MXPA00008466A - System and method for directing an adaptive antenna array - Google Patents

Abstract

A system for directing a receiving lobe of an adaptive antenna array toward an aircraft in flight includes an aircraft position vector calculator and an antenna weight vector generator. The aircraft position vector calculator receives aircraft position information from an aircraft tracking service and calculates, based upon the aircraft position information it receives, an aircraft position vector g. An antenna weight vector generator receives the aircraft position vector g from the aircraft position vector calculator and generates, based upon the aircraft position vector g, an antenna element weight vector w. The antenna weightvector w is applied to the elements of an adaptive antenna array to direct a receiving lobe of the array towards an aircraft in flight.

Description

SYSTEM AND METHOD FOR MANAGING AN ADAPTABLE ANTENNA PROVISION CROSS REFERENCE WITH RELATED REQUESTS. This invention claims priority over the provisional applications Nos. 60 / 076,666 filed 3/3/98, and 60 / 076,610 filed 3/3/98, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION The present invention relates to antennas for radio frequency telemetry applications, and more particularly to a system and method for directing an adaptive antenna arrangement in the direction of an aircraft in flight in order to establish a communication link of radio frequency (RF) between the aircraft in flight and a receiver. A significant problem found in the technique of in-flight telemetry is related to frequency and, more importantly, to the energy with which telemetry devices can transmit RF signals. Until approval by the Federal Communications Commission (FCC) of Part 15.247 of the FCC Rules and Regulations, aircraft telemetry systems were primarily limited to the VHF band (174-216 MHz), and could only operate at high energy Very low transmission rates of less than 0.1 milliwatts (mW) (FCC Part 15.241). This restriction on the transmission power has significantly limited the transmission range (ie, the maximum distance between the transmitter and the receiver) of the in-flight telemetry devices. Directional antennas, as well as those used in conventional RF communication receivers, have lobes or rays that represent areas of maximum receiver gain. The receiver gain is generally higher when these rays are placed in the direction of the signal source. Said antennas also typically have areas of no value, or areas of lower gain, for example, on the sides. Areas of no value are placed to desensitize the reaction to unwanted signals, based on their arrival address. The position of the lobes and the areas without value in said antennas is commonly fixed when installing them and they remain fixed with time. However, the position of an aircraft in flight constantly changes with respect to a given ground-based receiving antenna. Accordingly, there is a problem in the telemetry technique with respect to the reliable establishment of telecommunication links between an aircraft in flight and a ground-based receiver, especially under circumstances in which the output power of the on-board transmission antenna of the aircraft in flight is limited.

COMPENDIUM OF THE INVENTION The present invention solves this problem by providing a system and method for electronically directing the main lobe of a receiver antenna layout pattern in the direction of an aircraft in flight while simultaneously minimizing the sensitivity of the receiver to signals from other directions, including signals from interference from other directions and background noise from other directions. In an exemplary embodiment of the invention, an associated system and method for directing a main receiver lobe of an adaptive antenna arrangement toward an aircraft in flight comprises an aircraft position vector calculator and an antenna weight vector generator. The aircraft position vector calculator receives the position information of the aircraft for an aircraft, from aircraft tracking means as an aircraft tracking service. The aircraft position vector calculator calculates the aircraft position vector g, for a selected flight aircraft, and provides the position vector g to an exit. The antenna weight vector generator receives the aircraft position vector g from the aircraft position vector calculator and generates an antenna weight vector w, based on the position vector g. The weight vector generator provides the antenna weight vector w to the antenna elements of the adaptive antenna arrangement, so that a receiver lobe of the adaptive antenna arrangement is directed towards the aircraft in flight.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a block diagram of a system for directing an adaptive antenna arrangement according to the embodiment of the invention. Figure 2 is a flow diagram of the steps of a method for calculating the position vector g of an aircraft according to the embodiment of the invention. Figure 3 shows exemplary specifications for a communications link according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION A block diagram of an adaptive antenna array 50 and a system for directing the adaptive antenna array (referred to herein as antenna steering system 300) in accordance with one embodiment of the present invention is illustrated in FIG. used herein, the term "adaptive antenna arrangement" refers to an antenna arrangement capable of electronically directing a beam toward a desired signal, thereby increasing the signal-to-noise ratio of the desired signal. For a general discussion of common adaptive arrangements, see Antennas. John D. Krauss, Second Edition, Section 11-13, "Adaptive Arrays and Smart Antennas". The antenna steering system 300 of the present invention comprises an aircraft position vector calculator 315 coupled to a weight vector generator 320. A control unit 330 is coupled to the weight vector generator 320, so that the The control unit distributes the result w of the weight vector generator 320 to the individual elements of the arrangement 50. For purposes of this specification, bold letters are used to indicate the quantities of the vector. The amount of vector w comprises n complex elements (where n is the number of elements in the arrangement 50), that is, n magnitude and phase pairs, where each pair corresponds to an individual element of the arrangement 50. For example, w Controls element i of layout 50. In this way, the antenna management system 300 allows the antenna arrangement 50 to change electronically, or adapt its radiation pattern over time to optimize signal reception in the direction of aircraft 350.

The aircraft position vector calculator 315 is a programmable calculator, or processor, programmed to calculate a position vector g for an aircraft selected by a control unit 330. A position vector g is defined herein as a vector directed to along an axis of the antenna arrangement 50 to the selected aircraft 350. The position vector g is calculated from position data indicating the position of the selected aircraft 350. As used herein, the term "aircraft" includes all air vehicles such as helicopters, airplanes, remote control, gliders and balloons. In another embodiment of the present invention, the position data includes, but is not limited to, latitude, longitude and elevation information associated with the position of the aircraft 350. The position data may also include range or orientation data for the aircraft 350 as could be obtained by aircraft 350 by the on-board VHF Omni Ranging equipment (VOR), or other location or direction location instruments. In one embodiment of the present invention, the position data for aircraft 350 is supplied to system 300 by an aircraft tracking service 310. An example of a commercial aircraft tracking software provider suitable for use with the present invention is the RLM Software, of Boston Massachusetts. Another example of aircraft tracking service 310 is the Airtrak, an aircraft tracking program that can be obtained easily and commercially from METSYS Software & Services, Cropton, Pickering, North Yorkshire, YO18 8HL, England. The Airtrak program allows a user to generate maps for any area of the world, and present the maps with a latitude / longitude grid, report points, towns and airports. The Airtrak program diagrams the route of the requested flight as the flight progresses. However, it will be recognized that the Airtrak is one of many available aircraft position tracking means, suitable for use in the present invention. Other available means include the Global Positioning System (GPS), tracking means and satellite tracking means. The position vector calculator 315 employs calculations commonly applied in the navigation technique to calculate the relative position of one object with respect to another based on latitude, longitude and elevation information. An example of a calculation performed by the position vector calculator 315 in one embodiment of the invention is illustrated in Figure 2. First, the position information 333, i.e. the elevation (E), latitude (Li) and longitude (de) of aircraft 350 is obtained from the tracking service of aircraft 310 and stored in memory as shown in block 400. Also stored in memory are latitude (L2), length (? 2) and elevation (A) of antenna array 50 as shown in block 410. Distance D of antenna array 50 to aircraft 350 is calculated according to the relationship: D = 60 cos "1 [senL1senL2 + cosL1cosL2cos (? 2- ??)], is shown in block 420, where L ^ refers to the latitude of aircraft 350, L2 refers to the latitude of arrangement 50,? -i refers to the length of aircraft 350 and? 2 refers to to the length of arrangement 50.

Once D is obtained, the orientation H of the aircraft 350 of the arrangement of the antenna 50 is calculated according to the relationship: as shown in block 430. The orientation settings for the latitudes of the South and the latitudes of the East are made as shown in block 440. Finally, the elevation angle a is calculated according to the relationship: a = tan E-Al | _6076 * DJ as shown in block 450. Accordingly, the position vector g comprises the angle of elevation and orientation as calculated in Figure 2. As the aircraft moves, its position vector g changes and the arrangement weights optimal are recalculated to track these changes. This adaptive nature of the antenna steering system 300 allows it to perform well in a non-static environment. In one embodiment of the present invention, the antenna address system 300 is implemented in real time using a programmable Digital Signal Processor (DSP) chip. One embodiment of the present invention employs the TMS320C50, a DSP obtainable from Texas Instruments. Commonly, beam direction calculations, algorithms and devices are used to direct an antenna beam of an adaptive antenna array in a desired direction by weighing the individual elements of the antenna array. See, for example, Radar Handbook. Merrill I. Skolnik, Second Edition, particularly Chapter 7, "Phased Array Radar Antennas". As used herein, the term "weigh" as applied to an element of an antenna arrangement, refers to supplying a signal including a phase change angle and an amplitude, so that the beam of the antenna arrangement it is directed electronically in a desired direction. The system 300 of the present invention operates by weighing the antenna arrangement 50. According to the invention, the system 300 determines these weights on the basis ag, that is, the data about the latitude, longitude and elevation of the aircraft 350. This is, the vector generator 320 provides a result w based on the aircraft position vector g to provide desired radiation characteristics to the antenna arrangement 50. These characteristics include directivity and position of the main lobe in the direction g of the aircraft 350 along with low side lobes along other directions. In one embodiment of the invention, the weight vector w comprises the individual weights w i, that is, individual amplitude and phase values, or address values, for individual elements of the adaptive arrangement 50, such that a lobe or beam main receiver, of the adaptive arrangement 50 is directed, or carried in the direction g, that is, to the aircraft 350. In one embodiment of the present invention, the weight vector generator 320 employs a digital signal processor (DSP) programmed to perform the direction calculations that generate the weight vector w. The DSP may be the same DSP used to implement the position vector calculator 315. Alternative embodiments of the invention comprise other calculation means for generating the weight vector w, such as a computer or a microprocessor. During the operation, when you wish to receive communications from a particular aircraft in flight, like aircraft 350, control unit 330 sends a message 332 to aircraft tracking service 310, requesting position information related to aircraft 350. In one embodiment of the present invention, message 332 contains airline identification codes. standardized, as is commonly used in the airline industry to identify a particular aircraft for which position information has been requested. As described above, upon receiving the message 332, the aircraft tracking service 310 begins to provide position information 333, including latitude, longitude and elevation data for the aircraft 350 to place the vector calculator 315. The vector calculator of aircraft position 315 receives the position information 333 and calculates an aircraft position vector g based on the position information 333 and the known position information, that is, latitude, longitude and elevation, of the arrangement 50. weight vector generator 320 receives the aircraft position vector g and generates the weight vector w. The weight vector w is applied to the antenna arrangement 50 through the control unit 330, resulting in the elements of the antenna arrangement 50 being directed towards the aircraft 350. The construction of the control unit 330 is it knows in the radar signal processing technique, where it is common electronically to direct the individual elements of an array using amplitude and phase signal pairs obtained from a vector arrangement. With the approval of Part 15.247 in 1985, the FCC authorized the use of the Industrial, Scientific and Medical (ISM) band of 902-928 MHz, 2400-2483.5MHz and 5725-5850MHz. One embodiment of the invention takes advantage of the ISM band, an RF spectrum for which no license is required and which is relatively unoccupied and which is expected to remain in this manner for a reasonable period of time. In one embodiment of the present invention, the antenna arrangement 50 is adapted to establish an ISM band communication link with the aircraft 350. The specifications of the model communication link for a system mode 300 that includes a receiver adapted to establish an ISM band in a communication link during air-to-ground flight with aircraft 350 are given in Figure 3. In this embodiment of the invention, a reverse link (ground-to-air link) is not modeled and the model assumes a digital quadrature phase change keying modulation scheme (DQPSK) of a type generally known in the art. The transmit power of the model, the frequency wavelength of the carrier, the transmission antenna gain and the isotropic radiated energy (EIRP) for a modality of the invention are shown. The diameter of the receiving antenna element (indicated in Figure 2 in 50), the gain of the receiving antenna and the efficiency of the antenna are also shown. In this embodiment of the invention, a model for the adaptive arrangement 50 is composed of 16 elements. As indicated in Figure 3, the data rate in the general range of about one megabit per second is arranged. Another embodiment of this invention includes a ground-to-air link that has nominal and FCC parameter values allowed. This link establishes a reverse link in addition to an air-to-ground link. The ground-to-air data link is used to issue telemetry commands to aircraft 350. In one embodiment of the present invention, a typical control protocol is implemented using land-to-narrowband communications links that are already in use.; and another embodiment of the present invention uses an antenna and a modem that are already installed on the ground site for other purposes. An alternative embodiment of the present invention includes 5.7GHz band-receiver-receivers. Both the 2.4GHz band and the 5.7Ghz band are desirable modalities because there is not much activity in these bands at present. In addition, the most problematic source of interference within the 2.4GHz band is microwave ovens, of which the interference is almost negligible. It will be apparent to those skilled in the art that while the invention has been illustrated and described herein in accordance with the patent statutes, changes and modifications may be made to the described embodiments without departing from the true spirit and scope of the invention. Therefore, it should be understood that the appended claims are intended to cover all such modifications and changes insofar as they fall within the true spirit of the invention.

Claims (7)

1. A system for directing a receiving lobe of an adaptive antenna arrangement towards an aircraft in flight comprising: a position vector calculator for receiving position information from an aircraft tracking service, and for calculating, based on information from position, a position vector g; an antenna weight vector generator adapted to receive the position vector g of the position vector calculator and to generate, based on the position vector g, a weight vector of antenna element w; and an adaptive antenna arrangement comprising a plurality of antenna elements for receiving the weight vector of antenna element w and adjusting the respective weights of the elements according to the weight vector w, so that a receiving lobe of the arrangement Adaptive antenna is directed towards the aircraft in flight.

2. The system according to claim 1, wherein the aircraft position information comprises latitude, longitude and elevation of the aircraft.

3. The system according to claim 1, wherein the aircraft position information is provided by an Internet-based aircraft tracking service.

4. The system according to claim 1, wherein the antenna arrangement is adapted to receive radio frequency communications in the ISM band. The system according to claim 1, wherein the position vector calculator and the weight vector generator are implemented in a digital signal processor (DSP). The system according to claim 1, wherein the antenna arrangement comprises M arrangement elements for receiving radio frequency energy in the ISM band, wherein the gain of the Month? M0 arrangement element is proportional to the weight w¡ . 7. A method for directing a receiving lobe of an adaptive antenna arrangement toward an aircraft in flight comprising the steps of: providing an aircraft tracking service and obtaining aircraft position information thereof; calculating a position vector g based on the position information, the aircraft position vector g represents the aircraft direction of the adaptive antenna arrangement; calculate a weight vector w based on the position vector g; and providing the weight vector w to the elements of the adaptive antenna arrangement, such that a receiving lobe of the adaptive antenna arrangement is directed towards the aircraft.