Abstract:
A receiver system equipped with a first and second reception units for receiving a satellite radio broadcasting prevents a reception unit switching operations by using signal selection data that provides satellite availability for respective operation areas. The satellite radio broadcasting reception quality in each of the respective operation areas is improved because of the reduced chance of dropout or the like in the broadcasted contents of the satellite radio broadcasting received by the receiver system.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and claims the benefit of priority of Japanese Patent Application No. 2005-342406 filed on Nov. 28, 2005, the disclosure of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to a receiver system that receives a signal from a communication satellite.  
       BACKGROUND OF THE INVENTION  
       [0003]     In recent years, a satellite information service such as Global Positioning System or the like is widely available. In terms of utilization of the satellite information service, how a receiver can determine the positions of the satellites effortlessly is a key factor. Japanese patent application JP-A-2004-184121 discloses a process for determining the satellite position, that is, mask information is utilized to screen available satellites for speedy satellite selection.  
         [0004]     As a variety of the satellite information service, satellite radio broadcasting is now gaining popularity. The satellite radio broadcasting broadcasts a radio signal from a geostationary satellite that receives a source signal from a ground station. The satellite radio broadcasting provides radio programs such as music programs, traffic information programs and the like for a coverage that extends to a much greater area in comparison to the conventional ground broadcasting such as FM broadcasting or the like.  
         [0005]     The satellite radio broadcasting usually uses the geostationary satellites for broadcasting the radio signal, thereby providing for a user a relatively high readiness in terms of position determination in comparison to the positioning of GPS satellites. However, a satellite radio receiver suffers from a signal reception problem because the radio signal from the geostationary satellite is easily interrupted by a nearby building, an expressway on an elevated track or the like due to its straightness of propagation. In other words, continuation of service provision for the receiver in various conditions is a problem to be solved.  
         [0006]     In an attempt for an increased coverage and improved quality in terms of the service provision without interruption, the satellite radio broadcasting broadcasts the same program from the ground station of the FM broadcasting as a supplemental service provision scheme. That is, when the receiver receiving the satellite radio broadcasting comes behind the nearby building or under the raised expressway track, the receiver prevents the interruption of the service provision of the satellite radio program by alternatively tuning to the FM broadcasting from the ground station.  
         [0007]     In the above-described supplemental service provision scheme, the receiver of the satellite broadcasting still encounters a reception problem due to the time difference between the digital signal decryption for the satellite radio broadcasting signal and the analog signal decryption for the FM broadcasting. Further, the radio signal from the geostationary satellite transmits a far greater distance before being received by the receiver in comparison to the FM broadcasting. Therefore, even when the same program is sent out from a studio for broadcasting from both of the geostationary satellite and the ground station, the radio signal from the satellite and the radio signal from the FM station reach the receiver at respectively different times. As a result, the radio program may be interrupted even when the receiver switches from the satellite radio broadcasting to the FM broadcasting in order to avoid the reception problem. Furthermore, the reception switching time of the receiver may also contribute to an increase of the interruption time. Frequent switching of the broadcasting channel between the satellite and the ground station may further complicated the reception problem.  
       SUMMARY OF THE INVENTION  
       [0008]     In view of the above-described and other problems, the present disclosure provides a receiver system that prevents deterioration of broadcasting service quality when the receiver system switches broadcasting channels between a broadcasting from a broadcast satellite and from an FM station on the ground.  
         [0009]     The receiver system of the present disclosure includes a first receiver for receiving a first signal sent out from a communication satellite, a second receiver for receiving a second signal sent out from a ground facility, a signal selection data acquisition unit for acquiring signal selection data that controls selection of one of the first and second signals for broadcasting reception in a current operation area, and a control unit for controlling execution of a predetermined process that utilizes one of the first and second signals received by selecting one of the first receiver and the second receiver based on the signal selection data that is acquired by the signal selection data acquisition unit. In this case, the operation areas are defined based on municipalities such as a county or the like, or based on the coordinates such as the longitude and the latitude. In addition, the predetermined process is a process for demodulating the signal received by one of the two receivers and for outputting guidance voice or the like, or a process for extracting traffic information, weather information or the like from the signal. In this manner, the receiver system use the signal either from the satellite or the ground facility while the receiver system is in a certain operation area. Therefore, signal switching operation for switching signals from the first and the second receivers in the receiver system is prevented, thereby minimizing chances of broadcasted contents dropout due to the signal switching operation. In other words, the broadcasting service quality experienced by the user of the receiver system is kept from deteriorating by preventing the signal switching operation in each of the operation areas.  
         [0010]     The signal selection data acquisition unit may acquire the signal selection data from another device, or may acquired and store the signal selection data in the acquisition unit by retrieving the data from a storage medium. Further, the storage medium may be installed in the receiver system, or may be separately installed from the receiver system.  
         [0011]     The signal reception by the first receiver based on the-signal selection data may lead to the reception failure depending on the accuracy of the signal selection data or the like. For example, a newly built high-rise building in a certain operation area that is not yet reflected on the signal selection data may lead to the reception failure by the first receiver. Therefore, the control unit records an unsuccessful execution attempt of the predetermined process that utilizes the first signal received by the first receiver due to a signal reception failure by the first receiver as an failure record in association with the current operation area at a time of the signal reception failure, and the control unit controls a succeeding execution of the predetermined process to utilize the second signal received by the second receiver when an attempt of the succeeding execution of the predetermined process takes place in the current operation area that is recorded as the failure record in association with the unsuccessful execution attempt of the predetermined process by utilizing the first signal. In this manner, the signal selection data is updated appropriately for reflecting a change of environment such as a construction of a new building. Therefore, the chance of deterioration of the broadcasting service quality is further reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which:  
         [0013]      FIG. 1  shows a block diagram of a navigation system in an embodiment of the present disclosure;  
         [0014]      FIG. 2  shows a diagram of a satellite availability table for use in the navigation system;  
         [0015]      FIG. 3  shows a flowchart of a satellite radio reception process in the navigation system; and  
         [0016]      FIG. 4  shows an illustration of satellite radio reception in a real life situation. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Embodiments of the present disclosure are described with reference to the drawings. Like parts have like numbers in each of the embodiments.  
         [0018]      FIG. 1  shows a block diagram of a navigation system  20  in an embodiment of the present disclosure. The navigation system  20  includes a function of a receiver system of the present disclosure.  
         [0019]     The navigation system  20  is installed in a vehicle, and includes a position detector  21  for detecting a current position of the vehicle, operation switches  22  for inputting various instructions from a user, a remote controller  23   a  in a separate body for inputting various instructions as the operation switches  22 , a remote sensor  23   b  for receiving a signal from the remote controller  23   a , a map data input/output unit  25  for inputting map data from map data storage medium that stores map data, sound data and the like, a display unit  26  for displaying a map and/or other information, a speaker  27  for outputting a voice guidance and the like, a microphone  28  for outputting an electric signal based on a user&#39;s voice, an FM receiver  30  for receive an FM broadcast, a satellite receiver  31  for receiving a satellite radio broadcast, and a control unit  29  that controls above components for executing various process.  
         [0020]     The position detector  21  includes a GPS receiver  21   a  for receiving a radio wave from GPS satellites with a GPS antenna (not shown in the figure) and outputting a reception signal, a gyroscope  21   b  for detecting a rotation movement of the vehicle body, and a distance sensor  21   c  for detecting a travel distance of the vehicle based on an acceleration/deceleration in a front-rear direction. The control unit  29  calculates the current position, a travel direction, a speed and other condition of the vehicle based on the output from these sensors  21   a  to  21   c  and related devices. In this case, the current position of the vehicle is calculated based on the output of the reception signal from the GPS receiver  21   a  by using a point positioning method or a relative positioning method.  
         [0021]     The operation switches  22  are disposed on, for example, the display unit  26  as touch switches, mechanical switches or the like. The touch switches are integrally disposed on a display screen of the display unit  26 , and uses one of various detection methods such as a pressure sensing method, a electromagnetic induction method, a electrostatic capacitance method, and a combination of those methods.  
         [0022]     The map data input/output unit  25  is used to input various data from the map data storage medium (not shown in the figure) such as a hard disk drive or the like, and to output the data to the storage medium. The map data storage medium stores the map data including node data, link data, cost data, background data, road data, name data, mark data, intersection data, facility data and the like as well as guidance voice data, voice recognition data, satellite availability data and the like. The data mentioned above may also be retrieved from other source through a communication network.  
         [0023]     The display unit  26  is constructed by using, for example, a liquid crystal display, an organic EL display or the like, and is capable of displaying various colors. The display screen of the display unit  26  displays a current position mark of the vehicle at the current position on a map based on the signal from the position detector  21  and the map data from the map data input/output unit  25 . The display screen also displays a navigation route toward a destination of a travel, a location name, a landmark, a facility mark or the like on top of the map. In addition, facility guidance information may also be displayed on the display screen.  
         [0024]     The speaker  27  is used to output a radio broadcast voice, a guidance voice of the facility guidance information and the like that are inputted from the map data input/output unit  25 .  
         [0025]     The microphone  28  is used to input the user&#39;s voice, and then to output the electric signal (a sound signal) based on the inputted user&#39;s voice to the control unit  29 . The user controls the navigation system  20  by inputting various voice instructions to the microphone  28 .  
         [0026]     The FM receiver  30  is coupled with an FM antenna (not shown in the figure), and is used to receive the FM broadcast wave for demodulating the signal contained therein.  
         [0027]     The satellite receiver  31  is coupled with a satellite antenna (not shown in the figure), and is used to receive the satellite broadcast wave for demodulating the signal contained therein.  
         [0028]     The control unit  29  is constructed by using a well-known type microcomputer having a CPU, a ROM, a RAM, an SRAM, an I/O and a bus line for interconnection of these parts. The control unit  29  executes various processes based on programs stored in a storage such as the ROM, the RAM and the like. For example, the control unit  29  executes a process for calculating the current position of the vehicle as a combination of the coordinates and the travel direction based on the signals such as position detection signals and the like and for displaying on the display unit  26  a map around the current position by utilizing the map data inputted from the map data input/output unit  25 , a process for calculating an optimum route based on the map data stored in the map data input/output unit  25  and a destination specified by operating the operation switches  22 , the remote controller  23   a  and the like, a process for providing a route navigation by displaying the optimum route on the display unit  26  and/or outputting the guidance voice from the speaker  27  and other related processes.  
         [0029]      FIG. 2  shows a diagram of a satellite availability table for use in the navigation system  20 . The satellite availability table is stored on the map data storage medium to be accessed by the map data input/output unit  25 , and includes satellite availability data. The availability data is used in the following manner. That is, each of plural availability data records in the satellite availability table defines an area (a rectangular division in the map) in association with an area code, north east corner coordinates (a longitude and a latitude) of the area, south west corner coordinates (a longitude and a latitude) of the area, and the availability of the satellite radio broadcast in the area. The availability of the satellite radio broadcast in an area specifies one of OK or NG information. If the availability is specified as “OK,” the vehicle can receive the satellite radio broadcast on any location on the road in the defined area. If the availability is specified as “NG,” there is at least a portion of the road in the defined area where the vehicle cannot receive the satellite radio broadcast.  
         [0030]      FIG. 3  shows a flowchart of a satellite radio reception process in the navigation system  20 . Other processes in the navigation system  20  such as a route calculation process, a route guidance process or the like are well-known for the people in the art, thereby being omitted in the description of the present embodiment. The satellite radio reception process starts upon receiving an instruction of satellite radio reception from one of the operation switches  22  or the remote controller  23   a  after the navigation system  20  is turned on by receiving an electric power.  
         [0031]     The control unit  29  executes the process for satellite radio reception.  
         [0032]     In step S 105 , the process calculates the current position of the vehicle based on the signal derived from the position detector  21 .  
         [0033]     In step S 110 , the process acquires the satellite availability data from the data storage medium through the map data input/output unit  25 .  
         [0034]     In step S 115 , the process determines whether the satellite availability is OK or NG in the data. The process proceeds to step S 125  when the availability is OK (step S 115 : YES). The process proceeds to step S 120  when the availability is NG (step S 115 : NO).  
         [0035]     In step S 120 , the process controls circuitry to output a signal received by the FM receiver  30  to the speaker  27 . In addition, the process extracts traffic information from the signal received by the FM receiver  30  to be displayed on the display unit  26 . The process returns to step S 105  after step S 120 .  
         [0036]     In step S 125 , the process detects a satellite based on satellite orbit information stored in the control unit  29 .  
         [0037]     In step S 130 , the process determines whether the satellite is detected. The process proceeds to step S 140  when the satellite is detected (step S 130 : YES). The process proceeds to step S 135  when the satellite is not detected (step S 130 : NO).  
         [0038]     In step S 135 , the process updates the satellite availability data on the storage medium as NG by sending the data through the map data input/output unit  25 . The process returns to step S 120  after step S 135 .  
         [0039]     In step S 140 , the process determines whether plural satellites are detected. The process proceeds to step S 150  when the plural satellites are detected (step S 140 : YES). The process proceeds to step S 145  when the plural satellites are not detected, that is, when only one satellites is detected (step S 140 : NO).  
         [0040]     In step S 145 , the process selects one of the plural satellites for maximum availability. That is, for example, the process evaluates and selects one of the satellites based on an elevation angle for avoiding interruption by man-made structures such as a high-rise building or the like and for best visibility from the vehicle. The process proceeds to step S 150  after step S 145 .  
         [0041]     In step S 150 , the process controls circuitry to demodulate the signal received by the satellite receiver  31  for outputting it to the speaker  27  after D/A conversion. In addition, the process extracts the traffic information from the signal received by the satellite receiver  31  to be displayed on the display unit  26 . The process returns to step S 105  after step S 150 .  
         [0042]      FIG. 4  shows an illustration of satellite radio reception in a real life situation.  
         [0043]     Let&#39;s assume that all of the areas A 1  to A 4  are in a coverage by a satellite for the satellite radio broadcast, but a part of the navigation route in the areas A 1 , A 2 , and A 3  are blocked in terms of the satellite radio reception due to the high-rise buildings in a downtown district. That is, the satellite availability in the areas A 1  to A 3  is NG, while the availability in the area A 4  is OK.  
         [0044]     Now, the vehicle having the navigation system  20  is assumed to travel from the area A 4  toward the area A 1  through the areas A 3  and A 2 . The vehicle tunes in to the satellite broadcast by using the signal received by the satellite receiver  31  while traveling in the area A 4 , and then switches to the FM broadcast by tuning to the signal received by the FM receiver  30  when the vehicle proceeds to the area A 3 . The navigation system  20  keeps tuning in to the FM broadcast by using the signal received by the FM receiver  30  even when the satellite is visible between the high-rise buildings while the vehicle is traveling in the areas A 3 , A 2 , and A 1 .  
         [0045]     Therefore, while the vehicle is traveling in the areas A 3 , A 2 , and A 1 , the signal is not switched from the FM broadcast to the satellite broadcast, thereby providing an improved reception condition in comparison to a conventional switching scheme that suffers from interruption of the reception by frequent switching in the above-described situation.  
         [0046]     Further, when a newly built building in the area A 4  causes interruption of the satellite radio reception on a portion of the road in the area A 4 , the navigation system  20  in the vehicle updates a record of the satellite availability data to have NG attribute upon detecting satellite unavailability in the course of travel in the area A 4  as described as the process in steps S 130  and S 135  in the flowchart described above. In this manner, the reception of the satellite radio broadcast in the area A 4  will not be interrupted in the succeeding travel of the road in the area A 4 .  
         [0047]     Although the present disclosure has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.  
         [0048]     For example, the navigation system  20  having the satellite radio reception function may be used in a ship or other type of vehicle instead of an automobile for use on a ground.  
         [0049]     Such changes and modifications are to be understood as being within the scope of the present disclosure as defined by the appended claims.