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See detailEigenvalue Based Sensing and SNR Estimation for Cognitive Radio in Presence of Noise Correlation
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Vehicular Technology (2013), 62(8), 3671-3684

Herein, we present a detailed analysis of an eigenvalue based sensing technique in the presence of correlated noise in the context of a Cognitive Radio (CR). We use a Standard Condition Number (SCN) based ... [more ▼]

Herein, we present a detailed analysis of an eigenvalue based sensing technique in the presence of correlated noise in the context of a Cognitive Radio (CR). We use a Standard Condition Number (SCN) based decision statistic based on asymptotic Random Matrix Theory (RMT) for decision process. Firstly, the effect of noise correlation on eigenvalue based Spectrum Sensing (SS) is studied analytically under both the noise only and the signal plus noise hypotheses. Secondly, new bounds for the SCN are proposed for achieving improved sensing in correlated noise scenarios. Thirdly, the performance of Fractional Sampling (FS) based SS is studied and a method for determining the operating point for the FS rate in terms of sensing performance and complexity is suggested. Finally, a Signal to Noise Ratio (SNR) estimation technique based on the maximum eigenvalue of the received signal’s covariance matrix is proposed. It is shown that proposed SCN-based threshold improves sensing performance in correlated noise scenarios and SNRs up to 0 dB can be reliably estimated with less than 1 % normalized Mean Square Error (MSE) in the presence of correlated noise without the knowledge of noise variance. [less ▲]

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See detailFrequency Packing for Interference Alignment-based Cognitive Dual Satellite Systems
Chatzinotas, Symeon UL; Sharma, Shree Krishna UL; Ottersten, Björn UL

in Proceedings of IEEE 78th Vehicular Technology Conference: VTC2013-Fall (2013, September)

Interference Alignment (IA) has been considered a promising technique for spectral coexistence of different wireless systems in an underlay cognitive mode. Furthermore, Frequency Packing (FP) can be ... [more ▼]

Interference Alignment (IA) has been considered a promising technique for spectral coexistence of different wireless systems in an underlay cognitive mode. Furthermore, Frequency Packing (FP) can be considered as an important technique for enhancing the spectrum efficiency in spectrum-limited satellite applications. In this paper, we consider a spectral coexistence scenario of a multibeam satellite and a monobeam satellite with the monobeam satellite as primary and the multibeam satellite as secondary. In this context, this paper focuses on examining the effect of FP on the performance of multi-carrier based IA technique. For this purpose, different IA techniques such as coordinated IA, uncoordinated IA and static IA have been considered. The effect of FP on the performance of different IA techniques in the considered scenario is evaluated in terms of system sum rate and primary rate protection ratio. It is shown that the system sum rate increases with the FP factor for all the techniques and the primary rate is perfectly protected with the coordinated IA technique even with dense FP. [less ▲]

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See detailCognitive Radio Techniques for Satellite Communication Systems
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of IEEE 78th Vehicular Technology Conference: VTC2013-Fall (2013, September)

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast, multimedia and interactive services. In this context, cognitive satellite communications has received ... [more ▼]

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast, multimedia and interactive services. In this context, cognitive satellite communications has received important attention lately in the research community. Exploring efficient spectrum sharing techniques for enhancing spectral efficiency in satellite communication has become an important research challenge. In this paper, we study the main aspects of satellite cognitive communications and present possible practical scenarios for hybrid/dual cognitive satellite systems. Furthermore, suitable cognitive techniques for the considered scenarios are identified. More specifically, Spectrum Sensing (SS), interference modeling, and beamforming techniques are discussed for hybrid cognitive scenario and SS, interference alignment, and cognitive beamhopping techniques are discussed for dual satellite systems. This paper concludes by providing interesting open research issues in this domain. [less ▲]

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See detailCognitive Beamhopping for Spectral Coexistence of Multibeam Satellites
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Future Network and MobileSummit 2013 (2013, July)

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast and multimedia services. In this context, we consider the problem of enhancing spectral efficiency in ... [more ▼]

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast and multimedia services. In this context, we consider the problem of enhancing spectral efficiency in multibeam satellite networks. The spectral coexistence scenario of two multibeam satellites over a common coverage area is studied with a primary satellite having larger beams and a secondary satellite having smaller beams. Furthermore, a novel cognitive beamhopping satellite system is proposed. The system performance of the proposed system is evaluated and compared with that of conventional multibeam and beamhopping systems in terms of system throughput. It is shown that the proposed system significantly enhances the spectral efficiency in comparison to other systems. Moreover, the scenario of the presence of multiple secondary users within an inactive primary beam is considered with power control on the secondary transmission. The system performance is evaluated by considering partial and full frequency sharing approaches. It is noted that the total spectral efficiency increases with the number of secondary users in the full frequency reuse approach. [less ▲]

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See detailTransmit Beamforming for Spectral Coexistence of Satellite and Terrestrial Networks
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of 8th International Conference on Cognitive Radio Oriented Wireless Networks 2013 (2013, July)

Herein, we study transmit beamforming techniques in an underlay cognitive mode for the coexistence of satellite and terrestrial networks with the satellite forward link as primary and the terrestrial ... [more ▼]

Herein, we study transmit beamforming techniques in an underlay cognitive mode for the coexistence of satellite and terrestrial networks with the satellite forward link as primary and the terrestrial downlink as secondary. Since geostationary satellite terminals have predetermined propagation characteristics so that they always point towards the geostationary satellite, the interference received by the satellite terminals from the terrestrial Base Station (BS) is confined in an angular sector. Based on this a priori knowledge, we propose transmit beamforming techniques at the BS to maximize the Signal to Interference plus Noise Ratio (SINR) towards the desired secondary user and to mitigate the interference towards the primary satellite terminals. Different types of Linearly Constrained Minimum Variance (LCMV) techniques have been proposed for our considered scenario where the exact locations and the number of satellite terminals within a specific angular sector are not known while designing the beamformer. Furthermore, an optimization problem is formulated for maximizing the Secondary User (SU) rate and it is shown that the worst case SU rate depends on the Primary User (PU) distance, PU interference threshold and the angular separation of the desired SU from the region of interest. [less ▲]

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See detailSpatial Filtering for Underlay Cognitive SatComs
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in proceedings of 5th International Conference on Personal Satellite Services (2013, June)

Herein, we study an underlay beamforming technique for the coexistence scenario of satellite and terrestrial networks with the satel- lite return link as primary and the terrestrial uplink as secondary ... [more ▼]

Herein, we study an underlay beamforming technique for the coexistence scenario of satellite and terrestrial networks with the satel- lite return link as primary and the terrestrial uplink as secondary. Since satellite terminals are unique in that they always point towards the geo- stationary satellite, interference received by the terrestrial Base Station (BS) is concentrated in a specific angular sector. The priori knowledge that all the geostationary satellite terminals are facing south for the European coverage can be used in designing a beamformer at the ter- restrial BS. Based on this concept, we propose a receive beamformer at the BS to maximize the Signal to Interference plus Noise Ratio (SINR) towards the desired user and to mitigate the interference coming from the interfering satellite terminals. The performances of Minimum Vari- ance Distortionless (MVDR) and Linear Constrained Minimum Variance (LCMV) beamformers are compared for our considered scenario. It is shown that LCMV beamformer is better suited in rejecting interference even in case of Direction of Arrival (DoA) uncertainty of interfering satel- lite terminals as long as DoA range of the interfering sector is known to the beamformer. Furthermore, it is noted that MVDR beamformer is suitable for a large number of interferers. [less ▲]

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See detailThe Effect of Noise Correlation on Fractional Sampling based Spectrum Sensing
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Communications (ICC), 2013 IEEE International Conference on (2013, June)

This paper considers a Fractional Sampling (FS) technique to enhance the Spectrum Sensing (SS) efficiency of a Cognitive Radio (CR) using a decision statistic based on asymptotic Random Matrix Theory (RMT ... [more ▼]

This paper considers a Fractional Sampling (FS) technique to enhance the Spectrum Sensing (SS) efficiency of a Cognitive Radio (CR) using a decision statistic based on asymptotic Random Matrix Theory (RMT). Firstly, the effect of noise correlation on eigenvalue based SS is studied analytically and by numerical evaluation. Secondly, new bounds for the Standard Condition Number (SCN) are proposed to enhance the SS efficiency in correlated noise scenarios. It is shown that proposed FS method can enhance SS efficiency up to certain FS rates at the expense of receiver complexity and no performance advantage is obtained if the FS rate is increased beyond this limit. As a result, a method for determining the operating point for the FS rate in terms of sensing performance and complexity is suggested. [less ▲]

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See detailAsymptotic Analysis of Eigenvalue-based Blind Spectrum Sensing Techniques
Chatzinotas, Symeon UL; Sharma, Shree Krishna UL; Ottersten, Björn UL

in proceedings of International Conference on Acoustics, Speech, and Signal Processing (ICASSP) 2013 (2013, May)

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See detailMultiantenna Signal Processing for Cognitive Communications
Chatzinotas, Symeon UL; Sharma, Shree Krishna UL; Ottersten, Björn UL

in Proceedings of IEEE China Summit and International Conference on Signal and Information Processing (ChinaSIP) 2013 (2013)

Cognitive communications has attracted a large interest during the last decade due to spectrum scarcity. In combination with multiantenna techniques, cognitive communications have the ability to increase ... [more ▼]

Cognitive communications has attracted a large interest during the last decade due to spectrum scarcity. In combination with multiantenna techniques, cognitive communications have the ability to increase spectral efficiency by enabling the coexistence of a primary and secondary systems. In this paper, we focus in two specific cognitive approaches: a) Multiantenna Interference Alignment (IA) and b) Multiantenna Spectrum Sensing (SS). In the first case, we investigate how IA over multiple spatial dimensions can be exploited in order to lower harmful interference towards the primary system into acceptable levels. In the second case, we compare the sensing performance of different eigenvalue-based blind SS techniques. This paper concludes by presenting some interesting open problems in this area. [less ▲]

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See detailEigenvalue based SNR Estimation for Cognitive Radio in Presence of Channel Correlation
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of IEEE Globecom 2013 (2013)

In addition to spectrum sensing capability required by a Cognitive Radio (CR), Signal to Noise Ratio (SNR) estimation of the primary signals is crucial in order to adapt its coverage area dynamically ... [more ▼]

In addition to spectrum sensing capability required by a Cognitive Radio (CR), Signal to Noise Ratio (SNR) estimation of the primary signals is crucial in order to adapt its coverage area dynamically using underlay techniques. Furthermore, in practical scenarios, the fading channel may be correlated due to various causes such as insufficient scattering in the propagation path and antenna mutual coupling. In this context, we consider the SNR estimation problem for a CR in the presence of channel correlation. We study an eigenvaluebased SNR estimation technique for large-scale CR networks using asymptotic Random Matrix Theory (RMT). We carry out detailed theoretical analysis of the signal plus noise hypothesis to derive the asymptotic eigenvalue probability distribution function (a.e.p.d.f.) of the received signal’s covariance matrix in the presence of the correlated channel. Then an SNR estimation technique based on the derived a.e.p.d.f. is proposed for PU SNR in the presence of channel correlation and its performance is evaluated in terms of normalized Mean Square Error (MSE). It is shown that the PU SNR can be accurately estimated in the presence of channel correlation using the proposed technique even in low SNR region. [less ▲]

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See detailSatellite Cognitive Communications and Spectrum Regulation
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Hofmann, Mahulena (Ed.) International Regulations of Space Communications (2013)

Due to rapid increase of wireless users and the popularity of multimedia applications, the demand for wireless spectrum is increasing rapidly. However, due to current static spectrum policy, the available ... [more ▼]

Due to rapid increase of wireless users and the popularity of multimedia applications, the demand for wireless spectrum is increasing rapidly. However, due to current static spectrum policy, the available usable spectrum is becoming scarce while a significant amount of spectrum remains underutilized. In this aspect, cognitive communications can be considered as a promising technology to enhance spectrum usage efficiency by allowing the coexistence of heterogeneous networks within the same spectrum. In this paper, starting with the rationale of cognitive communication, we present two different coexistence scenarios in the context of satellite cognitive communication. We then present the current status of spectrum regulation in the context of Cognitive Radio (CR) and the relevant decisions of World Radio Conference 2012 (WRC-12). Finally, we present the technical aspects and regulatory challenges of this technology and provide some suggestions from research, industrial and regulatory perspectives. [less ▲]

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See detailEnhanced information throughput in multiple input multiple output orthogonal frequency division multiplexing based systems using fractional sampling and iterative signal processing
Sharma, Shree Krishna UL; Patwary, Mohammad; Abdel-Maguid, Mohamed

in Transactions on Emerging Telecommunications Technologies (2013)

Herein, we study the feasibility of enhanced information throughput capability of multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) based wireless communication systems ... [more ▼]

Herein, we study the feasibility of enhanced information throughput capability of multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) based wireless communication systems in the context of increasing wireless capacity demand. The concept of fractional sampling (FS) is exploited for this purpose to take advantage of diversity created because of it. Furthermore, a novel channel adaptive iterative sequence detector is proposed using the FS technique. The performance analysis of the proposed receiver is carried out, and a tighter performance bound is derived. It is found that the FS technique can improve bit error rate performance of MIMO and OFDM based systems provided that the noise samples are uncorrelated up to a certain level of FS rate. Moreover, it is observed that the performance improvement is a non-linear function of the FS rate. Besides this, the simulation results show that the proposed iterative receiver can significantly enhance the information throughput of MIMO-OFDM based wireless communication systems in comparison to conventional non-iterative receivers. [less ▲]

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See detailInterference alignment for spectral coexistence of heterogeneous networks
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in EURASIP Journal on Wireless Communications & Networking (2013), 2013(46),

The coexistence of heterogeneous networks within the same spectrum for enhancing the spectrum efficiency has attracted large interest lately in the research community. Furthermore, the research interest ... [more ▼]

The coexistence of heterogeneous networks within the same spectrum for enhancing the spectrum efficiency has attracted large interest lately in the research community. Furthermore, the research interest towards the deployment of small cells and multibeam satellites is increasing due to high capacity, easier deployment and higher energy efficiency. However, due to the scarcity of available spectrum and the requirement of additional spectrum for these systems, small cells need to coexist with macrocells and multibeam satellites need to coexist with monobeam satellites within the same spectrum. In this context, this contribution investigates an underlay spectral coexistence mechanism which exploits an interference alignment (IA) technique in order to mitigate the interference of cognitive transmitters towards the primary receivers in a normal uplink mode. More specifically, three types of IA techniques, namely static, uncoordinated and coordinated are investigated. The performance of the IA technique is evaluated and compared with primary only, resource division and no-mitigation techniques in terms of sum-rate capacity, primary to secondary rate ratio and primary rate protection ratio. It is shown that the coordinated IA technique perfectly protects the primary rate in both terrestrial and satellite coexistence scenarios. [less ▲]

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See detailSpectral efficient compressive transmission framework for wireless communication systems
Sharma, Shree Krishna UL; Patwary, Mohammad; Abdel-Maguid, Mohamed

in IET Signal Processing (2013)

Increasing demand of high-speed data rate is leading to a challenging task to provide services to the users within exponentially growing market for wireless multimedia services. Subsequently, the ... [more ▼]

Increasing demand of high-speed data rate is leading to a challenging task to provide services to the users within exponentially growing market for wireless multimedia services. Subsequently, the available radio resources are becoming scarce because of different factors such as spectrum segmentation and dedicated frequency allocation to existing wireless standards. Exploring new techniques for enhancing the spectral efficiency in wireless communication has been an important research challenge. In this study, the enhancement of spectral efficiency of wireless communication systems is considered. A framework is proposed to implement the concept of compressive sampling (CS) for compressing the natural random signals. The performance of proposed framework is evaluated in the context of multiple input multiple output orthogonal frequency division multiplexing system. Simulation-based results show that 25% of resources can be saved by marginal trade-off with the quality of service (QoS) requirement applying CS to the natural random signals. Furthermore, it can be claimed that this QoS trade-off can be optimised with dynamic selection of random measurement matrices. [less ▲]

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See detailSpectrum Sensing in Dual Polarized Fading Channels for Cognitive SatComs
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of IEEE Globecom Conference 2012 (2012, December)

Next generation networks are moving towards the convergence of mobile, fixed and broadcasting services in one standard platform, which requires the co-existence of satellite and terrestrial networks in ... [more ▼]

Next generation networks are moving towards the convergence of mobile, fixed and broadcasting services in one standard platform, which requires the co-existence of satellite and terrestrial networks in the same spectrum. This framework has motivated the concept of cognitive Satellite Communication (SatComs). In this aspect, the problem of exploiting Spectrum Sensing (SS) techniques for a dual polarized fading channel is considered. In this paper, the performance of Energy Detection (ED) technique is evaluated in the context of a co-existence scenario of a satellite and a terrestrial link. Diversity combining techniques such as Equal Gain Combining (EGC) and Selection Combining (SC) are considered to enhance the SS efficiency. Furthermore, analytical expressions for probability of detection (Pd) and probability of false alarm (Pf ) are presented for these techniques in the considered fading channel and the sensing performance is studied through analytical and simulation results. Moreover, the effect of Cross Polar Discrimination (XPD) on the sensing performance is presented and it is shown that SS efficiency improves for low XPD. [less ▲]

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See detailSatellite Cognitive Communications: Interference Modeling and Techniques Selection
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceeding of 6th Advanced Satellite Multimedia Systems Conference and the 12th Signal Processing for Space Communications Workshop (2012, September)

Due to increasing demand of high speed data rate for satellite multimedia and broadcasting services and spectrum scarcity problem in satellite bands, exploring new techniques for enhancing spectral ... [more ▼]

Due to increasing demand of high speed data rate for satellite multimedia and broadcasting services and spectrum scarcity problem in satellite bands, exploring new techniques for enhancing spectral efficiency in satellite communication has become an important research challenge. In this aspect, satellite cognitive communication can be considered as a promising solution to solve spectrum scarcity problem. In this paper, different cognitive techniques such as underlay, overlay, interweave and database related techniques are discussed by reviewing the current state of art. Exact beam patterns of a multi-beam satellite are plotted over the Europe map and interference modeling between terrestrial Base Station (BS) and satellite terminal is carried out on the basis of interference power level. Furthermore, suitable cognitive techniques are proposed in high and low interference regions in the context of satellite cognitive communication. [less ▲]

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See detailExploiting Polarization for Spectrum Sensing in Cognitive SatComs
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of 7th International Conference on Cognitive Radio Oriented Wireless Networks (2012, June)

Exploring new techniques for spectrum sensing (SS), which can detect the weak primary signals instantly, has been an important research challenge. In this paper, the problem of enhancing SS efficiency in ... [more ▼]

Exploring new techniques for spectrum sensing (SS), which can detect the weak primary signals instantly, has been an important research challenge. In this paper, the problem of enhancing SS efficiency in cognitive SatComs has been considered. The analysis of different combining techniques has been carried out for SS using dual polarized antenna. Furthermore, polarization states of received signals are exploited and based on obtained polarization states, Optimum Polarization Based Combining (OPBC) technique has been used for carrying out SS in the satellite terminal. The sensing performance of OPBC technique has been compared to selection combining (SC), equal gain combining (EGC) and maximum ratio combining (MRC) techniques. The simulation results show that OPBC technique achieves a great improvement in sensing efficiency over other considered techniques at the expense of complexity in a dual polarized AWGN channel. [less ▲]

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