Band Limited Signals Observed Over Finite Spatial and Temporal Windows: An Upper Bound to Signal Degrees of Freedom

The study of degrees of freedom of signals observed within spatially diverse broadband multipath fields is an area of ongoing investigation and has a wide range of applications, including characterising broadband MIMO and cooperative networks. However, a fundamental question arises: given a size limitation on the observation region, what is the upper bound on the degrees of freedom of signals observed within a broadband multipath field over a finite time window? In order to address this question, we characterize the multipath field as a sum of a finite number of orthogonal waveforms or spatial modes. We show that (i) the "effective observation time" is independent of spatial modes and different from actual observation time, (ii) in wideband transmission regimes, the "effective bandwidth" is spatial mode dependent and varies from the given frequency bandwidth. These findings clearly indicate the strong coupling between space and time as well as space and frequency in spatially diverse wideband multipath fields. As a result, signal degrees of freedom does not agree with the well-established degrees of freedom result as a product of spatial degrees of freedom and time-frequency degrees of freedom. Instead, analogous to Shannon's communication model where signals are encoded in only one spatial mode, the available signal degrees of freedom in spatially diverse wideband multipath fields is the time-bandwidth product result extended from one spatial mode to finite modes. We also show that the degrees of freedom is affected by the acceptable signal to noise ratio (SNR) in each spatial mode.Comment: Submitted to IEEE Transactions on Signal Processin

Impact of mechanical vibration on over-the-air link at upper mmW frequencies

Abstract. Mechanical vibrations will affect the performance of the wireless link especially with coming 6G systems, which will operate at significantly higher frequencies than current 5G networks. The mechanical vibrations affect the frequency generation circuitries of the radio equipment and thus the performance of the radio link. The amount mechanical vibration to the radio or any equipment has been standardized and a short summary of related standards has been given in the thesis. Some practical measurements have been performed to verify the effects of mechanical vibration on wireless link performance. The measurement has been done with a vector signal analyzer that measures the S-parameters of the wireless link. The phase response of the measured S-parameters has been studied to illustrate the phenomena. The mechanical vibration has been measured with a mobile phone application which detects the changes, vibrations, and location changes of the mobile phone when it was placed over the frequency extender. As a result of the selection of frequency extenders, the RF measurement equipment has been able to perform over a greater frequency range than was originally intended. The used mobile phone application was the G-force meter, which is freely available from application stores. The measured S-parameters S11 and S21 were analyzed with Matlab software which was provided for the purpose. The measured S-parameters and vibration results have been time synchronized in the Matlab result post-processing. The measurement results show clearly that mechanical vibrations influence the radio signal phase and thus it needs to be considered in the future development of 6G

Analysis of Degrees of Freedom of Wideband Random Multipath Fields Observed Over Time and Space Windows

In multipath systems, available degrees of freedom can be considered as a key performance indicator, since the channel capacity grows linearly with the available degrees of freedom. However, a fundamental question arises: given a size limitation on the observable region, what is the intrinsic number of degrees of freedom available in a wideband random multipath wavefield observed over a finite time interval? In this paper, we focus on answering this question by modelling the wavefield as a sum of orthogonal waveforms or spatial orders. We show that for each spatial order, (i) the observable wavefield is band limited within an effective bandwidth rather than the given bandwidth and (ii) the observation time varies from the given observation time. These findings show the strong coupling between space and time as well as space and bandwidth. In effect, for spatially diverse multipath wavefields, the classical degrees of freedom result of "time-bandwidth" product does not directly extend to "time-space-bandwidth" product.Comment: 9 pages, 2 figures, Accepted in 2014 IEEE Workshop on Statistical Signal Processin

Using decoys to block SPIT in the IMS

Includes bibliographical references (leaves 106-111)In recent years, studies have shown that 80-85% of e-mails sent were spam. Another form of spam that has just surfaced is VoIP (Voice over Internet Telephony) spam. Currently, VoIP has seen an increasing numbers of users due to the cheap rates. With the introduction of the IMS (IP Multimedia Subsystem), the number of VoIP users are expected to increase dramatically. This calls for a cause of concern, as the tools and methods that have been used for blocking email spam may not be suitable for real-time voice calls. In addition, VoIP phones will have URI type addresses, so the same methods that were used to generate automated e-mail spam messages can be employed for unsolicited voice calls. Spammers will always be present to take advantage of and adapt to trends in communication technology. Therefore, it is important that IMS have structures in place to alleviate the problems of spam. Recent solutions proposed to block SPIT (Spam over Internet Telephony) have the following shortcomings: restricting the users to trusted senders, causing delays in voice call set-up, reducing the efficiency of the system by increasing burden on proxies which have to do some form of bayesian or statistical filtering, and requiring dramatic changes in the protocols being used. The proposed decoying system for the IMS fits well with the existing protocol structure, and customers are oblivious of its operation

Development of Time Measuring Technique to Measure the Shock Speed during the Propagation in the Free Atmosphere

In the study of wave propagation in the free atmosphere, it is desirable to obtain time measurements to an accuracy of microsecond level. An experiment has been conducted to measure the wave speed during the propagation in the free atmosphere by the present technique. Due to sudden rupture of the diaphragm for the chamber pressure of 4.2 kg/cm2 and a wave generating in a shock tube travels with subsonic speed and the measured incident wave Mach number is 0.8 which leaves the shock tube in the free atmosphere. The measured travelling time of the incident wave to travel 61.5 cm distance in the shock tube is 2200 μsec and the same technique can apply to measure the shock wave speed. Several trigger points are installed at the exit of the shock tube in the open atmosphere to measure the strength of the wave propagation. It is observed that the wave strength decreases during the wave propagation in free atmosphere. Due to spherical expansion behind the wave, the pressure across the wave decreases. A numerical simulation is also conducted on supersonic shock wave to determine the shock speed and the travelling time in the free atmosphere. The pressures across shock wave at different locations of the shock wave are determined by solving the Euler equations and the simulation results indicate that the shock speed decreases during the propagation in the free atmosphere. In both experimental and numerical results, it is observed that the strength of the wave propagation in the free atmosphere decreases continuously due to spherical expansion.  The present technique can also be used to measure the supersonic jet velocity, the velocity of bullet and any particle velocity in subsonic or supersonic ranges

Capacity of Solid Waste Management of the Municipalities in North-West Region of Bangladesh: A Far Cry with Sustainable Development

The study addresses the overall waste management and drainage system of the Municipalities of Bangladesh. It also endeavors to compare the existing system with the requirements of making a sustainable city following the targets of SDG. It tries to highlight the shortcomings of the existing system of waste management and argues that this is never able to confine sustainability in the environment and the habitats of the Municipalities. The study is empirical in nature mainly based on primary data. Data have been collected from the officials and stakeholders of the three selected Municipalities of a North-west district of Bangladesh- Rajshahi through face to face interview and Focus Group Discussion. This paper identifies the fragile solid waste management capacity of the Municipalities of Bangladesh and argues that current practice is nothing but an inevitable setback for the country to achieve sustainable development

Reliability of the tools used to examine psychological distress, fear of COVID-19 and coping amongst migrants and non-migrants in Australia

Study tools examining psychological distress, fear of COVID-19 and coping amongst migrants and non-migrants in Australia are very limited. The aim of this research was to assess the psychometric properties and correlation of the English version of Kessler Psychological Distress Scale (K-10), Fear of COVID-19 Scale (FCSV-19S), and Brief Resilient Coping Scale (BRCS) tools during the COVID-19 pandemic situation in Australia. Data from a cross-sectional survey (n = 516) were utilized to examine reliability; 299 (57.9%) were migrants. High internal consistency, as evidenced by Cronbach’s alpha, was found for the K-10 (0.92), FCV-19S (0.87) and BRCS (0.66) tools. The corresponding values for migrants and non-migrants were (0.92, 0.87, 0.67) and (0.92, 0.86, 0.63), respectively. Item-total correlations ranged 0.57-0.78 for K-10, 0.62–0.69 for FCV-19S, and 0.39–0.50 for BRCS tools. EFA retained a single factor for each tool with adequate factor loadings. The scoring of K-10 was significantly predicted by the scoring of FCV-19S (r = 0.284, P < 0.001) and BRCS tool (r = 0.132, P < 0.01). Therefore, these tools can be used reliably amongst both migrant and non-migrant population in Australia. © 2021 John Wiley & Sons Australia, Ltd. **Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Muhammad Aziz Rahman and Wendy Cross" is provided in this record*

CAN MINOR FRUIT CULTIVATION CHANGE THE LIVELIHOOD OF THE MARGINAL PEASANTS? A CASE STUDY FROM BANGLADESH

Abstract Lemon (lebu) cultivation, a minor fruit production activity, is increasingly becoming popular among the marginal peasants. The present study aimed at exploring the potentials of lemon production and its impact on the changes in the livelihood pattern of the rural farmers as well as its impact on women empowerment. Based on qualitative and quantitative data collected from Mymensingh district in Bangladesh in 2015, this paper argues that life and livelihood of the citrus producer has significantly changed over the last decade. Income from the sale of lemon is the principal livelihood means and gender non-differentiated participation in the production process further enhanced the sustainability of the livelihoods. It also contributed to employment generation for those who are not directly involved in the lemon cultivation such as power tiller driver, irrigation pump driver, fertilizer &amp; pesticide retailer, small lemon collector, lemon supplier in the study area. Moreover, increased participation of women in the citrus cultivation has changed not only their economic well-being but also social status, honor, planning and decision making power, and self-esteem. This study also shows that marginal and vulnerable poor women including landless women, female member of women headed household and widows significantly benefited from citrus cultivation. Yet, lack of cooperative society, financial support, credit facility, technical support, storage facility and marketing support are identified as the potential problems to achieve a sustainable growth of lemon production activity

Recent changes in ecosystem services and human well-being in the Bangladesh coastal zone

This study takes an historical approach in order to establish how the form and function of the social-ecological system that represents the Bangladesh south-western coastal zone has changed over recent decades. Time series data for a range of ecosystem services and drivers are analysed to define the range of trends, the presence of change points, slow and fast variables and the significant drivers of change. Since the 1980s, increasing gross domestic product and per capita income mirror rising levels of food and inland fish production. As a result, the size of population below the poverty line has reduced by ~17 %. In contrast, non-food ecosystem services such as water availability, water quality and land stability have deteriorated. Conversion of rice fields to shrimp farms is almost certainly a factor in increasing soil and surface water salinity. Most of the services experienced statistically significant change points between 1975 and 1980, and among the services, water availability, shrimp farming and maintenance of biodiversity appear to have passed tipping points. An environmental Kuznets curve analysis suggests that the point at which growing economic wealth feeds back into effective environmental protection has not yet been reached for water resources. Trends in indicators of ecosystem services and human well-being point to widespread non-stationary dynamics governed by slowly changing variables with an increased likelihood of systemic threshold changes/tipping points in the near future. The results will feed into simulation models and strategies that can define alternative and sustainable paths for land management