• ETRI Journal
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• v.45 no.5
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• pp.874-886
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• 2023

A joint resource-optimization scheme is investigated for nonorthogonal multiple access (NOMA)-enhanced scalable video coding (SVC) multicast in unmanned aerial vehicle (UAV)-assisted radio-access networks (RANs). This scheme allows a ground base station and UAVs to simultaneously multicast successive video layers in SVC with successive interference cancellation in NOMA. A video quality-maximization problem is formulated as a mixed-integer nonlinear programming problem to determine the UAV deployment and association, RAN spectrum allocation for multicast groups, and UAV transmit power. The optimization problem is decoupled into the UAV deployment-association, spectrum-partition, and UAV transmit-power-control subproblems. A heuristic strategy is designed to determine the UAV deployment and association patterns. An upgraded knapsack algorithm is developed to solve spectrum partition, followed by fast UAV power fine-tuning to further boost the performance. The simulation results confirm that the proposed scheme improves the average peak signal-to-noise ratio, aggregate videoreception rate, and spectrum utilization over various baselines.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.56-65
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• 2002

This paper proposes a novel transmit diversity technique, namely symbol split orthogonal transmit diversity (SS-OTD). In this technique, full path diversity and temporal diversity are achieved by combining orthogonal transmit diversity technique (OTD) technique with the symbol splitting method proposed by Meyer. Its performances is simulated for fundamental channels associated with the forward link of the IS-2000 system, and then compared with those of OTD and space-time spreading (STS). Our proposed method offers a 0.5-7.7dB performance improvement over OTD under various simulation environments and its performance is similar to STS. Moreover, compares with that of STS, the peak-to-average power ratio (PAR) of transmitted signals in SS-OTD is reduced by a maximal 1.35dB, which decreases the complexity of base station RF devices, such as power amplifiers. Thus, SS-OTD is comparable to STS in performance and superior to STS in the cost and efficiency of base station RF devices.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.308-315
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• 2008

When operating in frequency-division duplex (FDD) mode, transmit beamforming in multiple-input single-output (MISO) wireless communication systems typically requires accurate knowledge of downlink channel state information (CSI) at the transmitter. In practical FDD systems, obtaining such downlink CSI at the transmitter is challenging, if not impractical. To circumvent such challenge and support user mobility, we present a new method for transmit beamforming based on simple beam-control commands (BCCs) in MISO FDD mobile systems. We then numerically evaluate the effects of BCC errors in terms of transmit power efficiency, system capacity, and outage probability.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.12
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• pp.2826-2834
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• 2013

In mobile ad hoc networks (MANET), power-saving technology of mobile nodes is divided into transmit power control (TPC), power-saving mode (PSM), and routing. TPC and PSM are operated in physical layer but the routing is managed in network layer, so the design of a joint algorithm is needed to provide better performance. Therefore, in this paper, we propose a joint power-saving and routing algorithm for maximizing the network lifetime while satisfying the end-to-end data rate in ad hoc networks. The proposed algorithm first applies the TPC or PSM to reduce the power consumption of mobile nodes and then performs the routing by considering the decided node lifetime in order to maximize the path lifetime. Simulation results show that the proposed algorithm maximize the lifetime while satisfying the required rate according to the number of mobile nodes and the level of interference.

• ETRI Journal
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• v.39 no.6
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• pp.782-793
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• 2017

This paper considers the use of the Partial Transmit Sequence (PTS) technique to reduce the Peak-to-Average Power Ratio (PAPR) of an Orthogonal Frequency Division Multiplexing signal in wireless communication systems. Search complexity is very high in the traditional PTS scheme because it involves an extensive random search over all combinations of allowed phase vectors, and it increases exponentially with the number of phase vectors. In this paper, a suboptimal metaheuristic algorithm for phase optimization based on an improved harmony search (IHS) is applied to explore the optimal combination of phase vectors that provides improved performance compared with existing evolutionary algorithms such as the harmony search algorithm and firefly algorithm. IHS enhances the accuracy and convergence rate of the conventional algorithms with very few parameters to adjust. Simulation results show that an improved harmony search-based PTS algorithm can achieve a significant reduction in PAPR using a simple network structure compared with conventional algorithms.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.83-84
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• 2007

Multiple-input multiple-output (MIMO) systems can achieve the increasing of performances by using an adaptive power allocation. The related previous work limited the transmit antenna number because orthogonal space-time block codes (OSTBCs) yield full transmit rate only for two transmit antennas. We extend a robust system under imperfect channel estimation for four transmission antennas with maintaining a full transmission rate.

• Journal of Korea Multimedia Society
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• v.20 no.12
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• pp.1849-1855
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• 2017

The main purpose of cooperative communications is improvement of communication quality and efficient use of transmission power. In this paper, a cooperative retransmission method is proposed, where neighbor nodes that receive messages correctly between transmit and receive nodes will participate in retransmission of the erroneous packet of the direct link. When the proposed retransmission method is used, the performance of the PER can be greatly improved. In case that the limited information is included in the NACK message, the transmit power of the retransmission packet can be reduced using the proper power control method.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1413-1418
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• 2004

This paper shows the analysis of the inductive power transfer system in conjunction with series resonant converter operating variable high frequency. Of particular interest is the sensitivity of the complete system to variations in operational frequency and parameters. In inductive power transfer system, electrical power is transferred from a primary winding in the form of a coil or track, to one or more isolated pick-up coils that may relative to the primary. The ability to transmit power without contact enables high reliability and easy maintenance that allows inductive power transfer system to be implemented in hostile environments. This technology has found application in many fields such as electric vehicles, PRT(Personal Rapid Transit) etc. The coupling between the primary and secondary is then presented to include the effects of parameter and operational frequency variation.

• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.4
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• pp.115-120
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• 2012

In multi-user multi-input multi-output (MU-MIMO) system, zero forcing beamforming (ZFB) is regarded as a realistic solution for transmitting scheme due to its low complexity and simple structure. However, ZFB shows a significant performance degradation when channel matrix has large condition number. In this case, the largest singular value of the channel inversion matrix has a dominant effect on transmit power. In this paper, we propose a perturbation method for reducing an effect of the dominant singular value. In the proposed algorithm, channel inverse matrix is first decomposed by SVD for the transmit signal to be expressed as a combination of singular vectors. Then, the transmit signal is perturbed to reduce the coefficient of the singular vector corresponding to the largest singular value. When a number of transmit antennas is 4, the simulation results of this paper shows that the proposed method shows 8dB performance enhancement at 10-3 uncoded bit error rate (BER) compared with conventional ZFB. Also, the simulation results show that the proposed method provides a comparable performance to Tomlinson-Harashima Precoding (THP) with much lower complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.360-370
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• 2010

In this paper, a distributed beamforming problem is considered in an amplify-and-forward (AF) wireless relay network consist of multiple source-destination pairs and relaying nodes. To exploit degree of freedom of the number of beamformers, in the first step, we proposed that the sources transmit their signals through orthogonal channels. During the second step, the relays transmit their received signals multiplied by complex weights to amplify and compensate for phase changes introduced by the backward channels through one common channel. The optimal beamforming vectors are obtained through minimization of the total relay transmit power while the signal-to-interference-plus-noise ratios (SINRs) at the destinations are above certain thresholds to meet a quality of services (QoSs) level. In the numerical example, it is shown that the proposed scheme needs less transmit power for moderate network data rates than other schemes, such as space division multiplexing or time-division multiplexing scheme.