Introduction. Nowadays, communication systems are mostly digital. One of the tasks of automatic gain control in digital receivers is to maintain analog signals at the appropriately fixed level, which prevents saturation of the analogto-digital converter. Most numerical algorithms are based on floating point arithmetic, and digital automatic gain control is usually implemented using fixed-point arithmetic devices such as programmable logic chips and signal processors. As consequence of fixed-point arithmetic and hardware constraints usage, the out-put significant bits should be truncated correctly. Although many studies mention digital automatic gain control, its characteristics are not considered in detail in terms of the finite capacity of calculators.

Objective. The purpose of the study is to analyze dynamic characteristics of digital automatic gain control implemented on a computer for operations on numbers with fixed-point.

Materials and methods. Within the frames of the study in Matlab software was developed a mathematical model of digital automatic gain control. The model was implemented on a programmable logic chip.

Results. The paper shows the difference in characteristics and features of the digital automatic gain control during operations on fixed-point numbers. The study provides the assessment of the effect of fixed-point signals on the stability of the digital automatic gain control and includes the analysis of causes of spurious oscillations of the control signal.

Conclusion. The study proposes the algorithm for compensation of the control signal oscillations by means of correction of the reference level of the digital automatic gain control. Further is required to verify the proposed algorithm on real signals. The results of the study are relevant in development of digital receivers for communication systems of various purposes.

Introduction. Satellite radar altimeter is an essential part of the Earth remote sensing space missions. Satellite altimeter on-board delay-lock loop, by a widely shared concept, is operationally just a tool of a reliable retaining of received echo-signal within the tracking window, while “fine” altimetric parameter (orbit height, significant wave height, scattering cross section per unit of a probed surface, etc.) measuring is committed to the ground-based retracking of data. In particular, in the course of retracking altimeter data are being filtered and/or smoothed.

Objective. The paper subject is study of retracking algorithms of altimeter data transmitted from the space vehicle to the ground segment.

Methods and materials. It is known that data filtering already presents on-board the space vehicle and is implemented in delay-lock loop based on the α–β-filter. However, at the stage of ground-based retracking it seems more appropriate to use the Kalman filter, which possesses a number of theoretical optimal features and is efficient as for utilization of the available computational resource.

Results and conclusions. In the paper implementation of filtering and smoothing via Kalman algorithm is described. On the ground of computer simulation data it is stated that Kalman filtering and smoothing make estimate accuracy two and more times higher depending on significant wave height.

Introduction. The modern technologies of virtual chromoendoscopy provide significant increase of diagnostic value of images considered by a doctor. The analysis of existing technologies shows that the existing solutions have significant disadvantages. Some of them require a complex preliminary calibration of the equipment for operation. Others use global transformations, making impossible consideration of local tissues characteristics and so on. In general, nowadays the technology of virtual chromoendoscopy, which suits the majority of potential users – doctors, does not exists, and, therefore, there it is a field for research.

Objective. Development of the method for virtual chromoendoscopy, with regard to disadvantages identified within the frames of carried out analysis of similar methods.

Methods and materials. For implementation of the research were used open endoscopic image data-bases, by the instrumentality of which, as a result of modeling and experiment, were evaluated quality characteris-tics of the proposed method.

Results. The new method of virtual chromoendoscopy. The main feature of the method is usage of nonlinear local transformation functions in transformation of RGB channels, as well as absence of calibration procedure for obtaining the effect of virtual chromoendoscopy. The proposed method is completely based on the technology of digital image processing and includes image brightness correction, which provides the possibility to obtain the necessary visual information both from very dark and overexposed fragments; image sharpening, contrasting small details and vessels.

Conclusion. The expert assessment of the obtained results shows that the visual effect of the proposed method corresponds, or in some cases, exceeds the visual effect of proprietary technologies of virtual endoscopy I-Scan and FICE.

Introduction. The modern approach for ensuring marine activities of necessary quality related to the assessment of current information on the state of the ocean environment in Russia is clearly insufficient. The development of operational methods and instruments of observation, as well as the assessment of the state of the ocean and its forecast naturally determine such an approach. Therefore, the development of the concept, tools and methods of obtaining data is an urgent task of the operational Oceanography formation.

Objective. The objective of the paper is to con-sider the concept of ocean surface monitoring using short-wave surface wave radar.

Methods and materials. The paper presents a number of specific Oceanologic examples that require operational monitoring of the state of coastal waters of the oceans and individual regions. Also, it describes observational systems used in other countries. The paper pays special attention for the development of radar sensing of surface waters, carried out in our country occasionally. The resonant nature of the reflections gives the opportunity to obtain maps of high-precision measurements of surface currents and wave characteristics on the long-range area in real time. The paper notes difficulties of the experiments implementation and the results interpretation, shows the insistent issues for the establishment of the ocean surface operational monitoring, and gives the approaches for solvation of the existing problems. The paper formulates the main task of the world ocean parameters forecast for ensuring of the sea transport safety from natural and anthropogenic threats, as well as formulates the problems solution of effective nature management.

Results. The paper shows that the optimal means of natural data acquisition is the creation of an observation network of coastal HF radars, which enables to assess surface currents and wave characteristics, as well as to solve the problem of monitoring. It is Important to develop an adequate coastal model and correlate its parameters with experimental data. The adaptive modeling and monitoring by modern technical means can overcome inadequacy of physical models to specific natural conditions can.

Conclusion. By assimilation in hydrodynamic and wave models, these data become applicable in spatial mapping of hydrophysical inhomogeneities of the water layer, sound velocity, and underwater acoustic noise.

Introduction. One of the classes of modern radio engineering systems are systems with spatial diversity of transmitting, receiving or transceiving elements. In such systems, an increase of the information content is achieved by signal coprocessing ensuring synchronization in time and phase of the carrier oscillation. Currently, the researchers do not pay enough attention to the requirements for the accuracy of synchronization of distributed systems of different applications, as well as simple and affordable ways to synchronize them.

Objective. The paper main objective is the search for technical solutions for clock and phase synchronization without atomic frequency standards and external sources of coordinate-time information.

Methods and materials. The paper considers a distributed radio engineering system with non-rigid structure. Each element of the system has reference signal from its own crystal oscillator. The oscillators are not physically aligned. The phases of their oscillations are periodically compared by the method of two-way transmission of synchronizing signals (from one element to another and vice versa). The synchronization technique (software algorithmic approach) is reduced to the coprocessing signal correction according to estimated frequency (phase) drifts. The testing of the proposed technical solution is presented on a hardware model consisting of ten receiving and transmitting modules.

Results. The experiment showed that RMS of synchronization errors does not exceeded 12 degrees by phase (for VHF), or 0.2 ns by time. These results are acquired for spatial diversity up to several hundred meters, mutual speed of the modules up to several meters per second and may be extended for higher frequencies (in particular, UHF).

Conclusion. The paper proposes a method of multilateral propagation to synchronize distributed radioengineering systems. Combined with software algorithmic technique this method enables to obtain synchronization accuracy in real-time sufficient for coherent diversity technique.

Introduction. Among acousto-optic spectrum analyzers with spatial integration, schemes based on optical interferometers provide the largest dynamic range. Nevertheless, they form the signal amplitude spectrum on a certain spatial carrier. Formation of quadrature components can eliminate this spatial carrier. The two-dimensionality of the transformations performed in optical processors provides this elimination by reading of the additional charge of matrix photosensor lines. A renowned method implements this approach using four lines, which in turn determines the estimation time of the signal spectrum.

Objective. The objective of the work is to study the possibility of time reduction of the spectrum estimation.

Materials and methods. The paper presents the description of two methods of forming the necessary components.The first method uses three photosensor lines, the charge distribution in which has the spatial carrier phaseshifted by 90 ° from line to line. The second method forms the necessary distributions sequentially in three accumulation cycles by means of variation of the initial phase of the reference signal. By the mathematical proof, three distributions with a 90 ° relative phase shift are sufficient to eliminate the spatial carrier.

Results. In the first method, reduction of the spectrum estimation time is insignificant, but the parallel distributions formation affords not to impose additional requirements on the signal spectrum. The second method, due to the possibility of using any three sequentially formed distributions for estimation, is potentially three times faster than the first method, but requires the stationary signal spectrum within three accumulation cycles. Researchers can implement this meth-od using a linear photosensor or TDI photosenor. In addition, the method is less demanding to optical scheme parameters.

Conclusion. The proposed quadrature components formation methods provide time reduction of the spectrum estimation in interference acousto-optic spectrum analyzers and simplify their design.