Sidelink configuration method and apparatus

A communication control method according to a first aspect is a method for controlling sidelink communication in a mobile communication system. The communication control method includes the steps of: broadcasting, by a base station of the mobile communication system, first resource information for indicating a carrier frequency or a radio resource pool utilizable in the sidelink communication; and transmitting, by the base station, first transmission type information associated with the first resource information. The first transmission type information is information for designating at least one of unicast, multicast, and broadcast as a transmission type in the sidelink communication using the carrier frequency or the radio resource pool.

TECHNICAL FIELD

The present disclosure relates to a communication control method for controlling sidelink communication in a mobile communication system.

BACKGROUND ART

In the existing Long Term Evolution (LTE) system of the 3rd Generation Partnership Project (3GPP), sidelink communication is defined, the sidelink communication being communication directly performed using a sidelink that is an interface between user equipments. Furthermore, V2X sidelink communication obtained by applying the sidelink communication to Vehicle-to-everything (V2X) service is also defined.

In recent years, New Radio (NR) as the 5th generation (5G) radio access technology has been standardized in 3GPP (for example, see Non-Patent Literature 1). Although the sidelink communication is not defined in the specifications of current NR system, 3GPP has started to discuss the introduction of the sidelink communication (in particular, V2X sidelink communication) into the NR system.

CITATION LIST

SUMMARY

A communication control method according to a first aspect is a method comprising: broadcasting, by a base station, a system information block including resource information related to a carrier frequency utilizable in sidelink communication; and transmitting, by user equipment to the base station, a sidelink UE information message for requesting individual allocation of a radio resource for the sidelink communication, which includes information indicating a carrier frequency which the user equipment desires to apply to the sidelink communication, based on the resource information. The sidelink UE information message includes, as transmission type corresponding to the radio resource requesting individual allocation, information indicating at least one of unicast, groupcast, and broadcast.

A user equipment according to a second aspect comprises: a receiver configured to receive, from a base station, a system information block including resource information related to a carrier frequency utilizable in sidelink communication; and a transmitter configured to transmit, to the base station, a sidelink UE information message for requesting individual allocation of a radio resource for the sidelink communication, which includes information indicating a carrier frequency which the user equipment desires to apply to the sidelink communication, based on the resource information. The sidelink UE information message includes, as transmission type corresponding to the radio resource requesting individual allocation, information indicating at least one of unicast, groupcast, and broadcast.

A chipset according to a third aspect is for controlling a user equipment. The chipset comprises: a processor and a memory coupled to the processor. The processor is configured to: receive, from a base station, a system information block including resource information related to a carrier frequency utilizable in sidelink communication; and transmit, to the base station, a sidelink UE information message for requesting individual allocation of a radio resource for the sidelink communication, which includes information indicating a carrier frequency which the user equipment desires to apply to the sidelink communication, based on the resource information. The sidelink UE information message includes, as transmission type corresponding to the radio resource requesting individual allocation, information indicating at least one of unicast, groupcast, and broadcast.

DESCRIPTION OF EMBODIMENTS

It is assumed that NR sidelink communication is defined based on LTE sidelink communication, and has additional advanced functions that are not included in the LTE sidelink communication. It is assumed that examples of the additional advanced functions include a function of retransmission control using delivery confirmation, and a function of multicast in addition to unicast and broadcast are added.

Accordingly, the present disclosure makes it possible to appropriately control NR sidelink communication.

A mobile communication system according to an embodiment will be described with reference to the drawings. In the descriptions of the drawings, the same or similar parts are given the same or similar reference numerals.

Mobile Communication System

First, a configuration of a mobile communication system according to an embodiment will be described. Although the mobile communication system according to the embodiment is a 5G system of 3GPP, LTE may be at least partially applied to the mobile communication system.

FIG.1is a diagram illustrating a configuration of the mobile communication system according to the embodiment.

As illustrated inFIG.1, the mobile communication system includes a User Equipment (UE)100, a 5G radio access network (Next Generation Radio Access Network (NG-RAN))10, and a 5G Core Network (5GC)20.

The UE100is a movable apparatus. The UE100may be any apparatus as long as the UE is utilized by a user. Examples of the UE100include a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or an apparatus provided on a sensor, a vehicle or an apparatus provided on a vehicle (Vehicle UE), or a flying object or an apparatus provided on a flying object (Aerial UE).

The NG-RAN10includes base stations (referred to as “gNBs” in the 5G system)200. The gNB200is also referred to as an NG-RAN node in some cases. The gNBs200are connected to each other via an Xn interface which is an inter-base station interface. The gNB200manages one or a plurality of cells. The gNB200performs wireless communication with the UE100that has established a connection with its own cell. The gNB200has a radio resource management (RRM) function, a function of routing user data (hereinafter simply referred to as “data”), and/or a measurement control function for mobility control and scheduling. A “cell” is used as a term to indicate a minimum unit of a wireless communication area. The “cell” is also used as a term to indicate a function or a resource for performing wireless communication with the UE100. One cell belongs to one carrier frequency.

Note that the gNB may be connected to the Evolved Packet Core (EPC), which is a core network of LTE, or a base station of LTE may be connected to the 5GC. Moreover, the base station of LTE and the gNB may be connected via the inter-base station interface.

In the following, a case in which the gNB200performs wireless communication with the UE100is mainly described, but an eNB may perform wireless communication with the UE100and control sidelink communication.

The 5GC20includes an Access and Mobility Management Function (AMF) and User Plane Function (UPF)300. The AMF performs various kinds of mobility control and the like for the UE100. The AMF manages information of the area in which the UE100exists by communicating with the UE100by using Non-Access Stratum (NAS) signaling. The UPF performs data transfer control. The AMF and UPF are connected to the gNB200via an NG interface, which is an interface between the base station and the core network.

FIG.2is a diagram illustrating a configuration of the UE100(user equipment).

As illustrated inFIG.2, the UE100includes a receiver110, a transmitter120, and a controller130.

The receiver110performs various kinds of reception under the control of the controller130. The receiver110includes an antenna and a reception device. The reception device converts a radio signal received through the antenna into a baseband signal (reception signal) and outputs the resulting signal to the controller130.

The transmitter120performs various kinds of transmission under the control of the controller130. The transmitter120includes an antenna and a transmission device. The transmission device converts a baseband signal (transmission signal) output by the controller130into a radio signal and transmits the resulting signal through the antenna.

The controller130performs various kinds of control in the UE100. The controller130includes at least one processor and at least one memory electrically connected to the processor. The memory stores a program executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a Central Processing Unit (CPU). The baseband processor performs modulation and demodulation, and coding and decoding of a baseband signal, and the like. The CPU executes the program stored in the memory and performs various kinds of processing.

FIG.3is a diagram illustrating a configuration of the gNB200(base station).

As illustrated inFIG.3, the gNB200includes a transmitter210, a receiver220, a controller230, and a backhaul communication unit240.

The transmitter210performs various kinds of transmission under the control of the controller230. The transmitter210includes an antenna and a transmission device. The transmission device converts a baseband signal (transmission signal) output by the controller230into a radio signal and transmits the resulting signal through the antenna.

The receiver220performs various kinds of reception under the control of the controller230. The receiver220includes an antenna and a reception device. The reception device converts a radio signal received through the antenna into a baseband signal (reception signal) and outputs the resulting signal to the controller230.

The controller230performs various kinds of control in the gNB200. The controller230includes at least one processor and at least one memory electrically connected to the processor. The memory stores a program executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, and coding and decoding of a baseband signal, and the like. The CPU executes the program stored in the memory and performs various kinds of processing.

The backhaul communication unit240is connected to the neighboring base station via the inter-base station interface. The backhaul communication unit240is connected to the AMF/UPF300via the interface between the base station and the core network. Note that the gNB may include a Central Unit (CU) and a Distributed Unit (DU) (i.e., each unit performs a separate function), and both the units may be connected via an F1 interface.

FIG.4is a diagram illustrating a configuration of a protocol stack of a radio interface of a user plane for handling data.

As illustrated inFIG.4, the radio interface protocol of the user plane includes a physical (PHY) layer, a Medium Access Control (MAC) layer, and a Radio Link Control (RLC) layer, a Packet Data Convergence Protocol (PDCP) layer, and a Service Data Adaptation Protocol (SDAP) layer.

The PHY layer performs coding and decoding, modulation and demodulation, mapping and demapping of antenna, and mapping and demapping of resource. Between the PHY layer of the UE100and the PHY layer of the gNB200, data and control information are transmitted via a physical channel.

The MAC layer performs priority control of data, retransmission processing by a hybrid ARQ (HARQ), random access procedure, and the like. Between the MAC layer of the UE100and the MAC layer of the gNB200, data and control information are transmitted via a transport channel. The MAC layer of the gNB200includes a scheduler. The scheduler determines a transport format (a transport block size, a modulation and coding scheme (MCS)) of an uplink and a downlink and an allocation resource block for the UE100.

The RLC layer uses the functions of the MAC layer and the PHY layer and transmits data to the RLC layer on the reception side. Between the RLC layer of the UE100and the RLC layer of the gNB200, data and control information are transmitted via a logical channel.

The PDCP layer performs header compression and expansion, and encryption and decryption.

The SDAP layer performs mapping between an IP flow which is a unit of QoS control by the core network performs and a radio bearer which is a unit of QoS control by an Access Stratum (AS). Note that when the RAN is connected to the EPC, the SDAP need not be provided.

FIG.5is a diagram illustrating a configuration of a protocol stack of a radio interface of a control plane for handling signaling (control signal).

As illustrated inFIG.5, the protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer illustrated inFIG.4.

Between the RRC layer of the UE100and the RRC layer of the gNB200, RRC signaling for various configurations is transmitted. The RRC layer controls the logical channel, the transport channel, and the physical channel in response to establishment, re-establishment, and release of the radio bearer. When there is a connection (RRC connection) between the RRC of the UE100and the RRC of the gNB200, the UE100is in an RRC connected mode. When there is no connection (RRC connection) between the RRC of the UE100and the RRC of the gNB200, the UE100is in an RRC idle mode. Furthermore, when the RRC connection is suspended, the UE100is in an RRC inactive mode.

The NAS layer higher than the RRC layer performs session management, mobility management, and the like. Between the NAS layer of the UE100and the NAS layer of the AMF300, NAS signaling is transmitted.

Note that the UE100has an application layer and the like other than the protocol of the radio interface.

The mobile communication system according to the embodiment supports sidelink communication, the side link communication being communication directly performed using a sidelink which is an interface between the UEs. The sidelink communication may be the V2X sidelink communication. Note that the sidelink may also be referred to as a PC5 interface.

The protocol stack of the sidelink communication has the physical layer, the MAC layer, the RLC layer, and the PDCP layer. The protocol stack of the sidelink communication may have the RRC layer in the control plane.

FIG.6is a diagram illustrating transmission types of sidelink communication according to the embodiment.

As illustrated inFIG.6, the transmission type of the sidelink communication includes unicast, multicast, and broadcast. In addition, feedback from a receiving UE100R to a transmitting UE100T may be introduced into the sidelink communication.

The feedback includes response information indicating whether or not the receiving UE100R has correctly received data from the transmitting UE100T. The feedback may include channel state information (CSI) indicating the state of a propagation channel between the transmitting UE100T and the receiving UE100R.

The response information may be response information of an Automatic repeat-request (ARQ) of the RLC layer, or may be response information of a Hybrid ARQ (HARQ) of the MAC layer. The response information includes ACK indicating that the data has been correctly received and NACK indicating that the data has not been correctly received (i.e., data reception has failed).

The unicast sidelink communication is one-to-one sidelink communication. The transmitting UE100T transmits data to the receiving UE100R, and the receiving UE100R transmits feedback information to the transmitting UE100T.

Note that the transmitting UE100T transmits control information for sidelink communication to the receiving UE100R prior to transmission of the data.

The multicast sidelink communication is one-to-many (one-to-specified large number) sidelink communication performed within a specific group. The multicast may also be referred to as a groupcast. The transmitting UE100T transmits data to the receiving UEs100R in the group, and each of the receiving UEs100R transmits feedback information to the transmitting UE100T.

Broadcast sidelink communication is one-to-unspecified large number sidelink communication. The transmitting UE100T transmits data without designating a specific destination UE or group.

First Embodiment

Next, a first embodiment will be described with the assumption of the mobile communication system and the sidelink communication described above.

In the first embodiment, the gNB200broadcasts first resource information indicating a carrier frequency or a radio resource pool utilizable for sidelink communication. The radio resource pool refers to a resource group including some of radio resources (time and frequency resources) within the carrier frequency. The radio resource pool may be some of bandwidth parts (BWPs) within the carrier frequency. As the radio resource pool, a radio resource pool for transmission and a radio resource pool for reception in the sidelink communication may be separately defined.

Furthermore, the gNB200transmits first transmission type information associated with the first resource information. The first transmission type information is information for designating any of unicast, multicast, and broadcast as a transmission type in the sidelink communication using the carrier frequency or the radio resource pool.

This allows the transmission type in the sidelink communication to be different for each carrier frequency or for each radio resource pool, so the sidelink communication using an optimum carrier frequency or radio resource pool for each transmission type is easily implemented.

For example, it becomes easier to implement an operation that allows subcarrier spacings to be different between the radio resource pool for unicast and the radio resource pool for multicast. In this case, the gNB200may transmit subcarrier spacing information associated with the first resource information. The subcarrier spacing information is information indicating subcarrier spacing of the corresponding carrier frequency or radio resource pool. The gNB200may transmit the subcarrier spacing information in addition to or instead of transmission of the first transmission type information.

In the first embodiment, the gNB200may include the first resource information and the first transmission type information in one system information block (SIB) and broadcast the one SIB. The one SIB may be a dedicated SIB used for NR sidelink communication. The gNB200may further include the subcarrier spacing information in the SIB. The SIB is receivable by the UE100in the RRC idle mode or in the RRC inactive mode, thus facilitating the sidelink communication by the UE100in the RRC idle mode and in the RRC inactive mode.

Alternatively, the gNB200may broadcast the first resource information by the SIB and transmit the first transmission type information in a unicast message (e.g., an RRC message). In this case, the UE100may be in the RRC connected mode.

In the first embodiment, the UE100having received the first resource information and the first transmission type information from the gNB200may make a request to the gNB200for individual allocation of a radio resource for sidelink communication on the basis of at least one of the first resource information or the first transmission type information. In this case, the UE100may be in the RRC connected mode. The UE100may make such a request by an RRC message.

This RRC message may be a sidelink UE information message that can be transmitted by the UE100in the RRC connected mode. Alternatively, the RRC message may be a message (RRC Request) for the UE100to transition from the RRC idle mode to the RRC connected mode, a message (RRC Resume Request) for the UE100to transition from the RRC inactive mode to the RRC connected mode, and/or a message (RRC Re-establishment) for the UE100which has detected radio link failure to perform reconnection.

When making the request to the gNB200for individual allocation of a radio resource for sidelink communication, the UE100may transmit second transmission type information to the gNB200on the basis of the first transmission type information. The second transmission type information is information for indicating any of unicast, multicast, and broadcast as a transmission type that the UE100desires to apply to sidelink communication. This allows the UE100to request the gNB200to allocate a radio resource (time and frequency resource) included in a carrier frequency or a radio resource pool that is suitable for the transmission type desired by the UE itself, among the transmission types utilizable by the UE itself.

Additionally, when making the request to the gNB200for individual allocation of a radio resource for sidelink communication, the UE100may transmit second resource information to the gNB200on the basis of the first resource information. The second resource information indicates a carrier frequency or a radio resource pool for which the individual allocation of the radio resource is requested. This allows the UE100to notify the gNB200of the carrier frequency or the radio resource pool that is suitable for the transmission type desired by the UE itself, making it easier for the gNB200to allocate a suitable radio resource (time and frequency resource).

Here, the second resource information (carrier frequency or radio resource pool) notified from the UE100to the gNB200may suggest the carrier frequency or the transmission type supported by the UE100. Specifically, the gNB200identifies a carrier frequency or a transmission type supported by the UE100on the basis of the carrier frequency or the radio resource pool notified from the UE100.

Alternatively, when making the request to the gNB200for individual allocation of a radio resource for sidelink communication, the UE100may not transmit the second resource information to the gNB200. The second resource information indicates a carrier frequency or a radio resource pool for which the individual allocation of the radio resource is requested. In this case, the UE100transmits the second transmission type information indicating the transmission type desired to be applied to the sidelink communication to the gNB200. The gNB200may assume that, as long as the carrier frequency or the radio resource pool corresponds to the transmission type desired by the UE100, any carrier frequency or any radio resource pool is supported by the UE100.

Note that the UE100having received the first resource information and the first transmission type information from the gNB200may select a radio resource (time and frequency resource) from the carrier frequency or the radio resource pool corresponding to the transmission type desired by the UE itself, and may autonomously perform sidelink communication. In this case, the UE100may be in the RRC idle mode or the RRC inactive mode.

Furthermore, the UE100in the RRC idle mode or the RRC inactive mode may perform cell reselection control such that cell reselection of a cell belonging to the carrier frequency corresponding to the transmission type desired by the UE itself is performed, on the basis of the first resource information and the first transmission type information received from the gNB200. For example, the UE100preferentially selects, by configuring a carrier frequency corresponding to the transmission type desired by the UE itself to a frequency having the highest priority of cell reselection, a cell belonging to the carrier frequency as a serving cell.

FIG.7is a diagram illustrating a specific example 1 of an operation according to the first embodiment.

As illustrated inFIG.7, in step S101, the gNB200broadcasts an SIB including an identifier of a carrier frequency (first resource information) and information for designating a transmission type in sidelink communication using the carrier frequency (first transmission type information).

Here, a list including one or a plurality of carrier frequency identifiers may be included in the SIB. The first transmission type information may be associated with each entry (identifier) in the list.

InFIG.7, an example is illustrated in which the unicast is associated with a carrier frequency A, the multicast is associated with a carrier frequency B, and the broadcast is associated with a carrier frequency C. Note that a plurality of transmission types may be associated with one carrier frequency.

In step S111, the UE100having received the first resource information and the first transmission type information from the gNB200may make a request to the gNB200for individual allocation of a radio resource for sidelink communication on the basis of the first resource information and the first transmission type information. The UE100may make such a request by an RRC message. Hereinafter, this message is referred to as a resource request message.

InFIG.7, an example is illustrated in which the UE100includes an identifier (second resource information) of the carrier frequency corresponding to the transmission type desired by the UE itself among carrier frequencies notified from the gNB200, in the resource request message. Additionally, illustrated is an example in which the UE100includes the second transmission type information indicating the transmission type desired by the UE itself in the resource request message. For example, in the above-described example, the UE100desiring multicast sidelink communication includes the identifier of the carrier frequency B and transmission type information indicating the multicast in the resource request message.

In step S112, the gNB200allocates, to the UE100, a radio resource for sidelink communication (time and frequency resource) included in the carrier frequency corresponding to the transmission type desired by the UE100on the basis of the resource request message from the UE100. The gNB200may perform such a resource allocation by either a Physical Downlink Control Channel (PDCCH) or a unicast RRC message (dedicated RRC message).

FIG.8is a diagram illustrating a specific example 2 of the operation according to the first embodiment.

As illustrated inFIG.8, in step S121, the gNB200broadcasts an SIB including an identifier of a radio resource pool (first resource information) and information for designating a transmission type in sidelink communication using the radio resource pool (first transmission type information).

Here, a list including one or a plurality of resource areas and identifiers of radio resource pools may be included in the SIB. The first transmission type information may be associated with each entry in this list.

InFIG.8, an example is illustrated in which the unicast is associated with a radio resource pool A, the multicast is associated with a radio resource pool B, and the broadcast is associated with a radio resource pool C. Note that a plurality of transmission types may be associated with one radio resource pool.

In step S131, the UE100having received the first resource information and the first transmission type information from the gNB200may make a request to the gNB200for individual allocation of a radio resource for sidelink communication on the basis of the first resource information and the first transmission type information.

InFIG.8, an example is illustrated in which the UE100includes an identifier (second resource information) of the radio resource pool corresponding to the transmission type desired by the UE itself among radio resource pools notified from the gNB200, in the resource request message. Additionally, illustrated is an example in which the UE100includes the second transmission type information indicating the transmission type desired by the UE itself in the resource request message. For example, in the above-described example, the UE100desiring multicast sidelink communication includes the identifier of the radio resource pool B and transmission type information indicating the multicast in the resource request message.

In step S132, the gNB200allocates, to the UE100, a radio resource for sidelink communication (time and frequency resource) included in the radio resource pool corresponding to the transmission type desired by the UE100on the basis of the resource request message from the UE100. The gNB200may perform such a resource allocation by either a PDCCH or a unicast RRC message (dedicated RRC message).

Modification 1 of First Embodiment

In the above-described first embodiment, an example in which the radio resource pool can be a BWP has been described. However, the radio resource pool may be a resource group including some radio resources (time and frequency resources) included in the BWP.

In this case, a set of the radio resource pool and the BWP may be configured, and the radio resource pool may be associated with the BWP. Specifically, the radio resource pool is defined in the BWP configured for the UE100.

The BWP is configured by the gNB200for the UE100. For example, the gNB200configures an Initial BWP by an SIB for the UE100and additionally and individually configures other BWPs for the UE100. The gNB200can variably configure subcarrier spacing and a cyclic prefix for each BWP additionally and individually configured for the UE100. Additionally, switching from one BWP to another BWP is controlled by the gNB200. For example, when a first BWP and a second BWP are configured for the UE100and the first BWP is active and the second BWP is inactive, the gNB200switches the active BWP from the first BWP to the second BWP.

Here, a radio resource pool corresponding to the active BWP may be active (usable) and a resource pool corresponding to the inactive BWP may be inactive (unusable). That is, active/inactive of the radio resource pool may be linked with active/inactive of the BWP.

Alternatively, a set of the radio resource pool and the BWP may not be configured, and the radio resource pool may be configured independently of the BWP. In this case, the radio resource pool may be configured in the BWP, may be configured outside the BWP, or may be configured across the boundary of the BWPs.

Here, when a radio resource pool at least partially overlaps with the BWP, active/inactive of the BWP can be linked with active/inactive of the radio resource pool at least partially overlapping with this BWP. Alternatively, active/inactive of the radio resource pool may not be linked with active/inactive of the BWP. Even if the BWP is inactive, as long as a radio resource pool is configured, the radio resource pool (frequency resource) may be made usable.

Modification 2 of First Embodiment

In the above-described first embodiment, the one example has been described which allows the gNB200to broadcast, as the first resource information, a list including identifiers of carrier frequencies utilizable for sidelink communication, by using SIB. The list may include an identifier of a neighboring carrier frequency different from the carrier frequency of the cell of the gNB200. In other words, the UE100receives, from the serving cell, a list including the identifier of the neighboring carrier frequency different from the carrier frequency of the serving cell.

In addition, the gNB200may broadcast, by the SIB, in addition to an identifier of a neighboring carrier frequency utilizable for sidelink communication, information for indicating a BWP utilizable for sidelink communication within the neighboring carrier frequency. This allows the UE100to recognize not only a neighboring carrier frequency utilizable for sidelink communication, but also a BWP utilizable for sidelink communication within the neighboring carrier frequency, on the basis of the SIB received from the serving cell.

For example, when the UE100receives (sidelink reception) data transmitted from another UE100that exists in a neighboring cell belonging to a neighboring carrier frequency, even if an SIB provided in the neighboring cell is not received, inter-frequency sidelink reception can be efficiently performed on the basis of the SIB (BWP information) from the serving cell.

In addition, the UE100recognizes a BWP and recognizes the properties (subcarrier spacing and a cyclic prefix) of the BWP. This allows the UE100to identify a BWP suitable for a Quality of Service (QoS) property of the sidelink communication desired by the UE itself, and determine, on the basis of the identified BWP, the necessity of the inter-frequency sidelink reception and the necessity of the resource request to the gNB200. Such a resource request is described in a modification 5 of the first embodiment.

Modification 3 of First Embodiment

In the above-described first embodiment, the gNB200may transmit, to the UE100, PDCP packet duplication-related information to be applied to sidelink communication in association with the first resource information.

In the PDCP packet duplication, the UE100transmits, on a sidelink, an identical PDCP packet redundantly in a plurality of independent transmission paths. For example, in the transmitting UE100T, an identical PDCP PDU is transmitted by a primary RLC entity (primary transmission), and is transmitted by a secondary RLC entity (secondary transmission).

In the present modification, by using radio resource pools different from each other in the primary transmission and the secondary transmission, independent transmission paths increase the reliability. When the PDCP packet duplication in the UE100is active, the gNB200transmits (configures), to (for) the UE100, information related to the primary transmission and the secondary transmission in association with the radio resource pool. Specifically, the gNB200configures, for the UE100, a first radio resource pool for the primary transmission and a second radio resource pool for the secondary transmission.

For example, the gNB200may transmit, to the UE100, information indicating that the radio resource pool is usable or unusable for the secondary transmission in association with the radio resource, by a dedicated RRC message or an SIB. The gNB200may transmit, to the UE100, information indicating that the radio resource pool is usable or unusable for the primary transmission in association with the radio resource, by a dedicated RRC message or an SIB.

Furthermore, the gNB200may configure, for the UE100, a radio resource pool for the primary transmission and a radio resource pool for the secondary transmission, by a dedicated RRC message. The gNB200may include, in association with each radio resource pool included in an SIB, in the SIB, information indicating whether the radio resource pool is for the primary transmission or for the secondary transmission.

In the present modification, the one example has been described which allows the radio resource pools different from each other to be used in the primary transmission and the secondary transmission, and carrier frequencies (cells) different from each other may be used in the primary transmission and the secondary transmission. In this case, the radio resource pool in the present modification may be replaced with the carrier frequency.

Modification 4 of First Embodiment

In the above-described first embodiment, the gNB200may transmit, to the UE100, information indicating the upper limit of the amount of transmission data in sidelink communication in association with the first resource information, by a dedicated RRC message or an SIB. The information indicating the upper limit of the amount of transmission data is information that indicates, for example, an upper limit not greater than 200 bytes per transmission or an upper limit of a bit rate not greater than 200 bps. This allows the UE100to select a radio resource pool (or carrier frequency) suitable for the amount of data transmitted by the UE itself and use the radio resource pool for sidelink communication.

Alternatively, the gNB200may transmit, to the UE100, information indicating a category of the size of transmission data in sidelink communication in association with the first resource information, by a dedicated RRC message or an SIB. The information indicating the category of the size of transmission data is information such as small packet transmission or large packet transmission. This allows the UE100to select a radio resource pool (or carrier frequency) suitable for the size of data transmitted by the UE itself and use the radio resource pool for sidelink communication.

Modification 5 of First Embodiment

In the above-described first embodiment, the example has been described which allows the second transmission type information indicating the transmission type that the UE100desires to apply to sidelink communication to be included in the resource allocation request transmitted from the UE100to the gNB200.

However, the resource allocation request may include at least one piece of information among 1) information indicating subcarrier spacing that the UE100desires to apply to sidelink communication, 2) information indicating a BWP that the UE100desires to apply to sidelink communication, 3) information indicating whether or not the UE100desires to apply PDCP packet duplication to sidelink communication, 4) information indicating a radio resource pool that the UE100desires to apply to primary transmission or secondary transmission, and 5) information indicating the amount (size) of data that the UE100desires to transmit in sidelink communication.

This allows the gNB200to perform resource allocation suitable for the situation of the UE100.

Note that the UE100may transmit these pieces of information to the gNB200on the basis of the SIB or the dedicated RRC message from the gNB200, or may spontaneously transmit these pieces of information to the gNB200not based on either the SIB or the dedicated RRC message from the gNB200.

Second Embodiment

Next, a second embodiment will be described while focusing on differences from the above-described first embodiment.

In the first embodiment, the example has been described which allows the resource allocation request transmitted from the UE100to the gNB200to be an RRC message. The RRC message is transmitted by a Physical Uplink Shared Channel (PUSCH) allocated by the gNB200for the UE100. However, such a method requires a PUSCH resource to be allocated by the gNB200for the UE100.

In the second embodiment, the resource allocation request is transmitted by a Physical Uplink Control Channel (PUCCH) or a Physical Random Access Channel (PRACH). This allows, even if no PUSCH resource is allocated by the gNB200for the UE100, the UE100to make a request to the gNB200for individual allocation of a radio resource for sidelink communication.

In the second embodiment, the UE100makes a request to the gNB200for individual allocation of a radio resource for sidelink communication via the PUCCH or the PRACH. Here, the UE100notifies the gNB200of any of unicast, multicast, and broadcast as a transmission type that the UE itself desires to apply to sidelink communication. This allows the UE100to make a request to the gNB200for individual allocation of a radio resource suitable for the transmission type that the UE itself desires to apply to sidelink communication.

FIG.9is a diagram illustrating a specific example 1 of an operation according to the second embodiment. In the present operation example, radio resources (time and frequency resources) or signal formats for a scheduling request (SR) are different between the unicast, the multicast, and the broadcast. A signal sequence may be included in the signal format. Note that the SR is a kind of uplink control information (UCI) transmitted on the PUCCH.

A mapping between the radio resource or the signal format for the SR and the transmission type may be broadcast from the gNB200by the SIB, may be notified to the UE100by a dedicated RRC message from the gNB200, or may be preconfigured in the UE100.

As illustrated inFIG.9, in step S201, the UE100selects an SR transmission method (radio resource or signal format) corresponding to a transmission type that the UE itself desires to apply to sidelink communication on the basis of the correspondence relationship described above.

In step S202, the UE100transmits an SR on the PUCCH to the gNB200by the SR transmission method selected in step S201. The gNB200having received the SR identifies a transmission type that the UE100desires to apply to sidelink communication, on the basis of the radio resource or the signal format used for transmission of the SR.

In step S203, the gNB200allocates, to the UE100, a radio resource for sidelink communication (time and frequency resource) corresponding to the transmission type desired by the UE100on the basis of the SR from the UE100. The gNB200may perform such a resource allocation by either a PDCCH or a unicast RRC message (dedicated RRC message).

FIG.10is a diagram illustrating a specific example 2 of the operation according to the second embodiment. In the present operation example, radio resources (time and frequency resources) or signal formats for a random access preamble are different between the unicast, the multicast, and the broadcast. The random access preamble is a signal transmitted on the PRACH.

A mapping between the radio resource or the signal format for the random access preamble and the transmission type may be broadcast from the gNB200by the SIB, may be notified to the UE100by a dedicated RRC message from the gNB200, or may be preconfigured in the UE100.

As illustrated inFIG.10, in step S211, the UE100selects a random access preamble transmission method (radio resource or signal format) corresponding to a transmission type that the UE itself desires to apply to sidelink communication on the basis of the mapping described above.

In step S212, the UE100transmits the random access preamble on the PRACH to the gNB200by the random access preamble transmission method selected in step S211. The gNB200having received the random access preamble identifies a transmission type that the UE100desires to apply to sidelink communication, on the basis of the radio resource or the signal format used for transmission of this random access preamble.

In step S213, the gNB200allocates, to the UE100, a radio resource for sidelink communication (time and frequency resource) corresponding to the transmission type desired by the UE100on the basis of the random access preamble from the UE100. The gNB200may perform such a resource allocation by either a PDCCH or a unicast RRC message (dedicated RRC message).

Third Embodiment

Next, a third embodiment will be described while focusing on differences from the above-described embodiments. The third embodiment is an embodiment related to ACK/NACK feedback from the receiving UE100R to the transmitting UE100T in sidelink communication.

In the third embodiment, the receiving UE100R receives data from the transmitting UE100T through sidelink communication. Furthermore, the receiving UE100R periodically transmits a sidelink signal for quality measurement (hereinafter referred to as a “quality measurement signal”) for sidelink communication. The quality measurement signal is a signal transmitted by each UE100for CSI measurement, and may be referred to as a discovery signal or a CSI reference signal. The quality measurement signal may include an identity of a transmission source UE of the quality measurement signal.

In the third embodiment, the receiving UE100R transmits a quality measurement signal including response information indicating whether or not data from the transmitting UE100T has been correctly received. The response information may be response information of an ARQ of the RLC layer, or may be response information of an HARQ of the MAC layer. The response information includes ACK indicating that the data has been correctly received and NACK indicating that the data has not been correctly received (i.e., data reception has failed). Note that the receiving UE100R may perform only NACK transmission without performing ACK transmission.

This makes it possible to carry the response information of the sidelink communication by the quality measurement signal without newly introducing a signal or a channel for response information of the sidelink communication, thus allowing the delivery confirmation of the sidelink communication to be introduced while saving radio resources.

In the third embodiment, the transmitting UE100T having received the quality measurement signal including the response information retransmits data that the receiving UE100R has not been able to correctly receive (i.e., data that the receiving UE100R has failed to receive) on the basis of this response information. This makes it possible to improve the reliability of the sidelink communication.

The receiving UE100R may determine whether or not all the data from the transmitting UE100T have been correctly received in a period from the time of transmission of the previous quality measurement signal to the time of transmission of the current quality measurement signal.

Then, when it is determined that at least part of the data has not been able to be correctly received from the transmitting UE100T in this period, the receiving UE100R may transmit the NACK as the response information included in the current quality measurement signal. The NACK may be a 1-bit flag.

This makes it possible to reduce the amount of response information to be included in the quality measurement signal. On the other hand, when it is determined that all the data have been able to be correctly received from the transmitting UE100T in this period, the receiving UE100R may not include the response information in the quality measurement signal of this time.

In this case, upon receiving the quality measurement signal including the NACK, in accordance with the reception of this NACK, the transmitting UE100T may retransmit all the data transmitted to the receiving UE100R in a period from the time of reception of the previous quality measurement signal to the time of reception of the current quality measurement signal.

FIG.11is a diagram illustrating a specific example of an operation according to the third embodiment. In the present operation example, the receiving UE100R transmits a quality measurement signal at a periodicity T. In addition, it is assumed that the transmitting UE100T performs data transmission three times in the periodicity T.

As illustrated inFIG.11, in step S301, the receiving UE100R transmits a quality measurement signal. The transmitting UE100T may estimate the CSI between the transmitting UE100T and the receiving UE100R on the basis of the quality measurement signal received from the receiving UE100R, and may adjust the MCS and the like (so-called link adaptation) in accordance with the estimated CSI.

In steps S302to S304, the transmitting UE100T transmits data #1 to #3 (initial transmission). Here, #1 to #3 correspond to sequence numbers of the data. The receiving UE100R correctly receives the data #1 to #3 (i.e., successfully decodes the data #1 to #3). In this case, the receiving UE100R does not perform ACK/NACK feedback.

In step S305, the receiving UE100R transmits the quality measurement signal. In steps S306to S308, the transmitting UE100T transmits data #4 to #6 (initial transmission). The receiving UE100R correctly receives the data #4 and #6, but does not correctly receive the data #5 (i.e., fails to decode the data #5). In this case, the receiving UE100R determines to perform the NACK feedback.

In step S309, the receiving UE100R transmits the quality measurement signal including the NACK. In steps S310to S312, the transmitting UE100T retransmits the data #4 to #6. The receiving UE100R correctly receives the data #4 to #6. In this case, the receiving UE100R does not perform the ACK/NACK feedback. In step S313, the receiving UE100R transmits the quality measurement signal.

Fourth Embodiment

Next, a fourth embodiment will be described while focusing on differences from the above-described embodiments. The fourth embodiment is an embodiment related to ACK/NACK feedback from the receiving UE100R to the transmitting UE100T in sidelink communication.

In the fourth embodiment, the gNB200allocates an identical radio resource for NACK transmission (hereinafter referred to as a “NACK transmission radio resource”) to a group including a plurality of UEs100that perform sidelink communication by multicast. Here, the NACK transmission radio resource may include not only a time and frequency resource but also a signal sequence.

One or a plurality of receiving UEs100R included in the group transmit, when data from the transmitting UE100T included in this group have not been able to be correctly received, the NACK to the transmitting UE100T by using the NACK transmission radio resource allocated from the gNB200.

In this way, by allocating the identical NACK transmission radio resource to the receiving UEs100R, radio resources can be saved in comparison with a case in which NACK transmission radio resources different from each other are allocated to the respective receiving UEs100R.

In the fourth embodiment, each receiving UE100R may perform only NACK transmission without performing ACK transmission. This allows the radio resource for ACK transmission to not be required, thus saving radio resources.

Note that if a plurality of receiving UEs100R transmit NACKs by using an identical NACK transmission radio resource, the NACKs are combined in the propagation channel, and the transmitting UE100T is not able to identify a receiving UE100R from which the NACK has been received. However, when receiving NACK from any of the receiving UEs100R in the group, the transmitting UE100T performs data retransmission by multicast, and thus it is not necessary to uniquely identify the receiving UE100R of the transmission source of the NACK.

FIG.12is a diagram illustrating a specific example of an operation according to the fourth embodiment. In the present operation example, it is assumed that one transmitting UE100T and two receiving UE100R1and UE100R2are present in the group.

As illustrated inFIG.12, in steps S401to S403, the gNB200transmits NACK resource information indicating a NACK transmission radio resource to each of the UEs100in the group. The gNB200may transmit, by unicast, the NACK resource information individually addressed to each of the UEs100, or may transmit, by multicast, the NACK resource information addressed to the group. Each of the UEs100in the group stores the NACK resource information received from the gNB200.

In steps S404and S405, the transmitting UE100T transmits data to the receiving UE100R1and UE100R2by multicast (initial transmission). In steps S406and S407, the receiving UE100R1and UE100R2correctly receive the data. In this case, the receiving UE100R1and UE100R2do not perform ACK/NACK feedback.

In steps S408and S409, the transmitting UE100T transmits data to the receiving UE100R1and UE100R2by multicast (initial transmission). In steps S410and S411, the receiving UE100R1and UE100R2fail to receive the data.

In this case, in steps S412and S413, the receiving UE100R1and UE100R2transmit NACK by using the NACK transmission radio resource allocated from the gNB200in steps S402and S403.

In steps S414and S415, in response to reception of the NACK, the transmitting UE100T retransmits the data having been transmitted in steps S408and S409by multicast. In steps S416and S417, the receiving UE100R1and UE100R2correctly receive the data. In this case, the receiving UE100R1and UE100R2do not perform the ACK/NACK feedback.

Other Embodiments

Each of the embodiments and modifications described above may not only be separately and independently implemented, but also be implemented in combination of two or more embodiments and/or two or more modifications.

In addition, in each of the embodiments described above, it is assumed that the UE100is located within the coverage of the gNB200, and the case where the UE100is located outside the coverage has not been particularly considered. However, in the first embodiment, the first resource information and the first transmission type information (and subcarrier spacing information) may be preconfigured in the UE100. For example, the first resource information and the first transmission type information (and subcarrier spacing information) may be stored in a Universal Integrated Circuit Card (UICC) of the UE100beforehand. Furthermore, in the fourth embodiment, the NACK resource information may be preconfigured in the UE100. For example, the NACK resource information may be stored in the UICC of the UE100beforehand.

In each of the embodiments described above, the 5G system (NR) is primarily described, but operations according to each embodiment may be applied to LTE. In such a case, the above-described RRC inactive mode may be replaced with a suspended state. The suspended state is one of the states of the RRC idle mode.

Note that a program for causing the computer to execute each processing performed by the UE100or the gNB200may be provided. The program may be recorded on a computer readable medium. By using the computer readable medium, it is possible to install the program in the computer. Here, the computer readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be a recording medium such as a CD-ROM, a DVD-ROM, or the like, for example.

In addition, circuits for executing the respective processes performed by the UE100or the gNB200may be integrated, and at least part of the UE100or the gNB200may be configured as a semiconductor integrated circuit (chipset, SoC).

An embodiment has been described in detail above with reference to the drawings, but the specific configuration is not limited to those described above, and various design modifications and the like can be made without departing from the gist.