• ETRI Journal
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• 제29권4호
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• pp.430-436
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• 2007

An OFDM/offset QAM (OQAM)-IOTA system uses the isotropic orthogonal transform algorithm (IOTA) function, which has good localization properties in the time and frequency domains. This is employed instead of the guard interval used in a conventional OFDM/QAM system in order to be robust for multi-path channels. However, the conventional channel estimation scheme is not valid for an OFDM/OQAM-IOTA system due to the intrinsic inter-symbol interference of the IOTA function. In this paper, a condition is derived to reduce the intrinsic interference of the IOTA function. This condition is obtained with the proposed pilot structure used for perfect channel estimation. We also derive the preamble structure appropriate for practical channel estimation of the OFDM/OQAM-IOTA system. Simulation results show that the OFDM/OQAM-IOTA system with the proposed preamble structure performs better than the conventional OFDM system, and it has the additional advantage of an increased data transmission rate which corresponds to the guard interval retrieval.

• 한국정보통신학회논문지
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• 제23권4호
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• pp.453-461
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• 2019

본 논문에서는 비효율적인 주파수 자원의 효율적인 사용을 위해 연구되고 있는 CRAHNs(Cognitive Radio Ad-hoc Networks)환경에, 데이터를 전달하기 전에 다수의 노드들이 여러 채널 중 하나의 공통 채널에서 만나는 연구에 초점을 맞춘다. 기존의 연구들은 대부분 두 개 노드의 채널 랑데부를 다루는데, 이를 3개 이상의 노드들에 적용하면 시간이 오래 걸리거나 통신이 불가능하다. 그래서 본 논문에서는 3개 이상의 다수 노드들이 빠른 시간 내에 하나의 채널에서 만나게 해주는 MNSEQ(Multi-Node Sequence)를 제안한다. 또한, 랑데부 후 데이터 교환을 위해 CSMA/CA 기법을 적용하였다. 기존 두 개의 노드 기반 랑데부 기법과 MNSEQ를 통신완료시간 및 전송의 효율성 관점에서 성능평가를 수행하여 MNSEQ가 기존의 기법보다 우수하다는 것을 보여 준다.

• Journal of Information Processing Systems
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• 제20권2호
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• pp.226-238
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• 2024

Recently, multi-access edge computing (MEC) has emerged as a promising technology to alleviate the computing burden of vehicular terminals and efficiently facilitate vehicular applications. The vehicle can improve the quality of experience of applications by offloading their tasks to MEC servers. However, channel conditions are time-varying due to channel interference among vehicles, and path loss is time-varying due to the mobility of vehicles. The task arrival of vehicles is also stochastic. Therefore, it is difficult to determine an optimal offloading with resource allocation decision in the dynamic MEC system because offloading is affected by wireless data transmission. In this paper, we study computation offloading with resource allocation in the dynamic MEC system. The objective is to minimize power consumption and maximize throughput while meeting the delay constraints of tasks. Therefore, it allocates resources for local execution and transmission power for offloading. We define the problem as a Markov decision process, and propose an offloading method using deep reinforcement learning named deep deterministic policy gradient. Simulation shows that, compared with existing methods, the proposed method outperforms in terms of throughput and satisfaction of delay constraints.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.457-459
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• 2004

The Channel Coding Unit (CCU) is an integral component of Payload Data Transmission System (PDTS) for the Multi-Spectral Camera (MSC) data. The main function of the CCU is channel coding and encryption. CCU has two channels (I & Q) for data processing. The input of CCU is the output of DCSU (Data Compression & Storage Unit). The output of CCU is the input of QTX which modulate data for RF communication. In this paper, there are the overview, short H/W description and operation concept of CCU.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.778-798
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• 2014

This paper proposes a novel exposed-terminal-eliminated medium access control (ETE-MAC) protocol by combining channel reservation, collision avoidance and concurrent transmissions to improve multi-access performance of the multihop wireless networks. Based on the proposed slot scheduling scheme, each node senses the control channel (CCH) or the data channel (DCH) to accurately determine whether it can send or receive the corresponding packets without collisions. Slot reservation on the CCH can be simultaneously executed with data packet transmissions on the DCH. Therefore, it resolves the hidden-terminal type and the exposed-terminal type problems efficiently, and obtains more spatial reuse of channel resources. Concurrent packet transmissions without extra network overheads are maximized. An analytical model combining Markov model and M/G/1 queuing theory is proposed to analyze its performance. The performance comparison between analysis and simulation shows that the analytical model is highly accurate. Finally, simulation results show that, the proposed protocol obviously outperforms the link-directionality-based dual-channel MAC protocol (DCP) and WiFlex in terms of the network throughput and the average packet delay.

• 대한전자공학회논문지TC
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• 제49권6호
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• pp.27-38
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• 2012

본 논문에서는 최근 스마트 폰의 급격한 보급과 음성 위주의 이동 통신 서비스가 무선 멀티미디어 콘텐츠를 중심으로 하는 데이터 위주의 서비스로 전환되고 있음을 보였고, 셀 서비스 문제인 음영(shadowing) 지역을 해결할 수 있는 방안으로 다중점 송수신(CoMP:Coordinated Multi-Point Transmission and Reception) 기법을 소개하였다. 간섭 신호의 영향을 줄이기 위해서는 원하지 않는 간섭 신호를 직교하도록 제어하는 것이 이상적이지만, 현실적인 응용에서는 간섭을 정렬하거나 회피하는 방법이 이용된다. 간섭을 적이 아닌 친구처럼 대할 수 있도록 하는 방법이 간섭 정렬 기법이다. 강한 간섭이 존재하는 가우시안 채널 에서 격자 부호가 랜덤 부호처럼 Shannon 채널 용량을 달성할 수 있음을 확인하였고, 세 명의 사용자가 존재하는 대칭 간섭 채널의 간섭 정렬에 격자 부호를 적용하여 채널 매개 변수 a와 자유도(DoF:Degree of Freedom)의 상관관계를 보였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.741-744
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• 2001

OFDM 방식은 전통적인 단일 반송파 전송방식과는 달리 전송할 데이터를 병렬적으로 변조하여 주어진 다중전송채널에 다수의 반송파를 실어보내므로 고속의 데이터전송을 수행하고 주파수를 직교적으로 오버랩 시킴으로써 높은 스펙트럼 효율을 제공할 수 있어 여러 분야에서 적용되고 있으며 계속해서 연구되고 있다. 본 논문에서는 컴퓨터 시뮬레이션을 통해서 변조방식에 따른 OFDM 무선통신시스템의 성능을 평가하였으며 변조방식으로서는 M-PSK, M-QAM을 사용하였다. 시뮬레이션은 다중로지연확산, 가우시안채널잡음, Peak Power Clipping, Frame Start Time Error 등이 포함된 가상의 채널환경과 실제채널환경에서 적용되었다. 시뮬레이션 결과 OFDM 시스템에서의 변조방식으로는 M-QAM 방식이 M-PSK 방식보다 우수함을 확인하였다.

• 한국정보통신학회논문지
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• 제5권2호
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• pp.251-256
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• 2001

OFDM 방식은 전통적인 단일 반송파 전송방식과는 달리 전송할 데이터를 병렬적으로 변조하여 주어진 다중전송채널에 다수의 반송파를 실어보내므로 고속의 데이터전송을 수행하고 주파수를 직교적으로 오버랩 시킴으로써 높은 스펙트럼 효율을 제공할 수 있어 여러 분야에서 적용되고 있으며 계속해서 연구되고 있다. 본 논문에서는 컴퓨터 시뮬레이션을 통해서 변조방식에 따른 OFDM 무선통신시스템의 성능을 평가하였으며 변조방식으로서는 M-PSK, M-QAM을 사용하였다. 시뮬레이션은 다중로지연확산, 가우시안채널잡음, Peak Power Clipping, Frame Start Time Error 등이 포함된 가상의 채널환경과 실제채널환경에서 적용되었다. 시뮬레이션 결과 OFDM 시스템에서의 변조방식으로는 M-QAM 방식이 M-PSK 방식보다 우수함을 확인하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(1)
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• pp.49-52
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• 2000

The Multi-Code CDMA systems that are proposed as an effective transmission methodology in the IMT-2000 systems allow higher rate services under the IS-95 CDMA infrastructure. The Multi-Code CDMA systems convert the higher rate data into the lower rate by serial to parallel operation and spread the converted data streams by the multiple walsh codes, and its mobile receiver needs multiple walsh generators and data correlators to demodulate simultaneously multiple walsh code channels. Therefore, the number of data correlators is increased as the number of traffic channels increases. In this paper, we proposed the new structure of the data correlators using walsh overlay coding, the shared accumulator, and FWHT(Fast Walsh Hadamard Transform) algorithm for reducing the bottle-neck effect resulting the increase of the number of data correlators.

• Journal of Information Processing Systems
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• 제13권5호
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• pp.1229-1242
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• 2017

In this paper, an interference aware distributed multi-channel MAC (IDMMAC) protocol is proposed for wireless sensor and actor networks (WSANs). The WSAN consists of a huge number of sensors and ample amount of actors. Hence, in the IDMMAC protocol a lightweight channel selection mechanism is proposed to enhance the sensor's lifetime. The IDMMAC protocol divides the beacon interval into two phases (i.e., the ad-hoc traffic indication message (ATIM) window phase and data transmission phase). When a sensor wants to transmit event information to the actor, it negotiates the maximum packet reception ratio (PRR) and the capacity channel in the ATIM window with its 1-hop sensors. The channel negotiation takes place via a control channel. To improve the packet delivery ratio of the IDMMAC protocol, each actor selects a backup cluster head (BCH) from its cluster members. The BCH is elected based on its residual energy and node degree. The BCH selection phase takes place whenever an actor wants to perform actions in the event area or it leaves the cluster to help a neighbor actor. Furthermore, an interference and throughput aware multi-channel MAC protocol is also proposed for actor-actor coordination. An actor selects a minimum interference and maximum throughput channel among the available channels to communicate with the destination actor. The performance of the proposed IDMMAC protocol is analyzed using standard network parameters, such as packet delivery ratio, end-to-end delay, and energy dissipation, in the network. The obtained simulation results indicate that the IDMMAC protocol performs well compared to the existing MAC protocols.