5 UDC 621.396 MODEM EQUIPMENT FOR THE NEW GENERATION COMPACT TROPOSCATTER STATIONS Serhii O. Kravchuk, Mikolay M. Kaydenko National Technical University of Ukraine “KPI”, Kyiv, Ukraine Background. Modem equipment of tropospheric communication lines is an important component of modern means of telecommunication. The theoretical and practical aspects of choosing a preferred embodiment of modem equipment, taking into account the aggregate indicators of quality. Objective. Presentation features the construction of modem equipment of the tropospheric stations of new generation that can provide high data transfer rates with guaranteed quality of service in complex stationary and non-stationary noise inherent in tropospheric channels. Methods. This goal is achieved by using new technical and architectural solutions to build a modem equipment, spectrally efficient modulation types and coding algorithms of effective adaptation to changing operating conditions. Feasibility of the proposed approaches to the construction of the modem hardware is fulfilled on a prototype of the equipment based on the HSMC ARRadio Daughter Card debugging modules. Results. The features of constructing of modem equipment of troposcatter stations with high data transfer rate are provided. To reach the limiting parameters of such stations proposed in the application of modem equipment of new technical and architectural solutions, spectrally efficient modulation types (OFDM plus linear modulation) and error-correcting coding, efficient algorithms of adaptation to changing conditions of work, the SDR technology, frame structures of physical layer. The variants of the configuration of modem equipment in relation to the modes of operation of compact troposcatter station. Conclusions. Ways of improving modem performance to improve the efficiency of modern compact troposcatter radiorelay stations. Keywords: tropospheric communication; modem equipment; adaptation; software-defined radio; channel configurations. Introduction inhomogeneities of the troposphere; at short intervals The troposphere is a lower layer of Earth's (less than 60...70 km) – diffraction propagation. So atmosphere. Its upper limit is at a height of about 10...12 stations are designed to work in the presence of both km. In the troposphere is always a local volume mechanisms of distribution, called for transhorizon heterogeneity caused by different physical processes communication systems. taking place in it. Radio waves UHF band and The main features of tropospheric propagation centimeter wavelengths (especially in the band 0.3...5.0 associated with the physical nature of this phenomenon GHz) can dissipate these inhomogeneities. Given the is fading very large area to spread and fading of the fact that heterogeneity are at high altitude, it is easy to signal at the receiver input, which are selective in imagine that they are scattered radio waves can extend frequency character [6-10]. This appears multipath for hundreds of kilometers. The effect of such a distant effect, due to the fact that the length of the rays passing tropospheric propagation was opened in the early 50s of through different parts of the volume, where the last century. Its practical application has made it possible scattering is different. This leads to distortion of signals to build a new type of microwave links - tropospheric transmitted form and volume scattering can be regarded radio relay lines with the distance between adjacent as quadripole, which has limited bandwidth. stations from 150 km to 300 km, and in some cases from In these conditions to provide stable connection have 600 km to 800 km and more. to raise energy parameters of equipment TRRS, achieved Despite the fact that troposcatter radio relay system an increase transmitter power, use larger antennas, use of (TRRS) is much more difficult to implement, and the low noise amplifier at the receiver input, and use of more capacity of lower than that of microwave systems (RRS) effective methods of formation and signal processing line of sight, thanks to length of flight TRRS found quite while taking in order to reduce the ratio signal to noise widely used, especially for military, special services, ratio at the receiver input at which performance rescue services and emergency situations [1-3]. standards are provided to the channel quality indicators Deploying troposcatter stations does not put forward and very high throughput. difficult requirements to terrain. No need to install high The disadvantages of traditional means of towers needed in case RRS for line of sight [4-5]. transhorizon communication relay include: poor The basis of troposcatter communication radiolines communication reliability in terms of interference; large are two mechanisms of propagation, at ranges of over size and power consumption and, consequently, a large 60...70 km - scattering of radio waves by the number of vehicles, no automatic antenna-mast devices; ISSN 2312-4121, Information and Telecommunication Sciences, 2016, Volume 7, Number 1 © 2016, National Technical University of Ukraine “Kyiv Polytechnic Institute” 6 INFORMATION AND TELECOMMUNICATION SCIENCES VOLUME 7 NUMBER 1 JANUARY ─ JUNE 2016 low characteristics of electromagnetic compatibility; use of multi-antenna technology and in particular - lack of unified radio relay stations with systems MIMO (Multiple Input - Multiple Output) technology; management and lack of effectiveness of functional interlayer, providing optimum utilization of adaptive control and diagnostics. One of cardinal decisions on modulation and coding and Hybrid automatic repeat leveling of the specified shortcomings of traditional request (HARQ) technologies. Adaptation of the station TRRS when saving necessary noise immunity in the to changing conditions of work must be carried out conditions of multipath fadings is creation of effective automatically with a minimal delay without interrupting portable TRRS of new generation which basic principles the session. There is a support of the high data transfer of creation were provided in [11-12]. rate of all operating modes of stations due to optimally Currently several companies presented their select the desired mode, the high reliability of data development of compact TRRS. Thus, the company transmission at a high availability factor of radio-line, TeleCommunication Systems Achieves Unprecedented high spectral efficiency of the communication channel Performance in partnership with Comtech Systems and continuous, non-destructive control of the presented the development TRRS «TCS 3T». Using a communication channel status on the basic parameters 500-watt solid state power amplifier and SSPAs (solid- and simultaneous transmission in the communication state power amplifiers) of Comtech, the system provides channel: information channel, channel of voice calls and data rates up to 50 Mbit / s over a distance of 100 miles. overhead information channel. Using of the packet The company since 2009 produces new seals digital transmission to support a plesiochronous digital equipment CSM8100, specifically designed for hierarchy. The automatic adjustment mode of antennas operation in the ground tropospheric lines and CS4400 - according to the built-in positioning system is supported. new frequency converter designed for operation on A simple, user-friendly interface to control the station is tropospheric lines and lines of sight. Raytheon Company present. Station control system should be built using the has developed TRRS BLOS-T (Beyond Line of Sight - Linux-based operating system. The station should have Troposcatter Communications) C-band [13]. block and modular architecture for providing creation of Implementation of the new generation of portable various options of a configuration of station to an TRRS has been treated with highly effective specific opportunity. The station should have the built-in system channel-forming equipment, based on a modem device of diagnostics of operability of all main units and [14]. modules. Time of deployment of station has to be The purpose of this article is to describe the main minimum possible. features of the construction of modem equipment of the B. Options configuration of the station equipments new generation of troposcatter stations. Such stations will be able to provide high data transfer rates with Modern troposcatter station should be able to work in guaranteed quality in complex stationary and non- three modes. Indirect visibility using tropospheric stationary noise inherent in tropospheric channels. scattering of radiowaves. This mode provides maximum communication range at the maximum transmitter power. Configuration of The Station Equipments Data transmission rate is minimal (from hundreds of kbps A. Requirements for modern troposcatter to 2 Mbps), due to the presence of deep frequency communication stations and them modem equipment selective fading including daily and seasonal nature. Indirect visibility using diffractive scattering by an When creating a modern troposcatter communication obstacle. In this mode, the range of up to 70 km at a station must be made number of specific requirements, maximum transmission power can be ensured. Data namely. The communication range determined by the transmission rate is average (to 4…8 Mbps) due to the destination station, and can be from tens to hundreds of indirect visibility and the inability to use a multi-position kilometers. Range of frequencies of work of station on modulation. Line of sight, in this mode, at low power of