• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.86-89
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• 2002

Recently, video conferencing, Web-casting service, and network sane service which use multicast-based service are popular in Internet. In order to support the broadband Internet services efficiently, more communication bandwidth are needed. The WDM single-hop broadcast network topology is coming into the spotlight in next-generation access networks area. In this paper, the new multicast scheduling algorithm, PGM, is proposed and is evaluated through the computer simulation. The PGM method shows the better performance comparing with existing multicast scheduling algorithm.

• ETRI Journal
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• v.36 no.6
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• pp.960-967
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• 2014

In this paper, an analytical framework is proposed for the optimization of network performance through joint congestion control, channel allocation, rate allocation, power control, scheduling, and routing with the consideration of fairness in multi-channel wireless multihop networks. More specifically, the framework models the network by a generalized network utility maximization (NUM) problem under an elastic link data rate and power constraints. Using the dual decomposition technique, the NUM problem is decomposed into four subproblems - flow control; next-hop routing; rate allocation and scheduling; power control; and channel allocation - and finally solved by a low-complexity distributed method. Simulation results show that the proposed distributed algorithm significantly improves the network throughput and energy efficiency compared with previous algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.5
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• pp.753-775
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• 2010

Greedy forwarding is a key mechanism of geographic routing using distance as a metric. As greedy forwarding only uses 1-hop neighbor node information, it minimizes routing overhead and is highly scalable. In existing greedy forwarding schemes, a node selects a next forwarding node based only on the distance. However, the signal strength in a realistic environment reduces exponentially depending on the distance, so that by considering only the distance, it may cause a large number of data packet retransmissions. To solve this problem, many greedy forwarding schemes have been proposed. However, they do not consider the unreliable and asymmetric characteristics of wireless links and thus cause the waste of limited battery resources due to the data packet retransmissions. In this paper, we propose a reliable and energy-efficient opportunistic greedy forwarding scheme for unreliable and asymmetric links (GF-UAL). In order to further improve the energy efficiency, GF-UAL opportunistically uses the path that is expected to have the minimum energy consumption among the 1-hop and 2-hop forwarding paths within the radio range. Comprehensive simulation results show that the packet delivery rate and energy efficiency increase up to about 17% and 18%, respectively, compared with the ones in PRR${\times}$Distance greedy forwarding.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.4
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• pp.17-22
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• 2013

In this paper, we propose a multi-hop cooperative transmission protocol over Rayleigh fading channels. In the proposed protocol, the multi-hop cooperative transmission is used to improve the system performance. Due to broadcast nature, we do not limit the receiving node to be only the next node, but the destination and all the nodes between the transmitting node and the destination. The proposed protocol can hence save the average transmit power, compared with multi-hop direct transmission protocol due to the skipped transmissions from some intermediate nodes or chosen relays. The proposed scheme is implemented and evaluated in mobile ad-hoc wireless networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.12-17
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• 2009

We consider an OFDM based multiple AF relaying systems. Since the channel between first hop (source station-relay station) and second hop (relay station -destination station) varies independently, the subcarrier in the first hop can be paired to another subcarrier in the second hop for the increase of the system capacity. The conventional pairing which uses the brute force searching requires large complexity while giving optimal pairing for maximum system capacity. In this paper, we present sub-optimal subcarrier pairing scheme with low complexity. Every RS firstly pairs the subcarrier with the highest channel gain in the first hop to the subcarrier with highest channel gain in the second hop. The pair with the highest SNR among all the pairs is determined as final selected pair and the corresponding subcarriers are not selected at other RSs in the next paring iteration. This process is repeated until all the subcarriers are paired. Simulation results show the proposed pairing scheme achieves near optimal performance with low complexity.

• The Journal of Korean Institute of Next Generation Computing
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• v.13 no.5
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• pp.51-70
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• 2017

The reliability of broadcasting over vehicular ad hoc networks (VANETs) is one of the most critical factors for driving safety applications. There exists limitations to improve the reliability of broadcast transmissions in saturated VANETs where previous proposals in literature tackle the problem by heuristically adapting the size of the contention window (CW). This paper considers improving the reliability by proposing a new probability model based on the counting methods of permutations and combinations, which counts all the possible cases of broadcast failures in a single-hop broadcast transmission for a given CW. From the model, we calculate the best CW size given the number of contention nodes, which significantly improves the reliability and satisfying the timely dissemination of emergency broadcasting messages. Through extensive VANET simulations with varying densities, we show that our model maintains near 100 percent success rate for single-hop broadcast as well as multi-hop broadcast (e.g. 40 hops) and achieves minimal broadcast delay.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5B
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• pp.539-548
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• 2011

We propose an efficient cooperative ARQ (Automatic Repeat reQuest) scheme for single-hop and multi-hop underwater acoustic communications, in which cooperative nodes are used to provide more reliable alternative paths for a specific source-to-destination connection. This alternative path has higher channel quality than that of the direct source-destination path. In addition, during a packet-relay through multiple hops, the typical acknowledgement (ACK) signal is replaced with overhearing data packet returned back from the next hop. The usage of overhearing as an ACK improves the system performance. In this paper, we evaluate the proposed scheme by comparing it with a conventional S&W ARQ in terms of throughput efficiency. Computer simulation results show that the proposed cooperative retransmission scheme can significantly improve the throughput by increasing the probability of successful retransmission.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.2
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• pp.189-197
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• 2016

Mobile ad-hoc networks (MANETs) experience frequent link disconnections due to non-uniform node distribution and mobility. Thus, end-to-end path establishment-based routing protocols cause frequent transmission failures in MANETs, resulting in heavy control messages for path reestablishment. While location-based MANET routing protocols, such as Greedy Perimeter Stateless Routing (GPSR), use location information to forward messages in a hop-by-hop routing fashion without an end-to-end path establishment procedure, such protocols encounter communication void problems when message forwarding to the next hop fails due to the absence of a relay node. Therefore, to solve this problem, this paper proposes a Delay Tolerant-GPSR (DT-GPSR) protocol, which combines Delay Tolerant Networking (DTN) technology with the GPSR protocol. The performance of DT-GPSR is compared with the performances of the original GPSR and PRoPHET routing protocols through simulation using NS-2. The simulation results confirm that DT-GPSR outperforms GPSR and PRoPHET in terms of the message delivery ratio and message delivery delay.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.10
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• pp.977-985
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• 2012

Recently, many countries have been developing new protocols to improve the performance of tactical ad hoc networks for implementing NCW (Network Centric Warfare). Combat net radio (CNR) networks are the most important communication infra for the ground forces such as infantry of Army. U.S. Army had developed MIL-STD-188-220D that is the Interoperability Standard for DMTDs (Digital Messages Transfer Device Subsystems) for voice and data communication in CNR. MIL-STD-188-220D is a candidate for MAC protocol of TMMR which is next radio and has a few constraints to used in TMMR. NAD (Network Access Delay) defined in MIL-STD-188-220D needs time synchronization to avoid collision. However, it is difficult for time synchronization to fit in multi-hop environment. We suggest the enhanced DAP (Deterministic Adaptable Priority)-NAD to prevent conflicts and decrease delays in multi-hop CNR. Simulation results show that the proposed scheme improves the performance in multi-hop CNR networks.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.7
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• pp.743-747
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• 2008

Hierarchical overlay of heterogeneous wireless cells is considered as a promising architecture for next-generation wireless networks. This paper considers a special form of such architecture, WWAN/WLAN two-hop wireless relay networks. We first describe an undesirable scheduling phenomenon that the conventional proportional fair algorithm can cause in such networks. We, then, propose an enhanced proportional fair scheduling to remedy this problem. We demonstrate the performance of the proposed scheme via a simulation of UMTS/WLAN networks using NS-2.