• Journal of Communications and Networks
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• v.16 no.2
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• pp.227-237
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• 2014

Throughput scaling laws for two coexisting ad hoc networks with m primary users (PUs) and n secondary users (SUs) randomly distributed in an unit area have been widely studied. Early work showed that the secondary network performs as well as stand-alone networks, namely, the per-node throughput of the secondary networks is ${\Theta}(1/\sqrt{n{\log}n})$. In this paper, we show that by exploiting directional spectrum opportunities in secondary network, the throughput of secondary network can be improved. If the beamwidth of secondary transmitter (TX)'s main lobe is ${\delta}=o(1/{\log}n)$, SUs can achieve a per-node throughput of ${\Theta}(1/\sqrt{n{\log}n})$ for directional transmission and omni reception (DTOR), which is ${\Theta}({\log}n)$ times higher than the throughput with-out directional transmission. On the contrary, if ${\delta}={\omega}(1/{\log}n)$, the throughput gain of SUs is $2{\pi}/{\delta}$ for DTOR compared with the throughput without directional antennas. Similarly, we have derived the throughput for other cases of directional transmission. The connectivity is another critical metric to evaluate the performance of random ad hoc networks. The relation between the number of SUs n and the number of PUs m is assumed to be $n=m^{\beta}$. We show that with the HDP-VDP routing scheme, which is widely employed in the analysis of throughput scaling laws of ad hoc networks, the connectivity of a single SU can be guaranteed when ${\beta}$ > 1, and the connectivity of a single secondary path can be guaranteed when ${\beta}$ > 2. While circumventing routing can improve the connectivity of cognitive radio ad hoc network, we verify that the connectivity of a single SU as well as a single secondary path can be guaranteed when ${\beta}$ > 1. Thus, to achieve the connectivity of secondary networks, the density of SUs should be (asymptotically) bigger than that of PUs.

• Journal of information and communication convergence engineering
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• v.9 no.6
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• pp.641-646
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• 2011

In this paper, we investigate a power control problem which is very critical in underlay-based spectrum sharing systems. Although an underlay-based spectrum sharing system is more efficient compared to an overlay-based spectrum sharing system in terms of spectral utilization, some practical problems obstruct its commercialization. One of them is a real-time-based power adaptation of secondary transmitters. In the underlay-based spectrum sharing system, it is essential to adapt secondary user's transmit power to interference channel states to secure primary users' communication. Thus, we propose a practical power control scheme for secondary transmitters. The feedback overhead of our proposed scheme is insignificant because it requires one-bit signaling, while the optimal power control scheme requires the perfect information of channel states. In addition, the proposed scheme is robust to feedback delay. We compare the performance of the optimal and proposed schemes in terms of primary user's outage probability and secondary user's throughput. Our simulation results show that the proposed scheme is almost optimal in terms of both primary user's outage probability and secondary user's throughput when the secondary user's transmit power is low. As the secondary user's transmit power increases, the primary user's outage probability of the proposed scheme is degraded compared with the optimal scheme while the secondary user's throughput still approaches that of the optimal scheme. If the feedback delay is considered, however, the proposed scheme approaches the optimal scheme in terms of both the primary user's outage probability and secondary user's throughput regardless of the secondary user's transmit power.

• Journal of electromagnetic engineering and science
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• v.12 no.1
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• pp.1-7
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• 2012

In this paper, we investigated the throughput of a cognitive radio network where two primary frequency channels (PCs) are sensed and opportunistically accessed by N secondary users. The sharing sensing member (SSM) protocol is introduced to sense both PCs simultaneously. According to the SSM protocol, N SUs (Secondary User) are divided into two groups, which allows for the simultaneous sensing of two PCs. With a frame structure, after determining whether the PCs are idle or active during a sensing slot, the SUs may use the remaining time to transmit their own data. The throughput of the network is formulated as a convex optimization problem. We then evaluated an iterative algorithm to allocate the optimal sensing time, fusion rule and the number of members in each group. The computer simulation and numerical results show that the proposed optimal allocation improves the throughput of the SU under a misdetection constraint to protect the PCs. If not, its initial date of receipt shall be nullified.

• Journal of Communications and Networks
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• v.11 no.2
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• pp.175-186
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• 2009

A new medium access control (MAC) scheme embedding physical channels into multiband carrier sense multiple access/collision avoidance (CSMA/CA) networks is proposed to provide strict quality of service (QoS) guarantee to high priority users. In the proposed scheme, two priority classes of users, primary and secondary users, are supported. For primary users physical channels are provided to ensure strict QoS, whereas secondary users are provided with best-effort service using CSMA/CA modified for multiband operation. The performance of the proposed MAC scheme is investigated using a new multiband CSMA/CA Markov chain model capturing the primary user activity and the operation of secondary users in multiple bands. The throughput of secondary users is obtained as a function of the primary user activity and other CSMA/CA parameters. It is shown that the new MAC scheme yields larger throughput than the conventional single-band CSMA/CA when both schemes use the same bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11A
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• pp.892-902
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• 2011

The opportunistic spatial orthogonalization (OSO) scheme, proposed by Cong Shen and Michael P. Fitz, allows the existence of secondary users during the period in which the primary user is occupying all licensed bands. This paper introduces an active secondary user selection algorithm which mitigates the interference from the primary user transmitter to the secondary user receiver based on single-input multi-output system without altering a primary user's transmission strategy. A proposed algorithm guarantees the minimum average throughput of the primary user and overcomes the average sum throughput of a conventional OSO. We have numerically analyzed the average throughput under various constraints.

• Korean Management Science Review
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• v.28 no.3
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• pp.15-29
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• 2011

In this paper, we consider a system working at both primary service and secondary service. A server can switch between the primary service and the secondary service or it can be assigned to secondary service as a dedicated server. A service policy is characterized by the number of servers dedicated to the secondary service and a rule for switching the remaining servers between two services. The primary service system is modelled as a Markovian queueing system and the throughput is a function of the number of servers, buffer capacity, and service policy. And the secondary service system has a service level requirement strategically determined to perform the service assigned. There is a revenue obtained from throughput and costs due to servers and buffers. We study the problem of simultaneously determining the optimal total number of servers, buffers, and service policy to maximize profit of the system subject to both an expected customer waiting time constraint of the primary service and a service level constraint of the secondary service and develop an algorithm which can be successfully applied with the small number of computations.

• ETRI Journal
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• v.34 no.2
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• pp.276-279
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• 2012

In this letter, a modified 802.11-based opportunistic spectrum access is proposed for single-channel cognitive radio networks where primary users operate on a slot-by-slot basis. In our opportunistic spectrum access, control frames are used to reduce the slot-boundary impact and achieve channel reservation to improve throughput of secondary users. An absorbing Markov chain model is used to analyze the throughput of secondary users. Simulation results show that the analysis accurately predicts the saturation throughput.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.9
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• pp.3075-3093
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• 2014

In this paper, we consider an advanced wireless user, called primary-secondary user (PSU) who is capable of harvesting renewable energy and connecting to both the primary network and cognitive radio networks simultaneously. Recently, energy harvesting has received a great deal of attention from the research community and is a promising approach for maintaining long lifetime of users. On the other hand, the cognitive radio function allows the wireless user to access other primary networks in an opportunistic manner as secondary users in order to receive more throughput in the current time slot. Subsequently, in the paper we propose the channel access policy for a PSU with consideration of the energy harvesting, based on a Partially Observable Markov decision process (POMDP) in which the optimal action from the action set will be selected to maximize expected long-term throughput. The simulation results show that the proposed POMDP-based channel access scheme improves the throughput of PSU, but it requires more computations to make an action decision regarding channel access.

• Journal of KIISE
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• v.43 no.12
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• pp.1412-1419
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• 2016

In cognitive radio sensor networks (CRSNs), secondary users (SUs) can occupy licensed bands opportunistically without causing interferences to primary users (PUs). SUs perform spectrum sensing to detect the presence of PUs. Sensing time is a critical parameter for spectrum sensing that can yield a tradeoff between sensing performance and secondary throughput. In this study, we investigate new approaches for spectrum sensing by exploring the tradeoff from a) spectrum sensing for PU detection (SSPD) and b) spectrum sensing for secondary throughput (SSST). In the proposed scheme, the first sensing result of the current frame determines the dynamic performance of the second spectrum sensing. Energy constraint in CRSNs leads to maximized network energy efficiency via optimization of sensing time. Simulation results show that the proposed scheme of SSPD and SSST improves network performance in terms of energy efficiency and secondary throughput, respectively.

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