HK1235167B - Method for dynamic csi feedback - Google Patents

Description

Method for dynamic CSI feedback

Technical Field

The present disclosure relates to channel state information (CSI) feedback in cellular communication networks.

Background Art

Long Term Evolution (LTE) uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)-spread OFDM in the uplink. Therefore, the basic LTE downlink physical resources can be viewed as a time-frequency grid as shown in Figure 1, where each resource element corresponds to an OFDM subcarrier during one OFDM symbol interval.

As shown in Figure 2, in the time domain, LTE downlink transmissions are organized into 10-millisecond (ms) radio frames, each consisting of ten equally sized subframes of length T _SUBFRAME = 1 ms. With a normal cyclic prefix, a subframe consists of 14 OFDM symbols. Each OFDM symbol has a duration of approximately 71.4 microseconds (μs).

Furthermore, resource allocation in LTE is typically described in terms of resource blocks (RBs), where an RB corresponds to one time slot (0.5 ms) in the time domain and 12 consecutive subcarriers in the frequency domain. A pair of two adjacent RBs (1.0 ms) in the time direction is called an RB pair. RBs are numbered in the frequency domain starting with 0 from one end of the system bandwidth.

Downlink transmissions are dynamically scheduled. Specifically, in each subframe, the base station sends control information related to the terminal (i.e., user equipment device (UE)) to which data is sent in the current downlink subframe. Control signaling carried by the physical downlink control channel (PDCCH) is usually sent in the first 1, 2, 3, or 4 OFDM symbols in each subframe, where the number n=1, 2, 3, or 4 is called a control format indicator (CFI). The downlink subframe also contains common reference symbols, which are known to the receiver and are used for coherent demodulation of control information, for example. A downlink system with CFI=3 OFDM symbols as control is shown in Figure 3.

From LTE Release 11 onwards, the above resource assignments can also be scheduled on the Enhanced Physical Downlink Control Channel (EPDCCH).For Release 8 to Release 10, only PDCCH is available.

The reference symbols shown in Figure 3 are cell-specific reference symbols (CRS). CRS is used to support a variety of functions, including fine time and frequency synchronization for certain transmission modes and channel estimation.

In cellular communication systems, there is a need to measure channel conditions in order to know what transmission parameters to use. These parameters include, for example, modulation type, coding rate, transmission rank, and frequency allocation. This applies to both uplink (UL) transmissions and downlink (DL) transmissions.

The scheduler that makes decisions about transmission parameters is typically located in the base station (i.e., an enhanced or evolved Node B (eNB)). Therefore, the scheduler can directly measure the channel properties for the UL using known reference signals transmitted by the terminals (i.e., UEs). These measurements then form the basis for UL scheduling decisions made by the eNB, which are then sent to the UE via the DL control channel. Conversely, for the DL, the scheduler receives channel state information (CSI) feedback from the terminals, which is taken into account by the scheduler when selecting transmission parameters for DL transmissions to those terminals.

In LTE Release 8, CRS is used in DL for CSI estimation and feedback, as well as for channel estimation for demodulation. CRS is transmitted in each subframe and is defined to support up to four antenna ports (APs). In LTE Release 10, in order to support up to 8 APs, a CSI reference signal (CSI-RS) is defined for UE to measure and feedback CSI related to multiple APs. Each CSI-RS resource consists of two resource elements (REs) on two consecutive OFDM symbols, and two different CSI-RSs (for two different APs) can share the same CSI-RS resource (two REs) through code division multiplexing (CDM). In addition, CSI-RS can be sent every 5, 10, 20, 40 or 80 ms, where this timing is called the CSI-RS period. Therefore, compared with CRS, CSI-RS has lower overhead and lower duty cycle. On the other hand, unlike CRS, CSI-RS is not used as a demodulation reference. Different CSI-RS can also be sent using different offsets in a subframe, where the offset of the CSI-RS within a subframe is called the CSI-RS subframe offset. When CSI-RS is configured, the UE measures the channel for a given AP at each time instant and can interpolate the channel between CSI-RS opportunities to estimate a dynamically changing channel, for example, by interpolating one sample every 1 ms instead of, for example, one measurement sample every 5 ms.

Figures 4A and 4B show examples of mappings from different CSI-RS configurations to REs in RB pairs. Figure 4A shows the mapping for one or two APs, where 20 configurations are possible. The two CSI-RSs of the two APs of a particular cell can be sent through configuration 0, for example, via CDM, while the CSI-RSs of the APs of other neighboring cells can be sent through configuration j (where 1≤j≤19) to avoid reference signal conflicts with the CSI-RSs in the cell. Figure 4B shows the mapping for four APs, where 10 configurations are possible. The four CSI-RSs of the four APs of a particular cell can be sent through configuration 0, for example, via CDM, while the CSI-RSs of the APs of other neighboring cells can be sent through configuration j, where 1≤j≤9.

The OFDM symbols used by two consecutive REs for one CSI-RS are quadrature phase shift keying (QPSK) symbols derived from a specified pseudo-random sequence. To randomize interference, the initial state of the pseudo-random sequence generator is determined by the detected cell identifier (ID) or the virtual cell ID configured to the UE through radio resource control (RRC) signaling. CSI-RS with such non-zero power OFDM symbols are called non-zero power (NZP) CSI-RS.

On the other hand, for the purpose of interference measurement (IM) (only in transmission mode 10 (TM10)) or for the purpose of improving CSI estimation in other cells (in transmission mode 9 (TM9) or TM10), zero-power (ZP) CSI-RS can also be configured to the UE via RRC. However, the CSI-RS mapping with four APs will always be used by ZP CSI-RS. For example, in Figure 4B, if cell A uses configuration 0 with NZP CSI-RS to estimate the CSI of two APs in cell A, configuration 0 with ZP CSI-RS (a total of four REs per RB pair) can be used by neighboring cell B to minimize DL interference to cell A on the four REs in configuration 0, so that the CSI estimation of the two APs in cell A can be improved.

In LTE TM10, up to four CSI processes and three NZP CSI-RS can be configured for a UE via RRC signaling. For example, these four CSI processes can be used to obtain CSI for APs in up to three different cells (or transmission points (TPs) within the same cell) in a coordinated multipoint (CoMP) framework. Array antennas capable of beamforming in azimuth, elevation, or both (i.e., two-dimensional (2D) beamforming) can also be used to assign the four CSI processes to multiple different beams transmitted from the same eNB. For the complete LTE specifications on how to establish CSI process and CSI-RS configurations, see 3rd Generation Partnership Project (3GPP) Technical Specifications (TS) 36.213 V12.3.0, 3GPP TS 36.331 V12.3.0, and 3GPP TS 36.211 V12.3.0. The beamforming of a transmitted signal, such as a CSI-RS, is obtained by transmitting the same signal from multiple antenna elements in an array, but with an individually controlled phase shift (and possibly amplitude gradient) for each antenna element. As a result, the resulting radiation pattern of the transmitted signal has a different beamwidth and main pointing direction compared to the antenna element radiation pattern. Thus, a beamformed signal, such as a beamformed CSI-RS, is obtained. Typically, the antenna elements at the transmitter are closely spaced to achieve correlated channels, which makes beamforming more efficient. The advantages of beamforming are reduced interference (due to the typically narrow beamwidth of the transmitted signal) and increased effective channel gain (due to the beamforming phase shift applied at the transmitter, which ensures coherent superposition of the signals from each transmitting antenna at the receiver).

In order for the UE to derive correct CSI, each CSI process in TM10 is associated with a signal hypothesis and an interference hypothesis (configured by RRC signaling). The signal hypothesis describes which NZP CSI-RS reflects the expected signal. Interference is measured in the configured CSI-IM resources, which are similar to CSI-RS with four REs per physical resource block (PRB), which the UE uses for interference measurement. To better support IM in CoMP, CSI-IM is standardized and based on ZP CSI-RS. Therefore, each of up to four CSI processes consists of one NZP CSI-RS and one CSI-IM.

For TM9 UEs, only a single CSI process can be configured, and CSI-IM is not defined. Therefore, IM is not specified in TM9. However, there is still the possibility of obtaining CSI feedback from two different subframe (SF) sets (SF Set 1 and SF Set 2). For example, based on almost blank subframe (ABS) information signaled on X2, for example, a pico eNB can configure the UE to feedback CSI for both protected (i.e., reduced power subframe (RPSF)) subframes (where the corresponding macro eNB has reduced activity) and unprotected subframes in two different CSI reports. This gives the pico eNB information to perform link adaptation differently in the two types of subframes, depending on whether they are protected subframes. UEs configured in TM10 can also use both subframe sets and multiple CSI processes.

In LTE, the format of CSI reports is specified in detail and can contain channel quality information (CQI), rank indicator (RI), and precoding matrix indicator (PMI). See 3GPP TS 36.213 V12.3.0. Reports can be wideband or applicable to subbands. They can be configured to be sent periodically or aperiodically by RRC messages, or triggered by control messages from the eNB to the UE. The quality and reliability of CSI are crucial for the eNB to make the best possible scheduling decision for the upcoming DL transmission.

The LTE standard does not specify how the UE should obtain and average CSI-RS and CSI-IM measurements from multiple time instances (i.e., subframes). For example, the UE may make measurements over a time frame of multiple subframes unknown to the eNB and combine several measurements in a UE-specific manner to create CSI values that are reported periodically or on a triggered basis.

In the context of LTE, the resources (i.e., REs) that can be used for the transmission of CSI-RS are called "CSI-RS resources." In addition, there are also "CSI-IM resources." The latter are defined according to the same set of possible physical locations in the same time/frequency grid as CSI-RS, but have zero power, and are therefore ZP CSI-RS. In other words, they are "silent" CSI-RS, and when the eNB is transmitting a shared data channel, it avoids mapping data to those REs used for CSI-IM. These are intended to give the UE the possibility to measure the power of any interference from another transmitter besides the UE's serving node.

Each UE can be configured with one, three, or four different CSI processes. Each CSI process is associated with one CSI-RS and one CSI-IM resource, where these CSI-RS resources have been configured to the UE via RRC signaling and are therefore transmitted/appear periodically with a period T and a given subframe offset relative to the start of the frame.

If only one CSI process is used, the CSI-IM is typically made to reflect the interference from all other eNBs, i.e., the serving cell uses ZP CSI-RS that overlaps with the CSI-IM, but in other neighboring eNBs, there is no ZP CSI-RS on these resources. In this way, the UE will use CSI-IM to measure interference from neighboring cells.

If an additional CSI process is configured for the UE, there is a possibility that the network will configure the UE in the serving eNB with ZP CSI-RS resources in a neighboring eNB that overlap with the CSI-IM resources used for that CSI process. In this way, the UE will also feedback accurate CSI for the case where the neighboring cell is not transmitting. Therefore, coordinated scheduling between eNBs is achieved by using multiple CSI processes, with one CSI process feedback CSI for the full interference case and the other CSI processes feedback CSI for the case when the (strong interfering) neighboring cell is muted. As described above, up to four CSI processes can be configured for the UE, enabling feedback of four different transmission hypotheses.

PDCCH/EPDCCH is used to carry downlink control information (DCI), such as scheduling decisions and power control commands. More specifically, DCI includes:

DL scheduling assignment, including physical downlink shared channel (PDSCH) resource indication, transport format, hybrid automatic repeat request (ARQ) information, and control information related to spatial multiplexing (if applicable). The DL scheduling assignment also includes commands for power control of the physical uplink control channel (PUCCH) for transmitting hybrid ARQ acknowledgements in response to the DL scheduling assignment.

UL Scheduling Grant, which includes Physical Uplink Shared Channel (PUSCH) resource indication, transport format, and Hybrid ARQ related information. The UL Scheduling Grant also includes commands for PUSCH power control.

• Power control commands for a set of terminals, in addition to the commands included in the scheduling assignment/grant.

The PDCCH/EPDCCH region carries one or more DCI messages, each of which has one of the formats described above. Since multiple terminals can be scheduled simultaneously on both the DL and UL, there must be the possibility of sending multiple scheduling messages within each subframe. Each scheduling message is sent on a separate PDCCH/EPDCCH physical resource. In addition, to support different radio channel conditions, link adaptation can be used, in which the PDCCH/EPDCCH code rate is selected by adapting the resource usage for the PDCCH/EPDCCH to match the radio channel conditions.

In this context, future cellular communication networks are expected to utilize beamforming, where the number of beams is expected to exceed the number of CSI-RS resources. In addition, existing and future cellular communication networks sometimes use a multi-layer radio access network that includes multiple coverage cells (e.g., macro cells controlled by an eNB) and multiple capacity cells (e.g., pico cells controlled by a pico eNB). Therefore, there is a need for systems and methods that enable improved CSI-RS configuration, particularly for cellular communication networks that utilize beamforming and/or a multi-layer radio access network.

Summary of the Invention

Systems and methods related to channel state information (CSI) feedback in cellular communication networks are disclosed. Although not limited thereto, the embodiments disclosed herein are particularly well-suited for improving CSI feedback in cellular communication networks that utilize beamformed CSI reference signals (CSI-RSs), such that the same CSI-RS resources can be reused in different beams over time.

Embodiments of a method for controlling operation of a base station of a cellular communication network for CSI-RS-based channel estimation at a wireless device are disclosed. In some embodiments, the method of operation of the base station includes disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes at the wireless device, and receiving one or more CSI reports from the wireless device, the CSI reports generated by the wireless device for which inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes is disabled in response to the base station disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes at the wireless device. In this manner, CSI feedback is improved, particularly in embodiments in which the base station transmits beamformed CSI-RS resources and reuses the same CSI-RS resources over time for different beams. In this case, without disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes, the wireless device may perform inter-subframe channel interpolation and/or filtering of CSI-RS estimates on specific CSI-RS resources transmitted on different beams in different subframes, which will in turn result in suboptimal CSI feedback.

In some embodiments, the wireless device uses two or more CSI processes for CSI reporting, and disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes includes disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes on a per-CSI-process basis. In other embodiments, the wireless device uses two or more CSI processes for CSI reporting, and disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes includes disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes for all of the two or more CSI processes.

In some embodiments, disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes comprises disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes via radio resource control (RRC) signaling. Furthermore, in some embodiments, disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes via RRC signaling comprises sending an indication that inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes for the CSI process of the wireless device is not allowed in an RRC information element configuring the CSI process of the wireless device.

In some embodiments, the method of operation of the base station further comprises disabling, at the wireless device, combining of CSI-interference measurement (CSI-IM) estimates across subframes.

In some embodiments, disabling inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes includes signaling an indication to the wireless device that inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes is not allowed.

In some embodiments, the method of operation of the base station further comprises configuring the wireless device with a set of CSI-RS resources. Furthermore, in some embodiments, receiving one or more CSI reports from the wireless device comprises receiving CSI reports for a subset of the set of CSI-RS resources configured for the wireless device. In some embodiments, configuring the wireless device with the set of CSI-RS resources comprises configuring the wireless device with the set of CSI-RS resources via RRC signaling. In other embodiments, configuring the wireless device with the set of CSI-RS resources comprises semi-statically configuring the wireless device with the set of CSI-RS resources. In some embodiments, the set of CSI-RS resources is specific to a CSI process of the wireless device.

In some embodiments, the base station transmits a beamformed CSI-RS, and the method of operation of the base station further comprises dynamically changing a beam used on a set of CSI-RS resources configured for the wireless device.

Also disclosed are embodiments of a base station that is enabled to control CSI-RS based channel estimation at a wireless device.In some embodiments, the base station operates according to any of the embodiments of the method of operation of a base station described herein.

Embodiments of a method of operation for providing CSI reports by a wireless device in a cellular communication network are disclosed. In some embodiments, the method of operation of the wireless device includes: receiving an indication from a base station of the cellular communication network to disable inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes, and in response, performing one or more CSI-RS measurements with the inter-subframe channel interpolation and/or filtering of CSI-RS estimates across subframes disabled. The method also includes: sending a CSI report to the base station based on the one or more CSI-RS measurements.

In some embodiments, the base station transmits beamformed CSI-RS resources and reuses the same CSI-RS resources for different beams over time.

In some embodiments, the wireless device uses two or more CSI processes for CSI reporting, and the indication received from the base station is an indication to disable inter-subframe channel interpolation and/or filtering of CSI-RS estimation for a specific CSI process across subframes. In other embodiments, the wireless device uses two or more CSI processes for CSI reporting, and the indication received from the base station is an indication to disable inter-subframe channel interpolation and/or filtering of CSI-RS estimation across subframes for all of the two or more CSI processes.

In some embodiments, receiving the indication comprises receiving the indication via RRC signaling. In some embodiments, the wireless device uses two or more CSI processes for CSI reporting, the indication received from the base station is for a specific CSI process of the wireless device, and an indication to disable inter-subframe channel interpolation and/or filtering of CSI-RS estimation across subframes is received, and receiving the indication comprises receiving the indication included in an RRC information element configuring the specific CSI process of the wireless device.

In some embodiments, the method of operation of the wireless device further includes receiving an indication from a base station to disable combining of CSI-IM estimates across subframes, and in response, performing one or more CSI-IM measurements with combining of CSI-IM estimates across subframes disabled.

In some embodiments, the method of operation of the wireless device further comprises: receiving a configuration of a set of CSI-RS resources for the wireless device. In some embodiments, the CSI report is for a subset of the set of CSI-RS resources configured for the wireless device. In some embodiments, receiving the configuration of the set of CSI-RS resources comprises: receiving the configuration of the set of CSI-RS resources from a base station via semi-static signaling (e.g., RRC signaling). In some embodiments, the set of CSI-RS resources is specific to a CSI process of the wireless device.

In some embodiments, the base station transmits beamformed CSI-RS, and the beam used on the set of CSI-RS resources configured for the wireless device is dynamically changed.

Embodiments of a wireless device for providing CSI reporting in a cellular communication network are disclosed. In some embodiments, the wireless device operates according to any of the embodiments of the method of operation of the wireless device described herein.

Those skilled in the art will understand the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the embodiments in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

Figure 1 shows the LTE downlink physical resources;

Figure 2 shows the LTE time domain structure;

FIG3 shows a downlink subframe;

4A and 4B illustrate configurations of channel state information reference signals (CSI-RS) for different numbers of antenna ports;

FIG5 illustrates an example of a cellular communication network implementing flexible channel state information (CSI) feedback according to some embodiments of the present disclosure;

FIG6 illustrates the operation of the base station and wireless device of FIG5 according to some embodiments of the present disclosure;

7 illustrates operations of the base station and wireless device of FIG. 5 to provide disabling of inter-subframe interpolation/filtering of CSI-RS estimates in accordance with some embodiments of the present disclosure;

FIG8 illustrates operations of the base station and wireless device of FIG5 for providing dynamic CSI feedback according to some embodiments of the present disclosure;

FIG9 illustrates operations of the base station and wireless device of FIG5 for providing dynamic CSI feedback via dynamic CSI-RS resource configuration according to some embodiments of the present disclosure;

FIG10 illustrates operations of the base station and wireless device of FIG5 for providing dynamic CSI feedback via dynamic CSI-RS resource configuration according to some other embodiments of the present disclosure;

FIG11 illustrates operations of the base station and wireless device of FIG5 to provide dynamic CSI feedback via dynamic CSI-RS resource configuration using downlink control information (DCI) messages according to some other embodiments of the present disclosure;

FIG12 illustrates operations of the base station and wireless device of FIG5 to provide dynamic CSI feedback via dynamic CSI-RS resource configuration using a Long Term Evolution (LTE) Medium Access Control (MAC) Control Element (CE) in accordance with some other embodiments of the present disclosure;

FIG13 illustrates operations of the base station and wireless device of FIG5 to provide dynamic CSI feedback via dynamic non-zero power (NZP) CSI-RS and CSI interference measurement (CSI-IM) resource configuration according to some other embodiments of the present disclosure;

FIG14 illustrates operations of the base station of FIG5 to dynamically configure CSI-RS resources for a wireless device from a set of K CSI-RS resources transmitted on adjacent beams, from the base station's perspective, in accordance with some embodiments of the present disclosure;

FIG15 is a block diagram of a base station according to some embodiments of the present disclosure;

FIG16 is a block diagram of a base station according to another embodiment of the present disclosure;

FIG17 is a block diagram of a wireless device according to some embodiments of the present disclosure; and

FIG18 is a block diagram of a wireless device according to other embodiments of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent information that enables those skilled in the art to practice the embodiments and illustrate the best modes for implementing the embodiments. When reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and will recognize applications of these concepts not specifically addressed herein. It should be understood that these concepts and applications fall within the scope of the present disclosure and the appended claims.

Note that although terminology from the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) has been used in this disclosure to illustrate embodiments of the present disclosure, this should not be considered to limit the scope of the concepts disclosed herein to only that system. Other wireless systems including Wideband Code Division Multiple Access (WCDMA), WiFi, WiMax, LTE for unlicensed bands, Ultra Mobile Broadband (UMB), and Global System for Mobile Communications (GSM) may also benefit from utilizing the concepts covered in this disclosure.

It should also be noted that terms such as enhanced or evolved Node B (eNB) and user equipment (UE) should be considered non-restrictive and, in particular, do not imply a hierarchical relationship between eNB and UE. In general, "eNB" or "transmission point (TP)" can be considered as device 1, "UE" as device 2, and the two devices communicate with each other via some radio channel. This disclosure also focuses on wireless transmission in the downlink, but the disclosure is equally applicable to the uplink.

Before describing the embodiments of the present disclosure, it is helpful to discuss some of the issues associated with conventional channel state information reference signals (CSI-RS). Some of the issues addressed in this disclosure relate to eNBs transmitting beamformed CSI-RS, where each CSI-RS is associated with a potentially narrow beam transmitted from, for example, an array antenna. In other words, each CSI-RS is transmitted using a different precoder or different beamforming weights.

Existing channel state information (CSI) feedback schemes have several problems that are addressed in the present disclosure. Reconfiguration of the CSI-RS on which measurements are performed requires radio resource control (RRC) signaling, which has two problems. First, there is a delay in setting up the reconfiguration, which can be as long as 10 milliseconds (ms). Second, it is uncertain when the UE has adopted the reconfiguration, so there is an uncertain period in system operation. Another problem with existing CSI feedback schemes is that the use of multiple CSI processes requires significant UE complexity, uplink signaling overhead, and power consumption, all of which are undesirable for network and UE implementations.

Another problem is that if beamformed CSI-RS is used and the UE moves in a tangential direction as seen from the eNB, the CSI-RS on which the UE measures needs to be frequently reconfigured as the UE moves from one main lobe of a beam to another. This problem is particularly severe in the case of high tangential UE speeds or narrow beams from the eNB (i.e., a large number of horizontal array antennas).

The Physical Downlink Control Channel (PDCCH) and Enhanced PDCCH (EPDCCH) can have relatively higher block error rates, which means that the network may not know whether a given Downlink Control Information (DCI) message was received correctly. Therefore, in the case where a DCI message changes the parameters used for periodic CSI reporting, because the UE can send periodic CSI reports using the same format and timing before and after receiving (or not receiving) the DCI message, the network may not know whether the parameters contained in the DCI are used in subsequent periodic CSI reports.

Disclosed are systems and methods relating to improved CSI feedback schemes that, at least in some embodiments, address the above-mentioned issues. In some embodiments, the eNB indicates to the UE, via higher layer signaling (e.g., RRC signaling) or in a DCI message, that the UE is not allowed to perform channel interpolation of CSI-RS estimates across subframes. In some embodiments, the eNB also indicates that averaging of CSI-IM estimates across subframes is not allowed. In other words, the indication that the UE is not allowed to perform channel interpolation of CSI-RS estimates across subframes ensures that inter-subframe filtering of channel estimates based on non-zero power (NZP) CSI-RS is not performed for the purpose of CSI feedback on the CSI process. The signaling may also indicate the CSI processes for which inter-subframe interpolation/filtering is disabled (e.g., all or a subset of the possible CSI processes). In some embodiments, the RRC information element used to configure the CSI process may be extended with a bit that controls whether inter-subframe NZP CSI-RS filtering is enabled or disabled.

Disabling inter-subframe interpolation/filtering of CSI-RS estimates can be particularly beneficial when CSI-RS resources are reused over time between different beams transmitted by the eNB. Specifically, when the eNB transmits beamformed CSI-RS and the number of beams is large (e.g., exceeds the number of available CSI-RS resources), it can be beneficial for the eNB to reuse the same CSI-RS resources on different beams over time. In other words, a specific CSI-RS resource may be used for a first beam during one subframe, and the same CSI-RS resource may be used for a second beam during another subframe. When CSI-RS resources are reused over time between different beams, the performance of a conventional inter-subframe interpolation/filtering scheme utilized by the UE to generate CSI-RS measurements will result in poor CSI-RS estimates because measurements from different beams will be combined. Therefore, by disabling the UE's inter-subframe interpolation/filtering of CSI-RS estimates, the eNB improves the resulting CSI feedback since the eNB will know exactly which subframe and CSI-RS, and hence which beam, a specific CSI feedback report is associated with.

In another embodiment of disabled inter-subframe filtering, the UE is monitoring a set of NZP CSI-RS configurations and selects a subset of those NZP CSI-RS configurations for reporting CSI. This selection can be based on, for example, an estimate of the channel strength of the monitored NZP CSI-RS configurations (e.g., a subset corresponding to the N strongest channels can be selected). The UE can be configured with such a monitoring set for each of its CSI processes (via, for example, a higher layer message). The monitoring set can be CSI process specific. With this embodiment, the network can now dynamically change the beam used on a (periodically recurring) set of NZP CSI-RS resources, which is significantly larger than the current maximum number of NZP CSI-RS configurations currently handled by a single UE (which is three), without forcing the UE to handle the additional complexity of calculating CSI for the entire monitoring set (calculating channel strength is significantly simpler than calculating CSI).

In some embodiments, the eNB configures a set of K CSI-RS resources (also referred to as a CSI-RS configuration) for the UE via higher layer signaling (eg, using an RRC message). The CSI-RS is potentially transmitted periodically with different periods.

In some embodiments, the K resources correspond to K different beam directions seen from the eNB.A typical number is K=20, since according to the LTE specification (3GPP TS 36.211 V12.3.0) 20 two-port CSI-RS can be transmitted in a single subframe.

The eNB may indicate to the UE, in an uplink scheduling grant message or some other form of message (e.g., a downlink assignment or a dedicated message on a downlink control channel), one of K CSI-RS resources (or configurations). This CSI resource is the one for which the UE should perform channel measurements (hence the CSI-RS may be referred to as NZP CSI-RS) and used for at least one subsequent CSI report. The CSI report sent on the uplink from the UE is then calculated using measurements on a single CSI-RS from the set of K possible CSI-RSs. Because a single CSI report and a single CSI process are used, UE complexity is reduced compared to using multiple CSI processes. In some embodiments, the signaling may take the form of associating the indicated CSI-RS resource (or configuration) with a CSI process, meaning that the CSI feedback for the corresponding CSI process will use the associated NZP CSI-RS. In other embodiments, the indicated CSI-RS resource (or configuration) may be associated with multiple CSI processes. In some embodiments, the same signaling message may contain multiple indications of an association between a CSI-RS resource (/configuration) and a CSI process. In some embodiments, the association may be maintained for a single CSI reporting instance (e.g., one CSI reporting instance associated with the signaling message). If an additional CSI report is sent thereafter, the corresponding CSI process may revert to using a default CSI-RS resource (/configuration). For example, such a default CSI-RS resource may be represented by a semi-statically configured CSI configuration that is associated with a CSI process according to the LTE Release 11 RRC mechanism (see 3GPP 36.331 V12.3.0 for more information). This may be the case for CSI on the Physical Uplink Shared Channel (PUSCH) (aperiodic) and/or the Physical Uplink Control Channel (PUCCH) (periodic). Alternatively, the association between a dynamically signaled CSI resource (/configuration) and a CSI process may be maintained until another association for that CSI process is signaled.

In some other embodiments, the eNB also indicates which of the K CSI-RS resources should be used as a CSI interference measurement (CSI-IM) resource.

In some embodiments, the UE assumes physical downlink shared channel (PDSCH) rate matching around all K CSI-RS resources indicated in the higher layer configuration.

In some other embodiments, periodic CSI reporting using the PUCCH is calculated based on the CSI-RS resource indicated in the downlink DCI message. The UE will use the selected CSI-RS resource for CSI feedback until the UE receives an indication of a new CSI-RS in the DCI message. In addition, the UE may provide an indication confirming which CSI-RS resource was measured, including an index of the measured CSI-RS resource, or alternatively, a bit confirming that the downlink DCI message was successfully received and that the CSI-RS resource in the DCI message was used for measurement.

In another embodiment, periodic CSI reporting using PUCCH is calculated based on the CSI-RS resources indicated in the LTE medium access control (MAC) control element. The UE may be expected to use the CSI-RS resources indicated in the MAC control element for the transport block containing the MAC control element no later than a predetermined number of subframes after sending a hybrid automatic repeat request acknowledgement (HARQ-ACK) on the PUCCH. In this way, the maximum length of the ambiguity period in which the measured prior CSI-RS will be measured may be determined, and thus the subframes in which the CSI-RS resources indicated by the MAC control element should be used for CSI reporting may be identified. Additionally or alternatively, the UE may provide an indication confirming which CSI-RS resource is measured, the indication comprising an index of the measured CSI-RS resource, or alternatively comprising a bit confirming that the MAC control element was successfully received and the CSI-RS resource was used for measurement.

In some other embodiments of the eNB, the CSI resources configured to the UE are sent in adjacent beams. Thus, the eNB can dynamically change the CSI measurement report from the UE for the current beam serving the UE and the adjacent beams to the serving beam.

As described above, embodiments of the present disclosure are implemented in a cellular communication network 10, such as that shown in FIG5 . As shown, the cellular communication network 10 includes a base station 12 (e.g., an eNB) and a wireless device 14 (e.g., a UE). Note that while the base station 12 is described as performing some of the functions disclosed herein, these concepts are equally applicable to any type of radio access node for which CSI measurements are desired to be configured by the wireless device 14. The base station 12 is connected to a core network (not shown).

FIG6 illustrates the operation of the base station 12 and wireless device 14 according to some embodiments of the present disclosure. As described above, in some embodiments, the base station 12 disables inter-subframe channel interpolation/filtering of the NZP CSI-RS and/or averaging of the CSI-IM for the CSI process belonging to the wireless device 14 (step 100). Note that in FIG6 , step 100 is optional, as indicated by the dashed line. It is worth noting that, after reading this disclosure, one of ordinary skill in the art will understand that inter-subframe interpolation and inter-subframe filtering are two different techniques for channel estimation based on inter-subframe CSI-RS. Inter-subframe interpolation uses CSI-RS estimates across subframes to interpolate additional CSI-RS estimates. In contrast, inter-subframe filtering filters or averages CSI-RS estimates across subframes. Therefore, “inter-subframe interpolation/filtering” refers to inter-subframe interpolation and/or inter-subframe filtering. In some embodiments, the base station 12 disables inter-subframe interpolation/filtering of the NZP CSI-RS and/or averaging of the CSI-IM in the uplink grant to the wireless device 14. In some embodiments, the base station 12 does this in an RRC message to the wireless device 14. In some embodiments, whether channel interpolation is done is encoded into an information element sent to the wireless device 14.

In some embodiments, the base station 12 configures the wireless device 14 with a set of K CSI-RS resources via higher layer signaling (e.g., using an RRC message) (step 102). Note that in FIG6 , step 102 is optional, as shown by the dashed line. The base station 12 then dynamically configures one (or more) of the CSI-RS resources in the set of K CSI-RS resources for subsequent CSI feedback (step 104). As used herein, a dynamic configuration is a configuration that changes at the subframe or at least frame level (e.g., from one subframe to another). In step 202, the base station 12 dynamically instructs the wireless device 14 on which CSI-RS resource(s) to perform measurements on for subsequent CSI feedback. In some embodiments, the indication includes an indication of at least one CSI-RS resource of the K CSI-RS resources to be used by the wireless device 14. In some embodiments, this is accomplished using an uplink grant to the wireless device 14.

The wireless device 14 then measures the indicated CSI-RS (step 106). In other words, the wireless device 14 performs one or more measurements on the one or more CSI-RS resources dynamically configured in step 104. The wireless device 14 then reports the selected CSI-RS to the base station 12 via a CSI report (step 110). In some embodiments, this is periodically scheduled CSI feedback. In some embodiments, this is aperiodic CSI feedback.

Figures 7 to 13 illustrate various embodiments described above. Specifically, Figure 7 illustrates the operations of a base station 12 and a wireless device 14 for enabling disabling of inter-subframe interpolation/filtering of NZP CSI-RS measurements according to some embodiments of the present disclosure. As shown, the base station 12 disables inter-subframe channel interpolation/filtering of NZP CSI-RS at the wireless device 14 (step 200). It is noteworthy that in this embodiment, disabling inter-subframe channel interpolation/filtering of NZP CSI-RS is performed on a per-wireless device basis. The base station 12 may disable inter-subframe channel interpolation/filtering of NZP CSI-RS at the wireless device 14 in response to certain triggering events (e.g., an increase in cell load, an increase in the number of beams transmitted by the base station, etc.). However, the triggering event may be any suitable triggering event. In some embodiments, the base station 12 disables inter-subframe channel interpolation/filtering of NZP CSI-RS at the wireless device 12 by sending an indication to the wireless device 14 that the wireless device 14 is not allowed to perform inter-subframe channel interpolation/filtering of NZP CSI-RS. The indication may be sent using any suitable signaling, such as higher layer signaling (e.g., RRC signaling).

In some embodiments, the base station 12 disables inter-subframe channel interpolation/filtering of NZP CSI-RS at the wireless device 14 for one or more specific CSI processes of the wireless device 12. For example, the base station 12 includes an indication that inter-subframe channel interpolation/filtering of NZP CSI-RS is to be disabled (i.e., not allowed) at the wireless device 14 for a specific CSI process within an RRC information element used to configure that CSI process. In this manner, the base station 12 can individually disable or enable inter-subframe channel interpolation/filtering of NZP CSI-RS for multiple CSI processes configured for the wireless device 14. In other embodiments, the base station 12 uses a single indicator to disable inter-subframe channel interpolation/filtering of NZP CSI-RS at the wireless device 14 for multiple CSI processes (e.g., two or more or even all CSI processes).

Optionally, in some embodiments, the base station 12 may also disable averaging of CSI-IM estimates at the wireless device (step 202). It is worth noting that while averaging of CSI-IM estimates is described as being disabled in some embodiments disclosed herein, the present disclosure is not limited to averaging. Averaging is merely one example of how CSI-IM estimates may be combined across subframes. Thus, in this regard, any combination (e.g., filtering or averaging) of multiple CSI-IM estimates across multiple subframes may be disabled. In other words, the base station 12 may also send an indication to the wireless device 14 indicating that the wireless device 14 will not perform averaging of CSI-IM estimates. This indication may be provided via higher layer signaling (e.g., RRC signaling). As discussed above with respect to step 200, the indication to disable averaging of CSI-IM estimates at the wireless device 14 may be provided separately for each of the multiple CSI processes, or a single indication may be used for multiple or even all CSI processes.

In response to receiving the indication from the base station 12 in step 200, the wireless device 14 performs CSI-RS measurements with inter-subframe channel interpolation/filtering of the NZP CSI-RS disabled (step 204). Similarly, if averaging of the CSI-IM estimates has been disabled, the wireless device 14 performs CSI-IM measurements with averaging of the CSI-IM estimates disabled (step 206). The wireless device 14 then provides CSI feedback to the base station 12 via CSI reports determined based on the measurements (step 208). Notably, if multiple CSI processes are present at the wireless device 14, CSI feedback can be reported to the base station 12 using a separate CSI report for each CSI process. Furthermore, if triggered (aperiodic) CSI reporting (e.g., using PUSCH in LTE) is used, the wireless device 14 can send multiple CSI reports together (stacked) in a single message (e.g., a single PUSCH message in LTE).

FIG8 illustrates operations of the base station 12 and wireless device 14 according to some embodiments of the present disclosure, wherein the base station 12 configures the wireless device 14 with a set of K CSI-RS resources, and the wireless device 14 selects a subset of the configured set of CSI-RS resources on which the wireless device 14 will perform measurements for CSI feedback. In some embodiments, the process of FIG8 is used in conjunction with the process of FIG7 (i.e., inter-subframe channel interpolation/filtering may be disabled for one or more or even all CSI processes).

As shown, the base station 12 configures the wireless device 14 with one or more sets of K CSI-RS resources (step 300). This configuration is static or semi-static. For example, the configuration can be semi-statically performed via higher layer signaling such as, for example, RRC signaling. In addition, a single set of K CSI-RS resources can be configured for all CSI processes of the wireless device 14 (i.e., the same set of K CSI-RS resources is used for all CSI processes). However, in other embodiments, a separate set of CSI-RS resources can be configured for each CSI process. In some specific embodiments, the base station 12 transmits CSI-RS to be beamformed, and the set of K CSI-RS resources configured for one CSI process or all CSI processes corresponds to K different beam directions or beams seen by the base station 12. In this case, K can be, for example, 20, because 20 two-port CSI-RS can be transmitted in a single subframe (3GPP TS 36.211 V12.3.0). Furthermore, the K beams may include a serving beam for the wireless device 14 and a plurality of adjacent beams to the serving beam for the wireless device 14 .

The wireless device 14 then dynamically selects a subset of the set of configured CSI-RS resources for CSI reporting (step 302). In embodiments where a different set of CSI-RS resources is configured for each CSI-RS process, for each CSI process, the wireless device 14 dynamically selects a subset of the set of configured CSI-RS resources for CSI reporting for that CSI process. For example, the selection may be based on an estimate of the channel strength for the configured CSI-RS resources (e.g., the subset may be selected to correspond to the N strongest channels, where 0<N≤K). The wireless device 14 performs measurements on the selected subset of the set of configured CSI-RS resources (step 304) and provides CSI feedback based on the measurements via the CSI report (step 306). Notably, the wireless device 14 may include an indication of the selected CSI-RS resources in the CSI report or provide such an indication to the base station 12 via a separate message. Steps 302-306 may be repeated periodically (eg, for periodic CSI reporting) or aperiodically (eg, for aperiodic CSI reporting). In contrast, the configuration of step 300 may be performed infrequently or only once.

FIG9 illustrates operations of a base station 12 and a wireless device 14 to enable dynamic CSI reporting according to some embodiments of the present disclosure. As shown, the base station 12 configures the wireless device 14 with one or more sets of K CSI-RS resources (step 400). This configuration is a static or semi-static configuration. For example, the configuration may be performed semi-statically via higher layer signaling, such as RRC signaling. In addition, a single set of K CSI-RS resources may be configured for all CSI processes of the wireless device 14 (i.e., the same set of K CSI-RS resources is used for all CSI processes). However, in other embodiments, a separate set of CSI-RS resources may be configured for each CSI process. In some specific embodiments, the base station 12 transmits beamformed CSI-RS, and the set of K CSI-RS resources configured for one CSI process or all CSI processes corresponds to K different beam directions or beams seen by the base station 12. In this case, K may be, for example, 20, since 20 two-port CSI-RSs may be transmitted in a single subframe (3GPP TS 36.211 V12.3.0). In addition, the K beams may include a serving beam for the wireless device 14 and multiple adjacent beams of the serving beam for the wireless device 14 .

After configuring the set of K CSI-RS resources, the base station 12 dynamically configures the CSI-RS resources for measurement from the CSI-RS resources (step 402). This dynamic configuration is performed by dynamically sending an indication to the wireless device 14 of which CSI-RS resource(s) from the set of CSI-RS resources configured for the wireless device 14 will be used for measurement. In some embodiments, the dynamic configuration is sent via an uplink scheduling grant message, a downlink assignment, a message on a dedicated control channel, a DCI message, or an LTE MAC control element (CE). The dynamic configuration is used for at least one subsequent CSI report. In some embodiments, the dynamic configuration will be used for only one subsequent CSI report. In other embodiments, the dynamic configuration will be used for multiple CSI reports until a new dynamic configuration is received.

After receiving the dynamic configuration, the wireless device 14 performs measurements on the dynamically configured CSI-RS resources (step 404) and sends a corresponding CSI report to the base station 12 (step 406). It is worth noting that the wireless device 14 can include an indication of the CSI-RS resources used for the CSI report (or some other indication that the dynamically configured CSI-RS resources are used for the CSI report) in the CSI report or provide such an indication to the base station 12 via a separate message. The CSI report can be a periodic CSI report or an aperiodic CSI report. As described above, the dynamic configuration is used for only one CSI report. In this case, the process proceeds to step 412, discussed below. However, in other embodiments, the dynamic configuration is applied until a new dynamic configuration is received. At this point, the wireless device 14 continues to perform measurements and send corresponding CSI reports, either periodically or aperiodically, until a new dynamic configuration is received (steps 408 and 410). Once the new dynamic configuration is sent by the base station 12 and received by the wireless device 14 (step 412), the wireless device 14 performs measurements on the newly configured CSI-RS resources and reports corresponding CSI reports to the base station 12 (steps 414 and 416). The process continues in this manner.

It is worth noting that in some embodiments, when performing measurements on dynamically configured CSI-RS resources, the wireless device 14 assumes PDSCH rate matching around the CSI-RS and CRS. PDSCH rate matching around the CSI-RS specifically refers to the case where the PDSCH is not mapped to any resource element (RE) in the union of the ZP CSI-RS and NZP CSI-RS resources in the set of configured CSI-RS resources. In other words, when mapping the PDSCH to REs for transmission at the base station 12, the PDSCH is not mapped to any RE included in the ZP CSI-RS and NZP CSI-RS resources in the set of configured CSI-RS resources.

FIG10 illustrates the operation of the base station 12 and wireless device 14 according to some embodiments, wherein after the CSI reporting on the dynamically configured CSI-RS resources is completed, the CSI-RS resource configuration reverts to a default configuration. In this example, steps 500-506 are identical to steps 400-406 of FIG9 , and therefore the details are not repeated. After sending a CSI report based on the dynamically configured CSI-RS resources in step 506, rather than continuing to report using the same dynamically configured CSI-RS resources, the wireless device 14 reverts to the default CSI-RS resources (step 506). Specifically, the wireless device 14 performs measurements on the default CSI-RS resources (step 508) and sends corresponding CSI reports to the base station 12 (step 510). The CSI reports can be periodic CSI reports or aperiodic CSI reports. In this example, the wireless device 14 continues to perform measurements and send corresponding CSI reports periodically or aperiodically based on the default CSI-RS resources until a new dynamic configuration is sent by the base station 12 and received by the wireless device 14 (step 512). Once the wireless device 14 receives the new dynamic configuration, it performs measurements on the newly configured CSI-RS resources and reports the corresponding CSI report to the base station 12 (steps 514 and 516). The process continues in this manner. It is worth noting that in some embodiments, when performing measurements on the dynamically configured CSI-RS resources, the wireless device 14 assumes that the PDSCH rate around the CSI-RS and CRS is matched.

FIG11 illustrates an embodiment in which CSI-RS resources are dynamically configured via DCI messages. Using DCI messages for dynamic configuration may be particularly well suited for aperiodic CSI reporting, but is not limited thereto. As shown, the base station 12 configures the wireless device 14 with one or more sets of K CSI-RS resources (step 600). As described above, the configuration is a static or semi-static configuration. For example, the configuration may be performed semi-statically via higher layer signaling, such as RRC signaling. In addition, a single set of K CSI-RS resources may be configured for all CSI processes of the wireless device 14 (i.e., the same set of K CSI-RS resources is used for all CSI processes). However, in other embodiments, a separate set of CSI-RS resources may be configured for each CSI process. In some specific embodiments, the base station 12 transmits beamformed CSI-RS, and the set of K CSI-RS resources configured for one CSI process or all CSI processes corresponds to K different beam directions or beams seen by the base station 12. In this case, K may be, for example, 20, since 20 two-port CSI-RSs may be transmitted in a single subframe (3GPP TS 36.211 V12.3.0). In addition, the K beams may include a serving beam for the wireless device 14 and multiple adjacent beams of the serving beam for the wireless device 14 .

After configuring the set of K CSI-RS resources, the base station 12 dynamically configures CSI-RS resources from the set of CSI-RS resources for measurement via a DCI message (step 602). The DCI message includes an indication (e.g., one or more indices) of the configured CSI-RS resources from the set of configured CSI-RS resources. After receiving the dynamic configuration, the wireless device 14 performs measurements on the dynamically configured CSI-RS resources (step 604) and sends a corresponding CSI report to the base station 12 (step 606), as described above. Although not limited to this, in this example, the wireless device 14 continues to use the same dynamically configured CSI-RS resources for one or more subsequent CSI reports (not shown). This may be the case, for example, if the CSI report is a periodic report. However, in other embodiments, the CSI report is aperiodic, and the CSI-RS resources to be used may be dynamically configured for each aperiodic CSI report, for example. Once the new dynamic configuration is sent by the base station 12 and received by the wireless device 14 (step 612), the wireless device 14 performs measurements on the newly configured CSI-RS resources and reports the corresponding CSI report (steps 614 and 616). The process continues in this manner. It is worth noting that in some embodiments, when performing measurements on the dynamically configured CSI-RS resources, the wireless device 14 assumes that the PDSCH rate around the CSI-RS is matched.

Figure 12 shows an embodiment in which CSI-RS resources are dynamically configured via LTE MAC CE. In this particular example, CSI reporting is periodic; however, the present disclosure is not limited thereto. As shown, the base station 12 configures the wireless device 14 with one or more sets of K CSI-RS resources (step 700). As described above, the configuration is a static configuration or a semi-static configuration. For example, the configuration can be performed semi-statically via higher layer signaling such as RRC signaling. In addition, a single set of K CSI-RS resources can be configured for all CSI processes of the wireless device 14 (i.e., the same set of K CSI-RS resources is used for all CSI processes). However, in other embodiments, a separate set of CSI-RS resources can be configured for each CSI process. In some specific embodiments, the base station 12 transmits beamformed CSI-RS, and the set of K CSI-RS resources configured for one CSI process or all CSI processes corresponds to K different beam directions or beams seen by the base station 12. In this case, K may be, for example, 20, since 20 two-port CSI-RSs may be transmitted in a single subframe (3GPP TS 36.211 V12.3.0). In addition, the K beams may include a serving beam for the wireless device 14 and multiple adjacent beams of the serving beam for the wireless device 14 .

After configuring the set of K CSI-RS resources, the base station 12 dynamically configures CSI-RS resources from the set of CSI-RS resources for measurement via an LTE MAC CE (step 702). The LTE MAC CE includes an indication (e.g., one or more indices) of the configured CSI-RS resources from the set of configured CSI-RS resources. In response to receiving the dynamic configuration, the wireless device 14 sends an acknowledgment (e.g., HARQ-ACK) to the base station 12 confirming receipt of the transport block containing the LTE MAC CE (step 704).

It takes a certain amount of time for the wireless device 14 to take effect of the dynamic configuration of the CSI-RS resources, i.e., to start measuring and reporting CSI measurements of the CSI-RS resources. Particularly for periodic CSI reporting, this results in an ambiguity period during which any CSI report received from the wireless device 14 is inaccurate (i.e., the CSI report is based on measurements on the previously configured CSI-RS resources, rather than on measurements on the newly configured CSI-RS resources). Therefore, in this example, the base station 12 discards any CSI reports received from the wireless device 14 during a predefined amount of time after receiving the acknowledgment from the wireless device 14 in step 704 (steps 706 and 708). This predefined amount of time is greater than or equal to the amount of time it takes for the wireless device 14 to take effect of the dynamic configuration of the CSI-RS resources received in step 702.

In response to receiving the dynamic configuration in step 702, the wireless device 14 performs measurements on the dynamically configured CSI-RS resources (step 710) and sends a corresponding CSI report to the base station 12 (step 712), as described above. Notably, the time required for the wireless device 14 to perform the measurements in step 710 may be part of the ambiguity time discussed above. Notably, the wireless device 14 may include an indication of the CSI-RS resources used for CSI reporting (or some other indication that the dynamically configured CSI-RS resources are used for CSI reporting) in the CSI report or provide such an indication to the base station 12 via a separate message. In this case, since the predefined amount of time has expired since receiving the acknowledgment in step 704, the base station 12 may determine that the CSI report is based on the CSI-RS resources configured in step 702. Thus, the base station 12 processes the CSI report (e.g., for selecting transmission parameters for the downlink to the wireless device 14 in a conventional manner) (step 714). Notably, in some embodiments, the CSI report includes an indication that the dynamically configured CSI-RS resources have been used for CSI reporting. The indication may be, for example, an indication (eg, an index) of a CSI-RS resource to be used for CSI reporting or any other suitable indication.

At this point, as described above, the wireless device 14 may continue to use the same dynamically configured CSI-RS resources for one or more subsequent CSI reports (not shown). This may be the case, for example, if the CSI report is a periodic report. However, in other embodiments, the CSI report is aperiodic, and the CSI-RS resources to be used may be dynamically configured for each aperiodic CSI report, for example. In other embodiments, the wireless device 14 may revert to a default CSI-RS resource until a new dynamic configuration is received. Notably, in some embodiments, when performing measurements on the dynamically configured CSI-RS resources, the wireless device 14 assumes that the PDSCH rate around the CSI-RS is matched.

While the embodiments described above with respect to Figures 9-12 focus on the dynamic configuration of general CSI-RS resources, it should be noted that in some embodiments, these CSI-RS resources are NZP CSI-RS resources, and in other embodiments, these CSI-RS resources are NZP CSI-RS resources and/or CSI-IM resources. In this regard, Figure 13 illustrates the operation of the base station 12 to dynamically configure NZP CSI-RS resources and CSI-IM resources according to some embodiments of the present disclosure. As shown, the base station 12 configures the wireless device 14 with one or more sets of K CSI-RS resources (step 800). As described above, this configuration is static or semi-static. For example, the configuration can be semi-static via higher layer signaling, such as RRC signaling. Furthermore, a single set of K CSI-RS resources can be configured for all CSI processes of the wireless device 14 (i.e., the same set of K CSI-RS resources is used for all CSI processes). However, in other embodiments, a separate set of CSI-RS resources can be configured for each CSI process. In some specific embodiments, the base station 12 transmits beamformed CSI-RS, and the set of K CSI-RS resources configured for one CSI process or all CSI processes corresponds to K different beam directions or beams seen by the base station 12. In this case, K can be, for example, 20, since 20 two-port CSI-RS can be transmitted in a single subframe (3GPP TS 36.211 V12.3.0). In addition, the K beams can include the serving beam of the wireless device 14 and multiple adjacent beams of the serving beam of the wireless device 14. In some embodiments, the set of CSI-RS resources includes a first set of NZP CSI-RS resources and a second set of CSI-IM resources (which can also be referred to as ZP CSI-RS resources).

After configuring the set of K CSI-RS resources, the base station 12 dynamically configures NZP CSI-RS resources and CSI-IM resources from the set of CSI-RS resources for measurement (step 802). The details of the dynamic configuration are as described above. For example, the dynamic configuration may include different NZP CSI-RS resources and CSI-IM resources for each of two or more CSI processes. In other words, the dynamic configuration may be CSI process specific. In addition, the dynamic configuration may be performed by sending an appropriate indication in, for example, a DCI message or an LTE MAC CE. In some embodiments, the set of CSI-RS resources configured in step 800 includes a set of NZP CSI-RS resources and a set of CSI-IM resources. Then, in step 802, the base station 12 dynamically configures one or more NZP CSI-RS resources from the set of NZP CSI-RS resources for measurement (e.g., one NZP CSI-RS resource is configured for each CSI process) and dynamically configures one or more CSI-IM resources from the set of CSI-IM resources for interference measurement (e.g., one CSI-IM resource is configured for each CSI process).

In response to receiving the dynamic configuration, the wireless device 14 performs measurements on the dynamically configured NZP CSI-RS resources and CSI-IM resources (step 804). Measurements on the NZP CSI-RS resources are measurements of the desired signal, while measurements on the CSI-IM resources are measurements of interference, as will be understood by those skilled in the art after reading this disclosure. The wireless device 14 sends a corresponding CSI report to the base station 12 based on the measurements on the dynamically configured CSI-RS resources and CSI-IM resources (step 806). It is worth noting that the wireless device 14 can include an indication of the NZP CSI-RS and CSI-IM resources used for the CSI report in the CSI report (or other indication of the dynamically configured NZP CSI-RS and CSI-IM resources) or provide such an indication to the base station 12 via a separate message.

At this point, as described above, the wireless device 14 may continue to use the same dynamically configured NZP CSI-RS resources and CSI-IM resources for one or more subsequent CSI reports (not shown). This may be the case, for example, if the CSI report is a periodic report. However, in other embodiments, the CSI report is aperiodic, and the CSI-RS resources to be used may be dynamically configured for each aperiodic CSI report, for example. In other embodiments, the wireless device 14 may revert to a default CSI-RS resource until a new dynamic configuration is received. Notably, in some embodiments, when performing measurements on the dynamically configured CSI-RS resources, the wireless device 14 assumes that the PDSCH rate around the CSI-RS is matched.

As described above, in some embodiments, the set of K CSI-RS resources configured for the wireless device 14 corresponds to K different beam directions from the perspective of the base station 12. Furthermore, in some embodiments, the K different beam directions include the beam direction of the serving beam of the wireless device 14 and the beam directions of multiple adjacent beams of the serving beam of the wireless device 14. Then, when the wireless device 14 switches from one beam to another (i.e., when the serving beam of the wireless device 14 changes), the base station 12 can dynamically configure (and reconfigure) the CSI-RS resources for measurement at the wireless device 14. In this regard, Figure 14 illustrates the operation of the base station 12 according to some embodiments of the present disclosure. As shown, the base station 12 configures the wireless device 14 with the set of K CSI-RS resources (step 900). As described above, the configuration can be performed via higher layer signaling (e.g., RRC signaling). Furthermore, the set of K CSI-RS resources may be used for multiple CSI processes (e.g., all CSI processes configured for the wireless device 14) or for a single CSI process (e.g., a separate set of CSI-RS resources may be configured for each CSI process). Here, the base station 12 transmits beamformed CSI-RS, and the set of K CSI-RS resources is transmitted by K adjacent beams. The adjacent beams include the serving beam of the wireless device 14 and multiple adjacent beams of the serving beam of the wireless device 14.

The base station 12 dynamically configures CSI-RS resources from a set of CSI-RS resources for measurement and CSI reporting for the serving beam and one or more neighboring beams of the wireless device 14 (step 902). The dynamic configuration can be performed via any suitable mechanism such as, for example, a DCI message or an LTE MAC CE. The base station 12 can configure one resource from the set of CSI-RS resources as an NZP CSI-RS for measurement on the serving beam and configure one or more other CSI-RS resources from the set as CSI-RS resources for interference measurement. As the wireless device 14 switches from one beam to another, the CSI-RS resources can continue to be dynamically configured so that different CSI-RS resources are configured for measurement and interference measurement.

15 is a block diagram of a base station 12 (e.g., an eNB) according to some embodiments of the present disclosure. As shown, the base station 12 includes a baseband unit 16, which includes at least one processor 18 (e.g., a central processing unit (CPU), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), etc.), a memory 20, and a network interface 22, and a radio unit 24 including a wireless or radio frequency (RF) transceiver 26, which includes one or more transmitters 28 and one or more receivers 30 coupled to one or more antennas 32. In some embodiments, the functionality of the base station 12 described herein is implemented in software stored in the memory 20 and executed by the at least one processor 18, whereby the base station 12 operates to, for example, configure a set of CSI-RS resources for the wireless device 14, configure measurement purposes for at least some resources in the configured set, and possibly all of the CSI-RS resources, etc.

In some embodiments, a computer program is provided, wherein the computer program includes instructions that, when executed on at least one processor (e.g., at least one processor 18), cause the at least one processor to perform the functionality of the base station 12 according to any one of the embodiments described herein. In some embodiments, a carrier embodying the computer program is provided, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium (e.g., a non-transitory computer-readable medium).

FIG16 illustrates a base station 12 according to another embodiment of the present disclosure. As shown, the base station 12 includes a disabling module 34 (in some embodiments only) and a CSI-RS indication module 36 (in some embodiments only), each of which is implemented in software. The disabling module 34 operates to disable inter-subframe channel interpolation/filtering of NZP CSI-RS belonging to a CSI process and/or averaging of CSI-IM for the wireless device 14, as described above, by, for example, sending an appropriate message or signal via an associated transmitter of the base station 12. The CSI-RS indication module 36 operates to indicate to the wireless device 14 which CSI-RS to measure, for example, by sending an appropriate message or signal via an associated transmitter of the base station 12. As described above, the indication of the CSI-RS resources that the wireless device 14 is to measure can be provided by first configuring the wireless device 14 with a static or semi-static set of CSI-RS resources (e.g., via RRC signaling), and then dynamically configuring the CSI-RS resources on which the wireless device 14 is to measure, for example, via a DCI message or LTE MAC CE.

17 is a block diagram of a wireless device 14 according to some embodiments of the present disclosure. As shown, the wireless device 14 includes at least one processor 40, memory 42, and a wireless or RF transceiver 44 including one or more transmitters 46 and one or more receivers 48 coupled to one or more antennas 50. In some embodiments, the functionality of the wireless device 14 described herein is implemented in software stored in the memory 42 and executed by the at least one processor 40.

In some embodiments, a computer program is provided, wherein the computer program includes instructions that, when executed on at least one processor (e.g., at least one processor 40), cause the at least one processor to perform the functions of the wireless device 14 according to any of the embodiments described herein. In some embodiments, a carrier embodying the computer program is provided, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium (e.g., a non-transitory computer-readable medium).

FIG18 illustrates a wireless device 14 according to some other embodiments of the present disclosure. As shown, the wireless device 14 includes a CSI-RS indication module 52, a metric calculation module 54, and a reporting module 56, each of which is implemented in software. The CSI-RS indication module 52 operates to receive, via a receiver (not shown) of the wireless device 14, an indication of which CSI-RS to measure. As described above, the CSI-RS indication module 52 may first receive a static or semi-static configuration of a set of CSI-RS resources (e.g., configuring a set of CSI resources for each CSI process, or configuring a set of CSI-RS resources for multiple CSI processes). The CSI-RS indication module 52 then receives, via a receiver (not shown) of the wireless device 14, a dynamic configuration of which CSI-RS resources in the configured set of CSI-RS resources the wireless device 14 is to measure on for CSI reporting. The metric calculation module 54 then calculates the measurements on the dynamically configured CSI-RS resources. The reporting module 56 then sends a CSI report based on the measurements to the network (eg, to the base station 12) via an associated transmitter (not shown) of the wireless device 14.

Embodiments of systems and methods for flexible CSI feedback are disclosed. In some embodiments, a network node (e.g., a radio access node such as, but not limited to, a base station) indicates to a wireless device (e.g., a UE) which CSI-RS resources to measure. In some embodiments, this is achieved by providing an uplink grant to the wireless device.

In one embodiment, the base station configures the wireless device with a set of K CSI-RS resources, for example, through higher layer signaling using, for example, an RRC message. The base station may then indicate to the wireless device in an uplink scheduling grant message or some other form of message (e.g., a downlink assignment, a MAC CE, or a dedicated message on a downlink control channel) at least one CSI-RS resource of the K CSI-RS resources to be used by the wireless device. The at least one CSI-RS resource is the CSI-RS resource for which the UE should perform channel measurements. The wireless device then calculates measurements on at least one CSI-RS resource in the set of K possible CSI-RS resources. In some embodiments, the K CSI-RS resources may correspond to K different beam directions seen by the base station. In one embodiment, K=20 because 20 dual-port CSI-RSs may be sent in a single subframe.

In some embodiments, the network node also indicates to the wireless device that the wireless device should disable inter-subframe channel interpolation/filtering of NZP CSI-RS belonging to a CSI process before indicating to the wireless device which CSI-RS resource to measure. In some embodiments, this is achieved via higher layer signaling such as RRC signaling or via a DCI message. In some embodiments, the base station also indicates that averaging of CSI-IM estimates across subframes is not allowed. In some embodiments, the signaling may also indicate which CSI processes this applies to (e.g., predetermined to be all or a subset of possible CSI processes). In some embodiments, the RRC information element used to configure the CSI process may be extended with a bit that controls whether inter-subframe NZP CSI-RS filtering is enabled or disabled.

In some embodiments, the wireless device then measures the indicated CSI-RS. The wireless device then reports the selected CSI-RS to the base station. In some embodiments, this is periodically scheduled CSI feedback. In some embodiments, this is aperiodic CSI feedback. In some embodiments, the aperiodic request is sent in an uplink grant.

In some embodiments, the wireless device is monitoring a set of NZP CSI-RS configurations and selects a subset of those NZP CSI-RS configurations for reporting CSI. In some embodiments, the selection may be based, for example, on an estimate of the channel strength of the monitored NZP CSI-RS configurations (e.g., the subset may be selected to correspond to the N strongest channels).

In some embodiments, the base station also indicates which of the CSI-RS resources should be used as the CSI-IM resource. In some embodiments, the wireless device shall assume PDSCH rate matching around all CSI-RS resources indicated in the higher layer configuration.

In some embodiments, periodic CSI reporting using the PUCCH is calculated based on the CSI-RS resource indicated in the downlink DCI message. The wireless device uses the selected CSI-RS resource for CSI feedback until the wireless device receives an indication of a new CSI-RS in the DCI message. Additionally, the wireless device may provide an indication of which CSI-RS resource was measured, including an index of the measured CSI-RS resource or, alternatively, a bit confirming that the downlink DCI message was successfully received and that the CSI-RS resource in the DCI message was used for measurement.

In some embodiments, periodic CSI reporting using the PUCCH is calculated based on the CSI-RS resource indicated in the LTE MAC CE. In some embodiments, the wireless device may provide an indication confirming which CSI-RS resource was measured, including an index of the measured CSI-RS resource, or alternatively, a bit confirming that the MAC CE was successfully received and that the CSI-RS resource was used for measurement.

In some embodiments, the CSI resources configured for the wireless device are sent in adjacent beams. Thus, the base station can dynamically change the CSI measurement report from the wireless device for the current beam serving the wireless device and the adjacent beams of the serving beam.

Embodiments of systems and methods for CSI feedback are disclosed. In one embodiment, a method for dynamic CSI feedback has low UE complexity and solves the above-mentioned problems:

o A signaling message is sent from the eNB to the UE so that the UE disables inter-subframe channel interpolation/filtering of the NZP CSI-RS belonging to the CSI process.

o Dynamically signaled messages (e.g., uplink grants scheduling (aperiodic) CSI reporting) contain an indicator that specifies on which CSI-RS resource the UE should perform measurements for subsequent aperiodic CSI feedback sent on the PUSCH.

• Since the uplink grant is transmitted by Layer 1, and since the UE only transmits aperiodic reports when triggered, there is no uncertainty as to when the UE has received the indication.

o After receiving the CSI-RS resource indicator carried by DCI, subsequent periodic CSI reports sent using PUCCH will be based on measurements on the indicated CSI-RS.

• A confirmation indicator of the CSI-RS resources may be included in the periodic CSI-RS report to verify that the DCI was received and that the measured CSI-RS resources are the CSI-RS resources carried by the DCI.

When operating in an environment where CSI-RS needs to be reconfigured frequently, such as in cases of many small cells or narrow beams and medium to high UE mobility, embodiments of the CSI feedback framework disclosed herein have greater benefits than the LTE CSI framework.

The following abbreviations are used throughout this disclosure.

μs microseconds

2D

3GPP Third Generation Partnership Project

ACK

ABS Almost Blank Subframe

AP antenna port

ARQ Automatic Repeat Request

ASIC Application-Specific Integrated Circuit

CDM Code Division Multiplexing

CE control components

CFI Control Format Indicator

CoMP Coordinated Multipoint

CPU Central Processing Unit

CQI Channel Quality Information

CRS Cell Specific Reference Symbol

CSI Channel State Information

CSI-RS Channel State Information Reference Signal

DCI Downlink Control Information

DFT Discrete Fourier Transform

DL Downlink

eNB Enhanced or evolved Node B.

EPDCCH Enhanced Physical Downlink Control Channel

FPGA Field Programmable Gate Array

GSM Global System for Mobile Communications

HARQ Hybrid Automatic Repeat Request

ID identifier

IM interference measurement

LTE Long Term Evolution

MAC Media Access Control

ms milliseconds

NZP Non-Zero Power

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

PMI Precoding Matrix Indicator

PRB Physical Resource Block

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

OFDM Orthogonal Frequency Division Multiplexing

QPSK Quadrature Phase Shift Keying

RB Resource Block

RE resource element

RF

RI rating indicator

RPSF Reduced Power Subframe

RRC Radio Resource Control

SF subframe

TM9 Transmission Mode 9

TM10 transmission mode 10

TS Technical Specifications

TP transmission point

UE User Equipment

UL uplink

UMB Ultra Mobile Broadband

WCDMA Wideband Code Division Multiple Access

ZP Zero Power

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure, and all such improvements and modifications are considered to be within the scope of the concepts disclosed herein.

Claims (29)

1. A method for controlling the operation of channel estimation based on Channel State Information Reference Symbols (CSI-RS) at a wireless device (14) in a base station (12) of a cellular communication network (10), comprising: Disable (200) inter-subframe channel interpolation of CSI-RS estimation across subframes at the wireless device (14); Disable the combination of CSI-IM estimation for cross-subframe CSI interference measurement at the wireless device (14); and Receive (208) one or more Channel State Information (CSI) reports from the wireless device (14), the one or more Channel State Information (CSI) reports being generated by the wireless device (14) having the following: inter-subframe channel interpolation of disabled cross-subframe CSI-RS estimates, and a combination of disabled cross-subframe CSI-IM estimates. 2. The method according to claim 1, wherein the base station (12) transmits beamformed CSI-RS resources and reuses the same CSI-RS resources over time for different beam directions, the beamformed CSI-RS resources corresponding to the beam direction. 3. The method according to claim 1 or 2, wherein the wireless device (14) uses two or more CSI processes for CSI reporting and disables (200) inter-subframe channel interpolation of CSI-RS estimation across subframes, comprising: disabling (200) inter-subframe channel interpolation and/or filtering of CSI-RS estimation across subframes on a per-CSI process basis. 4. The method according to claim 1 or 2, wherein the wireless device (14) uses two or more CSI processes for CSI reporting and disables (200) inter-subframe channel interpolation of CSI-RS estimation across subframes, comprising: disabling (200) inter-subframe channel interpolation of CSI-RS estimation across subframes for all CSI processes of the two or more CSI processes. 5. The method according to claim 1 or 2, wherein disabling (200) inter-subframe channel interpolation of CSI-RS estimation across subframes comprises: disabling (200) inter-subframe channel interpolation of CSI-RS estimation across subframes via Radio Resource Control (RRC) signaling. 6. The method of claim 5, wherein disabling (200) inter-subframe channel interpolation of CSI-RS estimation across subframes via RRC signaling comprises: In the RRC information element configuring the CSI process of the wireless device (14), an indication is sent that inter-frame channel interpolation for the CSI-RS estimation across subframes of the CSI process of the wireless device (14) is not allowed. 7. The method of claim 1 or 2, wherein disabling (200) inter-subframe channel interpolation of CSI-RS estimation across subframes comprises: signaling the wireless device (14) an indication that inter-subframe channel interpolation of CSI-RS estimation across subframes is not permitted. 8. The method according to claim 1 or 2, further comprising: configuring (300) the wireless device (14) using a set of CSI-RS resources. 9. The method of claim 8, wherein receiving (208) the one or more CSI reports from the wireless device (14) comprises: receiving CSI reports for a subset of the set of CSI-RS resources configured for the wireless device (14). 10. The method of claim 8, wherein configuring (300) the wireless device (14) using the set of CSI-RS resources comprises: configuring (300) the wireless device (14) using the set of CSI-RS resources via Radio Resource Control (RRC) signaling. 11. The method of claim 8, wherein configuring (300) the wireless device (14) using the set of CSI-RS resources comprises: semi-statically configuring (300) the wireless device (14) using the set of CSI-RS resources. 12. The method of claim 8, wherein the set of CSI-RS resources is specific to the CSI process of the wireless device (14). 13. The method of claim 8, wherein the base station (12) transmits beamformed CSI-RS, and the method further comprises: dynamically changing the beams used on the set of CSI-RS resources configured for the wireless device (14), each beam corresponding to a different beam direction. 14. A base station (12) of a cellular communication network (10), the base station (12) being enabled to control channel estimation based on Channel State Information Reference Symbols (CSI-RS) at a wireless device (14), the base station (12) comprising: At least one transmitter (28); At least one receiver (30); At least one processor (18); and Memory (20) storing software instructions executable by the at least one processor (18), thereby enabling the base station (12) to: Inter-subframe channel interpolation of CSI-RS estimation across subframes is disabled at the wireless device (14) via the at least one transmitter (28); The combination of CSI-IM estimation for cross-subframe CSI interference measurement is disabled at the wireless device (14) via the at least one transmitter (28); and The channel state information (CSI) report is received from the wireless device (14) via the at least one receiver (30). The channel state information (CSI) report is generated by the wireless device (14) in response to the disabling (200) of inter-subframe channel interpolation of cross-subframe CSI-RS estimation and the disabling (202) of the combination of cross-subframe CSI-IM estimation at the wireless device (14). 15. A computer-readable storage medium storing a computer program comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method according to any one of claims 1 to 13. 16. A method for a wireless device (14) in a cellular communication network (10) to provide a Channel State Information (CSI) report, comprising: Receive (200) an indication from the base station (12) of the cellular communication network (10) to disable inter-subframe channel interpolation estimated by the Channel State Information Reference Symbol (CSI-RS) across subframes; In response, one or more CSI-RS measurements are performed if inter-subframe channel interpolation of cross-subframe CSI-RS estimation is disabled; Receive (202) an indication from the base station (12) of the cellular communication network (10) to disable the combination of CSI-IM estimation for cross-subframe CSI interference measurement; In response, one or more CSI-IM measurements are performed (206) if the combination of CSI-IM estimates across subframes is disabled; and Send (208) a CSI report (208) to the base station (12) which is determined from the one or more CSI-RS measurements and the one or more CSI-IM measurements. 17. The method of claim 16, wherein the base station (12) transmits beamformed CSI-RS resources and reuses the same CSI-RS resources over time for different beams. 18. The method of claim 16 or 17, wherein the wireless device (14) uses two or more CSI processes for CSI reporting, and the indication received from the base station (12) is an indication to disable inter-subframe channel interpolation of CSI-RS estimation across subframes for a specific CSI process. 19. The method of claim 16 or 17, wherein the wireless device (14) uses two or more CSI processes for CSI reporting, and the indication received from the base station (12) is an indication to disable inter-subframe channel interpolation of CSI-RS estimation across subframes for all CSI processes of the two or more CSI processes. 20. The method of claim 16 or 17, wherein receiving (200) the indication comprises: receiving (200) the indication via Radio Resource Control (RRC) signaling. 21. The method of claim 20, wherein the wireless device (14) uses two or more CSI processes for CSI reporting, and the indication received from the base station (12) is an indication to disable inter-subframe channel interpolation of CSI-RS estimation across subframes for a specific CSI process of the wireless device (14), and receiving (200) the indication comprises: receiving (200) the indication included in an RRC information element, the RRC information element configuring the specific CSI process of the wireless device (14). 22. The method according to claim 16 or 17, further comprising: Receive (300) the configuration of the set of CSI-RS resources for the wireless device (14). 23. The method of claim 22, wherein the CSI report is for a subset of the set of CSI-RS resources configured for the wireless device (14). 24. The method of claim 22, wherein the configuration for receiving the set of (300) CSI-RS resources comprises: receiving the set of (300) CSI-RS resources from the base station (12) via Radio Resource Control (RRC) signaling. 25. The method of claim 22, wherein the configuration of the set of CSI-RS resources is semi-static. 26. The method of claim 22, wherein the set of CSI-RS resources is specific to the CSI process of the wireless device (14). 27. The method of claim 22, wherein the base station (12) transmits beamformed CSI-RS, and the beam used on the set of CSI-RS resources configured for the wireless device (14) is dynamically changed. 28. A wireless device (14) for providing Channel State Information (CSI) reports in a cellular communication network (10), comprising: At least one transmitter (46); At least one receiver (48); At least one processor (40); and Memory (42) storing software instructions executable by the at least one processor (40), thereby enabling the wireless device (14) to: The at least one receiver (48) receives from the base station (12) of the cellular communication network (10) an indication to disable inter-subframe channel interpolation estimated by the Channel State Information Reference Symbol (CSI-RS) across subframes; In response, one or more CSI-RS measurements are performed if inter-subframe channel interpolation of cross-subframe CSI-RS estimation is disabled; The at least one receiver (48) receives an instruction from the base station (12) of the cellular communication network (10) to disable the combination of CSI-IM estimation for cross-subframe CSI interference measurement; In response, one or more CSI-IM measurements are performed if the combination of CSI-IM estimates across subframes is disabled; and Send a CSI report to the base station (12) based on the CSI-RS measurements and the CSI-IM measurements. 29. A computer-readable storage medium storing a computer program comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method according to any one of claims 16 to 27.