Opportunistic Interference Alignment in MIMO Interference Channels

We present two interference alignment techniques such that an opportunistic point-to-point multiple input multiple output (MIMO) link can reuse, without generating any additional interference, the same frequency band of a similar pre-existing primary link. In this scenario, we exploit the fact that under power constraints, although each radio maximizes independently its rate by water-filling on their channel transfer matrix singular values, frequently, not all of them are used. Therefore, by aligning the interference of the opportunistic radio it is possible to transmit at a significant rate while insuring zero-interference on the pre-existing link. We propose a linear pre-coder for a perfect interference alignment and a power allocation scheme which maximizes the individual data rate of the secondary link. Our numerical results show that significant data rates are achieved even for a reduced number of antennas.Comment: To appear in proc. IEEE PIMRC 2008 - Workshop in Emerging Network Perspectives in Multiuser and Cooperative MIMO (NWMIMO). 5 pages and 4 figure

Performance Evaluation of an Actuator Dust Seal for Lunar Operation

Exploration of extraterrestrial surfaces (e.g. moon, Mars, asteroid) will require durable space mechanisms that will survive potentially dusty surface conditions in addition to the hard vacuum and extreme temperatures of space. Baseline tests with lunar simulant were recently completed at NASA GRC on a new Low-Temperature Mechanism (LTM) dust seal for space actuator application. Following are top-level findings of the tests completed to date in vacuum using NU-LHT-2M lunar-highlands simulant. A complete set of findings are found in the conclusions section.Tests were run at approximately 10-7 torr with unidirectional rotational speed of 39 RPM.Initial break-in runs were performed at atmospheric conditions with no simulant. During the break-in runs, the maximum torque observed was 16.7 lbf-in. while the maximum seal outer diameter temperature was 103F. Only 0.4 milligrams of NU-LHT-2M simulant passed through the sealshaft interface in the first 511,000 cycles while under vacuum despite a chip on the secondary sealing surface.Approximately 650,000 of a planned 1,000,000 cycles were completed in vacuum with NU-LHT-2M simulant.Upon test disassembly NU-LHT-2M was found on the secondary sealing surface

Clearing the Rf Smog: Making 802.11 Robust to Cross-Technology Interference

Recent studies show that high-power cross-technology interference is becoming a major problem in today’s 802.11 networks. Devices like baby monitors and cordless phones can cause a wireless LAN to lose connectivity. The existing approach for dealing with such high-power interferers makes the 802.11 network switch to a different channel; yet the ISM band is becoming increasingly crowded with diverse technologies, and hence many 802.11 access points may not find an interference-free channel. This paper presents TIMO, a MIMO design that enables 802.11n to communicate in the presence of high-power cross-technology interference. Unlike existing MIMO designs, however, which require all concurrent transmissions to belong to the same technology, TIMO can exploit MIMO capabilities to decode in the presence of a signal from a different technology, hence enabling diverse technologies to share the same frequency band. We implement a prototype of TIMO in GNURadio-USRP2 and show that it enables 802.11n to communicate in the presence of interference from baby monitors, cordless phones, and microwave ovens, transforming scenarios with a complete loss of connectivity to operational networks.National Science Foundation (U.S.) (NSF grant CNS-0831660)National Science Foundation (U.S.) (NSF grant CNS- 0721857)United States. Defense Advanced Research Projects Agency (DARPA ITMANET

A new unifying account of the roles of neuronal entrainment

Rhythms are a fundamental and defining feature of neuronal activity in animals including humans. This rhythmic brain activity interacts in complex ways with rhythms in the internal and external environment through the phenomenon of ‘neuronal entrainment’, which is attracting increasing attention due to its suggested role in a multitude of sensory and cognitive processes. Some senses, such as touch and vision, sample the environment rhythmically, while others, like audition, are faced with mostly rhythmic inputs. Entrainment couples rhythmic brain activity to external and internal rhythmic events, serving fine-grained routing and modulation of external and internal signals across multiple spatial and temporal hierarchies. This interaction between a brain and its environment can be experimentally investigated and even modified by rhythmic sensory stimuli or invasive and non-invasive neuromodulation techniques. We provide a comprehensive overview of the topic and propose a theoretical framework of how neuronal entrainment dynamically structures information from incoming neuronal, bodily and environmental sources. We discuss the different types of neuronal entrainment, the conceptual advances in the field, and converging evidence for general principles

Mathematical optimization techniques for resource allocation and spatial multiplexing in spectrum sharing networks

Due to introduction of smart phones with data intensive multimedia and interactive applications and exponential growth of wireless devices, there is a shortage for useful radio spectrum. Even though the spectrum has become crowded, many spectrum occupancy measurements indicate that most of the allocated spectrum is underutilised. Hence radically new approaches in terms of allocation of wireless resources are required for better utilization of radio spectrum. This has motivated the concept of opportunistic spectrum sharing or the so-called cognitive radio technology that has great potential to improve spectrum utilization. The cognitive radio technology allows an opportunistic user namely the secondary user to access the spectrum of the licensed user (known as primary user) provided that the secondary transmission does not harmfully affect the primary user. This is possible with the introduction of advanced resource allocation techniques together with the use of wireless relays and spatial diversity techniques. In this thesis, various mathematical optimization techniques have been developed for the efficient use of radio spectrum within the context of spectrum sharing networks. In particular, optimal power allocation techniques and centralised and distributed beamforming techniques have been developed. Initially, an optimization technique for subcarrier and power allocation has been proposed for an Orthogonal Frequency Division Multiple Access (OFDMA) based secondary wireless network in the presence of multiple primary users. The solution is based on integer linear programming with multiple interference leakage and transmission power constraints. In order to enhance the spectrum efficiency further, the work has been extended to allow multiple secondary users to occupy the same frequency band under a multiple-input and multiple-output (MIMO) framework. A sum rate maximization technique based on uplink-downlink duality and dirty paper coding has been developed for the MIMO based OFDMA network. The work has also been extended to handle fading scenarios based on maximization of ergodic capacity. The optimization techniques for MIMO network has been extended to a spectrum sharing network with relays. This has the advantage of extending the coverage of the secondary network and assisting the primary network in return for the use of the primary spectrum. Finally, instead of considering interference mitigation, the recently emerged concept of interference alignment has been used for the resource allocation in spectrum sharing networks. The performances of all these new algorithms have been demonstrated using MATLAB based simulation studies

Microtopography and stretch activated mechanotransduction in dermal fibroblasts and epithelia

Mechanical forces are key contributors to regulating cell function, development, homeostatic turnover, and repair of tissues. To date, the dynamic interactions between cell mechanics and their microenvironment. This study aims to reproduce a biomaterial scaffold that can carry dermal fibroblast and/or epithelia, combined with applied tissue engineering approaches to manipulate the mechanosensitive elements of cells to function for skin regeneration and wound healing. The major focus of this study provide insight into the mechanisms underlying the deformation of cell nuclei which have an impact on transcription factor control, cell memory, and behaviours. In an attempt to offer an effective biocompatible scaffold, one particular challenge lies in the delivery of functional mechanical stimuli to potential translational outcomes and promote regenerative characteristics of skin grafting and wound healing. This research project highlights how mechanical and biochemical microenvironments link the nuclear reorganization which reflects to functional consequences under mechanical regulation, imposed on nuclear overall shape and transcriptional activities. Two ways of delivering mechanical signals have been used to convey force to nuclear regulation which connect to the cytoskeleton and/or nucleoskeleton including; I) Externally applied force applications to activate cell growth or motility, with active stretch via microtopographic patterns and loading passive stretch by pulling on the cells. II) Adjusting nuclear force internally via the expression and activity of nuclear membrane proteins (i.e. emerin and binding partners; lamin A/C and BAF). The read-out of measuring at the end of dynamic changes in actin polymerisation direct to the nuclear entry of mechanosensitive transcription factor (TF), myocardin-related factor A (MRTF-A) have been addressed. As a result of the response of dermal fibroblasts to mechanical stimuli, immunofluorescent staining of n/c ratio showed that have significant enhanced nuclear import of MRTF-A by~2.0-fold and ~1.3-fold increased subjected to 4.2% unidirectional stretch and 5% cyclic stretch (0.05Hz, 90°grooves), respectively. However, the cells under lower mechanical force promoted the nuclear export of MRTF-A. Immunoblot results revealed that nuclear accumulation of MRTF-A in cell-lacking emerin to the range between 0.3-fold to 0.5-fold decreased confirmed by two knockout clones. The impact of reduced mechanical tension contributes to the nuclear mechanical properties and histone modification. Assessing the alteration of acetylation status of histones via HDAC3 gene expression was examined using real-time qPCR, with a significant decrease of half expression in knockout models of emerin both in BJ1 and HEK293 cells. With the stated results, the analysis of cell-induced environment deformations can imply chromatin remodelling and thus regulate cell behaviours. Increased mechanical properties lead to chromatin condensation and influence on cell contractility or even differentiation while, low mechanical forces link to chromatin unfold or decondensation with hyperproliferation. To conclude, this study represents the cell-based tissue-engineered platform which improved delivery via a biocompatible scaffold to offer an alternative artificial tissue layer for enhancing translational qualities in skin regeneration and wound healing. The results suggest condition favours with dynamic microenvironment to regulate cell behaviour specified to mechanical properties for cell contraction or proliferation. In addition to this, the work illustrates how mechanotransduction of cells sense and convert mechanical signals into changes in intracellular biochemistry and nuclear regulation including transcription factor translocation, TF activity, and chromatin reorganisation