• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.9
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• pp.741-749
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• 2012

Ad Hoc Self-Organizing TDMA (ASO-TDMA) has been proposed as a specification to support the multi-hop data communication service for ships over VHF band. It allows for organizing a multi-hop ad-hoc network in a distributed manner by sharing the radio resources among the ships navigating along the route. In this paper, Markov chain analysis is given to provide the average throughput performance for ASO-TDMA protocol Furthermore, the analytical results are verified with computer simulation, which shows that there exists the optimal transmission rate to maximize the average throughput as the subframe size and the number of ships are varying in each hop region.

• Journal of Communications and Networks
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• v.15 no.3
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• pp.266-275
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• 2013

The exact closed-form expressions for outage probability and bit error rate of spectrum sharing-based multi-hop decode-and-forward (DF) relay networks in non-identical Rayleigh fading channels are derived. We also provide the approximate closed-form expression for the system ergodic capacity. Utilizing these tractable analytical formulas, we can study the impact of key network parameters on the performance of cognitive multi-hop relay networks under interference constraints. Using a linear network model, we derive an optimum relay position scheme by numerically solving an optimization problem of balancing average signal-to-noise ratio (SNR) of each hop. The numerical results show that the optimal scheme leads to SNR performance gains of more than 1 dB. All the analytical expressions are verified by Monte-Carlo simulations confirming the advantage of multihop DF relaying networks in cognitive environments.

• ETRI Journal
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• v.36 no.3
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• pp.374-384
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• 2014

To achieve high-speed (giga-bit) connectivity for short-range wireless multimedia applications, the millimeter-wave (mmWave) wireless personal area networks with directional antennas are gaining increased interest. Due to the use of directional antennas and mmWave communications, the probability of non-interfering transmissions increases in a localized region. Network throughput can be increased immensely by the concurrent time allocation of non-interfering transmissions. The problem of finding optimum time allocation for concurrent transmissions is an NP-hard problem. In this paper, we propose two enhanced versions of previously proposed multi-hop concurrent transmission (MHCT) schemes. To increase network capacity, the proposed schemes efficiently make use of the free holes in the time-allocation map of the MHCT scheme; thus, making it more compact.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.7
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• pp.1406-1415
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• 2012

Though WiMedia supports the higher data rates than other WPAN technologies, a WiMedia device cannot reach other devices which are apart from it more than 10 meter; the limited transmission range of the WiMedia protocol. In this paper, we propose a multi-hop QoS routing protocol to enable WiMedia devices to transmit real-time data to devices that is located out of transmission range. The proposed routing protocol is a hybrid routing protocol, which is the mixed protocol of table-driven and on-demand routing algorithm. In the proposed protocol, a route for a device within 2-hop is established by using the table-driven routing algorithm and a route for the device beyond 2-hop is established by using the on-demand routing algorithm. We perform ns-2 simulation to investigate the performance of the proposed routing protocol with AODV and DSDV. The simulation results show that the proposed protocol's performance is better than AODV and DSDV in terms of the throughput and delay.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5A
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• pp.325-338
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• 2012

In this paper, a radio resource allocation scheme for a multi-hop relay transmission in cognitive radio (CR) system is proposed to support the employment of relay nodes in IEEE 802.22 standard for wireless regional area network (WRAN). An optimization problem is formulated to maximize the number of serving secondary users (SUs) under system constraints such as time-divided frame structure for multiplexing and a single resource-unit to every relay-hop. However, due to mathematical complexity, the optimization problem is solved with a sub-optimal manner instead, which takes three steps in the order of user selection, relay/path selection, and frequency selection. In the numerical analysis, this proposed solution is evaluated in terms of service rate denoting as the ratio of the number of serving SUs to the number of service-requesting SUs. Simulation results show the condition of adopting multi-hop relay and the optimum number of relaying hops by comparing with the performance of 1-hop system.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.259-259
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• 2004

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.84-84
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• 2004

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5A
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• pp.474-481
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• 2010

In this paper, we present an effective cross layer-based video transmission algorithm over multi-hop mobile ad hoc networks. The proposed algorithm selects the most efficient PHY mode of wireless LAN multi-rate service at each node in a distributed way based on the available information at application, MAC, and physical layers in order to minimize end-to-end delay and maintain packet loss rate in tolerable range at the receiver. Finally, experimental results are provided to show superior performance of the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4B
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• pp.584-591
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• 2010

In this paper, we propose an adaptive Relay Station (RS) coverage extension scheme for the Mobile Multi-hop Relay (MMR) systems. The MMR system with a non-transparent mode RS can be used to extend BS coverage using the remaining capacity of the Base Station(BS). Thus, the call blocking may occur in RSs when calls arrive very often in Multi-hop Relay Base Station (MR-BS). In the proposed scheme, RSs can be connected to the neighbor MMR system as the 2ndtier RSs if the neighbor MMR system services low traffic load when calls are frequently arrived in MR-BS or RSs. By doing so, the MMR system can accept a new call without call blocking. Through numerical results, we demonstrate that the proposed scheme outperforms the conventional MMR system in terms of the throughput and call blocking probability of MMR systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10B
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• pp.911-918
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• 2008

In this paper, we propose new cell structures using multi-hop Relay Station(RS) based on IEEE802.16j in Narrow-Beam Trisector Cell (NBTC) and Wide-Beam Trisector Cell (WBTC), which are two methods for cell sectorization using 3-sector directional antennas. Then, we analyze our proposed structures compared with the existing system which does not use any RS about the numbers of optimized Base Station (BS) and multi-hop relay, the extended BS coverage, and the deployment cost according to the traffic density using optimization model. According to the results, we know the reduction of total deployment cost of the proposed systems and that WBTC is suitable when the traffic density is high and NBTC is suitable when the traffic density is low in our proposed multi-hop based NBTC and WBTC structures.