Performance Study of Hybrid Spread Spectrum Techniques

This thesis focuses on the performance analysis of hybrid direct sequence/slow frequency hopping (DS/SFH) and hybrid direct sequence/fast frequency hopping (DS/FFH) systems under multi-user interference and Rayleigh fading. First, we analyze the performance of direct sequence spread spectrum (DSSS), slow frequency hopping (SFH) and fast frequency hopping (FFH) systems for varying processing gains under interference environment assuming equal bandwidth constraint with Binary Phase Shift Keying (BPSK) modulation and synchronous system. After thorough literature survey, we show that hybrid DS/FFH systems outperform both SFH and hybrid DS/SFH systems under Rayleigh fading and multi-user interference. Also, both hybrid DS/SFH and hybrid DS/FFH show performance improvement with increasing spreading factor and decreasing number of hopping frequencies

Relationship between split-step timing and leg stiffness in world-class tennis players when returning fast serves

International audienc

Performance Evaluation and Analysis of Effective Range and Data Throughput for Unmodified Bluetooth Communication Devices

The DoD and the Air Force continually seek to incorporate new technology in an effort to improve communication, work effectiveness, and efficiency. Office devices utilizing Bluetooth technology simplify device configuration and communication. They provide a means to communicate wirelessly over short distances thereby eliminating the need for different vendor specific cables and interfaces. One of the key concerns involved in incorporating new communication technology is security; the fundamental security concern of wireless communication is interception. Studies focusing on IEEE 802.11b have shown vulnerability zones around many DoD installations that reflect the ranges at which wireless communications using the 802.11b standard can be intercepted

Providing efficient services for smartphone applications

Mobile applications are becoming an indispensable part of people\u27s lives, as they allow access to a broad range of services when users are on the go. We present our efforts towards enabling efficient mobile applications in smartphones. Our goal is to improve efficiency of the underlying services, which provide essential functionality to smartphone applications. In particular, we are interested in three fundamental services in smartphones: wireless communication service, power management service, and location reporting service.;For the wireless communication service, we focus on improving spectrum utilization efficiency for cognitive radio communications. We propose ETCH, a set of channel hopping based MAC layer protocols for communication rendezvous in cognitive radio communications. ETCH can fully utilize spectrum diversity in communication rendezvous by allowing all the rendezvous channels to be utilized at the same time.;For the power management service, we improve its efficiency from three different angles. The first angle is to reduce energy consumption of WiFi communications. We propose HoWiES, a system-for WiFi energy saving by utilizing low-power ZigBee radio. The second angle is to reduce energy consumption of web based smartphone applications. We propose CacheKeeper, which is a system-wide web caching service to eliminate unnecessary energy consumption caused by imperfect web caching in many smartphone applications. The third angle is from the perspective of smartphone CPUs. We found that existing CPU power models are ill-suited for modern multicore smartphone CPUs. We present a new approach of CPU power modeling for smartphones. This approach takes CPU idle power states into consideration, and can significantly improve power estimation accuracy and stability for multicore smartphones.;For the location reporting service, we aim to design an efficient location proof solution for mobile location based applications. We propose VProof, a lightweight and privacy-preserving location proof scheme that allows users to construct location proofs by simply extracting unforgeable information from the received packets

Exploring the GDB-13 chemical space using deep generative models

Recent applications of recurrent neural networks (RNN) enable training models that sample the chemical space. In this study we train RNN with molecular string representations (SMILES) with a subset of the enumerated database GDB-13 (975 million molecules). We show that a model trained with 1 million structures (0.1% of the database) reproduces 68.9% of the entire database after training, when sampling 2 billion molecules. We also developed a method to assess the quality of the training process using negative log-likelihood plots. Furthermore, we use a mathematical model based on the “coupon collector problem” that compares the trained model to an upper bound and thus we are able to quantify how much it has learned. We also suggest that this method can be used as a tool to benchmark the learning capabilities of any molecular generative model architecture. Additionally, an analysis of the generated chemical space was performed, which shows that, mostly due to the syntax of SMILES, complex molecules with many rings and heteroatoms are more difficult to sample

Implementation of multi carrier-code division multiple access-frequency division multiple access with beyond 4G specifications

Hybrid code division multiple access techniques present the open door for the future of code division multiple access and wireless communications. Multicarrier CDMA is the most popular type of hybrid CDMA because of its robustness against multipath fading channels and flexible multiple access capability. MC-CDMA is a predictable technique for future high data rate wireless communication systems according to these appealed properties. The main drawback of MC-CDMA is the power level in uplink, i.e. the ratio of peak power to the average power is high and leads to high instantaneous power which is required in transmission of mobile station. However, there are many researchers working towards reducing the level of the transmitted power. This research presents new method of peak to average power ratio (PAPR) reduction. The proposed method is making use of the characteristics of uplink for current 4th Generation (single carrier frequency division multiple access) which has low PAPR into current MC-CDMA system to reproduce a new MC-CDMA system (MC-CDMA-FDMA) with low PAPR and keep all the characteristics of the basic MC-CDMA system. MC-CDMA-FDMA reduced the level of power from 10 dB to 2 dB in case of 64 FFT size and Walsh Hadamard code is used in spreading block. In addition bit error rate has been reduced from 96x10-5 bps to 82x10-5 bps comparing to SC-FDMA bit error rate. The proposed system also has high flexibility to deal with modern communication systems with minimum required hardware at the base station through optimization of FFT size. The simulation results show that MC-CDMA-FDMA system will be a good candidate for beyond 4th Generation for mobile communication

An integrative study of bird migration: From the migratory phenotype to its gene regulation mechanisms and back.

Life goes out of equilibrium; it is in constant movement. Animals, especially, move as part of their life cycle. An outstanding example is bird migration. Some birds adopt migration as a strategy to survive the harsh conditions of weather seasonality in temperate regions. Different sources of evidence indicate that seasonal migration is innate, and it can be inherited. Mutations in such heritable behaviour create an array of diversity in migratory traits: timing, orientation and distance. The diversity of migratory traits can affect ecological speciation. Migratory divides, for instance, are geographical areas where birds with different migratory orientations hybridise. If the differences in migratory behaviour are strong enough to create reproductive barriers, this could evolve into population divergence and eventually, speciation. However, to understand the potential processes of divergence caused by migratory behaviours, a crucial element is missing: the identity of the molecular mechanisms involved in migration. Genome-wide studies in bird species with migratory divides find several different genomic regions with species-specific signature. Similarly, gene expression approaches in different organs and species find groups of individual differentially expressed genes. These results suggest an intricate mechanism for the genetics of migration with potential species-specific characteristics. This thesis analyses the migratory behaviour from different angles spanning the phenotype to gene regulation, to contribute to the identification of mechanisms and evolution of migration. Most of the chapters of this thesis use the Eurasian blackcap ( Sylvia atricapilla) a species that comprise an extensive repertoire of orientation and distance traits, including entirely resident populations. With blackcaps, we studied the phenotypic variability of migration tracking individuals ithroughout the year (Chapter 2). We used light-level geolocators to obtain migratory routes of individuals from populations in Central Europe and the United Kingdom. We describe for the first time the orientation and timing patterns of individuals from a migratory divide and a recently adapted population in the UK. In chapter 4, we analyse the genomics and evolution patterns of blackcaps. Using whole-genome resequencing of populations covering all the differences in migratory traits, we describe population structure and demography in this species. We found that blackcaps show very little genomic differentiation. The most divergent populations are residents, while migratory populations comprise a single population at the genetic level. Chapter 5 is the first study of gene regulatory mechanisms in the context of bird migration. We characterised the chromatin accessibility landscape in three brain areas contrasting individuals during migration with individuals out of the migratory season. One of the findings is a general pattern of gene repression in relevant brain regions like the Cluster N. Moreover; we found cis-regulatory modules with particular evolutionary trajectories that may play a role in migration. Lastly, we did two comparative approaches to study macroevolutionary patterns related to migration. First, we analysed phylogenetic patterns and structural characteristics of previously proposed candidate genes (chapter 3). We found that the candidate genes do not have structural characteristics correlated with the presence of migration across the avian clade as it does within some species. The second comparative approach (Chapter 6), evaluates the repeatability patterns of genomic divergence in pairs of populations from migratory divides. Our results suggests that the degree of repeatability is mainly driven by how apart in the speciation continuum is the population pair located: if the pair is recently diverging, iifew repeatability is detected, while if the populations are further apart, repeatability is more plausible. Overall, this thesis highlights an essential feature for the study of complex traits like migration: integration of different sources of evidence. Ideally, in these cases, the analysis of phenotype, evolutionary patterns and regulatory mechanisms in the same individuals, should be the standard procedure. We are aware that this is an implausible scenario. However, the integration of different studies, help to guide the search of molecular elements involved in bird migration. This thesis is the first - at least that we are aware of - study compilating research on a variety of topics to understand bird migration. We are still far from getting a definitive understanding of bird migration. Nevertheless, confirming the heritability of the phenotype, describing macro and microevolutionary patterns of migration and specific regulatory elements, will improve the search for new candidate genes for this behaviou

Advanced data communication techniques for sub-sea applications

This thesis details research carried out in the through-water data communication field. An overview of the phenomena that prohibit acoustic communication in long-range shallow-water channels is constructed. Background research found that robust communications has not been achieved using single receiver reception in this environment. This work investigates the modulation technique itself and aims to improve on existing schemes (that have been applied to this environment). This is achieved with innovative techniques, based on multiple-frequency-shift-keying (MFSK) and space-frequency-shift-keying (SFSK). A number of industrial specified restrictions are placed on this work, including bandwidth restriction. Novel ways of intrinsically transmitting synchronisation information are therefore implemented. The development of appropriate systems is covered with general and platform specific implementation strategies being covered. A single modulation scheme (the three-chip four-frequency-shift-keying, 3C4FSK, scheme) has been put forward for consideration in any future research. Practical lab-based tests and the mathematical analysis is detailed. Conclusions recommend further funding of long-range shallow sea-water trails of the 3C4FSK scheme and for the industrial scope of this work to allow investigation into multiple receiver systems that allow spatial processing of the signal as these schemes have been shown lately to have potential in long-range channels