BATTERY CONSUMPTION CONTROL METHOD OF USER EQUIPMENT IN MOBILE COMMUNICATION SYSTEM

Abstract

A method and apparatus for controlling battery consumption of the User Equipment (UE) equipped with a feature such as Carrier Aggregation is provided. The battery consumption control method of a terminal operating in Semi-Persistent Scheduling (SPS) mode includes determining, when Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement (ACK) is received, whether a suspension restriction condition is fulfilled, and stopping, when the suspension restriction condition is fulfilled, suspension to flush an HARQ buffer and not monitor a retransmission grant. The battery consumption control method may improve Discontinuous Reception (DRX) efficiency and reduce an unnecessary waste of battery power.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of a U.S. Provisional application filed on Apr. 5, 2011 in the U.S. Patent and Trademark Office and assigned Ser. No. 61/471,872, and under 35 U.S.C. §119(a) of a Korean patent application filed on Apr. 5, 2012 in the Korean Intellectual Property Office and assigned Ser. No. 10-2012-0035570, the entire disclosure of each of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery control method and apparatus of a User Equipment (UE). More particularly, the present invention relates to a method and apparatus for controlling battery consumption of the UE equipped with a feature, such as Carrier Aggregation (CA), so as to improve functionality.

2. Description of the Related Art

Various research is being conducted to efficiently support Voice over Internet Protocol (VoIP) in recent mobile communication standards such as Long Term Evolution (LTE). Semi-Persistent Scheduling (SPS) is one of the representative techniques introduced to support VoIP. When a certain resource is allocated semi-persistently, a User Equipment (UE) transmits packets having a predetermined size at a predetermined Modulation and Coding Scheme (MCS) level on the semi-persistent transmission resource periodically. At this time, owing to the application of synchronous Hybrid Automatic Repeat Request (HARQ), the UE performs, if a HARQ Negative Acknowledgement (NACK) is received, retransmission of a packet using the same transmission resource at a time after the elapse of HARQ Round Trip Time (RTT).

The evolved Node B (eNB) may allocate a separate transmission resource for the retransmission. Such a HARQ retransmission performed using the resource different from the previously used resource is referred to as adaptive retransmission. The adaptive retransmission is indicated by the uplink grant message transmitted on a Physical Downlink Control Channel (PDCCH). Meanwhile, VoIP can operate in Discontinuous Reception (DRX) mode. At this time, the UE monitors the PDCCH every time the uplink grant message for packet retransmission can be received. Although it will be described later, this gives an effect of enforcing the UE to monitor the PDCCH at every 4 msec, resulting in a degradation of DRX efficiency and unnecessary battery consumption.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a battery control method and apparatus that is capable of improving DRX performance and avoiding an unnecessary waste of battery power by skipping active time when a specific condition is fulfilled.

In accordance with an aspect of the present invention, a method for controlling battery consumption of a terminal operating in Semi-Persistent Scheduling (SPS) mode is provided. The method includes determining, when Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement (ACK) is received, whether a suspension restriction condition is fulfilled, and stopping, when the suspension restriction condition is fulfilled, suspension to flush an HARQ buffer and not monitor a retransmission grant.

In accordance with another aspect of the present invention, a method for controlling battery consumption of a terminal in which a base station performs transmission in SPS mode is provided. The method includes determining, at the base station, whether a maximum number of transmissions is reached, determining, when the maximum number of transmissions is reached, whether the terminal fulfills a suspension restriction condition, and stopping, when the terminal fulfills the suspension restriction condition, suspension to flush a HARQ buffer and not transmit a retransmission grant.

In accordance with another aspect of the present invention, a terminal for supporting transmission in SPS mode to improve battery conservation is provided. The terminal includes a transceiver which receives data and control signals through a downlink channel of a serving cell and transmits data and control signals through an uplink channel, and a controller which controls to determine, when a HARQ ACK is received, whether a suspension restriction condition is fulfilled and stopping, when the suspension restriction condition is fulfilled, suspension to flush an HARQ buffer and not monitor a retransmission grant.

In accordance with still another aspect of the present invention, a base station for performing transmission in SPS mode to improve battery conservation of a terminal is provided. The base station includes a transceiver which transmits data and control signals on a downlink carrier and receives data and control signals on an uplink carrier, and a controller which determines whether a maximum number of transmissions is reached, determines, when the maximum number of transmissions is reached, whether the terminal fulfills a suspension restriction condition, and controls stopping, when the terminal fulfills the suspension restriction condition, suspension to flush a HARQ buffer and not transmit a retransmission grant.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an architecture of a Long Term Evolution (LTE) system according to an exemplary embodiment of the present invention;

FIG. 2 is a diagram illustrating a protocol stack of an LTE system according to an exemplary embodiment of the present invention;

FIG. 3 is a diagram illustrating an exemplary situation of carrier aggregation in an LTE system according to an exemplary embodiment of the present invention;

FIG. 4 is a diagram illustrating uplink transmission in view of time domain in an LTE system according to an exemplary embodiment of the present invention;

FIG. 5 is a diagram illustrating a principle of a battery power saving method of a User Equipment (UE) according to an exemplary embodiment of the present invention;

FIG. 6 is a flowchart illustrating a battery power control method of a UE according to an exemplary embodiment of the present invention;

FIG. 7 is a flowchart illustrating a battery consumption control method of a UE according to another exemplary embodiment of the present invention;

FIG. 8 is a flowchart illustrating an evolved Node B (eNB) procedure of a battery consumption control procedure according to an exemplary embodiment of the present invention;

FIG. 9 is a diagram illustrating a principle of a batter consumption control method of a UE according to an exemplary embodiment of the present invention;

FIG. 10 is a flowchart illustrating a battery consumption control method of a UE according to another exemplary embodiment of the present invention;

FIG. 11 is a block diagram illustrating a configuration a UE according to an exemplary embodiment of the present invention; and

FIG. 12 is a block diagram illustrating a configuration of an eNB according to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, description of well-known functions and constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.

FIG. 1 is a diagram illustrating an architecture of a Long Term Evolution (LTE) system according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a radio access network of a mobile communication system includes evolved Node Bs (eNBs) 105, 110, 115, and 120, a Mobility Management Entity (MME) 125, and a Serving-Gateway (S-GW) 130. User Equipment (UE) 135 connects to an external network via eNBs 105, 110, 115, and 120 and the S-GW 130.

In FIG. 1, the eNBs 105, 110, 115, and 120 correspond to legacy node Bs of the Universal Mobile Communications System (UMTS). The eNBs 105, 110, 115, and 120 allow the UE to establish a radio link and are responsible for more complicated functions than those performed by the legacy node B. In the LTE system, all the user traffic including real time services such as Voice over Internet Protocol (VoIP) are provided through a shared channel and thus there is a need of a device which is located in the eNB to schedule data based on the state information such as UE buffer conditions, power headroom state, and channel state. Typically, one eNB controls a plurality of cells. In order to secure the data rate of up to 100 Mbps, the LTE system adopts Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology. Also, the LTE system adopts Adaptive Modulation and Coding (AMC) to determine the modulation scheme and channel coding rate in adaptation to the channel condition of the UE. The S-GW 130 is an entity to provide data bearers so as to establish and release data bearers under the control of the MME 125. MME 125 is responsible for various control functions and is connected to a plurality of eNBs 105, 110, 115, and 120.

FIG. 2 is a diagram illustrating a protocol stack of an LTE system according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the protocol stack of the LTE system, as employed at a UE and an eNB, includes a Packet Data Convergence Protocol (PDCP) layer 205 and 240, a Radio Link Control (RLC) layer 210 and 235, a Medium Access Control (MAC) layer 215 and 230, and a Physical (PHY) layer 220 and 225. The PDCP layer 205 and 240 is responsible for Internet Protocol (IP) header compression/decompression, and the RLC layer 210 and 235 is responsible for segmenting the PDCP Protocol Data Unit (PDU) into segments in an appropriate size for Automatic Repeat Request (ARQ) operation. The MAC layer 215 and 230 is responsible for establishing connection to a plurality of RLC entities so as to multiplex the RLC PDUs into MAC PDUs and demultiplex the MAC PDUs into RLC PDUs. The PHY layer 220 and 225 performs channel coding on the MAC PDU and modulates the MAC PDU into OFDM symbols to transmit over a radio channel or performs demodulating and channel-decoding on the received OFDM symbols and delivers the decoded data to a higher layer.

The uplink transmission resource is essentially a frequency/time resource. In an LTE mobile communication system, the unit transmission resource is defined by a predetermined width of a band for a predetermined length of a timeslot.

FIG. 3 is a diagram illustrating an uplink transmission scheme in an LTE system according to an exemplary embodiment of the present invention.

Referring to FIG. 3, a square 305 is a unit of transmission resource and is referred to as resource block. The resource block has a length of 1 msec and may be referred to as a subframe or a Transmission Time Interval (TTI).

The eNB scheduler allocates an uplink transmission resource to the UE through a control channel referred to as Physical Downlink Control Channel (PDCCH), and the allocated resource is used for transmission and retransmission of the same packet at an interval of a Hybrid Automatic Repeat reQuest (HARQ) Round Trip Time (RTT) 310 on the time axis.

The UE performs initial transmission of uplink data on the allocated transmission resource 320, checks the HARQ feedback information received at a certain timing, and determines whether to perform HARQ retransmission. If it is determined that the HARQ feedback information is an HARQ Negative Acknowledgement (NACK) 345, the UE retransmits the data using the same resource at the next HARQ retransmission timing 325. Such data retransmission is repeated until an HARQ ACK is received. That is, if it is determined that the HARQ feedback information is an HARQ NACK as denoted by reference number 350, the UE retransmits the data using the same transmission resource 330 at the next HARQ retransmission timing.

Afterward, if an HARQ ACK 355 is received, the corresponding uplink HARQ process ends. As described above, if the HARQ NACK is received in the synchronous HARQ process, use of the uplink transmission resource is automatically permitted. However, since it is not preferred to retransmit the same data over a certain number of times in terms of transmission efficiency, the maximum number of retransmissions of the data is restricted. For example, if the maximum number of retransmissions is set to 3, the UE determines that the transmission resource has been released after three times of retransmission even though an HARQ ACK has not been received. That is, if the HARQ NACK is received repeatedly, the UE performs retransmission on the transmission resources (e.g., 325, 330, and 335) up to the maximum number of retransmissions and then regards that the resource (e.g., 340) as no longer valid so as to discard the data from the buffer.

The initial retransmissions are performed in the same HARQ process. The HARQ process includes a soft buffer for buffering the HARQ data such that the transmission part buffers the data to be transmitted and the reception part buffers the received data. If the data retransmitted in a certain HARQ process is received, the reception part performs soft combining on the buffered data and retransmission data received in the HARQ process.

An HARQ process is assigned an identifier. In the synchronous HARQ, the HARQ processor identifier corresponds to the data transmission/reception time one by one, and the initial transmission and retransmission is performed in the HARQ process identified by the same identifier. For example, when transmitting data on the allocated transmission resource as denoted by reference number 315, the transmission timing of the data transmitted on the transmission resource 320 is identified by a specific HARQ identifier, e.g., process 4, and the retransmission of the data is performed at the time points 360, 365, 370, and 375 in the HARQ process 4. If an HARQ ACK is received in the normal HARQ process, it is determined that the data has been transmitted successfully and a higher layer is notified of the completion of the transmission.

The uplink transmission is initiated at the time when the UE is allocated the uplink transmission resource from the eNB and acquires the information on the packet size and Modulation and Coding Scheme (MCS) information. This information is received in a control message referred to as an uplink grant which is transmitted in a predetermined format through a physical channel, i.e., a Physical Downlink Control Channel (PDCCH). The uplink grant can be used for indicating initial transmission or adaptive retransmission and has a field for discriminating between the initial transmission and adaptive retransmission.

FIG. 4 is a diagram illustrating uplink transmission in view of time domain in an LTE system according to an exemplary embodiment of the present invention.

Referring to FIG. 4, if the uplink grant indicating the initial transmission for a certain HARQ process is received at a certain timing 405, the UE performs initial transmission using the transmission resource allocated in the TTI arriving after 4 TTIs since the TTI at which the initial transmission uplink grant message has been received at timing 410. For example, if the reception timing of the initial transmission grant message is the y^th TTI, the actual initial transmission timing is (y+4)^th TTI. The UE may then perform HARQ retransmission of the MAC PDU at every 8^th TTI. The HARQ retransmission is permitted until the number of retransmissions reaches the maximum number of retransmissions. In an exemplary embodiment of the present invention the TTIs at which the UE can perform the HARQ transmission or retransmission in a certain HARQ process is referred to as a transmission occasion. Assuming that the maximum number of transmissions is set to 4, reference numbers 410, 420, 430, and 440 denote transmission occasions. In a case where a NACK has been received at a previous feedback occasion or a grant message indicating adaptive retransmission has been received at a retransmission grant occasion, the UE performs uplink transmission at the transmission occasion and, otherwise, skips uplink transmission even at the transmission occasion.

The feedback occasion is the time point arriving after 4 TTIs since the uplink transmission occasion. In FIG. 4, the time points 415, 425, 435, and 445 can be the feedback occasions or not depending on whether the uplink transmission has been performed at the transmission occasions. The retransmission grant occasion is the timings available for receiving a grant message indicating adaptive retransmission and corresponds to the TTIs arriving at an interval of a multiple of 8 from the reception timing of the initial transmission between the initial transmission grant reception timing 405 and the final transmission occasion 440. That is, reference number 415, 425, and 435 denote the retransmission grant occasion. It is noted that usually the retransmission grant occasion and the feedback occasion are identical with each other. This is because the feedback occasion follows a certain uplink transmission at an interval of 4 TTIs and the retransmission grant occasion precedes a certain uplink transmission at an interval of 4 TTIs.

As shown in FIG. 4, if the initial transmission grant message is received, the UE determines the transmission occasion and retransmission grant occasion as follows. In the following equation, y denotes the initial transmission grant message reception occasion, and n denotes the maximum number of transmissions.

Transmission occasion=(y+4)^th TTI, (y+4+1×8)^th TTI, (Y+4+2×8)^th TTI, . . . , (y+4+(n−1)×8)^th TTI

Retransmission grant occasion=(y+1×8)^th TTI, (y+2×8)^th TTI, . . . , (y+(n−1)×8)^th TTI

The UE increments the number of transmissions by 1 whenever the transmission occasion calculated by the above equation arrives, regardless of whether the transmission is actually performed, and decodes the PDCCH at every retransmission grant occasion to receive the grant message indicating adaptive retransmission.

Although there is no need to receive the uplink grant indicating an initial transmission in the transmission using the semi-persistent resource, the uplink transmission operation is identical with the normal uplink transmission. That is, after transmitting the packet on the semi-persistent resource at a certain occasion, the UE monitors the PDCCH at every retransmission grant occasion until the final transmission occasion of the packet passes.

The normal period of the semi-persistent resource for VoIP is 20 msec, and the maximum number of transmissions is about 5 or 6. By taking notice that the packet transmission succeeds typically after 2 or 3 attempts, although it may change depending on the UE's channel condition, it is inefficient in terms of battery consumption to monitor the PDCCH at every retransmission grant occasion until the last transmission. More particularly, for the battery power-constrained UE, the battery power consumption is more significant than the gain obtained with the adaptive retransmission. In order to reduce the unnecessary power consumption, a method and apparatus are proposed for restricting or disabling the adaptive retransmission of the battery power constrained UE, e.g., a UE operating in a Discontinuous Reception (DRX) mode, according to an exemplary embodiment of the present invention.

First Exemplary Embodiment

For convenience in explanation, the terms related to DRX are explained as follows.

In the following description, Active Time denotes a period determined for receiving the PDCCH in the DRX mode. In order for the UE to receive the adaptive retransmission grant, the time for receiving the PDCCH is included in the Active time. The active time can be defined in more detail as follows:

• • at least one of an onDurationTimer, a drx-InactivityTimer, a drx-RetransmissionTimer, and a mac-ContentionResolutionTimer is running (first type active time);
  • Scheduling Request is sent on the PUCCH and is pending (second type active time);
  • uplink grant for a pending HARQ retransmission can occur and there is data in the corresponding HARQ buffer (third type active time);
  • PDCCH indicating a new transmission addressed to the Cell-Radio Network Temporary Identifier (C-RNTI) of the UE has not been received after successful reception of a Random Access Response for the preamble not selected by the UE (fourth type active time).

For convenience in explanation, the first to last cases are referred to as the first type active time, the second type active time, the third type active time, and fourth type active time, respectively. Exemplary embodiments of the present invention are focused on the adjustment of the third type active time to improve battery saving performance of the UE. The onDurationTimer, drx-InactivityTimer, and drx-RetransmissionTimer are the times set by the eNB to trigger a UE's monitoring on the PDCCH when predetermined conditions are fulfilled.

In the following description, the term ‘Non-Active Time’ denotes a time duration for which PDCCH reception is idle in the DRX mode. That is, the non-active time is the sleep time in the entire period with the exception of the active time.

Typically, the UE operating in the DRX mode turns off the power to the transceiver at all times except for the active time so as to minimize power consumption. In a case where the UE is receiving a VoIP service with Semi-Persistent Scheduling (SPS) in the DRX mode, if the initial uplink transmission takes places every 20 msecs and if the UE transitions to the active time at each retransmission occasion up to the last transmission occasion for receiving PDCCH, this causes a waste of battery power for receiving the adaptive retransmission grant transmitted at a low incidence frequency.

In an exemplary embodiment of the present invention, the UE transitions to the active time at an interval of a predetermined number of retransmission grant occasions after receipt of an HARQ ACK so as to reduce the total active time duration, resulting in an improvement of DRX efficiency. The number of retransmission grant occasions may be set to 0, and the UE may apply this operation rule only when the active time is skipped by another condition, e.g., first, second, or fourth conditions.

FIG. 5 is a diagram illustrating a principle of a battery power saving method of a UE according to an exemplary embodiment of the present invention.

Referring to FIG. 5, for a certain reason, e.g., expiry of the onDurationTimer or the drx-InactivityTimer at subframe 520 and no activation of another drx-related timer, the UE operates in the active time up to the subframe 520.

If an HARQ ACK corresponding to a certain uplink transmission is received at subframe 505, the subframes 510 and 515 become the retransmission grant occasions. This means that the UE monitors the PDCCH to determine whether to perform adaptive retransmission at the subframes.

In the present exemplary embodiment, in spite of the retransmission grant occasion, if a predetermined condition is fulfilled, the UE skips transitioning to the active time, resulting in a reduction of battery consumption.

The active time skip condition can include the following three conditions:

[Condition 1]

If a DRX and UpLink (UL) grant are configured for the UE, if the configured UL resource is activated, and if the Transport Block (TB) is transmitted over the configured UL grant, then it is not an Active Time when an uplink grant for the pending HARQ retransmission can occur and the TB is stored in the corresponding HARQ buffer.

If the UL grant is configured in condition 1, this means that the SPS transmission resource is allocated to the UE such that the UE performs uplink transmission on the transmission resource. The TB means a layer 1 packet transmitted/received on the radio transmission resource of LTE.

If DRX is configured, this means that the UE has received a DRX-related parameter, e.g., at least one of the onDurationTimer, the drx-InactivityTimer, and the drx-RetransmissionTimer, and performs DRX using the parameter.

Accordingly, condition 1 means that, whether to regard the retransmission grant occasion for a certain transport block as an active time, is determined depending on whether the UE is in the DRX mode at the corresponding occasion and the transport block is transmitted over the configured uplink grant.

Condition 1 can be replaced by condition 2 as follows.

[Condition 2]

If DRX is configured and it is not an Active Time when an HARQ ACK is received for a TB and the TB has been transmitted in the configured UL resource, then it is not the Active Time when an uplink grant for the pending HARQ retransmission can occur and the TB is stored in the corresponding HARQ buffer.

In condition 2, it is also considered whether the HARQ ACK reception time is in the active time. By taking into account that the respective type of active times, with the exception of the third type of active time, are configured with contiguous subframes, if the HARQ ACK occasion is in the active time, the retransmission grant occasion is likely to be one of the onDurationTimer and the drx-InactivityTimer and, otherwise, if the HARQ ACK occasion is out of the active time, the retransmission grant occasion is also likely to be out of the active time.

As shown in FIG. 5, since the HARQ ACK occasion 505 is in the active time, the UE regards that the retransmission grant occasion is also in the active time. If the HARQ ACK is received at a timing out of the active time, the related-retransmission grant occasions are regarded as out of the active time. That is, if the retransmission grant occasion is out of the active time due to other reasons, the UE stops monitoring the PDCCH.

[Condition 3]

If DRX is configured, if it is not the Active time due to other reasons like the onDurationTimer running, the InactivityTimer running, the drxretransmissionTimer running, etc., at retransmission grant reception occasion, and if a TB has been transmitted in the configured UL resource, then it is not the Active Time when an uplink grant for the pending HARQ retransmission can occur and the TB is stored in the corresponding HARQ buffer.

In condition 3, the UE checks whether it is the active time (due to other reasons except for the pending HARQ retransmission) at a retransmission grant reception occasion but not at a HARQ feedback ACK reception occasion and determines whether to monitor the PDCCH at the retransmission grant occasion.

As shown in FIG. 5, since the onDurationTimer is running at the retransmission grant occasion 510 in the active time, there is no reason to skip receipt of the retransmission grant at the corresponding time point. Accordingly, a suspension operation is not disabled. For reference, the suspension operation is to retain the data until the number of transmissions reaches the maximum value even after the receipt of the HARQ ACK while monitoring to detect the receipt of the retransmission grant at every retransmission grant occasion for preparing adaptive retransmission.

Meanwhile, the timers for controlling the active time such as the onDurationTimer and the inactivityTimer are not running. That is, the UE has no reason to be in the active time with the exception of a pending HARQ retransmission and remains in a sleep time at the retransmission grant occasion 515. That is, the UE does not wake up to monitor the retransmission grant at the retransmission grant occasion. At this time, the UE may discard the transport block stored in the corresponding HARQ buffer to protect an abnormal retransmission afterward.

FIG. 6 is a flowchart illustrating a battery power control method of a UE according to an exemplary embodiment of the present invention.

The UE which retains the data of which number of retransmission times does not yet reach the maximum value in a certain HARQ process is in idle state at step 605. Afterward, the UE determines whether a condition used to determine whether to apply suspension is fulfilled at step 610. The configured condition may be at least one of the above described [condition 1], [condition 2], and [condition 3].

If it is determined that the condition is not fulfilled, the UE performs the suspension operation at step 615. That is, the UE monitors the PDCCH at the retransmission grant occasion. If it is determined that the condition is fulfilled, the UE stops the suspension operation for the HARQ process at step 620. That is, the UE stops monitoring the PDCCH if it is not an active time due to other reasons at the retransmission grant occasion. Next, the UE discards the data stored in the buffer of the HARQ process to avoid unnecessary retransmission afterward at step 625.

The above procedure can be modified slightly according to the condition applied. In an exemplary case of using condition 3, the UE can perform the operation of step 610 at a certain time prior to the retransmission grant occasion and, if the condition is fulfilled, the procedure proceeds to steps 620 and 625.

Also, if a predetermined timer expires, e.g., the onDurationTimer or the drx-InactivityTimer expires, the UE can discard the data stored in the HARQ buffer for a pending HARQ retransmission at a corresponding timing so as to stop the suspension operation for multiple HARQ buffers at a time. Also, it is possible to modify the procedure in such a way that predetermined timers, e.g., at least one of the onDurationTimer, the drx-InactivityTimer, the drx-retransmissionTimer, and the mac-ContentionResolutionTimer are categorized into a DRX timer set 1 such that, when the DRX timer set 1 expires, the UE determines whether there is a running timer among the timers except for the expired timers that belong to the DRX timer set 1, and determines, if the is no timer running, whether it is in the second type active time or the fourth type active time. If all the test results are true at the corresponding timing, the UE stores the data for the pending HARQ retransmission at the corresponding timing and discards data in all of the HARQ buffers so as to stop the suspension operation for the multiple HARQ buffers at a time.

FIG. 7 is a flowchart illustrating a battery consumption control method of a UE according to another exemplary embodiment of the present invention.

The UE is in a state where an UL grant is available for a current TTI at step 705. That is, the UE receives an uplink grant in the current TTI or configures an uplink grant for the current TTI with the UE Identifier. Next, the UE performs new transmission or retransmission according to a New Data Indicator (NDI) and waits for HARQ feedback at step 710. For this purpose, the UE delivers HARQ information (e.g., transport block size, Redundancy Version (RV), etc.) of the uplink grant to an HARQ entity and determines whether the NDI has been toggled in the corresponding HARQ process. NDI is a flag for discriminating between new transmission and retransmission. If NDI is transmitted and if the NDI has been toggled as compared to the previous value or if the uplink grant is configured for this TTI such that the NDI is regarded as toggled, the UE initialize the new transmission for the corresponding HARQ process. If the NDI has been toggled or regarded as toggled, the HARQ entity generates a new transmission according to the HARQ information for this HARQ process. If the NDI is not toggled, the HARQ entity generates adaptive retransmission according to the HARQ information for this HARQ process. Afterward, the UE waits to receive HARQ feedback and/or an uplink grant for the current HARQ process.

If an HARQ feedback is received, the UE determines whether the HARQ feedback is received along or together with an UL grant at step 715. If it is determined that the HARQ feedback is received together with the uplink grant at step 715, the UE ignores the HARQ feedback (because the uplink grant protected by Cyclic Redundancy Check (CRC) is more reliable information) at step 720 and then returns to step 705 to operate according to the receipt of uplink grant.

If it is determined that the HARQ feedback is received alone at step 715, the procedure goes to step 725 to determine whether the HARQ feedback is an ACK or a NACK. If the HARQ feedback is a NACK, the UE performs non-adaptive retransmission at step 730 and waits for HARQ feedback and/or an uplink grant for the present HARQ process and, if the HARQ feedback is received, the procedure returns to step 715.

If the HARQ feedback is an ACK at step 725, the UE determines whether DRX is configured and the configured UL resource is activated at step 735. This is the process for checking the condition to determine whether to apply the aforementioned suspension operation. That is, the UE determines whether one of [condition 1], [condition 2], and [condition 3] is fulfilled.

If the condition is not fulfilled at step 735, the UE determines whether the maximum number of transmissions is reached at step 740 and, if the maximum number of transmissions is reached, flushes the HARQ buffer to disable the suspension operation at step 745, resulting in an avoidance of the third type active time any longer. Afterward, the UE waits for the uplink grant to become available and returns the procedure to step 705. If the condition is fulfilled at step 735, the procedure goes to step 745.

FIG. 8 is a flowchart illustrating an eNB procedure of a battery consumption control procedure according to an exemplary embodiment of the present invention.

If the maxim number of HARQ transmissions is not reached yet in a certain HARQ process, the eNB waits for a pending HARQ retransmission for a HARQ process at step 805. Next, the eNB determines whether the conditions for determining whether to apply the suspension operation for the HARQ processor is fulfilled at step 810. The condition can be one of aforementioned [condition 1], [condition 2], and [condition 3].

If the condition is not fulfilled at step 810, the eNB performs a normal suspension operation as in a related art method at step 815. That is, the eNB transmits an uplink grant for adaptive retransmission at a retransmission grant occasion, if necessary. If the condition is fulfilled at step 810, the eNB stops suspension operation for the HARQ process at step 820.

Second Exemplary Embodiment

The traffic of a real-time service such as VoIP is generated in a regular pattern. For example, the pattern may alternate between a short on-period and an off-period. Meanwhile, since the active time of DRX is relatively long, this may cause a problem in that the UE maintains the on-period unnecessarily in an active time.

The second exemplary embodiment of the present invention proposes a method and apparatus for improving the battery efficiency of the UE by dividing the DRX structure into two layers.

The active time can be categorized into two patterns, namely first and second patterns. The first pattern corresponds to an active time, and the second pattern uses a part of the active time defined in the first pattern for an actual active period. The second pattern is not always enabled. That is, the second pattern may be enabled when a predetermined condition is fulfilled and disabled when another condition is fulfilled. If the second pattern is activated, the actual active time is the intersection of the first pattern active time and the second pattern active time.

FIG. 9 is a diagram illustrating a principle of a batter consumption control method of a UE according to an exemplary embodiment of the present invention.

Referring to FIG. 9, the onDurationTimer starts at a certain time point with the start of onDuration 905. Next, the drx-InactivityTimer starts due to a reason such as a DownLink (DL) assignment for a new transmission at a certain time point. That is, the UE enters the situation where downlink data occurs and maintains the active time while the onDurationTimer or the drx-InactivityTimer is running. If the data addressed to the UE has a repeating short on-duration like VoIP data, the eNB transmits a MAC Control Element (CE) to the UE to instruct the UE to apply the second pattern. If the MAC CE is received, the UE applies the pattern indicated by the MAC CE. The pattern is disabled when a predetermined condition is fulfilled, e.g., expiry of the drx-InactivityTimer.

The MAC CE can carry the information on the second pattern's period 925 and length 930. The start time point of the second pattern can be the time point derived from explicit information about the time point when the MAC CE has been received successfully. For example, the start time can be the subframe at which the value obtained through a modulo operation on an integer indicating the period of the pattern is 0.

For example, at timing ‘A,’ the on-duration starts. The eNB expects a limited amount of DL traffic to be delivered. Hence, the UE will not be scheduled continuously and continuous PDCCH monitoring is not required. The eNB chooses a proper pattern which fulfills the scheduling availability and reduces the UE power consumption. The pattern is consisted with the ‘duration’ and ‘periodicity’.

At ‘B’, the eNB sends and the UE receives a Scheduling Policy MAC CE containing the ‘duration’ and ‘periodicity’. Because a PDCCH for new transmission is also sent to UE at ‘B’, the inactivity timer starts to run.

At ‘C’ the UE successfully decodes the Scheduling Policy MAC CE. From then on, the UE applies the scheduling pattern. The UE monitors during a scheduling duration which occurs every ‘periodicity’. The starting point of the scheduling pattern is either the next subframe of the subframe when the Scheduling Policy MAC CE is first received (e.g., ‘B’), the next subframe of the subframe when Scheduling Policy MAC CE is successfully received (e.g., the subframe when the MAC PDU, which includes the Scheduling Policy MAC CE and is later successfully decoded after HARQ soft combining is received) or simply the first subframe of the on-duration or another moment.

The UE and eNB continue to apply the scheduling pattern (that UE monitors PDCCH during the scheduling duration and eNB schedule the UE during the scheduling duration) until either a next on-duration starts or an inactivity timer expires. This is because when the inactivity timer restarts when a PDCCH for a new transmission is received, the UE continues to apply the scheduling pattern unless a PDCCH for new transmission is not received for the duration equal to the length of inactivity timer.

FIG. 10 is a flowchart illustrating a battery consumption control method of a UE according to another exemplary embodiment of the present invention.

Referring to FIG. 10, DRX is configured at step 1005. The UE has received DRX parameters (e.g., the onDurationTimer, the drx-InactivityTimer, the drx-RetransmissionTimer, the drxStartOffset and the longDRX-Cycle, etc.) and acts upon the parameters such that the UE monitors a PDCCH only for a predetermined duration called an Active Time which is determined by the above parameters. Roughly speaking, the UE monitors the PDCCH for an on-Duration which occurs every DRX cycle. If the UE is scheduled during the on-Duration, the active time is extended by an inactivity time. The UE identifies the first subframe of the on-duration using the parameters like longDRX-Cycle and drxStartOffset.

The UE starts to monitor the PDCCH at the first subframe of on-duration at step 1010.

The UE checks whether a PDCCH for a new transmission is received before the end of the on-duration at step 1015. If so, the procedure proceeds to step 1025. If the PDCCH for new transmission is not received until the end of on-duration, the procedure goes to step 1020.

At step 1020, the UE ends the Active time and waits until the next active time starts (e.g., when the next on-duration starts).

The UE starts the inactivity timer at step 1025 when the PDCCH for new transmission is received.

The UE determines, while the inactivity timer is running, whether Scheduling Policy MAC CE is received at 1030. If the Scheduling Policy MAC CE is not received, the UE goes to step 1035. If the Scheduling Policy MAC CE is received, UE determines scheduling pattern as below.

The Scheduling Policy MAC CE is the control information originated and handled by MAC layer.

The Scheduling Policy MAC CE contains ‘scheduling duration’ information and ‘scheduling duration periodicity’ information.

The Scheduling duration occurs every scheduling duration periodicity, while the starting point of the scheduling duration is determined as below.

The Starting subframe of the scheduling duration is the subframe fulfilling the following condition:

[(SFN*10)+subframe number]modulo(scheduling periodicity)=starting offset

where the starting offset is either:

1) the subframe number of the subframe when the Scheduling Policy MAC CE is first received;

2) the subframe number of subframe when the Scheduling Policy MAC CE is successfully received; or

3) the subframe number of the subframe when the current on-duration has started.

It is possible that the Scheduling duration is fixed to a certain value (e.g., configured during DRX configuration procedure, or hard fixed in standard) and only the scheduling duration periodicity can be signaled in the Scheduling Period MAC CE.

While the inactivity timer is running, the UE continues monitoring the PDCCH at step 1035.

The UE applies the scheduling pattern until either the inactivity timer expires or a next on-duration starts at step 1040.

FIG. 11 is a block diagram illustrating a configuration a UE according to an exemplary embodiment of the present invention.

Referring to FIG. 11, the UE according to an exemplary embodiment of the present invention includes a transceiver 1105, a controller 1110, a multiplexer/demultiplexer 1120, a control message processor 1135, and higher layer processors 1125 and 1130.

The transceiver 1105 is responsible for receiving data and control signals through a downlink channel of the serving cell and for transmitting data and control signals through an uplink channel. In a case where multiple serving cells are configured, the transceiver 1105 transmits/receives data and control signals through multiple serving cells.

The multiplexer/demultiplexer 1120 multiplexes the data generated by the higher layer processors 1125 and 1130 and control message processor 1135 and demultiplexes the received data and delivers the demultiplexed data to the higher layer processors 1125 and 1130 and the control message processor 1135.

The higher layer processors 1125 and 1130 can be activated for respective services to process the data generated in the user services such as File Transfer Protocol (FTP) or VoIP and deliver the processed data to the multiplexer/demultiplexer 1120; and process the data delivered from the multiplexer/demultiplexer 1120 and deliver the processed data to the higher layer service applications.

The controller 1110 checks scheduling commands, e.g., uplink grants, received through the transceiver 1105 and controls the transceiver 1105 and the multiplexer/demultiplexer 1120 to perform uplink transmission on an appropriate resource at an appropriate timing. The controller 1110 also controls the transceiver 1105 in association with the DRX operation.

FIG. 12 is a block diagram illustrating a configuration of an eNB according to an exemplary embodiment of the present invention.

Referring to FIG. 12, the eNB includes a transceiver 1205, a controller 1210, a multiplexer/demultiplexer 1120, a control message processor 1235, higher layer processors 1225 and 1230, and a scheduler 1215.

The transceiver 1205 is responsible for transmitting data and control signals through a downlink carrier and receiving data and control signals through an uplink carrier. In a case where multiple carriers are configured, the transceiver 1205 performs data and control signal transmission/reception through multiple carriers.

The multiplexer/demultiplexer 1220 multiplexes the data generated by the higher layer processor 1225 and 1230 and the control message processor 1235 and demultiplexes the received data and delivers the demultiplexed data to the higher layer processors 1225 and 1230, control message processor 1235, and/or the controller 1210. The control message processor 1235 performs necessary actions for processing the control message transmitted by the UE and generates the control message addressed to the UE and delivers the controls message to lower layers.

The higher layer processors 1225 and 1230 can be configured for respective services and process the data generated by the user services such as FTP and VoIP and deliver the processed data to the multiplexer/demultiplexer 1220; and demultiplex the data delivered from the multiplexer/demultiplexer 1220 and delivers the demultiplexed data to higher layer service applications.

The controller 1210 determines the active time of the UE in consideration of DRX operation and notifies the scheduler of the active time information.

The scheduler 1215 allocates transmission resource to the UE at an appropriate time in consideration of buffer state, channel condition, and active time of the UE and controls the transceiver to process the signal received from the UE or the signal to be transmitted to the UE.

As described above, the battery control method and apparatus of exemplary embodiments of the present invention are capable of improving DRX efficiency and reducing battery power consumption.

While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims

1. A method for controlling battery consumption of a terminal operating in Semi-Persistent Scheduling (SPS) mode, the method comprising:

determining, when Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement (ACK) is received, whether a suspension restriction condition is fulfilled; and

stopping, when the suspension restriction condition is fulfilled, suspension to flush an HARQ buffer and not monitor a retransmission grant.

2. The method of claim 1, wherein the determining comprises checking a configuration of Discontinuous Reception (DRX) and an uplink grant.

3. The method of claim 2, wherein the determining comprises checking a reception timing of the HARQ ACK.

4. The method of claim 3, wherein the determining comprises determining when the reception timing of the HARQ ACK is in active time, that the suspension restriction condition is not fulfilled.

5. The method of claim 4, wherein the determining comprises determining, when the DRX and uplink grant are configured and the reception timing of the HARQ ACK is out of the active time, that the suspension restriction condition is fulfilled.

6. The method of claim 1, wherein the determining comprises checking a retransmission grant occasion.

7. The method of claim 6, wherein the determining comprises determining, when the retransmission grant occasion is out of an active time, that the suspension restriction condition is not fulfilled.

8. The method of claim 7, wherein the determining comprises determining, when a Discontinuous Reception (DRX) and uplink grant are configured and reception timing of the HARQ ACK is out of active time, that the suspension restriction condition is fulfilled.

9. A method for controlling battery consumption of a terminal in which a base station performs transmission in Semi-Persistent Scheduling (SPS) mode, the method comprising:

determining, at the base station, whether a maximum number of transmissions is reached;

determining, when the maximum number of transmissions is reached, whether the terminal fulfills a suspension restriction condition; and

stopping, when the terminal fulfills the suspension restriction condition, suspension to flush a Hybrid Automatic Repeat reQuest (HARQ) buffer and not transmit a retransmission grant.

10. The method of claim 9, wherein the determining comprises transmitting, when the terminal does not fulfill the suspension restriction condition, a retransmission grant at a retransmission occasion.

11. A terminal for supporting transmission in Semi-Persistent Scheduling (SPS) mode to improve battery conservation, the terminal comprising:

a transceiver which receives data and control signals through a downlink channel of a serving cell and transmits data and control signals through an uplink channel; and

a controller which controls to determine, when a Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement (ACK) is received, whether a suspension restriction condition is fulfilled and stopping, when the suspension restriction condition is fulfilled, suspension to flush an HARQ buffer and not monitor a retransmission grant.

12. The terminal of claim 11, wherein the controller determines, when Discontinuous Reception (DRX) and uplink grant are configured, that the suspension restriction condition is fulfilled.

13. The terminal of claim 12, wherein the controller checks a reception timing of the HARQ ACK.

14. The terminal of claim 13, wherein the controller determines, when the reception timing of the HARQ ACK is in active time, that the suspension restriction condition is not fulfilled.

15. The terminal of claim 14, wherein the controller determines, when the DRX and uplink grant are configured and the reception timing of the HARQ ACK is out of the active time, that the suspension restriction condition is fulfilled.

16. The terminal of claim 11, wherein the controller checks a retransmission grant occasion.

17. The terminal of claim 16, wherein the controller determines, when the retransmission grant occasion is out of an active time, that the suspension restriction condition is not fulfilled.

18. The terminal of claim 17, wherein the controller determines, when a Discontinuous Reception (DRX) and uplink grant are configured and reception timing of the HARQ ACK is out of active time, that the suspension restriction condition is fulfilled.

19. A base station for performing transmission in Semi-Persistent Scheduling (SPS) mode to improve battery conservation of a terminal, the base station comprising:

a transceiver which transmits data and control signals on a downlink carrier and receives data and control signals on an uplink carrier; and

a controller which determines whether a maximum number of transmissions is reached, determines, when the maximum number of transmissions is reached, whether the terminal fulfills a suspension restriction condition, and controls stopping, when the terminal fulfills the suspension restriction condition, suspension to flush a Hybrid Automatic Repeat reQuest (HARQ) buffer and not transmit a retransmission grant.

20. The base station of claim 19, wherein the controller controls transmitting, when the terminal does not fulfill the suspension restriction condition and retransmission is necessary, a retransmission grant at a retransmission occasion.