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See detailCooperative Power and DoT Estimation for a Directive Source
Maleki, Sina UL; Ciblat, Philippe; Chatzinotas, Symeon UL et al

in Asilomar Conference on Signals, Systems, and Computers 2015 (2015)

Reliable estimation of the source power as well as the direction of transmission (DoT) is required in a large number of applications, e.g. radio environment mapping for cognitive radios, security, system ... [more ▼]

Reliable estimation of the source power as well as the direction of transmission (DoT) is required in a large number of applications, e.g. radio environment mapping for cognitive radios, security, system performance and interference monitoring. In this paper, we develop a multi-sensor cooperative estimation algorithm for joint power and DoT estimation of a source with a known location and equipped with a directive antenna pattern. The source signal is assumed to be known, e.g. a training sequence, and the channel is modeled by the free-space path loss. Simulation results show that the developed algorithm can deliver a reliable estimation accuracy. [less ▲]

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See detailJoint Power Control in Wiretap Interference Channels
Kalantari, Ashkan UL; Maleki, Sina UL; Zheng, Gan et al

in IEEE Transactions on Wireless Communications (2015)

Interference in wireless networks degrades the signal quality at the terminals. However, it can potentially enhance the secrecy rate. This paper investigates the secrecy rate in a two-user interference ... [more ▼]

Interference in wireless networks degrades the signal quality at the terminals. However, it can potentially enhance the secrecy rate. This paper investigates the secrecy rate in a two-user interference network where one of the users, namely user 1, requires to establish a confidential connection. User 1 wants to prevent an unintended user of the network to decode its transmission. User 1 has to transmit such that its secrecy rate is maximized while the quality of service at the destination of the other user, user 2, is satisfied, and both user's power limits are taken into account. We consider two scenarios: 1) user 2 changes its power in favor of user 1, an altruistic scenario, 2) user 2 is selfish and only aims to maintain the minimum quality of service at its destination, an egoistic scenario. It is shown that there is a threshold for user 2's transmission power that only below or above which, depending on the channel qualities, user 1 can achieve a positive secrecy rate. Closed-form solutions are obtained in order to perform joint optimal power control. Further, a new metric called secrecy energy efficiency is introduced. We show that in general, the secrecy energy efficiency of user 1 in an interference channel scenario is higher than that of an interference-free channel. [less ▲]

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See detailMultiple Gateway Transmit Diversity in Q/V Band Feeder Links
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel et al

in IEEE Transactions on Communications (2015)

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q ... [more ▼]

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q/V band and an exploitation of multiple gateways (GW) as a transmit diversity measure for overcoming severe propagation effects are being considered. In this context, this contribution deals with the design of a feeder link comprising N + P GWs (N active and P redundant GWs). Towards provisioning the desired availability, a novel switching scheme is analysed and practical aspects such as prediction based switching and switching rate are discussed. Unlike most relevant works, a dynamic rain attenuation model is used to derive analytically average outage probability in the fundamental 1 + 1 gateway case. Building on this result, an analysis for the N +P scenario leading to a quantification of the end􀀀to􀀀end performance is provided. This analysis aids system sizing by illustrating the interplay between the number of active and redundant gateways on the chosen metrics : average outage and average switching rate. [less ▲]

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See detailLow Complexity Predistortion and Equalization in Nonlinear Multicarrier Satellite Communications
Zenteno, Efrain; Piazza, Roberto UL; Shankar, Bhavani UL et al

in EURASIP Journal on Advances in Signal Processing (2015)

Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint amplification of multiple carriers using a single high-power amplifier (HPA) is being considered ... [more ▼]

Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint amplification of multiple carriers using a single high-power amplifier (HPA) is being considered. In this scenario, a careful investigation of the resulting power efficiency is essential as amplification is nonlinear, and multicarrier signals exhibit enlarged peak-to-average power ratio. Thus, operating the amplifier close to saturation vastly increases signal distortion resulting in a severe degradation of performance, especially for higher order modulations. This paper proposes a reduced-complexity digital predistortion (DPD) scheme at the transmitter and a corresponding equalizer (EQ) at the receiver to mitigate these nonlinear effects. Scenarios include both the forward as well as the return links. In particular, the paper exploits the MIMO Volterra representation and builds on a basis pursuit approach using a LASSO (least absolute shrinkage and selection operator) algorithm to achieve an efficient basis representation, avoiding large computational complexity, to describe the selection of predistorter/equalizer model. The work further compares and contrasts the two mitigation techniques taking various system aspects into consideration. The gains in performance and amplification efficiency demonstrated by the use of DPD/ EQ motivate their inclusion in next-generation satellite systems. [less ▲]

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See detailA MIMO Symbol Rate Signal Digital Predistorter for Nonlinear Multicarrier Satellite Channels
Zenteno, Efrain; Piazza, Roberto UL; Shankar, Bhavani UL et al

in IET Communications (2015), 9(15), 20532059

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture ... [more ▼]

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture similar to data DPD schemes. However, it enhances the mitigation performance of data DPDs using a multi-rate processing algorithm to achieve spectrum broadening of non-linear operators. Compared to single carrier (single-input single-output) signal (waveform) DPD schemes, the proposed DPD has lower digital processing rate reducing the required hardware cost of the predistorter. The proposed DPD outperforms, in total degradation, both data and signal DPD schemes. Further, it performs closest to a channel bound described by an ideally mitigated channel with limited maximum output power. [less ▲]

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See detailGeneralized direct predistortion with adaptive crest factor reduction control
Piazza, Roberto UL; Bhavani Shankar, M. R.; Ottersten, Björn UL

in Proceedings of ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing (2015), 2015-August

Efficient power amplification is inherently a non linear operation that introduces unwanted interference in the amplified signal. Strong inter-symbol interference is generated when the amplifier non ... [more ▼]

Efficient power amplification is inherently a non linear operation that introduces unwanted interference in the amplified signal. Strong inter-symbol interference is generated when the amplifier non linearity is combined with channel memory effects. Further, signals with very high peak to average power ratio, typical of multiple carrier systems, are even more sensitive to the non linearities resulting in severe distortion effects. Signal pre-clipping (crest factor reduction) and predistortion are conventional countermeasure techniques to reduce the generated non linear distortion and improve power and spectral efficiency. In this work, novel optimization methods for predistortion and pre-clipping are analytically derived for a general non-linear communication channel with memory. A combined architecture in which crest factor reduction is followed by signal predistortion is proposed and the parameters are estimated resorting to iterative algorithms based on least squares method. Performance evaluation of the estimation techniques shows the effectiveness of the derived algorithms and significant gain compared to previously known methods. © 2015 IEEE. [less ▲]

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See detailMaximizing energy efficiency in multiple access channels by exploiting packet dropping and transmitter buffering
Butt, M. M.; Jorswieck, E. A.; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2015), 14(8), 4129-4141

Quality of service (QoS) for a network is characterized in terms of various parameters specifying packet delay and loss tolerance requirements for the application. The unpredictable nature of the wireless ... [more ▼]

Quality of service (QoS) for a network is characterized in terms of various parameters specifying packet delay and loss tolerance requirements for the application. The unpredictable nature of the wireless channel demands for application of certain mechanisms to meet the QoS requirements. Traditionally, medium access control (MAC) and network layers perform these tasks. However, these mechanisms do not take (fading) channel conditions into account. In this paper, we investigate the problem using cross layer techniques where information flow and joint optimization of higher and physical layer is permitted. We propose a scheduling scheme to optimize the energy consumption of a multiuser multi-access system such that QoS constraints in terms of packet loss are fulfilled while the system is able to maximize the advantages emerging from multiuser diversity. Specifically, this work focuses on modeling and analyzing the effects of packet buffering capabilities of the transmitter on the system energy for a packet loss tolerant application. We discuss low complexity schemes which show comparable performance to the proposed scheme. The numerical evaluation reveals useful insights about the coupling effects of different QoS parameters on the system energy consumption and validates our analytical results. © 2002-2012 IEEE. [less ▲]

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See detailView-Independent Enhanced 3D Reconstruction of Non-Rigidly Deforming Objects
Afzal, Hassan UL; Aouada, Djamila UL; Destelle, Francois et al

in 16th International Conference on Computer Analysis of Images and Patterns (2015)

In this paper, we target enhanced 3D reconstruction of non-rigidly deforming objects based on a view-independent surface representation with an automated recursive filtering scheme. This work improves ... [more ▼]

In this paper, we target enhanced 3D reconstruction of non-rigidly deforming objects based on a view-independent surface representation with an automated recursive filtering scheme. This work improves upon the KinectDeform algorithm which we recently proposed. KinectDeform uses an implicit viewdependent volumetric truncated signed distance function (TSDF) based surface representation. The view-dependence makes its pipeline complex by requiring surface prediction and extraction steps based on camera’s field of view. This paper proposes to use an explicit projection-based Moving Least Squares (MLS) surface representation from point-sets. Moreover, the empirical weighted filtering scheme in KinectDeform is replaced by an automated fusion scheme based on a Kalman filter. We analyze the performance of the proposed algorithm both qualitatively and quantitatively and show that it is able to produce enhanced and feature preserving 3D reconstructions. [less ▲]

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See detailPerformance Analysis of Underlay Cognitive Radio Systems: Estimation-Throughput Tradeoff
Kaushik, Ankit UL; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in arXiv preprint arXiv:1510.03353 (2015)

In this letter, we study the performance of cognitive Underlay Systems (USs) that employ power control mechanism at the Secondary Transmitter (ST). Existing baseline models considered for the performance ... [more ▼]

In this letter, we study the performance of cognitive Underlay Systems (USs) that employ power control mechanism at the Secondary Transmitter (ST). Existing baseline models considered for the performance analysis either assume the knowledge of involved channels at the ST or retrieve this information by means of a feedback channel, however, such situations hardly exist in practice. Motivated by this fact, we propose a novel approach that incorporates the estimation of the involved channels at the ST, in order to characterize the performance of USs under realistic scenarios. Moreover, we apply an outage constraint that captures the impact of imperfect channel knowledge, particularly on the interference power received at the primary receiver. Besides this, we employ a transmit power constraint at the ST to determine an operating regime for the US. Finally, we analyze an interesting tradeoff between the estimation time and the secondary throughput allowing an optimized performance of the US. [less ▲]

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See detailSensing-Throughput Tradeoff for Interweave Cognitive Radio System: A Deployment-Centric Viewpoint
Kaushik, Ankit UL; Sharma, Shree Krishna UL; Chatzinotas, Symeon UL et al

in Wireless Communications, IEEE Transactions on (2015), PP(99), 14

Secondary access to the licensed spectrum is viable only if the interference is avoided at the primary system. In this regard, different paradigms have been conceptualized in the existing literature ... [more ▼]

Secondary access to the licensed spectrum is viable only if the interference is avoided at the primary system. In this regard, different paradigms have been conceptualized in the existing literature. Among these, interweave systems (ISs) that employ spectrum sensing have been widely investigated. Baseline models investigated in the literature characterize the performance of the IS in terms of a sensing-throughput tradeoff, however, this characterization assumes perfect knowledge of the involved channels at the secondary transmitter, which is unavailable in practice. Motivated by this fact, we establish a novel approach that incorporates channel estimation in the system model, and consequently investigate the impact of imperfect channel knowledge on the performance of the IS. More particularly, the variation induced in the detection probability affects the detector’s performance at the secondary transmitter, which may result in severe interference at the primary receivers. In this view, we propose to employ average and outage constraints on the detection probability, in order to capture the performance of the IS. Our analysis reveals that with an appropriate choice of the estimation time determined by the proposed approach, the performance degradation of the IS can be effectively controlled, and subsequently the achievable secondary throughput can be significantly enhanced. [less ▲]

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See detailCognitive Zone for Broadband Satellite Communication in 17.3-17.7 GHz Band
Maleki, Sina UL; Chatzinotas, Symeon UL; Krause, Jens et al

in IEEE Wireless Communications Letters (2015)

Deploying high throughput satellite systems in Ka band to accommodate the ever increasing demand for high data rates hits a spectrum barrier. Cognitive spectrum utilization of the allocated frequency ... [more ▼]

Deploying high throughput satellite systems in Ka band to accommodate the ever increasing demand for high data rates hits a spectrum barrier. Cognitive spectrum utilization of the allocated frequency bands to other services is a potential solution. Designing a cognitive zone around incumbent broadcasting satellite service (BSS) feeder links beyond which the cognitive fixed satellite service (FSS) terminals can freely utilize the same frequency band is considered in this paper. In addition, we show that there is a rain rate called rain wall, above which cognitive downlink communications becomes infeasible. [less ▲]

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See detailEnergy Efficient Coordinated Beamforming for Multicell System: Duality-Based Algorithm Design and Massive MIMO Transition
He, Shiwen; Huang, Yongming; Yang, Luxi et al

in IEEE TRANSACTIONS ON COMMUNICATIONS (2015), 63(12), 4920-4935

In this paper, we investigate joint beamforming and power allocation in multicell multiple-input single-output (MISO) downlink networks. Our goal is to maximize the utility function defined as the ratio ... [more ▼]

In this paper, we investigate joint beamforming and power allocation in multicell multiple-input single-output (MISO) downlink networks. Our goal is to maximize the utility function defined as the ratio between the system weighted sum rate and the total power consumption subject to the users' quality of service requirements and per-base-station (BS) power constraints. The considered problem is nonconvex and its objective is in a fractional form. To circumvent this problem, we first resort to an virtual uplink formulations of the the primal problem by introducing an auxiliary variable and applying the uplink-downlink duality theory. By exploiting the analytic structure of the optimal beamformers in the dual uplink problem, an efficient algorithm is then developed to solve the considered problem. Furthermore, to reduce further the exchange overhead between coordinated BSs in a large-scale antenna system, an effective coordinated power allocation solution only based on statistical channel state information is reached by deriving the asymptotic optimization problem, which is used to obtain the power allocation in a long-term timescale. Numerical results validate the effectiveness of our proposed schemes and show that both the spectral efficiency and the energy efficiency can be simultaneously improved over traditional downlink coordinated schemes, especially in the middle-high transmit power region. [less ▲]

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See detailResource allocation for cognitive satellite uplink and fixed-service terrestrial coexistence in ka-band
Lagunas, E.; Sharma, Shree Krishna UL; Maleki, Sina UL et al

in Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST (2015), 156

This paper addresses the cognitive Geostationary Orbit (GSO) satellite uplink where satellite terminals reuse frequency bands of Fixed-Service (FS) terrestrial microwave links which are the incumbent ... [more ▼]

This paper addresses the cognitive Geostationary Orbit (GSO) satellite uplink where satellite terminals reuse frequency bands of Fixed-Service (FS) terrestrial microwave links which are the incumbent users in the Ka 27.5-29.5 GHz band. In the scenario considered herein, the transmitted power of the cognitive satellite user has to ensure that the interference impact on potentially present FS links does not exceed the regulatory interference limitations. In order to satisfy the interference constraint and assuming the existence of a complete and reliable FS database, this paper proposes a Joint Power and Carrier Allocation (JPCA) strategy to enable the cognitive uplink access to GSO Fixed Satellite Service (FSS) terminals. The proposed approach identifies the worst FS link per user in terms of interference and divides the amount of tolerable interference among the maximum number of FSS terminal users that can potentially interfere with it. In so doing, the cognitive system is guaranteed to never exceed the prescribed interference threshold. Subsequently, powers and carriers are jointly allocated so as to maximize the throughput of the FSS system. Supporting results based on numerical simulations are provided. It is shown that the proposed cognitive approach represents a promising solution to significantly boost the performance of conventional satellite systems. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2015. [less ▲]

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See detailFeasibility study of full-duplex relaying in satellite networks
Bhavani Shankar, M. R.; Zheng, G.; Maleki, Sina UL et al

in IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC (2015), 2015-August

With the successful implementation of full-duplex radio prototypes, traditional orthogonal half-duplex communications is deemed to be inefficient in certain terrestrial applications. While full-duplex ... [more ▼]

With the successful implementation of full-duplex radio prototypes, traditional orthogonal half-duplex communications is deemed to be inefficient in certain terrestrial applications. While full-duplex techniques are gaining interest in terrestrial communications, thanks to the trend of short-distance and low-power transmissions, their application to satellite communications has drawn little attention. Motivated by this, the paper explores the use of the full-duplex relaying operation on-board the satellite in a DVB-S2 compliant network. Self-interference, whose management is the key component of a full-duplex communication, is the focus of study in this paper. Modelling the effects of self-interference and power amplifier nonlinearities on the quality of the received signal in undertaken. Subsequently, closed-form expressions for the various interference components are derived. The numerical evaluations of derived expressions rely on realistic link budgets and indicate substantial gains in spectral efficiency when self-interference can be well calibrated and measured. This confirms that the satellite full-duplex communications could be a promising solution for the efficient use of satellite spectrum, at least from a technical point of view. © 2015 IEEE. [less ▲]

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See detailPower Allocation in Multibeam Satellite Systems: A Two-Stage Multi-Objective Optimization
Aravanis, Alexis; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel et al

in IEEE Transactions on Wireless Communications (2015)

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See detailMultiple-input multiple-output symbol rate signal digital predistorter for non-linear multi-carrier satellite channels
Zenteno, Efrain; Piazza, Roberto; Bhavani Shankar, M. R. et al

in Communications, IET (2015), 9(16), 2053--2059

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture ... [more ▼]

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture similar to data DPD schemes. However, it enhances the mitigation performance of data DPDs using a multi-rate processing algorithm to achieve spectrum broadening of non-linear operators. Compared to single carrier (single-input single-output) signal (waveform) DPD schemes, the proposed DPD has lower digital processing rate reducing the required hardware cost of the predistorter. The proposed DPD outperforms, in total degradation, both data and signal DPD schemes. Further, it performs closest to a channel bound described by an ideally mitigated channel with limited maximum output power. © 2015. The Institution of Engineering and Technology. [less ▲]

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See detailPrecoding in multibeam satellite communications: present and future challenges
Vázquez, Miguel Ángel; Pérez-Neira, Ana; Christopoulos, Dimitrios et al

in jourlib Journal (2015)

Whenever multibeam satellite systems target very aggressive frequency reuse in their coverage area, inter-beam interference becomes the major obstacle for increasing the overall system throughput. As a ... [more ▼]

Whenever multibeam satellite systems target very aggressive frequency reuse in their coverage area, inter-beam interference becomes the major obstacle for increasing the overall system throughput. As a matter of fact, users located at the beam edges suffer from a very large interference for even a moderately aggressive planning of reuse-2. Although solutions for inter-beam interference management have been investigated at the satellite terminal, it turns out that the performance improvement does not justify the increased terminal complexity and cost. In this article, we pay attention to interference mitigation techniques that take place at the transmitter (i.e. the gateway). Based on this understanding, we provide our vision on advanced precoding techniques and user clustering methods for multibeam broadband fixed satellite communications. We also discuss practical challenges to deploy precoding schemes and the support introduced in the recently published DVB-S2X standard. Future challenges for novel configurations employing precoding are also provided. [less ▲]

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See detailExample-Dependent Cost-Sensitive Logistic Regression for Credit Scoring
Correa Bahnsen, Alejandro UL; Aouada, Djamila UL; Ottersten, Björn UL

in 2014 13th International Conference on Machine Learning and Applications (2014, December 03)

Several real-world classification problems are example-dependent cost-sensitive in nature, where the costs due to misclassification vary between examples. Credit scoring is a typical example of cost ... [more ▼]

Several real-world classification problems are example-dependent cost-sensitive in nature, where the costs due to misclassification vary between examples. Credit scoring is a typical example of cost-sensitive classification. However, it is usually treated using methods that do not take into account the real financial costs associated with the lending business. In this paper, we propose a new example-dependent cost matrix for credit scoring. Furthermore, we propose an algorithm that introduces the example-dependent costs into a logistic regression. Using two publicly available datasets, we compare our proposed method against state-of-the-art example-dependent cost-sensitive algorithms. The results highlight the importance of using real financial costs. Moreover, by using the proposed cost-sensitive logistic regression, significant improvements are made in the sense of higher savings. [less ▲]

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See detailFeasibility of Positive Secrecy Rate in Wiretap Interference Channels
Kalantari, Ashkan UL; Maleki, Sina UL; Zheng, Gan et al

in IEEE Global Conference on Signal and Information Processing (GlobalSIP) (2014, December 03)

Interference usually is an adverse phenomenon in wireless networks. However, the interference can potentially be used to boost the secrecy rate in wireless interference channels. This work studies the ... [more ▼]

Interference usually is an adverse phenomenon in wireless networks. However, the interference can potentially be used to boost the secrecy rate in wireless interference channels. This work studies the secrecy rate in a two-user interference network where unintended user may overhear one of the users, namely user 1. User 1 tunes its transmission power in order to maximize its secrecy rate as well as to maintain the quality of service at the other user’s destination, user 2, while both user’s power limits are considered. It is demonstrated that achieving a positive secrecy rate for user 1 only depends on the channel conditions and user 2’s transmission power. Consequently, depending on the channel conditions, the exact threshold for user 2’s transmission power which leads to a positive secrecy rate for user 1 is derived. [less ▲]

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See detailSpatial Multiplexing in Optical Feeder Links for High Throughput Satellites
Gharanjik, Ahmad UL; Liolis, Konstantinos; Shankar, Bhavani UL et al

in Spatial Multiplexing in Optical Feeder Links for High Throughput Satellites (2014, December 02)

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the ... [more ▼]

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the architecture of a geostationary earth orbit (GEO) satellite system based on optical feeder links. To mitigate the effects of cloud coverage, which is the main availability-limiting factor, Optical Ground Station (OGS) diversity is employed. Moreover, a spatial multiplexing scheme is considered. Assuming an ON-OFF channel model, the number of required OGSs to ensure availability and throughput requirements is analyzed [less ▲]

Detailed reference viewed: 240 (21 UL)