Patent Document

CLAIM OF PRIORITY  
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application entitled SYSTEM FOR SYNCHRONIZING SATELLITE CLOCK IN BASE TRANSCEIVER STATION AND METHOD THERE FOR earlier filed in the Korean Intellectual Property Office on 25 Apr. 2003 and thereby duly assigned Serial No.2003-26506. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to synchronizing a satellite clock in a base transceiver station. More particularly, the present invention relates to synchronizing the satellite clock in base transceiver station wherein clocks of base transceiver stations are synchronized by efficiently distributing global positioning system (GPS) information to each base transceiver station in a wireless private exchange system in an office environment.  
           [0004]    2. Description of the Related Art  
           [0005]    When a GPS is used in a wireless private exchange system in an office environment, each customer base transceiver station has to be directly connected to a GPS antenna in a one-to-one manner or each customer base transceiver station has to be connected to a distributor distributing the GPS signal from one GPS antenna to each customer base transceiver in a one-to-many manner.  
           [0006]    Accordingly, if the customer base transceiver station and the GPS antenna are directly connected in the one-to-one manner, each customer base transceiver has to have a GPS antenna and a global positioning system receiver (referred to as a GPS receiver module, hereinafter).  
           [0007]    On the other hand, if each customer base transceiver station has to be directly connected to a GPS antenna in the one-to-many manner, a separate GPS distributor must be used and each customer base transceiver station must still have the GPS receiver module. Therefore, there is a problem in that this results in a high equipment cost.  
           [0008]    The following patents each discloses features in common with the present invention but do not teach or suggest the inventive features specifically recited in the present application: U.S. Pat. No. 6,243,372 to Petch et al., entitled METHODS AND APPARATUS FOR SYNCHRONIZATION IN A WIRELESS NETWORK, issued on Jun. 5, 2001; U.S. Pat. No. 6,452,541 to Zhao et al., entitled TIME SYNCHRONIZATION OF A SATELLITE POSITIONING SYSTEM ENABLED MOBILE RECEIVER AND BASE STATION, issued on Sep. 17, 2002; U.S. Pat. No. 6,377,517 to Tursich, entitled METHOD AND SYSTEM FOR SYNCHRONIZING A TIME OF DAY CLOCK BASED ON A STELLITE SIGNAL AND A COMMUNICATION SIGNAL, issued on Apr. 23, 2002; U.S. Pat. No. 6,344,821 to Norimatsu, entitled MOBILE COMMUNICATION SYSTEM AND INTER-BASES STATION SYNCHRONIZING METHOD, issued on Feb. 5, 2002; U.S. Pat. No. 6,674,730 to Moerder, entitled METHOD OF AND APPARATUS FOR TIME SYNCHRONIZATION IN A COMMUNICATION SYSTEM, issued on Jan. 6, 2004; U.S. Pat. No. 6,671,291 to Soliman, entitled METHOD AND APPARATUS FOR SEQUENTIALLY SYNCHRONIZED NETWORK, issued on Dec. 30, 2003; U.S. Pat. No. 6,665,541 to Kransner et al., entitled METHODS AND APPARAT USES FOR USING MOBILE GPS RECEIVERS TO SYNCHRONIZE BASE STATIONS IN CELLULAR NETWORKS, issued on Dec. 16, 2003; U.S. Pat. No. 6,647,246 to Lu, entitled APPARATUS AND METHOD OF SYNCHRONIZATION USING DELAY MEASUREMENTS, issued on Nov. 11, 2003; U.S. Pat. No. 6,628,628 to Yamazaki, entitled WIRELESS COMMUNICATION HAVING OPERATION TIME CORRECTING FUNCTION, issued on Sep. 30, 2003; U.S. Pat. No. 6,621,813 to Petch et al., entitled METHODS AND APPARATUS FOR SYNCHRONIZATION IN A WIRELESS NETWORK, issued on Sep. 16, 2003; U.S. patent application No. 2004/0047307 to Yoon et al., entitled APPARATUS AND METHOD OF FLYWHEEL TIME-OF-DAY (TOD) SYNCHRONIZATION, published on Mar. 11, 2004; U.S. patent application No. 2004/0028162 to Skahan, entitled MOBILE NETWORK TIME DISTRIBUTION, published on Feb. 12, 2004; U.S. patent application No. 2003/0214936 to Goff, entitled USING GPS SIGNALS TO SYNCHRONIZE STATIONARY MULTIPLE MASTER NETWORKS, published on Nov. 20, 2003; U.S. patent application No. 2003/0139898 to Mileretal., entitled METHOD FOR SYNCHRONIZING OPERATION ACROSS DEVICES, published on Jul. 24, 2003; U.S. patent application No. 2003/0109264 to Syjrarinne etal., entitled METHOD, APPARATUS AND SYSTEM FOR SYNCHRONIZING A CELLULAR COMMUNICATION SYSTEM TO GPS TIME, published on Jun. 12, 2003; U.S. patent application No. 2003/0058742 to Pikula et al., entitled WIRELESS SYNCHRONOUS TIME SYSTEM, published on Mar. 27, 2003; U.S. patent application No. 2002/0186716 to Eidson, entitled SYNCHRONIZING CLOCKS ACROSS SUB-NETS, published on Dec. 12, 2002; U.S. patent application No. 2002/0167934 to Carter et al., entitled METHOD AND SYSTEM FOR TIMEBASE SYNCHRONIZATION, published on Nov. 14, 2002; and U.S. patent application No. 2002/0001299 to Petch et al., entitled METHODS AND APPARATUS FOR SYNCHRONIZATION IN A WIRELESS NETWORK, published on Jan. 3, 2002.  
         SUMMARY OF THE INVENTION  
         [0009]    Therefore, the present invention has been made in view of the above problem, and it is an object of the present invention to provide a system and method of synchronizing a satellite clock in a base transceiver station wherein, in a private wireless exchange system in an office environment having a number of base transceiver stations, a GPS receiver module is installed in one base transceiver station and clock modules are installed in the remaining base transceiver stations. The GPS receiver module of the one base transceiver station receives a GPS signal through a GPS antenna and sends the GPS signal to the remaining base transceiver stations, so that the remaining base transceiver stations can operate with an inexpensive clock module.  
           [0010]    In accordance with an aspect of the present invention, there is provided a system of synchronizing a satellite clock between at least two base transceiver stations, the system comprising: a GPS receiver module adapted to extract clock information and time of date(TOD) information from a received GPS signal, to generate a first clock signal and first TOD data, and to output the first clock signal and first TOD data to a first base transceiver station and a base transceiver station of a next stage, the GPS receiver module being arranged within the first base-station transceiver; and a clock module adapted to generate a second clock signal and second TOD data synchronized with the first clock signal and first TOD data by performing a delay correction with one of the GPS receiver module of the first base transceiver station or the base transceiver station of a previous stage, and to output the second clock signal and second TOD data to its base transceiver station and a base transceiver station of the next stage upon the clock module receiving a first clock signal and first TOD data from one of the GPS receiver module of the first base transceiver station or the base transceiver station of the previous stage, the clock module being arranged within a base transceiver station other than the first base transceiver station.  
           [0011]    In accordance with another aspect of the present invention, there is provided a base station system having a synchronized satellite clock, comprising: a main base transceiver station having a GPS receiver module adapted to extract clock information and TOD information from a received GPS signal and to generate a clock signal and TOD data for operating its base transceiver station; and at least one sub-base transceiver station, each at least one sub-base transceiver station having a clock module adapted to receive a clock signal and TOD data from one of the GPS receiver module of the main base transceiver station or an adjacent base transceiver station through a daisy chain, and to generate a clock signal and TOD data synchronized with the clock signal and the TOD data of the main base transceiver station by performing a delay correction with one of the GPS receiver module which has transmitted the clock signal and the TOD data or the adjacent base transceiver station.  
           [0012]    In accordance with yet another aspect of the present invention, there is provided a method for synchronizing a satellite clock between at least two base transceiver stations forming a base station system, the method comprising: extracting clock information and TOD information from a received GPS signal with a first base transceiver station having a GPS receiver module; outputting a clock signal and TOD data used for operating the first base transceiver station from the extracted clock information and TOD information from the first base transceiver station; receiving clock signals and TOD data from one of the first base transceiver station or a base transceiver station of the previous stage through a daisy chain with a base transceiver station other than the first base transceiver station; measuring and correcting delays of the received clock signals and TOD data with a base transceiver station other than the first base transceiver station; and generating clock signals and TOD data synchronized with the clock signal and the TOD data of the first base transceiver station by correcting the received clock signals and TOD data in accordance with a value of the delay correction, and outputting the synchronized clock signals and TOD data to its base transceiver station and the base transceiver station of the next stage with a base transceiver station other than the first base transceiver station. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0014]    [0014]FIG. 1 is a view showing a construction of a customer base station system employing a system for synchronizing a satellite clock in base transceiver station in accordance with an embodiment of the present invention;  
         [0015]    [0015]FIG. 2 is a view showing a detailed construction block diagram of the GPS receiver module shown in FIG. 1; and  
         [0016]    [0016]FIG. 3 is a view showing a detailed construction block of a clock module shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0017]    Now, exemplary embodiments of the present invention will be described in detail with reference to the annexed drawings in order that those skilled in the art can embody the present invention with ease.  
         [0018]    [0018]FIG. 1 is a view showing a construction of a customer base station system employing a system for synchronizing a satellite clock in base transceiver station in accordance with an embodiment of the present invention.  
         [0019]    Referring to FIG. 1, a number of base transceiver stations  100 ,  200  and  300  are connected with one another through daisy chains. Each of the base transceiver station  100 ,  200  and  300  is connected to an Internet Protocol-Base Station Controller  30  (referred to as an IP-BSC, hereinafter) through an Ethernet switch  40 , and the IP-BSC  30  is connected to a Public Land Mobile Network  10  (PLMN) through a Mobile Switching Center  20  (referred to as an MSC, hereinafter).  
         [0020]    The base transceiver stations  100 ,  200  and  300  operate with the IP-BSC  30  to provide a wireless mobile communication service. FIG. 1 schematically shows that controllers  120 , 220  and  320  in the base transceiver stations  100 ,  200  and  300  control the wireless mobile communication service. The description of the function of the controllers  120 ,  220  and  320  has been abbreviated.  
         [0021]    Here, the description is restricted to the fact that the satellite clock is synchronized in each of the base transceiver stations  100 ,  200  and  300  according to the GPS signal, and the description of technical matters performed in the base transceiver stations has been abbreviated.  
         [0022]    As shown in FIG. 1, a number of the base transceiver stations  100 ,  200  and  300  can be divided into two types, that is, a base transceiver station  100  (referred to as a main base transceiver station, hereinafter) which receives a GPS signal through a GPS antenna and extracts a clock signal and Time Of Day (referred to as a TOD, hereinafter) necessary for operating its own base transceiver station from the GPS signal, and base transceiver stations  200  and  300  (referred to as sub-base transceiver station, hereinafter) which receive the clock signal and the TOD data from the main base transceiver station  100 , perform a delay correction to be used therein and provide a base transceiver station of the next stage with the clock signal and the TOD data.  
         [0023]    The main base transceiver station  100  has a GPS receiver module  110  receiving the GPS signal through the GPS antenna and processing it, and the sub-base transceiver stations  200  and  300  respectively have clock modules  210  and  310 .  
         [0024]    The GPS receiver module  110  installed in the mainbase transceiver station  100  extracts clock information and TOD information from the GPS signal received through the GPS antenna, generates the generated clock signal and TOD data for operating its own base transceiver station  100  and outputs the clock signal and the TOD data to its base transceiver station  100  and thebase transceiver station  200  of the next stage.  
         [0025]    The clock module  210  installed in the sub-base transceiver station  200  receives a clock signal and TOD data from the GPS receiver module  110  of the main base transceiver station through the daisy chain. The clock module  210  generates a clock signal and TOD data which are synchronized with the clock signal and the TOD data used in the main base transceiver station  100  by performing a delay correction with the GPS receiver module  110  of the main base transceiver station  100 , and outputs the clock signal and the TOD data to its own base transceiver station  200  and abase transceiver station of the next stage.  
         [0026]    The clock module  310  installed in the sub-base transceiver station  300  receives the clock signal and TOD data from a clock module (not shown) of a base transceiver station of the previous stage through the daisy chain. The clock module  310  then generates a clock signal and TOD data synchronized with the clock signal and the TOD data used in the main base transceiver station  100  by performing a delay correction with the clock module (not shown) of the base transceiver station of the previous stage, and outputs the clock signal and the TOD data to its own base transceiver station  300 .  
         [0027]    In order to measure a delay of a clock received from the GPS receiver module  110  of the main base transceiver station  100  or a base transceiver station of the previous stage (not shown), the clock modules  210  and  310  transmit delay correction signals to the GPS receiver module  110  of the main base transceiver station  100  or a base transceiver station (not shown) of the previous stage, and measure and correct delays using the returned signals.  
         [0028]    The delay must be corrected since a delay which occurs in a wireless communication system causes a phase synchronization difference so that a handoff may not be performed when the wireless terminal moves to another base station. Accordingly, the clock must be corrected in order to guarantee a stable handoff.  
         [0029]    The operation of synchronizing a GPS satellite clock in the above system is described below.  
         [0030]    The GPS antenna receives the GPS signal from a satellite and sends it to the main base transceiver station  100  using a cable. The GPS receiver module  110  in the main base transceiver station  100  extracts a clock signal and TOD data indicating time information from the GPS signal received in the GPS antenna.  
         [0031]    The extracted clock signal and TOD data are used in its own base transceiver station  100  and also transmitted to the next base transceiver station  200 . The main base transceiver station  100  sends back a delay correction signal to the next base transceiver station  200  in order to correct the delay which occurred during the clock transmission.  
         [0032]    On the other hand, each of clock modules  210  and  310  in the sub-base transceiver stations  200  and  300  receives the clock signal and the TOD data sent by the GPS receiver module  110  and generates clocks to be used in their base transceiver stations  200  and  300 . In order to measure the delay of the clocks sent by the GPS receiver module  110  or the clock module of the base transceiver stations  200  and  300 , each of the clock modules  210  and  310  sends a delay correction signal to the base transceiver station of the previous stage and performs a measurement and correction of the delay using a returned signal so that the clock signal to be used in its base transceiver station is corrected.  
         [0033]    Also, the base transceiver stations send the clock signal and the TOD data to the next base transceiver station so that the next base transceiver station can use the signal and the data. Then, since the clock module of the next base transceiver station also needs to perform the delay correction, it performs a function of returning the delay correction signal.  
         [0034]    The details of a GPS receiver module and a clock module are described with reference to FIGS. 2 and 3.  
         [0035]    [0035]FIG. 2 is a view showing a detailed block diagram of the GPS receiver module shown in FIG. 1. Referring to FIG. 2, the GPS receiver module  110  includes a GPS engine  111 , a processor  112 , a Phase Locked Loop module  113  (referred to as a PLL module, hereinafter), a driver  114  and a return module for delay correction  115 .  
         [0036]    The GPS engine  111  performs a function of extracting clock information and TOD information from the GPS signal received by a GPS antenna.  
         [0037]    The PLL logic  113  generates a clock signal and TOD data in accordance with the clock information and the TOD information extracted by the GPS engine  111 .  
         [0038]    The PLL module  113  is generally called a frequency synthesizer. The PLL module  113  forms a phase control loop, which continuously provides a phase of output signal coinciding with a phase of an input signal.  
         [0039]    Referring to FIG. 2, an Oven-controlled Oscillator (referred to as an OCXO, hereinafter) is shown together with the PLL module. The OCXO provides the entire system with a timing source. That is, the OCXO makes reverse use of the property that a crystal is heat sensitive and it constantly maintains the temperature around the crystal using an oven so as not to cause any clock error. Even though the OCXD has the best precision among crystal application products, it has a large size and uses various power sources such as 12V, 24V and 30V compared to other products using 3.3V or 5V so that it is generally used for a repeater or satellite communication equipment rather than personal hand-held communication equipment.  
         [0040]    The driver  114  outputs the clock signal and the TOD data generated by the PLL module  113  to its own base transceiver station  100  and the base transceiver station  200  of the next stage.  
         [0041]    The return module for delay correction  115  performs a function of sending back the delay  11  correction signal received from the clock module  210  of the next base transceiver station  200  in order to perform the delay correction of the next base transceiver station  200 .  
         [0042]    The processor  112  extracts the clock information and the TOD information with the help of the GPS engine  111  in case of receiving the GPS signal from the GPS antenna, generates a clock signal and TOD data with the help of the PLL module  113 , outputs the clock signal and TOD to its own base transceiver station  100  and the next base transceiver station  200  through the driver  114 , and processes a delay correction request sent from the base transceiver station  200  of the next stage with the help of the return module for delay correction  115 .  
         [0043]    An operation to perform a synchronization of the GPS satellite clock in the GPS receiver module  110  constructed as described above is explained below.  
         [0044]    On receiving the GPS signal from the GPS antenna, the GPS engine  111  extracts clock information and TOD information from the received GPS signal.  
         [0045]    The TOD data includes information on header and system time, state information, alarm information and leap second check sum.  
         [0046]    When clock information and the TOD information are extracted by the GPS engine  111 , the processor  112  controls the PLL module  113  to generate the clock and the TOD data to be used in its own base transceiver station  100 . The PLL module  113  receives the clock information and the TOD information extracted by the GPS engine  111 , and generates a clock signal and TOD data needed for the system in accordance with a specification already established by the processor  112 . For example, clock signals such as 10 MHz, Pulse Per 2 Second (PPP2S) and 19.6608 MHz are generated.  
         [0047]    Then, the driver  114  outputs the generated clock signal and TOD data to its own base transceiver station  100  and the clock module  210  of the base transceiver station  200  of the next stage.  
         [0048]    On the other hand, the clock module  210  of the base transceiver station  200  of the next stage sends a delay correction signal to correct a delay of the received clock signal to the GPS receiver module  110 . In such a case, the return module for delay correction  115  sends back to the sender the delay correction signal transmitted from the clock module of the base transceiver station of the next stage as is.  
         [0049]    The base transceiver station of the next stage corrects the delay of the clock received from the main base transceiver station using the signal returned from the return logic for delay correction  115 , and then generates a clock signal synchronized with the clock signal used in the main base transceiver station and provides its base transceiver station with the synchronized signal.  
         [0050]    [0050]FIG. 3 is a view showing a detailed block of the clock module shown in FIG. 1.  
         [0051]    Referring to FIG. 3, the clock module  210  includes a delay correction module  211  which measures a delay of the clock received from a main base transceiver station  100  and corrects the delay, a processor  212  for controlling the clock module  210 , a PLL module  213  for synchronizing using a clock from the GPS receiver module  110 , a driver  214  for sending out a clock and TOD, and a return module for delay correction  215  for sending back a delay correction signal sent by the next base transceiver station (not shown) in order to perform a delay correction of the next base-station transceiver.  
         [0052]    The delay correction module  211  receives the clock signal and the TOD data from the main base transceiver station  100 , and measures and corrects the delay of the received clock.  
         [0053]    The PLL module  213  receives the clock signal and the TOD data and a delay correction value received from the delay correction module  211 , and generates a clock signal and TOD data which reflects the delay correction.  
         [0054]    Referring to FIG. 3, a Temperature Compensated Crystal Oscillator (referred to as a TCXO, hereinafter) is shown together with the PLL module. The TCXO is a device outputting a very stable reference signal having a few to tens of MHz among constituents of a mobile communication terminal, which is embodied by an oscillating circuit controlling the oscillating frequency using the crystal oscillator. In order to perform a frequency temperature stabilization which is an important property in the TCXO, the ambient temperature must be in the range of −30˜85° C. and a frequency stability of a carrier required in the temperature is ±2.5 ppm and the room temperature deviation is established in ±0.2 ppm.  
         [0055]    On reviewing recent developments of TCXOs from an aspect of the temperature compensation scheme, a development of a D-TCXO to compensate the temperature using a digital circuit is in progress wherein a component or a circuitry whose reactance is changeable by external data is inserted into an oscillation loop of the crystal oscillation circuit so that the necessary temperature compensation can be obtained. From an aspect of miniaturization, a development of a D-TCXO is in progress wherein the crystal oscillator is embodied in a form of SMD and is covered in a form of a case on a board on which the basic circuit of the TCXO is mounted so that the area of the crystal oscillator is reduced.  
         [0056]    The driver  214  outputs the clock signal and the TOD data generated in the PLL module  213  to its base transceiver station  200  and a base transceiver station (not shown) of the next stage.  
         [0057]    The return module for delay correction  215  performs a function of sending back a delay correction signal received from the clock module of the next base transceiver station (not shown) in order to perform the delay correction of the next base transceiver station (not shown).  
         [0058]    The processor  210  performs the delay correction of the clock signal and the TOD data received from the main base transceiver station  100  by the delay correction module  211  and the PLL module  213 , outputs the corrected data to its base transceiver station  200  and the base transceiver station of the next stage (not shown) through the driver  214 , and controls each constituent to make the return module of delay correction  215  process a delay correction request sent by the base transceiver station of the next stage (not shown).  
         [0059]    Now, an operation for synchronizing GPS satellite clock in the clock module  210  constructed as described above will be explained.  
         [0060]    On receiving the clock signal and the TOD data from the previous base-station transceiver, that is, the GPS receiver module  110  of the main base transceiver station  100 , the delay correction module  211  transmits the delay correction signal to the GPS receiver module  110  of the main base transceiver station  100  in order to measure the delay of the received clock. More concretely, the delay correction signal is transmitted to the return module for delay correction  115 . And, the measurement and correction of the delay is performed using the returned signal from the return module for delay correction  115 .  
         [0061]    When the delay correction module  211  outputs the clock signal and the TOD data received from the GPS receiver module  110  of the main base transceiver station  100  and accordingly the correction control signal, the PLL module  213  corrects the clock signal and the TOD data received from the delay correction module  211  according to the correction control signal and generates a clock signal and TOD data synchronized with the clock signal and the TOD data used in the main base transceiver station  100 . Of course, the PLL module  213  generates a clock signal and TOD data required in the system in accordance with the specification established by the processor  212 .  
         [0062]    Then, the driver  214  outputs the generated clock signal and TOD data to its base transceiver station  200  and then outputs them to a clock module of a base transceiver station of the next stage.  
         [0063]    On the other hand, a clock module (not shown) of the base transceiver station (not shown) of the next stage transmits to the clock module  210  a delay correction signal to correct the received clock signal. In such a case, the return module for delay correction  215  sends back the delay correction signal transmitted from the clock module of the base transceiver station of the next stage as it is.  
         [0064]    The base transceiver station of the next stage corrects the delay of the clock received from the base transceiver station  200  using the signal returned from the return module for delay correction  215 , and accordingly and finally generates a clock signal synchronized with the clock signal used in the main base transceiver station and then provides its own base transceiver station with the clock signal.  
         [0065]    As described above, when the main base transceiver station  100  has one GPS receiver module  110  and the remaining base transceiver stations  200  and  300  have cheap clock modules  210  and  310 , it is possible to construct the customer wireless exchange system by connecting a number of base transceiver stations with one another.  
         [0066]    In a conventional customer wireless communication exchange system, each customer base transceiver station should be directly connected to a GPS antenna in a one-to-one manner, or many customer base transceiver stations should be connected to one GPS antenna in the one-to-many manner using a GPS distributor. At that time, each customer base transceiver station should have a GPS receiver module.  
         [0067]    In accordance with the present invention, however, since every customer base transceiver station can make use of a GPS signal with one GPS antenna, it does not need to install more than one GPS antenna and cables for that.  
         [0068]    Also, a system in accordance with the present invention is profitable economically since it is possible that the GPS receiver module having an expensive OCXO and a GPS engine is used only in one customer base transceiver station and remaining customer base transceiver stations use cheap clock modules.  
         [0069]    Also, a delay occurring due to the fact the customer base transceiver stations are connected with one another using a Daisy chain can be solved with a delay correction module, so that every customer base transceiver station can have the same clock phase as the nearest customer base transceiver station to the GPS antenna and a stable handoff can be performed between wireless base stations.

Technology Category: 5