Investigation of punctured LDPC codes and time-diversity on free-space optical links

In this paper, we analyze the behavior of DVB-S2 un-punctured/punctured low-density parity-check (LDPC) coded on-off-keying (OOK) under atmospheric turbulence conditions by utilizing time diversity. A performance characterization between these schemes is evaluated, where punctured LDPC code provides a penalty of around 0.1 to 0.2 dB against unpunctured LDPC codes but still provides a coding gain of several dB against uncoded OOK. The combination of channel coding and a bit interleaver results in performance improvements in turbulence conditions. For example, such a system can achieve a coding gain of 16.7 dB in moderate turbulence conditions compared to uncoded OOK

Re-routing Multicast Connections: A Distributed Approach

In virtual-circuit environments that provide a multicast capability, fixed routing algorithms provide solutions that are only efficient initially and for a short time due to dynamic nature of network environments. We propose a re-routing algorithm that continuously rearranges the topology of the initial connection, in response to changes in the destination set and network status. The re-routing algorithm is cost effective and minimally disruptive to the multicast session. It is based on a modified Steiner tree improvement technique, and it has been designed purposely to meet the requirements for distributed implementation in communications networks where only partial information is available to routing nodes

MAP Selection Algorithms Based on Future Movement Prediction Capability in Synthetic and Realistic Environment

Efficient mobility management involves micromobility principles. The performance of the Hierarchical Mobile IPv6 (HMIPv6) protocol, a representative micro-mobility approach, is affected by the Mobility Anchor Point (MAP) selection. In this paper, we propose a new selection method based on a prediction of the future movements of Mobile Nodes (MNs). The proposed algorithms exploit the information about the future availability of MAPs and choose those MAPs that assure a better service. An improvement to the evaluation methodology is also proposed. The algorithms are compared to each other not only in synthetic but also in realistic internet topologies, which has not been a practice in the past. The simulation results show promising improvements in terms of distance from chosen MAPs and frequency of MAP changes. Moreover, we showed that, for perceivable improvement of MAP selection, absolute accuracy of movement prediction is not required. As pioneers in the mobility management analysis in realistic environment, we ascertain that offering MAP services over more than one Autonomous System (AS) proves beneficial

SDL-Based Automatic Test Generation for GSM Services

The paper introduces automatic test scenario generation for GSM (Global System for Mobile communications) services. The first step of the test scenario generation, which cannot be fully automated, is to create an SDL (Specification and Description Language) description of a GSM service. We propose a methodology for transforming an informal service description to an SDL specification. The form and contents of the resulting specification are adapted to the properties of the test derivation method. The next three steps of the test scenario generation are abstraction of an EFSM (Extended Finite State Machine) to a FSM (Finite State Machine), generation of test sequences and translation to TTCN (Tree and Tabular Combined Notation). These steps are completely automated in the tool iATS. The process of the automatic test scenario generation is illustrated by the example of test scenario generation for the GSM call setup

Performance of BPSK subcarrier intensity modulation free-space optical communications using a log-normal atmospheric turbulence model

In this paper, we present simulation results for the bit error rate (BER) performance and the fading penalty of a BPSK - subcarrier intensity modulation (BPSK-SIM) free-space optical (FSO) communication link in a log-normal atmospheric turbulence model. The results obtained are based on the Monte-Carlo simulation. Multiple subcarrier modulation schemes offer increased system throughput and require no knowledge of the channel fading in deciding what symbol has been received. In an atmospheric channel with a fading strength 2 l ? of 0.1 obtaining a BER of 10-6 using a 2-subcarrier system will require a signal-tonoise (SNR) of 23.1 dB. The required SNR increases with the fading strength and at a BER of 10-9 the fading penalty due to the atmospheric turbulence is ~ 41 dB for 9 . 0 2 = l ? . The comparative studies of the OOK and BPSK-SIM schemes showed that for similar electrical SNR, BPSK-SIM offered improved performance across all range of turbulence variance

On the study of the FSO link performance under controlled turbulence and fog atmospheric conditions

In this paper, the effect of turbulence and fog on the free space optical (FSO) communication systems for on off keying (OOK), pulse amplitude modulation (PAM) and subcarrier intensity modulation (SIM) based on binary phase shift keying (BPSK) is experimentally investigated. The experiment is carried out in a controlled laboratory environment where turbulence and fog could be generated in a dedicated FSO chamber. In comparison to 4 PAM signal, the BPSK and OOK NRZ modulation signalling format are more robust against the fog and turbulence effects. In addition BPSK system is much less susceptible to the signal amplitude fluctuation due to turbulence compared to the other two modulation formats

Current optical technologies for wireless access

The objective of this paper is to describe recent activities and investigations on free-space optics (FSO) or optical wireless and the excellent results achieved within SatNEx an EU-framework 6th programme and IC 0802 a COST action. In a first part, the FSO technology is briefly discussed. In a second part, we mention some performance evaluation criterions for the FSO. In third part, we briefly discuss some optical signal propagation experiments through the atmosphere by mentioning network architectures for FSO and then discuss the recent investigations in airborne and satellite application experiments for FSO. In part four, we mention some recent investigation results on modelling the FSO channel under fog conditions and atmospheric turbulence. Additionally, some recent major performance improvement results obtained by employing hybrid systems and using some specific modulation and coding schemes are presented

RAMIFICATIONS OF MOBILE PHONE ADVANCED O/S ON SECURITY PERCEPTIONS AND PRACTICES

The present paper correlates advanced operating systems (O/S) in mobile phones to the security perceptions and practices of users. It is based upon the results of a survey that took place in 17 Universities of 10 Eastern and Southern Europe countries. 7172 questionnaires were gathered and processed with the results showing that there is a statistically significant connection between the type of the phone’s O/S (advanced or not) and the security feeling, awareness and practices of users. Users of advanced O/S believe they are more informed and feel more secure (both statistically proved). Unfortunately, even though they subjectively feel informed, their actual objective score in regards to awareness questions is lower than that of non advanced O/S users, while their actual security behavior, is just slightly better than that of other users. This false sense of security and awareness renders them more vulnerable than others. In any case, the overall percentages reveal general lack of awareness and moderate attention to security issues, with some even alarming findings. As such, the need for security education, combined with transparent security features in the phones is apparent. Furthermore, in regards to this specific research topic, there are not available any already validated questionnaires. Our research, apart from revealing the situation, aims at providing a basis for the formulation of similar questionnaires for future use