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Cognitive Radio Oriented Wireless Networks and Communications (CROWNCOM), 2011 Sixth International ICST Conference on

Date 1-3 June 2011

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Displaying Results 1 - 25 of 86
  • [Title page]

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  • [Copyright notice]

    Page(s): ii
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  • Contents

    Page(s): iii - ix
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  • Welcome from the general chairs

    Page(s): x - xiii
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  • Conference committees

    Page(s): xiv - xvi
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  • New robust sensing methods for DVB-T signals

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (481 KB) |  | HTML iconHTML  

    The regulations for operation in the TV white space (TVWS) have been developed and released in USA and UK It is believed that the ongoing TVWS related standardization projects, such as IEEE P802.19.1, IEEE P802.11af and IEEE P802.22, will encourage the regulation development in more countries and regions. Current regulations commonly require the TV band device (TVBD) or the sensing only TVBD to be capable of detecting incumbent TV signals of very low power level within a short time. To fulfill the strict requirements on both of sensitivity and sensing time while keeping the hardware implementation cost below a desired level, we propose two new sensing methods for DTV signals of DVB-T standard: the optimal one requires time synchronization and is therefore called The Proposed_Syn while the sub-optimal one requires no time synchronization and is called The Proposed_Asyn. Both computer simulation results and hardware testing results are shown in this paper. Simulation results show that for achieving a goal of high detection probability (≥90%) and low false alarm probability (≤1%) at a very low SNR (=-20dB) in AWGN channel, in comparison with conventional sensing methods, The Proposed_Syn reduces sensing time by 50% and both proposed methods can significantly reduce hardware implementation cost by potentially reducing multiplexer number more than 99%. Hardware sensing prototype testing results have further verified the improved performance by using the proposed sensing methods. View full abstract»

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  • A new spectrum sensing scheme using overlap FFT filter-bank for dynamic spectrum access

    Page(s): 6 - 10
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (652 KB) |  | HTML iconHTML  

    A periodogram scheme, a multi-taper scheme, and a filter-bank scheme are proposed for spectrum sensing for dynamic spectrum access. The filter-bank scheme is advantageous in hardware implementation since the hardware required for communications can be reused for spectrum sensing. However, it is difficult for the conventional filter-bank scheme to change the detection bandwidth, filter type and frequency channel since the conventional filter-bank is based on time domain signal processing. This paper proposes a new spectrum sensing scheme using overlap FFT filter-bank based on frequency domain signal processing, which can flexibly change the detection bandwidth, filter type and frequency channel. In addition, this paper proposes a windowing method to improve the false-detection performance and confirms its improvement by computer simulation. Furthermore, false-detection and miss-detection performance of the proposed spectrum sensing scheme are evaluated and compared with those of the periodogram scheme according to the roll-off factor of the filter and modulation scheme. View full abstract»

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  • Propagation based spectrum sensing: A novel beamforming detection method

    Page(s): 11 - 15
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (286 KB) |  | HTML iconHTML  

    This paper proposes a novel propagation based spectrum sensing method that utilizes beamforming for systems equipped with antenna arrays. Since rays are known to arrive in clusters, the arrival angles of the dominant ray clusters can be exploited to improve the spectral sensing performances. Moreover, from site-specific propagation characteristics, the dominant ray angles can be predicted without additional computational efforts in most practical environments. Numerical results based on ray-based channel models show that the proposed beamforming detection method (with or without dominant ray angle prediction) is superior to the conventional energy detection method. Numerical results also show that decreasing the angle spread, enhances the performance of the proposed method. The computational complexity and latency of the proposed method is the same as the conventional energy detection method when using dominant ray angle prediction, but increases slightly without prediction. View full abstract»

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  • B-SSCT: A block sequential spectrum sensing scheme for cognitive radio

    Page(s): 16 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    Recently, it has been shown that in comparison to the well-known energy detection scheme, the sequential shifted chi-square test (SSCT) is capable of delivering considerable reduction on the average sample number (ASN) while maintaining a comparable detection error performance for spectrum sensing. Nonetheless, SSCT needs to perform threshold comparisons on every received sample, which may be difficult or even infeasible in practice particularly when the sampling rate is high and/or the signal-to-noise ratio is low. This paper proposes an extension of SSCT, called block-wise SSCT (B-SSCT), to overcome this shortcoming. Numerical algorithms are applied to evaluate the false-alarm and miss-detection probabilities and the ASN of B-SSCT, in a recursive fashion. Simulation and numerical results show that compared to the original SSCT, B-SSCT is capable of achieving almost the same detection error performance with a significantly reduced number of threshold comparisons and a slightly increased ASN. An implementation example demonstrates potential practical feasibility of B-SSCT in a real environment. View full abstract»

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  • Impact of antenna selection on cognitive radio system capacity

    Page(s): 21 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    We examine the effect of transmit antenna selection on the secondary user (SU) and primary user (PU) capacity in a multiple-input single-output cognitive radio system. We consider antenna selection with the aim of improving SU and PU capacity and mitigating the effects of incomplete channel knowledge by the SU. Under a minimum PU signal-to-interference-and-noise ratio constraint, analytical and semi-analytical expressions for the permissible SU transmit power are derived, which are used in obtaining capacity cumulative distribution functions by means of simulations. We show that PU antenna selection is effective at reducing the SU blocking probability, the probability that it cannot transmit, while SU antenna selection leads to significant gains in its capacity. Antenna selection at the SU is also shown to effectively compensate for incomplete channel knowledge and can be used to achieve moderate improvements in PU capacity. View full abstract»

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  • Binary power control in dynamic spectrum access

    Page(s): 26 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (333 KB) |  | HTML iconHTML  

    In future wireless networks there is a need for distributed power allocation algorithms which are simple, but at the same time yields sufficient spectral efficiency. In this paper we investigate binary power control schemes in a wireless multiuser, multiband interference system, where each user is restricted to use only one frequency band. We explore different binary power control schemes, and show how knowledge of the other users can be used to construct a utility function which embodies the well being of others. Simulation results show that binary power control yields significant increase in sum rate compared to water filling with number of users ≥ 2, and in some scenarios yield sum-rates above those achieved with much more complex algorithms. View full abstract»

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  • Distributed scheduling algorithm for cooperative transmission with multiple relays

    Page(s): 31 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (275 KB) |  | HTML iconHTML  

    Cooperative transmission can improve the performance of wireless ad-hoc systems due to its spatial multiplexing gain. Given that multiple cooperative relays which belong to the same source-destination pair can transmit simultaneously in the cooperative transmission, it is different from normal data transmission in which only one source node transmits in a single source-destination pair. Therefore, a new distributed scheduling algorithm for wireless ad-hoc systems should be devised. To this end, we propose a distributed scheduling algorithm for wireless ad-hoc systems with cooperative transmission in which multiple cooperative relays can transmit at the same time by using Amplify-and-Forward or Decode-and-Forward scheme. By using the elastic exclusive distance which is the minimum distance between two active cooperative transmission sets, the outage probability of cooperative transmissions can be greatly reduced compared to that of conventional scheduling scheme. Through performance analysis and simulation results, we show that the proposed scheme can enhance the performance of the system. View full abstract»

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  • Cooperation based spectrum management scheme in ad-hoc cognitive radio system

    Page(s): 36 - 40
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    In cognitive radio (CR) ad-hoc systems, the performance of system can be increased by using cooperation between cognitive users. In this paper, we compare three cooperation schemes for CR ad-hoc systems which are non-cooperation, sensing-cooperation and full-cooperation of sensing and band, in which the spectrum information or the band can be cooperatively shared among cognitive users. Unlike other cooperative sensing schemes which focus on cooperative sensing on single band, our cooperation model focuses on cooperative sensing on multiple bands. We propose the concept of spectrum pool which is the common knowledge on spectrum among cognitive users and this spectrum pool is maintained by sharing sensing results of sensing users on different bands. Given that the cognitive users have more information on the spectrum compared to the case when there is no information sharing, the number of sensing attempts to find vacant band can be reduced and the performance of CR system can be improved. We analyze the performance of three cooperation schemes by using game theory and state transition diagram. Through simulation, we show that our analysis is well matched to simulation results. We also find that the throughput can be improved by utilizing spectrum pool and the throughput can be deteriorated due to the selfish behavior of cognitive users when band can be shared by the cognitive users. View full abstract»

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  • Statistical test for multiple primary user spectrum sensing

    Page(s): 41 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (305 KB) |  | HTML iconHTML  

    Spectrum sensing is a key component in cognitive radio networks. The existing results so far primarily focus on single primary user detection. Little is known in the most practical and critical setting when multiple primary users exist. In this paper, we aim to address this problem by studying an optimal detector in the presence of multiple primary users. Specifically, a simple and accurate analytical formula for its test statistics distribution is derived, which yields a useful tool in determining the decision threshold. Simulations are provided to show both the accuracy of the derived result and the superior detection performance in realistic sensing scenarios. View full abstract»

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  • Eigenvalue ratio detection based on exact moments of smallest and largest eigenvalues

    Page(s): 46 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (566 KB) |  | HTML iconHTML  

    Detection based on eigenvalues of received signal covariance matrix is currently one of the most effective solution for spectrum sensing problem in cognitive radios. However, the results of these schemes always depend on asymptotic assumptions since the close-formed expression of exact eigenvalues ratio distribution is exceptionally complex to compute in practice. In this paper, non-asymptotic spectrum sensing approach to approximate the extreme eigenvalues is introduced. In this context, the Gaussian approximation approach based on exact analytical moments of extreme eigenvalues is presented. In this approach, the extreme eigenvalues are considered as dependent Gaussian random variables such that the joint probability density function (PDF) is approximated by bivariate Gaussian distribution function for any number of cooperating secondary users and received samples. In this context, the definition of Copula is cited to analyze the extent of the dependency between the extreme eigenvalues. Later, the decision threshold based on the ratio of dependent Gaussian extreme eigenvalues is derived. The performance analysis of our newly proposed approach is compared with the already published asymptotic Tracy-Widom approximation approach. View full abstract»

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  • Low complexity cyclostationary feature detection method to compenstate cyclostationarity-degradation by guard interval insertion

    Page(s): 51 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1862 KB) |  | HTML iconHTML  

    In cognitive radio system, it is necessary for spectrum sensing technology to search for vacant channel. Cyclostationary feature detection method has superior noise-immune and recognition. However, since the mismatch between the detected signal and detection duration by guard interval (GI) insertion occurs, the cyclostationarity is degraded. In this paper, we propose a high accuracy and low complexity detection method based on cyclostationarity feature. The proposed method limits symbol detection time and makes multiple delay line detectors as units of the GI time. Computer simulation and analytical evaluation show the effectiveness of the proposed detection method compared to the conventional one. View full abstract»

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  • Multitaper spectrum sensing of OFDMA signals in frequency selective fading environment

    Page(s): 56 - 60
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    This paper considers the problem of how to quickly and accurately identify spectrum holes from downlink orthogonal frequency division multiple access (OFDMA) signals in frequency selective fading environment. We assume that the subcarrier assignment of primary users (PUs) in an OFDMA system is a priori known to the detector. Under this assumption, we formulate the original problem as the problem of detecting presence/absence of PUs, which requires less computational complexity than its original counterpart. We propose a spectrum sensing algorithm to detect presence/absence of a PU. In the proposed algorithm, we first apply the Thomson's multitaper spectrum estimation (MTSE) method to obtain spectral estimates at certain subcarriers of interest, and then we perform a simple threshold test. We present closed form results for false-alarm and miss-detection probabilities of the proposed algorithm. We study impacts of system/MTSE parameters on the detection performance via Monte Carlo simulation. View full abstract»

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  • Spectrum sensing in public safety applications: The 2-D LAD ACC method

    Page(s): 61 - 65
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB) |  | HTML iconHTML  

    Public safety communications (PSC) are invaluable in safety critical scenarios such as floods or earthquakes when commercial communication systems fall down. Cognitive radio (CR) approach that is independent of other communication systems provides flexibility and certainty. One of the key issues is to reliably find unused radio channels also in the situations when there is no a priori information about possible other users. In this paper, we propose using the two-dimensional localization algorithm based on double-thresholding with adjacent cluster combining (2-D LAD ACC) method for detecting free channels. It is low-complex, blind and able to operate in any frequency area. This paper applies the 2-D LAD ACC method for real-world channel measurement data for the first time. The indoor measurements at WLAN bands verify that the 2-D LAD ACC method is able to operate in the real-life situation. View full abstract»

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  • Spectrum sharing with interference coordination under outage probability constraint

    Page(s): 66 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (302 KB) |  | HTML iconHTML  

    In this paper we consider a cognitive radio (CR) communication system based on spectrum sharing schemes, where we have a secondary user (SU) link with multiple transmitting antennas and a single receiving antenna, coexisting with a primary user (PU) link with a single receiving antenna. At the SU transmitter (SU-Tx), the channel state information (CSI) of the SU link is assumed to be perfectly known; while the interference channel from the SU-Tx to the PU receiver (PU-Rx) is not perfectly known due to less cooperation between the SU and the PU. Considering a SU transmit power constraint, our design objective is to determine the transmit covariance matrix that maximizes the SU rate, while we protect the PU by enforcing both a PU average interference constraint and a PU outage probability constraint. This problem is formulated as a non-convex optimization problem with a non-explicit probabilistic constraint, which is then approximated as a mixed binary integer programming (MBIP) problem and solved with the Branch and Bound (BB) algorithm. The complexity of the BB algorithm is analyzed and numerical results are presented to show the performance of the CR system under consideration with our optimal solution. View full abstract»

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  • Distributed beam-forming and power control in multi-relay underlay cognitive radio networks: A game-theoretical approach

    Page(s): 71 - 75
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    In this paper, we propose a power control algorithm incorporating distributed beam-forming via multi-relay structure with underlay cognitive radio architecture. This problem is modeled as a non-cooperative game and a novel distributed algorithm is designed to achieve Nash equilibrium (NE). At each iteration, power and beam forming weights are determined while quality of service (QoS) of primary and secondary users are guaranteed in terms of interference threshold and signal to interference and noise (SINR) threshold levels, respectively. Convergence of the proposed algorithm to a unique and sub-optimal fixed point for any given initial resource allocation has been proved. Numerical simulations demonstrate significant improvement in average rate of secondary users in comparison with single-relay algorithms. View full abstract»

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  • A game-theoretic approach for opportunistic transmission scheme in cognitive radio networks with incomplete information

    Page(s): 76 - 80
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB) |  | HTML iconHTML  

    One of the key issues in cognitive transmission is for secondary users to dynamically acquire spare spectrum from the primary user and then select appropriate transmission schemes. The existing spectrum sharing scheme adopts a deterministic Cournot game to formulate this problem, of which the solution is Nash equilibrium. This formulation implicitly assumes that each secondary user is willing to fully exchange transmission parameters with all other users and hence knows the complete information of all others. However, this assumption may not be true in general. To remedy this, the present paper considers a more realistic assumption of incomplete information, i.e., each secondary user may choose to conceal its private information for achieving higher transmission benefit. Following this assumption, we adopt a probabilistic Cournot game to propose an opportunistic transmission scheme to maximize the transmission benefit of all secondary users. Bayesian equilibrium is considered as the solution of this game. Moreover, we rigorously prove that a secondary user can improve its expected transmission benefit by actively hiding its private transmission parameters and increasing the variance of its allocated spectrum. View full abstract»

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  • Distributed channel assignment algorithm based on simulated annealing for uncoordinated OSA-enabled WLANs

    Page(s): 81 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (410 KB) |  | HTML iconHTML  

    A promising approach to alleviate ISM band congestion problems in highly dense WLAN scenarios consists of exploiting opportunistic spectrum access (OSA) to underutilized bands under a primary-secondary model. This paper develops a distributed channel assignment algorithm valid for uncoordinated WLAN deployments where access points do not follow any specific planning and they could belong to different administrative domains. Unlike existing channel assignment schemes proposed for legacy WLANs, channel assignment mechanisms for OSA-enabled WLAN should address two distinguishing issues: channel prioritization and spectrum heterogeneity. Over such a basis, this paper develops and assesses the performance of a distributed channel assignment algorithm that is able to exploit both channel prioritization and spectrum heterogeneity concepts. In particular, the algorithm is based on a distributed adaptation of the simulated annealing metaheuristic algorithm commonly used in global optimization problems. View full abstract»

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  • Joint switched transmit diversity and adaptive modulation in spectrum sharing systems

    Page(s): 86 - 90
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    Under the scenario of an underlay cognitive radio network, we propose in this paper an adaptive scheme using switched transmit diversity and adaptive modulation in order to minimize the average number of switched branches at the secondary transmitter while increasing the capacity of the secondary link. The proposed switching efficient scheme (SES) uses the scan and wait (SWC) combining technique where a transmission occurs only when a branch with an acceptable performance is found, otherwise data is buffered. In our scheme, the modulation constellation size and the used transmit branch are determined to achieve the highest spectral efficiency with a minimum processing power, given the fading channel conditions, the required error rate performance, and a peak interference constraint to the primary receiver. Selected numerical examples show that the SES scheme minimizes the average number of switched branches for the average and the high secondary signal-to-noise ratio range. This improvement comes at the expense of a small delay introduced by the SWC technique. For reference, we also compare the performance of the SES scheme to the selection diversity scheme (SDS) where the best branch verifying the modulation mode and the interference constraint is always selected. View full abstract»

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  • A tree based recovery algorithm for block sparse signals

    Page(s): 91 - 95
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    The structure of block sparsity in multi-band signals is prevalent. Performance of recovery algorithms that taking advantage of the block sparsity structure is promising in the compressed sensing framework. In this paper, we propose a binary tree based recovery algorithm for block-sparse signals, where we exploit the fact that each block may have zero and nonzero elements both. The proposed algorithm improves the current algorithms through iteratively separating the recovered blocks of signals into two smaller blocks. Therefore, greedy searching based algorithm is possible to obtain more accurate basis for signal recovery. Simulations are performed and the results show the improvements over current block-based recovery algorithms. View full abstract»

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  • Optimized strategies for coordinated spectrum sensing in Cognitive Radio Networks

    Page(s): 96 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (330 KB) |  | HTML iconHTML  

    In Cognitive Radio Networks, coordinated spectrum sensing is a novel technique that the cognitive terminals are assigned to sense different channels in the same sensing slots in order to obtain the occupancy status of all the channels in every sensing period. In this paper the coordinated spectrum sensing strategies are discussed, the functional architecture is put forward, a Kuhn-Munkres based, alongside with a greedy based algorithm for coordinated sensing strategies arrangement is proposed. Simulation results show that the algorithms can significantly improve the overall sensing performance compared with a basic greedy based algorithm. View full abstract»

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