Abstract:
Disclosed is a method for obtaining a GPS signal by a user terminal operating in a time division duplex method, the user terminal receiving the GPS signal and a base station signal, the method includes setting a maximum window reception interval for attempting a GPS signal acquisition; setting within a frame an interval for attempting the GPS signal acquisition and attempting the GPS signal acquisition; exponentially increasing the time period for attempting the GPS signal acquisition and reattempting a GPS signal acquisition, when the GPS signal is not obtained in the set interval for the GPS signal acquisition; and ending the GPS signal acquisition attempts when the interval for the GPS signal acquisition is greater than or equal to the maximum window reception interval.

Description:
PRIORITY  
       [0001]     This application claims priority to an application entitled “Method For Obtaining GPS Signal For User Terminal” filed in the Korean Intellectual Property Office on Dec. 9, 2003 and assigned Serial No. 2003-89092, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a user terminal, and more particularly to a method for obtaining a global positioning system (GPS) signal for a user terminal.  
         [0004]     2. Description of the Related Art  
         [0005]     Recently, an IEEE 802.16e standard has been actively developed, which supports a user terminal mobility with technology similar to the mobile Internet technology. The IEEE 802.16e standard is a standard expanded from the IEEE 802.16a standard, which is a fixed broadband wireless connection standard using a frequency band of 2 to 11 GHz. The existing IEEE 802.16a does not support the user terminal mobility, but the IEEE 802.16e supports a handoff (or handover) between base stations, roaming, and the user terminal mobility, similarly to the Global System for Mobile Communication (GSM), the general packet radio service (GPRS), and the code division multiple access (CDMA) systems. This IEEE 802.16e standard is predicted to be used for providing a backhaul or Internet access service to various service areas to which many subscribers belong and to metropolitan areas.  
         [0006]     Further, with the development of mobile communication technology, users of user terminals (UTs) have demanded not only a communication service but also various supplementary services that are based on position information. Since user terminals are portable and can communicate wirelessly with other user terminals, carriers can provide users of the user terminals with various supplementary services by means of the position information. Recent supplementary services using terminal position information widely provided by carriers include a traffic information service, a map downloading service, a position information service, a weather information service, an emergency service, a vehicle navigation service, etc.  
         [0007]     As described above, various supplementary services provided on the basis of the position information of the user terminals are referred to as location-based services. Recently, in order to use location-based services, hardware for receiving GPS signals is provided within the user terminals. However, the IEEE 802.16e standard does not make reference to a GPS mode. The existing IEEE 802.16e standard does not include a description of a case in which a user terminal receives a GPS signal and a base station signal.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, an object of the present invention is to provide a method for efficiently obtaining a GPS signal for a user terminal according to an IEEE 802.16e time division duplex, without collision and during an ongoing radio communication.  
         [0009]     In order to accomplish the aforementioned object, according to one aspect of the present, there is provided a method for obtaining a GPS signal for a user terminal according to a time division duplex method, the user terminal receiving the GPS signal and a base station signal, the method including setting a maximum window reception interval for attempting a GPS signal acquisition; setting within a frame an interval for the GPS signal acquisition and attempting reception of the GPS signal; exponentially increasing the interval for the GPS signal acquisition and reattempting a GPS signal acquisition, when the GPS signal is not obtained in the set interval for the GPS signal acquisition; and ending the GPS signal acquisition attempts when the interval for the GPS signal acquisition is greater than or equal to the maximum window reception interval. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0011]      FIG. 1  is a block diagram showing a construction of a mobile communication system according to the present invention;  
         [0012]      FIG. 2  is a diagram showing a structure of a TDD frame;  
         [0013]      FIG. 3  is a block diagram showing a construction of a user terminal according to one embodiment of the present invention;  
         [0014]      FIG. 4  is a diagram showing a structure of a TDD frame according to the first reception for a GPS PN code according to the present invention;  
         [0015]      FIG. 5  is a diagram showing structure of a TDD frame for the second reception for a GPS PN code;  
         [0016]      FIG. 6  is a flowchart illustrating a method for obtaining a GPS signal for a time division duplex user terminal according to the present invention; and  
         [0017]      FIG. 7  is a diagram showing a structure of a TDD frame up to a maximum reception for a GPS PN code according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     Hereinafter, a preferred embodiment according to the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention.  
         [0019]      FIG. 1  is a block diagram showing a construction of a mobile communication system according to the present invention. As shown in  FIG. 1 , a user terminal (UT)  100  wirelessly communicates with a GPS satellite  110  and a base station (BS)  120 , and the base station  120  is connected to a mobile switching center (MSC)  130 .  
         [0020]     The user terminal  100  is connected to the base station  120  through an air interface. When an incoming call for a user terminal in a corresponding service area is received from the mobile switching center  130 , the base station  120  transmits the incoming call to a corresponding user terminal. In contrast, when an outgoing call is received from a user terminal, the base station  120  transmits the outgoing call to the mobile switching center  130 . Further, the base station  120  performs the general call processing for calls such as voice calls, circuit calls, and packet calls.  
         [0021]     The mobile switching center  130  performs a call connection exchange function for processing incoming/outgoing requests for the user terminal  100 , and a network interworking function with other mobile station centers. In such a mobile communication system, multiple access wireless communications between the base station  120  and the user terminal  100  is performed through the radio frequency (RF) channels that provide the physical routes to transmit the communication signals such as voice signals, data signals, and image signals. The user terminal  100  transmits/receives a frame according to a time division duplex (TDD) method of an IEEE 802.16e standard to/from the base station  120 . Further, an uplink channel is used in the case in which the user terminal  100  attempts to make a call through the base station  120  or responds to a control message from the base station  120 . In contrast, a downlink channel is used in the case in which the base station  120  transmits voice data or other data along with signal information to a predetermined user terminal  100 . Such an uplink channel and a downlink channel are contained in one wireless channel according to a TDD method of the IEEE 802.16e standard. One wireless channel includes one uplink channel and one downlink channel. A connection method in the aforementioned mobile communication system is essential when two-way simultaneous data transmission is required, that is, when voice communication is required.  FIG. 2  shows a structure of one frame a wireless channel.  
         [0022]      FIG. 2  is a diagram showing a structure of a TDD frame. As shown in  FIG. 2 , one frame  200  includes a downlink channel  210  and an uplink channel  230  as described above. Further, each frame  200  includes a TX/RX (transmission/reception) transition gap (TTG)  220  and a RX/TX (reception/transmission) transition gap (RTG)  240 .  
         [0023]     As shown in  FIG. 1 , the user terminal  100  includes, in addition to an RF module for UT-BS communications (not shown), a second RF module  20  for receiving a GPS pseudo random number (PN) code from the GPS satellite  110 . The GPS PN code contains positioning information used in a location-based service and a navigation service, etc. Recently the second RF module  20  for receiving a GPS signal has been provided within the user terminal  100 .  
         [0024]     A civilian GPS employs an L 1  carrier of 1.57542 GHz and uses a coarse acquisition (C/A) code as a pseudo random number (PN). Herein, the coarse acquisition code has a period of 1 ms and repeats 20 times.  
         [0025]     When a GPS receiver obtains the coarse acquisition code, the GPS receiver can be synchronized with satellite  110  and can obtain a pseudo range by means of this synchronization information. The GPS receiver can determine its own position.  
         [0026]     However, the frame according to the TDD method of the IEEE 802.16e standard shown in  FIG. 2  does not includes an interval for receiving or obtaining the GPS PN code.  
         [0027]     In the present invention, when the user terminal  100  must obtain the GPS PN code, an acquisition interval is arranged in each frame and the GPS PN code acquisition interval is exponentially increased, so that the GPS PN code can be obtained within a specified period of time up to a maximum window frame interval.  
         [0028]      FIG. 3  is a block diagram showing the construction of the user terminal  100  according to one embodiment of the present invention. As shown in  FIG. 3 , the user terminal  100  includes a first RF module  10  for radio communication with the base station  120 , the second RF module  20  for radio communication with the GPS satellite  110 , a baseband processor  30 , and a controller  40 . The baseband processor  30  performs baseband-processing for signals from the RF modules  10  and  20  or the controller  40 . When the GPS PN code must be obtained, the controller  40  assigns the GPS PN code acquisition interval to the frame. An operation of the controller  40  will be described in detail with reference to  FIG. 4 .  
         [0029]      FIG. 4  is a diagram showing a structure of a TDD frame according to the first reception of a GPS PN code according to the present invention. The upper part of  FIG. 4  shows a structure of the existing frame, and when one frame has a time period of 5 ms, a ratio between a downlink interval and an uplink interval is 13:9. The uplink interval has a time period of 2.03 ms, and the TX/RX transition gap and the RX/TX transition gap each have a time period of 20.14 μsec. The lower part of  FIG. 4  shows a structure of the TDD frame according to the first reception of the GPS PN code according to the present invention. As shown in  FIG. 4 , a data frame  300  as one unit includes a downlink channel interval  310 , a TX/RX transition gap  320 , a GPS signal reception interval  330  for the GPS PN code reception, and a RX/TX transition gap  340 . The GPS signal reception interval  330  according to the present invention substitutes for the existing uplink channel interval  330 .  
         [0030]     When a user orders a GPS mode, the controller  40  in the user terminal  100 , which is in a standby state after completing a synchronization procedure with the base station  120 , receives a signal from the base station  120  in the downlink channel interval  310  and receives a GPS signal in the GPS signal reception interval  330 , which is next to the TX/RX transition gap  320  and has been substituted for the uplink interval. Since the GPS signal reception interval  330  has the same time period of 2.03 ms as that of the uplink interval as described above, the coarse acquisition code with a period of 1 ms can be received twice within one sequence.  
         [0031]     The controller  40  replaces the uplink interval  330  with the GPS signal reception interval in one frame and receives a GPS signal in the GPS signal reception interval. When the GPS PN code is not obtained through such an initial attempt, the controller  40  attempts a second acquisition of the GPS PN code. After the initial attempt of the GPS PN code acquisition, in the immediate next frame, since the base station  120  may also transmit a short message or a received call to the user terminal  100 , or the user terminal  100  may also request communication with the base station  120 , a general communication must be performed between the base station  120  and the user terminal  100 . After such general communication, the controller  40  again tries a GPS PN code acquisition. Herein,  FIG. 5  shows a structure of a data frame when the controller  40  makes a second attempt for the GPS PN code acquisition.  
         [0032]      FIG. 5  is a diagram showing the structure of a TDD frame for the second reception of the GPS PN code. The upper part of  FIG. 5  shows a structure of the TDD frame  300  for the first reception of the GPS PN code, the central part of  FIG. 5  shows a structure of the existing frame  200  for general communication, and the lower part of  FIG. 5  shows a structure of a TDD frame for the second reception of the GPS PN code. As shown in the lower part of  FIG. 5 , an entire data frame  400  as a unit is used for the GPS PN code.  
         [0033]     That is, the controller  40  performs an acquisition by the frame from the second attempt. In the present invention, since an exponentially increased window is constructed for the GPS PN code reception in the frame, a frame interval T for the GPS PN code acquisition is set by Equation (1) 
 
frame length*2{circumflex over ( )}(count value−1)  (1) 
 
         [0034]     In the second attempt, a frame interval has a value of 5 ms*2{circumflex over ( )}(0), that is, 5 ms. For the 5 ms, the coarse acquisition code can be received five times during one sequence. In other words, since the coarse acquisition code is received within a period of 1 ms, the coarse acquisition code can be received five times in the sequence. Further, when the GPS PN code has not been obtained through this second attempt, the controller  40  attempts for a third time for the GPS PN code acquisition. After the second attempt of the GPS PN code acquisition, the controller  40  performs general communication with the base station  120  in the immediate next frame. After performing the general communication, the controller  40  makes the third attempt for the GPS PN code acquisition. As the acquisition attempt is performed, the counter value increases and a GPS signal reception interval increases. A control flow of the controller  40  for obtaining the GPS PN code will be described with reference to  FIGS. 6 and 7 .  
         [0035]      FIG. 6  is a flowchart illustrating a method for obtaining a GPS signal for a time division duplex user terminal according to the present invention, and  FIG. 7  is a diagram showing a structure of a TDD frame up to a maximum window in a GPS PN code.  
         [0036]     Referring to  FIGS. 6 and 7 , in step  702 , the controller  40  in the user terminal  100  completes the synchronization procedure with the base station  120 . That is, the controller  40  is synchronized with the base station  120  for transmitting/receiving a signal to/from the base station  120 . Next, in step  704 , the controller  40  resets a count value to zero and sets a maximum reception window to two seconds. Setting the maximum reception window to two seconds means that a frame interval for obtaining the GPS PN code may have a maximum value of two seconds. When it is assumed that one frame has a period of 5 ms, a maximum frame interval for obtaining the GPS PN code corresponds to 400 frames.  
         [0037]     Next, in step  706 , the controller  40  receives a base station signal in a downlink interval  310  of one frame  300  as shown in  FIG. 7 . Then, in step  708 , the controller  40  first receives a GPS signal in a GPS signal reception interval  330  having been substituted for an uplink interval. Then, in step  710 , the controller  40  determines whether or not the GPS PN code has been completely received. When the GPS PN code has been completely received, step  712  is performed. That is, the controller  40  communicates with the base station  120  in a normal mode. In contrast, when the first attempt for the GPS PN code acquisition fails, that is, the GPS PN code is not obtained, step  714  is performed. The controller  40  performs general communication with the base station  120  in a frame  200  next to the frame  300  as shown in  FIG. 7  so that the base station  120  can transmit a short message or a received call to the user terminal  100 , and the user terminal  100  can make a request for communication to the base station  120 . Next, after performing the general communication with the base station  120 , the controller  40  increases the count value by 1 in step  716  and determines a GPS PN code reception interval according to Equation (2) in step  718 . 
 
 T ( GPS PN  code reception interval)=frame length*2{circumflex over ( )}(count−1)  (2) 
 
         [0038]     In step  720 , the controller  40  determines whether or not an obtained GPS PN code reception interval exceeds the maximum reception window. That is, the controller  40  determines whether or not the GPS PN code reception interval has exceeded the two seconds set in step  704 . When the GPS PN code reception interval has not exceed the maximum reception window, step  730  is performed. That is, the controller  40  obtains or receives the GPS PN code for the GPS PN code reception interval. Then, step  710  is performed. Herein, when the maximum reception window has a value of two seconds and the GPS PN code has not been obtained, the controller  40  can reattempt the operation from step  714  to step  718 , that is, an acquisition operation for the GPS PN code, up to a maximum of seventeen times. When the GPS PN code has not been obtained by the completion of the 17 th  attempt for obtaining the GPS PN code, the controller  40  determines that the GPS PN code reception has failed.  
         [0039]     Meanwhile, from the result of the determination in step  720 , when the GPS PN code reception interval has exceeded the two seconds set in step  704 , step  722  is performed. That is, the controller  40  ends an operation for receiving the GPS PN code.  
         [0040]     Further, the controller  40  informs a user of the end of operation for receiving the GPS PN code and can ask the user whether to reattempt to receive the GPS PN code in step  724 .  
         [0041]     In another embodiment of the present invention, the controller  40  can be set to make an attempt to receive a GPS PN code for a predetermined number of times and automatically make an attempt to receive the GPS PN code up to the predetermined number of times.  
         [0042]     When it is not set to make a reattempt to receive the GPS PN code, the controller  40  releases a GPS mode in step  726 . The controller  40  performs a general communication with the base station  120  in frames  200  next to reception intervals  330 ,  400 ,  500 , and  600  of the GPS PN code as shown in  FIG. 7  so that the base station  120  can transmit a short message or a received call to the user terminal  100 , and the user terminal  100  can request a communication to the base station  120 .  
         [0043]     In the present invention, when a user terminal must obtain a GPS signal, a GPS signal acquisition interval is divided into a unit of a frame and the GPS signal acquisition interval is exponentially increased when the GPS signal acquisition has failed, to repeatedly attempt to obtain the GPS signal. Further, when a process for obtaining a GPS PN code in a user terminal according to the present invention is used, the synchronization with a GPS coarse acquisition code can be achieved without collision with a 802.16e communication method. In addition, this information is transmitted to a base station, so that position information can be used.  
         [0044]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.