WO2016182405A1

WO2016182405A1 - Method and apparatus of transmitting harq-ack in enhanced carrier aggregation systems

Info

Publication number: WO2016182405A1
Application number: PCT/KR2016/005123
Authority: WO
Inventors: Jingxing Fu; Yingyang Li; Shichang Zhang
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2015-05-14
Filing date: 2016-05-13
Publication date: 2016-11-17
Also published as: CN106301702A

Abstract

The present disclosure relates to a pre-5th-generation (5G) or 5G communication system to be provided for supporting higher data rates beyond 4th-generation (4G) communication system such as a long term evolution (LTE). The present disclosure discloses a method of transmitting a hybrid automatic repeat-request acknowledgement (HARQ-ACK) by a user equipment (UE) in an enhanced carrier aggregation (CA) system. The method includes: the UE determines the HARQ-ACK to be transmitted in an uplink subframe based on scheduled cells and downlink subframes scheduled in each of scheduled cells, and transmits the determined HARQ-ACK to an evolved Node B (eNB).

Description

METHOD AND APPARATUS OF TRANSMITTING HARQ-ACK IN ENHANCED CARRIER AGGREGATION SYSTEMS

The present invention relates to wireless communications systems, and particularly, to a method and apparatus of transmitting hybrid automatic repeat-request acknowledgement (HARQ-ACK) in an enhanced carrier aggregation (CA) system.

To meet the demand for wireless data traffic having increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.

The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, a massive multiple-input multiple-output (MIMO), a full dimensional MIMO (FD-MIMO), an array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.

In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, a coordinated multi-points (CoMP), reception-end interference cancellation and the like.

In the 5G system, an hybrid FSK and QAM modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and a filter bank multi carrier (FBMC), a non-orthogonal multiple access (NOMA), and a sparse code multiple access (SCMA) as an advanced access technology have been developed.

Long term evolution (LTE) supports two duplexing modes, i.e. frequency division duplexing (FDD) and time division duplexing (TDD). FIG. 1 is a schematic diagram illustrating the frame structure of a TDD system. Each radio frame has a length of 10ms and is equally divided into two half-frames of 5ms. Each half-frame includes 8 time slots and 3 special fields. Each of the 8 time slots has a duration of 0.5ms. The 3 special fields, i.e. downlink pilot time slot (DwPTS), guarding period (GP) and uplink pilot time slot (UpPTS), have a total duration of 1ms. Each sub frame is composed of two consecutive time slots, i.e., the k’th sub frame includes time slot 2k and time slot 2k+1. A TDD system supports 7 types of uplink/downlink (UL/DL) configurations, as shown in Table 1. In Table 1, D represents a downlink sub frame, U represents an uplink sub frame, and S represents a special sub frame including the 3 special fields.

In a TDD system, when downlink subframes are more than uplink subframes, hybrid automatic repeat-request acknowledgement (HARQ-ACK) for physical downlink shared channel (PDSCH) and physical downlink control channel (PDCCH)/ enhanced PDCCH (EPDCCH) for transmitting semi-persistent scheduling (SPS) release is transmitted in one uplink subframe, as shown in FIG. 2. The number of downlink subframes whose HARQ-ACK is transmitted within one uplink subframe is referred to as the size of an HARQ-ACK bundling window. An HARQ-ACK bundling window is determined by a TDD UL/DL configuration corresponding to an HARQ timing scheme adopted by a UE in HARQ-ACK feedback. An HARQ-ACK bundling window denotes all of downlink subframes whose HARQ-ACK is to be fed back in subframe n. Subframe index numbers of the downlink subframes are denoted as n-k_i, k_i ∈ K. The dimension M of the set K is referred to as the size of the bundling window. Sets K defined in conventional LTE standards for HARQ timing schemes of different TDD UL/DL configurations are as shown in Table 2. Table 2 represents Sets K: {k₀, k₁, ..., k_M _-1} determined for different HARQ timing schemes.

In an FDD system, the number of downlink subframes whose HARQ-ACK is transmitted within one uplink subframe is 1, i.e., the size of the HARQ-ACK bundling window is 1.

In order to increase transmission rate of users, the LTE-advanced (LTE-A) system is proposed. In LTE-A, multiple component carriers (CCs) are aggregated to obtain larger working bandwidth, i.e., carrier aggregation (CA). The aggregated carriers constitute downlink and uplink links in the communication system, therefore larger transmission rates can be achieved. For example, 5 CCs of 20MHz may be aggregated to obtain a bandwidth of 100MHz. Each CC is referred to as a cell. A base station may configure a UE to work in multiple CCs which include a primary CC (PCC or Pcell) and other CCs which are referred to as secondary CCs (SCC or Scell).

In such a CA system, downlink reference UL/DL configuration of a cell may be determined according to configurations in a UE regarding a cell transmitting HARQ-ACK and configurations of the cell. The configurations of the cell may include FDD and various TDD UL/DL configurations. Then, the HARQ-ACK bundling window and its size can be determined according to the downlink reference UL/DL configuration.

A UE may transmit HARQ-ACK feedback information using physical uplink control channel (PUCCH) format 3. PUCCH format 3 supports at most 5 cells and transmission of up to 22 bits. The 22 bits may include HARQ-ACK bits, channel state information (CSI) bits and scheduling request (SR) bits. PUCCH format 3 resource for HARQ transmission is determined as follows. A set of PUCCH format 3 resource is configured for a UE by higher layer signaling, and HARQ-ACK resource indicator (ARI) in (e)PDCCH in which PDSCH is scheduled is used to dynamically specify one of the set of PUCCH format 3 resources configured by higher layer signaling to be the PUCCH format 3 resource for HARQ-ACK transmission. The ARI is implemented by re-interpreting a transmission power control (TPC) field. The TPC field includes TPC field for scheduling (e)PDCCH in Scell and TPC field for scheduling PDCCH in which downlink downlink assignment indicator (DL DAI) is not 1 in Pcell. The resource indication method is as shown in Table 3. Table 3 represents PUCCH format 3 resource indication.

In conventional CA systems, if a UE is configured with PUCCH format 3 for HARQ-ACK transmission, HARQ-ACK bits and/or periodical CSI bits and/or SR bits are transmitted via PUCCH if the total number of the HARQ-ACK bits and/or periodical CSI bits and/or SR bits is within 22 bits; HARQ-ACK bits and/or periodical CSI bits and/or SR bits are processed through spatial bundling if the total number of the HARQ-ACK bits and/or periodical CSI bits and/or SR bits is within 22 bits; if the total number of the spatially bundled HARQ-ACK bits and/or periodical CSI bits and/or SR bits is within 22 bits, the HARQ-ACK bits and/or periodical CSI bits and/or SR bits are still transmitted via PUCCH; if the total number of the spatially bundled HARQ-ACK bits and/or periodical CSI bits and/or SR bits is larger than 22 bits, the UE only transmits HARQ-ACK bits and/or SR bits and does not transmit the periodical CSI bits.

If a UE is configured with plural cells, HARQ-ACK transmission using PUCCH format 3 includes performing HARQ-ACK transmission according to a transmission mode of each cell configured and the size of the HARQ-ACK bundling window. If the transmission mode configured in the cell is SIMO or MIMO with spatial bundling, a downlink subframe corresponds to a transmission block and transmits 1-bit HARQ-ACK. If the size of the HARQ-ACK bundling window of the cell is determined to be M according to downlink reference UL/DL configuration of the cell, M-bit HARQ-ACK is transmitted in the cell. If the transmission mode configured in the cell is MIMO, a downlink subframe corresponds to two transmission blocks, and 2-bit HARQ-ACK is transmitted. If the size of the HARQ-ACK bundling window of the cell is determined to be M according to downlink reference UL/DL configuration of the cell, 2*M-bit HARQ-ACK is transmitted in the cell. HARQ-ACK bits of the cells are arranged in ascending order of the index numbers of the cells. For each cell, HARQ-ACK bits of downlink subframes are arranged in ascending order of DL DAI. HARQ-ACK bits of PDSCH in SPS downlink subframes are arranged at the tail of HARQ-ACK bits of the cell. For example, for cell c, the transmission mode of is MIMO without spatial bundling, the downlink referent UL/DL configuration is TDD configuration 2, the size of the HARQ-ACK bundling window is 4, HARQ-ACK of downlink subframe n-km is transmitted in uplink subframe n. k_mincludes {k₁, k₂, k₃, k₄}. The HARQ-ACK of cell c has 8 bits, denoted as {a₀, a₁, a₂, a₃, a₄, a₅, a₆, a₇}. The HARQ-ACK of downlink subframe k_mis {a_2DAI _(km)-2, a_2DAI _(km)- ₁}. The DAI (k_m) represents the value of the DAI field in DCI in (e)PDCCH which schedules PDSCH of downlink subframe k_m, and specifies the sum of the accumulative number of (e)PDCCHs of already scheduled PDSCHs and the accumulative number of (e)PDCCHs indicating downlink SPS release.

In order to make full use of the wide spectrum which includes unlicensed bands, a UE may aggregate a CA system having more than 5 CCs to obtain larger bandwidth, e.g., aggregating a CA system having up to 32 cells.

Since a UE may be configured with a maximum of 32 cells and HARQ-ACK bits are remarkably greater than 22 bits, it is necessary to introduce a new PUCCH format to bear the HARQ-ACK bits. The new PUCCH format is herein referred to as PUCCH format X, and can bear a maximum of N’ bits. For example, N’ may be 64 or 128.

The present disclosure provides a method and apparatus of transmitting HARQ-ACK in an enhanced CA system. HARQ-ACK to be transmitted in an uplink subframe is determined according to scheduled cells of a UE and downlink subframes scheduled in each scheduled cell, and is transmitted to a base station.

To attain the above objectives, the present disclosure adopts the following technical schemes.

A method of transmitting HARQ-ACK in an enhanced CA system includes:

determining, by a UE, HARQ-ACK to be transmitted within an uplink subframe according to scheduled cells and downlink subframes scheduled in each scheduled cell; and

transmitting, by the UE, the determined HARQ-ACK to an eNB.

Preferably, the step of determining the HARQ-ACK includes:

determining, by the UE, the number of bits of the HARQ-ACK to be transmitted in the uplink subframe according to a value of a cell domain DL DAI defined in DL DCI in a PDCCH/EPDCCH scheduling PDSCH in the cell or in a PDCCH/EPDCCH scheduling downlink SPS release;

wherein the value of the cell domain DL DAI specifies the accumulative number of scheduled transmission blocks (TB) or of transmitted PDCCH/EPDCCH in a downlink subframe up to the cell which includes the DL DAI.

Preferably, the step of determining the HARQ-ACK includes:

determining, by the UE, the number of bits of the HARQ-ACK to be transmitted in the uplink subframe according to a value of a cell domain and time domain joint DL DAI defined in DL DCI in a PDCCH/EPDCCH scheduling PDSCH or in a PDCCH/EPDCCH scheduling downlink SPS release in the cell;

wherein the value of the cell domain and time domain joint DL DAI specifies the accumulative number of scheduled TBs or the accumulative number of PDCCH/EPDCCHs transmitted within a time-frequency bundling window up to the downlink subframe which includes the cell domain and time domain joint DL DAI; the time-frequency bundling window is a collection formed by all of downlink subframes whose HARQ-ACK is to be fed back in the same uplink subframe in all carriers of the UE.

Preferably, the number of bits of the HARQ-ACK may be determined further according to a value of a reverse DL DAI or reference DL DAI set in a PDCCH/EPDCCH scheduling PDSCH or in a PDCCH/EPDCCH indicating downlink SPS release in the cell;

the value of the reverse DL DAI is the sequence number of a cell which includes the DL DAI when all of the cells including the DL DAI in the downlink subframe arranged in a descending order of index numbers of the cells, and is for identifying a lost PDCCH/EPDCCH at the tail of the downlink subframe;

the value of the reference DL DAI indicates the total number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release or the total number of corresponding TBs when calculating the number of bits of the HARQ-ACK of the downlink subframe which includes the DL DAI, is for identifying a lost PDCCH/EPDCCH at the tail of the downlink subframe.

the value of the reverse DL DAI is the sequence number of a cell which includes the DL DAI when all of the cells in a time-frequency bundling window which includes the cell are arranged in a descending order of index numbers of the cells, and is for identifying a lost PDCCH/EPDCCH at the tail of the time-frequency bundling window;

the value of the reference DL DAI indicates the total number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release or the total number of corresponding TBs when calculating the number of bits of the HARQ-ACK in a time-frequency bundling window which includes the DL DAI, is for identifying a lost PDCCH/EPDCCH at the tail of the time-frequency bundling window.

Preferably, if all of cells configured for the UE is configured with SIMO as the transmission mode, or all cells configured with MIMO are also configured with spatial bundling of HARQ-ACK, the number of bits of HARQ-ACK determined is

; wherein

is the number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release when calculating the HARQ-ACK in the time-frequency bundling window, L is the number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release detected in the time-frequency bundling window and predicted by the UE according to the cell domain and time domain joint DL DAI, q is the number of bits of the cell domain and time domain joint DL DAI, and the cell domain and time domain joint DL DAI has the same number of bits with the reference DL DAI;

if the UE is configured with a cell whose transmission mode is MIMO without spatial bundling of HARQ-ACK, the number of bits of the HARQ-ACK determined is

; wherein

is the total number of scheduled TBs when calculating the HARQ-ACK of the time-frequency bundling window, L’ is the total number of scheduled TBs detected within the time-frequency bundling window and predicted according to the cell domain and time domain DL DAI by the UE.

Preferably, the method further includes: for each downlink subframe, when the number of bits of the determined HARQ-ACK is smaller than a pre-determined minimum HARQ-ACK bit number of the subframe, modifying the number of bits of the HARQ-ACK of the subframe to be the minimum HARQ-ACK bit number.

Preferably, the method further includes: after the UE transmits the HARQ-ACK, the eNB determines the number of bits of the HARQ-ACK actually transmitted by the UE through blind detection.

Preferably, when all of cells configured for the UE is configured with the transmission mode of SIMO, or all of cells configured with MIMO are configured with spatial bundling of HARQ-ACK, performing the blind detection by the eNB includes: performing blind detections respectively using L’, L’-1, ..., L’-I, ..., L’-S+1 as the number of HARQ-ACK bits; stopping performing the blind detections if HARQ-ACK is detected in a first blind detection and determining the number of HARQ-ACK bits of the first blind detection to be the number of bits of the HARQ-ACK actually transmitted by the UE; continuing performing the blind detections until a total of S times of blind detections are completed if HARQ-ACK is not detected; and

wherein, the L’ is the number of HARQ-ACK bits determined by the eNB, and the S is a pre-determined maximum number of blind detections.

Preferably, when the UE is configured with a cell whose transmission mode is MIMO without spatial bundling of HARQ-ACK, performing the blind detection by the eNB includes: performing blind detections respectively using L', L' - r₁, ..., L' - r_i, ..., L' - r_s _-1as the number of HARQ-ACK bits; stopping performing the blind detections if HARQ-ACK is detected in a first blind detection and determining the number of HARQ-ACK bits of the first blind detection to be the number of bits of the HARQ-ACK actually transmitted by the UE; continuing performing the blind detections until a total of S times of blind detections are completed if HARQ-ACK is not detected; and

wherein, the L’ is the number of HARQ-ACK bits determined by the eNB, the S is a pre-determined maximum number of blind detections, the r_iis the total number of HARQ-ACK bits of PDCCH/EPDCCHs scheduling PDSCH or indicating downlink SPS release from the last PDCCH/EPDCCH to the i’th PDCCH/EPDCCH transmitted by the eNB.

An apparatus of transmitting HARQ-ACK in an enhanced CA system may include: a feedback information determining unit and a transmitting unit;

the feedback information determining unit is configured to determine HARQ-ACK to be transmitted within an uplink subframe according to scheduled cells and downlink subframes scheduled in each scheduled cell; and

the transmitting unit is configured to transmit the determined HARQ-ACK to an eNB.

According to the above technical schemes, the UE of the present disclosure determines HARQ-ACK to be transmitted in an uplink subframe according to scheduled cells and downlink subframes scheduled in each scheduled cell, and transmits the determined HARQ-ACK to an eNB. The method can determine the number of HARQ-ACK bits according to cells actually scheduled and downlink subframes actually scheduled in each scheduled cell, can save PUCCH resources and improve PUCCH transmission performances.

FIG. 1 is a schematic diagram illustrating an LTE TDD frame structure;

FIG. 2 is a schematic diagram illustrating an HARQ-ACK timing scheme in an LTE TDD cell;

FIG. 3 is a flowchart illustrating a method of transmitting HARQ-ACK in an enhanced CA system of the present disclosure;

FIG. 4 is a schematic diagram illustrating a scenario where a time domain DL DAI co-exists with a cell domain DL DAI newly introduced in the present disclosure;

FIG. 5 is a schematic diagram illustrating a cell domain and time domain joint DL DAI newly introduced in the present disclosure;

FIG. 6 is a schematic diagram illustrating a cell domain DL DAI and a reverse DL DAI introduced in the present disclosure;

FIG. 7 is a schematic diagram illustrating determining HARQ-ACK according to a cell domain DL DAI and a reverse DL DAI;

FIG. 8 is a schematic diagram illustrating a cell domain DL DAI and a reference DL DAI introduced in the present disclosure;

FIG. 9 is a schematic diagram illustrating determining HARQ-ACK according to a cell domain DL DAI and a reference DL DAI;

FIG. 10 is a schematic diagram illustrating a situation where (e)PDCCHs in a downlink subframe are small in quantity and lost when a cell domain DL DAI is introduced in the present disclosure;

FIG. 11 is a schematic diagram illustrating a situation where (e)PDCCHs in a downlink subframe are small in quantity and lost when a cell domain DL DAI and a reference DL DAI are introduced in the present disclosure;

FIG. 12 is a schematic diagram illustrating a scenario where a cell domain and time domain joint DL DAI and a reference DL DAI are introduced according to embodiment two;

FIG. 13 is a first schematic diagram illustrating determining the actual number of HARQ-ACK bits through blind detection after a cell domain and time domain joint DL DAI is introduced according to embodiment four;

FIG. 14 is a second schematic diagram illustrating determining the actual number of HARQ-ACK bits through blind detection after a cell domain and time domain joint DL DAI is introduced according to embodiment four;

FIG. 15 is a first schematic diagram illustrating a scenario where a cell domain and time domain joint DL DAI and a reference DL DAI are introduced according to embodiment three;

FIG. 16 is a second schematic diagram illustrating a scenario where a cell domain and time domain joint DL DAI and a reference DL DAI are introduced according to embodiment three;

FIG. 17 is a third schematic diagram illustrating a scenario where a cell domain and time domain joint DL DAI and a reference DL DAI are introduced according to embodiment three; and

FIG. 18 is a schematic diagram illustrating a basic structure of an apparatus of transmitting HARQ-ACK in an enhanced CA system of the present disclosure.

In order to make the objectives, technical mechanisms and advantages of the present disclosure more clear and apparent, the present disclosure is described in detail as set forth below with reference to the accompanying drawings.

FIG. 3 is a flowchart illustrating a method of transmitting HARQ-ACK in an enhanced CA system according to the present disclosure. The method includes the following procedures.

In step 301, a UE determines HARQ-ACK to be transmitted in an uplink subframe according to scheduled cells and downlink subframes scheduled in each scheduled cell.

In this step, the UE may determine the number of bits of actually transmitted HARQ-ACK according to the number of actually scheduled cells and conditions of downlink subframes scheduled in the actually scheduled cells.

In step 302, the UE transmits the determined HARQ-ACK to an eNB.

With respect to step 301, the number of bits of actually transmitted HARQ-ACK is determined according to the number of actually scheduled cells and conditions of downlink subframes scheduled in the actually scheduled cells. When determining the number of bits, the present disclosure provides the following two basic mechanisms to ensure the eNB has the same understanding of the number of HARQ-ACK bits with the UE.

According to mechanism one, for a cell whose downlink reference UL/DL configuration is TDD configuration, in order to determine the number of HARQ-ACK bits in situations where multiple cells are scheduled, a cell domain DL DAI is newly introduced in DL DCI in a PDCCH/EPDCCH scheduling PDSCH and a PDCCH/EPDCCH indicating downlink SPS release in a cell to identify the accumulative number of transmitted PDCCH/EPDCCHs or scheduled transmission blocks (TBs) up to the current cell in a downlink subframe. The cell domain DL DAI includes q bits, and q is a positive integer, e.g., q=2 or 3. The time domain DL DAI may exist at the same time. Alternatively, there may be the cell domain DL DAI and no time domain DL DAI. If there is the time domain DL DAI, the cell domain DL DAI and the time domain DL DAI are calculated independently, as shown in FIG. 4. Restricted by the value of q, the value of the cell domain DL DAI is a result of (the number of actually transmitted PDCCH/EPDCCHs or the number of actually scheduled TBs) mod 2^q.

According to mechanism two, a cell domain and time domain joint DL DAI is introduced into the DL DCI in a PDCCH/EPDCCH scheduling PDSCH and a PDCCH/EPDCCH indicating downlink SPS release in a cell to specify the accumulative number of transmitted PDCCH/EPDCCHs or scheduled TBs within a time-frequency bundling window up to the PDCCH/EPDCCH scheduling PDSCH or the PDCCH/EPDCCH indicating downlink SPS release, as shown in FIG. 5. The cell domain and time domain joint DL DAI includes q bits, and q is a positive integer, e.g., q=2 or 3. The time-frequency bundling window is a collection formed by all of downlink subframes whose HARQ-ACK is to be fed back in uplink subframe n in carriers of the UE. The index c of a carrier bearing any downlink subframe in the time-frequency bundling window satisfies 0≤c<Nc. Carrier index numbers start from 0. The subframe sequence number is n-k_c, and k_c∈Kc. Kc is determined by the HARQ timing scheme applied to HARQ-ACK of the downlink subframe on carrier c to be fed back in uplink subframe n. If the HARQ timing scheme is certain TDD configuration, Kc is a collection corresponding to the TDD configuration in Table 2. Nc is the total number of downlink cells whose HARQ-ACK is to be fed back in uplink subframe n. All of downlink subframes within a time-frequency bundling window are arranged according to a pre-defined sorting rule, and the UE and the eNB have the same understanding of the sorted order. Preferably, HARQ-ACK bits of downlink subframes in a time-frequency bundling window are arranged first according to frequency domain then according to time domain, as shown in FIG. 5. Similar with the value of the above cell domain DL DAI, restricted by the value of q, the value of the cell domain and time domain joint DL DAI is the result of (the number of actually transmitted PDCCH/EPDCCH or scheduled TBs) mod 2^q.

In addition, the number of HARQ-ACK bits transmitted using PUCCH format 3 is related with the number of cells configured for the UE, the transmission mode of each configured cell and the size of the bundling window. According to the above two mechanisms, HARQ-ACK bits of the cells are arranged in ascending order of DL DAI. The number of HARQ-ACK bits transmitted in the PUCCH format 3 and the new PUCCH format X may be determined according to the number of scheduled cells and downlink subframes scheduled in each cell. According to the above two mechanisms, missing (e)PDCCHs at certain positions in (e)PDCCHs scheduling PDSCH and (e)PDCCHs indicating downlink SPS release within a downlink subframe or a time-frequency bundling window can be identified. The certain positions refer to positions other than the last several positions in the downlink subframe or the time-frequency bundling window. Since a UE may miss detection of the last several (e)PDCCH scheduled by the eNB, the UE and the eNB may have different understanding of the number of scheduled (e)PDCCHs and even different understanding of the number of HARQ-ACK bits. Preferably, a new reverse DL DAI or reference DL DAI may be introduced for facilitating identification of a lost subframe so that the UE and the eNB can have the same understanding of the number of HARQ-ACK bits. The number of bits of the reverse DL DAI or the reference DL DAI is q', and q' is a positive integer, e.g., q'=2 or 3.

For example, the accumulative number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release up to the current (e)PDCCH is specified using a cell domain DL DAI in a cell. The cell may be one of multiple FDD cells configured with a downlink reference UL/DL configuration and the transmission mode of the cells is MIMO with spatial bundling or SIMO. The value of the reverse DL DAI is the sequence number of each cell when the cells are arranged according to a descending order of cell index numbers, as shown in FIG. 6. If the (e)PDCCH of the last cell is lost, the UE receives a (e)PDCCH with a reverse DL DAI=2 and does not receive a (e)PDCCH with a reverse DL DAI=1. The UE makes a determination that the last (e)PDCCH is lost according to the reverse DL DAI and that the HARQ-ACK has 4 bits. As shown in FIG. 7, 1-bit HARQ-ACK is generated according to a PDCCH/EPDCCH with a DL DAI=1 which schedules PDSCH or indicates downlink SPS release, 1-bit HARQ-ACK is generated according to a PDCCH/EPDCCH with a DL DAI=2 which schedules PDSCH or indicates downlink SPS release, 1-bit HARQ-ACK is generated according to a PDCCH/EPDCCH with a DL DAI=3 which schedules PDSCH or indicates downlink SPS release, and there is another 1-bit HARQ-ACK which is NACK.

According to another method, a lost subframe may be identified using a reference DL DAI. The reference DL DAI specifies the total number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release when HARQ-ACK is calculated for each downlink subframe or for each time-frequency bundling window, as shown in FIG. 8. As such, if the (e)PDCCH of the last cell is lost, the UE receives a (e)PDCCH with a reference DL DAI=4 and only a total of 3 PDCCH/EPDCCHs including PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release. The UE makes a determination that the last (e)PDCCH is lost according to the reference DL DAI and that the HARQ-ACK has 4 bits. As shown in FIG. 9, 1-bit HARQ-ACK is generated according to a PDCCH/EPDCCH with a DL DAI=1 scheduling PDSCH or indicating downlink SPS release, 1-bit HARQ-ACK is generated according to a PDCCH/EPDCCH with a DL DAI=2 scheduling PDSCH or indicating downlink SPS release, 1-bit HARQ-ACK is generated according to a PDCCH/EPDCCH with a DL DAI=3 scheduling PDSCH or indicating downlink SPS release, and there is another 1-bit HARQ-ACK which is NACK. Similar with the value of the above cell domain DL DAI, restricted by the value of q, the value of the reverse DL DAI may be the result of sequence numbers of cells mod 2^q. The sequence numbers are determined by arranging cells in a descending order of cell index numbers. The value of the reference DL DAI may be the result of (the total number of PDCCH/EPDCCHs in the downlink subframe or time-frequency bundling window) mod 2^q.

Several preferred embodiments with the above different DL DAI designs are provided hereinafter to illustrate the HARQ-ACK transmission mechanism.

Embodiment one

In this embodiment, it is supposed a cell of a UE is configured with a TDD configuration as downlink reference UL/DL configuration and a cell domain DL DAI is introduced to specify the accumulative number of transmitted PDCCH/EPDCCHs or scheduled TBs up to the current cell in a downlink subframe. The cell domain DL DAI includes q bits, and q is a positive integer, e.g., q is 2 or 3. At the same time, the time domain DL DAI is still used. The cell domain DL DAI is independent from the time domain DL DAI, as shown in FIG. 4. A new reverse DL DAI or reference DL DAI is introduced in each subframe. When configured cells all have the same transmission mode which is SIMO, or all cells configured with MIMO are also configured with spatial bundling, the reverse DL DAI or reference DL DAI is for the cell. When the configured cells include a cell configured with SIMO as the transmission mode and a cell configured with MIMO without spatial bundling, the reverse DL DAI or reference DL DAI is for TBs. Reverse DL DAIs or reference DL DAIs of each subframe are counted independently, such that the UE can determine whether there is any lost PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release in each subframe and arrange HARQ-ACK bits by placing HARQ-ACK bits corresponding to cell domain ahead of HARQ-ACK bits corresponding to time domain. As stated above, the cell domain DL DAI introduced may facilitate detection of lost (e)PDCCHs at positions other than the last positions in a downlink subframe, and the reversed DL DAI or reference DL DAI introduced may facilitate detection of lost (e)PDCCH at the last positions in a downlink subframe. As such, a UE may determine the number of HARQ-ACK bits to be fed back in an uplink subframe, and feed back HARQ-ACK according to the number of bits to save system resources.

There may be the following situations according to the above processing manner. When there are a small number of PDCCH/EPDCCHs scheduling PDSCH or PDCCH/EPDCCHs indicating downlink SPS release in a downlink subframe, e.g., there is only one PDCCH/EPDCCH in a downlink subframe and the PDCCH/EPDCCH is not detected by the UE, the UE and the eNB may have different understanding of the number of HARQ-ACK bits and the order of the bits being arranged if the number of HARQ-ACK bits is determined according to the number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release. It is highly probable that the UE may miss a PDCCH/EPDCCH. As shown in FIG. 10, a downlink subframe is scheduled in subframe 2 and it is not detected by the UE. The HARQ-ACK bits may be arranged by the UE as: {HARQ-ACK bit of subframe 1, HARQ-ACK bit of subframe 3, HARQ-ACK bit of subframe 4}, while the order of the HARQ-ACK bits assumed by the eNB may be: {HARQ-ACK bit of subframe 1, HARQ-ACK bit of subframe 2, HARQ-ACK bit of subframe 3, HARQ-ACK bit of subframe 4}. As such, the eNB and the UE has different understanding of the number of HARQ-ACK bits and the order of the HARQ-ACK bits, and an error may occur.

In order to reduce the influence of a UE's miss detection of a PDCCH/EPDCCH scheduled by an eNB on the arrangement of HARQ-ACK bits, a minimum number of HARQ-ACK bits of a subframe may be set for each downlink subframe according to the minimum number M' of scheduled PDCCH/EPDCCHs or scheduled TBs in each subframe in order to determine the number of HARQ-ACK bits. That is, when more than M' PDCCH/EPDCCHs are actually scheduled, the number of HARQ-ACK bits of the subframe is calculated according to the actual number of PDCCH/EPDCCHs; when M' or less PDCCH/EPDCCHs are actually scheduled, M' bits may always be reserved. Because it is indefinite which cells are scheduled by the eNB and what are the downlink transmission modes of the cells, bits may be reserved always according to the 2-TB transmission mode. Or, when all of cells configured for a UE are configured with SIMO as the transmission mode, or all of cells configured with MIMO are also configured with spatial bundling, the UE and the eNB both regard the minimum number of PDCCH/EPDCCHs scheduled in each subframe to be M' (e.g., M'=4). Thus the number of HARQ-ACK bits of each subframe is max {the number of HARQ-ACK bits obtained according to PDCCH/EPDCCHs detected by the UE, M'}. The max {} denotes the operation of taking the larger one of two values. For example, as shown in FIG. 11, a DL DAI includes 2bits and a reference DL DAI includes 2bits. The UE may detect five scheduled PDCCH/EPDCCHs in the first subframe, one scheduled PDCCH/EPDCCH in the second subframe, two scheduled PDCCH/EPDCCHs in the third subframe, and four scheduled PDCCH/EPDCCHs in the fourth subframe. As such, the number of HARQ-ACK bits of the first subframe is max {5, 4}=5, and the HARQ-ACK bits are {O_(0,0), O_(0,1), O_(0,2), O_(0,3), O_(0,4)}. O₍ _0,i ₎ is the HARQ-ACK bit determined according to the (i+1)'th PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in the first subframe. The number of HARQ-ACK bits of the second subframe is max {1, 4}=4, and the HARQ-ACK bits are {O_(1,0), O_(1,1), O_(1,2), O_(1,3)}. O_(1,0) is the HARQ-ACK bit determined according to the first PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in the second subframe. O_(1,1), O_(1,2), O_(1,3) are all NACK because the UE only detects one PDCCH/EPDCCH in the subframe. The number of HARQ-ACK bits of the third subframe is max {2, 4}=4, and the HARQ-ACK bits are {O_(2,0), O_(2,1), O_(2,2), O_(2,3)}. O_(2,0) is the HARQ-ACK bit determined according to the first PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in the third subframe. O_(2,1) is the HARQ-ACK bit determined according to the second PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in the third subframe. O_(2,2), O_(2,3)are NACK because the UE detects only two PDCCH/EPDCCHs in the subframe. The number of HARQ-ACK bits of the fourth subframe is max {4, 4}=4, and the HARQ-ACK bits are {O_(3,0), O_(3,1), O_(3,2), O_(3,3)}. O₍ _3,i ₎ is the HARQ-ACK bit determined according to the (i+1)'th PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in the fourth subframe.

The above method can ensure that different understanding of the number of HARQ-ACK bits between a UE and an eNB can occur only when the UE misses detection of M' or more than M' PDCCH/EPDCCHs in a downlink subframe. Since there is little probability that a UE may miss detection of M' or more than M' PDCCH/EPDCCHs, thus there is little chance that different understanding of the number of HARQ-ACK bits occurs between the UE and the eNB resulted from inconsistency between the number of PDCCH/EPDCCHs detected by the UE and the number of PDCCH/EPDCCHs transmitted by the eNB.

Embodiment two

In this embodiment, it is assumed the downlink reference UL/DL configuration of a cell configured for a UE is a TDD configuration, and a cell domain and time-domain joint DL DAI is introduced to specify the accumulative number of transmitted PDCCH/EPDCCHs or scheduled TBs in a time-frequency bundling window up to the PDCCH/EPDCCH scheduling PDSCH or the PDCCH/EPDCCH indicating downlink SPS release. The cell domain and time domain joint DL DAI includes q bits, and q is a positive integer, e.g., q=2 or 3. As shown in FIG. 5, HARQ-ACK bits of downlink subframes in a time-frequency bundling window are arranged first according to frequency domain and then according to time domain. A new reverse DL DAI or reference DL DAI is introduced in each time-frequency bundling window, so as to ensure each UE can know that whether a PDCCH/EPDCCH scheduling PDSCH or a PDCCH/EPDCCH indicating downlink SPS release is lost in each time-frequency bundling window and arrange HARQ-ACK bits first according to frequency domain and then according to time domain. The reference DL DAI has q bits, and q is a positive integer, e.g., q=2 or 3. As shown in FIG. 12, the number of HARQ-ACK bits in a time-frequency bundling window is determined according to the reference DL DAI (denoted as

) in the time-frequency bundling window. When all of cells configured for a UE are configured with SIMO as the transmission mode or all of cells configured with MIMO are also configured with spatial bundling of HARQ-ACK, the number of HARQ-ACK bits in the time-frequency bundling window is

. The is the number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release detected by the UE in the time-frequency bundling window. The includes PDCCH/EPDCCHs at positions other than the last several positions in the bundling window and PDCCH/EPDCCHs indicating downlink SPS release that are determined to be lost by the UE according to the PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release detected by the UE in the time-frequency bundling window.

is the value of the cell domain and time domain joint DL DAI in a PDCCH/EPDCCH, and

is an operation of rounding up to the next integer. When a UE is configured both with cells configured with SIMO and cells configured with MIMO without spatial bundling, the number of HARQ-ACK bits in a time-frequency bundling window is

. The L is the number of scheduled TBs detected by the UE in the time-frequency bundling window,

is the value of the cell domain and time domain joint reference DL DAI in a PDCCH/EPDCCH,

is the operation of rounding up to the next integer. The number of TBs can be calculated in the following manner. If the cells are configured with SIMO as transmission mode, or all of cells configured with MIMO are also configured with spatial bundling of HARQ-ACK, the PDCCH/EPDCCH scheduling PDSCH or the PDCCH/EPDCCH indicating downlink SPS release detected by the UE includes a TB which corresponds to 1-bit HARQ-ACK. If the cells are configured with MIMO without spatial bundling, the PDCCH/EPDCCH scheduling PDSCH or the PDCCH/EPDCCH indicating downlink SPS release detected by the UE includes two TBs which correspond to 2-bit HARQ-ACK.

Embodiment three

In this embodiment, it is assumed the downlink reference UL/DL configuration of a cell configured for a UE is a TDD configuration, and a cell domain and time domain joint DL DAI is introduced to specify the accumulative number of transmitted PDCCH/EPDCCHs or scheduled TBs in a time-frequency bundling window up to the PDCCH/EPDCCH scheduling PDSCH or the PDCCH/EPDCCH indicating downlink SPS release. The cell domain and time domain joint DL DAI includes q bits, and q is a positive integer, e.g., q=2 or 3. HARQ-ACK bits of downlink subframe in a time-frequency bundling window are arranged first according to frequency domain and then according to time domain. Meanwhile, a new reverse DL DAI or reference DL DAI is introduced into each subframe. The reverse DL DAIs or reference DL DAIs in each subframe are counted independently, so that the UE can know whether there is a PDCCH/EPDCCH scheduling PDSCH or a PDCCH/EPDCCH indicating downlink SPS release lost in each subframe and arrange HARQ-ACK bits by placing bits corresponding to the cell domain ahead of bits corresponding to time domain, as shown in FIG. 15.

In order to reduce the influence of a UE's miss detection of PDCCH/EPDCCH scheduled by an eNB on the order of HARQ-ACK bits, similar to embodiment one, a minimum number of HARQ-ACK bits of a subframe may be set for certain downlink subframes according to the minimum number M' of PDCCH/EPDCCHs or TBs scheduled in each subframe to determine the number of HARQ-ACK bits. That is, when more than M' PDCCH/EPDCCHs are actually scheduled, the number of HARQ-ACK bits of the subframe is calculated according to the actual number of PDCCH/EPDCCHs; when M' or less PDCCH/EPDCCHs are actually scheduled, M' bits may always be reserved. Because it is indefinite which cells are scheduled by the eNB and what are the downlink transmission modes of the cells, bits may be reserved always according to the 2-TB transmission mode. Thus, the minimum number of HARQ-ACK bits in each downlink subframe can be determined. The downlink subframes refer to the downlink subframes whose successive downlink subframes do not include any subframe in which M' (e.g., M'=4) or more than M' PDCCH/EPDCCHs or TBs are scheduled. As shown in FIG. 16, there are no less than 4 PDCCH/EPDCCHs scheduled in subframe 0 and subframe 2. The number of HARQ-ACK bits of subframe 0, subframe 1 and subframe 2 may be calculated according to the actually scheduled PDCCH/EPDCCHs or according to M' TBs are scheduled in subframe 0, subframe 1 and subframe 2. There are less than 4 PDCCH/EPDCCHs scheduled in subframe 3, and no subsequent downlink subframe of subframe 3 schedules M' or more than M' PDCCH/EPDCCHs or TBs. Therefore, the number of HARQ-ACK bits of subframe 3 is calculated by assuming M' PDCCH/EPDCCHs or TBs are scheduled in subframe 3. For example, as shown in FIG. 17, a cell domain and time domain joint DL DAI includes 2 bits and a reference DL DAI includes 2 bits. The UE may detect five scheduled PDCCH/EPDCCHs in subframe 0, one scheduled PDCCH/EPDCCH in subframe 1, four scheduled PDCCH/EPDCCHs in subframe 2, and two scheduled PDCCH/EPDCCHs in subframe 3. As such, the number of HARQ-ACK bits of subframe 0 is 5, and the HARQ-ACK bits are {O_(0,0), O_(0,1), O_(0,2), O_(0,3), O_(0,4)}. O_(0,i) is the HARQ-ACK bit determined according to the (i+1)'th PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in subframe 0. Subframe 1 is corresponding to 1-bit HARQ-ACK which is {O_(1,0)}. {O_(1,0)} is the HARQ-ACK bit determined according to the first PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in subframe 1. Subframe 2 is corresponding to 4 HARQ-ACK bits which are {O_(2,0), O_(2,1), O_(2,2), O_(2,3)}. O₍ _2,i ₎ is the HARQ-ACK bit determined according to the (i+1)'th PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release detected in subframe 2. The fourth subframe is corresponding to max{4,2}=4 HARQ-ACK bits which are {O_(3,0), O_(3,1), O_(3,2), O_(3,3)}. O_(3,0)is the HARQ-ACK bit determined according to the first PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release in subframe 3. O_(3,1)is the HARQ-ACK bit determined according to the second PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release in subframe 3. O_(3,2), O_(3,3)are NACK.

The above method can ensure that different understanding of the number of HARQ-ACK bits between a UE and an eNB only occurs when the UE misses detection of M' or more than M' PDCCH/EPDCCHs in a downlink subframe. Since there is little probability that a UE may miss detection of M' or more than M' PDCCH/EPDCCHs, thus there is little chance that the UE and the eNB have different understanding of the number of HARQ-ACK bits due to inconsistency between the number of PDCCH/EPDCCHs detected by the UE and the number of PDCCH/EPDCCHs transmitted by the eNB.

Embodiment four

In this embodiment, it is assumed the downlink reference UL/DL configuration of a cell configured for a UE is a TDD configuration, and a cell domain and time-domain joint DL DAI is introduced to specify the accumulative number of transmitted PDCCH/EPDCCHs or scheduled TBs in a time-frequency bundling window up to the PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release. The cell domain and time domain joint DL DAI includes q bits, and q is a positive integer, e.g., q=2 or 3. As shown in FIG. 5, HARQ-ACK bits of downlink subframes in a time-frequency bundling window are arranged first according to frequency domain then according to time domain. If a cell is configured with SIMO or MIMO with spatial bundling, the number of HARQ-ACK bits in the time-frequency bundling window is the number L of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release detected by the UE in the time-frequency bundling window. If a UE is configured both with cells configured with SIMO and cells configured with MIMO without spatial bundling, the number of HARQ-ACK bits in the time-frequency bundling window is calculated according to the number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release detected by the UE in the time-frequency bundling window and transmission modes of the cells. The UE may, however, fail to detect a PDCCH/EPDCCH scheduling PDSCH or a PDCCH/EPDCCH indicating downlink SPS release in the time-frequency bundling window, as shown in FIG. 13. Therefore, the UE and the eNB may have different understanding of the number of HARQ-ACK bits. Thus the eNB needs to determine the number of HARQ-ACK bits sent by the UE through blind detection.

The blind detection process is as follows. The eNB may determine the number of HARQ-ACK bits actually sent by the UE through multiple blind detections. The more the blind detections performed, the more likely to find out the number of HARQ-ACK bits actually sent by the UE. But the increased number of blind detections may increase the implementation complexity of the eNB.

The blind detection may be as follows. If the cells are all configured with SIMO as transmission mode, or all of cells configured with MIMO are also configured with spatial bundling of HARQ-ACK, it is supposed the eNB determines the number L' of HARQ-ACK bits according to the number L of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release, the transmission mode of the cell of each PDCCH/EPDCCH, and whether spatial bundling is used. The maximum number of blind detections determined by the eNB is S, e.g., S=1, 3, 6. The eNB performs at most S blind detections respectively taking the number of HARQ-ACK bits to be L', L'-1, ..., L'-i, ..., L'-S+1. S=1 means the eNB performs detection only taking L' as the number of HARQ-ACK bits.

If the UE is configured both with cells whose transmission mode is SIMO and cells whose transmission mode is MIMO without spatial bundling, or all of the cells are configured with SIMO as transmission mode, or all cells configured which MIMO are also configured with spatial bundling, supposing the eNB determines the number L' of HARQ-ACK bits according to the number L of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release, the transmission mode of the cell of each PDCCH/EPDCCH, and whether spatial bundling is used. The number of blind detections determined by the eNB is S, e.g., S=1, 3, 6. The eNB performs at most S blind detections respectively taking the number of HARQ-ACK bits to be L', L' - r₁, ..., L' - r_i, ..., L' - r_s _- ₁. The r_i is the total number of HARQ-ACK bits from the last PDCCH/EPDCCH to the i'th PDCCH/EPDCCH scheduling PDSCH or tindicating downlink SPS release sent by the eNB. For example, S=3, and a situation of a PDCCH/EPDCCH scheduling PDSCH or a PDCCH/EPDCCH indicating downlink SPS release in the time-frequency bundling window is as shown in FIG. 14. The eNB first performs a blind detection by using L' as the number of HARQ-ACK bits, and stops performing the blind detections if HARQ-ACK is detected. If no HARQ-ACK is detected, another blind detection is performed using L'-2 as the number of HARQ-ACK bits because the number of HARQ-ACK bits of the last PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release is 2. The eNB stops performing the blind detections if HARQ-ACK is detected. If no HARQ-ACK is detected, another blind detection is performed using L'-2-1 as the number of HARQ-ACK bits because the number of HARQ-ACK bits of the last PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release is 2, the number of HARQ-ACK bits of the last but one PDCCH/EPDCCH scheduling PDSCH or indicating downlink SPS release is 1. The eNB stops performing the blind detections no matter whether HARQ-ACK is detected. S=1 means the eNB performs detection only taking L' as the number of HARQ-ACK bits.

The above are several embodiments of the HARQ transmission method of the present disclosure. The present disclosure also provides an apparatus of transmitting HARQ-ACK which can be configured to implement the above transmission method. FIG. 18 is a schematic diagram illustrating a basic structure of an apparatus of transmitting HARQ-ACK. As shown in FIG. 18, the apparatus includes: a feedback determining unit and a transmitting unit.

The feedback determining unit is configured to determine HARQ-ACK to be transmitted in an uplink subframe according to scheduled cells and downlink subframes configured in each scheduled cells. The transmitting unit is configured to transmit the determined HARQ-ACK to an eNB.

The foregoing are only preferred examples of the present disclosure and are not for use in limiting the protection scope thereof. All modifications, equivalent replacements or improvements in accordance with the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

A method of transmitting a hybrid automatic repeat-request acknowledgement (HARQ-ACK) by a user equipment (UE) in an enhanced carrier aggregation (CA) system, comprising:

determining the HARQ-ACK to be transmitted in an uplink subframe based on scheduled cells and downlink subframes configured in each of the scheduled cells; and

transmitting the determined HARQ-ACK to an evolved Node B (eNB).
The method of claim 1, wherein determining the HARQ-ACK comprising:

determining a number of bits of the HARQ-ACK based on a value of a cell domain downlink (DL) downlink assignment indication (DAI) in DL downlink control information (DCI) in a physical downlink control channel (PDCCH)/enhanced PDCCH (EPDCCH) scheduling a physical downlink shared channel (PDSCH) or in a PDCCH/EPDCCH indicating downlink semi-persistent scheduling (SPS) release in the scheduled cells;

wherein the value of the cell domain DL DAI specifies an accumulative number of transmitted PDCCH/EPDCCHs or scheduled transmission blocks (TBs) in a downlink subframe up to a cell which includes the cell domain DL DAI.
The method of claim 1, wherein determining the HARQ-ACK comprising:

determining a number of bits of the HARQ-ACK based on a value of a cell domain and time domain joint DL DAI in DL DCI in a PDCCH/EPDCCH scheduling a PDSCH or in a PDCCH/EPDCCH indicating downlink SPS release in the scheduled cells;

wherein the value of the cell domain and time domain joint DL DAI specifies an accumulative number of transmitted PDCCH/EPDCCHs or scheduled TBs in a time-frequency bundling window up to the downlink subframe which includes the cell domain and time domain joint DL DAI; the time-frequency bundling window is a collection of all of downlink subframes whose HARQ-ACK is to be transmitted in a same uplink subframe within all of carriers.
The method of claim 2 or 3, further comprising:

determining the number of bits of the HARQ-ACK based on a value of a reverse DL DAI or a value of a reference DL DAI in DL DCI of the PDCCH/EPDCCH scheduling the PDSCH or the PDCCH/EPDCCH indicating downlink SPS release in the scheduled cells;

wherein the value of the reverse DL DAI is a sequence number of a cell which includes the reverse DL DAI when all of cells including a cell in a downlink subframe are arranged in a descending order of index numbers of the cells, and is used for detecting a lost PDCCH/EPDCCH at the tail of the downlink subframe;

wherein the value of the reference DL DAI is an accumulative number of PDCCH/EPDCCHs scheduling PDSCH and PDCCH/EPDCCHs indicating downlink SPS release or an accumulative number of corresponding TBs when calculating the number of bits of the HARQ-ACK of the downlink subframe which includes the reference DL DAI, and is used for detecting a lost PDCCH/EPDCCH at the tail of the downlink subframe.
The method of claim 3, further comprising:

determining the number of bits of the HARQ-ACK based on a value of a reverse DL DAI or a value of a reference DL DAI in DL DCI in the PDCCH/EPDCCH;

wherein the value of the reverse DL DAI is a sequence number of a cell which includes the reverse DL DAI when all of cells including a cell in the time-frequency bundling window are arranged in a descending order of index numbers of the cells, and is used for detecting a lost PDCCH/EPDCCH at the tail of the downlink subframe;

wherein the value of the reference DL DAI is an accumulative number of PDCCH/EPDCCHs scheduling the PDSCH and the PDCCH/EPDCCHs indicating the downlink SPS release or an accumulative number of corresponding TBs when calculating the number of bits of the HARQ-ACK of the time-frequency bundling window which includes the reference DL DAI, and is used for detecting a lost PDCCH/EPDCCH at the tail of the time-frequency bundling window.
The method of claim 5, wherein

if cells configured for the UE have a same transmission mode which is a single input multiple output (SIMO) or all cells configured with a multiple input multiple output (MIMO) are also configured with spatial bundling of HARQ-ACK, the number of bits of the HARQ-ACK is determined based on the accumulative number of the PDCCH/EPDCCHs scheduling the PDSCH and the PDCCH/EPDCCHs indicating the downlink SPS release when calculating HARQ-ACK for the time-frequency bundling window, the number of the PDCCH/EPDCCHs scheduling the PDSCH and the PDCCH/EPDCCHs indicating the downlink SPS release detected in the time-frequency bundling window and predicted according to the cell domain and time domain joint DL DAI by the UE, the number of bits of the cell domain and time domain joint DL DAI, and the cell domain and time domain joint DL DAI has the same number of bits with the reference DL DAI;

if the cells configured for the UE include a cell configured with the MIMO without the spatial bundling of HARQ-ACK as an transmission mode, the number of bits of the HARQ-ACK is is determined the accumulative number of the scheduled TBs in the time-frequency bundling window when calculating the number of bits of the HARQ-ACK, a total number of scheduled TBs detected in the time-frequency bundling window and predicted according to the cell domain and time domain joint DL DAI by the UE.
The method of claim 2 or 3, further comprising: when the number of bits of HARQ-ACK determined for a downlink subframe is smaller than a pre-determined minimum number of HARQ-ACK bits of the subframe, determining a minimum number of HARQ-ACK bits as the number of bits of the HARQ-ACK of the downlink subframe.
The method of claim 3, further comprising: after transmitting the HARQ-ACK, determining, by the eNB, the number of bits of the HARQ-ACK transmitted by the UE through blind detection.
The method of claim 8, wherein when all of cells configured for the UE have a same transmission mode which is a SIMO or all of cells configured with a MIMO are configured with spatial bundling of HARQ-ACK, performing the blind detection comprises:

performing blind detections respectively using L', L'-1, ..., L'-i, ..., L'-S+1 as the number of HARQ-ACK bits, stopping performing the blind detections if an HARQ-ACK is detected in a first blind detection of the blind detections and determining a number of HARQ-ACK bits of the first blind detection to be the number of bits of the HARQ-ACK transmitted by the UE; continuing performing a next blind detection if no HARQ-ACK is detected until a total of S blind detections are completed;

wherein the L' is the number of HARQ-ACK bits determined by the eNB, and the S is a pre-determined maximum number of blind detections.
The method of claim 8, wherein when cells configured for the UE includes a cell configured with a transmission mode of a MIMO without spatial bundling of HARQ-ACK, performing the blind detection comprises:

performing blind detections respectively using L', L' - r₁, ..., L' - r_i, ..., L' - r_s _-1as the number of HARQ-ACK bits, stopping performing the blind detections if an HARQ-ACK is detected in a first blind detection of the blind detections and determining the number of HARQ-ACK bits of the first blind detection to be the number of bits of the HARQ-ACK transmitted by the UE; continuing performing a next blind detection if no HARQ-ACK is detected until a total of S blind detections are completed;

wherein the L' is the number of HARQ-ACK bits determined by the eNB, the S is a pre-determined maximum number of blind detections, the r_i is the total number of HARQ-ACK bits of PDCCH/EPDCCHs scheduling PDSCH or indicating downlink SPS release from the last PDCCH/EPDCCH to the i'th PDCCH/EPDCCH transmitted by the eNB.
A user equipment (UE) in an enhanced carrier aggregation (CA) system, the UE adapted to perform at least one of the methods described in claims 1 to 10.