Development of Aeronautical Communication System for
Air Traffic Control Using OFDM and
Computer Algebra Systems
Maja LUTOVAC1, Vladimir MLADENOVIĆ2, Miroslav LUTOVAC3
1 Lola Institute,
Kneza Višeslava 70a, Belgrade, 11000, Republic of Serbia
2 Higher Technical School of Professional Studies,
Nemanjina 2, Požarevac, 12000, Republic of Serbia
3 Singidunum University,
Danijelova 32, Belgrade, 11000, Republic of Serbia
Abstract: The future aeronautical communication system will have to provide more communications capacity and increased capabilities than the existing one. These systems should be able to provide the performance required in the long term. The improvements are necessary to be able to cope with the expected air traffic growth in future. In this paper we deal with the development of new algorithms for the new generation of communication systems based on digital signal processing. The main idea is to automate the design procedure starting from the block diagram of the system and carrying out the implementation code on the target hardware. The role and importance of symbolic computation in communication systems is exemplified on OFDM (Orthogonal Frequency Division Multiplexing). An original approach to algorithm development is illustrated using computer algebra system. The development tools are Mathematica, and application software SchematicSolver.
Keywords: Air Traffic, Computer Tools, Symbolic Processing, OFDM.
CITE THIS PAPER AS:
Maja LUTOVAC, Vladimir MLADENOVIĆ, Miroslav LUTOVAC, Development of Aeronautical Communication System for Air Traffic Control Using OFDM and Computer Algebra Systems, Studies in Informatics and Control, ISSN 1220-1766, vol. 22 (2), pp. 205-212, 2013. https://doi.org/10.24846/v22i2y201310
Two aeronautical communication systems, ATM (Air Traffic Management) and ATC (Air Traffic Control), were based mainly on analogue communication systems. They are using two types of modulations in the VHF range (Very High Frequency), AM (Amplitude Modulation) and DSBAM (Double Side-Band Amplitude Modulation). Due to the good propagation properties in the VHF band, new communications systems have to operate in the same frequency band. For new aeronautical communication systems, the B-VHF (Broadband VHF) system is planned. The B-VHF system is designed as an overlapping system based on OFDM (Orthogonal Frequency Division Multiplexing). This system can be implemented within the existing VHF system, but the interference between channels should be minimized as much as possible.
The simplified concept of the B-VHF overlapping system is shown in Figure 1 (a modified version of the figure from ). It can be seen that each channel in the VHF band covers exactly the current time and frequency position. The frequency transitions of the B-VHF system are met using OFDM-based modulation techniques because captured channels are excluded from the OFDM transmission.
The system can be flexibly adapted to the changes of the allocated spectrum simple using the OFDM subcarrier of B-VHF system [1-5].
The spectra of the individual subcarriers overlap and the information can be completely recovered without any interference from other subcarriers. From a mathematical point of view, this is a consequence of the orthogonality of the base functions of the Fourier series. This technique is very popular for many applications in wireless communication systems .
In order to prove some properties or to gain better insight into analysed phenomena, such as those produced by OFDM technique, the numeric simulation can be engaged as the most common in practice [7-8]. The drawback of the numeric-based tools is that they usually generate a tremendous amount of numeric data, and the user might easily lose insight into the phenomenon being investigated. Even more, some authors have noticed that simulation and the real-time measured results were similar but not identical for the same input data . In the case of OFDM, authors  only guess that different results are observed because they have used different FFT-IFFT blocks.
Figure 1. Overlapping concept of the VHF and B-VHF system
Usually, in many scientific papers typesetting errors in formulas exist, and intermediate results cannot be obtained, although the final result is correct . The numeric-based tools cannot be of larger help, except to provide very speed calculation.
In order to improve the usage of computer tools, a knowledge based approach can be introduced  that is based on computer algebra systems.
Post processing using the computer algebra systems successfully overcomes some problems encountered in the traditional numeric-only approach. We present an original step-by-step procedure for simulations of OFDM transmitter using computer algebra systems and symbolic signal processing (Mathematica and SchematicSolver) [11-12] in Broadband VHF range. The knowledge embedded in the symbolic object was used to simulate an example OFDM system and to generate the implementation code of some critical parts of the system.
The paper is organized as follows. Section 2 describes the OFDM principles applied in the B-VHF system and overlapping concept. Section 3 describes the general concept of symbolic processing and computer algebra system, as well as usage of Mathematica as a development environment. Section 4 illustrates an implementation and simulation model of OFDM transmitter using computer algebra system. Section 5 illustrates the concept of post-processing.
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