All or Nothing at All

We continue a study of unconditionally secure all-or-nothing transforms (AONT) begun in \cite{St}. An AONT is a bijective mapping that constructs s outputs from s inputs. We consider the security of t inputs, when s-t outputs are known. Previous work concerned the case t=1; here we consider the problem for general t, focussing on the case t=2. We investigate constructions of binary matrices for which the desired properties hold with the maximum probability. Upper bounds on these probabilities are obtained via a quadratic programming approach, while lower bounds can be obtained from combinatorial constructions based on symmetric BIBDs and cyclotomy. We also report some results on exhaustive searches and random constructions for small values of s.Comment: 23 page

A frequency reconfigurable multiband patch antenna for wireless applications

Copyright @ 2011 IEE

Widely tunable multiband reconfigurable patch antenna for wireless applications

The official published version can be obtained from the link below - Copyright @ EuCAP 2010A design of a low profile reconfigurable microstrip patch antenna is presented. The antenna consists of four suppatches connected to one feed line, each sub-patch generates a single band. By placing a variable capacitor at the input of the sub-patches, the impedance matching frequency of the antenna can be tuned over a wide range starting from 0.92 GHz to 2.98 GHz with total tunability rang of 2060 MHz. The proposed antenna designed to operate in the Global System for Mobile communication (GSM900, 880-960 MHz)/ Digital Communication System (DCS1800, 1710-1880 MHz)/ Universal Mobile Telecommunication System (UMTS, 1920-2170 MHz)/ Wireless Local Area Network (WLAN, 2400-2483.5 MHz)/ and Worldwide Interoperability for Microwave Access (WiMAX, 2495-2700 MHz). The total size of the proposed antenna is 50 x 50 mm2 which is suitable for small wireless devices

A reconfigurable H-shape antenna for wireless applications

The official published version of this article can be obtained from the link below - Copyright @ EuCAP2010This paper presents a novel H-Shaped reconfigurable microstrip patch antenna fed by a Grounded Coplanar Waveguide (GCPW) for wireless applications. The uniqueness in the presented antenna design relies in the ability to select the number of operating frequencies electronically by using a varactor diode. The antenna structure consists of coplanar waveguide (CPW) input with an H-shape printed on a PCB and a varactor diode for reconfigurability. By electronically varying the value of the diode capacitance, the antenna can operate in a single band mode to cover Global Position System (GPS), a dual band mode to cover GPS and Global System for Mobile communications (GSM1900) or a three-band mode to cover GPS, GSM1900 and Bluetooth or Wireless Local Area Networks (WLAN)

A reconfigurable CPW antenna for GPS, GSM and WLAN applications

Copyright @ 2011 IEEEMultiband reconfigurable antennas are receiving increasing importance in modern wireless communication systems supporting multiservice applications. The main advantage is the reduction in the size of wireless devices and allowing more space for other electronic components to be fitted. A widely tunable antenna using PIN switches was presented in [1]. Reconfigurable multiband antennas for wireless systems including satellite and terrestrial applications were reported in [2, 3]. This paper presents a new technique to electrically control the resonant frequencies by using a varactor diode. The antenna has an H-shape structure fed by a coplanar waveguide (CPW). It can generate and control up to three resonant frequencies to be used in GPS, GSM and Bluetooth/WLAN applications

Design and Measurements of a Five Independent Band Patch Antenna for Different Wireless Applications

This paper presents the design of a compact microstrip patch antenna with the ability of controlling the number of bands and the operating frequencies independently. Numerical equations are derived using a curve fitting technique to obtain the centre frequency of each band. The antenna comprises a main patch and four sub-patches fed by a 50 microstrip line. It is designed to generate up to five separate modes to cover the frequency range from 900MHz to 3GHz for the operation of wireless devices supporting multiple standards including Global System for Mobile communication (GSM900, 880-960 MHz), Digital Communication System (DCS1800, 1710-1880 MHz), Universal Mobile Telecommunication System (UMTS, 1920-2170 MHz), Wireless Local Area Network (WLAN, 2400-2483.5 MHz) and low band Worldwide Interoperability for Microwave Access (WIMAX, 2.5 to 2.8 GHz).NPL SMART chamber were supported by the Measurements for Innovators (MFI) program and the National Measurement Office, an Executive Agency of the Department for Business, Innovation and Skill

A reconfigurable wideband and multiband antenna using dual-patch elements for compact wireless devices

This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 IEEEA reconfigurable wideband and multiband C-Slot patch antenna with dual-patch elements is proposed and studied. It occupies a compact volume of 50 × 50 × 1.57 (3925 mm3), including the ground plane. The antenna can operate in two dual-band modes and a wideband mode from 5 to 7 GHz. Two parallel C-Slots on the patch elements are employed to perturb the surface current paths for excitation of the dual-band and the wideband modes. Two switches, implemented using PIN diodes, are placed on the connecting lines of a simple feed network to the patch elements. Dual-band modes are achieved by switching “ON” either one of the two patch elements, while the wideband mode with an impedance bandwidth of 33.52% is obtained by switching “ON” both patch elements. The frequencies in the dual-band modes can be independently controlled using positions and dimensions of the C-Slots without affecting the wideband mode. The advantage of the proposed antenna is that two dual-band operations and one wideband operation can be achieved using the same dimensions. This overcomes the need for increasing the surface area normally incurred when designing wideband patch antennas. Simulation results are validated experimentally through prototypes. The measured radiation patterns and peak gains show stable responses and are in good agreements. Coupling between the two patch elements plays a major role for achieving the wide bandwidth and the effects of mutual coupling between the patch elements are also studied

Measurements, processing functions and laboratory test-bed experiments for evaluating diversity in broadcast network

This paper presents a test-bed development and measurement plan for evaluating transmit diversity and on-channel repeaters in the Digital Video Broadcasting Network. Transmit diversity reduces the complexity and improves the power consumption of the personal receiving devices by enhancing the transmission of signals in NLOS cluttered environments. It is more practical than receive diversity due to the difficulty of locating two receive antennas far enough apart in a small mobile device. The on-channel repeater is to extend the coverage of the DVB-T/H network in areas where services are inaccessible by receiving the DVB-T/H signals off air, amplifying and then retransmitting it on the same frequency as received. Test service scenarios were developed to illustrate the benefits of such technologies so that effectiveness can be researched in a variety of service and terrain scenarios using purpose built test systems.The work presented in this paper was supported by the European Commission IST project PLUTO

Correlations in randomly stacked solids

Packing of spheres is a problem with a long history dating back to Kepler's conjecture in 1611. The highest density is realized in face-centred-cubic (FCC) and hexagonal-close-packed (HCP) arrangements. These are only limiting examples of an infinite family of maximal-density structures called Barlow stackings. They are constructed by stacking triangular layers, with each layer shifted with respect to the one below. At the other extreme, Torquato-Stillinger stackings are believed to yield the lowest possible density while preserving mechanical stability. They form an infinite family of structures composed of stacked honeycomb layers. In this article, we characterize layer-correlations in both families when the stacking is random. To do so, we take advantage of the H\"agg code -- a mapping between a Barlow stacking and a one-dimensional Ising magnet. The layer-correlation is related to a moment-generating function of the Ising model. We first determine the layer-correlation for random Barlow stacking, finding exponential decay. We next introduce a bias favouring one of two stacking-chiralities -- equivalent to a magnetic field in the Ising model. Although this bias favours FCC ordering, there is no long-ranged order as correlations still decay exponentially. Finally, we consider Torquato-Stillinger stackings, which map to a combination of an Ising magnet and a three-state Potts model. With random stacking, the correlations decay exponentially with a form that is similar to the Barlow problem. We discuss relevance to ordering in clusters of stacked solids and for layer-deposition-based synthesis methods.Comment: 6 page