Results 501-520 of 534.
Bookmark and Share    
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 215 (13 UL)
Full Text
Peer Reviewed
See detailMulti-User Detection in Multibeam Mobile Satellite Systems: A Fair Performance Evaluation
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Krause, Jens et al

in Proceedings of Vehicular Technology Conference, Spring 2013 (2013)

Multi-User Detection (MUD) techniques are currently being examined as promising technologies for the next generation of broadband, interactive, multibeam satellite communication (SatCom) systems. Results ... [more ▼]

Multi-User Detection (MUD) techniques are currently being examined as promising technologies for the next generation of broadband, interactive, multibeam satellite communication (SatCom) systems. Results in the existing literature have shown that when full frequency and polarization reuse is employed and user signals are jointly processed at the gateway, more than threefold gains in terms of spectral efficiency over conventional systems can be obtained. However, the information theoretic results for the capacity of the multibeam satellite channel are given under ideal assumptions, disregarding the implementation constraints of such an approach. Considering a real system implementation, the adoption of full resource reuse is bound to increase the payload complexity and power consumption. Since these novel techniques require extra payload resources, fairness issues in the comparison among the two approaches arise. The present contribution evaluates in a fair manner, the performance of the return link (RL) of a SatCom system serving mobile users that are jointly decoded at the receiver. In this context, the throughput performance of the assumed system is compared to that of a conventional one, under the constraint of equal physical layer resource utilization; thus the comparison can be regarded as fair. Results show, that even when systems operate under the same payload requirements as the conventional systems, a significant gain can be realized, especially in the high SNR region. Finally, existing analytical formulas are also employed to provide closed form descriptions of the performance of clustered systems, thus introducing insights on how the performance scales with respect to the system parameters. [less ▲]

Detailed reference viewed: 365 (49 UL)
Full Text
Peer Reviewed
See detailMMSE Performance Analysis of Generalized Multibeam Satellite Channels
Christopoulos, Dimitrios UL; Arnau, Jesus; Chatzinotas, Symeon UL et al

in IEEE Wireless Communications Letters (2013), 17(7), 1332-1335

Detailed reference viewed: 270 (21 UL)
Full Text
Peer Reviewed
See detailConstructive Interference in Linear Precoding Systems: Power Allocation and User Selection
Christopoulos, Dimitrios; Chatzinotas, Symeon UL; Krikidis, Ioannis et al

in IEEE GlobeCom (2013)

The exploitation of interference in a constructive manner has recently been proposed for the downlink of multiuser, multi-antenna transmitters. This novel linear precoding technique, herein referred to as ... [more ▼]

The exploitation of interference in a constructive manner has recently been proposed for the downlink of multiuser, multi-antenna transmitters. This novel linear precoding technique, herein referred to as constructive interference zero forcing (CIZF) precoding, has exhibited substantial gains over conventional approaches; the concept is to cancel, on a symbol-by-symbol basis, only the interfering users that do not add to the intended signal power. In this paper, the power allocation problem towards maximizing the performance of a CIZF system with respect to some metric (throughput or fairness) is investigated. What is more, it is shown that the performance of the novel precoding scheme can be further boosted by choosing some of the constructive multiuser interference terms in the precoder design. Finally, motivated by the significant effect of user selection on conventional, zero forcing (ZF) precoding, the problem of user selection for the novel precoding method is tackled. A new iterative, low complexity algorithm for user selection in CIZF is developed. Simulation results are provided to display the gains of the algorithm compared to known user selection approaches. [less ▲]

Detailed reference viewed: 103 (5 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 193 (13 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 194 (15 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 180 (7 UL)
Full Text
Peer Reviewed
See detailCognitive interference alignment between small cells and a macrocell
Chatzinotas, Symeon UL; Ottersten, Björn UL

in 19th International Conference on Telecommunications (ICT) 2012 (2012)

Detailed reference viewed: 159 (1 UL)
Full Text
Peer Reviewed
See detailCapacity Analysis of Dual-Hop Amplify-and-Forward MIMO Multiple-Access Channels
Chatzinotas, Symeon UL; Ottersten, Björn UL

in International Conference on Wireless Communications and Signal Processing, WCSP 2012 (2012)

Relay channels have been heavily studied during the last decades as a means of improving spectral efficiency, availability and coverage in combination with multiple antenna transceivers. Relay channels ... [more ▼]

Relay channels have been heavily studied during the last decades as a means of improving spectral efficiency, availability and coverage in combination with multiple antenna transceivers. Relay channels can comprise many hops but the most practical approach at the time being would be a dual-hop system. In addition, the simplest method of relaying in terms of complexity is amplify and forward. In this direction, we investigate the ergodic capacity of a dual-hop amplify-and-forward MIMO MAC and we derive asymptotic closed-form expressions based on the principles of free probability theory. We extend the current literature by proposing a analytical model which can accommodate variance-profiled Gaussian matrices. Numerical results are utilized to verify the accuracy of the derived closed-form expressions and evaluate the effect of the channel parameters. [less ▲]

Detailed reference viewed: 155 (1 UL)
Full Text
Peer Reviewed
See detailGeneric Optimization of Linear Precoding in Multibeam Satellite Systems
Zheng, Gan UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2012), 11(6), 2308-2320

Detailed reference viewed: 239 (18 UL)
Full Text
Peer Reviewed
See detailMulti-gateway cooperation in multibeam satellite systems
Zheng, Gan UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE 23rd International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC) (2012)

Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and ... [more ▼]

Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and precoding over multiple beams has shown great throughput potential in literature. However, feeding all this data from a single gateway is not feasible based on the current frequency allocations. In this context, we investigate a range of scenarios involving beam clusters where each cluster is managed by a single gateway. More specifically, the following cases are considered for handling intercluster interference: a) conventional frequency colouring, b) joint processing within cluster, c) partial CSI sharing among clusters, d) partial CSI and data sharing among clusters. CSI sharing does not provide considerable performance gains with respect to b) but combined with data sharing offers roughly a 40% improvement over a) and a 15% over b). [less ▲]

Detailed reference viewed: 181 (9 UL)
Full Text
Peer Reviewed
See detailFixed Full Duplex Relaying for Wireless Broadband Communication
Meng, Qingmin; Feng, Wei; Zheng, Gan UL et al

in Wireless Communications & Signal Processing (WCSP), 2012 International Conference on (2012)

We compare full duplex (FD) and half duplex (HD) relaying in terms of coverage range. We consider a practical FD relay model where both the dynamic ranges of transmitter and receiver and the level of the ... [more ▼]

We compare full duplex (FD) and half duplex (HD) relaying in terms of coverage range. We consider a practical FD relay model where both the dynamic ranges of transmitter and receiver and the level of the residual loop interference between transmitted and received signals are taken into account. We numerically evaluate the rate performance of the full duplex multi-hop (FD-MH) scheme and the half duplex decode-and-forward (HD-DF) scheme, where the former requires transmit power allocation under the dynamic range constraint. Results show that there is a tradeoff between these two relaying modes. [less ▲]

Detailed reference viewed: 200 (0 UL)
Full Text
Peer Reviewed
See detailLinear and nonlinear techniques for multibeam joint processing in satellite communications
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Zheng, Gan UL et al

in EURASIP Journal on Wireless Communications and Networking (2012), 2012(162),

Existing satellite communication standards such as DVB-S2 operate under highly-efficient adaptive coding and modulation schemes thus making significant progress in improving the spectral efficiencies of ... [more ▼]

Existing satellite communication standards such as DVB-S2 operate under highly-efficient adaptive coding and modulation schemes thus making significant progress in improving the spectral efficiencies of digital satellite broadcast systems. However, the constantly increasing demand for broadband and interactive satellite links emanates the need to apply novel interference mitigation techniques, striving towards Terabit throughput. In this direction, the objective of the present contribution is to investigate joint multiuser processing techniques for multibeam satellite systems. In the forward link, the performance of linear precoding is investigated with optimal non-linear precoding (i.e. Dirty Paper Coding) acting as the upper performance limit. To this end, the resulting power and precoder design problems are approached through optimization methods. Similarly, in the return link the concept of linear filtering (i.e. Linear Minimum Mean Square Error) is studied with the optimal successive interference cancellation acting as the performance limit. The derived capacity curves for both scenarios are compared to conventional satellite systems where beams are processed independently and interbeam interference is mitigated through a four color frequency reuse scheme, in order to quantify the potential gain of the proposed techniques. [less ▲]

Detailed reference viewed: 305 (29 UL)
Full Text
Peer Reviewed
See detailInterference Alignment for Clustered Multicell Joint Decoding
Chatzinotas, Symeon UL; Ottersten, Björn UL

in Interference Alignment for Clustered Multicell Joint Decoding (2011)

Detailed reference viewed: 144 (1 UL)
Full Text
Peer Reviewed
See detailClustered Multicell Joint Decoding under Cochannel Interference
Chatzinotas, Symeon UL; Ottersten, Björn UL

in Clustered Multicell Joint Decoding under Cochannel Interference (2011)

Detailed reference viewed: 127 (0 UL)
Full Text
Peer Reviewed
See detailInterference Mitigation Techniques for Clustered Multicell Joint Decoding Systems
Chatzinotas, Symeon UL; Ottersten, Björn UL

in EURASIP Journal on Wireless Communications and Networking (2011), 132

Detailed reference viewed: 179 (5 UL)
Full Text
Peer Reviewed
See detailJoint Precoding with Flexible Power Constraints in Multibeam Satellite Systems
Chatzinotas, Symeon UL; Zheng, Gan UL; Ottersten, Björn UL

in Joint Precoding with Flexible Power Constraints in Multibeam Satellite Systems (2011)

Detailed reference viewed: 177 (11 UL)