Results 341-360 of 748.
Bookmark and Share    
Full Text
Peer Reviewed
See detailPeak Power Minimization in Symbol-level Precoding for Cognitive MISO Downlink Channels
Alodeh, Maha UL; Spano, Danilo UL; Chatzinotas, Symeon UL et al

in IEEE Digital Signal Processing Conference (2016, October 16)

This paper proposes a new symbol-level precoding scheme at the cognitive transmitter that jointly utilizes the data and channel information to reduce the effect of nonlinear amplifiers, by reducing the ... [more ▼]

This paper proposes a new symbol-level precoding scheme at the cognitive transmitter that jointly utilizes the data and channel information to reduce the effect of nonlinear amplifiers, by reducing the maximum antenna power under quality of service constraint at the cognitive receivers. In practice, each transmit antenna has a separate amplifier with individual characteristics. In the proposed approach, the precoding design is optimized in order to control the instantaneous power transmitted by the antennas, and more specifically to limit the power peaks, while guaranteeing some specific target signal-to-noise ratios at the receivers and respecting the interference temperature constraint imposed by the primary system. Numerical results show the effectiveness of the proposed scheme, which outperforms the existing state of the art techniques in terms of reduction of the power peaks. [less ▲]

Detailed reference viewed: 540 (22 UL)
Full Text
Peer Reviewed
See detailTerminal-side interference mitigation for spectral coexistence of satellite and terrestrial systems in non-exclusive Ka-band
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in 34th AIAA International Communications Satellite Systems Conference (2016, October)

Detailed reference viewed: 167 (10 UL)
Full Text
Peer Reviewed
See detailUniversal Intelligent Small Cell for Next Generation Cellular Networks
Patwary, M.; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in Digital Communications and Networks (2016), 2(4), 167174

Exploring innovative cellular architectures to achieve enhanced system capacity and good coverage has become a critical issue towards realizing the next generation of wireless communications. In this ... [more ▼]

Exploring innovative cellular architectures to achieve enhanced system capacity and good coverage has become a critical issue towards realizing the next generation of wireless communications. In this context, this paper proposes a novel concept of Universal Intelligent Small Cell (UnISCell) for enabling the densification of the next generation of cellular networks. The proposed novel concept envisions an integrated platform of providing a strong linkage between different stakeholders such as street lighting networks, landline telephone networks and future wireless networks, and is universal in nature being independent of the operating frequency bands and traffic types. The main motivating factors for the proposed small cell concept are the need of public infrastructure re-engineering, and the recent advances in several enabling technologies. First, we highlight the main concepts of the proposed UnISCell platform. Subsequently, we present two deployment scenarios for the proposed UnISCell concept considering infrastructure sharing and service sharing as important aspects. We then describe the key future technologies for enabling the proposed UnISCell concept and present a use case example with the help of numerical results. Finally, we conclude this article by providing some interesting future recommendations. [less ▲]

Detailed reference viewed: 187 (25 UL)
Full Text
Peer Reviewed
See detailCentralized Power Control in Cognitive Radio Networks Using Modulation and Coding Classification Feedback
Tsakmalis, Anestis UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Cognitive Communications and Networking (2016), 2(3),

In this paper, a centralized Power Control (PC) scheme and an interference channel learning method are jointly tackled to allow a Cognitive Radio Network (CRN) access to the frequency band of a Primary ... [more ▼]

In this paper, a centralized Power Control (PC) scheme and an interference channel learning method are jointly tackled to allow a Cognitive Radio Network (CRN) access to the frequency band of a Primary User (PU) operating based on an Adaptive Coding and Modulation (ACM) protocol. The learning process enabler is a cooperative Modulation and Coding Classification (MCC) technique which estimates the Modulation and Coding scheme (MCS) of the PU. Due to the lack of cooperation between the PU and the CRN, the CRN exploits this multilevel MCC sensing feedback as implicit channel state information (CSI) of the PU link in order to constantly monitor the impact of the aggregated interference it causes. In this paper, an algorithm is developed for maximizing the CRN throughput (the PC optimization objective) and simultaneously learning how to mitigate PU interference (the optimization problem constraint) by using only the MCC information. Ideal approaches for this problem setting with high convergence rate are the cutting plane methods (CPM). Here, we focus on the analytic center cutting plane method (ACCPM) and the center of gravity cutting plane method (CGCPM) whose effectiveness in the proposed simultaneous PC and interference channel learning algorithm is demonstrated through numerical simulations. [less ▲]

Detailed reference viewed: 246 (29 UL)
Full Text
Peer Reviewed
See detailCognitive Interference Management Techniques for the Spectral Co-existence of GSO and NGSO Satellites
Pourmoghaddaslangroudi, Ameneh UL; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in International Conference on Wireless and Satellite Systems (WiSATS, formerly PSATS), Cardiff, UK, Sep 2016 (2016, September 19)

One of the main challenges in the co-existence of geostationary satellite orbit (GSO) and non-geostationary satellite orbit (NGSO) satellite networks is to mitigate the in-line interference caused by an ... [more ▼]

One of the main challenges in the co-existence of geostationary satellite orbit (GSO) and non-geostationary satellite orbit (NGSO) satellite networks is to mitigate the in-line interference caused by an NGSO satellite to the GSO earth terminal, while the NGSO satellite is crossing the GSO satellite's illumination zone. The method recommended in ITU-R S.1325-3 involves utilizing a range-based power control on the NGSO satellite for downlink communication to the NGSO earth terminals. In this paper, we investigate a cognitive range-based power control algorithm while taking into account the imposed interference level to the GSO fixed satellite service (FSS) system. Results show that the proposed cognitive power control algorithm can mitigate the harmful in-line interference on the GSO terminal receiver, while also providing the desired link quality for the NGSO system. More importantly, we formulate and solve an optimization problem with the objective of minimizing the inter-site distance (ISD) of the GSO-NGSO earth user-terminals. Finally, we develop an analytical method to calculate the ISD between GSO and NGSO earth terminals and validate this with the help of simulation results. [less ▲]

Detailed reference viewed: 258 (9 UL)
Full Text
Peer Reviewed
See detailOn the Performance Analysis of Underlay Cognitive Radio Systems: A Deployment Perspective
Kaushik, A.; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in IEEE Transactions on Cognitive Communications and Networking (2016), 2(3), 273-287

We study the performance of a cognitive underlay system (US) that employs a power control mechanism at the secondary transmitter (ST) from a deployment perspective. Existing baseline models considered for ... [more ▼]

We study the performance of a cognitive underlay system (US) that employs a power control mechanism at the secondary transmitter (ST) from a deployment perspective. Existing baseline models considered for performance analysis either assume the knowledge of involved channels at the ST or retrieve this information by means of a band manager or a feedback channel; however, such situations rarely exist in practice. Motivated by this fact, we propose a novel approach that incorporates estimation of the involved channels at the ST in order to characterize the performance of the US in terms of interference power received at the primary receiver and throughput at the secondary receiver (or secondary throughput). Moreover, we apply an outage constraint that captures the impact of imperfect channel knowledge, particularly on the uncertain interference. Besides this, we employ a transmit power constraint at the ST to classify the operation of the US in terms of an interference-limited regime and a power-limited regime. In addition, we characterize the expressions of the uncertain interference and the secondary throughput for the case where the involved channels encounter Nakagami-m fading. Finally, we investigate a fundamental tradeoff between the estimation time and the secondary throughput depicting an optimized performance of the US. [less ▲]

Detailed reference viewed: 139 (2 UL)
Full Text
Peer Reviewed
See detailLow Complexity Transmit Processing for Multibeam Satellite Systems with Non-Linear Channels
Mengali, Alberto UL; Kayhan, Farbod UL; Shankar, Bhavani UL et al

in Proceedings of ASMS Conference (2016, September)

Detailed reference viewed: 240 (8 UL)
Full Text
Peer Reviewed
See detailFrequency of Arrival-based Interference Localization Using a Single Satellite
Kalantari, Ashkan UL; Maleki, Sina UL; Chatzinotas, Symeon UL et al

in 8th Advanced Satellite Multimedia Systems Conference 14th Signal Processing for Space Communications Workshop (2016, September)

Intentional and unintentional interferences are an increasing threat for the satellite communications industry. In this paper, we aim to localize an interference with unknown location using frequency of ... [more ▼]

Intentional and unintentional interferences are an increasing threat for the satellite communications industry. In this paper, we aim to localize an interference with unknown location using frequency of arrival (FoA) technique by only relying on the measurements obtained through a single satellite. In each time instance, the satellite samples the interference and forwards it to the gateway to estimate its frequency. Since the satellite moves, each estimated frequency includes a Doppler shift, which is related to the location of the unknown interferer. The satellite's position, velocity, oscillator frequency, and the interference frequency are used at the gateway to build a location-related equation between the estimated frequency and the location of the unknown interference. Simultaneously with the interference signal, the satellite samples a reference signal to calibrate the estimated frequency and compensate for the mismatches between the available and real values of the satellite's position, velocity, and oscillator frequency. Multiple location-related equations obtained based on the FoA measurements, (at least two), along with the equation of the earth surface are used to localize the unknown interference. Simulations show that increasing the number of these equations, and the satellite velocity can improve the localization accuracy by 80% and 95%, respectively. [less ▲]

Detailed reference viewed: 216 (8 UL)
Full Text
Peer Reviewed
See detailSymbol-Level Precoding with Per-antenna Power Constraints for the Multi-beam Satellite Downlink
Spano, Danilo UL; Chatzinotas, Symeon UL; Krause, Jens et al

in 8th Advanced Satellite Multimedia Systems Conference (ASMS) (2016, September)

This paper tackles the problem of multi-user interference in the forward downlink channel of a multi-beam satellite system. A symbol-level precoding scheme is considered, where the data information is ... [more ▼]

This paper tackles the problem of multi-user interference in the forward downlink channel of a multi-beam satellite system. A symbol-level precoding scheme is considered, where the data information is used, along with the channel state information, in order to exploit the multi-user interference and transform it into useful power at the receiver side. In this framework, the max-min fair problem for constructive interference is formulated and solved, under per-antenna power constraints. The consideration of the power limitations individually for each transmitting RF chain is the novel aspect, and it is relevant in particular for systems suffering non-linear effects of the channel. This is the case of satellite systems, where the non-linear amplifiers should be properly driven in order to reduce the detrimental saturation effect. The proposed precoding design optimizes the system performance at the receiver side in terms of signal-to-noise ratio, whilst guaranteeing the system fairness and allowing a control over the power transmitted by each antenna, in particular reducing the power peaks. Numerical results are presented to validate the proposed scheme, and to show its effectiveness in terms of distribution of the transmitted power and peak-to-average power ratio. [less ▲]

Detailed reference viewed: 204 (14 UL)
Full Text
Peer Reviewed
See detailPerformance Analysis of Interweave Cognitive Radio Systems with Imperfect Channel Knowledge over Nakagami Fading Channels
Kaushik, A.; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in 2016 IEEE 84th Vehicular Technology Conference: VTC2016-Fall (2016, September)

Detailed reference viewed: 141 (2 UL)
Full Text
Peer Reviewed
See detailCompressive Sensing Based Energy Detector
Lagunas, Eva UL; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in European Signal Processing Conference (EUSIPCO) (2016, August)

Detailed reference viewed: 183 (12 UL)
Full Text
Peer Reviewed
See detailDirectional Modulation via Symbol-Level Precoding: A Way to Enhance Security
Kalantari, Ashkan UL; Soltanalian, Mojtaba; Maleki, Sina UL et al

in IEEE Journal of Selected Topics in Signal Processing (2016)

Wireless communication provides a wide coverage at the cost of exposing information to unintended users. As an information-theoretic paradigm, secrecy rate derives bounds for secure transmission when the ... [more ▼]

Wireless communication provides a wide coverage at the cost of exposing information to unintended users. As an information-theoretic paradigm, secrecy rate derives bounds for secure transmission when the channel to the eavesdropper is known. However, such bounds are shown to be restrictive in practice and may require exploitation of specialized coding schemes. In this paper, we employ the concept of directional modulation and follow a signal processing approach to enhance the security of multi-user MIMO communication systems when a multi-antenna eavesdropper is present. Enhancing the security is accomplished by increasing the symbol error rate at the eavesdropper. Unlike the information-theoretic secrecy rate paradigm, we assume that the legitimate transmitter is not aware of its channel to the eavesdropper, which is a more realistic assumption. We examine the applicability of MIMO receiving algorithms at the eavesdropper. Using the channel knowledge and the intended symbols for the users, we design security enhancing symbol-level precoders for different transmitter and eavesdropper antenna configurations. We transform each design problem to a linearly constrained quadratic program and propose two solutions, namely the iterative algorithm and one based on non-negative least squares, at each scenario for a computationally-efficient modulation. Simulation results verify the analysis and show that the designed precoders outperform the benchmark scheme in terms of both power efficiency and security enhancement. [less ▲]

Detailed reference viewed: 244 (30 UL)
Full Text
Peer Reviewed
See detailAn Iterative Approach to Nonconvex QCQP with Applications in Signal Processing
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Soltanalian, Mojtaba et al

in 2016 IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) (2016, July 10)

This paper introduces a new iterative approach to solve or to approximate the solutions of the nonconvex quadratically constrained quadratic programs (QCQP). First, this constrained problem is transformed ... [more ▼]

This paper introduces a new iterative approach to solve or to approximate the solutions of the nonconvex quadratically constrained quadratic programs (QCQP). First, this constrained problem is transformed to an unconstrained problem using a specialized penalty-based method. A tight upper-bound for the alternative unconstrained objective is introduced. Then an efficient minimization approach to the alternative unconstrained objective is proposed and further studied. The proposed approach involves power iterations and minimization of a convex scalar function in each iteration, which are computationally fast. The important design problem of multigroup multicast beamforming is formulated as a nonconvex QCQP and solved using the proposed method. [less ▲]

Detailed reference viewed: 147 (0 UL)
Full Text
Peer Reviewed
See detailJoint Compression and Feedback of CSI in Correlated multiuser MISO Channels
Alodeh, Maha UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in The 17th IEEE International workshop on Signal Processing advances in Wireless Communications (2016, July)

The potential gains of multiple antennas in wireless systems can be limited by the channel state information imperfections. In this context, this paper tackles the feedback in multiuser correlated ... [more ▼]

The potential gains of multiple antennas in wireless systems can be limited by the channel state information imperfections. In this context, this paper tackles the feedback in multiuser correlated multiple input single output (MU-MISO). We propose a framework to feedback the minimum number of bits without performance degradation. This framework is based on decorrelating the channel state information by compression and then quantize the compressed (CSI) and feedback it to the base station (BS). We characterize the rate loss resulted from the proposed framework. An upper bound on the rate loss is derived in terms of the amount of feedback and the statistics of the channel. Based on this characterization, we propose am adaptive bit allocation algorithm that takes into the account the channel statistics to reduce the rate loss induced by the quantization. Moreover, in order to maintain a constant rate loss with respect to the perfect CSIT case, it is shown that the number of feedback bits should scale linearly with the SNR (in dB) and to the rank of the user transmit correlation matrix. We validate the proposed framework by Monte-carlo simulations. [less ▲]

Detailed reference viewed: 208 (8 UL)
Full Text
Peer Reviewed
See detailDistributed coordinated beamforming for multi-cell multigroup multicast systems
Pennanen, Harri UL; Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL et al

in Communications (ICC), 2016 IEEE International Conference on (2016, July)

This paper considers coordinated multicast beam-forming in a multi-cell wireless network. Each multiantenna base station (BS) serves multiple groups of single antenna users by generating a single beam ... [more ▼]

This paper considers coordinated multicast beam-forming in a multi-cell wireless network. Each multiantenna base station (BS) serves multiple groups of single antenna users by generating a single beam with common data per group. The aim is to minimize the sum power of BSs while satisfying user-specific SINR targets. We propose centralized and distributed multicast beamforming algorithms for multi-cell multigroup systems. The NP-hard multicast problem is tackled by approximating it as a convex problem using the standard semidefinite relaxation method. The resulting semidefinite program (SDP) can be solved via centralized processing if global channel knowledge is available. To allow a distributed implementation, the primal decomposition method is used to turn the SDP into two optimization levels. The higher level is in charge of optimizing inter-cell interference while the lower level optimizes beamformers for given inter-cell interference constraints. The distributed algorithm requires local channel knowledge at each BS and scalar information exchange between BSs. If the solution has unit rank, it is optimal for the original problem. Otherwise, the Gaussian randomization method is used to find a feasible solution. The superiority of the proposed algorithms over conventional schemes is demonstrated via numerical evaluation. [less ▲]

Detailed reference viewed: 143 (6 UL)
Full Text
Peer Reviewed
See detailPerformance analysis of hybrid cognitive radio systems with imperfect channel knowledge
Kaushik, A.; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in Communications (ICC), 2016 IEEE International Conference on (2016, July)

In this paper, we study the performance of hybrid cognitive radio systems that combine the benefits of interweave and underlay systems by employing a spectrum sensing and a power control mechanism at the ... [more ▼]

In this paper, we study the performance of hybrid cognitive radio systems that combine the benefits of interweave and underlay systems by employing a spectrum sensing and a power control mechanism at the Secondary Transmitter (ST). Existing baseline models considered for performance analysis assume perfect knowledge of the involved channels at the ST, however, such situations hardly exist in practical deployments. Motivated by this fact, we propose a novel approach that incorporates channel estimation at the ST, and consequently characterizes the performance of Hybrid Systems (HSs) under realistic scenarios. To capture the impact of imperfect channel knowledge, we propose outage constraints on the detection probability at the ST and on the interference power received at the primary receiver. Our analysis reveals that the baseline model overestimates the performance of the HS in terms of achievable secondary user throughput. Finally, based on the proposed estimation-sensing-throughput tradeoff, we determine suitable estimation and sensing durations that effectively capture the effect of imperfect channel knowledge and subsequently enhance the achievable secondary user throughput. [less ▲]

Detailed reference viewed: 136 (3 UL)
Full Text
Peer Reviewed
See detailImpact of Transceiver Hardware Impairments on the Ergodic Channel Capacity for Rayleigh-Product MIMO Channels
Papazafeiropoulos, Anastasios; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in Proceedings of IEEE SPAWC 2016 (2016, July)

This paper aims at a realistic evaluation of Rayleighproduct multiple-input multiple-output (MIMO) systems. Specifically, by considering the residual transceiver hardware impairments into account, we ... [more ▼]

This paper aims at a realistic evaluation of Rayleighproduct multiple-input multiple-output (MIMO) systems. Specifically, by considering the residual transceiver hardware impairments into account, we derive the ergodic channel capacity of a MIMO system with optimal receivers in the case of insufficient scattering. Actually, motivated by the increasing interest for massive MIMO systems, we investigate the impact of transceiver hardware imperfections in systems with both finite (conventional) and large number of antennas under rank deficient channel matrix conditions by varying the severity of hardware quality. Among the interesting outcomes, we emphasize that the residual hardware transceiver impairments result to a saturation of the ergodic channel capacity within the high signal-to-noise ratio (SNR) regime. Furthermore, we observe that the higher the “richness” of the scattering environment, the higher the ergodic channel capacity till it gets saturated. [less ▲]

Detailed reference viewed: 187 (19 UL)
Full Text
Peer Reviewed
See detailSimilarity Metric For Curved Shapes In Euclidean Space
Demisse, Girum UL; Aouada, Djamila UL; Ottersten, Björn UL

in IEEE Conference on Computer Vision and Pattern Recognition (CVPR) 2016 (2016, June 26)

In this paper, we introduce a similarity metric for curved shapes that can be described, distinctively, by ordered points. The proposed method represents a given curve as a point in the deformation space ... [more ▼]

In this paper, we introduce a similarity metric for curved shapes that can be described, distinctively, by ordered points. The proposed method represents a given curve as a point in the deformation space, the direct product of rigid transformation matrices, such that the successive action of the matrices on a fixed starting point reconstructs the full curve. In general, both open and closed curves are represented in the deformation space modulo shape orientation and orientation preserving diffeomorphisms. The use of direct product Lie groups to represent curved shapes led to an explicit formula for geodesic curves and the formulation of a similarity metric between shapes by the $L^{2}$-norm on the Lie algebra. Additionally, invariance to reparametrization or estimation of point correspondence between shapes is performed as an intermediate step for computing geodesics. Furthermore, since there is no computation of differential quantities on the curves, our representation is more robust to local perturbations and needs no pre-smoothing. We compare our method with the elastic shape metric defined through the square root velocity (SRV) mapping, and other shape matching approaches [less ▲]

Detailed reference viewed: 408 (54 UL)
Full Text
Peer Reviewed
See detailEfficient sum-rate maximization for medium-scale MIMO AF-relay networks
Naghsh, M.M.; Soltanalian, M.; Stoica, P. et al

in IEEE Transactions on Wireless Communications (2016), 15(9), 6400-6411

We consider the problem of sum-rate maximization in multiple-input multiple-output (MIMO) amplify-and-forward relay networks with multi-operator. The aim is to design the MIMO relay amplification matrix ... [more ▼]

We consider the problem of sum-rate maximization in multiple-input multiple-output (MIMO) amplify-and-forward relay networks with multi-operator. The aim is to design the MIMO relay amplification matrix (i.e., the relay beamformer) to maximize the achievable communication sum rate through the relay. The design problem for the case of single-antenna users can be cast as a non-convex optimization problem, which, in general, belongs to a class of NP-hard problems. We devise a method based on the minorization-maximization technique to obtain quality solutions to the problem. Each iteration of the proposed method consists of solving a strictly convex unconstrained quadratic program. This task can be done quite efficiently, such that the suggested algorithm can handle the beamformer design for relays with up to ~70 antennas within a few minutes on an ordinary personal computer. Such a performance lays the ground for the proposed method to be employed in medium-scale (or lower regime massive) MIMO scenarios. [less ▲]

Detailed reference viewed: 139 (4 UL)