TRANSMISSION

Field of the Invention

The present invention relates to the technical field of communication, and more specifically, to a technology of reporting CSI (Channel Status Indicator) for superposition transmission.

BACKGROUND OF THE TNVFNTTON

In Rel-13, a study item to improve the performance of MU-MIMO (Multi

User-Multiple-Input Multiple-Output) was recently proposed, wherein Network Assisted Interference Cancellation & Suppression (NAICS) is employed. This new feature is called Superposition Transmission, where the main targeted scenario is MU-MIMO with near-far UEs (User Equipment). An example with two UEs is shown in Figure 1 where a first UE is close to the base station (e.g., eNodeB or eNB, evolved Node B) whilst a second UE is at the cell edge and the base station performs MU-MIMO pairing the first UE and the second UE. In such scenario, the signal to the second UE would be of higher power than that to the first UE and as a result the first UE would be highly interfered. However, since the interference consisting of signal to the second UE at the first UE is too strong, it is possible for the first UE to decode and cancel/ suppress this interference with information on decoding the signal of the second UE. Such information can be provided by the network (i.e., NAICS) and/or blindly decoded by the first UE.

It should be appreciated that Figure 1 is an example of superposition transmission and it is up to the base station to pair two such UEs and assign power allocation. One can view this as another form of MU-MIMO where the base station would decide which UE to pair and which precoding to use.

In the current system, CQI (Channel Quality Indicator) is based on the PDSCH (Physical Downlink Shared Channel) transport block size and MCS (Modulation and Coding Scheme) that the UE can decode with a BLER (Block Error Ratio) of 10%. The current reported CQI does not take into account interference cancellation/ suppression and a "pessimistic" CQI is reported leading to the base station to schedule a smaller than required TBS thereby not fully utilizing the benefits offered by NAICS. Although the outer loop link adaptation may eventually result in the base station to schedule the "right" TBS, this process is slow and requires that the interference condition remain the same during adaptation. During the Rel-12 NAICS WI (work item), this CQI issue was discussed extensively on whether any enhancement is required to the reporting. Several proposals were made, for example in one proposal the UE reports a Post-NAICS CQI and a Pre-NAICS CQI where in Post-NAICS CQI, the CQI is based on interference being removed whilst Pre-NAICS CQI is the CQI without interference being removed (i.e., legacy CQI). UE vendors argued that it is difficult to determine a Post-NAICS CQI, which leads to high UE complexity since a Post-NAICS CQI requires the UE to perform interference cancellation during CQI measurement. Furthermore it was unclear whether the CQI should be based on CRS RE (Cell-specific Reference Signal Resource Element) or PDSCH RE (Physical Downlink Shared Channel Resource Element) and if it is based on PDSCH RE, this creates further complication since the UE has to decode the PDSCH from its serving base station. Due to the complication, the WI concluded without any CQI enhancement. It is assumed that the UE would report the "correct" CQI and that RAN4 (Radio Access Network 4) may devise a test to ensure this. However, it is unclear currently how such a test can be used since the work is still under progress in RAN4.

The RANI is going to study superposition transmission schemes which can be classified as the worst case or practice of MU-MIMO and heavily rely on UE interference cancellation capability. Therefore, a similar issue in CQI reporting is expected and hence to find a solution to the technical problem that can provide CQI feedback on UE cancellation capability but avoid the complication of the Post-NAICS CQI is absolutely required.

Post-NAICS CQI is the known solution but this creates a lot of complication as described above. Moreover, the new SI (study item) of superposition transmission targets at dynamic multiuser transmission and pairing which may not be sufficiently supported by the concept of Post-NAICS CQI. STJMMARY OF THE TNVENTTON

An objective of the present invention is to provide a method and apparatus for reporting CSI for superposition transmission.

According to one aspect of the present invention, there is provided a method of implementing reporting CSI for superposition transmission in a first UE, wherein the method comprises:

a. reporting, based on a first BLER indicated by a corresponding base station, a first CSI corresponding to the first BLER to the base station;

b. reporting, based on at least one second BLER indicated by the base station, at least one second CSI corresponding to the at least one second BLER, to the base station, wherein the base station performs superposition transmission with the first UE and at least one second UE paired therewith, wherein a value of the at least one second BLER is different from a value of the first BLER.

Preferably, wherein the second CSI comprises a second CQI, wherein the step b comprises:

- calculating the second CQI based on at least one second BLER indicated by the base station in conjunction with power allocated by the base station for the first UE and the at least one second UE.

Preferably, wherein the method further comprises:

- determining, based on PMI/RI included in the first CSI, PMI/RI included in the at least one second CSI;

wherein the manner of determining includes any one of the following:

- the PMI/RI included in the at least one second CSI is identical to the PMI/RI included in the first CSI;

- the PMI/RI included in the at least one second CSI is a subarray of the PMI/RI included in the first CSI.

Preferably, wherein the second CSI only includes the second CQI.

According to another aspect of the present invention, there is further provided a method of facilitating implementation of reporting CSI for superposition transmission in a base station, wherein the method comprises:

- indicating a first BLER and at least one second BLER to a corresponding first UE, respectively, wherein a value of the at least one second BLER is different from a value of the first BLER.

Preferably, wherein the method further comprises:

- configuring, based on a first CSI and at least one second CSI reported by the first UE, a corresponding MCS for the first UE.

Preferably, wherein the method further comprises:

- configuring a corresponding MCS for the at least one second UE, respectively, based on the at least one second CSI reported by the first UE and a CSI reported by at least one second UE corresponding to the at least one second CSI.

According to a further aspect of the present invention, there is further provided a first UE implementing reporting CSI for superposition transmission, wherein the first UE comprises:

a first reporting device configured to report, based on a first BLER indicated by a corresponding base station, a first CSI corresponding to the first BLER to the base station;

a second reporting device configured to report, based on at least one second BLER indicated by the base station, at least one second CSI corresponding to the at least one second BLER, to the base station, wherein the base station performs superposition transmission with the first UE and at least one second UE paired therewith, wherein a value of the at least one second BLER is different from a value of the first BLER.

Preferably, wherein the second CSI comprises a second CQI, wherein the second reporting device is configured to:

- calculate the second CQI based on at least one second BLER indicated by the base station in conjunction with power allocated by the base station for the first UE and the at least one second UE.

Preferably, wherein the first UE further comprises:

a determining device configured to determine, based on PMI/RI included in the first CSI, PMI/RI included in the at least one second CSI;

wherein the manner of determining includes any one of the following:

- the PMI/RI included in the at least one second CSI is identical to the PMI/RI included in the first CSI;

- the PMI/RI included in the at least one second CSI is a subarray of the PMI/RI included in the first CSI.

Preferably, wherein the second CSI only includes the second CQI.

According to a further aspect of the present invention, there is further provided a base station facilitating implementation of reporting CSI for superposition transmission, wherein the base station comprises: an indicating device configured to indicate a first BLER and at least one second BLER to a corresponding first UE, respectively, wherein a value of the at least one second BLER is different from a value of the first BLER.

Preferably, wherein the base station further comprises:

a first configuring device configured to configure, based on a first CSI and at least one second CSI reported by the first UE, a corresponding MCS for the first UE.

Preferably, wherein the base station further comprises:

a second configuring device configured to configure a corresponding MCS for the at least one second UE, respectively, based on the at least one second CSI reported by the first UE and a CSI reported by at least one second UE corresponding to the at least one second CSI.

According to another further aspect of the present invention, there is further provided a system for implementing reporting CSI for superposition transmission, comprising a first UE above and a base station above.

Compared with the prior art, the present invention provides base information on the level of interference a victim UE can cancel under an MU-MIMO operation. The victim UE provides a first CSI based on an existing system and at least one second CSI corresponding to at least one paired UE, the second CSI being related to an interference cancellation capability of the victim UE; moreover, in the second CSI, a BLER different from that of the first CSI is utilized.

Different from the Post-NAICS CQI proposed in the Rel-12 NAICS, the present invention does not require the UE to perform interference cancellation/ suppression during a CQI measurement period for the second CSI. Therefore, the present invention does not have the complication as found in the Post-NAICS CQI. The present invention designs some restrictions and/or changes some existing standards when generating a CSI report, such that the report is more useful and more beneficial to the superposition transmission schemes, which enhances system efficiency and promotes user experience.

Further, in the present invention, the base station configures a corresponding MCS for the victim UE based on the first CSI and the second CSI reported by the victim UE; the base station further configures a corresponding MCS for the interferer UE based on the second CSI reported by the victim UE and the CSI reported by the interferer UE, which further enhances system efficiency and promotes user experience.

BRTEF DESCRIPTION OF THE DRAWINGS

Through reading the detailed depiction of the non-limiting embodiments with reference to the following drawings, other features, objectives and advantages of the present invention will become more apparent:

Fig. 1 shows a schematic diagram of a system performing MU-MIMO;

Fig. 2 shows a flow diagram of a method of reporting CSI for superposition transmission in a first UE according to one aspect of the present invention;

Fig. 3 shows a schematic diagram of an apparatus of reporting CSI for superposition transmission in a first UE according to another aspect of the present invention.

The same or like reference numerals in the drawings represent the same or corresponding components. DETAILED DESCRTPTTON OF THE PREFERRED EMBODTMENTS

While example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but on the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the claims. Like numbers refer to like elements throughout the description of the figures.

Before discussing example embodiments in more detail, it is noted that some example embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe the operations as sequential processes, many of the operations may be performed in parallel, concurrently or simultaneously. In addition, the order of operations may be re-arranged. The processes may be terminated when their operations are completed, but may also have additional steps not included in the figure. The processes may correspond to methods, functions, procedures, subroutines, subprograms, etc.

As used herein, the term "wireless device" or "device" may be considered synonymous to, and may hereafter be occasionally referred to, as a client, user equipment, mobile station, mobile user, mobile, subscriber, user, remote station, access terminal, receiver, mobile unit, etc., and may describe a remote user of wireless resources in a wireless communication network.

Similarly, as used herein, the term "base station" may be considered synonymous to, and may hereafter be occasionally referred to, as a Node B, evolved Node B, eNodeB, base transceiver station (BTS), RNC, etc., and may describe a transceiver in communication with and providing wireless resources to mobiles in a wireless communication network which may span multiple technology generations. As discussed herein, base stations may have all functionality associated with conventional, well-known base stations in addition to the capability to perform the methods discussed herein.

Methods discussed below, some of which are illustrated by the flow charts, may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine or computer readable medium such as a storage medium. A processor(s) may perform the necessary tasks.

Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.

It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

A basic idea of the present invention is that the UE provides at least two CSI reports, wherein the CSI report includes parameters such as CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator) or RI (Ranking Indication), where in each CSI, the parameters (CQI/ PMI/ RI) are based on different constraints. A UE providing the different CSI report, for example, is a UE close to the base station, e.g., the first UE performing interference cancellation in Fig. 1. Other UEs, e.g., the second UE, still measures a channel as usual. However, the scheduler at the base station should take into account the feedback reported from both the first UE and the second UE, and perform proper scheduling adjustment.

Preferably, when the first UE has a plurality of second UEs paired therewith, if the plurality of second UEs likewise need to perform interference cancellation, it may also report a plurality of CSIs at different BLERs.

For the sake of conciseness, detailed description will be provided with a first UE that needs to perform interference cancellation as an example.

It should be noted that in the 3 GPP standard, because it allows a UE vendor to implement its own receiver, derivation of the CQI is based on implementation of the UE. Besides the function as the receiver of the UE, the CQI is also a function of the radio propagation channel. Since the base station is not aware of individual UE's implementation and the radio channel propagation can change, it is very difficult (or impossible) for the base station to derive or determine the CQI of a UE at a specific BLER (e.g., 1%) based on a CQI of another BLER (e.g., 10%). It should also be noted that normally interpolation based on a single point (e.g., CQI at 10% BLER) is impossible.

Fig. 2 shows a flow diagram of a method of reporting CSI for superposition transmission in a first UE according to one aspect of the present invention.

Herein, in step S201, the first UE reports, based on a first BLER indicated by a corresponding base station, a first CSI corresponding to the first BLER to the base station.

Specifically, the base station, here for example eNB, indicates the first BLER to the first UE through pre-configuration or sending it to the first UE; the first UE, based on a first BLER indicated by the base station, performs channel measurement, obtains parameter information such as CQI, PMI or RI, generates a first CSI, and reports the first CSI to the base station with the first BLER.

In step S202, the first UE reports, based on at least one second BLER indicated by the base station, at least one second CSI corresponding to the at least one second BLER, to the base station, wherein the base station performs superposition transmission with the first UE and at least one second UE paired therewith, wherein a value of the at least one second BLER is different from a value different from the first BLER.

Specifically, besides indicating a first BLER to the first UE, the base station further indicates at least one second BLER to the first UE, a value of the at least one second BLER is different from a value of the first BLER. Preferably, a value of the at least one second BLER is lower than a value of the first BLER.

The first UE performs channel measurement based on the at least one second BLER indicated by the base station, and obtains parameter information such as CQI, PMI or RI, generates at least one second CSI, respectively, and reports the at least one second CSI to the base station based on the at least one second BLER, respectively.

Here, the base station performs superposition transmission between the first UE and the at least one second UE paired therewith, i.e., a plurality of pieces of information issued by the base station to the first UE and the at least one second UE is transmitted together. Therefore, the at least one second UE generates different levels of interference for the first UE.

Here, depending on the design of such as BLER and/or PMI and/or RI constraints, a higher-level signaling is needed to indicate a new constraint to the UE (for example the first UE herein) so that the first UE can follow new reporting criteria.

The second CSI effectively represents the probability that the interference would be cancelled or the probability that the first UE can achieve the first CSI.

Preferably, a value of the at least one second BLER is lower than a value of the first BLER. The values may be defined in a specification or notified by the network.

In one embodiment, the first UE has a plurality of second UEs paired therewith. For example, the first UE has three second UEs paired therewith, which are here called a second UE, a third UE, and a fourth UE. The base station performs superposition transmission with the first UE, the second UE, the third UE, and the fourth UE. Therefore, the second UE, the third UE, and the fourth UE generate interference with the first UE on different levels, respectively.

Preferably, the number of the second CSI corresponds to the number of the second UEs.

In this embodiment, because the first UE has three second UEs paired therewith, the first UE needs to report three corresponding second CSIs.

More preferably, the first UE sorts at least one interference based on a power level of the at least one interference generated by the at least one second UE, determines corresponding BLER from the at least one second BLER indicated by the base station in succession based on the sorting, and calculates the corresponding CSI.

In this embodiment, suppose the first UE is closest to the base station, and the second UE, the third UE, and the fourth UE are further away from the base station in succession. Therefore, in the MU-MIMO superposition transmission scheme, the power allocated by the base station to the fourth UE is the highest, then the power allocated to the third UE, then the power allocated to the second UE, and then the power allocated to the first UE, which is the lowest. Therefore, the fourth UE, the third UE and the second UE generate different levels of interference with the first UE, respectively. The first UE sorts these interferences based on the power levels of these interferences and determines the values of their corresponding BLERs. For example, the power level of the interference generated by the second UE is the lowest, while the value of its corresponding BLER is relatively high, the value of the BLER corresponding to the third UE is lower than that of the second UE, while the value of the BLER corresponding to the fourth UE is the lowest. Afterwards, the first UE calculates corresponding CSIs based on these BLERs and reports them to the base station.

In another embodiment, the first UE has a second UE paired therewith. The base station indicates a first BLER and a second BLER to the first UE, respectively, wherein a value of the second BLER is different from the value of the first BLER. For example, the value of the first BLER is 10%, and the value of the second BLER is 1%. The first UE first reports a first CSI corresponding to the first BLER to the base station based on the first BLER; next, the first UE reports a second CSI corresponding to the second BLER to the base station based on the second BLER.

With the scenario in Fig. 1 as an example, it is used for pairing near - far UEs, namely, for MU-MIMO transmission, the first UE and the second UE are paired. The base station configures the first UE to report 2 CSIs, wherein the first CSI is obtained based on the existing system, for example, based on a 10% BLER; the second CSI is obtained based on a different constraint, e.g., 1% BLER.

For the MU-MIMO, when the base station guarantees pairing a further UE (e.g., the second UE) for the first UE, the further UE (i.e., the second UE) may be scheduled, such that the MCS and TBS of the further UE (i.e., the second UE) do not exceed the MCS and TBS corresponding to the reported second CSI. It allows the victim UE (i.e., the first UE) to reliably cancel the interference from the further UE (i.e., the second UE).

Because generation of the CSI based on the current system does not take into account the interference of the MU-MIMO, if the interference of the MU-MIMO is completely cancelled or suppressed, the first CSI will effectively act as the CSI which the UE will experience. For the first CSI, the existing CQI/PMI/RI definition and feedback mechanisms do not change.

The second CSI represents interference that the UE may decode. The second CSI is relevant to the interference cancellation capability of the UE. The idea here is trying best to re-utilize the existing CQI/PMI/RI definition and feedback mechanism, but it needs some additional constraints or changes such that the second CSI may provide a reference to the interference cancellation for superposition transmission for the specific UE.

A different BLER is utilized in the second CSI with a reason that the UE can decode the interference based on the interference cancellation receiver on the symbol level or codeword level without any HARQ retransmission and without going through the whole decoding chain. That is, the UE needs to be able to decode this interference at a higher reliability, which would lead to the interferer UE (i.e., the second UE) having a lower MCS than that of the signal. In the near-far MU-MIMO scenario, since the interferer UE (i.e., the second UE) is at the cell edge, it is expected that the interferer UE has a lower MCS than the victim UE (for example the first UE closer to the base station) based on the superposition transmission scheme.

The difference lies in the Post-NAICS CQI proposed in Rel-12 NAICS, where the present invention does not need the UE to perform interference cancellation/ suppression during the CQI measurement for the second CSI. Therefore, the present invention does not have the complication as found in the Post-NAICS CQI. Further, the UE only needs to perform the same measurement (e.g., CRS) so as to generate two CSI reports.

Moreover, the two CSI reports here are not based on multiple CSI processing originally designed for the CoMP. When generating the CSI report, the present invention designs some constraints and/or changes some current criteria such that they become more useful and more beneficial to the superposition transmission scheme.

For the sake of conciseness, the instances provided hereinafter are described in a scenario where the first UE and the second UE are paired.

Preferably, the second CSI includes a second CQI, where in step S202, the first UE calculates the second CQI based on at least one second BLER indicated by the base station in conjunction with the power allocated by the base station for the first UE and the at least one second UE.

Specifically, because the CSI includes parameters such as CQI, PMI or RI, for the CQI therein, it may be derived from calculating the RSRP (Reference Signal Received Power) received from the base station and the BLER indicated by the base station. Here, since the base station performs superposition transmission with the first UE and the second UE paired therewith, the first UE, when calculating the CQI, may also consider the power allocated by the base station for the first UE and the second UE.

During superposition transmission, the base station allocates different power for different transmissions. With pairing the first UE and one second UE as an example, suppose the locations of the first UE and the second UE from the base station as shown in Fig. 1, then the base station may allocate 70% total power to the second UE, while only allocating 30% total power to the first UE. When calculating the CQI, the first UE takes the power allocation of the base station into account.

Here, the power size allocated to the first UE and the second UE is determined by the base station, and the calculation of the CQI may guarantee a certain power allocation.

Preferably, power split (e.g., between the first UE and the second UE) is notified to the first UE and the second UE, which acts as a part of the configuration or is prescribed in a specification.

Preferably, the first UE determines a PMI/RI included in the at least one second CSI based on the PMI/RI included in the first CSI;

wherein the manner of determining includes at least one of the following:

- the PMI/RI included in the at least one second CSI is identical to the PMI/RI included in the first CSI;

- the PMI/RI included in the at least one second CSI is a subarray of the PMI/RI included in the first CSI.

Here, the PMI/ RI included in the second CSI depends on the PMI/RI included in the first CSI. In the second manner of determining, i.e., when the PMI/RI included in the at least one second CSI is the subarray of the PMI/RI included in the first CSI, the RI will correspond to the size of the subarray, e.g., rank 1, and needs an additional indication to determine which layer or which layers correspond to the PMI included in the first CSI.

Preferably, the second CSI only includes the second CQI.

Here, depending on the constraint design of the PMI/RI included in the second CSI, the second CSI may only include the second CQI, namely, the first UE only reports CQI, without reporting PMI/RI. For example, when the PMI/RI included in the second CSI is identical to the PMI/RI included in the first CSI, the first UE only reports CQI, without reporting PMI/RI.

Preferably, the first CSI and the at least one second CSI are reported together to the base station in a new PUCCH (Physical Uplink Control Channel) format.

Preferably, the second CSI includes a differential value between the second CQI and a first CQI included in the first CSI.

Here, the second CQI may calculate, with the first CQI as a reference, to determine a differential value between the second CQI and the first CQI, and feed back to report the differential value in a short-term or long-term interval.

Preferably, the first CSI and the at least one second CSI are reported to the base station in a manner of time division multiplexing (TDM).

Here, this reporting manner allows use of the current PUCCH format, but different CSIs are reported at different times.

Preferably, the first CSI and the at least one second CSI are reported to the base station at different cycles.

Here, the first CSI and the second CSI have different periods. For example, the first CSI is reported to the base station more frequently than the second CSI.

Preferably, when there are a plurality of second CSIs, the plurality of second CSIs may also follow the above rules. For example, the plurality of second CSIs are reported together to the base station in a new PUCCH format, reported to the base station in a TDM manner, and reported to the base station at different cycles, etc.

According to another aspect of the present invention, there is further provided a method of facilitating implementation of reporting CSI for superposition transmission in a base station.

Herein, the base station indicates a first BLER and at least one second BLER to a corresponding first UE, respectively, wherein a value of the at least one second BLER is different from a value of the first BLER.

Here, besides a need of indicating the first BLER of the existing system to the first UE, the base station further needs to indicate a different second BLER for the interferer UE. The first BLER and the second BLER may be sent to the first UE, respectively, and may also be pre-sent to the first UE in the configuration.

Preferably, a value of the at least one second BLER is lower than a value of the first BLER.

Preferably, the base station configures a corresponding MCS for the first UE based on a first CSI and at least one second CSI reported by the first UE.

Different from an inter-cell NAICS (e.g., in Rel-12), in the present invention, the interference to be cancelled in the MU-MIMO is generated by a serving base station, namely, the serving base station controls a signal and interference to the victim UE (e.g., the first UE). The base station therefore may schedule UE pairing for the MU-MIMO.

With the first UE and one second UE paired therewith as an example, the base station (e.g., a scheduler within the base station) configures a corresponding MCS for the first UE based on the first CSI and the second CSI reported by the first UE. For example, based on equation CQI #1 - * CQI # 2, a corresponding MCS is configured for the first UE. Here, CQI#1 represents the first CQI included in the first CSI, CQI#2 represents the second CQI included in the second CSI, a denotes a coefficient, whose value may be adjusted slowly based on OLLA (Outer Loop Link Adaptation) and UE capability. Here, the MCS configured by the base station for the first UE does not exceed the MCS corresponding to the first CSI.

Preferably, the base station configures a corresponding MCS for the at least one second UE, respectively, based on the at least one second CSI reported by the first UE and a CSI reported by at least one second UE corresponding to the at least one second CSI.

With the first UE and one second UE paired therewith as an example, the base station configures a corresponding MCS for the second UE based on the second CSI reported by the first UE and the CSI reported by the second UE. Here, the MCS configured by the base station for the second UE does not exceed the MCS corresponding to the second CSI reported by the first UE.

Here, besides the second CSI reported by the first UE, the base station also directly considers the CSI feedback from the second UE, e.g., increasing a schedule priority for the second UE located at a cell edge.

More preferably, if the MCS configured by the base station for the second UE is higher than the MCS corresponding to the second CSI reported by the first UE, the base station configures a lower MCS for the first UE, because the first UE cannot cancel the interference generated by the second UE with a desired reliability. Of course, the MCSs configured for the first UE and the second UE depend on the base station, e.g., a scheduler within the base station.

Fig. 3 shows a schematic diagram of an apparatus of reporting CSI for superposition transmission in a first UE according to another aspect of the present invention. The first UE comprises a first reporting device 301 and a second reporting device 302.

Herein, the first reporting device 301 in the first UE reports, based on a first BLER indicated by a corresponding base station, a first CSI corresponding to the first BLER to the base station.

Specifically, the base station, here for example eNB, indicates the first BLER to the first UE through pre-configuration or sending it to the first UE; the first reporting device 301 in the first UE, based on a first BLER indicated by the base station, performs channel measurement, obtains parameter information such as CQI, PMI or RI, generates a first CSI, and reports the first CSI to the base station with the first BLER.

The second reporting device 302 in the first UE reports, based on at least one second BLER indicated by the base station, at least one second CSI corresponding to the at least one second BLER, to the base station, wherein the base station performs superposition transmission with the first UE and at least one second UE paired therewith, wherein a value of the at least one second BLER is different from a value different from the first BLER.

Specifically, besides indicating a first BLER to the first UE, the base station further indicates at least one second BLER to the first UE, a value of the at least one second BLER is different from a value of the first BLER. Preferably, a value of the at least one second BLER is lower than a value of the first BLER.

The second reporting device 302 in the first UE performs channel measurement based on the at least one second BLER indicated by the base station, and obtains parameter information such as CQI, PMI or RI, generates at least one second CSI, respectively, and reports the at least one second CSI to the base station based on the at least one second BLER, respectively. Here, the base station performs superposition transmission between the first UE and the at least one second UE paired therewith, i.e., a plurality of pieces of information issued by the base station to the first UE and the at least one second UE is transmitted together. Therefore, the at least one second UE generates different levels of interference for the first UE ₀

Here, depending on the design of such as BLER and/or PMI and/or RI constraints, a higher-level signaling is needed to indicate a new constraint to the UE (for example the first UE herein) so that the first UE can follow new reporting criteria.

The second CSI effectively represents the probability that the interference would be cancelled or the probability that the first UE can achieve the first CSI.

Preferably, a value of the at least one second BLER is lower than a value of the first BLER. The values may be defined in a specification or notified by the network.

In one embodiment, the first UE has a plurality of second UEs paired therewith. For example, the first UE has three second UEs paired therewith, which are here called a second UE, a third UE, and a fourth UE. The base station performs superposition transmission with the first UE, the second UE, the third UE, and the fourth UE. Therefore, the second UE, the third UE, and the fourth UE generate interference with the first UE on different levels, respectively.

Preferably, the number of the second CSI corresponds to the number of the second UEs.

In this embodiment, because the first UE has three second UEs paired therewith, the first UE needs to report three corresponding second CSIs.

More preferably, the first UE sorts at least one interference based on a power level of the at least one interference generated by the at least one second UE, determines corresponding BLER from the at least one second BLER indicated by the base station in succession based on the sorting, and calculates the corresponding CSI.

In this embodiment, suppose the first UE is closest to the base station, and the second UE, the third UE, and the fourth UE are further away from the base station in succession. Therefore, in the MU-MIMO superposition transmission scheme, the power allocated by the base station to the fourth UE is the highest, then the power allocated to the third UE, then the power allocated to the second UE, and then the power allocated to the first UE, which is the lowest. Therefore, the fourth UE, the third UE and the second UE generate different levels of interference with the first UE, respectively. The first UE sorts these interferences based on the power levels of these interferences and determines the values of their corresponding BLERs. For example, the power level of the interference generated by the second UE is the lowest, while the value of its corresponding BLER is relatively high, the value of the BLER corresponding to the third UE is lower than that of the second UE, while the value of the BLER corresponding to the fourth UE is the lowest. Afterwards, the first UE calculates corresponding CSIs based on these BLERs and reports them to the base station.

In another embodiment, the first UE has a second UE paired therewith. The base station indicates a first BLER and a second BLER to the first UE, respectively, wherein a value of the second BLER is different from the value of the first BLER. For example, the value of the first BLER is 10%, and the value of the second BLER is 1%. The first UE first reports a first CSI corresponding to the first BLER to the base station based on the first BLER; next, the first UE reports a second CSI corresponding to the second BLER to the base station based on the second BLER.

With the scenario in Fig. 1 as an example, it is used for pairing near - far UEs, namely, for MU-MIMO transmission, the first UE and the second UE are paired. The base station configures the first UE to report 2 CSIs, wherein the first CSI is obtained based on the existing system, for example, based on a 10% BLER; the second CSI is obtained based on a different constraint, e.g., 1% BLER.

For the MU-MIMO, when the base station guarantees pairing a further UE (e.g., the second UE) for the first UE, the further UE (i.e., the second UE) may be scheduled, such that the MCS and TBS of the further UE (i.e., the second UE) do not exceed the MCS and TBS corresponding to the reported second CSI. It allows the victim UE (i.e., the first UE) to reliably cancel the interference from the further UE (i.e., the second UE).

Because generation of the CSI based on the current system does not take into account the interference of the MU-MIMO, if the interference of the MU-MIMO is completely cancelled or suppressed, the first CSI will effectively act as the CSI which the UE will experience. For the first CSI, the existing CQI/PMI/RI definition and feedback mechanisms do not change.

The second CSI represents interference that the UE may decode. The second CSI is relevant to the interference cancellation capability of the UE. The idea here is trying best to re-utilize the existing CQI/PMI/RI definition and feedback mechanism, but it needs some additional constraints or changes such that the second CSI may provide a reference to the interference cancellation for superposition transmission for the specific UE.

A different BLER is utilized in the second CSI with a reason that the UE can decode the interference based on the interference cancellation receiver on the symbol level or codeword level without any HARQ retransmission and without going through the whole decoding chain. That is, the UE needs to be able to decode this interference at a higher reliability, which would lead to the interferer UE (i.e., the second UE) having a lower MCS than that of the signal. In the near-far MU-MIMO scenario, since the interferer UE (i.e., the second UE) is at the cell edge, it is expected that the interferer UE has a lower MCS than the victim UE (for example the first UE closer to the base station) based on the superposition transmission scheme.

The difference lies in the Post-NAICS CQI proposed in Rel-12 NAICS, where the present invention does not need the UE to perform interference cancellation/ suppression during the CQI measurement for the second CSI. Therefore, the present invention does not have the complication as found in the Post-NAICS CQI. Further, the UE only needs to perform the same measurement (e.g., CRS) so as to generate two CSI reports.

Moreover, the two CSI reports here are not based on multiple CSI processing originally designed for the CoMP. When generating the CSI report, the present invention designs some constraints and/or changes some current criteria such that they become more useful and more beneficial to the superposition transmission scheme.

For the sake of conciseness, the instances provided hereinafter are described in a scenario where the first UE and the second UE are paired.

Preferably, the second CSI includes a second CQI, where the second reporting device 302 in the first UE calculates the second CQI based on at least one second BLER indicated by the base station in conjunction with the power allocated by the base station for the first UE and the at least one second UE.

Specifically, because the CSI includes parameters such as CQI, PMI or RI, for the CQI therein, it may be derived from calculating the RSRP (Reference Signal Received Power) received from the base station and the BLER indicated by the base station. Here, since the base station performs superposition transmission with the first UE and the second UE paired therewith, the second reporting device 302 in the first UE, when calculating the CQI, may also consider the power allocated by the base station for the first UE and the second UE.

During superposition transmission, the base station allocates different power for different transmissions. With pairing the first UE and one second UE as an example, suppose the locations of the first UE and the second UE from the base station as shown in Fig. 1, then the base station may allocate 70% total power to the second UE, while only allocating 30% total power to the first UE. When calculating the CQI, the second reporting device 302 in the first UE takes the power allocation of the base station into account.

Here, the power size allocated to the first UE and the second UE is determined by the base station, and the calculation of the CQI may guarantee a certain power allocation.

Preferably, power split (e.g., between the first UE and the second UE) is notified to the first UE and the second UE, which acts as a part of the configuration or is prescribed in a specification.

Preferably, the first UE further comprises a determining device (not shown). The determining device determines a PMI/RI included in the at least one second CSI based on the PMI/RI included in the first CSI;

wherein the manner of determining includes at least one of the following:

- the PMI/RI included in the at least one second CSI is identical to the PMI/RI included in the first CSI;

- the PMI/RI included in the at least one second CSI is a subarray of the PMI/RI included in the first CSI.

Here, the PMI/ RI included in the second CSI depends on the PMI/RI included in the first CSI. In the second manner of determining, i.e., when the PMI/RI included in the at least one second CSI is the subarray of the PMI/RI included in the first CSI, the RI will correspond to the size of the subarray, e.g., rank 1, and needs an additional indication to determine which layer or which layers correspond to the PMI included in the first CSI.

Preferably, the second CSI only includes the second CQI.

Here, depending on the constraint design of the PMI/RI included in the second CSI, the second CSI may only include the second CQI, namely, the first UE only reports CQI, without reporting PMI/RI. For example, when the PMI/RI included in the second CSI is identical to the PMI/RI included in the first CSI, the first UE only reports CQI, without reporting PMI/RI.

Preferably, the first CSI and the at least one second CSI are reported together to the base station in a new PUCCH (Physical Uplink Control Channel) format.

Preferably, the second CSI includes a differential value between the second CQI and a first CQI included in the first CSI.

Here, the second CQI may calculate, with the first CQI as a reference, to determine a differential value between the second CQI and the first CQI, and feed back to report the differential value in a short-term or long-term interval.

Preferably, the first CSI and the at least one second CSI are reported to the base station in a manner of time division multiplexing (TDM).

Here, this reporting manner allows use of the current PUCCH format, but different CSIs are reported at different times.

Preferably, the first CSI and the at least one second CSI are reported to the base station at different cycles.

Here, the first CSI and the second CSI have different periods. For example, the first CSI is reported to the base station more frequently than the second CSI.

Preferably, when there are a plurality of second CSIs, the plurality of second CSIs may also follow the above rules. For example, the plurality of second CSIs are reported together to the base station in a new PUCCH format, reported to the base station in a TDM manner, and reported to the base station at different cycles, etc.

According to a further aspect of the present invention, there is further provided a base station facilitating implementation of reporting CSI for superposition transmission. The base station comprises an indicating device (not shown), a first configuring device (not shown) and a second configuring device (not shown).

Herein, the indicating device in the base station indicates a first BLER and at least one second BLER to a corresponding first UE, respectively, wherein a value of the at least one second BLER is different from a value of the first BLER.

Here, besides a need of indicating the first BLER of the existing system to the first UE, the indicating device in the base station further needs to indicate a different second BLER for the interferer UE. The first BLER and the second BLER may be sent to the first UE, respectively, and may also be pre-sent to the first UE in the configuration.

Preferably, a value of the at least one second BLER is lower than a value of the first BLER.

Preferably, the first configuring device in the base station configures a corresponding MCS for the first UE based on a first CSI and at least one second CSI reported by the first UE.

Different from an inter-cell NAICS (e.g., in Rel-12), in the present invention, the interference to be cancelled in the MU-MIMO is generated by a serving base station, namely, the serving base station controls a signal and interference to the victim UE (e.g., the first UE). The base station therefore may schedule UE pairing for the MU-MIMO. With the first UE and one second UE paired therewith as an example, the first configuring device in the base station (e.g., a scheduler within the base station) configures a corresponding MCS for the first UE based on the first CSI and the second CSI reported by the first UE. For example, based on equation CQI #1 - * CQI # 2, a corresponding MCS is configured for the first UE. Here, CQI#1 represents the first CQI included in the first CSI, CQI#2 represents the second CQI included in the second CSI, a denotes a coefficient, whose value may be adjusted slowly based on OLLA (Outer Loop Link Adaptation) and UE capability. Here, the MCS configured by the base station for the first UE does not exceed the MCS corresponding to the first CSI.

Preferably, the second configuring device in the base station configures a corresponding MCS for the at least one second UE, respectively, based on the at least one second CSI reported by the first UE and a CSI reported by at least one second UE corresponding to the at least one second CSI.

With the first UE and one second UE paired therewith as an example, the second configuring device in the base station configures a corresponding MCS for the second UE based on the second CSI reported by the first UE and the CSI reported by the second UE. Here, the MCS configured by the base station for the second UE does not exceed the MCS corresponding to the second CSI reported by the first UE.

Here, besides the second CSI reported by the first UE, the base station also directly considers the CSI feedback from the second UE, e.g., increasing a schedule priority for the second UE located at a cell edge.

More preferably, if the MCS configured by the base station for the second UE is higher than the MCS corresponding to the second CSI reported by the first UE, the base station configures a lower MCS for the first UE, because the first UE cannot cancel the interference generated by the second UE with a desired reliability. Of course, the MCSs configured for the first UE and the second UE depend on the base station, e.g., a scheduler within the base station.

It should be noted that the present invention may be implemented in software and/or a combination of software and hardware, for example, it may be implemented by an application-specific integrated circuit ASIC, a general purpose computer or any other similar hardware device. In one embodiment, the software program of the present invention may be executed through a processor to implement the steps or functions as mentioned above. Likewise, the software program of the present invention (including relevant data structure) may be stored in the computer-readable recording medium, for example, RAM memory, magnetic or optic driver or flappy disk or similar devices. Besides, some steps or functions of the present invention may be implemented by hardware, for example, as a circuit cooperating with the processor to execute various steps or functions.

To those skilled in the art, it is apparent that the present invention is not limited to the details of above exemplary embodiments, and the present invention can be implemented with other specific embodiments without departing the spirit or basic features of the present invention. Thus, from any perspective, the embodiments should be regarded as illustrative and non-limiting. The scope of the present invention is limited by the appended claims, instead of the above description. Thus, meanings of equivalent elements falling within the claims and all variations within the scope are intended to be included within the present invention. Any reference numerals in the claims should be regarded as limiting the involved claims. Besides, it is apparent that such terms as "comprise" and "include" do not exclude other units or steps, and a single form does not exclude a plural form. The multiple units or modules as stated in apparatus claims can also be implemented by a single unit or module through software or hardware. Terms such as first and second are used to represent names, not representing any specific sequence.

While example embodiments have been particularly shown and described, it will be understood by one of ordinary skill in the art that variations in form and detail may be made therein without departing from the spirit and scope of the claims. The protection sought herein is as set forth in the claims below. Those and other aspects of various embodiments are specified in the following numbered clauses:

1. A method of implementing reporting CSI for superposition transmission in a first UE, wherein the method comprises:

a. reporting, based on a first BLER indicated by a corresponding base station, a first CSI corresponding to the first BLER to the base station;

b. reporting, based on at least one second BLER indicated by the base station, at least one second CSI corresponding to the at least one second BLER, to the base station, wherein the base station performs superposition transmission with the first UE and at least one second UE paired therewith, wherein a value of the at least one second BLER is different from a value of the first BLER.

2. The method according to clause 1, wherein the second CSI comprises a second CQI, wherein the step b comprises:

- calculating the second CQI based on at least one second BLER indicated by the base station in conjunction with power allocated by the base station for the first UE and the at least one second UE.

3. The method according to clause 1, wherein the method further comprises: - determining, based on PMI/RI included in the first CSI, PMI/RI included in the at least one second CSI;

wherein the manner of determining includes any one of the following:

- the PMI/RI included in the at least one second CSI is identical to the PMI/RI included in the first CSI;

- the PMI/RI included in the at least one second CSI is a subarray of the PMI/RI included in the first CSI.

4. The method according to clause 1, wherein the second CSI only includes the second CQI.

5. The method according to clause 1, wherein number of the second CSI corresponds to number of the second UEs.

6. The method according to clause 1, wherein the method further comprises:

- sorting at least one interference based on a power level of the at least one interference generated by the at least one second UE;

- determining corresponding BLER from the at least one second BLER indicated by the base station in succession based on the sorting, and calculating the corresponding CSI.

7. The method according to clause 1, wherein a value of the at least one second BLER is lower than a value of the first BLER.

8. The method according to clause 1, wherein the first CSI and the at least one second CSI are reported together to the base station in a new PUCCH format.

9. The method according to clause 1, wherein the second CSI includes a differential value between the second CQI and a first CQI included in the first CSI.

10. The method according to clause 1, wherein the first CSI and the at least one second CSI are reported to the base station in a manner of time division multiplexing

(TDM).

11. The method according to clause 1, wherein the first CSI and the at least one second CSI are reported to the base station at different cycles.

12. A method of facilitating implementation of reporting CSI for superposition transmission in a base station, wherein the method comprises:

- indicating a first BLER and at least one second BLER to a corresponding first UE, respectively, wherein a value of the at least one second BLER is different from a value of the first BLER.

13. The method according to clause 12, wherein the method further comprises: - configuring, based on a first CSI and at least one second CSI reported by the first UE, a corresponding MCS for the first UE.

14. The method according to clause 12, wherein the method further comprises:

- configuring a corresponding MCS for the at least one second UE, respectively, based on the at least one second CSI reported by the first UE and a CSI reported by at least one second UE corresponding to the at least one second CSI.

15. A first UE implementing reporting CSI for superposition transmission, wherein the first UE comprises:

a first reporting device configured to report, based on a first BLER indicated by a corresponding base station, a first CSI corresponding to the first BLER to the base station;

a second reporting device configured to report, based on at least one second BLER indicated by the base station, at least one second CSI corresponding to the at least one second BLER, to the base station, wherein the base station performs superposition transmission with the first UE and at least one second UE paired therewith, wherein a value of the at least one second BLER is different from a value of the first BLER.

16. The first UE according to clause 15, wherein the second CSI comprises a second CQI, wherein the second reporting device is configured to:

- calculate the second CQI based on at least one second BLER indicated by the base station in conjunction with power allocated by the base station for the first UE and the at least one second UE.

17. The first UE according to clause 15, wherein the first UE further comprises: a determining device configured to determine, based on PMI/RI included in the first CSI, PMI/RI included in the at least one second CSI; wherein the manner of determining includes any one of the following:

- the PMI/RI included in the at least one second CSI is identical to the PMI/RI included in the first CSI;

- the PMI/RI included in the at least one second CSI is a subarray of the PMI/RI included in the first CSI.

18. The first UE according to clause 15, wherein the second CSI only includes the second CQI.

19. The first UE according to clause 15, wherein number of the second CSI corresponds to number of the second UEs.

20. The first UE according to clause 15, wherein the first UE further comprises a sorting device configured to:

- sorting at least one interference based on a power level of the at least one interference generated by the at least one second UE;

- determining corresponding BLER from the at least one second BLER indicated by the base station in succession based on the sorting, and calculating the corresponding CSI.

21. The first UE according to clause 15, wherein a value of the at least one second BLER is lower than a value of the first BLER.

22. The first UE according to clause 15, wherein the first CSI and the at least one second CSI are reported together to the base station in a new PUCCH format.

23. The first UE according to clause 15, wherein the second CSI includes a differential value between the second CQI and a first CQI included in the first CSI.

24. The first UE according to clause 15, wherein the first CSI and the at least one second CSI are reported to the base station in a manner of time division multiplexing (TDM).

25. The first UE according to clause 15, wherein the first CSI and the at least one second CSI are reported to the base station at different cycles.

26. A base station facilitating implementation of reporting CSI for superposition transmission, wherein the base station comprises:

an indicating device configured to indicate a first BLER and at least one second

BLER to a corresponding first UE, respectively, wherein a value of the at least one second BLER is different from a value of the first BLER.

27. The base station according to clause 26, wherein the base station further comprises:

a first configuring device configured to configure, based on a first CSI and at least one second CSI reported by the first UE, a corresponding MCS for the first UE.

28. The base station according to clause 26, wherein the base station further comprises:

a second configuring device configured to configure a corresponding MCS for the at least one second UE, respectively, based on the at least one second CSI reported by the first UE and a CSI reported by at least one second UE corresponding to the at least one second CSI.

29. A system for implementing reporting CSI for superposition transmission, comprising a first UE according to any one of clauses 15-25 and a base station according to any one of clauses 26-28.