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This paper adopts a relay among available secondary relays and exploits non-selected relays as jammers to maintain and secure legitimate secondary source-to-destination communications in energy harvesting underlay cognitive networks (EHUCNs) as their direct communications is in outage. All relays harvest radio frequency energy in signals transmitted by primary and secondary transmitters and consume the harvested energy for their jamming-and-relaying operations. Under Rayleigh fading, peak transmission power restriction, interference power restriction, primary interference and power splitting-based energy scavenging method, we propose exact closed-form formulas of outage and intercept probabilities to promptly assess both security and reliability performances of the suggested relay-and-jammers selection in EHUCNs. The suggested expressions are corroborated by computer simulations. Numerous results indicate the efficacy of the relay-and-jammers selection in improving both security and reliability for source–destination communications. Moreover, the security and reliability performances are saturated at large maximum transmit/interference powers and considerably degraded by the primary interference. Furthermore, the reliability performance can be optimized by splitting appropriately the received power for information decoding and energy harvesting at the relays. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) technology has been demonstrated as one of the key technologies that can provide the needed spectrum bands for supporting the emerging spectrum-hungry multimedia applications and services in next-generation wireless networks. Multicast routing technique plays a significant role in most of wireless networks that require multimedia data dissemination to a group of destinations through single-hop or multi-hop communication. Performing multimedia multicasting over CR networks can significantly improve the quality of multimedia transmissions by effectively exploiting the available spectrum, reducing network traffic and minimizing communication cost. An important challenge in this domain is how to perform a multi-cast transmissions over multiple hops in a dynamically varying CR environment while maintaining high-quality received video streaming to all multi-case CR receivers without affecting the performance of legacy primary radio networks (PRNs). In this paper, we investigate the problem of multicast multimedia streaming in multi-hop CR networks (CRNs). Specifically, we propose an intelligent multicast routing protocol for multi-hop ad hoc CRNs that can effectively support multimedia streaming. The proposed protocol consists of path selection and channel assignment phases for the different multi-cast receivers. It is based on the shortest path tree (SPT) that implements the expected transmission count metric (ETX). The channel selection is based on the ETX, which is a function of the probability of success (POS) over the different channels that depends on the channel-quality and availability. Simulation results verify the significant improvement achieved by the proposed protocol compared to other existing multicast routing protocols under different network conditions. [ABSTRACT FROM AUTHOR]

Energy harvesting has lately been of particular attention to researchers. In addition, cognitive radio networks (CRNs) are recognized as an attainable measure for the problem of radio spectrum shortage in next generation radio access. A combination of these two technologies, which forms energy harvesting CRNs (EHCRNs), allows wireless communication terminals to prolong their operation time in limited spectrum scenarios. Nonetheless, that CRNs create opportunities for secondary users to access primary users' spectrum induces vulnerability of message security. So far, security capability analysis of EHCRNs has been limited to Rayleigh fading whilst Nakagami-m fading is more common than Rayleigh fading and better reflects distinct fading severity degrees in practical scenarios. Accordingly, this paper firstly offers the precise security capability analysis of EHCRNs under interference power constraint, Nakagami-m fading, maximum transmit power constraint, and primary interference. Then, the offered analysis is ratified by computer simulations. Ultimately, multiple results reveal that the security capability is considerably improved with smaller primary interference and lower required security threshold. Moreover, the security capability is significantly impacted by channel severity and is optimized with appropriate selection of time percentage. [ABSTRACT FROM AUTHOR]

Routing in Cognitive Radio Ad Hoc Network (CRAHN) is a challenging task due to limited spectrum availability. To overcome this problem several researchers have proposed various routing schemes based on Quality of Service (QoS) and spectrum availability. These schemes choose a path that gives maximum QoS and spectrum level ignoring the required QoS level for a particular application which may be quite less than the maximum level. Thus, this paper proposes an integrated service model having eight classes instead of two for CRAHN to envisage the admission control at Primary User (PU) nodes thus reducing overhead on Secondary Users (SU) for various applications. The PU node first examines the spectrum availability and then checks whether the received packet can be granted user specific Quality of Service (QoS) or not to support Elastic plus Real Time Applications for (SU) nodes. To prove the efficacy of proposed scheme comparison with Cognitive Ad hoc On-demand Distance Vector (CAODV) or shortest spectrum aware path routing mechanism is done. The result exhibits that high performance rate for good reliability, low latency and high throughput with fair load distribution among all the nodes of the network. [ABSTRACT FROM AUTHOR]

In this paper, performance analysis of an asynchronous distributed space time block coded system with optimum combining at the cognitive radio receiver (CR-Rx) has been done in a cooperative underlay cognitive Internet of Things network under the influence of multiple co-channel primary users (PUs) interferers. The transmit power strategy being employed at the CR-Tx considers the PIP (peak interference power) at the PU-Rx and peak transmit power constraints at the CR-Tx, respectively. We have derived the probability density function of the signal-to-interference ratio (SIR) at the destination for the proposed system. The system is numerically and mathematically analyzed in terms of average post processed SIR (APPSIR), ergodic capacity ( C erg ), average bit error rate (ABER) and outage probability. All the numerical outcomes are in corroboration with its simulation counterpart. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) is introduced to efficiently and opportunistically use the limited spectrum to minimize the spectrum scarcity issues. Usually, service providers purchase the spectrum license from the policy-makers and spectrum regulator authority. The non-licensed users cannot utilize the licensed bands even though primary user is not transmitting. It sometimes results in under-utilization of frequency bands, which in turn decreases the spectral efficiency. The CR can opportunistically use the freely available licensed spectrum. To solve the spectrum scarcity problem, we implemented CR using software defined radio on frequency modulated radio band (88–108MHz), because of ease in access and availability. The proposed solution is equally valid for other frequency bands as well, because the printed circuit board adopted here supports frequency from 50MHz to 2.2GHz. The proposed solution uses energy-detection based spectrum-sensing technique for primary user (PU) detection, and afterwards secondary user starts the data transmission over the vacant frequency band. We presented real-time experimental results for the detection probabilities by testing under various false alarm probabilities to verify the efficiency of the designed system. Experimental results show that we can achieve high detection probability even at low receiver sensitivity. When PU becomes active, then the proposed system quickly shift the public-safety user to other available white spaces to avoid halting the licensed user transmission. This solution is beneficial for security and defense organization such as army, traffic wardens, city wardens, and police. [ABSTRACT FROM AUTHOR]

Cognitive radios have emerged as a key enabler for opportunistic spectrum access, in order to tackle the wireless spectrum scarcity and under utilization problems over the past two decades. In this paper, we aim to enhance the secondary user (SU) performance while maintaining the desired average packet delay for the primary user (PU). In particular, we investigate the trade-off between delay-constrained primary and secondary users in cog- nitive radio systems. In the first part of this work, we use the hard-sensing scheme to make a decision on the PU activity and maximize the SU effective capacity subject to an average PU delay constraint. Second, we propose a soft-sensing scheme by dividing the PU energy interval where the PU is decided to be idle into multiple decision. We also maximize the SU effective capacity subject to an average primary user delay constraint; then, we present three modifications for the proposed soft-sensing scheme to allow for low complexity implementation that is comparable to the complexity of the hard-sensing scheme, but with better performance. The numerical results reveal interesting insights comparing our soft sensing to the hard-sensing models in terms of the optimal performance obtained from our optimization solution compared to the unconstrained PU delay baseline system studied earlier in the literature. For instance, the hard sensing system in Akin and Gursoy (IEEE Trans Wirel Commun 9(11):3354–3364, 2010) and Abdel-Malek et al. (CrownCom 156:30–42, 2015) yields a SU effective capacity of only 50 % of the ideal, perfect sensing system. On the other hand, we show that the soft sensing system yields almost 87 % of the perfect sensing performance (at a primary user arrival rate of λ p = 0.1 ), which further increases for a larger number of decision sub-intervals. [ABSTRACT FROM AUTHOR]

Spectrum detecting is the essential and crucial mechanisms of cognitive radio (CR) to the invention the unemployed spectrum. CR system has been suggested as a conceivable resolution for enhancing the spectrum use by empowering unprincipled spectrum sharing. The principal prerequisite for enabling CR to utilize authorized range on an optional premise is not making interfering to primary users. The principal goal of CR is to use rare and limited natural resource efficiently with no obstruction to the primary users (PUs). This work presents an overview of CR architecture, discusses the characteristics and benefits of a CR. Energy identification, matched channel filter detection, and cyclostationary recognitions are most conventional techniques for spectrum sensing. The explanation behind picking energy detection procedure, it did not need any previous info from the primary user transmission. Additionally, the particular result of energy detection technique corrupts with a lower sign to noise ratio (SNR) level signal area. General detection performance of energy detection exceptionally depends upon noise, mainly while the SNR is low for PU. To consider this issue, this paper shows a remarkable, augmented threshold model for efficient energy detection procedure to improve the detection execution at low SNR level. The simulation results demonstrate the energy detection performance utilizing proposed system model is excellent than a fixed threshold at low SNR signal areas. [ABSTRACT FROM AUTHOR]

Underlay mode of cognitive radio networks (CRNs) permits secondary users (SUs) to simultaneously operate with primary users (PUs), inducing mutual interference between them. Nevertheless, primary interference (interference from PUs to SUs) is either neglected or treated as Gaussian noise in existing works. Moreover, artificial noise, which is deliberately introduced to harm signal reception of wire-tappers, can enhance information securing capability of CRNs. This paper analyzes a gap between reliability probability (successful decoding probability of legitimate receiver) and intercept probability (successful decoding probability of wire-tappers), which accounts for artificial noise, peak transmit power constraint, interference power constraint, and fading channels, and considers primary interference as non-Gaussian noise. Towards this end, exact closed-form expressions of reliability probability and intercept probability are first derived and then validated by computer simulations. Numerous results illustrate that both probabilities are saturated at either large peak interference power or large peak transmit power, the primary interference dramatically deteriorates them while the artificial noise creates a large gap between them, demonstrating its effectiveness in securing legitimate information. [ABSTRACT FROM AUTHOR]

This paper proposes a jamming technique which employs a self-powered secondary jammer to interfere a wire-tapper, who eavesdrops communications between a self-powered secondary source and a secondary destination in energy harvesting cognitive radio networks (EHCRNs). For generality, interference from a primary source, maximum transmit power constraint and interference power constraint are considered in analyzing security performance of the proposed jamming technique in terms of security-reliability compromise. Towards this end, exact expressions of detection/eavesdropping outage probabilities at the destination/the wire-tapper are first proposed and then verified by computer simulations. Finally, results are provided to demonstrate the efficacy of the jamming technique and the key effects (interference from the primary user, power constraints, interference power distribution factor, and time splitting factor) on security performance of EHCRNs. [ABSTRACT FROM AUTHOR]

In this paper, a frequency synthesizer, based on a type-2, third order phase locked loop (PLL), covering the frequency range of 0.9-5.4 GHz using three voltage controlled oscillators, is implemented using a 0.13-μm CMOS technology. The PLL has three modes of operation—a high bandwidth mode, a low bandwidth mode and a dynamic mode, in which the bandwidth dynamically changes from a low to a high value, during a frequency jump, and reverts back to low value, once the PLL settles. With a proper choice of bandwidth and timing synchronization during a frequency jump, a worst-case settling time of 3-μs has been obtained, which is one of the lowest in reported literature. The input clock of the PLL is set to 100 MHz, but it can go as low as 25 MHz without having any effect on its settling time. The PLL consumes 24 mW of power and occupies 0.8 mm2 of active area.This PLL is expected to be specially useful in wide-bandwidth cognitive radios that require large and fast transitions in the frequency of operation. [ABSTRACT FROM AUTHOR]

Underlay mechanism allows concurrent communications of primary users and secondary users in cognitive radio networks (CRNs), causing mutual interference between them. However, current literature neglects primary interference or considers it as Gaussian noise. In addition, artificial noise, which is intentionally generated to interfere eavesdroppers, can improve security performance of CRNs. This paper analyzes security performance of CRNs, accounting for artificial noise and considering primary interference as non-Gaussian noise, under maximum transmit power constraint, interference power constraint, and Rayleigh fading channels. The security performance is evaluated through proposed exact expressions of secrecy outage probability, non-zero achievable secrecy rate probability, and intercept probability, which are verified by Monte-Carlo simulations. Various results demonstrate that CRNs suffer security performance saturation in the range of large maximum transmit power or large maximum interference power, and primary interference significantly deteriorates security performance while artificial noise is useful in enhancing this performance. [ABSTRACT FROM AUTHOR]

This paper proposes an inter-frame dynamic double threshold (IF-DDT) spectrum sensing algorithm in order to improve the sensing performance based on energy detection (ED) in cognitive radios (CRs). Based on both the activity model of the primary user (PU) and the sensing mechanism of the secondary user (SU), the proposed algorithm exploits the relationship between two adjacent sensing frames and designs dynamic double thresholds for each sensing frame to enhance spectrum sensing performance when the received energy cannot give a reliable local decision. The detection probability and false alarm probability of the proposed sensing scheme are analyzed, and an algorithm for searching the optimal dynamic double thresholds is derived with very low complexity according to the Neyman-Pearson (NP) test criterion. Theoretical analysis and simulation results show that the proposed algorithm outperforms the ED algorithm. [ABSTRACT FROM AUTHOR]

Consider a multi-channel Cognitive Radio Network (CRN) with multiple Primary Users (PUs), and multiple Secondary Users (SUs) competing for access to the channels. In this scenario, it is essential for SUs to avoid collision among one another while maintaining efficient usage of the available transmission opportunities. We investigate two channel access schemes. In the first model, an SU selects a channel and sends a packet directly without Carrier Sensing (CS) whenever the PU is absent on this channel. In the second model, an SU invokes CS in order to avoid collision among co-channel SUs. For each model, we analyze the channel selection problem and prove that it is a so-called 'Exact Potential' game. We also formally state the relationship between the global optimal point and the Nash Equilibrium (NE) point as far as system capacity is concerned. Thereafter, to facilitate the SU to select a proper channel in the game in a distributed manner, we design a Bayesian Learning Automaton (BLA)-based approach. Unlike many other Learning Automata (LA), a key advantage of the BLA is that it is learning-parameter free. The performance of the BLA-based approach is evaluated through rigorous simulations and this has been compared with the competing LA-based solution reported for this application, whence we confirm the superiority of our BLA approach. [ABSTRACT FROM AUTHOR]

Deploying 5G technologies in a combination of smart homes and smart city opens for a new ecosystem with big potentials. The potentials lie in the creation of an advanced ICT infrastructure with support for connected and entangled services possibilities including technologies for efficient communication in an Internet of Things (5G) contexts. In this paper we discuss some of the key challenges that exist in the smart city and smart home networks in the light of possible 5G-solutions. Focus is on deploying cognitive radio technologies (5G) which enables the smart city networks to support interconnected infrastructure elements, to handle big-data from the smart homes, and to be compatible with existing infrastructures. The considered cognitive radio technology is based on pre-coded OFDM which offers the needed flexibility to deal with the key challenges found in the smart home networks. Thus, it is able to overcome the WiFi interferences and the wall penetration losses for a limited power cost. By simulation it has been found that power saving in the range of 10-23 % can be achieved for a small bandwidth cost. Additionally, it has been found that the choice of the smart home gateway location can change its power consumption with 99 %. The developed simulator incorporates interferences, wall losses, and packet error rates, which is elaborated in this paper. [ABSTRACT FROM AUTHOR]

This research work presents the design and the physical implementation of a power aware FFT core for OFDM-based, dynamic spectrum access (DSA) enabled cognitive radios. The FFT core is equipped with a pruning engine that allows the run-time removal of dummy operations (e.g. multiplications by a zero term) related to the pruning of sub-carriers of the communication systems. The pruning algorithm introduced by this research work utilizes a reduced size configuration matrix, which limits the memory requirements' overhead. Finally, the physical implementation of the FFT on a 45 nm technology node showed that, for a 8 % area overhead, the total power saving settles around 10 % when in the presence of a medium to high pruning level, justifying the silicon area overhead introduced by the pruning unit. [ABSTRACT FROM AUTHOR]

In this article, we present a unified perspective on the cognitive internet of things (CIoT). It is noted that within the CIoT design we observe the convergence of energy harvesting, cognitive spectrum access and mobile cloud computing technologies. We unify these distinct technologies into a CIoT architecture which provides a flexible, dynamic, scalable and robust network design road-map for large scale IoT deployment. Since the prime objective of the CIoT network is to ensure connectivity between things, we identify key metrics which characterize the network design space. We revisit the definition of cognition in the context of IoT networks and argue that both the energy efficiency and the spectrum efficiency are key design constraints. To this end, we define a new performance metric called the 'overall link success probability' which encapsulates these constraints. The overall link success probability is characterized by both the self-sustainablitiy of the link through energy harvesting and the availability of spectrum for transmissions. With the help of a reference scenario, we demonstrate that well-known tools from stochastic geometry can be employed to investigate both the node and the network level performance. In particular, the reference scenario considers a large scale deployment of a CIoT network empowered by solar energy harvesting deployed along with the centralized CIoT device coordinators. It is assumed that CIoT network is underlaid with a cellular network, i.e., CIoT nodes share spectrum with mobile users subject to a certain co-existence constraint. Considering the dynamics of both energy harvesting and spectrum sharing, the overall link success probability is then quantified. It is shown that both the self-sustainability of the link, and the availability of transmission opportunites, are coupled through a common parameter, i.e., the node level transmit power. Furthermore, provided the co-existence constraint is satisfied, the link level success in the presence of both the inter-network and intra-network interference is an increasing function of the transmit power. We demonstrate that the overall link level success probability can be maximized by employing a certain optimal transmit power. Characterization of such an optimal operational point is presented. Finally, we highlight some of the future directions which can benefit from the analytical framework developed in this paper. [ABSTRACT FROM AUTHOR]

In recent wireless network domains static spectrum access is a major concern. Generally, this access leads to spectrum scarcity problem by creating empty holes or white spaces. However, the scarcity is temporary and can be alleviated if spectrum access is performed dynamically and efficiently. One important step towards dynamic spectrum access is the development of cognitive radio (CR) technology, which senses nearby spectrum portions (or bands) and tries to use them either opportunistically or by negotiating with the neighboring users. Nonetheless, dynamic spectrum access raises several challenges which need to be addressed in detail. These challenges include efficient allocation of spectrum for users in order to maximize spectrum utilization and to avoid user level conflicts both under licensed and unlicensed bands. In this paper, considering the relative rarity of solutions for unlicensed spectrum access and their inadequacy, we propose a scheme, where the CR devices (equipped with agents) interact with their neighbors to form several coalitions over the unlicensed bands. These types of coalitions can provide a less-conflicted access as the agents mutually agree for spectrum sharing and they allow other CR users to enter in their vicinity of acquired spectrum via bilateral message exchanges. Further, we present continuous time Markov chains to model the spectrum access process in continuous time and derive important performance metric as the blocking probability for without and with queuing systems. Amongst others, the important comparisons we made between analytical and simulation results in terms of blocking probability verify that our proposed model is correct. In essence, our proposed solution aims to increase dynamic spectrum usage by enabling cooperation between the users. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) is used to overcome the spectrum scarcity problem, which results from fixed allocation of wireless bands. CR allows the unlicensed secondary users to exploit the idle spectrum, which is not occupied by any licensed primary user (PU), thus increasing the overall spectrum utilization. In this paper, we first propose a simple cooperative sensing algorithm, which combines the local decision at each CR along with a group decision received from a fusion center to produce a collective decision on the existence of the PU. The performance of the algorithm is investigated over ideal and non-ideal reporting channels, from the fusion center to the CR devices, both analytically and via simulations. Furthermore, the effect of cooperation delay, which causes the decisions received by the CR device from the fusion center to be outdated, is extensively studied, both analytically and via simulations. To overcome the significant performance degradation due to the effect of delay, an extra local sensing cycle is performed at the CR side upon reception of the group decision. Results show that the proposed algorithm outperforms the conventional hard decisions technique and exhibits a comparable performance to the soft decisions approach at a considerably lower complexity. Moreover, the algorithm is shown to enjoy more robustness against reporting channel errors than the conventional hard decisions-based algorithm. Finally, the extra sensing cycle is shown to dramatically improve the performance for different delay scenarios. [ABSTRACT FROM AUTHOR]

In order to detect the unused spectrum bands (the spectrum holes) efficiently in cognitive radios with low signal-to-noise radio (SNR), we propose to adopt two independent branches of wavelet to detect the singularities of the received signals' power spectrum density (PSD). The sensing structure is flexible such that we can use one or two branches to cope with different SNRs. Under low SNR condition, each branch uses distinct characteristics between noise and signals in the wavelet transform to eliminate the singularities generated by the noise. By using bandpass filter to calculate PSD values of the subbands which are distinguished by the signal's singularities, the subband with the minimum PSD value among all of the subbands could be found. Then, the results of the two branches are merged and analyzed in order to make the final decision. Finally, we use signal reconstruction to further remove the noise and then accurately detect the spectrum holes. When the SNR is high, only one branch through the denoising procedure is needed to get accurate sensing result. Our simulation results show that the two-branch wavelet method is more accurate than conventional approaches under given SNRs. [ABSTRACT FROM AUTHOR]

Opportunistic spectrum access (OSA) receives a constantly growing interest due to its potential to mitigate spectrum scarcity and meet the increasing communication needs of mobile users. OSA refers to identifying and exploiting spatiotemporal unused portions of licensed spectrum to allow communication among unlicensed-secondary users (SUs) without adverse impact to the licensees (primary users-PUs). Key parameters in OSA are the spectrum opportunities detection method used by the SUs, and the interference level perceived by the PUs. A spatial spectrum reuse framework is proposed, where broadcast messages of an infrastructure-based primary system are exploited and combined with location-aware methods to detect spectrum opportunities and establish interference-free secondary links. The study of secondary link establishment probabilities revealed a spectrum reuse of up to 25% for omni-directional and up to 90% for directional antennas. Moreover, increased throughput is achieved in both cases, with directional antennas attaining significantly better performance. [ABSTRACT FROM AUTHOR]

In this paper, we propose and analyze the outage probability of a two-way hybrid decode-and-amplify relaying scheme with relay selection for secondary spectrum access. In this scheme, a secondary network is co-located and uses the same spectrum as the primary network. The primary network is comprised of two primary terminals that attempt to transmit signals to one another; the secondary network is comprised of M secondary transmitter-receiver pairs (ST-SR). One of the secondary transmitters chosen to cooperate with the primary network uses a hybrid decode-and-amplify forward technique in order to relay primary and secondary signals. We derive expressions for the outage probability of the primary network as well as the secondary network over a Rayleigh fading channel. Simulation results are presented to verify theoretical analyses and to compare the performance of the proposed protocol to that of a two-way direct transmission protocol. [ABSTRACT FROM AUTHOR]

In this work, we first analyze the accuracy of different energy detector models in approximating the exact solution in AWGN. These models motivate us to develop approximation analysis to address energy detection for fading channels. Our analysis develops approximation that has almost the same performance as the exact solution in Rayleigh channels. Our new model is simple enough to derive the relationship between the required number of samples ( N) and the signal-to-noise ratio for a single Rayleigh channel similar to the one obtained for AWGN channels. We also define a fading margin for link budget calculations that relates N in fading channels to AWGN channels. Furthermore, we analyze the impact of multiple antennas for cognitive radios considering two receiver diversity schemes and quantify the improvement in performance regarding this margin. All the analytical results derived in this paper are verified by simulations. Finally, we have implemented and verified energy detection models in our multiple antenna wireless testbed. [ABSTRACT FROM AUTHOR]

Continuous rise in the number of users as well as the increased requirement of bandwidth per user has created a need to use the spectrum efficiently. Cognitive radios are solutions proposed to address the problem of using the spectrum efficiently. Regulatory bodies around the world, FCC included, have introduced specifications intended for cognitive radio applications. TV White Space devices, which operate in the spectrum holes caused by transition from analog to digital transmission, were the first targeted applications for cognitive radio specifications (IEEE 802.22, ECMA-392). However, to maximize the potential of the idea of cognitive radios it is desirable to be able to sense the spectrum across a wide band and accordingly transmit 'smartly'. This paper presents a possible transceiver architecture meant for integrated solutions while providing tentative block level specifications for the proposed architecture. Existing spectrum sensing techniques are discussed and an integrated low power system architecture at the PHY level suitable for waveform-based spectrum sensing technique that utilizes co-operative spectrum sensing methods is proposed. [ABSTRACT FROM AUTHOR]

A multiuser automatic modulation classifier (MAMC) is an important signal processing component of a multiantenna cognitive radio (CR) receiver that helps the radio in identifying modulation format employed by multiple users in a frequency band simultaneously. In a typical wireless communication, transmitted signals are subjected to multipath fading and interference from other users. Multipath fading not only affects symbol detection performance but also affects the performance of the automatic modulation classifier. A multi input multi output (MIMO) blind equalizer is another important component of a multiantenna CR receiver that improves symbol detection performance by reducing inter symbol interference and inter user interference. In a CR scenario it is preferable to consider the performance of the AMC also while adapting the parameters of the blind equalizer. In this paper we propose MIMO blind equalizers that improves the performance of both multiuser symbol detection and cumulants based MAMC. Computer simulations are provided to illustrate this concept and the proposed algorithm. [ABSTRACT FROM AUTHOR]

Cognitive radios (CRs) have been recently proposed for the problem of spectrum scarcity. The principle of CRs' operation is based on the opportunistic access to the frequency spectrum mainly dedicated to primary users (PUs). The statistical time pattern of PUs' channel usage and arrival can affect the usability of specific frequency bands for CRs. In this note, the effect of the arrival rate and channel holding time of PUs on the available times for CRs is analyzed. To this end, first, based on Poissonian arrivals, the available time for CRs is calculated. Then, assuming a gamma distribution for the inter-arrival times and a uniform distribution of channel holding time of PU in these intervals, the probability density function and moments of the available time for CRs are derived. Next, the effect of PUs statistical parameters on the average number of packets and the average symbol rate that a CR can transmit is analyzed. Also, taking that CR needs at least T seconds, the average waiting time is calculated. [ABSTRACT FROM AUTHOR]

Spectrum sensing is an important part of cognitive radio systems to find spectrum hole for transmission which enables cognitive radio systems coexist with the authorized radio systems without harmful interference. In this paper, an improved cyclostationary feature detection method is proposed to reduce computational complexity without loss of good performance based on the optimal parameter selection strategy for choosing detection parameters of cyclic frequency and lag. Taking binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) signals as examples, the theoretical analyses are presented for choosing the optimal parameters. Simulation results are given to certify the correctness of the proposed parameter selection strategy and show the performance of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we consider throughput maximization in cognitive radio systems with proper power control. In particular, we incorporate location-awareness into the power control design and maximize the average throughput of the cognitive system. As we shall show, the proposed approach effectively utilizes the 'spatial opportunity' to maximize the system throughput, which clearly outperforms traditional power control methods. Further, the proposed approach still exhibits significant throughput gain even considering imperfect position information, with appropriate robust design modifications. [ABSTRACT FROM AUTHOR]