Sungtae Kim

Sensing Performance of Energy Detector With Correlated Multiple Antennas

This paper describes the derivation of detection and false-alarm probabilities for energy detectors in cognitive radio networks when a sensing node of the secondary system has correlated multiple antennas. The sensing performance degradation due to the antenna correlation is then investigated based on the performance analysis. The conclusions of the analysis are verified by numerical simulation results.

Capacity enhancement of secondary links through spatial diversity in spectrum sharing

Previous investigations on capacity of secondary users in spectrum-sharing environments have determined the capacity of a secondary link based on the interference power threshold set at the primary receiver. In contrast to these previous works, we show that the capacity of a secondary link is determined based on a geographical relationship expressed as the ratio of the distance between the primary receiver and secondary transmitter to the distance between the secondary transmitter and receiver. Proceeding from that and in an effort, to enhance the capacity of the secondary user, which is limited by this distance-ratio, we adopt a secondary transmitter with M antennas. Furthermore, we analyze the capacity achieved using a simple antenna selection process.

Advanced sensing techniques of energy detection in cognitive radios

Recently, spectrum sensing has been intensively studied as a key technology in realizing the cognitive radio. There have been advances in the performance of spectrum sensing through both multi-antenna and cooperative sensing schemes. In this paper, the performances and complicated scenarios of the latest spectrum sensing schemes are analytically compared and arranged into a technical tree while considering practical concerns. This paper will give a macroscopic view of spectrum sensing and will also provide insight into future spectrum sensing works.

Capacity of Secondary Users Exploiting Multispectrum and Multiuser Diversity in Spectrum-Sharing Environments

In spectrum-sharing environments, secondary users are permitted to share the primary users spectrum only if limited interference to the primary user can be guaranteed. Hence, the capacity of the secondary link is limited by interference constraints given by the primary user. This fact motivated us to investigate selection diversity as a way of enhancing secondary link capacity. Selection diversity in conventional licensed wireless communication systems can be achieved only by selecting the user with the strongest channel gain. On the other hand, spectrum-sharing environments allow the secondary user to select not only the best secondary receiver with the strongest channel gain multiuser diversity (MUD) but the best primary spectrum with the weakest interference link gain multispectrum diversity (MSD) as well, thus doubling the opportunities for the secondary user. In this paper, we analyze the capacity gain of a secondary user exploiting MSD and MUD in spectrum-sharing environments in the form of a closed-form expression in a Rayleigh-fading channel. We then separately extract the MSD and MUD capacity gains, which results in an asymptotic capacity expression. Our results show that MSD and MUD play different roles in capacity enhancement in the spectrum-sharing environment, with capacity enhancement for secondary receivers as a whole and transmit capacity enhancement for the secondary transmitter.

Throughput Analysis and Optimization of Sensing-Based Cognitive Radio Systems With Markovian Traffic

This paper analyzes the secondary user throughput of a sensing-based cognitive radio system with Markovian traffic. Under the Markovian traffic assumption, imperfect packet capture, which occurs upon the random arrival of primary user packets, considerably affects the secondary user throughput. Considering both the primary user packet capture and energy detection of the captured packet, we derive the secondary user throughput. Additionally, using the tradeoff between the sensing accuracy and the secondary user throughput, we solve a joint optimization dealing with both the sensing duration and the sensing period to maximize the secondary user throughput with an interference constraint for the primary user.

Sensing threshold control for fair coexistence of heterogeneous systems in open spectrum

A critical problem in open-spectrum communications is fairness with respect to the coexistence of heterogeneous systems with different resource units and traffic models. In addition, the sensing performances of different systems can also lead to unfair resource utilization between systems. To address this problem, we derive a continuous-time Markov chain model to show the effect of sensing performance on system coexistence. The analysis derived from this model is then used as the basis for a sensing threshold control (STC) scheme to achieve fairness. The proposed STC determines the sensing threshold for each system as a way of balancing resource utilization among systems, while guaranteeing target detection probability. Numerical results on the amount of resource utilization by each system demonstrate that the proposed STC achieves a full degree of fairness.

Low bias frequency domain SNR estimator using DCT in mobile fading channels

The authors analyze the cause of bias in a fast Fourier transform (FFT)-based frequency domain signal-to-noise ratio (SNR) estimator by deriving the upper bound of the bias. The analysis is then used to propose a new frequency domain estimator using discrete cosine transform (DCT), which has lower bias. In addition, a criterion is proposed for use when maximum Doppler frequency information is available; it is based on the derived upper bound and can be used to improve the mean squared error (MSE) performance of the proposed DCT-based estimator. Simulation results show that the proposed estimator reduces the MSE remarkably by diminishing the bias..

Improved Frequency Domain SNR Estimator Using DCT in Mobile Fading Channels

Signal-to-noise ratio (SNR) measurement is required in many channel-adaptive techniques and radio resource management methods for mobile radio communication systems. In this paper, the factors that degrade the MSE performance of the conventional frequency domain SNR estimator in high SNR region are analyzed. Based on this analysis, we propose two improved frequency domain SNR estimators which employ windowing and discrete cosine transform (DCT) to suppress the leakage of the received fading signals frequency spectrum. The simulation results show that the proposed methods remarkably improve the MSE performance for high SNR region (ges15 dB) in mobile fading channels