• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.3
• /
• pp.749-761
• /
• 2014

Improving spectrum utilization efficiency is a fundamental goal of dynamic spectrum access technology. The definition of spectrum holes determines how to detect and exploit them. Current definitions of spectrum holes are ineffective in exploiting spatial-temporal spectrum holes. In this paper, a novel definition of spectrum holes is proposed, in which throughput loss indicates the impact of secondary users on primary users. The definition specifies spectrum holes, unifies the impact of secondary users on primary users and is effective exploiting spatial-temporal spectrum holes. Theoretical analysis and numerical simulations show that the new definition proposed in this paper significantly improves the spectrum utilization efficiency.

• Journal of information and communication convergence engineering
• /
• v.9 no.5
• /
• pp.515-522
• /
• 2011

In this paper, we investigate cooperative diversity in a spectrum sharing environment where secondary users utilize primary users' spectrum only if the interference power received at the primary users is maintained below a predetermined level. The outage probability of a selective decode-and-forward (DF) based cooperative diversity scheme in the secondary network is derived to analyze the effects of spectrum sharing on cooperative diversity. Our analytical and simulation results show that the outage probability is saturated at a certain level of transmit power of secondary users due to interference regulation, and, hence, cooperative diversity gains are lost. Through asymptotic analysis, we also identify the critical value of transmit SNR beyond which the outage probability is saturated.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.11
• /
• pp.3638-3654
• /
• 2014

Cognitive Radio (CR) users need to sense the environment or channel at regular time interval for sharing the spectrum band of the primary users (PUs). Once find the spectrum idle, CR users start their transmission through it. Even while transmitting, they need to continue the sensing process so that they can leave the spectrum immediately whenever find a PU wanting to use the band. Therefore, detecting PUs is one of the main functions of cognitive radio before transmission and higher the detection probability ensures better protection to the primary users. However, it is not possible to attain a high detection probability (or a low miss detection probability) and low false alarm probability simultaneously as there is a tradeoff between false alarm probability ($P_{fa}$) and the probability of detection ($P_d$). In this paper, the author has provided a comprehensive study on different sensing techniques and discussed their advantages and disadvantages. Moreover, it is expected that, with this article, readers can have a through understanding of sensing techniques in CR and the current research trends in this area.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.61 no.4
• /
• pp.629-631
• /
• 2012

In Cognitive Radio network, spectrum selection scheme is one of a important part to manage idle spectrums efficiently. However, in CR networks, they have to adopt time-varying channel availability to minimize the interference to primary users (PU), and be able to manage spectrum resources efficiently. In this paper, we proposed a modified PF scheduler which can be appropriate to schedule downlink CR users and channels, by considering the fairness and the throughput as well as the primary user characteristics of each channel.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.63 no.1
• /
• pp.34-39
• /
• 2014

In cognitive radios, secondary users can use the spectrum exclusively allocated to a primary wireless system if the secondary users detect the spectrum in idle states. Because the secondary users can utilize the idle state of the spectrum, the utilization rate of the spectrum can be improved. The idle states can be detected by using secondary users' sensing schemes. However, the wireless channel environment where secondary users perform the spectrum sensing is not very friendly to secondary users because the signal-to-noise ratio of the received primary signal is very low. Hence, cooperative sensing scheme where more than one secondary user take part in the spectrum sensing is generally used in cognitive radios. In this paper, we investigate the cooperative sensing performance for machine-to-machine communication devices operated by batteries with limited energy. In general, the energy consumed for the spectrum sensing increases as the length of the sensing period and the number of cooperative sensing nodes. Accordingly, even though the total amount of the consumed energy is the same, an energy allocation methodology how to distribute the energy to the sensing period and sensing nodes can achieve the optimum sensing performance, which is numerically analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.2A
• /
• pp.124-131
• /
• 2009

Cognitive radio has been proposed to mitigate the spectrum scarcity problem by allowing the secondary users to access the under-utilized frequency bands and opportunistically transmit. Spectrum sensing, as a key technology in cognitive radio, is required to reliably detect the presence of primary users to avoid the harmful interference. However, it would be very hard to reliably detect the presence of primary users due to the channel fading, shadowing. In this paper, we proposed a distributed cooperative spectrum sensing scheme based on conventional DF (decode-and-forward) cooperative diversity protocol. We fist consider the cooperation between two secondary users to illustrate that cooperation among secondary users can obviously increase the detection performance. We then compare the performance of DF based scheme with another conventional AF (amplify-and-forward) protocol based scheme. And it is found that the proposed scheme based on DF has a better detection performance than the one based on AF. After that, we extend the number of cooperative secondary users, and demonstrate that increasing the cooperation number can significantly improve the detection performance.

• Journal of electromagnetic engineering and science
• /
• v.11 no.2
• /
• pp.128-132
• /
• 2011

In interference tolerance based spectrum sharing systems, primary receivers (PRs) are protected by a predefined peak or average interference power constraint. To implement such systems, cognitive radio (CR) transmitters are required to adjust their transmit power so that the interference power received at the PR receivers is kept below the threshold value. Hence, a CR-transmitter requires knowledge of its channel and the primary receiver in order to allocate the transmit power. In practice, it is impossible or very difficult for a CR transmitter to have perfect knowledge of this channel state information (CSI). In this paper, we investigate the impact of imperfect knowledge of this CSI on the performances of both a primary and cognitive radio network. For fixed transmit power, average interference power (AIP) constraint can be maintained through knowledge of the channel distribution information. To maintain the peak interference power (PIP) constraint, on the other hand, the CR-transmitter requires the instantaneous CSI of its channel with the primary receiver. First, we show that, compared to the PIP constraint with perfect CSI, the AIP constraint is advantageous for primary users but not for CR users. Then, we consider a PIP constraint with imperfect CSI at the CR-transmitter. We show that inaccuracy in CSI reduces the interference at the PR-receivers that is caused by the CR-transmitter. Consequently the proposed schemes improve the capacity of the primary links. Contrarily, the capacities of the CR links significantly degrade due to the inaccuracy in CSI.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.11C
• /
• pp.1119-1126
• /
• 2007

In this paper, we examine the scheme that the CR (Cognitive Radio) user can coexist with primary user with obeying the concept of interference temperature proposed by FCC. Regarding to the capability of classifying the signals of primary user after the spectrum sensing, the interference temperature model can be discriminated by the ideal and generalized ones. And then, about each model, it can optimize the bandwidth and transmit power with satisfying predetermined capacity of CR user. Especially, it has been considered to allocate to CR user not to interfere to primary users for proper coexistence in conventional interference temperature multiple access technique, proposed by T. Clancy, but this paper proposes the scheme that considering QoS of not only primary users, but also CR user. The hill-climbing algorithm is employed to produce the bandwidth and transmit power subject to satisfying the required capacity.

• Journal of Korean Society for Geospatial Information Science
• /
• v.23 no.3
• /
• pp.49-55
• /
• 2015

Current medical delivery system in Korea has been distinguished into three types; primary medical facilities, secondary facilities, and tertiary facilities since 1989. This system prevents the waste of medical resources along with the maintenance of balance according to the medical treatment subjects. However, it is inevitable that the imbalance of the medical services among regions has been generated due to the concentration of the medical facilities on large cities. In this regard, this study attempted to evaluate the quality of the primary medical services, emphasizing accessibility and convenience targeting Jinju city, a small and medium-sized city, based on the distribution characteristics of the space. The study results show that cohesion index about the spatial distribution of the primary care facilities was 0~0.25. It conducted a correlation analysis between the location of the hospitals and users, based on the study results. Finally, it is demonstrated the correlation between the location of the hospitals and users tended to be low, while, the cohesion of the Oriental medicine clinics was high in other treatment subjects, and the accessibility to the Oriental medicine clinics was the highest because most Oriental medicine clinics were distributed to the places where users were many. However, on account that the locations of the medical facilities and users were varied in other treatment subjects except for the Oriental medicine clinics, problems were generated in terms of the accessibility. Therefore, it is judged that the preparation of the measures to improve the selection of lots in consideration of users, who use the primary medical services, is required.

• Journal of Broadcast Engineering
• /
• v.21 no.1
• /
• pp.113-116
• /
• 2016

Cognitive radio network technology is that secondary (unlicensed) users use the spectrum of primary (licensed) users without interfering primary communication. In this paper, we propose multiple access scheme for a cognitive radio network, where multiple secondary users access spectrum of one primary user. We consider two types of multiple access scheme, one is p-persistent and one is non-persistent, and apply these two schemes in the secondary network. For each multiple access scheme, total throughput of secondary network is derived and verified by Monte Carlo simulation. Simulation results show that maximum total throughput of the secondary network is achieved when channel access probability or the number of maximum waiting frames is chosen appropriately.