Abstract:
Apparatus having corresponding methods and computer-readable media comprise: a paging module configured to provide paging parameters for a mobile station, wherein the paging parameters include i) a paging listening interval length Lp for each paging listening interval, ii) a paging cycle period Pp, and iii) a paging cycle offset Qp; and a sleep module configured to determine sleep parameters for the mobile station based on the paging parameters, wherein the sleep parameters include i) a wakeup interval length Ls for each wakeup interval, ii) a sleep cycle period Ps, and iii) a sleep cycle offset Qs; and wherein the sleep module is further configured to determine the sleep parameters such that each paging listening interval overlaps one of the wakeup intervals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This disclosure claims the benefit of U.S. Provisional Patent Application Ser. No. 61/262,868, filed on Nov. 19, 2009, the disclosure thereof incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present disclosure relates generally to wireless communication systems. More particularly, the present disclosure relates to synchronization of paging and sleep cycles in wireless communication systems. 
     BACKGROUND 
     Mobile stations in wireless communications systems are generally powered by batteries. For this reason, manufacturers strive to reduce power consumption of mobile stations to enable the devices to be used for longer periods without replacing or recharging the batteries, for example by including idle modes, sleep modes, and the like. 
     In idle mode, a mobile station disconnects from a specific base station, but listens to periodic paging messages during paging listening intervals. The paging messages are broadcast by base stations in order to notify mobile stations of the arrival of downlink traffic and the like. 
     In sleep mode, a mobile station maintains a connection with a base station, but powers off except for periodic wakeup intervals. During each wakeup interval, a mobile station may decode broadcast messages, receive downlink packets, transmit uplink packets, measure base station signals, and the like. 
     In some wireless communications systems, such as WiMAX systems, the idle and sleep modes cannot be active at the same time. However, other wireless communications systems, such as 3GPP LTE, permit a mobile station to operate in both modes at the same time. 
     SUMMARY 
     In general, in one aspect, an embodiment features an apparatus comprising: a paging module configured to provide paging parameters for a mobile station, wherein the paging parameters include i) a paging listening interval length Lp for each paging listening interval, ii) a paging cycle period Pp, and iii) a paging cycle offset Qp; and a sleep module configured to determine sleep parameters for the mobile station based on the paging parameters, wherein the sleep parameters include i) a wakeup interval length Ls for each wakeup interval, ii) a sleep cycle period Ps, and iii) a sleep cycle offset Qs; and wherein the sleep module is further configured to determine the sleep parameters such that each paging listening interval overlaps one of the wakeup intervals. 
     In general, in one aspect, an embodiment features a method comprising: providing paging parameters for a mobile station, wherein the paging parameters include i) a paging listening interval length Lp for each paging listening interval, ii) a paging cycle period Pp, and iii) a paging cycle offset Qp; and determining sleep parameters for the mobile station based on the paging parameters, wherein the sleep parameters include i) a wakeup interval length Ls for each wakeup interval, ii) a sleep cycle period Ps, and iii) a sleep cycle offset Qs; and wherein the sleep parameters are determined such that each paging listening interval overlaps one of the wakeup intervals. 
     In general, in one aspect, an embodiment features computer-readable media embodying instructions executable by a computer to perform a method comprising: providing paging parameters for a mobile station, wherein the paging parameters include i) a paging listening interval length Lp for each paging listening interval, ii) a paging cycle period Pp, and iii) a paging cycle offset Qp; and determining sleep parameters for the mobile station based on the paging parameters, wherein the sleep parameters include i) a wakeup interval length Ls for each wakeup interval, ii) a sleep cycle period Ps, and iii) a sleep cycle offset Qs; and wherein the sleep parameters are determined such that each paging listening interval overlaps one of the wakeup intervals. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a conventional wireless communication schedule. 
         FIG. 2  shows a wireless communication schedule according to one embodiment. 
         FIG. 3  shows elements of a wireless communication system according to an embodiment where a mobile station selects its sleep parameters. 
         FIG. 4  shows a process operated by the wireless communication system of  FIG. 3  according to one embodiment. 
         FIG. 5  shows elements of a wireless communication system according to an embodiment where a base station selects sleep parameters for a mobile station. 
         FIG. 6  shows a process operated by the wireless communication system of  FIG. 5  according to one embodiment. 
     
    
    
     The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
     DETAILED DESCRIPTION 
     In conventional wireless communications systems that permit a mobile station to operate in sleep mode and idle mode contemporaneously, the paging cycles and sleep cycles are not coordinated. Therefore, a mobile station operating in both modes contemporaneously must be active during both paging listening intervals and wakeup intervals, which generally do not coincide. This problem is illustrated by schedule  100  of  FIG. 1 . 
     Referring to  FIG. 1 , schedule  100  includes a paging timeline  102  showing periodic paging listening intervals  104 , each preceded by an initialization interval  106 . Schedule  100  also includes a sleep timeline  108  showing periodic wakeup intervals  110 . Schedule  100  also shows an active timeline  112  showing the union of paging listening intervals  104 , initialization intervals  106 , and wakeup intervals  110  as active intervals  114 . As can be seen from  FIG. 1 , the active time represented by active timeline  112  is much greater than required by either paging timeline  102  or sleep timeline  108  alone. 
     The inventors have recognized that this situation presents a problem to be solved. The solutions disclosed herein involve synchronizing paging listening intervals  104  and wakeup intervals  110  so as to reduce the total active time required at the mobile station. In various embodiments, the sleep parameters for the mobile station are selected so that each paging listening interval  104  overlaps one of wakeup intervals  110 . Furthermore, in some embodiments, the sleep parameters for the mobile station are selected so that the end of each paging listening interval  104  is aligned with the end of one of wakeup intervals  110 . This alignment places some or all of each initialization interval  106  within one of wakeup intervals  110  as well. 
     These techniques provide numerous potential advantages. For example, battery power of the mobile station is conserved. As another example, the probability of the mobile station failing to receive paging messages from the base station is reduced. Therefore the processing delay is reduced in the case of the arrival of downlink data. 
       FIG. 2  shows an example schedule  200  according to one embodiment. Referring to  FIG. 2 , it can be seen that paging timeline  202  and sleep timeline  208  are synchronized such that each paging listening interval  104  overlaps one of wakeup intervals  110 . In addition, it can be seen that the end of each paging listening interval  104  is aligned with the end of one of wakeup intervals  110 . This alignment places some or all of each initialization interval  106  within one of the wakeup intervals  110 . As can be seen from schedule  200   FIG. 2 , the active time represented by active timeline  212  is much less than that required by schedule  100  of  FIG. 1 . 
       FIG. 2  also illustrates parameters used to describe various embodiments. The equations given below assume a discrete time interval t, where t is a non-negative integer. Discrete time interval t can be interpreted subframe with a duration of 1 ms for LTE. The period of the paging cycle is given by Pp≧0. The offset of the paging cycle is given by Qp≧0. The length of the paging listening interval is given by Lp≧0. Then the paging listening interval is described by equation (1), where np is a non-negative integer indicating periodic occurrence of paging listening intervals.
 
 Pp·np+Qp≦t&lt;Pp·np+Qp+Lp   (1)
 
     The period of the sleep cycle is given by Ps≧0. The offset of the sleep cycle is given by Qs≧0. The length of the wakeup interval is given by Lp≧0. Then the wakeup interval is described by equation (2), where ns is a non-negative integer indicating periodic occurrence of wakeup intervals.
 
 Ps·ns+Qs≦t&lt;Ps·s+Qs+Ls   (2)
 
     Idle mode generally has a longer period and shorter interval than sleep mode, as shown in equations (3) and (4).
 
 Pp≧Ps   (3)
 
 Lp≦Ls   (4)
 
     Now the selection of paging and sleep parameters is described in detail. In most cases, the paging parameters are set according to network requirements, Therefore, the sleep parameters are selected based on the paging parameters to synchronize idle and sleep modes. In some embodiments, the selection of sleep parameters is performed by the base station, which transmits the parameters to the mobile station. In other embodiments, the selection of sleep parameters is performed by the mobile station, which then transmits the parameters to the base station for confirmation. Both of these embodiments are described below. 
       FIG. 3  shows elements of a wireless communication system  300  according to an embodiment where a mobile station  302  selects its sleep parameters. Although in the described embodiments the elements of wireless communication system  300  are presented in one arrangement, other embodiments may feature other arrangements. For example, elements of wireless communication system  300  can be implemented in hardware, software, or combinations thereof. Furthermore, in some embodiments, wireless communication system  300  is implemented as a 3GPP LTE network. In other embodiments, wireless communication system  300  is implemented in other ways. 
     Referring to  FIG. 3 , wireless communication system  300  includes mobile station  302  and a base station  304 . Mobile station  302  includes a paging module  306 , a sleep module  308 , a transmitter  310 , and a receiver  312 . Base station  304  includes a receiver  314 , a transmitter  316 , and a controller  318 . 
       FIG. 4  shows a process  400  operated by wireless communication system  300  of  FIG. 3  according to one embodiment. Although in the described embodiments the elements of process  400  are presented in one arrangement, other embodiments may feature other arrangements. For example, in various embodiments, some or all of the steps of process  400  can be executed in a different order, concurrently, and the like. 
     In  FIG. 4 , processes of mobile station  302  are shown on the left, while processes of base station  304  are shown on the right. Process  400  begins at  402  where mobile station  302  is initialized, for example when powered on by a user. At  404  paging module  306  provides paging parameters for mobile station  302 . 
     The paging parameters include a paging listening interval length Lp for each paging listening interval, a paging cycle period Pp, and a paging cycle offset Qp. Paging listening interval length Lp is generally fixed for a given wireless communication system  300 . Paging cycle period Pp and paging cycle offset Qp are generally determined based on paging requirements such as delay and system parameters such as the total number of mobile stations  302 . Paging cycle period Pp is generally common among the mobile stations  302  within a cell. Paging cycle offset Qp is generally common among a group of mobile stations  302 , but may be different for each group when multiple groups are present. 
     At  406 , sleep module  308  determines sleep parameters for mobile station  302  based on the paging parameters. The sleep parameters include a wakeup interval length Ls for each wakeup interval, a sleep cycle period Ps, and a sleep cycle offset Qs. To ensure that each paging listening interval  104  overlaps one of wakeup intervals  110 , sleep module  308  determines the sleep parameters according to equation (5), where k is a positive integer.
 
 Pp/Ps=k   (5)
 
     To ensure that the end of each paging listening interval  104  is aligned with the end of one wakeup intervals  110 , sleep module  308  determines the sleep parameters according to equation (6), where m is a positive integer.
 
0 ≦Qs=Qp+Lp−Ls+mPs&lt;Ps   (6)
 
     At  408 , transmitter  310  of mobile station  302  transmits a message  320  representing a request for base station  304  to confirm the sleep parameters. At  410  receiver  314  of base station  304  receives message  320 . At  412 , controller  318  of base station  304  determines whether the sleep parameters are acceptable. If controller  318  determines the sleep parameters to be acceptable, at  414  transmitter  316  of base station  304  transmits a message  322  representing a confirmation of the sleep parameters. At  416  receiver  314  of mobile station  302  receives message  322 . At  418  mobile station  302  operates according to the sleep parameters. 
       FIG. 5  shows elements of a wireless communication system  500  according to an embodiment where a base station  504  selects sleep parameters for a mobile station  502 . Although in the described embodiments the elements of wireless communication system  500  are presented in one arrangement, other embodiments may feature other arrangements. For example, elements of wireless communication system  500  can be implemented in hardware, software, or combinations thereof. 
     Referring to  FIG. 5 , wireless communication system  500  includes mobile station  502  and base station  504 . Base station  504  includes a paging module  506 , a sleep module  508 , a transmitter  510 , and a receiver  512 . Mobile station  502  includes a transmitter  514  and a receiver  516 . 
       FIG. 6  shows a process  600  operated by wireless communication system  500  of  FIG. 5  according to one embodiment. Although in the described embodiments the elements of process  600  are presented in one arrangement, other embodiments may feature other arrangements. For example, in various embodiments, some or all of the steps of process  600  can be executed in a different order, concurrently, and the like. 
     In  FIG. 6 , processes of mobile station  502  are shown on the left, while processes of base station  504  are shown on the right. Process  600  begins at  602  where mobile station  502  is initialized, for example when powered on by a user. At  604 , transmitter  514  of mobile station  502  transmits a message  520  representing a request for sleep parameters. At  606  receiver  512  of base station  504  receives message  520 . 
     At  608  paging module  506  of base station  504  provides paging parameters for mobile station  502 . At  610 , sleep module  508  determines sleep parameters for mobile station  502  based on the paging parameters. The paging parameters and sleep parameters are determined as described above. 
     At  612 , transmitter  510  of base station  504  transmits a message  522  representing the sleep parameters and paging parameters. At  614  receiver  516  of mobile station  502  receives message  522 . At  616  mobile station  502  operates according to the sleep parameters. 
     Other embodiments are contemplated. For one example, the paging parameters can be determined by one or both of mobile station  502  and base station  504 . For another example, base station  504  can provide paging and sleep parameters without the explicit request at  604  of mobile station  502 . Various embodiments are independent of the manner in which the paging parameters are selected. 
     Now example parameters are described for a 3GPP LTE network. In a 3GPP LTE network, the parameters are determined by base station  304 , which is referred to as the evolved Node B (eNB), and transmitted to mobile station  302 , which is referred to as the user equipment (UE). The period of the paging cycle Pp can be 320, 640, 1280, or 2560 ms. The period of the sleep cycle Ps can be 10, 20, 32, 40, 64, 80, 128, 160, 256, 320, 512, 640, 1024, 1280, 2048, or 2560 ms. The paging listening interval Lp is 1 ms. The length of the wakeup interval Ls can be 1, 2, 3, 4, 5, 6, 8, 10, 20, 30, 40, 50, 60, 80, 100, or 200 ms. The offset of the paging cycle Qp is a function of the unique identification number UE_ID of the UE. The offset of the sleep cycle Qs can be any non-negative integer less than the period of the sleep cycle Ps. 
     Now an example of the selection of sleep parameters is described for a 3GPP LTE network. As mentioned above, the paging listening interval Lp is fixed at 1 ms. The eNB chooses the period of the paging cycle Pp based on its paging requirements, for example, Pp=1280 ms. The eNB and UE calculate the offset of the paging cycle Qp based on the UE_ID, for example, Qp=10 ms. The eNB chooses the wakeup interval Ls based on its sleep requirements, for example, Ls=4 ms. The eNB chooses the period of the sleep cycle Ps based on the already-chosen period of the paging cycle Pp and an equation, for example, Ps=Pp/4=320 ms. The eNB chooses the offset of the sleep cycle Qs based on the already-chosen parameters and equations, for example, Qs=Qp+Lp−Ls+m*Ps=10+1−4+0*320=7 ms. 
     Various embodiments can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions by operating on input data and generating output. Embodiments can be implemented in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     A number of implementations have been described. Nevertheless, various modifications may be made without departing from the scope of the disclosure. For example, one or more steps of methods described above can be performed in a different order (or concurrently) while still achieving desirable results. Accordingly, other implementations are within the scope of the following claims.