OFDM Waveform Optimisation for Joint Communications and Sensing

Radar systems are radios to sense objects in their surrounding environment. These operate at a defined set of frequency ranges. Communication systems are used to transfer information between two points. In the present day, proliferation of mobile devices and the advancement of technology have led to communication systems being ubiquitous. This has made these systems to operate at the frequency bands already used by the radar systems. Thus, the communication signal interferes a radar receiver and vice versa, degrading performance of both systems. Different methods have been proposed to combat this phenomenon. One of the novel topics in this is the RF convergence, where a given bandwidth is used jointly by both systems. A differentiation criterion must be adopted between the two systems so that a receiver is able to separately extract radar and communication signals. The hardware convergence due to the emergence of software-defined radios also motivated a single system be used for both radar and communication. A joint waveform is adopted for both radar and communication systems, as the transmit signal. As orthogonal frequency-division multiplexing (OFDM) waveform is the most prominent in mobile communications, it is selected as the joint waveform. Considering practical cellular communication systems adopting OFDM, there often exist unused subcarriers within OFDM symbols. These can be filled up with arbitrary data to improve the performance of the radar system. This is the approach used, where the filling up is performed through an optimisation algorithm. The filled subcarriers are termed as radar subcarriers while the rest as communication subcarriers, throughout the thesis. The optimisation problem minimises the Cramer--Rao lower bounds of the delay and Doppler estimates made by the radar system subject to a set of constraints. It also outputs the indices of the radar and communication subcarriers within an OFDM symbol, which minimise the lower bounds. The first constraint allocates power between radar and communication subcarriers depending on their subcarrier ratio in an OFDM symbol. The second constraint ensures the peak-to-average power ratio (PAPR) of the joint waveform has an acceptable level of PAPR. The results show that the optimised waveform provides significant improvement in the Cramer--Rao lower bounds compared with the unoptimised waveform. In compensation for this, the power allocated to the communication subcarriers needs to be reduced. Thus, improving the performances of the radar and communication systems are a trade-off. It is also observed that for the minimum lower bounds, radar subcarriers need to be placed at the two edges of an OFDM symbol. Optimisation is also seen to improve the estimation performance of a maximum likelihood estimator, concluding that optimising the subcarriers to minimise a theoretical bound enables to achieve improvement for practical systems

A Copula Model Approach to Identify the Differential Gene Expression

Deoxyribonucleic acid, more commonly known as DNA, is a complex double helix-shaped molecule present in all living organisms and hosts thousands of genes. However, only a few genes exhibit differential expression and play a vital role in a particular disease such as breast cancer. Microarray technology is one of the modern technologies developed to study these gene expressions. There are two major microarray technologies available for expression analysis: Spotted cDNA array and oligonucleotide array. The focus of our research is the statistical analysis of data that arises from the spotted cDNA microarray. Numerous models have been proposed in the literature to identify differentially expressed genes from the red and green intensities measured by the cDNA microarrays. Motivated by the Bayesian models described in Newton et al. (2001) and Mav and Chaganty (2004), we propose two models for the joint distribution of the red and green intensities using a Gaussian copula, which accounts for the dependence. In both models, we assume the marginals are distributed as gamma. The differentially expressed genes were identified by calculating the Bayes estimates of the differential expression under the first proposed copula model. The second copula model incorporates a latent Bernoulli variable, which indicates differential expression. The EM algorithm is applied to calculate the posterior probabilities of differential expression for the second model. The posterior probabilities rank the genes. We conducted two simulation studies to check the parameter estimation for the Gaussian copula-based models. We show that our models improve the models given in Newton et al. (2001) and Mav and Chaganty (2004). We have also studied the use of Weibull distribution instead of gamma distribution for the marginals. Our analysis shows that the copula models with Weibull marginals provide a better fit and improve the identification of genes. Finally, we illustrate the application of our models on samples of Escherichia coli microarrays data

The Role of Early Sampling in Age of Information Minimization in the Presence of ACK Delays

We study the structure of the optimal sampling policy to minimize the average age of information when the channel state (i.e., busy or idle) is not immediately perceived by the transmitter upon the delivery of a sample due to random delays in the feedback (ACK) channel. In this setting, we show that it is not always optimal to wait for ACKs before sampling, and thus, early sampling before the arrival of an ACK may be optimal. We show that, under certain conditions on the distribution of the ACK delays, the optimal policy is a mixture of two threshold policies

Financial Performance of the Firms and the Enterprise Risk Management: A Sri Lankan Perspective

Risk management and financial performances in organizations had been of mounting importance when it comes to the research arena during the past few decades and is still heavily discussed globally nowadays. The tendency is to take an all-risk encompassing overview of risk management instead of considering risk management from a narrow-based overview. This all-risk encompassing approach to risk management is usually mentioned as Corporate Risk Management. A noticeable dearth of research is there in the studies that have been done on the relationship between corporate risk management and financial performance in organizations. There are so many shreds of evidence for the statement that organizations will enhance their performance by using the corporate risk management concept. The main objective instigated during this study is that the proper match between corporate risk management and, therefore, the firm factors: namely, industry competition, firm size, firm complexity, and monitoring by the board of directors and the relationship among corporate risk management and firm performance. This study identifies the impact of corporate risk management on financial performances of Banks, Diversified Financials, Insurance, Energy, and Retailing sectors in the Colombo Stock Exchange, which include 86 companies, were considered as the population and supported a sample of 60 firms. The research began with a search for companies that indicated they were utilizing the corporate risk management concept in their annual reports covering their fiscal year 2018. The findings indicate that firms should consider the implementation of a corporate risk management system following structural variables affecting the firm. These findings will be interesting to the policymakers, future researchers, as well as to the general public and any third party who are keen on corporate risk and financial performance of Banks, Diversified Financials, Insurance, Energy, and Retailing sectors in Sri Lanka. Keywords: contingency theory, corporate risk management index, firm performance, Sri Lank

Waveform Design and Processing for Joint Wireless Communications and Sensing

Since the advent of radar/sensing systems, they have always had fixed frequencies for operation. Due to the exponential growth of communications systems, the need for dedicated spectrum for them also increased, causing spectrum scarcity for both communications and sensing. It was obvious that some form of flexible spectrum sharing was necessary between these two functionalities. Soon enough, this led the researchers to focus on joint communications and sensing (JCAS) systems that share spectral resources efficiently. The hardware convergence due to the similar functioning of the two systems complemented the frequency convergence of JCAS systems. In fact, JCAS is one of the prominent requirements in future sixth-generation (6G) communications systems. This thesis focuses on integrating the sensing functionality on top of wireless mobile communications systems, such as in fifth-generation (5G). To facilitate effective JCAS, the thesis provides signal processing techniques for designing waveforms that optimally share the spectral resources, for single-input single-output (SISO) as well as multiple-input multiple-output (MIMO) systems. In addition, novel radar processing techniques are investigated for MIMO systems to better detect the targets in the environment. The standard waveform in 5G, that is, orthogonal frequency-division multiplexing (OFDM), is also considered for joint waveform design. In such a communications system, the resources are usually not fully utilized and there exist unused subcarriers within the OFDM waveform. These subcarriers are filled with optimized samples to minimize the lower bounds of delay and velocity estimates’ error variances of sensing, for SISO JCAS systems. The simulations with standard-compliant 5G waveforms illustrate the improvements possible in sensing, while also helping to maximize the efficiency in the transmit power amplification process, along the same optimization scheme. The simulation results are complemented through practical radio-frequency measurements of an outdoor environment depicting the significant gains that can be obtained in the range–angle map of sensing, due to the waveform optimization. For MIMO JCAS systems, apart from conventional communications streams, separate transmit (TX) streams are used to improve sensing performance through two separate schemes. One scheme involves optimizing the sensing streams to minimize the lower bounds of delay and angle estimates’ error variances of sensing. Simulation results indicate that the errors of sensing can be minimized while striking a good balance with the communications capacity. The other scheme depicts that the target detection can be enhanced using sensing streams on top of a communications stream. Specifically, the number of false targets detected can be significantly reduced in comparison to single-stream communication. The antenna arrays in MIMO communications systems nowadays are a combination of analog and digital architectures, i.e., hybrid, instead of consisting of a fullydigital architecture, for reduced costs and power consumption. Radar processing in such a hybrid architecture with multiple TX streams is not straightforward in comparison to the conventional fully-digital MIMO radar. Hence, this thesis also provides novel radar processing techniques to obtain the range–angle and range–velocity maps of the sensed environment. The simulation results illustrate that the targets can be reliably detected through the proposed MIMO processing, while also providing super-resolution in the angular domain

Application of forward osmosis for the reduction of pre-treatment sludge volume in desalination: modelling and experiments.

Forward osmosis (FO) is a novel water treatment process that potentially can be used as an alternative technology for both sludge and brine treatment due to its low energy requirement. In the FO process, a solution of high salt concentration (known as draw solution) is utilized to generate an osmotic pressure gradient across a semipermeable membrane to extract freshwater from a solution with lower salt concentration (known as feed solution). The FO process requires low energy to operate as it capitalizes on the phenomenon of natural osmosis. FO has been given significant attention over the past few years due its superior characteristics. However, this technology is still in the developmental stages. A few studies have been carried out using FO for the treatment of industrial wastewater, landfill leachate and food industry effluents. However, to date, there has been no research on sludge treatment and brine management using the FO process, other than this research, which could be another promising application of FO. Therefore, in this study FO was proposed as an additional process to the seawater reverse osmosis (RO) process to dilute the brine before it is discharged back to the ocean and to reduce the volume of pre-treatment sludge before mechanical dewatering. Diluting of brine have number of advantages depending on the industrial requirements such as (1) it can increase the brine diffusion rate as the concentration is low (2) it can keep the same diffusion rate however adverse effect to flora and fauna near the diffusers are low as the salt concentration is low (3) it can be sent back to the RO desalting process to increase the overall water recovery as the diluted brine is already pre-treated. Most of the current seawater desalination plants have two-stage reverse osmosis (RO) processes. Therefore, the proposed FO systems utilize 1st stage RO concentrate (brine) as the draw solution (since osmotic pressure of brine is higher due to higher salinity) and pre-treatment sludge as feed solution (lower salt concentration). After passing through the FO system, as a consequence of water permeation from feed to draw solution, the pre-treatment sludge volume becomes lower and the brine gets diluted. Diluted brine can either be sent back to the 1st pass RO process to increase the overall water recovery or blended with the 2nd pass RO brine before being discharged to the ocean. By doing the latter, the diffusion rate of the brine within the water body can be increased. In this study, laboratory experiments to assess the viability of applying the FO process for an RO desalination system at different sludge conditions (pH, temperature) were conducted. Further, biofilm growth on the membrane surface up to 8 weeks of continuous filtration was analysed. In addition, mass balance calculations were used to predict the reduced sludge volume and power requirement arising from large scale (340 ML/day intake) and small scale (15 ML/day intake) hybrid FO/RO desalination plants. The electrical conductivity (EC) of the brine and seawater EC were 73.0 mS/cm and 44.5 mS/cm, respectively. As EC is directly proportional to osmotic pressure, there was a sufficient osmotic pressure difference between the draw and feed solutions to have adequate water flux through the FO system. However, the total organic carbon (TOC) of the brine and sludge were 3.10 mg/L and 8.92 mg/L, respectively. Therefore, there is a potential for biofilm growth on the membrane surface. When the pH of feed solution was increased from 6 to 8, there was a marginal change in water flux. Therefore, the as is pH (normally pH 8) of feed solution is recommended for the hybrid system. When the temperature increased from 20 to 40 oC, the average water flux slightly increased (5.6 to 6.0 LMH). However, considering the economic benefits, it is recommended to operate at room temperature. The water flux of continuous filtration experiments declined with time due to fouling as well as dilution of the draw solution. However, flux increased when the draw and feed solutions were replaced with the fresh solutions. This increased flux was lower than the initial flux of the previous batch and was due to fouling on the membrane. After one week of filtration, the flux declined further due to the thickened fouling layer deposited on the membrane. The layer may have contained microorganisms in addition to salt deposits as both draw and feed solutions contained salt ions. However, scanning electron microscopy (SEM) spectrum showed salt deposits on the membrane surface after 5 week of continuous filtration without cleaning in between. This fouling can easily be overcome by providing regular flushes at high cross flow velocities as deposited layers are thin and loose and therefore readily removed. After 8 weeks of continuous filtration large salt deposits were observed. Further, after 8 weeks there was no water permeation through membrane. After analysing SEM EDX images and spectra, weekly membrane cleaning is recommended to avoid biofouling and inorganic fouling. After analysing water flux values and the fouling behaviour during FO filtration, mathematical modelling was carried out for the proposed RO/FO systems. Since, daily pre-treatment sludge generation varies (both in volume and solids content) with the desalination plant size, calculations were made for two plant sizes: large-scale plants (LSP, 340 ML / day intake) and small-scale plants (SSP, 15 ML / day intake). When the membrane area is 100 m2 (minimum area considered in this study) it can reduce sludge volume up to 7% in a SSP, however this depends on the water flux through FO. When the membrane area increases, sludge volume reduction increases in both large and small scale plants. The sludge solids content can be increased from 3 to 10% TS with a small power requirement (17.3 kW h /day). Interestingly, when the membrane area of a LSP is increased to 900 m2, the sludge volume is reduced by 50%. This yields a sludge stream having a final solids content of 7.6%. Proposed system requires lower OPEX and CAPEX compared to existing system; however, they are marginal. With all the results obtained through laboratory scale experiments and mathematical modelling, it is evident that the proposed hybrid system is a promising technology to reduce the volume of pre-treatment sludge and increase the overall water recovery of RO process

EFFECT OF DIFFERENT LEVELS OF SALINITY ON GROWTH PERFORMANCES OF FOUR SELECTED TREE SPECIES

Salt affected soils are widespread in different parts of the world. In recent years significantamount of land extent were affected due to salinity rendering them biologically unproductive.The use of specific techniques for tnc amelioration of these lands for agriculture is taking placecontinuously. Reforestation of salt affected soils is possible given proper site preparation, choiceof suitable salt tolerant species and their proper nursery and cultural practices are achieved. Thepotentials of these soils for growing trees and woody vegetation have not been fully exploredyet.Therefore, four different pot experiments were conducted by using four selected tree speciesmainly available in the salt affected areas (i.e, Tamarind (Tamarindus indica), Katuandara(At:acia /eucop/oea), Castor (Ricinus communis) and Wood apple (Feronia /imonia) at theFaculty of Agriculture, University of Ruhuna Mapalana, Kamburupitiya during April to October200 1 to assess the influences of different levels of saline water (i.e. 0.13,2,4,6,8 and 12mmhos/cm) on growth and development of above four tree species. All the experiments wereconducted by using a Randomized Complete Design with four replicates. One month oldseedling raised in 6"x8" size polythene bags were used for the experiment. Seedlings weretransferred to lager Polythine bags (lO"x 12") at 2 months after planning without damage to theroot system to ensure enough space for root development. Plant height, shoot and root biomassyield were measured at every 2 weeks interval.The result revealed that the plant height, shoot and root biomass yield were not affectedsignificantly by different levels of saline water up to 12 mmhos /cm compared to the controlwhere normal water (O.13mmhosl em) is applied in all crop species. Therefore all four-treespecies, which were used for the experiment, may be recommended as salt tolerant tree speciesup salinity to the level of 12rnmhos/cm.

Influence of undergraduates activities on the waste composition and generation rates in a residential University – case study

The increase of waste generation and its disposal is a major problem and challenge faced by the most of the countries today.The uncontrolled disposal of different types of waste into environment is a great threat for the future of all living beings in the world. Therefore, it is essential to pay more attention for the waste management and disposal to avoid the detrimental impact on the environment. For the development of a proper treatment or disposal systems for waste management for any organization or municipality, it is essential to have the information with respect to waste composition, generation rate and its variation with time of that organization. Therefore, in this study, it was attempted to evaluate the composition and the variation of waste generation rate in the hostels of the undergraduates of University of Ruhuna with their activities.The study was conducted in the premises and surroundings of the hostels of the undergraduates for a period of one year (September to August). The waste samples were collected from each and every hostel once in two months. The waste samples were separated into different components (such as foods, paper, plastics, etc), weighed and determined the percentages of different components.  The different types of waste generation rate per head were calculated based on the waste generation for the total study period. It was found that food remains, papers, plastics and polythene are the major components. The types of waste found in hostels of girls were less in numbers than that of boys. Leather, textiles, metals, etc could not be found in hostels of girls.Over ~95 % of waste found in girls’ hostels were food remains and boys generate food waste about ~71%. Per capita food waste generation by girls was ~ 207 g/day while it was ~23 g/day by boys. The generation of other types of waste was higher in hostels of boys than that of girls’ hostels. It appears that the amount of waste generation varied in different months basically due to examinations and other activities of the students. During examination periods, it seems that the undergraduates may change their food habits. Based on this study, it can be concluded that major component of waste found in undergraduate hostels was food wastes and the generation rate slightly varies with the activities of undergraduates. When designing of a waste management systems for higher education institutes where students reside, higher priority should be given for the management of food wast