QC 20110427

In recent years, the main trend in wireless communications has been shifted from voice transmission to data-centric communication. This shift has caused an increase in the data rate requirements for future wireless communication systems. These requirements result in need for large bandwidth. Being a limited and thus expensive resource, wireless spectrum needs to be used efficiently. For higher spectral efficiency, new transmission techniques as well as new dynamic spectrum-allocationpolicies are needed. Cognitive radio is a promising approach for increasing spectral efficiency of wireless systems. By exploiting advanced signal processing techniques and sophisticated transmission schemes, cognitive radio devices allow to serve new wireless users within the existing crowded spectrum. Typically, a cognitive radio network is installed in parallel to an existing primary network, a legacy owner of the spectrum. The cognitive radio network adapts to its electro-magnetic environment in order to limit or even avoid the disturbance to the primary network. This thesis focuses on the underlay cognitive radio paradigm, which assumes that both the primary network and the ad hoc cognitive radio network operate within the same time and frequency band, as well as at the same geographic location. The cognitive network is able to estimate the interference caused to the primary network by means of channel training and possible feedback. This knowledge is then used to adjust the cognitive network’s transmissions in such a way that the disturbance to the primary network is below some acceptable threshold. In the first part of the thesis, we discuss the multi-hop line cognitive networks, in which the information content before reaching its destination passes through several hops from node to node within the cognitive network. In this way, transmission power at the source terminal may be decreased, thus producing less interference to the primary network. Moreover, the powers at each terminal within the cognitive network may be optimally allocated so that the interference constraint at the primary network is satisfied. This power allocation can be realized in both centralized and decentralized ways, depending on the available information about the channel state. We discuss both of these allocations subject to different interference constraints employed at the primary network. In the second part of the thesis, we discuss the reliability of transmission within the line cognitive ad hoc networks in terms of outage probability and diversity. We also illustrate the benefit of network coding for such networks and provide a heuristic algorithm for optimal scheduling. In the final part of the thesis, we study the uplink relay-assisted cellular cognitive radio scenario. Both, the cognitive network and the primary network, contain a set of multi-antenna users that communicate with a corresponding base station. The users create mutual interference and hence limit each other’s performance. Using certain mathematical tools originally developed within the field of statistical physics, we are able derive a closed-form expression for the ergodic mutual information for arbitrary channels inputs, which enables characterization of the achievable rate region of such scenario. / <p>QC 20120612</p>

The penetration of smart pocket-size devices that provide constant Internet connectivity, such as mobile phones, has significantly changed the way people obtain, view and share information. Content provision is not anymore a prerogative to professionals; individuals are not solely customers, but also act as content generators and distributors. This shift in social behavior requires changes in the way information is delivered to target audiences in an efficient, interest-based and location-aware manner. This thesis explores a solution for opportunistic content distribution in a content-centric network that primarily targets content dissemination among mobile users in urban areas. The term ’opportunistic’ here refers to a concept which rejects the assumption of always-connected user devices and instead allows nodes to leverage sporadic contacts which occur when two neighbors come into direct radio communication range. Such communication mode allows data exchanges to occur in areas with little or no infrastructure; moreover, it is a potential solution for offloading the increasing traffic volumes observed by mobile operators. The contributions of this thesis lie in three areas. We first outline a general architecture and design for opportunistic content-centric networking. We implement our proposal on the Google Android platform, and provide application scenarios which illustrate the potential of mobile peer-to-peer communication. Our tests however show that energy consumption turns out to be a major issue for opportunistic networks. Therefore, our second effort is in the area of energy-efficiency. We propose a dual-radio architecture for opportunistic communication, and evaluate it through extensive simulations on realistic human mobility traces. Our final study lies in the area of content dissemination when nodes in the network act altruistically and are willing to solicit data on behalf of other participants. We propose a number of relaying and caching strategies, and evaluate them through simulations in environments that exhibit different churn levels. / <p>QC 20120806</p>

Rapid mobile data traffic growth is becoming in a reality and several forecasts expect that it will be continued in upcoming years. It is expected that significant indoor investment will be made not only by traditional operators but also by facility owners for their own purposes. A key challenge to such local network providers is provisioning ever-increasing mobile traffic demand at the current level of production cost per bit. A popular deployment strategy so far is deploying WLAN networks. While denser indoor deployment is foreseen, the interference from inside of a network as well as other neighboring operators can be a limiting factor for higher capacity. Tighter interference management will certainly provide higher efficiency in network and spectrum usage. Nevertheless, costs to allow fast information sharing among access points are necessary for advanced interference coordination. Moreover, managing interference across networks owned by different operators raises not only infrastructure cost but also the network interrelatedness which operators are typically reluctant for business independency. When taking into account the cost and barriers for interference coordination, it is still not so obvious that coordination in wireless broadband systems will be advantageous to operators. In this thesis, we address the operator benefit of downlink interference coordination in two aspects: 1) multi-cell coordination with no interference from neighboring operators, and 2) inter-operator coordination in shared spectrum. In order to deal with interference and cost tradeoff analysis, we explicitly develop a techno-economic analysis framework and reform a traditional cost model. Numerical results indicate that the economic benefit of the multi-cell coordination significantly depends on propagation conditions and average user demand level. A self-deployed WLAN network can be the cheapest deployment option in closed areas up to certain average demand level. Over the demand level or in open areas, advanced joint processing schemes in a cellular domain may be a viable solution. The drawback is that it requires extremely accurate channel state information at transmitters for practical usage. When inter-operator interferences is present, asymmetric cellular networks will be likely to appear due to business independency and selfishly compete to access spectrum with no or little network-level coordination. A network designed for more fairness with higher transmission power will have more benefit against the other counterpart. Although asymmetric competition lets operators unfairly utilize spectrum, sharing spectrum with reasonable geographical separation can outperform over static coordination, i.e., traditional spectrum split. Tight cooperation to maximize a common objective can further offer the performance benefit to both involved partners. However, the cooperation gain quickly diminishes as network separation and size increases because self-interference becomes more dominant. / <p>QC 20121031</p> / The Mobile Broadband Project Phase 3: “More for less” (MBB++)

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>

No description available.

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