• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2607-2625
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• 2014

Previous studies on multiuser multiple-input multiple-output (MIMO) mostly assume a homogeneous signal-to-noise ratio (SNR), where each user has the same average SNR. However, real networks are more likely to feature heterogeneous SNRs (a random-valued average SNR). Motivated by this fact, we analyze a multiuser MIMO downlink with a zero-forcing (ZF) receiver in a heterogeneous SNR environment. A transmitter with Mantennas constructs M orthonormal beams and performs the SNR-based proportional fairness (S-PF) scheduling where data are transmitted to users each with the highest ratio of the SNR to the average SNR per beam. We develop a new analytical expression for the sum throughput of the multiuser MIMO system. Furthermore, simply modifying the expression provides the sum throughput for important special cases such as homogeneous SNR, max-rate scheduling, or high SNR. From the analysis, we obtain new insights (lemmas): i) S-PF scheduling maximizes the sum throughput in the homogeneous SNR and ii) under high SNR and a large number of users, S-PF scheduling yields the same multiuser diversity for both heterogeneous SNRs and homogeneous SNRs. Numerical simulation shows the interesting result that the sum throughput is not always proportional to M for a small number of users.

• 한국통신학회논문지
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• 제30권4A호
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• pp.296-303
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• 2005

본 논문에서는 기존의 한 개의 안테나를 가진 사용자에 $시\cdot공간$ 부호화된 두 개의 안테나를 가진 사용자가 추가되어 동일 채널을 공유할 경우 신호를 효과적으로 분리 및 검출할 수 있는 방법을 제안하고, 시스템 성능을 분석한다. 간섭 제거 방법을 적용하여 사용자를 구분하고 최대우도 방법을 통해 각 사용자 신호를 얻는 기법을 제안한다. 기존의 안테나 수가 같은 다중 사용자를 위한 신호 검출 방법인 최소평균제곱오차 방식이 안테나 수가 다른 MIMO 사용자의 경우 효과적으로 적용될 수 없는 단점을 설명하고 모의실험을 통해 확인한다. 또한 제안된 기법에 OFDM을 적용하여 시스템의 성능을 평가한다. 모의실험 결과 제안된 시스템의 단일 안테나 사용자는 기존의 단일 송수신 안테나를 가진 사용자의 성능과 유사하고 두 개의 안테나를 가진 MIMO 사용자의 경우 성능이 향상됨을 확인한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권2호
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• pp.628-649
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• 2017

Security and resource-saving are both demands of the fifth generation (5G) wireless networks. In this paper, we study the secrecy spectrum efficiency (SSE) and secrecy energy efficiency (SEE) of a K-tier massive multiple-input multiple-output (MIMO) enabled heterogeneous cellular network (HetNet), in which artificial noise (AN) are employed for secrecy enhancement. Assuming (i) independent Poisson point process model for the locations of base stations (BSs) of each tier as well as that of eavesdroppers, (ii) zero-forcing precoding at the macrocell BSs (MBSs), and (iii) maximum average received power-based cell selection, the tractable lower bound expressions for SSE and SEE of massive MIMO enabled HetNets are derived. Then, the influences on secrecy oriented spectrum and energy efficiency performance caused by the power allocation for AN, transmit antenna number, number of users served by each MBS, and eavesdropper density are analyzed respectively. Moreover, the analysis accuracy is verified by Monte Carlo simulations.

• Journal of Communications and Networks
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• 제8권4호
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• pp.401-409
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• 2006

Orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) technologies provide additional dimensions of freedom with spectral and spatial resources for radio resource management. Multi-dimensional radio resource management has recently been identified to exploit the full dimensions of freedom for more flexible and efficient utilization of scarce radio spectrum while provide diverse quality of service (QoS) guarantees. In this work, a multi-dimensional radio resource scheduling scheme is proposed to achieve above goals in hybrid orthogonal frequency division multiple access (OFDMA) and space division multiple access (SDMA) systems. Cochannel interference (CCI) introduced by frequency reuse under SDMA is eliminated by frequency division and time division between highly interfered users. This scheme maximizes system throughput subjected to the minimum data rate guarantee. for heterogeneous users and transmit power constraint. By numerical examples, system throughput and fairness superiority of the our scheduling scheme are verified.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.1841-1865
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• 2017

This paper proposes a new interference mitigation scheme for device-to-device (D2D) communications underlaying a cellular network. The object of the proposed scheme is to determine the number of data streams, a precoding matrix, and a decoding matrix of D2D networks so as to maximize the system capacity given the number of data streams of a cellular network while satisfying the constraint of the inter-system interference from D2D networks to the cellular network. Unlike existing interference mitigation schemes based on the interference alignment technique, the proposed scheme operates properly regardless of the number of data streams of a cellular network and moreover it does not require changing the precoding and decoding matrices of a cellular network. The simulation results demonstrate that the proposed scheme significantly increases the system capacity by mitigating the intra- and inter-system interference.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권3호
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• pp.794-815
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• 2023

The rapid development of mobile communication not only has made the industry gradually diversified, but also has enhanced the service quality requirements of users. In this regard, it is imperative to consider jointly network slicing and mobile edge computing. The former mainly ensures the requirements of varied vertical services preferably, and the latter solves the conflict between the user's own energy and harsh latency. At present, the integration of the two faces many challenges and need to carry out at different levels. The main target of the paper is to minimize the energy consumption of the system, and introduce a multi-slice joint task offloading and resource allocation scheme for massive multiple input multiple output enabled heterogeneous networks. The problem is formulated by collaborative optimizing offloading ratios, user association, transmission power and resource slicing, while being limited by the dissimilar latency and rate of multi-slice. To solve it, assign the optimal problem to two sub-problems of offloading decision and resource allocation, then solve them separately by exploiting the alternative optimization technique and Karush-Kuhn-Tucker conditions. Finally, a novel slices task offloading and resource allocation algorithm is proposed to get the offloading and resource allocation strategies. Numerous simulation results manifest that the proposed scheme has certain feasibility and effectiveness, and its performance is better than the other baseline scheme.

• 한국통신학회논문지
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• 제31권3A호
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• pp.254-266
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• 2006

최근에 OFDM 기반 셀룰러 시스템의 Throughput 및 셀 커버리지를 향상시키기 위하여 SDMA(Spatial Division Multiple Access) 방식을 적용하는 자원 할당 방식에 대한 연구가 시작되고 있으나, 대부분의 OFDM/SDMA 기반 자원 할당 방식에 대한 연구는 시스템 Throughput 만을 최적화시키거나 단일 셀 환경에서만 적응이 가능한 한계가 있다. 본 논문에서는 사용자가 요구하는 트래픽 특성에 맞는 High Layer QoS(Quality of Service) 파라미터를 고려하면서, 시스템의 Throughput의 손실을 최소화하고 인접 셀 간 간섭을 고려하여 다중 셀 환경에서도 적용이 가능한 하향 링크 OFDM/SDMA 기반 자원할당 알고리즘을 제안하고, Ped A 및 다중 안테나 채널모델인 SCME (Spatial Channel Model Extensions) 채널에서 제안된 알고리즘 성능을 분석한다.