• Journal of information and communication convergence engineering
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• 제13권1호
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• pp.7-14
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• 2015

In a multi-hop wireless network, connectivity is determined by the link that is established by the receiving signal strength computed by subtracting the path loss from the transmission power. Two path loss models are commonly used in research, namely two-ray ground and shadow fading, which determine the receiving signal strength and affect the link quality. Link quality is one of the key factors that affect network performance. In general, network performance improves with better link quality in a wireless network. In this study, we measure the network connectivity and performance in a shadow fading path loss model, and our observation shows that both are severely degraded in this path loss model. To improve network performance, we propose power control schemes utilizing link quality to identify the set of nodes required to adjust the transmission power in order to improve the network throughput in both homogeneous and heterogeneous multi-hop wireless networks. Numerical studies to evaluate the proposed schemes are presented and compared.

• ETRI Journal
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• 제40권1호
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• pp.101-110
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• 2018

In wireless positioning systems using range measurements non-line-of-sight (NLOS) links cause estimation errors. Several studies have attempted to improve the positioning performance by mitigating these NLOS errors. These studies, however, have focused on the performance of a dataset consisting of three or more links. Therefore, measurement errors induced by links are averaged, and a reliable link is not fully utilized in the dataset. This paper proposes a Link Reliability based on Range Measurement (LRRM) scheme, which specifies the relative reliability of each link using residuals. The link reliability becomes the input to a Link Residual Weighting (LRW) scheme, which is also proposed as a weighted positioning scheme. Moreover, LRRM and LRW constitute new turbo positioning, where the estimation errors are reduced considerably by iterative updates.

• 한국항행학회논문지
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• 제14권2호
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• pp.253-259
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• 2010

무선 메쉬 네트워크는 Base Station 기반과 더불어 애드혹 네트워크나 블루투스와 같이 유연성을 가진 네트워크이다. 하지만 무선 메쉬 네트워크는 높은 패킷 손실률을 보이고 TCP(Transport Control Protocol) 알고리즘은 무선 메쉬 네트워크의 패킷손실 원인을 네트워크 내의 혼잡으로 인식하기 때문에 TCP 혼잡제어 알고리즘(Congestion Control Algorithm)을 실행하게 된다. 이러한 TCP 동작은 혼잡 손실이 아닌 패킷 손실로 발생 할 경우, 상당한 성능 저하를 초래하게 된다. 본 논문에서는 무선 메쉬 네트워크에서 TCP 혼잡제어 알고리즘의 성능을 개선시키기 위해 혼잡 윈도우를 무선망에서도 적응력 있게 조절하는 연구를 제안하였다.

• 한국항행학회논문지
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• 제16권6호
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• pp.960-967
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• 2012

무선 센서 네트워크는 주변의 정보를 얻고자 하는 환경에 사용되며, 이러한 정보는 무선 링크를 통해 전송되기 때문에 재전송이 발생하여 노드의 에너지 소모가 크다는 단점이 있다. 이 때문에 신뢰성이 높고 에너지 효율이 좋은 링크를 선택하기 위해 LQI(link quality indication), hop count 등을 이용하여 무선 링크에 대한 품질을 추정하는 기법이 필요하다. 본 논문에서는 무선 센서 네트워크에서 노드들의 데이터 전송률을 높여 재전송을 줄임으로서 에너지 소모를 줄이는 라우팅을 위해 각 경로 내의 LQI를 구한 후 LQI 표준편차가 작은 경로를 선택하는 LQI 표준편차 라우팅 알고리즘을 제안한다. 또한 제안하는 알고리즘을 기존 LQI 알고리즘인 minimum-LQI. Hop-LQI weight과 RF 출력 -7dBm에서 비교하였다. 결과에 의하면 제안하는 알고리즘은 기존 알고리즘에 비해 경유 노드수, 재전송률, 네트워크 수명이 각각 우수하였다. 따라서 LQI 표준편차 라우팅 알고리즘을 에너지 소모에 제한적인 무선 센서 네트워크에 적용할 경우 에너지 소모를 효율적으로 줄일 수 있다.

• Journal of Communications and Networks
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• 제8권4호
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• pp.391-400
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• 2006

With the on-going wireless access technologies, the Internet has become accessible anytime anywhere. In wireless networks, link errors significantly degrade the performance of the transmission control protocol (TCP). To cope with this issue, this paper improves the recently-proposed terrestrial REFWA (T-REFWA) scheme by adding a new error recovery mechanism to its original design. In the T-REFWA scheme, senders are acknowledged with appropriate sending rates at which an efficient and fair utilization of network resources can be achieved. As the feedback values are computed independently of link errors, senders can keep transmitting data at high rates even in case of link error occurrences. Using this feature, the proposed error recovery mechanism can achieve high throughput in environments with high bit error rates. The throughput is further improved by disabling the exponential back-off algorithm of TCP so that long idle times are avoided in case of link errors. We show through simulations that the proposed method improves TCP performance in high bit error rates. Compared with several TCP variants, the proposed error recovery scheme exhibits higher link utilization and guarantees system fairness for different bit error rates.

• Journal of Information Processing Systems
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• 제11권1호
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• pp.57-75
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• 2015

In evaluating the performance of a dual-hop wireless link, the effects of large and small scale fading has to be considered. To overcome this fading effect, several schemes, such as multiple-input multiple-output (MIMO) with orthogonal space time block codes (OSTBC), different combining schemes at the relay and receiving end, and orthogonal frequency division multiplexing (OFDM) are used in both the transmitting and the relay links. In this paper, we first make compare the performance of a two-hop wireless link under a different combination of space diversity in the first and second hop of the amplify-and-forward (AF) case. Our second task in this paper is to incorporate the weak signal of a direct link and then by applying the channel model of two random variables (one for a direct link and another for a relayed link) we get very impressive result at a low signal-to-noise ratio (SNR) that is comparable with other models at a higher SNR. Our third task is to bring other three schemes under a two-hop wireless link: use of transmit antenna selection (TAS) on both link with weak direct link, distributed Alamouti scheme in two-hop link and single relay antenna with OFDM subcarrier. Finally, all of the schemes mentioned above are compared to select the best possible model. The main finding of the paper is as follows: the use of MIMO on both hops but application TAS on both links with weak direct link and the full rate OFDM with the sub-carrier for an individual link provide a better result as compared to other models.

• 대한산업공학회지
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• 제33권2호
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• pp.237-245
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• 2007

In this paper, a modified PCF (Point Coordination Function) MAC (Medium Access Control) Protocol is proposed to support the multiple direct link communication between STAs (STAtions) in infrastructure mode IEEE 802.11 wireless LANs. By the proposed MAC protocol, the direct link communication between STAs, which are located within the communication range of each other, is allowed without the use of AP (Access Point) as a relay. Moreover, when multiple direct data communication between STAs can be simultaneously performed with a sufficiently small interference, multiple simultaneous direct link communication is allowed for the efficient use of radio bandwidth. AP polls STAs to grant the transmission opportunities using the direct link communication by transmitting the polling frames to STAs. An efficient polling method for granting the transmission opportunities to STAs is proposed to reduce the number of the polling frame transmissions and enhance the PCF MAC performance.

• 한국통신학회논문지
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• 제35권2A호
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• pp.165-173
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• 2010

무선 메쉬 네트워크는 기존 무선랜에 비해 낮은 구축비용으로 네트워크 구성이 용이한 무선 백본 네트워크 기술이다. 대부분의 기존 무선 메쉬 관련 연구는 실제 구현 보다는 시뮬레이션을 통해 성능을 평가하였다. 구현 연구들도 존재하지만 링크 구성 유연성이나 다중 채널 등 링크 특성 활용 등의 측면에서 한계가 있다. 그 결과 무선 메쉬의 장점인 망 구성 유연성이 떨어지고 다중 홉 상황에서 성능이 악화되는 문제가 발생한다. 본 논문은 동적 링크 구성을 지원하며 다중 채널 등을 효과적으로 활용할 수 있는 리눅스 기반의 링크 계층 무선 메쉬 라우팅 시스템인 WBMR의 설계 및 구현에 관해 소개한다. 우리는 동적 링크 구성을 위해 무선랜 동작 모드의 하나인 WDS를, 링크 계층 라우팅을 위해 기존 리눅스 브릿지 모듈을 활용하고 변경하는 접근을 택했다. 실험을 통한 성능 평가 결과 WBMR은 빠르고 자율적인 망 구성을 지원하며 링크 특성 반영이 어려운 기존 접근법에 비해 다중 홉 환경에서 데이터 전송률을 크게 향상 시켰다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권4호
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• pp.651-669
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• 2013

In this paper, we study a novel routing algorithm based on load balancing for multi-channel wireless mesh networks. In order to increase the network capacity and reduce the interference of transmission streams and the communication delay, on the basis of weighted cumulative expected transmission time (WCETT) routing metric this paper proposes an improved routing metric based on load balancing and channel interference (LBI_WCETT), which considers the channel interference, channel diversity, link load and the latency brought by channel switching. Meanwhile, in order to utilize the multi-channel strategy efficiently in wireless mesh networks, a new channel allocation algorithm is proposed. This channel allocation algorithm utilizes the conflict graph model and considers the initial link load estimation and the potential interference of the link to assign a channel for each link in the wireless mesh network. It also utilizes the channel utilization percentage of the virtual link in its interference range as the channel selection standard. Simulation results show that the LBI_WCETT routing metric can help increase the network capacity effectively, reduce the average end to end delay, and improve the network performance.

• Journal of Information Technology Applications and Management
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• 제23권2호
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• pp.61-80
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• 2016

The wireless mesh network (WMN) is a next-generation technology for data networking that has the advantage in cost and the flexibility in its construction because of not requiring the infra-structure such as the ethernet. This paper focuses on the optimal link scheduling problem under the wireless mesh network to effectuate real-time streaming by using the constraint programming. In particular, Under the limitation of half-duplex transmission in wireless nodes, this paper proposes a solution method to minimize the makespan in scheduling packet transmission from wireless nodes to the gateway in a WMN with no packet transmission conflicts due to the half-duplex transmission. It discusses the conflicts in packet transmission and deduces the condition of feasible schedules, which defines the model for the constraint programming. Finally it comparatively shows and discusses the results using two constraint programming solvers, Gecode and the IBM ILOG CP solver.