Primary User

This paper explains the improved performance of spectrum sensing in cognitive radio networks using cluster based multistage relaying. It depicts that use of an enhanced energy detector instead of conventional energy detector results in better total error rate and optimizes the number of CR nodes. Enhanced energy detector is based on increased positive power as compared to the conventional energy detector whose decision statistics is based on square of signal amplitude. Further, the number of detection stages is optimized by using an expression derived for reducing the total error rate. On the contrary, to reduce the trade off sensing time, the required number of diversity branches is optimized. Clustering approach help to optimize the voting rule at every cluster head with objective to reduce the error probability. With the help of simulations, it is derived that use of MIMO systems achieves better reliability in detecting the vacant spectrum without interfering the primary user.

Cognitive Network is an intelligent network that is aware of its surrounding environment, and adapts the transmission or reception parameters of either a network or a wireless node to achieve efficient communication without interfering with primary users. For avoiding interference to primary users, cognitive users must be aware of primary users within the region of interest and disable themselves whenever primary user is active. However, it is not possible to identify the location of the passive listening primary users, and causes hidden node problem in cognitive networks. This paper applies leveling and sectoring based approach for localization, and then disable region is identified considering the communication range of both primary and cognitive user. This will avoid the interference caused by hidden node problem. The cognitive users within the disabled region are sent to sleep mode until a free channel is detected in that area by spectrum sensing module. This approach avoids interference with primary user and also saves energy of cognitive users. As this approach conserve energy of cognitive users as well as simple to implement, it is suitable for CWSN.

A project to create a Polish WordNet is under way. Rather than localise the English WordNet, we are constructing the lexical network from scratch, in two phases. First, we have established the linguistic principles, among them a list of semantic relations with detailed diagnostic tests. We have also implemented a client software tool that records the lexicographers' decisions in a central database. A core WordNet, populated with around 10,000 most frequent lexemes in the IPI PAN Corpus, will be a fully functional resource for Natural Language Processing in Polish. In the second phase, the enhanced software tool will detect candidate semantic relations in a much larger corpus, based on statistical methods of grouping words by semantic similarity. Lexicographers will review and approve such candidate relations.

In this paper, we describe the cognitive radios sharing the spectrum with licensed users and its effects on operational coexistence with unlicensed users. Due to the unlicensed spectrum band growing needs and usage by many IEEE 802.11 protocols, normal wireless radio operation sees high interference leading to high error rates on operational environments. We study the licensed bands and the characteristics of the unlicensed bands in general and more specific to radio characterization of individual radios and cognitive deployment of sensor networks and its effect on lifetime. No and also calculates the lower-bound of the combined value of secondary user interference for overlapping frequencies with the primary user. By using simulation, we detect the primary user when the radio frequencies are known a priori and compare it when the frequencies are unknown. In our analysis we exploit the similarity measure seen at each sub-channel frequency, which are due to multiple paths of the same reflected signal by maximizing the correlated information of the correlation matrix. For the general case the co-variance matrix for blind source separation, we use ICA de-correlation methods and show that cognitive radio can efficiently identify users in complex situations. The effects of large deployment and cognitive sensor network are studied for a family of 802.15.4 radios adapting to power-aware algorithms.

This paper analyses opportunistic access and pricing equilibrium of secondary user in cognitive radio networks. Secondary users opportunistically access (buy) the spectrum of primary user (sell) if the channel is idle. The primary users are admitted on channel within bounds which allows admission of secondary user packet. Within the bound primary user has preemptive priority over optimal secondary user, secondary users access the channel opportunistically, primary user does not need to care about the existence of secondary user when it has data to transmit. A time slotted is assumed in which the secondary user sense the state of spectrum at each of the beginning of slot to know if it is occupied or idle. If the slot is idle it is utilized for secondary transmission after satisfaction with price charged per slot. Sensing state of each slot minimize packet delay by preventing the interference with PU. The number of packets and their waiting time is calculated using M/D/1 queuing model. Through using bound as , the spectrum demand is determined. By using spectrum size, primary arrival in bounds, spectrum price and operation cost secondary service which depends on secondary packet arrived is calculated. Through market trade off basing on spectrum trading mechanism of selling and buying, size of spectrum equilibrium is calculated.

This paper addresses the spectrum-sharing for wireless communication where a cognitive or secondary user shares a spectrum with an existing primary user (and interferes with it). We propose two lower bounds, for the primary user mean rate, depending on the channel state information available for the secondary-user power control and on the type of constraint for spectrum access. Several power control policies are investigated and the achieved primary-user mean rates are compared with the lower bounds. Specially, assuming all pairs of transmitter-receiver are achieving real-time delay-sensitive applications, we propose a novel secondary-user power control policy to ensure for both users, at a given occurrence, predefined minimum instantaneous rates. This power control uses only the secondary-user direct links gains estimations (secondary-to-secondary link and secondary-to-primary link). We take into account all links in the network.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

In this work, a novel technique which allows every transmitter in an interference network to have global channel state information (CSI) is proposed. The key feature of the proposed technique is that each transmitter acquires global CSI purely through the available feedback channel (which is assumed here to be the received signal power). In the first step of the proposed technique, each transmitter uses several observations provided by the feedback channel to learn the channel gains perceived by its intended receiver. Secondly, this information is quantized, modulated, and transmitted to the other transmitters through the power levels used by the transmitters; the latter are indirectly observed through the received signal power. Hence, the interference is used as an implicit communication channel through which local CSI is exchanged. Once global CSI is acquired, it can be used to optimize any utility function which depends on it.

The aim of this study is to use the Discrete Cosine Transform (DCT) instead of the previous methods which used the discrete Fourier transform (DFT) to detect the signal of a primary user by the Bartlett periodogram method. In this study the Digital Video Broadcast-Terrestrial (DVB-T) signals are used as an application example to analyze and assess the proposed spectrum sensing algorithm in the frequency domain using the AWGN channel. The study concludes that an accurate performance analysis of energy detection, reducing the noise variance without decreasing the signal resolution compared with the Bartlett periodogram based on DFT. By using 16-QAM modulation it can be seen the average variance of the noise in the DCT in all the scenario is 0.3478, while in FFT is 5841.37. This is mainly due to DCT being a real transform possessing an energy compaction property and the leakage effect is not there for DCT as compared to DFT. The Monte Carlo trials are used to confirm the accuracy of the proposed analysis. To obtain good accuracy with low noise variance to implemented the system in low complexity, it is required to use some trade-off between Probability of Detection (PD) and the Probability of False Alarm (PFA).

Scientists at the International Rice Research Institute (IRRI), Philippines, generate a large volume of research results emanating from donor-funded projects. The main objective is to disseminate, as widely as possible, the results of IRRI's research. There is also a strong push to provide free open access to these information resources through modes convenient to researchers in both developing and developed countries. Certain instruments for open access (OA) are already in place at IRRI, including links to full-text publications posted on the Institute's Web site (http://www.irri.org/), especially via the Library branch site (http://ricelib.irri.cgiar.org/), the Rice Knowledge Bank (http://www.knowledgebank.irri.org/), and Rice Publications Archive (http://rice-publications.irri.org/). The joint initiatives of the Library and the Institute's main science publishing units, particularly Communication and Publications Services and the Training Center, typify a convergence ...

The quality of energy detector is quite challenging when the system parameters are not stable. On the other hand, in a cognitive radio network, primary users are licensed to use the desired radio spectrum band(s) and the throughput of the primary network has the highest priority to be kept satisfied. Therefore, it is quite important to secure the quality of primary service to a certain level, and it is worthless to blindly improve the throughput of the secondary network without taking its possible effects on the primary throughput into account. Hence, the mentioned issues motivate us to enhance the total throughput of the system when it suffers from an unstable primary network, due to a medium-traffic rate, and a random density of the secondary users, due to a stochastic-modeled secondary network, at the same time. By introducing a 1-persistent method in a cooperative spectrum sensing scheme, we show that how effective it can improve both primary and secondary throughputs, resulting higher total throughput of the system.

Cognitive radio methodologies have the potential to dramatically increase the throughput of wireless systems. Herein, control strategies which enable the superposition in time and frequency of primary and secondary user transmissions are explored in contrast to more traditional sensing approaches which only allow the secondary user to transmit when the primary user is idle. In this work, the optimal transmission policy for the secondary user when the primary user adopts a retransmission based error control scheme is investigated. The policy aims to maximize the secondary users' throughput, with a constraint on the throughput loss and failure probability of the primary user. Due to the constraint, the optimal policy is randomized, and determines how often the secondary user transmits according to the retransmission state of the packet being served by the primary user. The resulting optimal strategy of the secondary user is proven to have a unique structure. In particular, the optimal throughput is achieved by the secondary user by concentrating its transmission, and thus its interference to the primary user, in the first transmissions of a primary user packet. The rather simple framework considered in this paper highlights two fundamental aspects of cognitive networks that have not been covered so far: (i) the networking mechanisms implemented by the primary users (error control by means of retransmissions in the considered model) react to secondary users' activity; (ii) if networking mechanisms are considered, then their state must be taken into account when optimizing secondary users' strategy, i.e., a strategy based on a binary active/idle perception of the primary users' state is suboptimal.

A novel framework for the analysis and optimization of cognitive wireless networks with unslotted time operations and reactive primary users is proposed. In the considered network setting, primary users' channel access is regulated by a carrier sense-based contention mechanism. As the sensing mechanism cannot distinguish between primary and secondary signals, secondary users' activity may interfere with primary users' channel contention, thus biasing the statistics of the stochastic process modeling primary users' transmissions. In fact, a primary user which wakes up during a transmission from a secondary user may sense a busy channel and enter backoff or generate a collision. The proposed framework considers these effects and optimizes the fraction of time a secondary user is allowed to transmit according to a constraint on the minimum throughput achieved by the primary users. Numerical results are presented which illustrate fundamental behaviors and tradeoffs in a network with one primary and one secondary user. Extension to more general scenarios is also discussed.

Spectrum sensing is a critical function for enabling dynamic spectrum access (DSA) in wireless networks that utilize cognitive radio. In DSA networks, unlicensed secondary users can gain access to a licensed spectrum band as long as they do not interfere with primary users. Spectrum sensing is subject to errors in the form of false alarms and missed detections. False alarms cause spectrum under-use by secondary users, and missed detections cause interference to primary users. Although existing research has demonstrated the utility of a Markov chain for modeling the spectrum access pattern of primary users over time, little effort has been directed toward spectrum sensing based upon such models. In this paper, we develop several soft-input sequence detection algorithms of Markov sources in noise for spectrum sensing in DSA networks. We assign different Bayesian cost factors for missed detections and false alarms, and we show that a suitably modified forward-backward sequence detection algorithm is optimal in minimizing the detection risk. Two advanced sequence detection algorithms, complete forward algorithm and complete forward partial backward algorithm are introduced and their performance are compared as well. Along the way, we observe new fundamental limitations on sensing performance that we term the risk floor and the window length limitation of energy detection and coherent detection that arise from their mismatch with the PU's spectrum access pattern.

Spectrum sensing is a critical function for enabling dynamic spectrum access (DSA) in wireless networks that utilize cognitive radio (CR). In DSA networks, unlicensed secondary users can gain access to a licensed spectrum band as long as they do not cause harmful interfere to primary users. Spectrum sensing is subject to errors in the form of false alarms and missed detections. False alarms cause spectrum under-use by secondary users, and missed detections cause interference to primary users. Although existing research has demonstrated the utility of a Markov chain for modeling the spectrum access pattern of primary users over time, little effort has been directed toward spectrum sensing based upon such models. In this paper, we develop general sequence detection algorithms for Markov sources in noise for spectrum sensing in DSA networks. We assign different Bayesian cost factors for missed detections and false alarms, and we show that a suitably modified forwardbackward sequence detection algorithm is optimal in minimizing the detection risk. Two advanced sequence detection algorithms, the complete forward algorithm and the complete forward partial backward algorithm are introduced and their performances are compared as well. Along the way, we observe new fundamental limitations on sensing performance that we term the risk floor and the window length limitation of energy detection and coherent detection that arise from mismatch of their observation window with the PU's spectrum access pattern.

In this letter, we deal with the cognitive radio (CR) concept for legacy primary links optimized for non-interference surroundings. In this type of network, primary destinations are not able to deal with possible interference and a missed cognitive detection significantly reduces the system performance. The enhancement of the primary network with cooperative diversity in addition to the well-known diversity gain for the primary link improves the sensing ability of the system and protects the primary user from possible interference. The proposed solution provides CR benefits without complicated network modifications and seems to be an attractive solution for future legacy networks.

Two driving goals for cognitive radio (CR) technique are maximizing spectrum utilization and avoiding interference to primary users. In this paper, we deal with the CR concept for legacy primary links optimized for non-interference surroundings. In this type of network, primary destinations are not able to deal with possible interference and a missed cognitive detection significantly reduces the system performance. The enhancement of the primary network with cooperative diversity in addition to the well-known diversity gain for the primary link improves the sensing ability of the system and protects the primary user from possible interference. Both Amplify-Forward (AF) and Decode-Forward (DF) cooperative schemes are studied for the problem under consideration and a new DF policy which introduces a cognitive relay behavior is investigated. The proposed technique provides CR benefits without complicated network modifications and seems to be an attractive solution for future legacy networks with flexibility limitations.

The objective of this work is to obtain characteristic daily profiles of consumption, wind generation and electricity spot prices, needed to develop assessments of two different options commonly regarded under the smart grid paradigm: residential demand response, and small scale distributed electric energy storage. The approach consists of applying clustering algorithms to historical data, namely using a hierarchical method and a self-organizing neural network, in order to obtain clusters of diagrams representing characteristic daily diagrams of load, wind generation or electricity price. These diagrams are useful not only to analyze different scenarios of combined existence, but also to understand their individual relative importance. This study enabled also the identification of a probable range of variation around an average profile, by defining boundary profiles with the maximum and minimum values of any cluster prototypes.

Video is becoming vital to society and economy. It plays a key role in information distribution and access, and it is also becoming the natural form of communication on the Internet and via mobile devices. The massive increase in digital audiovisual information will pose high demands on advanced storage and retrieval engines, and it is certain that consumers and professionals will need advanced storage and search technologies for the management of large-scale video assets.

This paper proposes an optimal cooperative spectrum sensing scheme, based on the criterion of deflection coefficient maximization of the global decision statistic. Multiple cooperative secondary users serve in the cognitive radio network to provide space diversity for spectrum sensing. After the fusion center acquires the optimal fusion weights, an optimal global threshold setting strategy is utilized to obtain the final global decision. Since the proposed optimal cooperative sensing scheme requires precise estimations of primary user signal strengths and the noise variances at different cooperative secondary users, a recursive estimate algorithm is also proposed. Simulations illustrate the proposed optimal soft fusion scheme can significantly improve the spectrum sensing performance and outperform the conventional maximal-ratio combining and equal gain combining schemes. The recursive estimate algorithm can effectively approach the ideal performance of the proposed sensing scheme.

Channel allocation problem is a major challenge in wireless local area networks (WLANs), especially in dense deployments of access points (APs) where congestion of the unlicensed spectrum bands (i.e., ISM bands) could undermine achieved network performance. This paper analyses the possibility to alleviate congestion of the ISM band by allowing some APs to use additional channels located in licensed bands in an opportunistic manner whenever licensee services (i.e., primary users) are not affected. Availability of these additional channels in licensed bands is assumed not to be the same for all the APs. Based on this assumption, we formulate the problem for the channel assignment as a Binary Linear Programming (BLP) problem, which allows us to obtain an optimal solution despite an elevated execution time. We also develop a heuristic method based on building a Minimum Spanning Tree (MST) graph attending to interference conditions that is able to find nearoptimal solutions with a shorter execution time. Results are provided to assess the benefits of such a proposal under different WLAN deployment situations and primary channel availability conditions.

Collaborative spectrum sensing can significantly improve the detection performance of secondary unlicensed users (SUs). However, the performance of collaborative sensing is vulnerable to sensing data falsification attacks, where malicious SUs (attackers) submit manipulated sensing reports to mislead the fusion center's decision on spectrum occupancy. Moreover, attackers may not follow the fusion center's decision regarding their spectrum access. This paper considers a challenging attack scenario where multiple rational attackers overhear all honest SUs' sensing reports and cooperatively maximize attackers' aggregate spectrum utilization. We show that, without attack-prevention mechanisms, honest SUs are unable to transmit over the licensed spectrum, and they may further be penalized by the primary user for collisions due to attackers' aggressive transmissions. To prevent such attacks, we propose two novel attack-prevention mechanisms with direct and indirect punishments. The key idea is to identify collisions to the primary user that should not happen if all SUs follow the fusion center's decision. Unlike prior work, the proposed simple mechanisms do not require the fusion center to identify and exclude attackers. The direct punishment can effectively prevent all attackers from behaving maliciously. The indirect punishment is easier to implement and can prevent attacks when the attackers care enough about their long-term reward.

The choice of this topic was influenced from the concept that statistical analysis of different attributes representing certain endpoints of behavior during radio communication in cognitive networks was necessary to study the outliers occurring in those parameters. The importance of cognitive radio is explained in detail in the literature review section of this paper. The purpose of this report is to do an overview of emerging patterns in cognitive radio networks and seek an understanding of data by learning what kind of attributes that display outliers during estimation. During the course of this research, it has come to light that study of outliers require preprocessing of data during which certain anomalies of data are studied and then removed thus optimizing the dataset. In the process, two major attributes SNR and Lambda have emerged and statistically shown a pattern that helped with the estimation of outliers. Key words: SNR, Lambda, Outliers, PU, SU, CRs.

A realização deste projeto não seria possível sem o contributo e apoio de algumas pessoas, pelo que agradeço todo o auxílio e atenção atribuída. Em primeiro lugar, aos meus pais e a minha irmã por estarem sempre ao meu lado desde a minha entrada na universidade, sempre com confiança, apoio e compreensão em todas as etapas deste ciclo. As minhas orientadoras, a Professora Doutora Anabela Alves e a Professora Doutora Paula Carneiro, por todo apoio, disponibilidade e confiança demostrado ao longo do projeto e da realização da dissertação, com conselhos e críticas construtivas que foram essenciais ao longo do projeto. Ao meu orientador na empresa, Sr. António Gonçalves, ao diretor do departamento da qualidade, Sr. António Azevedo, aos meus colegas de trabalho e a todos os colaboradores da empresa Gestamp Cerveira Lda, pela oportunidade que me ofereceram em desenvolver este desafiante projeto, pela disponibilidade e por toda a partilha de conhecimentos. Ao Professor Doutor António Vieira, pela atenção, confiança e apoio atribuído no desenvolvimento do projeto da dissertação. Para terminar, mas não menos importante, quero agradecer aos meus amigos, pelo apoio e companheirismo ao longo desta etapa. A todos, o meu sincero obrigado! v DECLARAÇÃO DE INTEGRIDADE Declaro ter atuado com integridade na elaboração do presente trabalho académico e confirmo que não recorri à prática de plágio nem a qualquer forma de utilização indevida ou falsificação de informações ou resultados em nenhuma das etapas conducente à sua elaboração. Mais declaro que conheço e que respeitei o Código de Conduta Ética da Universidade do Minho. vi RESUMO O projeto foi desenvolvido no âmbito da dissertação do último ano do Mestrado em Engenharia Industrial numa empresa de componentes metálicos para automóveis. Este teve como principal objetivo a melhoria de processos logísticos e das condições de trabalho associadas utilizando princípios de Lean Thinking e de Ergonomia. A metodologia de investigação escolhida para este projeto, foi a Action-Research, permitindo um envolvimento direto do investigador com os colaboradores da empresa no projeto. Esta metodologia iniciou-se com o diagnóstico da situação atual para identificar os problemas. Em simultâneo, efetuou-se uma revisão bibliográfica sobre Lean Production, e Lean logístics, os princípios de ergonomia e a sua relação com a filosofia Lean. Após uma descrição da situação atual da unidade autonóma produtiva (UAP) em estudo e dos processos genéricos, dos fluxos de informação e de materiais e dos armazéns desta unidade, foi efetuada uma análise crítica de forma a diagnosticar e identificar os problemas existentes na UAP. Os principais problemas encontrados foram classificados em três categorias: problemas genéricos da UAP em estudo (e.g. esperas associadas ao problema da logística interna), problemas ergonómicos (e.g. manuseamento difícil dos contentores situados no suporte rolante) e problemas logísticos (e.g. não aproveitamento dos benefícios associados ao conceito Milk-Run). Por fim, tendo em conta a analise efetuada, foi traçado um plano de ação onde foram desenvolvidas as propostas de ações de melhoria para os problemas identificados. Este plano de ação foi desenvolvido a partir das três categorias de problemas, de modo a responder aos objetivos concretos do projeto de dissertação. De forma a comprovar as possíveis melhorias da logística interna, foi elaborado um projeto para implementar Automated Guided Vehicles (AGV), apoiado por uma simulação 3D, de forma a eliminar os desperdícios encontrados ao longo do projeto e obter uma poupança de 14% (cerca de 11025 € com o custo de aquisição no primeiro ano), e uma possível poupança anual de 40% (cerca de 31025 € no segundo ano) relativamente a implementação de AGVs na UAP em estudo.

In this paper, we focus on one of the ImageCLEF tasks that LIRIS-Imagine research group participated: visual concept detection and annotation. For this task, we firstly propose two kinds of textual features to extract semantic meanings from text associated to images: one is based on semantic distance matrix between the text and a semantic dictionary, and the other one carries the valence and arousal meanings by making use of the Affective Norms for English Words (ANEW) dataset. Meanwhile, we investigate efficiency of different visual features including color, texture, shape, high level features, and we test four fusion methods to combine various features to improve the performance including min, max, mean and score. The results have shown that combination of our textural features and visual features can improve the performance significantly.

A social ranking (solution) over a set N is defined as a map assigning to each coalitional relation (i.e. a ranking over subsets of N ) another ranking over the single elements in N . Differently, coalition formation situations, and, in particular, hedonic games, mainly focus on partitions of the set N into disjoint coalitions, which are in general referred to as coalition structures. A coalition structure may be stable according to various notions of stability and the objective is to understand under which conditions a coalition structure is stable. In this paper we merge the framework of coalition formation with the one of social rankings to keep into account the effect of hierarchies within coalitions on the stability of coalition structures. We consider alternative classes of coalition formation games where the preferences of the players over coalitions are induced by a social ranking. More precisely, players compare coalition structures keeping into account both the relative ranking of coalitions to which they belong (according to a coalitional relation) and their position in the social ranking within each coalition. Constructive characterizations of the set of stable coalition structures are provided for alternative classes of hedonic games, together with an impossibility result on the existence of stable coalition structures for (non-hedonic) coalition formation situations.

Cognitive Radio is an emerging wireless technology that has grabbed the attention of researchers, academicians, and telecommunication industries worldwide. Recent survey reports show that unlicensed frequency bands have become overcrowded from past few years with widespread acceptance of diverse wireless technology applications whereas, licensed frequency bands are being used intermittently. To deal with the conflicts between unlicensed spectrum overuse and underutilization of licensed frequency band, Cognitive Radio technology has been evolved eventually. It allows unlicensed subscribers to access licensed subscriber frequency band with some power constraints such that minimum or no interference should be experienced by primary user and its quality of service should not be affected while sharing its spectrum with unlicensed secondary subscriber. In this paper, distance based power control scheme has been analyzed for overlay ad-hoc cognitive radio network. It is shown that algorithm provides optimum power control as long as the separation between cognitive transmitter and receiver is greater than or equals to maximum decodable radius of primary transmitter.

In decentralized Cognitive Radio (CR) networks timing errors between secondary users cause increased interference during sensing periods. This kind of intra-network inteference inflicts significant performance degradation due to the growth of false alarm probabilities if energy-based incumbent detection is used, as shown in our previous study. Therefore, in this paper we propose a novel interference suppression algorithm, called Interference Suppression for Cognitive Radios (ISCR), to mitigate the impact of other CR users' transmissions on sensing. We show that by using ISCR the throughput of distributed CR networks under timing errors can be improved by minimizing the probability of false alarm while preserving sufficient protection for primary users. In addition to providing as much as 20 % throughput gain, ISCR is easy to implement and can be executed in real time.

While FCC proposes spectrum sharing between a legacy TV system and a cognitive radio network to increase spectrum utillization, one of the major concerns is that the interference from the cognitive radio network should not violate the QoS requirements of the primary users. In this paper, we consider the scenario where the cognitive radio network is formed by secondary users with low power personal/portable devices and when both systems are operating simultaneously. A power control problem is formulated for the cognitive radio network to maximize the energy efficiency of the secondary users and guarantee the QoS of both the primary users and the secondary users. The feasibility condition of the problem is derived and both centralized and distributed solutions are provided. Because the co-channel interference are from heterogeneous systems, a joint power control and admission control procedure is suggested such that the priority of the primary users is always ensured. The simulation results demonstrate the effectiveness of the proposed schemes.

Spectrum under-utilization calls for the open and dynamic spectrum access mechanism, which allows the unlicensed user equipped with cognitive radios to opportunistically sense and access the spectrum that not occupied by primary users. In practice due to the hardware limitations, each cognitive radio user may be only able to sense a portion of the interested wide span spectrum. Hence, a hardware-constrained cognitive MAC to conduct efficient and intelligent spectrum sense decision is desired. In this paper, we formulate the cognitive radio spectrum sensing problem under time-varying channels as an adversarial bandit problem without any assumption of the channel statistics. A fully distributed strategy is proposed to address the fundamental tradeoff between spectrum exploration and spectrum exploitation during the sensing periods. Simulation results demonstrate that significant performance gain can be achieved by the proposed algorithm when the channels are timevarying on small time-scales. A coordination scheme for the multi-user case is also presented and the effectiveness is also demonstrated by the simulation results. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2010 proceedings.

In this paper we describe the process that we undertook to build a configurable wireless platform that can be used to implement cognitive radio network (CRN) architectures. Consisting of a commodity IEEE 802.11 a/b/g (WiFi) router at the physical (PHY) layer and RF signal processing and IP traffic shaping circuitry, the resultant hybrid terminal (called the WiFi CR) becomes a building block that can implement cognitive femtocells, point to multipoint, mesh, and relay wireless networks. The IP addressable WiFi CR terminals can sense their radio environment, schedule IEEE 802.11 packet transmissions in space and time, and select channel, modulation rates, and transmit power. Intelligent operation is undertaken by a cognitive network management system (CR NMS) which controls a number of WiFi CR terminals and solicits sensor information from them. The CR NMS gathers the spectrum and sensed interference information and builds a memory map with such knowledge, thereby creating radio environment awareness for the CRN. Cognitive engines (the intelligent control algorithms) within the CR NMS use radio environment knowledge and other information (such as spectrum policy) to give the system a capability to seek white space spectrum, avoid interference, identify primary users, and take on other tasks associated with cognitive radio (CR). Designed around ISM band operation, this generic terminal, with proper RF modifications, can work in the TV bands, 3.65-3.70 GHz, and up to 60 GHz.

In opportunistic spectrum access, each secondary user selects a channel from a pool of multiple channels based on their local observations. The challenge here is to learn the best channel in terms of availability, as the channel availability statistics are unknown. In order to learn these unknown statistics, a novel decentralized multiuser learning technique termed as DSEE for channel selection in dynamic networks (DSEE-CSDN) has been proposed. DSEE-CSDN allows secondary users to enter the network during different time slots. Thus, the number of secondary users is not known beforehand. Moreover, the availability status of different independent channels is considered to be changing according to the two-state restless Markov chain model, which, in practice, is more realistic as compared to independent and identically distributed channel state model. Thus, the problem is formulated as a stochastic multiuser restless multiarmed bandit. The proposed algorithm achieves system-wide order-optimal performance under self-play. Results indicate that DSEE-CSDN is able to achieve a logarithmic order of regret. Furthermore, collisions and switching cost are just around 5% and 2% of total time slots, respectively. Also, DSEE-CSDN can achieve probabilistic fairness in channel selection without any preagreement among users. Index Terms-Opportunistic spectrum access (OSA), decentralized algorithms, cognitive radio (CR), reinforcement learning, restless multiarmed bandits (MABs). I. INTRODUCTION T HE demand for electromagnetic radio spectrum has increased exponentially in the last decade due to the introduction of new technologies, such as device-to-device communication and access paradigms, such as long-term evolution (LTE) and LTE-advanced networks [1]. The spectrum is a natural and limited resource; thus, its efficient utilization is the only option. It has been shown in [2] and [3] that the radio spectrum is massively underutilized with respect to time, frequency, and location. Cognitive radio (CR) overcomes the abovementioned limitations by accessing instantly available bands [4]. It senses the surrounding environment to collect information and reconfigure its parameters, such as transmission power, carrier frequency, modulation techniques, etc. This solution is known as opportunistic spectrum access (OSA) [5].

In creative collaboration, the primary focus of participants is creating "what if" scenarios that must be jointly imagined. Collaboration in strictly Physical Reality (PR) is constrained because of the limitations the real world places on shared imagination. As dynamic as Virtual Reality (VR) environments can be, subtle human-to-human interaction is severely limited in these totally synthetic environments, which provide such poor support for the physical expression of passion and personality. Augmented Reality (AR) can add virtual assets to the physical world, yet creative interaction cries out to escape the context of the physical world. With interpersonal imaginative interaction, Augmented Virtuality (AV), the augmentation of a virtual setting with real objects, provides a means to merge a richly layered, multi-modal, 3D real experience into a virtual environment. This class of Mixed Reality (MR), which represents a reversal of the more common AR concept, provides a change in paradigm that offers unique opportunities and novel tools for collaboration, the impact of which we will explore in this paper. The Mixed Simulation "Demo Dome," an innovative application of MR Head Mounted Displays (HMD) and unidirectional retro-reflective material, provides the next generation of immersive environment, one that is an easily deployable means of multi-modal AV collaboration. The technology associated with this environment will be discussed, along with the Mixed Reality Software Suite (MRSS), a system that supports the creation and delivery of nonlinear interactive experiences within such a dome. Examples of the use of this system and concept in team performance training, emergency planning, collaborative design, experience modeling, scientific virtualization and entertainment will be presented.

Energy-efficient design has become increasingly important to battery-powered wireless devices. In this work, we focus on the energy efficiency of a cognitive radio network, in which a secondary user senses the channels licensed to some primary users sequentially before it decides to transmit. Energy is consumed in both the channel sensing and transmission processes. The energy-efficient design calls for a careful design in the sensing-access strategies and the sensing order, with the sensing strategy specifying when to stop sensing and start transmission, the access strategy specifying the power level to be used upon transmission, and the sensing order specifying the sequence of channel sensing. The objective is to identify the sensing-access strategies and the sensing order that achieve the maximum energy efficiency. In this talk, joint design of the channel sensing order and the sensing-access strategies will be presented, together with performance evaluation of the proposed energy-efficient design.

A new flexible multiple access control (MAC) scheme embedding channelization in multi-band carrier sense multiple access / collision avoidance (CSMA/CA) systems is proposed to provide different priority classes among users, and its performance is investigated. In the proposed scheme, two priority classes of users, primary and secondary users, are considered; the classical CSMA/CA protocol is modified to multiband operation for secondary users, whereas channelization is provided for primary users to ensure the quality of service (QoS). The performance of the proposed MAC scheme is analyzed using a new multi-band CSMA/CA model based on a Markov chain capturing the primary user channel activity and the number of bands. The throughput of secondary users is obtained as a function of the primary user activity as well as other CSMA/CA parameters. It is shown that this mixed MAC scheme can guarantee the throughput of primary users certainly with minimal performance degradation to secondary users, especially when the number of available bands is large or the maximum contention window (CW) size for the CSMA/CA secondary users is small compared with the number of secondary users.

We study a framework that captures the interdependencies between spreading channelization and routing for a secondary multi-hop cognitive radio network that operates cognitively to coexist with primary users. We consider interactions between dynamic routing and code-division channelization functionalities for cognitive radio networks. With this respect, we study the effect of joint routing, spreading code and power allocation on the network throughput. A solution for joint routing and spread-spectrum channelization is proposed as a localized approximation of the throughput-maximizing problem. Specifically, power and spreading code are allocated to guarantee the quality of service of the on-going primary and secondary transmissions, while the routing algorithm dynamically selects relays based on the network traffic dynamics and on the achievable data rates on different secondary links.

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O objetivo deste estudo e aferir da aplicabilidade da filosofia Kaizen num contexto real, procurando perceber quais as dificuldades subjacentes a implementacao da tecnica dos 5’s e estudar o seu impacto e aceitacao no quotidiano de uma PME portuguesa. Seguindo a metodologia de estudo de caso, do tipo exploratorio, recolheram-se os dados com base na observacao direta e em entrevistas, e procedeu-se a analise qualitativa das respostas. Os resultados obtidos evidenciam uma diminuicao do tempo de movimentacao dos trabalhadores, uma melhoria na qualidade e condicoes de trabalho e um aumento da produtividade. Concluiu-se que a cultura e a comunicacao vertical nao foram fatores impeditivos na implementacao dos principios do kaizen e da tecnica 5’s.

An interference alignment (IA) scheme is presented that allows multiple opportunistic transmitters (secondary users) to use the same frequency band of a pre-existing primary link without generating any interference. The primary and secondary transmit-receive pairs are equipped with multiple antennas. Under power constraints on the primary transmitter, the rate of the primary user is maximized by water-filling on the singular values of its channel matrix leaving some eigen modes unused, and hence, the secondary users can align their transmitted signals to produce a number of interference-free dimensions at each secondary receiver without causing any interference to the primary user. An outer bound is developed on the degrees of freedom (DoF) of the secondary users. In the case of a symmetric secondary network with time-varying channel coefficients having M antennas at each node and operating in the presence of a primary link with d 0 active eigen modes, a precoding scheme is presented for the secondary transmitters that can asymptotically achieve the available (M 0 d 0 ) + =2 DoF per secondary user. An iterative algorithm is also presented that utilizes channel reciprocity to achieve the proposed cognitive IA scheme. For a cognitive 3-user secondary network with constant channel coefficients, a novel closed-form solution is derived for the precoding matrices of the secondary users.

A Caetano Bus é cliente do Instituto Kaizen e o projeto foi desenvolvido nessa empresa, com o intuito de apoiar a montagem de uma nova linha de produção de um novo produto. O produto foi um novo chassi elétrico, tendo como objetivo o desenho de layout e modelo de produção e logística interna da linha de produção de chassis elétricos, implementando uma linha piloto dimensionada para 1 chassi/dia, com uma redução de pelo menos 30% das horas iniciais de produção. O presente trabalho reflete o estudo de conceitos de desenho e implementação de linhas de montagem e também de criação de fluxo entre as várias operações que fazem parte da cadeia de valor, a partir de ferramentas como o Kaizen Diário. A criação de standards de trabalho e de postos de trabalho alinhados -para possibilitar o fluxo de materiais entre estes com o mínimo de desperdício possível -e o balanceamento de operações por posto de trabalho -tendo em consideração o tempo de saída do produto da linha previamente estabelecido -foram os pontos principais de análise e decisão. Foram definidos três postos de montagem e dois de pré-montagem, por forma a conseguirmos aumentar a cadência na linha produtiva e também obtermos maior fluxo entre as várias operações de montagem.

In this paper we describe how the annotation method- ology adopted in our approach allows us to explain the organization of indexed references in scientific research articles. We identify the semantic values of author judg- ments in the text segments containing indexed refer- ences. We use an automated semantic annotation plat- form to annotate our corpora. Exploiting this result, we obtain a representation of the annotation distribution on different scales. Finally, we present two evaluations of the annotation.

This paper presents the performance evaluation of the Energy Detector technique, which is one of the most popular Spectrum Sensing (SS) technique for Cognitive Radio (CR). SS is the ability to detect the presence of a Primary User (PU) (i.e. licensed user) in order to allow a Secondary User (SU) (i.e unlicensed user) to access PU's frequency band using CR, so that the available frequency bands can be used efficiently. We used for implementation an Universal Software Radio Peripheral (USRP), which is the most used Software Defined Radio (SDR) device for research in wireless communications. Experimental measurements show that the Energy Detector can obtain good performances in low Signal to Noise Ratio (SNR) values. Furthermore, computer simulations using MATLAB are closer to those of USRP measurements.

It is well known that secondary users can take advantages of spectrum opportunities from primary users via cognitive radio technology. However, general sense cognitive radio networks allow all users to cooperatively relay the packets, especially primary users are aware of existence and activity of secondary users. Secondary users may act as cooperative relays for primary traffic. We propose a relay selection criteria such that cooperation is beneficial to both primary and secondary systems. With the suitably chosen relays, power consumption in primary transmissions is reduced and simultaneously interference from primary traffic decreases exposing spectrum opportunities for secondary traffic. We characterize the performance improvement of secondary network due to the extra spectrum opportunities by analyzing the extension of its connectivity region through percolation theory. Such self-motivated cooperation leads the way toward self-organizing wireless networks.

Cognitive Radio technology releases the spectrum from shackles of authorized licenses and facilitates the trading of spectrum bands. In the spectrum market, primary service providers (PSPs) set prices for the vacant licensed bands of primary users (PUs) and sell/lease them for pecuniary gains, and the secondary service provider (SSP) can buy/rent the bands and support the secondary users (SUs) for their opportunistic spectrum accessing (OSA) when primary services are not active. However, due to the unpredictable activities of primary services, the SSP may suffer the monetary risk or failure to satisfy the traffic demands from the SUs. It is challenging for the SSP to measure the risk for OSA, to choose the bands to access, and to split the overall traffic on the band-mix, when there are multiple vacant bands and uncertain spectrum supply from PSPs. To address the concerns of the SSP, in this paper, we first introduce the X loss, an intuitive measurement to evaluate the risk for OSA at a given confidence level. Although the X loss is attractively simple, it theoretically underestimate the potential risk for OSA. Meanwhile, the X loss requires strong assumptions to support band-mix selection for traffic splitting, i.e., the primary services of different bands must satisfy normal distribution, which is not necessarily true in practice. To overcome the weakness of the X loss, we further propose a more suitable risk measurement, the expected X loss, which is theoretically subadditive and practically consistent with the SSP's perception of risk for OSA. Based on the proposed measurement, we formulate the band-mix selection problem for traffic splitting into an optimization problem and solve it by linear programming.

Cognitive Radio technology releases the spectrum from shackles of authorized licenses and facilitates the trading of spectrum bands. In the spectrum market, primary users (PUs) set prices for their vacant bands and sell them for monetary gains, and secondary users (SUs) buy the bands and opportunistically use them to satisfy their service demands when the PUs are not active. However, when there are multiple bands available for the SUs to access, the SU confronts the challenges of how to choose bands and how to split his traffic over them considering both the contention from peer SUs as well as the unpredictable activities of the PUs. In this paper, we propose a return and risk model to represent these concerns of the SU, and help the SU to make appropriate decisions of traffic distribution over available spectrum bands, either the bands belonging to SU itself or the bands shared with PUs. The simulation and analysis show that our spectrum sharing scheme is efficient in terms of maximum return for given risk or minimum risk for given return, and is also effective in improving the spectrum utilization and SUs' satisfactory degrees.