Cognitive Beamhopping for Spectral Coexistence of Multibeam Satellites

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 ▲]

Spatial Filtering for Underlay Cognitive SatComs

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 ▲]

Overloaded Satellite Receiver using SIC with Hybrid Beamforming and ML detection

in 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC) (2013, June)

In this paper, a new receiver structure that is intended to detect the signals from multiple adjacent satellites in the presence of other interfering satellites is proposed. We tackle the worst case ... [more ▼]

In this paper, a new receiver structure that is intended to detect the signals from multiple adjacent satellites in the presence of other interfering satellites is proposed. We tackle the worst case interference conditions, i.e., it is assumed that uncoded signals that fully overlap in frequency arrive at a multiple-element small-size parabolic antenna in a spatially correlated noise environment. The proposed successive interference cancellation (SIC) receiver, denoted by SIC Hy/ML, employs hybrid beamforming and disjoint maximum likelihood (ML) detection. Depending on the individual signals spatial position, the proposed SIC Hy/ML scheme takes advantage of two types of beamformers: a maximum ratio combining (MRC) beamformer and a compromised array response (CAR) beamformer. The performance of the proposed receiver is compared to an SIC receiver that uses only MRC beamforming scheme with ML detection for all signals, a joint ML detector, and a minimum mean square error detector. It is found that SIC Hy/ML outperforms the other schemes by a large margin. [less ▲]

Asymptotic Analysis of Eigenvalue-based Blind Spectrum Sensing Techniques

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

Improving Physical Layer Secrecy Using Full-Duplex Jamming Receivers

in IEEE Transactions on Signal Processing (2013), 20(61), 4962-4974

This paper studies secrecy rate optimization in a wireless network with a single-antenna source, a multi-antenna destination and a multi-antenna eavesdropper. This is an unfavorable scenario for secrecy ... [more ▼]

This paper studies secrecy rate optimization in a wireless network with a single-antenna source, a multi-antenna destination and a multi-antenna eavesdropper. This is an unfavorable scenario for secrecy performance as the system is interference-limited. In the literature, assuming that the receiver operates in half duplex (HD) mode, the aforementioned problem has been addressed via use of cooperating nodes who act as jammers to confound the eavesdropper. This paper investigates an alternative solution, which assumes the availability of a full duplex (FD) receiver. In particular, while receiving data, the receiver transmits jamming noise to degrade the eavesdropper channel. The proposed self-protection scheme eliminates the need for external helpers and provides system robustness. For the case in which global channel state information is available, we aim to design the optimal jamming covariance matrix that maximizes the secrecy rate and mitigates loop interference associated with the FD operation. We consider both fixed and optimal linear receiver design at the destination, and show that the optimal jamming covariance matrix is rank-1, and can be found via an efficient 1-D search. For the case in which only statistical information on the eavesdropper channel is available, the optimal power allocation is studied in terms of ergodic and outage secrecy rates. Simulation results verify the analysis and demonstrate substantial performance gain over conventional HD operation at the destination. [less ▲]

User Scheduling for Coordinated Dual Satellite Systems with Linear Precoding

in International Communications Conference, Budapest 2013 (2013)

Eigenvalue based SNR Estimation for Cognitive Radio in Presence of Channel Correlation

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 ▲]

Satellite Cognitive Communications and Spectrum Regulation

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 ▲]

Mutli-Frame Super-Resolution by Enhanced Shift & Add

in 8th International Symposium on Image and Signal Processing and Analysis (2013)

A critical step in multi-frame super-resolution is the registration of frames based on their motion. We improve the performance of current state-of-the-art super-resolution techniques by proposing a more ... [more ▼]

A critical step in multi-frame super-resolution is the registration of frames based on their motion. We improve the performance of current state-of-the-art super-resolution techniques by proposing a more robust and accurate registration as early as in the initialization stage of the high resolution estimate. Indeed, we solve the limitations on scale and motion inherent to the classical Shift & Add approach by upsampling the low resolution frames up to the super-resolution factor prior to estimating motion or to median filtering. This is followed by an appropriate selective optimization, leading to an enhanced Shift & Add. Quantitative and qualitative evaluations have been conducted at two levels; the initial estimation and the final optimized super-resolution. Results show that the proposed algorithm outperforms existing state-of-art methods. [less ▲]

Cooperative Communications against Jamming with Half-Duplex and Full-Duplex Relaying

in Vehicular Technology Conference (VTC Spring), 2013 IEEE 77th (2013)

This paper studies the impact of jamming on the design of three-node two-hop cooperative amplify-and-forward (AF) communications with both half-duplex and full-duplex relaying. For the half-duplex ... [more ▼]

This paper studies the impact of jamming on the design of three-node two-hop cooperative amplify-and-forward (AF) communications with both half-duplex and full-duplex relaying. For the half-duplex relaying, the jammer is smart such that it can optimally allocate jamming power between listening and forwarding phases. Given separate source and relay power constraints, we derive the optimal jamming power allocation; with a total source and relay power constraint, we model the interaction between the legitimate system and the jammer as a noncooperative game and prove the existence and uniqueness of the Nash Equilibrium (NE). It is found that due to the fact that the end performance is limited by the weaker phase, the legitimate systems tries to balance the performance of two phases while the jammer attacks the system by making the two hops imbalanced. While for the full-duplex relaying, we show that if the self-interference can be properly controlled, it can bring substantial performance gain. Simulation results verify our analysis. [less ▲]