Abstract:
A wireless communication network comprising a plurality of paging controllers capable of communication with a plurality of base stations within a coverage area of the network is provided. At least one of the plurality of paging controllers is configured to assign one or more paging identifications (PG IDs) to a subscriber station within a paging area when the subscriber station requests to enter idle mode, wherein each of the one or more PG IDs is associated with a paging offset, and transmit the one or more PG IDs to a base station in communication with the subscriber station. The subscriber station only monitors the PG ID having a shortest paging offset among the one or more PG IDs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION (S) AND CLAIM OF PRIORITY 
       [0001]    The present application is related to U.S. Provisional Patent No. 61/212,025, filed Apr. 6, 2009, entitled “METHOD FOR SUPPORTING MULTIPLE PAGING AREAS FOR ENHANCED POWER SAVING AND REDUCED PAGING OVERHEAD”. Provisional Patent No. 61/212,025 is assigned to the assignee of the present application and is hereby incorporated by reference into the present application as if fully set forth herein. The present application hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent No. 61/212,025. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present application relates generally to wireless communications and, more specifically, to a method and system for supporting multiple paging areas. 
       BACKGROUND OF THE INVENTION 
       [0003]    The operation of idle mode is described in IEEE 802.16e. Either a mobile station (MS) or a base station (BS) could initiate the idle mode operation using DREG-REQ and DREG-CMD messages, respectively. After an MS has entered the idle mode, the MS uses fixed parameters for the paging cycle, paging offset, paging listening interval and paging unavailable interval. If an MS is paged, the MS re-enters the radio access network using code based ranging and RNG-REQ/RSP messages. 
       SUMMARY OF TEE INVENTION 
       [0004]    A wireless communication network comprising a plurality of paging controllers capable of communication with a plurality of base stations within a coverage area of the network is provided. At least one of the plurality of paging controllers is configured to assign one or more paging identifications (PG IDs) to a subscriber station within a paging area when the subscriber station requests to enter idle mode, wherein each of the one or more PG IDs is associated with a paging offset, and transmit the one or more PG IDs to a base station in communication with the subscriber station. The subscriber station only monitors the PG ID having a shortest paging offset among the one or more PG IDs. 
         [0005]    A paging controller is provided. The paging controller is configured to assign one or more paging identifications (PG IDs) to a subscriber station within a paging area when the subscriber station requests to enter idle mode. Each of the one or more PG IDs is associated with a paging offset. The paging controller is also configured to transmit the one or more PG IDs to a base station in communication with the subscriber station. The subscriber station only monitors the PG ID having a shortest paging offset among the one or more PG IDs. 
         [0006]    A subscriber station is provided. The subscriber station is configured to receive one or more paging identifications (PG IDs) when the subscriber station requests to enter idle mode. Each of the one or more PG IDs is associated with a paging offset. The subscriber station is also configured to monitor only the PG ID having a shortest paging offset among the one or more PG IDs. 
         [0007]    A subscriber station is provided. The subscriber station is configured to start a timer when the subscriber station leaves a first primary paging group assigned to the subscriber station, perform a location update when the timer expires before the subscriber station enters a second primary paging group assigned to the subscriber station, and stop the timer when the subscriber station enters the second primary paging group before the timer expires. The first primary paging group is different from the second primary paging group. 
         [0008]    A method of paging a subscriber station is provided. The method comprises paging the subscriber station only in a particular primary paging group, while refraining from paging the subscriber station in other primary paging groups, when the subscriber station is in a primary paging group. The method also comprises paging the subscriber station in a first secondary paging group with a first shortest paging offset, while refraining from paging the subscriber station in primary paging groups, when the subscriber station is in a secondary paging group. 
         [0009]    A wireless communication network comprising a plurality of paging controllers capable of communication with a plurality of base stations within a coverage area of the network is provided. At least one of the plurality of paging controllers is configured to page a subscriber station only in a particular primary paging group and refrain from paging the subscriber station in other primary paging groups when the subscriber station is in a primary paging group. The at least one of the plurality of paging controllers is further configured to page the subscriber station in a first secondary paging group with a first shortest paging offset and refrain from paging the subscriber station in primary paging groups when the subscriber station is in a secondary paging group. 
         [0010]    A paging controller is provided. The paging controller is configured to page a subscriber station only in a particular primary paging group and refrain from paging the subscriber station in other primary paging groups when the subscriber station is in a primary paging group. The paging controller is further configured to page the subscriber station in a first secondary paging group with a first shortest paging offset and refrain from paging the subscriber station in primary paging groups when the subscriber station is in a secondary paging group. 
         [0011]    Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0013]      FIG. 1  illustrates an exemplary wireless network, which transmits messages according to the principles of the present disclosure; 
           [0014]      FIG. 2A  is a high-level diagram of an OFDMA transmitter according to one embodiment of the present disclosure; 
           [0015]      FIG. 2B  is a high-level diagram of an OFDMA receiver according to one embodiment of the present disclosure; 
           [0016]      FIG. 3  illustrates a system for supporting multiple paging areas according to an embodiment of this disclosure; 
           [0017]      FIG. 4  illustrates a table providing information regarding paging group ID assignments according to an embodiment of this disclosure; 
           [0018]      FIG. 5  illustrates a table providing information regarding paging group ID assignments along with paging offset indicators according to an embodiment of this disclosure; 
           [0019]      FIG. 6  illustrates a method of operating an idle mode according to an embodiment of this disclosure; and 
           [0020]      FIG. 7  illustrates a method of paging a mobile station according to an embodiment of this disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIGS. 1 through 7 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communication system. 
         [0022]      FIG. 1  illustrates an exemplary wireless network  100 , which transmits messages according to the principles of the present disclosure. In the illustrated embodiment, wireless network  100  includes base station (BS)  101 , base station (BS)  102 , base station (BS)  103 , and other similar base stations (not shown). Base station  101  is in communication with base station  102  and base station  103 . Base station  101  is also in communication with Internet  130  or a similar IP-based network (not shown). 
         [0023]    Base station  102  provides wireless broadband access (via base station  101 ) to Internet  130  to a first plurality of subscriber stations within coverage area  120  of base station  102 . The first plurality of subscriber stations includes subscriber station  111 , which may be located in a small business (SB), subscriber station  112 , which may be located in an enterprise (E), subscriber station  113 , which may be located in a WiFi hotspot (HS), subscriber station  114 , which may be located in a first residence (R), subscriber station  115 , which may be located in a second residence (R), and subscriber station  116 , which may be a mobile device (M), such as a cell phone, a wireless laptop, a wireless PDA, or the like. 
         [0024]    Base station  103  provides wireless broadband access (via base station  101 ) to Internet  130  to a second plurality of subscriber stations within coverage area  125  of base station  103 . The second plurality of subscriber stations includes subscriber station  115  and subscriber station  116 . In an exemplary embodiment, base stations  101 - 103  may communicate with each other and with subscriber stations  111 - 116  using OFDM or OFDMA techniques. 
         [0025]    Base station  101  may be in communication with either a greater number or a lesser number of base stations. Furthermore, while only six subscriber stations are depicted in  FIG. 1 , it is understood that wireless network  100  may provide wireless broadband access to additional subscriber stations. It is noted that subscriber station  115  and subscriber station  116  are located on the edges of both coverage area  120  and coverage area  125 . Subscriber station  115  and subscriber station  116  each communicate with both base station  102  and base station  103  and may be said to be operating in handoff mode, as known to those of skill in the art. 
         [0026]    Subscriber stations  111 - 116  may access voice, data, video, video conferencing, and/or other broadband services via Internet  130 . In an exemplary embodiment, one or more of subscriber stations  111 - 116  may be associated with an access point (AP) of a WiFi WLAN. Subscriber station  116  may be any of a number of mobile devices, including a wireless-enabled laptop computer, personal data assistant, notebook, handheld device, or other wireless-enabled device. Subscriber stations  114  and  115  may be, for example, a wireless-enabled personal computer (PC), a laptop computer, a gateway, or another device. 
         [0027]      FIG. 2A  is a high-level diagram of an orthogonal frequency division multiple access (OFDMA) transmit path.  FIG. 2B  is a high-level diagram of an orthogonal frequency division multiple access (OFDMA) receive path. In  FIGS. 2A and 2B , the OFDMA transmit path is implemented in base station (BS)  102  and the OFDMA receive path is implemented in subscriber station (SS)  116  for the purposes of illustration and explanation only. However, it will be understood by those skilled in the art that the OFDMA receive path may also be implemented in BS  102  and the OFDMA transmit path may be implemented in SS  116 . 
         [0028]    The transmit path in BS  102  comprises channel coding and modulation block  205 , serial-to-parallel (S-to-P) block  210 , Size N Inverse Fast Fourier Transform (IFFT) block  215 , parallel-to-serial (P-to-S) block  220 , add cyclic prefix block  225 , up-converter (UC)  230 . The receive path in SS  116  comprises down-converter (DC)  255 , remove cyclic prefix block  260 , serial-to-parallel (S-to-P) block  265 , Size N Fast Fourier Transform (FFT) block  270 , parallel-to-serial (P-to-S) block  275 , channel decoding and demodulation block  280 . 
         [0029]    At least some of the components in  FIGS. 2A and 2B  may be implemented in software while other components may be implemented by configurable hardware or a mixture of software and configurable hardware. In particular, it is noted that the FFT blocks and the IFFT blocks described in this disclosure document may be implemented as configurable software algorithms, where the value of Size N may be modified according to the implementation. 
         [0030]    Furthermore, although this disclosure is directed to an embodiment that implements the Fast Fourier Transform and the Inverse Fast Fourier Transform, this is by way of illustration only and should not be construed to limit the scope of the disclosure. It will be appreciated that in an alternate embodiment of the disclosure, the Fast Fourier Transform functions and the Inverse Fast Fourier Transform functions may easily be replaced by Discrete Fourier Transform (DFT) functions and Inverse Discrete Fourier Transform (IDFT) functions, respectively. It will be appreciated that for DFT and IDFT functions, the value of the N variable may be any integer number (i.e., 1, 2, 3, 4, etc.), while for FFT and IFFT functions, the value of the N variable may be any integer number that is a power of two (i.e., 1, 2, 4, 8, 16, etc.). 
         [0031]    In BS  102 , channel coding and modulation block  205  receives a set of information bits, applies coding (e.g., Turbo coding) and modulates (e.g., QPSK, QAM) the input bits to produce a sequence of frequency-domain modulation symbols. Serial-to-parallel block  210  converts (i.e., de-multiplexes) the serial modulated symbols to parallel data to produce N parallel symbol streams where N is the IFFT/FFT size used in BS  102  and SS  116 . Size N IFFT block  215  then performs an IFFT operation on the N parallel symbol streams to produce time-domain output signals. Parallel-to-serial block  220  converts (i.e., multiplexes) the parallel time-domain output symbols from Size N IFFT block  215  to produce a serial time-domain signal. Add cyclic prefix block  225  then inserts a cyclic prefix to the time-domain signal. Finally, up-converter  230  modulates (i.e., up-converts) the output of add cyclic prefix block  225  to RF frequency for transmission via a wireless channel. The signal may also be filtered at baseband before conversion to RF frequency. 
         [0032]    The transmitted RF signal arrives at SS  116  after passing through the wireless channel and reverse operations to those at BS  102  are performed. Down-converter  255  down-converts the received signal to baseband frequency and remove cyclic prefix block  260  removes the cyclic prefix to produce the serial time-domain baseband signal. Serial-to-parallel block  265  converts the time-domain baseband signal to parallel time domain signals. Size N FFT block  270  then performs an EFT algorithm to produce N parallel frequency-domain signals. Parallel-to-serial block  275  converts the parallel frequency-domain signals to a sequence of modulated data symbols. Channel decoding and demodulation block  280  demodulates and then decodes the modulated symbols to recover the original input data stream. 
         [0033]    Each of base stations  101 - 103  may implement a transmit path that is analogous to transmitting in the downlink to subscriber stations  111 - 116  and may implement a receive path that is analogous to receiving in the uplink from subscriber stations  111 - 116 . Similarly, each one of subscriber stations  111 - 116  may implement a transmit path corresponding to the architecture for transmitting in the uplink to base stations  101 - 103  and may implement a receive path corresponding to the architecture for receiving in the downlink from base stations  101 - 103 . 
         [0034]    An MS in idle mode is paged by the core network when there is an incoming call for the MS. The MS is not requested to perform a location update or be associated with any BS as long as the MS is moving inside the same paging area. One paging area could consist of hundreds or even thousands of BSs. When the core network needs to page an MS, traditionally all the BSs in the paging area would page the MS. This results in a large paging overhead for all the BSs. 
         [0035]    One way of reducing this paging broadcast overhead is by specifying a hierarchical paging structure that consists of two types of paging groups, a large paging and a small paging group. In such a structure, one large paging group covering a large geographical area is divided into a number of small geographical paging groups covering small portions of the large paging group geographical area. Through such a hierarchical paging structure, the paging controller is able to page specific small paging groups for only the intended MS. 
         [0036]    Nevertheless, the MS needs to perform a location update to manage the hierarchal paging structure whenever the MS moves to another small paging group. This incurs signaling overhead for a high mobility MS. Hence, to reduce such burden, a high mobility MS within a small paging group changes to the large paging group when the ‘small paging group change count’ for the MS exceeds a threshold within a predetermined time. 
         [0037]    When changing its paging state to a large paging group, the MS stops the location update process. However, the MS does perform a location update at the expiry of a location update timer, hence reducing overhead for location update. Thus, such a hierarchical paging structure may expect an increasing paging load when there are MSs that stay in the large paging group for a long period of time. If ‘the BS change count of the MS’ drops below a threshold over a long period, this implies a low mobilized or stationary MS. In this case, the MS is allowed to change from a large to a small paging group. Accordingly, the paging load of the network can be reduced. 
         [0038]    However, the disadvantage of such a hierarchal paging structure is that smaller paging areas result in more frequent location update. Furthermore, an MS may suffer from ping-pang effect when the paging area gets smaller. 
         [0039]    Another way of reducing the paging broadcast overhead is to have the network divide all of the BSs belonging to the same paging group into a number of groups. The network would page the MS through a first group of BSs. If no response is received from the MS, the network would then page the MS again using a next group of BS, and so on. Each page would occur in a different paging cycle. If the MS happens to be in the coverage of the first group of BSs, the paging overhead will be avoided in all the BSs of the remaining groups. If the MS is not in the first groups of BSs, the MS will not be paged again until one or more paging cycles later. 
         [0040]    Therefore, the drawback of this approach is the excessive paging delay for many MSs that are not in the first group of BSs or first several groups of BSs. 
         [0041]    Another approach to avoiding paging delay is to have all the BS groups, if necessary, finish paging the MS within one paging cycle. When an MS is assigned to more than one paging groups, one of the MS&#39;s paging groups is designated as the primary paging group and rest of the assigned paging groups are designated as secondary paging groups. 
         [0042]    The disadvantages of this approach are as follows: 
         [0043]    (a) It focuses on the distinction between the primary paging group and the second paging groups. However, in many scenarios, the essential for the paging operation is the order in which those groups of BSs conduct paging. 
         [0044]    (b) An MS could miss the paging message in some scenarios when the MS is in a primary paging area or a secondary paging area. 
         [0045]    (c) It does not specify the behavior when an MS has no primary paging group but multiple secondary paging groups. 
         [0046]    (d) It does not support the scenario that an MS could have multiple “primary” paging areas (e.g., one for the housing community where the subscriber lives, one for the office complex where the subscriber works, etc.). 
         [0047]    This disclosure provides a method and system for supporting multiple paging areas that balances the instances of MS location update with the paging overhead in a BS. 
         [0048]    In the method and system of this disclosure, an MS is assigned multiple paging groups before entering idle mode. Each paging group is associated with a paging group identifier (PG ID) and a paging offset relative to the beginning of each paging cycle. 
         [0049]    In one embodiment of this disclosure, the distance between two adjacent paging offset is long enough so that an MS paged in the first paging offset can respond to the network before the transmission of the next paging message at the next paging offset in the same paging cycle begins so that the network avoids any unnecessary paging of the MS in the next paging offset. 
         [0050]    In a particular embodiment, when an MS in idle-mode operation moves inside a cell or enters a new cell, if the BS of the cell broadcasts none of the PG IDs that have been assigned to the MS, the MS performs a location update, and the network assigns the MS with a new set of PG ID(s). If the BS of the cell broadcasts one or more of the PG IDs that have been assigned to the MS, the MS monitors the PG ID having shortest paging offset. 
         [0051]    This embodiment is different from the previous approach in that the MS does not differentiate between a primary paging group and the secondary paging groups. In this embodiment, the MS monitors only one PG ID that has the shortest paging offset among all the PG IDs assigned to the MS and broadcasted by the current BS. 
         [0052]      FIG. 3  illustrates a system for supporting multiple paging areas according to an embodiment of this disclosure. 
         [0053]    As shown in  FIG. 3 , a paging controller  301  pages mobile stations in a paging area  300 . Paging area  300  comprises a first paging group  303  comprising BS  1 - 100 , a second paging group  305  comprising BS  101 - 200 , and a third paging group  307  comprising BS  201 - 500 . The first paging group  303  carries two PG IDs that include PG ID_ 1  and PG ID_ 3 , the second paging group  305  carries two PG IDs that include PG ID  2  and PG ID_ 3 , and the third paging group  307  carries one PG ID that includes PG ID_ 3 . MS 1  is assigned PG ID_ 1  and PG ID_ 3  by the paging controller  301 . When MS 1  moves into the coverage area of the first paging group  303  and during the time MS 1  remains in this coverage area, MS 1  only monitors PG ID_ 1 . This is because all the BSs (i.e., BS  1 - 100 ) in this paging group carry PG ID_ 1 , and PG ID_ 1  has the shorter paging offset compared to PG ID_ 3 . When MS 1  leaves the first paging group  303  and moves into the second paging group  305  of BS  101 - 200  or the third paging group  307  of BS  201 - 500 , MS 1  only monitors PG ID_ 3 . It does not matter even though the second paging group  305  also carries the shorter PG ID_ 2  because MS 1  has not been assigned PG ID_ 2 . 
         [0054]    The situation for MS 2  is similar. In this embodiment, MS 2  is assigned PG ID_ 2  and PG ID_ 3  by the paging controller  301 . When MS 2  moves into the coverage area of the second paging group  305  of BS  101 - 200  and during the time MS 2  remains in this coverage area, MS 2  monitors only PG ID_ 2  because all the BSs in this paging group carries two PG IDs, and PG ID_ 2  has the shorter paging offset compared to PG ID_ 3 . When MS 2  leaves the coverage area of the second paging group  305  and moves into the coverage area of the first paging group  303  of BS  1 - 100  or the third paging group  307  of BS  201 - 500 , MS 2  only monitors PG ID_ 3 . It does not matter even though the first paging group  303  also carries the shorter PG ID_ 1  because MS 1  has not been assigned PG ID_ 1 . 
         [0055]    Both PG ID_ 1  and PG ID_ 2  can use the same paging offset because their coverage do not overlap. 
         [0056]    In this embodiment, MS 3  is assigned only PG ID_ 3  by the paging controller  301 , and as shown in  FIG. 3 , MS 3  only monitors PG ID_ 3 . It does not matter if MS 3  is in the first paging group, the second paging group  305 , or the third paging group  307 . 
         [0057]    In another embodiment, the network conducts the paging of an MS through groups of BSs in the order of increasing paging offsets until either the MS has successfully responded to the paging, or all of the paging groups have been exhausted in the current paging cycle. If all of the paging groups have been exhausted in the current paging cycle, the paging will restart in the next paging cycle. 
         [0058]    In such an embodiment, the network determines the number of PG IDs having been assigned to the MS. If the MS to be paged is assigned with only one PG ID, then all of the BSs with this PG ID would page the MS in the pre-determined paging offset starting from the beginning of the current paging cycle. 
         [0059]    If the MS to be paged is assigned with more than one PG ID, the network determines the PG ID with the shortest paging offset. All of the BSs with this PG ID would then page the MS in the paging offset starting from the beginning of the current paging cycle. If no response is received from the paged MS, the network would then determine the PG ID with the second shortest paging offset, and all of the BSs with this PG ID would then page the MS in the paging offset starting from the beginning of the current paging cycle. If no response is received from the paged MS, the network would continue the paging process in the order of increasing paging offset until all of the PG IDs have been exhausted in the current paging cycle. 
         [0060]    This embodiment is different from the previous approach because the network does not differentiate between a primary paging area from secondary paging areas. In this embodiment, the network pages the MS in the order of increasing paging offset in the current paging cycle. 
         [0061]      FIG. 4  illustrates a table  400  providing information regarding paging group ID assignments according to an embodiment of this disclosure. 
         [0062]    In a further embodiment, the paging controller, BSs and the MS have consistent information regarding the PG ID assignment and paging offset configuration. As shown in table  400 , the paging controller, BSs and the MS maintain the consistent configuration of the paging offset. 
         [0063]    In a particular embodiment, the paging controller, such as the paging controller  301 , informs the MS of the PG ID(s) assigned to it, together with the paging offset configuration for each PG ID. Each BS broadcasts the PG ID(s) it is assigned, and the BS broadcasts the paging message for a PG ID in its pre-determined paging offset in a paging cycle. The MS monitors the PG ID with the shortest paging offset in each cell. The paging controller then pages the MS using the BS groups in the order of increasing paging offset. 
         [0064]      FIG. 5  illustrates a table  500  providing information regarding paging group ID assignments along with paging offset indicators according to an embodiment of this disclosure. 
         [0065]    Alternatively, each BS broadcasts the PG ID(s) that the BS carries, together with the paging offset indicator as shown in table  500 . In this embodiment, the values of all the paging offsets are pre-defined. When an MS enters a cell, the MS detects whether the BS broadcasts any PG ID(s) that have been assigned to the MS. If none was detected, the MS performs a location update. Otherwise, the MS monitors the PG ID with the shortest paging offset. 
         [0066]    For example, MS 1  is assigned PG ID_ 1  and PG ID_ 3  by the paging controller  301 . When MS 1  moves into the coverage area of the first paging group  303  and during the time MS 1  remains in this coverage area, MS 1  detects the BSs broadcasting PG ID_ 1  and PG ID_ 3  with a Paging Offset Indicator of “11” as shown in table  500 . Therefore, the MS 1  monitors PG ID_ 1  at the first paging offset, which by default is zero. When the MS 1  enters the second paging group  305 , MS 1  detects the BSs broadcasting PG ID_ 2  and PG ID_ 3  with a Paging Offset Indicator of “11”. However, PG ID_ 2  is not assigned to the MS. Therefore, the MS 1  monitors PG ID_ 3  at the second paging offset. When MS 1  is in the third paging group  307 , MS 1  detects the BSs broadcasting only PG ID_ 3  with a Paging Offset Indicator of “01”. Therefore, the MS 1  monitors PG ID_ 3  at the second paging offset. 
         [0067]    In the previous embodiments, there is no differentiation of primary or secondary paging groups. The differentiation was in the order of the paging offsets of the paging groups. In the subsequent embodiments, paging groups are classified into two categories: primary paging group(s) and secondary paging group(s). 
         [0068]    In one embodiment, an MS is assigned zero or more primary paging groups, and one or more secondary paging groups. This is different from the previous approach where each MS has at most one primary paging group. 
         [0069]    In a particular embodiment, when an MS in idle-mode operation enters a primary paging area, the MS determines if a timer is running. If the timer is running, the MS stops the Timer. If the current primary paging area is different from the last primary paging area, the MS performs a location update and monitors the new PG ID of the current primary paging area. If the current primary paging area is the same as the last primary paging area, the MS monitors the PG ID of the current primary paging area, which is the same as that of the previous paging area. If the timer is not running, the MS performs a location update and monitors the PG ID of the current primary paging area. 
         [0070]    This embodiment is different from the previous approach in that it supports the scenario where the MS has multiple primary paging groups. In this case, when the MS leaves from one primary paging area and enters another primary paging area directly, the MS performs a location update to inform the paging controller. The MS could linger in a secondary paging area for some time after leaving a primary paging area and enters another primary paging area before the expiration of the timer, in such a case, the MS performs a location update just as before. Also, the MS starts the timer when the MS leaves a primary paging area. If the MS returns to the previous primary paging area before the timer expires, the MS stops the timer, but does not need to perform a location update. When the timer expires, the MS performs a location update. 
         [0071]      FIG. 6  illustrates a method  600  of operating an idle mode according to an embodiment of this disclosure. 
         [0072]    As shown in  FIG. 6 , an MS in active mode (block  601 ) enters idle mode and is assigned primary and secondary paging groups by a paging controller (block  603 ). The network then determines if the MS is currently in a primary paging group (block  605 ). The network deems the MS to be in a primary paging group if the MS has informed the network with a location update that the MS has entered a primary paging group and the MS has not informed the network regarding its exit of the primary paging group. If the MS is not determined to be in a primary paging group, the network and the MS know that the MS is in a secondary paging group (block  607 ). The MS then enters a primary paging group (block  609 ) where the MS performs a location update (block  611 ). 
         [0073]    The network and the MS now know that the MS is in a primary paging group (block  613 ). The MS then moves out of the primary paging group (block  615 ) and starts a timer (block  617 ). If the MS has not entered a primary paging group before the timer expires (block  619 ), the MS performs a location update (block  621 ) that lets the network and the MS know that the MS is in a secondary paging group (block  607 ). 
         [0074]    If the MS enters a primary paging group before the timer expires (block  623 ), the MS stops the timer ( 625 ). The MS then determines if the current primary paging group is the same as the last primary paging group (block  627 ). If the current primary paging group is the same as the last primary paging group, the MS does not perform a location update. Because no location update was performed, the network and the MS now assume that the MS is in the same primary paging group (block  613 ). It is possible that the MS may actually be in a neighboring secondary paging group while the network assumes that the MS is in the primary paging area if the MS has left the primary paging area and the timer has not expired. If the current primary paging group is not the same as the last primary paging group, the MS performs a location update (block  629 ) that allows the network and the MS to know that the MS is in a primary paging group (block  613 ). 
         [0075]    Even though not explicitly shown in  FIG. 6 , the MS performs a location update when the MS enters a cell that carries none of the PG IDs that had been assigned to the MS. In this case, the network re-assigns the MS with a new set of PG IDs. 
         [0076]    In another embodiment, the paging controller avoids having a primary paging group page the MS when the MS is not in this primary paging area. In this embodiment, the network determines the number of PG IDs that have been assigned to the MS. The network also determines whether the MS is in one of the primary paging areas. The network deems the MS to be in the primary paging area if the MS informed the network with a location update when the MS entered the primary paging area and the MS has not informed the network of an exit from the primary paging area. 
         [0077]    If the MS is in a primary paging area with a PG ID_x, the network skips all of other primary paging areas and pages the MS in this primary paging group. All of the BSs with this PG ID_x page the MS in the pre-determined paging offset starting at the beginning of the current paging cycle. If a response is received from the paged MS, the process is complete. Otherwise, the network continues to have the neighboring secondary paging areas page the MS. Only if all the attempts have failed in the current paging cycle, all of the BSs with this PG ID_x page the MS in the pre-determined paging offset starting at the beginning of the next paging cycle. 
         [0078]    If the MS is determined to be among the secondary paging groups, the network determines the PG ID with the shortest paging offset and has all of the BSs with this PG ID page the MS in the paging offset starting from the beginning of the current paging cycle. If no response is received from the paged MS and if there are more secondary paging groups, the network determines the PG ID with the second shortest paging offset and has all of the BSs with this PG ID page the MS in the paging offset starting from the beginning of the current paging cycle. If no response is received from the paged MS, the network continues the paging process in the order of increasing paging offset until all the PG IDs are exhausted in the current paging cycle. 
         [0079]    In some embodiments, the paging controller requests at most one primary paging group to page the MS because the system and method of this disclosure allow the paging controller to decide whether the MS is around one primary paging area, and the MS cannot be in two primary paging areas at the same time. 
         [0080]    If there is no primary paging group assigned to the MS, the paging controller requires only the secondary paging groups to page the MS. 
         [0081]    Even if the MS has been assigned one or more primary paging groups, if the paging controller is not informed that the MS is in one of the primary paging groups, the paging controller requests only the secondary paging groups to page the MS. 
         [0082]    When paging the MS using the secondary paging groups, the paging controller pages the MS using the secondary paging groups in the order of increasing paging offsets. 
         [0083]    In particular embodiments, the primary paging groups have paging offsets shorter than those of the secondary paging groups. All of the primary paging groups can use the same paging offset because at most only one of them will page the MS at any time. 
         [0084]      FIG. 7  illustrates a method  700  of paging a mobile station according to an embodiment of this disclosure. 
         [0085]    As shown in  FIG. 7 , a network determines that an MS needs to be paged (block  701 ). The network then determines if the MS is in a primary paging group (block  703 ). If the MS is not in a primary paging group, the MS skips paging the MS in all of the primary paging groups (block  705 ) and pages the MS in the secondary paging group with the shortest paging offset (block  707 ). The network then determines if the MS as responded to the paging (block  709 ). If the MS has responded, the paging process is complete (block  711 ). If the MS has not responded, the network determines if there are any remaining secondary paging groups (block  713 ). If there are any remaining secondary paging groups, the network pages the MS in the secondary paging group with the shortest paging offset among all of the remaining secondary paging groups (block  715 ) and determines if the MS has responded to the page (block  709 ). If there are no remaining secondary paging groups, the network continues paging in the next paging cycle (block  717 ). 
         [0086]    If the MS is in a primary paging group, the network skips paging the MS in the other primary paging groups (block  719 ) and pages the MS in the primary paging group with a PG ID_x (block  721 ). The network then determines if the MS has responded (block  723 ). If the MS has responded, the paging process is complete (block  711 ). If the MS has not responded, the network pages the MS in the secondary paging group with the shortest paging offset (block  707 ). 
         [0087]    This disclosure provides two idle mode mechanisms. 
         [0088]    The MS does not perform a location update as long as the MS is inside one of the paging groups that has been assigned to the MS. The consistency between the MS monitoring PG ID and the paging controller paging the MS guarantees that the MS is paged at most once in each paging cycle no matter which paging group the MS resides. There is minimum signaling overhead between the network and the MS. 
         [0089]    The network also skips the primary paging groups when the network knows that the MS is not in one of those primary paging groups. This dramatically reduces the paging broadcast overhead in those primary paging groups. The complete location update procedure not only handles ping-pang effect using the timer, but also guarantees both the network and the MS know whether the MS is in a primary or a secondary paging group at any time. 
         [0090]    Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.