Transmission

FIELD OF THE INVENTION

[0001] The present disclosure generally relates to the field of wireless communication, and more specifically relates to a method and apparatus for configuring an initial subframe for a Downlink (DL) burst data transmission in a base station to support Licensed Assisted Access (LAA). BACKGROUND OF THE INVENTION

[0002] It is expected that the amount of data traffic carried over cellular networks will dramatically increase in the coming years. More spectrums will be needed for mobile operators to meet the increasing demands. Therefore, it is desired to implement Licensed Assisted Access Using Long Term Evolution (LAA-LTE) by utilizing a large available bandwidth of unlicensed spectrum (see Bibliography [1]).

[0003] In consideration of the spectrum efficiency, the LAA-LTE should support transmission of data/control signals on a subset of the Orthogonal Frequency Division Multiplexing (OFDM) symbols in a DL subframe (i.e., partial Transmission Time Interval (Partial TTI)) (see Bibliography [2]). According to WF Rl-152222 (see Bibliography [2] ), it may be necessary to limit a starting position of a DL burst data transmission to a few OFDM symbol positions considering a tradeoff between complexity and performance. Meanwhile, the ending positions of the burst data transmission may also be flexible so as to fully utilize the channel resources. In RANl#82bis, it has been agreed to use a Downlink Pilot Timeslot (DwPTS) structure to transmit a DL transport block in the last subframe of the DL burst data transmission. However, no consensus has been reached regarding the starting position of the first data/control information of the DL burst data transmission (i.e., the starting position of the initial subframe of the DL burst data transmission).

SUMMARY OF THE INVENTION

[0004] At present, there is no LAA-supported solution for an initial subframe of a DL burst data transmission which can make a good tradeoff between the complexity and the performance.

[0005] In view of the above problems, in consideration of spectrum efficiency, complexity, and the effect on the current specifications, the present disclosure provides a framework design for an initial subframe of a DL burst data transmission.

[0006] According to one aspect of the present disclosure, there is provided a method for configuring an initial subframe of a DL burst data transmission in a base station to support LAA. The method includes transmitting a CRS at at least a first OFDM symbol in the initial subframe; and configuring a PDCCH from a first OFDM symbol of a first timeslot of the initial subframe if a starting position of DL burst data transmission is in the first timeslot; or configuring the PDCCH from a first OFDM symbol of a second timeslot of the initial subframe if the starting position of the DL burst data transmission is in the second timeslot.

[0007] According to one aspect of the present disclosure, there is provided an apparatus for configuring an initial subframe of a DL burst data transmission in a base station to support LAA. The apparatus includes a transmitting unit configured to transmit a CRS at at least a first OFDM symbol in the initial subframe; and a control signaling configuring unit configured to configure a PDCCH from a first OFDM symbol of a first timeslot of the initial subframe if a starting position of the DL burst data transmission is in the first timeslot, or to configure the PDCCH from a first OFDM symbol of a second timeslot of the initial subframe if the starting position of the DL burst data transmission is in the second timeslot.

[0008] With the initial subframe design for the DL burst data transmission according to the present disclosure, LAA may be supported and a good tradeoff among spectrum efficiency, complexity, and effect on current specifications may be achieved.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0009] The present disclosure will be better understood and the other objectives, details, features and advantages of the present disclosure will become apparent through depiction of the preferred embodiments of the present disclosure with reference to the accompanying drawings. In the accompanying drawings:

[0010] Fig. 1 illustrates a schematic diagram of two possible frame structures of an initial subframe for a DL burst data transmission according to the present disclosure; and

[0011] Fig. 2 illustrates a schematic diagram of an apparatus for configuring an initial subframe for a DL burst data transmission in a base station to support LAA according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Although the drawings illustrate the preferred embodiments of the present disclosure, it should be understood that the present disclosure may be implemented in various forms and should not be limited by the embodiments depicted herein. Instead, these embodiments are provided to make the present disclosure more thorough and complete so as to convey the scope of the present disclosure to those skilled in the art.

[0013] In the study item of LAA, it has been agreed to follow the Listen-Before-Talk (LBT) principle so as to reduce the adverse impact on other nearby co-existent systems. In other words, before data transmission, Clear Channel Assessment (CCA) will be performed by using "energy detection". The channel can only be accessed if the base station assesses that the channel is free.

[0014] The LBT mechanism enables the base station to sense a channel and accesses the channel when the channel is free. In order to reserve the channel till a transmission boundary (e.g., symbol or subframe boundary), it is needed to transmit a channel reservation signal between an instant when the base station completes the LBT procedure successfully and a starting position for the DL burst data transmission, which will incur overheads and affect the system spectrum efficiency. Particularly, if the Physical Downlink Shared Channel (PDSCH) is only allowed to start transmission from a symbol in a first timeslot, the overheads will be huge in the case of a smaller Maximum Channel Occupancy Time (MCOT). Therefore, as far as spectrum efficiency is concerned, it should be allowed to start PDSCH transmission not only from the first timeslot of the subframe.

[0015] On the other hand, the PDCCH transmission should start at an OFDM symbol with CRS so as to guarantee a decoding performance. For a normal Cyclic Prefix (CP) case, the potential starting positions may be any of symbols {0, 4, 7, 11} of the subframe (herein, in the case of a normal CP, each subframe includes two timeslots and each timeslot contains 7 symbols; therefore, each subframe includes symbols 0, 1, 2, 13); while for an extended CP case, the potential starting positions may be any one of symbols {0, 4, 6, 10} of the subframe (herein, in the case of an extended CP, each subframe includes two timeslots and each timeslot contains 6 symbols; therefore, each subframe includes symbols 0, 1, 2, 11). In addition, a User Equipment (UE) needs to perform blind detection so as to determine a starting position of the DL burst data transmission based on a reference signal (e.g., an initial signal and/or a Common Reference Signal (CRS)). Therefore, it is desirable to restrict candidate starting positions to reduce blind detection complexity.

[0016] To make a tradeoff between the blind detection complexity and the performance, the candidate starting position for downlink data/control transmission may be configured at a first symbol of a first timeslot or a second timeslot of the subframe. Therefore, the starting positions may be symbols {0, 7} of the subframe (for a normal CP) or {0, 6} (for an extended CP).

[0017] Fig. 1 illustrates a schematic diagram of two possible frame structures of an initial subframe for the DL burst data transmission according to the present disclosure.

[0018] As illustrated in Fig. 1, in the frame structure I, the base station performs a CCA procedure in the subframe N-l to determine that the channel is in a free state. The CCA procedure ends during a second timeslot of the subframe N-l. Next, the base station transmits a channel reservation signal before a frame boundary between the subframe N-l and the subframe N so as to reserve the channel for the DL burst data transmission. In such a frame structure, the starting position of the DL burst data transmission is in the first timeslot of the initial subframe (i.e., the subframe N in Fig. 1). More specifically, the starting position starts from symbol 0 of the subframe N so as to transmit data/control information.

[0019] In the frame structure II, the CCA procedure of the base station ends during a first timeslot of the subframe K. In this case, the base station may configure the second timeslot of the subframe K as the starting position of the DL burst data transmission. Therefore, after the end of the CCA procedure and before the second timeslot of the subframe K, the base station transmits a channel reservation signal so as to reserve the channel for the DL burst data transmission. For example, the starting position may be the first symbol of the second timeslot of the subframe K for transmitting data/control information.

[0020] In the present disclosure, for the case illustrated in the frame structure I, if the starting position of the DL burst data transmission is in the first timeslot of the initial subframe, this initial subframe is also termed as a full initial subframe. For the case illustrated in the frame structure II, if the starting position of the DL burst data transmission is in the second timeslot of the initial subframe, this initial subframe is also termed as a partial initial subframe.

[0021] Hereinafter, directed to the two frame structures, configuration of the initial subframe for the DL burst data transmission will be described from three aspects: transmission detection, control channel design and Transport Block Size (TBS) scaling factor.

[0022] Two options are provided for transmission detection of the initial subframe:

[0023] Option 1: an initial signal is configured before the DL burst data transmission. As part of the channel reservation signal, the initial signal may comprise at least one of a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), a Common Reference Signal (CRS), a Dedicated Reference Signal (DRS), and/or a Channel State Information Reference Signal (CSI-RS).

[0024] Option 2: the CRS signal is transmitted at at least a first OFDM symbol in the initial subframe. Here, different from conventionally transmitting the CRS signal only at port 0 or port 1, the base station may configure to transmit the CRS signal on both port 0 and port 1 at the at least first OFDM symbol of the initial subframe such that a UE receiving such a CRS signal can quickly detect the initial subframe for the DL burst data transmission.

[0025] For the partial initial subframe (e.g., the starting position of the initial subframe in the subframes is the first symbol of the second timeslot) and the full initial subframe (e.g., the starting position of the initial subframe in the subframes is the first symbol of the first timeslot), a similar detection mechanism of the initial subframe may be used.

[0026] With Option 1, a design based on an effective initial signal can perform a reliable and effective detection of the starting position of the DL burst data transmission. Moreover, transmission of the initial signal (e.g., including PSS/SSS/CRS, etc.) enables a good time/frequency synchronization and provides an Automatic Gain Control (AGC) reference for respective burst receptions.

[0027] With Option 2, by detecting the CRS signal on at least a first OFDM symbol of the initial subframe, the complexity of the UE can be greatly reduced and the UE power can be advantageously saved. This is quite helpful for the UE to wake up from a Discontinuous Reception (DRX).

[0028] In one implementation, the initial subframe configuration in the base station only adopts Option 2 for transmission detection of the initial subframe. For example, if it is not needed to perform AGC and time/frequency synchronization based on the initial signal, it may employ only Option 2.

[0029] In another implementation, the initial subframe configuration in the base station may employ a combination of Option 1 and Option 2. This may be a case of needing to perform AGC and time/frequency synchronization based on the initial signal. Moreover, in this implementation, even the UE misses the initial signal (i.e., failing to detect the Option 1 signal), the initial subframe for the DL burst data transmission can also be detected by detecting the CRS signal on the at least first OFDM symbol of the subframe.

[0030] Because for PDCCH and EPDCCH, transmission of a control signaling generally should start from symbol 0 and symbols 0-3 of the subframe, it is not supported to transmit a control signaling only in the second timeslot currently. For PDCCH, in order to guarantee least effect on the specifications and a lower blind detection complexity, the PDCCH may be transmitted in first several OFDM symbols of the initial subframe before the scheduled PDSCH. As an embodiment, the first 0-3 symbols may be configured for PDCCH transmission in the initial subframe as needed.

[0031] Therefore, for the frame structures I and II, the following solutions may be adopted for PDCCH control signaling transmission of the initial subframe, respectively:

[0032] For the frame structure I of the initial subframe, the base station starts configuring the PDCCH from the first symbol of the first timeslot of the initial subframe. In such a frame structure, the control channel actually needs no additional design since in the traditional control channel design, symbol 0 is a starting position of the PDCCH/PDSCH transmission in the DL burst data transmission. In this case, a self-carrier scheduling mechanism and a cross-carrier scheduling mechanism may be used for the initial subframe.

[0033] For the frame structure II of the initial subframe, the base station starts configuring the PDCCH from the first symbol of the second timeslot of the initial subframe. In such a frame structure, since data transmission starts from the second timeslot, the cross-carrier scheduling based on the current subframe cannot be used.

[0034] In order to support EPDCCH transmission within an initial subframe including a scheduled PDSCH, for the frame structures I and II, the following solutions may be employed for EPDCCH control signaling transmission of the initial subframe, respectively:

[0035] For the frame structure I of the initial subframe, the base station starts configuring the EPDCCH from the k ^th OFDM symbol of the first timeslot of the initial subframe.

[0036] For the frame structure II of the initial subframe, the base station starts configuring the PDCCH from the k ^th OFDM symbol of the second timeslot of the initial subframe.

[0037] Here, the value of k may be configured through a Radio Resource Control (RRC) signaling (e.g., in the EPDCCH-Config information element or other control information elements), or may be indicated based on detection of a Physical HARQ Indicator Channel (PFICH).

[0038] In other words, EPDCCH transmission starts after PDCCH, or if the PDCCH does not exist, the EPDCCH transmission starts from the first symbol of the initial subframe.

[0039] What has been discussed above is configuration of the starting position of EPDCCH. Hereinafter, specific design specifications of LAA-supported EPDCCH will be discussed.

[0040] In Rel-12, in a special subframe, at least 6 valid symbols in the subframe may support EPDCCH transmission. However, in the initial subframe, 3-7 symbols are needed to support EPDCCH transmission. Supposing an enhanced Resource Element Group (EREG) mapping in a Physical Resource Block (PRB) pair maintains unchanged, similar to Rel-12, in the case of partial initial subframe, the amount of valid Resource Elements (REs) in each enhanced Control Channel Element (ECCE) will be less than the amount of valid REs for normal subframe EPDCCH transmission. To ensure the performance of EPDCCH, the following specific designs for EPDCCH in the initial subframe may be considered.

[0041] Solution 1: if the number of valid symbols in the initial subframe for EPDCCH transmission is smaller than a specific value, in the EPDCCH, one PRB pair only has one ECCE therein.

[0042] In Rel-12, dependent on the frame structure type, CP length and special frame configuration, the PRB pair has 4 or 2 ECCEs. In view that the number of valid REs becomes less for EPDCCH transmission in the initial subframe, it is recommended in solution 1 that the number of valid symbols in the initial subframe for EPDCCH transmission is less than a specific value, such that the EPDCCH should support that one PRB pair only has one ECCE therein.

[0043] Solution 2: If the number of valid symbols in the initial subframe for EPDCCH transmission is less than a specific value, a higher aggregation level may be used in EPDCCH.

[0044] For example, if the number of valid symbols in the initial subframe for EPDCCH transmission is less than the specific value, the maximum aggregation level as used may be twice of the conventional maximum aggregation level.

[0045] In one implementation, for both solution 1 and solution 2, the specific value may be a positive integer less than 7, e.g., it may be 6.

[0046] Further, since the design of the initial subframe for the DL burst data transmission according to the present disclosure includes two possible types of frame structures, different Transport Block Sizes (TBSs) may be configured for Transport Blocks (TBs) in the two types of frame structures. [0047] Since the interval between TB preparation and transmission might be only several milliseconds, the size of the transport block in the initial subframe should be determined before the TB transmission. Further, since the actual length of the initial subframe when the TB is determined is unknown, transport blocks with different TBSs should be prepared in advance for the frame structures I and II.

[0048] In one implementation, for the frame type I, a first TBS is configured for the transport block, while for the frame type II, a second TBS different from the first TBS is configured for the transport block, wherein the second TBS is determined by a scaling factor.

[0049] For PDSCH transmission in a normal DL subframe, the TBS is determined based on a resource allocation size (NPRB) and a Modulation Coding Scheme (MCS) index. For PDSCH transmission in the DwPTS, the TBS may also be adjusted to adapt a scenario with less number of OFDM symbols available for PDSCH so as to provide a more effective DL transmission. Here, for all special subframe configurations, TBS adjustment is done by multiplying the NPRB with a factor 0.75.

[0050] For the initial subframe configuration, only 4 ~ 7 (for the normal CP) or 3~6 (for the extended CP) valid OFDM symbols may be used for PDSCH transmission. In this case, since the factor 0.75 usually corresponds to 0.75 x 12=9 OFDM symbols, it cannot reflect the number of available OFDM symbols configured for the partial initial subframe.

[0051] Considering the case of the frame type II, the initial subframe only occupies one timeslot of the subframe; therefore, the scaling factor may be determined based on the number of available symbols in the initial subframe.

[0052] In one implementation, if the initial subframe spans over 7 OFDM symbols while the

PDCCH spans over 2 OFDM symbols, the scaling factor may be set to 5/12.

[0053] Fig. 2 illustrates a schematic diagram of an apparatus 200 for configuring an initial subframe for the DL burst data transmission in a base station according to the present disclosure.

[0054] As illustrated in Fig. 2, the apparatus 200 comprises a transmitting unit 210 configured to transmit a CRS at at least a first OFDM symbol in the initial subframe; and a control signaling configuring unit 220 configured to configure PDCCH from a first OFDM symbol of a first timeslot of the initial subframe if a starting position of the DL burst data transmission is in the first timeslot, or to configure the PDCCH from a first OFDM symbol of a second timeslot of the initial subframe if the starting position of DL burst data transmission is in the second timeslot.

[0055] In one implementation, the control signaling configuring unit 220 is further configured to configure an initial signal before the DL burst data transmission for AGC and/or time/frequency synchronization.

[0056] In one implementation, the initial signal includes at least one reference signal of SSS, PSS, CRS, DRS and CSI-RS.

[0057] In one implementation, the apparatus further comprises a CCA unit 230 configured to perform CCA before the initial subframe so as to determine whether the starting position of the DL burst data transmission is in the first timeslot or the second timeslot of the initial subframe.

[0058] In one implementation, if the starting position of the DL burst data transmission is in the second timeslot of the initial subframe, the control signaling configuring unit 220 configures the EPDCCH from a kth OFDM symbol of the second timeslot, wherein a value of k is indicated to the UE through a RRC signaling or indicated based on PRICH detection.

[0059] In one implementation, if a number of valid symbols in the initial subframe for EPDCCH transmission is smaller than a specific value, then in the EPDCCH, one PRB pair only has one ECCE.

[0060] In one implementation, if a number of valid symbols in the initial subframe for EPDCCH transmission is smaller than a specific value, a higher aggregation level is used in the EPDCCH.

[0061] In one implementation, the specific value is a positive integer smaller than 7.

[0062] In one implementation, if the starting position of the DL burst data transmission is in the first timeslot of the initial subframe, a first transport block size is configured for the transport blocks; and if the starting positon of the DL burst data transmission is in the second timeslot of the initial subframe, a second transport block size different from the first transport block size is configured for the transport blocks, wherein the second transport block is determined by a scaling factor.

[0063] The proposed design for initial subframe for the DL burst data transmission can support

LAA and realize a good tradeoff between the complexity and the performance.

[0064] In one or more exemplary designs, the functions of the present application may be implemented using hardware, software, firmware, or any combinations thereof. In the case of implementation with software, the functions may be stored on a computer readable medium as one or more instructions or codes, or transmitted as one or more instructions or codes on the computer readable medium. The computer readable medium comprises a computer storage medium and a communication medium. The communication medium includes any medium that facilitates transmission of the computer program from one place to another. The storage medium may be any available medium accessible to a general or specific computer. The computer-readable medium may include, for example, but not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disc storage devices, magnetic disk storage devices, or other magnetic storage devices, or any other medium that carries or stores desired program code means in a manner of instructions or data structures accessible by a general or specific computer or a general or specific processor. Furthermore, any connection may also be considered as a computer-readable medium. For example, if software is transmitted from a website, server or other remote source using a co-axial cable, an optical cable, a twisted pair wire, a Digital Subscriber Line (DSL), or radio technologies such as infrared, radio or microwave, then the co-axial cable, optical cable, twisted pair wire, Digital Subscriber Line (DSL), or radio technologies such as infrared, radio or microwave are also covered by the definition of medium.

[0065] The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any normal processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0066] Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0067] The above depiction of the present disclosure is to enable any of those skilled in the art to implement or use the present disclosure. For those skilled in the art, various modifications of the present disclosure are obvious, and the general principle defined herein may also be applied to other transformations without departing from the spirit and protection scope of the present disclosure. Thus, the present disclosure is not limited to the examples and designs as described herein, but should be consistent with the broadest scope of the principle and novel characteristics of the present disclosure.

Bibliographies:

[1]. 3GPP TR 36.889, "Study on Licensed-assisted access to unlicensed spectrum", V13.0.0.

[2]. Rl-152222, "WF on Start and end position of DL transmission in LAA", LGE, Samsung, NTT DOCOMO, 3GPP RANl#80bis, Belgrade, Serbia, 20th -24th April, 2015

[3]. RANI Chairman's Notes, 3GPP TSG RAN WG1 Meeting #82bis, Oct. 5th-9th 2015