Patent Publication Number: US-2004057395-A1

Title: Channel recovery method and mobile communication system

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a channel recovery method and, more particularly, to a channel recovery method for a case wherein a channel trouble occurs between a radio base station and a radio base station control station in a mobile communication system.  
       [0002] The arrangement of a conventional mobile communication system will be described with reference to FIG. 7.  
       [0003] In the mobile communication system, a plurality of radio base station control stations  2  are connected to one maintenance/monitoring console  1 , and a plurality of radio base stations  3  are connected to each radio base station control station  2 . A plurality of mobile units  4  are connected to each radio base station  3 .  
       [0004] The maintenance/monitoring console  1  and the radio base station control stations  2  are connected to each other through wires. The radio base station control stations  2  and the radio base stations  3  are connected to each other through wires. The radio base stations  3  and the mobile units  4  are wirelessly connected to each other.  
       [0005] The radio base station control stations  2  and the radio base stations  3  are basically connected to each other through wires. However, in a place where a cable is difficult to lay, the radio base station control station  2  and the radio base station  3  are connected to each other through a simple radio apparatus installed between them.  
       [0006] A plurality of channels are connected per station between the radio base station control stations  2  and the radio base stations  3 . The radio base station  3  is constituted by a plurality of cards having different functions.  
       [0007] As a synchronization scheme in the radio base station  3 , a master-slave timing scheme of receiving clocks from the radio base station control station  2  or a simple radio apparatus is used.  
       [0008] For this reason, when a channel goes out of synchronization due to an instantaneous clock interruption or the like in the radio base station  3  which is receiving clocks from the simple radio apparatus, the radio base station  3  cannot establish channel synchronization with the radio base station control station  2  at the timing when the channel has lost synchronization. If, therefore, a channel trouble occurs, a maintenance person goes to the in-situ station and performs recovery operation.  
       [0009] The following problems are posed in this mobile communication system.  
       [0010] First, when channel synchronization cannot be established between a radio base station and a radio base station control station, it cannot be discriminated whether this is caused by a channel synchronization loss or the absence of clocks from the radio base station control station to the radio base station. This makes it necessary for the maintenance person to goes to the site.  
       [0011] Second, radio base stations are dispersed in various areas, and some installation place is difficult to visit, resulting in much time spent to perform recovery operation at the occurrence of a trouble.  
       [0012] In the above conventional mobile communication system, if channel synchronization cannot be established between a radio base station and a radio base station control station, the maintenance person must visit the radio base station.  
       [0013] In addition, the maintenance person cannot easily visit a radio base station depending on the installation place, it takes much time to perform recovery operation at the occurrence of a trouble.  
       SUMMARY OF THE INVENTION  
       [0014] It is an object of the present invention to provide a mobile communication system which determines a channel synchronization loss, if a channel trouble caused between a radio base station and a radio base station control station is not recovered even after a lapse of a predetermined period of time, and tries channel re-synchronization control upon shifting the timing of a channel synchronization clock when the radio base station communicates with the remote radio base station control station so as to realize channel re-synchronization with the radio base station control station, thereby reducing the number of times a maintenance person visits the in-situ station.  
       [0015] In order to achieve the above object, according to the present invention, there is provided a channel recovery method comprising the steps of monitoring whether no synchronization is established for a predetermined period of time between a radio base station and a radio base station control station which constitute a mobile communication system, and trying channel re-synchronization upon shifting a timing of a channel synchronization clock used for communication between the radio base station and the radio base station control station. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016]FIG. 1 is a block diagram showing the arrangement of a mobile communication system according to the present invention;  
     [0017]FIG. 2 is a block diagram showing an embodiment of a radio base station to which a channel recovery method of the present invention is applied;  
     [0018]FIG. 3 is a flow chart for explaining a method of monitoring an operation state in a radio base station in FIG. 1;  
     [0019]FIG. 4 is a flow chart showing procedures for re-synchronization establishment processing and channel trouble notification processing in a radio base station in FIG. 1;  
     [0020]FIG. 5 is a flow chart showing system startup processing and the flow from detection of a channel disconnection to channel trouble notification in a radio base station in FIG. 1;  
     [0021]FIG. 6 is a flow chart showing procedures for updating operation parameters in a radio base station in FIG. 1; and  
     [0022]FIG. 7 is a block diagram showing the arrangement of a general mobile communication system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0023] An embodiment of the present invention will be described next with reference to FIGS. 1 and 2.  
     [0024] A mobile communication system shown in FIG. 1 includes a maintenance/monitoring console  101  which monitors the overall operation information of the system, radio base station control stations  102  which are connected to the maintenance/monitoring console  101  and control a plurality of subordinate radio base stations  103 , the plurality of radio base stations  103  connected to the radio base station control stations  102  through wires, and a plurality of mobile units  104  wirelessly connected to the radio base stations  103 .  
     [0025] As shown in FIG. 2, the radio base station  103  includes a central monitoring/control section  11  which monitors and controls the overall operation of the radio base station  103 , channel monitoring/control sections  60  to  6   n  which communicate with the radio base station control stations  102  serving as host stations through networks  80  to  8   n , and radio transmission/reception units  20  to  2   n  which communicate with mobile units in radio zones.  
     [0026] The radio base station  103  also includes a plurality of cards  30  to  3   n  which constitute the radio base station  103  and have different functions, and a current-system SDM (Static Direct Memory)  40  and standby-system SDM  41  which constitute a redundant arrangement and store control programs for the operation of the radio base station  103  and operation parameters for monitoring an operation state between the radio base station  103  and the radio base station control station  102 .  
     [0027] The radio base station  103  also includes a shared memory  45  for the expansion of operation parameters, a card state monitoring timer value  42  for monitoring the operation states of the cards  30  to  3   n  constituting the radio base station  103  in a predetermined cycle, and a channel synchronization loss protection stage count  43  for determining, when a channel disconnection has occurred, whether the channel disconnection has been caused by an instantaneous interruption or synchronization loss.  
     [0028] In addition, the radio base station  103  includes a synchronization failure protection stage count  44  for defining the maximum trial time for channel re-synchronization control, re-synchronization monitoring flags  50  to  5   n  for identifying a card subjected to a channel disconnection at the time of occurrence of a channel disconnection, and synchronization timing updating timer values  70  to  7   n  which are connected to the channel monitoring/control sections  60  to  6   n  and define a unit time for a trial of channel re-synchronization control at the time of occurrence of a channel synchronization loss.  
     [0029] The components connected to the central monitoring/control section  11  include the channel monitoring/control sections  60  to  6   n , radio transmission/reception units  20  to  2   n , cards  30  to  3   n , current-system SDM  40 , standby-system SDM  41 , shared memory  45 , card state monitoring timer value  42 , channel synchronization loss protection stage count  43 , synchronization failure protection stage count  44 , re-synchronization monitoring flags  50  to  5   n , and central monitoring/control section  11 .  
     [0030] The central monitoring/control section  11  further includes a comparing section  11   a , a specifying section  11   b  connected to the comparing section  11   a , a determining section  11   c  connected to the specifying section  11   b , a re-synchronization establishing section  11   d  connected to the determining section  11   c , a channel trouble notifying section  11   e  connected to the re-synchronization establishing section  11   d , and a radio transmission/reception switching section  11   f  connected to the channel trouble notifying section  11   e . The central monitoring/control section  11  includes an updating section  11   g.    
     [0031] The comparing section  11   a  monitors the operation state of each card. Upon detecting a state change, the comparing section  11   a  checks whether the detected contents are identical to those previously detected. If the detected contents differ from those previously detected, the comparing section  11   a  stores the contents. The specifying section  11   b  determines a card whose state change has been detected. The determining section  11   c  determines whether or not the contents of the state change correspond to a channel disconnection during the operation of the card.  
     [0032] The re-synchronization establishing section  11   d  prompts one of the channel monitoring/control sections  60  to  6   n  which has undergone a channel disconnection to perform channel re-synchronization, and checks a channel state. If a channel disconnection has occurred, the re-synchronization establishing section  11   d  registers a synchronization timing updating timer again.  
     [0033] The re-synchronization establishing section  11   d  also tries channel re-synchronization control upon shifting the timing of a channel synchronization clock in communicating with the radio base station control station  102 . If a channel has been or is being established when the synchronization timing updating timer expires, the re-synchronization establishing section  11   d  cancels the operation of the synchronization failure timer upon reception of a channel re-synchronization establishment notification sent out from the channel monitoring/control section during channel establishment.  
     [0034] When channel re-synchronization establishment fails, the channel trouble notifying section  11   e  notifies the maintenance/monitoring console  101  of the corresponding information.  
     [0035] The radio transmission/reception switching section  11   f  stops one of the radio transmission/reception units  20  to  2   n  which is performing call connection using a troubled channel and switches to another radio communication means. If there is no normal channel, the radio transmission/reception switching section  11   f  restarts (resumes) the home station to prevent a call connection failure due to a channel trouble, and stands by until a channel with the radio base station control station  102  recovers.  
     [0036] The updating section  11   g  downloads operation parameters from the radio base station control station  102  and writes them in the standby-system SDM  41 .  
     [0037] The channel synchronization loss protection stage count  43  includes a synchronization loss detection timer  43   a  for setting a time during which a state change is to be monitored. The synchronization failure protection stage count  44  includes a synchronization failure timer  44   a  for setting the maximum trial time for channel re-synchronization control upon shifting the timing of a channel synchronization clock.  
     [0038] Networks  81  to  8   n  can be connected for four channels at maximum between the radio base station  103  and the radio base station control station  102 . If, for example, each of the networks  81  to  8   n  is constituted by a combination of a control channel and speech communication channel, two channels can be connected at the maximum.  
     [0039] The operation of a radio base station based on a channel recovery method of the present invention will be described in detail next with reference to FIGS.  3  to  5 .  
     [0040] Of the steps to be described below, steps S 301  to S 322  will be described with reference to FIG. 3, steps S 401  to S 418  will be described with reference to FIG. 4, and steps S 501  to S 513  will be described with reference to FIG. 5.  
     [0041] (System Startup Processing)  
     [0042] In starting services by the system, control programs and operation parameters are externally written in advance in the current-system SDM  40  and standby-system SDM  41  in equal number.  
     [0043] The central monitoring/control section  11  loads the control programs written in the current-system SDM  40 , and activates the channel monitoring/control sections  60  to  6   n  which communicate with the radio base station control station  102  through wires, the radio transmission/reception units  20  to  2   n  which performs signal transmission/reception in radio zones, and the cards  30  to  3   n  which constitute the radio base station  103  and have different functions, thereby starting operation (steps S 501  and S 502 , steps S 601  and S 602 , and steps S 629  and S 630 ).  
     [0044] Upon completion of the startup of the radio base station  103 , the central monitoring/control section  11  reads out operation parameters for re-synchronization establishment from the current-system SDM  40 , and expands the card state monitoring timer value  42 , channel synchronization loss protection stage count  43 , synchronization failure protection stage count  44 , and synchronization timing updating timer values  70  to  7   n  in the shared memory  45  (steps S 503  to S 507 , steps S 603  to S 607 , and steps S 631  to S 635 ).  
     [0045] Upon expanding the operation parameters in the shared memory  45 , the central monitoring/control section  0 . 11  transmits re-synchronization establishment parameters to the channel monitoring/control sections  60  to  6   n  and receive the corresponding responses (steps S 508  and S 509 , steps S 608  and S 609 , and steps S 636  and S 637 ).  
     [0046] (Card State Monitoring Processing)  
     [0047] The central monitoring/control section  11  reads out the card state monitoring timer value  42  expanded in the shared memory and registers it in a timer section  46  in order to monitor the operation state of each of the cards  30  to  3   n  constituting the radio base station  103  (steps S 301  and S 302 ).  
     [0048] When the timer in which the card state monitoring timer value  42  is registered expires, the central monitoring/control section  11  loads the operation state of each of the cards  30  to  3   n  constituting the radio base station  103  (steps S 303  to S 305 ).  
     [0049] The comparing section  11   a  of the central monitoring/control section  11  compares the operation state of each of the cards  30  to  3   n  having different functions with the corresponding previous state. If there is no change, the comparing section  11   a  checks the next card. Upon detecting a state change, the comparing section  11   a  checks whether the detected contents are identical to those previously detected.  
     [0050] If it is determined upon comparison that the contents are identical, the comparing section  11   a  of the central monitoring/control section  11  checks the next card. If the contents differ from each other, the corresponding contents are stored (steps S 306  and S 307 ).  
     [0051] After the contents of the state change are stored, the specifying section  11   b  of the central monitoring/control section  11  determines a specific card having a specific function from which the state change has been detected. If a trouble has occurred in one of the channel monitoring/control sections  60  to  6   n , the determining section  11   c  of the central monitoring/control section  11  determines whether or not the trouble corresponds to a channel disconnection during the operation of the card (steps S 308  and S 309 ).  
     [0052] If the trouble corresponds to a channel disconnection, the corresponding one of the re-synchronization monitoring flags  50  to  5   n  respectively held in the channel monitoring/control sections  60  to  6   n  is checked (step S 310 ). If the corresponding re-synchronization monitoring flag is OFF, it is checked whether the channel disconnection has been caused by an instantaneous interruption or synchronization loss.  
     [0053] The channel synchronization loss detection timer value is read out from the channel synchronization loss protection stage count  43  and registered in the timer section  46 , and the corresponding re-synchronization monitoring flag is turned on (steps S 311  to S 313 ).  
     [0054] If the corresponding re-synchronization monitoring flag is ON, the operation state of the next card is checked (step S 317 ).  
     [0055] If it is determined in step S 309  that no channel disconnection has occurred, the corresponding re-synchronization monitoring flag is checked.  
     [0056] If the corresponding re-synchronization monitoring flag is ON, it is determined that the state change corresponds to a recovery from a channel disconnection. The re-synchronization monitoring flag is then turned off and the channel synchronization loss detection timer is stopped (steps S 314  to S 316 ). If the corresponding re-synchronization monitoring flag is OFF, the operation state of the next card is checked (step S 317 ).  
     [0057] According to the above description, when the operation state of one of the channel monitoring/control sections  60  to  6   n  has changed, which has been caused by a channel disconnection during the operation of the card, and the corresponding re-synchronization monitoring flag is OFF, it is checked whether a channel disconnection is an instantaneous interruption.  
     [0058] A channel synchronization loss detection timer value is therefore read out and registered in the timer section  46 . When the operation state of the channel monitoring/control section with the same card changes and the corresponding re-synchronization monitoring flag is OFF, it is determined that the change corresponds to a recovery from a channel disconnection, and the corresponding channel synchronization loss detection timer is interrupted (canceled).  
     [0059] This channel synchronization loss detection timer value is set to a time during which steps S 303  to S 317  are executed a predetermined number of times. If a recovery from a channel disconnection cannot be made within the time set in the timer, the timer is stopped, and control is passed to the procedure for channel re-synchronization establishment (steps S 320  and S 513 ).  
     [0060] When a channel disconnection occurs during the operation of a card, the channel synchronization loss detection timer is started, and the operation state of each card is monitored a plural number of times until the expiration of the timer, thereby determining whether or not a recovery is made, i.e., an instantaneous interruption or channel synchronization loss.  
     [0061] (Re-Synchronization Establishment Processing)  
     [0062] When the registered channel synchronization loss detection timer expires, a synchronization failure timer value is read out from the synchronization failure protection stage count  44  and registered in the timer section  46  (steps S 318  and S 319  and steps S 401  and S 402 ).  
     [0063] The synchronization failure timer value is used, in the event of a channel re-synchronization failure, as a standard for the timing of transmission of a channel trouble notification to the maintenance/monitoring console  101  for the sake of prompting it to check the channel for which channel re-synchronization cannot be established owing to a channel trouble. Alternatively, this value is used as the maximum trial time for channel re-synchronization control.  
     [0064] After the channel re-synchronization failure timer is registered, the re-synchronization establishing section  11   d  of the central monitoring/control section  11  sends out a re-synchronization establishment request to a channel monitoring/control section  6   k  (k=1 to n) subjected to the channel disconnection (step S 403 ).  
     [0065] Upon reception of the re-synchronization establishment request, the channel monitoring/control section  6   k  reads out a synchronization timing updating timer value  6   k  of the re-synchronization establishment parameters received from the central monitoring/control section  11 , and registers it in the timer section  46  (steps S 404  to S 407 ).  
     [0066] When the synchronization timing updating timer expires, the channel monitoring/control section  6   k  checks a channel state with a network  8   k  (step S 408 ).  
     [0067] If a channel disconnection state is determined, the channel monitoring/control section  6   k  registers a synchronization timing updating timer again, and tries channel re-synchronization control upon shifting the timing of a channel synchronization clock in communicating with the radio base station control station  102  (steps S 409  and S 410 ).  
     [0068] When the synchronization timing updating timer expires, the channel monitoring/control section  6   k  checks the channel state with the network  8   k.    
     [0069] If it is determined that a channel has been or is being established, the channel monitoring/control section  6   k  sends out a channel re-synchronization establishment notification to the central monitoring/control section  11 . Upon reception of the channel re-synchronization establishment notification, the central monitoring/control section  11  stops (cancels) the synchronization failure timer (steps S 411  and S 412 ).  
     [0070] If the registered synchronization failure timer expires without channel synchronization establishment (step S 321 ), the central monitoring/control section  11  checks the states of the networks  80  to  8   n  between the radio base station  103  and the radio base station control station  102  (step S 413 ).  
     [0071] If the presence of a normal channel is determined, the channel trouble notifying section  11   e  of the central monitoring/control section  11  transmits a channel trouble notification to the maintenance/monitoring console  101  through the corresponding channel to prompt the maintenance/monitoring console  101  to make a channel check. In addition, the central monitoring/control section  11  stops a radio transmission/reception unit which is performing call connection using a troubled channel (steps S 414  to S 416 ).  
     [0072] If no available channel is present in the networks  80  to  8   n  with the radio base station control station  102 , the radio base station  103  is resumed and set in the standby state until a channel with the radio base station control station  102  is recovered in order to prevent a call connection failure due to a channel trouble (step S 418 ).  
     [0073] As described above, in this embodiment, after the central monitoring/control section  11  which monitors/controls the radio base station  103  starts the radio base station  103 , the operation states of the cards  30  to  3   n  are monitored at intervals of a card state monitoring timer value.  
     [0074] If a channel trouble is detected in one of the channel monitoring/control sections  60  to  6   n , the re-synchronization monitoring flag held in the channel monitoring/control section in which the trouble has been detected is turned on to monitor a state change within the time of a channel synchronization loss detection timer value.  
     [0075] If the trouble is recovered afterward, the corresponding re-synchronization monitoring flag is turned off again, and the channel synchronization loss detection timer is interrupted.  
     [0076] If the channel synchronization loss detection timer expires while the corresponding re-synchronization monitoring flag is kept on, i.e., the channel trouble is not recovered, the channel monitoring/control section corresponding to the channel trouble is caused to start re-synchronization control upon shifting the timing of a channel synchronization clock.  
     [0077] If the synchronization failure timer expires without channel establishment, the channel trouble notifying section  11   e  of the central monitoring/control section  11  transmits a channel trouble notification to the maintenance/monitoring console  101 .  
     [0078] The radio transmission/reception switching section  11   f  of the central monitoring/control section  11  stops one of the radio transmission/reception units  20  to  2   n  which is performing call connection by using the troubled channel, and switches the mobile unit to another normal radio transmission/reception unit.  
     [0079] The above operation makes it possible to decrease the number of times the maintenance/monitoring console  101  is notified of the occurrence of a trouble and recovery in the event of a trouble due to a channel disconnection. Of the resources of the maintenance/monitoring console  101 , therefore, the capacity used for the notification of troubles can be saved and assigned to another use.  
     [0080] (Updating of Operation Parameters)  
     [0081] A case wherein the operation parameters which are being used by the radio base station  103  are updated will be described next with reference to FIG. 6.  
     [0082] The maintenance person transmits a station data download start request signal from the radio base station control station  102  to the channel monitoring/control sections  60  to  6   n  through the networks  80  to  8   n  under the control of the maintenance/monitoring console  101 .  
     [0083] Upon reception of the station data download start request signal through the channel monitoring/control sections  60  to  6   n , the updating section  11   g  of the central monitoring/control section  11  sets the standby-system SDM  41  in a write enable state, and returns a station data download start response signal (steps S 610  to S 612 ). The updating section  11   g  then receives the station data download request signal transmitted from the radio base station control station  102 , and writes the contents of the signal in the standby-system SDM  41 . After this write operation is complete, the updating section  11   g  transmits a station data download response signal to the radio base station control station  102  (steps S 613  to S 618 ).  
     [0084] Upon reception of a station data download end request signal from the radio base station control station  102 , the updating section  11   g  of the central monitoring/control section  11  restores the standby-system SDM  41  to a write disable state, and returns a station data download end response signal to the radio base station control station  102  (steps S 619  to S 621 ).  
     [0085] Upon transmission of the station data download end response signal, the updating section  11   g  reads out the update operation parameter written in the standby-system SDM  41 , and writes the parameter in the current-system SDM  40  after setting the current-system SDM  40  in a write enable state.  
     [0086] After the write operation, the updating section  11   g  restores the current-system SDM  40  to a write disable state, thus making the contents of the current-system SDM  40  and standby-system SDM  41  identical (steps S 622  to S 625 ).  
     [0087] When the maintenance person instructs the radio base station  103  to update the operation parameter at a proper update timing, the radio base station control station  102  transmits an operation parameter update request signal to the radio base station  103  in accordance with the operation parameter update request from the maintenance person (step S 626 ).  
     [0088] Upon reception of the operation parameter update request signal, the radio base station  103  returns an operation parameter update request response to the radio base station control station  102 , and resumes the radio base station  103 , thus completing the operation parameter updating operation (steps S 627  to S 637 ).  
     [0089] As has been described above, according to the channel recovery method and mobile communication system of the present invention, if a synchronization is not established between a radio base station and a remote radio base station control station for a predetermined period of time, the radio base station tries channel re-synchronization control upon shifting the timing of a channel synchronization clock in communicating with the remote radio base station control station. This makes it possible to obtain the following effects.  
     [0090] First, when the radio base station periodically monitors each card, and a channel trouble occurs, the station determines whether the trouble is caused by an instantaneous interruption or channel synchronization loss. If it is determined that the trouble is caused by a channel synchronization loss, the channel connection failure can be quickly solved.  
     [0091] Second, when a temporary trouble such as an instantaneous interruption occurs or a channel is established by a re-synchronization trial, the maintenance/monitoring console is notified of nothing. This makes it possible to easily specify a radio base station in which a channel trouble has occurred.