• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.11
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• pp.937-942
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• 2012

In cognitive radio (CR) systems, the secondary user (SU) performs the spectrum sensing to determine the presence of the primary user (PU) on the PU's frequency band. In practical cases, the PU would arrive and depart randomly in the sensing duration of the SU, which is referred to as the high traffic circumstance. In this paper, we propose a cyclostationarity-based spectrum sensing scheme for CR systems in high traffic circumstances. From numerical results, it is confirmed that the proposed scheme outperforms both the energy detector proposed for high traffic circumstances and the conventional cyclostationarity-based spectrum sensing scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7C
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• pp.459-466
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• 2011

This paper addresses the problem in the acquisition of binary offset carrier (BOC) signals employed in global navigation satellite systems, which is caused by the multiple side-peaks of the BOC autocorrelation function. We first observe that the side-peaks arise due to the fact that the BOC autocorrelation is made up of the sum of the sub-correlations shaped irregularly, and then, propose a novel acquisition scheme based on a recombination of the sub-correlations with cyclostationarity. The proposed scheme is demonstrated to remove the side-peaks completely for any type of BOC signal and to provide a performance improvement over the conventional schemes in terms of the mean acquisition time.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1998.11a
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• pp.420-423
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• 1998

최근 이동 통신이나 위성통신과 같은 많은 디지털 통신 시스템에서 시스템의 용량을 증가시키고 인접 채널간 간섭을 줄이기 위해 많은 연구가 진행되고 있으며, 그 중에서 어레이 빔 형성 기법에 대한 연구가 활발하게 진행되고 있다. 이에 본 논문에서는 원하는 신호의 입사방향을 모르더라도 정상 동작이 가능한 블라인드 빔 형성 기법 중에서 신호의 cyclostationarity를 이용한 방법을 사용하여 원하는 사용자 신호의 cyclic 주파수만큼 천이된 신호와 수신신호 사이의 상호상관 행렬을 구하고 이를 이용하여 계수벡터를 구하는 알고리즘을 제시한다.

• Journal of Communications and Networks
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• v.17 no.1
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• pp.1-11
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• 2015

In this paper, the transmission of an improper-complex second-order stationary data sequence is considered over a strictly band-limited frequency-selective channel. It is assumed that the transmitter employs linear modulation and that the channel output is corrupted by additive proper-complex cyclostationary noise. Under the average transmit power constraint, the problem of minimizing the mean-squared error at the output of a widely linear receiver is formulated in the time domain to find the optimal transmit and receive waveforms. The optimization problem is converted into a frequency-domain problem by using the vectorized Fourier transform technique and put into the form of a double minimization. First, the widely linear receiver is optimized that requires, unlike the linear receiver design with only one waveform, the design of two receive waveforms. Then, the optimal transmit waveform for the linear modulator is derived by introducing the notion of the impropriety frequency function of a discrete-time random process and by performing a line search combined with an iterative algorithm. The optimal solution shows that both the periodic spectral correlation due to the cyclostationarity and the symmetric spectral correlation about the origin due to the impropriety are well exploited.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7C
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• pp.672-679
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• 2006

Cognitive radio, which is designed to dynamically adapt its transmission to the environments, is believed to be one of the fundamental techniques for future spectrum utilization. As the first step of cognitive radio, spectrum sensing is treated as the most important technique, through which cognition is well explained. In this paper, we propose a spectral correlation based detection method for spectrum sensing. An unlicensed secondary user system operating in TV broadcast bands is taken as an example. Based on the cyclostationarity of communication signals, spectral correlation function is used to minimize the effect of random noise and interference. Energy measurement and peak detection based criteria are proposed. Simulation results show that the proposed detection method outperforms the energy detection and is more suitable for spectrum sensing in cognitive radios.

• Journal of Communications and Networks
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• v.16 no.6
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• pp.600-612
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• 2014

In this paper, we consider the problem of spectrum sensing for advanced television systems committee (ATSC) digital television (DTV) signal detection. To exploit the cyclostationarity of the ATSC DTV signals, we employ spectral correlation density (SCD) as the decision statistic and propose an optimal detection algorithm. The major difficulty is in obtaining the probability distribution functions of the SCD. To overcome the difficulty, we probabilistically model the pilot frequency location and employ Gaussian approximation for the SCD distribution. Then, we obtain a practically implementable detection algorithm that outperforms the industry leading systems by 2-3 dB. We also propose various techniques that greatly reduce the system complexity with performance degradation by only a few tenths of decibels. Finally, we show how robust the system is to the estimation errors of the noise power spectral density level and the probability distribution of the pilot frequency location.

• Journal of Communications and Networks
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• v.15 no.3
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• pp.245-251
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• 2013

This paper addresses the issue of time-difference-of-arrival (TDOA) estimation for complex noncircular signals. First, under the wide-sense stationary assumption, we derive the maximum likelihood (ML) estimator and the Cramer-Rao lower bound for Gaussian noncircular signals in Gaussian circular noise. The ML estimator uses the second-order statistics information of a noncircular signal more comprehensively when compared with the cross-correlation (CC) and the conjugate CC estimators. Further, we present a scheme to modify the traditional signal-selective TDOA methods for noncircular signals on the basis of the cyclostationarity of man-made signals. This scheme simultaneously exploits the information contained in both the cyclic cross-correlation (CCC) and the conjugate CCC of a noncircular signal.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.8
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• pp.2763-2782
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• 2014

In this paper, a generalized likelihood ratio test (GLRT) is proposed for cyclostationary multi-antenna spectrum sensing in cognitive radio systems, which takes into account the cyclic autocorrelations obtained from all the receiver antennas and the cyclic cross-correlations obtained from all pairs of receiver antennas. The proposed GLRT employs a different hypotheses problem formulation and a different asymptotic covariance estimation method, which are proved to be more suitable for multi-antenna systems than those employed by the $Dandawat{\acute{e}}$-Giannakis algorithm. Moreover, we derive the asymptotic distributions of the proposed test statistics, and prove the constant false alarm rate property of the proposed algorithm. Extensive simulations are conducted, showing that the proposed GLRT can achieve better detection performance than the $Dandawat{\acute{e}}$-Giannakis algorithm and its extension for multi-antenna cases.

• Journal of Communications and Networks
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• v.16 no.2
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• pp.162-171
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• 2014

Spectrum sensing is a key technical challenge for cognitive radio (CR). It is well known that multicycle cyclostationarity (MC) detection is a powerful method for spectrum sensing. However, a conventional MC detector is difficult to implement because of its high computational complexity. This paper considers reducing computational complexity by simplifying the test statistic of a conventional MC detector. On the basis of this simplification process, an improved MC detector is proposed. Compared with the conventional detector, the proposed detector has low-computational complexity and high-accuracy sensing performance. Subsequently, the sensing performance is further investigated for the cases of Rayleigh, Nakagami-m, Rician, and Rayleigh fading and lognormal shadowing channels. Furthermore, square-law combining (SLC) is introduced to improve the detection capability in fading and shadowing environments. The corresponding closed-form expressions of average detection probability are derived for each case by the moment generation function (MGF) and contour integral approaches. Finally, illustrative and analytical results show the efficiency and reliability of the proposed detector and the improvement in sensing performance by SLC in multipath fading and lognormal shadowing environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.1C
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• pp.92-98
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• 2005

In this paper, blind synchronization algorithm is developed for estimating jointly timing and frequency offset of OFDM system. The proposed estimator exploits the second-order cyclostationarity of received signals, and then uses the information of symbol timing and carrier frequency offset appeared in the cyclic correlation. As a bling estimator, the information of impulse response of channel and training symbols are not required. The performance of the proposed method is consistent in spite of channel conditions in mean squre error sense, and simulation results prove it. For more accurate estimaion, the method that averages cyclic correlation is applied. In this case, the performance of averaging method is better.