91 research outputs found
An overview of optimal and sub-optimal detection techniques for a non orthogonal spectrally efficient FDM
Spectrally Efficient non orthogonal Frequency Division Multiplexing (SEFDM) Systems occupy less bandwidth than equivalent orthogonal FDM (OFDM). However, enhanced spectral efficiency comes at the expense of an increased complexity in the signal detection. In this work, we present an overview of different detection techniques that trade the error performance optimality for the signal recovery computational effort. Linear detection methods like Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE) offer fixed complexity but suffer from a significant degradation of the Bit Error Rate (BER). On the other hand optimal receivers like Sphere Decoders (SD) achieve the optimal solution in terms of error performance. Notwithstanding, their applicability is severely constrained by the SEFDM signal dimension, the frequency separation between the carriers as well as the noise level in the system
Spectrally efficient multicarrier communication systems: signal detection, mathematical modelling and optimisation
This thesis considers theoretical, analytical and engineering design issues relating
to non-orthogonal Spectrally Efficient Frequency Division Multiplexing (SEFDM)
communication systems that exhibit significant spectral merits when compared to Orthogonal
FDM (OFDM) schemes. Alas, the practical implementation of such systems
raises significant challenges, with the receivers being the bottleneck.
This research explores detection of SEFDM signals. The mathematical foundations
of such signals lead to proposals of different orthonormalisation techniques as required
at the receivers of non-orthogonal FDM systems. To address SEFDM detection, two
approaches are considered: either attempt to solve the problem optimally by taking
advantage of special cases properties or to apply sub-optimal techniques that offer reduced
complexities at the expense of error rates degradation. Initially, the application
of sub-optimal linear detection techniques, such as Zero Forcing (ZF) and Minimum
Mean Squared Error (MMSE), is examined analytically and by detailed modelling. To
improve error performance a heuristic algorithm, based on a local search around an
MMSE estimate, is designed by combining MMSE with Maximum Likelihood (ML)
detection. Yet, this new method appears to be efficient for BPSK signals only. Hence,
various variants of the sphere decoder (SD) are investigated. A Tikhonov regularised
SD variant achieves an optimal solution for the detection of medium size signals in
low noise regimes. Detailed modelling shows the SD detector to be well suited to the
SEFDM detection, however, with complexity increasing with system interference and
noise. A new design of a detector that offers a good compromise between computational
complexity and error rate performance is proposed and tested through modelling
and simulation. Standard reformulation techniques are used to relax the original optimal
detection problem to a convex Semi-Definite Program (SDP) that can be solved
in polynomial time. Although SDP performs better than other linear relaxations, such
as ZF and MMSE, its deviation from optimality also increases with the deterioration
of the system inherent interference. To improve its performance a heuristic algorithm
based on a local search around the SDP estimate is further proposed. Finally, a modified
SD is designed to implement faster than the local search SDP concept. The new
method/algorithm, termed the pruned or constrained SD, achieves the detection of
realistic SEFDM signals in noisy environments
A practical system for improved efficiency in frequency division multiplexed wireless networks
Spectral efficiency is a key design issue for all wireless communication systems. Orthogonal frequency division multiplexing (OFDM) is a very well-known technique for efficient data transmission over many carriers overlapped in frequency. Recently, several studies have appeared that describe spectrally efficient variations of multi-carrier systems where the condition of orthogonality is dropped. Proposed techniques suffer from two weaknesses: firstly, the complexity of generating the signal is increased. Secondly, the signal detection is computationally demanding. Known methods suffer either unusably high complexity or high error rates because of the inter-carrier interference. This study addresses both problems by proposing new transmitter and receiver architectures whose design is based on using the simplification that a rational spectrally efficient frequency division multiplexing (SEFDM) system can be treated as a set of overlapped and interleaving OFDM systems. The efficacy of the proposed designs is shown through detailed simulation of systems with different signal types and carrier dimensions. The decoder is heuristic but in practice produces very good results that are close to the theoretical best performance in a variety of settings. The system is able to produce efficiency gains of up to 20% with negligible impact on the required signal-to-noise ratio
Light-Induced Reversible DNA Ligation of Gold Nanoparticle Superlattices
DNA-mediated self-assembly of nanoparticles has been of great interest because it enables access to nanoparticle superstructures that cannot be synthesized otherwise. However, the programmability of higher order nanoparticle structures can be easily lost under DNA denaturing conditions. Here, we demonstrate that light can be employed as an external stimulus to master the stability of nanoparticle superlattices (SLs) via the promotion of a reversible photoligation of DNA in SLs. The oligonucleotides attached to the nanoparticles are encoded to ligate using 365 nm light, effectively locking the SLs and rendering them stable under DNA denaturing conditions. The reversible process of unlocking these structures is possible by irradiation with light at 315 nm, recovering the structures to their natural state. Our work inspires an alternative research direction toward postassembly manipulation of nanoparticle superstructures using external stimuli as a tool to enrich the library of additional material forms and their application in different media and environments
Vrabas. The Effect of Natural and Artificial Grass on Sprinting Performance in Young Soccer Players
Abstract: The sprint performance on natural and artificial grass of 5 th generation was assessed. Sixty eight young male soccer players, which were divided in two groups according to their age [children (n=36; 12.1±0.5y) and adolescents (n=32; 14.2±0.4y)], performed 30-m sprint tests with and without handling the ball on natural and artificial grass. The performance was recorded during 0-10m, 10-30m, and 0-30m running distances. It was found that children were significantly faster during 0-10m running distance on the artificial compared to natural grass when handling the ball while adolescents revealed no differences in sprint performance between the surfaces irrespectively of the ball condition. In running distances 10-30m and 0-30m, children were significant faster in the artificial compared to the natural grass either with or without ball, while the adolescents were significantly faster in the artificial grass only without handling the ball. Children run faster on artificial than natural grass while adolescent soccer players are faster in artificial grass when they do not have to handle the ball. It is clear that children should be more careful when play soccer on artificial grass because the ball is moving faster and greater skill is needed in order to avoid injuries
PEG Branched Polymer for Functionalization of Nanomaterials with Ultralong Blood Circulation
Nanomaterials have been actively pursued for biological and medical
applications in recent years. Here, we report the synthesis of several new
poly(ethylene glycol) grafted branched-polymers for functionalization of
various nanomaterials including carbon nanotubes, gold nanoparticles (NP) and
gold nanorods (NRs), affording high aqueous solubility and stability for these
materials. We synthesize different surfactant polymers based upon
poly-(g-glutamic acid) (gPGA) and poly(maleic anhydride-alt-1-octadecene)
(PMHC18). We use the abundant free carboxylic acid groups of gPGA for attaching
lipophilic species such as pyrene or phospholipid, which bind to nanomaterials
via robust physisorption. Additionally, the remaining carboxylic acids on gPGA
or the amine-reactive anhydrides of PMHC18 are then PEGylated, providing
extended hydrophilic groups, affording polymeric amphiphiles. We show that
single-walled carbon nanotubes (SWNTs), Au NPs and NRs functionalized by the
polymers exhibit high stability in aqueous solutions at different pHs, at
elevated temperatures and in serum. Morever, the polymer-coated SWNTs exhibit
remarkably long blood circulation (t1/2 22.1 h) upon intravenous injection into
mice, far exceeding the previous record of 5.4 h. The ultra-long blood
circulation time suggests greatly delayed clearance of nanomaterials by the
reticuloendothelial system (RES) of mice, a highly desired property for in vivo
applications of nanomaterials, including imaging and drug delivery
Potentiating angiogenesis arrest in vivo via laser irradiation of peptide functionalised gold nanoparticles
Inorganic hierarchical nanostructures induced by concentration difference and gradient
A practical system for improved efficiency in frequency division multiplexed wireless networks
Analysis of Sub-optimum detection techniques for a bandwidth efficient multi-carrier communication system.
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