Facilitating Flexible Link Layer Protocols for Future Wireless Communication Systems

This dissertation addresses the problem of designing link layer protocols which are flexible enough to accommodate the demands offuture wireless communication systems (FWCS).We show that entire link layer protocols with diverse requirements and responsibilities can be composed out of reconfigurable and reusable components.We demonstrate this by designing and implementinga novel concept termed Flexible Link Layer (FLL) architecture.Through extensive simulations and practical experiments, we evaluate a prototype of the suggested architecture in both fixed-spectrumand dynamic spectrum access (DSA) networks. FWCS are expected to overcome diverse challenges including the continual growthin traffic volume and number of connected devices.Furthermore, they are envisioned to support a widerange of new application requirements and operating conditions.Technology trends, including smart homes, communicating machines, and vehicularnetworks, will not only grow on a scale that once was unimaginable, they will also become the predominant communication paradigm, eventually surpassing today's human-produced network traffic. In order for this to become reality, today's systems have to evolve in many ways.They have to exploit allocated resources in a more efficient and energy-conscious manner.In addition to that, new methods for spectrum access and resource sharingneed to be deployed.Having the diversification of applications and network conditions in mind, flexibility at all layers of a communication system is of paramount importance in order to meet the desired goals. However, traditional communication systems are often designed with specific and distinct applications in mind. Therefore, system designers can tailor communication systems according to fixedrequirements and operating conditions, often resulting in highly optimized but inflexible systems.Among the core problems of such design is the mix of data transfer and management aspects.Such a combination of concerns clearly hinders the reuse and extension of existing protocols. To overcome this problem, the key idea explored in this dissertation is a component-based design to facilitate the development of more flexible and versatile link layer protocols.Specifically, the FLL architecture, suggested in this dissertation, employs a generic, reconfigurable data transfer protocol around which one or more complementary protocols, called link layer applications, are responsible for management-related aspects of the layer. To demonstrate the feasibility of the proposed approach, we have designed andimplemented a prototype of the FLL architecture on the basis ofa reconfigurable software defined radio (SDR) testbed.Employing the SDR prototype as well as computer simulations, thisdissertation describes various experiments used to examine a range of link layerprotocols for both fixed-spectrum and DSA networks. This dissertation firstly outlines the challenges faced by FWCSand describes DSA as a possible technology component for their construction.It then specifies the requirements for future DSA systemsthat provide the basis for our further considerations.We then review the background on link layer protocols, surveyrelated work on the construction of flexible protocol frameworks,and compare a range of actual link layer protocols and algorithms.Based on the results of this analysis, we design, implement, and evaluatethe FLL architecture and a selection of actual link layer protocols. We believe the findings of this dissertation add substantively to the existing literature on link layer protocol design and are valuable for theoreticians and experimentalists alike

Clinical correlations with Lewy body pathology in LRRK2-related Parkinson disease

IMPORTANCE: Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of genetic Parkinson disease (PD) known to date. The clinical features of manifesting LRRK2 mutation carriers are generally indistinguishable from those of patients with sporadic PD. However, some PD cases associated with LRRK2 mutations lack Lewy bodies (LBs), a neuropathological hallmark of PD. We investigated whether the presence or absence of LBs correlates with different clinical features in LRRK2-related PD. OBSERVATIONS: We describe genetic, clinical, and neuropathological findings of 37 cases of LRRK2-related PD including 33 published and 4 unpublished cases through October 2013. Among the different mutations, the LRRK2 p.G2019S mutation was most frequently associated with LB pathology. Nonmotor features of cognitive impairment/dementia, anxiety, and orthostatic hypotension were correlated with the presence of LBs. In contrast, a primarily motor phenotype was associated with a lack of LBs. CONCLUSIONS AND RELEVANCE: To our knowledge, this is the first report of clinicopathological correlations in a series of LRRK2-related PD cases. Findings from this selected group of patients with PD demonstrated that parkinsonian motor features can occur in the absence of LBs. However, LB pathology in LRRK2-related PD may be a marker for a broader parkinsonian symptom complex including cognitive impairment

Effects of L-dopa during Auditory Instrumental Learning in Humans

<div><p>The dopaminergic neurotransmitter system is critically involved in promoting plasticity in auditory cortex. We combined functional magnetic resonance imaging (fMRI) and a pharmacological manipulation to investigate dopaminergic modulation of neural activity in auditory cortex during instrumental learning. Volunteers either received 100 mg L-dopa (Madopar) or placebo in an appetitive, differential instrumental conditioning paradigm, which involved learning that a specific category of frequency modulated tones predicts a monetary reward when fast responses were made in a subsequent reaction time task. The other category of frequency modulated tones was not related to a reward. Our behavioral data provides evidence that dopaminergic stimulation differentially impacts on the speed of instrumental responding in rewarded and unrewarded trials. L-dopa increased neural BOLD activity in left auditory cortex to tones in rewarded and unrewarded trials. This increase was related to plasma L-dopa levels and learning rate. Our data thus provides evidence for dopaminergic modulation of neural activity in auditory cortex, which occurs for both auditory stimuli related to a later reward and those not related to a reward.</p> </div

Averaged beta values as a function of group and condition in regions of interest to illustrate the results shown in <b>Figure 3</b>.

<p>Note that neural activity in the left auditory cortex was significantly enhanced in the L-dopa group compared to the placebo group without any significant differences between CS+ and CS− trials. Differences in CS+ and CS− trials were evident in dopaminergic brain regions (B and C). The plots further illustrates higher neural responses in the midbrain under L-dopa. Black bars show rewarded (CS+) trials, gray bars unrewarded (CS−) trials. Statistically significant differences are marked by asterisks (two factorial ANOVA corrected for multiple comparisons).</p

Behavioral data.

<p>(A) Learning curves: Cumulative sum of correct answers to reward expectations as function of trial number for each individual subject. Bold lines (blue and red) indicate the mean of each group (L-dopa and placebo, respectively). Bold black lines indicate 100% and 50% (chance) correct answers. (B) Speed of instrumental responding: Reaction times in the number comparison task in rewarded (CS+, solid lines) and unrewarded (CS−, dashed lines) as function of trial number for each group.</p

Results of the linear regression analysis using the slope of the individual learning curves: (A) L-dopa group, (B) placebo group and (C) differences between placebo and L-dopa.

<p>Results of the linear regression analysis using the slope of the individual learning curves: (A) L-dopa group, (B) placebo group and (C) differences between placebo and L-dopa.</p

Neural activity for main effect of group (A) and condition (B).

<p>Neural activity for (A) main effect of group, which yields stronger activation in the auditory cortex (AC), inferior frontal gyrus (Broca’s area) and anterior cingulate cortex (ACC)/left medial frontal gyrus for the L-dopa treated group compared to the placebo group. (B) Main effect of condition which shows stronger activation for rewarded (CS+) compared to non-rewarded tones (CS−), in several dopaminergic brain areas, such as nucleus accumbens (NAC) and midbrain regions (SN/VTA), as well as insula.</p

Results of the full factorial ANOVA with effects of drug treatment (A) and reward anticipation (B).

<p>Results of the full factorial ANOVA with effects of drug treatment (A) and reward anticipation (B).</p

Clinical Correlations With Lewy Body Pathology in LRRK2-Related Parkinson Disease.

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of genetic Parkinson disease (PD) known to date. The clinical features of manifesting LRRK2 mutation carriers are generally indistinguishable from those of patients with sporadic PD. However, some PD cases associated with LRRK2 mutations lack Lewy bodies (LBs), a neuropathological hallmark of PD. We investigated whether the presence or absence of LBs correlates with different clinical features in LRRK2-related PD