인지무선 시스템을 위한 거리기반 가중결합을 이용한 협력 광대역 스펙트럼 센싱

Cognitive radio (CR) is seen as a promising technology to make radio spectrum usage more effective by providing an opportunistic access for secondary users to the licensed spectrum areas. CR systems need to detect the presence of a primary user (PU) signal by continuously sensing the spectrum area of interest. Radiowave propagation effects like fading and shadowing often complicate sensing of spectrum holes because the PU signal can be weak in a particular area. Cooperative spectrum sensing is seen as a prospective solution to enhance the detection of PU signals. This paper studies distributed spectrum sensing in a cognitive radio context. We investigate distributed energy detection schemes without using any fusion center. We propose the usage of distributed, diffusion least mean square (LMS) type of power estimation algorithms. In this paper an Adapt and Combine (ATC) diffusion based power estimation scheme is proposed and the performance is compared with the Combine and Adapt (CTA) and ring-around schemes in a common framework. The PU signal is assumed to be slowly fading. We analyse the resulting energy detection performance and verify the theoretical findings through simulations.

In this paper, a new spectrum sensing method based on energy detection is proposed and analyzed in a cognitive radio(CR) system. We employ a delay diversity receiver for sensing the primary user's spectrum with reasonable cost and complexity. Conventional CR with the receiver equipping multiple antennas requires additional hardware and space for installing multiple antennas in accordance with increase in the number of antennas. If the number of antennas increases, detection probability as well as hardware complexity and cost rise. Then, it is difficult to make a primary user detector practically. Therefore, we adopt a delay diversity receiver for solving problems of the conventional spectrum detector utilizing multiple antennas. We derive analytical expressions for the spectrum sensing performance of the proposed system. From the simulation results, it is demonstrated that the primary user detector with the delay diversity receiver has almost half the complexity and shows similar or improved performance as compared with that employing multiple antennas. Therefore, the proposed spectrum sensing structure can be a practical solution for enhancing the detection capacity in CR system operations. The results of this paper can be applied to legacy CR systems with simple modifications.

Cognitive radio (CR) systems have been proposed for efficient usage of spare spectrum licensed to primary systems. This leads to the issue of providing as much spectrum to CR users as possible while not degrading the quality of service (QoS) of primary users of the spectrum. This paper proposes a novel cooperation scheme between primary and CR users to guarantee QoS of primary users up to the cell edge while making the licensed spectrum available for opportunistic access by the CR users. Thus the proposed method can provide a so called ¿win-win strategy¿ by benefiting both primary and CR users. The proposed scheme solves efficiently the Gaussian multiple access problem for power allocation of primary systems that cooperates with CR systems. We show that the Gaussian multiple access problem can be formulated as a standard semi-definite programming (SDP) problem. Numerical results show that the QoS of primary users at the cell edge is improved by the proposed cooperative access scheme.

In a cognitive radio (CR) system, an achievable throughput of secondary users (SU) primarily depends on the activity level of primary users (PU) in the channels. More the PU are active in the channels, lesser the opportunity of SU transmission. Protecting the PU from a harmful interference introduced by SU is also a challenging task specifically when multiple PU and SU exist in the system. The trade-off between SU sum throughput and PU occupancy level has been thoroughly analysed considering a zero interference tolerance of an interweave CR system. PU activity level in the channel is measured in terms of duty cycle (DC). The interplay between DC of PU and throughput of SU is presented here for Poisson and binomial distribution based SU arrival processes. The results identify the opportunistic channels when SU aims a particular sum throughput and find the optimal numbers of SU in the channels for various DC.

Selection of appropriate detection threshold (λ) is a very critical task in energy detection scheme based cognitive radio (CR) system. λ is mainly selected by using two principles called as constant detection rate (CDR) in which λ is calculated by taking fixed value of probability of detection (P d ) and constant false alarm rate (CFAR) in which λ is calculated by taking fixed value of probability of false alarm P fa . The CDR principle is mostly adopted to sufficiently protect the primary users (PUs), but it lags in exploiting the best spectrum utilization opportunities mainly when CR user is located far away where chances of interfering a PU communication are least. This overprotective nature of CR in CDR principle leads to a decrease in its achievable throughput. To overcome it, this article proposes an approach in which the location information of PU is efficiently used to access the spectrum using “opportunistic spectrum access scheme under the CDR principle” and the “scheme of spectrum sharing”. Under the proposed approach, the CR achieves a significant gain in its throughput compared to the approach in which the CDR and CFAR principles are used blindly.

In cognitive radio systems, the main requirement of the architectures is the ability to detect the presence of the primary user with fast speed and precise accuracy. In a cognitive radio system, signal detection mechanism is required for spectrum sensing in order to identify occupied and vacant channels and hence to detect the availability of the vacant spectra. To achieve this we have simulated the energy detection technique for cognitive radio system out of the three deferent techniques. In this paper we have emphasis on sensing the vacant channel for FM band using energy detection method and then the simulation results are ratified.

To improve the efficiency of bandwidth usage, the cognitive radios concept has emerged. Spectrum sensing is a pivotal function in cognitive radio systems so that the secondary users can be able to access the free spectrum holes without interfering with primary users. Energy detection is the most common and easiest spectrum sensing technique for cognitive radios. In this paper, the conventional energy detection receiver operating characteristic curve and performance metrics are simulated under additive white Gaussian noise (AWGN) environment by using Monte Carlo simulation. Also, the performance of energy detection is analyzed under different types of M-ary modulation. The analysis of performance will carry the assumption of noise uncertainty. This performance gain is compared with conventional energy detection without any noise effect. In addition, the relation between a number of samples and signal to noise ratio wall (SNR wall) is provided and simulated. The simulation tool used in the analysis is MATLAB software. Finally, the implementation of energy detection technique in the time domain and frequency domain is designed on Xilinx Spartan-3E (XC3S500E-FG320) Field Programmable Gate Array (FPGA) kit by using Verilog language and Xilinx ISE Simulator version 14.1.

Cognitive radio (CR) systems make efficient use of the frequency spectrum by opportunistically exploiting unoccupied or under-utilized frequency bands. However, the frequency bands used by CR systems are expected to suffer from various forms of noise and interference with non-Gaussian distributions, such as narrowband and co-channel interference caused by the primary user and other CRs, respectively, and man-made impulsive noise. To mitigate the harmful effects of non-Gaussian noise and interference, we propose a robust L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -norm metric for CR systems that employ the popular combination of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM). For the considered CR system we provide an approximate upper bound and an asymptotic closed-form approximation for the bit error rate (BER). Our results show that the proposed L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -norm metric can achieve large performance gains compared to the conventional L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -norm metric in non-Gaussian noise and interference.

In this paper, we consider the performance of received signal strength (RSS) and time of arrival (TOA) under different areas of primary user (PU) position estimation. The areas of PU position can be separated into two cases: inner area and outer area of boundary of secondary user (SU) nodes. This boundary is created by convex hull algorithm. In simulation result, we found that RSS is appropriated to use in inner area and TOA is suitable to use in outer area. Therefore, in this paper, we propose two hybrid location estimation techniques that combine RSS and TOA in cognitive radio (CR) system. The proposed techniques include the hybrid TOA/RSS in serial and the hybrid TOA/RSS in parallel technique. Simulation results show that the proposed techniques have better performance than the methods that use only RSS or TOA. Moreover, the proposed techniques are faster than TOA about 60%.

Wire cleaner

The optimal admission strategy for secondary users (SUs) in a cognitive radio (CR) system with two types of primary users (PUs) is investigated in this paper. When an SU comes to the system, it will decide to either enter the system or give up its service and leave the system based on the current state (number of PUs and SUs) of the system. SUs can access the spectrum in an opportunistic way without interfering with the PUs. When any PU arrives, however, if the band is occupied by a SU, the SU’s service on the band is interrupted and this SU is placed back to the waiting queue. Admitting each SU would bring a reward to the system provider but holding each US in the system would also incur some expenses (or cost) to the provider. We concentrate on the optimization problems of when to admit or reject a SU when all bandwidth are being used in order to achieve the maximum total discounted expected reward for any initial state. By developing a continuous time Markov decision process model, we verify that the optimal policy for admitting SUs is a state-related control limit policy. Our numerical results explained in both tables and diagrams are consistent with our theoretic results.

Cognitive radio (CR) technology is a potential solution to the spectrum scarcity problem. In CR systems, the availability of the licensed spectrum portion is monitored by the spectrum sensing process and strategies are applied to use this licensed portion without interfering with active primary users (PU). CR provides a flexible system that secondary users (SU) can make decisions about the spectrum usage at any time by simply configuring corresponding transmission parameters. However, implementation of CR systems can be a challenging task due to characteristic difficulties of the wireless channels introduced by fading. Especially spectrum sensing process is affected by changing channel conditions, which should be considered in order to create a high performance CR system. Robust spectrum sensing is essential for a CR system due to its vital role in the efficient usage of the spectrum. Therefore, several algorithms that are proposed for this issue should contain suitable properties considering realistic channel conditions. Implementation of these algorithms can be realized through software defined radios (SDRs). SDR is a core component of the CR technology and it allows a practical development process with modification on the software rather than hardware. Thus, SDR based approaches to CR problems are quite effective. In this chapter, the state of the art of CR systems are explained in detail by highlighting essential components of the existing studies. Effective approaches to the implementation using SDR systems are given. Moreover, an energy detection based spectrum sensing implementation for 2.4 GHz ISM band is given as an implementation example and channel based spectrum usage is analyzed by using SDR tools LabVIEW and NI USRP-2921 hardware in real-time.

Energy detection (ED) technique is a vastly used sensing technique in CRNs because of its operational simplicity. However at low SNR, the performance of ED is badly degraded. Matched Filter (MF) detection is an alternate sensing technique at low SNR, as it increases SNR of the received signal. MF detector gives far better performance when compared to ED at low SNR. But the problem with MF detector is that it must have priori knowledge about Primary User (PU) signal, therefore we need dedicated MF detector for each PU. Motivated by above drawback of ED and MF in this paper we proposed a new MF technique by which requirement of priori knowledge about PU signal can be eliminated as well as performance at low SNR is improved. At the MF detector front end, we perform blind estimation of PU signal parameters and accordingly update the coefficient of MF transfer function. Blind Estimation of signal parameters solves the problem of having priori information about PU signal for MF detector. Performance analysis and comparison of ED, conventional MF detector and proposed MF detector also have been done in this paper which show that the proposed MF detector perform better than ED and almost same as the conventional MF detector.

Two points need to be considered on power loading policy of cognitive radio (CR) systems. The first is to maximize the channel capacity over the given frequency band, which is detected usable for CR systems. The second is the out-of-band interference suppression of the CR systems. In the paper based on the mathematical expression of the interference power caused by MB-OFDM based CR systems, the relationship of the symbols on the sub-carriers can be obtained. To realize the relationship the sub-carrier weighting method can be adopted. With the effect of the weighting factors, the symbols relationship can be satisfied, and simultaneously the maximum channel capacity can be achieved on certain degree. The simulation results of the relationship among the three parameters, channel capacity, interference power and total transmission power, also shows that a better tradeoff can be achieved between the channel capacity and the interference power.

In a cognitive radio (CR) network, the channel sensing scheme to detect the appearance of a primary user (PU) directly affects the performances of both CR and PU. However, in practical systems, the CR is prone to sensing errors due to inefficient sensing scheme. This may lead to interfering with primary user and low system performance. In this paper, we present a learning based scheme for channel sensing in CR network. Specifically, we formulate the channel sensing problem as a partially observable Markov decision process (POMDP), where the most likely channel state is derived by a learning process called Fuzzy Q-Learning (FQL). The optimal policy is derived by solving the problem. The simulation results show the effectiveness and efficiency of our proposed scheme.