• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6A
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• pp.506-514
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• 2009

To minimize energy consumption, most of MAC Protocols in WSNs exploit low duty cycling. Among those, RMAC [4] allows a node to transmit a data packet for multiple hops in a single duty cycle, which is made possible by exploiting a control frame named Pioneer (PION) in setting up the path. In this paper, we present a MAC Protocol called Hop Extended MAC (HE-MAC) that transmits the data packet for more multiple hops in a single duty cycle. It employs an EXP (Explorer) frame to set up the multiple hop transmission, which contains the information of the maximum hop that a packet can be transmitted. With the use of the information in EXP and an internal state of Ready to Receive (RTR), HEMAC extends the relay of the packet beyond the termination of the data period by two more hops compared to RMAC. Along with our proposed adaptive sleeping method, it also reduces power consumption and handles heavy traffic efficiently without experiencing packet inversion observed in RMAC. We analytically obtain the packet delivery latency in HE-MAC and evaluate the performance through ns-2 simulations. Compared to RMAC, HE-MAC achieves 14% less power consumption and 20% less packet delay on average for a random topology of 300 nodes.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10d
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• pp.525-530
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• 2007

기술의 발전과 함께 최근의 모바일 장치들은 복수의 서로 다른 우선 인터페이스를 동시에 장착한 멀티라디오 환경을 가지게 되었고, 이러한 장치들로 구성된 애드 혹 네트워크는 유비쿼터스 컴퓨팅 환경에서 새로운 요구와 항께 다양한 활용 가능성을 가지고 있다. 유비쿼터스 컴퓨팅 환경에서는 사용자나 서비스, 장치에 따라 상황정보가 다양하게 나타날 수 있고, 그것을 네트워킹에 반영하기 위한 수단으로 멀티라디오 환경이 사용될 수 있으므로, 멀티 라디오 환경의 특성을 정확히 파악하고 어떻게 그 특성을 활용 할 수 있는가를 분석하는 것이 필요하다. 본 연구에서는 멀티 라디오 애드 혹 네트워킹에 관한 관련 연구 분석과 함께 기존의 연구가 지원하지 못한 멀티 라디오 환경의 특성을 지적하고, 시뮬레이션을 통하여 멀티 라디오 환경의 특성과 활용 요소에 대여 분석하였다. 시뮬레이션 결과는 시나리오에 따라 인터페이스의 선택이 가지는 trade-off를 보여주고 서로 다른 인터페이스의 혼합된 사용이 네트워크에 미치는 영향에 대해 설명하고 있으며 결과적으로 시뮬레이션을 통해 얻은 멀티 라디오의 특성을 상황인지 애드 혹 네트워킹에 활용할 수 있는 시스템 디자인을 제안한다.

• Journal of KIISE:Information Networking
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• v.30 no.5
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• pp.631-640
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• 2003

Because of multi-hop wireless communication, P2P applications in ad hoc networks suffer poor performance. We Propose neighbor caching strategy to overcome this shortcoming and show it is more efficient than self caching that nodes store data in theirs own cache individually. A node can extend its caching storage instantaneously with neighbor caching by borrowing the storage from idle neighbors, so overcome multi-hop wireless communications with data source long distance away from itself. We also present the ranking based prediction that selects the most appropriate neighbor which data can be stored in. The node that uses the ranking based prediction can select the neighbor that has high possibility to keep data for a long time and avoid caching the low ranked data. Therefore the ranking based prediction improves the throughput of neighbor caching. In the simulation results, we observe that neighbor caching has better performance, as large as network size, as long as idle time, and as small as cache size. We also show the ranking based prediction is an adaptive algorithm that adjusts times of data movement into the neighbor, so makes neighbor caching flexible according to the idleness of nodes

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2B
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• pp.250-262
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• 2004

In IPv6 environment, the Internet Telephony, VoD(Video on Demand) and high capacity file exchange service will be more increased than IPv4. Therefore, the strict guarantee of QoS based on End-to-End and differentiated quality control schemes are simultaneously required. This paper proposes the flow control schemes on IPv6 network that the traffic is identified by flow and the QoS of multi-service is improved by QoS information in IPv6 hop-by-hop option header. The object of flow control includes not only non-default QoS traffic, which uses the flow label, but also best-effort or encrypted traffic. Therefore, the guarantee of real-time service is strengthened and the flow, which abuses unnecessarily the network resources, is effectively controlled. Also, this paper proposes the mapping scheme between the flow and MPLS by reflecting the minimum change of the existed network resource and the status of backbone network of ISP(Internet Service Provider). In the simulation result, It is shown that the proposed scheme is effective in the side of QoS on real-time services and utilization of backbone resources.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.103-113
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• 2010

In this paper, a tradeoff between the total energy consumption-per-bit and the end-to-end rate under spatial reuse in wireless multi-hop network is developed and analyzed. The end-to-end rate of the network is the number of information bits transmitted (end-to-end) per channel use by any node in the network that is forwarding the data. In order to increase the bandwidth efficiency, spatial reuse is considered whereby simultaneous relay transmissions are allowed provided there is a minimum separation between such transmitters. The total energy consumption-per-bit includes the energy transmitted and the energy consumed by the receiver to process (demodulate and decoder) the received signal. The total energy consumption-per-bit is normalized by the distance between a source-destination pair in order to be consistent with a direct (single-hop) communication network. Lower bounds on this energy-bandwidth tradeoff are analyzed using convex optimization methods. For a given location of relays, it is shown that the total energy consumption-per-bit is minimized by optimally selecting the end-to-end rate. It is also demonstrated that spatial reuse can improve the bandwidth efficiency for a given total energy consumption-per-bit. However, at the rate that minimizes the total energy consumption-per-bit, spatial reuse does not provide lower energy consumption-per-bit compared to the case without spatial reuse. This is because spatial reuse requires more receiver energy consumption at a given end-to-end rate. Such degraded energy efficiency can be compensated by varying the minimum separation of hops between simultaneous transmitters. In the case of equi-spaced relays, analytical results for the energy-bandwidth tradeoff are provided and it is shown that the minimum energy consumption-per-bit decreases linearly with the end-to-end distance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10B
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• pp.1043-1049
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• 2009

Broadcast of sink node is used for network management, data collection by query and synchronization in wireless sensor networks. Simple flooding scheme induces the broadcast storm problem. The MPR based broadcast schemes reduce redundant retransmission of broadcast packets. MPR is a set of one hop neighbor nodes which have to relay broadcast message to cover all two hop neighbors. Though MPR can reduce redundant retransmission remarkably, it still suffers from energy waste problem caused by collision and duplicate packets reception. This paper proposes a new MPR based sink broadcast scheme using 3-channel. The proposed scheme reduces energy consumption by avoiding duplicate packet reception, while increases reliability by reducing collision probability remarkably. The results of analysis and simulation show that the proposed scheme is more efficient in energy consumption compared to the MPR based scheme. The result also shows that the proposed scheme reduces delivery latency by evading a contention with other relay nodes and improves reliability of broadcast message delivery by reducing collision probability.

• Journal of Communications and Networks
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• v.10 no.4
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• pp.412-421
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• 2008

We observe simultaneous transmission of relay stations (RSs) allowed in current IEEE 802.16j draft standard for multi-hop relay networks may involve severe interference among the RSs, hence leading to throughput degradation. Allowing only 1/3 of the RSs to simultaneously transmit instead of 1/2 RSs as in the current draft standard reduces the interference but results in reduced throughput. To remedy this problem, we devise schemes to incorporate network coding at link-layer level (decode-and-forward) into the simultaneous transmission of RSs. Data movement is rearranged to maximize coding gain. Formula is derived to dictate exact movement of packets traveling between base station (BS) and mobile stations (MSs) via intermediate RSs. The frame structure in the current IEEE 802.16j draft standard does not allow broadcast needed for network coding. We devise a new frame structure which supports the broadcast. A new R-MAP (pointers to the burst data) is introduced to implement the broadcast. Since our new frame structure is used only for BS to RS or RS to RS communication, our schemes retain backward compatibility with legacy MSs based on IEEE 802.16e standard. Simulation based on simple configuration of RSs shows considerable improvement in terms of system throughput and round trip delay. For a 4-hop relay network with 1 BS and 4 RSs with symmetric traffic in uplink (UL) and downlink (DL), throughput is improved by 49% in DL and by 84% in UL traffic compared with IEEE 802.16j draft standard under the assumption that omni-directional antennae are used in BS and RSs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.12
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• pp.1128-1137
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• 2012

In this paper, we propose an improved MPR selection method considering mobility and density of nodes for ad-hoc networks. In Optimized Link State Routing(OLSR), a node selects 1-hop Multi-Point Relay(MPR) nodes to cover all 2-hop neighbor nodes. In a high population area, many nodes are likely to be selected as MPR nodes by their neighbors. This leads to increase in contention among MPR nodes and may decrease overall performance of the network. In addition, when an MPR node leaves the communication range of its MPR selector node, it can no longer perform as the MPR node and the performance of the network may also decrease. In this paper, we propose an MPR selection method which measures the mobility and density of nodes by exchanging the hello messages and gives the priorities to the nodes for MPR selection. Performance evaluation results using OPNET show that the proposed method is superior to OLSR or the MPR candidate method in terms of connectivity and throughput.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.3
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• pp.463-474
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• 2015

Future Ground Control Stations (GCSs) for Unmanned Aerial Vehicles (UAVs) teleoperation targets better situational awareness by providing extra motion cues to stimulate the vestibular system. This paper proposes a new virtual environment for long range Unmanned Aerial Vehicle (UAV) control via Non-Line-of-Sight (NLoS) communications, which is based on motion platforms. It generates motion cues for the teleoperator for extra sensory stimulation to enhance the guidance performance. The proposed environment employs the distributed component simulation over GSM network as a simulation platform. GSM communications are utilized as a multi-hop communication network, which is similar to global satellite communications. It considers a UAV mathematical model and wind turbulence effects to simulate a realistic UAV dynamics. Moreover, the proposed virtual environment simulates a Multiple Axis Rotating Device (MARD) as Human Machine Interface (HMI) device to provide a complete delay analysis. The demonstrated measurements cover Graphical User Interface (GUI) capabilities, NLoS GSM communications delay, MARD performance, and different software workload. The proposed virtual environment succeeded to provide visual and vestibular feedbacks for teleoperators via GSM networks. The overall system performance is acceptable relative to other Line-of-Sight (LoS) systems, which promises a good potential for future long range, medium altitude UAV teleoperation researches.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4C
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• pp.485-493
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• 2004

The system performance of 2-Dimensional wavelength hopping/time spreading optical CDMA systems is found to be limited by the occurrence of the beat noise between the components of the signal and the multiple user interference. This paper shows that the performance is analyzed under the beat noise and no beat noise to blow impact of the beat noise. To overcome this problem, the OHL(Optical Hard-Limiter) is used in the receiver. The performance is calculated for a optical CDMA system employing asymmetric and symmetric prime-hop 2-Dimensional codes, respectively The analysis results show that the performance improved 3.5 times of simultaneous users of before and after inserting OHL in the case of no beat noise. In the case of beat noise the performance improved 1.5 times of simultaneous users of before and after inserting OHL. The performance marked use of symmetric prime-hop code.