WO2016148544A1

WO2016148544A1 - Method and apparatus for performing direct communication among multiple users via group relaying in wireless communication system

Info

Publication number: WO2016148544A1
Application number: PCT/KR2016/002783
Authority: WO
Inventors: Yunjung Yi; Hanbyul Seo
Original assignee: Lg Electronics Inc.
Priority date: 2015-03-18
Filing date: 2016-03-18
Publication date: 2016-09-22

Abstract

A method and apparatus for performing device-to-device (D2D) transmission in a wireless communication system is provided. A first device which belongs to a first group of devices, transmits a first signal by using a first resource used for initial transmission of the first group of devices, receives a second signal by using a second resource used for initial transmission of a second group of devices, and relays the second signal by using a third resource used for relaying of the second group of devices.

Description

METHOD AND APPARATUS FOR PERFORMING DIRECT COMMUNICATION AMONG MULTIPLE USERS VIA GROUP RELAYING IN WIRELESS COMMUNICATION SYSTEM

The present invention relates to wireless communications, and more particularly, to a method and apparatus for performing direct communication among multiple users via group relaying in a wireless communication system.

3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

Recently, there has been a surge of interest in supporting proximity-based services (ProSe). Proximity is determined ("a user equipment (UE) is in proximity of another UE") when given proximity criteria are fulfilled. This new interest is motivated by several factors driven largely by social networking applications, and the crushing data demands on cellular spectrum, much of which is localized traffic, and the under-utilization of uplink frequency bands. 3GPP is targeting the availability of ProSe in LTE rel-12 to enable LTE become a competitive broadband communication technology for public safety networks, used by first responders. Due to the legacy issues and budget constraints, current public safety networks are still mainly based on obsolete 2G technologies while commercial networks are rapidly migrating to LTE. This evolution gap and the desire for enhanced services have led to global attempts to upgrade existing public safety networks. Compared to commercial networks, public safety networks have much more stringent service requirements (e.g., reliability and security) and also require direct communication, especially when cellular coverage fails or is not available. This essential direct mode feature is currently missing in LTE.

Vehicle-to-everything (V2X) communication is the passing of information from a vehicle to any entity that may affect the vehicle, and vice versa. This information exchange can be used for a host of safety, mobility and environmental applications to include driver assistance and vehicle safety, speed adaptation and warning, emergency response, safety, traveler information, navigation, traffic operations and demand management, personal navigation, commercial fleet planning and payment transactions. There is significant societal benefit and commercial value to delivering safety, mobility and convenience applications that rely on V2X.

The wide variety of use cases cannot only be met with a short-range radio solution working in a peer to peer manner. Some V2X use cases require infrastructure assistance for communication, and some use cases can make use of smaller scale infrastructure such as small cells or methods such as relaying. For this, the 3GPP has a role to play in defining, examining and acting on the variety of use cases to support the V2X effort. 3GPP infrastructure and 3GPP ProSe can act in support and enhancement to dedicated short range communications (DSRC) to fulfil many use cases. There is also the opportunity for 3GPP to investigate modifications and enhancements to ProSe to meet or improve the performance of short range communications in terms of spectral efficiency, effective range, bandwidth and throughput, error resiliency, and improved latency.

Since ProSe may apply to V2X communication, m-to-m communication/discovery may be possible. However, some mechanism may be required for efficient m-to-m communication/discovery.

The present invention provides a method and apparatus for performing direct communication among multiple users via group relaying in a wireless communication system. The present invention discusses mechanisms to enable m-to-m communication among devices using direct communication, particularly in case devices are assumed as half-duplex devices (i.e. the device may receive or transmit in a frequency at a given time).

In an aspect, a method for performing, by a first device which belongs to a first group of devices, device-to-device (D2D) transmission in a wireless communication system is provided. The method includes transmitting a first signal by using a first resource used for initial transmission of the first group of devices, receiving a second signal by using a second resource used for initial transmission of a second group of devices, and relaying the second signal by using a third resource used for relaying of the second group of devices.

In another aspect, a first device which belongs to a first group of devices in a wireless communication system is provided. The first device includes a memory, a transceiver, and a processor coupled to the memory and the transceiver. The processor is configured to control the transceiver to transmit a first signal by using a first resource used for initial transmission of the first group of devices, control the transceiver to receive a second signal by using a second resource used for initial transmission of a second group of devices, and control the transceiver to relay the second signal by using a third resource used for relaying of the second group of devices.

Efficient coordination between devices can be achieved when multiple devices perform device-to-device (D2D) transmission.

FIG. 1 shows a wireless communication system.

FIG. 2 shows structure of a radio frame of 3GPP LTE.

FIG. 3 shows a resource grid for one downlink slot.

FIG. 4 shows structure of a downlink subframe.

FIG. 5 shows structure of an uplink subframe.

FIG. 6 shows an example of multiple devices served by the same cell or operator.

FIG. 7 shows an example of transmission by multiple devices served by the same cell or operator.

FIG. 8 shows an example of multiple devices served by different cells or operators.

FIG. 9 shows an example of transmission by multiple devices served by different cells or operators.

FIG. 10 shows an example of grouping of devices according to an embodiment of the present invention.

FIG. 11 shows an example of transmission by multiple devices according to an embodiment of the present invention.

FIG. 12 shows another example of transmission by multiple devices according to an embodiment of the present invention.

FIG. 13 shows another example of transmission by multiple devices according to an embodiment of the present invention.

FIG. 14 shows example of multiple devices served by different cells or operators according to an embodiment of the present invention.

FIG. 15 shows another example of transmission by multiple devices according to an embodiment of the present invention.

FIG. 16 shows another example of transmission by multiple devices according to an embodiment of the present invention.

FIG. 17 shows example of multiple devices according to an embodiment of the present invention.

FIG. 18 shows another example of transmission by multiple devices according to an embodiment of the present invention.

FIG. 19 shows another example of transmission by multiple devices according to an embodiment of the present invention.

FIG. 20 shows a method for performing, by a device which belongs to a first group of devices, D2D transmission according to an embodiment of the present invention.

FIG. 21 shows a wireless communication system to implement an embodiment of the present invention.

Techniques, apparatus and systems described herein may be used in various wireless access technologies such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. The CDMA may be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. The TDMA may be implemented with a radio technology such as global system for mobile communications (GSM)/general packet radio service (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMA may be implemented with a radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved-UTRA (E-UTRA) etc. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved-UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE employs the OFDMA in downlink (DL) and employs the SC-FDMA in uplink (UL). LTE-advance (LTE-A) is an evolution of the 3GPP LTE. For clarity, this application focuses on the 3GPP LTE/LTE-A. However, technical features of the present invention are not limited thereto.

FIG. 1 shows a wireless communication system. The wireless communication system 10 includes at least one evolved NodeB (eNB) 11. Respective eNBs 11 provide a communication service to particular

geographical areas

15a, 15b, and 15c (which are generally called cells). Each cell may be divided into a plurality of areas (which are called sectors). A user equipment (UE) 12 may be fixed or mobile and may be referred to by other names such as mobile station (MS), mobile terminal (MT), user terminal (UT), subscriber station (SS), wireless device, personal digital assistant (PDA), wireless modem, handheld device. The eNB 11 generally refers to a fixed station that communicates with the UE 12 and may be called by other names such as base station (BS), base transceiver system (BTS), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongs is called a serving cell. An eNB providing a communication service to the serving cell is called a serving eNB. The wireless communication system is a cellular system, so a different cell adjacent to the serving cell exists. The different cell adjacent to the serving cell is called a neighbor cell. An eNB providing a communication service to the neighbor cell is called a neighbor eNB. The serving cell and the neighbor cell are relatively determined based on a UE.

This technique can be used for DL or UL. In general, DL refers to communication from the eNB 11 to the UE 12, and UL refers to communication from the UE 12 to the eNB 11. In DL, a transmitter may be part of the eNB 11 and a receiver may be part of the UE 12. In UL, a transmitter may be part of the UE 12 and a receiver may be part of the eNB 11.

The wireless communication system may be any one of a multiple-input multiple-output (MIMO) system, a multiple-input single-output (MISO) system, a single-input single-output (SISO) system, and a single-input multiple-output (SIMO) system. The MIMO system uses a plurality of transmission antennas and a plurality of reception antennas. The MISO system uses a plurality of transmission antennas and a single reception antenna. The SISO system uses a single transmission antenna and a single reception antenna. The SIMO system uses a single transmission antenna and a plurality of reception antennas. Hereinafter, a transmission antenna refers to a physical or logical antenna used for transmitting a signal or a stream, and a reception antenna refers to a physical or logical antenna used for receiving a signal or a stream.

FIG. 2 shows structure of a radio frame of 3GPP LTE. Referring to FIG. 2, a radio frame includes 10 subframes. A subframe includes two slots in time domain. A time for transmitting one subframe is defined as a transmission time interval (TTI). For example, one subframe may have a length of 1ms, and one slot may have a length of 0.5ms. One slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain. Since the 3GPP LTE uses the OFDMA in the DL, the OFDM symbol is for representing one symbol period. The OFDM symbols may be called by other names depending on a multiple-access scheme. For example, when SC-FDMA is in use as a UL multi-access scheme, the OFDM symbols may be called SC-FDMA symbols. A resource block (RB) is a resource allocation unit, and includes a plurality of contiguous subcarriers in one slot. The structure of the radio frame is shown for exemplary purposes only. Thus, the number of subframes included in the radio frame or the number of slots included in the subframe or the number of OFDM symbols included in the slot may be modified in various manners.

FIG. 3 shows a resource grid for one downlink slot. Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols in time domain. It is described herein that one DL slot includes 7 OFDM symbols, and one RB includes 12 subcarriers in frequency domain as an example. However, the present invention is not limited thereto. Each element on the resource grid is referred to as a resource element (RE). One RB includes 12×7 resource elements. The number N^DL of RBs included in the DL slot depends on a DL transmit bandwidth. The structure of a UL slot may be same as that of the DL slot. The number of OFDM symbols and the number of subcarriers may vary depending on the length of a CP, frequency spacing, etc. For example, in case of a normal cyclic prefix (CP), the number of OFDM symbols is 7, and in case of an extended CP, the number of OFDM symbols is 6. One of 128, 256, 512, 1024, 1536, and 2048 may be selectively used as the number of subcarriers in one OFDM symbol.

FIG. 4 shows structure of a downlink subframe. Referring to FIG. 4, a maximum of three OFDM symbols located in a front portion of a first slot within a subframe correspond to a control region to be assigned with a control channel. The remaining OFDM symbols correspond to a data region to be assigned with a physical downlink shared chancel (PDSCH). Examples of DL control channels used in the 3GPP LTE includes a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of a subframe and carries information regarding the number of OFDM symbols used for transmission of control channels within the subframe. The PHICH is a response of UL transmission and carries a HARQ acknowledgment (ACK)/non-acknowledgment (NACK) signal. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes UL or DL scheduling information or includes a UL transmit (Tx) power control command for arbitrary UE groups.

The PDCCH may carry a transport format and a resource allocation of a downlink shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information on a paging channel (PCH), system information on the DL-SCH, a resource allocation of an upper-layer control message such as a random access response transmitted on the PDSCH, a set of Tx power control commands on individual UEs within an arbitrary UE group, a Tx power control command, activation of a voice over IP (VoIP), etc. A plurality of PDCCHs can be transmitted within a control region. The UE can monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate based on a state of a radio channel. The CCE corresponds to a plurality of resource element groups.

A format of the PDCCH and the number of bits of the available PDCCH are determined according to a correlation between the number of CCEs and the coding rate provided by the CCEs. The eNB determines a PDCCH format according to a DCI to be transmitted to the UE, and attaches a cyclic redundancy check (CRC) to control information. The CRC is scrambled with a unique identifier (referred to as a radio network temporary identifier (RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UE may be scrambled to the CRC. Alternatively, if the PDCCH is for a paging message, a paging indicator identifier (e.g., paging-RNTI (P-RNTI)) may be scrambled to the CRC. If the PDCCH is for system information (more specifically, a system information block (SIB) to be described below), a system information identifier and a system information RNTI (SI-RNTI) may be scrambled to the CRC. To indicate a random access response that is a response for transmission of a random access preamble of the UE, a random access-RNTI (RA-RNTI) may be scrambled to the CRC.

FIG. 5 shows structure of an uplink subframe. Referring to FIG. 5, a UL subframe can be divided in a frequency domain into a control region and a data region. The control region is allocated with a physical uplink control channel (PUCCH) for carrying UL control information. The data region is allocated with a physical uplink shared channel (PUSCH) for carrying user data. When indicated by a higher layer, the UE may support a simultaneous transmission of the PUSCH and the PUCCH. The PUCCH for one UE is allocated to an RB pair in a subframe. RBs belonging to the RB pair occupy different subcarriers in respective two slots. This is called that the RB pair allocated to the PUCCH is frequency-hopped in a slot boundary. This is said that the pair of RBs allocated to the PUCCH is frequency-hopped at the slot boundary. The UE can obtain a frequency diversity gain by transmitting UL control information through different subcarriers according to time.

UL control information transmitted on the PUCCH may include a HARQ ACK/NACK, a channel quality indicator (CQI) indicating the state of a DL channel, a scheduling request (SR), and the like. The PUSCH is mapped to a UL-SCH, a transport channel. UL data transmitted on the PUSCH may be a transport block, a data block for the UL-SCH transmitted during the TTI. The transport block may be user information. Or, the UL data may be multiplexed data. The multiplexed data may be data obtained by multiplexing the transport block for the UL-SCH and control information. For example, control information multiplexed to data may include a CQI, a precoding matrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Or the UL data may include only control information.

Proximity-based services (ProSe) are described. "ProSe" may be used mixed with "D2D"(i.e. device-to-device). ProSe direct communication means a communication between two or more UEs in proximity that are ProSe-enabled, by means of user plane transmission using E-UTRA technology via a path not traversing any network node. ProSe-enabled UE means a UE that supports ProSe requirements and associated procedures. Unless explicitly stated otherwise, a ProSe-enabled UE refers both to a non-public safety UE and a public safety UE. ProSe-enabled public safety UE means a ProSe-enabled UE that also supports ProSe procedures and capabilities specific to public safety. ProSe-enabled non-public safety UE means a UE that supports ProSe procedures and but not capabilities specific to public safety. ProSe direct discovery means a procedure employed by a ProSe-enabled UE to discover other ProSe-enabled UEs in its vicinity by using only the capabilities of the two UEs with 3GPP LTE rel-12 technology. EPC-level ProSe discovery means a process by which the EPC determines the proximity of two ProSe-enabled UEs and informs them of their proximity. ProSe UE identity (ID) is a unique identity allocated by evolved packet system (EPS) which identifies the ProSe enabled UE. ProSe application ID is an identity identifying application related information for the ProSe enabled UE.

UE performs ProSe direct communication on subframes defined over the duration of sidelink control period.　The sidelink control period is the period over which resources allocated in a cell for sidelink control and sidelink data transmissions occur.　Within the sidelink control period, the UE sends a sidelink control followed by data. Sidelink control indicates a layer 1 ID and characteristics of the transmissions (e.g. modulation and coding scheme (MCS), location of the resource(s) over the duration of sidelink control period, timing alignment).

For ProSe direct communication, the UE supporting ProSe direct communication can operate in two modes for resource allocation, which include Mode 1 (scheduled resource allocation) and Mode 2 (UE autonomous resource selection). In Mode 1, the UE needs to be RRC_CONNECTED in order to transmit data. The UE requests transmission resources from the eNB. The eNB schedules transmission resources for transmission of sidelink control and data. The UE sends a scheduling request (dedicated scheduling request (D-SR) or random access) to the eNB followed by a ProSe buffer status report (BSR). Based on the ProSe BSR, the eNB can determine that the UE has data for a ProSe direct communication transmission and estimate the resources needed for transmission. The eNB can schedule transmission resources for ProSe direct communication using configured sidelink radio network temporary identifier (SL-RNTI). In Mode 2, a UE on its own selects resources from resource pools to transmit sidelink control and data.

ProSe direct discovery is defined as the procedure used by the UE supporting direct discovery to discover other UE(s) in its proximity, using E-UTRA direct radio signals via PC5. ProSe direct discovery is supported only when the UE is served by E-UTRAN.

There are two types of resource allocation for discovery message announcement, which include Type 1 (UE autonomous resource selection) and Type 2 (scheduled resource allocation). Type 1 is a resource allocation procedure where resources for announcing of discovery message are allocated on a non UE specific basis. In Type 1, the eNB provides the UE(s) with the resource pool configuration used for announcing of discovery message. The configuration may be signaled in broadcast or dedicated signaling. The UE autonomously selects radio resource(s) from the indicated resource pool and announce discovery message. The UE can announce discovery message on a randomly selected discovery resource during each discovery period. Type 2 is a resource allocation procedure where resources for announcing of discovery message are allocated on per UE specific basis. In Type 2, the UE in RRC_CONNECTED may request resource(s) for announcing of discovery message from the eNB via radio resource control (RRC). The eNB assigns resource(s) via RRC. The resources are allocated within the resource pool that is configured in UEs for monitoring.

D2D communication, which allows direct communication among devices without going through infrastructure (i.e. network), has wide-range of potential applications including vehicle-to-vehicle (V2V) communication, proximity communication, etc. For example, cars may exchange situation information such as traffic load, accidents information, etc., periodically to enhance the situation awareness. In most cases, multiple devices may be required to receive and transmit from other devices, in other words, m-to-m communication/discovery may be possible. Assuming only one frequency is used for D2D communication/discovery, m-to-m communication/discovery may not be directly achieved without considering some other mechanisms such as relaying.

FIG. 6 shows an example of multiple devices served by the same cell or operator. Referring to FIG. 6, it is assumed that there are five devices, i.e. D1, D2, D3, D4 and D5. Those five devices are served by the same cell or operator which shares the same resource pool.

FIG. 7 shows an example of transmission by multiple devices served by the same cell or operator. FIG. 7 shows transmission by five devices described in FIG. 6. If devices are randomly select the resource(s) to transmit D2D communication and/or discovery, some devices, which are not transmitting, may listen to D2D communication and/or discovery from other devices at the same time. However, devices, which are transmitting, cannot receive the D2D communication and/or discovery from other devices at the same time. For example, referring to FIG. 7, D1 and D4 perform transmission by using the same resource simultaneously. D4 cannot receive D2D communication and/or discovery from D1, and D1 cannot receive D2D communication and/or discovery from D4. Likewise, D3 cannot receive D2D communication and/or discovery from D2, and D2 cannot receive D2D communication and/or discovery from D3.

In this case, to allow message exchange between D1 and D4, another transmission mechanism or repeated transmission mechanism may be necessary. For example, a round-robin fashion transmission mechanism, where only one device which has the token can transmit at a given time, may be considered. However, this mechanism may not easily applicable to D2D communication/discovery when multi-hop transmissions may occur. Also, for this mechanism, a type of clustering/grouping may be necessary, but grouping over multiple high-speed moving devices may be challenging.

FIG. 8 shows an example of multiple devices served by different cells or operators. Referring to FIG. 6, it is assumed that there are five devices, i.e. D1, D2, D3, D4 and D5. Among those five devices, D1 and D3 are served by the first cell (or first operator) which uses the first resource pool for the first cell (or first operator). D2, D4 and D5 are served by the second cell (or second operator) which uses the second resource pool for the second cell (or second operator).

FIG. 9 shows an example of transmission by multiple devices served by different cells or operators. FIG. 9 shows transmission by five devices described in FIG. 8. When devices are served by different cells or operators, the issue described above becomes more complicated. Referring to FIG. 9, the D2D communication/discovery transmission from D1 may be heard only by D3, which belongs to the same cell as D1, unless some coordination among different cells are achieved and the devices listen on resources of other cells as well. However, since the resource pools are overlapped between two cells, unless tight synchronization between cells are assumed/achieved, one device may not be able to listen on resource pool(s) belonging to different cells/operators. Furthermore, if cells/operators use different frequencies for D2D operation, listening on devices served by different cells/operators becomes more challenging.

In order to solve the problem described above, a method for performing D2D communication/discovery among multiple users according to embodiments of the present invention is described. The present invention proposes m-to-m communication/discovery mechanism utilizing one of the following cases.

(1) Single frequency with different resource set and relay functionality: according to one embodiment of the present invention, devices may be divided into 'm' groups, and resource pool may be shared/used in a round-robin fashion among 'm' groups. To address half-duplex issue, additional resources may be reserved/used for relaying.

FIG. 10 shows an example of grouping of devices according to an embodiment of the present invention. Referring to FIG. 10, it is assumed that there are five devices, i.e. D1, D2, D3, D4 and D5. Those five devices are served by the same cell or operator which shares the same resource pool. Devices are divided into two groups. D1, D3 and D5 belong to group 1, and D2 and D4 to group 2.

FIG. 11 shows an example of transmission by multiple devices according to an embodiment of the present invention. FIG. 11 shows transmission by five devices described in FIG. 10. Resource pool may be used in a round-robin fashion. That is, resource pool for each group may be configured by time division multiplexing (TDM) manner. Referring to FIG. 11, the first resource pool is used by group 1 and the second resource pool is used by group 2. D1/D3/D5 may transmit discovery signals by using the first resource pool and D2/D4 may transmit discovery signals by using the second resource pool. By using the resource pool allocate to each group, each device in the corresponding group may transmit D2D communication/discovery. The device may or may not transmit by using the allocated resource depending on its traffic and/or others' traffic.

Each group may select resource pool based on group ID. Or, each device may choose its group based on UE ID. For example, some devices with even IDs may be grouped into one group with group ID=2, and another devices with odd IDs may be grouped into another group with group ID=1. Devices belongs to group with group ID=1 (i.e. devices with odd ID) may transmit by using the first resource pool, and devices belong to group with group ID=2 (i.e. devices with even ID) may transmit by using the second resource pool. Alternatively, explicit signaling of resource pool may be configured by the cell via SIB along with grouping rule(s). For example, SIB may indicate the number of groups intended to be supported (i.e. 'm'), and UE ID may be used as a rule for grouping. Or, for V2V communication, different rules may be applied to each car maker. For example, group 1 may be used for Honda made cars, and group 2 may be used for Toyota made cars, etc.

Further, to support devices to be able to listen on other devices which perform transmission at the same time, repetition/relaying may occur at least one time. For example, D1 transmits discovery signals by using the first resource pool, and those discovery signals may be received by other devices, e.g. D2. D2 may transmit discovery signals received from D1 by using the fourth resource pool via relaying/retransmission, which can be heard by D3/D5 which belong to the same group as D1 so that it may not receive the data from D1. Similarly, D2 transmits discovery signals by using the second resource pool, and those discovery signals may be received by other devices, e.g. D1. D1 may transmit discovery signals received from D2 by using the third resource pool via relaying/retransmission. To avoid possible collisions of relay operation, a device may be selected as a relay node in each group and only that device may perform relaying. The selected device may relay/retransmit all the received signals.

FIG. 12 shows another example of transmission by multiple devices according to an embodiment of the present invention. Referring to FIG. 12, D1 and D2 are selected as relaying nodes, so only D1 and D2 perform relaying operation.

The same techniques described above may also be utilized for multiple cells/operators. Devices served by one cell may form a group, and each group may relay/retransmit signals from another group(s) by using different resource pools. Accordingly, devices belonging to the same group may listen signals from devices of the same group.

(2) Multiple frequencies with different resource set and relay functionality

FIG. 13 shows another example of transmission by multiple devices according to an embodiment of the present invention. Two different or 'm' different frequencies may be used by one device. One frequency may be mainly used for transmission and the other frequency(s) may be mainly used for reception. Referring to FIG. 13, D1/D2/D3 uses F1 as transmitting frequency and F2 as receiving frequency. On the other hand, D4/D5 uses F2 as transmitting frequency and F1 as receiving frequency. Each device may transmit by using the allocated resource pool, and the resource pool may be different per frequency or the same across frequencies.

In one frequency, a device may take a turn between initial transmissions and relay transmissions. For example, D1 can listen on D4 which transmits data on F2 by using the first resource pool, and D1 may retransmit/relay the received data from D4 on F1 by using the second resource pool. That is, devices listening on F1 may listen data from devices transmitting on F2. Similarly, D4 can listen on D2 which transmits data on F1 by using the first resource pool, and D4 may retransmit/relay the received data from D2 on F2 by using the second resource pool. That is, devices listening on F2 may listen data from devices transmitting on F1. For each frequency, the network may select one or a few devices as relaying node(s). Or, a pre-determined rule may be used to select relaying node(s). Otherwise, each device may assume that it may operate as a relay node. In this case, some type of system frame number (SFN)-ed transmission among relays may be assumed or channel sensing among relay nodes may be used to minimize the collision among relay nodes.

For selecting which frequency to be used, random selection may be used. Or, frequency may be selected based on UE ID. For example, devices with even UE ID may select the first frequency as the transmitting frequency, and devices with odd UE ID may select the second frequency as the transmitting frequency. Furthermore, each cell may also transmit information on grouping rules or whether devices are allowed for transmission in a frequency via SIB or higher layer. For example, a cell may indicate that some devices are able to transmit in a given frequency via UE-specific higher layer signaling. Other cells, even without explicit signaling or indication, may listen on that frequency based on the resource pool configuration by the cell.

The same techniques described above may also be utilized for multiple cells/operators. Devices belonging to one cell/operator may listen on resource(s) configured by different cells/operators and relay/retransmit the received data from devices serviced by different cells/operators. In this case, the grouping mechanism which is described in FIG. 10 and FIG. 11 may also be used together.

FIG. 14 shows example of multiple devices served by different cells or operators according to an embodiment of the present invention. Referring to FIG. 14, it is assumed that there are five devices, i.e. D1, D2, D3, D4 and D5. Among those five devices, D1 and D3 are served by the first cell (or first operator) which uses the first resource pool for the first cell (or first operator). Frequency F1 is used for D2D in the first cell (or first operator). D2, D4 and D5 are served by the second cell (or second operator) which uses the second resource pool for the second cell (or second operator). Frequency F2 is used for D2D in the second cell (or second operator).

FIG. 15 shows another example of transmission by multiple devices according to an embodiment of the present invention. Referring to FIG. 15, two resource pool may be used for relaying operation, one of which is for relaying operation for devices belonging to the same cell/operator or utilizing the same frequency, and the other is for relaying operation for devices belonging to different cells/operators or utilizing different frequencies. For example, D1 may perform relaying of data received from devices belonging to the same cell/operator or utilizing the same frequency by using the third resource pool, and D1 may also perform relaying of data received from devices belonging to the different cells/operators or utilizing the different frequencies by using the fifth resource pool. Relay node(s) for each purpose (i.e. relaying operation for devices belonging to the same cell/operator, and relaying operation for devices belonging to different cells/operators) may be configured separately. The resource pool used for each relaying operation may be configured separately, also independently for each purpose.

(3) Multiple frequencies with transmit/receive switching

FIG. 16 shows another example of transmission by multiple devices according to an embodiment of the present invention. Referring to FIG. 16, similar to the embodiment of FIG. 13, multiple frequencies are used for initial transmission and relay transmission along with grouping. However, in this embodiment case, frequency may be switched between initial transmission and relaying transmission. Referring to FIG. 16, D1/D2/D3 uses F1 as transmitting frequency and F2 as receiving frequency for initial transmission. Further, D1/D2/D3 uses F2 as transmitting frequency for relaying transmission. On the other hand, D4/D5 uses F2 as transmitting frequency and F1 as receiving frequency. Further, D4/D5 uses F1 as transmitting frequency for relaying transmission. D1 can listen on D4 which transmits data on F2 by using the first resource pool, and D1 may retransmit/relay the received data from D4 on F2, not on F1, by using the second resource pool. Similarly, D4 can listen on D2 which transmits data on F1 by using the first resource pool, and D4 may retransmit/relay the received data from D2 on F1, not on F2, by using the second resource pool. This embodiment may be useful in case of different timing is used per each frequency or more than two frequencies are used for D2D operations.

(4) Different device types and separate resource

FIG. 17 shows example of multiple devices according to an embodiment of the present invention. Referring to FIG. 17, it is assumed that there are five devices, i.e. D1, D2, D3, D4 and D5. Those five devices are divided into two categories, i.e. normal nodes and relay nodes. In this embodiment, D2 is assigned to a relay node.

FIG. 18 shows another example of transmission by multiple devices according to an embodiment of the present invention. FIG. 18 shows transmission by five devices described in FIG. 17. Resource pools may be configured separately among normal nodes and relay nodes. Relay nodes may utilize only resource pools configured for relay nodes. Otherwise, the relay nodes may listen to other normal nodes. Relay nodes may transmit initial transmission as well as relaying transmission in the allocated resource pool only which will be listened by other normal nodes. Referring to FIG. 18, resource pool for normal nodes (D1/D3/D4/D5) and resource pool for relay nodes (D2) are configured separately. Relay node D2 may perform initial transmission or relaying transmission by using the allocated resource pool for relay nodes.

However, this embodiment may not allow a relay node to listen on other relay node(s) if there are more than one relay node(s). Furthermore, relay node(s) may be infrastructure rather than device(s). For example, relay node may be a base station or road side unit (RSU) used for V2V communication. In this case, the base station and/or RSU may broadcast whatever listened on D2D resource pool in a dedicated resource pool for relaying/retransmission. Furthermore, this dedicated resource pool may be configured in different time and/or frequency from D2D resource used by normal node(s).

(5) Selecting a relay node

FIG. 19 shows another example of transmission by multiple devices according to an embodiment of the present invention. Assuming devices are grouped into multiple groups where different group may use different resource pools (i.e. time and/or frequency) for transmission, devices belonging to one group may listen on devices belonging to other group(s). To avoid possible collision for relaying operation, relay node may be selected dynamically. For this, each device may select another UE as a potential relay node which then each node belongs to different group or uses different resource pool. Referring to FIG. 19, D1 and D4 may make a pair where D1 and D4 negotiate to use different resource pools. D1 and D4 may perform relaying for each other. When D1 transmits, D4 may perform relaying operation for D1. Once D4 selects a resource pool, D4 may make another pair other than D1, yet, the other node should not utilize the same resource pool with D4. For example, D5 may make a pair with D4, then D1 and D5 may utilize the same resource and D4 may perform relaying operation for either D1 or D5. In this embodiment, D1/D5 and D4 are paired, and D2 and D3 are paired. D4, since it has more than one pairings, may select a relay node when transmitting data. For example, D4 may select D5 as a relay node where D5 performs relaying operation at the resource pool configured for relaying operation. The pairing may be performed between devices belonging to different cells/operators. For example, cars in the same lane may form a pairing or a car may request a pairing with car in the right lane.

In summary, the present invention proposes the followings:

- Devices may be divided into different groups where different group may utilize different resource pools in terms of frequency and/or time.

- All or partial devices who are able to listen on other devices' transmission may perform relaying operation to allow devices which were transmitting at the same time to receive data.

- Selecting relay node(s) may be higher layer configured or determined based on pre-determined rule(s) or dynamic grouping/paring mechanism.

- Relay node(s) may be infrastructure, i.e. base station or RSU.

- Resource pool used for initial transmission and relay retransmission may be separately configured or determined based on a predetermined rule.

FIG. 20 shows a method for performing, by a device which belongs to a first group of devices, D2D transmission according to an embodiment of the present invention. The D2D transmission may include at least one of a D2D communication or D2D discovery.

In step S100, the device transmits a first signal by using a first resource used for initial transmission of the first group of devices. In step S110, the device receives a second signal by using a second resource used for initial transmission of a second group of devices. In step S120, the device relays the second signal by using a third resource used for relaying of the second group of devices. The first group of devices and the second group of devices may be served by the same cell or the same operator. Or, the first group of devices and the second group of devices may be served by different cells or different operators from each other.

The first resource, the second resource and the third resource may be allocated on a single frequency. This corresponds to option (1) described above, which may refers to FIG. 10 and FIG. 11. Or, the first resource and the third resource may be allocated on a first frequency, and the second resource may be allocated on a second frequency. This corresponds to option (2) described above, which may refers to FIG. 13. Or, the first resource may be allocated on a first frequency, and the second resource and the third resource may be allocated on a second frequency. This corresponds to option (3) described above, which may refers to FIG. 16.

The first resource, the second resource and the third resource may be allocated on different time intervals from each other. The first resource used for initial transmission of the first group of devices may be determined based on a group ID of the first group of devices, and the second resource used for initial transmission of the second group of devices may be determined based on a group ID of the second group of devices. The device may belong to the first group of devices based on a UE ID of the device. The first resource, the second resource and the third resource may be configured by a network via SIB.

Further, the first signal may be relayed by a relay node by using a fourth resource used for relaying transmission of the first group of devices. The relay node may be selected by a higher layer or a pre-determined rule. Or, the relay node may be a base station or a RSU in V2V communication.

A first device 800 may include a processor 810, a memory 820 and a transceiver 830. The processor 810 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 810. The memory 820 is operatively coupled with the processor 810 and stores a variety of information to operate the processor 810. The transceiver 830 is operatively coupled with the processor 810, and transmits and/or receives a radio signal.

A second device 900 may include a processor 910, a memory 920 and a transceiver 930. The processor 910 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 910. The memory 920 is operatively coupled with the processor 910 and stores a variety of information to operate the processor 910. The transceiver 930 is operatively coupled with the processor 910, and transmits and/or receives a radio signal.

The

processors

810, 910 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The

memories

820, 920 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. The

transceivers

830, 930 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in

memories

820, 920 and executed by

processors

810, 910. The

memories

820, 920 can be implemented within the

processors

810, 910 or external to the

processors

810, 910 in which case those can be communicatively coupled to the

processors

810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope and spirit of the present disclosure.

Claims

A method for performing, by a first device which belongs to a first group of devices, device-to-device (D2D) transmission in a wireless communication system, the method comprising:

transmitting a first signal by using a first resource used for initial transmission of the first group of devices;

receiving a second signal by using a second resource used for initial transmission of a second group of devices; and

relaying the second signal by using a third resource used for relaying of the second group of devices.
The method of claim 1, wherein the first resource, the second resource and the third resource are allocated on a single frequency.
The method of claim 1, wherein the first resource and the third resource are allocated on a first frequency, and

wherein the second resource is allocated on a second frequency.
The method of claim 1, wherein the first resource is allocated on a first frequency, and

wherein the second resource and the third resource are allocated on a second frequency.
The method of claim 1, wherein the first resource, the second resource and the third resource are allocated on different time intervals from each other.
The method of claim 1, wherein the first resource used for initial transmission of the first group of devices is determined based on a group ID of the first group of devices, and

wherein the second resource used for initial transmission of the second group of devices is determined based on a group ID of the second group of devices.
The method of claim 1, wherein the device belongs to the first group of devices based on a user equipment (UE) ID of the device.
The method of claim 1, wherein the first resource, the second resource and the third resource are configured by a network via system information block (SIB).
The method of claim 1, wherein the first signal is relayed by a relay node by using a fourth resource used for relaying transmission of the first group of devices.
The method of claim 10, wherein the relay node is selected by a higher layer or a pre-determined rule.
The method of claim 10, wherein the relay node is a base station or a road side unit in vehicle-to-vehicle (V2V) communication.
The method of claim 11, wherein the first group of devices and the second group of devices are served by the same cell or the same operator.
The method of claim 11, wherein the first group of devices and the second group of devices are served by different cells or different operators from each other.
The method of claim 1, wherein the D2D transmission includes at least one of a D2D communication or D2D discovery.
A first device which belongs to a first group of devices in a wireless communication system, the first device comprising:

a memory;

a transceiver; and

a processor coupled to the memory and the transceiver,

wherein the processor is configured to:

control the transceiver to transmit a first signal by using a first resource used for initial transmission of the first group of devices,

control the transceiver to receive a second signal by using a second resource used for initial transmission of a second group of devices, and

control the transceiver to relay the second signal by using a third resource used for relaying of the second group of devices.