The traffic volume in wireless communication has grown dramatically in the last decade and is predicted to keep increasing in the future. In this thesis, we focus on the densification dimension for capacity improvement, which has been proved to be the most effective in the past. The current gain of network densification mainly comes from cell splitting, thereby serving more user equipments (UEs) simultaneously. This trend will decelerate as base station (BS) density gets closer to or even surpass UE density which forms an ultra-dense network (UDN). Thus, it is crucial to understand the behavior of ultra-densification for future network provisioning.   We start from comparing the effectiveness of densification with spectrum expansion and multi-antenna systems. Our findings show that deploying more BSs provides a substantial gain in sparse network but the gain decreases progressively in a UDN. The diminishing gain appears in a UDN make us curious to know if there exists a terminal on the way of densification. Such uncertainty leads to the study on the asymptotic behavior of densification. We incorporate a sophisticated bounded dual-slope path loss model and practical UE densities in our analysis. By using stochastic geometry, we derive the expressions and prove the convergence of the coverage probability of a typical UE and network area spectral efficiency (ASE). Considering the large portion of dormant BSs in a UDN, it is an interesting question whether we can utilize these dormant BSs to improve system performance is an interesting question. To this end, we employ joint transmission (JT) techniques into a UDN. Two types of cooperation schemes are investigated: non-coherent JT and coherent JT depending on the availability of channel state information (CSI). Our results reveal that non-coherent JT is not beneficial in a UDN while coherent JT are able to increase UE spectral efficiency (SE) depending on the environmental parameters. / <p>QC 20170117</p>

The next generation of mobile communication (5G) is upon us, and with that newtypes of technologies are needed for improved data rates, reliability, response timeand increased utilization. In this report, two highly efficient linear power amplifiersare characterized and tested with simulated communication signals. The purpose ofthe amplifiers is to be integrated into antenna arrays that will transmit amplifiedcommunication signals to mobile users.One of the amplifiers is tested with modulated communication signals with anoptimized gate bias value. The amplifier shows during the final tests high-efficiencylevels of up to 40% and is still able to behave linearly with&gt;20 dB gain and lowerror vector magnitude below 1%.The fundamental theory for signal processing is described at the beginning of thereport, followed by an overview of the experimental setup built during the thesis formeasuring modulated signals through amplifiers.

Society as we know it today would not have been possible without the explosive and astonishing development of telecommunications systems, and optical fibers have been one of the pillars of these technologies. Despite the enormous amount of data being transmitted over optical networks today, the trend is that the demand for higher bandwidths will also increase. Given this context, a central element in the design of telecommunications networks will be data security, since information can often be confidential or private. Quantum information emerges as a solution to encrypt data by quantum key distribution (QKD) between two users. This technique uses the properties of nature as the fundamentals of operation rather than relying on mathematical constructs to provide data protection. A popular alternative to performing QKD is to use the relative phase between two individual photon paths for information encoding. However, this method was not practical over long distances. The time-bin- based scheme was a solution to the previous problem given its practical nature, however, it introduces intrinsic losses due to its design, which increases with the dimension of the encoded quantum system. In this thesis we have designed and tested a fiber-optic platform using spatial-division- multiplexing techniques. The use of few-mode fibers and photonic lanterns are the cornerstone of our proposal, which also allow us to support orbital angular momentum (OAM) modes. The platform builds on the core ideas of the phase-coded quantum communication system and also takes advantage of the benefits proposed by the time-bin scheme. We have experimentally tested our proposal by successfully transmitting phase-coded single-photon states over 500 m few-mode fiber, demonstrating the feasibility of our scheme. We demonstrated the successful creation of OAM states, their propagation and their successful detection in an all in-fiber scheme. Our platform eliminates the post-selection losses of time-bin quantum communication systems and ensures compatibility with next-generation optical networks and opens up new possibilities for quantum communication.

Passive Internet-of-Things (IoT), a new paradigm based on battery-free devices, is a promising technology to enable several use cases that require connectivity with stringent requirements in terms of cost, complexity, and energy efficiency. These use cases span critical sectors, such as healthcare, transportation, and agriculture. Passive IoT relies on the development of technologies such as radio frequency (RF) energy harvesting, low-power computing, and backscatter communication. Particularly, backscatter communication allows devices to modulate its information on external RF signals that are backscattered to the receiver or reader. BC considers the following elements: a carrier emitter (CE), a reader, and a backscatter device (BD). The main BC configurations are monostatic BC (MoBC), ambient BC (AmBC) and bistatic BC (BiBC). In a MoBC setup, the CE and reader are co-located and share parts of the same infrastructure. A monostatic system suffers from round-trip path loss, and requires full-duplex technology if the same antennas are simultaneously used for transmission and reception. In an AmBC setup, CE and reader are in different locations, while the CE is not considered dedicated. AmBC uses ambient sources to transmit information, such as Wi-Fi, Bluetooth, and TV signals. In BiBC, the CE and reader are also spatially separated from each other, but there is a dedicated CE. In addition, BiBC can operate in half duplex mode, thus avoiding the complexity associated to the full-duplex operation. Due to the double path-loss effect on the two-way backscatter link, the received backscattered signal is typically weak compared to the direct link interference (DLI) from a CE. This requires a high dynamic range of the circuitry in the reader. As a result, a high-resolution analog-to-digital converter (ADC) is required to detect the weak backscattered signal under heavy DLI; this represents a great limitation because ADCs are major power consumers. Nonetheless, the benefits provided by multiple-antenna and distributed multiple-input multiple-output (MIMO) technologies can be explored to circumvent the limitations of BiBC, which is the main focus of this thesis. In this context, the contributions of this thesis are two-fold. First, we propose a novel transmission scheme that includes a protocol for channel estimation at the multiple-antenna CE as well as a transmit beamformer design to suppress the DLI between the two ends of a bistatic link (namely CE and reader) and increase the detection performance of the BD symbol. Further, we derive a generalized log-likelihood ratio test (GLRT) to detect the symbol/presence of the BD and provide an iterative algorithm to estimate the unknown parameters in the GLRT. Simulation results show that the required dynamic range of the system is significantly decreased while the detection performance of the BD symbol is increased, by the proposed algorithm compared to a system not using beamforming at the CE. For the second part, we consider BiBC in the context of cell-free MIMO networks by exploring the optimal selection of CE and reader among multiple access points, leveraging prior knowledge about the area where the BD is located. First, a maximum a posteriori probability (MAP) detector to decode the BD information bits is derived. Then, the exact probability of error for this detector is obtained. In addition, an algorithm to select the best CE-reader pair for serving the specified area is proposed. Finally, simulation results show that the error performance of the backscatter communication (BC) is improved by the proposed algorithm compared to the benchmark scenario.

Digital communication has gone through much development in the past decade. The literature in this field has developed and improved as well, but the educational materials still lack illustrative descriptions. The modulation techniques are a very complex area that needs practical implementation to facilitate intuitive understanding for engineering students. This thesis presents an educational application where users conduct experiments in digital modulation techniques, ASK, PSK, QAM, and OFDM. The product is a simulation application of the transmission of information from transmitter to receiver with a theoretical description. The application is programmed within the MATLAB environment, and the result is presented with a GUI that contains signal diagrams for each step of the modulation and demodulation process. This tool provides an illustrative description of the modulation techniques without any need for more extensive mathematical knowledge. / Digital kommunikation har genomgått mycket utveckling under det senaste decenniet. Litteraturen inom detta område har utvecklats och förbättrats, men utbildningsmaterialet saknar fortfarande illustrativa beskrivningar. Digitala Modulation teknikerna är ett mycket komplext område som kräver praktisk implementering för att underlätta intuitiv förståelse för ingenjörsstudenter. Denna studie presenterar en pedagogisk applikation där användare genomföra experiment inom digital modulerings-tekniker som ASK, PSK, QAM och OFDM. Produkten är en simulerings applikation för överföring av information från sändare till mottagare med teoretisk beskrivning. Applikationen är programmerad i Matlab utvecklingsmiljö, och resultatet presenteras med ett GUI som innehåller signal diagram för varje steg i modulerings- och demoduleringsprocessen. Detta verktyg ger en illustrativ beskrivning av modulerings-teknikerna utan behov av mer omfattande matematiska kunskaper.

This thesis evaluated the performance of four different virtual private networks (VPNs): IP security (IPsec), OpenVPN, SSH port forwarding and SSH using virtual interfaces. To evaluate these VPNs, three comparative performance tests were carried out in which the maximum throughput of each VPN was measured. In every test, a specific parameter was varied to observe how it affected the VPNs throughput. The parameters varied were the type of transport layer protocol used, the encryption algorithm used and whether the VPN used compression or not. The results showed, among others, that when TCP traffic was transferred through the VPN and AES-128 was used as encryption algorithm in a Gigabit Ethernet network, the throughput for SSH port forwarding was 168 Mbit/s, 165 Mbit/s for IPsec, 95,0 Mbit/s for SSH using virtual interfaces and 83,3 Mbit/s for OpenVPN. These results are to be compared to the through put measured when no VPN was used, 940 Mbit/s. Three conclusions are drawn from the results of the performance tests. The first conclusion is that the throughput of a VPN depends on the technology the VPN solution is based on, the encryption method that is used and the type ofdata that is sent over the VPN. The second conclusion is that IPsec and SSH port forwarding are the most effective VPNs of the ones compared in this thesis, while OpenVPN and SSH using virtual interfaces are less effective. Lastly, it is concluded that although the different parameters affected the throughput of each VPN, the relation between the VPNs is the same in almost every test. In other words a VPN that performs well in one test performs well in every test.

No description available.

Abstract This thesis presents a comparative analysis of two network automation tools, Ansible and Netmiko, within a virtualized environment. The primary objective is to evaluate and contrast the performance, scalability, and user complexity associated with each tool, providing insights that can help network engineers make informed decisions regarding their automation strategies. The study was conducted by setting up a controlled virtual network topology in which both network automation tools could be assessed. GNS3 and VirtualBox were used to set-up the virtual network topologies and simulate real-world network scenarios. Findings from the experiments indicate that Ansible, while slower in configuring a sole router, scales more efficiently as network complexity increases, benefiting from its parallel execution capability. In contrast, Netmiko shows strengths in environments where processing power is a significant consideration and for when the network is extremely congested. In terms of user complexity, configuring small-scale environments with the same tasks requires fewer symbols for Netmiko than Ansible though this result represents only a narrow use-case and further research is needed.

Several aspects of the control of large-scale systems communicating over digital channels are considered. In particular, the issue of delay, quantization, and packet loss is addressed with the help of dynamic quantization. New small-gain results suitable for networked control systems are introduced and it is shown that many of the known small-gain conditions are equivalent. The issue of bandwidth limitations is addressed with the help of event-triggered control. A novel approach termed parsimonious triggering is introduced, which helps to rule out the occurrence of an infinite number of triggering events within finite time. Moreover, the feasibility of the presented approaches is demonstrated by numerical examples. / Es werden großskalige Netzwerke betrachtet, bei denen die Zustandsrückführung über digitale Kommunikationskanäle erfolgt. Typische Effekte digitaler Kommunikation wie Totzeiten, Quantisierung und Paketverlust werden mithilfe der sogenannten dynamischen Quantisierung bearbeitet. Im Kontext der Netzwerkkontrollsysteme werden neue small-gain Ergebnisse eingeführt, die auf den Bedarf der digitalen Kommunikation eingehen. Des Weiteren wird gezeigt, dass viele der aus der Literatur bekannten small-gain Ergebnisse äquivalent sind. Eventbasierte Kontrollstrategien werden vorgestellt, um das Problem der Bandbreitenbeschränkung zu umgehen. Ein neuer Ansatz, parsimonious triggering genannt, wird vorgestellt, um das Problem des unendlich oft Schaltens in endlicher Zeit zu umgehen. Abschließend wird anhand von numerischen Beispielen die Anwendbarkeit der vorgestellten Methoden demonstriert.

Universiẗat, Diss.--St. Gallen, 1996.