Enerji hasadı yapan kablosuz ağlarda kullanıcı işbirliği ve kaynak tahsisi

Yeni nesil haberleşme sistemlerinde, pillere ya da şehir elektriğine bağımlı olarak çalışan klasik haberleşme bileşenlerinin yerlerini, enerjilerini çevreden hasat eden, çevreye duyarlı ve uzun kullanım ömrüne sahip bileşenlere bırakacağı öngörülmektedir. Bu nedenle, bilinen haberleşme protokollerinin, enerjinin aralıklı olarak geldiği, ve gönderilerin anlık enerji kısıtlarına tabi olduğu durumlara uygun olarak baştan ele alınması, ve enerji hasadı koşulları altında kuramsal performans üst limitlerinin baştan belirlenmesi gerekmektedir. Bu projede, tüm enerjilerini doğadan hasat eden işbirlikli haberleşme ağlarında, kaynakları etkin kullanarak ağ performansını artıran ve ömrünü uzatan gönderim protokolleri tasarlanmıştır. Böylece, işbirlikli kablosuz ağlarda basit çoklu erişim ya da aktarım kanal modellerinin ötesine geçilmiş; farklı kullanıcılarda anlık olarak farklı miktarlarda biriktirilen enerjinin beraberinde getirdiği enerji çeşitleme kazancı ile işbirliği kazancından bir arada faydalanılması sağlanmıştır. Düğümlerin kendi enerjilerini iletim sırasında çevrelerinden temin ettikleri, ve biribirleri ile gerek veri, gerekse enerji aktarımı ile yardımlaşabildikleri durumlar için, • Bilgi kuramsal bir yaklaşım kullanılarak, gerek gecikme kısıtlı, gerekse gecikmeye toleranslı durumlar için, blok Markov kodlama ve geriye doğru kodçözme tabanlı yeni işbirlikli kodlama teknikleri geliştirilmiş, ve karşılık gelen erişilebilir veri hızları elde edilmiş, • Toplam veri hızı veya veri gönderim bölgelerini enbüyükleyen kaynak tahsisi algoritmaları geliştirilmiş, • Hasat edilen enerji ve kanal durumlarının gönderim, aktarım, ya da enerjinin depolanması kararlarını nasıl etkilediği incelenmiş, temel bazı ödünleşimler belirlenmiş, • Verinin ve hasat edilen enerjinin gönderi devam ederken aralıklı geldiği durumda en iyi veri hızı ve güç çizelgelemesi bulunmuş, • İşbirlikli haberleşme için kritik olan, hem alıcı hem de verici olarak davranan düğümlerdeki kodçözme maliyeti kısıtları dikkate alınarak işbirliğinden net kazancı eniyileyen politikalar geliştirilmiş, • Düğümlerin biribirlerine enerji de gönderebildikleri durumda, işbirlikli veri iletişimi ile enerji transferi yoluyla işbirliği senaryoları birlikte incelenip, en iyi kaynak tahsisi stratejisi belirlenmiş, • Hasat edilen kaydedildiği bataryaların sınırlı kapasitesi olması durumunda gelen enerjinin ziyan edilmemesini garanti eden en iyi kaynak yönetimi algoritmaları önerilmiştir. Elde edilen sonuçlar, gerek veri, gerekse enerji işbirliğinin, enerji hasat eden sistemlerde, özellikle enerji çeşitlemesinden kazanç sağlamak için çok faydalı yaklaşımlar olduğuna işaret etmektedir.In new generation wireless systems, traditional communication components which rely on batteries or the electrical grid are expected to ve replaced by more environment-conscious, energy harvesting components with longer lifetime. Therefore, known communication protocols need to be reconsidered from scratch to adapt to situations where the transmissions are subject to instantaneous energy constraints caused by intermittent energy arrivals, and their theoretical performance upper bounds need to be re-derived under energy harvesting constraints. In this project, we design transmission protocols that maximize the network performance and lifetime by efficiently allocating resources, for communication networks that rely only on energy harvested from their surroundings. We go beyond simple multiple access or relay models, and jointly take advantage of the energy diversity provided by the variable nature of the energy arrivals at different users, and cooperative diversity. For scenarios where the nodes harvest their own enery during transmission, and are able to cooperate both at data and battery level, • we approach the system from an information theoretic perspective and develop new encoding and decoding techniques, based on block Markov coding and backward decoding, that can be used in delay constrained and delay tolerant communication; and characterize their achievable rates, • we develop resource allocation algorithms that maximize the total rate or departure region, • we investigate the effect of energy arrival profiles and channel qualities on transmission, bi-directional relaying and energy saving decisions, and determine some fundamental tradeoffs, • we find the optimal power and rate scheduling policy when data, as well as energy arrives intermittently during transmission, • we obtain the optimal policies that maximize the net gain from cooperation, taking into account the decoding costs at the transceiver nodes, • we develop jointly optimal energy and data cooperation strategies, when energy can be exchanged wirelessly • we propose scheduling optimization algorithms that guarantee that energy is not wasted, taking into account practical battery limitations at the energy harvesting nodes. The results obtained point to the conclusion that data and energy cooperation are significantly useful approaches that take advantage of the inherent energy diversity provided by the energy harvesting communication systems.TÜBİTA

Resource management techniques for sustainable networks with energy harvesting nodes

Premi extraordinari doctorat UPC curs 2015-2016, àmbit Enginyeria de les TICThis dissertation proposes novel techniques for assigning resources of wireless networks by considering that the coverage radii are small, implying that some power consumption sinks not considered so far shouldnow be introduced, and by considering that the devices are battery-powered terminals provided with energy harvesting capabilities. In this framework, two different configurations in terms of harvesting capabilities are considered. First, we assume that the energy source is external and not controllable, e.g. solar energy. In this context, the proposed design should adapt to the energy that is currently being harvested. We also study the effect of having a finite backhaul connection that links the wireless access network with the core network. On the other hand, we propose a design in which the transmitter feeds actively the receivers with energy by transmitting signals that receivers use for recharging their batteries. In this case, the power transfer design should be carried out jointly with the power control strategy for users that receive information as both procedures, transfer of information and transfer of power, are implemented at the transmitter and make use of a common resource, i.e., power. Apart from techniques for assigning the radio resources, this dissertation develops a procedure for switching on and off base stations. Concerning this, it is important to notice that the traffic profile is not constant throughout the day. This is precisely the feature that can be exploited to define a strategy based on a dynamic selection of the base stations to be switched off when the traffic load is low, without affecting the quality experienced by the users. Thanks to this procedure, we are able to deploy smaller energy harvesting sources and smaller batteries and, thus, to reduce the cost of the network deployment. Finally, we derive some procedures to optimize high level decisions of the network operation in which variables from several layers of the protocol stack are involved. In this context, admission control procedures for deciding which user should be connected to which base station are studied, taking into account information of the average channel information, the current battery levels, etc. A multi-tier multi-cell scenario is assumed in which base stations belonging to different tiers have different capabilities, e.g., transmission power, battery size, end energy harvesting source size. A set of strategies that require different computational complexity are derived for scenarios with different user mobility requirements.Aquesta tesis doctoral proposa tècniques per assignar els recursos disponibles a les xarxes wireless considerant que els radis de cobertura són petits, el que implica que altres fonts de consum d’energia no considerades fins al moment s’hagin d’introduir dins els dissenys, i considerant que els dispositius estan alimentats amb bateries finites i que tenen a la seva disposició fonts de energy harvesting. En aquest context, es consideren dues configuracions diferents en funció de les capacitats de l’energia harvesting. En primer lloc, s’assumirà que la font d’energia és externa i incontrolable com, per exemple, l’energia solar. Els dissenys proposats han d’adaptar-se a l’energia que s’està recol·lectant en un precís moment. En segon lloc, es proposa un disseny en el qual el transmissor és capaç d’enviar energia als receptors mitjançant senyals de radiofreqüència dissenyats per aquest fi, energia que és utilitzada per recarregar les bateries. A part de tècniques d’assignació de recursos radio, en aquesta tesis doctoral es desenvolupa un procediment dinàmic per apagar i encendre estacions base. És important notar que el perfil de tràfic no és constant al llarg del dia. Aquest és precisament el patró que es pot explotar per definir una estratègia dinàmica per poder decidir quines estaciones base han de ser apagades, tot això sense afectar la qualitat experimentada pels usuaris. Gràcies a aquest procediment, es possible desplegar fonts d'energy harvesting més petites i bateries més petites. Finalment, aquesta tesis doctoral presenta procediments per optimitzar decisions de nivell més alt que afecten directament al funcionament global de la xarxa d’accés. Per prendre aquestes decisions, es fa ús de diverses variables que pertanyen a diferents capes de la pila de protocols. En aquest context, aquesta tesis aborda el disseny de tècniques de control d’admissió d’usuaris a estacions base en entorns amb múltiples estacions base, basant-se amb la informació estadística dels canals, i el nivell actual de les bateries, entre altres. L'escenari considerat està format per múltiples estacions base, on cada estació base pertany a una família amb diferents capacitats, per exemple, potència de transmissió o mida de la bateria. Es deriven un conjunt de tècniques amb diferents costos computacionals que són d'utilitat per a poder aplicar a escenaris amb diferents mobilitats d’usuaris.Award-winningPostprint (published version

Transmission strategies for wireless energy harvesting nodes

Over the last few decades, transistor miniaturization has enabled a tremendous increase in the processing capability of commercial electronic devices, which, combined with the reduction of production costs, has tremendously fostered the usage of the Information and communications Technologies (ICTs) both in terms of number of users and required data rates. In turn, this has led to a tremendous increment in the energetic demand of the ICT sector, which is expected to further grow during the upcoming years, reaching unsustainable levels of greenhouse gas emissions as reported by the European Council. Additionally, the autonomy of battery operated devices is getting reduced year after year since battery technology has not evolved fast enough to cope with the increase of energy consumption associated to the growth of the node¿s processing capability. Energy harvesting, which is known as the process of collecting energy from the environment by different means (e.g., solar cells, piezoelectric generators, etc.), has become a potential technology to palliate both of these problems. However, when energy harvesting modules are placed in wireless communication devices (e.g., sensor nodes or hand-held devices), traditional transmission strategies are no longer applicable because the temporal variations of the node¿s energy availability must be carefully accounted for in the design. Apart from not considering energy harvesting, traditional transmission strategies assume that the transmission radiated power is the unique energy sink in the node. This is a reasonable assumption when the transmission range is large, but it no longer holds for low consumption devices such as sensor nodes that transmit to short distances. As a result, classical transmission strategies become suboptimal in short-range communications with low consumption devices and new strategies should be investigated. Consequently, in this dissertation we investigate and design transmission strategies for Wireless Energy Harvesting Nodes (WEHNs) by paying a special emphasis on the different sinks of energy consumption at the transmitter(s). First, we consider a finite battery WEHN operating in a point-to-point link through a static channel and derive the transmission strategy that minimizes the transmission completion time of a set of data packets that become available dynamically over time. The transmission strategy has to satisfy causality constrains in data transmission and energy consumption, which impose that the node cannot transmit data that is not yet available nor consume energy that has not yet been harvested. Second, we consider a WEHN that has an infinite backlog of data to be transmitted through a point-to-point link in a time-varying linear vector Gaussian channel and study the linear precoding strategy that maximizes the mutual information given an arbitrary distribution of the input symbols while satisfying the Energy Causality Constraints (ECCs) at the transmitter. Next, apart from the transmission radiated power, we take into account additional energy sinks in the power consumption model and analyze how these energy sinks affect to the transmission strategy that maximizes the mutual information achieved by a WEHN operating in a point-to-point link. Finally, we consider multiple transmitter and receiver pairs sharing a common channel and investigate a distributed power allocation strategy that aims at maximizing the network sum-rate by taking into account the energy availability in the different transmitters and a generalized power consumption model.Durant les últimes dècades, la miniaturització del transistor i la reducció dels seus costos de fabricació han provocat un augment substancial del nombre de terminals de comunicacions i del tràfic de dades requerit per aquests dispositius. Així doncs, el consum energètic del sector de les Tecnologies de la Informació i Comunicacions ha incrementat notablement. A més a més, s’espera que aquest consum segueixi creixent durant els propers anys arribant a nivells insostenibles d’emissions de gasos d’efecte hivernacle segons ha informat el Consell Europeu. D’altra banda, la tecnologia de les bateries no ha evolucionat suficientment ràpid com per fer front a l’augment del consum energètic associat al creixement de la capacitat de processament dels dispositius. Això ha ocasionat que l’autonomia dels dispositius que operen amb bateries empitjori any rere any. Les energies renovables (per exemple, energia solar, cinètica, etc.) s’han convertit en una solució potencial per pal•liar aquests dos problemes. No obstant això, quan els dispositius de comunicació sense fils incorporen mòduls de captació d’energies renovables, les estratègies tradicionals de transmissió deixen de ser vàlides, ja que les variacions temporals de la disponibilitat d’energia en el dispositiu han de ser considerades en el disseny. A més a més, les estratègies de transmissió tradicionals assumeixen que la potència radiada és l’única font de consum energètic del node. Aquesta és una suposició raonable per distàncies de transmissió llargues, però deixa de ser vàlida quan es consideren dispositius de baix consum que transmeten en distàncies curtes. Com a resultat, les estratègies de transmissió clàssiques són subòptimes en comunicacions de curt abast amb dispositius de baix consum i per això, s’han d’investigar noves estratègies. En conseqüència, en aquesta tesi doctoral s’investiguen i es dissenyen noves estratègies de transmissió per nodes sense fils que operen amb energies renovables (WEHN) posant un èmfasi especial en les diferents fonts de consum d’energia en el transmissor. En primer lloc, la tesi investiga l’estratègia de transmissió en un enllaç¸ punt a punt a través d’un canal estàtic que minimitza el temps de transmissió d’un conjunt de paquets de dades que s’adquireixen al llarg del temps. L’estratègia de transmissió ha de satisfer les limitacions per causalitat en la transmissió de dades i en el consum d’energia les quals imposen que el node no pot transmetre dades que no han estat encara obtingudes o utilitzar energia que encara no ha estat adquirida. En segon lloc, es considera un WEHN que sempre disposa de dades per a transmetre a través d’un enllaç¸ punt a punt en un canal lineal Gaussià amb variacions temporals. En aquest escenari i, també, donada una distribució arbitrària dels símbols d’entrada, s’estudia l’estratègia de precodificació lineal que maximitza la informació mútua alhora que satisfà la causalitat d’energia en el transmissor. A continuació, a part de la potència radiada en transmissió, s’inclouen en el model de consum energètic els costos d’activació per accés al canal i per portadora. Donat aquest model, s’analitza com aquestes fonts de consum addicionals afecten a l’estratègia de transmissió que maximitza la informació mútua d’un WEHN que opera en un enllaç punt a punt. Finalment, la tesi considera diversos parells transmissor i receptor que comparteixen un canal comú i investiga una estratègia d’assignació de potència distribuïda la qual té com a objectiu maximitzar la suma de les taxes de transmissió dels diferents nodes tenint en compte la disponibilitat energètica en cada transmissor que està basada en un model de consum energètic generalitzat