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Cognitive Radio Oriented Wireless Networks and Communications, 2009. CROWNCOM '09. 4th International Conference on

Date 22-24 June 2009

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Displaying Results 1 - 25 of 63
  • Capacity achievable by spectrum sharing with adaptive transmit power control: Based on field measurements

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (187 KB) |  | HTML iconHTML  

    We conduct field measurements to assess the effectiveness of the spectrum sharing method using adaptive transmit power control [2]. This investigation assumes a fixed satellite service as the victim and an IMT-Advanced system as the interferer. We evaluate the capacities achieved by adaptive transmit power control in a comparison with fixed-level transmit power control. The results show that adaptive transmit power control attains higher capacities, especially in severe sharing conditions such as the victim receiver operates near a interfering transmitter. We also discuss the impact of introducing interference criteria based on desired signal level at the victim receiver instead of the long-standing noise-based criteria. View full abstract»

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  • A study on the application of wavelet packet transforms to Cognitive Radio spectrum estimation

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (505 KB) |  | HTML iconHTML  

    Spectrum sensing is an important functionality of cognitive radio (CR). Accuracy and speed of estimation are the key indicators to select the appropriate spectrum sensing technique. Conventional spectrum estimation techniques which are based on short time Fourier transform (STFT) suffer from familiar problems such as low frequency resolution, variance and high side lobes/leakages. In this article, the possibility of employing wavelet packet decomposition as a basis for new spectrum sensing approach is investigated. Three types of sources, namely partial band, single tone and swept tone, are used to investigate the performance of the proposed wavelet based approach. Swept tone source is a special kind of source devised to simulate the temporal dynamics in cognitive radio. The results of the experiments show that the wavelet based approach is quite promising for spectral estimation and can be a suitable technology for CR applications. View full abstract»

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  • A context-aware and Intelligent Dynamic Channel Selection scheme for cognitive radio networks

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (167 KB) |  | HTML iconHTML  

    The tremendous growth in ubiquitous low-cost wireless applications that utilize the unlicensed spectrum bands has laid increasing stress on the limited and scarce radio spectrum resources. Given that the licensed or Primary Users (PUs) are oblivious to the presence of unlicensed or Secondary Users (SUs), Cognitive Radio (CR) is a new paradigm in wireless communication that allows the SUs to detect and use the underutilized licensed spectrums opportunistically and temporarily. In this paper, we propose a Context-aware and Intelligent Dynamic Channel Selection scheme that helps SUs to select channel adaptively for data transmission to enhance QoS, particularly throughput and delay. Our scheme is suitable for CR networks with mobile hosts. We formulate and design our scheme using Reinforcement Learning that offers a simple and yet practical solution. Channel heterogeneity, which is a feature unique to CR networks that has been ignored in previous studies, is considered in this paper. Simulation results reveal that the proposed scheme achieves very good performance. View full abstract»

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  • Wavelet Packet Multi-carrier modulation MIMO architecture for spectrum pooling systems

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (546 KB) |  | HTML iconHTML  

    In this paper we demonstrate the operation of a wavelet packet multi-carrier modulation (WPMCM) based cognitive radio (CR) on a multiple-input and multiple-output (MIMO) platform. The wavelet packets are derived from multistage tree-structured paraunitary filter banks. To enable the WPMCM system to co-exist with other licensed users (LU), the WPMCM transmission waveform characteristics are shaped to communicate in the idle time-frequency gaps of the LUs. This is done by vacating WPMCM carriers in and near the region of the LU spectrum. Furthermore, a spectrum estimation unit is tagged to the WPMCM transceiver structure by exploiting the filter bank infrastructure used for wavelet packet demodulation. Thus spectrum analysis is done at no additional cost. Through simulation studies the effectiveness of the system is demonstrated. View full abstract»

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  • A quantitative assessment of wireless spectrum measurements for dynamic spectrum access

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (271 KB) |  | HTML iconHTML  

    In this paper, we provide a qualitative assessment of the spectrum usage across five geographically separated sites in four mid-size metropolitan centers located in the United States. Specifically, the variations in spectrum occupancy across space, time and frequency are investigated and compared between different sites within the city as well as with other cities. We show that the variation at different locations within the same city is considerably high. Furthermore, we present a simple four-state Markov model that characterizes time-varying behavior of the spectral occupancy of a frequency channel. View full abstract»

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  • Performance comparison of time delay estimation for whole and dispersed spectrum utilization in cognitive radio systems

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (148 KB) |  | HTML iconHTML  

    In cognitive radio systems, information is transmitted and received over multiple dispersed bands using dispersed spectrum utilization approach whereas information is transmitted and received over a single band using whole spectrum utilization approach. In this paper, performance of both approaches are compared theoretically considering CRLB and maximum likelihood (ML) method for time delay estimation. The results show that dispersed spectrum utilization methods have a great potential to exploit the efficiency of spectrum utilization and support goal driven and autonomous cognitive radio systems. View full abstract»

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  • Research project concerning cooperative heterogenious radio networks for reliability improvements

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (235 KB) |  | HTML iconHTML  

    In Japan, several new Research and Development (R & D) projects have been started, whose main purpose is to attain the efficient use of the restricted resources of frequency bands. This paper introduces the objective and outline of the project in which we have been engaged. The test-bed facility has been developed and their features, specifications and some experimental results are also described. Our project focuses on cooperative heterogeneous radio networks to improve the reliability on the radio communication link. The technology developed in the project is considered to be advanced network technology that includes the cognitive radio system being studied in many research organizations. View full abstract»

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  • User clusters based hierarchical cooperative spectrum sensing in cognitive radio networks

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    This paper investigates secondary user clusters based cooperative spectrum sensing. Secondary users in the cognitive radio network are grouped into multiple clusters and the cooperative spectrum sensing is performed on a hierarchical architecture of these user clusters, through two levels of user collaborations. The low level cooperation is carried out within each cluster while the high level one is accomplished inside the cluster of the clusterheads. We propose soft fusion and hard fusion according to the bandwidth constraints of the control channels and the spectrum sensing agility requirement. An optimal soft fusion scheme and a double-threshold strategy are proposed to improve the overall spectrum sensing performance in soft fusion and hard fusion, respectively. Analysis and simulations verify that the proposed hierarchical cooperative spectrum sensing schemes can significantly improve the spectrum sensing performance. View full abstract»

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  • A novel algorithm for blind adaptive recognition between 8-PSK and π/4-shifted QPSK modulated signals for software defined radio applications

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (309 KB) |  | HTML iconHTML  

    In this paper, we propose a new method to recognizing and distinguishing among 8-PSK modulated signal and pi/4-shifted QPSK, from the samples of received noisy and faded PSK signal. The proposed algorithm is based on computation of relative Euclidean distance and relative phase difference among the received symbols in a frame. Prior to recognition, the constant modulus (CM) equalization is performed. Based on simulation results, this method can perform recognition task with high accuracy even at low signal to noise ratio (SNR) values and employing fairly small number of data samples. To the best of our knowledge in comparison with other methods of distinguishing among QPSK variants, this algorithm do well specially in practical systems which have a limited time to make the decision and use small number of samples of receiving signal. View full abstract»

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  • Enhancing cognitive radios with spatial statistics: From radio environment maps to topology engine

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (132 KB) |  | HTML iconHTML  

    Radio environment maps are a promising architectural concept for storing environmental information for use in cognitive wireless networks. However, if not applied carefully their use can lead to large amounts of measurement data communicated over wireless links, causing substantial overhead. We propose enhancing the basic radio environment map concept by spatial statistics and probabilistic models, enabling applications to benefit from environment data while reducing overhead. In this paper we discuss the development of a topology engine, an agent in the CWN collecting and processing spatial information about the environment for storage in the REM. We discuss both technical and architectural issues in enabling such an approach, and outline some of the potential application scenarios for the topology engine. View full abstract»

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  • Traffic studies for DSA policies in a simple cellular context with packet services

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (414 KB) |  | HTML iconHTML  

    DSA (dynamic spectrum allocation) techniques are very challenging when the quality of service has to be guaranteed in a flexible spectrum situation. In this paper, we present and analyze DSA policies for packet services in cellular context. A centralized model, where a meta-operator shares a common spectrum among different operators, is considered. We focus on two criteria for the policies design: the total welfare (sum of operators' rewards), and the blocking probability. We go through two steps to pass from the actual FSA (fixed spectrum allocation) situation into DSA. First, DSA algorithms depend on the arrival rates. Second, DSA algorithms depend on both the arrival rates as well as the number of active users. Targeting the reward maximization shows to be inefficient when the blocking probability has to be guaranteed. However policies targeting a blocking probability threshold, achieve greater rewards then FSA rewards. We also present a heuristic DSA algorithm that takes into consideration: the arrival rates, the number of active users and the blocking probability. The algorithm gives a very close blocking probability to the one achieved using FSA, while the obtained reward significantly exceeds the FSA reward. View full abstract»

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  • A frequency rendezvous approach for decentralized dynamic spectrum access networks

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (139 KB) |  | HTML iconHTML  

    In this paper, we propose a transmission frequency rendezvous approach for secondary users deployed in decentralized dynamic spectrum access networks. Frequency rendezvous is a critical step in bootstrapping a wireless network that does not possess centralized control. Current techniques for enabling frequency rendezvous in decentralized dynamic spectrum access networks either require pre-existing infrastructure or use one of several simplifying assumptions regarding the architecture, such as the use of regularly spaced frequency channels for communications. Our proposed approach is designed to be operated in a strictly decentralized wireless networking environment, where no centralized control is present and the spectrum does not possess pre-defined channels. This is accomplished via a combination of receiver pilot tones, a tone scanning protocol, and transmitter/receiver handshaking process. In our proposed rendezvous algorithm, the most important step is pilot tone detection and receiver query. In order to realize a shortest search time for the target receiver, an efficient scanning rule should be employed. In this paper, three scanning rules are proposed and evaluated, namely: frequency sequence scanning, pilot tone strength scanning, and cluster scanning. To validate our result, we test our scanning rules with actual paging band spectrum measurements. View full abstract»

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  • Cyclostationary multitone beacon signal for opportunistic spectrum access

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (821 KB) |  | HTML iconHTML  

    Cognitive radio is a promising solution to the problem of spectrum scarcity by means of allowing secondary radio networks access the spectrum opportunistically. One of the most important issues in cognitive radio is how to detect existing over-the-air signals reliably. Not a few literatures have reported that signals could be detected via their inherent or embedded properties. However, these may not be reliable and flexible enough for all kinds of signals with different modulation types. In this paper, we propose a multitone beacon signal carrying cyclostationary signatures, which is able to strengthen the reliability and efficiency of signal detection at low cost of spectrum overhead. This beacon not only can indicate the presence or absence of user signal but also can reveal some other information helpful to opportunistic spectrum access through the bit word modulated in its cyclostationary signatures. It could be applied to device/network identification, indication of spectrum allocation and spectrum rendezvous, both for primary and secondary users. The generation and detection algorithm of the beacon signal are presented firstly in this paper, then an initial simulation analysis and experiments with radio devices are illustrated to discuss the performance. View full abstract»

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  • Optimal power allocation in joint spectrum underlay and overlay cognitive radio networks

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (105 KB) |  | HTML iconHTML  

    In this paper, we investigate the optimal power allocation strategy in the joint spectrum overlay and underlay cognitive radio network where a licensee and multiple unlicensed users coexist and operate in the same spectrum. We propose an optimal power allocation scheme which achieves the maximum system utility while satisfying the QoS requirement of SUs and interference constrains of the PU. Particularly, since the unlicensed users adopting the overlay strategy do not necessarily have perfect sensing knowledge regarding the licensee, we modify the optimal power allocation scheme with the imperfect sensing knowledge. Moreover, we propose a QoS sensitivity based admission control algorithm to deal with the case that the optimal power allocation scheme is infeasible. The simulation results show that the proposed algorithm achieves better performance. View full abstract»

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  • Cognitive radio with reinforcement learning applied to heterogeneous multicast terrestrial communication systems

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (166 KB) |  | HTML iconHTML  

    This paper shows how channel assignment in heterogeneous multicast terrestrial communication systems can be improved using intelligence based on reinforcement learning. Two novel distributed channel assignment schemes with reinforcement learning applied are shown, which efficiently improves the speed and quality of channel assignment by limiting the reassignments, blocking and dropping rates. A weighting factor is used in this paper to determine the highest priority channels, and to help to control the performance of the system. It is found that reinforcement learning provides an efficient approach to reduce the needs of reassignments. At the same time, reassignment is a very good alternative to using blocking of new assignments to control dropping. Learning is categorized into 3 stages depending on the degree of effect it has on behavior. View full abstract»

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  • On regulation of spectrum sharing: An analysis supporting a distributed pilot channel

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB) |  | HTML iconHTML  

    This paper argues in favor of introducing a standardized distributed pilot channel to improve spectrum sharing between heterogeneous technologies in unlicensed and possibly licensed bands with incumbent users. The main features of such a distributed pilot channel are sketched and a simple distributed algorithm for optimization of spectrum sharing is introduced. The pilot channel serves as a supplement to spectrum sensing and can improve spectrum sharing in unlicensed and licensed bands. View full abstract»

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  • Coexistent intra-symbol SMSE waveform design: Variation in waveform update latency and update rate

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1178 KB) |  | HTML iconHTML  

    The impact of variation in waveform update latency and update rate is investigated for Spectrally Modulated, Spectrally Encoded (SMSE) waveform designs in a coexistent environment containing multiple 802.11 Primary User (PU) systems. As previously demonstrated for no latency with a fixed update rate, the SMSE waveform design process can exploit statistical knowledge of PU spectral and temporal behavior to maximize SMSE system throughput (bits/second) while adhering to SMSE and PU bit error rate constraints with mutual coexistent interference limited to manageable levels. Building upon this previous work, a sensitivity analysis is conducted here through parametric variation in both waveform update latency and update rate. Relative to a spectrally-only adapted waveform, the spectrally-temporally adapted waveform provides significant performance improvement. Maximum improvement is achieved using statistic-based prediction of channel temporal conditions and appropriate updating of the SMSE waveform design. View full abstract»

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  • A partial spectrum transmission method for dynamic spectrum access

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    This paper proposes a partial spectrum transmission (PST) method for dynamic spectrum access (DSA). For DSA, it is preferable to select modulation scheme which is appropriate for the low-priority user's condition and radio environment by taking into account the required Eb/N0, frequency efficiency and PARR. When received SINR condition is better, QAM is selected for high-speed packet communication. However, QAM may cause link performance degradation due to the shorter Euclidean distance. On the other hand, PSK is capable of preventing such performance degradation. In this paper, we propose a PST method using PSK. It is shown by computer simulations that the required Eb/N0 at a BLER of 10-2 and the PAPR for the proposed PST (1/2) are approximately maximum 1dB better than those of 16QAM respectively. View full abstract»

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  • The smart radio channel change protocol a primary user avoidance technique for dynamic spectrum sharing cognitive radios to facilitate co-existence in wireless communication networks

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (275 KB) |  | HTML iconHTML  

    This paper details the design, implementation, simulation, and testing of the Smart Radio Channel Change Protocol (CCP), a primary user avoidance technique for dynamic spectrum sharing cognitive radios in wireless communication networks. The CCP enables a digital cognitive radio to detect the presence of legacy analog or digital radios, and to facilitate channel-change procedures to use an alternate, vacant block of spectrum. This allows primary and secondary users to co-exist in the same band with minimal interference and reductions in quality of service (QoS). The CCP also provides an advantage to other systems' frequency management schemes in terms of simplicity of design and execution. We evaluate the CCP's performance through OMNeT++ simulations and experiments in a five node laboratory network testbed. We present our results in terms of the CCP's ability to detect and avoid the primary user and record its improvement to user QoS. View full abstract»

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  • Eigenvalues based spectrum sensing against untrusted users in cognitive radio networks

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (137 KB) |  | HTML iconHTML  

    Spectrum sensing is an essential mechanism for a cognitive radio system. However, the security aspects of spectrum sensing receive little attention so far. In this paper, we identify two kinds of untrusted secondary users which are called dasiaAlways Yespsila users and dasiaAlways Nopsila users. These untrusted secondary users can degrade detection performance greatly, especially when conventional data fusion rules are applied. To counter these threats, for the correlated primary signals, an eigenvalues based detection scheme with double thresholds and revised data fusion rules is proposed. Maximum eigenvalues are proved to be very effective to detect the correlated primary signals and to find the untrusted users. By using the revised data fusion rules, simulation shows that our method has a better detection performance than the conventional method. View full abstract»

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  • An approach for realizing Future Internet with cognitive technologies

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (563 KB) |  | HTML iconHTML  

    Telecommunications and information technology will be parts of the Future Internet infrastructures. It will be characterized by powerful and complex network infrastructures, advanced applications, services and content, efficient power management as well as extensions in the business model. These characteristics entail that the management of the Future Internet world will be more complex, compared to today. The introduction of cognitive systems is believed to be an efficient response to the complexity. In this respect, the aims and contribution of this paper is to provide an approach for realizing the Future Internet era by means of cognitive systems. The basis and foundation will be work conducted in the area of cognitive wireless networks. This work constitutes a solid basis, on which the Future Internet era can be realized, through suitable expansions. View full abstract»

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  • Performance of spectrum sensing using Welch's periodogram in rayleigh fading channel

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (149 KB) |  | HTML iconHTML  

    In this paper we present theoretical performance evaluation of spectrum sensing with energy detection using Welch's periodogram for cognitive radio systems. We generalize the theoretical expressions for the probability of detection and the probability of false alarm of energy detection in Rayleigh fading channel to the case of Welch's periodogram. We verify the theoretical results by simulations both in single node and cooperative sensing scenarios. In particular, cooperation is crucial in fading environment. Protection of primary systems from harmful interference is the key requisite for the introduction of cognitive radio systems into the future spectrum regulatory framework if the systems are deployed on the same spectrum bands. The primary user's concern is how often it could be susceptible to potential interference from the cognitive radio system, which, as we show, is dependent on the probability of detection. Therefore, performance evaluation and in particular the probability of detection is critical in assessing the potential capabilities of the future cognitive radio systems. View full abstract»

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  • Interference-throughput tradeoff in dynamic spectrum access: Analysis based on discrete-time queuing subjected to bursty preemption

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (129 KB) |  | HTML iconHTML  

    This article considers the issue of dynamic spectrum access in time domain, in which the secondary user seeks spectrum vacancy between bursty transmissions of the primary user to communicate. Since spectrum sensing and data transmission can not be done simultaneously in the same band, the secondary user should employ the sense-then-transmit strategy to detect the presence of primary user before accessing the licensed band. We model the behavior of the secondary user as a discrete-time queuing subjected to bursty preemption, which is an abstraction of temporal channel unavailability due to the random presence of the primary user. We formulate an interference-throughput tradeoff problem under the discrete-time queuing framework, and find the optimal slot duration to maximize the throughput of the secondary user, yet to ensure the primary interfered time ratio (PITR) is less than a tolerable threshold. Finally, the computer simulation results validate our theoretical approach. View full abstract»

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  • Aggregated interference control for cognitive radio networks based on multi-agent learning

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (225 KB) |  | HTML iconHTML  

    This paper deals with the problem of aggregated interference generated by multiple cognitive radios (CR) at the receivers of primary (licensed) users. In particular, we consider a secondary CR system based on the IEEE 802.22 standard for wireless regional area networks (WRAN), and we model it as a multi-agent system where the multiple agents are the different secondary base stations in charge of controlling the different secondary cells. We propose a solution for the aggregated interference problem based on a form of real-time multi-agent reinforcement learning known as decentralized Q-learning, so that the multi-agent system is designed to learn an optimal policy by directly interacting with the surrounding environment in a distributed fashion. Simulation results reveal that the proposed approach is able to fulfil the primary users interference constraints, without introducing signalling overhead in the system. View full abstract»

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  • Performance evaluation of cognitive radio spectrum sensing using multitaper-singular value decomposition

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    Cognitive radio (CR) is a promising technology for the efficient use of available spectrum. Reliable detection of primary user (PR) signals and spectrum sensing are the most important challenges which meet the implementation of the CR. In CR's communications, the PR user must be protected from the interference from the CR users. This can be achieved only by using an optimal spectrum sensing. In this paper we apply the multitaper method with singular value decomposition (MTMSVD) in the estimation of the power spectrum density and the decision about the presence or the absence of PR transmission. Our system model consists of a licensed PR user transmits QPSK-OFDM signal in a specific band, and a number of CR's sensors that detect the PR user's signal and this information is used by a CR base station to facilitate the CR user's communications through AWGN channel. We will compare the MTM-SVD technique with the conventional method of power spectrum density estimation (periodogram). Our results show that the MTM-SVD has a better performance in low SNR compared with the energy detection method. Furthermore, MTM-SVD is a powerful method that combines the mutual information using a number of sensors and different tapers. The decision process has a large threshold margin, which increases the probability of the correct decision. Increasing the sensors improves the performance of the spectral sensing in a low SNR environment. View full abstract»

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