Adaptive blind channel equalization based on constellation information of MPSK signal

In this paper, we propose a new adaptive algorithm for the blind equalization of an FIR (finite impulse response) channel excited by an M-ary phase shift keying (MPSK) signal. Different from the conventional constant modulus algorithm (CMA), which exploits the amplitude information of the input signal, the proposed algorithm exploits the full constellation information of the input signal. Theoretical analysis shows that the new algorithm has less mean square error (MSE), namely better equalization performance, in steady state than the CMA. Numerical simulations show the effectiveness of the new algorithm

Differential encoding technique for multi-antenna systems with correlated Rayleigh fading channels

Differential space-time modulation (DSTM) techniques developed for multi-antenna systems allow the receiver to detect the transmitted signal without the knowledge of the fading channels. It can be viewed as an extension of differential phase-shift keying (DPSK) in single antenna systems. In this paper, we derived the pairwise error probability upper bound of differential space-time coded systems with spatially correlated Rayleigh fading channels. Based on the performance analysis, we develop a novel DSTM scheme which can exploit the spatial correlation in the fading channels. It is found that by carefully designing the initial transmitted signal matrix, the performance of the differential space-time coded systems can be significantly improved.

Blind equalization of non-irreducible channels driven by MPSK signals

This paper deals with the problem of blind equalization of finite-impulse-response (FIR) and multiple-input multiple-output (MIMO) channels excited by M-ary phase shift keying (MPSK) signals. It is known that the algorithms based on the constant modulus (CM) criterion can equalize an FIR MIMO channel that is irreducible. The irreducible condition is restrictive since it requires that all source signals arrive at the receiving antennas simultaneously. In this paper, we show that the CM criterion can also be used to construct a zero-forcing equalizer for a channel that is non-irreducible. We also derive a lower bound for the order of the equalizer. The proposed result is validated by numerical simulations.

A new blind-equalization algorithm for an FIR SIMO system driven by MPSK signal

We consider the problem of blind equalization of a finite impulse response and single-input multiple-output system driven by an M-ary phase-shift-keying signal. The existing single-mode algorithms for this problem include the constant modulus algorithm (CMA) and the multimodulus algorithm (MMA). It has been shown that the MMA outperforms the CMA when the input signal has no more than four constellation points, i.e., Mles4. In this brief, we present a new adaptive equalization algorithm that jointly exploits the amplitude and phase information of the input signal. Theoretical analysis shows that the proposed algorithm has less mean square error, i.e., better equalization performance, at steady state than the CMA regardless of the value of M. The superior performance of our algorithm to the CMA and the MMA is validated by simulation examples

Climate change impacts and adaptation in Bangladesh : an agent-based approach

Bangladesh exemplifies the complex challenges facing densely populated coastal regions. The
pressures on the country are immense: around 145 million people live within an area of just 145,000 sq-km at
the confluence of three major river systems: the Ganges, the Brahmaputra and the Meghna. While progress
has been made, poverty remains widespread, with around 39% of children under five malnourished. Most of
its land-mass lies below 10m above sea level with considerable areas at sea level, leading to frequent and
prolonged flooding during the monsoons. Sea level rise is leading to more flooding as storm surges rise off
higher sea levels, pushing further inland. Higher sea levels also result in salt-water intrusion into freshwater
coastal aquifers and estuaries, contaminating drinking water and farmland. Warmer ocean waters are also
expected to lead to an increase in the intensity of tropical storms.
Bangladesh depends on the South Asian summer monsoon for most of its rainfall which is expected to
increase, leading to more flooding. Climate scientists are also concerned about the stability of monsoon and
the potential for it to undergo a nonlinear phase shift to a drier regime. Bangladesh faces an additional
hydrological challenge in that the Ganges and Brahmaputra rivers both rise in the Himalaya-Tibetan Plateau
region, where glaciers are melting rapidly. The Intergovernmental Panel on Climate Change (IPCC)
concluded that rapid melting is expected to increase river flows until around the late-2030s, by which time
the glaciers are expected to have shrunk from their 1995 extent of 500,000 sq-km to an expected 100,000 sqkm.
After the 2030s, river flows could drop dramatically, turning the great glacier-fed rivers of Asia into
seasonal monsoon-fed rivers. The IPCC concluded that as a result, water shortages in Asia could affect more
than a billion people by the 2050s. Over the same period, crop yields are expected to decline by up to 30% in
South Asia due to a combination of drought and crop heat stress. Bangladesh is therefore likely to face
substantial challenges in the coming decades.
In order to adequately understand the complex, dynamic, spatial and nonlinear challenges facing Bangladesh,
an integrated model of the system is required. An agent-based model (ABM) permits the dynamic
interactions of the economic, social, political, geographic, environmental and epidemiological dimensions of
climate change impacts and adaptation policies to be integrated via a modular approach. Integrating these
dimensions, including nonlinear threshold events such as mass migrations, or the outbreak of conflicts or
epidemics, is possible to a far greater degree with an ABM than with most other approaches.
We are developing a prototype ABM, implemented in Netlogo, to examine the dynamic impacts on poverty,
migration, mortality and conflict from climate change in Bangladesh from 2001 to 2100. The model employs
GIS and sub-district level census and economic data and a coarse-graining methodology to allow model
statistics to be generated on a national scale from local dynamic interactions. This approach allows a more
realistic treatment of distributed spatial events and heterogeneity across the country. The aim is not to
generate precise predictions of Bangladesh’s evolution, but to develop a framework that can be used for
integrated scenario exploration. This paper represents an initial report on progress on this project. So far the
prototype model has demonstrated the desirability and feasibility of integrating the different dimensions of
the complex adaptive system and, once completed, is intended to be used as the basis for a more detailed
policy-oriented model.

Seasonal periodicity of serum vitamin D and parathyroid hormone, bone resorption, and fractures : the Geelong Osteoporosis Study

In this population-based study, seasonal periodicity was seen with reduced serum vitamin D, increased serum PTH, and increased bone resorption in winter. This was associated with an increased proportion of falls resulting in fracture and an increased risk of wrist and hip fractures.

Introduction: In a population of women who reside in a temperate climate and do not generally receive dietary vitamin D supplementation, we investigated whether seasonal vitamin D insufficiency is associated with increased risk of fracture.

Materials and Methods: An observational, cross-sectional, population-based study set in southeastern Australia (latitude 38–39° S). Participants were drawn from a well-defined community of 27,203 women ≥55 years old: 287 randomly selected from electoral rolls, 1635 with incident fractures, and 1358 presenting to a university hospital with falls. The main outcome measures were annual periodicities of ultraviolet radiation, serum 25-hydroxyvitamin D [25(OH)D], serum parathyroid hormone (PTH), serum C-telopeptide (CTx), BMD, falls, and fractures.

Results: Cyclic variations in serum 25(OH)D lagged 1 month behind ultraviolet radiation, peaking in summer and dipping in winter (p < 0.001). Periodicity of serum PTH was the inverse of serum 25(OH)D, with a phase shift delay of 1 month (p = 0.004). Peak serum CTx lagged peak serum PTH by 1–2 months. In late winter, a greater proportion of falls resulted in fracture (p < 0.001). Seasonal periodicity in 439 hip and 307 wrist fractures also followed a simple harmonic model (p = 0.078 and 0.002, respectively), peaking 1.5–3 months after the trough in 25(OH)D.

Conclusions: A fall in 25(OH)D in winter is accompanied by increases in (1) PTH levels, (2) bone resorption, (3) the proportion of falls resulting in fracture, and (4) the frequency of hip and wrist fracture. Whether vitamin D supplementation in winter can reduce the population burden of fractures requires further investigation.

Behavioural flexibility allows an invasive vertebrate to survive in a semi-arid environment

Plasticity or evolution in behavioural responses are key attributes of successful animal invasions. In northern Australia, the invasive cane toad (Rhinella marina) recently invaded semi-arid regions. Here, cane toads endure repeated daily bouts of severe desiccation and thermal stress during the long dry season (April-October). We investigated whether cane toads have shifted their ancestral nocturnal rehydration behaviour to one that exploits water resources during the day. Such a shift in hydration behaviour could increase the fitness of individual toads by reducing exposure to desiccation and thermal stress suffered during the day even within terrestrial shelters. We used a novel method (acoustic tags) to monitor the daily hydration behaviour of 20 toads at two artificial reservoirs on Camfield station, Northern Territory. Remarkably, cane toads visited reservoirs to rehydrate during daylight hours, with peaks in activity between 9.00 and 17.00. This diurnal pattern of rehydration activity contrasts with nocturnal rehydration behaviour exhibited by adult toads in their native geographical range and more mesic parts of Australia. Our results demonstrate that cane toads phase shift a key behaviour to survive in a harsh semi-arid landscape. Behavioural phase shifts have rarely been reported in invasive species but could facilitate ongoing invasion success.

Interplay among nocturnal activity, melatonin, corticosterone and performance in the invasive cane toad (Rhinella marinus)

Most animals conduct daily activities exclusively either during the day or at night. Here, hormones such as melatonin and corticosterone, greatly influence the synchronization or regulation of physiological and behavioral cycles needed for daily activity. How then do species that exhibit more flexible daily activity patterns, responses to ecological, environmental or life-history processes, regulate daily hormone profiles important to daily performance? This study examined the consequences of (1) nocturnal activity on diel profiles of melatonin and corticosterone and (2) the effects of experimentally increased acute melatonin levels on physiological and metabolic performance in the cane toad (Rhinella marinus). Unlike inactive captive toads that had a distinct nocturnal melatonin profile, nocturnally active toads sampled under field and captive conditions, exhibited decreased nocturnal melatonin profiles with no evidence for any phase shift. Nocturnal corticosterone levels were significantly higher in field active toads than captive toads. In toads with experimentally increased melatonin levels, plasma lactate and glucose responses following recovery post exercise were significantly different from control toads. However, exogenously increased melatonin did not affect resting metabolism in toads. These results suggest that toads could adjust daily hormone profiles to match nocturnal activity requirements, thereby avoiding performance costs induced by high nocturnal melatonin levels. The ability of toads to exhibit plasticity in daily hormone cycles, could have broad implications for how they and other animals utilize behavioral flexibility to optimize daily activities in response to natural and increasingly human mediated environmental variation.

The unintended consequences of simplifying the sea: making the case for complexity

Many over-exploited marine ecosystems worldwide have lost their natural populations of large predatory finfish and have become dominated by crustaceans and other invertebrates. Controversially, some of these simplified ecosystems have gone on to support highly successful invertebrate fisheries capable of generating more economic value than the fisheries they replaced. Such systems have been compared with those created by modern agriculture on land, in that existing ecosystems have been converted into those that maximize the production of target species. Here, we draw on a number of concepts and case-studies to argue that this is highly risky. In many cases, the loss of large finfish has triggered dramatic ecosystem shifts to states that are both ecologically and economically undesirable, and difficult and expensive to reverse. In addition, we find that those stocks left remaining are unusually prone to collapse from disease, invasion, eutrophication and climate change. We therefore conclude that the transition from multispecies fisheries to simplified invertebrate fisheries is causing a global decline in biodiversity and is threatening global food security, rather than promoting it.

Achievable rate and error performance of an amplify and forward multi-way relay network in the presence of imperfect channel estimation

In this paper, we investigate the impact of channel estimation error on the achievable common rate and error performance of amplify and forward (AF) multi-way relay networks (MWRNs). Assuming lattice codes with large dimensions, we provide the analytical expressions for the end-to-end SNR at the users and obtain upper bounds on the achievable common rate for an AF MWRN. Moreover, considering binary phase shift keying (BPSK) modulation as the simplest case of lattice codes, we obtain the average bit error rate (BER) for a user in an AF MWRN. The analysis shows that the average BER is a linearly increasing function and the achievable common rate is a linearly decreasing function of the channel estimation error. On the other hand, the average BER decreases and the achievable common rate increases with increasing correlation between the true and the estimated channel. Also, we observe that the AFprotocol is robust against increasing number of users in terms of error performance. We show that when the decoding user has better channel conditions compared to other users, AF relaying gives a better error performance and common rate. Finally, simulation results are provided to verify the validity of our analysis.

Ion conduction and phase morphology in sulfonate copolymer ionomers based on ionic liquid–sodium cation mixtures

A series of sulfonate based copolymer ionomers based on a combination of ionic liquid and sodium cations have been prepared in different ratios. This system was designed to improve the ionic conductivity of ionomers by partially replacing sodium cations with bulky cations that are less associated with anion centres on the polymer backbone. This provides more conduction sites for sodium to ‘hop’ to in the ionomers. Characterization showed the glass transition and 15N chemical shift of the ionomers did not vary significantly as the amount of Na+ varied, while the ionic conductivity increased with decreasing Na+ content, indicating conductivity is increasingly decoupled from Tg. Optical microscope images showed phase separation in all compositions, which indicated the samples were inhomogeneous. The introduction of low molecular weight plasticizer (PEG) reduced the Tg and increased the ionic conductivity significantly. The inclusion of PEG also led to a more homogeneous material.