JP6010666B2 - Communication control method and radio base station - Google Patents

Description

  The present invention relates to a communication control method and a radio base station in a mobile communication system that constitutes a DRX cycle (intermittent reception cycle) having an on period in which a downlink signal transmitted from a serving cell should be monitored and an off period other than the on period.

  In a next-generation communication system such as LTE (Long Term Evolution), a technique called DRX (Discontinuous Reception) is adopted in order to reduce power consumption of a wireless terminal (for example, Non-Patent Document 1).

  In DRX, an ON period in which a downlink signal (for example, PDCCH: Physical Downlink Control Channel) transmitted from a serving cell should be monitored and an OFF period other than the ON period (Opportunity for) within a DRX cycle (DRX Cycle). DRX) is provided. The radio base station transmits a dedicated signal addressed to the radio terminal only during a period in which the radio terminal is on. Thus, the wireless terminal is configured to monitor the downlink signal transmitted from the wireless base station only during the on period, and it is considered that the receiver is powered down during the off period. In addition, as the DRX cycle, two cycles (a short DRX cycle and a long DRX cycle) can be configured. Further, the DRX mode can be configured in a state (RRC connected state) in which an RRC connection is set between the wireless terminal and the wireless base station. That is, it should be noted that the off period of the DRX cycle is different from the RRC idle state. In the 3GPP standard, the long DRX cycle is a mandatory and the short DRX cycle is optional.

  By the way, in recent years, wireless terminals equipped with various applications are increasing. The application is configured to periodically transmit and receive a predetermined message such as a keep alive message or a status update message to a communication partner such as a server. In such a case, every time a predetermined message is transmitted / received, transmission / reception of a control signal resulting from the transition of the RRC state occurs, resulting in tight network resources.

  On the other hand, in order to prevent such tightness of network resources, it is considered to provide a DRX cycle having a longer cycle (for example, an extended DRX cycle) than an existing DRX cycle (for example, a short DRX cycle and a long DRX cycle). (For example, Non-Patent Document 2).

TS36.321 V10.0.0 RP-110454

  By the way, a period of several seconds or more is assumed as the extended DRX period, and the extended DRX period is very long compared to the short DRX period and the long DRX period. Therefore, it is assumed that the off period of the extended DRX cycle is also very long.

  Therefore, it is considered that various measures are necessary when the extended DRX cycle is configured. For example, since the incoming call process cannot be performed during the off period, the delay of the incoming call process increases.

  Therefore, the present invention has been made to solve the above-described problem, and it is possible to suppress a problem associated with a prolonged off period when a DRX cycle such as an extended DRX cycle is configured. It aims to provide a method.

  A mobile communication method according to a first feature includes an on period in which a downlink signal transmitted from a serving base station is to be monitored in an RRC connected state in which an RRC connection is established between a radio terminal and a radio base station, and A DRX cycle having an off period other than the on period is configured. In the mobile communication method, when the DRX cycle is configured for the radio terminal, the radio base station transmits a paging signal for notifying an incoming call of the radio terminal at a predetermined timing even in the off period. A step A for transmitting to the wireless terminal; and a step B for monitoring the paging signal at the predetermined timing in the off period when the wireless terminal is configured with the DRX cycle.

  In the first feature, the mobile communication method includes a step C in which the radio terminal cancels the DRX cycle in response to reception of the paging signal.

  In the first feature, the step C includes a step in which the wireless terminal releases the DRX cycle and continuously monitors the downlink signal.

  In the first feature, the step C includes a step in which the wireless terminal cancels the DRX cycle and configures a DRX cycle shorter than the DRX cycle.

  In the first feature, the step C includes a step in which the radio terminal starts a reconnection procedure for the radio base station in response to reception of the paging signal.

  The wireless terminal according to the second feature receives a downlink signal in the mobile communication system. In an RRC connected state in which an RRC connection is established between a radio terminal and a radio base station, the mobile communication system is configured to monitor an downlink period signal transmitted from a serving base station and an off period other than the on period. A DRX cycle having a period is configured. The wireless terminal includes a control unit that monitors a paging signal at a predetermined timing in the off period when the DRX cycle is configured.

FIG. 1 is a diagram showing a mobile communication system 100 according to the first embodiment. FIG. 2 is a diagram illustrating a radio frame according to the first embodiment. FIG. 3 is a diagram illustrating radio resources according to the first embodiment. FIG. 4 is a diagram illustrating a short DRX cycle according to the first embodiment. FIG. 5 is a diagram illustrating a long DRX cycle according to the first embodiment. FIG. 6 is a diagram illustrating an extended DRX cycle according to the first embodiment. FIG. 7 is a block diagram showing the UE 10 according to the first embodiment. FIG. 8 is a sequence diagram showing the mobile communication method according to the first embodiment.

  Hereinafter, a mobile communication system according to an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

  However, it should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Therefore, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

[Outline of Embodiment]
The mobile communication method according to the embodiment includes an on-period in which a downlink signal transmitted from a serving base station is to be monitored and the on-state in an RRC connected state in which an RRC connection is established between the radio terminal and the radio base station. A DRX cycle having an off period other than the period is configured. In the mobile communication method, when the DRX cycle is configured for the radio terminal, the radio base station transmits a paging signal for notifying an incoming call of the radio terminal at a predetermined timing even in the off period. A step A for transmitting to the wireless terminal; and a step B for monitoring the paging signal at the predetermined timing in the off period when the wireless terminal is configured with the DRX cycle.

  In the embodiment, when the DRX cycle is configured in the RRC connected state, the radio base station transmits the paging signal at a predetermined timing even in the off period, and the radio terminal is in the RRC connected state. The paging signal is monitored at a predetermined timing in the off period of the DRX cycle configured as described above.

  As a result, even if a very long DRX cycle is configured, the incoming call processing can be performed by receiving the paging signal in the off period.

[First Embodiment]
(Mobile communication system)
The mobile communication system according to the first embodiment will be described below. FIG. 1 is a diagram showing a mobile communication system 100 according to the first embodiment.

  As shown in FIG. 1, the mobile communication system 100 includes a mobile terminal 10 (hereinafter, UE 10) and a core network 50. The mobile communication system 100 includes a first communication system and a second communication system.

  The first communication system is a communication system that supports, for example, LTE (Long Term Evolution). The first communication system includes, for example, a radio base station 110 (hereinafter, eNB 110) and an MME 120. In the first communication system, a first RAT (EUTRAN; Evolved Universal Terrestrial Access Network) is used.

  The second communication system is a communication system compatible with WCDMA (registered trademark) (Wideband Code Division Multiple Access), for example. The second communication system includes a radio base station 210, an RNC 220, and an SGSN 230. In the second communication system, a second RAT (UTRAN; Universal Terrestrial Access Network) is used.

  The UE 10 is a device (User Equipment) configured to communicate with the first communication system and the second communication system. For example, the UE 10 has a function of performing wireless communication with the eNB 110 and a function of performing wireless communication with the wireless base station 210.

  The eNB 110 is a device (evolved NodeB) that includes the cell 111 and performs radio communication with the UE 10 existing in the cell 111.

  The MME 120 is a device (Mobility Management Entity) that manages the mobility of the UE 10 that has set up a wireless connection with the eNB 110. The MME 120 is provided in the core network 50.

  The radio base station 210 has a cell 211 and is a device (NodeB) that performs radio communication with the UE 10 existing in the cell 211.

  The RNC 220 is connected to the radio base station 210 and is a device (Radio Network Controller) that sets up a radio connection (RRC Connection) with the UE 10 existing in the cell 211.

  The SGSN 230 is a device (Serving GPRS Support Node) that performs packet switching in the packet switching domain. The SGSN 230 is provided in the core network 50. Although omitted in FIG. 1, a device (MSC: Mobile Switching Center) that performs circuit switching in the circuit switching domain may be provided in the core network 50.

  In the following, the first communication system will be mainly described. However, the following description may be applied to the second communication system. Further, the cell should be understood as a function of performing radio communication with the UE 10. However, the cell may be considered as a service area indicating a range in which communication with the cell is possible.

  Here, in the first communication system, an OFDMA (Orthogonal Frequency Division Multiple Access) scheme is used as a downlink multiplexing scheme, and an SC-FDMA (Single-Carrier Frequency Division Multiplex) is used as an uplink multiplexing scheme. A method is used.

  In the first communication system, an uplink control channel (PUCCH; Physical Uplink Channel), an uplink shared channel (PUSCH; Physical Up Shared Channel), and the like exist as uplink channels. In addition, as downlink channels, there are a downlink control channel (PDCCH), a downlink shared channel (PDSCH), and a physical downlink shared channel (PDSCH).

  The uplink control channel is a channel that carries a control signal. The control signal is, for example, CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), RI (Rank Indicator), SR (Scheduling Request), ACK / NACK, or the like.

  The CQI is a signal that notifies a recommended modulation method and coding rate to be used for downlink transmission. PMI is a signal indicating a precoder matrix that is preferably used for downlink transmission. The RI is a signal indicating the number of layers (number of streams) to be used for downlink transmission. SR is a signal for requesting allocation of uplink radio resources (resource blocks to be described later). ACK / NACK is a signal indicating whether or not a signal transmitted via a downlink channel (for example, PDSCH) has been received.

  The uplink shared channel is a channel that carries a control signal (including the control signal described above) and / or a data signal. For example, the uplink radio resource may be allocated only to the data signal, or may be allocated so that the data signal and the control signal are multiplexed.

  The downlink control channel is a channel that carries a control signal. The control signal is, for example, Uplink SI (Scheduling Information), Downlink SI (Scheduling Information), or a TPC bit.

  The Uplink SI is a signal indicating uplink radio resource allocation. Downlink SI is a signal indicating allocation of downlink radio resources. The TPC bit is a signal instructing increase / decrease in power of a signal transmitted through an uplink channel.

  The downlink shared channel is a channel that carries a control signal and / or a data signal. For example, the downlink radio resource may be allocated only to the data signal, or may be allocated so that the data signal and the control signal are multiplexed.

  A control signal transmitted via the downlink shared channel includes TA (Timing Advance). TA is transmission timing correction information between the UE 10 and the eNB 110, and is measured by the eNB 110 based on an uplink signal transmitted from the UE 10.

  Moreover, ACK / NACK is mentioned as a control signal transmitted via channels other than a downlink control channel (PDCCH) downlink shared channel (PDSCH). ACK / NACK is a signal indicating whether or not a signal transmitted via an uplink channel (for example, PUSCH) has been received.

(Radio frame)
Hereinafter, a radio frame in the first communication system will be described. FIG. 2 is a diagram illustrating a radio frame in the first communication system.

  As shown in FIG. 2, one radio frame is composed of 10 subframes, and one subframe is composed of two slots. The time length of one slot is 0.5 msec, the time length of one subframe is 1 msec, and the time length of one radio frame is 10 msec.

  One slot is configured by a plurality of OFDM symbols (for example, six OFDM symbols or seven OFDM symbols) in the downlink direction. Similarly, one slot is configured by a plurality of SCFDMA symbols (for example, six SC-FDMA symbols or seven SC-FDMA symbols) in the uplink direction.

(Radio resource)
Hereinafter, radio resources in the first communication system will be described. FIG. 3 is a diagram illustrating radio resources in the first communication system.

  As shown in FIG. 3, the radio resource is defined by a frequency axis and a time axis. The frequency is composed of a plurality of subcarriers, and a predetermined number of subcarriers (12 subcarriers) are collectively referred to as a resource block (RB). As described above, the time includes units such as OFDM symbols (or SC-FDMA symbols), slots, subframes, radio frames, and the like.

  Here, the radio resource can be allocated for each resource block. Also, it is possible to divide and allocate radio resources to a plurality of users (for example, user # 1 to user # 5) on the frequency axis and the time axis.

  Radio resources are allocated by the eNB 110. The eNB 110 is assigned to each UE 10 based on CQI, PMI, RI, and the like.

(Intermittent reception)
In the following, discontinuous reception (DRX) will be described. 4 to 6 are diagrams for explaining intermittent reception. The UE 10 can configure intermittent reception in order to suppress power consumption. Here, a case will be described in which intermittent reception is configured in a state where an RRC connection is set between the UE 10 and the eNB 110 (RRC connected state).

  As shown in FIGS. 4 to 6, in discontinuous reception (DRX), an ON period in which a downlink signal transmitted from a serving cell is to be monitored and an off period other than the ON period are monitored within a DRX cycle (DRX Cycle). A period (opportunity for DRX) is provided. The eNB 110 transmits a dedicated signal addressed to the UE 10 only in a period in which the UE 10 is on. In this way, the UE 10 is configured to monitor the downlink signal (for example, PDCCH: Physical Downlink Control Channel) transmitted from the eNB 110 only in the on period, and the receiver 10 is turned on in the off period. It is thought to have dropped.

  Note that a plurality of types of cycles can be configured as the DRX cycle. Here, three DRX cycles (short DRX cycle, long DRX cycle, extended DRX cycle) will be described.

  As shown in FIG. 4, the short DRX cycle is a short cycle. The length of the short DRX cycle is not particularly limited, but is on the order of several milliseconds (for example, 80 msec).

  For example, the short DRX cycle is configured according to an instruction (DRX Command) received from the eNB 110. Alternatively, the short DRX cycle is configured when a predetermined period has elapsed since the last reception of a downlink signal (for example, PDCCH). Note that the short DRX cycle is optional, and the short DRX cycle may not be set.

  As shown in FIG. 5, the long DRX cycle is longer than the short DRX cycle. The length of the long DRX cycle is not particularly limited, but is on the order of several milliseconds (for example, 160 msec).

  For example, when configuring a long DRX cycle, a configuration parameter (DRX Config.) Is notified from the eNB 110. The long DRX cycle is configured when a predetermined period has elapsed since the last reception of a downlink signal (for example, PDCCH). Alternatively, the long DRX cycle is configured when a predetermined period elapses after the short DRX cycle is configured.

  As shown in FIG. 6, the extended DRX cycle is a longer cycle than the long DRX cycle. The length of the extended DRX cycle is not particularly limited, but is a cycle that is much longer than the short DRX cycle and the long DRX cycle, for example, on the order of several seconds. For example, the extended DRX cycle is equivalent to the cycle (Paging Channel Monitoring Cycle) for monitoring the paging signal for notifying the UE 10 when the RRC connection is not set between the UE 10 and the eNB 110 (RRC idle state). is there. Alternatively, the extended DRX cycle is longer than the cycle for monitoring the paging signal for notifying the UE 10 in the RRC idle state.

  For example, when configuring the extended DRX cycle, the configuration parameter (DRX Config.) Is notified from the eNB 110. The extended DRX cycle is configured according to the eNB 110 permission for the request from the UE 10. Alternatively, the extended DRX cycle is configured when a predetermined period has elapsed since the last reception of a downlink signal (for example, PDCCH). Alternatively, the extended DRX cycle is configured when a predetermined period elapses after the short DRX cycle or the long DRX cycle is configured. In another example, the UE 10 knows static configuration parameters in advance, and the extended DRX cycle may be configured according to the eNB 110 permission for a request from the UE 10.

  As the number of UEs 10 equipped with various applications increases, the transition of the RRC state due to an increase in transmission / reception of a predetermined message increases. As a result, radio resources such as RACH (Random Access Channel) are expected to be tight, so that an extended DRX cycle is configured to suppress frequent RRC state transition of the UE 10 and suppress network resource tightness. . The predetermined message is a message (keep alive message or status update message) transmitted by various applications mounted on the UE 10 to the communication partner.

(Wireless terminal)
Hereinafter, the wireless terminal according to the first embodiment will be described. FIG. 7 is a block diagram showing the UE 10 according to the first embodiment. As illustrated in FIG. 7, the UE 10 includes a communication unit 11 and a control unit 12.

  The communication unit 11 receives a signal from the eNB 110 (or the radio base station 210). Alternatively, the communication unit 11 transmits a signal to the eNB 110 (or the radio base station 210). Note that the communication unit 11 includes, for example, an antenna (a plurality of antennas when MIMO is used), a demodulation unit, a modulation unit, and the like.

  The control unit 12 controls the UE 10. For example, the control unit 12 controls on / off of the communication unit 11 when discontinuous reception (DRX) is configured. That is, the control unit 12 turns on the communication unit 11 and monitors a downlink signal (for example, PDCCH) transmitted from the eNB 110 in an on period in which the downlink signal transmitted from the serving cell is to be monitored. The control unit 12 turns off the communication unit 11 and does not monitor the downlink signal (for example, PDCCH) transmitted from the eNB 110 in the off period other than the on period in which the downlink signal transmitted from the serving cell is to be monitored.

  Specifically, when the DRX cycle is configured in the RRC connected state, the control unit 12 performs a predetermined timing in a period other than the on period (that is, the off period) in which the downlink signal transmitted from the serving cell is to be monitored. To monitor the paging signal. The predetermined timing is sometimes referred to as PO (Paging Occlusion), and is composed of one or more subframes. In addition, since the control part 12 is monitoring PDCCH in the ON period of the DRX period comprised by the RRC connected state, of course, it can receive a paging signal.

  It should be noted that in the prior art, the paging signal is not transmitted to the UE 10 in the RRC connected state. In the first embodiment, it should be noted that the eNB 110 transmits the paging signal to the UE 10 at a predetermined timing in the off period of the DRX cycle configured in the RRC connected state.

  Here, the control unit 12 may monitor the paging signal in the off period only when the extended DRX cycle is configured. That is, when the short DRX cycle and the long DRX cycle are configured, the control unit 12 does not have to monitor the paging signal in the off period.

  Further, the control unit 12 cancels the DRX cycle in response to reception of the paging signal. For example, the control unit 12 may cancel the DRX cycle and shift to a mode in which the downlink signal is continuously monitored. Or the control part 12 may cancel | release DRX period (for example, extended DRX period), and may comprise DRX period (for example, short DRX period and long DRX period) shorter than DRX period. Or the control part 12 may cancel | release DRX period and may start the reconnection procedure (Reestablish Procedure) with respect to eNB110.

(Mobile communication method)
Hereinafter, the mobile communication method according to the first embodiment will be described. FIG. 8 is a sequence diagram showing the mobile communication method according to the first embodiment.

  As illustrated in FIG. 8, in step 10, the UE 10 transmits a connection request (RRC Connection Request) to the eNB 110.

  In step 20, the eNB 110 transmits a connection setting (RRC Connection Setup) to the UE 10.

  In step 30, the UE 10 transmits a connection completion (RRC Connection Complete) to the eNB 110.

  In step 40, the UE 10 configures DRX. For example, the UE 10 configures an extended DRX cycle.

  In Step 50A to Step 50C, the UE 10 monitors the paging signal at a predetermined timing in a period other than the on period (that is, the off period) in which the downlink signal transmitted from the serving cell is to be monitored.

  In Step 60, the UE 10 monitors the downlink signal (for example, PDCCH) in the on period in which the downlink signal transmitted from the serving cell is to be monitored.

  In Step 70, the eNB 110 transmits a paging signal at a predetermined timing in a period other than the on period (that is, the off period) in which the downlink signal transmitted from the serving cell is to be monitored.

  In step 80, the UE 10 monitors the paging signal at a predetermined timing in the on period in which the downlink signal transmitted from the serving cell is to be monitored. Moreover, UE10 receives a paging signal.

  In step 90, the UE 10 releases the DRX cycle in response to receiving the paging signal. For example, UE10 may cancel | release DRX period and may transfer to the mode which monitors a downstream signal continuously. Or UE10 may cancel | release DRX period (for example, extended DRX period), and may comprise DRX period (for example, short DRX period, long DRX period, and continuous reception) shorter than DRX period. Or UE10 may cancel | release DRX period and may start the reconnection procedure (Reestablish Procedure) with respect to eNB110.

(Function and effect)
In the embodiment, the eNB 110 transmits the paging signal at a predetermined timing in a period other than the on period (that is, the off period) in which the downlink signal transmitted from the serving cell is to be monitored, and the UE 10 is transmitted from the serving cell. The paging signal is monitored at a predetermined timing in a period other than the on period in which the downstream signal is to be monitored (ie, the off period).

  As a result, even if a very long DRX cycle is configured, the paging signal is received in a period other than the on period (that is, the off period) in which the downlink signal transmitted from the serving cell is to be monitored. It can be carried out.

  In particular, when an extended DRX cycle having a very long DRX cycle is configured, a paging signal is transmitted at a predetermined timing in a period other than an on period (that is, an off period) in which a downlink signal transmitted from a serving cell is to be monitored. It is effective to monitor with.

  As described above, the extended DRX cycle suppresses frequent transition of the RRC state of the UE 10 when the frequency of transmission / reception of a predetermined message is longer than the cycle for monitoring the paging signal in the RRC idle state (Paging Channel Monitoring Cycle). Configured to reduce the strain on network resources.

[Other Embodiments]
Although the present invention has been described with reference to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, the extended DRX cycle is configured to reduce the power consumption of the UE 10 when the frequency of transmission / reception of a predetermined message is longer than the cycle (Paging Channel Monitoring Cycle) for monitoring a paging signal in the RRC idle state. Alternatively, the extended DRX cycle is for reducing the power consumption of the UE 10 when the power consumption necessary for the on period in which the downlink signal transmitted from the serving cell is to be monitored is larger than the power consumption necessary for monitoring the paging signal. Configured.

  Although not particularly mentioned in the embodiment, the configuration (Configuration) necessary for monitoring the paging signal in a period other than the on period (that is, the off period) in which the downlink signal transmitted from the serving cell is to be monitored is the eNB 110. To UE 10 before the DRX cycle is configured. The configuration necessary for monitoring the paging signal includes, for example, a condition for starting the process of monitoring the paging signal, and paging in a period other than the on period (that is, the off period) in which the downlink signal transmitted from the serving cell is to be monitored. This is the signal monitoring cycle. The configuration necessary for monitoring the paging signal may be notified to the UE 10 by RRC signaling or may be notified to the UE 10 by a broadcast channel, for example. The broadcast channel is a channel broadcast from the eNB 110, and carries an MIB (Master Information Block) and an SIB (System Information Block).

  As an example, when a DRX cycle (particularly, an extended DRX cycle) is configured, a DRX cycle setting request is transmitted from the UE 10 to the eNB 110, and the eNB 110 permits the UE 10 to set the DRX cycle. The case where it is transmitted is considered. In such a case, it is considered that the configuration necessary for monitoring the paging signal is included in the setting permission transmitted from the eNB 110 to the UE 10.

  Although not particularly mentioned in the embodiment, when the extended DRX cycle includes a cycle for monitoring a paging signal (Paging Channel Monitoring Cycle), when the timing for monitoring the paging signal overlaps with the ON period, the PDCCH is changed. If the timing for monitoring and monitoring the paging signal overlaps with the off period, only the paging signal may be monitored.

  In order to receive a paging signal, it is necessary to receive a dedicated PDCCH. However, in the embodiment, reception of such a dedicated PDCCH is omitted.

ADVANTAGE OF THE INVENTION According to this invention, when DRX periods, such as an extended DRX period, are comprised, the mobile communication method and radio | wireless terminal which can suppress the problem accompanying prolongation of an off period can be provided.

Claims (2)

A communication control method in a radio base station in a mobile communication system capable of configuring a DRX cycle having an on period in which a radio terminal should monitor a downlink signal and an off period other than the on period,
The wireless base station transmits a first configuration related to timing for the wireless terminal to monitor a paging signal to the wireless terminal,
The radio base station transmits, to the radio terminal, a second configuration related to an extended DRX cycle that constitutes a cycle longer than a long DRX cycle,
The communication control method, wherein the radio base station transmits the paging signal to the radio terminal at a predetermined timing corresponding to the first configuration in an off period of the extended DRX cycle. A radio base station in a mobile communication system capable of configuring a DRX cycle having an on period in which a radio terminal should monitor a downlink signal and an off period other than the on period,
Comprising a control unit, a first Configuration concerning timing for the wireless terminal monitors a paging signal, and a second Configuration regarding extended DRX cycle constituting the longer period than the long DRX cycle the Configuration transmission processing to be transmitted to the wireless terminal;
After the Configuration transmission processing configuration in the OFF period of the extended DRX cycle, to perform, and paging signal transmitting process of transmitting to the wireless terminal at a predetermined timing corresponding to the paging signal to the first Configuration wireless base stations.