WO2021205611A1

WO2021205611A1 - Communication device, communication method, and communication system

Info

Publication number: WO2021205611A1
Application number: PCT/JP2020/016009
Authority: WO
Inventors: フィテンチェン; 剛史下村; 紅陽陳; 青木　信久; ジヤンミンウー
Original assignee: 富士通株式会社
Priority date: 2020-04-09
Filing date: 2020-04-09
Publication date: 2021-10-14

Abstract

The present invention improves the communication qualities in D2D communication systems for supporting retransmission procedures using feedbacks. A communication device according to the present invention supports Device-to-Device (D2D) communications, and comprises a resource selection region determining unit, a resource selecting unit and a radio transmitting unit. The resource selection region determining unit determines a first resource selection region and a second resource selection region that is to be set up away from the first resource selection region by an interval equal to or greater than a predetermined interval. The resource selecting unit selects, from at least one of the first resource selection region or the second resource selection region, a resource for transmitting D2D data. The radio transmitting unit transmits the D2D data by using the resource selected by the resource selecting unit.

Description

Communication equipment, communication methods, and communication systems

The present invention relates to a communication device, a communication method, and a communication system.

Currently, most of the network resources are occupied by the traffic used by mobile terminals (including smartphones or future phones). In addition, the traffic used by mobile terminals is expected to continue to increase.

On the other hand, in line with the development of IoT (Internet of things) services (for example, monitoring systems for transportation systems, smart meters, devices, etc.), it is required to support services with various requirements. Therefore, in the 5th generation mobile communication (5G or NR (New Radio)) standard, the standard technology of the 4th generation mobile communication (4G (LTE: Long Term Evolution)) (for example, Non-Patent Documents 1 to 12) ), There is a demand for technology that realizes higher data rates, larger capacities, and lower delays. The 5th generation mobile communication standard is being examined by the working group of 3GPP (Third Generation Partnership Project) (for example, TSG-RAN WG1, TSG-RAN WG2, etc.), and the standard document will be published at the end of 2017. The first edition has been published (for example, Non-Patent Documents 13 to 39).

In addition, the 3GPP working group is also discussing V2X (Vehicle to Everything) communication. V2X is V2V (Vehicle to Vehicle) that communicates between automobiles, V2P (Vehicle to Pedestrian) that communicates between automobiles and pedestrians, and V2I (Vehicle to Infrastructure) that communicates between automobiles and road infrastructure. , Includes V2N (Vehicle to Network) that communicates between the car and the network. The provisions regarding V2X are described in, for example, Non-Patent Document 1. Further, Patent Document 1 describes D2D / V2X.

Furthermore, in NR (New Radio) -V2X, a feedback channel (PSFCH: Physical Sidelink Feedback CHannel) has been introduced in order to improve the quality of the side link. Feedback channels are used to request data retransmissions. For example, it is assumed that the source terminal transmits a V2X signal and the destination terminal fails to receive / decode the V2X signal. In this case, the destination terminal uses the feedback channel to transmit a NACK signal indicating reception failure. Then, when the source terminal receives the NACK via the feedback channel, it retransmits the V2X signal. A wireless communication method for appropriately receiving downlink data and transmitting HARQ-ACK has been proposed (for example, Patent Document 2).

Special table 2020-505841 WO2018 / 158923

In a system that improves communication quality by feedback, the source terminal performs the following operation after receiving an ACK / NACK signal from the destination terminal. For example, when the source terminal receives the NACK signal from the destination terminal, it retransmits the V2X data.

On the other hand, in V2X communication, the range in which resources for data transmission for satisfying the delay can be selected (hereinafter, selectable resource range) may be limited. Moreover, the selectable resource range may be further limited, for example, in order to reduce power consumption. When the retransmission is performed by feedback, the initial transmission and the corresponding retransmission are preferably separated at regular time intervals for the transmission / reception of the ACK / NACK signal and the preparation process for the retransmission. However, the resource for retransmission is set after the resource for initial transmission. Therefore, the resource for retransmission is selected from a limited range within the selectable resource range. Therefore, the source terminal may not be able to acquire the resource for retransmission. Alternatively, if the resource for retransmission and the resource used by another terminal overlap, packet collision occurs. In any case, the communication quality may deteriorate. It should be noted that this problem does not occur only in V2X communication, but may occur in arbitrary D2D (Device-to-Device) communication.

An object relating to one aspect of the present invention is to improve communication quality in a D2D communication system that supports a feedback retransmission procedure.

The communication device according to one aspect of the present invention supports D2D (Device-to-Device) communication. This communication device includes a resource selection area determination unit that determines a first resource selection area and a second resource selection area that is set at a distance of a predetermined interval or more from the first resource selection area, and the first resource selection unit. A resource selection unit that selects a resource for transmitting D2D data from at least one of the area or the second resource selection area, and a wireless transmission unit that transmits D2D data using the resource selected by the resource selection unit. And.

According to the above aspect, the communication quality is improved in the D2D communication system that supports the retransmission procedure by feedback.

It is a figure which shows an example of the wireless communication system which concerns on embodiment of this invention. It is a figure which shows an example of the method of determining a resource based on sensing. It is a figure which shows another example of the method of determining a resource based on sensing. It is a figure which shows an example of the arrangement of a feedback channel. It is a figure which shows an example of the transmission timing of the feedback signal in HARQ feedback. It is a figure which shows an example of the selection candidate slot set. It is a figure which shows the example of the retransmission by HARQ feedback. It is a figure (the 1) which shows the example of arrangement of a resource selection area. It is a figure (the 2) which shows the example of the arrangement of the resource selection area. It is a figure (the 3) which shows the example of the arrangement of the resource selection area. It is a figure (the 1) which shows the example of the minimum HARQ round trip time. It is a figure (the 2) which shows the example of the minimum HARQ round trip time. It is a figure which shows the example of the table for searching the minimum HARQ round trip time. It is a flowchart which shows an example of the communication method which concerns on embodiment of this invention. It is a flowchart which shows an example of the process which sets a plurality of subsets in a selection window. It is a figure which shows the example of the procedure of making a gap between a subset. It is a flowchart which shows another example of the process which sets a plurality of subsets in a selection window. It is a figure which shows the example of the table for searching the gap time between a subset. It is a figure which shows the variation of the method of setting a subset. It is a figure which shows the example of the resource which can be selected for transmission and retransmission. It is a figure which shows the effect by an embodiment of this invention. It is a figure which shows an example of the structure of a base station. It is a figure which shows an example of the structure of a communication device.

The issues and examples in this specification are examples, and do not limit the scope of rights of the patent application. For example, even if the expressions described are different, the technology of the present patent application can be applied as long as they are technically equivalent. In addition, the embodiments described in the present specification can be combined within a consistent range.

The terms and technical contents used in this specification are those described in the specifications (for example, 3GPP TS 38.211 V16.0.0 (2019-12)) or contributions as standards for communication such as 3GPP. May be done.

FIG. 1 shows an example of a wireless communication system according to an embodiment of the present invention. As shown in FIG. 1, the wireless communication system 100 includes a base station 1 and a plurality of communication devices 2.

The base station 1 controls the cellular communication (uplink / downlink communication via the Uu interface) of the communication device 2. That is, the base station 1 receives the uplink signal (control signal and data signal) from the communication device 2. Further, the base station 1 transmits a downlink signal (control signal and data signal) to the communication device 2.

The communication device 2 can communicate with another communication device via the base station 1. Further, the communication device 2 can also communicate with another communication device without going through the base station 1. That is, the communication device 2 supports D2D (Device-to-Device) communication. D2D communication transmits signals via, for example, a PC5 interface. Note that D2D communication is sometimes called "side link communication". Further, the communication device 2 may be referred to as a "UE (User Equipment)".

When transmitting data by D2D communication, the communication device 2 determines a resource for transmitting the data. At this time, the communication device 2 detects a resource reserved by another communication device in a resource (that is, a resource pool) preset for D2D communication. Then, the communication device 2 determines a free resource based on the resource reservation information and the interference level measured for a certain period of time, selects a resource from the determined free resources, and transmits data. In the following description, the process of detecting a resource reserved by another communication device in the resource pool for D2D communication may be referred to as "sensing".

FIG. 2 shows an example of a method of determining a resource based on sensing. Here, it is assumed that a resource (re) selection trigger is generated in the subframe n. The resource (re) selection trigger corresponds to, for example, an instruction to determine a resource for transmitting data generated by an application implemented in the communication device 2.

The communication device 2 sets a selection window and a sensing window for the resource (re) selection trigger. The selection window represents the range of resources that can be selected. That is, the communication device 2 can select a resource for transmitting data from the resources in the selection window. When a resource (re) selection trigger is generated in subframe n, the range of the selection window is subframe "n + T1, n + T2". The range of the parameters T1 and T2 is set in advance, for example. Alternatively, the range of the parameters T1 and T2 is notified from the base station 1. The communication device 2 determines the parameters T1 and T2 within a given range. The determined parameter T2 needs to meet the delay requirement.

The sensing window represents the range in which the communication device 2 performs sensing. That is, the communication device 2 senses each resource in the sensing window. Here, the communication device 2 senses, for example, 1000 subframes immediately before the resource (re) selection trigger. In this case, when it is predicted that a resource (re) selection trigger will be generated in subframe n, the range of the sensing window is subframe "n-1000, n-1".

In the sensing process, the communication device 2 decodes PSCCH (Physical Sidelink Control Channel), which is a control channel transmitted in the sensing window, and measures the received power of PSCH (Physical Sidelink Shared Channel), which is the corresponding data channel. do. For example, side link control information (SCI: Sidelink Control Information) including information related to reservation of the corresponding data channel (PSSCH: Physical Sidelink Shared Channel) resource and transmission resource is mapped to the PSCCH resource. In the received power measurement, for example, the received power (RSRP: Reference Signal Received Power) and / or RSSI (Received Signal Strength Indicator) of the reference signal is measured.

In NR-V2X, the control channel (PSCCH: Physical Sidelink Control Channel) and the data channel (PSSCH: Physical Sidelink Shared Channle) are multiplexed by TDM (Time Division Multiplexing) or FDM (Frequency Division Multiplexing). Further, in order to improve the channel quality of the side link, a feedback channel (PSFCH: Physical Sidelink Feedback Channel) has been introduced.

In the example shown in FIG. 2, some of the resources in the selection window are reserved by other communication devices (UE1 and UE2). In this case, the communication device 2 excludes the reserved resources from the resources in the selection window and the received power is higher than the predetermined threshold value, and determines the resource for transmitting data from the remaining resources. do. The sensing shown in FIG. 2 is described in Release 14 of 3GPP.

However, in the method shown in FIG. 2, since sensing is continuously performed over a long period of time, the power consumption of the communication device 2 becomes large. On the other hand, in many cases, the battery capacity of a communication device carried by a pedestrian is small. Therefore, there is a demand for a sensing method with low power consumption.

FIG. 3 shows another example of how to determine resources based on sensing. Here, it is assumed that the D2D communication transmits packets at a predetermined cycle. Specifically, in D2D communication, packets are transmitted at intervals of k × 100 msec. k is not particularly limited, but in this example, it is 1, 2, 5, or 10.

In this case as well, the communication device 2 sets the selection window and the sensing window corresponding to the resource (re) selection trigger, as in the case shown in FIG. However, the communication device 2 sets a selection candidate slot set in the selection window. In this example, the selection candidate slot set consists of Y consecutive slots. In FIG. 3, Y = 5, and the selection candidate slot set is composed of five consecutive slots.

Here, when the resources in the selection candidate slot set are used by the periodic traffic of another communication device, the previous transmission should have been performed at a time dating back k × 100 msec from the selection candidate slot set. Therefore, if sensing is performed on the resource k × 100 msec before the selection candidate slot set, the communication device 2 has another resource in the selection candidate slot set when the resource (re) selection trigger is generated. It can be determined whether or not the reservation is made by the periodic traffic of the communication device.

Therefore, the communication device 2 sets a sensing section corresponding to the selection candidate slot set in the sensing window. Specifically, as shown in FIG. 3, the sensing section is set k × 100 msec before the selection candidate slot set as a reference. The length of each sensing interval is the same as the selection candidate slot set. That is, each sensing section is composed of Y slots.

When the resource (re) selection trigger is generated in the slot m, the communication device 2 performs sensing in the four sensing sections shown in FIG. In this case, the communication device 2 receives the control signals (eg, SCI) transmitted from the UE 1 and the UE 2, respectively, so that the periodic traffic of the UE 1 and the UE 2 reserves a predetermined resource in the selection candidate slot set. Is detected. Further, the communication device 2 measures the received power of the PSCH corresponding to the control signal. Then, the communication device 2 excludes the resources reserved by the UE1 / UE2 from the resources in the selection candidate slot set and whose received power is higher than the predetermined threshold value, and transmits data from the remaining resources. Determine the resources for. The sensing shown in FIG. 3 is also described in Release 14 of 3GPP.

HARQ (hybrid automatic repeat request) -ACK / NACK feedback is supported in NR-V2X. That is, when the source device transmits V2X data, the destination device transmits a feedback signal indicating whether or not the data reception is successful. Then, when the source device receives the feedback signal (that is, the NACK signal) indicating that the data reception has failed, the data is retransmitted. Here, the feedback signal is transmitted via PSFCH (Physical Sidelink Feedback Channel).

FIG. 4 shows an example of the arrangement of feedback channels. The feedback channel (ie, PSFCH) is set at a predetermined cycle. For example, the feedback channel is set every 1 slot, every 2 slots, or every 4 slots. In FIG. 4, the feedback channel is represented by a shaded area. In addition, the slot is composed of 14 symbols in this embodiment.

The period in which the feedback channel is set is represented by the parameter N in this example. The parameter N is set in advance for each resource pool in each communication device 2, for example. Alternatively, the base station 1 notifies the communication device 2 of the parameter N. In this case, the base station 1 notifies the communication device 2 of the parameter N for each resource pool by using PDCCH (Physical Downlink Control Channel) or RRC (Radio Resource Control).

FIG. 5 shows an example of the transmission timing of the feedback signal in HARQ feedback. In the example shown in FIG. 5, N = 2. That is, a feedback channel is set every two slots.

When the communication device 2 receives the V2X data via the PSCH (Physical Sidelink Shared Channel), the communication device 2 transmits a feedback signal indicating whether or not the data reception was successful to the V2X data source device. However, the transmission timing of the feedback signal is defined by the parameter K. The parameter K represents the minimum interval between PSCH reception and the corresponding HARQ feedback. Here, the parameter K is represented by the number of slots. Then, when the communication device 2 receives the V2X data via the PSCH, the communication device 2 determines the feedback timing for transmitting the feedback signal so that the interval between the PSCH reception and the corresponding HARQ feedback is K slot or more. ..

The parameter K that indicates the feedback timing is 2 or 3 in this embodiment. Then, the parameter K is set in advance in each communication device 2, for example. Alternatively, the base station 1 notifies the communication device 2 of the parameter K. In this case, the base station 1 notifies the communication device 2 of the parameter K by using PDCCH, RRC, or the like.

For example, it is assumed that the communication device 2 receives V2X data in slot n + 1 via PSCH. Here, it is assumed that K = 2. In this case, the communication device 2 can transmit the hoodback signal in the slot two or more slots after the slot n + 1. Therefore, the communication device 2 transmits the hoodback signal in the slot n + 3.

Similarly, when V2X data is received in slot n, the communication device 2 can transmit a hoodback signal in a slot two or more slots after slot n. However, the hoodback channel is not set in slot n + 2. Therefore, in this case, the communication device 2 transmits the hoodback signal in the slot n + 3.

As described above, in the HARQ feedback system, the feedback channel is set at a predetermined cycle. Further, the communication device 2 determines whether or not to perform retransmission after receiving the footback signal. Therefore, the resources that can be selected by the communication device 2 for retransmission are reduced in the system that performs HARQ feedback as compared with the system that does not perform HARQ feedback. As a result, the probability of packet collision may increase.

Here, with reference to FIGS. 6 to 7, a case where the probability of packet collision is increased by performing HARQ feedback will be described. In this example, as shown in FIG. 6, slots S1 to S9 are set as selection candidate slot sets. This candidate slot set includes four subchannels in the frequency domain. In the following description, one resource is composed of one slot and one subchannel. In this case, the selection candidate slot set is composed of 36 resources.

The communication device 2 cannot use the resources reserved by other communication devices even if the resources are in the selection candidate slot set. Therefore, the communication device 2 extracts a predetermined number of resources that are not reserved by other communication devices from the resources in the selection candidate slot set. In this embodiment, it is assumed that 20% or more of the resources in the selection candidate slot set are extracted. As an example, it is assumed that the eight resources R1 to R8 shown in FIG. 6 have been extracted.

In the following description, it is assumed that N = 4 and K = 3. That is, a feedback channel is set every 4 slots. Within the selection candidate slot set, a feedback channel is set for the penultimate symbol of slot S4 and slot S8. In FIG. 6, the frequency channel is represented by a region. Further, the time required for processing the feedback channel is shorter than one symbol time.

It is assumed that the communication device 2 sets the above-mentioned selection candidate slot set and extracts resources R1 to R8 from the selection candidate slot set. Further, as shown in FIG. 7A, the communication device 2 shall transmit V2X data by using the resource R1. Here, the parameter K representing the feedback timing is 3. In this case, the destination terminal of the V2X data transmits the feedback signal via the feedback channel set in the slot S4. That is, the communication device 2 receives the feedback signal via the feedback channel set in the slot S4. On the other hand, the communication device 2 can retransmit the V2X data after receiving the feedback signal. Therefore, when the V2X data is transmitted using the resource R1, the communication device 2 can retransmit the V2X data using any of the resources R5 to R8.

In the example shown in FIG. 7B, the communication device 2 transmits V2X data using the resource R2. In this case, the destination terminal of the V2X data cannot transmit the feedback signal via the feedback channel set in the slot S4, and transmits the feedback signal via the feedback channel set in the slot S8. That is, the communication device 2 receives the feedback signal via the feedback channel set in the slot S8. Therefore, when the V2X data is transmitted using the resource R2, the communication device 2 can retransmit the V2X data using the resource R8.

In the example shown in FIG. 7C, the communication device 2 transmits V2X data using the resource R5. In this case, the destination terminal of the V2X data transmits the feedback signal via the feedback channel set in the slot S12. That is, the communication device 2 receives the feedback signal via the feedback channel set in the slot S12. Therefore, when the V2X data is transmitted using the resource R5, the communication device 2 cannot retransmit using the resources in the selection candidate slot set. In this case, the communication device 2 performs a new resource selection process in order to perform retransmission. The resource selection process sets the selection candidate slot set and determines the resource based on the sensing results in the corresponding sensing interval. However, when a new resource selection process is performed, the power consumption of the communication device 2 and the delay of data transmission increase.

In this way, in a communication system that performs HARQ feedback, the resources that can be selected for retransmission are reduced. As an example, a case where HARQ feedback is performed and a case where HARQ feedback is not performed are compared.

HARQ feedback shall not be performed in the selection candidate slot set shown in FIG. In this case, when the resource R1 is used for the first transmission, the communication device 2 can select a resource for retransmission from the resources R2 to R8. That is, the number of resources that can be selected for retransmission is 7. Further, when the resource R2 is used for the first transmission, the communication device 2 can select a resource for retransmission from the resources R4 to R8. That is, the number of resources that can be selected for retransmission is five. Similarly, when the first transmission is performed using the resources R3, R4, R5, R6, R7, and R8, the number of resources that can be selected for retransmission is 5, 4, 3, 2, 1, respectively. , 0. Therefore, the total number of resource combinations that can realize initial transmission and retransmission in the selection candidate slot set shown in FIG. 6 is 27.

Subsequently, HARQ feedback shall be performed in the selection candidate slot set shown in FIG. In this case, when the resource R1 is used for the first transmission, the communication device 2 can select a resource for retransmission from the resources R5 to R8 as shown in FIG. 7A. That is, the number of resources that can be selected for retransmission is four. Further, when the resource R2 is used for the first transmission, as shown in FIG. 7B, the communication device 2 can select the resource 8 for the retransmission. That is, the number of resources that can be selected for retransmission is 1. Similarly, when the first transmission is performed using the resource R3 or the resource R4, the number of resources that can be selected for retransmission is 1. Further, when the resource R4 is used for the first transmission, as shown in FIG. 7C, the communication device 2 cannot perform the retransmission in the selection candidate slot set. Similarly, when the resources R5 to R8 are used for the first transmission, the communication device 2 cannot perform the retransmission in the selection candidate slot set. Therefore, the total number of resource combinations that can realize initial transmission and retransmission in the selection candidate slot set shown in FIG. 6 is 7.

In this way, in the communication system that performs HARQ feedback, the resources that can be selected for retransmission in the selection candidate slot set are reduced. Then, there is a high probability that a plurality of communication devices in the communication system will select the same resource. As a result, the probability of packet collisions increases. Therefore, the communication device according to the embodiment of the present invention has a function of increasing the resources that can be selected for retransmission in the selection candidate slot set in the communication system that performs HARQ feedback.

<Embodiment>
8 to 10 show an example of arranging the resource selection area. In this example, as in FIG. 6, the selection window consists of 20 slots. The selection candidate slot set also includes nine slots. Further, the feedback channel PSFCH is set every 4 slots.

The selection candidate slot set includes multiple Cebu sets. In the example shown in FIG. 8, the selection candidate slot set is composed of two subsets. Each subset is an example of a resource selection area. That is, the communication device 2 can select a resource for transmitting or retransmitting V2X data from each subset.

There is a gap between the subsets. The gap is an example of a resource non-selected area. That is, the communication device 2 does not select resources in the gap to transmit or retransmit V2X data.

The width of the gap is determined based on the HARQ round trip time. Specifically, the gap G is determined by the equation (1).
G ≧ min ( _TRTT ) -1 ... (1)

“Min ( _TRTT )” represents the minimum value of the HARQ round trip time. The HARQ round trip time represents the time from transmission of V2X data to retransmission corresponding to the transmission in the HARQ feedback procedure. For example, in FIG. 7A, when the first transmission is performed in the slot S1, the retransmission can be performed after the feedback channel set in the slot S4. That is, the retransmission is performed in slot S5 in the earliest case. Therefore, in this case, the minimum HARQ round trip time is 4 slots. Further, in FIG. 7B, when the first transmission is performed in the slot S2, the retransmission can be performed after the feedback channel set in the slot S8. That is, the retransmission is performed in slot S9 in the earliest case. Therefore, in this case, the minimum HARQ round trip time is 7 slots. The "-1" in the above calculation formula represents "1 slot" and is provided to obtain a "gap" between subsets. Thus, the time between the last slot of the subsystem and the first slot of the next subset corresponds to the minimum round trip time.

In the example shown in FIG. 9, the selection candidate slot set is composed of three subsets. As described above, the number of subsets that can be set in the selection window is not particularly limited.

In the example shown in FIG. 10, each subset is composed of a plurality of non-consecutive slots. In this case, the communication device 2 can select only the resources represented by the diagonal lines. For example, the communication device 2 selects a resource from the first, second, and fourth slots when performing the first transmission.

In the cases shown in FIGS. 9 to 10, the communication device 2 may be set to retransmit once for the first transmission, or may be set to retransmit twice for the first transmission. good. That is, the following retransmission patterns can be set.
Initial transmission: Subset 1, Retransmission: Subset 2
Initial transmission: Subset 1, Retransmission: Subset 3
Initial transmission: Subset 2, Retransmission: Subset 3
First transmission: Subset 1, First retransmission: Subset 2, Second retransmission: Subset 3

11 to 12 show an example of the minimum HARQ round trip time. Here, the minimum HARQ round trip time is determined based on the parameters N, K, Np, and the transmission timing. N represents the period in which the feedback channel is set, which is "4" in this example. K represents the minimum interval between PSCH reception and the corresponding HARQ feedback, which is "3" in FIG. 11 and "2" in FIG. Np represents the feedback processing time. Here, Np is represented by the number of slots. In this example, Np is "0". That is, the time required for feedback processing is shorter than one symbol time. The transmission timing represents a slot in which V2X data is transmitted. In FIGS. 11 to 12, the transmission timing is represented by "Tx".

Also, in this example, a slot number that identifies each slot in the resource pool is given. In FIGS. 11 to 12, slot numbers "0" to "11" are assigned to the 12 slots. In the following description, the slot in which V2X data is transmitted may be referred to as a “transmission slot”. A slot in which a feedback channel is set is sometimes called a "feedback slot". In FIG. 11,

slots

3, 7, and 11 are feedback slots.

FIG. 11 shows a case where slots 0 to 3 are transmission slots in a communication system in which K = 3. FIG. 12 shows a case where slots 0 to 3 are transmission slots in a communication system in which K = 2.

As shown in FIGS. 11 to 12, when the number of slots from the transmission slot to the first feedback slot (hereinafter referred to as the first feedback slot) set after the transmission slot is K or more, the feedback slot is used. The feedback signal comes back. That is, in Case 1 shown in FIG. 11 and

Cases

1 and 2 shown in FIG. 12, the feedback signal is returned in the first feedback slot. Thus, in these cases, at the earliest, retransmissions occur in the slot following the first feedback slot.

On the other hand, when the number of slots from the transmission slot to the first feedback slot is smaller than K, the feedback signal is returned in the second feedback slot from the transmission slot. That is, in cases 2 to 4 shown in FIG. 11 and cases 3 to 4 shown in FIG. 12, the feedback signal is returned in the second feedback slot. Therefore, in these cases, the retransmission is performed in the slot next to the second feedback slot at the earliest.

In this way, the minimum HARQ round trip time can be determined based on the number of slots from the transmission slot to the first feedback slot. It is also possible to calculate the minimum HARQ round trip time using the following equation based on the parameters described above. In the following equation, "() modN" represents an operator that divides the numerical value in parentheses by N to calculate the remainder. “N” represents the slot number of the transmission slot in the resource pool.
When (n + K + 1) modN = 0: min ( _TRTT ) = K + Np + 1
Otherwise: min ( _TRTT ) = K + Np + N + 1-{(n + K + 1) modN}

Here, the minimum HARQ round trip time represents the minimum value of the time required from transmission to retransmission corresponding to the transmission in the HARQ feedback system. Therefore, no retransmission is performed during the period from the transmission slot to the "minimum HARQ round trip time-1 slot".

Therefore, the width of the gap between the subsets shown in FIGS. 8 to 10 is set to "minimum HARQ round trip time-1 slot" or more. Then, immediately after the subset for selecting the transmission resource, a gap interval in which no retransmission occurs is provided. That is, the slots constituting the selection candidate slot set are not arranged in the section where retransmission is not performed. Therefore, when the number of slots used as the selection candidate slot set is determined, the slots constituting the selection candidate slot set can be arranged in the section where retransmission can be performed.

Therefore, more resources can be selected for resending in the selection window. Then, since the probability that a plurality of communication devices in the communication system select the same resource is low, the probability that packet collision occurs is low.

As described above, the minimum HARQ round trip time can be calculated from the feedback channel period N, feedback timing K, and processing time Np. Here, N and K are set in advance for each resource pool, or are notified from the base station 1 by RRC signaling. Further, the processing time Np is set in advance based on the capability of the communication device 2, or is notified from the base station 1 by RRC signaling.

Also, the minimum HARQ round trip time is determined for the subset set in the selection window. In this case, the table shown in FIG. 13 (a) or FIG. 13 (b) is prepared. The table is set in the communication device 2 in advance, or is notified from the base station 1 by RRC signaling. Then, the communication device 2 acquires the minimum HARQ round trip time by searching the table. At this time, "n" represents the slot number of the last slot of the subset set before the gap.

FIG. 14 is a flowchart showing an example of a communication method according to the embodiment of the present invention. The processing of this flowchart is executed, for example, when a resource (re) selection trigger is generated in the communication device 2, or periodically.

In S1, the communication device 2 sets a selection window corresponding to the resource (re) selection trigger. The parameters for setting the selection window (T1, T2, etc. in FIG. 3) are predetermined or notified from the base station 1.

In S2, the communication device 2 sets a selection candidate slot set in the selection window. The number of slots included in the selection candidate slot set is predetermined or notified by the base station 1. Here, the selection candidate slot set includes a plurality of subsets as shown in FIGS. 8 to 10. That is, in S2, a plurality of subsets are set in the selection window. Each subset is an example of a resource selection area. How to set up multiple subsets will be described in detail later.

In S3, the communication device 2 sets a sensing section. The sensing section is not particularly limited, but is set by the method described with reference to FIG. 3, for example. In S4, the communication device 2 performs sensing in the sensing section and analyzes the result. Specifically, the control information (for example, SCI) is decoded for each resource in the sensing section, and the received power (for example, RSRP of PSCCH or RSRP or RSSI of PSCH) is calculated. The result of sensing is saved in memory.

The processes of S5 to S9 are executed for each subset. In S5 to S6, the communication device 2 extracts a resource reserved by another communication device and whose received power is larger than the threshold value, based on the sensing result. When the communication device (here, the communication device Z) reserves a resource for V2X communication, the communication device (here, communication device Z) notifies the surrounding devices of the content of the reservation by using SCI. At this time, this notification reaches each communication device located around the communication device Z. Therefore, the communication device 2 can detect the resource reservation by sensing. Then, the communication device 2 excludes the resources extracted based on the reserved and received power from the resources in the selection candidate slot set.

In S7, the communication device 2 determines whether or not a predetermined amount or more of resources remain in each subset. The predetermined amount is, for example, 20 percent of the total amount of resources in the initial state of the subset. Then, when the amount of the remaining resources is less than the predetermined amount, the communication device 2 increases the threshold value in S8. At this time, the threshold value is incremented by, for example, 3 dB. After that, the processing of the communication device 2 returns to S5. That is, the processes S6 to S9 are repeatedly executed until the amount of resources remaining in the subset becomes a predetermined amount or more. Then, when the amount of resources remaining in the subset exceeds a predetermined amount, the processing of the communication device 2 proceeds to S9.

In S9, the communication device 2 selects a resource for transmitting data from the resources remaining in each subset. Then, the communication device 2 transmits data using the selected resource.

FIG. 15 is a flowchart showing an example of a process of setting a plurality of subsets in the selection window. In the following description, it is assumed that the number Y of slots extracted as the selection candidate slot set in the selection window is specified in advance. Further, the processing of this flowchart corresponds to S2 shown in FIG. That is, it is assumed that the selection window is set before the processing of this flowchart is executed.

In S11, the communication device 2 initializes the variable i to "1". The variable i identifies the subset. In S12, the communication device 2 selects consecutive Ni slots constituting the subset i in the selection window, as shown in FIG. 16A. The communication device 2 can select consecutive Ni slots at arbitrary positions in the selection window.

In S13, the communication device 2 sets the gap X for the first slot of the subset i, and excludes the slots belonging to the gap X from the selection target slots. In this example, the first slot of the subset i also belongs to the gap X, but the first slot of the subset i remains selected and is not excluded. In the example shown in FIG. 16A, four slots are excluded. The method of determining the width of the gap X will be described later.

In S14, the communication device 2 sets the gap Y for the last slot of the subset i, and excludes the slots belonging to the gap Y from the selection target slots. In this example, the last slot of the subset i also belongs to the gap Y, but the first slot of the subset i remains selected and is not excluded. In the example shown in FIG. 16A, three slots are excluded. The width of the gap Y is the minimum HARQ round trip time described with reference to FIGS. 11 to 13.

In S15, the communication device 2 increments the variable i. In S16, the communication device 2 selects consecutive Ni slots constituting the next subset i in the selection window. At this time, the communication device 2 does not select the slots excluded in S13 to S14. Further, the communication device 2 does not select the previously selected slot.

In S17, the communication device 2 compares the total number of slots ΣNi selected as the subset i with the predetermined number Ntotal. As described above, Ntotal represents the number of slots extracted as the selection candidate slot set in the selection window. Then, when ΣNi is smaller than Ntotal, the communication device 2 returns the slots excluded in S13 to S14 to a selectable state in S18. After that, the processing of the communication device 2 returns to S13. That is, the processes S13 to S18 are repeatedly executed until ΣNi becomes Ntotal or more. Then, when ΣNi becomes Ntotal or more, the process of setting the subset ends.

FIG. 17 is a flowchart showing another example of the process of setting a plurality of subsets in the selection window. In this example, each subset contains non-contiguous slots, as shown in FIG. 16 (b).

The procedure for setting the subset in the selection window is almost the same in FIGS. 15 and 17. However, in S12b and S16b executed in place of S12 and S16, the communication device 2 selects Ni non-contiguous slots as the subset i. At this time, the interval between the slots selected as the subset i is shorter than the minimum HARQ round trip time. Further, the communication device 2 excludes the slots located between the slots selected as the subset i in S21 from the selection target slots.

The width of the gap X is calculated based on the period N in which the feedback channel is set, the feedback timing K, and the processing time Np, similarly to the gap Y (that is, the minimum HARQ round trip time). For example, the width of the gap X is calculated by the following equation.
When (n + 1) modN = 0: Gap X = K + N + Np-1
Otherwise: Gap X = K + Np + {(n + 1) modN} -1

Further, the width of the gap X may be obtained by referring to the table shown in FIG. 18 (a) or FIG. 18 (b). The table is set in the communication device 2 in advance, or is notified from the base station 1 by RRC signaling. Then, the communication device 2 acquires the width of the gap X by searching the table. At this time, "n" represents the slot number of the first slot of each subset.

In the example shown in FIG. 15 or 17, a subset is set using gap X and gap Y, but the invention is not limited to this method. For example, in the example shown in FIG. 19, a subset is set using _{"minimum HARQ round trip time TRTT -1".} In the following description, it is assumed that the feedback channel PSFCH is set every 4 slots as shown in FIG. 19A. That is, N = 4. The K representing the minimum interval between PSCH reception and the corresponding HARQ feedback is 3. The HARQ processing time Np is 0. That is, the time required for HARQ processing is shorter than one symbol time. The number Y of slots selected as the selection candidate slot set from the selection window is 9.

First, as shown in FIG. 19B, subset 1 is set. Subset 1 is set at the top of the selection window, but is not particularly limited. Also, in this example, subset 1 includes three slots.

Subset 2 is set to have a " _TRTT -1" slot gap between

subsets

1 and 2, as shown in FIG. 19 (c). Here, the slot number of the last slot of the subset 1 is "2". That is, the time from the last slot of subset 1 to the feedback slot closest to subset 1 is one slot. Therefore, the minimum HARQ round trip time is determined according to Case 3 shown in FIG. Specifically, since the minimum HARQ round trip time is "6", " _TRTT -1 = 5" can be obtained. Therefore, subset 2 starts at slot 8. In other words, the time between the last slot of Subset 1 and the first slot of Subset 2 is the minimum HARQ round trip time. Also, in this example, subset 2 includes three slots. Then, since the total number of slots included in the

subsets

1 and 2 is 6, which is less than the value of Y (that is, 9), the communication device 2 sets the next subset.

Subset 3 is set to have a " _TRTT -1" slot gap between

subsets

2 and 3, as shown in FIG. 19 (d). Here, the slot number of the last slot of the subset 2 is "10". That is, the time from the last slot of the subset 2 to the feedback slot closest to the subset 2 is one slot. Therefore, the minimum HARQ round trip time is determined according to Case 3 shown in FIG. That is, " _TRTT -1 = 5" is obtained. Therefore, subset 3 starts at slot 16. Also, in this example, subset 3 includes three slots. Then, the total number of slots included in the subsets 1 to 9 is "9", which is Y or more, so that the process of setting the subset ends.

Next, the effect of the embodiment of the present invention will be described. Here, the total number of resource combinations that can realize initial transmission and retransmission is compared for the following four cases.
Case 1: No HARQ feedback in the selection candidate slot set shown in FIG. 6: HARQ feedback is performed in the selection candidate slot set shown in FIG. 6: Case 3:

Subsets

1 and 2 shown in FIG. 20 (a).
Case 4: Subsets 1 to 3 shown in FIG. 20 (b)

The total number of combinations of Case 1 and Case 2 is 27 and 7, respectively, as described with reference to FIGS. 6 to 7. That is, in the selection candidate slot set shown in FIG. 6, when HARQ feedback is performed, the number of selectable resources decreases and the probability of packet collision increases.

In case 3, as shown in FIG. 20A,

subsets

1 and 2 are set. Here, in each of the

subsets

1 and 2, 20% or more of the resources are selected as selectable resources. Specifically, resources R1 to R4 are selected in subset 1, and resources R5 to R8 are selected in subset 2. Also, the time from the last slot of Subset 1 to the first slot of Subset 2 corresponds to the minimum HARQ round trip time.

Therefore, when the first transmission is performed in the subset 1, the corresponding retransmission can be performed in the subset 2. For example, when the first transmission is performed using the resource R1, the communication device 2 receives the feedback signal in the slot S4. In this case, the communication device 2 can select a resource for retransmission from the selectable resources in slots S5 and thereafter. That is, the communication device 2 can select any one of the resources R5 to R8 for retransmission. Therefore, when the first transmission is performed using the resource R1, the number of combinations of resources that can realize the first transmission and the retransmission is four. Similarly, when the first transmission is performed using the resource R2, the number of combinations of resources that can realize the first transmission and the retransmission is four.

When the first transmission is performed using the resource R3, the communication device 2 receives the feedback signal in the slot S8. In this case, the communication device 2 can select a resource for retransmission from the selectable resources in slots S9 and thereafter. That is, the communication device 2 can select any one of the resources R5 to R8 for retransmission. Therefore, even when the first transmission is performed using the resource R2, the number of combinations of resources that can realize the first transmission and the retransmission is four. Similarly, when the first transmission is performed using the resource R4, the number of combinations of resources that can realize the first transmission and the retransmission is four. Therefore, in Case 3, the total number of resource combinations that can realize the initial transmission and the retransmission is 16 as shown in FIG.

In case 4, as shown in FIG. 20 (b), subsets 1 to 3 are set. Here, in each of the subsets 1 to 3, 20% or more of the resources are selected as selectable resources. Specifically, resources R1 to R3 are selected in subset 1, resources R4 to R6 are selected in subset 2, and resources R7 to R9 are selected in subset 3. Also, the time from the last slot of subset 1 to the first slot of subset 2 corresponds to the minimum HARQ round trip time, and the time from the last slot of subset 2 to the first slot of subset 3 is also the minimum HARQ round trip time. Corresponds to.

Therefore, when the first transmission is performed in the subset 1, the corresponding retransmission can be performed in the subset 2 or the subset 3. That is, when the first transmission is performed using the resource R1, it is possible to perform the retransmission using any of the resources R4 to R9. The same applies when the first transmission is performed using the resources R2 and R3. Therefore, when the first transmission is performed in the subset 1, the total number of resource combinations that can realize the first transmission and the retransmission is 18.

Further, when the first transmission is performed in the subset 2, the corresponding retransmission can be performed in the subset 3. That is, when the first transmission is performed using the resource R4, it is possible to perform the retransmission using any of the resources R7 to R9. The same applies when the first transmission is performed using the resources R5 and R6. Therefore, when the first transmission is performed in the subset 2, the total number of resource combinations that can realize the first transmission and the retransmission is nine. Therefore, in Case 4, the total number of resource combinations that can realize the initial transmission and the retransmission is 27, as shown in FIG.

As described above, in cases 3 to 4 according to the embodiment of the present invention, the total number of combinations of resources capable of realizing initial transmission and retransmission is larger than that in case 2. That is, by dividing the selection candidate slot set into a plurality of subsets, the probability that a plurality of communication devices in the communication system select the same resource is reduced. As a result, the probability of packet collisions is low. In addition, the communication method according to the embodiment of the present invention is premised on the partial sensing shown in FIG. That is, the communication method according to the embodiment of the present invention can suppress packet collision while reducing power consumption and improving reliability by HARQ feedback.

FIG. 22 shows an example of the configuration of the base station 1. The base station 1 is, for example, a next-generation base station apparatus (gNB: Next generation NodeB). Then, as shown in FIG. 22, the base station 1 includes a control unit 11, a storage unit 12, a network interface 13, a radio transmission unit 14, and a radio reception unit 15. The base station 1 may have other circuits or functions not shown in FIG. 22.

The control unit 11 controls the cellular communication provided by the base station 1. Further, the control unit 11 may determine parameters for D2D communication (that is, side link communication) performed by the communication device 2. For example, the control unit 11 may determine parameters T1 and T2 representing the arrangement of the selection window shown in FIG. 5, parameter Y representing the number of slots in the selection candidate slot set, and the like. Further, the control unit 11 may determine a parameter N representing the period of the feedback channel, a parameter K representing the minimum interval between the PSCH reception and the corresponding HARQ feedback, and the like. The determined parameter is notified to the communication device 2 by, for example, PDCCH or RRC. The control unit 11 is realized by the processor in this embodiment. However, some of the functions of the control unit 11 may be realized by a hardware circuit.

The storage unit 12 stores a software program executed by the processor. Further, the storage unit 12 stores data and information necessary for controlling the operation of the base station 1. The storage unit 12 is realized by, for example, a semiconductor memory. The network interface 13 provides an interface for connecting to the core network. That is, the base station 1 can be connected to another base station 1 or a network management system that controls the base station 1 via the network interface 13.

The wireless transmission unit 14 transmits a wireless signal for cellular communication according to an instruction given from the control unit 11. That is, the wireless transmission unit 14 transmits a downlink signal to the communication device 2 located in the cell. The radio receiving unit 15 receives the radio signal of cellular communication according to the instruction given from the control unit 11. That is, the wireless receiving unit 15 receives the uplink signal transmitted from the communication device 2 located in the cell. Note that cellular communication is provided, for example, using the 2.4 GHz band and / or the 4 GHz band.

FIG. 23 shows an example of the configuration of the communication device 2. The communication device 2 supports cellular communication and D2D communication. Note that D2D communication is realized by using a frequency band different from that of cellular communication. For example, D2D communication is provided using the 6 GHz band. However, the D2D communication may share the same frequency band as the uplink of the cellular communication. The communication device 2 includes a control unit 21, a storage unit 22, a wireless transmission unit 23, a wireless reception unit 24, a wireless transmission unit 25, and a wireless reception unit 26. The communication device 2 may have other circuits or functions not shown in FIG.

The control unit 21 controls the cellular communication and the D2D communication provided by the communication device 2. The control unit 21 is realized by the processor in this embodiment. In this case, the control unit 21 provides a function of controlling cellular communication and D2D communication by executing a software program stored in the storage unit 22. For example, the control unit 21 executes a program that describes the processing of the flowchart shown in FIG. 14 (including the processing of the flowchart shown in FIG. 15 or 17). In this case, the control unit 21 executes, for example, the processing of the flowchart shown in FIG. 14 in response to the resource (re) selection trigger in the communication device 2. Further, the control unit 21 provides a function of a resource area determination unit that determines a plurality of subsets as a resource selection area and a resource selection unit that selects a resource for transmitting a D2D signal from the resource selection area. A part of the function of the control unit 21 may be realized by a hardware circuit.

The storage unit 22 stores a software program executed by the processor. Further, the storage unit 22 stores data and information necessary for controlling the operation of the communication device 2. The storage unit 22 is realized by, for example, a semiconductor memory.

The wireless transmission unit 23 transmits a wireless signal for cellular communication according to an instruction given from the control unit 21. That is, the wireless transmission unit 23 transmits an uplink signal to the base station 1. The radio receiving unit 24 receives the radio signal of cellular communication according to the instruction given from the control unit 21. That is, the wireless receiving unit 24 receives the downlink signal transmitted from the base station 1. At this time, the wireless reception unit 24 may receive parameters related to resource selection for D2D communication from the base station 1.

The wireless transmission unit 25 transmits a wireless signal for D2D communication according to an instruction given from the control unit 21. That is, the wireless transmission unit 25 transmits a D2D signal to another communication device by using the resource selected by the communication device 2 by itself. The radio receiving unit 26 receives a radio signal for D2D communication according to an instruction given from the control unit 21. That is, the wireless receiving unit 26 receives the D2D signal transmitted from another communication device. The D2D signal includes V2X data and V2X control information in this embodiment. The sensing process of S4 shown in FIG. 14 is executed by the wireless receiving unit 26. That is, the wireless receiving unit 26 has a sensing function. In this case, the wireless receiving unit 26 may include a processor that executes the sensing process.

In the example shown in FIG. 23, the wireless communication unit for cellular communication and the wireless communication unit for D2D communication are provided separately from each other, but the communication device 2 is not limited to this configuration. .. For example, the wireless communication unit for cellular communication and the wireless communication unit for D2D communication may be shared. In this case, the wireless transmission unit 25 and the wireless reception unit 26 are unnecessary. Then, the wireless transmission unit 23 transmits the cellular signal and the D2D signal, and the wireless reception unit 24 receives the cellular signal and the D2D signal. Further, the wireless receiving unit 24 has a sensing function.

1 Base station 2 Communication device 11 Control unit 12 Storage unit 13 Network interface 14 Wireless transmission unit 15 Wireless reception unit 21 Control unit 22

Storage unit

23, 25

Wireless transmission unit

24, 26 Wireless reception unit 100 Wireless communication system

Claims

A communication device that supports D2D (Device-to-Device) communication.
A resource selection area determination unit that determines a first resource selection area and a second resource selection area set at a distance of a predetermined interval or more from the first resource selection area, and a resource selection area determination unit.
A resource selection unit that selects a resource for transmitting D2D data from at least one of the first resource selection area or the second resource selection area, and a resource selection unit.
A wireless transmission unit that transmits D2D data using the resources selected by the resource selection unit, and
A communication device equipped with.
The resource selection unit is characterized by selecting a resource for transmitting D2D data from the first resource selection area and selecting a resource for retransmitting the D2D data from the second resource selection area. The communication device according to claim 1.
The predetermined interval is based on at least one of the period in which the feedback channel for transmitting the feedback signal is set, or the minimum interval between PSCH (Physical Sidelink Shared Channel) reception and the corresponding HARQ (hybrid automatic repeat request) feedback. The communication device according to claim 1, wherein the communication device is determined.
The predetermined interval is determined based on a round trip time representing the time from when the D2D data is transmitted until the retransmission of the D2D data based on the feedback signal corresponding to the D2D data becomes possible. The communication device according to claim 1.
The communication device according to claim 4, wherein the time between the last slot of the first selection area and the first slot of the second resource selection area is the round trip time.
The communication device according to claim 4 or 5, wherein the round trip time is determined based on a period in which a feedback channel for transmitting a feedback signal is set.
The claim is characterized in that the round trip time is determined based on the period and the time between the transmission slot in which the D2D data is transmitted and the slot including the feedback channel initially set after the transmission slot. The communication device according to 6.
A communication method executed by a communication device that supports D2D (Device-to-Device) communication.
A first resource selection area and a second resource selection area set apart from the first resource selection area by a predetermined interval or more are determined.
Select a resource for transmitting D2D data from at least one of the first resource selection area or the second resource selection area, and select a resource.
A communication method characterized in transmitting D2D data using selected resources.
A communication system including a plurality of communication devices that support D2D (Device-to-Device) communication.
The first communication device among the plurality of communication devices is
A first resource selection area and a second resource selection area set apart from the first resource selection area by a predetermined interval or more are determined.
A resource for transmitting D2D data is selected from the first resource selection area, and a resource for retransmitting the D2D data is selected from the second resource selection area.
Using the resource selected from the first resource selection area, the D2D data is transmitted to the second communication device among the plurality of communication devices.
The second communication device transmits a feedback signal indicating whether the reception of the D2D data was successful or unsuccessful to the first communication device.
When the second communication device receives a feedback signal indicating whether the reception of the D2D data has failed from the second communication device, the second communication device uses the resource selected from the second resource selection area. A communication system characterized in that D2D data is retransmitted to the second communication device.