Methods and arrangements for CSI reporting

Abstract

A method in a wireless device for reporting Channel State Information (CSI). The wireless device is comprised in a wireless communications system. The method includes receiving a CSI process configuration and a request for CSI information from a network node. The method further includes reporting CSI for one or more CSI processes. The CSI reflects the state of the channel for a CSI reference resource. According to the method, the CSI reference resource is determined based on the number of configured CSI processes. Related devices are also disclosed.

Claims

1. A method, in a wireless device, for reporting Channel State Information (CSI), the wireless device being comprised in a wireless communications system, the method comprising: receiving a CSI process configuration and a request for CSI from a network node; determining a CSI reference resource based on a numerical indicator indicating a total number of configured CSI processes; and reporting CSI for one or more CSI processes, wherein the CSI reflects a state of a channel for the CSI reference resource; wherein determining the CSI reference resource comprises determining, as a function of how many CSI processes are configured for the wireless device, a location of the CSI reference resource.

2. The method of claim 1, wherein the determining the CSI reference resource comprises determining the CSI reference resource further based on a total number of configured CSI-RS resources configured for the wireless device.

3. The method of claim 1, further comprising: prioritizing a first CSI process over a second CSI process; determining a rank indicator and/or a precoding matrix indicator for the first CSI process; and reusing the determined rank indicator and/or precoding matrix indicator for the second CSI process.

4. The method of claim 1, further comprising: performing measurements on reference signal resources corresponding to the configured CSI processes; and determining the CSI based on the measurements.

5. The method of claim 1, wherein the CSI is determined based on measurements performed in and/or prior to the CSI reference resource.

6. The method of claim 1, wherein the request for CSI is a request for a periodic CSI report.

7. The method of claim 1, wherein the request for CSI is a request for an aperiodic CSI report.

8. The method of claim 1, further comprising: performing measurements on interference measurement resources corresponding to the configured CSI processes; and determining the CSI based on the measurements.

9. The method of claim 1, wherein each CSI process corresponds to a reference signal resource and an interference measurement resource.

10. A wireless device for reporting Channel State Information (CSI), the wireless device comprising: memory comprising instructions; and processing circuitry operatively connected to the memory and configured, when executing the instructions, to cause the wireless device to: receive, from a network node, a CSI process configuration and a request for CSI; determine a CSI reference resource based on a numerical indicator indicating a total number of configured CSI processes; and report CSI for one or more CSI processes, wherein the CSI reflects a state of a channel for the CSI reference resource; wherein determining the CSI reference resource comprises determining, as a function of how many CSI processes are configured for the wireless device, a location of the CSI reference resource.

11. The wireless device of claim 10, wherein the wireless device is a user equipment.

12. The wireless device of claim 10, wherein the processing circuitry, when executing the instructions, is further configured to determine the CSI reference resource further based on a total number of configured CSI-RS resources configured for the wireless device.

13. The wireless device of claim 10, wherein the processing circuitry, when executing the instructions, is further configured to: prioritize a first CSI process over a second CSI process; determine a rank indicator and/or a precoding matrix indicator for the first CSI process; and reuse the determined rank indicator and/or precoding matrix indicator for the second CSI process.

14. The wireless device of claim 10, wherein the processing circuitry, when executing the instructions, is further configured to: perform measurements on reference signal resources corresponding to the configured CSI processes; and determine the CSI based on the measurements.

15. The wireless device of claim 10, wherein the processing circuitry, when executing the instructions, is further configured to determine the CSI based on measurements performed in and/or prior to the CSI reference resource.

16. The wireless device of claim 10, wherein the processing circuitry, when executing the instructions, is further configured to: perform measurements on interference measurement resources corresponding to the configured CSI processes; and determine the CSI based on the measurements.

17. A computer program product stored on a non-transitory, computer readable medium and comprising program instructions, which when executed by at least one processor, causes the at least one processor to: receive, from a network node, a CSI process configuration and a request for CSI; determine a CSI reference resource based on a numerical indicator indicating a total number of configured CSI processes; and report CSI for one or more CSI processes, wherein the CSI reflects a state of a channel for the CSI reference resource; wherein determining the CSI reference resource comprises determining, as a function of how many CSI processes are configured for the wireless device, a location of the CSI reference resource.

18. The wireless device of claim 10, wherein the processing circuitry is operatively connected to the memory and is configured, when executing the instructions, to cause the wireless device to determine, as a function of how many CSI processes are configured for the wireless device, a location of the CSI reference resource.

19. The method of claim 1, wherein the reporting CSI comprises transmitting the CSI report in a given subframe; and wherein the determining a CSI reference resource comprises determining, based on the numerical indicator indicating a total number of configured CSI processes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments will now be described in more detail in relation to the enclosed drawings, in which:

(2) FIG. 1 is a diagram of a time frequency grid of resource elements.

(3) FIG. 2 is a block diagram of precoded spatial multiplexing.

(4) FIG. 3 is a diagram of resource elements in a downlink subframe.

(5) FIG. 4 is a diagram of resource element patterns.

(6) FIG. 5 is a diagram of a wireless communication system in accordance with one or more embodiments.

(7) FIG. 6 is a signalling diagram of channel state information (CSI) reporting.

(8) FIG. 7 is a signalling diagram of CSI reporting in accordance with one or more embodiments.

(9) FIG. 8 is a signalling diagram of CSI reporting in accordance with one or more embodiments.

(10) FIG. 8a is a signalling diagram of CSI reporting in accordance with one or more embodiments.

(11) FIG. 8b is a signalling diagram of CSI reporting in accordance with one or more embodiments.

(12) FIG. 8c is a flowchart of a method in a wireless device of reporting CSI in accordance with one or more embodiments.

(13) FIG. 8d is a flowchart of a method in a wireless device of reporting CSI in accordance with one or more embodiments.

(14) FIG. 8e is a flowchart of a method in a network node of performing link adaptation and/or scheduling based on received CSI in accordance with one or more embodiments.

(15) FIG. 8f is a flowchart of a method in a network node of performing link adaptation and/or scheduling based on received CSI in accordance with one or more embodiments.

(16) FIG. 9 is a signalling diagram between a network node and a wireless device of one or more embodiments.

(17) FIG. 10 is a flowchart of a method in a wireless device of transmitting CSI in accordance with one or more embodiments.

(18) FIG. 11 is a flowchart of a method in a wireless device of transmitting CSI in accordance with one or more embodiments.

(19) FIG. 12 is a flowchart of a method in a wireless device of transmitting CSI in accordance with one or more embodiments.

(20) FIG. 13 is a flowchart of a method in a network node in accordance with one or more embodiments related to transmitting a CSI request.

(21) FIG. 14 is a block diagram illustrating a network node in accordance with one or more embodiments.

(22) FIG. 15 is a block diagram illustrating a wireless device in accordance with one or more embodiments.

(23) FIG. 16 is a flowchart of a method in a wireless device of reporting CSI in accordance with one or more embodiments.

DETAILED DESCRIPTION

(24) A typical processing in a UE involved for determining a CSI report for a specific CSI process can be divided as:

(25) 1) Receiving at least one reference signal that defines a desired effective channel for said specific CSI process.

(26) 2) Receiving interference and noise on a specific interference measurement resource (IMR) associated with said specific CSI process.

(27) 3) Estimating/determining a desired effective channel from said received at least one reference signal.

(28) 4) Estimating a received interference and noise covariance, or level, from said received interference and noise

(29) 5) Assessing the performance of each transmission rank and precoder in a codebook

(30) 6) Selecting the PMI and RI corresponding to the highest performance (typically the PMI and RI combination that results in the highest throughput without exceeding a target BLER or 10%)

(31) 7) Determining a CQI (or multiple in case of rank >1) for the selected PMI/RI, involving selecting the highest CQI (recommended transport block size) that does not exceed a target BLER of 10%.

(32) Each of these steps involves a non-negligible processing load in a typical UE implementation. In particular steps 5) to 7) above involves substantial processing. Moreover, these demanding steps cannot be performed prior to steps 1) through 4).

(33) The UE is required to process CSI within a certain time frame after receiving a specific reference signal, or performing a specific interference measurement. This requirement may be encoded into a standard, e.g. the standard may mandate that the UE must be capable to report CSI a certain number of subframes (e.g. 4 subframes) after the subframe wherein the corresponding CSI-RS is transmitted. It should be noted that according to the prior art, this timing requirement is static and the same timing requirement applies to all UEs and all CSI reports. For example, in 3GPP LTE the processing time frame is determined by the so-called CSI reference resource with occurs 4 subframes prior to the time frame in which the CSI report is transmitted (or the first valid downlink subframe prior to this instance). Strictly speaking the CSI reference resource specifies, or is defined by <, a specific subframe for which the CSI report should accurately reflect the state of the channel; this implies that the UE should base the CSI report on the reference signals and interference and noise received within this subframe and prior to this subframe. See also FIG. 8a.

(34) In a scenario where the UE is configured with multiple CSI processes, it is possible that some or all of the corresponding reference signal resources and IMRs occur in the same subframe, in which case it may become difficult for the UE to determine all the required CSI information within the specified time frame.

(35) From a UE processing budget perspective, the worst case scenario is that all IMRs and all reference signals associated with a plurality of CSI processes all occur in a single subframe, because then all CSI processes must be computed simultaneously. Such a scenario could occur e.g. if all zero-power CSI-RS configured for a UE would share the same subframe offset and periodicity configuration, since this would imply that muting could only be configured for a single subframe within a period. Since the transmission of a CSI-RS should typically be matched by a corresponding muting in neighboring transmission points (to boost the SINR on the received CSI-RS signals), the transmission of a CSI-RS would in practice be confined to the same subframe as the muting configurations. Hence, it is quite possible that the worst-case scenario could occur in practice.

(36) Such a situation is illustrated in FIG. 6, where the UE is required to finalize the CSI processing during a predetermined processing time after the reception (steps 1 and 2 above), so that reporting after the processing time will contain updated reports. Designing a UE to manage this worst case scenario may lead to very high implementation cost. This problem becomes particularly severe if large CoMP Measurement Set sizes are supported in the standard, and/or if a large number of parallel CSI processes are supported by the standard.

(37) Thus, a possible solution to the problems described above would be to limit the size of the CoMP measurement set and/or the number of parallel CSI processes. This would reduce the processing requirements on the UE, but on the other hand means that the potential benefits of CoMP cannot be fully exploited.

(38) A basic concept of some embodiments is therefore to reduce the peak processing requirement of a wireless device for CSI reporting by introducing a processing time window, also referred to as a maximum CSI processing time, which may either device-specific or CSI-process-specific. The maximum processing time may be expressed e.g. in subframes or milliseconds. The length of the time window may e.g. be dependent on the total number of CSI processes, or the number of CSI-RS resources, configured for the wireless device. For example, a CSI reference resource may depend on the number of configured CSI-RS resources or number of CSI processes.

(39) FIG. 5 illustrates an example wireless communications system 500 in which various embodiments of the invention may be implemented. The three transmission points 510, 520 and 530 form a CoMP coordination cluster. In the following, for purposes of illustration and not limitation, it will be assumed that the communications system 500 is an LTE system. Transmission points 510, 520 and 530 are remote radio units (RRU), controlled by eNodeB 560. In an alternative scenario (not shown), the transmission points could be controlled by separate eNodeBs. It should be appreciated that, generally speaking, each network node, e.g. eNodeB, may control one or more transmission points, which may either be physically co-located with the network node, or geographically distributed. In the scenario shown in FIG. 5, it is assumed that the transmission points 510, 520 and 530 are connected to eNodeB 560, e.g. by optical cable or a point-to-point microwave connection. In the case where some or all of the transmission point forming the cluster are controlled by different eNodeBs, those eNodeBs would be assumed to be connected with each other e.g. by means of a transport network, to be able to exchange information for possible coordination of transmission and reception.

(40) It should be appreciated that although examples herein refer to an eNodeB for purposes of illustration, the invention applies to any network node. The expression “network node” as used in this disclosure is intended to encompass any radio base station, e.g. an eNodeB, NodeB, Home eNodeB or Home NodeB, or any other type of network node that controls all or part of a CoMP cluster.

(41) The communications system 500 further comprises two wireless devices 540 and 550. Within the context of this disclosure, the term “wireless device” encompasses any type of wireless node which is able to communicate with a network node, such as a base station, or with another wireless device by transmitting and/or receiving wireless signals. Thus, the term “wireless device” encompasses, but is not limited to: a user equipment, a mobile terminal, a stationary or mobile wireless device for machine-to-machine communication, an integrated or embedded wireless card, an externally plugged in wireless card, a dongle etc. The wireless device may also be a network node, e.g. a base station. Throughout this disclosure, whenever the term “user equipment” is used this should not be construed as limiting, but should be understood as encompassing any wireless device as defined above.

(42) In some embodiments (see FIG. 8c), a wireless device reports CSI for a CSI process.

(43) The wireless device receives CSI process configuration, and a CSI request, from a network node.

(44) The wireless device performs measurements on CSI-RS resources and interference measurement resources corresponding to the configured CSI processes. When a measurement is performed in a certain subframe, the wireless device will begin processing the received information for the purpose of determining channel state information for the corresponding CSI process. However, as mentioned above, this processing will take a certain amount of time to complete. It should be noted that a particular interference measurement resource may be shared by multiple CSI processes, in which case the interference measurement only has to be performed once in a particular subframe.

(45) Similarly, the desired signal reference signal resource may be shared by multiple CSI processes, in which case the associated channel estimation only need to be performed once in a particular subframe.

(46) The wireless device subsequently reports CSI for one or more processes, wherein the CSI is determined based on measurements performed in and/or or prior to a CSI reference resource. The wireless device determines the CSI reference resource depending on one or more of: the number of configured CSI-RS resources, the number of configured CSI processes, or the number of configured CSI-RS resources that occur in the same subframe.

(47) For instance, the wireless device may determine a number n.sub.CQI_ref based on the number of configured CSI-RS resources, and/or based on the number of configured CSI processes, where n.sub.CQI_ref represents the location of the CSI reference resource relative to the subframe in which the CSI report is transmitted (as shown in FIG. 8a). In a particular example, n.sub.CQI_ref increases with the number of configured CSI processes. Stated differently, if the number of configured CSI processes increases, n.sub.CQI_ref also increases.

(48) As a specific example, if the number of configured CSI-RS (or number of configured CSI processes) exceeds 2, n.sub.CQI_ref is set to 5, whereas otherwise, n.sub.CQI_ref is set to 4. This accounts for the additional processing time that is required in the wireless device for the larger number of CSI-RS (or CSI processes). Stated differently, if the number of configured CSI-RS (or number of configured CSI processes) exceeds 2, the CSI reference resource is determined to be 5 subframes prior to the subframe when CSI is reported, and otherwise, the CSI reference resource is determined to be 4 subframes prior to the subframe when CSI is reported.

(49) In one variant, the CSI reference resource is specific to the wireless device. For example, the wireless device determines one number n.sub.CQI_ref which is applied to all CSI processes configured for the device.

(50) In some embodiments, the CSI reference resource is CSI-process-specific, see FIG. 8d. For example, the wireless device obtains or determines a different value n.sub.CQI_ref for each CSI process, as exemplified in FIG. 8b.

(51) In a particular variant, the wireless device receives information indicating the CSI reference resource for each CSI process from a network node. As a specific example, the wireless device receives a value n.sub.CQI_ref for each CSI process from a network node, e.g. as part of downlink control information, or comprised in CSI process configuration information, or in a separate message, such as an RRC message. This allows the network node to prioritize between different CSI processes, or, stated differently, to control which CSI processes are processed first.

(52) Another possibility is that the wireless device receives or determines a priority indication for each CSI process. As will be described below, the priority indication may be determined based on a causality between different CSI processes. For example, two CSI processes may be related such that the rank of the first CSI process can be reused for the second CSI process, in which case the first CSI process would have a higher priority (indicating that it should be processed before the second process). The CSI reference resource for each CSI process is then determined based on the priority.

(53) FIGS. 8e-8f show corresponding embodiments in a network node.

(54) The methods illustrated in FIGS. 8c-8f may be implemented in the network shown in FIG. 5.

(55) Some embodiments provide a processing time window for a specific CSI report of a CSI process, wherein the length of the processing time window increases when the CSI reporting configuration corresponds to a computational complexity heavy configuration. For example, the processing time window may increase with an increased number of configured CSI processes and/or configured CSI-RSs. The processing time window may also be referred to as a “maximum CSI processing time” or “allowed CSI processing time”.

(56) Alternatively, the processing time window of a CSI report of a specific CSI process increases with the number of CSI reports that are associated with a higher priority than the specific CSI process.

(57) The UE can then not be expected to update a CSI report based on new measurements, prior to said time window has passed after the corresponding measurement.

(58) One embodiment of the invention is illustrated in FIG. 7. Here the total processing time, before a complete CSI report based on the measurements can be expected from the terminal, is extended. The duration of the extended processing time relates to the expected computational complexity of determining the CSI report(s) for the CSI processes. For example, it is a function of the number of configured CSI processes and/or the number of CSI-RSs configured. The extended processing time could, for example be standardized and determined from a look up table from known parameters.

(59) In another embodiment, a specific processing time window can be determined for a specific CSI process, so that a CSI report for said CSI process triggered after said specific processing time window is updated with the new measurements.

(60) Such an embodiment is illustrated in FIG. 8, where the processing time window of CSI Process 1 is one subframe, the processing time window of CSI Process 2 is 2 subframes, and the processing time window of CSI Process 3 is 3 subframes. Hence, after 2 subframes a CSI report can only be expected to contain updated information for CSI Processes 1 and 2, whereas any information relating to CSI Process 3 cannot be expected to account for the new measurements. Only reports triggered after at least 3 subframes can be expected to be updated with new measurements for all CSI Processes.

(61) In one embodiment a minimum processing capability of the terminal is mandated by the standard, in terms of the number of CSI Processes that it should be capable of determining in a specified timeframe. For example, it could be mandated that the terminal should be able to processes N CSI Processes in M subframes. For example, it could be mandated that a terminal shall be capable of determining a report for two CSI Processes in each subframe.

(62) In a further embodiment, the UE is capable of processing more than the mandated minimums number of CSI Processes in a given subframe.

(63) In one embodiment there is a prioritization between multiple CSI Processes identifying in which order the UE is expected to processes multiple configured CSI Processes.

(64) In one embodiment the reporting prioritization is configurable by the network. In one such embodiment, each CSI Process is assigned a priority indicator that determines in which order the CSI Processes should be computed.

(65) It should be noted that a particular interference measurement resource may be shared by multiple CSI processes, in which case the interference measurement only has to be performed once.

(66) Similarly, the desired signal reference signal resource may be shared by multiple CSI processes, in which case the associated channel estimation only need to be performed once.

(67) Also, a RI and/or a PMI, may be determined as part of a first CSI process (assuming the associated desired effective channel and interference measurement) and reused also in a second CSI process. In this case, the PMI and RI do not involve any processing in the determining of the second CSI process. However, the CQI of the second CSI process should be determined using the interference measurements, and desired signal reference signals, of the second CSI process.

(68) In one such embodiment, the prioritization is such that said first CSI process is prioritized over, implying that it should be processed prior to, said second CSI process. In a further embodiment, it is mandated by the standard that the first CSI process is prioritized over the second CSI process.

(69) This has the advantage that UE may exploit that the reporting of the CSI processes is aligned with the causality of the dependencies of the CSI processes; that is, for the processing of the second CSI processes, the assumed the RI and/or PMI are available, since they were already determined as part of the reporting for the first CSI process.

(70) An advantage of some embodiments is that the required peak processing capability of a UE can be reduced, while maintaining acceptable support also for large CoMP feedback configurations.

(71) FIG. 9 is a combined signaling diagram and flowchart illustrating the interaction between a network node and a wireless device in some embodiments.

(72) FIGS. 10-12 illustrate methods in a wireless device according to some embodiments.

(73) Referring to FIG. 10, a method is provided in a wireless device for reporting channel state information, CSI, to a network node. This method may be implemented in the wireless network shown in FIG. 5.

(74) The wireless device receives a CSI process configuration for one or more CSI processes from the network node. Each CSI process corresponds to a reference signal resource and an interference measurement resource. The reference signal resource comprises a set of resource elements in which one or more reference signals corresponding to a desired signal are received. “Desired signal” in this context means a signal intended for reception by the wireless device. The interference measurement resource comprises a set of resource elements in which one or more signals assumed to be interfering with the desired signal are received. In particular embodiments the reference signal resource is a CSI-RS resource. However, the reference signal resource may be any other type of RS resource which may be used to estimate a desired signal, e.g. a CRS resource.

(75) The wireless device further receives a request for CSI information from the network node. The CSI request may e.g. be comprised in downlink control information (DCI) in the form of a flag, or it may be comprised in a higher-layer message e.g. an RRC message. The CSI request may be a request for an aperiodic, or a periodic CSI report.

(76) The wireless device determines a maximum CSI processing time based e.g. on the number of configured CSI processes or the number of configured CSI-RS resources. The maximum CSI processing time may also be referred to as an “allowed CSI processing time”. In a variant, the maximum CSI processing time is CSI-process-specific, i.e. each CSI process is associated with a maximum CSI processing time.

(77) The wireless device performs measurements based on one or more reference signals received in the reference signal resource for each configured CSI process, e.g. based on one or more CSI-RS. Depending on the CSI process configuration for the wireless device, some or all of the reference signal resources may be received in the same subframe. In addition, the wireless device estimates interference e.g. based on measurements on an IMR, as described above.

(78) The wireless device then determines CSI information for each configured CSI process, within the allowed CSI processing time. In the variant where each CSI process is associated with a maximum CSI processing time, the wireless device will determine CSI information for each configured CSI process within the maximum processing time for that process. Thus, in this variant, the wireless device may start by determining CSI information for the processes that have the shortest maximum processing time, to ensure that the timing restrictions can be met.

(79) Finally, the wireless device transmits CSI to the network node. Such a transmission can be requested by the network in an aperiodic CSI request (scheduled in a DCI block) or it could be scheduled to occur periodically in specific subframes.

(80) FIG. 11 illustrates a similar embodiment, but in the method of FIG. 11 the wireless device also determines a priority order for the configured CSI processes, and determines CSI information for each CSI process according to the priority order. The prioritization may involve identifying a causal relationship between certain CSI processes, wherein one or more CSI values from one process can be reused for another process, as was described above.

(81) FIG. 12 is a further variant of the method in FIG. 11. Here, the wireless device also determines a priority order, and determines CSI for the process with the highest priority within the maximum processing time (as shown in FIG. 8). In a variant, an indication of the priority order may be received from the network. For example, the wireless may receive, as part of the CSI process configuration, a priority indicator or index for each CSI process.

(82) If the wireless device cannot determine CSIs for all CSI processes within the maximum processing time, the remaining CSI information will be based on previous measurements.

(83) It should be noted that the network node has performed the corresponding prioritization (and optionally communicated this prioritization of CSI processes to the wireless device) and therefore knows which CSI processes it should expect to be updated within the maximum processing time, and which CSI processes are expected to be outdated.

(84) FIG. 13 illustrates a method in a network node for CSI reporting.

(85) The network node, e.g. an eNodeB, transmits, to a wireless device, e.g. an UE, a CSI process configuration for one or more CSI processes. Each CSI process corresponds to a reference signal resource and an interference measurement resource. The reference signal resource comprises a set of resource elements in which one or more reference signals corresponding to a desired signal are received. “Desired signal” in this context means a signal intended for reception by the wireless device. The interference measurement resource comprises a set of resource elements in which one or more signals assumed to be interfering with the desired signal are received. In particular embodiments the reference signal resource is a CSI-RS resource. However, the reference signal resource may be any other type of RS resource which may be used to estimate a desired signal, e.g. a CRS resource.

(86) The network node further transmits a request for CSI information to the wireless device. The CSI request may e.g. be comprised in downlink control information (DCI) in the form of a flag, or it may be comprised in a higher-layer message e.g. an RRC message. The CSI request may be a request for an aperiodic, or a periodic CSI report.

(87) The network node further determines a maximum CSI processing time based e.g. on the number of configured CSI processes or the number of configured CSI-RS resources. In a variant, the maximum CSI processing time is CSI-process-specific, i.e. each CSI process is associated with a maximum CSI processing time.

(88) Optionally, the network node also determines a priority order for the CSI processes. As described above, the priority order may be determined based on a causality relationship between CSI processes.

(89) The network node receives CSI information corresponding to the CSI processes from the wireless device, within the maximum CSI processing time. In the variant where a priority order is determined, the network node may receive CSI information for some CSI processes (having a higher priority) within the maximum processing time, and receive the remaining CSI information at a later point in time.

(90) Optionally, the network node performs link adaptation and/or makes a scheduling decision based on the received CSI.

(91) Referring to FIG. 16, according to some embodiments a method is provided in a wireless device for reporting channel state information, CSI. This method may be implemented in the wireless device 540 shown in FIG. 5. The wireless device is comprised in a wireless network, e.g. wireless communications system 500 of FIG. 5. In some variants, the wireless device is a user equipment, UE.

(92) The wireless device receives 1610 a CSI process configuration and a request for CSI information from a network node 560. The request for CSI information may be a request for a periodic CSI report, or a request for an aperiodic CSI report. The wireless device then reports 1620 CSI for one or more CSI processes, wherein the CSI is determined such as to reflect the state of the channel for a CSI reference resource. The CSI reference resource is determined based on the number of configured CSI processes. Optionally, the CSI reference resource is also determined based on the number of configured CSI-RS resources.

(93) The wireless device may determine CSI based on measurements performed on reference signal resources corresponding to the configured CSI processes. In a particular variant, the CSI is determined based on measurements performed in and/or prior to the CSI reference resource. As described above, determining the CSI may further comprise performing measurements on interference measurement resources corresponding to the configured CSI processes, and determine the CSI based on these measurements.

(94) In some variants, the wireless device determines a number n.sub.CQI_ref representing the location of the CSI reference resource relative to the subframe in which the CSI report is transmitted. The wireless device may determine one number n.sub.CQI_ref which is applied to all CSI processes configured for the device. Alternatively, different numbers n.sub.CQI_ref may be determined for different CSI processes. In some variants, the number n.sub.CQI_ref increases when the number of configured CSI processes exceeds a certain threshold. In another variant, n.sub.CQI_ref increases with the number of configured CSI processes.

(95) Optionally, the wireless device prioritizes a first CSI process over a second CSI process, e.g. based on a CSI process index or identity. The wireless device then determines a rank indicator and/or a precoding matrix indicator for the first CSI process, and reuses the determined rank indicator and/or precoding matrix indicator for the second CSI process.

(96) Although the described solutions may be implemented in any appropriate type of telecommunication system supporting any suitable communication standards and using any suitable components, particular embodiments of the described solutions may be implemented in an LTE network, such as that illustrated in FIG. 5.

(97) As shown in FIG. 5, the example network may include one or more instances of user equipment (UEs) and one or more base stations capable of communicating with these UEs, along with any additional elements suitable to support communication between UEs or between a UE and another communication device (such as a landline telephone). Although the illustrated UEs may represent communication devices that include any suitable combination of hardware and/or software, these UEs may, in particular embodiments, represent devices such as the example UE illustrated in greater detail by FIG. 15. Similarly, although the illustrated base stations may represent network nodes that include any suitable combination of hardware and/or software, these base stations may, in particular embodiments, represent devices such as the example base station illustrated in greater detail by FIG. 14.

(98) With reference to FIG. 15, some embodiments provide a wireless device 1500 for reporting Channel State Information, CSI. The wireless device may be a user equipment. The wireless device is adapted to receive a CSI process configuration and a request for CSI information from a network node, and to report CSI for one or more CSI processes. The CSI is determined such as to reflect the state of the channel for a CSI reference resource, and the CSI reference resource is determined based on the number of configured CSI processes.

(99) Optionally, the wireless device is adapted to determine the CSI reference resource also based on the number of configured CSI-RS resources.

(100) The wireless device may further be adapted to determine CSI based on measurements performed on reference signal resources corresponding to the configured CSI processes. In a particular variant, the wireless device is adapted to determine CSI based on measurements performed in and/or prior to the CSI reference resource. The wireless device may be further adapted to determine the CSI by performing measurements on interference measurement resources corresponding to the configured CSI processes, and determine the CSI based on these measurements.

(101) In some variants, the wireless device is adapted to determine a number n.sub.CQI_ref representing the location of the CSI reference resource relative to the subframe in which the CSI report is transmitted. The wireless device may further be adapted to determine one number n.sub.CQI_ref which is applied to all CSI processes configured for the device. Alternatively, the wireless device may be adapted to determine different numbers n.sub.CQI_ref for different CSI processes. In some variants, the wireless device is adapted to determine the number n.sub.CQI_ref such that it increases when the number of configured CSI processes exceeds a certain threshold. In another variant, the wireless device is adapted to determine the number n.sub.CQI_ref such that it increases with the number of configured CSI processes.

(102) Optionally, the wireless device is adapted to prioritize a first CSI process over a second CSI process, e.g. based on a CSI process index or identity. The wireless device is then further adapted to determine a rank indicator and/or a precoding matrix indicator for the first CSI process, and to reuse the determined rank indicator and/or precoding matrix indicator for the second CSI process.

(103) Referring again to FIG. 15, some embodiments provide a user equipment 1500 for reporting Channel State Information, CSI, the user equipment 1500 comprising a processor 1520 and a memory 1530, the memory 1530 comprising instructions executable by said processor whereby said user equipment 1500 is operative to receive a CSI process configuration and a request for CSI information from a network node, and to report CSI for one or more CSI processes, wherein the CSI is determined such as to reflect the state of the channel for a CSI reference resource, and the CSI reference resource is determined based on the number of configured CSI processes.

(104) Optionally, the instructions, when executed, cause the user equipment 1500 to be operative to determine the CSI reference resource also based on the number of configured CSI-RS resources.

(105) In some embodiments the instructions, when executed, cause the user equipment 1500 to be operative to determine CSI based on measurements performed on reference signal resources corresponding to the configured CSI processes. In a particular variant, the wireless device is caused to be operative to determine CSI based on measurements performed in and/or prior to the CSI reference resource. The wireless device may be further caused to be operative to determine the CSI by performing measurements on interference measurement resources corresponding to the configured CSI processes, and determine the CSI based on these measurements.

(106) In some variants, the instructions, when executed, cause the user equipment 1500 to be operative to determine a number n.sub.CQI_ref representing the location of the CSI reference resource relative to the subframe in which the CSI report is transmitted. The wireless device may further be caused to be operative to determine one number n.sub.CQI_ref which is applied to all CSI processes configured for the device. Alternatively, the wireless device may be caused to be operative to determine different numbers n.sub.CQI_ref for different CSI processes. In some variants, the wireless device is caused to be operative to determine the number n.sub.CQI_ref such that it increases when the number of configured CSI processes exceeds a certain threshold. In another variant, the wireless device is caused to be operative to determine the number n.sub.CQI_ref such that it increases with the number of configured CSI processes.

(107) Optionally the instructions, when executed, cause the user equipment 1500 to be operative to prioritize a first CSI process over a second CSI process, e.g. based on a CSI process index or identity. The wireless device is then further operative to determine a rank indicator and/or a precoding matrix indicator for the first CSI process, and to reuse the determined rank indicator and/or precoding matrix indicator for the second CSI process.

(108) As shown in FIG. 15, the example UE includes a processor, a memory, a transceiver, and an antenna. In particular embodiments, some or all of the functionality described above as being provided by mobile communication devices or other forms of UE may be provided by the UE processor executing instructions stored on a computer-readable medium, such as the memory shown in FIG. 15. Alternative embodiments of the UE may include additional components beyond those shown in FIG. 15 that may be responsible for providing certain aspects of the UE's functionality, including any of the functionality described above and/or any functionality necessary to support the solution described above.

(109) As shown in FIG. 14, the example base station includes a processor, a memory, a transceiver, and an antenna. In particular embodiments, some or all of the functionality described above as being provided by a mobile base station, a base station controller, a node B, an enhanced node B, and/or any other type of mobile communications node may be provided by the base station processor executing instructions stored on a computer-readable medium, such as the memory shown in FIG. 14. Alternative embodiments of the base station may include additional components responsible for providing additional functionality, including any of the functionality identified above and/or any functionality necessary to support the solution described above.

(110) When using the word “comprise” or “comprising” it shall be interpreted as non-limiting, i.e. meaning “consist at least of”.

(111) The present invention is not limited to the above-describe preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.