International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / The analysis of multiple-input multiple-output (MIMO) communication systems often assumes a static, or quasi-static, environment. Platform motion and changes in the environment makes this an unreasonable assumption for many telemetry applications. This paper uses computer simulations to characterize the time variation of MIMO channel parameters when there is relative motion between the transmitter and receiver. These simulation results yield explicit time intervals over which a MIMO channel can be considered static for a given relative velocity and propagation environment. These results can be used to predict the practical limitations of proposed MIMO system algorithms.

In 2001, the Federal Communications Commission made available a large block of spectrum known as the 60 GHz band. The 60 GHz band is attractive because it provides the opportunity of multi-Gbps data rates with unlicensed commercial use. One of the main challenges facing the use of this band is poor propagation characteristics including high path loss and strong attenuation due to oxygen absorption. Antenna arrays have been proposed as a means of combating these effects. This thesis provides an analysis of array processing for communication systems operating in the 60 GHz band. Based on measurement campaigns at 60 GHz, deterministic modeling of the channel through ray tracing is proposed. We conduct a site-specific study using ray tracing to model an outdoor and an indoor environment on the Virginia Tech campus. Because arrays are required for antenna gain and adaptability, we explore the use of arrays as a form of equalization in the presence of channel-induced intersymbol interference. The first contribution of this thesis is to establish the expected performance achieved by arrays in the outdoor environment. The second contribution is to analyze the performance of adaptive algorithms applied to array processing in mobile indoor and outdoor environments. / Master of Science

The Human brain consists of mutually connected neuronal populations that build anatomically and functionally separated structures. To understand human brain activity and connectivity, it is crucial to describe how these structures are connected and how information is spread. Commonly used methods often work with data from scalp EEG, with a limited number of contacts, and are incapable of observing dynamic changes during cognitive processes or different behavioural states. In addition, connectivity studies almost never analyse pathological parts of the brain, which can have a crucial impact on pathology research and treatment. The aim of this work is connectivity analysis and its evolution in time during cognitive tasks using data from intracranial EEG. Physiological processes in cognitive stimulation and the local connectivity of pathology in the epileptic brain during wake and sleep were analysed. The results provide new insight into human brain physiology research. This was achieved by an innovative approach which combines connectivity methods with EEG spectral power calculation. The second part of this work focuses on seizure onset zone (SOZ) connectivity in the epileptic brain. The results describe the functional isolation of the SOZ from the surrounding tissue, which may contribute to clinical research and epilepsy treatment.

No description available.

With the increasing maturity of unmanned aerial vehicles (UAVs), also known as drones, wireless ecosystem is experiencing an unprecedented paradigm shift. These aerial platforms are specifically appealing for a variety of applications due to their rapid and flexible deployment, cost-effectiveness, and high chance of forming line-of-sight (LoS) links to the ground nodes. As with any new technology, the benefits of incorporating UAVs in existing cellular networks cannot be characterized without completely exploring the underlying trade space. This requires a detailed system-level analysis of drone cellular networks by taking the unique features of UAVs into account, which is the main objective of this dissertation. We first focus on a static setup and characterize the performance of a three-dimensional (3D) two-hop cellular network in which terrestrial base stations (BSs) coexist with UAVs to serve a set of ground user equipment (UE). In particular, a UE connects either directly to its serving terrestrial BS by an access link or connects first to its serving UAV which is then wirelessly backhauled to a terrestrial BS (joint access and backhaul). We consider realistic antenna radiation patterns for both BSs and UAVs using practical models developed by the third generation partnership project (3GPP). We assume a probabilistic channel model for the air-to-ground transmission, which incorporates both LoS and non-LoS links. Assuming the max-power association policy, we study the performance of the network in both amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols. Using tools from stochastic geometry, we analyze the joint distribution of distance and zenith angle of the closest (and serving) UAV to the origin in a 3D setting. Further, we identify and extensively study key mathematical constructs as the building blocks of characterizing the received signal-to-interference-plus-noise ratio (SINR) distribution. Using these results, we obtain exact mathematical expressions for the coverage probability in both AF and DF relaying protocols. Furthermore, considering the fact that backhaul links could be quite weak because of the downtilted antennas at the BSs, we propose and analyze the addition of a directional uptilted antenna at the BS that is solely used for backhaul purposes. The superiority of having directional antennas with wirelessly backhauled UAVs is further demonstrated via extensive simulations. Second, we turn our attention to a mobile setup and characterize the performance of several canonical mobility models in a drone cellular network in which UAV base stations serve UEs on the ground. In particular, we consider the following four mobility models: (i) straight line (SL), (ii) random stop (RS), (iii) random walk (RW), and (iv) random waypoint (RWP), among which the SL mobility model is inspired by the simulation models used by the 3GPP for the placement and trajectory of UAVs, while the other three are well-known canonical models (or their variants) that offer a useful balance between realism and tractability. Assuming the nearest-neighbor association policy, we consider two service models for the UEs: (i) UE independent model (UIM), and (ii) UE dependent model (UDM). While the serving UAV follows the same mobility model as the other UAVs in the UIM, it is assumed to fly towards the UE of interest in the UDM and hover above its location after reaching there. We then present a unified approach to characterize the point process of UAVs for all the mobility and service models. Using this, we provide exact mathematical expressions for the average received rate and the session rate as seen by the typical UE. Further, using tools from the calculus of variations, we concretely demonstrate that the simple SL mobility model provides a lower bound on the performance of other general mobility models (including the ones in which UAVs follow curved trajectories) as long as the movement of each UAV in these models is independent and identically distributed (i.i.d.). Continuing our analysis on mobile setups, we analyze the handover probability in a drone cellular network, where the initial positions of the UAVs serving the ground UEs are modeled by a homogeneous Poisson point process (PPP). Inspired by the mobility model considered in the 3GPP studies, we assume that all the UAVs follow the SL mobility model, i.e., move along straight lines in random directions. We further consider two different scenarios for the UAV speeds: (i) same speed model (SSM), and (ii) different speed model (DSM). Assuming nearest-neighbor association policy, we characterize the handover probability of this network for both mobility scenarios. For the SSM, we compute the exact handover probability by establishing equivalence with a single-tier terrestrial cellular network, in which the BSs are static while the UEs are mobile. We then derive a lower bound for the handover probability in the DSM by characterizing the evolution of the spatial distribution of the UAVs over time. After performing these system-level analyses on UAV networks, we focus our attention on the air-to-ground wireless channel and attempt to understand its unique features. For that, we first study the impact of UAV wobbling on the coherence time of the wireless channel between UAVs and a ground UE, using a Rician multi-path channel model. We consider two different scenarios for the number of UAVs: (i) single UAV scenario (SUS), and (ii) multiple UAV scenario (MUS). For each scenario, we model UAV wobbling by two random processes, i.e., the Wiener and sinusoidal processes, and characterize the channel autocorrelation function (ACF) which is then used to derive the coherence time of the channel. For the MUS, we further show that the UAV-UE channels for different UAVs are uncorrelated from each other. One key observation that is revealed from our analysis is that even for small UAV wobbling, the coherence time of the channel may degrade quickly, which may make it difficult to track the channel and establish a reliable communication link. Finally, we develop an impairments-aware air-to-ground unified channel model that incorporates the effect of both wobbling and hardware impairments, where the former is caused by random physical fluctuations of UAVs, and the latter by intrinsic radio frequency (RF) nonidealities at both the transmitter and receiver, such as phase noise, in-phase/quadrature (I/Q) imbalance, and power amplifier (PA) nonlinearity. The impact of UAV wobbling is modeled by two stochastic processes, i.e., the canonical Wiener process and the more realistic sinusoidal process. On the other hand, the aggregate impact of all hardware impairments is modeled as two multiplicative and additive distortion noise processes, which is a well-accepted model. For the sake of generality, we consider both wide-sense stationary (WSS) and nonstationary processes for the distortion noises. We then rigorously characterize the ACF of the wireless channel, using which we provide a comprehensive analysis of four key channel-related metrics: (i) power delay profile (PDP), (ii) coherence time, (iii) coherence bandwidth, and (iv) power spectral density (PSD) of the distortion-plus-noise process. Furthermore, we evaluate these metrics with reasonable UAV wobbling and hardware impairment models to obtain useful insights. Similar to our observation above, this work again demonstrates that the coherence time severely degrades at high frequencies even for small UAV wobbling, which renders air-to-ground channel estimation very difficult at these frequencies. / Doctor of Philosophy / With the increasing maturity of unmanned aerial vehicles (UAVs), also known as drones, wireless ecosystem is changing dramatically. Owing to their ease of deployment and high chance of forming direct line-of-sight (LoS) links with the other UAVs and ground users, they are very appealing for numerous wireless applications. As with any new technology, exploring the full extent of the benefits of UAVs requires careful exploration of the underlying trade space. Therefore, in this dissertation, our main focus is on the analysis of such aerial networks, their interplay with the current terrestrial networks, and the unique features of UAVs that make them different from conventional ground nodes. One important aspect of aerial communication systems is their integration into our current cellular networks. Clearly, the addition of these new aerial components has the potential of benefiting both the ground users (such as mobile users watching a concert who need cellular connectivity to share the moments) and the cellular base station (BS). Therefore, careful analysis of these ``aerial-terrestrial" networks is of utmost importance. In the first phase of this dissertation, we perform this analysis by interpreting the network as a combination of one-hop (from the BS to the user) and two-hop (from the BS to the UAV and then from the UAV to the UE) links. Since the locations of BSs, UAVs, and users are irregular in general, we use tools from stochastic geometry to carry out our analysis, which is a field of mathematics that studies random shapes and patterns. Also, because existing terrestrial BSs are primarily designed to serve the ``ground", we propose the addition of a separate set of antennas at the BS site that is solely used to serve the ``air", i.e., to communicate with the UAVs, and demonstrate the benefits of this additional infrastructure in detail. One of our assumptions in the first phase of this dissertation was that the considered network was static, i.e., the UAVs were hovering in the air and the BSs/users were also not moving. In the second phase, on the other hand, we explore the benefits and challenges of a mobile network of UAVs and characterize the performance of several canonical mobility models in a drone cellular network. In particular, one of the models that we studied extensively is the so-called straight line (SL) mobility model, which was inspired by the simulation models used by the third generation partnership project (3GPP) for the placement and trajectory of UAVs. Since the locations of UAVs could be assumed random in general, we use tools from stochastic geometry and present a unified approach to characterize the point process of UAVs, using which we obtained exact mathematical expressions for the average received rate (i.e., throughput) as seen by the users. Continuing our analysis on mobile setups and using the SL mobility model, we also analyze the handover probability in a drone cellular network, which is defined as the event when the serving UAV of a user changes. By establishing equivalence between our aerial setup with a terrestrial cellular network, we compute the exact handover probability in drone cellular networks. In the final phase of this dissertation, we focus our attention on the air-to-ground wireless channel and attempt to understand its unique features. For that, we propose an impairments-aware unified channel model for an air-to-ground wireless communication system and extensively analyze the link between a hovering UAV in the air and a static user on the ground. In particular, we consider two different types of impairments: (i) UAV wobbling, and (ii) hardware impairments, where the former is caused by random physical fluctuations, and the latter by intrinsic radio frequency (RF) nonidealities at both the transmitter and receiver. Using appropriate models for each type of impairment, we rigorously characterize the autocorrelation function (ACF) of the wireless channel, using which we provide a comprehensive analysis of key channel-related metrics, such as coherence time and coherence bandwidth. One key observation that is revealed from our analysis is that even for small UAV wobbling and low hardware impairment levels, the coherence time of the channel may degrade quickly at high frequencies, which could make it difficult to track the channel and establish a reliable communication link at these frequencies.

"Many current and future medical devices are wearable, using the human body as a conduit for wireless communication, which implies that human body serves as a crucial part of the transmission medium in body area networks (BANs). Implantable medical devices such as Pacemaker and Cardiac Defibrillators are designed to provide patients with timely monitoring and treatment. Endoscopy capsules, pH Monitors and blood pressure sensors are used as clinical diagnostic tools to detect physiological abnormalities and replace traditional wired medical devices. Body-mounted sensors need to be investigated for use in providing a ubiquitous monitoring environment. In order to better design these medical devices, it is important to understand the propagation characteristics of channels for in-body and on- body wireless communication in BANs. The IEEE 802.15.6 Task Group 6 is officially working on the standardization of Body Area Network, including the channel modeling and communication protocol design. This thesis is focused on the propagation characteristics of human body movements. Specifically, standing, walking and jogging motions are measured, evaluated and analyzed using an empirical approach. Using a network analyzer, probabilistic models are derived for the communication links in the medical implant communication service band (MICS), the industrial scientific medical band (ISM) and the ultra- wideband (UWB) band. Statistical distributions of the received signal strength and second order statistics are presented to evaluate the link quality and outage performance for on-body to on- body communications at different antenna separations. The Normal distribution, Gamma distribution, Rayleigh distribution, Weibull distribution, Nakagami-m distribution, and Lognormal distribution are considered as potential models to describe the observed variation of received signal strength. Doppler spread in the frequency domain and coherence time in the time domain from temporal variations is analyzed to characterize the stability of the channels induced by human body movements. The shape of the Doppler spread spectrum is also investigated to describe the relationship of the power and frequency in the frequency domain. All these channel characteristics could be used in the design of communication protocols in BANs, as well as providing features to classify different human body activities. Realistic data extracted from built-in sensors in smart devices were used to assist in modeling and classification of human body movements along with the RF sensors. Variance, energy and frequency domain entropy of the data collected from accelerometer and orientation sensors are pre- processed as features to be used in machine learning algorithms. Activity classifiers with Backpropagation Network, Probabilistic Neural Network, k-Nearest Neighbor algorithm and Support Vector Machine are discussed and evaluated as means to discriminate human body motions. The detection accuracy can be improved with both RF and inertial sensors."

On demand single-photon and entangled-photon sources are key building-blocks for many proposed photonic quantum technologies. For practical device applications, epitaxially grown quantum dots (QDs) are of increasing importance due to their bright photon emission with sharp line width. Particularly, they are solid-state systems and can be easily embedded within a light-emitting diode (LED) to achieve electrically driven sources. Therefore, one would expect a full-fledged optoelectronic quantum network that is running on macroscopically separated, QD-based single- and entangled-photon devices. An all-electrically operated wavelength-tunable on demand single-photon source (SPS) is demonstrated first. The device consists of a LED in the form of self-assembled InGaAs QDs containing nanomembrane integrated onto a piezoelectric crystal. Triggered single photons are generated via injection of ultra-short electrical pulses into the diode, while their energy can be precisely tuned over a broad range of about 4.8 meV by varying the voltage applied to the piezoelectric crystal. High speed operation of this single-photon emitting diode up to 0.8 GHz is demonstrated. In the second part of this thesis, a fast strain-tunable entangled-light-emitting diode (ELED) is demonstrated. It has been shown that the fine structure splitting of the exciton can be effectively overcome by employing a specific anisotropic strain field. By injecting ultra-fast electrical pulses to the diode, electrically triggered entangled-photon emission with high degree of entanglement is successfully realized. A statistical investigation reveals that more than 30% of the QDs in the strain-tunable quantum LED emit polarization-entangled photon-pairs with entanglement-fidelities up to f+ = 0.83(5). Driven at the highest operation speed ever reported so far (400 MHz), the strain-tunable quantum LED emerges as unique devices for high-data rate entangled-photon applications. In the end of this thesis, on demand and wavelength-tunable LH single-photon emission from strain engineered GaAs QDs is demonstrated. Fourier-transform spectroscopy is performed, from which the coherence time of the LH single-photon emission is studied. It is envisioned that this new type of LH exciton-based SPS can be applied to realize an all-semiconductor based quantum interface in the foreseeable distributed quantum networks.

In the upcoming era of communication systems, there is an anticipated shift towards using lower-grade hardware components to optimize size, cost, and power consumption. This shift is particularly beneficial for multiple-input multiple-output (MIMO) systems and internet-of-things devices, which require numerous components and extended battery lifes. However, using lower-grade components introduces impairments, including various non-linear and time-varying distortions affecting communication signals. Traditionally, these distortions have been treated as additional noise due to the lack of a rigorous theory. This thesis explores new perspective on how distortion structure can be exploited to optimize communication performance. We investigate the problem of distortion-aware beamforming in various scenarios.  In the first part of this thesis, we focus on systems with limited fronthaul capacity. We propose an optimized linear precoding for advanced antenna systems (AAS) operating at a 5G base station (BS) within the constraints of a limited fronthaul capacity, modeled by a quantizer. The proposed novel precoding minimizes the mean-squared error (MSE) at the receiver side using a sphere decoding (SD) approach.  After analyzing MSE minimization, a new linear precoding design is proposed to maximize the sum rate of the same system in the second part of this thesis. The latter problem is solved by a novel iterative algorithm inspired by the classical weighted minimum mean square error (WMMSE) approach. Additionally, a heuristic quantization-aware precoding method with lower computational complexity is presented, showing that it outperforms the quantization-unaware baseline. This baseline is an optimized infinite-resolution precoding which is then quantized. This study reveals that it is possible to double the sum rate at high SNR by selecting weights and precoding matrices that are quantization-aware.  In the third part and final part of this thesis, we focus on the signaling problem in mobile millimeter-wave (mmWave) communication. The challenge of mmWave systems is the rapid fading variations and extensive pilot signaling. We explore the frequency of updating the combining matrix in a wideband mmWave point-to-point MIMO under user equipment (UE) mobility. The concept of beam coherence time is introduced to quantify the frequency at which the UE must update its downlink receive combining matrix. The study demonstrates that the beam coherence time can be even hundreds of times larger than the channel coherence time of small-scale fading. Simulations validate that the proposed lower bound on this defined concept guarantees no more than 50 \% loss of received signal gain (SG). / I den kommande eran av kommunikationssystem finns det en förväntad förändringmot att använda hårdvarukomponenter av lägre kvalitet för att optimera storlek, kostnad och strömförbrukning. Denna förändring är särskilt fördelaktig för MIMO-system(multiple-input multiple-output) och internet-of-things-enheter, som kräver många komponenter och förlängd batteritid. Användning av komponenter av lägre kvalitet medfördock försämringar, inklusive olika icke-linjära och tidsvarierande förvrängningar sompåverkar kommunikationssignaler. Traditionellt har dessa förvrängningar behandlatssom extra brus på grund av avsaknaden av en rigorös teori. Denna avhandling utforskarett nytt perspektiv på hur distorsionsstruktur kan utnyttjas för att optimera kommunikationsprestanda. Vi undersöker problemet med distorsionsmedveten strålformning iolika scenarier. I den första delen av detta examensarbete fokuserar vi på system med begränsadfronthaulkapacitet. Vi föreslår en optimerad linjär förkodning för avancerade antennsystem (AAS) som arbetar vid en 5G-basstation (BS) inom begränsningarna av en begränsad fronthaulkapacitet, modellerad av en kvantiserare. Den föreslagna nya förkodningen minimerar medelkvadratfelet (MSE) på mottagarsidan med användning av ensfäravkodningsmetod (SD). Efter att ha analyserat MSE-minimering, föreslås en ny linjär förkodningsdesignför att maximera summahastigheten för samma system i den andra delen av dennaavhandling. Det senare problemet löses av en ny iterativ algoritm inspirerad av denklassiska vägda minsta medelkvadratfel (WMMSE)-metoden. Dessutom presenterasen heuristisk kvantiseringsmedveten förkodningsmetod med lägre beräkningskomplexitet, som visar att den överträffar den kvantiseringsomedvetna baslinjen. Denna baslinje är en optimerad förkodning med oändlig upplösning som sedan kvantiseras. Dennastudie avslöjar att det är möjligt att fördubbla summahastigheten vid hög SNR genomatt välja vikter och förkodningsmatriser som är kvantiseringsmedvetna. I den tredje delen och sista delen av denna avhandling fokuserar vi på signaleringsproblemet i mobil millimetervågskommunikation (mmWave). Utmaningen medmmWave-system är de snabba blekningsvariationerna och omfattande pilotsignalering.Vi utforskar frekvensen av att uppdatera den kombinerande matrisen i en bredbandsmmWave punkt-till-punkt MIMO under användarutrustning (UE) mobilitet. Konceptet med strålkoherenstid introduceras för att kvantifiera frekvensen vid vilken UE:nmåste uppdatera sin nedlänksmottagningskombinationsmatris. Studien visar att strålkoherenstiden kan vara till och med hundratals gånger större än kanalkoherenstiden försmåskalig fädning. Simuleringar bekräftar att den föreslagna nedre gränsen för dettadefinierade koncept inte garanterar mer än 50 % förlust av mottagen signalförstärkning(SG) / <p>QC 20240219</p>

Le but principal du présent travail est ainsi de réaliser une expérience de mélange par la turbulence, dans laquelle il est possible de déterminer et de quantifier les temps de cohérence des différentes échelles spatiales des fluctuations du champ de vitesse et du champ de concentration qu'il transporte et mélange. La turbulence est ici voisine de la situation idéale statistiquement homogène et isotrope, et la configuration est conçue pour qu'il en soit de même pour le champ de concentration. La turbulence est créée par une grille placée perpendiculairement à un écoulement uniforme à l'extérieur des couches limites qui se développent le long des parois de la veine d'essais à section carrée constante. L'écoulement de la présente étude est un écoulement d'eau, dans lequel le champ de concentration est celui d'une solution de Rhodamine B injectée au niveau de la grille à travers des injecteurs équi-répartis le long des barreaux de celle-ci. Ce choix, dicté par la technique de mesure du champ de concentration par Fluorescence Induite par Laser, permet en outre de mesurer le champ de vitesse par une autre technique optique, elle aussi non-intrusive. Pour se rapprocher le plus de la théorie d'un mélange idéal statistiquement homogène et isotrope sans vitesse moyenne, on considère dans l'expérience, conformément à l'hypothèse de Taylor, que toutes les échelles associées à chacun de ces champs, sont convectés à la vitesse moyenne U de l'écoulement, et l'on suit une "boîte de turbulence" qui se déplace à cette vitesse le long de la veine. Par suite déterminer l'état de la turbulence en un point donné de cette boite à l'instant t et à l'instant t'=t+dt, revient à l'étudier dans l'expérience à t à l'abscisse x de la veine d'essai, et à t' à l'abscisse x+dx , avec dx=Udt, où se trouve le point de la boîte aux deux instants successifs. Les résultats expérimentaux concernant les échelles pour lesquelles l'isotropie statistique est satisfaite, permettent alors de vérifier une phénoménologie de l'évolution de la cohérence temporelle des diverses échelles spatiales du champ des fluctuations de concentration fondée sur les idées de Comte-Bellot et Corrsin. Cette expérience, est en outre l'occasion de donner des résultats sur les densités de probabilité de diverses propriétés statistiques des champs de fluctuation de vitesse. / The main purpose of this work is to make an experiment of mixing by turbulence, in which it is possible to determine and quantify the coherence time of the different spatial scales of fluctuations of a scalar field. We measure concentration fluctuations of rhodamine B by Planar Laser Induced Fluorescence (PLIF) which is transported and mixed by velocity fluctuations. These latter ones are generated by a grid placed perpendicularly to the flow in a water channel and are measured by Particle Image Velocimetry (PIV). The concentration field is injected in the flow by injectors regularly spaced on the grid so that it is a situation where both the velocity and the concentration fields are statistically homogeneous and isotropic. To get as close as the theory of statistically homogeneous and isotropic turbulence with no mean velocity, we consider, according to Taylor's hypothesis, that all scales associated with each of these fields are convected with the mean velocity U of the flow, and we follow a "turbulent box" that moves at U along the channel. As a result determining the state of turbulence at a given point of the box at time t and time t ' = t + dt, is like studying in the experiment at time t and space x of test section, and time t' and space x + dx of the test section, with dx = U dt. When statistical isotropy is satisfied, we can verify a phenomenology of the evolution of the temporal coherence of various space scales of the concentration fluctuation fields based on the ideas of Comte-Bellot and Corrsin. This experiment is also an opportunity to give results on probability densities of various statistical properties of fluctuating velocity fields.

On demand single-photon and entangled-photon sources are key building-blocks for many proposed photonic quantum technologies. For practical device applications, epitaxially grown quantum dots (QDs) are of increasing importance due to their bright photon emission with sharp line width. Particularly, they are solid-state systems and can be easily embedded within a light-emitting diode (LED) to achieve electrically driven sources. Therefore, one would expect a full-fledged optoelectronic quantum network that is running on macroscopically separated, QD-based single- and entangled-photon devices. An all-electrically operated wavelength-tunable on demand single-photon source (SPS) is demonstrated first. The device consists of a LED in the form of self-assembled InGaAs QDs containing nanomembrane integrated onto a piezoelectric crystal. Triggered single photons are generated via injection of ultra-short electrical pulses into the diode, while their energy can be precisely tuned over a broad range of about 4.8 meV by varying the voltage applied to the piezoelectric crystal. High speed operation of this single-photon emitting diode up to 0.8 GHz is demonstrated. In the second part of this thesis, a fast strain-tunable entangled-light-emitting diode (ELED) is demonstrated. It has been shown that the fine structure splitting of the exciton can be effectively overcome by employing a specific anisotropic strain field. By injecting ultra-fast electrical pulses to the diode, electrically triggered entangled-photon emission with high degree of entanglement is successfully realized. A statistical investigation reveals that more than 30% of the QDs in the strain-tunable quantum LED emit polarization-entangled photon-pairs with entanglement-fidelities up to f+ = 0.83(5). Driven at the highest operation speed ever reported so far (400 MHz), the strain-tunable quantum LED emerges as unique devices for high-data rate entangled-photon applications. In the end of this thesis, on demand and wavelength-tunable LH single-photon emission from strain engineered GaAs QDs is demonstrated. Fourier-transform spectroscopy is performed, from which the coherence time of the LH single-photon emission is studied. It is envisioned that this new type of LH exciton-based SPS can be applied to realize an all-semiconductor based quantum interface in the foreseeable distributed quantum networks.