With the rise of mobile devices claiming a greater and greater portion of internet traffic, optimizing performance of data fetching becomes more important. A common technique of communicating between subsystems of online applications is through web services using the REpresentational State Transfer (REST) architectural style. However, REST is imposing restrictions in flexibility when creating APIs that are potentially introducing suboptimal performance and implementation difficulties. One proposed solution for increasing efficiency in data fetching is through the use of frameworks for declarative data fetching. During 2015 two open source frameworks for declarative data fetching, Falcor and Relay+ GraphQL, were released. Because of their recency, no information of how they impact performance could be found. Using the experimental approach, the frameworks were evaluated in terms of latency, data volume and number of requests using test cases based on a real world news application. The test cases were designed to test single requests, parallel and sequential data flows. Also the filtering abilities of the frameworks were tested. The results showed that Falcor introduced an increase in response time for all test cases and an increased transfer size for all test cases but one, a case where the data was filtered extensively. The results for Relay+GraphQL showed a decrease in response time for parallel and sequential data flows, but an increase for data fetching corresponding to a single REST API access. The results for transfer size were also inconclusive, but the majority showed an increase. Only when extensive data filtering was applied the transfer size could be decreased. Both frameworks could reduce the number of requests to a single request independent of how many requests the corresponding REST API needed. These results led to a conclusion that whenever it is possible, best performance can be achieved by creating custom REST endpoints. However, if this is not feasible or there are other implementation benefits and the alternative is to resort to a "one-size-fits-all" API, Relay+GraphQL can be used to reduce response times for parallel and sequential data flows but not for single request-response interactions. Data transfer size can only be reduced if filtering offered by the frameworks can reduce the response size more than the increased request size introduced by the frameworks. / Alteftersom användningen av mobila enheter ökar och står för en allt större andel av trafiken på internet blir det viktigare att optimera prestandan vid datahämtning. En vanlig teknologi för kommunikation mellan delar internet-applikationer är webbtjänster användande REpresentational State Transfer (REST)-arkitekturen. Dock introducerar REST restriktioner som minskar flexibiliteten i hur API:er bör konstrueras, vilka kan leda till försämrad prestanda och implementations-svårigheter. En möjlig lösning för ökad effektivitet vid data-hämtning är användningen av ramverk som implementerar deklarativ data-hämtning. Under 2015 släpptes två sådana ramverk med öppen källkod, Falcor och Relay+GraphQL. Eftersom de nyligen introducerades kunde ingen information om dess prestanda hittas. Med hjälp av den experimentella metoden utvärderades ramverken beträffande svarstider, datavolym och antalet anrop mellan klient och server. Testerna utformades utifrån en verklig nyhetsapplikation med fokus på att skapa testfall för enstaka anrop och anrop utförda både parallellt och sekventiellt. Även ramverkens förmåga att filtrera svarens data-fält testades. Vid användning av Falcor visade resultaten på en ökad svarstid i alla testfall och en ökad datavolym för alla testfall utom ett. I testfallet som utgjorde undantaget utfördes en mycket omfattande filtrering av datafälten. Resultaten för Relay+GraphQL visade på minskad svarstid vid parallella och sekventiella anrop, medan ökade svarstider observerades för hämtningar som motsvarades av ett enda anrop till REST API:et. Även resultaten gällande datavolym var tvetydiga, men majoriteten visade på en ökning. Endast vid en mer omfattande filtrering av datafälten kunde datavolymen minskas. Antalet anrop kunde med hjälp av båda ramverken minskas till ett enda oavsett hur många som krävdes vid användning av motsvarande REST API. Dessa resultat ledde till slutsatsen att när det är möjligt att skräddarsy REST API:er kommer det att ge den bästa prestandan. När det inte är möjligt eller det finns andra implementations-fördelar och alternativet är att använda ett icke optimerat REST API kan användande av Relay+ GraphQL minska svarstiden för parallella och sekventiella anrop. Däremot leder det i regel inte till någon förbättring för enstaka interaktioner. Den totala datavolymen kan endast minskas om filtreringen tar bort mer data från svaret än vad som introduceras genom den ökade anrops-storleken som användningen av ett frågespråk innebär.

A significant security risk of modern vehicles is their vulnerability to relay attacks, due to challenge-response methods, such as those employed in Passive Keyless Entry (PKE) used by most commercial cars, being inherently exposed. This class of attacks are where communication between a vehicle and its key is relayed by an attacker over long range - thereby bypassing any encryption and unlocking the vehicle without requiring direct access to the key. While a multitude of defenses have been proposed in recent years, many lack either robustness or practicality. Any viable system will likely have to rely on an environmental parameter which is not easily manipulated. Moreover, the system has to be: cost effective; easily implementable; and take user comfort, such as the key’s battery life, into account. This thesis implements and evaluates a PKE system resistant to relay attacks, analyses a multitude of proposed strategies in literature for feasibility, as well as suggests a novel method: Approach Curve Matching. It is concluded that the most promising strategies are: Immobility Detection, Distance Bounding Protocols, and Approach Curve Matching - the first of which is chosen to be implemented in the prototype PKE system. The project develops a PKE system and implements the communication protocol using Bluetooth, as opposed to the conventional RFID. Immobility Detection, using an accelerometer, is then implemented. The final system is then tested and evaluated. It is concluded that while Immobility Detection is not comprehensively effective, it is easily implementable, cost-effective, and can greatly increase the security of PKE systems. Finally, it is proposed that Immobility Detection should be employed promptly by manufacturers while investigating potentially more effective, albeit uncertain, strategies. / En betydande säkerhetsbrist av moderna fordon är deras sårbarhet mot så kallade ’relay attacker’. Dessa typer av attacker, där signaler mellan bilen och nyckeln vidarebefordras, kringgår all kryptering och låser upp bilen utan att ha direkt tillgång till nyckeln. En stor del av kommersiella fordon tillämpar ’Passive Keyless Entry’ (PKE) som bygger på ’challenge-response’ metoder som visats vara särskilt utsatta för dessa attacker. En mängd olika skyddssystem har föreslagits på senare år, men många saknar erforderlig robusthet eller genomförbarhet. Ett lämpligt system bör uppfylla en rad olika kriterier. Strategin måste grundas på en omgivningsparameter som är både oföränderlig och tillräckligt rymdberoende att två nära positoner kan skiljas åt. Dessutom ska systemet vara kostnadseffektivt, implementerbart, och ta hänsyn till användarkomfort såsom batteritid. Projektets huvudsyfte är konstruktionen och analysen av ett ’relay attack’ resistent PKE system. I detta projekt ingår också en analys av ett antal föreslagna försvar och ett förslag om en ny metod: ’Approach Curve Matching’. Slutsatsen dras att de mest lovande taktikerna är: analys av Jaccard indexet av Wi-Fi hotspots, ’Distance Bounding Protocols’, ’Approach Curve Matching’ och ’Immobility Detection’ som också implementeras i prototyp PKE systemet. Projektet utvecklar först ett PKE system med två Raspberry Pis som agerar som bilens och nyckelns mikrodatorer och implementerar kommunikationsprotokollet med hjälp av Bluetooth. ’Immobility Detection’ är sedan implementerad genom en inbyggd accelerometer i nyckeln. Slutligen testas och utvärderas systemet. Det konkluderas att trots att ’Immobility Detection’s effektivitet inte är helt omfattande är den lätt att implementera, kostnadseffektiv, och kan bidra till en betydlig ökning av säkerheten hos PKE system. Vidare observerade projektet att Bluetooths ’Received Signal Strength Indicator’ (RSSI) mätningar är utsatta för avsevärd ostadighet och är allmänt omgivningsberoende. Därför anses Bluetooth RSSI inte lämplig för PKE tillämpningar även om andra metoder för avståndsmätning med Bluetooth kan ha högre prestanda. Det föreslås att ’Immobility Detection’ tillämpas av tillverkare omgående medans andra potentiellt mer effektiva strategier utreds.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Aerocross Systems, Inc. is developing a low-cost unmanned airborne telemetry relay system to augment the USAF Air Armament Center’s Eglin Gulf Range instrumentation resources. The system is designed to remotely autotrack and relay S-Band telemetry and VHF/UHF voice communications from test articles beyond the line-of-sight of land-based instrumentation. The system consists of a medium altitude/endurance Unmanned Aerial Vehicle (UAV), a Mission Control Station, and a remotely operated telemetry/voice tracking and relay instrumentation suite. Successfully developed and deployed, the system will contribute to lower range costs while enhancing range instrumentation performance.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / The primary objective of the NASA Space-Based Range Demonstration and Certification program was to develop and demonstrate space-based range capabilities. The Flight Demonstration 2 flights at NASA Dryden Flight Research Center were conducted to support Range Safety (commanding and position reporting) and high-rate (5 Mbps) Range User (video and data) requirements. Required ground support infrastructure included a flight termination system computer, the ground-data distribution network to send range safety commands and receive range safety and range user telemetry data and video, and the ground processing systems at the Dryden Mission Control Center to process range safety and range user telemetry data and video.

The focus of this thesis is peak-to-average power ratio (PAPR) reduction in cooperative wireless networks which exploit orthogonal frequency division multiplexing in transmission. To reduce the PAPR clipping is employed at the source node. The first contribution focuses upon an amplify-and-forward (AF) type network with four relay nodes which exploits distributed closed loop extended orthogonal space frequency block coding to improve end-to-end performance. Oversampling and filtering are used at the source node to reduce out-of-band interference and the iterative amplitude reconstruction decoding technique is used at the destination node to mitigate in-band distortion which is introduced by the clipping process. In addition, by exploiting quantized group feedback and phase rotation at two of the relay nodes, the system achieves full cooperative diversity in addition to array gain. The second contribution area is outage probability analysis in the context of multi-relay selection in a cooperative AF network with frequency selective fading channels. The gains of time domain multi-path fading channels with L paths are modeled with an Erlang distribution. General closed form expressions for the lower and upper bounds of outage probability are derived for arbitrary channel length L as a function of end-to-end signal to noise ratio. This analysis is then extended for the case when single relay selection from an arbitrary number of relay nodes M is performed. The spatial and temporal cooperative diversity gain is then analysed. In addition, exact form of outage probability for multi-path channel length L = 2 and selecting the best single relay from an arbitrary number of relay nodes M is obtained. Moreover, selecting a pair of relays when L = 2 or 3 is additionally analysed. Finally, the third contribution context is outage probability analysis of a cooperative AF network with single and two relay pair selection from M available relay nodes together with clipping at the source node, which is explicitly modelled. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of algorithms and methods.

This thesis presents new methodologies to improve performance of wireless cooperative networks using the Golden Code. As a form of space-time coding, the Golden Code can achieve diversity-multiplexing tradeoff and the data rate can be twice that of the Alamouti code. In practice, however, asynchronism between relay nodes may reduce performance and channel quality can be degraded from certain antennas. Firstly, a simple offset transmission scheme, which employs full interference cancellation (FIC) and orthogonal frequency division multiplexing (OFDM), is enhanced through the use of four relay nodes and receiver processing to mitigate asynchronism. Then, the potential reduction in diversity gain due to the dependent channel matrix elements in the distributed Golden Code transmission, and the rate penalty of multihop transmission, are mitigated by relay selection based on two-way transmission. The Golden Code is also implemented in an asynchronous one-way relay network over frequency flat and selective channels, and a simple approach to overcome asynchronism is proposed. In one-way communication with computationally efficient sphere decoding, the maximum of the channel parameter means is shown to achieve the best performance for the relay selection through bit error rate simulations. Secondly, to reduce the cost of hardware when multiple antennas are available in a cooperative network, multi-antenna selection is exploited. In this context, maximum-sum transmit antenna selection is proposed. End-to-end signal-to-noise ratio (SNR) is calculated and outage probability analysis is performed when the links are modelled as Rayleigh fading frequency flat channels. The numerical results support the analysis and for a MIMO system maximum-sum selection is shown to outperform maximum-minimum selection. Additionally, pairwise error probability (PEP) analysis is performed for maximum-sum transmit antenna selection with the Golden Code and the diversity order is obtained. Finally, with the assumption of fibre-connected multiple antennas with finite buffers, multiple-antenna selection is implemented on the basis of maximum-sum antenna selection. Frequency flat Rayleigh fading channels are assumed together with a decode and forward transmission scheme. Outage probability analysis is performed by exploiting the steady-state stationarity of a Markov Chain model.

International Telemetering Conference Proceedings / October 17-20, 1988 / Riviera Hotel, Las Vegas, Nevada / By making use of NC212-200 commuter aircraft as an airborne container, the ADReS, a short for airborne data relay system, had been configured and tested in an experimental status during the year of 1987. A kind of test on EMC, EMI, RFI and telemetry data link were applied to the system. Prior to the IPTN's flight test program in the year of 1988 - 1992, the ADReS is designed not only to receive and to relay the data, but also planed to be able to process the data for quick data analysis purposes on board. This paper describes the ADReS system concept and its experimental status system - the Phase One system configuration.

International Telemetering Conference Proceedings / October 17-20, 1988 / Riviera Hotel, Las Vegas, Nevada / This paper discusses one approach to determine a characteristic of West - Java's air and ground segment as a block-box to accomodate radio waves propagation, especially in L-band ranges, by evaluating both the topographical data and radio reception pattern as measured from ground based telemetry receiving-end system. All the measured signals are random and assumed to be stationair and ergodic. In order to characterize the channel for polarization diversity reception, some statistical analysis are applied to the signal strength measured of both - RHCP and LHCP components of 1531 MHz propagated waves as transmitted fr om NC212-200 PK-NZJ-aircraft. Some computer calculated correlograms of measured data are shown herewith, it is focused for a certain radio corridor at radial 265E relative to the ground based receiving antenna. More over some curves of predicted multipath gain factor are also presented to gain more theoretical back ground. When this paper is written, a further field experiments on the matter concerned is beeing conducted.

Efficiently allocating the scarce and expensive radio resources is a key challenge for advanced radio communication systems. To this end, cognitive radio (CR) has emerged as a promising solution which can offer considerable improvements in spectrum utilization. Furthermore, cooperative communication is a concept proposed to obtain spatial diversity gains through relays without requiring multiple antennas. To benefit from both CR and cooperative communications, a combination of CR networks (CRNs) with cooperative relaying referred to as cognitive cooperative relay networks (CCRNs) has recently been proposed. CCRNs can better utilize the radio spectrum by allowing the secondary users (SUs) to opportunistically access spectrum, share spectrum with primary users (PUs), and provide performance gains offered by cooperative relaying. In this thesis, a performance analysis of underlay CRNs and CCRNs in different fading channels is provided based on analytical expressions, numerical results, and simulations. To allocate power in the CCRNs, power allocation policies are proposed which consider the peak transmit power limit of the SUs and the outage probability constraint of the primary network. Thus, the impact of multiuser diversity, peak transmit power, fading parameters, and modulation schemes on the performance of the CRNs and CCRNs can be analyzed. The thesis is divided into an introduction and five research parts based on peer-reviewed conference papers and journal articles. The introduction provides fundamental background on spectrum sharing systems, fading channels, and performance metrics. In the first part, a basic underlay CRN is analyzed where the outage probability and the ergodic capacity of the network over general fading channels is derived. In the second part, the outage probability and the ergodic capacity of an underlay CRN are assessed capturing the effect of multiuser diversity on the network subject to Nakagami-m fading. Considering the presence of a PU transmitter (PU-Tx), a power allocation policy is derived and utilized for CRN performance analysis under Rayleigh fading. In the third part, the impact of multiple PU-Txs and multiple PU receivers (PU-Rxs) on the outage probability of an underlay CCRN is studied. The outage constraint at the PU-Rx and the peak transmit power constraint of the SUs are taken into account to derive the power allocation policies for the SUs. In the fourth part, analytical expressions for the outage probability and symbol error probability for CCRNs are derived where signal combining schemes at the SU receiver (SU-Rx) are compared. Finally, the fifth part applies a sleep/wake-up strategy and the min(N; T) policy to an underlay CRN. The SUs of the network operate as wireless sensor nodes under Nakagami-m fading. A power consumption function of the CRN is derived. Further, the impact of M/G/1 queue and fading channel parameters on the power consumption is assessed.

Wireless devices have become an integral part of our everyday lives. Cell-phones, PDA's, Wi-Fi enabled laptops, smart homes and appliances, and automated highway systems are some of the examples of wireless devices and networks in common use. More and more applications and functionalities are constantly being added to these devices, and to support these new applications high data rate communication is required between the wireless devices. Achieving high data rates with wireless communication is impeded by severe fluctuations in the received signal strength (called fading) due to mobility, the exponential attenuation of signal power with distance (called path loss), and interference due to simultaneous transmissions by different users at the same time or over same frequency band. Two of the promising techniques to mitigate the effects of fading, path loss, and interference are: using multiple antennas at the transmitter and receiver, and employing extra nodes (called relays) in between the transmitter and its receiver to relay the transmitter's message to its receiver. This dissertation identifies the optimal transmit and receive strategy with multiple antennas that maximizes the transmission capacity of an ad-hoc wireless network. The transmission capacity is defined as the maximum number of transmitter-receiver pairs that can simultaneously communicate under a per transmission quality of service constraint. This dissertation also presents novel relay transmission strategies for multiple antenna equipped relay based communication that achieve near optimal performance, with Shannon capacity and diversity-multiplexing tradeoff (DMT) as the performance metrics. The Shannon capacity is defined as the maximum rate of reliable communication, while the DMT characterizes the maximum diversity gain for a given value of multiplexing gain in a multiple antenna system. DMT is used as the benchmark, since transmission strategies that meet the DMT are guaranteed to leverage both the advantages of multiple antenna systems. / text