• East Asian mathematical journal
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• 제29권1호
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• pp.101-107
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• 2013

We consider a cognitive network with a primary and a secondary channel. Primary users have higher priority on the usage of the primary channel, and secondary users are allowed to opportunistically access the primary channel at times when the channel is not occupied by primary users. The secondary channel is dedicated only to secondary users. An analytical model is presented to obtain the performance of an opportunistic spectrum access using both the primary and secondary channels, and is validated by simulations.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2009년도 정보 및 제어 심포지움 논문집
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• pp.284-286
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• 2009

In this paper, we consider a cognitive radio system operating as secondary user. It uses an empty channel that is not currently used by primary users having the license to the channel. In the previous works, secondary user looks for an empty channel by choosing any channel in order or randomly and by sensing the channel to distinguish whether primary users are using. But if primary user is fixed type, we will find an empty channel faster than the mentioned channel selecting methods by using a method considering prior information about cases that primary user used the channel, since it is possible to analogize the channel access possibility of primary user according to regular time and position. Therefore, we propose a channel searching method based on the channel list for the purpose of reducing the channel searching time and improving throughput of secondary users. Firstly, we determine a weighting value of each channel based on the history of channel activities of primary users. This value is added to current channel state buffer and we search an empty channel from channel with smallest value to one with the biggest value. Finally, we compare the performances of the proposed method with those of the sequential channel searching and the random channel searching methods in terms of the average channel searching time and the average number of transmissions of secondary user.

• 전기학회논문지
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• 제60권9호
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• pp.1767-1769
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• 2011

In a CR (cognitive radio) network, channel selection is one of the important issues for the efficient channel utilization. When the CR user exploits the spectrum of primary network, the interference to the primary network should be minimized. In this paper, we propose a spectrum hole prediction based channel selection scheme to minimize the interference to the primary network. To predict spectrum hole, statistic properties of primary user's traffic is used. By using the predicted spectrum hole, channel is selected and it can reduce the possibility of interference to the primary user and increase the efficiency of spectrum utilization. The performance of proposed channel selection scheme is evaluated by the computer simulation.

• Journal of electromagnetic engineering and science
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• 제11권2호
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• pp.128-132
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• 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.

• 전기학회논문지
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• 제65권6호
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• pp.1080-1082
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• 2016

In a multi-hop CR (Cognitive Radio) network, each node find a path to destination node through several links. If links have the same frequency channel, there can be a serious interference among the links and it can reduce the network capacity. In multi-channel CR networks, each channel has different capacity according to the inter-link interference, and each channel has different traffic properties of primary users. In this paper, we propose channel scheduling scheme to minimize channel interferences and collision with primary users. Simulation results show the improvement of channel capacity and collision rate with primary users.

• 한국통신학회논문지
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• 제21권11호
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• pp.2817-2827
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• 1996

In this paper, we propose a new channel assignment scheme considering traffic characteristics in the CDMA cellular system. The object of proposed method is to reduce the hard handoff of data calls which are very sensitive to transmission errors. In this algorithm, we use three channel assignment policies. First, all of the data calls are assigned to the primary CDMA channel if possible. Second, priority for primary CDMA channel is given to data calls by assigning some primary CDMA traffic channels exclusively for data calls. Third, data calls are assigned to the CDMA channel most served by neighbor cells, when all of the primary CDMA traffic channels are used. A performance analysis shows the minimum soft handoff probability of data calls in handoff which is guarantied any cellconfiguration is increased above 40% by the adopting proposed algorithm.

• Journal of Communications and Networks
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• 제16권1호
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• pp.56-66
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• 2014

We propose a novel opportunistic access scheme for cognitive radios in an interweave cognitive system, that considers the channel gain as well as the predicted idle channel probability (primary user occupancy: Busy/idle). In contrast to previous work where a cognitive user vacates a channel only when that channel becomes busy, the proposed scheme requires the cognitive user to switch to the channel with the next highest idle probability if the current channel's gain is below a certain threshold. We derive the threshold values that maximize the long term throughput for various primary user transition probabilities and cognitive user's relative movement.

• 한국정보통신학회논문지
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• 제13권7호
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• pp.1422-1428
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• 2009

독립형 무선 인지 시스템은 보통 채널에 대한 면허를 가지는 기사용자가 사용하지 않는 빈 채널을 사용하는 2차 사용자로서 동작한다. 기존연구에서는 이와 같은 2차 사용자가 가용한 채널을 찾을 때, 순차 혹은 무작위로 채널을 선택하여 기사용자의 사용 유무를 확인하였다. 하지만 이러한 방법은 무선 채널의 특성에 맞지 않다. 그러므로 본 논문에서는 이전에 채널을 기사용자가 사용한 경우를 고려하여 가중치 값을 결정하고, 각 채널별 상태 값 중에서 작은 순서대로 채널을 선택함으로써 빈 채널을 찾는데 소요되는 시간을 줄이는 방법을 제안하고, 2차 사용자의 평균 채널 찾기 시간과 평균 전송 횟수의 관점에서 순차적, 무작위적 방법과 그 성능을 비교 분석 한다.

• Journal of Communications and Networks
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• 제16권2호
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• pp.209-216
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• 2014

Cognitive radio (CR) has been proposed to solve the spectrum utilization problem by dynamically exploiting the unused spectrum. In CR networks, a spectrum selection scheme is an important process to efficiently exploit the spectrum holes, and an efficient channel allocation scheme must be designed to minimize interference to the primary network as well as to achieve better spectrum utilization. In this paper, we propose a multichannel selection algorithm that uses spectrum hole prediction to limit the interference to the primary network and to exploit channel characteristics in order to enhance channel utilization. The proposed scheme considers both the interference length and the channel capacity to limit the interference to primary users and to enhance system performance. By using the proposed scheme, channel utilization is improved whereas the system limits the collision rate of the CR packets.

• Journal of Communications and Networks
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• 제11권2호
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• pp.104-114
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• 2009

In this paper, a technique is proposed that enables secondary users to evaluate channel availability in cognitive radio networks. Here, secondary users estimate the utilization of channels via predicting the traffic pattern of primary user, and select a proper channel for radio transmission. The proposed technique reduces the channel switching rate of secondary users (the rate of switching from one channel to another) and the interference on primary users, while maintaining a reasonable call blocking rate of secondary users.