• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.8
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• pp.1786-1804
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• 2013

We consider a specific interference-limited wireless relay system that comprises several cooperation units (CUs) which are defined as a source and destination node pair with an associated relay node. In the wireless relay system, all source nodes simultaneously transmit their own signals and the relay node in each CU then forwards the received signal to the destination node, causing co-channel interference at both the relay node and the destination node in each CU. The co-channel interference at the relay node is closely related to that at the destination node in each CU. We first derive the end-to-end outage probability in a CU over Rayleigh slow-fading channels with interference for the decode-and-forward (DF) relaying strategy. Then, on the assumption that each CU is allocated with equal power we design an optimal power allocation between the source node and the relay node in each CU to minimize the outage probability of the investigated CU. At last, in the case that each CU is not allocated with equal power and the sum of their power is constrained, we present an optimal power allocation between CUs to minimize the sum of the outage probability of all CUs. The analytical results are verified by simulations.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.445-450
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• 2020

Cooperative networks provides the benefits of performance improvements and capacity increment when the source node transmits signal to the destination node using several relay nodes. In this paper, we consider the cooperative network where the transmission scheme between the source node and relay node use conventional binary signaling, whereas the transmission scheme between thee relay node and destination node adopt the differential space time coding signaling. We analyze the performance of the system depending on the modulation scheme, i.e., coherent and differential modulation, at the source-relay links. The performance depending on the relay location is also compared by considering modulation scheme and the number of relay node.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1549-1555
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• 2009

The Relay node placement problem is one of the most important requirements for many wireless sensor networks because the lifetime of sensor networks is closely related with the placement of relay nodes which receive sensed data from sensor nodes and forward them to the base station. Relay node placement problem has focused at minimization of dissipated total energy of the sensor nodes in whole networks. However, minimum total energy causes the unbalance of consumed energy in sensor nodes due to different distances between relay nodes and sensor nodes. This paper proposes the concept of energy balance ratio and finds the locations of relay nodes using objective functions which maximize the energy balance ratio. Maximizing this ratio results in maximizing the network lifetime by minimizing the energy consumption of large-scale sensor networks. However, finding a solution to relay node placement problem is NP-hard and it is very difficult to get exact solutions. Therefore, we get approximate solutions to EBR-RNP problem which considers both energy balance ratio and relay node placement using constraint programming.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.5
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• pp.436-442
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• 2013

The diversity-multiplexing tradeoff (DMT) function of a special half-duplex (HD) dynamic decode and forward (DDF) relay protocol with more than two antennas at the source node, two antennas at the relay node, and two antennas at the destination node is derived. This protocol is compared to a HD NAF protocol with the same number of source antennas and a HD DDF relay protocol with two antennas at the source node, more than two antennas at the relay node, and two antennas at the destination node.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.108-110
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• 2015

In this paper, we proposed the relay node selection scheme using property of node such as velocity, direction in Delay Tolerant Networks. the existing selection scheme is caused the problem increasing the transmission delay and packet loss, if select the relay node for different mobile with destination. To overcome this problem, we proposed the relay node selection scheme using the property of mobile node. the proposed scheme represents and shares the property of mobile node. The proposed algorithm assumed the sketchy position of node from mobile node delivering property of destination. In addition, the propose algorithm recognizes and analyzes the context of mobile node to provide the relay node transferring the data efficiently. The simulation result provides the better result in terms of transmission delay and packet delivery ratio by selecting transmission by relay node according property of node.

• International journal of advanced smart convergence
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• v.6 no.3
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• pp.9-16
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• 2017

In this paper, we propose a new routing protocol for wireless sensor networks. This protocol improves energy consumption of ML-LEACH by reducing the transmission distance of member node via Relay Node. Since clusters of each Layer in ML-LEACH are randomly formed, the distance, between member node and cluster head may be longer than specific distance, distance threshold value. To improve this, we propose the new routing protocol using 2-Hop transmission via Relay Node depending on the transmission distance of the member node.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.6
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• pp.15-26
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• 2012

In this paper, we perform interference cancellation in multiuser MIMO (Multiple Input Multiple Output) relay network with improved Amplify-and-Forward (AF) and Decode-and-Forward (DF) relay protocols. The work of interference cancellation is followed by evolved NodeB (eNB), Relay Node (RN) and User Equipment (UE) to improve the error performance of whole transmission system with the explicit use of relay node. In order to perform interference cancellation, we use Dirty Paper Coding (DPC) and Thomilson Harashima Precoding (THP) allied with detection techniques Zero Forcing (ZF), Minimum Mean Square Error (MMSE), Successive Interference Cancellation (SIC) and Ordered Successive Interference Cancellation (OSIC). These basic techniques are studied and improved in the proposal by using the functions of relay node. The performance is improved by Decode-and-Forward which enhance the cancellation of interference in two layers at the cooperative relay node. The interference cancellation using weighted vectors is performed between eNB and RN. In the final results of the research, we conclude that in contrast with the conventional algorithms, the proposed algorithm shows better performance in lower SNR regime. The simulation results show the considerable improvement in the bit error performance by the proposed scheme in the LTE-Advanced system.

• Journal of Korea Society of Digital Industry and Information Management
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• v.16 no.4
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• pp.9-17
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• 2020

When IoT sensor nodes are deployed in areas where data collection is challenging, sensors must be relocated if sensing holes occur due to improper placement of sensors or energy depletion, and data collection is impossible. The sensing hole's cluster header transmits a request message for sensor relocation to an adjacent cluster header through a specific relay node. However, since a specific relay node is frequently used, a member sensor located in a specific cluster area adjacent to the sensing hole can continuously receive the movement message. In this paper, we propose a method that avoids the situation in which the sensing hole cluster header monopolizes a specific relay node and allows the cluster header to use multiple relay nodes fairly. Unlike the existing method in which the relay node immediately responds to the request of the header, the method proposed in this paper solves a ping-pong problem and a problem that the request message is concentrated on a specific relay node by applying a method of responding to the request of the header using a timer. OMNeT++ simulator was used to analyze the performance of the proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7B
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• pp.517-527
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• 2012

This paper considers a cooperative communication system with a single relay node, where two-layer superposition coding and successive decoding is employed to reduce the expected distortion of a Gaussian source delivered. For the system, we propose a relay scheme which forwards an appropriate relay signal at the relay node, based on the local decoding result of layers and the decoding result of layers at the destination node fed back to the relay node. In the scheme, the relay signal is designed not only by applying decode-and-forward but also by applying amplify-and-forward to reduce the outage probability in final decoding of each layer. The performance of the proposed scheme is evaluated numerically in terms of the expected distortion at various relay locations using outage probabilities derived. The results show that the proposed scheme outperforms the conventional schemes in most cases of the relay location and the gain gets larger when the relay node is closer to the source node in particular.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.8
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• pp.2894-2909
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• 2015

As the number of mobile devices such as smart phones and tablets explodes, the need for new services or applications is also rapidly increasing. Smart class application is one of the emerging applications, in which most of contents are distributed to all members of a class simultaneously. It is highly required to select relay nodes to cover shadow area of radio as well as extend coverage, but existing algorithms in a smart class environment suffer from high control packet overhead and delay for exchanging topology information among all pairs of nodes to select relay nodes. In addition, the relay selection procedure should be repeated in order to adapt to the dynamic topology changes caused by link status changes or device's movement. This paper proposes the learning based relay selection algorithm to overcome aforementioned problems. The key idea is that every node keeps track of its relay quality in a fully distributed manner, where RQI (Relay Quality Indicator) is newly defined to measure both the ability of receiving packets from content source and the ability of successfully relaying them to successors. The RQI of each node is updated whenever it receives or relays broadcast packet, and the node having the higher RQI is selected as a relay node in a distributed and run-time manner. Thus, the proposed algorithm not only removes the overhead for obtaining prior knowledge to select relay nodes, but also provides the adaptability to the dynamic topology changes. The network simulation and experimental results prove that the proposed algorithm provides efficient and reliable content distribution to all members in a smart class as well adaptability against network dynamics.