CN106465338B

CN106465338B - Contention-based resource allocation method and apparatus for low power D2D communication

Info

Publication number: CN106465338B
Application number: CN201580015481.6A
Authority: CN
Inventors: 薛鹏; 朴承勋; 柳贤锡; 朴廷镐; 崔相元
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2014-03-21
Filing date: 2015-03-23
Publication date: 2020-01-10
Anticipated expiration: 2035-03-23
Also published as: KR20150110269A; KR102235369B1; CN106465338A

Abstract

A contention-based resource allocation method and apparatus for use in low power device-to-device (D2D) communication is provided. The resource allocation method of the device-to-device (D2D) terminal of the present disclosure includes: selecting an available resource in a frame, monitoring while a back-off timer is running to detect that a signal is received, and performing D2D communication using the available resource when no signal is received on the available resource before the back-off timer expires.

Description

Contention-based resource allocation method and apparatus for low power D2D communication

Technical Field

The present disclosure relates to contention-based resource allocation methods and apparatus for use in low power device-to-device (D2D) communications.

Background

With the increase of smart phones, mobile data services are rapidly increasing. By focusing on the increase in the number of smartphone users and the consequent increase in various application services such as Social Network Service (SNS) and games, it is expected that mobile data traffic will grow faster than before. Also, if human-to-machine and machine-to-machine communication is popularized in addition to human-to-human communication, it is likely that traffic concentrated on a base station is increased to an uncontrollable extent.

Therefore, a technique for solving this problem is required. One such technique is device-to-device (D2D) communication. D2D communication is a promising technology in both licensed band communication systems, such as cellular systems, and unlicensed band communication systems, such as Wireless Local Area Networks (WLANs).

In the field of mobile communications, D2D communications are of particular interest in increasing the traffic capacity of base stations. The advantages of D2D communication are: since User Equipments (UEs) located in the same cell or a neighboring cell may establish a D2D connection for direct data communication without the participation of an evolved node b (eNB), the number of communication links is reduced from 2 (UE1-eNB and eNB-UE2 links) to 1 (UE-UE link).

The LTE based D2D communication includes a D2D discovery phase and a D2D communication phase. D2D discovery is the process by which a UE checks the identity and attention of a neighboring UE and broadcasts its identity and attention to the neighboring UE. The identity and attention may be identified by a UE Identifier (ID), an application identifier or a service identifier, depending on the D2D service and operational scenario.

The UE protocol stack includes a D2D application layer, a D2D management layer, and a D2D transport layer. The D2D application layer is responsible for D2D-specific services running on an Operating System (OS), the D2D management layer is used to convert discovery information generated by the D2D application services into a format suitable for the D2D transport layer, and the D2D transport layer corresponds to the physical/media access control (PHY/MAC) layer of the LTE or Wi-Fi wireless communication standard. The D2D discovery process may be performed as follows. When the D2D application is executed, the application layer generates discovery information to the D2D management layer. The management layer converts the discovery information into a management layer message. The management layer message is transmitted by means of the transport layer and the neighboring UEs receive and process the management message in the reverse order of the transmission.

AS indicated above, the purpose of D2D communication is for UEs to directly transfer data without infrastructure such AS enbs and access points (AS). The D2D communication may be performed based on the results of the D2D discovery process (with other UEs) or without a discovery process. Whether the D2D discovery process is required depends on the D2D service and operational scenario.

D2D service scenarios are divided into business services (or non-public safety services) and public safety services. Examples of services include advertisements, Social Networking Services (SNS), games, and public safety and emergency network services.

1) Advertising: network operators supporting D2D communications allow pre-registered stores, cafes, theaters, restaurants, etc. to broadcast their identities to nearby D2D users through D2D discovery and D2D communications procedures. The concerns include promotions, event information, and discount offers of the advertiser. When the identity matches the user's attention, the user accesses the corresponding store for detailed information via a legacy cellular communication network or D2D communication. In another example, a user discovers a rental car located near the user through a D2D discovery process and exchanges data regarding the user's destination and rental fare through legacy cellular communication or D2D communication.

2) Social Network Service (SNS): the user sends the current application and application specific attention to other users located in the vicinity of the user. The identities and concerns used in D2D discovery include application-specific lists of friends and application identifiers. The user performs D2D discovery and then shares content such as photos and movies through D2D communication.

3) And (3) playing: the user discovers the user and the game application through the D2D discovery process to play a mobile game with other nearby users and performs D2D communication for exchanging game data.

4) Public safety service: police and fire fighters use D2D communication technology for public safety purposes. For example, in an emergency such as a fire, a landslide, or when cellular communication is cut off due to a cellular network interruption caused by a natural disaster such as an earthquake, a fire mountain burst, and a tsunami, police and firefighters use D2D communication to find nearby coworkers and share emergency information with nearby users.

The 3GPP LTE D2D standardization is advancing in both D2D discovery and D2D communication, but the standardization category of both is different. Both D2D discovery and D2D communications were developed for commercial use and must only be designed within the range of network coverage. D2D found not to support a no-eNB environment or non-eNB coverage. D2D communication was developed for public safety and emergency network services in addition to commercial services, and must support all scenarios, such as within or outside of network coverage and within partial network coverage (communication in cases where some UEs are within eNB coverage and others are outside eNB coverage). In public safety and emergency network services, D2D communication without D2D discovery procedure needs to be performed.

Both D2D discovery and D2D communication at standardized LTE D2D are performed in association with LTE uplink subframes. That is, the D2D transmitter transmits the D2D discovery signal and the D2D communication data in the uplink subframe, and the D2D receiver receives the signal and the data in the uplink subframe. In the current LTE system, D2D operates differently from the legacy LTE, since the UE receives data and control information from the eNB in downlink and transmits data and control information to the eNB in uplink. For example, a UE that does not support D2D functionality must have a receiver based on an Orthogonal Frequency Division Multiplexing (OFDM) implementation for receiving downlink data and control information from an eNB and a transmitter based on a single carrier-frequency division multiplexing (SC-FDM) implementation for transmitting uplink data and control information to the eNB. However, since it must support both the cellular mode and the D2D mode, the D2DUE must have an SC-FDM receiver for receiving D2D data and control information in the uplink and an OFDM-based receiver for receiving downlink signals from the eNB and an SC-FDM transmitter for transmitting uplink data and control information to the eNB and D2D data and control information to the counterpart D2D UE.

The current LTE D2D specifies two types of D2D discovery schemes that are selectively used according to a resource allocation method.

1) Discovery in category 1: the eNB broadcasts information on an uplink resource pool available for D2D discovery through a System Information Block (SIB) for reception by UEs within the cell. The size of the available communication resources (such as x consecutive frames) and the resource period (such as y seconds) for D2D are signaled. Upon receiving this information, the receiving D2D UE selects resources for use in a distributed manner and transmits a D2D discovery signal using the selected resources. Meanwhile, the receiving D2D device must receive all D2D discovery signals transmitted in the resource pool indicated by the SIB.

2) Discovery in category 2: the eNB informs the receiving D2D UE of the resource pool for the discovery signal through the SIB. The discovery signal resources for transmitting D2D UEs are scheduled by the eNB. At this time, the eNB performs scheduling in a semi-persistent manner or a dynamic manner.

Like the D2D discovery process, the D2D communication process can be divided into two modes depending on the resource allocation type:

1) mode 1: the base station informs the D2D transmitter of the data transmission resources of the D2D communication that can be directly used.

2) Mode 2: the eNB informs the D2D of the pool of resources available to the transmitter to enable the UE to select resources to signal in a distributed manner.

Another feature of LTE-based D2D communication is: unlike cellular communications, which focuses on unicast communications, it addresses public safety scenarios to support broadcast-based communications. Therefore, LTE D2D communication does not support feedback, such as channel measurement reports and hybrid automatic repeat request positive acknowledgement/negative acknowledgement (HARQ ACK/NACK). From this point of view, the pending problem with D2D broadcast communication is to provide high reliability link quality for ensuring seamless D2D communication without the help of eNB and any feedback. Especially in the case where UEs operate in a distributed manner without the help of an eNB, it is important to solve the problem of resource collision due to contention between UEs occupying the same resources.

As described above, since D2D communication for a public safety network must be operated in an environment where no eNB is assisted and no feedback is transmitted by UEs participating in D2D communication, a method capable of effectively controlling D2D resources between UEs is required.

There are several well-known resource allocation methods for D2D communication.

Legacy Wi-Fi or ZIGBEE-based peer-to-peer/sensor networks use carrier sense multiple access/collision avoidance (CSMA-CA) as the basic contention-based resource access scheme without the concept of scheduling-based resource allocation. CSMA-CA has the following characteristics: when the number of UEs is small, communication is performed in a hover transmission manner to avoid collision without additional complicated network management, and thus is widely used. However, in areas where Wi-Fi users are concentrated, it shows a disadvantage of a significant drop in data rate, increasing user complaints, and thus an enhanced method capable of replacing CSMA-CA is required.

Unlike the D2D distributed resource access method described above, Time Division Multiple Access (TDMA) is a very efficient resource access scheme when the master node manages resources. However, in the case where multiple master nodes are present, resource allocation between the multiple nodes needs to be controlled, and this creates additional control signal overhead and delay. Therefore, TDMA is not suitable for a network that can be extended to cover a wide area such as a D2D communication network.

The FlashLinQ of QUALCOMM modifies the request-to-Send (RTS) and clear-to-Send (CTS) control signals used in CSMA-CA for accessing TCMA resources. It is well known that FlashLinQ exhibits a 5-fold improvement in performance over Wi-Fi in certain environments when applying signal-to-interference ratios (SIR) measured using RTS and CTS to terminals operating in synchronous networks based on OFDM.

Disclosure of Invention

Technical problem

In the conventional art, a contention-based method such as CSMA-CA exhibits good scalability but low efficiency, while a resource access method such as TDMA exhibits high efficiency but low scalability. FlashLinQ, which is conceived to solve these problems, introduces a concept of time slot like in TDMA for efficiency, and uses a round robin scheme for allocating time slot resources.

D2D broadcast communication for public safety networks in question in 3GPP is similar to Wi-FI in that no connection setup is required, and to FlashLinQ in that it runs on licensed bands and establishes synchronization between terminals.

Therefore, there is a need for a method of efficiently allocating D2D resources by means of a base station in a network area while minimizing a collision probability in contention-based resource allocation in consideration of D2D communication (or D2D broadcasting) characteristics.

Technical scheme

According to an aspect of the present disclosure, there is provided a resource allocation method of a device-to-device (D2D) terminal. The resource allocation method comprises the following steps: selecting an available resource in a frame, monitoring to detect a signal while a back-off timer is running, and performing D2D communication using the available resource when no signal is received on the available resource before the back-off timer expires.

According to another aspect of the present disclosure, a terminal operating in a device-to-device (D2D) communication mode is provided. The terminal includes: a communication unit responsible for data communication; and a control unit that selects an available resource in a frame, monitors to detect a signal while a back-off timer is running, and controls the communication unit to perform D2D communication using the available resource when a signal is not received on the available resource before the back-off timer expires.

Before proceeding with the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation; the term "or" is inclusive, meaning and/or; the phrases "associated with …" and "associated with …," and derivatives thereof, may refer to include, be included within, interconnected with …, contained within, connected to or connected with …, coupled to or coupled with …, communicable with …, cooperative with …, staggered, juxtaposed, proximate to …, bound to or bound with …, having … characteristics, or the like; the term "controller" refers to any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or a combination of at least two of the foregoing. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

Advantageous technical effects

To address the above-described deficiencies, a primary objective is to provide a method of efficiently allocating resources while minimizing access delay for a backoff operation that avoids collisions, by focusing on receiving terminals operating at low power, particularly when allocating resources to transmitting terminals in a distributed manner. Meanwhile, the present disclosure is directed to providing a method of transmitting signaling between terminals capable of avoiding collision in a backoff operation.

The present disclosure is applicable to terminals operating outside of network coverage and within partial network coverage. Also, the present disclosure is applicable to a terminal using both frames with and without a control region.

Drawings

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like reference numbers represent like parts:

fig. 1 illustrates low power operation of a receiving UE in a frame including a control region according to various embodiments of the present disclosure;

fig. 2 illustrates low power operation of a receiving UE in a frame without a control region according to various embodiments of the present disclosure;

fig. 3 illustrates a resource allocation method of a transmitting UE in a frame having a control region according to various embodiments of the present disclosure;

fig. 4 illustrates a resource allocation method of a transmitting UE in a frame without a control region according to various embodiments of the present disclosure;

fig. 5 illustrates a conflict in a contention-based resource allocation method according to various embodiments of the present disclosure;

fig. 6 illustrates a backoff operation of a transmitting UE according to various embodiments of the present disclosure;

FIG. 7 illustrates a resource allocation method according to various embodiments of the present disclosure;

fig. 8 illustrates a backoff operation using a frame as a time unit for backoff according to various embodiments of the present disclosure;

fig. 9 illustrates a backoff operation using a subframe as a time unit for backoff according to various embodiments of the present disclosure;

FIG. 10 illustrates a resource allocation method according to various embodiments of the present disclosure;

FIG. 11 illustrates a resource allocation method according to various embodiments of the present disclosure;

FIG. 12 illustrates a resource allocation method according to various embodiments of the present disclosure;

FIG. 13 illustrates a resource allocation method according to various embodiments of the present disclosure;

FIG. 14 illustrates a resource allocation method according to various embodiments of the present disclosure;

fig. 15 illustrates a Reserve to Transmit (RT) transmission method according to various embodiments of the present disclosure;

FIG. 16 illustrates an asynchronous D2D resource allocation method, according to various embodiments of the present disclosure;

fig. 17 illustrates a configuration of a UE according to various embodiments of the present disclosure;

FIG. 18 illustrates a resource allocation method according to various embodiments of the present disclosure; and

fig. 19 illustrates a resource allocation method according to various embodiments of the present disclosure.

Detailed Description

Figures 1 through 19, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those of ordinary skill in the art will understand that: the principles of the present disclosure may be implemented in any suitably arranged wireless communication device. The present disclosure is directed to D2D broadcast, although minor modifications may be made to apply to other types of wireless communications without departing from the scope of the present disclosure. The disclosed embodiments are also applicable to various types of broadcast-based services and are not limited to D2D broadcasts.

The present disclosure may be implemented by a D2D UE. In certain embodiments of the present disclosure, the UE operates as a transmitting UE. It is determined whether the UE operates as a transmitting UE or a receiving UE according to information from the eNB or a predetermined rule. In the following description, the term "transmitting and receiving UE" may be used interchangeably with the terms "some UEs and other UEs", "terminals and other terminals", and "first and second sets of terminals".

In the present disclosure, the D2D communication is performed in a frame unit as a basic unit. The frames are referred to as a repetition period, and a D2D frame. The term "frame" is conceptually the same as that specified in LTE, and may or may not be identical in structure and format. The frame is 20ms or 40ms on the time axis, but is not limited thereto. The frame includes a plurality of Resource Blocks (RBs) in the frequency domain. Referring to the LTE standard, resources used by a UE are counted in units of Transmission Time Intervals (TTIs), and one TTI is 1ms, which is identical in time to one subframe. In some embodiments, assuming that 5 RBs corresponds to one D2D RB, the UE uses one of 10D 2D RBs in one subframe.

The frame is composed of a control area and a data area (shared area) (based on control access) or only a data area (distributed access).

The control region and the data region are notified to the UE by the eNB or predetermined to be used in an area outside the network where the eNB's signal cannot reach. In some embodiments, the control and data regions are resources that are independent or shared with each other.

For ease of explanation of the disclosed embodiments, a frame structure is defined. The terminology and structure associated with a frame may be varied widely without departing from the spirit and scope of the disclosure.

In a specific embodiment of the present disclosure, resources that are basic units selected by a user for data transmission or reception are referred to as resources, radio resources, resource blocks, communication resources, D2D resources, etc., and resources in a control region of a frame are referred to as control regions and resources in a data region are referred to as data resources.

The eNB controls and supports resource allocation operations of the UE. Although the description is directed to UE operation outside the network without control of the eNB, the present disclosure may also be used within a network coverage area or a portion of a network coverage area in which an eNB and a UE communicate, with minor modifications, without departing from the scope of the present disclosure. In various embodiments of the present disclosure, a UE functions as a coordinator in an environment without an eNB.

Exemplary embodiments of the present disclosure are described in detail with reference to the accompanying drawings. The same reference numbers will be used throughout the drawings to refer to the same or like parts. A detailed description of known functions and configurations incorporated herein may be omitted to avoid obscuring the subject matter of the present disclosure. Also, the following terms are defined in consideration of the functions of the present disclosure, and vary according to the intention and usage of a user or operator, or the like. Therefore, the definition should be made based on the entire contents of the present specification.

When synchronization is not established between the UEs, the receiving UE listens to an external signal to receive a signal transmitted by the transmitting UE. In order to reduce power consumption, the UE operates in an active state for a predetermined period of time between time-synchronized UEs, is in an idle state for the remaining period of time with a low duty cycle time, and in order to support low power operation, the transmitting UE transmits a control signal and a data signal for the active period of the receiving terminal and transmits a remaining data signal immediately preceding the control signal or an initial data signal for the idle period of time.

Fig. 1 illustrates low power operation of a receiving UE in a frame (repeating time period) containing a control region according to various embodiments of the present disclosure. As shown in fig. 1, when the repetition period is composed of a control region and a data region, the receiving UE listens to a signal in the control region, and when the control signal is not detected, enters an idle state in the data region. When a control signal transmitted by a transmitting UE is detected in a control region, a receiving UE decodes the control signal and determines whether data corresponding to the control signal is received based on information acquired from the control signal. When data corresponding to the control signal is transmitted thereto, the receiving UE remains in an active state to receive data in the data region.

Fig. 2 illustrates low power operation of a receiving UE in a frame without a control region according to various embodiments of the present disclosure. When the repetition period consists of only the data region without any control region, the receiving UE listens during the data region 1 in the active state, and enters and remains in the idle state during the period of the data region 2 to the data region 5 when no data is detected. When a data signal transmitted by a transmitting UE is detected in the data region 1, the receiving UE receives the data signal. The receiving UE determines whether the data immediately following the data signal is sent to it based on the information contained in the data signal. The sending UE is preconfigured to repeatedly send data during the time period of data region 1 to data region 5, and the receiving UE detects that the sending UE sends data in data regions 2 to 5 without additional control information. When it is determined that the subsequent data is transmitted to the receiving UE based on the information contained in the first data signal, the receiving UE maintains an active state to receive the data signal during the remaining data regions 2 to 5.

Although the following embodiments are applicable to an environment considering a repetition period with and without a control area as shown in fig. 1 and 2, for convenience of explanation, in each embodiment, one of the two environments of fig. 1 and 2 is selectively described. The following embodiments are applicable to both the environments of fig. 1 and 2.

For a receiving UE operating in a low power mode, a normal transmission operation of a transmitting UE is described.

Fig. 3 illustrates a resource allocation method of a transmitting UE in a frame having a control region according to various embodiments of the present disclosure.

The D2D broadcast communication mode is designed primarily to support voice services. The repetition D2D frame (frame or repetition period) is set to 30ms by focusing on the voice over ip (voip) packet period (20ms or 40 ms). Embodiments of the present disclosure are described based on the LTE standard. The resources used by the UE are Transmission Time Intervals (TTIs), one TTI corresponding to one subframe with a length of 1 ms.

The embodiment of fig. 3 is directed to the case where a frame is composed of a control area and a data area in a state where D2D synchronization is established. The control region and the data region are composed of a plurality of D2D resource blocks as viewed from the frequency domain. For example, in an LTE system having an entire uplink band divided into 50 basic Resource Blocks (RBs) and in which 5 basic RBs constitute one D2D RB, as viewed from the frequency domain, a UE uses one of a total of 10D 2D resource blocks of one subframe.

At least one transmitting UE transmits a control signal in a control region. In certain embodiments of the present disclosure, the control signal is a Scheduling Assignment (SA) control signal.

In fig. 3, each of UE1 and UE2 transmits one SA control signal and 3 data packets. The UE3 performs energy sensing in the control region of the first D2D frame and detects that resource 3# and resource 4# are empty. The UE3 selects resource #3 between the two empty resources to send the SA signal followed by the data. The SA includes identification information (such as a transmitting UE ID, a receiving UE ID, and a group ID) and a resource index of data immediately following the SA.

Fig. 4 illustrates a resource allocation method of a transmitting UE in a frame without a control region according to embodiments of the present disclosure.

Fig. 4 is directed to a case in which a frame does not have a control region in a state in which D2D synchronization is established. Each of UE1 and UE2 sent 3 data packets. The UE3 performs energy sensing in the first D2D frame and detects that resource 3# and resource 4# are empty. The UE3 selects resource #3 between two empty resources of the second D2D frame to transmit data.

The collision occurring in the transmission operation of fig. 3 and 4 is described below.

Fig. 5 illustrates a conflict in a contention-based resource allocation method according to embodiments of the present disclosure.

As described in the embodiments of fig. 3 and 4, the transmitting UE1 and the transmitting UE2 transmit control signals using different control resources as shown in the upper half of fig. 5, and the location of data resources is predetermined depending on the location of the control resources. That is, when the control signals of two UEs are transmitted on different control resources, the two UEs also transmit data on different data communication resources.

As shown in the lower half of fig. 5, however, when the transmitting UE1 and the transmitting UE2 transmit control signals on the same control resource, there is a high possibility that collision occurs in the data region as well as the control region. When there is no feedback corresponding to the control signal in the D2D communication, there is no way to avoid collisions by using the feedback information. Especially because the control area is shorter in time than the data area for low power operation, the probability of collision increases compared to the situation where the entire data area is used for contention based access.

To reduce the collision probability, the UE performs a backoff operation.

Fig. 6 illustrates a backoff operation of a transmitting UE according to embodiments of the present disclosure.

To reduce the collision probability during D2D contention based access, the UE uses a back-off mechanism. When the UE transmits data, as shown in the embodiment of fig. 5, the UE1 and the UE2 receive the same control signal. When UE1 and UE2 attempt to randomly select a resource (such as an available resource) on which no control signal is transmitted, UE1 and UE2 select the same resource, thereby causing a collision. To avoid collisions, UE1 and UE2 set the backoff counters to different values so that each UE selects an available resource when its own backoff counter expires. In certain embodiments, UE1 and UE2 select resources in different frames, thereby reducing the likelihood of collisions.

Fig. 6 is for an exemplary case where UE1 and UE2 set their backoff counters to 1 and 3, respectively, to avoid collisions.

The backoff operation of the UE is advantageous in reducing the collision probability, but disadvantageous in causing as many access delays as multiples between the backoff counter and the repetition period.

The present disclosure provides a resource allocation method of D2D capable of minimizing the possibility of collision and access delay during contention-based resource access.

Various embodiments of the present disclosure are applicable to a case where area information of transmitting and receiving UEs match each other (synchronization is acquired) and the UEs operate based on individual area information (synchronization is not acquired). A case in which the area information of the transmitting and receiving UEs are matched and a case in which the UEs operate using the respective area information are described. When the area information of the transmitting and receiving UEs match, the receiving UE operates in a low power mode.

In various embodiments of the present disclosure, a transmitting UE and a receiving UE are distinguished by a resource access operation. Voice services for public safety networks operate mainly in a push-to-talk (PTT) mode, and when a sender pushes a button, a corresponding UE operates as a sending UE, and other UEs operate as receiving UEs.

The control signal proposed by the present disclosure includes Scheduling Assignment (SA) and Reservation Transmission (RT). The SA signal is used in the control region and the RT signal is used in the data region. In some embodiments, other control signals are used in the control zone. For example, the control signal is a bidirectional signal such as a scheduling request and a scheduling response. The control signal is other bi-directional signal such as a request to send or a clear to send. The control signals are transmitted in the form of sequences, tones or messages. In embodiments of the present disclosure, the control signal is transmitted in the form of a message.

In some embodiments, frames spanning 40ms are utilized as the basic resource unit for communication. The term "frame" may be used interchangeably with the terms "repetition period," repetition duration, "and" D2D frame. Referring to the LTE standard, the resource used by a UE is a Transmission Time Interval (TTI), and one TTI corresponds to one subframe having a length of 1 ms.

The frame is composed of a control area and a data area (shared area) (based on control access) or composed of only a data area (distributed access).

The control region and the data region are notified to the UE by the eNB or predetermined to be used in the outside of the network where the eNB's signal cannot reach. In some embodiments, the control region and the data region are separate resources or shared resources.

Typically, in a distributed resource selection mode, a transmitting UE performs energy sensing to determine whether another transmitting UE occupies the resource and transmits data on unoccupied resources and whether this would cause a collision when multiple transmitting UEs occupy the same resource. To reduce the collision probability, the transmitting UE waits for a different back-off timer after sensing operation and accesses the corresponding resource for use. To reduce the probability of collision within the restricted control region, the resource allocation time delay is increased when the UE transmits control signals in different control regions. Various embodiments of the present disclosure present methods of resolving conflict issues in the same repetition time period. Various embodiments of the present disclosure propose a signaling method capable of allowing at least one transmitting UE to select a resource within a repetition period and immediately transmit a signal on the selected resource of the next repetition period.

The resource allocation method comprises the following steps: the resource allocation status of the other UEs is checked on the transmitting UE by energy sensing in the control region or the first data region, and contention-based resource allocation is performed using available resources in the data region that are not occupied by the other UEs based on the resource allocation status. The resource allocation method of the present disclosure is designed in consideration of two situations: a situation in which the time region of the transmitting UE occupying the resource transmitting the control signal or the first data signal matches the duration the receiving UE is listening in the active state (region synchronization situation); another scenario, where the time regions of the UEs do not match (region unsynchronized case).

Fig. 7 illustrates a resource allocation method according to some embodiments of the present disclosure.

Referring to fig. 7, a UE3, a UE4, and a UE5 perform energy sensing in a first region of a frame, such as a control region (or a first data region). When the UE1 and the UE2 have occupied resources to transmit control Signals (SAs) in the first region, the UE3, the UE4, and the UE5 detect SA signals of the UE1 and the UE 2. The UE3, the UE4, and the UE5 check resources (data resources corresponding to control resources) occupied by the UE1 and the UE2 based on the detected SA signal. The UE3, UE4, and UE5 check the resources occupied by the UE1 and UE2 based on the resource index explicitly contained in the SA signal or based on the location of the control resources implicitly indicated in the SA signal.

UE3, UE4, and UE5 check resources not occupied by UE1 and UE2 and randomly select one of the available resources. In fig. 7, UE3 and UE4 select available resource #3, while UE5 selects available resource # 4.

In the region of the first region immediately following the repetition period, UE3, UE4, and UE5 transmit RT signals using resources corresponding to available resources #3 or #4 to inform neighboring UEs of the resource selection for occupation. When the back-off timer expires, the UE3, UE4, and UE5 set the respective back-off timers to transmit the RT signal.

While the back-off timer (back-off counter) is running, the UE3, UE4, and UE5 perform energy sensing. The UE3, UE4, and UE5 determine whether they win contention for the selected resource according to whether other UEs' RTs are detected through energy sensing before the back-off timer expires.

In certain embodiments of fig. 7, when UE3 and UE4 select the same available resource #3, they contend for resource # 3.

When contention for the same resource occurs as shown in fig. 7, a UE that has occupied a resource block corresponding to the resource index wins the contention. When contention for the same resource occurs, its backoff timer first expires and a UE transmitting an RT for the corresponding resource wins the contention and occupies the corresponding resource. Each UE performs energy sensing to sense RTs transmitted by other UEs while its back-off timer is running, determines that it loses contention when RTs transmitted by other UEs are detected on the selected resource, or otherwise determines that it wins contention.

In fig. 7, when the UE3 has transmitted an RT signal for resource #3, it wins contention, and the UE4 loses contention for resource # 3. The UE3 that has won the contention transmits data using the selected resources in the next repetition period.

According to the resource allocation method of some embodiments of the present disclosure, the UE4 that has lost contention relinquishes the corresponding resource. Thereafter, the UE4 performs a contention-based resource allocation operation to select available resource # 1.

In fig. 7, when the UE5 does not detect the RTs of other UEs while its back-off timer is running, it transmits data using the selected resource #4 in the next repetition period.

Fig. 8 illustrates a backoff operation using a time unit of a frame for backoff according to various embodiments of the present disclosure.

In an exemplary backoff operation, the unit of time for backoff is a resource block in the resource indicated by the selected resource index. In some embodiments, the UE decrements the back-off timer by 1 per resource block, as shown in fig. 8.

For example, the UE3 determines the resource index used in the sensing period, sets the backoff counter to 2, and decrements the backoff timer by 1 when the first available resource block arrives at resource # 3. When the second available resource block arrives, the UE3 decrements the backoff timer to 0. When the back-off timer reaches 0, the UE3 sends an RT signal.

The back-off timer is set to span one or more D2D frames. Since the backoff timer is decremented by 1 per available resource block, when another UE pre-occupies the corresponding resource, the UE suspends the decremental backoff timer for the pre-occupied resource, and when the corresponding resource is withdrawn, resumes the decremental backoff timer.

Fig. 9 illustrates a backoff operation in units of time of subframes for backoff use according to embodiments of the present disclosure.

In an exemplary backoff operation, the time unit for backoff is a subframe. In some embodiments, the UE decrements the backoff timer by 1 every subframe, as shown in fig. 9.

Although the UE transmits the RT signal on the entire available resources in the subframe, the actual resource location is not determined depending on the location of the RT transmission, and thus the resource index is explicitly transmitted in the RT signal. The backoff timer determined after the sensing period is decremented by 1 every subframe.

When all resource indices are in use based on the pre-occupied resource index and the resource indices contained in other RT signals of the transmitting UE, the UE suspends decrementing the backoff timer until the resource indices are retracted.

Fig. 10 illustrates a resource allocation method according to embodiments of the present disclosure.

In step 1001, the UE determines to transmit data;

in step 1003, the UE monitors a first region, such as a control region or a first data region of the current frame, to detect neighbor's signals. The neighbor signal is a control signal, particularly an SA signal.

In step 1005, the UE determines whether there is any available resource in the current frame based on the detected SA signal.

In step 1007, when there is no available resource, such as when the entire resource is occupied by other UEs as a result of SA signal monitoring, the UE gives up the corresponding resource in the current frame.

In step 1009, when there is any available resource, the UE selects a certain available resource.

In step 1011, the UE sets and starts a backoff timer. The UE continues monitoring to detect neighbor signals (energy sensing) while the back-off timer runs. The neighbor signal is an RT signal. The UE decrements the back-off timer by 1 per time unit.

When receiving an RT signal of a resource selected by the UE before the back-off timer expires in step 1013, the UE determines that it has lost contention for the resource and abandons the corresponding resource in the current frame in step 1007.

In step 1015, when the RT signal of the selected resource is not received before the back-off timer expires in step 1013, the UE transmits the RT signal on the selected available resource.

In step 1017, the UE transmits D2D broadcast data on the selected available resource in the next frame.

Fig. 11 illustrates a resource allocation method according to various embodiments of the present disclosure.

Referring to fig. 11, a UE3, a UE4, and a UE5 perform energy sensing in a first region of a frame, such as a control region or a first data region. When the UE1 and the UE2, which have occupied resources, transmit control Signals (SAs) in the first area, the UE3, the UE4, and the UE5 detect SA signals of the UE1 and the UE 2. The UE3, the UE4, and the UE5 check resources (data resources corresponding to control resources) occupied by the UE1 and the UE2 based on the detected SA signal. The UE3, UE4, and UE5 check the resources occupied by the UE1 and UE2 based on the resource index explicitly contained in the SA signal or based on the location of the control resources implicitly indicated in the SA signal.

UE3, UE4, and UE5 check resources not occupied by UE1 and UE2 and randomly select one of the available resources. In fig. 11, UE3 and UE4 select available resource #3, and UE5 selects available resource # 4.

In the region of the first region immediately following the repetition period, UE3, UE4, and UE5 send RT signals to inform neighboring UEs of occupied resource selection using resources corresponding to available resources #3 or # 4. The UE3, UE4, and UE5 set respective backoff timers to transmit an RT signal when the backoff timers expire.

The UE3, UE4, and UE5 perform energy sensing while the back-off timer (back-off counter) is running. The UE3, UE4, and UE5 determine whether they win contention for the selected resource depending on whether other UEs' RTs are detected by energy sensing before the back-off timer expires.

In the embodiment of fig. 11, since UE3 and UE4 select the same available resource #3, they contend for available resource # 3.

As shown in fig. 11, when contention for the same resource occurs, a UE that has occupied a resource block corresponding to the resource index wins the contention. When contention for the same resource occurs, the backoff timer first expires and thus the UE transmitting the RT of the corresponding resource wins the contention and occupies the corresponding resource. Each UE performs energy sensing to sense RTs transmitted by other UEs while the backoff timer is running, determines that it loses contention when an RT transmitted by other UEs is detected on the selected resource, or otherwise determines that it wins contention.

In fig. 11, when the UE3 has transmitted an RT signal of resource #3, it wins contention, and the UE4 loses contention for resource # 3. The UE3 that has won the contention transmits data using the selected resource for the next repetition period.

In a resource allocation method according to an embodiment of the present disclosure, the UE4 that has lost contention selects other available resource indexes at the corresponding time point to resume the backoff operation. The UE4 selects resource #4 as another available resource to resume the backoff operation. The back-off timer is decremented or reset to the new timer value as before.

In some embodiments of fig. 11, the UE4 newly selects another available resource index #4 to perform the back-off timer reduction operation.

In certain embodiments, UE4 competes with UE5 for newly selected resource # 4. When the backoff timer of UE5 expires before the UE4 backoff timer expires and thus UE5 transmits the RT, UE4 loses contention for resource # 4. When there are no more resources available, the UE4 stops the contention operation in the current repetition period. The UE4 performs a contention resource allocation operation for the next repetition period to select the available resource # 1.

In fig. 11, when no RT is detected from other UEs while the backoff timer of the UE5 is running, the UE5 transmits data using the selected resource #4 in the next repetition period.

Fig. 12 illustrates a resource allocation method according to embodiments of the present disclosure.

In step 1201, the UE determines to transmit data;

in step 1203, the UE monitors a first area (such as a control region or a first data region of the current frame) to detect a neighbor signal. The neighbor signal is a control signal, particularly an SA signal.

In step 1205, the UE determines whether there are any available resources in the current frame based on the detected SA signal.

In step 1207, when there is no available resource, such as when the entire resource is occupied by other UEs as a result of SA signal monitoring, the UE gives up the resource occupation in the current frame.

In step 1209, when any resources are available, the UE selects some available resource.

In step 1211, the UE sets and starts a back-off timer, which the UE continues to monitor for neighbor signals (energy sensing) while running. The neighbor signal is an RT signal, and the UE decrements the backoff timer by 1 every time unit.

When receiving the RT signal of the selected resource before the back-off timer expires in step 1213, the UE detects that it has lost the resource allocation contention and determines whether there are other available resources in step 1215.

When there are no other available resources in step 1215, the UE relinquishes the corresponding resources in the current frame in step 1207.

In step 1217, the UE selects a portion of the available resources when there are other available resources.

The UE repeats steps 1211 to 1217 until the back-off timer expires.

In step 1219, when the RT signal of the selected resource is not received before the back-off timer expires in step 1213, the UE transmits the RT signal on the selected resource at the expiration of the back-off timer.

In step 1221, the UE transmits D2D broadcast data on the selected resource in the next frame.

Fig. 13 illustrates a resource allocation method according to embodiments of the present disclosure.

Referring to fig. 13, a UE3, a UE4, and a UE5 perform energy sensing in a first region of a frame, such as a control region or a first data region. In fig. 13, when the UE1 and the UE2, which have occupied resources, transmit a control Signal (SA) in the first region, the UE3, the UE4, and the UE5 detect SA signals of the UE1 and the UE 2. The UE3, the UE4, and the UE5 check resources (data resources corresponding to control resources) occupied by the UE1 and the UE2 based on the detected SA signal. UE3, UE4, and UE5 check the resources occupied by UE1 and UE2 based on the resource index explicitly contained in the SA signal or based on the location of the control resources implicitly indicated in the SA signal.

In certain embodiments of the present disclosure, the UE3, UE4, and UE5 check resources not occupied by the UE1 and UE2, such as available resources, and generate a list containing available resources #3 and # 4.

Next, the UE3, the UE4, and the UE5 set back-off timers that are decremented by time units, and transmit an RT signal when the back-off timers reach 0. Each of the UE3, UE4, and UE5 selects one of the available resources listed in the list to transmit an RT signal on the corresponding resource when the backoff timer expires.

Each UE3, UE4, and UE5 continues energy sensing while the backoff timer or backoff counter is running. Each UE3, UE4, or UE5 determines whether to detect RTs transmitted by other UEs before expiration of its backoff timer. Upon receiving any RT, the UE determines that the corresponding resource has been occupied by other transmitting UEs, and removes the index of the resource pre-occupied by other UEs from the available resource list. When all available resource indices are removed from the list, such as when there are no further available resources, the UE suspends its backoff timer until any available resource indices are reclaimed. The following operation is the same as that described in the first and second embodiments.

Fig. 14 illustrates a resource allocation method according to embodiments of the present disclosure.

In step 1401, the UE determines to transmit data.

In step 1403, the UE monitors a first region (such as a control region or a first data region of a current frame) to detect a neighbor signal. The neighbor signal is a control signal, particularly an SA signal.

In step 1405, the UE determines whether there are any available resources in the current frame based on the detected SA signal.

In step 1407, when there is no available resource, such as when the entire resource is occupied by other UEs as a result of SA signal monitoring, the UE gives up the corresponding resource in the current frame.

In step 1409, when any resources are available, the UE updates the available resources list by adding the available resources to the available resources list.

In step 1411, the UE sets and starts a backoff timer, while the backoff timer runs, the UE continues to monitor to detect neighbor signals (energy sensing). The neighbor signal is an RT signal, and the UE decrements the backoff timer by 1 every time unit.

In step 1413, when an RT signal of the selected resource is received before the back-off timer expires, the UE removes an available resource corresponding to the RT signal from an available resource list in step 1415. The UE repeats the above operations until the back-off timer expires.

In step 1417, the UE determines whether any available resources remain unremoved from the available resources list.

When there is no available resource left in the available resource list, the UE determines that it has lost the resource allocation contention and gives up the corresponding resource in the current frame in step 1407.

In step 1419, when any available resource remains in the available resource list, the UE transmits an RT signal on the selected available resource in the list.

In step 1421, the UE transmits D2D broadcast data using the selected resource in the next frame.

Fig. 15 illustrates a method of Reservation Transmission (RT) transmission according to various embodiments of the present disclosure.

When the back-off timers of the plurality of transmitting UEs are set to the same value, the transmitting UEs transmit their RT signals on the same resource. When RT signals of different UEs are transmitted on the same resource, the receiving UE cannot correctly receive the RT signals due to collision. From the transmitting UE perspective, this would cause a half-duplex problem where one transmitting UE cannot receive RT signals transmitted on the same resource by other transmitting UEs.

To alleviate such problems, the transmitting UE transmits the RT signal in the mode as shown in fig. 15. The transmitting UEs transmit their RT signals at different intervals at multiple times. In some embodiments, it may be difficult for the transmitting UE to select the same back-off timer and the same mode, resulting in a minimized probability of collisions.

Referring to fig. 15, although their first RT signals collide on the same resource, since RT signals of UE3 and UE4 are transmitted at different intervals, UE4 hears the RT signal of UE 3.

The UE4 operates as described in the embodiments above. In fig. 15, the RT signal includes a contention index to win contention for a UE transmitting an RT signal with a high contention index, not for a UE transmitting the RT signal first.

In the RT signal transmission mode for resolving contention with different time intervals, all RT signals (except the first RT signal) include a first RT signal timing or a backoff timer. In the fig. 15 embodiment, the second data packet of the UE3 includes a value of-1 when it is transmitted after a number of resource blocks corresponding to one backoff timer from the first data packet. Another transmitting UE that has received the RT signal of UE3 checks the value-1 and detects that the first RT signal was transmitted one resource block ago.

The above embodiments are mainly directed to operations between UEs without involving the network.

In the case of partial network coverage, the UE allocated resources from the eNB has a higher priority than the UE of autonomously selected resources outside the eNB coverage. Therefore, UEs inside the eNB do not contend but transmit the SA signal on the resource allocated by the eNB. The out-of-coverage UE first senses the SA signal to select resources, and thus there is no problem. When unoccupied resources are selected (allocated to UEs) by out-of-coverage UEs, collisions may occur when UEs inside the eNB attempt to use the corresponding resources. To solve this problem, the UE inside the eNB transmits an RT signal to select the occupied resources. For example, the UE inside the eNB transmits an RT signal including an index and priority of resources allocated by the eNB or information informing that it is the UE inside the eNB. Under the condition that the UE outside the coverage is not assumed to set its backoff timer to 0, the UE inside the eNB transmits an RT signal whose backoff timer is set to 0. When a UE inside the eNB wins contention with an out-of-coverage UE and is thus allocated resources, it requests to reclaim resources expected to be used with the SA signal.

Fig. 16 illustrates an asynchronous D2D resource allocation method according to embodiments of the disclosure.

The UE1 performs sensing in data region 1 to detect unoccupied resource #6 and turns on the back-off timer from 2. UE2 and UE3 are synchronized in time. The UE2 performs sensing in data region 1 and starts a back-off timer from 0 to immediately transmit an RT signal in the next data region 2. The UE3 whose backoff timer is being decremented sends an RT signal when the backoff timer reaches 0 in data region 2. When consecutive RT signal patterns used by the UE2 and the UE3 are not identical to each other, the UE3 receives the RT signal of the UE2 transmitted in the data region 3 and abandons transmission in resource #6 of the current repetition period and performs sensing in the data region 1 of the next repetition period. The UE1 receives the RT signal of the UE2 or UE3, suspends the backoff operation of the corresponding resource #6, and performs sensing in the next repetition period, restarts the backoff operation in the unoccupied resource #15 to transmit the RT signal in the data region 2 where the backoff is finished.

Although the above description is mainly directed to an SA and a data resource allocation method using unoccupied resources, an SA resource allocation method in which resource selection (resource allocation) is directly indicated in an SA transmission period (control region or first data region) may be used in various embodiments. In some embodiments, all UEs sense and decode all SAs. When selecting SA resources for transmitting SA signals, the UE decodes the received SAs to check available SA resources. The UE selects one of the available SA resources to transmit the SA signal.

In some embodiments, there is a reservation interval comprising a plurality of SA time periods to prevent collisions prior to SA signal transmission. The UE selects one SA time period for transmitting the SA signal and selects an indication (reservation indication) and notifies that the corresponding SA resource is reserved for transmitting data after the SA reservation interval is finished. This information informs other UEs that the corresponding SA resource was selected by the UE and that other UEs cannot use the SA resource to avoid collisions. When the UE detects that other UEs occupy the SA resource, it detects invalidity of the corresponding SA resource and considers selecting one of the other available SA resources.

Fig. 18 illustrates a resource allocation method according to embodiments of the present disclosure.

Referring to fig. 18, SA1 in SA/data period 0 is used by UE 1.

When SA/data period 0 arrives, UE2 and UE3 perform decoding on SA resources to detect SA2, SA3, and SA4 as available SA resources. Within the SA reservation interval, the UE2 selects SA2 of SA/data period 2, and the UE3 selects SA3 of SA/data period 3.

When SA/data period 1 arrives, the UE4 decodes the SA signal to detect SA2, SA3, and SA4 as available SA resources. Within the reservation interval, the UE4 decodes SA2 and SA3, and SA2 and SA3 are not selected. Finally, the UE4 selects SA4 of SA/data period 4.

After the SA reservation interval, the UE transmits an SA signal on the selected SA resource without collision.

Fig. 19 illustrates a resource allocation method according to embodiments of the present disclosure.

Referring to fig. 19, the scheduling interval configured by the system includes N SA/data periods. When the UE selects an SA and a data resource, it performs transmission in at least one scheduling interval. Each scheduling interval has a reservation interval comprising M SA/data time periods. In some embodiments, N and M are set by signaling with a System Information Block (SIB), M being equal to or less than N.

In the embodiment of fig. 19, the scheduling interval is equal in length to the reservation interval. N-M-4. In scheduling interval 0, the UE1 uses SA 1. When SA/data period 0 arrives, UE2 and UE3 decode the received SA signal to detect that SA2, SA3, and SA4 are available SA resources. In the next scheduling interval, UE2 and UE3 select SA resources within the reservation interval. The UE2 selects SA2 in SA/data period 4 and the UE3 selects SA3 in SA/data period 6.

The UE transmits an SA reservation containing information about the selected SA resources. The UE repeatedly transmits the SA reservation in the SA/data period after transmitting the SA reservation in the current SA/data period before the end of the reservation interval. For example, the UE2 transmits SA reservations in SA/

data time periods

4, 5, 6, and 7; the UE3 transmits the SA reservation in SA/data periods 6 and 7. When SA reservation is detected, other UEs cannot select the reserved SA resources to avoid collision.

According to the above embodiments, UE2 and UE3 each transmit an SA signal on the selected SA resource without collision in the subsequent scheduling interval.

The SA reservation indication method is described in detail hereinafter.

The SA signal includes important information as listed in table 1.

TABLE 1

SA field name	Length of	Application method
			ID	8	RX (group) ID and/or TX ID
Data resource frequency indexing	5-13	Data resource RB index (BW dependent)
			Data resource time indexing	7	Data resource subframe index
MCS and RV	5	Common to all TB
			TX timing information	6	Timing Advance (TA) values are indicated
Flag bit for SPS indication	1	Whether SPS is or is not
			TPC indication	1	Power control information
Indication of SA reservations	1	Indicating that the SA is used only for reservation or for data transfer

In embodiments of the present disclosure, both explicit and implicit indication methods are used.

Option 1: explicit indication

The simplest explicit indication method is to explicitly include an indication parameter in the SA signal. As shown in table 1, the indication field of the SA reservation of 1 bit explicitly indicates that the SA resource is selected for data transmission. In some embodiments, other fields are reused to send other useful information. For example, the other fields include selected data resources for data transmission and a selected length such that other UEs do not select corresponding data resources within the selected length.

Option 2: implicit indication

In various embodiments, in addition to using a 1-bit indicator, it is possible to indicate in various ways that SA resources are reserved for data transmission. Some fields are set to a specific value for indicating the reservation of the SA resources. For example, the "ID" field is set to "00000000" for indicating SA resource reservation. The "MCS" and "RV" fields are set to "11111" for indicating SA resource reservation. The "ID" resource and "MCS and RV" fields are set to "00000000" and "11111" respectively for a combination indicating SA resource reservation. It is also possible to set other fields to predetermined values for indicating SA resource reservation. SA resource reservation is implicitly indicated without using a 1-bit indicator.

Fig. 17 illustrates a configuration of a UE according to embodiments of the present disclosure.

Referring to fig. 17, a UE 1700 according to some embodiments of the present disclosure includes a communication unit 1701 and a control unit 1703.

The communication unit 1701 is responsible for data transmission. For example, the communication unit 1701 transmits control signals such as SA and RT signals and D2D broadcast data. The communication unit 1701 simultaneously monitors the medium to receive control signals of other UEs.

A control unit 1703 controls the components of UE 1700 for D2D communication. Control unit 1703 controls the components comprising communication unit 1701 to perform resource allocation operations according to some embodiments of the present disclosure. The control unit 1703 operates as described above.

As described above, the resource allocation method of the present disclosure is advantageous in preventing collisions between transmitting terminals and reducing access delay in allocating resources for D2D broadcast resources between terminals outside network coverage and within partial network coverage.

Meanwhile, the resource allocation method disclosed by the invention is beneficial in that the terminal which allocates the resources in advance is not influenced by the newly added terminal, and the resources can be yielded to the newly added terminal when the terminals have different priorities.

Those of ordinary skill in the art will understand that: variations and modifications may be made to the described embodiments without departing from the techniques of this disclosure. Accordingly, it should be understood that the above-described embodiments are merely illustrative in nature and are not intended to be limiting in any way.

Although the present disclosure has been described with exemplary embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure cover such changes and modifications as fall within the scope of the appended claims.

Claims

1. A method of resource allocation for a device-to-device (D2D) terminal, the method comprising:

receiving a control signal in a first region of a frame;

identifying available resources in a second region of the frame based on the control signal;

monitoring while the back-off timer is running to detect signals received on the available resources; and is

Performing D2D communication using the available resource if no signal is received on the available resource before the back-off timer expires.

2. The method of claim 1, further comprising: skipping D2D communication using the available resource if a signal is received on the available resource before the back-off timer expires.

3. The method of claim 1, further comprising:

determining whether there is additional available resource in the frame if a signal is received on the available resource before the back-off timer expires;

in the event that there are additional available resources in the frame, selecting one of the additional available resources; and is

Performing D2D communication using the available resource in a next frame if no signal is received on the available resource before the back-off timer expires.

4. The method of claim 3, further comprising: in the event that no further available resources exist in the frame, D2D communication using the available resources in the frame is skipped.

5. The method of claim 1, further comprising:

in the case where a signal is received before the back-off timer expires, removing an available resource corresponding to the signal from an available resource list;

determining whether there are available resources remaining in the available resource list if the backoff timer expires; and is

Performing D2D communication using the available resource if available resources remain in the available resource list.

6. The method of claim 1, wherein identifying available resources comprises:

selecting at least a portion of the available resources.

7. The method of claim 1, wherein performing D2D communications comprises: transmitting a transmission reservation signal on the available resource if no signal is received on the available resource before expiration of a back-off timer.

8. The method of claim 7, wherein transmitting the transmission reservation signal comprises transmitting the transmission reservation signal in a transmission mode formed based on a transmission interval and a number of times.

9. The method of claim 1, wherein the backoff timer is decremented by 1 per available resource block or subframe.

10. A terminal operating in a device-to-device (D2D) communication mode, the terminal comprising:

a transceiver; and

at least one processor coupled to the transceiver and configured to:

receiving a control signal in a first region of a frame;

monitoring while the back-off timer is running to detect that a signal is received on an available resource; and is

11. The terminal of claim 10, wherein the at least one processor is further configured to skip D2D communication using the available resource if a signal is received on the available resource before a back-off timer expires.

12. The terminal of claim 10, wherein the at least one processor is further configured to:

determining whether additional available resources are present in the frame if a signal is received on the available resources before the back-off timer expires;

13. The terminal of claim 12, wherein the at least one processor is further configured to skip D2D communication using the available resources in the frame if no additional available resources exist in the frame.

14. The terminal of claim 10, wherein the at least one processor is further configured to:

determining whether available resources remain in the list of available resources if a backoff timer expires; and is

Performing D2D communication using the available resource if available resources remain in the list of available resources.

15. The terminal of claim 10, wherein the at least one processor is further configured to:

selecting at least a portion of the available resources.

16. The terminal of claim 10, wherein the at least one processor is further configured to: transmitting a transmission reservation signal on the available resource if no signal is received on the available resource before the back-off timer expires.

17. The terminal of claim 16, wherein the at least one processor is further configured to transmit the transmission reservation signal in a transmission mode formed based on a transmission interval and number.

18. The terminal of claim 10, wherein the backoff timer is decremented by 1 per available resource block or subframe.