Abstract:
Logical coverage areas are dynamically rearranged to meet the traffic needs of a wireless switching system. Further, the logical coverage areas do not have to be initially provisioned during deployment of the wireless switching system since the initial determination of the logical coverage areas is automatically performed. Once the logical coverage areas are established, the logical coverage areas adapt to the changing needs of the community of wireless handsets. A first embodiment allows the base stations to control the rearrangements, and a second embodiment allows a system wireless controller controlling the wireless switching system to control the rearrangements.

Description:
TECHNICAL FIELD 
     This invention relates to telecommunications switching and, in particular, to wireless switching systems. 
     BACKGROUND OF THE INVENTION 
     A problem in the installing, provisioning, and deploying of in-building or campus personal communications systems (PCS) is the small physical size of the cells provided by the base stations. This is a problem because as an individual walks through a building with their wireless handset, the wireless handset is continuously re-registering on different base stations as it loses contacts with the previous base station. Such movements cause a large amount of traffic for the base stations as well as for the central controller that is providing overall control and switching for the wireless system. Since the central controller must be informed on which base station each wireless handset is registered, there is an advantage in the central controller knowing the exact base station on which a wireless handset is registered. When an incoming call is received for the handset, the wireless system controller can immediately set up the call via the base station to the wireless handset. If the wireless system controller simply knows that the wireless handset is registered on one of the base stations in the wireless system, then, the wireless system controller must attempt to set up the incoming call via all the base stations. 
     Within the prior art these problems have been resolved by the utilization of logical coverage areas. Base stations are grouped into logical coverage areas, and the wireless system controller is only informed that a wireless handset is registered on a base station within a particular logical coverage area. When an incoming call is received for the wireless handset, the wireless system controller only attempts to establish a connection to the wireless handset through the base stations that make up the logical coverage area of the wireless handset. Within a logical coverage area, if a wireless handset moves from one base station to another, the wireless handset does not re-register on the other base station since it is in the same logical coverage area. This greatly reduces the number of re-registrations and assists in the amount of work that must be done to route incoming calls to a wireless handset. 
     Logical coverage areas are used in many wireless protocols such as PHS, DECT, or PWT. However, problems do exist with the utilization of logical coverage areas. First, the use of logical coverage areas complicates the provisioning and deploying of new PCS wireless networks since a great deal of time and effort must be spent in determining which base stations should be placed in which logical coverage areas. Further, within a building or a campus, people do not move in constant and uniform patterns. Rather, people enter the wireless system in the morning and leave in the evening. People go to a cafeteria for lunch, or go to an auditorium for a large meeting. The result is that no matter how carefully the provisioning and deployment of the logical coverage areas is performed, a static deployed logical coverage areas are not efficient for all conditions in most installations. 
     SUMMARY OF THE INVENTION 
     The foregoing problems are solved, and a technical advance is achieved, by an apparatus and method that dynamically rearrange logical coverage areas to meet the traffic needs of a wireless switching system. Once the logical coverage areas are established, the logical coverage areas adapt to the changing needs of the community of wireless handsets. Advantageously, in a first embodiment, the adaptation is controlled by individual base stations, or in a second embodiment, the adaptation is controlled by a system wireless controller that controls the wireless switching system. 
     In the first embodiment, a base station in a first logical coverage area determines when it should join a second logical coverage area by monitoring the frequency of registrations of wireless handsets from all other logical coverage areas. When registrations from the second logical coverage area exceed a predetermined threshold rate, the base station joins the second logical coverage area. To join the second logical coverage area, the base station requests permission from another base station within the second logical coverage area. If the number of base stations in the second logical coverage area does not exceed a predetermined threshold number, the other base station gives the base station permission to join the second logical coverage area. 
     In the second embodiment, the system wireless controller maintains a frequency table for each base station. The frequency table records the rate of registrations from other logical coverage areas to the base station. When registrations from a second logical coverage area to a base station in a first logical coverage area exceed a predetermined threshold rate, the system wireless controller transfers the base station from the first logical coverage area to second logical coverage area if the number of base stations already in the second logical coverage area does not exceed a predetermined threshold. 
    
    
     Other and further aspects of the present invention will become apparent during the course of the following description and by reference to the accompanying drawing. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1-4 illustrate, in block diagram form, a wireless switching system for use with the invention; 
     FIGS. 5-9 illustrate, in flow chart form, steps performed by a base station in implementing a first embodiment of the invention; and 
     FIGS. 10-12 illustrate, in flow chart form, steps performed by a system wireless controller in implementing a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a wireless switching system that has wireless handsets (WH)  113 - 133  which are capable of registering and placing and receiving calls on base stations (BS)  101 - 112 . The base stations are interconnected by fixed links not illustrated in FIG. 1 to system wireless controller  100 . System wireless controller  100  provides overall control of the wireless system and provides the necessary switching of audio information between the wireless handsets. FIG. 1 illustrates the initial state of the system before logical coverage areas are established. Cells  134 - 141  illustrate the radio coverage of individual base stations. For example, cell  134  is the radio coverage area of base station  108 . Double-ended arrows attaching a wireless handset to a base station indicate that the wireless handset is registered on that base station. In a first embodiment of the invention, base stations initially interrogate each wireless handset registered on the base station to determine in which other cells, the wireless handset is registered. For example, base station  108  interrogates its registered wireless handset and determine that wireless handset  122  is within cell  136  of base station  107 . Base station  108  then communicates with base station  107  via the fixed links through system wireless controller  100  to determine that base stations  107  and  108  should be in a logical coverage group. Base station  106  performs a similar operation with respect to wireless handset  114 . The logical coverage area that results from the communication between base stations  106 - 108  is logical coverage area  201  as illustrated in FIG.  2 . Similarly, base stations  109 - 112  establish coverage area  202  as illustrated in FIG.  2 . The reason that logical coverage area  202  is established is because wireless handsets  128  and  126  are within cell  141  of base station  112  but are registered on base stations  109  and  111 , respectively. Similarly, base stations  101  and  102  also have a common wireless handset, although not illustrated, and form coverage area  203 . Similarly, coverage area  204  is formed to include base stations  103  and  104 . After a group of base stations such as base stations  106 - 108  have determined they should be in a logical coverage area, this fact must be communicated to system wireless controller  100  so that it can assign a logical coverage area number to the determined logical coverage area and know the identity of the base stations in the determined logical coverage area. 
     In a second embodiment of the invention, the previously described operations of forming the logical coverage areas are performed by system wireless controller  100  using information received from base stations  101 - 112 . 
     When wireless handset  121  is in logical coverage area  201  and system wireless controller  100  receives a call for wireless handset  121 , system wireless controller  100  sends call setup messages to base stations  106 - 108  since system wireless controller  100  sends setup messages to all of the base stations in logical coverage area  201 . If logical coverage areas were not utilized, system wireless controller  100  would either have to send call. setup messages to all of the base stations illustrated in FIG. 1, or each time, wireless handset  121  re-registered on a base station, this re-registration would have to be reported back to system wireless controller  100 . 
     Using logical coverage areas, if wireless handset  121  moves into cell  137  of base station  106 , wireless handset  121  will not re-register because it detects that it has not left logical coverage area  201 . Wireless handset  121  knows that it has not left logical coverage area  201  because base stations  106 - 108  each broadcast on the broadcast control channel (BCCH) the logical coverage area number. Hence, when wireless handset  121  moves into cell  137  it is aware from information contained in the BCCH broadcasted by base station  107  that it is still in logical coverage area  201 . If wireless handset  121  had entered cell  139  of base station  109 , wireless handset  121  would re-register since it detects from information transmitted by base station  109  that it had changed its logical coverage area. This re-registration of wireless handset  121  on base station  109  involves operations by system wireless controller  100  and base station  109 . In addition, wireless handset  121  expends a large amount of electrical energy from its battery in performing its portion of the re-registration operation. 
     Consider now an example of the dynamic rearrangement of logical coverage areas based on the movement of wireless handsets. Assume that wireless handsets  124  and  129  leave cells  138  and  139 , respectively, and enter cell  134  in a short period of time as illustrated in FIG.  3 . Upon detecting the registration of wireless handsets  124  and  129 , base station  108  uses this fact as an indication that there will be a general movement of wireless handsets to cell  134  from logical coverage area  202 . 
     In response to the rapid registration of wireless handsets  124  and  129  from logical coverage area  202 , base station  108  determines that it should be part of logical coverage area  202  in anticipation of more wireless handsets from logical coverage area  202  registering on base station  108 . First, base station negotiates its entry into logical coverage area  202  with base stations  109 - 112  by the transmission of messages to these base stations via system controller  100  and the wired links that the base stations maintain to system wireless controller  100 . Second, after the negotiations have been successfully completed with base stations  109 - 112 , base station  108  communicates to base stations  106  and  107  of logical coverage area  201  that base station  108  is transferring out of coverage area  201 . Third, base station  108  via its BCCH transmits to wireless handsets  121 ,  122 ,  124 , and  129  that they are no longer part of logical coverage area  201  and are part of logical coverage area  201 . Base station  108  also specifies that the handsets do not have to re-register. Finally, base station  108  transmits to system wireless controller  100  a message for each of its presently registered wireless handsets that informs system wireless controller  100  that these wireless handsets are now part of logical coverage area  202 . FIG. 4 illustrates the configuration of the wireless switching system after base station  108  becomes part of logical coverage area  202 . 
     In the second embodiment of the invention, system wireless controller  100  performs the control operations performed by base station  108  in the first embodiment of the invention, and automatically adjusts the logical coverage areas as previously described. 
     FIGS. 5 and 6 illustrate the steps performed by a base station in initially establishing a logical coverage area. Once started from block  500 , the base station first determines the number of registered handsets that are registered on the base station in block  501 . Then, decision block  502  determines if there are any registered handsets. If the answer is no, normal processing is performed in block  505  before control is transferred back to block  501 . If the answer in decision block  502  is yes, decision block  503  determines if any of the registered handsets are unreported. If the answer in decision block  503  is yes, block  504  requests that a registered handset report other base stations in the radio coverage area of the registered handset before transferring control to decision block  506 . The latter decision block waits until the requested handset reports and then transfers control to block  603  of FIG.  6 . 
     Block  603  requests the identification of the other base stations from the requested handset. Block  604  selects one of the base stations identified in block  603 . Decision block  606  then determines if the selected base station is already in a logical coverage area with the base station that is performing the steps of FIGS. 5 and 6. If the answer is yes, control is transferred back to block  604 . If the answer is no, control is transferred by decision block  606  to decision block  607  that determines whether the selected base station is already in another logical coverage area. If the answer is yes in decision block  607 , control is transferred back to block  604 . If the answer is no in decision block  607 , block  608  contacts the selected base station and forms it into a new logical coverage area before transferring control to decision block  609 . The latter decision block determines if there are any more unselected base stations reported by the reporting handset that supplied a list of base stations in block  603 . If the answer is yes, control is transferred back to block  604  so that a new base station can be selected. If the answer is no in decision block  609 , control is transferred back to decision block  503  of FIG.  5 . 
     When all of the handsets that are registered on the base station executing the steps of FIGS. 5 and 6 have reported, this fact is determined by decision block  503  which transfers control to block  601  of FIG.  6 . Block  601  requests a number for the new logical coverage area that is being formed from the system wireless controller, and block  602  transmits this logical coverage area number to the other base stations that are being formed into the new logical coverage area. These are the base stations that were determined and designated in block  608 . 
     FIGS. 7-9 illustrate, in flow chart form, the steps performed by a base station in automatically transferring to a different logical coverage area. Returning to FIG. 6, after execution of block  602 , control is transferred to decision block  701  that examines a frequency table that is maintained by each base station. The frequency table maintains the frequency of transfers of wireless handsets from other logical coverage area to the base station. Decision block  701  determines if the transfer rate from any logical coverage area listed in the frequency table exceeds the threshold for such transfers. If the answer is yes, the base station will join the logical coverage area exceeding the threshold. If the answer is no in decision block  701 , control is transferred to decision block  702  which determines if a wireless handset is in the process of registering on the base station. If the answer is yes, decision block  703  determines if the wireless handset is already in the logical coverage area of the base station. If the answer is yes in decision block  703 , control is transferred to block  707  which processes the registration operation with the wireless handset in a normal manner before returning control back to decision block  701 . If the answer is no in decision block  703 , control is transferred to block  704  which determines from the wireless handset the logical coverage area and base station from which the wireless handset came before transferring control to block  706 . The latter block updates the frequency table with the information about the determined logical coverage area from block  704  and records the base station information before transferring control to block  707 . 
     Returning to decision block  701 , if a logical coverage area in the frequency table exceeds the threshold, control is transferred to block  801  of the FIG.  8 . Block  801  selects a base station associated with the determined logical coverage area to be contacted before transferring control to block  802 . The latter block sends a message to the selected base station in the determined logical coverage area requesting permission to join the logical coverage area and to receive the logical coverage area number. If the selected base station returns the logical coverage area number, this means that permission has been granted to join the logical coverage area. The steps performed by a base station such as the selected base station in block  802  are illustrated in FIG.  9 . After execution of block  802 , block  803  determines if the logical coverage area number has been received from the selected base station of block  801 . If the answer is no, control is transferred to decision block  804  that determines if there is another base station that has been associated in the frequency table with the determined logical coverage area. If the answer is yes in decision block  804 , block  807  selects another base station from the frequency table and returns control to block  802 . If the answer in decision block  804  is no, block  806  deletes the determined logical coverage area with its associated base stations from the frequency table before transferring control back to decision block  701  of FIG.  7 . 
     Returning to decision block  803 , if the logical coverage area number is received back from the selected base station of block  801 , control is transferred to block  808 . Block  808  sends a message to all of the wireless handsets registered on the base station, performing the step of block  808 , informing these wireless handsets that they are now in the determined logical coverage area as defined by the logical coverage area number received in block  803 . The message transmitted in block  808  also informs the registered wireless handsets that the wireless handsets do not have to re-register. After execution of block  808 , control is transferred to block  809  that sends messages to the system wireless controller for the base station and each of the registered handsets informing the system wireless controller that the base station and all of its registered handsets are now in the determined logical coverage area before transferring control to block  811 . Block  811  informs the other base stations of the former or departed logical coverage area that the base station is no longer part of that logical coverage area before transferring control back to decision block  701  of FIG.  7 . 
     FIG. 9 illustrates, in flow chart form, the steps performed by a base station upon receiving a message from another base station requesting permission to join the logical coverage area of the base station executing the steps of FIG.  9 . Returning to FIG. 7, if a wireless handset registration is not determined in decision block  702 , control is transferred to decision block  901  of FIG.  9 . Decision block  901  determines if a message is being received from another base station is requesting permission to join the logical coverage area of the base station executing decision block  901 . If the answer is no, control is transferred to block  906  which processes the stimuli being received by the base station in a normal manner before transferring control back to decision block  701  of FIG.  7 . If the answer in decision block  901  is yes, control is transferred to decision block  902  that determines if the logical coverage area is at the threshold for the number of base stations that are allowed to be in a logical coverage area. If the answer is yes, control is transferred back to decision block  701  of FIG.  7 . If the answer in decision block  902  is no, block  903  transmits the logical coverage area number to the requesting base station, and identifies the requesting base station to the other base stations in the logical coverage area before transferring control back to decision block  701  of FIG.  7 . 
     FIG. 10 illustrates the steps performed by system wireless controller  100  in initially establishing logical coverage areas for the base stations. Once start from block  1000 , system wireless controller  100  determines the total number of registered handsets by execution of block  1001 . Decision block  1002  determines if there are any registered handsets. If the answer is no, block  1003  performs normal processing before returning control back to block  1001 . If the answer in decision block  1002  is yes, block  1004  requests that all handsets report all base stations within the radio coverage area of each wireless handset before transferring control to decision block  1006 . The latter decision block waits until all wireless handsets have reported before transferring control to block  1007 . The latter block groups the stations into logical coverage areas. A logical coverage area initially consists of those base stations that have common handsets. After execution of block  1007 , block  1008  transmits the logical coverage area numbers to the base stations. Finally, decision block  1009  determines when a predefined amount of time that is allowed for the initialization phase has elapsed. If the time has not elapsed yet, decision block  1009  transfers control back to block  1001 . If the time has elapsed, decision block  1009  transfers control to block  1101  of FIG.  11 . 
     Block  1101  creates a frequency table for each base station. The frequency table lists the frequency of registrations being received from particular logical coverage areas. Decision block  1102  examines the frequency tables to determine if a logical coverage area in a frequency table for a base station has exceeded the threshold. If the answer is no in decision block  1102 , decision block  1103  determines if a wireless handset has just registered on the wireless switching system. If the answer is no, block  1111  performs normal processing before transferring control back to decision block  1102 . If the answer in decision block  1103  is yes, decision block  1104  determines if the handset has merely re-registered on a base station within its present logical coverage area. If the answer is yes, control is transferred to block  1109  which processes the registration in a normal manner before transferring control back to decision block  1102 . If the answer in decision block  1104  is no, block  1106  determines the logical coverage area and base station from which the wireless handset came, and block  1107  determines the present logical coverage area and base station on which the wireless handset is presently registered. Then, block  1108  updates the frequency table for the base station with information about the determined logical coverage area before transferring control to block  1109 . 
     Returning to decision block  1102 , if a logical coverage area for a particular base station has exceeded the threshold, control is transferred to block  1201  of FIG.  12 . Block  1201  sends messages to the handsets registered on the base station selected in decision block  1102 . (The selected base station is the one whose frequency table had a logical coverage area that has exceeded the threshold as determined in block  1102 .) The messages inform the wireless handsets that they are being switched to the determined logical coverage area but that they should not re-register. Then, block  1202  sends a message to the selected base station requesting that it switch to the new logical coverage area, and messages are sent to the base stations in the new logical coverage area informing them that the selected base station is joining that logical coverage area. Next, block  1203  sends messages to the base stations in the new logical coverage area that the selected base station will be joining the new logical coverage area. Finally, block  1204  sends messages to the base stations in the departed logical coverage area informing these base stations that the selected base station is leaving the departed logical coverage area before transferring control back to  1102  of FIG.  11 . 
     Of course, various changes and modifications to the illustrative embodiments described above will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the invention and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the following claims except insofar as limited by the prior art.