Patent Description:
Existing Long Term Evolution (LTE) systems have a maximum bandwidth of <NUM> which cannot meet the requirement of higher data rates. Currently, in order to increase transmission rates of users, LTE-Advanced (LTE-A) has been proposed, based on LTE. In LTE-A systems, multiple Component Carriers (CCs) are combined to provide a wide working bandwidth and form a downlink and uplink of a communication system, so as to provide higher transmission rates. This technique is referred to as a Carrier Aggregation (CA) technique. For example, in order to support <NUM> bandwidth, five CCs of <NUM> may be combined. Hereinafter, each CC is referred to as a Cell.

Among multiple downlink Cells configured by a base station, one is a Primary Cell (Pcell) and others are Secondary Cells (Scells). The base station configures the UE to receive downlink data from multiple CCs through higher layer signaling. The number of Cells actually scheduled in one subframe may be less than or equal to the number of Cells configured by the higher layer. For example, in <FIG>, two Cells are configured by the higher layer, respectively, Cell <NUM> and Cell <NUM>, whereas the base station actually schedules one Cell, i.e. Cell <NUM>.

The data transmission in one downlink Cell may be scheduled by a Physical Downlink Control CHannel (PDCCH) transmitted in another Cell, which is referred to as cross-carrier scheduling. The data transmission in one downlink Cell may also be scheduled by the PDCCH transmitted in the same Cell, which is referred to as non-cross-carrier scheduling, as shown in <FIG>.

Based on the CA technique, the base station transmits downlink data to the same UE on multiple Cells. Accordingly, the UE needs to return HARQ-ACK information in response to the downlink data transmitted on the multiple Cells. According to current discussions involving LTE-A, the HARQ-ACK information of the downlink data of Cells within one CA is transmitted in one uplink Cell (i.e. uplink Pcell). In order to support the transmission of HARQ-ACK information of multiple bits, at most <NUM> bits of HARQ-ACK information may be transmitted in LTE-A adopting a channel selection based method, which has been used in LTE Time Division Duplexing (TDD) systems. When the channel selection of a single antenna is considered, the number of bits of HARQ-ACK information to be allocated is equal to the number of the HARQ-ACK bits. For simplicity, suppose there are M bits of HARQ-ACK information, and M HARQ-ACK channels are allocated accordingly. Since each HARQ-ACK channel has four available Quadrature Phase Shift Keying (QPSK) constellations, <NUM> channel and constellation resources are obtained. Appropriate channel and constellation resources may be selected from the <NUM> resources for returning the M bits information.

Such HARQ ACK transmission for data received on a number of cells is disclosed by document <NPL>.

According to the current discussions regarding LTE-A, in LTE-A Frequency Division Duplexing (FDD) systems, the channel selection method supports only aggregation of two Cells and each Cell may return <NUM>-bit or <NUM>-bit HARQ-ACK information. The method for allocating the HARQ-ACK channel resource is as follows.

For a downlink Pcell, the HARQ-ACK channel used by the HARQ-ACK information of the Pcell is determined according to a Control Channel Element (CCE) index of the PDCCH via a connotative method.

For a downlink Scell, if the Scell is not cross-carrier scheduled from the PDCCH of the Pcell, the HARQ-ACK channel used by the HARQ-ACK information of the Scell is determined according to a HARQ-ACK Resource Information (ARI) in the PDCCH of the Scell; if the Scell is cross-carrier scheduled from the PDCCH of the Pcell, the HARQ-ACK channel used by the HARQ-ACK information of the Scell is determined via a connotative method according to the CCE index of the PDCCH.

If the Cell is configured with a Single Input Multiple Output (SIMO) transmission mode, since it is only required to return one HARQ-ACK with respect to one Transmission Block (TB) of the Cell, one HARQ-ACK channel needs to be allocated. Accordingly, if the Cell is configured with a Multiple Input Multiple Output (MIMO) transmission mode, two HARQ-ACK need to be returned with respect to two TBs of the Cell. Therefore, two HARQ-ACK channels need to be allocated. As to the situation of allocating HARQ-ACK channels via the connotative method, the HARQ-ACK channel used by the HARQ-ACK information of one Cell is obtained through the PDCCH scheduling the data transmission of the Cell. In particular, the index of a first CCE of the PDCCH is denoted as nCCE. If one HARQ-ACK channel needs to be allocated, the HARQ-ACK channel may be mapped according to the index nCCE of the first CCE. If two HARQ-ACK channels need to be allocated, the two HARQ-ACK channels may be mapped according to the first CCE index nCCE and the second CCE index nCCE +<NUM>. According to the current discussions regarding LTE or LTE-A Release <NUM> (Rel-<NUM>), if two Cells are both configured with the MIMO transmission mode, four HARQ-ACK bits will be generated. If the Physical Uplink Control CHannel (PUCCH) format 1b with channel selection is adopted for transmission, four PUCCH resources are required. If a Spatial Orthogonal Resource Transmission Diversity (SORTD) method is adopted, eight PUCCH resources are required. According to the discussions regarding LTE-A, the number of PUCCH resources does not exceed <NUM> when transmission diversity is adopted.

The above and other aspects, features and advantages of the present invention will be more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:.

In the following description, identical elements will be designated by identical reference numerals throughout the drawings. Further, in the following description of the present invention, a detailed description of associated known functions or elements will be omitted for the sake of clarity and conciseness.

The present invention is applicable to a scenario in which a UE is configured with two serving-Cells and the base station configures the UE to transmit HARQ-ACK information adopting the transmission diversity technique. As previously noted, each component carrier (CC) is referred to in the following description as a "Cell".

For the above scenario, the present invention provides a method for transmitting HARQ-ACK information based on transmission diversity. In the method, the number of Cells scheduled by the base station in the same downlink subframe is dynamically indicated by the PDCCH, and the UE determines whether to implement spatial bundling to the HARQ-ACK information according to the number of Cells scheduled by the base station. If two Cells are scheduled, spatial bundling is performed on the HARQ-ACK information of the Cell configured with a MIMO transmission mode and the HARQ-ACK information is transmitted adopting the transmission diversity technique. If only one Cell is scheduled, spatial bundling is not performed on the HARQ-ACK information and the HARQ-ACK information is directly transmitted adopting the transmission diversity technique.

Thus, performing spatial bundling on the HARQ-ACK information is avoided when there is only one Cell is scheduled. Confusion between the UE and the base station is also avoided.

During spatial bundling, the two bits of {ACK, NACK} or {NACK, ACK} will be bundled into one bit of {NACK}, and two bits of {ACK, DTX} or {DTX, ACK} will be bundled into one bit of {DTX}, which results in that a downlink subframe having been correctly received has to be retransmitted with a downlink subframe not correctly received. In contrast to this, the present invention avoids unnecessary spatial bundling of the HARQ-ACK information, thereby reducing unnecessary retransmission of downlink data and improving throughput of downlink data.

Referring now to <FIG> is a flowchart illustrating a method according to an embodiment of the present invention.

In Step <NUM>, the UE obtains the number of Cells scheduled by the base station in one downlink subframe from PDCCH.

When a downlink subframe of a Cell is scheduled, the base station has to transmit a corresponding PDCCH to realize the scheduling. Based on this, the present invention provides that, when the downlink subframe of a Cell is scheduled, the base station indicates whether another Cell is scheduled in the downlink subframe through the PDCCH scheduling the downlink subframe, i.e., indicating data of another CC is scheduled in the downlink subframe. Thus, the UE may be aware of the number of CCs scheduled by the base station in the downlink subframe.

Suppose the CA system configures two Cells, one being the Pcell and the other being the Scell. HARQ-ACK information is transmitted using PUCCH format 1b with channel selection, and the HARQ-ACK information is transmitted adopting the transmission diversity technique of SORTD.

In order to indicate the number of Cells scheduled by the base station in the same downlink subframe through PDCCH, the present invention provides two preferable indicating methods.

The first indicating method is applicable for FDD systems and TDD systems with a HARQ-ACK bundling window of <NUM>. Through adding one information bit in the PDCCH or utilizing one padding bit of the PDCCH, it is able to indicate whether one Cell or two Cells are scheduled in the current subframe. This bit is referred to as a Number of Scheduling Cells (NSC) bit.

For example, it may be defined that the value "<NUM>" of the NSC denotes that only one Cell is scheduled in the current subframe, and the value "<NUM>" of the NSC denotes that two Cells are scheduled in the current subframe. If only the Pcell is scheduled in the current subframe and the Scell is not scheduled, the NSC of the PDCCH scheduling the Pcell data is configured to <NUM>. If only the Scell is scheduled in the current subframe and the Pcell is not scheduled, the NSC of the PDCCH scheduling the Scell data is also configured to <NUM>. If both the Pcell and the Scell are scheduled in the current subframe, the NSC in the PDCCH scheduling the Pcell data and the NSC in the PDCCH scheduling the Scell data are respectively configured to <NUM>.

The second indicating method is applicable for only TDD systems with a HARQ-ACK bundling window of <NUM>. Through redefining a Downlink Assignment Index (DAI) field of the PDCCH, it is able to indicate whether one Cell or two Cells are scheduled in the current subframe. In the present invention, the DAI field is redefined as the Number of Scheduling Cells (NSC).

For example, it may be defined that, value "<NUM>" of the NSC denotes that only one Cell is scheduled in the current subframe, the value "<NUM>" of the NSC denotes that two Cells are scheduled in the current subframe, and the value "<NUM>" and "<NUM>" of the NSC are reserved for later use. If only the Pcell is scheduled in the current subframe and the Scell is not scheduled, the NSC in the PDCCH scheduling the Pcell data is configured to "<NUM>". If only the Scell is scheduled in the current subframe and the Pcell is not scheduled, the NSC in the PDCCH scheduling the Scell data is also configured to "<NUM>". If both the Pcell and the Scell are scheduled in the current subframe, the NSC in the PDCCH scheduling the Pcell data and the NSC in the PDCCH scheduling the Scell data are respectively configured to "<NUM>".

In Step <NUM>, the UE receives from the downlink subframe downlink data transmitted by the base station, and generates HARQ-ACK information according to the number of Cells scheduled by the base station in the downlink subframe and according to whether the downlink data is correctly received.

If the first indicating method in step <NUM> is adopted, in this step, the processing of the UE includes,
if the UE receives the PDCCH information of one Cell and the NSC in the PDCCH is "<NUM>", the UE determines that the base station schedules only one Cell. At this time, if the Cell is configured with the SIMO transmission mode, one HARQ-ACK bit is generated based on whether the downlink subframe is correctly received; if the Cell is configured with the MIMO transmission mode, two HARQ-ACK bits are generated based on whether the downlink subframe is correctly received.

If the UE receives from the base station PDCCH information of one Cell but the NSC value in the PDCCH is "<NUM>", the UE determines that the base station schedules both the Pcell and the Scell and the Cell corresponding to the PDCCH information not received has not been detected. At this time, if the Cell corresponding to the received PDCCH information is configured with the SIMO transmission mode, one HARQ-ACK bit is generated based on whether the downlink subframe corresponding to the Cell is correctly received. If the Cell corresponding to the received PDCCH information is configured with the MIMO transmission mode, two HARQ-ACK bits are generated based on whether the downlink subframe corresponding to the Cell is correctly received, and the two HARQ-ACK bits are bundled into one HARQ-ACK bit through spatial bundling. At the same time, HARQ-ACK information denoted as "DTX" or "not received" is generated for the Cell that has failed to be detected.

If the UE received from the base station the PDCCH information of both the Pcell and the Scell and the NSC values in both the PDCCH of the Pcell and the Scell are "<NUM>", the UE determines that the base station schedules both the Pcell and the Scell. At this time, for a Cell configured with the SIMO transmission mode, one HARQ-ACK bit is generated based on whether the downlink subframe corresponding to the Cell is correctly received. For a Cell configured with the MIMO transmission mode, two HARQ-ACK bits are generated based on whether the downlink subframe corresponding to the Cell is correctly received, and the two HARQ-ACK bits are bundled into one HARQ-ACK bit through spatial bundling. Thus, the final result is that one HARQ-ACK bit is generated for each Cell and there are two HARQ-ACK bits for the two Cells.

If the second indicating method in Step <NUM> is adopted, in this step, the processing of the UE includes:
If the UE receives the PDCCH information of one Cell and the NSC value in the PDCCH is "<NUM>", the UE determines that the base station schedules only one Cell. At this time, if the Cell is configured with the SIMO transmission mode, one HARQ-ACK bit is generated according to whether the downlink subframe is correctly received; if the Cell is configured with the MIMO transmission mode, two HARQ-ACK bits are generated according to whether the downlink subframe is correctly received.

If the UE receives from the base station PDCCH information of one Cell but the NSC value in the PDCCH is "<NUM>", the UE determines that the base station schedules both the Pcell and the Scell, and the Cell corresponding to the PDCCH information that is not received is undetected. At this time, if the Cell corresponding to the received PDCCH information is configured with the SIMO transmission mode, one HARQ-ACK bit is generated based on whether the downlink subframe corresponding to the Cell is correctly received. If the Cell corresponding to the received PDCCH information is configured with the MIMO transmission mode, two HARQ-ACK bits are generated based on whether the downlink subframe corresponding to the Cell is correctly received, and the two HARQ-ACK bits are bundled into one HARQ-ACK bit through spatial bundling. At the same time, HARQ-ACK information designated as DTX is generated for the Cell that has failed to be detected.

If the UE received from the base station the PDCCH information of both the Pcell and the Scell, and the NSC values in both the PDCCH of the Pcell and the Scell are "<NUM>", the UE determines that the base station schedules both the Pcell and the Scell. At this time, for a Cell configured with the SIMO transmission mode, one HARQ-ACK bit is generated based on whether the downlink subframe corresponding to the Cell is correctly received. For a Cell configured with the MIMO transmission mode, two HARQ-ACK bits are generated based on whether the downlink subframe corresponding to the Cell is correctly received, and the two HARQ-ACK bits are bundled into one HARQ-ACK bit through spatial bundling. Thus, the final result is that one HARQ-ACK bit is generated for each Cell and there are two HARQ-ACK bits for the two Cells.

In Step <NUM>, the UE transmits the HARQ-ACK information generated in Step <NUM> to the base station adopting the transmission diversity technique.

If only the Pcell is scheduled, the transmission of the HARQ-ACK information to the base station includes the following two cases.

Case <NUM>: If the Pcell is configured with the SIMO transmission mode, one HARQ-ACK bit is generated. Adopting the SORTD method, the one HARQ-ACK bit is transmitted in duplicate on antenna <NUM> and antenna 1on different channels.

Suppose the index of the first CCE of the corresponding PDCCH is nCCE, two HARQ-ACK channels may be mapped according to nCCE and nCCE+<NUM>. The two HARQ-ACK channels are used for two transmission antennas, i.e., antenna <NUM> transmits on the HARQ-ACK channel mapped according to nCCE, and antenna <NUM> transmits on the HARQ-ACK channel mapped according to nCCE+<NUM>. The HARQ-ACK information transmitted on the two antennas are the same.

Alternatively, if the current subframe of the Pcell transmits a Semi-Persistent Scheduling (SPS) service, two HARQ-ACK channels are semi-statically configured by a higher layer. The two HARQ-ACK channels are denoted as CH_1 and CH_2. Adopting the SORTD method, i.e., the one HARQ-ACK bit is transmitted in duplicate on antenna <NUM> and antenna <NUM> on different channels. Antenna <NUM> transmits on CH_1 and antenna <NUM> transmits on CH_2. The HARQ-ACK information transmitted on the two antennas are the same.

Case <NUM>: If the Pcell is configured with the MIMO transmission mode, two HARQ-ACK bits are generated. The two HARQ-ACK bits are transmitted in duplicate on antenna <NUM> and antenna <NUM> on different channels adopting the SORTD method.

Suppose the index of the first CCE of the PDCCH is nCCE, two HARQ-ACK channels can be mapped according to nCCE and nCCE+<NUM>. The two HARQ-ACK channels are used for the two antennas, i.e., antenna <NUM> transmits on the HARQ-ACK channel mapped according to nCCE, and antenna <NUM> transmits on the HARQ-ACK channel mapped according to nCCE+<NUM>. The HARQ-ACK information transmitted on the two antennas are the same.

If only the Scell is scheduled, and the Scell is configured with the SIMO transmission mode, one HARQ-ACK bit is generated. The one HARQ-ACK bit is transmitted in duplicate on antenna <NUM> and antenna <NUM> on different channels adopting the SORTD method. With respect to different scheduling methods, the mapping method of the PUCCH resource transmitting the HARQ-ACK information of the Scell includes the following two cases:.

If only the Scell is scheduled, and the Scell is configured with the MIMO transmission mode, two HARQ-ACK bits are generated. The two HARQ-ACK bits are transmitted in duplicate on antenna <NUM> and antenna <NUM> on different channels adopting the SORTD method. With respect to different scheduling methods, the mapping method of the PUCCH resource transmitting the HARQ-ACK information of the Scell includes the following two cases:.

If the Pcell and the Scell are scheduled at the same time, and the Pcell is configured with the SIMO transmission mode, one HARQ-ACK bit is generated. If the Pcell is configured with the MIMO transmission mode, two bits of HARQ-ACK information are generated and the two bits of HARQ-ACK information are bundled into one bit through spatial bundling. Whether the Pcell is configured with the SIMO transmission mode or MIMO transmission mode, one HARQ-ACK bit is finally generated for the Pcell, denoted as HARQ-ACK(<NUM>). Similarly, whether the Scell is configured with the SIMO transmission mode or the MIMO transmission mode, one HARQ-ACK bit is finally generated for the Scell, denoted as HARQ-ACK(<NUM>). Thus, two HARQ-ACK bits are generated for the Pcell and the Scell, denoted as {HARQ-ACK(<NUM>), HARQ-ACK(<NUM>)}. Two channels are mapped for the Pcell and the Scell respectively adopting the SORTD method. There are four channels altogether.

In particular, the mapping method of the two channels of the Pcell is as follows: if the current subframe of the Pcell transmits an SPS service, the two channels of the Pcell is obtained by semi-static configuration of the higher layer, denoted as CH_1 and CH_2; otherwise, the two channels of the Pcell are mapped according to the index nCCE of first CCE of the PDCCH scheduling the PDSCH of the Pcell and the index nCCE+<NUM> of the second CCE of the PDCCH scheduling the PDSCH of the Pcell, also denoted as CH_1 and CH_2;.

The mapping method of the two channels of the Scell is as follows: if the PDSCH of the Scell is cross-carrier scheduled by the PDCCH of the Pcell, the two channels of the Scell is mapped according to the first CCE index nCCE and the second CCE index nCCE+<NUM> of the PDCCH of the Pcell scheduling the PDSCH of the Scell, denoted as CH_3 and CH_4; if the PDSCH of the Scell is non-cross-carrier scheduled from the PDCCH of the Scell, the two channels of the Scell are indicated by the ARI in the PDCCH scheduling the PDSCH of the Scell, also denoted as CH_3 and CH_4.

For FDD systems, bit mapping and resource mapping relationships when HARQ-ACK information is transmitted on antenna <NUM> adopting the SORTD technique are shown in Table <NUM>:.

Bit mapping and resource mapping relationships when HARQ-ACK information is transmitted on antenna <NUM> are shown in Table <NUM>:.

For TDD systems with HARQ-ACK bundling window of <NUM>, bit mapping and resource mapping relationships when HARQ-ACK information is transmitted on antenna <NUM> adopting the SORTD technique are shown in Table <NUM>:.

It can be seen from the above that, in the method provided by the present invention, through indicating in the PDCCH whether data of another CC is scheduled in the same subframe, the UE is able to know the number of Cells scheduled by the base station in the same downlink subframe and to generate HARQ-ACK information based on the number of Cells. Then the UE transmits the generated HARQ-ACK information to the base station adopting the transmission diversity technique. According to the present invention, spatial bundling is prevented from being used when there is only one CC is scheduled. Thus, unnecessary downlink data retransmission is reduced and throughput of downlink data is improved.

Claim 1:
A method for transmitting, by a user equipment, UE, hybrid automatic retransmission request acknowledgement, HARQ-ACK, information on a physical uplink control channel, PUCCH, in a communication system, wherein the UE is configured with at least two cells by a base station, the at least two cells comprising a primary cell and a secondary cell, the method comprising:
identifying at least one of first information, second information, or third information, wherein the first information is related to whether a first physical downlink shared channel, PDSCH, in a downlink subframe is scheduled by a first physical control channel, PDCCH, of the primary cell, and the second information is related to whether a second PDSCH in the downlink subframe is scheduled by a second PDCCH of the secondary cell, wherein the third information is related to whether a third PDSCH in the downlink subframe is scheduled by the primary cell, and wherein the third PDSCH includes semi-persistent scheduling, SPS, data;
receiving, from the base station, downlink data of the at least two cells in the downlink subframe;
generating HARQ-ACK information for the downlink data based on a number of the at least two cells; and
transmitting (<NUM>) the HARQ-ACK information to the base station by using a first resource for a first antenna port and a second resource for a second antenna port,
wherein the first resource for the first antenna port and the second resource for the second antenna port are defined respectively based on at least one of the first information, the second information, or the third information.