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In high-resolution Earth observation imagery, Low Earth Orbit (LEO) satellites capture and transmit images to ground to create an updated map of an area of interest. Such maps provide valuable information for meteorology and environmental monitoring, but can also be employed for real-time disaster detection and management. However, the amount of data generated by these applications can easily exceed the communication capabilities of LEO satellites, leading to congestion and packet dropping. To avoid these problems, the Inter-Satellite Links (ISLs) can be used to distribute the data among multiple satellites and speed up processing. In this paper, we formulate a satellite mobile edge computing (SMEC) framework for real-time and very-high resolution Earth observation and optimize the image distribution and compression parameters to minimize energy consumption. Our results show that our approach increases the amount of images that the system can support by a factor of 12× and 2× when compared to directly downloading the data and to local SMEC, respectively. Furthermore, energy consumption was reduced by 11% in a real-life scenario of imaging a volcanic island, while a sensitivity analysis of the image acquisition process demonstrates that energy consumption can be reduced by up to 90%., This work was partially funded by SatNEx-V, co-funded by the European Space Agency (ESA). The work of Ana Perez-Neira is partially supported by Project IRENE- (PID2020-115323RB-C31) funded by MCIN/AEI/10.13039/501100011033., Peer Reviewed, Postprint (author's final draft)

Modern satellites deployed in low Earth orbit (LEO) accommodate processing payloads that can be exploited for edge computing. Furthermore, by implementing inter-satellite links, the LEO satellites in a constellation can route the data end-toend (E2E). These capabilities can be exploited to greatly improve the current store-and-forward approaches in Earth surveillance systems. However, they give rise to an NP-hard problem of joint communication and edge computing resource management (RM). In this paper, we propose an algorithm that allows the satellites to select between computing the tasks at the edge or at a cloud server and to allocate an adequate power for communication. The overall objective is to minimize the energy consumption at the satellites while fulfilling specific service E2E latency constraints for the computing tasks. Experimental results show that our algorithm achieves energy savings of up to 18% when compared to the selected benchmarks with either 1) fixed edge computing decisions or 2) maximum power allocation., Part of the research has been supported by the project SatNEx-V, co-funded by the European Space Agency (ESA). This work has also received funding by the Spanish ministry of science and innovation under project IRENE (PID2020-115323RB-C31 / AEI / 10.13039/501100011033) and grant from the Spanish ministry of economic affairs and digital transformation and of the European union – NextGenerationEU [UNICO-5G I+D/AROMA3D-Space (TSI-063000-2021-70)., Peer Reviewed, Postprint (author's final draft)

This paper investigates a novel closed-form noniterative precoding technique for multicast multibeam satellite systems. Next-generation satellite systems will be benefited from the flexible use of the satellite resources especially its power flexible allocation among beams. Intending to obtain a low-computational complexity design, we revisit the well-known signal-to-leakage-and-noise ratio design for multicast transmission. Two alternatives are introduced considering both the physical meaning of the ratio and certain multicast channel vector mapping. We observe the benefits of these techniques in satellite flexible payloads. The proposed technique shows a substantial gain compared to the benchmark according to the numerical simulations. Intuitive insights on the precoding behaviour are also presented., This work is funded by Ministry of Science, Innovation and Universities, Spain, under project TERESA -TEC2017-90093-C3-1-R (AEI/FEDER, UE) and by Catalan government under the grant 2017-SGR-01479., Peer Reviewed, Postprint (author's final draft)

Low-complexity suboptimal solutions are widely accepted to design spatial precoders that mitigate the resulting co-channel interference in multibeam high throughput satellites, which is caused by the aggressive frequency reuse. The most widely accepted solution, due to its simplicity and robustness to different channel conditions, is the so-called minimum Mean Square Error (MMSE) precoder. This work reviews the different rationals that support this technique and presents an alternative that maximizes the directivity. With this new point of view we propose a solution that is suitable for both the unicast and the multicast scenario. The latter is quite unexplored in the existing literature, partly explained by its loss of performance with respect to the unicast case. The proposed technique presents a practical and more clear design than the MSE, and the numerical simulations proof its gains compared to the benchmark., This work is supported by the Spanish ministry of science and innovation under project IRENE (PID2020-115323RB-C31 / AEI / 10.13039/501100011033) and from the Catalan Government (2017-SGR1479)., Peer Reviewed, Postprint (author's final draft)

Zero-Forcing (ZF) and Regularized Zero-Forcing (RZF) precoding are low-complexity sub-optimal solutions widely accepted in the satellite communications community to mitigate the resulting co-channel interference caused by aggressive frequency reuse. However, both are sensitive to the conditioning of the channel matrix, which can greatly reduce the achievable gains. This paper brings the attention to the benefits of a design that allows some residual received interference power at the co-channel users. The motivation behind this approach is to relax the dependence on the matrix inversion procedure involved in conventional precoding schemes. In particular, the proposed scheme aims to be less sensitive to the user scheduling, which is one of the key limiting factors for the practical implementation of precoding. Furthermore, the proposed technique can also cope with more users than satellite beams. In fact, the proposed precoder can be tuned to control the interference towards the co-channel beams, which is a desirable feature that is not met by the existing RZF solutions. The design is formulated as a non-convex optimization and we study various algorithms in order to obtain a practical solution. Supporting results based on numerical simulations show that the proposed precoding implementations are able to outperform the conventional ZF and RZF schemes., This work has been partially supported by the Luxembourg National Research Fund (FNR) under the project FlexSAT (C19/IS/13696663) and by the ministry of Science, Innovation and Universities, Spain, under project TERESA-TEC2017-90093- C3-1-R (AEI/FEDER, UE)., Peer Reviewed, Postprint (published version)

This paper tackles the problem of user scheduling in satellite content delivery networks with precoding. The clustering process has to consider two crucial and independent characteristics of the user terminals. On the one hand, users belonging to the same group shall have a reduced Euclidean norm between their channel vectors in order to obtain the maximum precoding gain. On the other hand, with the aim of exploiting the multicast capabilities of the system, user terminals grouped in the same cluster shall have requested the same content. The resulting clustering problem is formulated as a multigraph (also known as multiview) spectral clustering problem. The paper shows that this unsupervised learning framework is able to capture the different peculiarities of the mentioned problem. Two different techniques are introduced and validated in a close-to-real numerical simulation., This work has received funding from the Spanish ministry of Science, Innovation and Universities under project TERESA-TEC2017-90093-C3-1-R (AEI/FEDER,UE), and by the Catalan Government under grant 2017-SGR01479., Peer Reviewed, Postprint (author's final draft)

The use of multi-antenna transmitters is emerging as an essential technology of the future wireless communication systems. While Zero-Forcing Beamforming (ZFB) has become the most popular low-complexity transmit beamforming design, it has some drawbacks basically related to the effort of "trying" to invert the channel coefficients towards the interfered users. In particular, ZFB performs poorly in the low Signal-to-Noise Ratio (SNR) regime and does not work when the interfered users outnumber the transmit antennas. In this paper, we study in detail an alternative transmit beamforming design framework, where we allow some residual received-interference power instead of trying to null it completely out. Subsequently, we provide a close-form non-iterative optimal solution that avoids the use of sophisticated convex optimization techniques that compromise its applicability onto practical systems. Supporting results based on numerical simulations show that the proposed transmit beamforming is able to perform close to the optimal with much lower computational complexity., This work was partially supported by the Luxembourg FNR, under the CORE projects ECLECTIC and PROSAT, and the FNR-Bridges DISBUS; and it has been partially funded by the ministry of Science, Innovation and Universities, Spain, under project TERESA - TEC2017-90093-C3-1-R (AEI/FEDER, UE)., Peer Reviewed, Postprint (author's final draft)

This paper investigates the application of multicast non-orthogonal multiple access (MC-NOMA) schemes to the forward link of a satellite communication system. In multicast transmission each frame contains information of multiple users. To benefit from the theory developed in NOMA, the proposed scheme creates two groups of users within each beam. The analysis conducted in this work reveals that the user grouping has an impact on the performance. In the light of this observation, power allocation and user clustering techniques have been derived to either maximize the sum-rate or achieve max-min fairness. The numerical simulation results show that MC-NOMA outperforms multicast orthogonal multiple access (MC-OMA) schemes, where different groups are served in orthogonal resources. Moreover, the gain of MC-NOMA over the MC-OMA becomes more prominent as number of users per group and the transmit power increases. The results show the minimum-rate and the sum-rate of MC-NOMA can be increased by a factor 2 and 1.45 with respect to MC-OMA, respectively., Peer Reviewed, Postprint (author's final draft)

The adoption of artificial intelligence (AI) techniques entails a substantial change in the wireless ecosystem where data as well as their owners become crucial. As a result, the roll out of AI techniques in wireless systems raises a plethora of questions. In this context, we describe the challenges observed by the wireless stakeholders when deploying AI. Furthermore, we introduce the recent discussion in field of ethics that appear when managing wireless communications data., Peer Reviewed, Postprint (published version)

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Non-orthogonal transmission is a promising technology enabler to meet the requirements of 5G communication systems. Seminal papers demonstrated that non-orthogonal multiplexing techniques outperform orthogonal schemes in terms of capacity, latency, and user fairness. Since it is envisioned that satellites will be an integral component of the 5G infrastructure, it is worth studying how satellite communication systems can benefit from the application of non-orthogonal transmission schemes as well. Contrary to common perception, current communications through a satellite present a different architecture and face different impairments than those in the wireless terrestrial links. In particular, this work aims to describe different non-orthogonal schemes that are suitable for the forward link (i.e., satellite to user). In contrast with the return link of the satellite (i.e., user to satellite), where the use of non-orthogonal transmission schemes has been widely studied, less effort has been devoted to the forward link. In light of this, this article provides an overview and a novel taxonomy that is based on the forward link of different non-orthogonal multibeam transmission schemes. Finally, guidelines that open new avenues for research in this topic are provided., Peer Reviewed, Postprint (author's final draft)

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., The field of satellite communications (SatCom) is enjoying renewed attention in the global telecommunications market, and high-throughput satellites, with their multiple spot beams, are critical components for delivering the rates that will be demanded in the future. In this article, we present the state of the art and the open research challenges in the area of high-throughput satellites, with a focus on signal processing approaches for efficient interference mitigation., Peer Reviewed, Postprint (author's final draft)

Interference Management is a vast topic present in many disciplines. The majority of wireless standards suffer the drawback of interference intrusion and the network efficiency drop due to that. Traditionally, interference management has been addressed by proposing signal processing techniques that minimize their effects locally. However, the fast evolution of future communications makes difficult to adapt to new era. In this paper we propose the use of Deep Learning techniques to present a compact system for interference management. In particular, we describe two subsystems capable to detect the presence of interference, even in high Signal to Interference Ratio (SIR), and interference classification in several radio standards. Finally, we present results based on real signals captured from terrestrial and satellite networks and the conclusions unveil the courageous future of AI and wireless communications., Peer Reviewed, Postprint (published version)

This paper introduces the notion of beam-free satellite systems and it investigates different scheduling algorithms for this architecture. Attending to the current satellite gateway cloudification, this paper assumes that users from different beams can be scheduled over the same frame. Indeed, considering full frequency reuse among beams and on ground precoding, we show that whenever the scheduler is able to freely group users independently of their beam location, large attainable rates are obtained. In addition, we also consider that the gateway is able to select a number of simultaneous transmissions which leads to a substantial sum-rate increase. A scheduling scheme based on spectral clustering is proposed and it shows a higher performance compared to other state-of-the-art alternatives. In addition, our method is able to deal with different user terminal traffic classes. Based on the numerical results obtained considering a close-to-real multibeam satellite pattern, we point out that the current per-beam scheduling process is an inefficient network management for multi-beam satellite systems using precoding., Peer Reviewed, Postprint (published version)

This paper deals with the problem of sparse beamforming for interference mitigation in milimiter wave (mm Wave) frequency bands. Multiantenna solutions in mmWave are generally implemented with phase shifters which are known to have good interference rejection capabilities. However, phase shifters are power-demanding components and, depending on their resolution, they require bulky hardware solutions able to accommodate the control lines. On the other hand, the use of switches leads to a cost-efficient alternative able to provide a sufficiently large interference rejection while substantially reducing the hardware cost and power consumption. This work proposes a beamforming scheme able to maximize the signal-to-interference-plus-noise ratio (SINR) assuming that the beamforming weights can only take 0 and 1 values. The resulting optimization problem is a binary quadratic fractional problem which is a difficult non-convex problem. Two optimization approaches are proposed; namely, the semidefinite relaxation and the penalized convex-concave procedure. We show that both techniques behave well in the considered scenarios and their performance is close to the optimization problem upper bound value., Peer Reviewed, Postprint (published version)

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., This paper deals with the problem of precoding in multibeam satellite system with rate splitting (RS). In contrast to the single-stream (SS) case where a unique private frame is transmitted towards each beam, in RS we consider the simultaneous transmission of a public frame to all intended users superimposed with each private frames. In this context, every user terminal (UT) firstly decodes the public frame which contains data from all UTs at all beams and; posteriorly, its intended private frame which is only decodable by a set of users. With this, each UT receives information from both the public and the private frame, leading to a system sum-rate increase in some cases. This performance increase is evaluated by computing an upper bound of the attainable rates. Moreover, a low-complexity precoding alternative is proposed considering a decoupled design of the precoding of the private frames and public frames. This technique is evaluated considering a real multibeam satellite system. A substantial gain with respect to the current benchmark technique is identified., Peer Reviewed, Postprint (published version)

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Current satellite and terrestrial backhaul systems are deployed in disjoint frequency bands. This fact precludes an efficient use of the spectrum and limits the evolution of wireless backhauling networks. In this paper, we propose an interference mitigation technique in order to allow the spectrum coexistence between satellite and terrestrial backhaul links. This interference reliever is implemented at the terrestrial backhaul nodes, which are assumed to be equipped with multiple antennas. Due to the large bandwidth and huge number of antennas required in these systems, we consider pure analog beamforming. Precisely, we assume a phased array beamforming configuration so that the terrestrial backhaul node can only reduce the interference by changing the phases of each beamforming weight. Two cases are considered: the 18 and 28 GHz band where transmit and receive beamforming optimization problems shall be tackled, respectively. In both cases, the optimization problem results in a nonconvex problem that we propose to solve via two alternative convex approximation methods. These two approaches are evaluated and they present less than 1 dB array gain loss with respect to the upper bound solution. Finally, the spectral efficiency gains of the proposed spectrum sharing scenarios are validated in numerical simulations., Peer Reviewed, Postprint (published version)

An aggressive frequency reuse is expected within the next years in order to increase the spectral ef¿ciency. Multiuser interference by all in-band transmitters can create a communication bottleneck and, therefore, it is compulsory to control it by means of radiated power regulations. In this work we consider received power as the main way to properly measure radiated power, serving at the same time as a spectrum sharing mechanism. Taking into account the constraints on the maximum total receive-power and maximum transmit-power, we ¿rst obtain the transmit powers that attain the Pareto-ef¿cient rates in an uncoordinated network. Among these rates, we identify the maximum sum-rate point for noise-limited scenarios. Next, in order to reach this working point using as less power as possible, we design a novel beamformer under some practical considerations. This beamformer can be calculated in a non-iterative and distributed fashion (i.e. transmitters do not need to exchange information). We evaluateour designby meansof Monte Carlosimulations, compare it with other non-iterative transmit beam formers and show its superior performance when the spectrum sharing receive-power constraints are imposed., Peer Reviewed, Postprint (published version)

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., This paper deals with the problem of analog-digital transmit beamforming under spectrum sharing constraints for backhaul systems. In contrast to fully digital designs, where the spatial processing is done at baseband unit with all the flexible computational resources of digital processors, analog-digital beamforming schemes require that certain processing is done through analog components, such as phase-shifters or switches. These analog components do not have the same processing flexibility as the digital processor, but on the other hand, they can substantially reduce the cost and complexity of the beamforming solution. This paper presents the joint optimization of the analog and digital parts, which results in a nonconvex, NP-hard, and coupled problem. In order to solve it, an alternating optimization with a penalized convex-concave method is proposed. According to the simulation results, this novel iterative procedure is able to find a solution that behaves close to the fully digital beamforming upper bound scheme., Peer Reviewed, Postprint (author's final draft)

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works, This paper deals with the problem of precoding, scheduling and link adaptation in next generation mobile interactive multibeam satellite systems. In contrast to the fixed satellite services, when the user terminals move across the coverage area, additional challenges appear. Due to the time varying channel, the gateway has only access to a delayed version of the channel state information (CSI) which can eventually limit the overall system performance. However, in contrast to general multiuser multipleinput- multiple-output terrestrial systems, the CSI degradation in multibeam mobile applications has a very limited impact for typical fading channel and system assumptions. Under realistic conditions, the numerical results show that precoding can offer an attractive gain in the system throughput compared to conservative frequency reuse allocations., Peer Reviewed, Postprint (author's final draft)

Current satellite standards do not employ multi-carrier modulations due to its high peak to average power. Consequently, satellite communication systems can not get benefited from the rate granularity and multiuser capabilities of these modulations. Furthermore, it is of great interest to satellite operators to use multi-carrier modulations as they are used in current cellular standard and, eventually, an air interface convergence could be obtained. The performance evaluation of this modulations is done in terms of bit error rate, out of band power and peak to average power ratio. As it is described in the document, multi-carrier modulations present different trade-offs and in some cases they do not perform better than the current filtered multitone scheme used in most of the standards., Los actuales estándares de satélite no utilizan modulaciones multiportadoras debido a la elevada relación entre el pico y la media de potencia. Consiguientemente, los sistemas de comunicación satélite no se pueden beneficiar de la granularidad de las tasas de datos y la capacidad de servir diferentes usuarios simultáneamente de forma eficiente. Además, es de gran interés para los operadores de satélite el uso de modulaciones multiportadoras tal y como usan en los estándares celulares, de tal modo que una convergencia con la interfaz de aire puede ser lograda. La evaluación del funcionamiento se ha hecho en términos de ratio de error de bit y relación entre el pico y la media de potencia. Como está descrito en este documento, las modulaciones multiportadoras presentan diferentes compensaciones y en algunos casos no actúan mejor que el esquema de filtrado de multitonos usado en muchos de los estándares., Els actuals estàndards de satèl·lit no utilitzen modulacions multiportadores degut a l'elevada relació entre el pic y la potencia mitja. Consegüentment, els sistemes de comunicació satèl·lit no es poden beneficiar de la granularitat de les taxes de dades i la capacitat de servir diferents usuaris simultaneament de forma eficient. A més, és de gran interès per las operadores de satèl·lit l'ús de modulacions multiportadores tal com usen en els estàndards cel·lulars, de manera que una convergència amb la interfície d'aire pot ser obtinguda. L'avaluació del funcionament d'aquestes modulacions s'ha fet en termes de ràtio de error de bit i relació entre el pic y la mitjana de potència. Como està descrit en aquest document, les modulacions multiportadores presenten diferents compensacions i en alguns casos no actuen millor que l'esquema de filtrat de multitons usat en molts dels estàndards.

In order to provide wireless services for the current demand of high data rate mobile applications, more spectrally efficient systems are needed. As a matter of fact, the current wireless systems are limited by a frequency splitting spectrum management which in one hand minimizes the multiuser interference but; on the other hand, it precludes the use of wider bandwidth signals. As a more aggressive frequency reuse is targeted (ideally, all transmitters might eventually share the same frequency band), the use of multiple antennas for interference reliving, jointly with a smart power allocation is compulsory. In addition, novel spectrum management regulatory policies are required for ensuring a peaceful coexistence between adjacent spectrum sharing networks and for promoting their development. The aim of this dissertation is provide a beamforming and power allocation design for these novel spectrum sharing systems which are meant to exponentially increase the spectral efficiency of the systems. A mathematical framework based on multicriteria optimization for analyzing the beamforming design is provided which serves as a fundamental tool for describing the state-of-the-art studies in multiantenna interference networks. Indeed, the achievable rates are described and several ways of computing the Pareto rate region of MISO interference channel (i.e. the communication model that represents the spectrum sharing network when the transmitters use multiple antennas) are studied. Nevertheless, as the system designer aims to work in a single efficient rate point, the sum-rate optimal beamforming design is studied. Curiously, it results that under some realistic assumptions on both the desired and interference power levels, the obtained beamformer is the reciprocal version of a known receiving one and it optimizes a notion of antenna directivity for multiuser communications. Neverthelss, it is important to remark that the higher transmit power is used, the more interference domi, Postprint (published version)

[ANGLÈS] This thesis deals with the problem of finding optimal precoding techniques that, considering multiple antennas at the transmitter side, will be able to increase the data rate of future interference networks. First, we present a transmit beamformer that obtains higher sum-rates of the current decentralized designs in asymmetric channel link gains yet preserving a good performance in the general case. From a more theoretical perspective, we derive the achiveable rates of the multiple-input-single-output interference channel via the mathematical framework of multicriteria optimization. Although few results have appeared for solving this problem, we show that all of them can be reformulated as a multicriteria optimization problem and we show their equivalence. Finally, we consider the problem of confidential communication in interference networks that might be required by several wireless communication applications. Relaying on physical layer formulation of the security, we obtain the weighted region when the nonintended receivers do not collude. This is, once each eavesdropper has a weighting factor, we derive the maximum rates that the transmitter can securely communicate with the intended receiver., [CASTELLÀ] Esta tesis versa sobre el problema de encontrar las técnicas óptimas de precodificación que, teniendo en cuenta múltiples antenas en el lado del transmisor, será capaz de aumentar la velocidad de datos de redes de injerencia en el futuro. En primer lugar, se presenta un formador de haces de transmisión que obtiene mayor suma de las tasas de los diseños actuales descentralizados de enlace de canal asimétrica, sin embargo, las ganancias preservan una buena actuación en el caso general. Desde una perspectiva más teórica, se derivan las tasas de achiveable de la interferencia de canales múltiples de entrada y salida única a través de la estructura matemática de la optimización multicriterio. Aunque pocos resultados han aparecido para resolver este problema, nos muestran que todos ellos pueden ser reformulados como un problema de optimización multicriterio y mostramos su equivalencia. Por último, consideramos el problema de la comunicación confidencial en redes de injerencia que podrían ser necesarias por varias aplicaciones de comunicación inalámbrica. La retransmisión en la formulación de la capa física de la seguridad, se obtiene la región ponderada cuando los receptores nonintended no concuerdan. Esto es, una vez al espía tiene un factor de ponderación, se derivan las tasas máximas que el transmisor de forma segura se pueden comunicar con el receptor previsto., [CATALÀ] Aquesta tesi tracta el problema de trobar les tècniques òptimes de precodificació que, tenint en compte múltiples antenes en el costat del transmissor, serà capaç d'augmentar la velocitat de dades de xarxes d'ingerència en el futur. En primer lloc, es presenta un formador de feixos de transmissió que obté una major suma de les taxes dels dissenys actuals descentralitzats d'enllaç de canal asimètrica, però, els guanys preserven una bona actuació en el cas general. Des d'una perspectiva més teòrica, es deriven les taxes d'achiveable de la interferència de canals múltiples d'entrada i sortida única a través de l'estructura matemàtica de l'optimització multicriteri. Encara que pocs resultats han aparegut per resoldre aquest problema, ens mostren que tots ells poden ser reformulats com un problema d'optimització multicriteri i mostrem la seva equivalència. Finalment, considerem el problema de la comunicació confidencial en xarxes d'ingerència que podrien ser necessàries per diverses aplicacions de comunicació sense fils. La retransmissió en la formulació de la capa física de la seguretat, s'obté la regió ponderada quan els receptors nonintended no concorden. Això és, un cop l'espia té un factor de ponderació, es deriven les taxes màximes que el transmissor de forma segura es poden comunicar amb el receptor previst.

Projecte fet en col.laboració amb el Department of Electrical and Information Technology. Lund University, The high peak-to-average power ratio (PAPR) and the high out-of-band power (OBP) are two major drawbacks of multicarrier communication systems. Many PAPR reduction and OBP supression techniques have been proposed in the literature whereas not much has been proposed regarding the jointly reduction performance. This thesis focuses on joint reducing time-domain peaks and out-of-band leakage of OFDM signals. The resulting algorithm combines the bene ts of both methods and yields better results than each method does separately.