Abstract:
A method and apparatus for efficient paging of user equipment (UE) in an LTE network is disclosed. In addition to storing the Last Seen eNodeB (LSeNB) for each UE attached to a mobility management entity (MME), the MME also maintains an LSeNB List of the eNodeBs seen immediately before the LSeNB for each UE. When a notification for a UE arrives at the MME, then MME can select from several paging methods, including paging only the LSeNB to locate the UE and sending a paging request LSeNB as well as to the list of eNodeBs seem immediately before the LSeNB. The MME can send a paging request to more than a single eNodeB but less than a full Tracking Area. Efficient paging is especially needed for voice over internet protocol (VoIP) calls where a call will go to voice mail if a page isn&#39;t answered quickly.

Description:
This invention relates generally to tracking user equipment in a long term evolution network and more particularly to efficient paging of user equipment. 
     BACKGROUND 
     A service area of a wireless telecommunications network is typically broken up into contiguous geographic regions called cells. In 4G networks, commonly known a long term evolution (LTE) networks, each cell is associated with an eNodeB (eNB), or base station and each cell is assigned to a tracking area. A cell is associated with a specific geographic service area and multiple cells can be associated with a specific tracking area. Also, an eNodeB may be associated with more than one cell. Consequently, a tracking area covers a geographic service area made up of the set of cells that are assigned to that tracking area. A mobility management entity (MME), similarly to an MSC in a 3G network, is responsible for managing the communications of UEs through a plurality of eNBs in one or more tracking areas. 
     As each UE moves through a geographic area, it transmits a tracking are update (TAU) request when it detects that it has entered a tracking area where it is not registered. The MME associated with the tracking area receives the TAU requests and maintains a record with information associated with the UE. When the MME receives a request to connect with a registered UE, the MME sends out a paging request to alert the UE that a connection is desired. 
     LTE providers have found that they need to increase the size of tracking areas in order to reduce the frequency of TAU procedures. In other words, if UEs change their tracking area less often, fewer TAU procedures will be using communication bandwidth. Unfortunately, while this increase in the size of tracking areas reduces the number of TAU procedures performed, it significantly increases the amount of paging traffic that must be handled by each eNodeB for connecting with individual UEs. Typically, the last seen eNodeB is part of the information the MME maintains for each UE and when a request to connect is received, the MME initially sends a paging request to this eNodeB. If the paging request fails, however, the MME then sends a paging request to all the eNodeBs within the same tracking area as the last seen eNodeB. If this paging request fails, a paging request can be sent out to all the eNBs in the same tracking area as well as one or more neighboring tracking areas. As the size of tracking areas increases, they encompass more eNodeBs and each eNodeB receives more paging requests. 
     Thus, a need exists for to support paging of more than a single eNodeB but less than a full Tracking Area. There is also a need to select a subset of eNodeBs to be paged where the UE is most likely to be present. The need for efficient paging is especially acute with regard to voice over internet protocol (VoIP) calls where a call will go to voice mail if a paging request isn&#39;t answered in a given amount of time. 
     SUMMARY 
     This section will be corrected when claims are finalized. The invention in one implementation encompasses a method and apparatus for improving paging in an LTE network. An MME maintains a small list of several last seen eNodeBs for each UE in the order in which they were visited, newest to oldest. 
     In one embodiment, there is provided a method, executed in a wireless network having base stations and wireless mobility managers controlling the base stations, which includes the steps of maintaining a Last Seen list of one or more base stations in the order in which they were visited by a user equipment (UE) for each UE attached to the wireless mobility managers, receiving a message requesting access to a requested UE, sending a first paging request to the base stations on the Last Seen list for the requested UE and if that paging request fails, sending a second paging request to a larger group of base stations. 
     In another embodiment, there is provided method of paging a user equipment (UE) using at least one mobility management entity (MME) operatively coupled to a plurality of eNodeBs (eNBs) in a LTE (Long Term Evolution) network, which includes the steps of maintaining a last seen eNB list of one or more eNBs in the order in which they were last seen by a user equipment for each UE attached to the MME, receiving a notification requesting access to a requested UE, sending a first paging request to the one or more eNBs on the last seen eNB list and if the first paging request fails, sending a second paging request to a larger group of eNBs. 
     Some embodiments of the above methods further include wherein the length of the list may be flexibly provisioned with the maximum number of eNBs to be paged. 
     Some embodiments of the above methods further include wherein the list of one or more eNBs is maintained so that it does not contain any duplicate entries. 
     Some embodiments of the above methods further include wherein the list is cleared when a UE reattaches to the wireless mobility managers. 
     Some embodiments of the above methods further include wherein a plurality of eNBs are grouped into tracking areas and a UE is capable of moving between eNBs within one tracking area, or between eNBs in different tracking areas. 
     Some embodiments of the above methods further include wherein the first and second paging requests are related to paging methods in a paging policy table, the method further including the steps of maintaining a paging policy table for the MME that determines which one or more paging methods are used in response to different types of notifications and accessing the paging policy table when a notification is received to determine how one or more paging methods to follow, said paging methods including any of accessing the last seen eNB, accessing a list of the last seen eNBs, accessing the last seen tracking area and accessing the last seen tracking area and neighboring tracking areas. 
     Some embodiments of the above methods further include the steps of maintaining a database of UE mobility patterns, said database storing the number of times one eNB is visited immediately after another eNB for pairs of eNBs within a set, generating a mobility patterns list, in response to the notification request, of likely eNBs the requested UE would visit by accessing the database with the requested UE&#39;s most recently visited eNB, and combining the last seen eNB list and the mobility pattern list into a final list for use in selecting eNBs to receive the first paging request for the requested UE. 
     Some embodiments of the above methods further include the step of accessing the database of UE mobility patterns with information indicating the last known direction of movement of the requested UE. 
     Some embodiments of the above methods further include wherein the database of UE mobility patterns is organized according to time of day and the step of generating a supplemental list further includes the step of accessing the database of UE mobility patterns to retrieve mobility data for the same time of day as the current time. 
     Some embodiments of the above methods further include wherein the paging method used for the first paging request can vary based on the type of notification. 
     In another embodiment, there is provided as apparatus for use in an LTE network for paging a user equipment (UE) using at least one mobility management entity (MME), said apparatus configured to perform the steps of maintaining a last seen eNB list of one or more eNBs in the order in which they were last seen by a user equipment for each UE attached to the MME, receiving a notification requesting access to a requested UE, sending a first paging request to the one or more eNBs on the last seen eNB list and if that paging request fails, sending a second paging request to a larger group of eNBs. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Features of example implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which: 
         FIG. 1  is a representation of one implementation of an apparatus that comprises that performs an efficient paging process. 
         FIG. 2  is a representation of on message flow for the paging procedure of the apparatus of  FIG. 1 . 
         FIG. 3  is a representation of the mobility pattern data derived using the apparatus of  FIG. 1 . 
         FIG. 4  is a representation of partial view of the geographic service area supported by the apparatus of  FIG. 1 . 
         FIG. 5  is a flow chart depicting the operation of the apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A high level view of LTE network  100  is depicted in  FIG. 1 . Network  100  is not a full LTE network but only depicts a few elements that may be used during paging of a wireless device that allows service on LTE network. Such a wireless device is known as a UE (user equipment) in LTE terminology.” At a basic level, an LTE network includes a plurality of eNodeBs (eNBs)  110  or base stations, which are responsible for handling communications with UEs in a certain geographic region. A representative UE is shown at  120 . The eNodeBs is associated with one or more cells, and each cell is assigned to a tracking area. A cell is associated with a specific geographic service area and multiple cells can be associated with a specific tracking area. Consequently, a tracking area covers a geographic service area made up of the set of cells that are assigned to that tracking area. In  FIG. 1 , several eNodeBs  110  are shown grouped into tracking areas  115  and  125 . Since cells associated with different tracking areas may be assigned to a single eNodeB, it is also possible that an eNodeB  110  may appear in two different tracking areas. Also, the number of eNodeBs in each tracking area is just an example. Typically, tracking areas may include a flexible number of eNodeBs. Each eNodeB  110  may be communicatively coupled via a backhaul connection with a mobile management entity (MME)  130  and a serving gateway (SGW)  140 . The MME  130  and SGW  140  may be nodes in the network  100  or they may be physical computer components, such as a circuit board, that reside on a computer node in the network  100 . The functions of the MME  130  and serving gateway  135  as described herein may be implemented in hardware, firmware or software in combination with associated hardware. The MME  130  may perform UE paging operations and it may also perform interoperability functionality with 3GPP networks  140 . The SGW  135  may act as a mobility anchor during inter eNodeB handovers, provide interoperability communication with non-3GPP networks  150  and forward user data packets to various IP networks  145 . 
     As the UE  120  moves through the network  100 , the UE  120  may perform tracking area update procedures. That is, when the UE  120  detects that it is in a new tracking area, the UE  120  may send a tracking area update (TAU) request to the MME  130  to inform the MME  130  of the UE&#39;s  120  new location. If UE  120  is within tracking area  125  and transmits a tracking area update request, one of the eNodeBs  110  may receive the message, and forward the message to the MME  130  and the MME  130  may save the location of the UE  120  as within tracking area  120 . The MME also saves an ID of the eNodeB which forwarded the message. This is referred to as the “Last Seen eNodeB.” Whenever the UE  120  is attached to an LTE network—that is, the UE  120  has successfully registered with the MME  130 —the UE  120  transmits a TAU request when the UE  120  detects that it has entered a tracking area where it is not currently registered. Upon receipt of a TAU request, the MME  130  notes the tracking area and eNodeB where the UE  120  has registered. MME  130  also stores the eNodeB ID that is reported during other procedures such as Service Request and Handover. 
       FIG. 2  depicts the general message flow for a paging procedure. A DDN for a particular UE  120  is sent from a Packet Gateway (P-GW)  210  to a Signaling Gateway (S-GW)  220  when there is data available for UE  120 . This could comprise an incoming voice call, incoming text message, notification for a social networking app, etc. S-GW  130  forwards the DDN to MME  130 . Then MME  130  sends a paging request to the Last Seen eNodeB which is registered to UE  120 . If UE  120  is still in the cell served by eNodeB  110 , it receives the paging request and returns a service request to MME  130 . In response to the service request, MME  130  returns a DDN Acknowledge signal to S-GW  220  and transfer of the data proceeds. 
     If UE  120  has moved and is no longer served by the Last Seen eNodeB known to MME  130 , the UE will fail to respond to the initial page attempt and MME  130  will need to continue the paging process with additional page attempts. Typically, MME  130  will perform a series of page attempts as necessary, gradually expanding the size of the area in which the UE is paged. The set of eNodeBs where the UE is paged is a function of the paging method that has been specified for each page attempt within a Paging Policy table. As an example, when a paging request to the Last Seen eNodeB fails to reach UE  120 , the next policy in the Paging Policy table could require MME  130  to send the paging request to all eNodeBs  110  in the Last Seen Tracking Area. As another example, if this second paging attempt fails, MME  130  could move to a third paging process that sends the paging request to all eNodeBs in the Last Seen Tracking Area as well its neighboring tracking areas. This would result in a very large amount of paging traffic in the LTE network. 
     In a preferred embodiment, a new paging method called the Last Seen eNB List method is provided. For this method, the MME  130  maintains a small list of Last Seen eNodeBs which are paged instead of just the single Last Seen eNB. Allowing MME  130  to page more than one eNodeB  110  but less than all the eNodeBs in an entire tracking area allows MME  130  to reach UE  120  with relatively high effectiveness without generating an excessive amount of paging message traffic. As explained above, an MME can flexibly use a variety of paging methods to respond to a notification for accessing a UE. The specific sequence of paging methods is stored in the Paging Policy Table. It is also possible to adjust the Paging Policy Table based on the type of notification received. For some types, a single Last Seen eNB may be paged, followed by the Last Seen Tracking Area, then the Last Seen Tracking Area and its neighbors. It is also possible that MME  130  will use the Last Seen eNodeB List paging method in place of the Last Seen eNodeB paging method in cases where MME  130  needs to be more aggressive in its paging efforts (e.g., paging for incoming VoIP calls). The Paging Policy Table may be flexibly configured in a variety of ways, including the number of eNBs to maintain on the Last Seen eNB List. 
     For the Last Seen eNodeB List paging method, MME  130  constructs a list of eNodeBs  110  based on the UE  120  mobility history in terms of the eNodeBs that have served the UE. Paging this subset of eNodeBs is effective because UEs will frequently return to previously visited eNodeBs due to a variety of factors such as RF toggling and the high relative occurrence of “round trips” in movement patterns within a cellular network (i.e., cyclical movement). 
     The MME  130  shall track the mobility history of each UE by saving the following information:
         a. The last seen eNodeB (i.e., the current eNodeB that was serving the UE during the last mobility-related procedure)   b. The old last seen eNodeB (i.e., the eNodeB where the UE was observed prior to the last one)   c. The older last seen eNodeB (i.e., the eNodeB where the UE was observed prior to the old last seen eNodeB)       

     Please note that MME  130  will manage this information to ensure that these values are unique. Duplicate values are not saved. Any old mobility history is cleared when the UE re-attaches to the LTE network or when UE  120  returns from another MME. 
     The Last Seen eNodeB List is generated using the collected mobility history. The length of Last Seen eNodeB List should be configurable. For example, if the maximum length of Last Seen eNodeB List is 1, then only the ‘last seen eNodeB’ will be included. If the maximum length of Last Seen eNodeB List is 3, then it may include the ‘last seen eNodeB’, the ‘old last seen eNodeB’, and the ‘older last seen eNodeB’. For larger maximum lengths, the list would be extended similarly. 
     In a further embodiment, MME  130  creates a Mobility Pattern List of eNodeBs that have a higher likelihood of successfully completing a paging request. This Mobility Pattern List can be combined with the Last Seen eNodeB List to create a list of a somewhat larger group of eNodeBs that is still smaller than the total number of eNodeBs in a tracking area. The Mobility Pattern List contains the set of eNodeBs that are the most likely next eNodeB to be visited based on the movement patterns for all UEs served by the MME  130 . While the Last Seen eNodeB List accounts for the high relative occurrence of “round trips” in movement patterns within a cellular network (i.e., cyclical movement), the Mobility Pattern List accounts for forward movement of a UE through a service area, i.e., linear movement such as moving along a highway or commuter rail line. 
     To generate the Mobility Pattern List, MME  130  analyzes the mobility patterns for UEs served by an eNodeB by tracking the number of times eNodeB ‘Y’ was visited when the ‘last seen eNodeB was eNodeB ‘X’. This information can be collected for an entire day or for specific periods of the day. This compiled data of mobility patterns can then be used to construct the top ranked ‘next likely’ eNodeB for predicting where the UE may have moved. An example of the data structure which could store the information regarding mobility patterns for a set of 8 eNodeBs is shown in  FIG. 3 . This figure is a representation of the mobility pattern data derived using the apparatus of  FIG. 1  and illustrates the relatively frequency of movement of UEs between specific eNodeBs. The full data set of mobility pattern data would cover all eNodeBs associated with the MME  130  and would include data from all UEs served by the MME  130 . 
     The Mobility Pattern List is generated using the top ranked ‘next likely’ eNodeBs for a UE based on its ‘last seen eNodeB’ value and mobility pattern data from the data structure of  FIG. 3 . The length of the Mobility Pattern List should be configurable. For example, if the maximum length of the Mobility Pattern List is 1, then only the top ranked ‘next eNodeB’ will be included in the Mobility Pattern List. If the Mobility Pattern List length is 7, then the top 7 ‘next likely’ eNodeBs will be included. Inter-eNB mobility data would be collected for all eNBs served by the MME and could be generated using Per-Call Measurement Data (PCMD) collected by MME  130 . 
     An example of the generation of the Last Seen eNodeB List and the Supplemental List will now be described in conjunction with the data structure of  FIG. 3 . 
     Assume the following parameter values for Predictive eNB Paging (are in use:
         Max Last Seen eNodeB List Length=2   Max Supplemental List Length=4       

     Assume the UE&#39;s mobility history is as follows:
         Last Seen eNB=1   Old Last Seen eNB=4   Older Last Seen eNB=6       

     Given this scenario, the sublists and final eNB paging lists would be as follows:
         eNB Last Seen eNodeB List=1, 4   eNB Supplemental List=2, 4, 5, 7       

     A combination of the Last Seen eNodeB List and the Mobility Pattern List causes MME  130  to page eNBs 1, 2, 4, 5 and 7. Duplicates between the two lists will be eliminated. It should be noted that the Last Seen eNodeB List and the Mobility Pattern List can be used together or each can be used alone to accomplish an embodiment. 
       FIG. 4  depicts an arrangement of eNodeBs that further illustrates the example given above. Assume for example that a major road runs through the service areas of eNBs 7, 3, 1, 4 and 6. If the Last Seen eNodeB for a UE is eNB 1 in service area  410 , then the most likely eNBs for the UE to travel to next would be eNB4 in service area  420 , eNB2 in service area  430 , eNB7 in service area  440  and eNB5 in service area  450 . This configuration is shown in the mobility patterns in row 1 of the data structure of  FIG. 3 . The inclusion of eNB5 in service area  450  could be due to the presence of an exit on the major road. 
     In another embodiment, the mobility patterns used to generate the Mobility Pattern List may take into consideration the last known direction of movement in addition to the last known position when processing data for the generation of the Mobility Pattern List. In other words, the top ‘next likely’ eNodeBs would be retrieved for the case where the last known position (i.e., last seen eNodeB) is ‘Y’ and the previous location before that (i.e., old last seen eNodeB) was ‘X’. 
     As a further embodiment, the Mobility Pattern List may be generated while taking into consideration the current time, thus utilizing only mobility history data when generating the Supplemental List that is from the current time of day (e.g., morning rush hour, evening rush hour, late night, etc). 
     An illustrative description of operation of the apparatus  100  is presented, for explanatory purposes in connection with  FIG. 5 . As shown in step  510 , an MME maintains a Last Seen eNB List of one or more of the last seen eNBs for each UE attached to the MME. When the MME received a notification requesting access to a UE in step  520 , it sends a paging request to the Last Seen eNB in step  530 . If that paging request does not succeed in step  540 , a second paging request is sent to a larger group of eNBs, either all the eNBs in the Last Seen Tracking Area or all the eNBs in the Last Seen Tracking Area as well as adjacent tracking areas in step  550 . Once a paging request succeeds or the possible paging methods are exhausted, the paging process is completed in step  560 . 
     The apparatus  100  in one example comprises a plurality of components such as one or more of electronic components, hardware components, and computer software components. A number of such components can be combined or divided in the apparatus  100 . An example component of the apparatus  100  employs and/or comprises a set and/or series of computer instructions written in or implemented with any of a number of programming languages, as will be appreciated by those skilled in the art. 
     The steps or operations described herein are just for example. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. 
     Although example implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.