• Journal of Information Processing Systems
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• 제13권3호
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• pp.630-642
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• 2017

In this paper, we propose the opportunistic non-orthogonal multiple access (NOMA)-based cooperative relaying system (CRS) with channel state information (CSI) available at the source, where CSI for the source-to-destination and source-to-relay links is used for opportunistic transmission. Using the CSI, for opportunistic transmission, the source instantaneously chooses between the direct transmission and the cooperative NOMA transmission. We provide an asymptotic expression for the average achievable rate of the opportunistic NOMA-based CRS under Rayleigh fading channels. We verify the asymptotic analysis through Monte Carlo simulations, and compare the average achievable rates of the opportunistic NOMA-based CRS and the conventional one for various channel powers and power allocation coefficients used for NOMA.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(II)
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• pp.833-836
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• 1987

The error probability for coherent frequency-hopped spread-spectrum multiple-access communications is computed. We employ PSK as a modulation scheme. The channel capacity is performance measure and the minimum bit signal-to-noise ratio for reliable communications is obtained.

• 한국정보과학회논문지:정보통신
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• 제27권1호
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• pp.22-29
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• 2000

본 논문에서는 유럽의 ETSI(European Telecommunication Standards Institute)에서 표준화를 진행 중에 있는 유럽형 고속 무선 근거리 통신망인 HIPERLAN(HIgh PErformance Radio Local Area Network) 타입 1의 채널접근제어 프로토콜인 EY-NPMA(Elimination Yield - Non-preemptive Priority Multiple Access)프로토콜의 성능을 분석하였다. 본 논문에서는 EY-NPMA 프로토콜의 분석을 위해 시스템 모델을 설정하였으며, 채널접근 시도에서 성공할 확률과 경쟁 단계의 평균 길이를 분석하였다. 또한 M/G/1 대기행렬 모델을 사용하여 정규화된 지연시간과 처리율을 근사화 하였으며, 이러한 분석결과를 시뮬레이션을 통해 검증하였다.

• 한국통신학회논문지
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• 제24권9A호
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• pp.1425-1433
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• 1999

본 논문은 ETSI에 의해 정의된 무선 LAN(Wireless LAN)의 표준안인 HIPERLAN(HIgh PErformance Radio LAN) 타입 1의 매체 접근 제어 프로토콜에 관하여 해석적으로 분석한다. HIPERLAN의 채널 접근 계층(Channel Access Control layer)에서 사용하는 EY-NPMA(Elimination Yield-Nonpreemptive Priority Multiple Access)의 채널 경쟁 단계 중에서 제어 단계(Elimination phase)와 양보 단계(Yield phase)의 무선 가입자 모델에 대하여 분석한다. 그리고, 분석 결과를 이용하여 전송 단계(Transmission phase)에서 패킷 전송의 성공확률을 해석적으로 구한 후, 시뮬레이션을 이용한 성능 평가를 통하여 분석 결과를 검증한다.

• 한국전자파학회논문지
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• 제12권5호
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• pp.755-764
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• 2001

본 논문에서는 M-ary 직교 변조를 사용하는 직접 확산 코드 분할 다중 접속 (DS/CDMA: Direct Sequence/Code Division Multiple Access) 시스템을 위한 최대 근사 (Maximum Lkelihood : ML) 결정 궤환 채널 추정(Decision Feedback Channel Estimation : DFCE) 시스템을 제안한다. 제안된 시스템은 결정 궤환 정보로서 RAKE 수신기의 최대 결합 출력을 사용한다. 제안된 시스템으로부터 추정된 채널 값을 이용하면 파일럿의 삽입없이 RAKE 수신기에서 동기 검파 (coherent demodulation)를 할 수 있고, 동시에 최대 비 결합(Maximum Ration Combining : MRC) 기법을 사용할 수 있다. 그러나 제안된 DFCE 다중 사용자 환경에서 다중 사용자 간섭 (Multiple Access Interference: MAI)으로 인해 심각한 성능의 저하가 발생한다. 이런 문제를 해결하기 위해 다단 병렬 간섭 제거기(Multistage Parallel Interference Cancellation : PIC)를 제안된 시스템과 결합해 본다. 제안된 DFCE에서 추정된 정확한 채널 값은 동기식 검파뿐 아니라 PIC에서 다중 사용자 간섭 신호의 재 생성(regeneration)을 위해서도 쓰인다. 이럴 경우 PIC와 EFCF간에 서로 도움을 주는 이중 효과를 얻게 된다. 실험결과에 의하면 제안된 시스템은 기존의 비동기 검파(noncoherent demodulation) 방식에 비해 다단 PIC를 쓰지 않는 동기 검파의 경우 IE-02의 E$_{b}$/N$_{0}$에서 수용 가능한 사용자 수가 5명에서 약 10으로 2배 증가함을 확인할 수 있었으며, 다단 PIC를 사용한 동기 검파의 경우 약 30명으로 6배 정도가 증가함을 확인할 수 있었다.

• 전기전자학회논문지
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• 제16권1호
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• pp.51-55
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• 2012

본 논문에서는 순환천이변조 (CCSK: cyclic code shift keying) 시퀀스로 삼진 시퀀스를 적용하는 것을 제안하였다. 그리고 순환천이변조를 적용한 주파수도약대역확산/시분할다중접속 (FHSS/TDMA: frequency hopping spread spectrum/time division multiple access) 시스템에서 성능을 모의실험 하였다. 실험에서 무선 채널은 레일레이(Rayleigh) 페이딩 채널로 모델링하였다. 모의 실험 결과로부터 순환천이변조 시퀀스로 무작위 시퀀스를 사용한 시스템보다 삼진 시퀀스를 적용한 시스템이 더 높은 성능을 보이는 것이 증명되었다.

• 대한전자공학회논문지
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• 제26권10호
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• pp.1462-1470
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• 1989

This paper aims at investigating the Demand Assigned Multiple Access(DAMA) system for the packet-switched Satellite Communication. An onboard processor of the multisport beam satellite incorporates the ground controller to macimize the packet transmissions for each slot. 'Request Following' trnasmission mode is introduced as a transmission strategy of ground station under the control of its zone controller. The combined scheme of reservation channel access and contention channel access was proposed by Lee & Mark[3] for improving the Delay-Throughput performance. Our scheme provides less communication delay of approximately max. 200msec for achieving the corresponding throughput than the Lee & Mark's work does. Delay versus Throughput curves as well as Delay versus Traffic parameter curves are obtained. Numerical results obtained through the analysis and by the computer simulation show that the proposed scheme provides the low average packer delay even under the condition that the number of transponders (M)is below the half of the number of zones(N).

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권6호
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• pp.2240-2254
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• 2021

We investigate the channel allocation problem in an ultra-dense device-to-device (D2D) enabled cellular network in underlaying mode where multiple D2D users are forced to share the same channel. Two kinds of low complexity solutions, which just require partial channel state information (CSI) exchange, are devised to resolve the combinatorial optimization problem with the quality of service (QoS) guaranteeing. We begin by sorting the cellular users equipment (CUEs) links in sequence in a matric of interference tolerance for ensuring the SINR requirement. Moreover, the interference quota of CUEs is regarded as one kind of communication resource. Multiple D2D candidates compete for the interference quota to establish spectrum sharing links. Then base station calculates the occupation of interference quota by D2D users with partial CSI such as the interference channel gain of D2D users and the channel gain of D2D themselves, and carries out the channel allocation by setting different access priorities distribution. In this paper, we proposed two novel fast matching algorithms utilize partial information rather than global CSI exchanging, which reduce the computation complexity. Numerical results reveal that, our proposed algorithms achieve outstanding performance than the contrast algorithms including Hungarian algorithm in terms of throughput, fairness and access rate. Specifically, the performance of our proposed channel allocation algorithm is more superior in ultra-dense D2D scenarios.

• International Journal of Internet, Broadcasting and Communication
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• 제15권3호
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• pp.43-51
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• 2023

Slotted ALOHA (S-ALOHA) is a classical medium access control protocol widely used in multiple access communication networks, supporting distributed random access without the need for a central controller. Although stability and delay have been extensively studied in existing works, most of these studies have assumed ideal channel conditions or independent fading, and the impact of time-correlated wireless channels has been less addressed. In this paper, we investigate the queueing delay performance in S-ALOHA networks under time-correlated channel conditions by utilizing a Gilbert-Elliott model. Through simulation studies, we demonstrate how temporal correlation in the wireless channel affects the queueing delay performance. We find that stronger temporal correlation leads to increased variability in queue length, a larger probability of having queue overflows, and higher congestion levels in the S-ALOHA network. Consequently, there is an increase in the average queueing delay, even under a light traffic load. With these findings, we provide valuable insights into the queueing delay performance of S-ALOHA networks, supplementing the existing understanding of delay in S-ALOHA networks.

• ETRI Journal
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• 제45권2호
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• pp.213-225
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• 2023

Physical layer security (PLS) can improve the security of both terrestrial and nonterrestrial wireless communication networks. This study proposes a simplified framework for nonterrestrial cyclic prefixed orthogonal variable spreading factor (OVSF)-encoded multiple-input and multiple-output nonorthogonal multiple access (NOMA) systems to ensure complete network security. Various useful methods are implemented, where both improved sine map and multiple parameter-weighted-type fractional Fourier transform encryption schemes are combined to investigate the effects of hybrid PLS. In addition, OVSF coding with power domain NOMA for multi-user interference reduction and peak-toaverage power ratio (PAPR) reduction is introduced. The performance of $\frac{1}{2}$-rated convolutional, turbo, and repeat and accumulate channel coding with regularized zero-forcing signal detection for forward error correction and improved bit error rate (BER) are also investigated. Simulation results ratify the pertinence of the proposed system in terms of PLS and BER performance improvement with reasonable PAPR.