Method and apparatus for performing a random access (RA) procedure for device to-device (D2D) service in a wireless communication system

A method and apparatus are disclosed for performing a RA procedure for at least a first D2D communication session and a second D2D communication session in a wireless communication system. The method includes a UE transmitting a first message to a network, wherein the first message is a preamble. The method also includes the UE receiving a second message from the network after transmission of the first message, wherein the second message contains a first UL resource. The method further includes the UE using the first UL resource to transmit a third message to the network after reception of the second message, wherein the third message includes at least a BSR MAC CE. In addition, the method includes the UE determining that the RA procedure is successful if the UE receives a fourth message, wherein the fourth message contains either a second UL resource or at least a D2D resource depending on whether or not the BSR MAC CE is associated with the first D2D communication session and the second D2D communication session.

FIELD

This disclosure generally relates to wireless communication networks, and more particularly, to a method and apparatus for performing a RA procedure for D2D service in a wireless communication system.

BACKGROUND

An exemplary network structure for which standardization is currently taking place is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput in order to realize the above-noted voice over IP and multimedia services. The E-UTRAN system's standardization work is currently being performed by the 3GPP standards organization. Accordingly, changes to the current body of 3GPP standard are currently being submitted and considered to evolve and finalize the 3GPP standard.

SUMMARY

A method and apparatus are disclosed for performing a RA procedure for at least a first D2D communication session and a second D2D communication session in a wireless communication system. The method includes a UE transmitting a first message to a network, wherein the first message is a preamble. The method also includes the UE receiving a second message from a network after transmission of the first message, wherein the second message contains a first UL (Uplink) resource. The method further includes the UE using the first UL resource to transmit a third message to the network after reception of the second message, wherein the third message includes at least a buffer status report (BSR) medium access control (MAC) control element (CE). In addition, the method includes the UE determining that a contention resolution of the RA procedure is successful if the UE receives a fourth message, wherein the fourth message contains either a second UL resource or at least a D2D resource depending on whether or not the BSR MAC CE is associated with the first D2D communication session and the second D2D communication session.

DETAILED DESCRIPTION

In particular, the exemplary wireless communication systems devices described below may be designed to support one or more standards such as the standard offered by a consortium named “3rd Generation Partnership Project” referred to herein as 3GPP, including the RAN1#77 Chairman's Notes; the RAN2#85 Chairman's Notes; SP-110638, “WID on Proposal for a study on Proximity-based Services”; R2-142229, “D2D BSR Triggering and Sending Mechanism”, Huawei and HiSilicon; and TS 36.321 V11.2.0, “Medium Access Control (MAC) protocol specification”. The standards and documents listed above are hereby expressly incorporated by reference in their entirety.

3GPP SP-110638 proposes a new study item on proximity-based services (ProSe), or D2D services. 3GPP SP-110638 describes the justification and objective of the study item as follows:

Proximity-based applications and services represent a recent and enormous socio-technological trend. The principle of these applications is to discover instances of the applications running in devices that are within proximity of each other, and ultimately also exchange application-related data. In parallel, there is interest in proximity-based discovery and communications in the public safety community.
Current 3GPP specification are only partially suited for such needs, since all such traffic and signalling would have to be routed in the network, thus impacting their performance and adding un-necessary load in the network. These current limitations are also an obstacle to the creation of even more advanced proximity-based applications.
In this context, 3GPP technology, has the opportunity to become the platform of choice to enable proximity-based discovery and communication between devices, and promote a vast array of future and more advanced proximity-based applications.
4 Objective
The objective is to study use cases and identify potential requirements for an operator network controlled discovery and communications between devices that are in proximity, under continuous network control, and are under a 3GPP network coverage, for:1. Commercial/social use2. Network offloading3. Public Safety4. Integration of current infrastructure services, to assure the consistency of the user experience including reachability and mobility aspects
Additionally, the study item will study use cases and identify potential requirements for5. Public Safety, in case of absence of EUTRAN coverage (subject to regional regulation and operator policy, and limited to specific public-safety designated frequency bands and terminals)
Use cases and service requirements will be studied including network operator control, authentication, authorization, accounting and regulatory aspects.
The study does not apply to GERAN or UTRAN.

As discussed in 3GPP RAN2#85 Chairman's Notes, it was agreed in the RAN2#85 meeting that UE can request D2D resource from network via RA procedure as follows:2 In Mode 1, a UE requests transmission resources from an eNB. The eNB schedules transmission resources for transmission of scheduling assignment(s) and data.2a In Mode 1, the UE sends a scheduling request (D-SR or RA) to the eNB followed by a BSR based on which the eNB can determine that the UE intends to perform a D2D transmission as well as the required amount resources.

As discussed in the 3GPP RAN1#77 Chairman's Notes, RAN1#77 meeting assumed that a D2D RNTI (Radio Network Temporary Identifier) is used to distinguish a grant for UL (Uplink) or D2D as follows:

For Mode 1, DCI format which is same size as existing DCI format 0 is used for allocating D2D Data and SASame grant for D2D Data and SAFor Mode 1, a D2D RNTI is used to distinguish a grant for WAN from grant from D2D

3GPP R2-142229 proposed that UE shall consider the RACH (Random Access Channel) successful if it receives a D2D grant after sending a D2D BSR (Buffer Status Report) in Msg3 as follows:

If there is no dedicated PUCCH resource available for SR, RACH should be used to send D2D BSR as shown inFIG. 1. In this case, the D2D BSR shall be transmitted in MSG3. Upon reception of the D2D BSR in MSG3, the eNB may schedule D2D resources for the UE. Thus, the UE can consider the RACH successful if it receives a D2D grant.
Proposal 5: The UE shall consider the RACH successful if it receives a D2D grant contained in a PDCCH transmission after sending a D2D BSR in MSG3.
[FIG. 1 of 3GPP R2-142229 has been reproduced asFIG. 5]

3GPP TS 36.321 V11.2.0 introduced the Random Access procedure as follows:

5 MAC Procedures

5.1 Random Access Procedure

5.1.3 Random Access Preamble Transmission

The random-access procedure shall be performed as follows:

set PREAMBLE_RECEIVED_TARGET_POWER to preambleInitialReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE—COUNTER−1)*powerRampingStep;instruct the physical layer to transmit a preamble using the selected PRACH, corresponding RA-RNTI, preamble index and PREAMBLE_RECEIVED_TARGET_POWER.
5.1.4 Random Access Response Reception
Once the Random Access Preamble is transmitted and regardless of the possible occurrence of a measurement gap, the UE shall monitor the PDCCH of the PCell for Random Access Response(s) identified by the RA-RNTI defined below, in the RA Response window which starts at the subframe that contains the end of the preamble transmission [7] plus three subframes and has length ra-ResponseWindowSize subframes. The RA-RNTI associated with the PRACH in which the Random Access Preamble is transmitted, is computed as:
RA-RNTI=1+t_id+10*f_id
Where t_id is the index of the first subframe of the specified PRACH (0≦t_id<10), and f_id is the index of the specified PRACH within that subframe, in ascending order of frequency domain (0≦f_id<6). The UE may stop monitoring for Random Access Response(s) after successful reception of a Random Access Response containing Random Access Preamble identifiers that matches the transmitted Random Access Preamble.If a downlink assignment for this TTI has been received on the PDCCH for the RA-RNTI and the received TB is successfully decoded, the UE shall regardless of the possible occurrence of a measurement gap:if the Random Access Response contains a Backoff Indicator subheader:set the backoff parameter value in the UE as indicated by the BI field of the Backoff Indicator subheader and Table 7.2-1.else, set the backoff parameter value in the UE to 0 ms.if the Random Access Response contains a Random Access Preamble identifier corresponding to the transmitted Random Access Preamble (see subclause 5.1.3), the UE shall:consider this Random Access Response reception successful and apply the following actions for the serving cell where the Random Access Preamble was transmitted:process the received Timing Advance Command (see subclause 5.2);indicate the preambleInitialReceivedTargetPower and the amount of power ramping applied to the latest preamble transmission to lower layers (i.e., (PREAMBLE_TRANSMISSION_COUNTER−1)*powerRampingStep);process the received UL grant value and indicate it to the lower layers;if ra-Preamblelndex was explicitly signalled and it was not 000000 (i.e., not selected by MAC):consider the Random Access procedure successfully completed.else, if the Random Access Preamble was selected by UE MAC:set the Temporary C-RNTI to the value received in the Random Access Response message no later than at the time of the first transmission corresponding to the UL grant provided in the Random Access Response message;if this is the first successfully received Random Access Response within this Random Access procedure:if the transmission is not being made for the CCCH logical channel, indicate to the Multiplexing and assembly entity to include a C-RNTI MAC control element in the subsequent uplink transmission;obtain the MAC PDU to transmit from the “Multiplexing and assembly” entity and store it in the Msg3 buffer.NOTE: When an uplink transmission is required, e.g., for contention resolution, the eNB should not provide a grant smaller than 56 bits in the Random Access Response.NOTE: If within a Random Access procedure, an uplink grant provided in the Random Access Response for the same group of Random Access Preambles has a different size than the first uplink grant allocated during that Random Access procedure, the UE behavior is not defined.
If no Random Access Response is received within the RA Response window, or if none of all received Random Access Responses contains a Random Access Preamble identifier corresponding to the transmitted Random Access Preamble, the Random Access Response reception is considered not successful and the UE shall:increment PREAMBLE_TRANSMISSION_COUNTER by 1;If PREAMBLE_TRANSMISSION_COUNTER=preambleTransMax+1:if the Random Access Preamble is transmitted on the PCell:indicate a Random Access problem to upper layers;if the Random Access Preamble is transmitted on an SCell:consider the Random Access procedure unsuccessfully completed.if in this Random Access procedure, the Random Access Preamble was selected by MAC:based on the backoff parameter in the UE, select a random backoff time according to a uniform distribution between 0 and the Backoff Parameter Value;delay the subsequent Random Access transmission by the backoff time;proceed to the selection of a Random Access Resource (see subclause 5.1.2).
5.1.5 Contention Resolution
Contention Resolution is based on either C-RNTI on PDCCH of the PCell or UE Contention Resolution Identity on DL-SCH.
Once Msg3 is transmitted, the UE shall:start mac-ContentionResolutionTimer and restart mac-ContentionResolutionTimer at each HARQ retransmission;regardless of the possible occurrence of a measurement gap, monitor the PDCCH until mac-ContentionResolutionTimer expires or is stopped;if notification of a reception of a PDCCH transmission is received from lower layers, the UE shall:if the C-RNTI MAC control element was included in Msg3:if the Random Access procedure was initiated by the MAC sublayer itself and the PDCCH transmission is addressed to the C-RNTI and contains an UL grant for a new transmission; orif the Random Access procedure was initiated by a PDCCH order and the PDCCH transmission is addressed to the C-RNTI:consider this Contention Resolution successful;stop mac-ContentionResolutionTimer;discard the Temporary C-RNTI;consider this Random Access procedure successfully completed.else if the CCCH SDU was included in Msg3 and the PDCCH transmission is addressed to its Temporary C-RNTI:if the MAC PDU is successfully decoded:stop mac-ContentionResolutionTimer;if the MAC PDU contains a UE Contention Resolution Identity MAC control element; andif the UE Contention Resolution Identity included in the MAC control element matches the CCCH SDU transmitted in Msg3:consider this Contention Resolution successful and finish the disassembly and demultiplexing of the MAC PDU;set the C-RNTI to the value of the Temporary C-RNTI;discard the Temporary C-RNTI;consider this Random Access procedure successfully completed.elsediscard the Temporary C-RNTI;consider this Contention Resolution not successful and discard the successfully decoded MAC PDU.if mac-ContentionResolutionTimer expires:discard the Temporary C-RNTI;consider the Contention Resolution not successful.if the Contention Resolution is considered not successful the UE shall:flush the HARQ buffer used for transmission of the MAC PDU in the Msg3 buffer;increment PREAMBLE_TRANSMISSION_COUNTER by 1;If PREAMBLE_TRANSMISSION_COUNTER=preambleTransMax+1:indicate a Random Access problem to upper layers.based on the backoff parameter in the UE, select a random backoff time according to a uniform distribution between 0 and the Backoff Parameter Value;delay the subsequent Random Access transmission by the backoff time;proceed to the selection of a Random Access Resource (see subclause 5.1.2).

In the legacy LTE, if a UE has new data for UL transmission while there is no PUCCH (Physical Uplink Control Channel) resource for SR (Scheduling Request) available, the UE shall initiate a RA procedure and transmits Msg3 with LTE BSR to the network. After that, the UE would consider the RA procedure successful if the UE receives a UL grant for new transmission in Msg4.

For D2D communication, a UE may host multiple D2D sessions. Those multiple D2D sessions may trigger multiple D2D BSRs, which would make the UE performs a RA procedure for requesting D2D grant(s) from the network. Since the network will not distinguish the intention of the UE after receiving preamble, the network would not schedule sufficient random access response (RAR) grant(s) for the UE. Thus, it is quite possible that the UE would not be able to accommodate all of multiple D2D BSRs in Msg3 with the received RAR grant(s). After the reception of Msg3 with partial D2D BSR(s), if the network could understand that UE has remaining D2D BSR(s) to be transmitted (as discussed in U.S. Provisional Application Ser. No. 61/991,082), it is quite reasonable that the network would schedule UL grant(s) for the UE to transmit the remaining D2D BSR(s) for scheduling purposes. Besides, the network would also schedule D2D grant(s) for the D2D BSR(s) reported successful. Therefore, it would be possible for UE to receive UL grant(s) or D2D grant(s) in a RA procedure which is performed for requesting D2D grant(s).

3GPP R2-142229 proposed that UE shall determine a RA procedure performed for requesting D2D grant successful if it receives a PDCCH transmission for a D2D grant after sending an Msg3 with D2D BSR. This new mechanism of RA procedure may generally be fine for the case of UE accommodating one D2D BSR in Msg3. However, the mechanism should be further modified if the above concern is taken into account.

FIG. 7is a flow chart700in accordance with one exemplary embodiment from the perspective of a UE. In general,FIG. 7illustrates a method of the UE performing a RA procedure for at least a first D2D communication session and a second D2D communication session. In step705, the UE transmits a first message to a network, wherein the first message is a preamble, especially could be a random access preamble.

In step710, the UE receives a second message from the network after transmission of the first message, wherein the second message contains a first uplink (UL) resource. In one embodiment, the first UL resource could be a UL grant. The first UL resource also could be a RA response grant.

In step715, the UE uses the first UL resource to transmit a third message to the network after reception of the second message, wherein the third message includes at least a buffer status report (BSR) medium access control (MAC) control element (CE). In one embodiment, the third message could be an Msg3. Furthermore, the BSR MAC CE could be a D2D BSR MAC CE.

In step720, the UE determines that the RA procedure is successful if the UE receives a fourth message from the network, wherein the fourth message contains either a second UL resource or at least a D2D resource depending on whether or not the BSR MAC CE is associated with the first D2D communication session and the second D2D communication session. The second UL resource could be a UL grant.

In one embodiment, the UE determines that the RA procedure is successful when the UE receives the second UL resource if the BSR MAC CE is not associated with the first D2D communication session and the second D2D communication session. More specifically, if the first UL resource is insufficient, the BSR MAC CE may be only associated with the first D2D communication session or with the second D2D communication session. The BSR MAC CE could be a truncated BSR MAC CE. Moreover, the truncated BSR MAC CE could be a truncated D2D BSR MAC CE.

Alternatively, the UE determines that the RA procedure is successful when the UE receives the D2D resource if the BSR MAC CE is associated with both the first D2D communication session and the second D2D communication session simultaneously in the third message. The D2D resource could be a D2D grant. The BSR MAC CE may not be a truncated BSR MAC CE.

In one embodiment, the fourth message could include the D2D resource. Furthermore, the fourth message could be a PDCCH transmission addressed to a first identification. More specifically, the first identification could be a D2D-RNTI (Device-to-Device Radio Network Temporary Identifier).

In another embodiment, the fourth message could include the second UL resource. Furthermore, the fourth message could be a PDCCH transmission addressed to a second identification. More specifically, the second identification could be a C-RNTI (Cell Radio Network Temporary Identifier).

Referring back toFIGS. 3 and 4, the device300includes a program code312stored in memory310of a UE. The CPU308could execute program code312to enable the UE to (i) transmit a first message to a network, wherein the first message is a preamble; (ii) receive a second message from the network after transmission of the first message, wherein the second message contains a first uplink (UL) resource; (iii) use the first UL resource to transmit a third message to the network after reception of the second message, wherein the third message includes at least a buffer status report (BSR) medium access control (MAC) control element (CE); and (iv) determine that RA procedure is successful when receiving a fourth message from the network, wherein the fourth message contains either a second UL resource or at least a D2D resource depending on whether or not the BSR MAC CE is associated with at least the first D2D communication session and the second D2D communication session.

FIG. 8is a flow chart800in accordance with one exemplary embodiment from the perspective of a UE. In general,FIG. 8illustrates a method of the UE performing a RA procedure for at least a first D2D communication session and a second D2D communication session. In step805, a UE transmits a first message to a network, wherein the first message is a preamble, especially could be a random access preamble.

In step810, the UE receives a second message from the network after transmission of the first message, wherein the second message contains a first UL resource. In one embodiment, the first UL resource could be a UL grant. The first UL resource also could be a RA response grant.

In step815, the UE uses the first UL resource to transmit a third message to the network after reception of the second message, wherein the third message includes at least a BSR MAC CE. In one embodiment, the third message could be an Msg3. Furthermore, the BSR MAC CE could be a D2D BSR MAC CE.

In step820, the UE determines that the RA procedure is successful (i) when the UE receives at least a D2D resource from the network if the BSR MAC CE is associated with the first D2D communication session and the second D2D communication session OR (ii) when the UE receives a second UL resource from the network if the BSR MAC CE is not associated with the first D2D communication session and the second D2D communication session. The BSR MAC CE could be a D2D BSR MAC CE.

In one embodiment, the method further comprises that the UE receives a fourth message from the network after transmission of the third message, wherein the fourth message is a PDCCH (Physical Downlink Control Channel) transmission addressed to a first identification, and the fourth message contains at least a D2D resource. The first identification could be a D2D-RNTI (Device-to-Device Radio Network Temporary Identifier).

In the other embodiment, the method further comprises that the UE receives a fourth message from the network after transmission of the third message, wherein the fourth message is a PDCCH transmission addressed to a second identification, and the fourth message contains the second UL resource. The second identification is a C-RNTI (Cell Radio Network Temporary Identifier).

Referring back toFIGS. 3 and 4, the device300includes a program code312stored in memory310of a UE. In one embodiment, the CPU308could execute program code312to enable the UE to (i) transmit a first message to a network, wherein the first message is a preamble; (ii) receive a second message from the network after transmission of the first message, wherein the second message contains a first uplink (UL) resource; (iii) use the first UL resource to transmit a third message to the network after reception of the second message, wherein the third message includes at least a buffer status report (BSR) medium access control (MAC) control element (CE); and (iv) determine that the RA procedure is successful when the UE receives at least a D2D resource from the network if the BSR MAC CE is associated with at least the first D2D communication session and the second D2D communication session and that the RA procedure is successful when the UE receives a second UL resource from the network if the BSR MAC CE is not associated with the first D2D communication session and the second D2D communication session.

Referring back toFIGS. 3 and 4, the device300includes a program code312stored in memory310of a UE. In one embodiment, the CPU308could execute program code312to enable the UE (i) to receive a second message from a network, wherein the second message contains a first UL resource, and (ii) to determine that a RA procedure is successful if the UE receives at least a D2D resource from the network in case the first UL resource accommodates at least a BSR MAC CE which is associated with at least the first D2D communication session and the second D2D communication session in a third message. In one embodiment, the CPU could further execute program code312to enable the UE to determines that the RA procedure is successful if the UE receives a second UL resource from the network in case the first UL resource accommodates at least the BSR MAC CE which cannot be associated with both the first D2D communication session and the second D2D communication session simultaneously in the third message.

In addition, the CPU308could execute the program code312to perform all of the above-described actions and steps or others described herein.