Patent Description:
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.

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.

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.

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.

Relevant prior art disclosures in this technical field are: "<NPL>;<CIT> and <CIT>.

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.

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:.

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.

<FIG> shows a wireless communication system <NUM> in accordance with one embodiment. The system <NUM> includes a plurality of WTRUs <NUM> and an eNB <NUM>. As shown in <FIG>, the WTRUs <NUM> are in communication with the eNB <NUM>. Although three WTRUs <NUM> and one eNB <NUM> are shown in <FIG>, it should be noted that any combination of wireless and wired devices may be included in the wireless communication system <NUM>. The eNB <NUM> and the WTRUs <NUM> may communicate while in DRX mode and may have coordinated DRX cycles.

<FIG> is a functional block diagram <NUM> of a WTRU <NUM> and the eNB <NUM> of the wireless communication system <NUM> of <FIG>. As shown in <FIG>, the WTRU <NUM> is in communication with the eNB <NUM>. Both WTRU <NUM> and eNB <NUM> may operate in DRX mode.

In addition to the components that may be found in a typical WTRU, the WTRU <NUM> includes a processor <NUM>, a receiver <NUM>, a transmitter <NUM>, and an antenna <NUM>. The processor <NUM> may be configured to adjust DRX cycle length as necessary. The receiver <NUM> and the transmitter <NUM> are in communication with the processor <NUM>. The antenna <NUM> is in communication with both the receiver <NUM> and the transmitter <NUM> to facilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical eNB <NUM>, the eNB <NUM> includes a processor <NUM>, a receiver <NUM>, a transmitter <NUM>, and an antenna <NUM>. The processor <NUM> is configured to communicate with the receiver <NUM> and transmitter <NUM> to adjust DRX cycles as necessary. The receiver <NUM> and the transmitter <NUM> are in communication with the processor <NUM>. The antenna <NUM> is in communication with both the receiver <NUM> and the transmitter <NUM> to facilitate the transmission and reception of wireless data.

In order to improve battery life, but not limit the eNB <NUM> and WTRU <NUM> 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 <NUM> is in a LTE_ACTIVE DRX state.

Approximately half of WTRU <NUM> to eNB <NUM> interaction involves WTRU <NUM> requests and reports and eNB <NUM> responses while the WTRU <NUM> is in LTE_ACTIVE DRX mode. When the WTRU <NUM> measures a particular scenario, measurement events may be reported to the eNB <NUM>, and the eNB <NUM> may respond to the situation by commanding the WTRU <NUM> 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 <NUM> and eNB <NUM> system performance during LTE_ACTIVE DRX mode may suffer. However, certain measurement events may make good candidates for the anticipated network downlink commands.

<FIG> shows an implicit DRX transition state machine <NUM> in accordance with one embodiment. The state machine <NUM>, as well as associated transition mechanisms and parameter values, may be configured by the eNB (<NUM> of <FIG>). The state machine <NUM> may have a life span, also configured by the eNB <NUM>. Each state may be applied at the WTRU (<NUM> of <FIG>) and at the eNB <NUM>, 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 <NUM> and the eNB <NUM> operations.

The DRX cycle length transition rules may be based on WTRU <NUM> and eNB <NUM> experiences. Given a certain elapsed time, or a given set of measurement values, the WTRU <NUM> and the eNB <NUM> 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 <NUM> for a WTRU <NUM>/eNB <NUM> system that permits implicit transition operation and consistent DRX actions for both the WTRU <NUM> and the eNB <NUM>. The eNB <NUM> can prescribe DRX states for service and mobility conditions with the potential for continuous improvement and learned traffic patterns upon every invocation.

<FIG> shows <NUM> defined DRX levels, <NUM>, <NUM>, <NUM> and an undefined DRX level <NUM>. In DRX level <NUM><NUM>, the WTRU <NUM> is operating in a normal DRX cycle. The actual length of the normal state may be defined by the eNB <NUM>. DRX level <NUM><NUM> is a shorter cycle length than DRX level <NUM><NUM>, and is associated with more frequent activity than normal. The eNB <NUM> may also define the cycle length for DRX level <NUM><NUM>, 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 <NUM> may return to DRX level <NUM><NUM> operation, unless the WTRU <NUM> is commanded to do otherwise.

DRX level <NUM> has the shortest DRX cycle length, and may be used by a WTRU <NUM> or eNB <NUM> to handle predicted immediate downlink commands and when uplink traffic patterns are recognized by the WTRU <NUM> and the eNB <NUM> as requiring immediate downlink action, such as during a handover event, for example.

A DRX level n <NUM> may be configured with longer DRX cycles than that for the DRX Level <NUM><NUM>. The eNB <NUM> 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.

For a WTRU <NUM> at DRX level <NUM><NUM>, a timer or counter trigger may be defined to trigger a transition to DRX Level <NUM><NUM> if the eNB <NUM> determines that the WTRU <NUM> 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 <NUM> from DRX level-<NUM><NUM> to DRX Level <NUM> 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.

If the WTRU <NUM> in DRX Level <NUM><NUM> state receives a RB Reconfiguration command, the current DRX Level <NUM> state is over. If the WTRU <NUM> at DRX Level <NUM> state <NUM> 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 <NUM> at a particular time while the WTRU <NUM> 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.

The eNB <NUM> may configures 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 <NUM> from time to time and loaded to a particular WTRU <NUM> via higher layer signaling before an intended DRX mode period.

Transitions between different states may be signaled in an information element. An example of a skeleton for signaling an implicit DRX cycle transition if shown in Table <NUM>. As shown in Table <NUM>, the Implicit DRX Transition List is mandatory and is limited to a value indicating a maximum number of DRX states.

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 <NUM> at start-up.

To aid with easier DRX cycle length transition and maintain DRX cycle length synchronization between the WTRU <NUM> and the eNB <NUM>, 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:
<MAT> where n = <NUM>, <NUM>, <NUM>. such that the resulting DRX-cycle-len does not exceed a maximum DRX cycle length. The shortest DRX cycle length possible occurs when n=<NUM>, and is a fraction of a longer DRX cycle length.

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 <NUM> and eNB <NUM>. When DRX periods are defined as multiples of each other, and when DRX periods become mismatched between the WTRU <NUM> and the eNB <NUM>, 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.

Typically, a WTRU <NUM> in DRX Level <NUM><NUM> 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-<NUM> DRX Cycle Length; where Level-k cycle length is the length of the DRX cycle before the WTRU <NUM> enters DRX Level <NUM>. Alternatively, the network may configure n for the "resume method".

Transitions from state to state may be initiated by a trigger. Table <NUM> 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 <NUM>. The CHOICE mechanism allows the network to configure the WTRU <NUM> 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 <NUM>. 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 <NUM> may remain in an elevated state without receiving a command to move back to normal state.

<FIG> is a signal flow diagram for implicit DRX transition <NUM> in accordance with one embodiment. A WTRU <NUM> may receive an RRC message or an IE <NUM> from the E-UTRAN <NUM> that triggers the WTRU <NUM> to enter DRX mode. The WTRU <NUM> may enter DRX mode <NUM> at a default level which may be a normal cycle length DRX level <NUM> (<NUM> of <FIG>). Both the WTRU <NUM> and the E-UTRAN <NUM> enter DRX mode (<NUM>, <NUM> respectively). The WTRU <NUM> may receive another RRC message or IE <NUM> that triggers the WTRU <NUM> to enter a faster DRX cycle mode (DRX level <NUM> of <FIG>). The WTRU <NUM> and the E-UTRAN <NUM> enter the DRX level <NUM> (<NUM>, <NUM> respectively). A WTRU timer <NUM>, 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 <NUM> triggers the WTRU <NUM> and the E-UTRAN <NUM> to return to normal DRX level. The WTRU <NUM> returns <NUM> to DRX level-<NUM><NUM> at the same time that the E-UTRAN <NUM> returns <NUM> to DRX level-<NUM><NUM>.

<FIG> is a flow diagram of a method of implicit signaling <NUM> in accordance with one embodiment. At step <NUM> the WTRU is in normal operating mode, or Level-<NUM>. At step <NUM>, 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 <NUM>, the WTRU remains in normal state. If the WTRU detects a time out signal or a trigger at step <NUM>, at step <NUM>, the WTRU determines if it should move to DRX Level <NUM> or DRX level <NUM>. If the WTRU determines that the trigger is a level-<NUM> trigger, at step <NUM> the WTRU moves to DRX Level <NUM>. At step <NUM>, the WTRU determines that the resume period has ended, and returns to DRX level-<NUM>. If, however, the WTRU, at step <NUM>, determines that it received a level <NUM> trigger, at step <NUM>, the WTRU goes into a DRX level <NUM>. At step, <NUM>, the WTRU determines if it has received a Radio Bearer Reconfiguration message. If not, the WTRU, at step <NUM>, waits for the resume period to end and returns to normal operation at step <NUM>. If, however, at step <NUM>, the WTRU receives a radio bearer reconfigure message, at step <NUM>, the WTRU returns to normal DRX cycle operation.

<FIG> is a flow diagram of an implicit DRX method <NUM> in accordance with another embodiment. At step <NUM>, the WTRU is in normal or DRX Level-<NUM> mode. At step <NUM>, the WTRU conducts a traffic volume measurement. At step <NUM>, the WTRU compares the traffic volume measurement with a threshold. It if the volume is below the threshold, at step <NUM>, the WTRU takes no action and remains in DRX Level-<NUM> mode. However, if, at step <NUM>, the WTRU determines that the traffic is above a threshold, at step <NUM>, the WTRU changes mode to a shorter DRX cycle. Based on the traffic, the new DRX mode may be DRX level-<NUM> or DRX level-<NUM>. At step <NUM>, the WTRU determines if a command or message has been received. If yes, at step <NUM>, the WTRU returns to Level-<NUM> mode. If not, the WTRU, at step <NUM> the WTRU waits the resume period before returning to level-<NUM> mode at step <NUM>. 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.

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 <NUM>, <NUM> of <FIG>, for example) in order to receive the network command. The network, when receiving the predetermined measurement event, may determine the WTRU'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".

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> is a flow diagram of a method of implicit DRX signaling <NUM> in accordance with an alternative embodiment. At step <NUM>, the WTRU is in normal DRX level <NUM> state. At step <NUM>, the WTRU determines that a serving cell measurement is below a threshold. The WTRU may then determine that an intra-frequency measurement is high <NUM>, 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 <NUM>. As another alternative, the WTRU may determine that a non-LTE system measures the best <NUM>.

At step <NUM>, the WTRU, due to the measurements, may anticipate a handover command. At step <NUM>, the WTRU reports the measurement event. This may invoke, at step <NUM>, an implicit DRX transition trigger that causes the WTRU to go to a Level-<NUM> DRX state in order to receive the possible handover command from the network. At step <NUM>, the WTRU receives the handover command. At step <NUM>, the WTRU transitions back to its original DRX state.

<FIG> is a flow diagram of a method of implicit DRX cycle signaling <NUM> in accordance with yet another embodiment. At step <NUM>, the WTRU is level-<NUM> mode. At step <NUM>, the WTRU begins to monitor a Level <NUM>/Level <NUM> control channel to intercept anticipated downlink commands. At step <NUM>, the WTRU determines if an anticipated network command is received. If received, at step <NUM>, 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 <NUM>, the WTRU transitions back to its original DRX state before entering the Level-<NUM> state.

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).

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.

Claim 1:
A method implemented by a wireless transmit/receive unit, WTRU, (<NUM>) the method comprising:
receiving discontinuous reception, DRX, configuration parameters, the DRX configuration parameters comprising an indication of a first DRX cycle length, an indication of a second DRX cycle length, an indication of a value for a first WTRU timer, and an indication of a value for a second WTRU timer;
operating the WTRU at the first DRX cycle length;
using the first WTRU timer to trigger a transition to the second DRX cycle length;
setting the second WTRU timer based on beginning DRX operation at the second DRX cycle length;
operating the WTRU at the second DRX cycle length;
determining that the second WTRU timer has expired; and
operating the WTRU at the first DRX cycle length based on determining that the second WTRU timer has expired, wherein the first DRX cycle length is a multiple of the second DRX cycle length.