• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.49 no.8
• /
• pp.19-24
• /
• 2012

In this paper, we analyze the maximum throughput of opportunistic routing along a long-haul multi-hop wireless network path for a single data stream, while considering link-level interference among the network nodes. Surprisingly, we find out that opportunistic routing does not provide much improvement in throughput for long-haul paths. The results of this research show that when we compare the extra cost for the complex implementation of the opportunistic routing scheme to the performance improvement obtained from it, opportunistic routing scheme needs to be applied to only short-haul multi-hop wireless network paths.

• Journal of Preventive Medicine and Public Health
• /
• v.42 no.3
• /
• pp.177-182
• /
• 2009

Objectives : Both organized and opportunistic screening programs have been widely used in Korea. This paper examined the determinants of the use of opportunistic screening programs in Korea. Methods : The subjects were a national stratified random sample of 10,254 people aged 45 or older from the first wave of the Korean Longitudinal Study of Ageing in 2006. A logit model was used to examine the determinants of the use of opportunistic screening programs in terms of the demographic and socioeconomic characteristics, the type of health insurance and the health status. Results : Thirteen point seven percent of the individuals received opportunistic screening programs within 2 years from the time the survey was conducted in 2006. The individuals who graduated from college or who had even more education were 3.0 times more likely to use opportunistic screening programs compared with the individuals who were illiterate. The individuals who resided in urban areas and who had religious beliefs were more likely to receive opportunistic screening programs compared with their counterparts. Those who were in the first quartile for the total household assets were 2.6 times more likely to use opportunistic screening programs than those who were in the fourth quartile for the total household assets. Privately insured people were 1.6 times more likely to use opportunistic screening programs than those who were not insured. Finally, the individuals who self-assessed their health status as worst were 2.1 times more likely to use opportunistic screening programs compared individuals who self-assessed their health status as best. Conclusions : This study suggests that opportunistic screening programs can be an indicator for whether or not an individual is among the advantaged group in terms of their socioeconomic characteristics and type of health insurance.

• Journal of Information Processing Systems
• /
• v.13 no.3
• /
• pp.630-642
• /
• 2017

In this paper, we propose the opportunistic non-orthogonal multiple access (NOMA)-based cooperative relaying system (CRS) with channel state information (CSI) available at the source, where CSI for the source-to-destination and source-to-relay links is used for opportunistic transmission. Using the CSI, for opportunistic transmission, the source instantaneously chooses between the direct transmission and the cooperative NOMA transmission. We provide an asymptotic expression for the average achievable rate of the opportunistic NOMA-based CRS under Rayleigh fading channels. We verify the asymptotic analysis through Monte Carlo simulations, and compare the average achievable rates of the opportunistic NOMA-based CRS and the conventional one for various channel powers and power allocation coefficients used for NOMA.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.8 no.4
• /
• pp.25-33
• /
• 2008

The performance of power constrained cooperative multi-relay system with/without opportunistic transmission is considered in Rayleigh fading. The three power allocation methods are considered to maximize the system performance when the total network power is limited. It is analyzed that the opportunistic power allocation strategy has the best performance enhancement compared to the other power allocation strategies. The opportunistic relays increases with the total network power, which induce the higher diversity order of the opportunistic cooperative diversity, consequently improves the end-to-end outage probability.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.10 no.5
• /
• pp.2029-2046
• /
• 2016

Energy consumption is an important index in mobile ad hoc networks. Data packet transmission increases among nodes, particularly in big data communication. However, nodes may be unable to transmit data packets because of energy over-consumption. Consequently, information may be lost and network communication may block. While opportunistic network is a kind of mobile ad hoc networks, researchers do not focus on energy consumption in opportunistic network communication. This study proposed an effective sensor energy supply scheme that can be applied in opportunistic networks. This scheme considers nodes sensor requests and communication model. In this scheme, nodes do not only accomplish energy supply in communication, but also extend communication time in opportunistic networks. Compared with the Spray and Wait algorithm and the Binary Spray and Wait algorithm in simulations, the proposed scheme extends communication time, increases data packet transmission, and accomplishes energy supply among nodes.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.2A
• /
• pp.191-197
• /
• 2008

For the efficient transmission of burst data in the time varying wireless channel, opportunistic scheduling is one of the important techniques to maximize multiuser diversity gain. In this paper, we propose a distributed opportunistic scheduling scheme for wireless LAN network. A proportional fair scheduling, which is one of the opportunistic scheduling schemes, is used for centralized networks, whereas we design distributed proportional fair scheduling (DPFS) scheme and medium access control with distributed manner. In the proposed DPFS scheme, each receiver estimates channel condition and calculates independently its own priority with probabilistic manner, which can reduce excessive probing overhead required to gather the channel conditions of all receivers. We evaluate the proposed DPFS using extensive simulation and simulation results show that DPFS obtains higher network throughput than conventional scheduling schemes and has a flexibility to control the fairness and throughput by controlling the system parameter.

• Journal of information and communication convergence engineering
• /
• v.12 no.3
• /
• pp.135-139
• /
• 2014

Opportunistic routing was originally introduced in various multihop network environments to reduce the number of hops in such a way that, among the relays that decode the transmitted packet for the current hop, the one that is closest to the destination becomes the transmitter for the next hop. Unlike the conventional opportunistic routing case where there is a single active S-D pair, for an ad hoc network in the presence of fading, we investigate the performance of parallel opportunistic multihop routing that is simultaneously performed by many source-destination (S-D) pairs to maximize the opportunistic gain, thereby enabling us to obtain a logarithmic gain. We first analyze a cut-set upper bound on the throughput scaling law of the network. Second, computer simulations are performed to verify the performance of the existing opportunistic routing for finite network conditions and to show trends consistent with the analytical predictions in the scaling law. More specifically, we evaluate both power and delay with respect to the number of active S-D pairs and then, numerically show a net improvement in terms of the power-delay trade-off over the conventional multihop routing that does not consider the randomness of fading.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37B no.10
• /
• pp.929-937
• /
• 2012

In this paper, we introduce three types of opportunistic interference management strategies in multi-cell uplink networks with time-invariant channel coefficients. First, we propose two types of opportunistic interference mitigation techniques, where each base station (BS) opportunistically selects a set of users who generate the minimum interference to the other BSs, and then their performance is analyzed in terms of degrees-of-freedom (DoF). Second, we propose a distributed opportunistic scheduling, where each BS opportunistically select a user using a scheduler designed based on two threshold, and then its performance is analyzed in terms of throughput scaling law. Finally, numerical evaluation is performed to verify our result.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.1A
• /
• pp.76-83
• /
• 2009

In this paper, we provide opportunistic scheduling schemes for elastic services in OFDMA systems with fairness constraints for each user. We adopt the network utility maximization framework in which a utility function is defined for each user to represent its level of satisfaction to the service. Since we consider elastic services whose degree of satisfaction depends on its average data rate, we define the utility function of each user as a function of its average data rate. In addition, for fair resource allocation among users, we define fairness requirements of each user by using utility functions. We first formulate an optimization problem for each fairness requirement that aim at maximizing network utility, which is defined as the sum of utilities of users. We then develop an opportunistic scheduling scheme for each fairness requirement by solving the problem using a dual approach and a stochastic sub-gradient algorithm.

• Journal of Communications and Networks
• /
• v.11 no.2
• /
• pp.187-195
• /
• 2009

The application of mathematical analysis to the study of wireless ad hoc networks has met with limited success due to the complexity of mobility, traffic models and the dynamic topology. A scenario based universal mobile telecommunications system (UMTS) time division duplex (TDD) opportunistic cellular system with an ad hoc behaviour that operates over UMTS frequency division duplex (FDD) licensed cellular network is considered. In this paper, we present a new routing metric which overall improves system performance in terms of interference and routing which operate in an ad hoc network in an opportunistic manner. Therefore we develop a simulation tool that addresses the goal of analysis and assessment of UMTS TDD opportunistic radio system with ad hoc behavior in coexistence with a UMTS FDD primary cellular networks.