• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제9권1호
• /
• pp.50-67
• /
• 2015

The Cognitive Radio (CR) paradigm in tactical ad hoc networks is an important element of future military communications for network-centric warfare. This paper presents a novel Cognitive Link State Routing protocol for CR-based tactical ad hoc networks. The proposed scheme provides prompt and reliable routes for Primary User (PU) activity through procedures that incorporate two main functions: PU-aware power adaptation and channel switching. For the PU-aware power adaptation, closer multipoint relay nodes are selected to prevent network partition and ensure successful PU communication. The PU-aware channel switching is proactively conducted using control messages to switch to a new available channel based on a common channel list. Our simulation study based on the ns-3 simulator demonstrates that the proposed routing scheme delivers significantly improved performance in terms of average end-to-end delay, jitter, and packet delivery ratio.

• ETRI Journal
• /
• 제44권6호
• /
• pp.915-924
• /
• 2022

In this paper, we present a two-stage scalable channel estimator (TSCE), a deep learning (DL)-based scalable, and robust channel estimator for wireless cellular networks, which is made up of two DL networks to efficiently support different resource allocation sizes and reference signal configurations. Both networks use the transformer, one of cutting-edge neural network architecture, as a backbone for accurate estimation. For computation-efficient global feature extractions, we propose using window and window averaging-based self-attentions. Our results show that TSCE learns wireless propagation channels correctly and outperforms both traditional estimators and baseline DL-based estimators. Additionally, scalability and robustness evaluations are performed, revealing that TSCE is more robust in various environments than the baseline DL-based estimators.

• 한국인터넷방송통신학회논문지
• /
• 제13권5호
• /
• pp.249-258
• /
• 2013

다중-홉 애드 혹 네트워크(multi-hop ad hoc networks)에서 실효 대역폭과 단-대-단 처리량을 높이기 위한 방법으로 다중-인터페이스 다중-채널 구조가 주목을 받고 있다. 그러나 단일 인터페이스 기반 네트워크를 위해서 설계된 기존의 라우팅 메트릭들은 다중-인터페이스 다중-채널 기반 네트워크의 특성을 정확히 반영할 수 없으므로, 처리량 개선의 효과를 기대할 수 없다. 따라서 채널 다양성, 인터페이스 전환 비용과 같은 메트릭들을 사용하여 높은 처리량을 갖는 경로를 발견하는 MCR이 제안되었다. 하지만 MCR은 트래픽 부하의 영향을 반영하지 않기 때문에 혼잡한 네트워크에서 성능이 저하되는 문제점이 있다. 본 논문에서는 MCR에 채널 접근 시간 메트릭을 결합하여 혼잡한 조건에서도 높은 처리량을 갖는 경로를 선택하는 MAMCR 메트릭을 제안하고, ns-2 시뮬레이션을 통해 성능 개선 효과를 확인한다.

• 한국통신학회논문지
• /
• 제33권7B호
• /
• pp.538-549
• /
• 2008

최근 IEEE 802.22 WRAN 워킹 그룹에서는 부족해지는 주파수 부족의 해결을 위해 CR (Cognitive Radio)의 기술개발을 진행 중에 있다. 채널을 센싱하는 방법에 따라 기존의 시스템 (IS: Incumbent System)의 보호에 상당한 영향을 미치기 때문에 네트워크 상황에 따른 최적의 센싱 방법을 선택하는 것이 중요하다. 이에 IEEE 802.22에서 fine sensing을 제안하고 있지만 아직까지는 다양한 네트워크에 효율적으로 적용할 수 없다. 따라서 본 논문에서는 네트워크 환경에 따라 효율적인 센싱 방법을 선택하기 위한 무선인지 네트워크에서 정책기반 채널 센싱구조 및 알고리즘 (Policy-based Channel Sensing Architecture and Algorithms for Cognitive Radio Networks)을 제안한다. 본 논문에서는 제안하는 채널 센싱 방법 및 알고리즘의 효율성을 확인하기 위하여 제시한 모의실험 결과는 각 센싱 방법에 따라 차이점을 보였지만 제안하는 채널 센싱 방법이 전체적으로 기존의 시스템 검출 시간 및 QP(Quiet Period)를 줄일 수 있었다. 제안하는 방법 중에 클러스터를 이용한 센싱 방법(Channel division round robin sensing)의 경우 IEEE 802.22에서 제안하는 fine sensing에 비교하여 70%정도 평균 검출시간을 줄일 수 있었다.

• 한국인터넷방송통신학회논문지
• /
• 제8권3호
• /
• pp.57-70
• /
• 2008

This paper introduces a new paradigm of physical layer security through channel coding for wireless networks. The well known spread spectrum based physical layer security in wireless network is applicable when code division multiple access (CDMA) is used as wireless air link interface. In our proposal, we incorporate the proposed security protocol within channel coding as channel coding is an essential part of all kind of wireless communications. Channel coding has a built-in security in the sense of encoding and decoding algorithm. Decoding of a particular codeword is possible only when the encoding procedure is exactly known. This point is the key of our proposed security protocol. The common parameter that required for both encoder and decoder is generally a generator matrix. We proposed a random selection of generators according to a security key to ensure the secrecy of the networks against unauthorized access. Therefore, the conventional channel coding technique is used as a security controller of the network along with its error correcting purpose.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 1998년도 하계종합학술대회논문집
• /
• pp.74-77
• /
• 1998

We consider connection-oriented wireless cellular networks. These networks employ dedicated radio channels for the transmission of signaling information. A forward signaling channel is a common signaling channel assigned to carry the multiplexed stream of paging and channel allocation(virtual circuit allocation) packets from a base station to mobile stations. The delay levels experienced by paging and channel allocation packets have serious effect on the utilization level of the limited radio channel capacity. While a slotted mode operation is used to reduce the power consumption level at mobile stations, it may induce an increase in packet delay levels. In this paper, we thus consider a multiplexing scheme for paging and channel allocation packets under which slots are dynamically allocated for the paging packet transmission. For this dynamic scheme, we develop an analytical method for deriving the delay characteristics exhibited by paging and channel allocation packets, and investigate the effect of network parameters on the delay level by using this method.

• Journal of Communications and Networks
• /
• 제16권2호
• /
• pp.209-216
• /
• 2014

Cognitive radio (CR) has been proposed to solve the spectrum utilization problem by dynamically exploiting the unused spectrum. In CR networks, a spectrum selection scheme is an important process to efficiently exploit the spectrum holes, and an efficient channel allocation scheme must be designed to minimize interference to the primary network as well as to achieve better spectrum utilization. In this paper, we propose a multichannel selection algorithm that uses spectrum hole prediction to limit the interference to the primary network and to exploit channel characteristics in order to enhance channel utilization. The proposed scheme considers both the interference length and the channel capacity to limit the interference to primary users and to enhance system performance. By using the proposed scheme, channel utilization is improved whereas the system limits the collision rate of the CR packets.

• Journal of Communications and Networks
• /
• 제11권2호
• /
• pp.104-114
• /
• 2009

In this paper, a technique is proposed that enables secondary users to evaluate channel availability in cognitive radio networks. Here, secondary users estimate the utilization of channels via predicting the traffic pattern of primary user, and select a proper channel for radio transmission. The proposed technique reduces the channel switching rate of secondary users (the rate of switching from one channel to another) and the interference on primary users, while maintaining a reasonable call blocking rate of secondary users.

• 한국통신학회논문지
• /
• 제36권11A호
• /
• pp.870-877
• /
• 2011

IEEE 802.11 장비가 널리 사용되고 있으며, 저비용 IEEE 802.11 장비들이 보급됨에 따라 단말들은 다중 IEEE 802.11 라디오를 장착할 수 있게 되었다. 최신 IEEE 802.11 장비들은 다수 채널 (multi-channel)과 전송률 (multi-rate)을 제공한다. 실제 다중 채널 네트워크에서는 같은 노드에 대해 채널들이 서로 다른 신호 특성을 가지는 채널 이질성 (channel heterogeneity)이 있으므로, 네트워크 용량을 향상시키기 위해 다수의 채널을 효율적으로 할당해야 한다. 또한, 다중 전송률 네트워크에서는 같은 채널 상의 낮은 전송률 링크가 높은 전송률 링크의 성능을 심각히 저하시키는 성능 이상 (performance anomaly) 현상이 발생한다. 따라서, 본 논문에서는 채널 이질성과 성능 이성을 반영하여 네트워크 성능을 향상시키는 HACA (Heterogeneity Aware Channel Assignment) 알고리즘을 제안한다. NS-2 시뮬레이션을 통해 HACA 알고리즘이 채널 이질성을 반영하지 못하는 기존 채널 할당 알고리즘에 비해 향상된 성능을 보임을 검증하였다.

• Journal of Communications and Networks
• /
• 제13권6호
• /
• pp.639-654
• /
• 2011

In this paper, we present a channel access mechanism, referred to as the enhanced mesh coordinated channel access (eMCCA) mechanism, for IEEE 802.11s-based wireless mesh networks. The current draft of IEEE 802.11s includes an optional medium access control (MAC), denoted as MCCA, which is designed to provide collision-free and guaranteed channel access during reserved periods. However, the MCCA mechanism fails to achieve the desired goal in the presence of contending non-MCCA nodes; this is because non-MCCA nodes are not aware of MCCA reservations and have equal access opportunities during reserved periods. We first present a probabilistic analysis that reveals the extent to which the performance of MCCA may be affected by contending non-MCCA nodes. We then propose eMCCA, which allows MCCA-enabled nodes to enjoy collision-free and guaranteed channel access during reserved periods by means of prioritized and preemptive access mechanisms. Finally, we evaluate the performance of eMCCA through extensive simulations under different network scenarios. The simulation results indicate that eMCCA outperforms other mechanisms in terms of success rate, network throughput, end-to-end delay, packet-loss rate, and mesh coordinated channel access opportunity-utilization.