Patent Application
20150077290
The present disclosure relates generally to managing interference using an adjustable phased array antenna, and more particularly to systems and methods for locating the source of and mitigating the effects of interference using an adjustable phased array antenna.
Antenna arrays can be used to estimate the direction-of-arrival (DOA) of incoming signals employing one or more signal processing algorithms. These methods measure and process received signals to determine the direction-of-arrival information. In one class of approaches for geolocation, known as beamspace processing, the signal processing is formed after beamforming Existing beamspace processing approaches are either noncoherent or coherent. In noncoherent geolocation one or two antenna beams point near but not directly at the direction of an interferer. This can be accomplished by a spiral scan or grid scan. A gain slope of the antenna pattern provides directional sensitivity. Coherent geolocation uses two or more antenna beams pointed in different directions. A phase difference between interferer signals received in the two antenna beams reveals one angle of arrival. Repeating this process for north-south and east-west separated beam centers reveals the complete direction of arrival from the interferer. Both of these approaches interrupt communication service in the beams employed. Noncoherent geolocation is relatively slow, requiring movement of the beam centers. Coherent geolocation is faster and more accurate than noncoherent geolocation but it still requires pre-emption (i.e., interruption) of communication service.
Given that known geolocation systems currently require dedication of one or more receiving antenna beam, thereby removing the beam or beams from communication service, a system that enables geolocation to be performed while allowing communication service to continue would be beneficial.
In one aspect, a method for mitigating interference using a phased array receiving antenna is provided. The method includes perturbing a first communications beam and a second communications beam received at the phased array receiving antenna to generate a first composite beam and a second composite beam, cross-correlating the first composite beam and the second composite beam, receiving communications data using the first composite beam and the second composite beam, and determining a direction of a received interference signal based on the cross-correlation of the first composite beam and the second composite beam.
In another aspect, a communications satellite comprising a phased array receiving antenna is provided. The communications satellite is configured to perturb a first communications beam and a second communications beam received at the phased array receiving antenna to generate a first composite beam and a second composite beam, cross-correlate the first composite beam and the second composite beam, receive communications data using the first composite beam and the second composite beam, and determine a direction of a received interference signal based on the cross-correlation of the first composite beam and the second composite beam.
In another aspect, a non-transitory computer-readable medium having computer-executable instructions embodied thereon is provided. When executed by a communications satellite comprising a phased array receiving antenna and at least one processor in communication with the phased array receiving antenna, the computer-executable instructions cause the communications satellite to perturb a first communications beam and a second communications beam received at the phased array receiving antenna to generate a first composite beam and a second composite beam, cross-correlate the first composite beam and the second composite beam, receive communications data using the first composite beam and the second composite beam, and determine a direction of a received interference signal based on the cross-correlation of the first composite beam and the second composite beam.
Processor 504 may include any type of conventional processor, microprocessor, or processing logic that interprets and executes instructions. Main memory 506 may include a random access memory (RAM) or another type of dynamic storage device that stores information and instructions for execution by processor 504. ROM 508 may include a conventional ROM device or another type of static storage device that stores static information and instructions for use by processor 504. Storage device 510 may include a magnetic and/or optical recording medium and its corresponding drive.
Input device 512 may include a conventional mechanism that permits computing device 500 to receive commands, instructions, or other inputs from a user, including visual, audio, touch, button presses, stylus taps, etc. Additionally, input device may receive location information. Accordingly, input device 512 may include, for example, a camera, a microphone, one or more buttons, and/or a touch screen. Output device 514 may include a conventional mechanism that outputs information to a user, including a display (including a touch screen) and/or a speaker. Communication interface 516 may include any transceiver-like mechanism that enables computing device 500 to communicate with other devices and/or systems. For example, communication interface 516 may include mechanisms for communicating with another device, such as phased array receiving antenna 300, communication sources 104, 106, 108 and/or other devices (not shown).
As described herein, computing device 500 facilitates mitigating interference from at least one interference source, such as interference source 110, at least by transmitting instructions to phase shifters 318, 320, 322, 324, 326, 328, 330, and 332 and attenuators 334, 336, 338, 340, 342, 344, 346, and 348 of phased array receiving antenna 300 to generate multiple composite beams 124 and 126, and determine a direction of a received interference signal 118 by cross-correlating first composite beam 124 and second composite beam 126. Computing device 500 may perform these and other operations in response to processor 504 executing software instructions contained in a computer-readable medium, such as memory 506. A computer-readable medium may be defined as a physical or logical memory device and/or carrier wave. The software instructions may be read into memory 506 from another computer-readable medium, such as data storage device 510, or from another device via communication interface 516. The software instructions contained in memory 506 may cause processor 504 to perform processes described herein. In other implementations, hardwired circuitry may be used in place of or in combination with software instructions to implement processes consistent with the subject matter herein. Thus, implementations consistent with the principles of the subject matter disclosed herein are not limited to any specific combination of hardware circuitry and software.
More specifically, in at least some implementations, communications satellite 102 receives communications data as described above concurrently with determining the direction of received interference signal 118. In other words, the perturbations to the beams, for example first communications beam 112 and second communications beam 114, are small enough to maintain sufficient link margin such that there are no communications service interruptions while determining the direction of interference signal 118 received from interference source 110 (i.e., “the geolocation process”). Accordingly, communications satellite 102 performs the geolocation process in the background as regular communications are in progress. In perturbing a communications beam, for example first communications beam 112, communications satellite 102 modifies a set of beamforming coefficients for a corresponding beamport, for example beamport 352, in a way that generates a sub-beam, for example sub-beam 120, under the base communications beam (e.g., first communications beam 112). This process may be referred to as “beam-under-beam processing.” Beamport 352 then carries a superposition of the perturbed communications beam (e.g., first communications beam 112) and sub-beam 120 as a composite beam, for example first composite beam 124. Second composite beam 126 is generated in a similar manner.
In one example implementation, the sub-beam, for example first sub-beam 120, is of a fan-shaped type that is generated using one row (e.g., first row 478) or one column (e.g., first column 460) of phased array receiving antenna 300. The magnitude of first sub-beam 120 is lower than the magnitude of first communications beam 112 such that a link margin required to continue receiving communications data from first communications source 104 is maintained. First sub-beam 120 provides the necessary information for geolocation when used in conjunction with a second beamport (e.g. beamport 354) similarly configured with a second sub-beam (e.g., second sub-beam 122). Each beamport 352 and 354 steps through a predetermined set of directions for each corresponding sub-beam 120 and 122 and communications satellite 102 generates a covariance matrix. Each element of the covariance matrix encapsulates the cross-correlation between first sub-beam 120, which is pointed is a first direction and has a first orientation, and second sub-beam 122, which is pointed in a second direction and has a second orientation.
In another example implementation, a sub-beam, for example first sub-beam 120 is pseudo-random in nature and is generated by selective phase reversals of selected array elements along a periphery of phased array receiving antenna 300. As described above, array elements 400-407, 415-316, 302-314, and 408-448 form a periphery of phased array receiving antenna 300. Communications satellite 102 selects a subset of array elements 400-407, 415-316, 302-314, and 408-448 to generate first sub-beam 120 such that the link margin described above is maintained for receiving communications data from first communications source 104. Likewise, communications satellite 102 selects a subset of array elements 400-407, 415-316, 302-314, and 408-448 for generating second sub-beam while maintaining the link margin required for communications. The link margin may be predetermined as required for communications.
In another example implementation, communications satellite 102 replaces coefficients of first communications beam 112 with 1 s and −1 is in a checkerboard pattern with corresponding attenuators 334, 336, 338, 340, 342, 344, 346, 348 set at their maximum level to generate a low level sub-beam (e.g., first sub-beam 120) over a region of interest. Only one feed is excited, with low or no attenuation, to capture the signals of that feed. A similar process may be performed to generate second sub-beam 122. This implementation enables element-space processing using beamformer 350 and may be employed for a relatively short period of time interleaved with receiving communications data from communications source 104. The pattern of coefficients suppresses received signals for all but one feed.
In all of the above example implementations, the correlation between beamports 352 and 354 is computed. As described above, beamport 352 receives first composite beam 124 and beamport 354 receives second composite beam 126. Beamport 352 has two components: a first component that is formed by excitation coefficients for first communications beam 112 and a second component that is formed by excitation coefficients for first sub-beam 120. More specifically, the excitation coefficients used for first sub-beam 120 are replacement excitation coefficients to normal excitation coefficients used for first communications beam 112. The replacement excitation coefficients are applied to a subset of array elements of phased array receiving antenna 300, and thereby excite the subset of array elements, to form first sub-beam 120. Likewise, a similar process applies to second communications beam 114 and second sub-beam 122. Accordingly, beamport 354 has two components: a first component that is formed by excitation coefficients for second communications beam 114 and a second component that is formed by excitation coefficients for second sub-beam 122. In some implementations, phases of the replacement excitations are synchronously varied. Additionally, in some implementations, the subset of array elements used for first sub-beam 120 are disjoint from the subset of array elements used for second sub-beam 122. A desired correlation is between first sub-beam 120 and second sub-beam 122.
Communications satellite 102 may use the following process to extract the correlation: Let the signal of beamport 352 be S1=A+X, where A represents a signal of first communications beam 112 and X represents a signal of first sub-beam 120. Let the signal of beamport 354 be S2=B+Y, where B represents second communications beam 114 and Y represents second sub-beam 122. What is needed is the correlation between X and Y (i.e., <XY>). The direct correlation of beamports 352 and 354, <S1S2>, which is also representative of the correlation between first composite beam 124 and second composite beam 126, produces <AB>+<AY>+<XB>+<XY>. To extract <XY>, three additional correlations are formed by flipping the signs of the signals of sub-beams 120 and 122. In this manner, the following four correlations are formed: C1=<(A+X)(B+Y)>, C2=<(A+X)(B−Y)>, C3=<(A−X)(B+Y)>, and C4=<(A−X)(B−Y)>. After these measurements, <XY> is proportional to C1-C2-C3+C4. As previously mentioned, phases of the replacement excitations may be varied. Thus, for example, the process may include varying the phases of the first set of replacement excitations and varying the phases of the second set of replacement excitations through: normal first sub-beam excitations and normal second sub-beam excitations, normal first sub-beam excitations and inverted second sub-beam excitations, inverted first sub-beam excitations and inverted second sub-beam excitations, and inverted first sub-beam excitations and normal second sub-beam excitations.
In some implementations, in determining a direction of a received interference signal, such as interference signal 118, communications satellite 102 estimates an angle of arrival of interference signal 118. Also, in some implementations, in estimating the angle of arrival, communications satellite 102 geolocates interference signal 118 and/or interference source 110. Also, in some implementations, communications satellite 102 determines a pointing direction of phased array receiving antenna 300 based on the estimated angle of arrival. Additionally, in some implementations, communications satellite 102 determines a pointing direction of a spacecraft attitude based on the estimated angle of arrival.
In the above example implementations, only two beamports are used. However, because link performance is maintained for any beamports used for geolocation, additional beams can optionally be used without affecting system resources. If more beamports are allocated to this process, the covariance matrix can be computed faster and more accurately, resulting in an alternative implementation that improves geolocation cycle time at the expense of additional processing complexity.
A technical effect of systems and methods described herein includes at least one of: (a) perturbing a first communications beam and a second communications beam received at a phased array receiving antenna to generate a first composite beam and a second composite beam; (b) cross-correlating the first composite beam and the second composite beam; (c) receiving communications data using the first composite beam and the second composite beam; and (d) determining a direction of a received interference signal based on the cross-correlation of the first composite beam and the second composite beam.
As compared to known methods and systems for geolocating or otherwise mitigating a source of an interference signal, the methods and systems described herein facilitate geolocating or otherwise mitigating a source of an interference signal received at a communications satellite while enabling communication service to continue through the communications satellite.
The description of the different advantageous implementations has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the implementations in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous implementations may provide different advantages as compared to other advantageous implementations. The implementation or implementations selected are chosen and described in order to best explain the principles of the implementations, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various implementations with various modifications as are suited to the particular use contemplated. This written description uses examples to disclose various implementations, which include the best mode, to enable any person skilled in the art to practice those implementations, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
