No. 2 (2013)

Preface

The paper covers development and importance of mobile (cellular) telecommunication services, which developed during last about 20 years and are currently the most important and profitable telecommunication sector. The development of mobile telecommunications becomes essential factor of economic growth in many countries, especially in developing countries. Currently due to the scientific and technological progress as well as the implementation a new standard known as LTE system, cellular telecommunication becomes the basic element of the modern broadband telecommunication infrastructure and internet services. Growing importance of the mobile systems is also connected with great popularity of new mobile terminals – smartphones and tablets. These terminals together with the technology known as cloud computing changed also the ICT market. The paper relates to the situation in many countries, but mainly to Poland.

Broadband fixed wireless access, local multipoint distribution service networks are promising wireless solutions to connect fixed users to the backbone network instead of wired copper or fiber optic networks, via point-to-multipoint cellular networks. Channel capacity is of primary importance in broadband fixed wireless access networks due to increasing demand for multimedia services and possibility of providing wireless internet. Modern radio transmission systems are specifically designed for meeting two main objectives: to provide a solution for long distance networks with high transmission capacity, and to guarantee the highest link quality. Availability of a radio-relay system is very important and dependent on many factors, particularly propagation conditions in the troposphere. The article describes wave propagation that determines the performance of a radio-relay path at 6 GHz. Attenuation of received signal level measured in this frequency range depends on propagation condition on terrestrial path. Examples of measured fading duration of are presented.

In this paper a novel configuration of broadband multi slot antenna for C/X bands is presented and analyzed. By cutting two diamond slots in the middle of the rectangular patch and three triangular slots in the right side of the patch, resonances can be created. Microstrip feed line is used in the down side region of the patch. Antenna characteristics were simulated using a finite element method (HFSS). According to simulations, the proposed multiple slot antennas can provide two separated impedance bandwidths of 970 MHz (about 11.96% centred at 8.11 GHz band) and 890 MHz (about 9.76% centred at 9.42 GHz band) and stable radiation patterns, promising for satellite systems.

In the last decade a new idea has been suggested for receivers of communication systems, namely, in microwave receivers’ architecture. Though superheterodyne radio-frequency receivers are best suited to the needs of contemporary wireless communication, however stray radiation of their local oscillator (heterodyne) interferes with neighboring radio-devices and permits to locate the covert receiver. To overcome this drawback the signal transfer to optical range has been suggested. By this conversion, not only an elimination of receiver’s stray radiation is attained but also vast advantages of photonic signal processing become available. The key element of existing microwave-photonic receivers is electro-optical microdisk modulator. However, its realization is complicated and as an alternative an electro-optical modulator based on high Q-factor Fabry-Perot microresonator is suggested. Comparative analysis of both types of modulators is performed, and advantages of high Q-factor Fabry-Perot microresonator based modulator are highlighted.

Mobile Telecommunication is one of the fastest growing technologies in the world. The effects of its high frequencies and complex modulations to the exposed population are considered in this paper. Experimental studies examining a variety of effects on all levels of the organism, ranging from effects on single cells to effects which manifest themselves as reactions of the entire body, there have been a number of epidemiological studies in order to establish the possible causal correlations between higher exposures to HF EMFs. Recommendations on the reduction of the effects of EMFs of Mobile Telecommunication on humans was presented.

This paper presents speech enhancement technique based on Spectral Subtraction (SS) method. SS is a renowned noise reduction technique that works on the principle that noise spectrum estimate over the entire speech spectrum can be subtracted from the noisy signal. On the contrary, most of the noise encountered in the real-world conditions is majorly colored. Unlike Additive White Gaussian Noise (AWGN), colored noise does not affect the speech signal uniformly over the entire spectrum. To mitigate effects of colored noise on the processed signal, we propose a Multi-Band Spectral Subtraction (MBSS) method using novel Adaptive-Control Factor (ACF). The spectrum is divided into frequency sub bands based on a nonlinear multi-band frame and various signal-to-noise ratios (SNRs) are considered. The proposed scheme results in better system performance with quality signal and unlike the basic SS method. It mitigates the effects of anomaly known as “musical” tones artifacts in the processed signal that result in residual noise and speech distortion. The computational complexity involved is minimal. Furthermore, simulation results show that the proposed algorithm removes more colored noise without removing the relatively low amplitude speech signal over the entire speech spectrum. Subjective listening tests, with clean speech signals and different noise levels, show discernable performance of our proposed method when compared with the conventional SS approach.

Object and service identification is considered as one of the main challenges in the field of Internet of Things (IoT), which can be solved by the introduction of the so called ID (IDentifier) layer. The objective of this layer is to expose IoT objects and services offered by them, to users. Common approach for ID layer is to create it in overlay manner, on the top of existing network. This paper presents a novel architecture of the ID layer, which is characterized by embedding ID layer functionality into the network plane. Moreover, this approach takes advantage of the Name-Oriented Networking (NON) paradigm. To gain easy access to the IoT objects and services, as well as native support for multicast service, human readable ID-based unified addressing with hierarchical structure was exploited. Additionally, in-network caching of forwarded IoT data, inherited from the NON, helps to reduce total network load and supports applications during collaboration with energy-constrained sensors. Such sensors may enter sleep mode to save energy and then the network nodes can serve requests for sensing data, arrived from applications, by using data stored in nodes’ cache. The paper shows the concept of NON-based ID layer and describes functional architecture of network node paying attention on modules and mechanisms related with ID layer functionality. Primary ID layer processes, i.e., object/service registration, resolution and data forwarding are explained in detail. Moreover, the ID-aware network node was implemented on Linux-based platform and tested to check its forwarding characteristics. The tests showed the performance of the of ID network node in data plane operations, which are the more sensitive for scalability issues.

In this paper, an application of Evolutionary Multiagent Systems (EMAS) and its memetic version to the optimization of advisory strategy (in this case, Sudoku advisory strategy) is considered. The problem is tackled using an EMAS, which has already proven as a versatile optimization technique. Results obtained using EMAS and Parallel Evolutionary Algorithm (PEA) are compared. After giving an insight to the possibilities of decision support in Sudoku solving, an exemplary strategy is defined. Then EMAS and its memetic versions are discussed, and experimental results concerning comparison of EMAS and PEA presented.