in OFDMA cellular systems. Under three frequency plannings, UCA algorithms allocate frequency channels to UEs(User Equipments). Proposed UCA algorithms require the information of received signal power from home sector and neighbor sectors respectively. We compare all possible combinations of UCA algorithms and frequency plannings through compute simulation. A primary performance measure is the low 5th percentile of SINR at UEs. The proposed UCA algorithms can avoid the interference to neighbor cells by allocating relatively low transmit power to centrally-located UEs and cancel inter-cell interference at cell-edge UEs by a coordinated symbol repetition. We show that UCA algorithm 2 applied in frequency planning 1 is promising among other combinations of UCA algorithms and frequency palnnings in terms of the low 5th percentile of SINR at UEs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.13-23
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• 2007

In this paper, a packet scheduling scheme that supports real-time traffic having multi-level delay constraints in OFDMA systems is proposed. The proposed scheme pursues to satisfy the delay constraint first, and then manage the residual radio resource in order to enhance the overall throughput. A parameters named tolerable delay time (TDT) is newly defined to deal with the differentiated behaviors of packet scheduling according to the delay constraint level. Assuming that the packets violating the delay constraint are discarded, the proposed scheme is evaluated in terms of the packet loss probability, throughput, channel utilization. It is then compared with existing schemes for real-time traffic support such as the Exponential Scheduling (EXP) scheme, the Modified Largest Weighted Delay First (M-LWDF) scheme, and the Round robin scheme. The numerical results show that the proposed scheduling scheme performs much better than the aforementioned scheduling schemes in terms of the packet loss probability, while slightly better in terms of throughput and channel utilization.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.382-384
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• 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 Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.225-228
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• 2010

본 논문은 CoMP 기법이 적용된 다중 사용자 MIMO-OFDMA 시스템을 위한 자원할당 알고리즘을 제안한다. 제안된 알고리즘에서는 eNode B가 RRE와 UE간의 채널 정보를 이용하여 전체 송신 전력 제한을 가지면서 전체 데이터 레이트가 최대가 되도록 자원을 할당한다. 자원할당 알고리즘을 통해 얻어진 결과를 이용하여 부반송파에 다수의 UE들이 할당된다. 할당된 UE들은 각각 MIMO 채널을 통해 다수의 공간경로를 갖고 각 공간경로에서는 할당된 전력에 따라 QPSK, 16QAM, 64QAM 중 하나를 선택하여 전송한다.