On PAPR Reduction of OFDM using Partial Transmit Sequence with Intelligent Optimization Algorithms

In recent time, the demand for multimedia data services over wireless links has grown up rapidly. Orthogonal Frequency Division Multiplexing (OFDM) forms the basis for all 3G and beyond wireless communication standards due to its efficient frequency utilization permitting near ideal data rate and ubiquitous coverage with high mobility. OFDM signals are prone to high peak-to-average-power ratio (PAPR). Unfortunately, the high PAPR inherent to OFDM signal envelopes occasionally drives high power amplifiers (HPAs) to operate in the nonlinear region of their characteristic leading out-of-band radiation, reduction in efficiency of communication system etc. A plethora of research has been devoted to reducing the performance degradation due to the PAPR problem inherent to OFDM systems. Advanced techniques such as partial transmit sequences (PTS) and selected mapping (SLM) have been considered most promising for PAPR reduction. Such techniques are seen to be efficient for distortion-less signal processing but suffer from computational complexity and often requires transmission of extra information in terms of several side information (SI) bits leading to loss in effective data rate. This thesis investigates the PAPR problem using Partial Transmit Sequence (PTS) scheme, where optimization is achieved with evolutionary bio-inspired metaheuristic stochastic algorithms. The phase factor optimization in PTS is used for PAPR reduction. At first, swarm intelligence based Firefly PTS (FF-PTS) algorithm is proposed which delivers improved PAPR performance with reduced searching complexity. Following this, Cuckoo Search based PTS (CS-PTS) technique is presented, which offers good PAPR performance in terms of solution quality and convergence speed. Lastly, Improved Harmony search based PTS (IHS-PTS) is introduced, which provides improved PAPR. The algorithm has simple structure with a very few parameters for larger PTS sub-blocks. The PAPR performance of the proposed technique with different parameters is also verified through extensive computer simulations. Furthermore, complexity analysis of algorithms demonstrates that the proposed schemes offer significant complexity reduction when compared to standard PAPR reduction techniques. Findings have been validated through extensive simulation tests

Impact of step size on convergence in swarmalator systems

openGroup robotics is one of the key areas of the development of robotic systems. This is due to the fact that for a wide class of practical tasks, the use of a group of relatively simple robots is much more efficient than using a single large multi-purpose device. The modern development of computer technology and communication systems opens up wide opportunities for the construction of such systems. The most progressive and effective approach is the implementation of the collective behavior of robots according to the swarm principle, when each of them interacts only with neighboring individuals, synchronously exchanging the collected information about the environment and their condition. Such a group compensates for the weakness of its detection and communication devices by joining a team. The problems of introducing group robotics into the modern world are studied in this thesis. If they combine two concepts, synchronization and swarming, they are called a swarmalator. In swarmalator systems, the movement of the robots is governed by differential equations. These equations are solved with the Euler method, where the location and phase are determined. The Euler method is time-discrete and allows the integration of first-order differential equations. Therefore, there is a step size to be chosen. The main task is to study group movement, which is based on transmitting information with a definite step size. The step value affects how often the swarmalators share their location and phase. Three main conclusions are made. The first research is what happens when varying the step size - is it most optimal to use with small step sizes? The second conclusion is that when increasing the step size with a small increment or using randomization of the step size. Such methods are typically, more optimal to use with a gradual increase in the step size because the convergence time is lower. The third is when decreasing the step size using a small increment. The results showed that this method is optimal to use when the step size exceeds 1. The states converge at a rather large interval, compared with previous results, but at the same time with a large value of the convergence time. The values of optimal step sizes are presented and analyzed. As performance criteria, we consider the computational power that is required, the average convergence time, the coupling probability and the step size. The behavior of all parameters is graphically represented in plots. The conclusions are based on the simulations done for the results.Group robotics is one of the key areas of the development of robotic systems. This is due to the fact that for a wide class of practical tasks, the use of a group of relatively simple robots is much more efficient than using a single large multi-purpose device. The modern development of computer technology and communication systems opens up wide opportunities for the construction of such systems. The most progressive and effective approach is the implementation of the collective behavior of robots according to the swarm principle, when each of them interacts only with neighboring individuals, synchronously exchanging the collected information about the environment and their condition. Such a group compensates for the weakness of its detection and communication devices by joining a team. The problems of introducing group robotics into the modern world are studied in this thesis. If they combine two concepts, synchronization and swarming, they are called a swarmalator. In swarmalator systems, the movement of the robots is governed by differential equations. These equations are solved with the Euler method, where the location and phase are determined. The Euler method is time-discrete and allows the integration of first-order differential equations. Therefore, there is a step size to be chosen. The main task is to study group movement, which is based on transmitting information with a definite step size. The step value affects how often the swarmalators share their location and phase. Three main conclusions are made. The first research is what happens when varying the step size - is it most optimal to use with small step sizes? The second conclusion is that when increasing the step size with a small increment or using randomization of the step size. Such methods are typically, more optimal to use with a gradual increase in the step size because the convergence time is lower. The third is when decreasing the step size using a small increment. The results showed that this method is optimal to use when the step size exceeds 1. The states converge at a rather large interval, compared with previous results, but at the same time with a large value of the convergence time. The values of optimal step sizes are presented and analyzed. As performance criteria, we consider the computational power that is required, the average convergence time, the coupling probability and the step size. The behavior of all parameters is graphically represented in plots. The conclusions are based on the simulations done for the results

Fast data acquisition for silicon tracking detectors at high rates

Silicon tracking detectors play a key role in many current high energy physics experiments. To enhance experimental sensitivities for searches for new physics, beam energies and event rates are constantly being increased, which leads to growing volumes of detector data that have to be processed. This thesis covers high-speed data acquisition for silicon tracking detectors in the context of the Mu3e experiment and future hadron collider experiments. For the Mu3e experiment, a vertical slice of the trigger-less readout system is realized as a beam telescope consisting of 8 layers of pixel sensors that are read out using a prototype of the Mu3e front-end board. The performance of the full readout system is studied during beam tests. Sensor hit rates of up to 5 MHz can be handled without significant losses. Hence, the system fulfils the requirements for the first phase of the experiment. To fully exploit the potential of silicon tracking detectors at future hadron collider experiments, the implementation of high-speed data links is mandatory. Wireless links operating at frequencies of 60 GHz and above present an attractive alternative to electrical and optical links, as they offer high bandwidth, small form factor and low power consumption. This thesis describes readout concepts for tracking detectors applying wireless data transfer and presents studies of wireless data transmission

Decentralized Ultra-Reliable Low-Latency Communications through Concurrent Cooperative Transmission

Emerging cyber-physical systems demand for communication technologies that enable seamless interactions between humans and physical objects in a shared environment. This thesis proposes decentralized URLLC (dURLLC) as a new communication paradigm that allows the nodes in a wireless multi-hop network (WMN) to disseminate data quickly, reliably and without using a centralized infrastructure. To enable the dURLLC paradigm, this thesis explores the practical feasibility of concurrent cooperative transmission (CCT) with orthogonal frequency-division multiplexing (OFDM). CCT allows for an efficient utilization of the medium by leveraging interference instead of trying to avoid collisions. CCT-based network flooding disseminates data in a WMN through a reception-triggered low-level medium access control (MAC). OFDM provides high data rates by using a large bandwidth, resulting in a short transmission duration for a given amount of data. This thesis explores CCT-based network flooding with the OFDM-based IEEE 802.11 Non-HT and HT physical layers (PHYs) to enable interactions with commercial devices. An analysis of CCT with the IEEE 802.11 Non-HT PHY investigates the combined effects of the phase offset (PO), the carrier frequency offset (CFO) and the time offset (TO) between concurrent transmitters, as well as the elapsed time. The analytical results of the decodability of a CCT are validated in simulations and in testbed experiments with Wireless Open Access Research Platform (WARP) v3 software-defined radios (SDRs). CCT with coherent interference (CI) is the primary approach of this thesis. Two prototypes for CCT with CI are presented that feature mechanisms for precise synchronization in time and frequency. One prototype is based on the WARP v3 and its IEEE 802.11 reference design, whereas the other prototype is created through firmware modifications of the Asus RT-AC86U wireless router. Both prototypes are employed in testbed experiments in which two groups of nodes generate successive CCTs in a ping-pong fashion to emulate flooding processes with a very large number of hops. The nodes stay synchronized in experiments with 10 000 successive CCTs for various modulation and coding scheme (MCS) indices and MAC service data unit (MSDU) sizes. The URLLC requirement of delivering a 32-byte MSDU with a reliability of 99.999 % and with a latency of 1 ms is assessed in experiments with 1 000 000 CCTs, while the reliability is approximated by means of the frame reception rate (FRR). An FRR of at least 99.999 % is achieved at PHY data rates of up to 48 Mbit/s under line-of-sight (LOS) conditions and at PHY data rates of up to 12 Mbit/s under non-line-of-sight (NLOS) conditions on a 20 MHz wide channel, while the latency per hop is 48.2 µs and 80.2 µs, respectively. With four multiple input multiple output (MIMO) spatial streams on a 40 MHz wide channel, a LOS receiver achieves an FRR of 99.5 % at a PHY data rate of 324 Mbit/s. For CCT with incoherent interference, this thesis proposes equalization with time-variant zero-forcing (TVZF) and presents a TVZF receiver for the IEEE 802.11 Non-HT PHY, achieving an FRR of up to 92 % for CCTs from three unsyntonized commercial devices. As CCT-based network flooding allows for an implicit time synchronization of all nodes, a reception-triggered low-level MAC and a reservation-based high-level MAC may in combination support various applications and scenarios under the dURLLC paradigm

Optical Wireless Data Center Networks

Bandwidth and computation-intensive Big Data applications in disciplines like social media, bio- and nano-informatics, Internet-of-Things (IoT), and real-time analytics, are pushing existing access and core (backbone) networks as well as Data Center Networks (DCNs) to their limits. Next generation DCNs must support continuously increasing network traffic while satisfying minimum performance requirements of latency, reliability, flexibility and scalability. Therefore, a larger number of cables (i.e., copper-cables and fiber optics) may be required in conventional wired DCNs. In addition to limiting the possible topologies, large number of cables may result into design and development problems related to wire ducting and maintenance, heat dissipation, and power consumption. To address the cabling complexity in wired DCNs, we propose OWCells, a class of optical wireless cellular data center network architectures in which fixed line of sight (LOS) optical wireless communication (OWC) links are used to connect the racks arranged in regular polygonal topologies. We present the OWCell DCN architecture, develop its theoretical underpinnings, and investigate routing protocols and OWC transceiver design. To realize a fully wireless DCN, servers in racks must also be connected using OWC links. There is, however, a difficulty of connecting multiple adjacent network components, such as servers in a rack, using point-to-point LOS links. To overcome this problem, we propose and validate the feasibility of an FSO-Bus to connect multiple adjacent network components using NLOS point-to-point OWC links. Finally, to complete the design of the OWC transceiver, we develop a new class of strictly and rearrangeably non-blocking multicast optical switches in which multicast is performed efficiently at the physical optical (lower) layer rather than upper layers (e.g., application layer). Advisors: Jitender S. Deogun and Dennis R. Alexande