Abstract:
A mobile satellite radio equipped with a phased array antenna configures the phased array antenna in one or more non-directional operating modes in order to initially detect a signal from a communication satellite. Once a signal has been received from the satellite, frequency information determined in the course of operating in the one or more non-directional modes is used to configure the mobile satellite radio for operation in a subsequent stage when the phased array antenna is configured in a directional mode. In the subsequent stage the phased array antenna is used to scan a solid angle space to determine the direction of the satellite. Thereafter the antenna is used in the directional mode for satellite communication.

Description:
RELATED APPLICATION DATA 
       [0001]    This application is based on provisional U.S. patent application Ser. No. 61/799,183 filed Mar. 15, 2013. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to satellite communications. 
       BACKGROUND 
       [0003]    While cellular telephone networks and wireless local area networks (LANs) provide ready access to global communication networks from cities, suburbs and even rural areas in the developed world, there are still vast areas of the world where access to communication via the aforementioned wireless communications or via regular telephone networks is not available. In such instances communications via satellites is a viable option. Satellite communications can be useful to a variety of civilian and military users. 
         [0004]    Various companies and consortia have placed constellations of communication satellites in orbit around the earth for the purpose of providing communication in remote locations. Some such satellites are in geosynchronous orbits and some are in lower, shorter period orbits. 
         [0005]    Geosynchronous satellites have the advantage that they provide persistent communications for the area that they serve. Disadvantageously, there is a lag in communications through geosynchronous satellites due to time required for signals to travel to and from satellites in geosynchronous orbits. Additionally geosynchronous satellites by virtue of their location at or near the equatorial plane do not provide service to the polar regions. 
         [0006]    Communications satellites in lower, shorter period orbits resolve the communication lag issue and are able to serve the polar region. However disadvantageously, the shorter period orbits do not provide persistent communication connectivity because the satellite rapidly traverses from horizon to horizon while communications are taking place. For example from a user&#39;s perspective a short period satellite might traverse from horizon to horizon in a few minutes. 
         [0007]    To communicate with the communication satellites, a mobile satellite radio is used. The mobile satellite radio can be a handheld device or attached to a mobile object such as, for example, a sea, land or air conveyance. Such mobile satellite radios either include an affixed antenna or are adapted to connect to an external antenna. The antenna may be an omnidirectional antenna or a directional antenna. A directional antenna offers the advantage of higher directivity or gain which leads to a higher link budget. With a directional antenna, higher data rates can be attained for a given transmit power or for a given receiver sensitivity. On the other hand directional antennas must be properly oriented towards a satellite with which they are communicating. 
         [0008]    Operation of a mobile satellite radio may be initiated when location of the radio is not known and the terrain may be sloped. In these circumstances the direction of satellite, even if it is fixed, is not known. Additionally, satellites may serve different zones with different frequencies and the zone and corresponding frequency of any given geographic location where it is desired to initiate satellite communication may not be known at the outset. Thus for a directional antenna one would need to try different frequencies and for each frequency one would need to scan the aiming direction of the antenna through a solid angle search space (i.e., varying both elevation and azimuth directions). For geostationary satellites it is possible, if the position of the satellite and longitude and latitude of the terminal are known, to determine the correct pointing direction. However, it can be a time consuming process and may be burdensome especially in the case of time sensitive, mission critical communications. 
         [0009]    What is needed is a method to rapidly establish satellite communications. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0010]    The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
           [0011]      FIG. 1  is a schematic representation of a satellite communication system; 
           [0012]      FIG. 2  is a block diagram of a mobile satellite radio; 
           [0013]      FIG. 3  is a block diagram of a modular mobile satellite radio according to an alternative embodiment of the invention; 
           [0014]      FIG. 4  is a perspective view of an antenna element array of a phased array antenna according to an embodiment of the invention; 
           [0015]      FIG. 5  is 3-D directivity plot for the antenna element array shown in  FIG. 4  when configured to operate in a first non-directional mode; 
           [0016]      FIG. 6  is 3-D directivity plot for the antenna element array shown in  FIG. 4  when configured to operate in a second non-directional mode; and 
           [0017]      FIG. 7  is a flowchart of a method of operating the mobile satellite radios shown in  FIGS. 1-3  according to an embodiment of the invention. 
       
    
    
       [0018]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
       DETAILED DESCRIPTION 
       [0019]      FIG. 1  is a schematic representation of a satellite communication system  100 . The satellite communication system  100  includes a constellation of communication satellites  102 . A mobile satellite radio  104  is used to communicate with and through the satellites  102 . The mobile satellite radio  104  is communicatively coupled to a laptop computer  106 , so that computer communications such as videoconferencing, email, and World Wide Web browsing may be conducted via satellite. The satellites  102  communicate with one or more ground stations  108  (only one of which is shown). The ground stations  108  are coupled to the regular terrestrial telephone network or other network (not shown). The satellites  102  will relay communications from the mobile satellite radio  104  to the ground station  108  from which they will be coupled to terrestrial or other networks. Communications will also flow in the reverse direction. 
         [0020]      FIG. 2  is a block diagram of a mobile satellite radio  200  according to an embodiment of the invention.  FIG. 2  shows one possible embodiment of the mobile radio  104  shown in  FIG. 1 . The mobile satellite radio  200  includes a controller  202  coupled to a transceiver  204  and to a digital phase shifter array  206  of a phased array antenna  208 . 
         [0021]    The transceiver  204  comprises an input/output (I/O) interface  210  coupled to an encoder  212  and a decoder  214 . The I/O interface  210  is useful for coupling to external data sources and/or data sinks such as the laptop computer  106 . The I/O interface  210  may, for example, comprise an industry standard interface such as a Universal Serial bus (USB) port. 
         [0022]    The encoder  212  is coupled to a modulator  216 . At least one local oscillator  218  is also coupled to the modulator  216 . The modulator  216  modulates a carrier signal generated by the local oscillator  218  based on input from the encoder  212 . The output of the modulator  216  is coupled to a power amplifier  220 . 
         [0023]    A low noise amplifier  222  is coupled to a demodulator  224 . The at least one local oscillator  218  is also coupled to the demodulator  224 . The output of the demodulator  224  is coupled to the decoder  214 . 
         [0024]    Both the power amplifier  220  and the low noise amplifier  222  are coupled to the digital phase shifter array  206 . The digital phase shifter array  206  suitably comprises one digitally controlled phase shifter for each antenna element ( 402 ,  FIG. 4 ) of an antenna element array  226 . 
         [0025]    The controller  202  is coupled to the at least one local oscillator  218  and is able to set the at least one local oscillator  218  to one of multiple operating frequencies so as to configure the transceiver  204  to receive signals in one of multiple frequency bands. The controller  202  is also coupled to the digital phase shifter array  206  and is able to set the phase shift of signals coupled to and from each element  402  ( FIG. 4 ) of the antenna element array  226 . By appropriately setting the phase shift for each antenna element the controller  202  is able to configure the phased array antenna  208  into a directional antenna configuration and steer the aim direction of maximum gain to different directions. Operation of a phased array antenna in a directional configuration is known to person&#39;s of ordinary skill in the art. 
         [0026]    The controller  202  can also set the phase shift for each antenna element  402  ( FIG. 4 ) to such relative values as to configure the phased array antenna  208  into a non-directional configuration. 
         [0027]    When the antenna is set to a non-directional mode it is able to receive signals from a greater range of directions, and in principle could detect satellites situated somewhere in such a range of direction, however in such a non-directional mode the signal output by the phased array antenna  208  will be much weaker and in certain cases too weak for relatively high data rate communications, due to the lower link budget. Nonetheless the transceiver  204  (and transceiver  320  shown in  FIG. 3 , and internal receiver  306  shown in  FIG. 4 ) can be used to detect the signal. 
         [0028]      FIG. 3  is a block diagram of a modular mobile satellite radio  300  according to an alternative embodiment of the invention.  FIG. 3  shows another possible embodiment of the mobile radio  104  shown in  FIG. 1 . The modular mobile satellite radio  300  includes a separate phased array antenna  302  that includes a directional coupler  304  the routes a portion of received signals that are output by the digital phase shifter array  206  to an internal receiver  306 . Within the internal receiver  306  signals received from the directional coupler  304  are routed to a mixer  308  which also receives signals from a tunable second local oscillator  310 . The tunable second local oscillator  310  is coupled to and receives frequency control signals from an antenna controller  312 . The mixer  308  is coupled to and outputs signals to a band pass filter  314 . The band pass filter  314  is coupled to and outputs signals to a log amplifier  316  which in turn is coupled to and output signals to analog-to-digital converter  318 . The antenna controller  312  is also coupled the digital phase shifter array  206  and can set the phase delays of each phase shifter in the digital phase shifter array  206  to steer the gain pattern when the phased array antenna  302  is configured in a directional mode or to configure the phased array antenna  302  into one or more non-directional modes. The modular satellite mobile radio  300  has a main transceiver  320  that in addition to the components included in the transceiver  204  shown in  FIG. 2  has an internal controller  322 . The antenna controller  312  is coupled to the internal controller  322  of the transceiver  320  and communicates frequency information so that the internal controller  322  of the main transceiver  320  is able to tune the transceiver to an active satellite frequency based on information received from the antenna controller  312 . The phased array antenna  302  is detachably coupled to the main transceiver  320  through a set of connectors  324 . Thus the phased array antenna  302 , having the advanced functionality described herein can be used with existing equipment. 
         [0029]    In operation the antenna controller  312  sets phase delays of the digital phase shifter array  206  so as to put the phased array antenna  302  into one or more non-directional modes and then successively tunes the tunable local oscillator  310  to a set of frequency channels while monitoring the output of the analog-to-digital converter  318  to which it is coupled in order to search the set of frequency channels for an active satellite channel. According to certain embodiments the antenna controller  312  simply checks for any signals having energy meeting a predetermined threshold. According to other embodiments the antenna controller checks for signals having a certain envelope modulation pattern. After an active satellite channel has been located while operating the phased array antenna  302  in one or more non-directional modes, the antenna controller  312  reconfigures the phased array antenna  302  into a directional mode and begins a search through a solid angle search space in order to determine the angular coordinates of the satellite that emitted the signals that were detected while operating the antenna  302  in the one or more non-directional modes. If the satellite is not in geosychronous orbit, or if the modular mobile satellite radio  300  is itself in motion the antenna controller  312  can then operate the phased array antenna  302  to track the satellite. 
         [0030]      FIG. 4  is a perspective view of an antenna element array  400  of the phased array antennas  208 ,  302  according to an embodiment of the invention.  FIG. 4  shows one possible embodiment of the antenna element array  226  shown in  FIG. 2  and  FIG. 3 . As shown in  FIG. 4  the antenna element array  400  is a 4 by 4 array of antenna elements  402  (only three of which are numbered to avoid crowding the drawing). Each antenna element  402  of the antenna element array  400  is a quadrifilar helical antenna. According to alternative embodiments of the invention array sizes other than 4 by 4 are used. Also the array  400  need not necessarily be a square array, but could be rectangular, circular, hexagonal or have a different configuration. According to alternative embodiments, in lieu of quadrifilar helical antenna elements, different types of antenna elements are used, for example, patch antenna elements or slot antenna elements. 
         [0031]      FIG. 5  is 3-D directivity plot  500  for the antenna element array  400  shown in  FIG. 4  when configured to operate in a first non-directional mode. This first non-directional pattern is distinguished from the usual directional patterns which are produced by phased array antennas. A set of phase shifts that can be established by the digital phase shifter array  206  in order to configure the phased array antenna  208  to produce the directivity pattern shown in  FIG. 5  is shown in table I below. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
             
             
               
                   
                 105° 
                   0° 
                   0° 
                 105° 
               
               
                   
                  0° 
                 −105° 
                 −105° 
                  0° 
               
               
                   
                  0° 
                 −105° 
                 −105° 
                  0° 
               
               
                   
                 105° 
                   0° 
                   0° 
                 105° 
               
               
                   
                   
               
             
          
         
       
     
         [0032]    The position of the entries in table I and table II below correspond to position of the antenna elements  402  in the antenna element array  400 . The set of phase shifts shown in Table I includes a first group of equal phase shifts of a first value (−105° applied to a first group of antenna elements  302  located at the center of the array of antenna elements, a second group of equal phase shifts of a second value (105°) applied to a second group of antenna elements  302  located at corners of the array of antenna elements and a third group of phase shifts having values (0°) that are between said first value and said second value applied to a third group of remaining antenna elements  302 . 
         [0033]      FIG. 6  is 3-D directivity plot  600  for the antenna element array  400  shown in  FIG. 4  when configured to operate in a second non-directional mode. This second non-directional pattern is also distinguished from the usual directional patterns which are produced by phased array antennas. A set of phase shifts that can be established by the digital phase shifter array  206  in order to configure the phased array antenna  208  to produce the directivity pattern shown in  FIG. 6  is shown in table II below. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE II 
               
               
                   
                   
               
             
             
               
                   
                 −105° 
                   0° 
                   0° 
                  105° 
               
               
                   
                   0° 
                  105° 
                 −105 
                   0° 
               
               
                   
                   0° 
                 −105° 
                  105° 
                   0° 
               
               
                   
                  105° 
                   0° 
                   0° 
                 −105° 
               
               
                   
                   
               
             
          
         
       
     
         [0034]    The set of phase shifts shown in Table II include phase shifts for elements in a block of four elements at the center of the array of elements, including phase shifts for an upper left element and a lower right element in the block having a first value and phase shifts for a upper right and lower left element in the block having a second value; phase shifts for elements at corners of the array of elements, including phase shifts for the upper right corner element and lower left corner element having the first value, and phase shifts for the upper left corner element and lower right corner element having the second value; and phase shifts for remaining elements having values that are between the first value and the second value. 
         [0035]      FIG. 7  is a flowchart of a method  700  of operating the mobile satellite radios  104 ,  200 ,  300  shown in  FIG. 1 ,  FIG. 2  and  FIG. 3  according to an embodiment of the invention. Block  702  is the top of a loop that runs through each K TH  non-directional beam pattern of a plurality of N non-directional beam patterns. Two non-directional beam patterns are shown in  FIG. 5  and  FIG. 6 . In certain embodiments only one non-directional beam pattern may be used, while in other embodiments more than one non-directional beam pattern may be used. One reason to use more than one non-directional beam pattern, is if each non-directional beam pattern for a particular antenna has certain angular regions of weak gain that are stronger in at least one other non-directional beam pattern. 
         [0036]    Block  704  is the top of a loop that runs through each J TH  of a plurality of M frequency bands. In the case of certain embodiments the satellites  102  may be transmitting on an a priori unknown frequency out of a set of possible frequencies, thus the mobile satellite radio  104 ,  200 ,  300  may need to check multiple frequencies before finding a frequency that can be used for communications. As discussed above in the background section a satellite may cover different zones with different frequency bands and the mobile satellite radio may not have foreknowledge of the zone in which it is situated and the corresponding frequency band. 
         [0037]    In block  706  the receiver (e.g.,  306  or included in transceivers  204 ,  320 ) is operated to try to receive a signal. The LNA  222  in combination with the demodulator  224 , decoder  214  and the local oscillator  218  can be said to constitute a receiver. Many other receiver architectures are known and can be used as alternatives. The outcome of succeeding decision block  708  depends on whether a signal was received in block  706 . If the outcome of decision block  708  is negative meaning that no signal was received then the method proceeds to decision block  710  the outcome of which depends on whether more of the M frequencies remain to be tried. 
         [0038]    If the outcome of decision block  710  is positive then in block  712 , the method  700  advances to a next available frequency and thereafter loops back to block  706  to check for communications in a corresponding frequency band. If on the other hand, the outcome of decision block  710  is negative meaning that there are no more frequencies to be tried, then the method  700  branches to decision block  714  the outcome of which depends on whether there are more non-directional beam patterns to be tried. 
         [0039]    If the outcome of decision block  714  is positive meaning that are more non-directional beam patterns to be tried then in block  716  the phased array antenna is reconfigured to the next non-directional beam pattern and thereafter the method returns to block  704  to begin checking through the plurality of M frequencies. 
         [0040]    If on the other hand the outcome of decision block  714  is negative meaning that there are no more non-directional beam patterns to be checked then the method may loop back to block  702  to restart the process described above. Although not shown, a limit may be imposed on the number of re-executions of the entire search that are performed without user intervention. After a pre-programmed number of executions of the loop commenced in block  702  a user interface device (e.g., display screen, indicator light) may be used to alert the user that the search for a satellite signal was unsuccessful. 
         [0041]    When the outcome of block  708  is positive meaning that a signal was received in block  706 , the method  700  branches to block  718  in which the receiver (e.g.,  306  or those included in transceivers  204 ,  320 ) is set to a frequency which was received in block  706  or is set to a frequency specified in the signal that was received in block  706  and decoded. In the latter case, in certain embodiments, the signal received in block  706  may be a control channel e.g., a broadcast control channel which bears information on available frequencies. Such a control channel may have higher energy per information symbol (e.g., bit) and thus may be more easily detected using a non-directional beam pattern. Additionally it should be noted that in certain embodiments when one is merely seeking to detect the frequency of a signal the higher error rate arising from the use of a non-directional antenna as opposed to a directional antenna may be tolerable. 
         [0042]    Next in block  720  the phased array antenna is configured in a directional mode by proper selection of phase shifts established by the digital phase shifter array  206  as known in the art and the antenna aiming direction is scanned through a solid angle (e.g., scanned in both azimuth and elevation angle) to locate the satellite angularly. Thereafter in block  722  communication with and through the satellite is carried out. A program that performs the method  700  can be executed by the controllers  202 ,  312 ,  322  of the mobile satellite radios  104 ,  200 ,  300 . 
         [0043]    In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.