Abstract:
A method for controlling discontinuous reception in a wireless transmit/receive unit includes defining a plurality of DRX levels, wherein each DRX level includes a respective DRX cycle length and transitioning between DRX levels based on a set of criteria. The transitioning may be triggered by implicit rules.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/535,915, filed Jun. 28, 2012, which is a continuation of U.S. patent application Ser. No. 12/022,233, filed Jan. 30, 2008; which issued as U.S. Pat. No. 8,238,260 on Aug. 7, 2012, which claims the benefit of U.S. Provisional Patent Application No. 60/887,276, filed Jan. 30, 2007, the contents of which are incorporated by reference herein. 
     
    
     FIELD OF DISCLOSURE 
       [0002]    The present invention is in the field of wireless communications. 
       BACKGROUND 
       [0003]    A goal of the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) program is to develop new technology, new architecture and new methods for settings and configurations in wireless communication systems in order to improve spectral efficiency, reduce latency and better utilize the radio resource to bring faster user experiences and richer applications and services to users with lower costs. 
         [0004]    In a typical LTE network, a wireless transmit/receive unit (WTRU) may operate in a number of modes. While in LTE_ACTIVE mode, the WTRU may operate in a discontinuous reception (DRX) mode. DRX mode allows the WTRU to operate in a low power, or sleep mode, for a preset time, and then switch to a full power, or awake, mode for another preset time in order to reduce battery consumption. The DRX cycle lengths are generally configured by the enhanced universal terrestrial radio access network (E-UTRAN) so that an enhanced Node B (eNB) and the WTRU are synchronized on a consistent sleep and wake-up cycle. 
         [0005]    Live traffic situations and WTRU mobility may require frequent adjustment of the DRX cycle length in order to balance system performance, WTRU performance and WTRU power savings. However, relying only on WTRU/E-UTRAN signaling to make the fine DRX cycle adjustment may incur a heavy system and WTRU signaling load. 
         [0006]    Implicit rules for DRX cycle length adjustment may be used for smooth LTE_ACTIVE DRX operations to reduce battery power consumption while not effecting system or WTRU performance issues. Implicit rules may assist the implicit DRX cycle length transitions between the WTRU and the E-UTRAN without using excessive explicit signaling. 
       SUMMARY 
       [0007]    A method and apparatus are disclosed for controlling discontinuous reception in a WTRU. The method may include defining a plurality of DRX levels, wherein each DRX level includes a respective DRX cycle length, and transitioning between DRX levels based on a set of criteria. Transitioning may be triggered by implicit rules. Triggering may be invoked by a measurement event, a timer, a counter or a downlink command, for example. The transitions between DRX states may occur without explicit signaling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A more detailed understanding may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
           [0009]      FIG. 1  shows a wireless communications system in accordance with one embodiment; 
           [0010]      FIG. 2  is a functional block diagram of a WTRU and an e Node B (eNB) in accordance with one embodiment; and 
           [0011]      FIG. 3  is a state diagram of implicit DRX transition in accordance with one embodiment; 
           [0012]      FIG. 4  is a signal flow diagram for implicit DRX transition in accordance with one embodiment; 
           [0013]      FIG. 5  is a flow diagram for a method of implicit DRX signaling in accordance with one embodiment; 
           [0014]      FIG. 6  is a flow diagram for a method of implicit DRX signaling in accordance with another embodiment; 
           [0015]      FIG. 7  is a flow diagram for a method of implicit DRX signaling in accordance with an alternative embodiment; and 
           [0016]      FIG. 8  is a flow diagram for a method of implicit DRX signaling in accordance with another alternative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    When referred to hereafter, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “base station” includes but is not limited to a Node-B, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. 
         [0018]      FIG. 1  shows a wireless communication system  100  in accordance with one embodiment. The system  100  includes a plurality of WTRUs  110  and an eNB  120 . As shown in  FIG. 1 , the WTRUs  110  are in communication with the eNB  120 . Although three WTRUs  110  and one eNB  120  are shown in  FIG. 1 , it should be noted that any combination of wireless and wired devices may be included in the wireless communication system  100 . The eNB  120  and the WTRUs  110  may communicate while in DRX mode and may have coordinated DRX cycles. 
         [0019]      FIG. 2  is a functional block diagram  200  of a WTRU  110  and the eNB  120  of the wireless communication system  100  of  FIG. 1 . As shown in  FIG. 1 , the WTRU  110  is in communication with the eNB  120 . Both WTRU  110  and eNB  120  may operate in DRX mode. 
         [0020]    In addition to the components that may be found in a typical WTRU, the WTRU  110  includes a processor  215 , a receiver  216 , a transmitter  217 , and an antenna  218 . The processor  215  may be configured to adjust DRX cycle length as necessary. The receiver  216  and the transmitter  217  are in communication with the processor  215 . The antenna  218  is in communication with both the receiver  216  and the transmitter  217  to facilitate the transmission and reception of wireless data. 
         [0021]    In addition to the components that may be found in a typical eNB  120 , the eNB  120  includes a processor  225 , a receiver  226 , a transmitter  227 , and an antenna  228 . The processor  225  is configured to communicate with the receiver  226  and transmitter  227  to adjust DRX cycles as necessary. The receiver  226  and the transmitter  227  are in communication with the processor  225 . The antenna  228  is in communication with both the receiver  226  and the transmitter  227  to facilitate the transmission and reception of wireless data. 
         [0022]    In order to improve battery life, but not limit the eNB  120  and WTRU  110  performance, transitions between DRX cycle length states may be defined implicitly, rather than explicitly. The implicit rules may be implemented at the radio resource control (RRC) and the medium access control (MAC) levels while the WTRU  110  is in a LTE_ACTIVE DRX state. 
         [0023]    Approximately half of WTRU  110  to eNB  120  interaction involves WTRU  110  requests and reports and eNB  120  responses while the WTRU  110  is in LTE_ACTIVE DRX mode. When the WTRU  110  measures a particular scenario, measurement events may be reported to the eNB  120 , and the eNB  120  may respond to the situation by commanding the WTRU  110  to start a new service, mobility activity, and the like. If the downlink command transmission or reception is limited by a relatively long DRX cycle length, WTRU  110  and eNB  120  system performance during LTE_ACTIVE DRX mode may suffer. However, certain measurement events may make good candidates for the anticipated network downlink commands. 
         [0024]      FIG. 3  shows an implicit DRX transition state machine  300  in accordance with one embodiment. The state machine  300 , as well as associated transition mechanisms and parameter values, may be configured by the eNB ( 120  of  FIG. 1 ). The state machine  300  may have a life span, also configured by the eNB  120 . Each state may be applied at the WTRU ( 110  of  FIG. 1 ) and at the eNB  120 , so that operation is consistent and synchronized. At each defined and configured DRX state, a different DRX cycle length is associated with both the WTRU  110  and the eNB  120  operations. 
         [0025]    The DRX cycle length transition rules may be based on WTRU  110  and eNB  120  experiences. Given a certain elapsed time, or a given set of measurement values, the WTRU  110  and the eNB  120  may learn and predict traffic patterns. These learned and predicted traffic patterns may be superimposed on a general model for a state machine, resulting in the DRX state machine  300  for a WTRU  110 /eNB  120  system that permits implicit transition operation and consistent DRX actions for both the WTRU  110  and the eNB  120 . The eNB  120  can prescribe DRX states for service and mobility conditions with the potential for continuous improvement and learned traffic patterns upon every invocation. 
         [0026]      FIG. 3  shows 3 defined DRX levels,  302 ,  304 ,  306  and an undefined DRX level  308 . In DRX level  3   306 , the WTRU  110  is operating in a normal DRX cycle. The actual length of the normal state may be defined by the eNB  120 . DRX level  2   304  is a shorter cycle length than DRX level  3   306 , and is associated with more frequent activity than normal. The eNB  120  may also define the cycle length for DRX level  2   304 , and may also set a “resume” period. A resume period is a length of time in which there are no new transmissions and after which the WTRU  110  may return to DRX level  3   306  operation, unless the WTRU  110  is commanded to do otherwise. 
         [0027]    DRX level  1   302  has the shortest DRX cycle length, and may be used by a WTRU  110  or eNB  120  to handle predicted immediate downlink commands and when uplink traffic patterns are recognized by the WTRU  110  and the eNB  120  as requiring immediate downlink action, such as during a handover event, for example. 
         [0028]    A DRX level n  308  may be configured with longer DRX cycles than that for the DRX Level  3   306 . The eNB  120  can redefine the DRX cycle lengths for each state at the end of the DRX configuration life span but may observe a DRX cycle length rule that lower level DRX states have shorter DRX lengths. 
         [0029]    For a WTRU  110  at DRX level  3   306 , a timer or counter trigger may be defined to trigger a transition to DRX Level  2   304  if the eNB  120  determines that the WTRU  110  should periodically transition to a “busy” cycle to check downlink data. This may be considered a trigger based on a measurement event. Another trigger based on a measurement event can also be defined to transition a WTRU  110  from DRX level- 3   306  to DRX Level  1  when a traffic volume event on a certain radio bearer accumulating a larger amount of uplink data than a threshold is reported and an anticipated Radio Bearer (RB) Reconfiguration command is imminent. 
         [0030]    If the WTRU  110  in DRX Level  1   302  state receives a RB Reconfiguration command, the current DRX Level  1  state is over. If the WTRU  110  at DRX Level  1  state  302  does not receive the anticipated command for the defined “resume period”, it can go back to its original DRX state and resume the power saving DRX cycle. Regular timers and counters may be used during a DRX mode to trigger the implicit DRX cycle length transition. The choice between the timers and counters and the values of the timers or counters may be based on learned traffic patterns and models with respect to the mobility and/or service state of the WTRU  110  at a particular time while the WTRU  110  is in LTE_ACTIVE DRX mode. The timer or counter triggers may be used as transition triggers to bring up the DRX cycle length as well as to bring down the DRX cycle length as the DRX state changes. 
         [0031]    The eNB  120  may configure DRX parameters based on a network traffic monitoring operation and analysis. Several methods exist to select the parameter values, such as by including a default system value set that is defined for implicit DRX transition operation. Optionally, the parameters may be published in system information broadcasts, or they can be determined by the eNB  120  from time to time and loaded to a particular WTRU  110  via higher layer signaling before an intended DRX mode period. 
         [0032]    Transitions between different states may be signaled in an information element (IE). An example of a skeleton for signaling an implicit DRX cycle transition is shown in Table 1. As shown in Table 1, the Implicit DRX Transition List is mandatory and is limited to a value indicating a maximum number of DRX states. 
         [0033]    The DRX cycle length IE is mandatory, and is an integer. The trigger mechanisms are optional, and may be a trigger to move up a DRX state level, or move down a DRX state level. The Implicit DRX Transition configured life Span IE is mandatory, and sets the resume period for non-normal states. The Initial DRX state is optional, and may set the DRX state of the WTRU  110  at start-up. 
         [0034]    To aid with easier DRX cycle length transition and maintain DRX cycle length synchronization between the WTRU  110  and the eNB  120 , the DRX cycle length definition may be given as a function of the shortest DRX base number (L). Then various DRX length values may be: 
         [0000]      DRX-cycle-len= L ×2 n ,  Equation (1)
 
         [0000]    where n=0, 1, 2 . . . such that the resulting DRX-cycle-len does not exceed a maximum DRX cycle length. The shortest DRX cycle length possible occurs when n=0, and is a fraction of a longer DRX cycle length. 
         [0035]    The use of DRX cycle lengths that are multiples of each other reduces the probability that DRX periods may be mismatched and provides an efficient mechanism to resynchronize DRX periods between the WTRU  110  and eNB  120 . When DRX periods are defined as multiples of each other, and when DRX periods become mismatched between the WTRU  110  and the eNB  120 , each entity can determine the period of the other by increasing or decreasing the cycle length to determine the period being used by the other entity, and resynchronizing the entities accordingly. 
         [0036]    Typically, a WTRU  110  in DRX Level  1   302  may count n times before it transits back to the original DRX state. The default may be given as: n=(Level-k DRX Cycle Length or original DRX cycle length)/Level- 1  DRX Cycle Length; where Level-k cycle length is the length of the DRX cycle before the WTRU  110  enters DRX Level  1   302 . Alternatively, the network may configure n for the “resume method”. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Information 
                   
                   
                   
                   
               
               
                 Element/ 
                   
                   
                 Type and 
                 Semantics 
               
               
                 Group name 
                 Need 
                 Multi 
                 reference 
                 description 
               
               
                   
               
             
             
               
                 Implicit DRX 
                 MP 
                 maxDR 
                   
                   
               
               
                 Transition 
                   
                 Xstates 
               
               
                 List 
                   
                 (TBD) 
               
               
                 DRX Cycle 
                 MP 
                   
                 Integer 
               
               
                 Length 
                   
                   
                 (TBD) 
               
               
                 Trigger-UP-1 
                 OP 
                   
                 Trigger 
                 To next upper level 
               
               
                   
                   
                   
                 Mechanism 
                 DRX State 
               
               
                   
                   
                   
                 A.B.C.D 
               
               
                 Trigger-UP-2 
                 OP 
                   
                 Trigger 
                 Used by Level-1 for 
               
               
                   
                   
                   
                 Mechanism 
                 resume 
               
               
                   
                   
                   
                 A.B.C.D 
               
               
                 Trigger-Down-1 
                 OP 
                   
                 Trigger 
                 To next lower level 
               
               
                   
                   
                   
                 Mechanism 
                 DRX state 
               
               
                   
                   
                   
                 A.B.C.D 
               
               
                 Trigger-Down-2 
                 OP 
                   
                 Trigger 
                 To Level-1 trigger 
               
               
                   
                   
                   
                 Mechanism 
               
               
                   
                   
                   
                 A.B.C.D 
               
               
                 Implicit DRX 
                 MP 
                   
                 TBD 
                 Time in seconds 
               
               
                 Transition 
               
               
                 configured 
               
               
                 life span 
               
               
                 Initial DRX state 
                 OP 
                   
                 TBD 
               
               
                   
               
             
          
         
       
     
         [0037]    Transitions from state to state may be initiated by a trigger. Table 2 shows an example of transition trigger IEs. Each of the IEs is mandatory, except for the resume period. The Transition Trigger is mandatory and is specified by the network if specified as shown in Table 1. The CHOICE mechanism allows the network to configure the WTRU  110  for implicit DRX operational triggers. The trigger Timer value may be in units of absolute time, LTE frames or transmission time intervals (TTIs) and is used to monitor or regulate ON and OFF periods for network signaling channel activities or data channel activities for the WTRU  110 . The Counter values may be an integer value used to check the occurrences of certain trigger events. The measurement event may enumerate the event that causes the trigger. The resume period may be a time period given in seconds, DRX cycles, or some other value, that denotes the total time a WTRU  110  may remain in an elevated state without receiving a command to move back to normal state. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Information 
                   
                   
                   
                   
               
               
                 Element/ 
                   
                   
                 Type and 
                 Semantics 
               
               
                 Group name 
                 Need 
                 Multi 
                 reference 
                 description 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Transition 
                 MP 
                   
                   
               
               
                 Trigger 
               
               
                 CHOICE 
                 MP 
               
               
                 mechanism 
               
               
                 Timer 
               
               
                 Timer Value 
                 MP 
                 Integer TBD 
               
               
                 Counter 
               
               
                 Counts 
                 MP 
                 Integer TBD 
               
               
                 Measurement 
               
               
                 Event 
               
               
                 measurement 
                 MP 
                 Enumerated 
               
               
                 Event-Id 
                   
                 (TBD) 
               
               
                 resume period 
                 CV- 
                 TBD 
                 Could be default in 
               
               
                   
                 Trigger- 
                   
                 Level-1 State. 
               
               
                   
                 UP-2 
                   
                 Default is to stay n 
               
               
                   
                   
                   
                 Level-1 cycles so the 
               
               
                   
                   
                   
                 total length is 
               
               
                   
                   
                   
                 equivalent to its 
               
               
                   
                   
                   
                 original DRX state 
               
               
                   
                   
                   
                 DRX length 
               
               
                   
               
             
          
         
       
     
         [0038]      FIG. 4  is a signal flow diagram for implicit DRX transition  400  in accordance with one embodiment. A WTRU  402  may receive an RRC message or an IE  406  from the E-UTRAN  404  that triggers the WTRU  402  to enter DRX mode. The WTRU  402  may enter DRX mode  408  at a default level which may be a normal cycle length DRX level  3  ( 306  of  FIG. 3 ). Both the WTRU  402  and the E-UTRAN  404  enter DRX mode ( 408 ,  410  respectively). The WTRU  402  may receive another RRC message or IE  412  that triggers the WTRU  402  to enter a faster DRX cycle mode (DRX level  1   302  of  FIG. 3 ). The WTRU  402  and the E-UTRAN  404  enter the DRX level  1  ( 414 ,  416  respectively). A WTRU timer  418 , synchronized with an E-UTRAN timer (not shown), expires. As the timers are synchronized, no notice of timer expiration is required. The expiration of the timer  418  triggers the WTRU  402  and the E-UTRAN  404  to return to normal DRX level. The WTRU  402  returns  422  to DRX level- 3   306  at the same time that the E-UTRAN  404  returns  424  to DRX level- 3   306 . 
         [0039]      FIG. 5  is a flow diagram of a method of implicit signaling  500  in accordance with one embodiment. At step  502  the WTRU is in normal operating mode, or Level- 3 . At step  504 , the WTRU checks to see if a timer has timed-out, or a trigger has been received that would force the WTRU to move to another DRX state. If no, at step  506 , the WTRU remains in normal state. If the WTRU detects a time out signal or a trigger at step  504 , at step  508 , the WTRU determines if it should move to DRX Level  1  or DRX level  2 . If the WTRU determines that the trigger is a level- 2  trigger, at step  510  the WTRU moves to DRX Level  2 . At step  512 , the WTRU determines that the resume period has ended, and returns to DRX level- 3 . If, however, the WTRU, at step  508 , determines that it received a level  1  trigger, at step  514 , the WTRU goes into a DRX level  1 . At step,  516 , the WTRU determines if it has received a Radio Bearer Reconfiguration message. If not, the WTRU, at step  518 , waits for the resume period to end and returns to normal operation at step  522 . If, however, at step  516 , the WTRU receives a radio bearer reconfigure message, at step  520 , the WTRU returns to normal DRX cycle operation. 
         [0040]      FIG. 6  is a flow diagram of an implicit DRX method  600  in accordance with another embodiment. At step  602 , the WTRU is in normal or DRX Level- 3  mode. At step  604 , the WTRU conducts a traffic volume measurement. At step  606 , the WTRU compares the traffic volume measurement with a threshold. If the volume is below the threshold, at step  608 , the WTRU takes no action and remains in DRX Level- 3  mode. However, if, at step  606 , the WTRU determines that the traffic is above a threshold, at step  610 , the WTRU changes mode to a shorter DRX cycle. Based on the traffic, the new DRX mode may be DRX level- 2  or DRX level- 1 . At step  612 , the WTRU determines if a command or message has been received. If yes, at step  614 , the WTRU returns to Level- 3  mode. If not, at step  616  the WTRU waits the resume period before returning to level- 3  mode at step  618 . Optionally, the E-UTRAN may determine the traffic volume measurement reporting threshold level for DRX state transition triggering. Once the defined traffic volume measurement event occurs, the DRX state transition is triggered. 
         [0041]    While in LTE_ACTIVE DRX mode, a WTRU may perform traffic volume measurements for uplink traffic. The E-UTRAN may configure the WTRU to report the events on threshold crossing. Based on learned traffic patterns, the E-UTRAN determines that there is a large volume change, which may means that an RB addition, an RB reconfiguration or an RB release command is imminent. Therefore, the traffic volume event reports may be used as implicit DRX transition triggers. For example, a large volume change may be used to trigger the WTRU into the shortest DRX cycle (DRX level  1 ,  302  of  FIG. 3 , for example) in order to receive the network command. The network, when receiving the predetermined measurement event, may determine the WTRU&#39;s DRX state via implicit DRX transition rules and either sends the anticipated command to the WTRU or wait for the WTRU to return to its previous DRX state with the specified “resume period”. 
         [0042]    By way of another example, the WTRU, while in LTE_ACTIVE mode, may use configured handover measurements. Certain measurement event reports may indicate that a handover (HO) command is imminent for intra-frequency, inter-frequency or an inter-radio access technology (RAT) handover. Depending on handover measurement events, certain other measurement events may act as triggers for DRX transition control.  FIG. 7  is a flow diagram of a method of implicit DRX signaling  700  in accordance with an alternative embodiment. At step  702 , the WTRU is in normal DRX level  3  state. At step  704 , the WTRU determines that a serving cell measurement is below a threshold. The WTRU may then determine that an intra-frequency measurement is high  706 , meaning that an intra-frequency neighbor is measuring as the best cell. Alternatively, the WTRU may determine that an inter-frequency band measures to be the best  708 . As another alternative, the WTRU may determine that a non-LTE system measures the best  710 . 
         [0043]    At step  712 , the WTRU, due to the measurements, may anticipate a handover command. At step  714 , the WTRU reports the measurement event. This may invoke, at step  716 , an implicit DRX transition trigger that causes the WTRU to go to a Level- 1  DRX state in order to receive the possible handover command from the network. At step  718 , the WTRU receives the handover command. At step  720 , the WTRU transitions back to its original DRX state. 
         [0044]      FIG. 8  is a flow diagram of a method of implicit DRX cycle signaling  800  in accordance with yet another embodiment. At step  802 , the WTRU is level- 1  mode. At step  804 , the WTRU begins to monitor a Level  1 /Level  2  control channel to intercept anticipated downlink commands. At step  806 , the WTRU determines if an anticipated network command is received. If received, at step  808 , the WTRU will follow the command to end the DRX mode or will receive instruction on the next DRX activity with the command. If the command is not received, at step  810 , the WTRU transitions back to its original DRX state before entering the Level- 1  state. 
         [0045]    Although the features and elements are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0046]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0047]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) module.