Quantization Effects in OFDM Systems

The advantage of using orthogonal frequency division multiplexing (OFDM) over the single-carrier modulation is its ability to mitigate interference and fading without complex equalization filters in the receiver. OFDM systems have a high peak-to-average ratio (PAPR) which results in a high requirement for the resolution of AD converters. High-resolution AD converters are therefore widely used in OFDM receivers. However, the power consumption is proportional to the resolution of the AD converters. In this paper we investigate the quantization effects in OFDM systems. Quantization is a nonlinear function which happens in the time domain, so the quantization effect in the frequency domain (important for OFDM) is not simple. Here, we derive a model for the quantization effect in the frequency domain. Further, we investigate whether it is possible to apply low-resolution AD converters in reliable communications based on OFDM. Simulations with an AWGN channel reveal that the proposed model predicts the quantization noise in the frequency domain very well. Difference in $\sigma_\mathrm{q}^2$ between simulation outcomes and our model is less than 0.6\%. Also, simulations show that 5-bits AD resolution is required for OFDM communication over an AWGN channel

Reliable Download Delivery in a Terrestrial DAB Network

Reliable file transfer is important in broadcast networks. In this paper, we have investigated if it is useful to extend the DAB standard with Fountain codes. To evaluate this, results from measurements in a live Single Frequency Network (SFN) were used. Our results show that the existing error correction algorithms provide already reliable file delivery, so there is no need to extend the DAB standard

MIMO System Setup and Parameter Estimation

There is a rat race in wireless communication to achieve higher spectral efficiency. One technique to achieve this is the use of multiple antenna systems i.e. MIMO systems. In this paper we describe a wireless 4x4 Multiple Input Multiple Output (MIMO) testbed in the 2.2 GHz band including results from live experiments. MIMO systems have several advantages compared to SISO (Single Input Single Output) systems. The most important ones are higher reliability and/or higher throughput per Herz. In this testbed we used the 802.11a OFDM Wireless LAN standard as a basis for the MIMO system. The experiments have been conducted at 2.2 GHz carrier using 5 MHz bandwidth. These can be divided into several subjects: antenna spacing experiments, effects for increasing antennas, AD accuracy and performance for different antenna topologies. Moreover, the performance of the Zero Forcing (ZF), Minimum Mean Square Error (MMSE) and Vertical Bell labs LAyered Space Time (VBLAST) have been evaluated

Optimal Teleportation Based on Bell Measurement

We study optimal teleportation based on the Bell measurements. An explicit expression for the quantum channel associated with the optimal teleportation with an arbitrary mixed state resource is presented. The optimal transmission fidelity of the corresponding quantum channel is calculated and shown to be related to the fully entangled fraction of the quantum resource, rather than the singlet fraction as in the standard teleportation protocol.Comment: 7 pages, latex, no figure

Separability and entanglement in 2x3xN composite quantum systems

The separability and entanglement of quantum mixed states in \Cb^2 \otimes \Cb^3 \otimes \Cb^N composite quantum systems are investigated. It is shown that all quantum states $\rho$ with positive partial transposes and rank $r(\rho)\leq N$ are separable.Comment: Latex, 15 page

A Pontine Region is a Neural Correlate of the Human Affective Processing Network

The in vivo neural activity of the pons during the perception of affective stimuli has not been studied despite the strong implications of its role in affective processing. To examine the activity of the pons during the viewing of affective stimuli, and to verify its functional and structural connectivity with other affective neural correlates, a multimodal magnetic resonance imaging methodology was employed in this study. We observed the in vivo activity of the pons when viewing affective stimuli. Furthermore, small-world connectivity indicated that the functional connectivity (FC) between the pons and the cortico-limbic affective regions was meaningful, with the coefficient λ being positively associated with self-reported emotional reactivity. The FC between the pons and the cortico-limbic-striatal areas was related to self-reported negative affect. Corroborating this finding was the observation that the tract passing through the pons and the left hippocampus was negatively related to self-reported positive affect and positively correlated with emotional reactivity. Our findings support the framework that the pons works conjunctively with the distributed cortico-limbic-striatal systems in shaping individuals' affective states and reactivity. Our work paves the path for future research on the contribution of the pons to the precipitation and maintenance of affective disorders.published_or_final_versio

Decoherence and Relaxation of a Quantum Bit in the Presence of Rabi Oscillations

Dissipative dynamics of a quantum bit driven by a strong resonant field and interacting with a heat bath is investigated. We derive generalized Bloch equations and find modifications of the qubit's damping rates caused by Rabi oscillations. Nonequilibrium decoherence of a phase qubit inductively coupled to a LC-circuit is considered as an illustration of the general results. It is argued that recent experimental results give a clear evidence of effective suppression of decoherence in a strongly driven flux qubit.Comment: 14 pages; misprints correcte

Cosmic Evolution in Brans-Dicke Chameleon Cosmology

We have investigated the Brans-Dicke Chameleon theory of gravity and obtained exact solutions of the scale factor $a(t)$, scalar field $\phi(t)$, an arbitrary function $f(\phi)$ which interact with the matter Lagrangian in the action of the Brans-Dicke Chameleon theory and potential $V(\phi)$ for different epochs of the cosmic evolution. We plot the functions $a(t)$, $\phi(t)$, $f(t)$ and $V(\phi)$ for different values of the Brans-Dicke parameter. In our models, there is no accelerating solution, only decelerating one with $q>0$. The physical cosmological distances have been investigated carefully. Further the statefinder parameters pair and deceleration parameter are discussed.Comment: To be appear in "The European Physical Journal - Plus (EPJ Plus)",Extended version,15 pages, 17eps figure

Correlation between centrality metrics and their application to the opinion model

In recent decades, a number of centrality metrics describing network properties of nodes have been proposed to rank the importance of nodes. In order to understand the correlations between centrality metrics and to approximate a high-complexity centrality metric by a strongly correlated low-complexity metric, we first study the correlation between centrality metrics in terms of their Pearson correlation coefficient and their similarity in ranking of nodes. In addition to considering the widely used centrality metrics, we introduce a new centrality measure, the degree mass. The m order degree mass of a node is the sum of the weighted degree of the node and its neighbors no further than m hops away. We find that the B_{n}, the closeness, and the components of x_{1} are strongly correlated with the degree, the 1st-order degree mass and the 2nd-order degree mass, respectively, in both network models and real-world networks. We then theoretically prove that the Pearson correlation coefficient between x_{1} and the 2nd-order degree mass is larger than that between x_{1} and a lower order degree mass. Finally, we investigate the effect of the inflexible antagonists selected based on different centrality metrics in helping one opinion to compete with another in the inflexible antagonists opinion model. Interestingly, we find that selecting the inflexible antagonists based on the leverage, the B_{n}, or the degree is more effective in opinion-competition than using other centrality metrics in all types of networks. This observation is supported by our previous observations, i.e., that there is a strong linear correlation between the degree and the B_{n}, as well as a high centrality similarity between the leverage and the degree.Comment: 20 page

Quantum information processing with superconducting qubits in a microwave field

We investigate the quantum dynamics of a Cooper-pair box with a superconducting loop in the presence of a nonclassical microwave field. We demonstrate the existence of Rabi oscillations for both single- and multi-photon processes and, moreover, we propose a new quantum computing scheme (including one-bit and conditional two-bit gates) based on Josephson qubits coupled through microwaves.Comment: 7 pages, 1 figur