Patent Publication Number: US-2007099576-A1

Title: Method and apparatus for base station management

Description:
TECHNICAL FIELD  
      This invention relates generally to wireless communication systems and more particularly to wireless communication systems that manage base stations to facilitate mobile station transfers between base stations.  
     BACKGROUND  
      Many wireless communication systems are known in the art. In such systems, a mobile station, such as a phone, wirelessly networked computer, or other wireless communication device transmits data to and from a stationary transceiver. The stationary transceiver, commonly known as a base transceiver station, is connected to a network such that information may be shared with other systems. Because the mobile stations move relative to the base transceiver stations, eventually the wireless signal will weaken to the point that the mobile station will need to switch its wireless communication to another base transceiver station.  
      Wireless communication systems employ various known techniques to facilitate the transfer of a mobile station from one base transceiver station to another. Certain wireless communication systems will wait until the system determines that the mobile station needs to transfer base transceiver stations to begin a transfer of data. In such a system, the transfer cannot occur until the mobile station signals to the system that a transfer should occur. In a typical system, at that time, a controller will then forward the data to be sent to the mobile station to the target base station transceiver instead of the primary base station transceiver. Waiting for this data transfer results in a delay in the operation of the system for the mobile station user.  
      In certain high speed networks, a central server will forward the data to be sent to a mobile station to every base transceiver station in the active area of the mobile station at a given frequency or at certain times or intervals to reduce the delay experienced during a handoff. In other words, the system will send the data to not only the base transceiver station with which the mobile station is communicating, the primary base transceiver station, but also to every base transceiver station to which the mobile station may switch its communication surrounding that primary base transceiver station. This flooding technique results in larger data traffic volumes within the network as data is needlessly sent to multiple base transceiver stations. The larger data volumes, in turn, can overly tax the system&#39;s resources.  
      Further, when a mobile station experiences a handoff in such a high speed system, the target base transceiver station will send all the data previously received by the target base transceiver station for that mobile station. Often, the mobile station had previously received much of this data from the primary base transceiver station prior to the handoff. Sending synchronization signals to the base transceiver stations neighboring the primary base transceiver station to synchronize the data at the neighboring base transceiver stations with the data at the primary base transceiver station can reduce the redundancy in resending data to the mobile station during handoffs. Sending too many synchronization signals to too many base transceiver stations, however, can introduce further inefficiencies and burdens on the system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above needs are at least partially met through provision of the method and apparatus for base station management described in the following detailed description, particularly when studied in conjunction with the drawings, wherein:  
       FIG. 1  is a block diagram of a wireless communication system as configured in accordance with various embodiments of the invention;  
       FIG. 2  is a block diagram of a portion of the wireless communication system of  FIG. 1  as configured in accordance with various embodiments of the invention;  
       FIG. 3  is a flow diagram depicting a method as configured in accordance with various embodiments of the invention;  
       FIG. 4  is a flow diagram depicting a method as configured in accordance with various embodiments of the invention;  
       FIG. 5  is a block diagram of a wireless communication system as configured in accordance with various embodiments of the invention; and  
       FIG. 6  is a flow diagram depicting a method as configured in accordance with various embodiments of the invention. 
    
    
      Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the arts will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.  
     DETAILED DESCRIPTION  
      Generally speaking, pursuant to these various embodiments, an apparatus and method for determining a quality of channel factor for a base transceiver station of an active set of base transceiver stations is provided such that it may be determined whether the base transceiver station should be assigned to a prefill set of base transceiver stations at least in part according to a predetermined function of the quality of channel factor. The active set of base transceiver station(s) is typically a set of one or more base transceiver stations in communication with a mobile station. The prefill set of base transceiver station(s) is a set of one or more base transceiver stations from the active set that appear most likely to receive a handoff from a primary base transceiver station. The identity and number of base transceiver stations in the active and prefill sets typically changes over time depending on various conditions such as, for example, the quality of channel between the base transceiver stations and a mobile station or the rate at which a mobile station travels relative to the base transceiver station locations. The prefill set of base transceiver stations will typically receive synchronization signals because these base transceiver stations are typically more likely to accept a handoff of a given mobile station from the primary base transceiver station.  
      Advantageously, this method and apparatus for managing base stations allows for adaptation of the set of base transceiver stations which receive synchronization signals to optimize the performance of the wireless communication system. For example, fewer system resources need be used by tailoring the number of base transceiver stations which receive synchronization data to the needs of the mobile station.  
      Referring now to the drawings, and in particular to  FIG. 1 , a wireless communication system  100  is provided including a mobile station  110  in wireless communication with a primary base transceiver station  120 . The primary base transceiver station  120  is identical to or similar to the neighboring base transceiver stations  130  elsewhere in the wireless communication system  100 . The base transceiver stations are networked or otherwise in communication with a base station controller  140 . A wireless communication zone  150  is defined around the primary base transceiver station  120 . Similarly, wireless communication zones  151 ,  152 ,  153 ,  154 ,  155 , and  156  are defined around each base transceiver station  130 . A mobile station in a zone will likely have as its primary base transceiver station the base transceiver station for that zone, and the mobile station will likely transfer its communications via a known handoff procedure to a new base transceiver station when the mobile station moves to a new zone within the wireless communication system  100 .  
      A typical embodiment of the invention will be described with reference to  FIG. 2 . The mobile station  110  is in wireless communication with the primary base transceiver station  120 . The mobile station  110  includes a transceiver  210 , a monitor circuit  215 , and a processor circuit  217 . The monitor circuit  215  typically includes one or more of the following: a peak hour time monitor, a quality of service factor monitor, a quality of channel factor monitor, a mobility factor monitor, a transmission rate monitor, and/or other appropriate monitor.  
      The primary base transceiver station  120  may include several components such as a transceiver  220  that is responsive at least in part to a data send buffer  225  and a processor circuit  230 . The data send buffer  225  is also responsive to the processor circuit  230 , and the processor circuit  230  is responsive to a memory circuit  235  and a monitor circuit  240 . The monitor circuit  240  is capable of monitoring one or more factors relative to the wireless communication system  100 . The monitor circuit  240  may comprise one or more of the following: a peak hour time monitor, a primary base transceiver station, a quality of channel factor monitor, a neighboring base transceiver station a quality of channel factor monitor, a quality of service factor monitor, a sent data monitor, a buffer monitor, a transmission rate monitor, and/or other appropriate factor monitor. A synchronization signal generator circuit  245  is responsive to the processor circuit  230  and the monitor circuit  240 . Similarly, the neighboring base transceiver station  130  may include a monitor circuit (not shown).  
      A base station controller  140  is in communication with a plurality of base transceiver stations  120  and  130 . Typically, the base station controller  140  is in communication with each base transceiver station  130  that neighbors the primary base transceiver station  120 . The base station controller  140  also may include a monitor circuit  250 , a data controller circuit  255 , and a processor circuit  260 . The monitor circuit  250  may comprise one or more of the following: a peak hour time monitor, a traffic load for a sector monitor, a quality of service factor monitor, a quality of channel factor monitor, a mobility factor monitor, a sent data monitor, a transmission rate monitor, and/or other appropriate factor monitor. The synchronization signal generator circuit  245  may be responsive to the monitor circuit  250  and/or the processor circuit  260 .  
      One skilled in the art will recognize that the various individual circuits, monitors, and elements described herein, even when combined as described to form an embodiment of the invention, are readily designed by one skilled in the art and may operate in conjunction with various software elements to perform according to this description. For example, the various monitors are typically processor circuits operating in conjunction with certain software elements. Other enabling structure can be applied by those skilled in the art as desired as well.  
      It will be further understood that the various monitor circuits  215 ,  240 , and/or  250  will output a signal corresponding to the factor being monitored. This signal will be communicated to the synchronization signal generator circuit  245 , typically through the processor circuit  230 , such that the synchronization signal generator circuit  245  may send synchronization signals in part in response to a function of the factors monitored by the monitor circuits  215 ,  240 , and/or  250 . For example, for a factor monitored by a first monitor circuit  215 , a signal from this monitor circuit  215  will be sent wirelessly during the normal operation of the mobile station  110  to the primary base transceiver station  120  whereupon it will be received by the processor circuit  230 . Similarly, for a factor monitored by a second monitor circuit  250 , a signal from this second monitor circuit  250  will be transmitted during the normal operation of the base station controller  140  to the primary base transceiver station  120  whereupon it will be received by the processor circuit  230 . The processor circuit  230  in coordination with the synchronization signal generator circuit  245  will then apply the predetermined function to the factor based on the received signal, and the synchronization signal generator circuit  245  will generate synchronization signals according to the function. One skilled in the art will recognize that the processor circuit  230  and the synchronization signal generator circuit  245  may be separate structures or contained within the same circuitry or structure.  
      The operation of a typical embodiment for sending synchronization signals will be further described with reference to  FIG. 3 . The monitor circuit  215 ,  240 , and/or  250  monitors  310  at least one factor relating to a wireless communication system  100 . The synchronization signal generator circuit  245  sends  320  a synchronization signal to at least one base transceiver station  130  neighboring a primary base transceiver station  120  at least in part according to a predetermined function of the at least one factor. The synchronization signal may be any signal to the neighboring base transceiver stations  130  that facilitates synchronization with the primary base transceiver station  120  such that redundancy in data transmission is lessened during a handoff of a mobile station  110  from the primary base transceiver station  120  to a neighboring base transceiver station  130 .  
      For example, the step of sending  320  the synchronization signal may include sending a signal corresponding to an indication of data at a front end of the data send buffer circuit  225  corresponding to the primary base transceiver station  120 . In such an embodiment, the neighboring base transceiver stations  130  receive data to send to the mobile station  110  in case the mobile station  110  transitions to one of the neighboring base transceiver stations  130 . The processor circuit  230  reads the data send buffer circuit  225  to determine the data portions at the front end of the buffer that are then most likely to be sent. The synchronization signal generator circuit  245  in conjunction with the processor circuit  230  generates the synchronization signal which is sent to and notifies the neighboring base transceiver stations  130  as to which data portion is close to being sent by the primary base transceiver station  120 . In this manner, the neighboring base transceiver stations  130  may arrange the data stored at the neighboring base transceiver stations  130  to place the indicated data at the front end of the buffer.  
      In an alternative embodiment, the step of sending  320  the synchronization signal may include sending a signal corresponding to a mapping of data stored in a data send buffer circuit  225  corresponding to the primary base transceiver station  120 . In this embodiment, the processor circuit  230  reads the data send buffer circuit  225  to map the data in the buffer. The synchronization signal generator circuit  245  in conjunction with the processor circuit  230  generates the synchronization signal which provides a data map of the data in the data send buffer circuit  225  such that the neighboring base transceiver stations  130  may arrange their data to be identical or substantially the same as the data in the primary base transceiver station  120 .  
      In another embodiment, the step of sending  320  the synchronization signal may include the processor circuit&#39;s  230  determining at the primary base transceiver station  120  a transmission rate history for a mobile station  110 , the processor circuit&#39;s  230  predicting in accordance with the transmission rate history a data set that will be at a front end of a data send buffer circuit  225  corresponding to the primary base transceiver station  120  when a neighboring base transceiver station  130  receives the synchronization signal, and the synchronization signal generator circuit&#39;s  245  sending a signal corresponding to the data set. In this embodiment, the processor circuit  230 , in conjunction with a memory circuit  235 , tracks the transmission history for data sent to the mobile station  110 . By analyzing that transmission history stored in the memory circuit  235  using known algorithms, the processor circuit  230  can predict what data in the data send buffer circuit  225  will most likely be next to send to the mobile station  110  when a synchronization signal reaches a neighboring base transceiver station  130 . Therefore, the synchronization signal generator circuit  245  in conjunction with the processor circuit  230  will send a signal to one or more neighboring base transceiver stations  130  that indicates to the stations what data is most likely to be sent next to the mobile station  110 .  
      In yet another embodiment, the step of sending  320  the synchronization signal may include the processor circuit&#39;s  230  determining at the primary base transceiver station  120  a transmission rate history for a mobile station  110 , the processor circuit&#39;s  230  predicting in accordance with the transmission rate history a certain data set that will be at a front end of a data send buffer circuit  225  corresponding to the primary base transceiver station  120  when a neighboring base transceiver station  130  receives the synchronization signal, and the synchronization signal generator circuit&#39;s  245  sending a signal corresponding to the certain data set. Similar to the other embodiments, the neighboring base transceiver stations  130  receive data to send data to the mobile station  110  in case the mobile station  110  transitions to one of the neighboring base transceiver stations  130 . Then, in this embodiment, the processor circuit  230 , in conjunction with a memory circuit  235 , tracks the transmission history and/or call type for data sent to the mobile station  110 . By analyzing that call type (e.g. a streaming service) or transmission history stored in the memory circuit  235  using known algorithms, the processor circuit  230  can predict the certain data set in the data send buffer circuit  225  that will be next sent to the mobile station  110  when a synchronization signal reaches a neighboring base transceiver station  130  or force that certain data set to be the next to be sent to the mobile station  110 . Therefore, the synchronization signal generator circuit  245  in conjunction with the processor circuit  230  will send a signal to one or more neighboring base transceiver stations  130  that indicates to the stations the certain data set to be sent next to the mobile station  110  upon receipt of the synchronization signal or over the next time interval.  
      This embodiment can be applied to streaming services, for example, where the synchronization signal indicates to the neighboring base transceiver stations  130  that exactly one additional packet will be sent by the end of each 200 millisecond interval, starting at a given time. Additionally, the synchronization signal can indicate that each of those packets will not be sent earlier than 200 milliseconds before the time by which they are guaranteed to be delivered. In other words, in this example, the packet is guaranteed to be delivered sometime during a specific 200 millisecond interval. Thus, in this case, if a reselection or handoff occurs on one of these 200 millisecond boundaries, then the target base transceiver station can know exactly which data has been transmitted from the previous primary base transceiver station.  
      In yet another alternative embodiment, the step of sending  320  the synchronization signal may include the processor circuit&#39;s  230  determining at the primary base transceiver station  120  a transmission rate history for a mobile station  110  and the synchronization signal generator circuit&#39;s  245  sending a signal corresponding to the transmission rate history. Similar to the other embodiments, the neighboring base transceiver stations  130  receive data to send to the mobile station  110  in case the mobile station  110  transitions to one of the neighboring base transceiver stations  130 . Then, in this embodiment, the processor circuit  230 , in conjunction with a memory circuit  235 , tracks the transmission history for data sent to the mobile station  110 . The synchronization signal generator circuit  245  in conjunction with the processor circuit  230  will send a signal to the one or more neighboring base transceiver stations  130  that corresponds to the transmission history. By analyzing that transmission history using known algorithms, a processor circuit in the neighboring base transceiver stations  130  can determine according to the transmission rate history discardable data that need not be sent to the mobile station  110  because such data will be redundant. The neighboring base transceiver stations  130  then may discard  330  the discardable data. In this way, the neighboring base transceiver stations  130  may determine and set the data that will be the next sent to the mobile station  110  at a given time.  
      Similarly, under any of the above embodiments, the neighboring base transceiver stations  130  may discard  330  data in response to receiving the synchronization signal. In this way, the neighboring base transceiver stations  130  may discard  330  whatever data will not need to be sent to the mobile station  110  should the mobile station  110  transition into active communication with the neighboring base transceiver station  130 . Therefore, redundant data is eliminated, lessening the volume of data transmitted in the system.  
      In another alternative, the step of sending  330  the synchronization signal is performed in conjunction with sending data other than the synchronization signal to a base station controller  140  from the primary base transceiver station  120 . One skilled in the art will recognize that to send a synchronization signal from the primary base transceiver station  120  to one or more neighboring base transceiver stations  130 , the primary base transceiver station  120  will typically send the synchronization signal to the base station controller  140  that in turn will direct the synchronization signal to the appropriate neighboring base transceiver station(s)  130 . By piggy-backing the synchronization signal along with other data sent to the base station controller  140  during the normal operation of the primary base transceiver station  120 , this embodiment will conserve the resources involved in sending multiple messages to the base station controller  140  from the primary base transceiver station  120 .  
      Also, under any of the above embodiments, the step of sending  320  the synchronization signal may be performed in conjunction with sending updated data to the one or more neighboring base transceiver stations  130 . This alternative streamlines the process of sending the synchronization signals by associating such signals with the data sent to the neighboring base transceiver stations  130  for the purpose of speeding up the handoff procedure. In one such embodiment, the synchronization signal is sent to the base station controller  140  which stores the synchronization signal until the data controller circuit  255  determines that data should be sent to one or more neighboring base transceiver stations  130 . Thus, the synchronization signal may be sent with such data.  
      The sending of the synchronization signal may be controlled by a predetermined function of one or more factors of the wireless communication system. As noted above, any number of monitors  215 ,  240 , and/or  250  at the mobile station  110 , a base transceiver station  120  and/or  130 , and/or at a base station controller  140  may monitor  310  any number of the factors. Depending on the factors monitored, the predetermined function determines when or how often synchronization signals are sent to the one or more neighboring base transceiver stations  130  that receive the signals.  
      In one alternative, the peak hour time monitor monitors whether the wireless communication system  100  is operating at a peak hour time. The peak hour time is a time during which the system  100  typically experiences the highest call and/or data traffic volumes, and the peak hour time can be previously determined based on the system&#39;s history or can be determined by the base station controller  140  or other structure on a periodic basis. The peak hour time monitor can be located at the base station controller  140 , the primary base transceiver station  120 , the mobile station  110 , or other appropriate location. In operation, the peak hour time monitor typically monitors the peak hour time and is in communication with the processor circuit  230  and/or the synchronization signal generator circuit  245  such that the synchronization signal generator circuit  245  sends synchronization signals at a predetermined rate when the peak hour time monitor detects that the wireless communication system  100  is operating at the peak hour time. The predetermined rate will be at a rate less than the rate at which synchronization signals are sent when the wireless communication system  100  operates at a time outside of the peak hour time so that the synchronization signals do not place further strain on the system  100  when the system  100  experiences high traffic volumes.  
      In another embodiment, the traffic load monitor monitors the traffic load for at least a portion of the wireless communication system  100 . The traffic load monitor can be located at the base station controller  140 , the primary base transceiver station  120 , or other appropriate location. In operation, the traffic load monitor, as typically located at the base station controller  140 , monitors the traffic load for the group of base transceiver stations controlled by the base station controller  140 . Alternatively, the traffic load monitor when located at the primary base transceiver station  120  monitors the traffic load for the primary base transceiver station  120 . Based upon the monitored traffic load, the synchronization signal generator circuit  245  in communication with the traffic load monitor sends synchronization signals at a predetermined rate when detecting that the traffic load for a sector exceeds a predetermined level. The predetermined level is set according to the traffic capacity for the particular portion of the wireless communication system  100  monitored by the traffic load monitor. Therefore, the predetermined rate will be at a rate less than the rate at which synchronization signals are sent when the traffic load is below the predetermined level so that the synchronization signals do not further over burden the system  100  when experiencing high signal traffic volumes.  
      In yet another embodiment, a primary base transceiver station quality of channel factor monitor and a neighboring base transceiver station quality of channel factor monitor will monitor the signal strength or other appropriate factors relating to the quality of the communication channel between the primary base transceiver station  120  and the mobile station  110  and between a neighboring base transceiver station  130  and the mobile station  110 . The primary base transceiver station quality of channel factor monitor is typically located at the primary base transceiver station  120 , and the neighboring base transceiver station quality of channel factor monitor is typically located at a neighboring base transceiver station  130 . Alternatively, the quality of channel factor monitor may be located at the mobile station  110  for monitoring each communication channel.  
      The quality of channel factor monitors typically detect the signal strength using any known circuitry and associated algorithms to detect the signal strength between a given mobile station  110  and a base transceiver station. The processor circuit  230  using known or readily developable algorithms monitors the relationship between the primary base transceiver station&#39;s  120  monitored quality of channel factor relative to the mobile station  110  and the neighboring base transceiver station&#39;s  130  monitored quality of channel factor relative to the mobile station  110 . Based upon this relationship, the synchronization signal generator circuit  245  in communication with the processor circuit  230  sends synchronization signals at a predetermined rate when detecting that the quality of channel factor of the at least one base transceiver station  130  neighboring the primary base transceiver station  120  exceeds a predetermined level relative to the primary base transceiver station quality of channel factor. The predetermined level is typically based upon a signal strength ratio that indicates that the mobile station is likely to soon experience a handoff from the primary base transceiver station  120  to a neighboring base transceiver station  130 . Therefore, the predetermined rate will be at an increased level when the neighboring base transceiver station signal strength exceeds a predetermined level relative to the primary base transceiver station signal strength to increase the efficiency of the handoff when the handoff to the neighboring base transceiver station  130  occurs. Alternatively, the synchronization signal generator circuit  245  in communication with the processor circuit  230  sends synchronization signals at a predetermined rate when detecting that the quality of channel factor of the primary base transceiver station  120  exceeds a predetermined level because at higher quality levels, the mobile station  110  is unlikely to experience a handoff.  
      In a similar embodiment, a quality of service factor monitor monitors a quality of service factor for the mobile station  110 . Typically, the quality of service factor monitor detects one or more factors relative to the quality of service for the mobile station  110  relative to the primary base transceiver station  120  during data transmission such as bit error rate and so forth. Alternatively, the quality of service factor monitor may detect one or more quality of service factors for the mobile station  110  relative to one or more neighboring base transceiver stations  130 . The quality of service factor monitor may be located in the mobile station  110  for any case, in the primary base transceiver station  120  to monitor the quality of service between the primary base transceiver station  120  and the mobile station  110 , or in a neighboring base transceiver station  130  to monitor the quality of service between the neighboring base transceiver station  130  and the mobile station  110 .  
      In communication with the quality of service factor monitor and/or the processor circuit  230 , the synchronization signal generator circuit  245  sends synchronization signals at a predetermined rate when detecting that the quality of service factor exceeds a predetermined level. For example, the quality of service factor monitor measures the error rate between the mobile station  110  and the primary base transceiver station  120 . When the error rate drops below a predetermined level indicating that the quality of service between the mobile station  110  and the primary base transceiver station  120  is better than the predetermined level, the synchronization signal generator circuit  245  will send synchronization signals at a lesser rate than when the error rate exceeds the predetermined level. In other words, the synchronization signals will be sent less often when the quality of service between the primary base transceiver station and the mobile station is high because it is unlikely that the mobile station will need a handoff when the quality of service is high. Such an embodiment is particularly useful when the mobile station  110  is receiving streaming data because the quality of service strongly affects the quality of the mobile station  110  user&#39;s experience.  
      In still another embodiment, a mobility factor monitor monitors a mobility factor for a given mobile station  110 . Typically, the mobility factor monitor is located in a base station controller  140  or in the mobile station  110 . The mobility factor monitor measures, for example, the rate at which the mobile station  110  is moving thereby necessitating handoffs between base transceiver stations. In communication with the mobility factor monitor and/or the processor circuit  230 , the synchronization signal generator circuit  245  sends synchronization signals at a predetermined rate when detecting that the mobility factor exceeds a predetermined level. Typically, the predetermined rate is an increased rate when the mobility factor exceeds the predetermined level because a mobile station that has a high mobility will likely experience more handoffs. Therefore, sending more synchronization signals for that mobile station increases the efficiency when the handoffs do occur.  
      In another alternative embodiment, a sent data monitor monitors a data amount sent to a given mobile station  110  from the primary base transceiver station  120 . The sent data monitor is typically located at the primary base transceiver station  120  but may also be located at the base station controller  140 . In communication with the sent data monitor and/or the processor circuit  230 , the synchronization signal generator circuit  245  sends synchronization signals at a predetermined rate when detecting that the data amount sent to the mobile station  110  from the primary base transceiver station  120  exceeds a predetermined level. In this way, synchronization signals typically are sent more often when the mobile station  110  receives higher volumes of data. This arrangement increases efficiencies by ensuring that a lesser volume of old data is sent to the mobile station  110  upon a handoff.  
      In another alternative, a buffer monitor monitors a buffer data size stored in a buffer corresponding to the primary base transceiver station  120 . The buffer monitor is often at the primary base transceiver station  120  and in communication with a data send buffer  225 . In communication with the buffer monitor and/or the processor circuit  230 , the synchronization signal generator circuit  245  sends synchronization signals at a predetermined rate when detecting that the buffer data size stored in the data send buffer  225  exceeds a predetermined level. Typically then, synchronization signals are sent less often when the buffer data size exceeds certain levels because larger amounts of data are yet to be sent to the mobile station  110 . Conversely, synchronization signals may be sent more often when the buffer data size decreases because less data will be sent. In this way, the synchronization signals are sent more often when there is less data to manage during a handoff of the mobile station  110  thereby increasing efficiency. In other words, the synchronization signals are sent more often when the rate of data being sent to the mobile station  110  is higher. This is advantageous because if data is sent to the mobile station  110  more rapidly, a larger discrepancy can arise between the data sent from the primary base transceiver station  120  and the synchronization data at the neighboring base transceiver station(s)  130 .  
      In still another alternative, a transmission rate monitor monitors a transmission rate from the primary base transceiver station  120  to the mobile station  110 . The transmission rate monitor is typically at the primary base transceiver station  120  and in communication with a data send buffer  225 . In communication with the transmission rate monitor and/or the processor circuit  230 , the synchronization signal generator circuit  245  sends synchronization signals at a predetermined rate when detecting that the transmission rate exceeds a predetermined level. Typically then, synchronization signals are sent more often when the transmission rate exceeds certain levels because larger amounts of data are being sent to the mobile station  110 . Conversely, synchronization signals may be sent less often when the transmission rate decreases because less data is being sent. In this way, the synchronization signals are sent more often when there is more data passing to the mobile station  110  thereby increasing efficiency or the accuracy of the synchronization signal. In other words, the synchronization signals are sent more often when the rate of data being sent to the mobile station  110  is higher. This is advantageous because if data is sent to the mobile station  110  more rapidly, a larger discrepancy can arise between the data sent from the primary base transceiver station  120  and the synchronization data at the neighboring base transceiver station(s)  130 .  
      In yet another alternative, one or more predetermined mobile station handoff times are monitored such that the synchronization signal generator circuit  245  sends synchronization signals at a time that corresponds to the predetermined mobile station handoff time. In certain wireless communication systems  100 , the mobile station  110  will handoff at certain predetermined times or intervals. Therefore, in this embodiment, the synchronization signal generator circuit  245  will send a synchronization signal a certain number of seconds prior to the predetermined mobile station handoff time to maximize the efficiency of the handoff. In other words, the synchronization signal will be sent such that it arrives at approximately, and typically exactly, the same time as the predetermined handoff time.  
      In a variation on the above alternative, the primary base transceiver station  120  sends a signal indicating that certain packets will not be transmitted until a predetermined packet sending time when the predetermined function of the at least one factor comprises sending the synchronization signal at predetermined times. In this alternative, the neighboring base transceiver station(s)  130  will have a record of which packets the primary base transceiver station  120  sent to the mobile station  110  at which time. Therefore, the neighboring base transceiver station(s)  130  will be able to quickly provide unsent packets to the mobile station  110  upon a handoff.  
      In several of the above embodiments, it will be understood that the rate at which synchronization signals are sent may vary along with the monitored factors instead of changing only upon a certain factor&#39;s reaching a predetermined amount. For example, in the embodiment where a monitor circuit monitors the signal strength between the mobile station  110  and the primary base transceiver station  120 , the rate at which the synchronization signals are sent may vary in a reverse proportional manner with the signal strength between the mobile station  110  and primary base transceiver station  120 . Such a continuously varying relationship between the synchronization signal rate and monitored factor may be employed for any monitored factor. Similarly, the synchronization signal rate may vary according to a combination of factors as may be determined by one skilled in the art.  
      By so tailoring the sending of synchronization signals, the wireless communication system effectively reduces the amount of redundant data sent to the mobile station during a handoff. Further, the wireless communication system experiences lessened traffic burdens by limiting unnecessary synchronization signals. Thus, overall efficiency in the wireless communication system is improved.  
      Further efficiencies may be gained through management of the base transceiver stations. For instance, the wireless communication system can determine a quality of channel factor for a base transceiver station of an active set of base transceiver stations and then determine, according to a predetermined function of the quality of channel factor, whether the base transceiver station should be assigned to a prefill set. The system may determine the quality of channel factor for assigning base transceiver stations to the prefill set in a number of ways including, for example, monitoring the signal quality between a mobile station and one or more base transceiver stations or by executing an anticipative signal strength algorithm.  
      By determining a prefill set of the active set, the wireless communication system can limit the amount of resources used to send synchronization signals to the base transceiver stations that are most likely to benefit from the signals. Further, the prefill and active sets may be utilized by the wireless communication system  100  to maximize efficiencies in communication between mobile stations such as by determining a target base transceiver station for a receiving mobile station at least in part by which base transceiver stations are in an active or prefill set for a sending mobile station.  
      The operation of a typical embodiment for managing the base transceiver stations will be described with reference to  FIG. 4 . A quality of channel factor for a base transceiver station  130  of an active set is determined  410 . Then, a processor circuit  217 ,  230 , or  260  determines  420  whether the base transceiver station  130  should be assigned to a prefill set at least in part according to a predetermined function of the quality of channel factor. With momentary reference to  FIG. 5 , an active set of base transceiver stations will typically include those base transceiver stations  530  within communication range of the mobile station  110  such as those located in zones denoted by reference numerals  151 ,  152 ,  153 ,  154 ,  557 , and  558  surrounding the zone  150  in which the mobile station  110  operates. Other, typically more distance, base transceiver stations  560  such as those in more distant zones  555  and  556  with typically poor communication with the mobile station  110  will be omitted from the active set. The base transceiver stations  530  and  560  are identical to or similar to the neighboring base transceiver stations  130  elsewhere in the wireless communication system  100 . The prefill set, then, is typically a subset, designated for illustration purposes with the letter P in  FIG. 5 , of the active set of base transceiver stations  530  with improved communication with the mobile station  110  as compared with other base transceiver stations  530  of the active set. One skilled in the art will appreciate that the methods described herein are typically applied to each base transceiver station  530  of the active set to determine the prefill set. For simplicity, the embodiments of the invention will be described herein with reference to a single base transceiver station  530  of the active set.  
      Referring again to  FIGS. 4 and 5 , typically, determining  410  the quality of channel factor will include monitoring  412  the quality of channel factor between the mobile station  110  and the base transceiver station  530 . Using this single monitored factor, the determination  420  of whether the base transceiver station  530  should be assigned to the prefill set may be made using a predetermined algorithm such as comparing the quality of channel factor against an absolute signal strength or other appropriate factor relating to the communication quality. The quality of channel factor may be monitored  412  by monitor circuit  215  or by a corresponding monitor in base transceiver station  530 .  
      Alternatively, a monitor circuit  215  or  235  will monitor  414  a first quality of channel factor between the mobile station  110  and the primary base transceiver station  120 . In this embodiment, the predetermined function of the quality of channel factor will include, at least in part, a function of the first quality of channel factor.  
      In one such embodiment, the predetermined function includes assigning  425  the base transceiver station  530  to the prefill set when the quality of channel factor for the base transceiver station  530  reaches a predetermined threshold, for example, relative to the first quality of channel factor. Generally, the predetermined threshold will define a quality of communication between the mobile station  110  and base transceiver station  530  such that the base transceiver station  530  is likely to be a target for the mobile station  110  upon the mobile station&#39;s next handoff. Typically, the predetermined threshold is when the quality of channel factor reaches about 80% of the first quality of channel factor when the quality of channel factor is a signal strength measurement. Alternatively, the predetermined threshold is when the quality is at least about three decibels below the first quality of channel factor when the quality of channel factor is a signal strength measurement.  
      Another alternative method of determining  410  the quality of channel factor includes executing an anticipative signal strength algorithm  416  to predict a signal strength between the mobile station  110  and the base transceiver station  530  such that the quality of channel factor is, at least in part, a function of the anticipative signal strength algorithm. The anticipative signal strength algorithm will typically be a known or readily developed algorithm based upon known or typical patterns of signal strength for the mobile station  110 . For example, by analyzing a signal strength history stored in the mobile station  110  using known algorithms, the processor circuit  217  or  230  can predict the signal strength for the mobile station  110  given certain known conditions. In this manner, the quality of channel factor can be the output of the anticipative signal strength algorithm or include the output as part of other monitored conditions. One skilled in the art will recognize a variety of ways to determine the quality of channel factor using an anticipative signal strength algorithm in combination with certain monitored factors.  
      In an additional variation on the alternative ways to determine the quality of channel factor, an offset may be added  418  to the quality of channel factor wherein the offset is specific to each base transceiver station  530 . In one such embodiment, the offset is determined at least in part according to a function of a relative load for a base transceiver station  530  of the active set. For example, the wireless communication system  100  may monitor the load for each base transceiver station  530  of the active set. As a way to help distribute the overall traffic load for the system, offsets may be assigned to each base transceiver station  530  such that the quality of channel factor disfavors assigning base transceiver stations  530  to the prefill set when the traffic load for the base transceiver station  530  exceeds a given amount. In this way, already loaded base transceiver stations  530  do not also receive synchronization signals because the base transceiver station  530  is not assigned to the prefill set.  
      Various alternatives are available for determining  420  whether the base transceiver station  530  should be assigned to the prefill set. For instance, this step may include executing the predetermined function at the mobile station  110  when the mobile station  110  monitors the first quality of channel factor with the primary base transceiver station  120  and the quality of channel factor with each base transceiver station  530  of the active set. In such an embodiment, the mobile station  110  sends a signal, typically through the primary base transceiver station  120 , to the base station controller  140  that indicates an outcome of the predetermined function. In this embodiment, the base station controller  140  will control the assignment of base transceiver stations to the active set and prefill set for the mobile station  110  using the outcome, and various signals and other traffic in the wireless communication will be directed by the base station controller  140  accordingly.  
      Alternatively, the mobile station  110  and/or the various base transceiver stations may send the first quality of channel factor and quality of channel factor for the base transceiver stations of the active set to the base station controller  140 . The base station controller  140 , then, executes the predetermined function. In one such embodiment, the signal sent to the base station controller  140  includes at least a pilot strength measurement for each of the first quality of channel factor and quality of channel factor for the base transceiver station(s)  530  of the active set. Then, the base station controller  140  will control the assignment of base transceiver stations to the active set and prefill set for the mobile station  110  using the outcome of the predetermined function.  
      The wireless communication system  100  may use the prefill set in any number of ways. In one typical embodiment, the primary base transceiver station  120  will be notified  430  of the prefill set. Then, the base transceiver stations of the prefill set are prefilled  435 , and the primary base transceiver station  120  sends  440  synchronization signals to each base transceiver station of the prefill set. Typically, the base transceiver stations of the prefill set will receive the same data to be sent to the mobile station  110  as that received by the primary base transceiver station  120 . Thus, the sending of synchronization signals as described herein may be applied to the base transceiver stations of the prefill set thereby achieving further efficiencies by sending the synchronization signals only to those base transceiver stations identified in the prefill set.  
      In one further alternative embodiment, a target base transceiver station is determined  450  for the mobile station  110  at least in part according to the outcome of the predetermined function of the quality of channel factor. In this embodiment, a signal is sent to the mobile station  110  or other structure that determines the target base transceiver station during a handoff procedure indicating either an output of the predetermined function or an identity of the base transceiver stations  530  of the active set or prefill set. Typically, the mobile station  110  will be handed off to the base transceiver station with the best output of the predetermined function such that the target base transceiver station has the best quality of channel for the mobile station  110  or has the best combination of quality of channel and allocation of resources for the wireless communication system  100 . Thus, the predetermined function of the quality of channel may further improve the quality of experience for the user and/or improve the efficiencies of the system during handoff operations.  
      A further embodiment of the invention will be described in reference to  FIGS. 5 and 6 . The wireless communication system  100  determines  610  the active set of base transceiver stations  530  for a sending mobile station  110  as known in the art or using the various methods described herein regarding the determination of a prefill set. Then, a target base transceiver station for a receiving mobile station  510  is selected  620  from the active set of the sending mobile station  110 . Typically, the step of selecting the target base transceiver station will include selecting the target base transceiver station with a maximum transmission capability from the sending mobile station  110  and an acceptable communication link with the receiving mobile station  510 , usually a base transceiver station of the prefill set of the receiving mobile station  510 . The maximum transmission capability is easily monitored; thus, the receiving mobile station  510  may experience the maximum quality of channel from the sending mobile station  110  such that the data stream from the sending mobile station  110  is not impeded during sending from the sending mobile station  110 . In such a situation, the data may be relayed by the target base transceiver station without downloading the data back from the base station controller  140  and without sending the data to the base station controller  140 . In this way, the wireless communication system  100  reduces system traffic by eliminating the need to send data down the communication chain when the data is already accessible within a given zone. In other words, this embodiment typically reduces any latency in the communication.  
      Thus, utilization of the various methods described herein in connection with the active and prefill sets of base transceiver stations can increase the efficiencies of a wireless communication system. Further, these methods will typically improve the quality of channel experienced by users of the system.  
      Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.