• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.9
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• pp.1117-1122
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• 2019

In this paper, a power allocation scheme is proposed to improve the fairness of user data rates in downlink non-orthogonal multiple access systems with one base station and two users. In particular, the power allocation scheme is presented to maximize the fairness of average user data rates assuming independent Rayleigh fading channels, where the fairness maximization is achieved when the average user data rates are equal. For the fairness evaluation, hence approximate expressions for the average user data rates and the average sum date rate of the proposed scheme are provided by using high signal-to-noise ratio approximation. Through simulation investigation, the derived approximate expressions for the average data rates are verified, and it is shown that the proposed scheme is superior to the conventional power allocation schemes in terms of the fairness of the average user data rates.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2003.11a
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• pp.215-218
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• 2003

본 논문에서는 다수의 셀로 구성된 CDMA 시스템의 순방향 링크를 대상으로 지연 및 PRER 제약과 전송출력 제약 하에서 데이터 전송률과 사용자간 형평성을 반영한 총효용을 최대화하기 위한 각 기지국의 총평균전송출력과 각 사용자의 데이터 전송률 할당 체계를 제시한다. 실험을 통해 모든 셀을 동시에 고려하는 OPARS(Optimal Power and Rate Allocation Scheme)가 각 셀을 개별적으로 고려하는 SPRAS(Separate Power and Rate Allocation Scheme)에 비해 더 좋은 해를 제공한다는 것을 알 수 있었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.11
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• pp.1407-1413
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• 2019

In this paper, we assume that another transmitter can transmit its data signal in the same frequency band in order to maximize the frequency efficiency of non-orthogonal multiple access(NOMA) systems. We also focus on the improvement in fairness performance of receiver's data rates, not the maximization of sum data rate for NOMA systems. Thus, in this paper, we propose a power allocation scheme to enhance the fairness performance of average data rates of receivers considering the NOMA systems in the presence of interference. Assuming Rayleigh fading channels, the average data rates of receivers are defined, and the power allocation coefficients to improve the data-rate fairness are derived by using high signal-to-noise power ratio approximation. In addition, through simulations, it is shown that the proposed power allocation scheme can improve the data-rate fairness in the NOMA system with interference.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.7
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• pp.1040-1046
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• 2022

In this paper, we consider a system with massive user equipments (UEs) in a cell and assume path loss and Rayleigh fading channels between the base station (BS) and UEs. In addition, it is assumed that the system bandwidth consists of multiple identical frequency subchannels. Under such assumptions, we propose a channel state information (CSI) feedback scheme and a resource allocation scheme for non-orthogonal multiple access (NOMA) transmission in order to reduce the feedback overhead of CSI generated by massive UEs and to reduce the complexity of resource allocation. In particular, for the proposed schemes, we analyze the sum data rate achievable by massive UEs in a cell and the outage probability with which the UEs in a cell do not meet the target data rate. Through the simulation results, we show that the proposed schemes can provide the superior outage probability, although it degrades the average sum data rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1560-1566
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• 2015

To enable the efficient use of energy, the environment where unscheduled receivers can harvest energy from the transmitted signal is considered in next-generation wireless communication systems. In this paper, we propose a scheme for allocating subchannel and power to maximize the system throughput and harvested energy simultaneously using optimization techniques. Through simulations, we verify that the proposed scheme can increase the system throughput and harvested energy harmoniously. In particular, the proposed scheme improves the harvested energy remarkably with a negligible degradation of system throughput, compared with conventional scheme, as a result, energy can be used efficiently in the system.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10c
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• pp.175-177
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• 2003

본 논문에서는 직교 주파수 분할 다중화 전송방식(OFDM:Orthogonal Frequency Division Multiplexing)에서 비트 오류율(BER)과 시스템에서 사용할 수 있는 총 송신 파워가 제한된 상태에서 데이터 전송률을 최대화 시키는 기법을 제안한다. 제안한 기법은 미리 계산된 비트수별 신호대잡음비 임계값(threshold)과 부반송파의 신호대잡음비를 비교한 후 부반송파별 송신 파워를 최적화 시켜 비트를 할당한다. 이 기법은 송신 파워 및 비트를 할당하는 최적의 기법이라고 알려진 Hughes­Hartogs 기법과 거의 동일한 데이터 전송률을 가질 수 있으면서, 부반송파의 송신 파워 및 비트수를 할당하기 위해 필요한 반복작업을 줄일 수 있다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.490-492
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• 2018

This paper presents an analysis of the AMR speech data as a basic work to study the technique of inputting and transmitting AMR voice data which is widely used in the public cell phone. AMR consists of HEADER and Speech Data, and it is transmitted in bit format and has 8 bit-rate modes in total. HEADER contains mode information of Speech Data, and the length of Speech Data differs depending on the mode. We chose the best mode which is best to input into QR code and analyzed that mode. It is a goal to show a higher compression ratio for voice data by the analysis and experiments. This analysis shows improvement in that it can transmit voice data more effectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.9
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• pp.1340-1346
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• 2022

In this paper, we consider a downlink non-orthogonal multiple access (NOMA) using multiple transmit antennas, where the transmit antenna selection scheme is used to reduce the system complexity. Thus, in this paper, we propose radio resource allocation and receiver selection schemes in order to improve the outage probability performance of the downlink NOMA system using the transmit antenna selection scheme. In particular, the receiver selection scheme is a method of grouping the receivers to improve the outage probability performance, and the radio resource allocation scheme is a method of allocating radio resources to each group in order to enhance the outage probability performance. In addition, through the computer simulation under the assumption of independent Rayleigh fading channels, we show that the proposed radio resource allocation and receiver selection schemes can improve the outage probability performance at the expense of the sum rate performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.666-673
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• 2006

In this paper, we evaluated the performance of 4 types of ARQ algorithms that have been adopted to offer reliable transmission between MAC layers. First of all, we implemented IEEE 802.16 ARQ algorithms with NS-2 network simulator and then evaluated the performances in various channel states. We used two performance measures to evaluate those performances. First, we used the total number of ARQ block in bytes that have been received without error. Second, we used ACK_Efficiency that is newly defined in this paper. From the results of simulation, we could be aware that each ARQ algorithm has different performance in a various channel states. For improving the transmission data rate in a specific channel state, we have to choose the right ACK interval as well as a suitable ARQ algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1A
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• pp.8-18
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• 2011

Visible light communication (VLC) using optical sources which can be simultaneously utilized for illumination and communication is currently an attractive option for wireless personal area network. Improving the data rate in optical wireless communication system is challenging due to the limited bandwidth of the optical sources. In this paper, we design the singular value decomposition (SVD)-based multiplexing multi-input multi-output (MIMO) system to support two data streams in optical wireless channels. In order to improve the spectral efficiency, the rate adaptation using multi-level pulse amplitude modulation (PAM) is applied according to the channel condition and we propose the method to allocate the optical power, the offset and the size of modulation scheme theoretically under the constraints of the nonnegativity of the modulated signals, the aggregate optical power and the bit error rate (BER) requirement. The simulation results show that the proposed allocation method gives the better performance than the method to allocate the optical power equally for each data stream.