• ETRI Journal
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• v.36 no.6
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• pp.953-959
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• 2014

This paper studies the uplink resource allocation for multiple radio access (MRA) in reconfigurable radio systems, where multiple-input and multiple-output (MIMO) multicarrier-code division multiple access (MC-CDMA) and MIMO orthogonal frequency-division multiple access (OFDMA) networks coexist. By assuming multi-radio user equipment with network-guided operation, the optimal resource allocation for MRA is analyzed as a cross-layer optimization framework with and without fairness consideration to maximize the uplink sum-rate capacity. Numerical results reveal that parallel MRA, which uses MC-CDMA and OFDMA networks concurrently, outperforms the performance of each MC-CDMA and OFDMA network by exploiting the multiuser selection diversity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.12
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• pp.3237-3256
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• 2012

In the context of effective usage of a scarce spectrum resource, emerging wireless communication standards will demand spectrum sharing with existing systems as well as multiple access with higher spectral efficiency. We mathematically analyze the sum throughput of a spectrum sharing space-division multiple access (SDMA) system, which forms a transmit null in the direction of other coexisting systems while satisfying orthogonal beamforming constraints. For a large number of users N, the SDMA throughput scales as log N at high signal-to-noise ratio (SNR) ((J-1) loglog N at normal SNR), where J is the number of transmit antennas. This indicates that multiplexing gain of the spectrum sharing SDMA is $\frac{J-1}{J}$ times less than that of the non-spectrum sharing SDMA only using orthogonal beamforming, whereas no loss in multiuser diversity gain. Although the spectrum sharing SDMA always has lower throughput compared to the non-spectrum sharing SDMA in the non-coexistence scenario, it offers an intriguing opportunity to reuse spectrum already allocated to other coexisting systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.6
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• pp.648-653
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• 2011

In this paper, coordinated space division multiple access(SDMA) technology is proposed to mitigate inter-cell interference by using partial channel state information in cooperative wireless communications system with limited feedback. Each AT selects an optimal cluster transmission mode and sends it back to a cluster scheduler, and at the cluster scheduler, ATs are scheduled within a AT group with the identical cluster transmission mode, and the optimal transmission mode and the corresponding scheduled ATs are determined to maximize scheduling priority. Also, in order to enhance multiuser diversity gain, an extended transmission feedback method is proposed to feed back multiple preferred cluster transmission modes at each AT. It is shown that the proposed coordinated SDMA scheme outperforms existing non-coordinated SDMA schemes in terms of the average system throughput.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.1
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• pp.43-48
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• 2021

One of the effective ways to increase data transmission rate is to use massive antenna technique where tens or hundreds of antennas are deployed in base station and spatial diversity gain is improved by multiuser method. If multiuser method is applied, there will be inter-user interference and maximal ratio combiner (MRC) is conventionally used to reduce the complexity of the receiver and to eliminate interference. However, as the number of mobile devices increases, the performance of the conventional receiver becomes deteriorated. To solve this problem, we propose a new detector that completely eliminates the interference from the registered devices and reduces that from the unregistered devices. Then, to reduce the complexity of the proposed scheme, we propose adaptive algorithm of the proposed scheme. Through simulation, we show that the proposed scheme has better bit error rate performance than the conventional scheme.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.1-8
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• 2008

In this paper, we analyze the symbol error rate (SER) performance of maximum likelihood (ML) joint detection in downlink multiple-input multiple-output (MIMO) multicarrier code division multiple access (MC-CDMA) systems by deriving a tight union bound on the symbol error rate (SER). The union bound for ML joint detection is utilized to demonstrate the performance of MIMO MC-CDMA systems quantitatively in multiuser and frequency selective Rayleigh fading environments. An analysis of the diversity order of the systems shows the effects of multiple users, spread subcarriers, and multiple antennas on the ML joint detection performance. Furthermore, the analysis shows that MIMO MC-CDMA systems without full loading can achieve more diversify than MIMO orthogonal frequency division multiplexing (OFDM) systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.9-14
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• 2008

In this paper, we propose a collision avoidance scheduling to increase the multiuser diversity gains in the adaptive orthogonal frequency division multiple access (OFDMA) system. The scheduling policy is based on the minimum collision criterion which investigates the differences of user channels. The paper includes the derivation of capacity expressions for the adaptive OFDMA system with the proposed scheduling. The analysis shows that the capacity of the system depends on the number of collisions between the selected users to be simultaneously served. Numerical results show that the proposed scheduling provides improved capacity performance over existing ones.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.130-139
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• 2010

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. This paper addresses a number of multiple input multiple output (MIMO) precoding and scheduling techniques across the PHY and MAC layers that can operate under a reduced link budget and collectively improve the transmit power efficiency of a base station, while maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity in both the time, frequency as well as the space domain, are examined. Several fairness-aware resource allocation algorithms are applied to the considered MIMO schemes and a detailed analysis of the tradeoffs between power efficiency and quality of service is presented. This paper explicitly examines the performance of a system serving real-time, VoIP traffic under different traffic loading conditions and transmit power levels. It is demonstrated that by use of efficient scheduling and resource allocation techniques significant savings in terms of consumed energy can be achieved, without compromising QoS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9A
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• pp.856-867
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• 2006

This paper proposes a new algorithm for opportunistic scheduling that take advantage of both multiuser diversity and power control. Motivated by the multicast RTS and priority-based CTS mechanism of OSMA protocol, we propose an opportunistic packet scheduling with power control scheme based on IEEE 802.11 MAC protocol. The scheduling scheme chooses the best candidate receiver for transmission by considering the SINR at the nodes. This mechanism ensures that the transmission would be successful. The power control algorithm on the other hand, helps reduce interference between links and could maximize spatial reuse of the bandwidth. We then formulate a convex optimization problem for minimizing power consumption and maximizing net utility of the system. We showed that if a transmission power vector satisfying the maximum transmission power and SINR constraints of all nodes exist, then there exists an optimal solution that minimizes overall transmission power and maximizes utility of the system.

• Journal of Communications and Networks
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• v.13 no.3
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• pp.221-231
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• 2011

A joint multipath routing algorithm and channel allocation and scheduling for wireless multihop and multichannel systems is discussed. In packet transmission, distribution of packets to multiroutes makes it possible to reduce the transmission cost of the channels. Cross-layer cooperation of routing, channel allocation, and scheduling is an effective method of packet distribution. As a framework for the cooperation, we propose a multiroute distance vector routing (MDVR) scheme. In the MDVR scheme, the routing table is logically placed in between the routing and link layers, and the table plays the role of a service access point between these two layers. To evaluate the performance of MDVR, simulation is performed in a multichannel, multihop environment. The simulation results show that the MDVR framework can be efficiently implemented in the form of a distributed routing algorithm. It is also shown that in MDVR, the system-wise channel efficiency is almost 25% higher than that in a conventional single-route routing approach.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8A
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• pp.601-611
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• 2012

In this paper, we first study the spatial multiplexing gain for the 3-cell interfering broadcast channels (IFBC) where all base stations and mobile users are equipped with multiple antennas. Then, we present the IA scheme in conjunction with user selection which outperforms the TDMA technique in the IFBC environment. The optimal scheduling method utilizes multiuser diversity to achieve a significant fraction of sum capacity by using an exhaustive search algorithm. To reduce the computational complexity, a suboptimal scheduling method is proposed based on a coordinate ascent approach.