On computing fixpoints in well-structured regular model checking, with applications to lossy channel systems

We prove a general finite convergence theorem for "upward-guarded" fixpoint expressions over a well-quasi-ordered set. This has immediate applications in regular model checking of well-structured systems, where a main issue is the eventual convergence of fixpoint computations. In particular, we are able to directly obtain several new decidability results on lossy channel systems.Comment: 16 page

Space-Frequency Equalization for Broadband Single Carrier MIMO Systems

In this paper, a frequency domain (FD) receiver architecture implemented using estimated channel parameters is derived for broadband single carrier modulations. Co-channel and inter-symbol interferences are compensated by a minimum mean squared error based integrated space-frequency-equalizer (SFE) using the estimated parameters. The integrated SFE in the FD consists of coupled FIR structures, that are jointly optimized by maximizing the desired signal to interference plus noise ratio. We develop analytical expressions and present simulation results for the integrated SFE. Simulation results demonstrate that excellent receiver performance is achieved even for channels with large ISI spans. The proposed SC-SFE outperforms previous layered space frequency (LSF) receivers with imperfect channel knowledge. Further, the parallel receiver architecture yields equal diversity gains to all data streams without the error propagation that is common to most LSF schemes

Improved Information Outage Rate in Certain MIMO Systems

We propose a simple class of encoding/decoding techniques which can be used to improve the information outage rate of certain multiple-input multiple-output (MIMO) systems. Gains in outage rate can be achieved at low to moderate signal to noise ratios in MIMO systems which have fewer receive antennas than transmit antennas. This performance improvement is due to extra ``virtual'' receive antennas which are created with low complexity signal processing. A simple space-time block code system using virtual receive antennas is also investigated

Cooperative Relaying with CPFSK and Distributed Space-Time Trellis Codes

Cooperative relaying allows single antenna users to achieve diversity and coding gains by utilizing nearby users' transmitting capabilities. We consider a relay system employing constant envelope continuous phase frequency shift keying. Distributed space-time trellis codes are implemented with a novel multiple relay protocol

Cooperative Relaying with CPFSK and Distributed Space-Time Trellis Codes

Cooperative relaying allows single antenna users to achieve diversity and coding gains by utilizing nearby users' transmitting capabilities. We consider a relay system employing constant envelope continuous phase frequency shift keying. Distributed space-time trellis codes are implemented with a novel multiple relay protocol

Two-user Cooperative Transmission Using Superposition Modulation and Soft Information Combining

We propose a cooperative transmission scheme for two users with one common relay using superposition modulation. It uses distributed Turbo codes (DTCs) for each user. The relay always decodes, then interleaves and re-encodes the decoded data. A new packet is formed by combining the re-encoded packets from both users using superposition modulation. This packet is forwarded to the destination with the average receive SNRs of each user. The destination uses the cooperative Turbo decoder of [1] to improve performance. Simulation results show the proposed scheme outperforms XOR based schemes and is simple to implement

Peter Waterman and T-Matrix Methods

This paper summarizes the scientific legacy of Peter C. Waterman (1928-2012) who introduced concepts and theoretical techniques that have had a major impact on the fields of scattering by particles and particle groups, optical particletcharacterization, radiative transfer, and remote sensing. A biographical sketch is also included

Hypersingular integral equations over a disc: Convergence of a spectral method and connection with Tranter's method

Two-dimensional hypersingular equations over a disc are considered. A spectral method is developed, using Fourier series in the azimuthal direction and orthogonal polynomials in the radial direction. The method is proved to be convergent. Then, Tranter's method is discussed. This method was devised in the 1950s to solve certain pairs of dual integral equations. It is shown that this method is also convergent because it leads to the same algebraic system as the spectral method

Multiple scattering by random configurations of circular cylinders: second-order corrections for the effective wavenumber

A formula for the effective wavenumber in a dilute random array of identical scatterers in two dimensions is derived, based on Lax's quasi-crystalline approximation. This formula replaces a widely-used expression due to Twersky, which is shown to be based on an inappropriate choice of pair-correlation function

Dynamics of avian species and functional diversity in secondary tropical forests

Deforestation for agriculture in the tropics, followed by abandonment, has resulted in large areas of secondary forest. Some authors have suggested that this secondary regrowth could help prevent mass extinction in the tropics by providing habitat for forest species. However, there is little generalised understanding of the biodiversity value of secondary forest. To address this knowledge gap, we conducted an analysis of avian responses to secondary forest succession, comparing data from 44 tropical secondary forest sites with nearby primary forest sites and investigating both species and functional diversity based metrics. Total species richness in secondary forests was 12% lower than in primary forests and was not related to secondary forest age. In contrast, forest specialist species richness increased with time since disturbance, reaching 99% of primary forest values after 100 years. In terms of functional diversity, functional dispersion (FDis) and functional divergence (FDiv) were similar in primary and secondary forests. However, functional evenness (FEve) was 5% higher in secondary than in primary forests. The standardized effect size of functional diversity (sesFD) was higher in young secondary forests than primary forests and declined with time since disturbance. Overall, these results suggest that secondary tropical forests can support provision of ecosystem services but that these services may be less stable in young forests. Therefore, secondary tropical forests, particularly older regrowth, have biodiversity value and can support important ecosystem functions. These secondary forests should be protected from further disturbance but preserving primary forest is vital for supporting overall and forest specialist species richness