Spatial Localization of Radio Wave Emission Sources Using SDF Technology

Transcription

1 Spatial Localization of Radio Wave Emission Sources Using SF Technology Jan M. Kelner, Piotr Gajewski, Cezary Ziółkowski Military University of Technology, Warsaw, Poland, {jkelner, pgajewski, Abstract: The paper is devoted to the question of locating of radio wave emission sources by using of SF technology. The generalized algorithm to estimate the radio transmitter coordinates has been presented. The oppler characteristics are the basis to determine the location coordinates of a source. They are obtained as the result of measuring of instantaneous frequency of a signal received on board of an airplane. Keywords: location techniques, oppler shift, Signal oppler Frequency (SF), 3 localization I. Introduction The localization of mobile radio waves transmitters is more and more interesting service both for networks users of and for operators of Electronic Warfare (EW) systems. Many location techniques have been already studied and described, mainly [6]-[1]: CoO (Cell of Origin), AoA (Angle of Arrival), RSS (Received Signal Strength), TOA (Time of Arrival), ToA (Time ifference of Arrival), GPS/A-GPS (Assisted GPS), FoA (Frequency ifference of Arrival) as well as the so-called hybrid methods. Above methods have some advantages and disadvantages for using in practical systems. Mostly, the location in two dimensions () is these methods main limitation. The article presents an idea of the method for location in 3 that use the values of signal oppler shift which is measured on the mobile flying platform (helicopters, planes, drones). The SF (Signal oppler Frequency) technology [] is based on the analytical description of the oppler effect [1]. It uses the distinctive nature of oppler curves resulting from the reciprocal location of signal sources and receiver in relation to the movement of the objects trajectory. Because of using the oppler effect, the SF method is compared to FoA one. However, the SF and FoA methods present considerably different approaches to the location techniques. The possibility of object spatial 3 localizations is a main advantage of the SF technology, which is presented below.

2 368 Military Communications and Information Technology... Moreover, the main propriety of SF method is its high precision as well as independency for the time-frequency structure of signals emitted by objects being localised. It gives the possibility to use the method universally and autonomously in numerous practical applications. Several applications of the SF technology have been presented till now, among others in the area of: reconnaissance and electronic warfare, spectrum monitoring, sea and land rescue, and navigation. II. Characteristic of SF method The SF technology bases on the analytical description of the oppler frequency [1]. The expression describing the variability of the oppler frequency has the following form [1]: k xvt f x, t k f 0 1k xvt 1k y z, (1) where: k vc, the difference of velocity between a signal source and the receiver, the electromagnetic wave propagation speed in the medium, the carrier frequency of the emitted signal, x xyz,, coordinates of the signal source location. Above formula shows that the value of the oppler frequency shift is a function of signal source location coordinates. This fact has become the essence of elaborated method is a measurement of the instantaneous value of the signal frequency by a moving measurement receiver. Basing on (1), particular coordinates x, y, z of the transmitter location can be determined as the functions of the oppler frequency shift measured in various time moments. In the case, when the receiver is moving on a fixed height above the flat terrain, the coordinates are known and fixed values. Making elementary transformations of the equation (1) we achieve formulas describing the coordinates x and y of the signal source []-[5]: x v tat At tat 1 1 At 1, () y 1 1 v t t At At 1 1 k At1 At z, (3) where: 1 F t f t 1k At, Ft k. (4) Ft f k So, in order to determine coordinates of signal source, it is necessary to measure the oppler frequency value in two moments and. Therefore, it is 0

3 Chapter 8: Localization Techniques 369 possible to determine locations of emitting radio wave sources during the receiver movement, basing on the measurement of the oppler frequency shift. The idea of SF 3 method is described below. III. SF spatial localization method The algorithm of localization procedure is presented in the Fig. 1. The following simplifications were assumed in the analysed scenario []: the signal generated by the localised transmitter is received at any point of the space where the localization stand (LS) is placed; the localised signal source is immovable and it is placed on the flat Earth surface; the LS is moving at a defined height over the Earth, what means that only the direct component is taken into account in the signal coming from the source to the receiver; the operator of the LS knows the frequency of the signal transmitted by the localised source. Figure 1. Algorithm of the SF spatial localization procedure

4 370 Military Communications and Information Technology... Here, the several possible situations of localization using an aircraft are taken into account. They depend on the knowledge of an approximated direction for the transmitter. So, Algorithm contents three blocks. Block (A) corresponds to the situation, when the LS operator knows the approximated direction to the signal source. Block (B) is using if the LS operator does not know the approximated direction to the signal source, and the stand is moving in the direction, for which is not possible the coordination determining. And finally block (C) corresponds to the situation where the LS operator does not know the approximate direction to signal source, but he is able to determine transmitter coordinates x and y on the flying route. The task of part B is to define the precise coordinates of the transmitter using procedure Z, presented in the Fig. []. Figure. Illustration of Z-procedure The Z procedure is brought to define 3-phase flight route of LS between the points (1) () (3) (4). In the first phase between the points (1) (), the ap-

5 Chapter 8: Localization Techniques 371 proximate transmitter s coordinations can be determined. Knowing the approximated direction to the localised transmitter, it is possible to select a suitable flight direction within the first phase of the procedure Z. This direction should be established so that the oppler frequency shift changed []. In the point (), the change of the movement direction takes place in the OXY plane by the angle (Fig. ) defined by the formula []: y s 1 xy s arctg arccos xvt xvt s arccos arccos, xy where: xvt y, s the length of the route segment between point () xy and point (X) (Fig. ), where the oppler frequency is equal to zero. This phase of the Z procedure allows to achieve the coordinate values of the transmitter position with high accuracy. It is resulted from the suitable selection of the route where almost symmetrical part of the oppler curve is achieved around the value of. The point (X) in the Fig. is called the Point of the Closest Approach PCA [1]. The selection of the length s of the route segment between the points () (3) depends on the distance of the localization stand to the signal source. The question of selection of the measurement segment s is presented in the references [,13]. In the point (3) the next change in the movement direction takes place in the plane OXY by the angle of (Fig. ) described by formula []: xy xy (5) y ' vt ' x' arctg y' y', (6) where: x', y', z ' coordinates of the signal source position determined in the second phase of the procedure Z, the time measured from the moment of changing the movement direction in the point (), y' y ' a factor responsible for the sign of the angle and providing the proper change of the direction (to the right or to the left) in the point (3). Within the third phase of the procedure Z the plane flights in the direction to the transmitter. The change in the direction for the route (3) (5) (Fig. ) is executed similarly to the point () of the procedure Z. The precise coordinate values of the source position are determined in this way. When the direction to the transmitter is not known and oppler shift does not changed, the block (B) is worked out. Here, three situations can be distinguished: a) the stand moves away from the transmitter that is in a large distant from the receiver ( f t fmax ), b) the stand moves closer to the transmitter, but is in a large distant from it ( f t fmax ),

6 37 Military Communications and Information Technology... c) the stand moves (closer or away) in small distant of the source, but the flight direction overlaps (with a margin) the direction to the signal source ( f t fmax ). The Fig. presents an example of such situation by moving the LS between the points (6) (7). Then, the diametrical change in the movement direction is required in the plane OXY by the angle of ±90 related to the present movement direction. Next, the procedure Z is executed. The segment (7) () corresponds to the (1) () one in the procedure Z as for the situation (A). The last block (C) corresponds to the situation where the LS operator does not know the approximate direction to signal source, but he is able to determine coordinates x and y of the source position on the route of his movement (the segment (1) () in the Fig.. The coordinate y is then defined ambiguously. It is not known if the signal source is on the right or on the left side of the LS movement trajectory (the segment (1) () in the Fig. ). Therefore, the LS direction change in the point () can be done in the incorrect direction. In such a case, the movement of the receiver in the direction () (8) will cause that f t fmax. The return (8) () and further continuation of the flight according to the procedure Z is required in such situation. IV. Simulation results The SF method was verified by simulations and measurements for localization. Some results have been presented in [4],[5]. The procedure Z has been positively verified by simulation tests for the rescue action scenario [14]. Some simulation results are presented below. Figure 3. Simulation scenario

7 Chapter 8: Localization Techniques 373 Fig. 3 shows the simulation scenario and the flight trajectory in. The aircraft position is in geographical UMT standard. At the top, the positioning accuracy results obtained for the point F is shown. This is the point with the best accuracy of location because of the most distinguish change of oppler frequency (Fig. 4). Figure 4. oppler frequency courses Figure 5. Localization accuracy The r localization accuracy is shown in Fig. 5. The best results are obtained during the flight in sector EF, after few changes of flight route. V. Summary The paper shows the possibility of using the space platform to spatial localization of the radio emission sources (both stationary and movable). The SF method in the spatial localization can find wide applications in air and sea rescue systems as well as in national security agencies. Installing the localization

8 374 Military Communications and Information Technology... stand on helicopters and aircrafts increases the range and accuracy of the method in relation to the ground localization. The exact characteristics of this method, the many experiments should be worked out. At present, the preparations are in progress to develop the new research project. Within this grant it is expected to carry out researches and the attempt to implement the SF technology on an aircraft from the Navy Sea Rescue Unit. The expected better precision of the oppler localization method in the case of placing the localization stand on aircraft than placed on land vehicles allows to infer of high capacities of the method, which can be also used for air navigation, particularly within aircraft landing systems in reduced visibility conditions. The possibility to use the SF method to navigation purposes is presented, among others, in [],[13]. References [1] J. Rafa, C. Ziółkowski, Influence of transmitter motion on received signal parameters Analysis of the oppler effect, Wave Motion, vol. 45, no. 3, pp , January 008. [] J.M. Kelner, Analiza dopplerowskiej method lokalizacji źródeł emisji fal radiowych (Analysis of the oppler location method of the radio waves emission source), Ph.. thesis, Military University of Technology, Warsaw, Poland, 010, (in Polish). [3] P. Gajewski, J.M. Kelner, C. Ziółkowski, Subscriber location in radio communication nets, Journal of Telecommunications and Information Technology, no., pp. 88-9, 008. [4] J.M. Kelner, C. Ziółkowski, L. Kachel, The empirical verification of the location method based on the oppler effect, 17th International Conference on Microwaves, Radar and Wireless Communications MIKON 008, Wroclaw, Poland, vol. 3, pp , May 008. [5] P. Gajewski, C. Ziółkowski, J.M. Kelner, Mobile location method of radio wave emission sources, Progress in Electromagnetics Research Symposium PIERS 009, Moscow, Russia, August 009. [6] A. Amar, A.J. Weiss, Localization of narrowband radio emitters based on oppler frequency shifts, IEEE Transactions on Signal Processing, vol. 56, no. 11, pp , 008. [7] Y. Zhao, Standardization of mobile phone positioning for 3G systems, IEEE Communications Magazine, vol. 40, no. 7, pp , 00. [8] M. Vossiek, L. Wiebking, P. Gulden, J. Wieghardt, C. Hoffmann, P. Heide, Wireless local positioning, IEEE Microwave Magazine, vol. 4, no. 4, pp , 003. [9] I.J. Gupta, Stray signal source location in far-field antenna/rcs ranges, IEEE Antennas and Propagation Magazine, vol. 46, no. 3, pp. 0-9, 004. [10] A. Küpper, Location-based services. Fundamentals and operation, John Wiley & Sons, Chichester, UK, 005.

9 Chapter 8: Localization Techniques 375 [11] K.W. Kołodziej, J. Hjelm, Local positioning system. LBS applications and services, CRC Press, Boca Raton, FL, USA, 006. [1] N. Levanon, M. Ben-Zaken, Random error in ARGOS and SARSAT satellite positioning systems, IEEE Transaction on Aerospace and Electronic System, vol. AES-1, no. 6, pp , [13] P. Gajewski, C. Ziółkowski, J.M. Kelner, Influence of length and location of the measurement route on location accuracy of the radio waves sources using the SF method, Przegląd Telekomunikacyjny i Wiadomości Telekomunikacyjne, vol. LXXXIII, no. 8-9, pp , August-September 010 (in Polish). [14] C. Ziółkowski, J.M. Kelner, Using the oppler methodology for object location estimation in lifeboat service, 6th International Conference on: Perspectives and evelopment of Rescue, Safety and efence Systems in the 1st Century RSS 008, Gdansk, Poland, June 008.