WO2017134527A1

WO2017134527A1 - Method and apparatus for uplink frame transmission

Info

Publication number: WO2017134527A1
Application number: PCT/IB2017/000169
Authority: WO
Inventors: Tao Tao; Jianguo Liu; Yan Meng; Sigen Ye; Junrong GU
Original assignee: Alcatel Lucent
Priority date: 2016-02-05
Filing date: 2017-01-24
Publication date: 2017-08-10
Also published as: CN107046732A; CN107046732B

Abstract

Embodiments of the present disclosure provide a method and apparatus for uplink frame transmission. The method comprises: reserving a specific time-domain resource immediately preceding an OFDM symbol for transmission of a Sounding Reference Signal (SRS); and performing a Clear Channel Assessment (CCA) check with the reserved time-domain resource. The method may further comprise: reserving a further specific time-domain resource immediately preceding an OFDM symbol for transmission of PUSCH data; and performing a CCA check with the further reserved time-domain resource. The embodiments of the present disclosure further disclose a corresponding apparatus for uplink frame transmission. The embodiments of the present disclosure propose a solution of SRS transmission and PUSCH transmission in a Licensed Assisted Access (LAA), which enhances reliability and effectiveness of SRS transmission and PUSCH transmission.

Description

METHOD AND APPARATUS FOR UPLINK FRAME TRANSMISSION FIELD

[0001] Embodiments of the present disclosure generally relate to the field of wireless communications, and more specifically, to a method and apparatus for uplink frame transmission.

BACKGROUND

[0002] In current LTE system, data transmission occurs on a licensed spectrum. However, with dramatic increase of communication traffics, the licensed spectrum may not satisfy needs of the increasing traffics. The 3GPP work item has started studying LTE deployment on an unlicensed spectrum and proposed a concept of LAA (License Assisted Access) which utilizes unlicensed bands with assistance of LTE licensed spectrums. Communication on the LAA needs to apply a LBT (Listen Before Talk) mechanism, i.e., applying a CCA (Clear Channel Assessment) before using the unlicensed spectrum communication so as to listen whether the channel is available, thereby preventing communication interference on the unlicensed band.

[0003] SRS (Sounding Reference Signal) transmission on the LTE system uplink is for maintaining uplink timing and facilitating an eNB (Evolved Node B) to perform uplink and downlink scheduling, based on channel estimation, using channel interchangeability. Therefore, due to the same reasons, it is desirable to support SRS transmission on the unlicensed band for uplink transmission.

[0004] As the SRS signal is not necessarily transmitted along with any uplink physical channel, transmission of SRS mainly involves two transmission scenarios, i.e., the SRS is transmitted within a same subframe with PUSCH (Physical Uplink Shared Channel) data, or the SRS is separately transmitted within a subframe without PUSCH transmission. The communication on LAA needs to apply an LBT mechanism, however, there is no solution that supports the two SRS transmission scenarios in the LAA so far. SUMMARY

[0005] In view of the problems above, embodiments of the present disclosure propose a solution of supporting SRS and PUSCH transmission in an LAA by reserving specific time-domain resources before transmitting SRS and taking into account the support of an LBT procedure of PUSCH data transmission, thereby enhancing reliability and effectiveness of SRS transmission and PUSCH transmission.

[0006] According to a first aspect of the present disclosure, there is provided a method for uplink frame transmission, the method comprising: reserving a specific time-domain resource immediately preceding an Orthogonal Frequency Division Multiplexing (OFDM) symbol for transmission of a Sounding Reference Signal (SRS); and performing a Channel Assessment (CCA) check with the reserved time-domain resource.

[0007] According to embodiments of the present disclosure, the method further comprises: reserving a further specific time-domain resource immediately preceding an OFDM symbol for transmission of Physical Uplink Shared Channel (PUSCH) data; and performing a CCA check with the further reserved time-domain resource.

[0008] According to embodiments of the present disclosure, the method further comprises: configuring a cell-specific SRS subframe to enable the SRS to be transmitted in a last OFDM symbol or a first OFDM symbol of the cell-specific SRS subframe.

[0009] According to embodiments of the present disclosure, the method further comprises: if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe, reserving a time-domain resource in an end portion of a subframe immediately preceding the cell-specific SRS subframe so as to support the CCA check for the transmission of the SRS.

[0010] According to embodiments of the present disclosure, the method further comprises: if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe, reserving a time-domain resource in an end portion of each uplink subframe so as to support the CCA check for the transmission of the SRS and/or the CCA check for the transmission of the PUSCH data.

[0011] According to embodiments of the present disclosure, if the SRS is transmitted in the first OFDM symbol of the cell- specific SRS subframe and the PUSCH data is transmitted in the cell-specific subframe, the PUSCH data is transmitted immediately following the SRS.

[0012] According to embodiments of the present disclosure, the method further comprises: if the SRS is transmitted in the last OFDM symbol of the cell-specific SRS subframe, reserving a time-domain resource in an initial portion of each uplink subframe, and reserving a portion of time-domain resource immediately preceding the OFDM symbol for the transmission of the SRS, so as to support the CCA check for the transmission of the SRS and/or the transmission of the PUSCH data. [0013] According to embodiments of the present disclosure, the reserved time-domain resource includes a time-domain resource temporally corresponding to one OFDM symbol, or corresponding to more than one OFDM symbol, or corresponding to less than one OFDM symbol.

[0014] According to embodiments of the present disclosure, the method further comprises: configuring a downlink-uplink switching subframe, such that if only one OFDM symbol in the downlink-uplink switching subframe is used for uplink, the SRS is not transmitted in the downlink-uplink switching subframe.

[0015] According to embodiments of the present disclosure, the method further comprises: reserving the last OFDM symbol of the downlink-uplink switching subframe so as to support a CCA check for uplink subframe transmission subsequent to the downlink-uplink switching subframe.

[0016] According to embodiments of the present disclosure, the method further comprises: if a downlink-uplink switching subframe is used and two OFDM symbols in the downlink-uplink switching subframe are used for uplink, transmitting the SRS in the last OFDM of the downlink-uplink switching subframe, and reserving the second-to-last OFDM symbol of the downlink-uplink switching subframe so as to support the CCA check for the transmission of the SRS.

[0017] According to a second aspect of the present disclosure, there is provided an apparatus for uplink frame transmission, the apparatus comprising: a transmission unit configured to reserve a specific time-domain resource immediately preceding an Orthogonal Frequency Division Multiplexing (OFDM) symbol for transmission of a Sounding Reference Signal (SRS); and a CCA check unit configured to perform a Clear Channel Assessment (CCA ) check with the reserved time-domain resource.

[0018] According to embodiments of the present disclosure, the transmission unit is also configured to reserve a further specific time-domain resource immediately preceding an OFDM symbol for transmission of Physical Uplink Shared Channel (PUSCH ) data; and the CCA check unit is further configured to: perform a CCA check with the further reserved time-domain resource.

[0019] According to embodiments of the present disclosure, the transmission unit is also configured to configure a cell- specific SRS subframe to enable the SRS to be transmitted in a last OFDM symbol or a first OFDM symbol of the cell-specific SRS subframe.

[0020] According to embodiments of the present disclosure, the transmission unit is also configured to, if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe, reserve a time-domain resource in an end portion of a subframe immediately preceding the cell-specific SRS subframe so as to support the CCA check for the transmission of the SRS.

[0021] According to embodiments of the present disclosure, the transmission unit is also configured to, if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe, reserve a time-domain resource in an end portion of each uplink subframe so as to support the CCA check for the transmission of the SRS and/or the CCA check for the transmission of the PUSCH data.

[0022] According to embodiments of the present disclosure, the transmission unit is also configured to, if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe and the PUSCH data is transmitted in the cell-specific subframe, transmit the PUSCH data immediately following the SRS.

[0023] According to embodiments of the present disclosure, the transmission unit is also configured to, if the SRS is transmitted in the last OFDM symbol of the cell-specific SRS subframe, reserve a time-domain resource in an initial portion of each uplink subframe, and reserve a portion of time-domain resource immediately preceding the OFDM symbol for the transmission of the SRS, so as to support the CCA check for the transmission of the SRS and/or the transmission of the PUSCH data.

[0024] According to embodiments of the present disclosure, the reserved time-domain resource includes a time-domain resource temporally corresponding to one OFDM symbol, or corresponding to more than one OFDM symbol, or corresponding to less than one OFDM symbol.

[0025] According to embodiments of the present disclosure, the transmission unit is also configured to configure a downlink-uplink switching subframe, such that if only one OFDM symbol in the downlink-uplink switching subframe is used for uplink, the SRS is not transmitted in the downlink-uplink switching subframe.

[0026] According to embodiments of the present disclosure, the transmission unit is also configured to reserve the last OFDM symbol of the downlink-uplink switching subframe so as to support a CCA check for uplink subframe transmission subsequent to the downlink-uplink switching subframe.

[0027] According to embodiments of the present disclosure, the transmission unit is also configured to, if a downlink-uplink switching subframe is used and two OFDM symbols in the downlink-uplink switching subframe are used for uplink, transmit the SRS in the last OFDM of the downlink-uplink switching subframe, and reserve the second-to-last OFDM symbol of the downlink-uplink switching subframe so as to support the CCA check for the transmission of the SRS.

[0028] Considering the need of transmitting SRS and PUSCH data in the LAA, the embodiments of the present disclosure implements application of the LBT mechanism before transmission, thereby enhancing reliability and effectiveness of SRS transmission and PUSCH transmission and improving accuracy of channel measurement and channel estimation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of the present disclosure will be better understood through detailed depiction of the non-limiting embodiments provided with reference to the accompanying drawings, and other objectives, details, features, and advantages of the embodiments of the present disclosure will become more apparent. In the accompanying drawings:

[0030] Figure 1 illustrates SRS transmission with CCA check carried out in an existing LTE system;

[0031] Figure 2 illustrates a flowchart of a method for uplink frame transmission according to embodiments of the present disclosure;

[0032] Figure 3 illustrates uplink frame transmission according to an embodiment of the present disclosure;

[0033] Figure 4 illustrates uplink frame transmission according to another embodiment of the present disclosure;

[0034] Figure 5 illustrates uplink frame transmission according to a further embodiment of the present disclosure;

[0035] Figure 6 illustrates an exemplary scenario of supporting different uplink transmissions according to embodiments of the present disclosure; and

[0036] Figure 7 illustrates a block diagram of an apparatus for uplink frame transmission according to embodiments of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0037] Now, detailed depiction will be made to the embodiments of the present disclosure in conjunction with the accompanying drawings. The accompanying drawings only disclose specific embodiments capable of implementing the present disclosure in an exemplary manner, and the exemplary embodiments are not intended to exhaust all embodiments of the present disclosure. Those skilled in the art may obtain alternative embodiments from the depiction below so as to make structural or logical modifications without departing from the spirit and protection scope of the embodiments of the present disclosure. Therefore, the specific depiction below is not limitative, and the scope of the embodiments of the present disclosure is limited by the appended claims. It should be noted that although steps of relevant methods of the embodiments of the present disclosure have been described in a specific sequence, it does not require or imply that these operations have to be executed according to the specific sequence, or all operations that have been illustrated must be carried out to achieve the expected results. On the contrary, the order of carrying out the steps as described herein may be changed. Additionally or alternatively, some steps may be omitted; a plurality of steps may be merged into one step to execute, and/or one step may be split into a plurality of steps to execute.

[0038] In the LTE system, an SRS signal is usually transmitted in the last OFDM symbol of a cell-specific SRS subframe. Meanwhile, as previously mentioned, the SRS is not necessarily transmitted along with any uplink physical channel. In LTE Rel-12, two SRS transmission scenarios are allowed from the perspective of a user equipment (UE), namely: SRS being transmitted with the PUSCH data within a same subframe, or SRS is transmitted independently within one subframe without PUSCH transmission. However, when the SRS is transmitted with other physical channel (e.g., PUSCH), the SRS transmitted by one UE in a specific subframe may overlap in frequency domain with a PUSCH transmitted by another UE within the cell. In order to avoid conflict between SRS transmission and PUSCH transmission of different UEs, the SRS subframe configuration is performed at a cell level, such that all UEs are aware of the cell-specific SRS subframe configuration. Thus no UE in the cell transmits PUSCH data in an OFDM symbol for SRS transmission in the cell-specific SRS subframe.

[0039] It is required to apply the LBT mechanism on the LAA such that an LTE device listens and detects a clear channel on an unlicensed frequency band. The LBT mechanism requires listening the channel during CCA (Clear Channel Assessment). When an unlicensed frequency band is detected clear, an unlicensed frequency band will be occupied for starting data transmission.

[0040] According to the regulations on LBT in the EU standard, SRS may be considered as "short control signaling transmission", which may be transmitted by UE without LBT operation. With this option, the UE can transmit the SRS regardless of channel state, and the SRS transmission opportunities will increase. However, in this case, channel measurement and estimation may be inaccurate, because the interference level in an ideal channel has a great difference as that in a busy channel while the real interference level is not estimated. Meanwhile, without LBT operation, the SRS transmission may conflict with transmission from inter-cell or other technologies (e.g., Wi-Fi), or may suddenly deteriorate on-going transmission from a co-existing network. In general, in the LAA, LBT must be applied to SRS transmission in order to enhance channel measurement accuracy and avoid possible conflict with other nodes.

[0041] Figure 1 illustrates a schematic diagram of directly employing an LBT mechanism on an existing LTE communication, i.e., the LBT procedure for the SRS transmission is performed with a current frame structure. Figure 1 schematically shows transmission of three UEs (UE 1, UE 2, UE 3) with different transmission configurations in two subframes, wherein the first subframe is a cell-specific SRS subframe, and the second subframe is a non-SRS subframe. UE 1 and UE 2 are configured or triggered to transmit the SRS in the first subframe. UE 1 also transmits PUSCH data in the same subframe while UE 2 does not have PUSCH transmission in the subframe. Therefore, UE 2 has to transmit SRS on its own. UE 3 is not configured or triggered to transmit SRS in the first subframe, but configured to transmit PUSCH data in the two subframes. In this case, because of the PUSCH transmission performed by other nodes (e.g., UE 1 and UE 3), UE 2 has high chance to detect that the channel is busy, which would cause failure of CCA check and thus the SRS signal cannot be transmitted.

[0042] In addition, UE 3 which is not configured with SRS transmission has to interrupt PUSCH transmission to protect SRS transmission from intra-cell nodes. In order to resume the PUSCH transmission, UE 3 should check channel availability again. However, because the LBT procedure is blocked by intra-cell SRS transmissions and accordingly its CCA check result is likely to be very busy, PUSCH transmission cannot be resumed.

[0043] Therefore, there is a need for a novel frame structure and transmission scheme to support SRS transmission in LAA. Embodiments of the present disclosure provide a method for uplink frame transmission to support channel check for SRS transmission and PUSCH transmission on an unlicensed carrier while maintaining advantages of the existing LTE frame structure.

[0044] Figure 2 illustrates a flow diagram of a method according to the embodiments of the present disclosure.

[0045] In step S201, according to one embodiment of the present disclosure, a specific time-domain resource immediately preceding an OFDM symbol for transmitting an SRS signal is reserved so as to support CCA check for SRS transmission. In this step, in order to support the SRS transmission to be performed, no signal may be transmitted with the reserved time-domain resource.

[0046] In step S202, a CCA check is performed with the reserved time-domain resource. In this step, the UE may perform the CCA check using, for example, "energy detection," with the reserved time-domain resource. For example, the UE detects the channel with the reserved time-domain resource. If an energy level in the channel exceeds a power level threshold, it is believed that the channel is occupied; if it is found that the channel is clear, transmission may be performed immediately.

[0047] According to another embodiment of the present disclosure, a specific time-domain resource immediately preceding an OFDM symbol for transmitting PUSCH data is reserved and a CCA check is performed with the reserved time-domain resource. The procedure is similar to the procedure of CCA check that supports SRS transmission.

[0048] Because each UE in the cell is provided to perform CCA check with the reserved time-domain resource before transmitting the SRS or PUSCH data, interference of uplink transmission of each UE with other device transmission on the unlicensed frequency band is reduced, enabling effective transmission of the SRS and PUSCH data based on the channel state.

[0049] It should be noted that the reserved time-domain resource may be reasonably arranged according to specific application scenarios, e.g., in consideration of the capability of the UE, LAA system capacity, or loads of other communication systems on the unlicensed frequency band, etc. The reserved time-domain resource may be a time-domain resource that for example, temporally corresponds to one OFDM symbol, or temporarily corresponds to more than one OFDM symbol, or even temporally corresponds to less than one OFDM symbol.

[0050] Hereinafter, reservation of the time-domain resource involved in the embodiments of the present disclosure will be specifically described for the following three subframe scenarios.

• Scenario of Cell-Specific SRS Subframe

[0051] According to one embodiment of the present disclosure, in the cell-specific SRS subframe, a certain time-domain resource immediately preceding the configured SRS symbol is reserved. For example, the uplink transmission may be blanked in the corresponding reserved OFDM symbol. Therefore, in the cell-specific SRS subframe, regardless of stand-alone SRS transmission, SRS transmission with PUSCH, or PUSCH transmission without configuring the SRS, the reserved time-domain resource will provide an opportunity to perform the LBT procedure for CCA check.

[0052] As a specific example, in consideration that the SRS is always transmitted in the last OFDM symbol in the current LTE system, the reserved time-domain resource may be the resource preceding the last OFDM symbol in the SRS subframe configured for the current SRS in the LTE system, e.g., the second-to-last OFDM symbol in the subframe.

[0053] As another specific example, the SRS transmission position may be moved to the first OFDM symbol of the subframe. In this case, the reserved time-domain resource may be the time-domain resource in an end portion of the preceding subframe, e.g., the last OFDM symbol located in the preceding subframe. This will be beneficial to position the LBT location in the uplink subframe. In this example, the reserved time-domain resource may be located in the last OFDM symbol of the uplink subframe.

[0054] According to another embodiment of the present disclosure, in case that the UE is not configured or triggered to perform SRS transmission in the cell- specific SRS subframe and is scheduled to perform PUSCH transmission immediately following the SRS symbol, the UE still performs an LBT procedure with the reserved time-domain resource; and if the LBT procedure succeeds, the reserved signal is transmitted in the symbol for transmitting the SRS so as to hold the channel for subsequent PUSCH transmission. In this case, the UE transmits the reserved signal while not affecting SRS transmission performed by other UEs. This will be beneficial such that the PUSCH transmission configured for the UE will not be interrupted.

[0055] According to a further embodiment of the present disclosure, in order to be capable of CCA check for PUSCH transmission and SRS transmission, respectively, an initial portion of time-domain resource for each cell-specific subframe and a portion of time-domain resource immediately preceding the SRS symbol may be reserved.

• The scenario of non-SRS (common) subframe

[0056] According to one embodiment of the present disclosure, the time-domain resource immediately preceding the next potential transmission start point of PUSCH (e.g., subframe boundary or OFDM symbol #1) will be reserved. As a specific example, for the purpose of CCA check for SRS transmission or PUSCH transmission, an end portion of time-domain resource for each non-SRS subframe is reserved, e.g., the last OFDM symbol of each non-SRS subframe is reserved. As another specific example, for the purpose of CCA check for PUSCH transmission, the initial portion of time-domain resource for each uplink subframe, e.g., the first OFDM symbol of each uplink subframe is reserved. • The scenario of downlink-uplink switching subframe

[0057] According to one embodiment of the present disclosure, for a downlink-uplink switching subframe, e.g., the special subframe in LTE TDD, if there is only one symbol for uplink, the SRS transmission proposed in the present disclosure should not be configured or triggered in this downlink-uplink switching subframe, because the UE would not have enough time to perform the LBT procedure.

[0058] If there are more than two symbols for uplink, the SRS may be configured or triggered in the downlink-uplink switching subframe. If the SRS transmission is configured or triggered, for example, the second-to-last symbol in the downlink-uplink switching subframe is reserved for the LBT procedure of the SRS, while the last symbol is for SRS transmission. Alternatively, only part of time-domain resource corresponding to the second-to-last symbol may be reserved.

[0059] As mentioned above, in order to follow the LBT procedure on the unlicensed carrier, the UE should perform CCA check before the SRS transmission, and the SRS is only transmitted when the channel is clear. The solution proposed in the present disclosure implements CCA check for both SRS and PUSCH transmissions, and solves the problem that CCA check may be unreliable and the SRS transmission may be blocked when the UE is performing channel detection while UEs in other cell are transmitting data.

[0060] Hereinafter, a plurality of preferred embodiments will be described with reference to Figures 3-5 so as to understand the principle and essence of the present disclosure more clearly. It should be noted that the embodiments of the present disclosure are only for ease of understanding, to describe a plurality of embodiments in an exemplary manner, rather than limitative, let alone exhaustive.

[0061] Additionally, at the ease of depiction, only taking an example that reservation of the time-domain resource corresponds to one OFDM symbol. As mentioned above, for reservation of the time-domain resource, embodiments of the present disclosure are not limited to the scenario of corresponding to one OFDM symbol. Those skilled in the art will understand that a plurality of different specific implementations may exist, without departing from the spirit or basic feature of the embodiments of the present disclosure,.

[0062] Figure 3 is a schematic diagram of uplink frame transmission according to an embodiment of the present disclosure. Here, a TDD special subframe in the LTE system is taken as an example of the downlink-uplink switching subframe. UpPTS only occupies one OFDM symbol; transmission of PUSCH data is configured in the non-SRS subframe, and transmissions of PUSCH data and SRS signal are configured in the SRS subframe. [0063] In this embodiment, because UpPTS in the special subframe only occupies one OFDM symbol, SRS transmission is not allowed in the special subframe. However, the LBT procedure for next uplink subframe transmission may be performed in the UpPTS. Therefore, the symbol in the UpPTS is reserved. Transmission of PUSCH data is configured in the non-SRS subframe, and the last OFDM symbol of this subframe is reserved for CCA check. In the SRS subframe, the second-to-last OFDM symbol is reserved for CCA check, and the last OFDM symbol is reserved for SRS transmission.

[0064] It may be seen from this embodiment that the LBT procedure may be performed in the last OFDM symbol or the second-to-last OFDM symbol of the subframe. According to another embodiment of the present disclosure, in order to locate the position of LBT in the SRS subframe and the non-SRS subframe, the position of the SRS transmission may be moved to the first OFDM symbol of the cell- specific SRS subframe, as illustrated in Figure 4. In this case, the last symbol of each subframe is reserved for the LBT. If the SRS is transmitted together with the PUSCH, subsequent PUSCH transmission of the UE may continue without affecting SRS transmission due to the fact that other users in the cell transmit the SRS in the first OFDM symbol of the subframe. therefore, after the SRS transmission, the PUSCH data may be directly transmitted.

[0065] In another embodiment, the first OFDM symbol of each uplink subframe is reserved for the purpose of CCA check for PUSCH transmission. Moreover, for the purpose of CCA check for SRS transmission, the OFDM symbol immediately preceding the SRS symbol is reserved. This situation is shown in Figure 5. In Figure 5, two OFDM symbols of the SRS subframe are reserved. In a worst situation, if each uplink subframe has SRS to be transmitted, the transmission overheads will increase considerably. However, the uplink frame configuration in this embodiment has least impact on the existing LTE frame structure.

[0066] It should be understood that what has been discussed above is only an uplink frame transmission solution proposed by the present disclosure in a non-exhaustive manner with different specific examples, so as to support channel check for SRS transmission and PUSCH transmission on an unlicensed carrier. Those skilled in the art will easily know that, without departing from the spirit or basic feature of the embodiments of the present disclosure, a plurality of different uplink frame transmission schemes may also exist, which can implement the embodiments of the present disclosure in other specific forms.

[0067] Figure 4 illustrates an example of how the technical solution proposed by the present disclosure supports different uplink transmission scenarios. As illustrated in Figure 6, the first subframe is an uplink subframe configured with cell/ user-specific SRS subframe, and the second subframe is a common uplink subframe. Suppose the following scenarios:

- UE 1 is scheduled for PUSCH transmission in two subframes, and its SRS transmission is configured in the first subframe;

- UE 2 is configured with SRS transmission in the first subframe, and is not scheduled for PUSCH transmission in this subframe;

- UE 3 is scheduled for PUSCH transmission in two subframes;

- UE 4 is scheduled for PUSCH transmission only in the second subframe;

- in the first subframe, PUSCH transmissions of UE 1 and UE 3 are multiplexed in the frequency domain; in the second subframe, PUSCH transmissions of UE 1, UE 3 and

UE 4 are multiplexed in the frequency domain.

[0068] According to the solution proposed in the embodiments of the present disclosure, the uplink transmission for each UE may be provided below.

[0069] For UE 1, the LBT procedure for PUSCH transmission in the first subframe is performed in the last OFDM symbol of a preceding normal subframe. The PUSCH transmission takes OFDM symbols #0 - #11 of the SRS subframe. The LBT procedure for the SRS transmission is performed in the second-to-last OFDM symbol of the first subframe.

Because UE 1 is also scheduled for PUSCH transmission in the second subframe, the

PUSCH now can be directly transmitted in the second subframe after the SRS transmission. In this case, the last OFDM symbol of the second subframe is reserved for CCA check for subsequent transmissions, i.e., for performing PUSCH transmission in OFDM symbols

#0-#12 in the non-SRS subframe.

[0070] For UE 2, it detects channel availability in the second-to-last OFDM symbol of the first subframe. If the channel is detected clear, the stand-alone SRS of UE 2 may be transmitted.

[0071] For UE 3, it is not configured or triggered for SRS transmission. The LBT procedure is performed in the second-to-last OFDM symbol in the SRS subframe and the last OFDM symbol in the non-SRS subframe. In this case, because data transmission is not allowed in the last OFDM symbol of the SRS subframe so as to protect SRS transmissions from other UEs in the cell, the reserved signal should be transmitted by UE 3 to occupy the channel. For example, the reserved signal may be a UE specific sequence transmitted with the PUSCH resource so as to reserve the channel.

[0072] For UE 4, it is scheduled with only PUSCH transmission in the non-SRS subframe. Its uplink transmission is similar to the procedure of UE 3. [0073] Figure 7 is a schematic diagram of an apparatus for uplink frame transmission according to embodiments of the present disclosure. According to one embodiment of the present disclosure, there is provided an apparatus for uplink frame transmission, the apparatus comprising: a transmission unit 701 configured to reserve a specific time-domain resource immediately preceding an OFDM symbol for transmitting an SRS; and a CCA check unit 702 configured to perform a CCA check with the reserved time-domain resource.

[0074] According to embodiments of the present disclosure, the transmission unit 701 is further configured to reserve a further specific time-domain resource immediately preceding an OFDM symbol for transmitting PUSCH data; and the CCA check unit 702 is further configured to perform a CCA check with the further reserved time-domain resource.

[0075] According to embodiments of the present disclosure, the transmission unit 701 is further configured to configure a cell-specific SRS subframe to enable the SRS to be transmitted in a last OFDM symbol or a first OFDM symbol of the cell-specific SRS subframe.

[0076] According to embodiments of the present disclosure, the transmission unit 701 is further configured to, if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe, reserve a time-domain resource in an end portion of a subframe immediately preceding the cell-specific SRS subframe so as to support the CCA check for the transmission of the SRS.

[0077] According to embodiments of the present disclosure, the transmission unit 701 is further configured to, if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe, reserve a time-domain resource in an end portion of each uplink subframe so as to support the CCA check for the transmission of the SRS and/or the CCA check for the transmission of the PUSCH data.

[0078] According to embodiments of the present disclosure, the transmission unit 701 is further configured to, if the SRS is transmitted in the first OFDM symbol of the cell-specific SRS subframe and the PUSCH data is transmitted in the cell-specific subframe, transmit the PUSCH data immediately following the SRS.

[0079] According to embodiments of the present disclosure, the transmission unit 701 is further configured to, if the SRS is transmitted in the last OFDM symbol of the cell-specific SRS subframe, reserve a time-domain resource in an initial portion of each uplink subframe, and reserve a portion of time-domain resource immediately preceding the OFDM symbol for the transmission of the SRS, so as to support the CCA check for the transmission of the SRS and/or the transmission of the PUSCH data. [0080] According to embodiments of the present disclosure, the reserved time-domain resource includes a time-domain resource temporally corresponding to one OFDM symbol, or corresponding to more than one OFDM symbol, or corresponding to less than one OFDM symbol.

[0081] According to embodiments of the present disclosure, the transmission unit 701 is further configured to configure a downlink-uplink switching subframe, such that if only one OFDM symbol in the downlink-uplink switching subframe is used for uplink, the SRS is not transmitted in the downlink-uplink switching subframe.

[0082] According to embodiments of the present disclosure, the transmission unit 701 is further configured to reserve the last OFDM symbol of the downlink-uplink switching subframe so as to support a CCA check for uplink subframe transmission subsequent to the downlink-uplink switching subframe.

[0083] According to embodiments of the present disclosure, the transmission unit 701 is further configured to if a downlink-uplink switching subframe is used and two OFDM symbols in the downlink-uplink switching subframe are used for uplink, transmit the SRS in the last OFDM of the downlink-uplink switching subframe, and reserve the second-to-last OFDM symbol of the downlink-uplink switching subframe so as to support the CCA check for the transmission of the SRS.

[0084] Through the teachings provided in the depictions above and relevant drawings, many modifications and other embodiments of the present disclosure provided here will be appreciated by those skilled in the art, and the modifications and other embodiments are intended to be included within the scope of the present disclosure. In addition, although the depictions above and relevant drawings describe the exemplary embodiments under the background of some exemplary combinations of the components and/or functions, it should be appreciated that alternative embodiments may provide different combinations of the components and/or functions without departing from the scope of the present disclosure. As far as this point is concerned, for example, other combinations forms of components and/or functions that differ from the explicit depiction above are also expected to be within the scope of the present disclosure. Although specific terms are used here, they are only used in general and descriptive meanings, not intended to limit.

Claims

I/We Claim:

L A method for uplink frame transmission, comprising:

reserving a specific time-domain resource immediately preceding an Orthogonal Frequency Division Multiplexing (OFDM) symbol for transmission of a Sounding Reference Signal (SRS); and

performing a Clear Channel Assessment (CCA) check with the reserved time-domain resource.

2. The method according to claim 1, further comprising:

reserving a further specific time-domain resource immediately preceding an OFDM symbol for transmission of Physical Uplink Shared Channel (PUSCH) data; and

performing a CCA check with the further reserved time-domain resource.

3. The method according to claim 1 or 2, further comprising:

configuring a cell-specific SRS subframe to enable the SRS to be transmitted in a last OFDM symbol or a first OFDM symbol of the cell-specific SRS subframe.

4. The method according to claim 3, further comprising:

if the SRS is transmitted in the first OFDM symbol of the cell- specific SRS subframe, reserving a time-domain resource in an end portion of a subframe immediately preceding the cell-specific SRS subframe so as to support the CCA check for the transmission of the SRS.

5. The method according to claim 3, further comprising:

if the SRS is transmitted in the first OFDM symbol of the cell- specific SRS subframe, reserving a time-domain resource in an end portion of each uplink subframe so as to support the CCA check for the transmission of the SRS and/or the CCA check for the transmission of the PUSCH data.

6. The method according to claim 3, wherein:

if the SRS is transmitted in the first OFDM symbol of the cell- specific SRS subframe and the PUSCH data is transmitted in the cell-specific subframe, the PUSCH data is transmitted immediately following the SRS.

7. The method according to claim 3, further comprising: if the SRS is transmitted in the last OFDM symbol of the cell-specific SRS subframe, reserving a time-domain resource in an initial portion of each uplink subframe, and reserving a portion of time-domain resource immediately preceding the OFDM symbol for the transmission of the SRS, so as to support the CCA check for the transmission of the SRS and/or the transmission of the PUSCH data.

8. The method according to claim 1, wherein the reserved time-domain resource includes a time-domain resource temporally corresponding to one OFDM symbol, or corresponding to more than one OFDM symbol, or corresponding to less than one OFDM symbol.

9. The method according to claim 1, further comprising:

configuring a downlink-uplink switching subframe, such that if only one OFDM symbol in the downlink-uplink switching subframe is used for uplink, the SRS is not transmitted in the downlink-uplink switching subframe.

10. The method according to claim 9, further comprising:

reserving the last OFDM symbol of the downlink-uplink switching subframe so as to support a CCA check for uplink subframe transmission subsequent to the downlink-uplink switching subframe.

11. The method according to claim 1, further comprising:

if a downlink-uplink switching subframe is used and two OFDM symbols in the downlink-uplink switching subframe are used for uplink, transmitting the SRS in the last OFDM of the downlink-uplink switching subframe, and reserving the second-to-last OFDM symbol of the downlink-uplink switching subframe so as to support the CCA check for the transmission of the SRS.

12. An apparatus for uplink frame transmission, comprising:

a transmission unit configured to reserve a specific time-domain resource immediately preceding an Orthogonal Frequency Division Multiplexing (OFDM) symbol for transmission of a Sounding Reference Signal (SRS); and

a CCA check unit configured to perform a Clear Channel Assessment (CCA ) check with the reserved time-domain resource.

13. The apparatus according to claim 12, wherein the transmission unit is further configured to reserve a further specific time-domain resource immediately preceding an OFDM symbol for transmission of Physical Uplink Shared Channel (PUSCH ) data; and the CCA check unit is further configured to perform a CCA check with the further reserved time-domain resource.

14. The apparatus according to claim 12 or 13, wherein the transmission unit is further configured to:

configure a cell- specific SRS subframe to enable the SRS to be transmitted in a last

OFDM symbol or a first OFDM symbol of the cell-specific SRS subframe.

15. The apparatus according to claim 14, wherein the transmission unit is further configured to:

if the SRS is transmitted in the first OFDM symbol of the cell- specific SRS subframe, reserve a time-domain resource in an end portion of a subframe immediately preceding the cell-specific SRS subframe so as to support the CCA check for the transmission of the SRS.

16. The apparatus according to claim 14, wherein the transmission unit is further configured to:

if the SRS is transmitted in the first OFDM symbol of the cell- specific SRS subframe, reserve a time-domain resource in an end portion of each uplink subframe so as to support the CCA check for the transmission of the SRS and/or the CCA check for the transmission of the PUSCH data.

17. The apparatus according to claim 14, wherein the transmission unit is further configured to:

if the SRS is transmitted in the first OFDM symbol of the cell- specific SRS subframe and the PUSCH data is transmitted in the cell-specific subframe, transmit the PUSCH data immediately following the SRS.

18. The apparatus according to claim 14, wherein the transmission unit is further configured to:

if the SRS is transmitted in the last OFDM symbol of the cell-specific SRS subframe, reserve a time-domain resource in an initial portion of each uplink subframe, and reserve a portion of time-domain resource immediately preceding the OFDM symbol for the transmission of the SRS, so as to support the CCA check for the transmission of the SRS and/or the transmission of the PUSCH data.

19. The apparatus according to claim 12, wherein the reserved time-domain resource includes a time-domain resource temporally corresponding to one OFDM symbol, or corresponding to more than one OFDM symbol, or corresponding to less than one OFDM symbol.

20. The apparatus according to claim 12, wherein the transmission unit is further configured to:

configure a downlink-uplink switching subframe, such that if only one OFDM symbol in the downlink-uplink switching subframe is used for uplink, the SRS is not transmitted in the downlink-uplink switching subframe.

21. The apparatus according to claim 20, wherein the transmission unit is further configured to:

reserve the last OFDM symbol of the downlink-uplink switching subframe so as to support a CCA check for uplink subframe transmission subsequent to the downlink-uplink switching subframe.

22. The apparatus according to claim 12, wherein the transmission unit is further configured to:

if a downlink-uplink switching subframe is used and two OFDM symbols in the downlink-uplink switching subframe are used for uplink, transmit the SRS in the last OFDM of the downlink-uplink switching subframe, and reserve the second-to-last OFDM symbol of the downlink-uplink switching subframe so as to support the CCA check for the transmission of the SRS.