• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권6호
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• pp.3029-3045
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• 2017

The main processes of a cognitive radio system include spectrum sensing, spectrum decision, spectrum sharing, and spectrum conversion. Experimental results show that these stages introduce a time delay that affects the spectrum sensing accuracy, reducing its efficiency. To reduce the time delay, the frequency spectrum prediction was proposed to alleviate the burden on the spectrum sensing. In this paper, the deep recurrent neural network (DRNN) was proposed to predict the spectrum of multiple time slots, since the existing methods only predict the spectrum of one time slot. The continuous state of a channel is divided into a many time slots, forming a time series of the channel state. Since there are more hidden layers in the DRNN than in the RNN, the DRNN has fading memory in its bottom layer as well as in the past input. In addition, the extended Kalman filter was used to train the DRNN, which overcomes the problem of slow convergence and the vanishing gradient of the gradient descent method. The spectrum prediction based on the DRNN was verified with a WiFi signal, and the error of the prediction was analyzed. The simulation results proved that the multiple slot spectrum prediction improved the spectrum efficiency and reduced the energy consumption of spectrum sensing.

• 한국전자파학회논문지
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• 제26권3호
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• pp.305-310
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• 2015

본 논문에서는 RF단에서의 프로세싱에 의한 무선 스펙트럼 인지 시스템을 제안하였다. 기존의 Cognitive Radio 시스템이 신호의 하향 변환과 복조의 과정을 거쳐 수신된 신호를 분석함에 의해 스펙트럼과 신호를 인지하는데 반해, 제안된 시스템은 RF 단 프로세싱에 의한 신호 수신 및 검출에 의한 센싱 방법을 제안하였다. 이를 위해 제안된 수신기는 초재생(super-regeneration) 회로 방식으로 설계되었으며, FDM에 활용할 수 있는 채널 선택성과 채널 가변성을 갖도록 하여 기존 초재생 회로가 단일 채널로만 사용이 가능하였던 한계를 극복하였다. 제작된 제안 시스템은 퀸칭(quenching) 신호를 이용한 채널 할당 최적화를 위한 설계를 수행하였으며, 실험결과 5 MHz의 채널 간격에 대한 채널 선택성을 검증하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권7호
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• pp.1777-1791
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• 2012

This paper considers a downlink cognitive radio (CR) network where one secondary user (SU) and one primary user (PU) share the same base station (BS). The spectrum of interest is divided into a set of independent, orthogonal subchannels. The communication of the PU is of high priority and the quality of service (QoS) is guaranteed by the minimum rate constraint. On the other hand, the communication of the SU is of low priority and the SU opportunistically accesses the subchannels that were previously discarded by the PU during power allocation. The BS assigns fractions ?? and 1 ?? of the total available transmit power to the PU and the SU respectively. Two power allocation schemes with opportunistic subchannel access are proposed, in which the optimal values of ??'s are also obtained. The objective of one scheme is to maximize the rate of the SU, and the objective of the other scheme is to maximize the sum rate of the SU and the PU, both under the PU minimum rate constraint and the total transmit power constraint. Extensive simulation results are obtained to verify the effectiveness of the proposed schemes.

• IEIE Transactions on Smart Processing and Computing
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• 제3권4호
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• pp.181-190
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• 2014

This paper reports a cognitive radio network architecture based on overloaded multicarrier direct sequence code division multiple access (O-MC-DS-CDMA). The O-MC-DSCDMA technique combines CDMA with a multicarrier modulation technique to overcome the channel fading effects. In this technique, secondary users are enabled to share the available bandwidth with the existing primary users. Two sets of orthogonal Gold codes are used to support the primary and secondary users simultaneously. The orthogonality between the spreading codes is lost due to the non-zero cross correlation between the codes and the timing synchronization error in the uplink transmission, which causes interference between primary and secondary users. This paper proposes two modified hybrid parallel/successive interference cancellation techniques for primary and secondary user base station receivers with multiple antennas to suppress the interference among users. Interference among the same group of users is cancelled by parallel interference cancellation and the interference among groups is cancelled using successive interference cancellation. The simulation results confirmed that the proposed modified interference cancellation techniques show better BER performance over conventional interference cancellation techniques.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.123-145
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• 2017

Due to the increasing demand for spectrum resources, cognitive radio networks and dynamic spectrum access draw a lot of research into efficiently utilizing limited spectrum resources. To set up cluster-based CR ad-hoc common channels, conventional methods require a relatively long time to successfully exchange the initialization messages. In this paper, we propose a fast and reliable common channel initialization protocol for CR ad-hoc networks. In the proposed method, the cluster head sequentially broadcasts a system activation signal through its available channels with a predetermined correlation pattern. To detect the cluster head's broadcasting channels and to join the cluster, each member node implements fast Fourier transform (FFT) and computes autocorrelation of an FFT bin sequence for each available channel of the member node. This is compared to the predetermined reference pattern. The join request and channel decision procedures are also presented in this paper. In a simulation study, the performance of the proposed method is evaluated.

• ETRI Journal
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• 제40권5호
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• pp.613-623
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• 2018

The instability of operational channels on cognitive radio networks (CRNs), which is due to the stochastic behavior of primary users (PUs), has increased the complexity of the design of the optimal routing criterion (ORC) in CRNs. The exploitation of available opportunities in CRNs, such as the channel diversity, as well as alternative routes provided by the intermediate nodes belonging to routes (internal backup routes) in the route-cost (or weight) determination, complicate the ORC design. In this paper, to cover the channel diversity, the CRN is modeled as a multigraph in which the weight of each edge is determined according to the behavior of PU senders and the protection of PU receivers. Then, an ORC for CRNs, which is referred to as the stability probability of communication between the source node and the destination node (SPC_SD), is proposed. SPC_SD, which is based on the obtained model, internal backup routes, and probability theory, calculates the precise probability of communication stability between the source and destination. The performance evaluation is conducted using simulations, and the results show that the end-to-end performance improved significantly.

• 한국인터넷방송통신학회논문지
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• 제10권3호
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• pp.167-172
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• 2010

본 논문은 ATSC DTV (advanced television system committee digital television) 신호를 검출하기 위해 고속 퓨리에 변환 (FFT : fast Fourier transform) 기반의 파일럿 신호를 검출하는 알고리즘의 성능을 파라미터를 변화시켜가면서 분석하였다. DTV 신호를 검출하기 위한 요구사항을 분석하였으며, 센싱 회수 및 시간에 따라서 성능을 비교하였다. 실험 결과 센싱 횟수가 증가할수록 신호 검출 성능이 향상되는 것을 확인할 수 있었다. 본 논문의 결과는 DTV 주파수 대역의 인지 라디오 (CR : cognitive radio) 시스템을 구현하는데 참고자료로 활용될 수 있다.

• 한국정보전자통신기술학회논문지
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• 제3권4호
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• pp.49-69
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• 2010

이 논문에서는 수신 다양성을 쓰는 인지 무선통신에 알맞은 새로운 주파수 검출 기법을 제안한다. 제안한 기법은 일반화된 비슷함비 검정 검파기와 비선형 다양성 결합 기법을 바탕으로 둔 바, 충격성 환경에서도 주파수 검출 성능이 꽤 뛰어나다. 제안한 주파수 검출 기법이 이제껏 널리 쓰이던 주파수 검출 기법들보다 검출 성능이 안정적이며 특히 충격성 환경에서 성능이 뛰어나다는 것을 이론적인 분석과 모의실험으로 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권1호
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• pp.58-78
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• 2016

Compressed sensing (CS) possesses the potential benefits for spectrum sensing of wideband signal in cognitive radio. The sparsity of signal in frequency domain denotes the number of occupied channels for spectrum sensing. This paper presents a scheme of adaptively adjusting the number of compressed measurements to reduce the unnecessary computational complexity when priori information about the sparsity of signal cannot be acquired. Firstly, a method of sparsity estimation is introduced because the sparsity of signal is not available in some cognitive radio environments, and the relationship between the amount of used data and estimation accuracy is discussed. Then the SNR of the compressed signal is derived in the closed form. Based on the SNR of the compressed signal and estimated sparsity, an adaptive algorithm of adjusting the number of compressed measurements is proposed. Finally, some simulations are performed, and the results illustrate that the simulations agree with theoretical analysis, which prove the effectiveness of the proposed adaptive adjusting of compressed measurements.

• Journal of Communications and Networks
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• 제15권5호
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• pp.486-495
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• 2013

In this article, we suggest a two-dimensional genetic algorithm (GA) method that applies a cognitive radio (CR) decision engine which determines the optimal transmission parameters for multicarrier communication systems. Because a CR is capable of sensing the previous environmental communication information, CR decision engine plays the role of optimizing the individual transmission parameters. In order to obtain the allowable transmission power of multicarrier based CR system demands interference analysis a priori, for the sake of efficient optimization, a two-dimensionalGA structure is proposed in this paper which enhances the computational complexity. Combined with the fitness objective evaluation standard, we focus on two multi-objective optimization methods: The conventional GA applied with the multi-objective fitness approach and the non-dominated sorting GA with Pareto-optimal sorting fronts. After comparing the convergence performance of these algorithms, the transmission power of each subcarrier is proposed as non-interference emission with its optimal values in multicarrier based CR system.