Abstract: One of the main requirements of future all Internet protocol based multimedia networks
is to provide Quality of Service (QoS). In such networks, QoS is based on the concept of policy-based admission control. The admission control uses information about user session, resource availability, subscriber profile and operator defined policy. Session Initiation Protocol (SIP) is used to negotiate QoS parameters of multimedia sessions while Diameter protocol is used for authorization and usage monitoring of resources intended for multimedia traffic. In this paper, protocol models of QoS resources assigned to multimedia session are suggested. The models reflect the SIP and Diameter protocol views. The models are formally presented and it is proved that both models expose a synchronized behavior.
Key words: Quality of Service, Internet Protocol Multimedia Subsystem, Labeled Transition Systems, Behavioral equivalence
Ilia Iliev, Stanio Kolev, Stoicho Manev
Abstract: This work proposes a methodology for the synthesis of optimal correlative codes to
reduce inter-carrier interference (ICI) in OFDM systems and maintain good BER performance at
large frequency offsets. For the synthesis of codes an objective function is used, that combines two
criteria – the first minimizes ICI by frequency offset and the second minimizes the BER for
Maximum Likelihood Sequence Detection (MLSD). The simulation studies are made with the
proposed polynomials for frequency offset ɛ = 0, 0.1 and 0.2, which confirm the expected results for
the BER and ICI.
Key words: PRS, OFDM, lCl, MLSD, Correlative coding, OFDM, Frequency offset
Boyan Kehayov, Ilia Iliev
Abstract: A quasi-optimal algorithm for MIMO based on consecutively direct search is proposed.
Functional dependence between the number of the iterations and the error rate performance by M-QAM modulations are studied. BER performance of the algorithm is compared with the well-known
V-BLAST successive interference cancellation detectors: zero forcing, minimum of mean square
error and maximum likelihood. Computer simulations show high computational speed and
acceptable BER precision of the algorithm.
Key words: MIMO, V-BLAST algorithm, MMSE detectors, ZF detectors, multl user detection.
Abstract: The development of efficient emergency vehicle to vehicle communications systems
requires an understanding of the underlying propagation channels.
Measurements were performed at a carrier frequency of 5.2 GHz with the communicating vehicles
travelling on the highway in opposite direction.
Keywords: Channel measurements, radio channel characterization
Abstract: In the presented work two of the most popular algorithms for power control for 4G
wireless networks are considered and investigated. The first algorithm uses equal distribution of
power through all subchannels and features very low computational complexity. The second one,
known as water-filling, has higher complexity but reveals better characteristics especially for low
SNR conditions. Extensive simulations according two scenarios are implemented. The first
scenario considers fixed customers while the second one – customers moving with speed of 50
km/h. The obtained results prove the advantages of water-filling method in both cases. The
spectral efficiency and as a result the transmission data rate for the second algorithm are
considerably better in SNR range from – 10 dB to 10 dB.
Key words: wireless networks, power control, algorithms for optimization, algorithms for power distribution
Daniela Minkovska, Ludmila Stoyanova
Abstract: The paper presents the investigation and the analysis of the results received from the
students‘ knowledge and skills assessment in Informatics in the mechanical engineering faculties at
the Technical University of Sofia. The investigation has been conducted in order to analyze the
relevance of inclusion of the programming language C for the future mechanical specialists. The
organization of the assessment process is introduced according the interdisciplinary relations. The
investigation of students’ results has been conducted before and after the change of the
programming language. Certain conclusions have been drawn about the benefits and
appropriateness of this change.
Key words: education, informatics, mechanical engineering, assessment, programming language
Dragi Kimovski, Plamenka Borovska
Abstract: The flow control mechanism is crucial element for attaining optimal allocation of the
communicational resources and achieving high communicational performance. In this paper the
current flow control mechanisms have been examined in more details and new highly effective flow
control mechanism has been proposed. The behavior and the effectiveness of the proposed ”Step-
Back-On-Blocking“ flow control mechanism have been verified on the basis of numerous simulation
experiments conducted in the OMNeT++ simulation environment.
Keywords: Flow control methods, system area networks, high performance computing systems.
Tasho Tashev, Adelina Aleksieva-Petrova, Milen Petrov
Abstract: Moodle is oriented toward the delivery and management of web based e-learning
courses. The system is open source and has ability to add new plugin to the system which
contribute to its widespread use. The main objective of this paper is to define the core system
functionality and propose database implementation of the teachers’ personal profile module in the
Key words: CV, AJAX, moodle, personal page.
Plamenka Borovska, Ivailo Georgiev
Abstract: An investigation of the service oriented architecture in order to design the architecture of
high performance computing portal is presented in this paper. The designed portal provides
services as follows: security, parallel program execution, database access on compact
heterogeneous computer cluster. The portal architecture consists of four layers: interface, security,
software tools, and resources.
Key words: web portal, portlet, high performance computing, service oriented architecture.
Abstract: This paper describes some problems of the IPv4 and how they are solved by IPv6. IPv4
and IPv6 addressing and address auto configuration are analyzed. The content includes the
addressing model for IPv4 and IPv6, definitions for different address types and address formats.
The autoconfiguration process is described. An algorithm presents the steps a host takes in
deciding how to auto configure its interfaces in IPv6.
Keywords: IPv4 and IPv6 addressing, lP autoconfiguration