• ETRI Journal
• /
• 제45권6호
• /
• pp.963-973
• /
• 2023

Non-orthogonal multiple access (NOMA) is considered a key candidate technology for next-generation wireless communication systems due to its high spectral efficiency and massive connectivity. Incorporating the concepts of multiple-input-multiple-output (MIMO) into NOMA can further improve the system efficiency, but the hardware complexity increases. This study develops an energy-efficient (EE) subchannel assignment framework for MIMO-NOMA systems under the quality-of-service and interference constraints. This framework handles an energy-efficient co-training-based semi-supervised learning (EE-CSL) algorithm, which utilizes a small portion of existing labeled data generated by numerical iterative algorithms for training. To improve the learning performance of the proposed EE-CSL, initial assignment is performed by a many-to-one matching (MOM) algorithm. The MOM algorithm helps achieve a low complex solution. Simulation results illustrate that a lower computational complexity of the EE-CSL algorithm helps significantly minimize the energy consumption in a network. Furthermore, the sum rate of NOMA outperforms conventional orthogonal multiple access.

• ETRI Journal
• /
• 제28권2호
• /
• pp.227-230
• /
• 2006

There has been a growing need for increased capacity in cellular systems. This has resulted in the adoption of the code division multiple access (CDMA) system as a multiple channel access method. Thus, it is important to obtain the phase offsets of binary codes in the CDMA system because distinct phase offsets of the same code are used to distinguish signals received at the mobile station from different base stations. This letter proposes an efficient algorithm to compute the phase offset of a binary code in the CDMA system through the use of the basic facts of number theory and a new notion of the subcodes of a given code. We also formulate the algorithm in a compact form.

• 한국통신학회논문지
• /
• 제33권12C호
• /
• pp.1075-1081
• /
• 2008

본 논문에서는 optical orthogonal code를 (OOC) 사용하는 optical 부호 분할 다중 접속 (code division multiple access: CDMA) 시스템에 알맞은 부호 획득 알고리즘을 제안한다. 일반적으로 부호 획득 알고리즘의 평균 부호 획득 시간이 (mean acquisition time: MAT) 짧을수록 알고리즘의 성능이 뛰어나다고 말할 수 있다 기존의 Multiple-shift (MS) 알고리즘은 부호 획득을 두 단계로 나누어 수행함으로써, serial-search (SS) 알고리즘에 비해 빠른 부호 획득이 가능하였다. 본 논문에서 제안한 enhanced multiple-shift (EMS) 알고리즘은 기존의 MS 알고리즘과는 달리 여러 개의 문턱값을 씀으로써 MS 알고리즘에 비해 더 짧은 MAT를 갖는다. 모의실험을 통해 제안한 EMS 알고리즘의 MAT 성능을 MS 알고리즘의 MAT 성능과 비교해 본 결과, 단일 사용자 환경 및 다중사용자 환경 모두에서 EMS 알고리즘이 MS 알고리즘에 비해 더 짧은 MAT를 갖는 것을 확인할 수 있었다.

• 한국통신학회논문지
• /
• 제34권6C호
• /
• pp.649-655
• /
• 2009

평균 부호 획득 시간은 (mean acquisition time: MAT) 부호 획득 시스템의 성능을 나타내는 가장 중요한 지표이며, MAT가 짧을수록 부호 획득 시스템의 성능이 좋다고 일컬어진다. 광 부호 분할 다중 접속 (optical code division multiple access: O-CDMA) 시스템의 부호 획득을 위해 Keshavarzian과 Salehi가 제안한 multiple-shift (MS) 알고리즘은 부호 획득을 두 단계로 나누어 수행함으로써, 기존 serial-search (SS) 알고리즘에 비해 짧은 MAT를 제공한다. 본 논문에서는 효율적으로 결합된 로컬 신호와 그에 따른 상관값 및 부호를 이용하여 기존 MS 알고리즘에 비해 더 짧은 MAT를 제공할 수 있는 알고리즘을 제안한다. 또한, 모의실험을 통해 제안한 알고리즘이 기존 MS 알고리즘에 비해 더 짧은 MAT를 제공함을 보인다.

• ETRI Journal
• /
• 제30권2호
• /
• pp.301-307
• /
• 2008

As broadband access is evolving from digital subscriber lines to optical access networks, Ethernet passive optical networks (EPONs) are considered a promising solution for next generation broadband access. The point-to-multipoint topology of EPONs requires a time-division multiple access MAC protocol for upstream transmission. In this paper, we propose a new enhanced dynamic bandwidth allocation algorithm with fairness called EFDBA for multiple services over EPONs. The proposed algorithm is composed of a fairness counter controller and a fairness system buffer in the optical line terminal. The EFDBA algorithm with fairness can provide increased capability and efficient resource allocation in an EPON system. In the proposed EFDBA algorithm, the optical line termination allocates bandwidth to the optical network units in proportion to the fairness weighting counter number associated with their class and queue length. The proposed algorithm provides efficient resource utilization by reducing the unused remaining bandwidth made by idle state optical network units.

• Journal of Communications and Networks
• /
• 제18권3호
• /
• pp.439-445
• /
• 2016

In this paper, we consider subcarrier-index modulation (SIM) for precoded orthogonal frequency division multiplexing (OFDM) with a few activated subcarriers per user and its generalization to multi-carrier multiple access systems. The resulting multiple access is called sparse index multiple access (SIMA). SIMA can be considered as a combination of multi-carrier code division multiple access (MC-CDMA) and SIM. Thus, SIMA is able to exploit a path diversity gain by (random) spreading over multiple carriers as MC-CDMA. To detect multiple users' signals, a low-complexity detection method is proposed by exploiting the notion of compressive sensing (CS). The derived low-complexity detection method is based on the orthogonal matching pursuit (OMP) algorithm, which is one of greedy algorithms used to estimate sparse signals in CS. From simulation results, we can observe that SIMA can perform better than MC-CDMA when the ratio of the number of users to the number of multi-carrier is low.

• 정보통신설비학회논문지
• /
• 제8권4호
• /
• pp.201-206
• /
• 2009

The third generation mobile communications system requiring the reliable multimedia data transmission has provided with the reliable voice, data and video services over the variable propagation environment. However the broadband wireless multiple access technologies cause Inter Symbol Interference (ISI) or Multiple Access Interference (MAI) to degrade the performance of W-CDMA (Code Division Multiple Access) system. Constant Modulus Algorithm (CMA) which is frequently used as the adaptive blind equalizers to remove the interfering signal has ill-convergence phenomenon without proper initialization. In this paper, new blind equalization method based on conventional CMA is proposed to improve the channel efficiency, and through computer simulation this is tested over the time varying fading environment of mobile communication system. Consequently, new blind equalization method into concatenated Kalman filter with CMA is verified better than conventional CMA through adopting minimum mean square errors and eye-pattern obtained from algorithm are compared.

• 한국통신학회논문지
• /
• 제34권12A호
• /
• pp.998-1005
• /
• 2009

OFDMA (Orthogonal Frequency Division Multiple Access) 방식을 기반으로 하는 M-WiMAX(Mobile-Worldwide Interoperability for Microwave Access) 시스템의 상향링크에서는 여러 사용자들이 전송하는 각각의 신호가 서로 다른 지연시간으로 인해 한 OFDMA 심볼 내에 선형적인 위상 성분이 발생하고, 이 위상 성분들이 합성되어 다중 접속 간섭 (Multiple Access Interference : MAI) 으로 기지국에서의 레인징 코드 검출 및 지연시간 추정 성능을 열화 시키는 원인이 된다. 따라서, 본 논문에서는 각 사용자에 의해 발생되는 MAI 를 최소화하고, 레인징 코드 검출 및 지연시간 추정 성능을 향상시키기 위해 기존의 방법에 직렬 간섭 제거(Successive Interference Cancellation : SIC) 를 적용한 레인징 기법을 제안한다. 모의 실험을 통해 기존의 방법보다 향상된 성능을 보였으며, 3GPP LTE 의 랜덤 액세스와의 비교를 통해 M-WiMAX 의 레인징 성능 한계를 확인하였다.

• 전자공학회논문지A
• /
• 제33A권7호
• /
• pp.55-63
• /
• 1996

In this paper, a multiple-access algorithm for PCN is proposed. The proposed algorithm provides th integrated service of information soruces and can be operated stably in high load state. Given bandwidth is efficiently used for it in the microcell environment. And system performance can be improved through the statistical-multiplexing technque. In order to process the speech signal usually requiring real-tiem processing, we adopt a random access of AlOHA type for th ebasic protocol sturcture and assume the form of ALOHA-reservation. We have analyzed the performance of the proposed algorithm through system throughput and packet delay in the microcell environment.

• 한국통신학회논문지
• /
• 제38A권11호
• /
• pp.938-943
• /
• 2013

본 논문에서는 동적 스펙트럼 접근을 위한 유전자 알고리즘 기반 전송 매개변수 최적화 기법을 제안한다. 구체적으로는 전송 매개변수 최적화를 위해 다목적 적합도 함수를 단일 목적 적합도 함수들의 가중합으로 표현하고, 유전자 알고리즘을 이용하여 주어진 전송 시나리오에 최적화된 전송 매개변수 값을 얻는다. 모의실험을 통하여 제안한 다목적 적합도 함수를 이용하여 주어진 시나리오에 따라 전송 매개변수를 최적화한 결과를 보인다.