Multiple CSI reports for multi-user superposition transmission

Abstract

According to an aspect, a radio access network node supports the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first UE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The radio access network node receives multiple CSI reports from the first UE for a first reporting instance. One or more of the received multiple CSI reports correspond to one or more respective multi-user superposition transmission states. The radio access network node also determines whether to use multi-user superposition transmission or an orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports.

Claims

1. A method, in a radio access network node configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first user equipment (UE) and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding, the method comprising: receiving multiple channel-state information (CSI) reports from the first UE for a first reporting instance, wherein one or more of the received multiple CSI reports correspond to one or more respective multi-user superposition transmission states; and determining whether to use multi-user superposition transmission or an orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports.

2. A method, in a first user equipment (UE) configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for the first UE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding, the method comprising: receiving one or more configuration messages, the one or more configuration messages indicating number of channel quality indicators (CQIs) to be reported by the first UE, each CQI corresponding to a different rank for data transmission to the first UE; and sending multiple CSI reports for a first reporting instance, wherein one or more of the transmitted multiple CSI reports correspond to one or more respective multi-user superposition transmission states.

3. A radio access network node configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first user equipment (UE) and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding, the radio access network node comprising: a transceiver circuit configured to send and receive transmissions; and a processing circuit configured to: receive a channel-state information (CSI) report from the first UE, via the transceiver circuit, the received CSI report being based on an assumption that a transmission power for a physical channel is lower than a minimum transmission power that is assumed when multi-user superposition transmission is not used; and control the transceiver circuit to transmit a multi-user superposition transmission to the UE, based on the received CSI report.

4. The radio access network node of claim 3, wherein the processing circuit is configured to use the transceiver circuit to signal to the UE, for configuring the UE to send the CSI report, a selected parameter indicating a ratio of a Physical Downlink Shared Channel (PDSCH) energy per resource element to a CSI reference symbol (CSI-RS) energy per resource element, wherein the selected parameter is selected from a range having a minimum value corresponding to a ratio below 8 dB.

5. The radio access network node of claim 3, wherein the processing circuit is configured to use the transceiver circuit to signal to the UE, for configuring the UE to send the CSI report, a selected parameter indicating a ratio of a Physical Downlink Shared Channel (PDSCH) energy per resource element to a cell-specific reference symbol (CRS) energy per resource element, wherein the selected parameter is selected from an extended range having a minimum value corresponding to a ratio below 6 dB.

6. The radio access network node of claim 5, wherein the extended range has a minimum value corresponding to a ratio of about 19.21 dB.

7. A user equipment (UE) configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for the UE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding, the UE comprising: a transceiver circuit configured to send and receive transmissions; and a processing circuit configured to: receive one or more configuration messages from a radio access network node, via the transceiver circuit, the one or more configuration messages directing the UE to transmit a channel-state information (CSI) report, the one or more configuration messages comprising at least one of (a) a selected parameter indicating a ratio of a Physical Downlink Shared Channel (PDSCH) energy per resource element to a CSI reference symbol (CSI-RS) energy per resource element, wherein the selected parameter is selected from a range having a minimum value corresponding to a ratio below 8 dB, or (b) a selected parameter indicating a ratio of a Physical Downlink Shared Channel (PDSCH) energy per resource element to a cell-specific reference symbol (CRS) energy per resource element, wherein the selected parameter is selected from an extended range having a minimum value corresponding to a ratio below 6 dB; send, using the transceiver circuit, a channel-state information (CSI) report, in accordance with the one or more configuration messages; wherein the transceiver circuit is further configured to receive a multi-user superposition transmission from the radio access network node.

8. A radio access network node configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first user equipment (UE) and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding, the radio access network node comprising: a transceiver circuit configured to send and receive transmissions; and a processing circuit configured to: receive, via the transceiver circuit, multiple channel-state information (CSI) reports from the first UE for a first reporting instance, wherein one or more of the received multiple CSI reports correspond to one or more respective multi-user superposition transmission states; and determine whether to use multi-user superposition transmission or an orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports.

9. The radio access network node of claim 8, wherein the processing circuit is configured to first send one or more configuration messages, via the transceiver circuit, to the first UE, the one or more configuration messages directing the first UE to provide multiple channel state information (CSI) reports for at least the first reporting instance such that one or more of the multiple CSI reports correspond to one or more respective multi-user superposition transmission states for a transmission to the first UE.

10. The radio access network node of claim 9, wherein the multiple CSI reports are received on request, in response to the one or more configuration messages.

11. The radio access network node of claim 8, wherein the processing circuit is configured to schedule the first UE based on said determining whether to use multi-user superposition transmission or an orthogonal multiple access transmission, and to send a scheduling message, via the transceiver circuit, to the first UE.

12. The radio access network node of claim 8, wherein a first one of the received multiple CSI reports comprises a channel quality indicator (CQI) corresponding to a full-power or substantially full-power data transmission to the first UE, and wherein the processing circuit is configured to determine whether to use multi-user superposition transmission or an orthogonal multiple access transmission by being configured to: obtain a CSI report from a second UE, the CSI report from the second UE comprising a CQI corresponding to a full-power or substantially full-power data transmission to the second UE; and determine that multi-user superposition transmission to the first and second UEs is feasible by being configured to determine that said CQI for the first UE is greater than said CQI for the second UE by a predetermined factor or threshold, and determine that a precoder matrix indicator (PMI) corresponding to the CSI report from the second UE matches at least one PMI corresponding to one of the received multiple CSI reports from the first UE other than said first one of the received multiple CSI reports.

13. The radio access network node of claim 12, wherein the processing circuit is configured to obtain the CSI report from the second UE by being configured to: transmit, in an interference measurement resource (IMR) for the second UE, an interference component corresponding to a potential power share allocated to the first UE in a multi-user superposition transmission to the first and second UEs, wherein said interference component is transmitted using the same antennas and the same antenna precoding intended for the multi-user superposition transmission to the first and second UEs; and receive, from the second UE, said CQI corresponding to a full-power or substantially full-power data transmission to the second UE, wherein said CQI reflects the interference component transmitted in the IMR for the second UE.

14. The radio access network node of claim 8, wherein the received multiple CSI reports from the first UE correspond to different power-sharing hypotheses for multi-user superposition transmission to the first UE.

15. The radio access network node of claim 14, wherein one or more configuration messages sent to the first UE indicate one or more of the different power-sharing hypotheses.

16. The radio access network node of claim 8, wherein the received multiple CSI reports from the first UE correspond to different ranks for data transmission to the first UE.

17. The radio access network node of claim 16, wherein one or more configuration messages sent to the first UE indicate a number of channel quality indicators (CQIs) to be reported by the first UE, each CQI corresponding to a different rank for data transmission to the first UE.

18. The radio access network node of claim 17, wherein one or more configuration messages sent to the first UE indicate the number of CQIs to be reported by the first UE by indicating, for each desired CSI report, a corresponding transmission rank by indicating a set of precoders that are restricted to the corresponding transmission rank.

19. The radio access network node of claim 8, wherein the received multiple CSI reports from the first UE comprise N CSI reports, the N CSI reports comprising the N best channel quality indicators (CQIs) and wherein each of the N CSI reports includes a corresponding precoding matrix indicator (PMI) and rank indicator (RI).

20. A first user equipment (UE) configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for the first UE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding, the first UE comprising: a transceiver circuit configured to send and receive transmissions; and a processing circuit configured to: receive one or more configuration messages, the one or more configuration messages indicating number of channel quality indicators (CQIs) to be reported by the first UE, each CQI corresponding to a different rank for data transmission to the first UE; and send, via the transceiver circuit, multiple CSI reports for a first reporting instance, wherein one or more of the transmitted multiple CSI reports correspond to one or more respective multi-user superposition transmission states.

21. The first UE of claim 20, wherein the one or more configuration messages direct the first UE to provide multiple channel state information (CSI) reports for at least the first reporting instance such that one or more of the multiple CSI reports correspond to one or more respective multi-user superposition transmission states for a transmission to the first UE.

22. The first UE of claim 21, wherein the processing circuit is configured to send the multiple CSI reports on request, in response to receiving the one or more configuration messages.

23. The first UE of claim 20, wherein the processing circuit is configured to receive a scheduling message based on the sent multiple CSI reports, the scheduling message scheduling a multi-user superposition transmission to the first UE.

24. The first UE of claim 20, wherein a first one of the sent multiple CSI reports comprises a channel quality indicator (CQI) corresponding to a full-power or substantially full-power data transmission to the first UE.

25. The first UE of claim 20, wherein the sent multiple CSI reports correspond to different power-sharing hypotheses for multi-user superposition transmission to the first UE.

26. The first UE of claim 25, wherein one or more configuration messages received by the first UE indicate one or more of the different power-sharing hypotheses.

27. The first UE of claim 20, wherein the sent multiple CSI reports correspond to different ranks for data transmission to the first UE.

28. The first UE of claim 20, wherein the one or more configuration messages received by the first UE indicate the number of CQIs to be reported by the first UE by indicating, for each desired CSI report, a corresponding transmission rank by indicating a set of precoders that are restricted to the corresponding transmission rank.

29. The first UE of claim 20, wherein the sent multiple CSI reports comprise N CSI reports, the N CSI reports comprising the N best channel quality indicators (CQIs) and wherein each of the N CSI reports includes a corresponding precoding matrix indicator (PMI) and rank indicator (RI).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a generalized illustration of a MUST transmitter with two superposed UEs.

(2) FIG. 2 is a generalized illustration of MUST receiver processing with two superposed information streams intended for two UEs respectively.

(3) FIG. 3 illustrates an example of superposed NOMA constellation.

(4) FIG. 4 illustrates another example of superposed SOMA constellation.

(5) FIG. 5 illustrates an example of 16-QAM superposed REMA constellation.

(6) FIG. 6 illustrates a request-based CQI reporting by a UE with multiple RI/PMT/CQI configurations for MUST transmission, according to some embodiments.

(7) FIG. 7 illustrates a block diagram of a radio access network node, according to some embodiments.

(8) FIG. 8 illustrates a method of receiving multiple CSI reports for determining whether to use multi-user superposition transmission or an orthogonal multiple access transmission, according to some embodiments.

(9) FIG. 9 illustrates a block diagram of a UE, according to some embodiments.

(10) FIG. 10 illustrates a method of sending multiple CSI reports, according to some embodiments.

(11) FIG. 11 illustrates an example functional implementation of a radio access network node, according to some embodiments.

(12) FIG. 12 illustrates an example functional implementation of a UE, according to some embodiments.

(13) FIG. 13 is a process flow diagram illustrating an example method according to some embodiments.

(14) FIG. 14 is a process flow diagram illustrating another example method according to some embodiments.

DETAILED DESCRIPTION

(15) Reference may be made below to specific elements, numbered in accordance with the attached figures. The discussion below should be taken to be exemplary in nature, and not as limiting of the scope of the present invention. The scope of the present invention is defined in the claims, and should not be considered as limited by the implementation details described below, which as one skilled in the art will appreciate, can be modified by replacing elements with equivalent functional elements.

(16) Embodiments of the present invention provide for allowing multiple CSI reports to be sent by the UE for the purpose of MUST. The multiple CSI reports may correspond to different data transmission power levels, different rank restrictions, or different precoders with the best and the second best measured quality CQI values.

(17) For example, a radio access network node, such as an LTE eNodeB, or eNB, is configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first UE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The radio access network node receives multiple CSI reports from the first UE for a first reporting instance. One or more of the received multiple CSI reports correspond to different possible multi-user superposition transmission states, where a multi-user superposition transmission state is a particular combination of allocated transmission power and transmit antenna precoding. The different possible multi-user superposition transmission states may foe example be one or more respective multi-user superposition transmission states corresponding to the one or more of the received multiple CSI reports. The radio access network node is also configured to determine whether to use multi-user superposition transmission or orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports.

(18) Multiple CSI reports of a reporting instance can be considered to be associated with one another, in that they generally correspond to the same interval of time and/or the same radio channel measurements. Reporting instances may be periodic, according to configuration instructions provided to the UE, but in some embodiments may also or instead be aperiodic, in response to a request from the radio access network node or another node.

(19) Example methods of receiving multiple CSI reports include where the precoding matrix indicators, PMIs, of the multiple CSI reports from one UE that correspond to different data transmission power levels, different rank restrictions, or different qualities are compared to a PMI of another CSI report from another UE for the purpose of identifying valid MUST UE pairs.

(20) In some cases, the first UE can be configured to send CSIs when the UE is configured to receive multi-user superposition transmissions. This can include, for example, providing a power ratio value selected from a first set of power ratio values, where the first set of power ratio values contains smaller power ratios than a second set of power ratio values, and where the second set of power ratio values may be used for UEs that are not configured to receive multi-user superposition transmissions, and where the power ratios are ratios of PDSCH energy to reference signal energy. In this case, Physical Downlink Shared Channel, PDSCH, can be extended to a reference signal energy per resource element, RS EPRE, ratio range in CSI reports.

(21) In another example, the first UE can be configured to report multiple CSIs when the UE is configured to receive multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting a modulation symbol intended for a second UE using the same precoding and on the same antennas as a modulation symbol intended for the UE. A plurality of parameters corresponding to different potential multi-user superposition transmission states can be provided, the plurality of parameters comprising a set of transmission powers, a set of transmission rank restrictions, and/or a set of precoder restrictions.

(22) It is noted that for some cases one of the CSI reports is not specific to MUST, perhaps to support dynamic switching between MUST and non-MUST transmissions. In other cases, the UE may not receive an explicit configuration message specific to MUST. In such cases, the existing signaling, not specific to MUST, can be used to realize rank restricted multiple CSI reports.

(23) Continuing with the example of configuring the UE, in some cases, superposition hypotheses may only include serving PDSCH parameters, where superposition is defined as using the same precoding. All of the parameters may indicate one or more potential states of a transmission intended for the UE. In other examples, the UE is configured to send the multiple CSI reports aperiodically when requested by the eNodeB. Each CSI report may correspond to different data transmission power levels.

(24) Additional examples include methods where one of the CSI reports corresponds to full data transmission power level (this corresponds to OMA CQI, which is important for dynamic switching between OMA and MUST). The UE may assume ideal interference cancellation for the CSI reports corresponding to non-full data transmission power levels. Each CSI report may correspond to different rank restrictions or CSI measurements of different quality.

(25) Methods may include indicating a configuration of multiple CSI reports to a UE for the purposes of MUST where each configuration indication may contain one or more of a power ratio parameter with extended range to support MUST (radio resource control, RRC, signaling), a list of power ratio parameters with extended range to support MUST (RRC signaling), and/or a bit string indicating the restricted set of precoders to be considered during CSI measurements and feedback.

(26) In some embodiments, a signal corresponding to the interference from a first UE to a second UE is transmitted on the interference measurement resource of the second UE where the first UE is configured to receive multi-user superposition transmissions. The interference component is transmitted using the same precoding and on the same antennas as the modulation symbols intended for the first and second UEs.

(27) Three embodiments will be described in more detail below, but in general, it should be understood that multi-user superposition is distinct from multi-user multiple-input and multiple-output, MIMO, as used in LTE in that for multi-user superposition transmissions, the same antenna patterns and precoding (or same effective antenna) are used for the transmissions intended for the different UEs. Multi-user MIMO, on the other hand, relies on spatial multiplexing between the users, which is achieved by using different antennas and/or antenna precoding. To facilitate multi-user superposition transmissions, the CSI feedback should accurately predict the needed transmission parameters to obtain good downlink throughput given this same effective antenna behavior

(28) CSI feedback comprises at least channel quality information, CQI, indicating a modulation and coding rate that could be used for a PDSCH transmitted to the UE providing the feedback at a predetermined block error rate. A CSI report may also comprise additional feedback such as precoding matrix indications, rank indications, etc. Therefore, in some cases, a UE is configured to send multiple CSI reports for the purpose of multi-user superposition transmission. The CSI reports may comprise at least a channel quality indication.

(29) In some instances, a plurality of parameters corresponding to different potential multi-user superposition transmission states are hypothesized in CSI feedback. In general, the amount of feedback overhead and UE computational complexity grows in proportion to the number of parameters and multi-user transmission states for which the UE provides CSI feedback. Therefore, it is generally desirable to provide a small number of parameters that provides as much performance gain as possible.

(30) If N parameter settings are jointly and independently hypothesized for M users in a multi-user transmission, the number of parameter settings is on the order of N.sup.M. One approach to avoiding this exponential growth of the number of parameter hypotheses is to provide parameters corresponding only to hypotheses of the PDSCH intended for the UE, rather than those for both the intended and interfering PDSCHs, and to have the UE assume that single user transmission is used. In this case, it is still possible to have accurate CSI feedback when an interfering PDSCH is transmitted, so long as it is transmitted in the same way (i.e., using the precoding, etc.) as the desired PDSCH. This allows dynamic switching between multi-user superposition and single-user transmission.

(31) Because parameters or the presence of the interfering far UE transmission are not part of the hypotheses, the UE should calculate the CSI assuming that a superposed far UE PDSCH does not interfere with the received near UE PDSCH. Therefore, in some embodiments, when calculating the MUST specific CQIs, a UE that employs interference cancellation (i.e., a near UE, UE.sub.1) may assume that the interference component in Equation 6 can be completely cancelled.

Example Embodiment 1

(32) A first embodiment will now be described in more detail. In this embodiment, an eNodeB generally configures the UE(s) to send multiple CSI reports where one of the CSI reports corresponds to the OMA mode and one or more other CSI reports correspond to the MUST mode. Having one CSI report for OMA and one or more CSI report(s) for MUST ensures that the proposed solution supports dynamic switching between OMA and MUST modes. That is, the scheduler in the proposed scheme can more accurately decide whether OMA or MUST should be employed in a given scheduling band depending on which scheme provides the highest PF rate. To reduce uplink feedback overhead, the eNodeB may configure only the near UE(s) to send multiple CSI reports for the purposes of MUST; the far UE(s) may be configured to send only a single OMA CSI report. The eNodeB may use Reference Signal Received Power, RSRP, reports and/or uplink pathloss measurements to distinguish between the near and far UEs.

(33) The eNodeB configures the OMA CSI report such that full transmission power allocation is assumed when the UE measures CQI. In the CSI report(s) configured specifically for MUST, the eNodeB configures the UE(s) such that each of the MUST specific CQIs corresponds to a different power share value. The steps involved in this embodiment are summarized below. Although these steps are described using one near UE and one far UE, the solution proposed in this embodiment is applicable to a plurality of near and far UEs.

(34) Step 1:

(35) The eNodeB configures a near UE UE.sub.1 to send Q>1 CSI reports. One of the reports contains a CQI denoted by CQI.sub.UE1.sup.0 that corresponds to the OMA CQI (i.e., assumes full transmission power). The remaining Q1 CSI reports contain CQIs denoted by CQI.sub.UE1.sup.1, CQI.sub.UE2.sup.2, . . . , CQI.sub.UE1.sup.Q1 that respectively correspond to Q1 different MUST power share values .sub.1, .sub.2, . . . , .sub.Q1 (note that .sub.1, .sub.2, . . . , .sub.Q1 are assumed to be in non-decreasing order here). Additionally, the eNodeB configures a far UE UE.sub.2 to send a single OMA CSI report containing a CQI that is denoted by CQI.sub.UE2.sup.0.

(36) Step 2:

(37) UE.sub.1 calculates the CSI reports (including the CQIs) according to the power share hypotheses, and then sends the Q CSI reports to the eNodeB. Similarly, UE.sub.2 sends the OMA CSI report to the eNodeB. When calculating the MUST specific CSIs, UE.sub.1 may assume that the interference component in Equation 6 can be completely cancelled.

(38) Step 3:

(39) For each scheduling band, the eNodeB scheduler first checks if CQI.sub.UE1.sup.0 is sufficiently higher than CQI.sub.UE2.sup.0. Additionally, the scheduler checks the combination of precoders among these UEs when deciding whether UE.sub.1 and UE.sub.2 can be valid MUST pairs. This is done by comparing the PMI corresponding to CQI.sub.UE2.sup.0 with the PMIs corresponding to CQI.sub.UE1.sup.1, CQI.sub.UE1.sup.2, . . . , CQI.sub.UE1.sup.Q1. If the PMI of CQI.sub.UE2.sup.0 matches or is sufficiently close to the PMI of CQI.sub.UE1.sup.q where 1q(Q1), then UE.sub.1 and UE.sub.2 can be valid MUST pairs with near UE power share parameter close to .sub.q.

(40) Step 4:

(41) If UE.sub.1 and UE.sub.2 are deemed a valid MUST pair, then the eNodeB scheduler can select a near UE power share parameter {tilde over ()} close to .sub.q. The parameter {tilde over ()} is selected from a set A of predetermined power share parameter values (i.e., {tilde over ()}A).

(42) Step 5:

(43) For the selected C value, calculate the scheduling SINRs for MUST using SINR.sub.UE.sub.1 and SINR.sub.UE.sub.2, corresponding to CQI reports CQI.sub.UE1.sup.q and CQI.sub.UE2.sup.0 with the following approximations: UE.sub.1's scheduling SINR for MUST is calculated as

(44) $\begin{array}{cc}\frac{\stackrel{~}{}}{{}_q}{\mathrm{SINR}}_{\mathrm{UE}1}^q& \mathrm{Equation}13\end{array}$ UE.sub.2's scheduling SINR for MUST is calculated as

(45) $\begin{array}{cc}\frac{1-\stackrel{~}{}}{\stackrel{~}{}+\frac{1}{{\mathrm{SINR}}_{\mathrm{UE}2}^0}}& \mathrm{Equation}14\end{array}$

(46) Step 6:

(47) The scheduler then calculates the MUST PF metric corresponding to the MUST UE pair under consideration as

(48) $\begin{array}{cc}\underset{{\mathrm{UE}}_{i}U}{.Math.}\left(\frac{R\left(i|U,\stackrel{~}{},{}_q\right)}{L\left(i\right)}\right)& \mathrm{Equation}15\end{array}$

(49) where R(i|U, {acute over ()}, .sub.q) and L(i) respectively denote the instantaneous throughput and the average throughput of UE.sub.i. In Equation 15, R(i|U, {tilde over ()}, .sub.q) is a function of MUST scheduling SINRs computed in Equation 13-Equation 14, and hence R(i|U, {tilde over ()}, .sub.q) also depends on the power share parameters {tilde over ()} and .sub.q. The candidate user set U contains the MUST UE pair under consideration.

(50) Step 7:

(51) The steps 3-6 are repeated for all valid MUST UE pairs with all .sub.q that yield matching PMIs and all {tilde over ()} values in the set A. Additionally, the OMA PF metrics corresponding to each UE belonging to the serving cell are also calculated using the reported OMA CQIs (i.e., CQI.sub.UE1.sup.0 and CQI.sub.UE2.sup.0) as is currently done in LTE.

(52) Step 8:

(53) From Step 7, the scheduler decides whether OMA or MUST should be employed in the current scheduling band depending on which scheme provides the highest PF rate. The UE(s) corresponding to the highest PF metric are scheduled. In case the MUST scheme is scheduled in the scheduling band, the power share parameter pair ({tilde over ()}, .sub.q) that yields the highest PF rate is chosen.

(54) In one variant of this embodiment, the eNodeB, in Step 1, may configure a far UE UE.sub.2 using LTE transmission mode 10 to send a single CSI report containing a CQI while at the same time transmitting the interference term {square root over (P)}g.sub.F(k)x.sub.N(k) (see Equation 9) in UE.sub.2's interference measurement resource (IMR). The far UE UE.sub.2 may not be aware of the superposed interference from UE.sub.1 and may not be configured to receive multi-user superposition transmission. Since transmitting the interference term on the IMR improves a UE's interference estimate without requiring any a-priori knowledge of the interference characteristics, the CSI feedback from a far UE served by multi-user superposition transmission can be improved without any additional UE complexity. There may be further improvements for the CSI estimate of the far UE if the CSI report of UE.sub.2 is configured with a MUST power share value of (1) as well. Note that since the power offset values used for CSI in LTE Rel-12 (for example, P.sub.c described in further detail below) may cover the range needed for the far UE served by MUST transmissions, the far UE may not need to be aware that its power share value of (1) is for the purpose of MUST transmission

(55) It should be noted that MUST specific CSI (i.e., CQI.sub.UE1.sup.q) is used in this solution for identifying valid MUST pairs (Step 3), calculating near UE's MUST scheduling SINR (Step 5), and computing the MUST PF metrics (Step 6). As a result, the problems of rank mismatch, CQI mismatch, and PMI mismatch are alleviated in this solution. In addition, the solution of Embodiment 1 also supports dynamic switching between OMA and MUST modes. That is, the scheduler in the proposed scheme can more accurately decide whether OMA or MUST should be employed in a given scheduling band depending on which scheme provides the highest PF rate.

(56) The RRC signaling required to support the solution of Embodiment 1 in LTE transmission mode 10, TM10, can be realized in a few different ways. In current LTE, a parameter P.sub.c is signaled by the eNodeB to the UE to indicate the ratio of the PDSCH energy per resource element (EPRE) to CSI-RS EPRE. In other words, the P.sub.c parameter indicates the ratio of the downlink data transmitted power per resource element to the channel state information reference symbol power per resource element. The UE uses the P.sub.c parameter to determine the reference data transmission power during CSI feedback. Currently, P.sub.c takes values in the range of [8, 15] dB with 1 dB step size. However, to support the solution of Embodiment 1, the range of P.sub.c should be extended to cover the desired near UE power share {tilde over ()} values in dB. For instance, the range of near UE power share values in Table 1 should be covered. So if the range of P.sub.c is extended to [19, 15] dB then all the possible REMA cases in Table 1 should be covered. However, if extending the range of P.sub.c value to 19 dB is an overkill, then a more reasonable range extension for P.sub.c would be [13, 15] dB which covers a majority of superposed REMA constellations in Table 1.

(57) An example using RRC signaling of the CSI-Process information element with the range-extended P.sub.c parameter (which is denoted as p-C-r11) is shown in Table 2. With the CSI-Process information element of Table 2, an eNodeB can currently configure a UE to report 2 MUST specific CQIs and 1 OMA CQI (a total of Q=3 CSI reports). This is because in current LTE it is possible to configure a maximum of 3 CSI-RS processes per UE in TM10 (i.e., the maxCQI-ProcEt-r11 parameter can be currently set to 3, for example). However, if maxCQI-ProcExt-r11 is further increased, it is possible to have more than 2 MUST specific CQIs (i.e., Q>3).

(58) Alternatively, if subframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured (i.e. csi-SubframePatternConfig is configured), then the UE can be configured to send two CSI reports per CSI process in the two CSI measurement subframe sets currently supported in LTE. In each CSI process, two different P.sub.c values can be set in the two CSI measurement subframe sets by having two entries in p-C-AndCBSRList-r11. This can be exploited to configure up to Q=6 CSI reports in LTE TM10 (i.e., 2 CSI reports per CSI process3 CSI processes). Hence, by configuring subframe patterns for CSI reporting, it is possible for the eNodeB to configure a near UE to report up to 5 MUST specific CSIs and 1 OMA CSI.

(59) Yet another alternative is to introduce a new sequence called p-C-List in the CSI-Process information element. This sequence will contain a configurable number (for instance, say Q) of entries of type P.sub.c. In this alternative, the eNodeB will configure the UE to report Q CSI measurements from the same CSI process (thus, reducing the CSI-RS overhead from having to use multiple CSI processes). Each of the Q CST reports will correspond to one of P.sub.c values contained in p-C-List. Thus, with this alternative, Embodiment 1 can be realized in LTE TM10 with a flexibly configurable number Q of CSI reports.

(60) TABLE-US-00002 TABLE 2 CSI-Process information element -- ASN1START CSI-Process-r11 ::= SEQUENCE { csi-ProcessId-r11 CSI-ProcessId-r11, csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11, csi-IM-ConfigId-r11 CSI-IM-ConfigId-r11, p-C-AndCBSRList-r11 SEQUENCE (SIZE (1..2)) OF P-C-AndCBSR-r11, cqi-ReportBothProc-r11 CQI-ReportBothProc-r11 OPTIONAL, -- Need OR cqi-ReportPeriodicProcId-r11 INTEGER (0..maxCQI-ProcExt-r11)OPTIONAL, -- Need OR cqi-ReportAperiodicProc-r11 CQI-ReportAperiodicProc-r11 OPTIONAL, -- Need OR .... [[ alternativeCodebookEnabledFor4TXProc-r12 ENUMERATED {true} OPTIONAL, -- Need ON csi-IM-ConfigIdList-r12 CHOICE { release NULL, setup SEQUENCE (SIZE (1..2)) OF CSI-IM-ConfigId- r12 } OPTIONAL, -- Need ON cqi-ReportAperiodicProc2-r12 CHOICE { release NULL, setup CQI-ReportAperiodicProc-r11 } OPTIONAL -- Need ON ]] } P-C-AndCBSR-r11 ::= SEQUENCE { p-C-r11 INTEGER (13..15), codebookSubsetRestriction-r11 BIT STRING } -- ASN1STOP
CSI-Process field descriptions are as follows.
alternativeCodebookEnabledFor4TXProc

(61) Indicates whether code book in TS 36.213 Table 7.2.4-0A to Table 7.2.4-0D is being used for deriving CSI feedback and reporting for a CSI process. EUTRAN may configure the field only if the number of CSI-RS ports for non-zero power transmission CSI-RS configuration is 4.

(62) cqi-ReportAperiodicProc

(63) If csi-MeasSubframeSets-r12 is configured for the same frequency as the CSI process, cqi-ReportAperiodicProc

(64) applies for CSI subframe set 1. If csi-MeasSubframeSet1-r10 or csi-MeasSubframeSet2-r10 are configured for the same frequency as the CSI process, cqi-ReportAperiodicProc applies for CSI subframe set 1 or CSI subframe set 2. Otherwise, cqi-ReportAperiodicProc applies for all subframes

(65) cqi-ReportAperiodicProc2

(66) cqi-ReportAperiodicProc2 is configured only if csi-MeasSubframeSets-r12 is configured for the same frequency as the CSI process. cqi-ReportAperiodicProc2 is for CSI subframe set 2. E-UTRAN shall set cqi-ReportModeAperiodic-r11 in cqi-ReportAperiodicProc2 the same as in cqi-ReportAperiodicProc.

(67) cqi-ReportBothProc

(68) Includes CQI configuration parameters applicable for both aperiodic and periodic CSI reporting, for which CSI process specific values may be configured. E-UTRAN configures the field if and only if cqi-ReportPeriodicProcId is included and/or if cqi-ReportAperiodicProc is included.

(69) cqi-ReportPeriodicProcId

(70) Refers to a periodic CQI reporting configuration that is configured for the same frequency as the CSI process. Value 0 refers to the set of parameters defined by the REL-10 CQI reporting configuration fields, while the other values refer to the additional configurations E-UTRAN assigns by CQI-ReportPeriodicProcExt-r11 (and as covered by CQI-ReportPeriodicProcExtId).

(71) csi-IM-ConfigId

(72) Refers to a CSI-IM configuration that is configured for the same frequency as the CSI process.

(73) csi-IM-ConfigIdList

(74) Refers to one or two CSI-IM configurations that are configured for the same frequency as the CSI process. csi-M-ConfigIdList can include 2 entries only if csi-MeasSubframeSets-r12 is configured for the same frequency as the CSI process. UE shall ignore csi-IM-ConfigId-r11 if csi-IM-ConfigIdList-r12 is configured.

(75) csi-RS-ConfigNZPId

(76) Refers to a CSI RS configuration using non-zero power transmission that is configured for the same frequency as the CSI process.

(77) p-C

(78) Parameter: P.sub.c, see TS 36.213.

(79) p-C-AndCBSRList

(80) A p-C-AndCBSRList including 2 entries indicates that the subframe patterns configured for CSI (CQI/PMI/PTI/RI) reporting (i.e. as defined by field csi-MeasSubframeSet1 and csi-MeasSubframeSet2, or as defined by csi-MeasSubframeSets-r12) are to be used for this CSI process, while a single entry indicates that the subframe patterns are not to be used for this CSI process. E-UTRAN does not include 2 entries in p-C-AndCBSRList with csi-MeasSubframeSet1 and csi-MeasSubframeSet2 for CSI processes concerning a secondary frequency. E-UTRAN includes 2 entries in p-C-AndCBSRList when configuring both cqi-pmi-ConfigIndex and cqi-pmi-ConfigIndex2.

(81) The RRC signaling required to support the solution of Embodiment 1 in LTE transmission mode 9, TM9, can be realized in a few different ways. An example RRC signaling of the CSI-RS-Config information element is shown in Table. Here, a new optional integer p-C2 is introduced in the CSI-RS-Config information element with range [13, 15] dB which covers a majority of the superposed REMA constellations in Table 1. If subframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured (i.e. csi-SubframePatternConfig is configured), then the existing integer p-C-r10 is only used in the first CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet1) and the newly introduced integer p-C2 is only used in the second CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet2). This way the eNodeB can configure a near UE in TM9 to send one OMA CSI report on the first CSI-MeasSubframeSet and one MUST CSI report on the second CSI-MeaSubframeSet. Note that the parameter p-C2 is only signaled if the eNodeB wants to enable multiple CSI reports for the purposes of MUST. Hence, with this RRC signaling approach, the solution of Embodiment 1 can be supported in LTE TM9 with Q=2.

(82) An alternative RRC signaling approach is to introduce a new sequence called p-C-List in the CSI-RS-Config information element. This sequence will contain a configurable number (for instance, say Q) of entries of type P.sub.c. The range of values for P.sub.c will be extended to cover the MUST near UE power share values of interest (for instance, this range can be set to [13, 15] dB as discussed above). In this alternative, the eNodeB will configure the UE to report Q CSI measurements per CSI-RS-Config. Each of the Q CSI reports will correspond to one of P values contained in p-C-List. Thus, with this alternative, Embodiment 1 can be realized in LTE TM9 with a flexibly configurable number Q of CSI reports.

(83) TABLE-US-00003 TABLE 3 CSI-RS-Config information element -- ASN1START CSI-RS-Config-r10 ::= SEQUENCE { csi-RS-r10 CHOICE { release NULL, setup SEQUENCE { antennaPortsCount-r10 ENUMERATED {an1, an2, an4, an8}, resourceConfig-r10 INTEGER (0..31), subframeConfig-r10 INTEGER (0..154), p-C-r10 INTEGER (8..15), p-C2 INTEGER (13..15) } } OPTIONAL, -- Need ON zeroTxPowerCSI-RS-r10 ZeroTxPowerCSI-RS-Conf-r12 OPTIONAL -- Need ON } CSI-RS-Config-v1250 ::= SEQUENCE { zeroTxPowerCSI-RS2-r12 ZeroTxPowerCSI-RS-Conf-r12 OPTIONAL, -- Need ON ds-ZeroTxPowerCSI-RS-r12 CHOICE { release NULL, setup SEQUENCE { zeroTxPowerCSI-RS-List-r12 SEQUENCE (SIZE (1..maxDS-ZTP-CSI- RS-r12)) OF ZeroTxPowerCSI-RS-r12 } } OPTIONAL -- Need ON } ZeroTxPowerCSI-RS-Conf-r12 ::= CHOICE { release NULL, setup ZeroTxPowerCSI-RS-r12 } ZeroTxPowerCSI-RS-r12::= SEQUENCE { zeroTxPowerResourceConfigList-r12 BIT STRING (SIZE (16)), zeroTxPowerSubframeConfig-r12 INTEGER (0..154) } -- ASN1STOP
CSI-RS-Config field descriptions will be provided.
ds-ZeroTxPowerCSI-RS

(84) Parameter for additional zeroTxPowerCSI-RS for a serving cell, concerning the CSI-RS included in discovery signals.

(85) zeroTxPowerCSI-RS2

(86) Parameter for additional zeroTxPowerCSI-RS for a serving cell. E-UTRAN configures the field only if csi-MeasSubframeSets-r12 and TM 1-9 are configured for the serving cell.

(87) p-C

(88) Parameter: P.sub.c, see TS 36.213 (See Section 7.2.5).

(89) p-C2

(90) Additional P.sub.c parameter (see Section 7.2.5) only signalled when subframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured and when multiple CQI reports for the purposes of MUST are desired. If signalled, p-C is only used in the first (CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet1) and p-C2 is only used in the second CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet2).

(91) resourceConfig

(92) Parameter: CSI reference signal configuration, see TS 36.211 (See Tables 6.10.5.2-1 and 6.10.5.2-2)

(93) subframeConfig

(94) Parameter: I.sub.CSI-RS, see TS 36.211 (See Tables 6.10.5.3-1).

(95) zeroTxPowerResourceConfigList

(96) Parameter: ZeroPowerCSI-RS, see TS 36.213 (See Section 7.2.7).

(97) zeroTxPowerSubframeConfig

(98) Parameter: I.sub.CSI-RS, see TS 36.211 (See Table 6.10.5.3-1).

(99) The RRC signaling required to support the solution of Embodiment 1 in LTE transmission mode 4, TM4, can be realized in a few different ways. In current LTE, a parameter P.sub.A is signaled by the eNodeB to the UE which is used to define the ratio of the PDSCH EPRE to cell specific RS (CRS) EPRE. In TM4, the UE uses the P.sub.A parameter to determine the reference data transmission power during CSI feedback. Currently, P.sub.A can take on values of {6 dB, 4.77 dB, 3 dB, 1.77 dB, 0 dB, 1 dB, 2 dB, 3 dB}. However, to support the solution of Embodiment 1, the range of P.sub.A should be extended to cover the desired near UE power share {tilde over ()} values in dB. For instance, the range of near UE power share values in Table 1 should be covered. So if additional values of 19.21 dB, 13.19 dB, 12.29 dB, and 6.9867 dB can be added to the list of possible P.sub.A values then all the possible REMA cases in Table 1 should be covered. If this is overkill, a subset of these additional values can be added to the list of possible P.sub.A values so that most of the superposed REMA constellations in Table 1 can be supported.

(100) One alternative is to define a new information element, IE, called MUST-AssistanceInfo as shown in Table 4. This new IE will be part of the dedicated RRC signaling. The IE contains a sequence servCellp-aList of size maxP-a-PerServCell-r13 (containing P.sub.A values) to be signaled when multiple CSI reports for the purposes of MUST are desired. In this alternative, the eNodeB will configure the UE to report Q CSI measurements where Q is equal to maxP-a-PerServCell-r13. Each of the Q CQIs in the CSI reports will correspond to one of Pa values contained in servCellp-aList. Thus, with this alternative, Embodiment 1 can be realized in LTE TM4 with a flexibly configurable number Q of CSI reports.

(101) In another alternative, the size of servCellp-aList in Table 4 can be set to 2 If subframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured (i.e., csi-SubframePatternConfig is configured), then the first P.sub.A value in servCellp-aList is only used in the first CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet1) and the second P.sub.A value in servCellp-aList is only used in the second CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet2). This way the eNodeB can configure a near UE in TM4 to send one OMA CSI report on the first CSI-MeasSubframeSet and one MUST CSI report on the second CSI-MeasSubframeSet. Hence, with this RRC signaling approach, the solution of Embodiment 1 can be supported in LTE TM4 with Q=2.

(102) TABLE-US-00004 TABLE 4 MUST-AssistanceInfo information element MUST-AssistanceInfo-r13 ::= CHOICE { release NULL, setup SEQUENCE { servCellp-aList-r13 SEQUENCE (SIZE (1..maxP-a-PerServCell-r13)) OF P-a OPTIONAL -- Need ON } } P-a ::- ENUMERATED { dB-13dot19, dB-6, dB-4dot77, dB-3, dB-1dot77, dB0, dB1, dB2, dB3}
MUST-AssitanceInfo field descriptions are defined as the following.
P-a

(103) Parameter: P.sub.A, see TS 36.213 (see Section 5.2). Value dB-6 corresponds to 6 dB, dB-4dot77 corresponds to 4.77 dB etc.

(104) servCellp-aList

(105) Indicates the list of P.sub.A parameters to be only signalled when multiple CSI reports for the purposes of MUST are desired.

Embodiment 2

(106) In this embodiment, the eNodeB generally configures the UE(s) to send multiple CSIs for the purposes of MUST wherein each of several CQIs among the CSI reports corresponds to different rank restrictions. If the eNodeB is equipped with N.sub.Tx transmit antennas and each UE has N.sub.Rx receive antennas, then the maximum transmission rank possible is given by
R.sub.max=min(N.sub.Tx,N.sub.Rx). Equation 16

(107) Hence, in this embodiment, the eNodeB may configure the UE to report R.sub.max CQIs. For instance, when R.sub.max=2, the UE will report 2 CQIs where the first CQI will be restricted to rank 1 and the second CQI will be restricted to rank 2. The UE will assume full data transmission power is allocated to the UE when calculating CSI feedback. Furthermore, the eNodeB can easily determine the OMA CSI by choosing the CSI report with the CQI that provides the best instantaneous throughput among the R.sub.max CSI reports. To reduce uplink feedback overhead, the eNodeB may configure only the near UE(s) to send multiple CQI reports for the purposes of MUST, the far UE(s) may be configured to send only a single OMA CSI report. The eNodeB may use RSRP reports and/or uplink pathloss measurements to distinguish between the near and far UEs. The steps involved in this embodiment are summarized below. Although these steps are described using one near UE and one far UE, the solution proposed in this embodiment is applicable to a plurality of near and far UEs.

(108) Step 1:

(109) The eNodeB configures a near UE UE.sub.1 to send R.sub.max>1 CSI reports. The r.sup.th CSI report with CQI.sub.UE1.sup.r of UE.sub.1 is restricted to rank r where 1rR.sub.max. Additionally, the eNodeB configures a far UE UE.sub.2 to send a single OMA CSI report that contains a CQI denoted by CQI.sub.UE2.

(110) Step 2:

(111) UE.sub.1 sends the R.sub.max CSI reports to the eNodeB. Similarly, UE.sub.2 sends the OMA CSI report to the eNodeB. When measuring the R.sub.max CSIs, UE.sub.1 will assume full data transmission power is allocated to itself.

(112) Step 3:

(113) For each scheduling band, the eNodeB scheduler first determines the OMA CSI (containing a CQI denoted by CQI.sub.UE1) corresponding to UE.sub.1. This is done by choosing the CQI from the CSI reports that provides the best instantaneous throughput among CQI.sub.UE1.sup.1, CQI.sub.UE1.sup.2, . . . , CQI.sub.UE1.sup.R.sup.max.

(114) Step 4:

(115) For each scheduling band, the eNodeB scheduler checks if CQI.sub.UE1 is sufficiently higher than CQI.sub.UE2. Additionally, the scheduler checks the combination of precoders among these UEs when deciding whether UE.sub.1 and UE.sub.2 can be valid MUST pairs. This is done by comparing the PMI corresponding to CQI.sub.UE2 with the PMIs corresponding to CQI.sub.UE1.sup.1, CQI.sub.UE1.sup.2, . . . , CQI.sub.UE1.sup.R.sup.max. If the PMI of CQI.sub.UE2 matches the PMI of CQI.sub.UE1.sup.r where 1rR.sub.max, then UE.sub.1 and UE.sub.2 can be valid MUST pairs.

(116) Step 5:

(117) If UE.sub.1 and UE.sub.2 are deemed a valid MUST pair, then the eNodeB scheduler can select a near UE power share parameter {tilde over ()}. The parameter {tilde over ()} is selected from a set A of predetermined power share parameter values (i.e., {tilde over ()}A).

(118) Step 6:

(119) For the selected C value, calculate the scheduling SINRs for MUST using SINR.sub.UE.sub.1 and SINR.sub.UE.sub.2, corresponding to CQI reports CQI.sub.UE1.sup.r and CQI.sub.UE2 with the following approximations: UE.sub.1's scheduling SINR for MUST is calculated as
{tilde over ()}SINR.sub.UE1.sup.r Equation 17 UE.sub.2's scheduling SINR for MUST is calculated as

(120) $\begin{array}{cc}\frac{1-\stackrel{~}{}}{\stackrel{~}{}+\frac{1}{{\mathrm{SINR}}_{\mathrm{UE}2}}}& \mathrm{Equation}18\end{array}$

(121) Step 7:

(122) The scheduler then calculates the MUST PF metric corresponding to the MUST UE pair under consideration as

(123) $\begin{array}{cc}\underset{{\mathrm{UE}}_{i}U}{.Math.}\left(\frac{R\left(i|U,\stackrel{~}{}\right)}{L\left(i\right)}\right)& \mathrm{Equation}19\end{array}$

(124) where R(i|U, {tilde over ()}) and L(i) respectively denote the instantaneous throughput and the average throughput of UE.sub.i. In Equation 19, R(i|U, {tilde over ()}) is a function of MUST scheduling SINRs computed in Equation 17-Equation 18, and hence R(i|U, {tilde over ()}) also depends on the power share parameters {tilde over ()}. The candidate user set U contains the MUST UE pair under consideration.

(125) Step 8:

(126) The steps 3-7 are repeated for all valid MUST UE pairs with all rank (i.e., all r) values that yield matching PMIs and all {tilde over ()} values in the set A. Additionally, the OMA PF metrics corresponding to each UE belonging to the serving cell are also calculated using the reported OMA CQIs (i.e., CQI.sub.UE1 and CQI.sub.UE2) as is currently done in LTE.

(127) Step 9:

(128) From Step 8, the scheduler decides whether OMA or MUST should be employed in the current scheduling band depending on which scheme provides the highest PF rate. The UE(s) corresponding to the highest PF metric are scheduled. In case the MUST scheme is scheduled in the scheduling band, the power share parameter {tilde over ()} and the rank value r that yield the highest PF rate are chosen.

(129) It should be noted that since the best CQI corresponding to all possible ranks (i.e., all r) are taken into account in this embodiment, the problems of rank mismatch, CQI mismatch, and PMI mismatch are alleviated. In addition, the solution of Embodiment 2 also supports dynamic switching between OMA and MUST modes. That is, the scheduler in the proposed scheme can more accurately decide whether OMA or MUST should be employed in a given scheduling band depending on which scheme provides the highest PF rate. If very high ranks are unlikely due to the channel conditions, this embodiment can also be used with a rank R<R.sub.max.

(130) The RRC signaling required to support the solution of Embodiment 2 in LTE TM10 can be realized in a few different ways. In current LTE, a parameter codebookSubsetRestriction is signaled by the eNodeB to the UE to indicate the restricted set of precoders to be considered during CSI measurements/feedback. The eNodeB could use this parameter to implement different rank restrictions of Embodiment 2 on different CSI reports.

(131) The existing RRC signaling of the CSI-Process information element is shown in Table 5. With the CSI-Process information element of Table 5, an eNodeB can currently configure a UE to send up to R.sub.max=3 CSI reports each with different rank restrictions. This is because in current LTE it is possible to configure a maximum of 3 CSI-RS processes per UE in TM10 (i.e., the maxCQI-ProcExt-r11 parameter can currently be set to 3, for example). However, if maxCQI-ProcExt-r11 is further increased, it is possible to have more than 3 rank restricted CSI reports (i.e., R.sub.max>3).

(132) Alternatively, if subframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured (i.e. csi-SubframePatternConfig is configured), then the UE can be configured to send two CSI reports per CSI process in the two CSI measurement subframe sets currently supported in LTE. (Note that PTI stands for precoding type indicator.) In each CSI process, two different rank restrictions can be set in the two CSI measurement subframe sets by having two entries in p-C-AndCBSRList-r11 with appropriate codebookSubsetRestriction bit strings. This can be exploited to configure up to R.sub.max=6 CSI reports in LTE TM10 (i.e., 2 CQI reports per CSI process3 CSI processes). Hence, by configuring subframe patterns for CSI reporting, it is possible for the eNodeB to configure a near UE to send up to 6 rank restricted CSI reports.

(133) Yet another alternative is to introduce a new sequence called CBSR-List in the CSI-Process information element. This sequence will contain a configurable number (for instance, say R.sub.max) of entries of type codebookSubsetRestriction. In this alternative, the eNodeB will configure the UE to report R.sub.max CSI measurements from the same CSI process (thus, reducing the CSI-RS overhead from having to use multiple CSI processes). Each of the R.sub.max CSI reports will correspond to a different rank restriction indicated by one of the codebookSubsetRestriction bit strings contained in CBSR-List. Thus, with this alternative, Embodiment 2 can be realized in LTE TM10 with a flexibly configurable number R.sub.max of CSI reports.

(134) TABLE-US-00005 TABLE 5 CSI-Process information elements -- ASN1START CSI-Process-r11 ::= SEQUENCE { csi-ProcessId-r11 CSI-ProcessId-r11, csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11, csi-IM-ConfigId-r11 CSI-IM-ConfigId-r11, p-C-AndCBSRList-r11 SEQUENCE (SIZE (1..2)) OF P-C-AndCBSR-r11, cqi-ReportBothProc-r11 CQI-ReportBothProc-r11 OPTIONAL, -- Need OR cqi-ReportPeriodicProcId-r11 INTEGER (0..maxCQI-ProcExt-r11) OPTIONAL, -- Need OR cqi-ReportAperiodicProc-r11 CQI-ReportAperiodicProc-r11 OPTIONAL, -- Need OR ..., [[alternativeCodebookEnabledFor4TXProc-r12 ENUMERATED {true} OPTIONAL, -- Need ON csi-IM-ConfigIdList-r12 CHOICE { release NULL, setup SEQUENCE (SIZE (1..2)) OF CSI-IM-ConfigId- r12 } OPTIONAL, -- Need ON cqi-ReportAperiodicProc2-r12 CHOICE { release NULL setup CQI-ReportAperiodicProc-r11 } OPTIONAL -- Need ON ]] } P-C-AndCBSR-r11 ::= SEQUENCE { p-C-r11 INTEGER (8..15), codebookSubsetRestriction-r11 BIT STRING } -- ASN1STOP
CSI-Process field descriptions are described above.

(135) The RRC signaling required to support the solution of Embodiment 2 in LTE TM4 and TM9 can be realized in a few different ways. One alternative is to define a new IE called MUST-AssistanceInfo as shown in Table 6. This new IE will be part of the dedicated RRC signaling. The IE contains a sequence CBSRList of size maxCBSR-r13 (containing codebookSubsetRestriction values) to be signaled when multiple CSI reports for the purposes of MUST are desired. In this alternative, the eNodeB will configure the UE to report R.sub.max CSI measurements where R.sub.max is equal to maxCBSR-r13. Each of the R.sub.max CSI reports will correspond to a different rank restriction indicated by one of the codebookSubsetRestriction bit strings contained in CBSRList. Thus, with this alternative, Embodiment 2 can be realized in LTE TM4 and TM9 with a flexibly configurable number R.sub.max of CSI reports.

(136) In another alternative, the size of CBSRList in Table 6 can be set to 2. If subframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured (i.e. csi-SubframePatternConfig is configured), then the rank restriction indicated by the first codebookSubsetRestriction bit string in CBSRList is only used in the first CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet1) and the rank restriction indicated by the second codebookSubsetRestriction bit string in CBSRList is only used in the second CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet2). This way the eNodeB can configure a near UE in TM4 or TM9 to report one rank-1 CQI on the first CSI-MeasSubframeSet and one rank-2 CQI on the second CSI-MeasSubframeSet. Hence, with this RRC signaling approach, the solution of Embodiment 2 can be supported in LTE TM4 and TM9 with R.sub.max=2.

(137) TABLE-US-00006 TABLE 6 MUST-AssistanceInfo information element MUST-AssistanceInfo-r13 ::= CHOICE { release NULL, setup SEQUENCE { CBSRList-r13 SEQUENCE (SIZE(1..maxCBSR-r13)) OF codebookSubsetRestriction OPTIONAL -- Need ON } } codebookSubsetRestriction BIT STRING OPTIONAL
MUST-AssistanceInfo field descriptions are described as follows.
codebookSubsetRestriction Parameter: codebookSubsetRestriction, see TS 36.213 (see Section 7.2) and TS 36.211 (see Section 6.3.4.2.3). The number of bits in the codebookSubsetRestriction for applicable transmission modes is defined in TS 36.213 (see Table 7.2-1b). If the UE is configured with transmission lode tm8, E-UTRAN configures the field codebookSubsetRestriction if PMI/RI reporting is configured. If the UE is configured with transmissionMode tm9, E-UTRAN configures the field codebookSubsetRestriction if PMI/RI reporting is configured and if the number of CSI-RS ports is greater than 1. E-UTRAN does not configure the field codebookSubsetRestriction in other cases where the UE is configured with transmissionMode tm8 or tm9.
servCellp-aList Indicates the list of codebookSubsetRestriction parameters to be only signalled when multiple CSI reports for the purposes of MUST are desired.

(138) In some cases, it may be desirable to configure the UE so that it provides a mixed-rank CSI in addition to one or more rank-restricted CSIs, particularly when the maximum supportable rank is high. For instance, if there are there three CST processes and up to four ranks, then the UE might be configured, using the above techniques, to report a rank-1 CSI for the first CSI process, a rank-2 CSI for the second CSI process, and a joint rank3-rank4 restriction on the third process (meaning that the third CSI process can consider both rank-3 and rank-4). This way embodiment 2 can be supported for higher rank cases without increasing the number of CSI processes.

Embodiment 3

(139) In this embodiment, the eNodeB configures the UE(s) to send Z>1 CSI reports for the purposes of MUST wherein the z.sup.th CSI report contains the z.sup.th best CQI (the corresponding PMI and RI are also included in the report). The UE will assume full data transmission power is allocated to the UE during CSI measurement corresponding to all CSI reports. To reduce uplink feedback overhead, the eNodeB may configure only the near UE(s) to send multiple CSI reports for the purposes of MUST; the far UE(s) may be configured to send only a single OMA CSI report. The eNodeB may use RSRP reports and/or uplink pathloss measurements to distinguish between the near and far UEs The steps involved in this embodiment are summarized below. Although these steps are described using one near UE and one far UE, the solution proposed in this embodiment is applicable to a plurality of near and far UEs.

(140) Step 1:

(141) The eNodeB configures a near UE UE.sub.1 to send Z>1 CSI reports. One of the CQIs in the reports denoted by CQI.sub.UE1.sup.0 corresponds to the OMA CQI (i.e., the best CQI). The remaining Z1 CQIs in the reports are denoted by CQI.sub.UE1.sup.1, CQI.sub.UE1.sup.2, . . . , CQI.sub.UE1.sup.Z1, where the z.sup.th CSI report with CQI.sub.UE1.sup.z contains the z.sup.th best CQI. Additionally, the eNodeB configures a far UE UE.sub.2 to report a single OMA CSI report that contains a CQI that is denoted by CQI.sub.UE2.sup.0.

(142) Step 2:

(143) UE.sub.1 sends the Z CSI reports to the eNodeB. Similarly, UE.sub.2 sends the OMA CSI report to the eNodeB. When measuring the Z CSIs, UE.sub.1 will assume full data transmission power is allocated to itself.

(144) Step 3:

(145) For each scheduling band, the eNodeB scheduler first checks if CQI.sub.UE1.sup.0 is sufficiently higher than CQI.sub.UE2.sup.0. Additionally, the scheduler checks the combination of precoders among these UEs when deciding whether UE.sub.1 and UE.sub.2 can be valid MUST pairs. This is done by comparing the PMI corresponding to CQI.sub.UE2.sup.0 with the PMIs corresponding to CQI.sub.UE1.sup.0, CQI.sub.UE1.sup.2, . . . , CQI.sub.UE1.sup.Z1. If the PMI of CQI.sub.UE2.sup.0 matches the PMI of CQI.sub.UE1.sup.z where 0z(Z1), then UE.sub.1 and UE.sub.2 can be valid MUST pairs.

(146) Step 4:

(147) If UE.sub.1 and UE.sub.2 are deemed a valid MUST pair, then the eNodeB scheduler can select a near UE power share parameter {tilde over ()}. The parameter {tilde over ()} is selected from a set A of predetermined power share parameter values (i.e., {tilde over ()}A).

(148) Step 5:

(149) For the selected {tilde over ()} value, calculate the scheduling SINRs for MUST using SINR.sub.UE.sub.1 and SINR.sub.UE.sub.2, corresponding to CQI reports CQI.sub.UE1.sup.z and CQI.sub.UE2.sup.0 with the following approximations: UE.sub.1's scheduling SINR for MUST is calculated as
{tilde over ()}SINR.sub.UE1.sup.z Equation 20 UE.sub.2's scheduling SINR for MUST is calculated as

(150) $\begin{array}{cc}\frac{1-\stackrel{~}{}}{\stackrel{~}{}+\frac{1}{{\mathrm{SINR}}_{\mathrm{UE}2}^0}}& \mathrm{Equation}21\end{array}$

(151) Step 6:

(152) The scheduler then calculates the MUST PF metric corresponding to the MUST UE pair under consideration as

(153) $\begin{array}{cc}\underset{{\mathrm{UE}}_{i}U}{.Math.}\left(\frac{R\left(i|U,\stackrel{~}{}\right)}{L\left(i\right)}\right)& \mathrm{Equation}22\end{array}$

(154) where R(i|U, {tilde over ()}) and L(i) respectively denote the instantaneous throughput and the average throughput of UE.sub.i. In Equation 22, R(i|U, {tilde over ()}) is a function of MUST scheduling SINRs computed in Equation 20-Equation 21, and hence R(i|U, {tilde over ()}) also depends on the power share parameter {tilde over ()}. The candidate user set U contains the MUST UE pair under consideration.

(155) Step 7:

(156) The steps 3-6 are repeated for all valid MUST UE pairs with all possible z values that yield matching PMIs and all {tilde over ()} values in the set A. Additionally, the OMA PF metrics corresponding to each UE belonging to the serving cell are also calculated using the reported OMA CQIs (i.e., CQI.sub.UE1.sup.0 and CQI.sub.UE2.sup.0) as is currently done in LTE.

(157) Step 8:

(158) From Step 7, the scheduler decides whether OMA or MUST should be employed in the current scheduling band depending on which scheme provides the highest PF rate. The UE(s) corresponding to the highest PF metric are scheduled. In case the MUST scheme is scheduled in the scheduling band, the power share parameter {tilde over ()} and the z value that yield the highest PF rate are chosen.

(159) It should be noted that since Z best CQIs corresponding to the near UE are taken into account in this embodiment, the problems of rank mismatch, CQI mismatch, and PMI mismatch are alleviated. In addition, the solution of Embodiment 3 also supports dynamic switching between OMA and MUST modes. That is, the scheduler in the proposed scheme can more accurately decide whether OMA or MUST should be employed in a given scheduling band depending on which scheme provides the highest PF rate.

(160) Aperiodic CSI Feedback for MUST Transmission

(161) Reporting multiple RI/PMI/CQIs periodically for a UE means increased uplink feedback overhead. One solution to reduce the feedback overhead is to only feedback/report the multiple configured RI/PMI/CQI when requested. In other words, a UE only reports multiple RI/PMI/CQIs when it is requested by the serving eNodeB or a network node. The request can be dynamically indicated to the UE by the eNodeB. A UE may be configured with one RI/PMI/CQI hypothesis assuming full transmit power (existing LTE CQI configuration) and with additional RI/PMI/CQI hypothesis as discussed in the previous embodiments using RRC signaling. A UE only report a new RI/PMI/CQI based on one of the additional hypothesis when requested by the eNodeB as shown in FIG. 6. The request can be triggered in a subframe by subframe basis. For example, when a potential UE pair is identified for MUST transmission, the eNodeB may send a request to the near UE for a CQI report based on a reduced transmit power to get better CQI (and/or RI) estimation for MUST transmission.

(162) Since the CQI mismatch during MUST scheduling mainly occurs to near UEs with large transmit power reduction (i.e., the UEs that feedback higher rank CSI when assuming full transmit power allocation), the requests from the eNodeB may only be sent to near UEs and the feedback may be restricted to rank 1 PMI/CQI reports.

(163) FIG. 7 illustrates a diagram of a radio access network node 30, such as a base station or a base station operating in coordination with a base station controller, according to some embodiments. The radio access network node 30 includes one or more communication interface circuits 38 in order to communicate with network nodes or peer nodes. The radio access network node 30 provides an air interface to wireless devices, which is implemented via one or more antennas 34 and a transceiver circuit 36. The transceiver circuit 36 may include transmitter circuits, receiver circuits, and associated control circuits that are collectively configured to transmit and receive signals according to a radio access technology for the purposes of providing communication services. According to various embodiments, the radio access network node 30 can communicate with one or more peer nodes or core network nodes. The transceiver circuit 36 is configured to communicate using cellular communication services operated according to wireless communication standards (e.g. Global System for Mobile communication (GSM), General Packet Radio Services (GPRS), Wideband Code Division Multiple Access (WCDMA), High Speed Downlink Packet Access (HSDPA), LTE and LTE-Advanced).

(164) The radio access network node 30 also includes one or more processing circuits 32 that are operatively associated with the communication interface circuit(s) 38 and/or the transceiver circuit 36. The processing circuit 32 comprises one or more digital processors 42, e.g., one or more microprocessors, microcontrollers, Digital Signal Processors or DSPs, Field Programmable Gate Arrays or FPGAs, Complex Programmable Logic Devices or CPLDs, Application Specific Integrated Circuits or ASICs, or any combination thereof. More generally, the processing circuit 32 may comprise fixed circuitry, or programmable circuitry that is specially configured via the execution of program instructions implementing the functionality taught herein, or may comprise some combination of fixed and programmable circuitry. The processor(s) 42 may be multi-core.

(165) The processing circuit 32 also includes a memory 44. The memory 44, in some embodiments, stores one or more computer programs 46 and, optionally, configuration data 48. The memory 44 provides non-transitory storage for the computer program 46 and it may comprise one or more types of computer-readable media, such as disk storage, solid-state memory storage, or any combination thereof. By way of non-limiting example, the memory 44 may comprise any one or more of Static Random-Access Memory (SRAM), Dynamic Random-Access Memory (DRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), and FLASH memory, which may be in the processing circuit 32 and/or separate from the processing circuit 32. In general, the memory 44 comprises one or more types of computer-readable storage media providing non-transitory storage of the computer program 46 and any configuration data 48 used by the node 30.

(166) The radio access network node 30 is configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first UE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The processing circuit 32 is configured to receive multiple CSI reports from the first UE for a first reporting instance, wherein one or more of the received multiple CSI reports correspond to different possible multi-user superposition transmission states. The processing circuit 32 is configured to determine whether to use multi-user superposition transmission or an orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports. Furthermore, the processing circuit 32 is configured to perform any of the operations described in the embodiments above for the radio access network node. This functionality may be represented or carried out by scheduling circuitry 40.

(167) Regardless of the implementation, the processing circuit 32 is configured to perform operations, as described in the above embodiments. For example, the processing circuit 32 is configured to perform method 800 illustrated by the flowchart in FIG. 8. The method 800 operates in a radio access network node 30 configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first LIE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The method 800 includes receiving multiple CSI reports from the first UE for a first reporting instance, wherein one or more of the received multiple CSI reports correspond to different possible multi-user superposition transmission states (block 802). The method 800 also includes determining whether to use multi-user superposition transmission or an orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports (block 804).

(168) In some cases, the first UE is sent scheduling messages or configuration messages, the configuration messages directing the first UE to provide multiple CSI reports for at least the first reporting instance.

(169) A first one of the received multiple CSI reports may include a CQI corresponding to a full-power or substantially full-power data transmission to the first UE. Note that first does not limit the embodiment or the claims to any type of order or sequence of receiving CQI reports.

(170) The radio access network node 30 then determines whether to use multi-user superposition transmission or an orthogonal multiple access transmission. According to some embodiments, this determination is made by obtaining a CSI report from a second UE, the CSI report from the second UE comprising a CQI corresponding to a full-power or substantially full-power data transmission to the second UE, determining that multi-user superposition transmission to the first and second UEs is feasible, in that transmission to both UEs can be performed using the same antennas and antenna precoding and with a power allocation such that the signal can be successfully received and decoded by both UEs.

(171) This feasibility determination is made by determining that said CQI for the first UE is greater than said CQI for the second UE by a predetermined factor or threshold, and determining that a precoder matrix indicator, PMI, corresponding to the CSI report from the second UE matches at least one PMI corresponding to one of the received multiple CSI reports from the first UE other than said first one of the received multiple CST reports.

(172) Obtaining the CSI report from the second UE may include transmitting, in an interference measurement resource, IMR, for the second UE, an interference component corresponding to a potential power share allocated to the first UE in a multi-user superposition transmission to the first and second UEs. The interference component is transmitted using the same antennas and the same antenna preceding intended for the multi-user superposition transmission to the first and second UEs. An antenna preceding is as a mapping of one or more signals to multiple antennas, according to preceding weights. Obtaining the CSI report may further include receiving, from the second UE, the CQI corresponding to a full-power or substantially full-power data transmission to the second UE, wherein said CQI reflects the interference component transmitted in the IMR for the second UE.

(173) The multiple CSI reports may correspond to different power-sharing hypotheses for multi-user superposition transmission to the first UE, and/or different ranks for data transmission to the first UE. Likewise, configuration messages may indicate different power-sharing hypotheses, and/or a number of CQIs to be reported by the first UE, each CQI corresponding to a different rank for data transmission to the first UE. In further instances, the configuration messages may signal, for each desired CSI report, a corresponding transmission rank by indicating a set of precoders that are restricted to the corresponding transmission rank. Restricted precoders can mean that a precoder is for use with only one rank. Thus, if three indicated precoders are all rank-1 precoders, then it can be inferred by the UE that a CSI is wanted that is specific to rank 1. Likewise, if three indicated precoders are all rank-2 precoders, then the UE knows that a CSI specific to rank 2 is desired.

(174) In some cases, it may be desirable to configure the UE so that it provides a mixed-rank CSI in addition to one or more rank-restricted CSIs, particularly when the maximum supportable rank is high. For instance, if there are there three CSI processes and up to four ranks, then the UE might be configured, using the above techniques, to report a rank-1 CSI for the first CSI process, a rank-2 CSI for the second CSI process, and a joint rank3-rank4 restriction on the third process.

(175) In some embodiments, the multiple CSI reports from the first UE may also include N CSI reports, the N CSI reports comprising the N best channel quality indicators, CQIs, and wherein each of the N CSI reports includes a corresponding precoding matrix indicator, PMI, and rank indicator, RI. In some cases, signaling may indicate whether one or more of the CSI reports are for Coordinated MultiPoint, CoMP, transmissions and/or MUST transmissions.

(176) FIG. 9 illustrates a diagram of a wireless device, such as UE 50, according to some embodiments. To ease explanation, the user equipment 50 may also be considered to represent any wireless devices that may operate in a network. The UE 50 herein can be any type of wireless device capable of communicating with a network node or another UE over radio signals. The UE 50 may also be radio communication device, target device, device to device-(D2D), UE, machine type UE or UE capable of machine to machine communication (M2M), a sensor equipped with UE, personal digital assistant (PDA), Tablet, mobile terminal, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), Universal Serial Bus (USB) dongles, Customer Premises Equipment (CPE), etc.

(177) The UE 50 communicates with a radio node or base station, such as the radio access network node 30, via antennas 54 and a transceiver circuit 56. The transceiver circuit 56 may include transmitter circuits, receiver circuits, and associated control circuits that are collectively configured to transmit and receive signals according to a radio access technology, for the purposes of providing cellular communication services.

(178) The UE 50 also includes one or more processing circuits 52 that are operatively associated with the transceiver circuit 56. The processing circuit 52 comprises one or more digital processing circuits, e.g., one or more microprocessors, microcontrollers, Digital Signal Processors or DSPs, Field Programmable Gate Arrays or FPGAs, Complex Programmable Logic Devices or CPLDs, Application Specific Integrated Circuits or ASICs, or any mix thereof. More generally, the processing circuit 52 may comprise fixed circuitry, or programmable circuitry that is specially adapted via the execution of program instructions implementing the functionality taught herein, or may comprise some mix of fixed and programmed circuitry. The processing circuit 52 may be multi-core.

(179) The processing circuit 52 also includes a memory 64. The memory 64, in some embodiments, stores one or more computer programs 66 and, optionally, configuration data 68. The memory 64 provides non-transitory storage for the computer program 66 and it may comprise one or more types of computer-readable media, such as disk storage, solid-state memory storage, or any mix thereof. By way of non-limiting example, the memory 64 comprises any one or more of SRAM, DRAM, EEPROM, and FLASH memory, which may be in the processing circuit 52 and/or separate from processing circuit 52. In general, the memory 64 comprises one or more types of computer-readable storage media providing non-transitory storage of the computer program 66 and any configuration data 68 used by the user equipment 50.

(180) The UE 50 is configured to perform at least the modulation and demodulation techniques described above. For example, the processor 62 of the processing circuit 52 may execute a computer program 66 stored in the memory 64 that configures the processor 62 to operate as a first UE 50 configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for the first UE 50 and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The processing circuit 52 is configured to send multiple CSI reports for a first reporting instance, wherein one or more of the received multiple CSI reports correspond to different possible multi-user superposition transmission states. Furthermore, the processing circuit 52 is configured to perform any of the operations described in the embodiments above for the UE. Such functionality is represented by or carried out by reporting circuitry 60.

(181) The processing circuit 52 of the UE 50 is configured to perform a method, such as method 1000 of FIG. 10. The method 1000 operates in a first UE, such as the UE 50, that is configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for the first UE 50 and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The method 1000 includes sending multiple CSI reports for a first reporting instance, wherein one or more of the received multiple CSI reports correspond to different possible multi-user superposition transmission states (block 1002).

(182) FIG. 11 illustrates an example functional module or circuit architecture as may be implemented in the radio access network node 30, e.g., based on the scheduling circuitry 40. The illustrated embodiment at least functionally includes a receiving module 1102 for receiving multiple CSI reports from the first UE for a first reporting instance, wherein one or more of the received multiple CST reports correspond to different possible multi-user superposition transmission states. The implementation also includes a determining module 1104 for determining whether to use multi-user superposition transmission or an orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports.

(183) The scheduling circuitry 40 also includes a configuration module 1106 for sending one or more configuration messages, via the transceiver circuit 36, to the first UE. In some embodiments, the one or more configuration messages direct the first UE to provide multiple CSI reports for at least the first reporting instance such that one or more of the multiple CSI reports correspond to different possible multi-user superposition transmission states for a transmission to the first UE. The scheduling circuitry still further includes a scheduling module 1108 for scheduling the first UE, based on the determination of whether to use multi-user superposition transmission or an orthogonal multiple access transmission. The scheduling module 1108 thus sends a scheduling message, via the transceiver circuit 36, to the first UE.

(184) FIG. 12 illustrates an example functional module or circuit architecture as may be implemented in UE 50, e.g., based on the reporting circuitry 60. The illustrated embodiment at least functionally includes a sending module 1202 for sending multiple CSI reports for a first reporting instance, wherein one or more of the received multiple CSI reports correspond to different possible multi-user superposition transmission states. The illustrated embodiment further comprises a configuration module 1204, which in some embodiments is for receiving one or more configuration messages, the one or more configuration messages directing the first UE to provide multiple CST reports for at least the first reporting instance such that one or more of the multiple CSI reports correspond to different possible multi-user superposition transmission states for a transmission to the first UE. The illustrated embodiment still further comprise a receiving module 1206 for receiving a scheduling message based on the sent multiple CSI reports, the scheduling message scheduling a multi-user superposition transmission to the first UE.

(185) As described in detail above, multiple CSI reports are used in various embodiments of the disclosed techniques and apparatus for identifying valid MUST pairs, calculating near UE's MUST scheduling SINR, and computing the MUST proportional fair scheduling metrics. As a result, the problems of rank mismatch, CQI mismatch, and PMI mismatch are alleviated in this solution. In addition, the proposed solution also supports dynamic switching between OMA and MUST modes. Additionally, some embodiments of the proposed solution can be implemented in an LTE standard transparent manner.

(186) In additional or alternative embodiments, a single CSI report is also conceivable, for example in form of a method, in a radio access network node configured to support the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first user equipment, UE, and a second modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The method comprises receiving a CSI report from the first UE, wherein the received CSI report assumes a transmission power for a physical channel, the transmission power being lower than a minimum transmission power that is assumed when multi-user superposition transmission is not used.

(187) FIG. 13 illustrates a process flow 1300 according to this additional or alternative embodiment. As shown at block 1304, the illustrated method comprises receiving a CSI report from the first UE, the received CSI report being based on an assumption that a transmission power for a physical channel is lower than a minimum transmission power that is assumed when multi-user superposition transmission is not used. As shown at block 1306, the method further comprises transmitting a multi-user superposition transmission to the UE, where the transmitting is based on the received CSI report. As discussed above, CSI reporting according to the techniques described herein may be facilitated by providing for an extended range for one or more parameters provided to the UE in configuration messages, where the range is extended compared to conventional signaling ranges. Thus, some embodiments of the method shown in FIG. 13 comprise configuring the UE to send the CSI report, where said configuring comprises signaling a selected parameter indicating a ratio of a PDSCH energy per resource element to a CSI reference symbol (CSI-RS) energy per resource element, wherein the selected parameter is selected from a range having a minimum value corresponding to a ratio below 8 dB, e.g., somewhere between 8 dB and 19 dB, such as 13 dB. Alternatively or additionally, the configuring may comprise signaling a selected parameter indicating a ratio of a PDSCH energy per resource element to a cell-specific reference symbol (CRS) energy per resource element, where the selected parameter is selected from an extended range having a minimum value corresponding to a ratio below 6 dB, e.g., corresponding to a ratio of about 19.21 dB. This configuration step is illustrated at block 1302 of FIG. 13.

(188) It will be appreciated that the method shown in FIG. 13 may be carried out by the radio access network node 30 illustrated in FIGS. 7 and 11, for example, and more specifically using at least the transceiver circuit 36, receiving module 1102, and configuration module 1106.

(189) FIG. 14 illustrates a corresponding method 1400 as implemented in a UE configured to support the transmission of multi-user superposition transmissions. As shown at block 1402, the illustrated method comprises receiving one or more configuration messages from a radio access network node, the one or more configuration messages directing the UE to transmit a CSI report. These one or more configuration messages comprise at least one of (a) a selected parameter indicating a ratio of a PDSCH energy per resource element to a CSI-RS energy per resource element, where the selected parameter is selected from a range having a minimum value corresponding to a ratio below 8 dB, such as somewhere between 8 dB and 19 dB or (b) a selected parameter indicating a ratio of a PDSCH energy per resource element to a CRS energy per resource element, where the selected parameter is selected from an extended range having a minimum value corresponding to a ratio below 6 dB, e.g., about 19.2 dB.

(190) The illustrated method further comprises transmitting a CSI report, in accordance with the one or more configuration messages, as shown at block 1404, and receiving a multi-user superposition transmission from the radio access network node, as shown at block 1406. Once again, it will be appreciated that the method shown in FIG. 14 may be carried out by the UE 50 illustrated in FIGS. 9 and 12, for example, and more specifically using at least the transceiver circuit 56, receiving module 1206, and configuration module 1204.

(191) Notably, modifications and other embodiments of the disclosed invention(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention(s) is/are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.