Alexander Vavoulas

Weather effects on FSO network connectivity

The use of relays is one of the most promising methods for mitigating impairments of the performance of free-space optical (FSO) systems and extending their limited transmission range. However, several factors contribute to significant link performance degradation. Most severe is the influence of the adverse atmospheric conditions that frequently appear, thus making the design of strongly connected networks a demanding issue. In this paper, we consider a multiple-hop FSO network, where the nodes are distributed at fixed positions on a given path-link. We take account of the most critical weather phenomena, i.e., fog, rain, and snow, and derive analytical expressions for the node isolation probability, assuming a suitable path loss model. Next, we find the number of transceivers for a given path-link in order to achieve reliable performance. We also examine the reverse case; i.e., we find the total service length for a known number of FSO transceivers. The effect of the prime FSO modulation formats is also considered. The addressed analytical framework offers significant insights into the main factors that degrade the performance of FSO networks. It constitutes a valuable tool for telecom researchers to design such networks in practice.

Connectivity Issues for Ultraviolet UV-C Networks

This paper focuses on the connectivity issues of a non-line-of-sight (NLOS) optical wireless network operating in the ultraviolet UV-C spectral region. NLOS UV-C transmitters have a limited effective coverage and, hence, a dense node distribution is required in order to efficiently cover a large geographical area. Under this assumption, the concept of connectivity is more than important since it provides a strong indication of the network reliability and robustness. In the present study, we consider transmission with on-off keying and pulse position modulation schemes assuming both Gaussian and Poisson noise and adopt an effective experimental path loss model. Then, we evaluate the k-connectivity properties in terms of several network parameters. More precisely, we present and analyze the trade-off between node density and the degree of k-connectivity against other parameters (i.e., transmitted power, supported data rate, and error probability). The derived results are depicted using appropriate figures and tables and constitute the theoretical basis for the design and implementation of a reliable UV-C network in practice.

Node Isolation Probability for Serial Ultraviolet UV-C Multi-hop Networks

Non-line-of-sight optical wireless transmission, operated in the unlicensed ultraviolet UV-C band, has been recently suggested as an alternative means of communication. However, due to limited coverage, relayed UV-C networks need to be deployed in order to supply communication services at large distances. In this paper, we consider a serial multi-hop UV-C network where the nodes are distributed at fixed positions on a given service interval. We adopt a suitable path loss model and derive analytical expressions for the node isolation probability assuming on-off keying and pulse position modulation formats. Moreover, we investigate the node density required to achieve connectivity for several geometrical transceiver configurations. The numerical results of this paper are of significant value for telecom researchers working toward a flexible UV-C network deployment in practice.

Underwater Optical Wireless Networks: A

In this paper, optical wireless has been addressed as a promising technology to provide high-bandwidth services for underwater communications. However, the significant attenuation degree due to high absorption and scattering of optical transmission in the water confines the achievable range of optical links to only few meters. One way to achieve transmission at long distances is to employ a dense network configuration where information can be transferred through a series of intermediate nodes acting as relays. In this study, we consider optical wireless network arrangements where nodes are floating at different depths into a service aquatic medium. We deploy an effective path loss model which incorporates the key factors that deteriorate the optical power, and we derive the achievable transmission range to satisfy connectivity criteria assuming intensity-modulation direct detection (IM/DD) with on-off keying (OOK). A set of numerical results is presented in order to reveal the interaction between various parameters such as error probability, wavelength, node density, transmitted power, data rate, etc., in order to achieve k-connectivity. The proposed analysis could be the basis of deploying reliable underwater optical networks suitable to deliver broadband services at far distances.

k

It is evidence that the demand for Asymmetric Digital Subscriber Line (ADSL) connections increases day by day in all European countries as much as worldwide and it is well known that Internet’s penetration is considerably amazing. At the same time, due to the fierce competition among ADSL connections providers, several packages are offered in attractive tariffs. As a product consists of various characteristics that consumers value, the question that arise could be summarized to the following: How should consumers’ choices and preferences for ADSL connections affect tariffs and what are the more significant and powerful characteristics that shape tariffs of ADSL connections?This paper provides a hedonic price analysis of ADSL connections for the European market. A problem which is posed is the selection of the best model. So, in order to estimate prices a sliced inverse regression (SIR) is performed, without knowing the shape of the function. Then by applying Local Polynomial Regression (LPR) a possible shape of the hedonic function is given. Among several candidate hedonic models and by applying Akaike Information Criterion (AIC), the best one is derived. In order to evaluate the proposed methodology, tariffs’ data have been collected from 15 European countries over the period from 2003 to 2005. Apart from tariffs, information on characteristics such as supported data rate (DR), maximum consumed data volume (V) and maximum allowed minutes on line (T) have been collected and analyzed.

-Connectivity Analysis

This paper considers the impact of dual polarization adoption on the performance for a fixed wireless access (FWA) network. The major limiting factor of the performance in these systems is co-channel interference (CCI) originating from intracell and intercell concurrent transmissions. The proposed framework combines an appropriate time domain radio resource allocation technique with a dual polarization pattern to mitigate CCI and enhance the obtained signal to interference plus noise ratio (SINR). Simulation results present the performance of the proposed framework against various terrain categories and sector antenna characteristics. Copyright

Nonparametric estimation of a hedonic price index for ADSL connections in the European market using the Akaike Information Criterion

An improved radio resource allocation scheme with avoidance of major interferers is proposed and analyzed for the downlink of Fixed Broadband Wireless Access (FBWA) systems with full frequency reuse. The scheme is based on Enhanced Staggered Resource Allocation (ESRA) and permits the enhancement of the throughput per sector. Simulation results show a maximum downlink throughput per sector in excess of 44% and an increase of 10% with respect to ESRA is achieved, with Base Station (BS) selection procedure, while meeting a 15 dB signal-to-interference ratio (SIR).

Performance improvement of fixed wireless access networks by conjunction of dual polarization and time domain radio resource allocation technique

Underwater optical wireless communications (UOWC) have gained a considerable interest during the last years as an alternative means for broadband inexpensive submarine communications. UOWC present numerous similarities compared to free space optical (FSO) communications or laser satellite links mainly due to the fact that they employ optical wavelengths to transfer secure information between dedicated point-to-point links. By using suitable wavelengths, high data rates can be attained. Some recent works showed that broadband links can be achieved over moderate ranges. Transmissions of several Mbps have been realized in laboratory experiments by employing a simulated aquatic medium with scattering characteristics similar to oceanic waters. It was also demonstrated that UOWC networks are feasible to operate at high data rates for medium distances up to a hundred meters. However, it is not currently available as an industrial product and mainly test-bed measurements in water test tanks have been reported so far. Therefore, extensive research is expected in the near future, which is necessary in order to further reveal the “hidden” abilities of optical spectrum to transfer broadband signals at higher distances. The present work summarizes the recent advances in channel modeling and system analysis and design in the area of UOWC.

A Radio Resource Allocation Scheme for Fixed Broadband Wireless Access Systems with Avoidance of Major Interferers

Fixed wireless access (FWA) networks recently attracted increased attention as a means to accommodate the demand for high data rate broadband services. However, co-channel interference (CCI) imposes constraints of quality of service (QoS) requirements in terms of signal to interference ratio (SIR). Efficient scheduling algorithms along with terminal classification procedure have been proposed so as to compensate CCI and improve system performance. However, it has been observed that the terminal classification procedure induces a SIR margin for a significant number of terminals. The objective of this paper is to examine potential exploitation of the SIR margin by adopting multiple modulation modes. Simulation results show that a significant performance improvement in terms of the maximum throughput per sector is achieved.

Underwater Optical Wireless Communication Systems: A Concise Review

Fixed cellular systems, supporting a high level of scalability, may provide ubiquitous broadband access and fulfill the growing demand for high Internet access and a wide range of other broadband services. High performance and spectral efficiency are essential to accomplish the required Quality of Service (QoS) and the research for efficient co-channel interference (CCI) management is of great interest. This paper presents an integrated scheduling of the intracell and intercell transmissions and polarization alternation pattern so as to minimize the total amount of interference and enhance the service quality. The proposed scheme minimizes the impact of dominant interferers for the downlink of such a system and performs a significant increase of the maximum throughput per sector.