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The purpose of the work is to study solutions of the problems connected with environmental control of state of environment at design of systems like «smart city». It is supposed that management of the urban environment will be inefficient and even dangerous to inhabitants if doesn’t include, as an organic component, the block of environmental monitoring. As the «smart city» system is represented as the big information system relying on the universal database (or the knowledge base), an important role is played by the effective organization of the base of ecological data supporting the monitoring block. The main objective of work is the analysis of the general and private requirements to the organization of collection of information, to control methods of the importance of the used indicators, to the organization of storage of collected data in the format convenient for the automated processing. It is shown that traditional DBMS have no potential, specially focused on processing of the big ecological data obtained by means of the modern technical means and focused on the modern systems of making management decisions. Being based on the known data from literature, the special information model providing effective data storage of biomonitoring and their processing with use of the relevant methods «date mining» is offered. The model is constructed proceeding from the analysis of the main properties and a biomonitoring process component. The general models of information exchanges, the principles of selection of representative bioindicator data and planning of monitoring activity in time and space, the modern principles of the organization of databases were used. Further development of model is supposed towards closer integration into the existing projects of systems of the «smart city». It assumes, in particular, further adaptation of structure of data to opportunities of their processing by methods of artificial intelligence.

Background The correlation of Clostridium difficile infection (CDI) with in-hospital morbidity is important in hospital settings where broad-spectrum antimicrobial agents are routinely used, such as in Greece. The C. DEFINE study aimed to assess point-prevalence of CDI in Greece during two study periods in 2013. Methods There were two study periods consisting of a single day in March and another in October 2013. Stool samples from all patients hospitalized outside the ICU aged ≥18 years old with diarrhea on each day in 21 and 25 hospitals, respectively, were tested for CDI. Samples were tested for the presence of glutamate dehydrogenase antigen (GDH) and toxins A/B of C. difficile; samples positive for GDH and negative for toxins were further tested by culture and PCR for the presence of toxin genes. An analysis was performed to identify potential risk factors for CDI among patients with diarrhea. Results 5,536 and 6,523 patients were screened during the first and second study periods, respectively. The respective point-prevalence of CDI in all patients was 5.6 and 3.9 per 10,000 patient bed-days whereas the proportion of CDI among patients with diarrhea was 17% and 14.3%. Logistic regression analysis revealed that solid tumor malignancy [odds ratio (OR) 2.69, 95% confidence interval (CI): 1.18-6.15, p = 0.019] and antimicrobial administration (OR 3.61, 95% CI: 1.03-12.76, p = 0.045) were independent risk factors for CDI development. Charlson's Comorbidity Index (CCI) >6 was also found as a risk factor of marginal statistical significance (OR 2.24, 95% CI: 0.98-5.10). Median time to CDI from hospital admission was shorter with the presence of solid tumor malignancy (3 vs 5 days; p = 0.002) and of CCI >6 (4 vs 6 days, p = 0.009). Conclusions The point-prevalence of CDI in Greek hospitals was consistent among cases of diarrhea over a 6-month period. Major risk factors were antimicrobial use, solid tumor malignancy and a CCI score >6. © 2017 Skoutelis et al.

An Optical Code Division Multiple Access (OCDMA) Passive Optical Network (PON) is a highly promising PON configuration, thanks to the potential of OCDMA technology in eliminating channel contention and efficiently supporting multi-rate traffic with different QoS requirements. In this paper, we provide a mathematical framework for a call-level performance analysis of an OCDMA PON that accommodates multiple service-classes of bursty traffic with retries. Blocked calls of random arrivals may immediately retry several times, by requesting less resources (number of codewords) each time, in order to be admitted for service. The bursty nature of traffic is denoted by the fact that in-service calls may alternate between transmission and no-transmission periods. Our analysis takes into account user activity and the various components of additive noise. An approximate recursive formula is derived for the efficient calculation of call-level performance measures. The proposed analytical model is further extended to assess the performance of an OCDMA PON that provides QoS differentiation, through the utilization of multiple-weight optical codes. Both proposed models are verified through simulation and found to be absolutely satisfactory. Moreover, comparison of the new models with a model without retries shows the necessity and effectiveness of the new models.

Optical Code Division Multiple Access (OCDMA) provides increased security communications with large dedicated bandwidth to end users and simplified network control. We analyse the call-level performance of an OCDMA Passive Optical Network (PON) configuration, which accommodates multiple service-classes with finite traffic source population. The considered user activity is in accordance with the bursty nature of traffic, so that calls may alternate between active (steady transmission of a burst) and passive states (no transmission at all). Parameters related to multiple access interference, additive noise, user activity and number of traffic sources are incorporated to our analysis, which is based on a two-dimensional Markov chain. An approximate recursive formula is derived for efficient calculation of call blocking probability. Furthermore, we determine the burst blocking probability; burst blocking occurs when a burst delays its returning from passive to active state. The accuracy of the model is completely satisfactory and is verified through simulation. Moreover, we reveal the consistency and necessity of the proposed model.

We present an analytical model for the determination of blocking probabilities in an OCDMA Passive Optical Network (PON) that accommodates multiple service-classes, under a code reservation policy. The analysis considers fixed-length and fixed-weight codewords, while the provision of multi-rate differentiation is realized through the application of the parallel mapping technique. The user activity and different sources of additive noise are incorporated in our study. The model accuracy is completely satisfactory and is verified through simulation.

We propose a new teletraffic loss model for the calculation of blocking probabilities in an OCDMA Passive Optical Network (PON) configuration that supports multiple service-classes according to the parallel mapping technique of data rate differentiation. Our analysis includes parameters related to both the local and hard blocking, as well as to Multiple Access Interference and user activity. We form a two-dimensional Markov chain, and solve it to derive recursive formulas for the efficient calculation of blocking probabilities. To evaluate the proposed model, the analytical results are compared with simulation results. The comparison reveals that the accuracy of the proposed analysis is quite satisfactory.

We present a new way of operation for the convolutional interleaver of an asynchronous digital subscriber line (ADSL) modem, exploiting the single latency path through the modem. A combined buffer is added after the Reed-Solomon (RS) coders in order to support the parallel way of operation. On the other hand, the combined buffer increases the correcting capabilities of the structure in case the fast path through the modem used, as it serves as an interleaver with a depth of two. The interleaving process is of the double byte kind. The proposed structure offers a performance equivalent to that achieved by a conventional interleaver with a depth of interleaving of double size, reducing thus significantly the delay caused by the interleaver. The gains achieved range from 50% to even a 100%.

Future access networks will have to meet the ever increasing demand for capacity. Optical access systems are now considered as a viable alternative solution to the xDSL technologies for delivering future integrated broadband services. Nowadays, passive optical networks are the most promising and cost-effective class of fiber access systems. In this paper we develop teletraffic loss models for calculating connection failure probabilities (due to unavailability of a wavelength) and call blocking probabilities (due to the restricted bandwidth capacity of a wavelength) in hybrid TDM-WDM passive optical networks with dynamic wavelength allocation. The optical access network accommodates bursty services of ON-OFF (transmission or no transmission) type. The proposed models are derived from one-dimensional Markov chains which describe the wavelengths occupancy in the optical access network. The accuracy of the proposed models is validated by simulation and was found to be quite satisfactory.

An analytical development of the magnetic vector potential is used in order to investigate the skin effect inside a conductor. The current distribution in electrical wires is affected by the skin effect and the field created by adjacent wires (proximity effect). This field depends on the current distribution in conductors, resulting in a closed-form problem. In this paper, we obtain the vector potential outside a conductor and we estimate the effect of induced currents in the field shape over the neighbouring conductors. Broadband over power line communication systems (BPLC) are using the medium voltage power lines as a broadband access network. Since the signal attenuates over the line, with higher losses at higher frequencies, the profound knowledge of skin effect is important because it can compromise the performance of BPLC.

The performance of the Reed Solomon coder/decoder for an ADSL modem is studied. The proposal incorporates a new faster parallel structure for the RS coding/decoding part of the modem that exploits the single latency operation of the device. The modem is fully compatible with the existing standard of T1E1.4 ANSI Standard Group and ADSL Forum requirements. The proposed structure was simulated and the results confirmed significant savings. Only the coding/decoding part of the modem was simulated. The simulation results of the parallel structure showed approximately 50% improvement in the speed of the RS coding/decoding operation. The correcting possibilities of the RS code were also confirmed and shown in the simulation results. The paper is organized as follows. The specific structure of the modem is presented. A brief introduction to Reed Solomon codes for ADSL applications is then given. Finally, the simulation results are presented.

A Reed-Solomon coder/decoder combined with a trellis encoder for an ADSL modem for ATM applications is presented and its performance is studied. The proposal incorporates a faster structure for the RS coding/decoding part of the modem that exploits the single latency operation of the device. The modem, as well as the proposed changes in it, is fully compatible with the existing standard of the T1E1.4 ANSI Standard Group. The proposed structure and the results obtained confirmed the significant savings that can be achieved by its application. Here, the coding/decoding part of the modem was simulated, only. The simulation results showed an approximate 50% improvement in the speed of the RS coding/decoding operation. Due to the operation speed up, deeper interleaving or faster transmission could be achieved leading to an improvement in the performance of the whole system. For further gains, a trellis encoder was added to the RS coder in a concatenated scheme. The paper is organized as follows: first, the introduction and the proposed modem structure are given; then follow the Reed Solomon and trellis codes used in the simulations; finally, we give the simulation method, results and conclusions.

In this paper we present the simulation results of a concatenated Reed Solomon-convolutional encoder scheme. The structure proposed was designed with the purpose of being used in ADSL applications. RS (255,239) is used as the outer code, which is proposed by the ANSI T1E1.4 Standard Group. The role of the inner code is undertaken by a convolutional encoder, which protects the outer one from random errors, while the RS code is responsible for the correction of burst errors. The noise model used, AWGN, is generally accepted as the worst case for ADSL transmission. A burst impulsive noise was also simulated proving the correcting capabilities of the RS code. The paper is organized as follows: After the introduction, a description of the simulated system is given. Next, the simulation method is described. The results from the simulation are represented, and, finally, the conclusions and some proposals for the improvement of the system are given.

The traditional waveform coding techniques for digital communication systems convert the original analog input signal into a digital bit stream using uniform sampling in the time domain, i.e. PCM, DM, ADPCM. We propose the time code modulation (TCM) technique as an alternative coding scheme, where information is extracted from the signal, only at the time instants when necessary. This results in a variable sampling rate, where its mean value is significantly less than the Nyquist rate. In addition we suggest a general theoretical model for TCM and we present simulation results for various implementations of TCM coders and decoders. A theoretical estimation of SNR vs. sampling rate performance is also presented.

Optical access systems are now considered a feasible alternative to the predominant broadband access technologies, while, at the same time, passive optical networks (PONs) are viewed as an attractive and promising type of fiber access system. In this paper we present and analyze three basic dynamic wavelength allocation scenarios for a hybrid wavelength division multiplexing-time division multiple access (WDM-TDMA) PON. We propose new teletraffic loss models for calculating call-level performance measures, like connection failure probabilities (due to unavailability of a wavelength) and call blocking probabilities (due to the restricted bandwidth capacity of a wavelength). The PON accommodates bursty service-classes of ON-OFF traffic. The proposed models are extracted from one-dimensional Markov chains, which describe the wavelength occupancy in the PON, and two-dimensional Markov chains, which describe the bandwidth occupancy inside a wavelength. The accuracy of the proposed models is validated through simulation and is found to be quite satisfactory. Moreover, these models are computationally efficient because they are based on recursive formulas.

A faster structure for an asynchronous digital subscriber line (ADSL) modem is presented. The simulation results show an improvement of up to 50%, depending on the application. The structure exploits the path remaining idle in single latency transmission, through the Reed Solomon codecs, improving the correcting capabilities without increasing the latency.