Gosan Noh

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.

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.

Reporting Order Control for Fast Primary Detection in Cooperative Spectrum Sensing

Although cooperative spectrum sensing improves sensing accuracy in cognitive radio systems, additional reporting time is required to report the local test statistics until the existence of the primary user is verified, resulting in detection delay. To reduce the reporting time, we propose controlling the reporting order of the local test statistics, so that the local test statistics are reported to the fusion center in descending order of magnitude. As a result, the global test statistic at the fusion center accumulates faster than the case without reporting order control, reducing the reporting time needed to determine when the threshold for detecting the primary user has been exceeded. To do this, we propose, based on distributed access control, a combination of order identification, which finds the order of the local test statistic, and transmission probability calculation according to the identified order. Simulation results show that the proposed reporting order control significantly reduces the reporting time for detecting the primary user.

Exact Capacity Analysis of Spectrum Sharing Systems: Average Received-Power Constraint

This letter presents an exact closed-form expression for the ergodic capacity of the secondary user in a spectrum sharing environment under an average received-power constraint, considering the effect of the interference from the primary user. Using capacity maximizing water-filling power allocation, we provide the closed-form expressions for the ergodic capacity and the average received-power assuming Rayleigh fading channels. Numerical results show that the primary user interference significantly affects the ergodic capacity of the secondary user. The obtained formulas can be used when predicting whether spectrum sharing is beneficial in a practical channel environment.

Goodness-of-Fit-Based Malicious User Detection in Cooperative Spectrum Sensing

Cooperative spectrum sensing improves sensing accuracy in primary user detection, but can be threatened by malicious users. Malicious users may try to falsify the sensing result to indicate that the primary user exists even when there is no primary user in order to monopolize the spectrum usage, thereby depriving other users of their spectrum opportunities. To address this, we propose a malicious user detection scheme where the malicious users are identified and cut off from the cooperative sensing process. The proposed scheme exploits the Anderson-Darling (AD) goodness-of-fit technique which tests whether the empirical distribution of the sensing data from each secondary user fits the expected distribution for a malicious user. In addition, we derive false alarm and detection probabilities for when malicious users are cut off by the malicious user detection scheme. Simulation results show that the proposed goodness-of-fit-based malicious user detection significantly improves sensing performance in comparison with conventional outlier detection-based schemes.

A New Spectrum Sensing Scheme using Cyclic Prefix for OFDM-Based Cognitive Radio Systems

In cognitive radio systems, spectrum sensing schemes for detecting primary users in a licensed spectrum are essential to utilize the spectrum effectively. As a matter of fact, sensing accuracy is regarded as the most important factor for spectrum sensing with the intension of sufficient protection for the primary user. In this paper, we propose a new spectrum sensing scheme which exploits the cyclic prefix of an orthogonal frequency-division multiplexing (OFDM) symbol as well as idle period containing no information symbols. Redundant information in the cyclic prefix enables spectrum sensing to be more accurate and efficient. With analysis and simulation, we show that the proposed scheme can improve sensing accuracy and increase system throughput compared with the conventional system which uses only idle period.

Stochastic Multichannel Sensing for Cognitive Radio Systems: Optimal Channel Selection for Sensing with Interference Constraints

This paper considers the problem of sensing and transmission strategy of multiple parallel channels owned by the primary user, referred as stochastic multichannel sensing. The traffic parameters follow the Markovian traffic assumption and are not identically distributed among the channels. In order to obtain the optimal probabilities of channel selection for sensing, we formulate a maximization problem for the secondary user throughput with interference constraints to the primary user. The solution to the problem is obtained via linear programming. Numerical results show that the proposed stochastic sensing achieves higher normalized effective throughput and lower av- erage collision probability than the conventional deterministic sensing in a non-identical traffic environment. Additionally, the proposed method greatly reduces computational overheads and memory space. Index Terms—Cognitive radio, dynamic spectrum access, spec- trum sensing, throughput maximization, linear programming. I. INTRODUCTION

Mobile TV White Space with Multi-Region Based Mobility Procedure

Current regulations require that portable unlicensed devices operating in TV white space perform a channel availability query (CAQ) before transmitting whenever they move more than 100m. Since this mobility constraint gives rise to frequent CAQs, the Federal Communications Commission allows a region-based mobility procedure (RMP) to help reduce the number of CAQs. Since the performance of the RMP cannot be precisely evaluated based only on the number of CAQs, in this letter, we formulate an achievable throughput in terms of the average number of available channels, the effective data transmission time, and the TV band database fees. We discover that the achievable throughput for the conventional single RMP is degraded when the radius of the region is not properly determined. In order to alleviate this performance degradation, we propose a multi-RMP using multiple radii in order to obtain multiple available channel lists. Simulation results show that the proposed multi-RMP can mitigate the performance degradation. In addition, the use of multi-RMP enhances the maximum throughput compared to the single RMP.

Joint Beamforming and Power Control Algorithm for Cognitive Radio Network with the Multi-Antenna Base Station

Cognitive radio (CR) has been studied as a useful solution for efficient utilization of scarce radio spectrums. For it to succeed, two conflicting challenges are imposed on the secondary users: one is to ensure the quality of service (QoS) of the primary link, and the other is to maximize their own transmit throughput. To balance this tradeoff, beamforming and power control employing the multi-antenna in the base station (BS) of the CR network have been introduced. In the perfect beamforming situation, the power control algorithms suitable in the CR network with a multi-antenna BS (MBS) have been proposed in previous works. However, those algorithms are meaningless for realizing a practical CR network with the MBS since perfect beamforming is impossible. Therefore, unlike previous works, this paper proposes a joint beamforming and power control algorithm as a more practical strategy for realizing a CR network with the MBS. The algorithm is proposed so as to maximize the sum-rate of secondary users, while not degrading QoS for the primary link. Numerical results verify its effectiveness in a CR network with the MBS.

Optimal Tone Space Selection Scheme for OFDMA-VTS in Carrier Aggregation

In this paper, we propose an optimal tone space selection scheme for orthogonal frequency division multiple access with variable tone spaces (OFDMA-VTS) in carrier aggregation based on user-specific channels. We begin by analyzing inter-symbol interference (ISI) and inter-carrier interference (ICI) in non-contiguous carrier aggregation, which differ according to the delay and Doppler spreads associated with each user, as well as the tone space that each user utilizes. Based on that, we propose an optimal tone space selection scheme as a way to minimize both ISI and ICI. We also derive an upper bound on OFDMA-VTS capacity when it is applied to the proposed scheme. Furthermore, we investigate the effect of inter-user interference (IUI) in contiguous carrier aggregation and show that the proposed scheme can be applied to OFDMA-VTS in contiguous carrier aggregation as a suboptimal solution. Numerical results demonstrate that the proposed scheme maximizes OFDMA-VTS capacity by minimizing the total ISI and ICI interference, thereby enhancing the system capacity over what is possible with conventional OFDMA.