Abstract:
A satellite communication system for aircraft having other than top-mounted satellite communication antennas, wherein the system includes an ability to optimize the operation of the system depending on the existence of other than top-mounted antennas and/or the angular distance between a normal line of such antennas and a line drawn from the antenna to a satellite.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention relates to copending application entitled “DUAL MODE SATELLITE TERMINAL FOR EMERGENCY OPERATION” filed on even date herewith by the same inventor and assigned to the same assignee. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to satellite communication systems and more particularly relates to airborne satellite communications systems and even more particularly relates to airborne satellite communication systems with a satellite antenna mounted on an aircraft at a position other than the top of the aircraft. 
     In the past, airborne satellite communication systems have been used extensively for aircraft to communicate, via satellite, to terrestrial positions. In many areas of the earth, a typical satellite communications system may have several satellites between which to choose for its communication path. Often these systems make their selection between these several satellites primarily upon the elevation angle of the satellite above the horizon. 
     While use of elevation angle for satellite selection has some beneficial aspects, especially for top-mounted antennas, it does have serious drawbacks, especially for antennas mounted in positions other than the top of the aircraft. 
     Consequently, there exists a need for improved satellite communication systems which utilize other than top mounted antennas. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to increase the capacity of airborne satellite communication systems. 
     It is a feature of the present invention to use side mounted antennas and an algorithm selecting satellites based upon their orthogonality with respect to the plane of the antenna on the aircraft. 
     It is an advantage of the present invention to increase the effectiveness of satellite communication antennas by improving the cross-sectional area of the antenna capable of capturing signals incident thereon. 
     It is another object of the present invention to reduce the time required for satellite selection. 
     It is another feature of the present invention to eliminate the need for mapping each antenna upon initialization of the satellite communication system. 
     It is another advantage of the present invention to allow airlines to maintain their telephone service in operation for longer time periods, thereby increasing revenues and profits. 
     It is yet another object of the present invention to provide for a more versatile satellite communication transmitter. 
     It is yet another feature of the present invention to include a satellite selection feature which will bias the satellite selection based upon particular characteristics of the antenna system in use. 
     It is yet another advantage of the present invention to reduce reconfirmation expense associated with reconfirming the satellite communication transmitter for differing aircraft installations and antenna characteristics. 
     The present invention is a method and apparatus for selecting among several available satellites by a satellite communications system, which system includes at least some antennas other than top-mounted antennas which is designed to satisfy the aforementioned needs, provide the previously stated objects, include the above listed features and achieve the already articulated advantages. 
     Accordingly, the present invention is a method and apparatus including a satellite selection algorithm which utilizes information relating to the types and locations of antennas on the aircraft and to the angle between an antenna normal line and a line to a satellite. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more fully understood by reading the following description of the preferred embodiments of the invention in conjunction with the appended drawings wherein: 
     FIG. 1 is a schematic diagram of a prior art satellite communication system. 
     FIG. 2 is a flow diagram of a method of satellite selection of the present invention. 
     FIG. 3 is a more detailed flow diagram of the “side-mount handover” section of FIG.  2 . 
     FIG. 4 is a more detailed flow diagram of the “select GES/Satellite-side-mount antenna” block of FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawings, wherein like numerals refer to like matter throughout, and more particularly to FIG. 1, there is shown a schematic representation of a satellite communication system, generally designated  100  of the prior art, including an airborne earth station segment  102 , a satellite segment  120 , and a ground earth station segment  140 . 
     Airborne earth station segment  102  is shown having an antenna  104 , which is typically disposed on the exterior surface of the aircraft and is typically designed for communicating with the satellite segment  120 , using RF communication in the L band; however, other frequencies could be readily substituted. Antenna  104  is coupled through amplifier  106  to transmitter/receiver  108 . An ACARS Management Unit (ACARS MU)  110  is shown coupled with transmitter/receiver  108  having a crew headset  112  coupled thereto. A cabin terminal unit (CTU)  109  is shown coupling the passenger headsets  114  with the transmitter/receiver  108 . Airborne earth station segments  102  are well known in the art, and numerous modifications and variations of that which is depicted herein are also readily known. 
     The satellite segment  120  of the satellite communication system  100  is shown having three satellites  122 ,  124  and  126 . Satellite systems may have varying numbers of satellites, and three are shown here only for purposes of simplicity. First satellite  122  is generally depicted in a position above the airborne earth station segment  102 . As situated, it is intended to depict a satellite having the highest elevation angle above the horizon. Satellite  124  has an elevation angle between satellite  122  and satellite  126 . Satellite  126  is intended to depict a satellite whose elevation above the horizon is a smaller angle than either satellite  122  or  124 . 
     Ground earth station segment  140  is shown as a ground based satellite antenna  142  positioned at a terrestrial location and typically communicating with satellite segment  120  over the C band; however, other frequencies could be readily substituted. Signals received by ground based satellite antenna  142  are then provided over some terrestrial based communication network  144 , which could be any type of communication system known in the art. An end user station  146  can be any type of end user operating any type of communication equipment, such as a telephone, computer, etc. 
     In operation, the prior art satellite communication system  100  may operate as follows: passengers or members of the flight crew on board an aircraft desirous of communicating with an end user station  146 , initiate a voice or data call from crew and passenger headsets  112  and  114  respectively. These signals are processed by transmitter/receiver  108  and amplifier  106  and emitted through antenna  104  to a satellite in the satellite segment  120 . One of the satellites, acting as a relay station, typically receives signals transmitted from the airborne earth station segment  102  on one frequency, and then relays it to a ground based satellite antenna  142  on another frequency. Signals from the crew and passenger headsets  112  and  114  respectively continue over communication network  144  and are ultimately delivered to end user station  146 . 
     Now referring to FIG. 2, there is shown a flow diagram, generally designated  200 , of the present invention which includes three possible events which could initiate a new inquiry into satellite selection process including the expiration of a timer  202  (which may be a three-minute timer), the signal loss of the P channel as shown in block  204 , as well as a degradation in the P channel as shown in the block  206 . If either of the events  202 ,  204  or  206  occurs, then the satellite communication system will perform the remaining functions, the first of which would be a determination in block  208  of whether the satellite communication system utilizes a high gain antenna or an intermediate gain antenna. If the answer to this determination is “no”, then a low gain antenna handover algorithm  210  would be followed. These low gain antenna handover algorithms are currently in use and are well known in the industry. If the determination from block  208  is that a high gain or intermediate gain antenna is in use, then decision  212  must be addressed, and that is whether there is a top mount antenna. If the answer to the top mount antenna question  212  is “yes”, then block  216  should be followed, which depicts the top mount handover algorithm. Top mount handover algorithm  216  is currently in use in the industry and is well known. However, if the top mount antenna determination  212  results in a decision of “no”, then, as shown in block  214 , a side mount handover algorithm is implemented. 
     Now referring to FIG. 3, there is shown a detailed flow diagram of the side mount handover  214  of FIG. 2 which begins with a block  302  entitled “select GES/satellite-side mount antenna”, which is the subject of FIG.  4  and its accompanying discussion. Once the algorithm  302  is performed, a spot beam selection is made pursuant to block  304 . An inquiry  306  as to whether or not you are communicating with the same ground earth station GES is made. If the answer is “yes”, then proceed to decision point  308 . However, if the answer is “no”, and you are not in the same GES, you should, in accordance with decision mode  310 , determine whether or not there are any calls in process. If there are calls in process, then proceed to decision point  308 . If there are no calls in process, then decision point  312  is next considered. Decision Point  312  involves determining whether the current antenna gain is greater than 9 dB, a user definable value. If the answer is “no”, then the process goes to log off current GES block  314 . However, if the decision from decision point  312  is “yes”, and the current antenna gain is greater than 9 dB, a user definable value, then decision point  316  further inquires whether the antenna elevation angle is greater than 6 degrees, a user definable value. If the answer is “yes” to decision  316 , then the process proceeds to decision block  308 . However, if the answer is “no”, and the elevation angle of the satellite is less than or equal to 6 degrees, a user definable value, then it is believed that the satellite is too near the horizon to be considered for use in the future and the process proceeds to the log off current GES block  314 . Once the log off occurs, the next step is Step  318 , which would involve logging on to a new GES beam. However, if the process were directed to decision point  308 , then a determination there must be made as to whether the current aircraft location is outside the current spot beam in use. If the answer is “no”, then the process will remain logged on to the current GES and spot beam. However, if the answer is “yes”, then the log on renew function  320  is performed. Logon renew function involves resetting certain parameters relating to events  202 ,  204 , and  206  of FIG.  2 . 
     Now referring to FIG. 4, there is shown a more detailed flow diagram of the block  302  of FIG.  3 . The first process of block  302  involves the process  402  sorting the GES&#39;s according to highest look angle to horizon. Next, a sorting of GES&#39;s according to smallest angle to the normal to the antenna is performed in accordance with block  404 . Thereafter, in accordance with block  406 , a sorting is done of GES&#39;s according to user specified priorities. Finally, in accordance with block  408 , a determination of a GES is made based upon satellites with the highest priority, with the smallest angle to antenna normal and the best look angle. The order of GES selection is such that the highest priority GES will always be chosen. However, if two or more GES&#39;s have the same priority, then the GES chosen will have the smallest angle to antenna normal. However, in the event that GES&#39;s with the same priority have approximately the same angle to the antenna normal, then the GES with the highest elevation angle is preferred. 
     It is thought that the method and apparatus of the present invention will be understood from the foregoing description and that it will be apparent that various changes may be made in the form, construction, steps and arrangements of the parts and steps thereof, without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred or exemplary embodiment thereof.