The first decade of twenty-first century has witnessed the spread of innovative wireless technologies: novel wireless network architectures and services; operations in unlicensed bands, advanced mobile devices and smartphones. All these have pondered growing demand for wireless broadband services, so that more spectra are required. Consequently,the advent of flat-rate service pricing for mobile broadband services plus continuous investments in a network infrastructure and shortage of licensed spectrum make it more difficult for current wireless operators (OPs) to financially sustain themselves in a competitive environment. Since existing, fixed spectrum allocation (FSA), mechanism offers very limited flexibility, dynamic spectrum access from the market point of view is exploited here to support such flexibility. A framework of competitive spectrum access, where available spectrum can be leased based on the outcome of competition between heterogeneous wireless operators in a short-term fashion, is reviewed in this thesis. The main objectives are: (1) to maximize spectrum efficiency by utilizing market mechanisms in a heterogeneous setting, and (2) to identify which conditions and criteria should be applied to allow heterogeneous wireless networks to be viable in the marketplace. Under the competitive spectrum access framework, we explore three directions to tackle these objectives for a case of a two-operators system. First, we will look at how an inter-operator competition can affect the operator profits under an asymmetry in their networks. Then, we will analyze which deployment strategies in a heterogeneous environment should be utilized. Finally, we will consider which pricing strategies can be applied by competing OPs to sustain themselves. Through analysis and extensive simulations, we show that heterogeneous access architectures and the scalable infrastructure deployment could improve not only spectrum utilization efficiency, but also facilitate viability of spectrum allocation in a competitive environment. As a conclusion, we believe that techno-economical approach used to assess a feasibility of the framework could help in the designing of future wireless systems to efficiently utilize both the infrastructure and the spectrum resources. / <p>QC 20120529</p> / QUASAR

The rapid development of electronic components has resulted in the emergence of newmobile applications targeted at industry and hospital sectors. Moreover, a lack of availablewireless frequencies as result of the growth of wireless systems is becoming a problem.In this thesis we characterize industrial and hospital environments in order to provide theknowledge necessary to asses present and future development of critical wireless applications.Furthermore, we investigate the possibility of using TV white space by analysingthe interference from secondary to primary user in home environments. Some of the wireless solutions used in industries and hospitals come directly fromsystems designed for home or office, such asWLAN and Bluetooth. These systems are notprepared to handle problems associated with interference of impulsive character found inindustrial processes and electrical systems. Typically, industrial environments have been classified as reflective environments dueto the metallic structure present in the buildings. In this thesis, we demonstrate that althoughthis may be generally true, some locations in the industry may have special propertieswith wave propagation characteristics in the opposite direction. Stored materials canabsorb wireless signals, resulting in a coverage problem. From the measurement campaignwe are able to distinguish three main classes of indoor environments (highly reflective,medium reflective and low reflective) with different propagation characteristics. Improving spectrum efficiency can be a solution to the growing demand for wirelessservices and can increase a system’s robustness against interference, particularly in criticalapplications in industrial and hospital environments. One improvement in spectrum efficiencycan be for secondary consumers to reuse unassigned portions of the TV spectrum ata specific time and geographical location. This thesis studies the effect of inserting whitespace devices in the TV broadcast spectrum. Note that any new model must state the maximumpower allocated to secondary users to avoid harmful interference with the primarysignal. The content of this thesis is divided into three parts. The first part is the most comprehensiveand addresses electromagnetic interference and multipath characterization ofindustrial environments. In this part, we have developed a method for channel characterizationfor complex electromagnetic environments and have produced results from differentindustrial environments. The second part presents a preliminary study that characterizesthe electromagnetic interference in a hospital environment. The third part is a study ofsecondary users reusing the TV white spaces. / QC 20120119

A recent trend is to integrate sensing, communication, and computation into every aspect of our daily life, ranging from various user devices to physical environment. The goal is to give computer systems an awareness of the users and their situations, so that they can support their diverse interaction needs at anytime, any place. A major problem hindering achieving this promising goal is that the users usually play a passive role in these systems with little possibility to interfere with the processing. Additionally, there is no option for the user to prevent being monitored by the system. This drawback stems from the lack of an independent and consistent user oriented viewpoint in current ubiquitous computing systems, which can easily result in the occurrence of user privacy invasion and misinterpretation of the user. To overcome this problem, this thesis proposes a Person-Centric Context Aware System architecture, helping to preserve an independent representation for each individual user to different computer systems. The main idea embraced in this system architecture is that the users are the owners of their personal information, thus they should have the control of how their information will be used by others. In the design of this system architecture, a number of important issues have been addressed with their corresponding solutions in terms of different system components. Among these issues, three are identified as the most crucial ones, and hence these issues have received most of our efforts to provide better solutions: Context Data Communication, Location Detection, and Communication Anonymity support. A prototype system constructed during the process of developing each specific solution is also presented. Together these comprise the main contributions of this thesis work. Finally, our concluding remarks are presented together with our planned future work, based on the current implementation of a Person-Centric Context Aware System. / QC 20101118

With the advent of multi-radio access (MRA), an integration of differentradio access technologies (RATs) into a heterogeneous radio access network(RAN) becomes feasible. Such integration allows a user to be at any instantof time served by one or multiple radio accesses (RAs) concurrently, where anRA constitutes an independent radio resource, such as a carrier or a channel,implemented by a single RAT. It also allows a user´s service demands to bemapped onto the aggregated network resources in a transparent and efficientway. An approach for the realization of such multi-radio integrated environmentsis through a unifying generic link layer (GLL) that provides joint radiolink processing and enables communication between nodes and devices acrossdifferent radio accesses.Based on the requirements on multi-access, an architecture that supportsMRA is suggested and the functions of GLL that aims at integrating andutilising multiple RATs are defined. We explore the potential for performanceimprovements through novel extensions of the transmission diversityparadigm which builds on GLL functions that enable multi-radio access selection.Multi-radio transmission diversity (MRTD) is defined as the dynamicselection of radio access for the transmission of a user´s data and it can bethought of as consisting of a packet scheduler operating across multiple radiointerfaces. Different MRTD schemes may be envisaged through combinationsof access re-selection rate, transmission parallelism and transmission redundancy.The re-selection rate refers to the rate at which radio access selectionis performed. It may range from multiple IP packets to one single MACframe. Switched MRTD corresponds to an access selection scheme where auser transmits via one RA at a time, while parallel MRTD corresponds to ascheme where simultaneous transmissions over multiple RAs are scheduled.Finally, redundancy refers to the transmission of copies of the same data overmultiple RAs to increase the possibility of correct reception.The benefits of MRTD are investigated by simulation studies on two multiradiocase scenarios, based on generic RATs and on specific RATs respectively.In the RAT generic scenario, switched MRTD has been evaluated for networktopologies of collocated and non-collocated RAs consisting of macroand pico-cells. In the case of collocated RAs, spectral efficiency is increasedby exploiting diversity in multi-path fading while in non-collocated RAs, thespectral efficiency increase is due to diversity exploitation in both shadowingand multi-path fading. Simulation results show that switched MRTD is mostadvantageous when the RAs provide comparable throughputs. Furthermore,when combined with multi-radio ARQ, MRTD significantly reduces packetloss and packet transmission delays. This is also shown in the specific radioaccesssimulation scenario where a delay sensitive voice service is studied. Inaddition, switched MRTD provides comparable gains to parallel MRTD interms of average packet transmission delay and packet loss, while using lessradio resources. In all cases, it is concluded that maximum performance isconditioned on the reporting delays of the channel quality indicator (CQI).Reporting delays of CQI that are half the channel coherence time render sucha complex MRTD mechanism less effective. / <p>QC 20130531</p>

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Cellular wireless communication like GSM and WLAN has become an important part of the infrastructure. The next generation of wireless systems is believed to be based on multiple-input multiple-output (MIMO), where all units are equipped with multiple antennas. In contrast to the single antenna case, MIMO systems may exploit beamforming to concentrate the transmission in the direction of the receiver. The receiver may in turn use beamforming to maximize the received signal power and to suppress the interference from other transmissions. The capacity of a MIMO system has the potential of increasing linearly with the number of antennas, but the performance gain is limited in practice by the lack of channel information at the transmitter side. This thesis considers downlink strategies where the transmitter utilizes channel norm feedback to perform beamforming that maximizes the signal-to-noise ratio (SNR) for a single beam. Two optimal strategies with feedback of, either the channel squared norm to each receive antenna, or the maximum of them are introduced and analyzed in terms of conditional covariance, eigenbeamforming, minimum mean-square error (MMSE) estimation of the SNR and the corresponding estimation variance. These strategies are compared under fair conditions to the upper bound and strategies without feedback or with pure SNR feedback. Simulations show that both strategies perform well, even if spatial division multiple access (SDMA) is required to exploit the full potential. The beamforming strategies are generalized to the multiuser case where a scheduler schedule users in time slots in which their channel realization seems to be strong and thereby support high data rates. The gain of exploiting multiuser diversity is shown in simulations. The thesis is concluded by a generalization to a multi-cell environment with intercell interference. Optimal and suboptimal receive beamforming is analyzed and used to propose approximate beamforming strategies based on channel norm feedback. / Master of Science Thesis in Engineering Mathematics at Lund University, in cooperation with KTH Royal Institute of Technology

Originally, the main purpose of the wired Internet was to interconnect hosts on different networks in order to allow them to communicate. Although this is still an important service, the Internet has evolved and today its predominant application is to provide its users with access to contents. This evolution is also taking place in the wireless domain and is to a large extent being pushed by advances in mobile platforms which now commonly have advanced multimedia capabilities. Today, contents are therefore both being consumed and produced by users on the move which calls for efficient dissemination of information to and from the mobile devices.  This thesis considers content-centric networking, particularly in the context of mobile wireless networks. The main focus is on opportunistic distribution of content where mobile nodes directly exchange content items when they are within communication range. This opportunistic communication mode allows for networking in the absence of fixed infrastructure and it has several other benefits in terms of scalability, network-neutrality, locality and more.  The contributions of this thesis lie in three areas. Firstly we study the feasibility of opportunistic content distribution among mobile nodes in urban areas using both analytic models and simulations. Our findings show that if nodes cooperate by sharing, even in a limited manner, content can spread efficiently in a number of common case scenarios. Secondly we present our design of PodNet: a middleware architecture for a mobile peer-to-peer content distribution. On the Internet, PodNet uses single source multicast to implement scalable and efficient delivery of published content to subscribers over the current unchanged Internet architecture. In the wireless domain, PodNet uses a decentralized content solicitation scheme that allows the distribution of content between mobile devices without requiring Internet connectivity and infrastructure support. Key components of the design are the content structure, multicast distribution, solicitation protocol, service discovery and an API based on the publish/subscribe paradigm. Thirdly we perform a thorough system evaluation to dimension important system parameters and to assess system performance. Our evaluation uses both experimental connectivity traces and a detailed simulator implementation that utilizes a realistic mobility model of pedestrians in an urban area. / QC 20100507

Recent surveys conducted in the context of industrial automation have outlined that reliability concerns represent today one of the major barriers to the diffusion of wireless communications for sensing and control applications: this limits the potential of wireless sensor networks and slows down the adoption of this new technology. Overcoming these limitations requires that awareness on the causes of unreliability and on the possible solutions to this problem is created. With this respect, the main factor responsible for the perceived unreliability is radio interference: low-power communications of sensor nodes are in fact very sensitive to bad channel conditions and can be easily corrupted by transmissions of other co-located devices. In this thesis we investigate different techniques that can be exploited to avoid interference or mitigate its effects.We first consider interference avoidance through dynamic spectrum access: more specifically we focus on the idea of channel surfing and design algorithms that allow sensor nodes to identify interfered channels, discover their neighbors and maintain a connected topology in multi-channel environments. Our investigation shows that detecting and thus avoiding interference is a feasible task that can be performed by complexity and power constrained devices. In the context of spectrum sharing, we further consider the case of networked estimation and aim at quantifying the effects of intranetwork interference, induced by contention-based medium access, over the performance of an estimation system. We show that by choosing in an opportune manner their probability of transmitting, sensors belonging to a networked control system can minimize the average distortion of state estimates.In the second part of this thesis we focus on frequency hopping techniques and propose a new adaptive hopping algorithm. This implements a new approach for frequency hopping: in particular rather than aiming at removing bad channels from the adopted hopset our algorithm uses all the available frequencies but with probabilities that depend on the experienced channel conditions. Our performance evaluation shows that this approach outperforms traditional frequency hopping schemes as well as the adaptive implementation included in the IEEE 802.15.1 radio standard leading to a lower packet error rate.Finally, we consider the problem of sensor networks reprogramming and propose a way for ingineering a coding solution based on fountain codes and suitable for this challenging task. Using an original genetic approach we optimize the degree distribution of the used codes so as to achieve both low overhead and low decoding complexity. We further engineer the implementation of fountain codes in order to allow the recovery of corrupted information through overhearing and improve the resilience of the considered reprogramming protocol to channel errors.

This master thesis has been done at Ericsson AB (2018) in collaboration with LeonardoPadial Torán. Microwave filters for the future 5G have become an increasingly interesting researchtopic. The conventional design theory of microwave filters is no longer valid. Newmodels have to be implemented that meet the challenges imposed by demands ofcompact size, low insertion losses, low cost and high performance.In this thesis work, stripline band pass filters with a 28 GHz center frequency havebeen designed and simulated for 5G wireless communication systems. Many designtechniques have been investigated in order to achieve the goal requirements and toovercome the design rules limitation. In particular two different filter categories havebeen designed and simulated:Uniform Impedance Resonator (UIR) configurations. There are various possibletopologies to implement UIR using stripline technology such as parallel-coupled,hairpin, interdigital and combined filters.Here, a parallel-coupled λ/2-line band pass filter was chosen and investigated by theinsertion loss method. This filter, however, displayed an undesired pass band at twicethe designed central frequency.Step Impedance Resonator (SIR) configurations. In order to suppress the secondharmonic, three different types of (SIR) band pass filters have been investigated: theparallel-coupled SIR filter, the hairpin SIR filter and, finally, a filter comprising fourcross-coupled hairpin SIR filters. Advanced Design System (ADS) has been used for the initial filter design and AnsysHFSS has been used for the electromagnetic (EM) simulation part, includingparameter optimization.

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