A wireless relay network consists of multiple source nodes, multiple destination nodes, and possibly many relay nodes in between to facilitate its transmission. It is clear that the performance of such networks highly depends on information for- warding strategies adopted at the relay nodes. This dissertation studies a particular information forwarding strategy called compute-and-forward. Compute-and-forward is a novel paradigm that tries to incorporate the idea of network coding within the physical layer and hence is often referred to as physical layer network coding. The main idea is to exploit the superposition nature of the wireless medium to directly compute or decode functions of transmitted signals at intermediate relays in a net- work. Thus, the coding performed at the physical layer serves the purpose of error correction as well as permits recovery of functions of transmitted signals. For the bidirectional relaying problem with Gaussian channels, it has been shown by Wilson et al. and Nam et al. that the compute-and-forward paradigm is asymptotically optimal and achieves the capacity region to within 1 bit; however, similar results beyond the memoryless case are still lacking. This is mainly because channels with memory would destroy the lattice structure that is most crucial for the compute-and-forward paradigm. Hence, how to extend compute-and-forward to such channels has been a challenging issue. This motivates this study of the extension of compute-and-forward to channels with memory, such as inter-symbol interference. The bidirectional relaying problem with parallel Gaussian channels is also studied, which is a relevant model for the Gaussian bidirectional channel with inter-symbol interference and that with multiple-input multiple-output channels. Motivated by the recent success of linear finite-field deterministic model, we first investigate the corresponding deterministic parallel bidirectional relay channel and fully characterize its capacity region. Two compute-and-forward schemes are then proposed for the Gaussian model and the capacity region is approximately characterized to within a constant gap. The design of coding schemes for the compute-and-forward paradigm with low decoding complexity is then considered. Based on the separation-based framework proposed previously by Tunali et al., this study proposes a family of constellations that are suitable for the compute-and-forward paradigm. Moreover, by using Chinese remainder theorem, it is shown that the proposed constellations are isomorphic to product fields and therefore can be put into a multilevel coding framework. This study then proposes multilevel coding for the proposed constellations and uses multistage decoding to further reduce decoding complexity.

Mjukvara i datorer styr många viktiga funktioner i dagens samhälle och används i stor utsträckning för att kommunicera men även för att styra utrustning. För att mjukvara ska fungera tillförlitligt behöver den byggas korrekt och testas utförligt. För att uppnå tillförlitlighet kan en byggserver används för att automatiskt bygga och testa mjukvaran. Den här rapporten beskriver hur en prototyp av ett övervakningssystem för byggservrar skapats. Systemet sköter övervakningen genom en övervakningstjänst som hämtar information från en byggserver av typen CruiseControl.NET [10] och presenterar informationen på en webbportal. Informationen som hämtas ut från byggservern går från en hög abstraktionsnivå ner till minsta detalj som är baserad på loggfiler från bygget, med exempelvis information om kompileringsfel. Utvecklingen av övervakningssystemet har haft fokus på att göra det möjligt att använda molntjänster och på det sättet inte begränsa vart en byggserver finns placerad. En av de molntjänster som använts är Service Bus Relay [27] som hanterar kommunikationen mellan en övervakningstjänst och webbportalen. Webbportalen har utvecklats för att vara responsiv [34] för på så sätt stödja mobila enheter och ge användaren frihet att besöka webbportalen oavsett enhet. Webbportalen använder sig av en databas för att lagra informationen som bland annat möjliggör övervakning av flera byggservrar, och den välutvecklade användarhanteringen. Det har gjorts flera lärdomar, bland annat genom upptäckt av en bugg i Microsofts implementation av meddelandehanteringen i Service Bus Relay. / Software in computers control many important functions in today's society and are widely used for communication but also to control equipment. For the software to work reliably it needs to be built correctly and tested extensively. To achieve reliability, a build server can be used to automatically build and test the software. This report describes how a prototype of a monitoring system for the build servers was created. The system will be monitored by a monitoring service that retrieves information from a build server using the CruiseControl.NET [10] software. The information gathered by the monitoring service will be presented on a web portal. The information retrieved from build the server goes from a high level of abstraction down to the smallest detail that is based on the log files from the build server, for example, information about compilation errors. The development of the monitoring system has been focused on making it possible to use cloud services and thus not restrict where a build server is located. One of the cloud services used is the Service Bus Relay [27] that handles the communication between a monitoring service and the web portal. The web portal is developed to be responsive [34] and provide support for mobile devices which give the user the freedom to visit the web portal from whatever device. The web portal uses a database to store information which enables monitoring of multiple build servers. A well-developed user management system is used on the web portal which provides administrators with an effective tool for user management. There have been several lessons learned, including the discovery of a bug in the Microsoft implementation of message handling in the Service Bus Relay.

At present, there is a widespread use of alternative measurement technologies in electrical networks that include current and voltage sensors. Their use is closely related to the use of IEC 61850-9-2 for data transfer of measured values within the substation for the purpose of protection and measurement. The use of sensors and communication standard IEC 61850 together with high-speed Ethernet will simplify the concept of the arrangement of protection terminals in substations and enable the development of a new protection system based on central protection. The dissertation is focused on protection algorithms, which use the SV according to IEC 61850-9-2, and their implementation into the central protection model. Thesis describes development in the field of protection of substations and the currently available solutions using IEC 61850-9-2 and the principle of central protection. Thesis explains algorithms for selected protection functions - overcurrent protection, negative sequence overcurrent protection, logic busbar protection and differential protection. Further, thesis deals with the programming of protection function algorithms in LabView development environment in the form of a central protection model. The model processes data from a process bus according to IEC 61850-9-2 and sends a GOOSE message over Ethernet in the event of a failure. To verify the correct function of the programmed protection algorithms, a testing procedure was developed using OMICRON 256plus, the current sensor and the merging unit. The results of the testing of the central protection model and the proposed algorithms were compared with the results of testing the currently used protections. At the end, the thesis deals with the assessment of the benefits of central protection for protecting substations and the possibility of further utilization of the central protection model. The thesis highlights a new way of protecting the electrification system using digital data from MU transferred via the process bus described in IEC 61850-9-2.

Non-orthogonal multiple access (NOMA), with its exceptional spectrum efficiency, was thought to be a promising technology for upcoming wireless communications. Physical layer security has also been investigated to improve the security performance of the system. Power-domain NOMA has been considered for this paper, where multiple users can share the same spectrum which bases this sharing on distinct power values. Power allocation is used to allocate different power to the users based on their channel condition. Data signals of different users are superimposed on the transmitter's side, and the receiver uses successive interference cancellation (SIC) to remove the unwanted signals before decoding its own signal. There exist an eavesdropper whose motive is to eavesdrop on the confidential information that is being shared with the users. The network model developed in this way consists of two links, one of which considers the relay transmission path from the source to Near User to Far User and the other of which takes into account the direct transmission path from the source to the destination, both of which experience Nakagami-m fading. To degrade the eavesdropper's channel, the jamming technique is used against the eavesdropper where users are assumed to be in a full-duplex mode which aims to improve the security of the physical layer. Secrecy performance metrics such as secrecy outage probability, secrecy capacity, etc. are evaluated and analyzed for the considered system. Mathematical analysis and simulation using MATLAB are done to assess, analyze and visualize the system's performance in the presence of an eavesdropper when the jamming technique is applied. According to simulation results, the active jamming approach enhances the secrecy performance of the entire system and leads to a positive improvement in the secrecy rate.

Cooperative relaying is a promising diversity achieving technique to provide reliable transmission, high throughput and extensive coverage for wireless networks in a variety of applications. Two-way relaying is a spectrally efficient protocol, providing one solution to overcome the half-duplex loss in one-way relay channels. Moreover, incorporating the multiple-input-multiple-output (MIMO) technology can further improve the spectral efficiency and diversity gain. A lot of related work has been performed on the two-way relay network (TWRN), but most of them assume perfect channel state information (CSI). In a realistic scenario, however, the channel is estimated and the estimation error exists. So in this thesis, we explicitly take into account the CSI error, and investigate its impact on the performance of amplify-and-forward (AF) TWRN where either multiple distributed single-antenna relays or a single multiple-antenna relay station is exploited. For the distributed relay network, we consider imperfect self-interference cancellation at both sources that exchange information with the help of multiple relays, and maximal ratio combining (MRC) is then applied to improve the decision statistics under imperfect signal detection. The system performance degradation in terms of outage probability and average bit-error rate (BER) are analyzed, as well as their asymptotic trend. To further improve the spectral efficiency while maintain the spatial diversity, we utilize the maximum minimum (Max-Min) relay selection (RS), and examine the impact of imperfect CSI on this single RS scheme. To mitigate the negative effect of imperfect CSI, we resort to adaptive power allocation (PA) by minimizing either the outage probability or the average BER, which can be cast as a Geometric Programming (GP) problem. Numerical results verify the correctness of our analysis and show that the adaptive PA scheme outperforms the equal PA scheme under the aggregated effect of imperfect CSI. When employing a single MIMO relay, the problem of robust MIMO relay design has been dealt with by considering the fact that only imperfect CSI is available. We design the MIMO relay based upon the CSI estimates, where the estimation errors are included to attain the robust design under the worst-case philosophy. The optimization problem corresponding to the robust MIMO relay design is shown to be nonconvex. This motivates the pursuit of semidefinite relaxation (SDR) coupled with the randomization technique to obtain computationally efficient high-quality approximate solutions. Numerical simulations compare the proposed MIMO relay with the existing nonrobust method, and therefore validate its robustness against the channel uncertainty. / Graduate

Cooperative relay systems have emerged as promising techniques to boost the performance of wireless systems. Recent studies have confirmed that interferences, co-channel interferences (CCIs) and self-interferences, have a huge impact on cooperative relay systems and can cause significant performance degradation. Two problems were observed in this research. Firstly, previous studies on performance analysis of Amplify-and-Forward (AF) relay systems in presence of CCIs have only focused on a specific interference channel model. However, in practical design scenarios, such an assumption is not a realistic proposition. Secondly, analyses of overheads introduced by a time-based relay selection protocol in distributed cooperative systems have been based on an over-pessimistic assumption where all packets involved in a collision are destroyed. Nevertheless, collisions due to the protocol overheads cause the system performance to be degraded but this does not mean that the failure of end-to-end transmission certainly occurs. The thesis aims to analyse the performance of practical cooperative relay systems in the presence of CCIs and self-interferences, by developing exact mathematical methods. A new unified mathematical method for AF relay systems in presence of a random number of arbitrary non-identical CCIs was developed. The obtained new approach derived in terms of a moment generating function of the aggregate interferences' power led to the derivation of new explicit expressions. The new results greatly simplify evaluation of average error rates over diverse practical interference scenarios. Moreover, a new exact mathematical analysis for distributed cooperative relay systems employing a time-based relay selection protocol based on an accurate interference model was presented. This approach led to the derivation of new exact expressions for the spectral efficiency which accounts for both self-interferences and the protocol overheads as well as for different fading scenarios and arbitrary relay locations. This approach provided several advantages over direct approaches, one of which is that it significantly simplified averaging-out the joint random variables involved.

Spatial diversity is an effective technique to combat the effects of severe fading in wireless environments. Recently, cooperative communications has emerged as an attractive communications paradigm that can introduce a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. In this thesis, a new approach to cooperative communications via distributed extended orthogonal space-time block coding (D-EO-STBC) based on limited partial feedback is proposed for cooperative relay networks with three and four relay nodes and then generalized for an arbitrary number of relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain, and it has certain properties that make it alluring for practical systems such as orthogonality, flexibility, low computational complexity and decoding delay, and high robustness to node failure. Versions of the closed-loop D-EO-STBC scheme based on cooperative orthogonal frequency division multiplexing type transmission are also proposed for both flat and frequency-selective fading channels which can overcome imperfect synchronization in the network. As such, this proposed technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, this scheme is extended for two-way relay networks through a three-time slot framework. On the other hand, to substantially reduce the feedback channel overhead, limited feedback approaches based on parameter quantization are proposed. In particular, an optimal one-bit partial feedback approach is proposed for the generalized D-O-STBC scheme to maximize the array gain. To further enhance the end-to-end bit error rate performance of the cooperative relay system, a relay selection scheme based on D-EO-STBC is then proposed. Finally, to highlight the utility of the proposed D-EO-STBC scheme, an application to cognitive radio is studied.

Bilen är en av de saker som många människor använder dagligenoch för att underlätta användandet kommer det hela tiden nya funk-tioner som underlättar användandet. Ett exempel är trådlösa nycklar.Många moderna bilar använder en teknik som kallas för “keyless” vilketinnebär att bilnycklarna under intervaller sänder ut radiosignaler. Detger en möjlighet att inte behöva hålla i nyckeln när bilen ska användasoch bilägaren har det lättare att öppna bilen och lasta in saker, utanatt aktivt behöva använda nycklen.Men är det tillräckligt säkert med helt trådlösa nycklar? Signaler-na är öppen för alla som kan avlyssna dem. Signalerna mellan bil ochnyckel skickas trådlöst och obehöriga kan lyssna av innehållet. I dettaprojekt undersöker vi möjligheten att spela in signalen och därefterspela upp den igen i syfte att låsa upp en bil, utan tillgång till denverkliga nyckeln. Vi utför experiment på X fordon, med olika nycklaroch olika signalfrekvenser. Om det är öppet för alla borde det ock-så gå att spela in dessa signaler och sända ut dem med hjälp utaven radiosändare. Det kallas för en relay-attack och där kommer syftetmed detta arbete, nämligen en studie om hur attackerna går till ochhur enkelt det egentligen är att göra dem själva. Samt att ett experi-ment utförs på en mängd olika bilar med olika typer av bilnycklar medvarierande frekvenser. / On a daily basis the car is frequently used, and a lot of people arein need of their cars. New technologies are developed to make it easierfor car owners to unlock the car and drive away without making theeffort of using the car keys. A technology called “keyless” car keys areimplemented in modern cars, the car keys sends out radio frequenciesin an interval on a couple of seconds.But is a complete wireless key system secure enough? The radiosignals are open to whoever wants to listen to them, and that couldhave devastating consequences. If it is open to everyone, then it shouldalso be possible to record these signals and send them out using a radiotransmitter. It’s called a relay attack and the purpose of this report isto get broader perspective of how an attack like that works and howeasy it is to execute the attack. The experiment was performed ondifferent types of cars and their keys with varying frequencies.

Recently, cooperative relay networks have emerged as an attractive communications technique that can generate a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. To achieve cooperative diversity single-antenna terminals in a wireless relay network typically share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission, interference and outage. Therefore, the focus of this thesis is to exploit cooperative relay networks within two-way transmission schemes. Such schemes have the potential to double the data rate as compared to one-way transmission schemes. Firstly, a new approach to two-way cooperative communications via extended distributed orthogonal space-time block coding (E-DOSTBC) based on phase rotation feedback is proposed with four relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain. Then, distributed orthogonal space-time block coding (DOSTBC) is applied within an asynchronous two-way cooperative wireless relay network using two relay nodes. A parallel interference cancelation (PIC) detection scheme with low structural and computational complexity is applied at the terminal nodes in order to overcome the effect of imperfect synchronization among the cooperative relay nodes. Next, a DOSTBC scheme based on cooperative orthogonal frequency division multiplexing (OFDM) type transmission is proposed for flat fading channels which can overcome imperfect synchronization in the network. As such, this technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, a closed-loop EDOSTBC approach using through a three-time slot framework is proposed. A full interference cancelation scheme with OFDM and cyclic prefix type transmission is used in a two-hop cooperative four relay network with asynchronism in the both hops to achieve full data rate and completely cancel the timing error. The topic of outage probability analysis in the context of multi-relay selection for one-way cooperative amplify and forward networks is then considered. Local measurements of the instantaneous channel conditions are used to select the best single and best two relays from a number of available relays. Asymptotical conventional polices are provided to select the best single and two relays from a number of available relays. Finally, the outage probability of a two-way amplify and forward relay network with best and Mth relay selection is analyzed. The relay selection is performed either on the basis of a max-min strategy or one based on maximizing exact end-to-end signal-to-noise ratio. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of new algorithms and methods.

Relay-assisted cooperative communications are promising solutions for error-performance improvement and cell coverage extension. In this thesis, we propose several efficient cooperative relay communication schemes. First, an efficient space-time coded cooperative relay communications scheme that employs linear precoding and transmission-pattern selection is proposed. This is built upon an existing block linear precoding technique for conventional multiple-input multiple-output systems in order to improve the diversity performance of a multihop relay network. Second, we consider several multiuser cooperative relay communication schemes employing layered modulations, such as hierarchical modulation and superposition coding. Conventional cooperative relay communication is effective in mitigating fading effects. However, additional resources, such as time slots or frequency bands are required for the relay, which reduce the overall throughput. Reduction of throughput will become more severe as the number of users increases. In order to overcome this limitation, multiuser cooperative relaying schemes that employ hierarchical modulation and superposition coding are proposed. These schemes exploit the superimposed message for users in the network and allow the system to transmit two or more independent data streams simultaneously. The proposed schemes do not require additional resources than the conventional schemes, while improving the error performance by flexibly controlling the power division coefficient of superposition coding or the distance parameter of hierarchical modulation. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Sept. 28, 2011 - Sept. 28, 2012