-
[show abstract]
[hide abstract]
ABSTRACT: Beside providing solutions to the interoperability problem of the first responders, location awareness feature of the cognitive radios can be beneficial for victim and first responder location estimation under extreme conditions. Location and environment based services can be employed to detect and locate victims even when the core wireless communications networks are down. In this paper, a location awareness framework is proposed for victim signal detection and direction estimation. A wideband, multi-channel sensing method is proposed along with a two-antenna multiple signal classification (MUSIC) direction finding algorithm. The performance evaluation of proposed methods are discussed with both simulation and measurement results.
Wireless and Microwave Technology Conference (WAMICON), 2011 IEEE 12th Annual; 05/2011
-
[show abstract]
[hide abstract]
ABSTRACT: In order to perform reliable communications, a system needs to have sufficient information about its operational environment, such as spectral resources and propagation characteristics. Cognitive-radio technology has capabilities for acquiring accurate spectrum, location, and environmental information, due to its unique features such as spectrum, location, and environmental awareness. The goal of this paper is to give a comprehensive review of the implementation of these concepts. In addition, the dynamic nature of cognitive-radio systems - including dynamic spectrum utilization, transmission, the propagation channel, and reception - is discussed, along with performance limits, challenges, mitigation techniques, and open issues. The capabilities of cognitive-radio systems for accurate characterization of operational environments are emphasized. These are crucial for efficient communications, localization, and radar systems.
IEEE Antennas and Propagation Magazine 09/2010; · 0.97 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Opportunistic spectrum access feature of cognitive radio systems is a method to improve frequency underutilization of wireless spectrum. One of the techniques for detecting the unused bands is the energy detection for which selection of the threshold defines detection performance. In this paper, the adaptive threshold method is proposed as an alternative approach to estimate the threshold as a function of first and second order statistics of recorded signals. The proposed method does not require estimation of noise variance or signal to noise ratio and aims to minimize the effects of impairments introduced by wireless channel and non-stationary noise. The simulation results indicate that adaptive threshold has low false alarm and missed detection rates that can satisfy the detection requirements of multi-channel cognitive radios for either narrow or wideband spectrum sensing, when the standard deviation coefficient is selected properly.
Telecommunications (ICT), 2010 IEEE 17th International Conference on; 05/2010
-
[show abstract]
[hide abstract]
ABSTRACT: In cognitive radio systems, secondary users can utilize multiple dispersed bands that are not used by primary users. In this paper, time delay estimation of signals that occupy multiple dispersed bands is studied. First, theoretical limits on time delay estimation are reviewed. Then, two-step time delay estimators that provide trade-offs between computational complexity and performance are investigated. In addition, asymptotic optimality properties of the two-step time delay estimators are discussed. Finally, simulation results are presented to explain the theoretical results.
Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2009 3rd IEEE International Workshop on; 01/2010
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Cognitive Radio Oriented Wireless Networks and Communications, 2009. CROWNCOM '09. 4th International Conference on; 07/2009
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, fundamental limits on time delay estimation are studied for cognitive radio systems, which facilitate opportunistic use of spectral resources. First, a generic Cramer-Rao lower bound (CRLB) expression is obtained in the case of unknown channel coefficients and carrier-frequency offsets (CFOs) for cognitive radio systems with dispersed spectrum utilization. Then, various modulation schemes are considered, and the effects of unknown channel coefficients and CFOs on the accuracy of time delay estimation are quantified. Finally, numerical studies are performed in order to verify the theoretical analysis.
IEEE Transactions on Wireless Communications 02/2009; · 2.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, theoretical limits on time delay estimation are studied for ultra-wideband (UWB) cognitive radio systems. For a generic UWB spectrum with dispersed bands, the Cramer-Rao lower bound (CRLB) is derived for unknown channel coefficients and carrier-frequency offsets (CFOs). Then, the effects of unknown channel coefficients and CFOs are investigated for linearly and nonlinearly modulated training signals by obtaining specific CRLB expressions. It is shown that for linear modulations with a constant envelope, the effects of the unknown parameters can be mitigated. Finally, numerical results, which support the theoretical analysis, are presented.
Ultra-Wideband, 2008. ICUWB 2008. IEEE International Conference on; 10/2008
-
[show abstract]
[hide abstract]
ABSTRACT: The detection issues of ultrawideband (UWB) signals depend on the type of modulation scheme that is used during the transmission. Cross-modulation interference (CMI) is a problem that is specific to UWB pulse-position-modulation (PPM) signaling. In this paper, the effects of CMI on the performance of noncoherent UWB receivers are analyzed. The probabilities of error for transmitted-reference (TR) and energy detector (ED) receivers in the presence and absence of CMI are derived. Optimal and suboptimal CMI avoidance algorithms, which are based on novel acquisition techniques, are proposed for Rake receivers. The results show that the performance degradation in both receivers, which is due to the CMI effects, can be significant, depending on the modulation index. TR receivers still can be functional in the presence of CMI, and the target performance level determines the modulation index to be used. It is unlikely that effects of CMI on the performance of ED receivers in the presence of CMI are more severe relative to TR receivers, and the performance level is not acceptable. As a result, PPM signaling is not an appropriate modulation technique for ED receivers that are operating in the CMI region, unless CMI mitigation algorithms can be developed. Furthermore, the proposed optimal and suboptimal algorithms are two promising schemes for avoiding the CMI effects and, consequently, for improving the performance of Rake receivers operating in the CMI region.
IEEE Transactions on Vehicular Technology 04/2008; · 1.92 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Location awareness is one of the essential characteristics of cognitive radios. In this paper, an innovative cognitive positioning system (CPS) that achieves accuracy adaptation in both indoor and outdoor environments is proposed as a step towards realization of location awareness in cognitive radios. The proposed CPS is composed of two modes; bandwidth determination and enhanced dynamic spectrum management (EDSM). Bandwidth determination equations are derived through Cramer-Rao Lower Bound (CRLB) for both additive white Gaussian noise (AWGN) and multipath channels. An EDSM system providing the optimum available bandwidth to the CPS is proposed. Overlay spectrum access based EDSM (O-EDSM) and hybrid overlay and underlay spectrum access based EDSM (H-EDSM) are two schemes that are introduced. A switching mechanism that manages the transition between underlay and overlay spectrum usage modes for the H-EDSM algorithm is presented. The theoretical analysis of the mechanism is carried out using Two-slope model. Simulation results, challenges and complexity options for the implementation of the CPS are outlined. Our study reveals the existence of a trade-off between the accuracy and complexity in the cognitive positioning systems.
IEEE Transactions on Wireless Communications 01/2008; · 2.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Location awareness is an essential characteristic of cognitive radios as well as networks. In this article a location awareness engine architecture is proposed for the realization of location awareness in cognitive radios and networks. The proposed architecture consists of location estimation and/or sensing, seamless positioning and interoperability, statistical learning and tracking, security and privacy, mobility management, and location-based applications. However, the focus of this article is on location-based applications where we demonstrate the utilization of location information in cognitive wireless networks by presenting some representative location-assisted network optimization applications such as location-assisted spectrum management, network planning and expansion, and handover. Our study unveils that location information can be used in cognitive wireless networks to optimize network performance. Possible solutions to the implementation issues are proposed, and the remaining open issues are also addressed.
IEEE Wireless Communications 09/2007; · 2.58 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Theoretical analysis of time-of-arrival (TOA)-based high-precision ranging algorithm for the dynamic spectrum access networks (DSANs) is performed. The asymptotic frequency-domain Cramer-Rao bound (CRB) of the ranging algorithm that takes the frequency-dependent feature (FDF) and phase of multipath components (MPCs) into account is derived through Whittle formula. The effects of FDF-MPCs and related parameters such as absolute bandwidth and operating center frequency on the ranging accuracy are investigated. The results show that the impacts of the FDF-MPCs on the ranging accuracy can be significant and it is recommended utilizing as large absolute bandwidth as possible at low operating center frequencies to obtain high-precision distance information of the users in the DSANs
IEEE Communications Letters 06/2007; · 0.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Location awareness is a prominent characteristic of cognitive radio technologies. Realizing such awareness in cognitive radios require an underlying advanced positioning system that have cognition capabilities. In this paper, an innovative cognitive positioning system (CPS) that have cognition capabilities by means of adjusting positioning accuracy adaptively in both indoor and outdoor environments is proposed. Bandwidth determination and hybrid overlay and underlay enhanced dynamic spectrum management (H-EDSM) are two main components that form the proposed CPS technique. Bandwidth determination equations are derived through Cramer-Rao lower bound (CRLB) for additive white Gaussian noise (AWGN). H-EDSM that provides optimum available bandwidth to the CPS is proposed. A switching mechanism that manages the transition between overlay and underlay spectrum usage modes for the H-EDSM algorithm is presented. Theoretical analysis of the mechanism is carried out using two-slope model. Simulation results, challenges and complexity options for the implementation of the CPS are outlined. Our study reveals the existence of a trade-off between accuracy and complexity in the adaptive positioning systems for cognitive radios.
New Frontiers in Dynamic Spectrum Access Networks, 2007. DySPAN 2007. 2nd IEEE International Symposium on; 05/2007
-
[show abstract]
[hide abstract]
ABSTRACT: The detection issues of UWB signals depend on the type of modulation scheme used during the transmission. The cross-modulation interference (CMI) for pulse position modulated (PPM) UWB signaling is introduced. The effects of CMI on the detection mechanism of selective-Rake (SRake), transmitted-reference (TR) and energy detector (ED) receivers are analyzed. The bit-error-rate (BER) performance of all three receivers in the presence and absence of CMI are studied through computer simulations. The results show that the CMI amount varies according to the modulation index and the performance degradation due to CMI can be extremely severe depending on the modulation index for all three receivers. The validity of the conventional optimal and orthogonal PPM criteria are checked considering the CMI effects. The results demonstrate that the conventional orthogonal PPM for all three receivers and the conventional optimal PPM criterion for N-SRake and TR receivers can be used in the presence of CMI. On the other hand, the BER performance of ED receivers using the conventional optimal PPM criterion result in error floor and this criterion is not valid to be used for ED receivers
Military Communications Conference, 2005. MILCOM 2005. IEEE; 11/2005
-
[show abstract]
[hide abstract]
ABSTRACT: Detecting the ultra-short pulses in ultra-wideband radios requires rapid and accurate timing acquisition. An optimal data-aided timing acquisition algorithm based on minimum probability of error criterion is proposed. The estimation of timing offset parameter is derived in closed form. The cross-modulation interference (CMI) due to multipath components during the transmission of pulse position modulated (PPM) signal is introduced. A suboptimal data-aided timing acquisition algorithm is derived from the optimal algorithm for practical implementations. The BER performances of the proposed and conventional algorithms are simulated. The results show that optimal algorithm performs better than suboptimal algorithm in CMl channel whereas the suboptimal algorithm performs as good as the optimal algorithm in CM4 channel. Both proposed algorithms outperform the conventional algorithm in both channels.
Ultra-Wideband, 2005. ICU 2005. 2005 IEEE International Conference on; 10/2005
