Abstract:
Signal acquisition methods and receivers utilizing such signal acquisition methods are disclosed. More specifically, a signal acquisition method may include: identifying a list of available beam patterns that an antenna unit is configured to provide; iteratively searching for satellite signals by controlling the antenna unit to utilize one of the list of available beam patterns in each iteration; determining whether a satellite signal is detected in each iteration; collecting ephemeris data of a satellite producing the satellite signal when the satellite signal is detected in each iteration; and controlling beamforming operations of the antenna unit for satellite signal acquisition based on the ephemeris data collected.

Description:
BACKGROUND 
       [0001]    Satellite navigation systems, such as the Global Positioning System (GPS), utilize satellites to provide location and time information to GPS receivers. During initial acquisition of satellite signals, however, a GPS receiver may not have the precise time, satellite almanac, and user location information necessary to perform antenna beamforming operations to acquire satellite signals. A GPS receiver may therefore default to a “search the sky” mode of operation to search for all available satellites in the sky above the GPS receiver. 
         [0002]    A GPS receiver typically performs the “search the sky” mode of operation by passing through and not manipulating its antenna gain pattern at all in order to simulate an omnidirectional gain pattern. It is noted, however, that the simulated omnidirectional gain pattern provided in this manner often incur significantly reduced gain, inhibiting the ability of the GPS receiver to acquire satellite signals even without presence of jamming signals. The problem may be particularly noticeable if the antenna is installed on an aircraft, especially if the antenna is recessed into the skin of the aircraft. 
       SUMMARY 
       [0003]    In one aspect, embodiments of the inventive concepts disclosed herein are directed to a signal acquisition method. The method may include identifying a list of available beam patterns that an antenna unit is configured to provide; iteratively searching for satellite signals by controlling the antenna unit to utilize one of the list of available beam patterns in each iteration; determining whether a satellite signal is detected in each iteration; collecting ephemeris data of a satellite producing the satellite signal when the satellite signal is detected in each iteration; and controlling beamforming operations of the antenna unit for satellite signal acquisition based on the ephemeris data collected. 
         [0004]    In a further aspect, embodiments of the inventive concepts disclosed herein are directed to a receiver. The receiver may include an antenna unit and at least one processor in communication with the antenna unit. The least one processor may be configured to: identify a list of available beam patterns that the antenna unit is configured to provide; iteratively search for satellite signals by controlling the antenna unit to utilize one of the list of available beam patterns in each iteration; determine whether a satellite signal is detected in each iteration; collect ephemeris data of a satellite producing the satellite signal when the satellite signal is detected in each iteration; and control beamforming operations of the antenna unit for satellite signal acquisition based on the ephemeris data collected. 
         [0005]    In another aspect, embodiments of the inventive concepts disclosed herein are directed to a GPS receiver. The GPS receiver may include an antenna unit and at least one processor in communication with the antenna unit. The least one processor may be configured to: identify a list of available beam patterns that the antenna unit is configured to provide; iteratively search for GPS signals by controlling the antenna unit to utilize one of the list of available beam patterns in each iteration; determine whether a GPS signal is detected in each iteration; collect ephemeris data of a GPS satellite producing the GPS signal when the GPS signal is detected in each iteration; and control beamforming operations of the antenna unit for GPS signal acquisition based on the ephemeris data collected. 
         [0006]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the inventive concepts disclosed and claimed herein. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the inventive concepts and together with the general description, serve to explain the principles and features of the inventive concepts disclosed herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The numerous objects and advantages of the inventive concepts disclosed herein may be better understood by those skilled in the art by reference to the accompanying figures in which: 
           [0008]      FIG. 1  is a block diagram depicting a satellite signal receiver according to an exemplary embodiment of the inventive concepts disclosed herein; 
           [0009]      FIG. 2  is an illustration depicting beam patterns that may be formed by an antenna unit of a satellite signal receiver; 
           [0010]      FIG. 3  is an illustration depicting a summation of the beam patterns shown in  FIG. 2 ; and 
           [0011]      FIG. 4  is a flow diagram depicting a satellite signal acquisition method according to an exemplary embodiment of the inventive concepts disclosed herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Reference will now be made in detail to exemplary embodiments of the inventive concepts disclosed herein, examples of which are illustrated in the accompanying drawings. 
         [0013]    Embodiments in accordance with the inventive concepts disclosed herein are directed to satellite signal acquisition techniques and receivers utilizing such satellite signal acquisition techniques. More specifically, beamforming antenna electronics may be configured to splay the beams in an optimal fashion to provide maximum sky coverage and significant gain improvement, allowing a receiver configured in accordance with the inventive concepts disclosed herein to take advantages of the beamforming abilities of the antenna electronics when searching for satellites. 
         [0014]    Referring to  FIG. 1 , a simplified block diagram depicting a receiver  100  configured according to an exemplary embodiment of the inventive concepts disclosed herein is shown. For illustrative purposes, specific references to the Global Positioning System (GPS) may be utilized in some of the examples described below. It is to be understood, however, that the receiver  100  and the signal acquisition method utilized by the receiver  100  may be applicable to acquire other types of signals without departing from the broad scope of the inventive concepts disclosed herein. 
         [0015]    As shown in  FIG. 1 , the receiver  100  may include an antenna unit  102  in communication with a processor unit  104 . The processor unit  104  may include one or more processors configured to control operations of the antenna unit  102  and to process signals received at the antenna unit  102 . It is contemplated that the one or more processors may be implemented as dedicated processing devices, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or various other types of processors or processing devices. 
         [0016]    The antenna unit  102  may include one or more antennas with beamforming abilities. The beamforming abilities of the antenna unit  102  may allow the antenna unit  102  to form a number of beam patterns. In case of GPS receivers, for example, the antenna unit  102  may include a controlled reception pattern antenna (CRPA). 
         [0017]      FIG. 2  is an illustration depicting various beam patterns that may be provided for the GPS L 1  frequency utilizing an exemplary antenna unit  102 . For illustrative purposes, an exemplary sixteen-beam connection between the antenna unit  102  and the processor unit  104  is depicted, where eight of the sixteen beam patterns may be used for the GPS L 1  frequency and the other eight of the sixteen beam patterns may be used for the GPS L 2  frequency. It is noted that only the GPS L 1  frequency is depicted in  FIG. 2  because the GPS L 1  frequency is utilized by the GPS satellites to transmit Coarse/Acquisition (C/A) code for signal acquisition purposes. It is to be understood that beam patterns may be provided for other frequencies without departing from the broad scope of the inventive concepts disclosed herein. It is also to be understood that the antenna unit  102  may be able to form beam patterns that are different from those depicted in  FIG. 2  (in terms of numbers and/or coverage areas) without departing from the broad scope of the inventive concepts disclosed herein. 
         [0018]    For illustrative purposes, however, suppose the antenna unit  102  is capable of providing eight beam patterns labeled patterns A through H for the GPS L 1  frequency as shown in  FIG. 2 . It is noted that while each particular beam pattern shown in  FIG. 2  may be focused primarily on a relatively small portion of the sky, the sum of the coverage provided by all of the beam patterns A through H, as depicted in  FIG. 3 , may effectively cover substantially the entire sky above the antenna unit  102 . Therefore, instead of using the antenna unit  102  in a pass through mode to provide an omnidirectional gain pattern in an attempt to search the sky, an iterative process may be utilized to iteratively search for satellite signals one beam pattern at a time until desired satellite signals have been acquired successfully and/or until all available beam patterns have been exhausted. It certain implementations, the iterative search process may be repeated until at least the desired number of satellite signals have been acquired. 
         [0019]    It is noted that searching for satellite signals one beam pattern at time allows the antenna unit  102  to produce significantly more gain within a given portion of the sky in comparison to the gain provided within the same portion of the sky if an omnidirectional pattern is utilized. It is noted that providing more gain effectively improves the ability of the receiver  100  to acquire satellite signals, and any shortcomings associated with limited coverage areas may be effectively mitigated as the result of the iterative process, which eventually covers substantially the same area as an omnidirectional pattern would. It may therefore be beneficial to configure the antenna unit  102  to carry out the iterative search process as described above. 
         [0020]      FIG. 4  is a flow diagram depicting a satellite signal acquisition method  400  that may be utilized by the processor unit  104  to control the operations of the antenna unit  102  during satellite signal acquisition. Referring generally to  FIGS. 1-4 , a list of available beam patterns A through H that the antenna unit  102  is capable of providing may be identified in a step  402 . A step  404  may be carried out iteratively to activate one particular beam pattern out of the list of available beam patterns for the purpose of searching for satellite signals. If it is determined in a step  406  that no satellite signal is detected utilizing the particular beam pattern activated in the step  404 , the step  404  may be repeated to activate another beam pattern out of the list of available beam patterns. On the other hand, if satellites signal(s) have been detected utilizing the beam pattern activated in the step  404 , ephemeris data of the satellite(s)  108  producing the detected satellite signal(s) may be collected and stored in one or more non-transitory processor-readable memories  106  in a step  408 . The method  400  may repeat again from the step  404  until all available beam patterns have been exhausted, or repeat until ephemeris data of at least a predetermined number of satellites have been successfully collected (e.g., four or more satellites in case of GPS receivers), in which case the method  400  may terminate in a step  410 . Subsequently, the ephemeris data of the various satellites collected may be utilized to control beamforming operations of the antenna unit  102  to acquire satellite signals in a step  412 . 
         [0021]    It is contemplated that the satellite signal acquisition method  400  may be utilized as long as the location and attitude of the receiver  100  remain relatively static or deterministic for the duration of the acquisition process. It is noted that a GPS receiver  100  installed on an aircraft may utilize the satellite signal acquisition method  400  without any significant concerns because modern implementations of GPS receivers  100  may be able to complete the acquisition process within a period of time that the location and attitude of the aircraft (and hence the GPS receiver  100  installed on the aircraft) may be considered relatively static. It is also noted that even if an aircraft changes its position very rapidly during the acquisition process, the satellite signal acquisition method  400  may still be applicable by compensating for the location and/or attitude changes of the aircraft (e.g., determined utilizing an inertial navigation system or the like co-located on the aircraft). 
         [0022]    It is to be understood that the specific references to GPS receivers in the examples above are merely exemplary and are not meant to be limiting. It is contemplated that any satellite signal receiver  100  utilizing antennas  102  with beamforming abilities may implement the satellite signal acquisition method  400  without departing from the broad scope of the inventive concepts disclosed herein. It is also to be understood that the specific references to receivers installed on aircraft are merely exemplary and are not meant to be limiting. It is contemplated that receivers  100  configured in accordance with the inventive concepts disclosed herein may be utilized by various mobile and/or stationary platforms without departing from the broad scope of the inventive concepts disclosed herein. 
         [0023]    It is also to be understood that the specific references to GPS satellites in the examples above are merely exemplary. It is contemplated that receivers  100  configured in accordance with the inventive concepts disclosed herein may be utilized to acquire signals from other types of satellites and/or satellite constellations, including satellites that orbit in Low Earth Orbit (LEO). It is also contemplated that receivers  100  configured in accordance with the inventive concepts disclosed herein may be utilized in other types of systems (in addition to navigation systems). For instance, a communication system that supports two-way data transmissions with one or more satellites may utilize one or more receivers  100  without departing from the broad scope of the inventive concepts disclosed herein. It is further contemplated that the receivers  100  may be adapted to search for signals originated from other sources in addition to satellite signals without departing from the broad scope of the inventive concepts disclosed herein. 
         [0024]    Further, it is to be understood that the specific reference to a sixteen-beam antenna unit  102  capable of forming eight beam patterns in the GPS L 1  frequency to facilitate satellite signal acquisition is merely exemplary. It is contemplated that antenna units  102  capable of forming more (or less) than eight beam patterns may be utilized to facilitate satellite signal acquisition without departing from the broad scope of the inventive concepts disclosed herein. In certain instances, the abilities to form more beam patterns with closer angular spacing may be appreciated. 
         [0025]    It is to be understood that embodiments of the inventive concepts disclosed herein may be conveniently implemented in forms of a software, hardware or firmware package. Such a package may be a computer program product which employs a computer-readable storage medium including stored computer code which is used to program a computer to perform the disclosed function and process of the present invention. The computer-readable medium may include, but is not limited to, any type of conventional floppy disk, optical disk, CD-ROM, magnetic disk, hard disk drive, magneto-optical disk, ROM, RAM, EPROM, EEPROM, magnetic or optical card, or any other suitable media for storing electronic instructions. 
         [0026]    It is to be understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. It is to be understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the broad scope of the inventive concepts disclosed herein. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
         [0027]    It is believed that the inventive concepts disclosed herein and many of their attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction, and arrangement of the components thereof without departing from the broad scope of the inventive concepts or without sacrificing all of their material advantages. The form herein before described being merely an explanatory embodiment thereof, it is the intention of the following claims to encompass and include such changes.