Patent Description:
LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform-spread (DFT-spread) OFDM in the uplink. <FIG> illustrates the basic LTE downlink physical resource can thus be seen as a time-frequency grid, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.

<FIG> illustrates LTE downlink transmissions in the time domain. The LTE downlink transmissions are organized into radio frames of <NUM>, each radio frame consisting often equally-sized subframes of length Tsubframe = <NUM>.

Furthermore, the resource allocation in LTE is typically described in terms of resource blocks (RBs), where a resource block corresponds to one slot (<NUM>) in the time domain and twelve contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with zero from one end of the system bandwidth.

<FIG> illustrates an example downlink subframe. Downlink transmissions are dynamically scheduled. In other words, in each subframe the base station transmits control information about to which terminals data is transmitted and upon which resource blocks the data is transmitted in the current downlink subframe. This control signaling is typically transmitted in the first <NUM>, <NUM>, <NUM> or <NUM> OFDM symbols in each subframe. For example, <FIG> illustrates a downlink system with <NUM> OFDM symbols as control.

In LTE, a number of physical downlink (DL) channels and transmission modes are supported. A downlink physical channel corresponds to a set of resource elements carrying information originating from higher layers. The following are some of the physical channels supported in LTE:.

PDSCH is used mainly for carrying user traffic data and higher layer messages. PDSCH is transmitted in a DL subframe outside of the control region as shown in <FIG>. Both PDCCH and EPDCCH are used to carry Downlink Control Information (DCI) such as physical resource block (PRB) allocation, modulation level and coding scheme (MCS), precoder used at the transmitter, and other information. PDCCH is transmitted in the first one to four OFDM symbols in a DL subframe, which is the control region, while EPDCCH is transmitted in the same region as PDSCH.

Different DCI formats are defined in LTE for DL and uplink (UL) data scheduling. For example, as provided in 3GPP TS <NUM>, DCI formats <NUM> and <NUM> are used for UL data scheduling while DCI formats <NUM>, 1A, 1B, 1C, 1D, <NUM>, 2A, 2B, 2C, 2D, <NUM>/3A are used for DL data scheduling. There are two search spaces defined for PDCCH, i.e. a common search space and a user equipment (UE) specific search space. The common search space consists of PDCCH resources over which all UEs monitor for PDCCH(es). A PDCCH intended for all or a group UEs is always transmitted in the common search space so all UE can receive it. UE specific search space consists of PDCCH resources that can vary from UE to UE. A UE monitors both the common search space and the UE specific search space associated with it for PDCCH(es). DCI 1C carries information for PDSCH intended for all UEs or for UEs that have not been assigned with a Radio Temporary Network Identifier (RNTI). Thus, DCI 1C is always transmitted in the common search space. DCI <NUM> and DCI 1A can be transmitted on either common or UE specific search space. DCI 1B, 1D, <NUM>, 2A, 2C, and 2D are always transmitted on UE specific search space.

In DL, which DCI format is used for data scheduling is associated with a DL transmission scheme and/or the type of message to be transmitted. The following are some of the transmission schemes supported in LTE.

PDCCH is always transmitted with either the single-antenna port or Transmit Diversity scheme while PDSCH can use any one of the transmission schemes. In LTE, a UE is configured with a transmission mode (TM), rather than a transmission scheme. There are <NUM> TMs, i.e. TM1 to TM10, defined so far for PDSCH in LTE. Each TM defines a primary transmission scheme and a backup transmission scheme. The backup transmission scheme is either single antenna port or TxD. The primary transmission schemes in LTE include:.

In TM1 to TM6, cell specific reference signal (CRS) is used as the reference signal for both CSI feedback and for demodulation at a UE. While in TM7 to TM10, UE specific demodulation reference signal (DMRS) is used as the reference signal for demodulation.

Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a multiple-input multiple-output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO.

A core component in LTE is the support of MIMO antenna deployments and MIMO related techniques. Currently, up to <NUM>-layer spatial multiplexing in the downlink with <NUM>,<NUM>,<NUM>,<NUM> transmit (Tx) antenna ports laid out in one dimension or <NUM>,<NUM>, and <NUM> transmit antenna ports laid out in two dimensions (2D) is supported in LTE with channel dependent precoding; The spatial multiplexing mode is aimed for high data rates in favorable channel conditions.

<FIG> illustrates an example spatial multiplexing operation. As depicted, the information carrying symbol vector, s, is multiplied by an NT x r precoder matrix W, which serves to distribute the transmit energy in a subspace of the NT (corresponding to NT antenna ports) dimensional vector space. The precoder matrix is typically selected from a codebook of possible precoder matrices, and typically indicated by means of a precoder matrix indicator (PMI), which specifies a unique precoder matrix in the codebook for a given number of symbol streams. Symbol vector, s, is a rx1 vector with r data symbols each corresponding to a data layer and r is referred to as the transmission rank. In this way, spatial multiplexing is achieved since multiple symbols can be transmitted simultaneously over the same time/frequency resource element (TFRE). The number of symbols r is typically adapted to suit the current channel properties.

LTE uses OFDM in the downlink (and DFT precoded OFDM in the uplink) and hence the received NR × <NUM> (NR is number of receive antennas at a UE) vector yn for a certain TFRE on subcarrier n (or alternatively data TFRE number n) is thus modeled by <MAT> where Hn is a NRxNT MIMO channel matrix, sn is a r × <NUM> transmitted data symbol vector, and en is a noise/interference vector. The precoder, W, can be a wideband precoder, which is constant over frequency, or frequency selective (i.e. it may be different from one RB to another).

The precoder matrix is often chosen to match the characteristics of the NRxNT MIMO channel matrix Hn, resulting in so-called channel dependent precoding. This is also commonly referred to as closed-loop precoding and essentially strives for focusing the transmit energy into a subspace which is strong in the sense of conveying much of the transmitted energy to the UE. In addition, the precoder matrix may also be selected to strive for orthogonalizing the channel, meaning that after proper linear equalization at the UE, the inter-layer interference is reduced.

The transmission rank, and thus the number of spatially multiplexed layers, is reflected in the number of columns of the precoder. For efficient performance, it is important that a transmission rank that matches the channel properties is selected.

When all the data layers are transmitted to one UE, it is referred to as single user MIMO or SU-MIMO. On the other hand, when the data layers are transmitted to multiple UEs, it is referred to as multi-user MIMO or MU-MIMO. MU-MIMO is possible when, for example, two UEs are located in different areas of a cell such that they can be separated through different precoders (or beamforming) at the eNodeB (eNB) (a network node in LTE), the two UEs may be served on the same time-frequency resources (i.e. PRBs) by using different precoders or beams. In DMRS based transmission modes <NUM> and <NUM>, different DMRS ports and/or the same DMRS port with different scrambling codes can be assigned to the different UEs for MU-MIMO transmission. In this case, MU-MIMO is transparent to UE. For example, a UE is not informed about the co-scheduling of another UE in the same PRBs.

MU-MIMO requires much more accurate downlink channel information than in SU-MIMO in order for the eNB to use precoding to separate the UEs, i.e. reducing cross interference to the co-scheduled UEs by forming nulls toward the co-scheduled UEs.

In closed loop MIMO transmission schemes such as TM9 and TM10, a UE estimates and feeds back the downlink CSI to the eNB. The eNB uses the feedback CSI to transmit downlink data to the UE. The CSI consists of a transmission rank indicator (RI), a precoding matrix indicator (PMI) and a channel quality indicator(s) (CQI). A codebook of precoding matrices is used by the UE to find out the best match between the estimated downlink channel Hn and a precoding matrix in the codebook based on certain criteria, for example, maximizing the UE throughput. The channel Hn is estimated based on a Non-Zero Power CSI reference signal (NZP CSI-RS) transmitted in the downlink for TM9 and TM10.

Together, the CQI, RI, and PMI provide the downlink channel state of the UE. This is also referred to as implicit CSI feedback since the estimation of Hn is not fed back directly. The CQI/RI/PMI can be wideband or sub-band depending on which reporting mode is configured.

The RI corresponds to a recommended number of streams/layers that are to be spatially multiplexed and thus transmitted in parallel over the downlink channel. The PMI identifies a recommended precoding matrix codeword (in a codebook which contains precoders with the same number of rows as the number of CSI-RS ports) for the transmission, which relates to the spatial characteristics of the channel. The CQI represents a recommended transport block size such as, for example, code rate, and LTE supports transmission of one or two simultaneous (on different layers) transmissions of transport blocks (i.e. separately encoded blocks of information) to a UE in a subframe. There is thus a relation between a CQI and an SINR of the spatial stream(s) over which the transport block or blocks are transmitted.

Codebook of up to <NUM> antenna ports has been defined in LTE. Both one-dimension (1D) and two-dimension (2D) antenna array are supported. For LTE Rel-<NUM> UE and earlier, only a codebook feedback for a 1D port layout is supported, with <NUM>, <NUM> or <NUM> antenna ports. Hence, the codebook is designed assuming these ports are arranged on a straight line. In LTE Rel-<NUM>, codebooks for 2D port layouts were specified for the case of <NUM>, <NUM>, or <NUM> antenna ports. In addition, a codebook 1D port layout for the case of <NUM> antenna ports was also specified in LTE Rel-<NUM>.

In LTE Rel-<NUM>, two types of CSI reporting were introduced. Specifically, 3GPP <NUM> specifies Class A and Class B as the two types of CSI reporting. In Class A-CSI reporting, a UE measures and reports CSI based on a new codebook for the configured 2D antenna array with <NUM>, <NUM> or <NUM> antenna ports. The CSI consists of a RI, a PMI and a CQI or CQIs.

In Class B-CSI reporting, in one scenario (also referred to as "K><NUM>"), the eNB may preform multiple beams in one antenna dimension. There can be multiple ports (<NUM>, <NUM>, <NUM>, or <NUM> ports) within each beam on the other antenna dimension. "beamformed" CSI-RS are transmitted along each beam. A UE first selects the best beam from a group of beams configured and then measures CSI within the selected beam based on the legacy codebook for <NUM>, <NUM>, or <NUM> ports. The UE then reports back the selected beam index and the CSI corresponding to the selected beam. In another scenario (also referred to as "K=<NUM>"), the eNB may form up to <NUM> (2D) beams on each polarization and "beamformed" CSI-RS is transmitted along each beam. A UE measures CSI on the "beamformed" CSI-RS and feedback CSI based on a new Class B codebook for <NUM>, <NUM>, <NUM> ports.

In LTE, two types of CSI feedbacks are supported, i.e. period feedback and aperiodic feedback. In periodic CSI feedback, a UE is configured to report CSI periodically on certain preconfigured subframes, and the feedback information is carried on the UL PUCCH channel. In aperiodic CSI feedback, a UE only report CSI when it is requested. The request is signaled in a UL grant such as, for example, either in DCI <NUM> or DCI <NUM> carried on PDCCH or EPDCCH.

Channel State Information-Reference Signal (CSI-RS) was introduced in LTE for downlink CSI estimation in transmission modes <NUM> and <NUM>. CSI reference signals can be transmitted on <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> antenna ports (ports # <NUM> to <NUM>). The antenna ports will also be referred to as CSI-RS ports. <FIG> illustrates the resource elements (REs) available for CSI-RS allocations in a PRB. Up to <NUM> REs can be configured for CSI-RS.

For <NUM>, <NUM>, and <NUM> antenna ports, CSI-RS associated with each antenna port is allocated with two adjacent REs per PRB on the same subcarrrier and in two adjacent OFDM symbols. Two CSI-RS signals are multiplexed using two orthogonal cover codes (OCC) of length two, also referred to as OCC2. So for <NUM> antenna ports, there are <NUM> different patterns available within a subframe.

<FIG> and <FIG> illustrate CSI-RS patterns or resource configurations for <NUM> and <NUM> antenna ports, respectively. REs shaded similarly form one CSI-RS resource configuration. As depicted, there are <NUM> and <NUM> CSI-RS resource patterns or resource configurations, respectively. For TDD, some additional CSI-RS patterns are available.

<FIG> and <FIG> illustrate one example of a CSI-RS pattern or resource configuration for <NUM> and <NUM> antenna ports, respectively. For <NUM> antenna ports, a CSI-RS resource is obtained by aggregating three <NUM> ports CSI-RS resources, as shown in <FIG>. Similarly, for <NUM> antenna ports, a CSI_RS resource is obtained by aggregating two <NUM> ports CSI-RS resources, as shown in <FIG>. With increased number of CSI-RS ports, the number of CSI-RS resource configurations is reduced. For example, for <NUM> CSI-RS ports, only three CSI-RS resource configurations are available in a subframe. For <NUM> CSI-RS ports, only two CSI-RS resource configurations are available.

The complex CSI reference-signal sequence is defined as <MAT> where ns is the slot number within a radio frame and l is the OFDM symbol number within the slot. c(i) is pseudo-random sequence initialized at the start of each OFDM symbol. Furthermore, <MAT> i is the largest downlink bandwidth configuration supported by LTE. This sequence is mapped to each of the CSI-RS REs.

For <NUM>, <NUM>, and <NUM> antenna ports, there is an option to multiplex either two ports over two REs using OCC2 (CDM2) or four ports on four REs using OCC4 (CDM4). <FIG> and <FIG> illustrate an example of port multiplexing with OCC4 (CDM4) for a <NUM> port resource and a <NUM> port resource, respectively. As shown, the four REs with the same letter are in one OCC4 group. The benefit of using OCC4 is that up to <NUM> dB processing gain can be achieved for channel estimation if the channel doesn't change fast in either time or frequency domain.

CSI-RS can be transmitted periodically on certain subframes, also referred as CSI-RS subframes. A CSI-RS subframe configuration consists of a subframe periodicity and a subframe offset. The periodicity is configurable at <NUM>, <NUM>, <NUM>, <NUM> and <NUM> in LTE.

A CSI-RS configuration consists of a CSI-RS resource configuration and a CSI-RS subframe configuration. A UE can also be configured with one or multiple zero power (ZP) CSI-RS resources. A ZP CSI-RS subframe configuration is also associated with each ZP CSI-RS configuration.

To improve channel estimation in adjacent cells, an eNB may not transmit any signals in certain CSI-RS REs, referred as zero-power CSI-RS or ZP CSI-RS. The CSI-RS used for CSI estimation is also referred to as non-zero power CSI-RS or NZP CSI-RS. Only CSI-RS REs for four antenna ports can be allocated to ZP CSI-RS. A ZP CSI-RS subframe configuration is also associated with ZP CSI-RS. It can be the same as or different from a NZP CSI-RS configuration.

The concept of CSI process is introduced in TM10. A CSI process is associated with a NZP CSI-RS resource and a CSI interference measurement (CSI-IM) resource. A CSI-IM resource is defined by a ZP CSI-RS resource and a ZP CSI-RS subframe configuration. A UE can be configured with multiple CSI processes. The multiple CSI processes was introduced to support Coordinated Multi-Point (COMP) transmission in which a UE measures and feeds back CSI associated with each transmission point (TP) to an eNB. Based on the received CSIs, the eNB may decide to transmit data to the UE from one of the TPs.

Measurement restriction was introduced in LTE release <NUM> for TM9 and TM10, in which CSI measurement for a UE may be restricted to a CSI-RS resource or a CSI-IM resource in one subframe. Measurement restriction can be configured in the form of channel measurement restriction or interference measurement restriction or both.

For a UE in transmission mode <NUM> or <NUM> and for a CSI process, if the UE is configured with parameter CSI-Reporting-Type by higher layers, and CSI-Reporting-Type is set to 'CLASS B', and parameter channelMeasRestriction is configured by higher layers, the UE shall derive the channel measurements for computing the CQI value reported in uplink subframe n and corresponding to the CSI process, based on only the most recent, no later than the CSI reference resource, non-zero power CSI-RS within a configured CSI-RS resource associated with the CSI process.

For a UE in transmission mode <NUM> and for a CSI process, when parameters CSI-Reporting-Type and interferenceMeasRestriction is configured by higher layers, the UE shall derive the interference measurements for computing the CQI value reported in uplink subframe n and corresponding to the CSI process, based on only the most recent, no later than the CSI reference resource, configured CSI-IM resource associated with the CSI process.

Channel measurement restriction to one CSI-RS subframe is needed in Class B in which the precoding for CSI-RS may be different in different CSI-RS subframes.

Patent application <CIT> discloses a method for processing a Channel State Information Reference Signal (CSI-RS) in a wireless communication system based on a multiple access scheme. The CSI-RS transmission method defines a plurality of CSI-RS patterns, assigns the CSI-RS patterns to individual cells, uses the CSI-RSs alternately per Physical Resource Block (PRB) so as to utilize the transmission powers of all antenna ports for transmitting CSI-RSs, transmits Coordinated Multi Point (CoMP) CSI-RSs and non-CoMP CSI-RSs separately, and mutes specific resources in association with the CSI-RS pattern of adjacent cells.

Patent application <CIT> discloses an apparatus for wireless communication. The apparatus may be a UE. The UE determines a first CSI subframe set including a first set of subframes of a frame and a second CSI subframe set including a second set of subframes of the frame. Subframes in the first set of subframes are different than subframes in the second set of subframes. The UE determines a semi-statically configured CSI reference subframe in one of the first CSI subframe set or the second CSI subframe set. The UE measures CSI in the semi-statically configured CSI reference subframe. The UE receives an aperiodic CSI request in a triggering subframe in one of the first CSI subframe set or the second CSI subframe set. The triggering subframe is after the semi-statically configured CSI reference subframe.

To address the foregoing problems with existing solutions, the present application discloses devices and methods for flexible channel state signal transmission.

The invention is defined and limited by the appended set of independent claims.

According to aspects of the present disclosure, methods for restricting channel state information (CSI) and corresponding wireless devices and network nodes are provided according to the independent claims. Preferred embodiments are recited in the dependent claims.

For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, on which:.

In LTE Rel-<NUM>, up to thirty-two antenna ports are to be supported in the downlink (DL). However, there are maximum forty Channel State Information-Reference Signal (CSI-RS) resource elements (REs) available per physical resource block (PRB) in a CSI-RS subframe. As such, only one <NUM>-port CSI-RS configuration can be supported per CSI-RS subframe. To avoid CSI-RS collision in adjacent cells, CSI-RS in adjacent cells may be configured in different subframes. For example, CSI-RS may be time division multiplexed (TDM). In this case, CSI-RS would collide with PDSCH data in adjacent cells. If zero power (ZP) CSI-RS is also configured to improve wireless device channel estimation in adjacent cells, then the resource overhead would be very high. To support more than thirty-two antenna ports, more CSI-RS REs are needed per PRB in each CSI-RS subframes. As such, there is a CSI-RS resource limitation issue for supporting <NUM> or more antenna ports. How to reduce CSI-RS overhead is clearly a problem.

Secondly, the current CSI-RS subframes are semi-statically configured. CSI-RS is transmitted regardless if there are wireless devices receiving a given CSI-RS transmission or not. The CSI-RS subframes are common to all wireless devices in a cell. To support wireless devices with different mobilities, smaller CSI-RS subframe periodicity is commonly used such that more frequent CSI feedback can be supported for medium to high mobility wireless devices, which means more CSI-RS resource overhead even there is only low mobility wireless devices in a cell.

To support multiple user multiple-input multiple-output (MU-MIMO), more accurate CSI feedback is required. However, more accurate CSI feedback means higher uplink overhead. Currently, the same CSI granularity is supported in both periodic and aperiodic CSI feedback. In the current system, a network node, such as an eNB, may request CSI feedback at any subframe by triggering an aperiodic CSI feedback from a wireless device. However, the CSI granularity is the same for CSI fed back at different times.

Certain embodiments provide frequency domain CSI measurement restriction to reduce the required CSI-RS REs for large number of antennas. Specifically, a UE can be requested to measure CSI over a fraction of the PRBs within the system bandwidth in a CSI-RS subframe. This can be achieved through CSI measurement restriction. For example, CSI measurements may be performed on a subset of PRBs that is indicated to a wireless device. The measurement restriction can be semi-statically or dynamically transmitted to a wireless device.

A wireless device may consider the CSI-RS REs in other PRBs as used for another purpose. For example, CSI-RS REs in other PRBs may be used for CSI-RS transmission targeting other wireless devices. Thus, a network node such as an eNB may transmit CSI-RS on one subset of PRBs to a group of wireless devices while transmitting CSI-RS on another subset of PRBs to a different group of wireless devices. The CSI-RS on the two subsets of PRBs may have different configurations, for example, with different CSI-RS reporting types (i.e. CLASS A or CLASS B) or the same Class B reporting type but different CSI-RS precodings.

As another example, CSI-RS REs may be used as zero-power CSI-RS. In other words, nothing may be transmitted on the REs. Adjacent cells may coordinate CSI-RS transmission. For example, different cells may transmit CSI-RS on different subsets of PRBs to improve channel estimation based on CSI-RS.

Certain embodiments may include antenna port level CSI measurement restriction. To reduce the required CSI-RS REs for a large number of antennas, a wireless device may be requested to measure CSI over a subset of the configured antenna ports in a CSI-RS subframe. For example, a UE may be requested to measure CSI based on only eight out of thirty-two antenna ports. In a particular embodiment, the subset of antenna ports can be preconfigured. In particular embodiments, the request can be either semi-statically configured or dynamically indicated/signaled. For example, semi-static configuration may be used for periodic CSI report. Dynamic signaling can be used for aperiodic CSI reports in between periodic reports. The CSI feedback can be based on a codebook of the subset antenna ports (e.g. <NUM> ports) or a codebook of full antenna ports (e.g. <NUM> ports).

Certain embodiments may provide scheduled CSI transmission without CSI-RS subframe configuration. Specifically, CSI-RS transmission may occur in a non-CSI-RS subframe. A wireless device can be dynamically signaled in a subframe whether CSI-RS is present or not in the subframe. If CSI-RS is present in a subframe, a wireless device maybe further instructed to measure CSI based on the CSI-RS transmitted in the subframe. In a particular embodiment, the dynamic scheduling can be done through a DL DCI message. A wireless device may be further signaled to report the measured CSI in a future subframe. In a particular embodiment, the signaling can be done through a UL grant.

To reduce the required CSI-RS REs for a large number of antenna ports, a wireless device can be requested to measure CSI using CSI-RS in a fraction of the PRBs within the system bandwidth in a CSI-RS subframe.

<FIG> illustrates an example method <NUM> by a wireless device for restricting CSI measurement, according to certain embodiments. In a particular embodiment, the wireless device may include wireless device <NUM> described below with respect to <FIG> and <FIG>.

The method may begin at step <NUM> when wireless device <NUM> receives information identifying a first subset of CSI-RS resources to be used in performing CSI measurements. According to certain embodiments, the information may be received from a network node such as network node <NUM> described below with respect to <FIG> and <FIG>. The information may be received in semi-static signaling or in dynamic signaling, according to various embodiments. According to a particular embodiment, the information may be received as downlink control information (DCI). Additionally, the DCI may be received in a common control channel search space or a UE-specific search space. According to certain embodiments, the first subset of CSI-RS resources is associated with a first portion of a frequency band that is less than the entire frequency band. According to a particular embodiment, the frequency band may include a system bandwidth in a CSI-RS subframe.

According to a particular embodiment, the frequency band may consist of a plurality of PRBs. For example, a first portion of the frequency band may consist of a first subset of PRBs in the frequency band, and the first subset of CSI-RS resources may include CSI-RS resources in the first subset of PRBs. Additionally, a second subset of CSI-RS resources that is different from the first subset of CSI-RS resources may be associated with a second subset of PRBs that is not to be used when performing CSI measurements. In another embodiment, the second subset of CSI-RS resources may be associated with a second portion of the frequency band that is less than the entire frequency band, and the second subset of CSI-RS resources may also be used in performing CSI measurements.

In a particular embodiment, for example, the information identifying the first subset of CSI-RS resources may include one or more parameters identifying the first subset of PRBs. According to a particular embodiment, wireless device <NUM> may transmit CSI feedback that includes one or more values associated with the CSI measurements performed in the first subset of CSI-RS resources.

At step <NUM>, wireless device <NUM> performs CSI measurements in the first subset of CSI-RS resources that are associated with the first portion of the frequency band. According to a particular embodiment, the information identifying the first subset of CSI-RS resources may include a set of antenna ports. In such an embodiment, wireless device <NUM> may perform the CSI measurements in the first subset of CSI-RS resources associated with the set of antenna ports.

According to a particular embodiment, the information identifying the first subset of CSI-RS resources may additionally or alternatively include a set of even number PRBs or a set of odd number PRBs in the frequency band. Wireless device <NUM> may perform the CSI measurements on the first subset of CSI-RS resources configured on the set of even number PRBs or the set of odd number PRBs. According to a particular embodiment, the information identifying the first subset of CSI-RS resources may include every M PRBs in the frequency band, where M is greater than one. According to another particular embodiment, the information identifying the first subset of CSI-RS resources may include a subset of precoding resource block groups (PRGs).

According to a particular embodiment, the method may additionally include transmitting, from the wireless device <NUM> to network node <NUM>, CSI feedback that includes one or more values associated with the CSI measurements performed in the first subset of CSI-RS resources. Additionally, according to certain embodiments, the CSI feedback may also include one or more values associated with the CSI measurements performed in the second subset of CSI-RS resources, where the second subset of CSI-RS resources is identified. In a particular embodiment, the information identifying the first subset of CSI-RS resources may be associated with a first CSI reporting type, and the CSI feedback may include a report of the first CSI reporting type. Likewise, the second subset of CSI-RS resources may be associated with a second CSI reporting type, and the CSI feedback may include a report of the second CSI reporting type. In a particular embodiment, the first type of CSI report may be associated with a first set of PRBS while the second type of CSI report is associated with a second set of PRBs.

According to certain embodiments, the information received in step <NUM> may identify a first subframe in which the CSI measurements are to be performed. Additionally, in a particular embodiment, wireless device <NUM> may receive information identifying a second subset of CSI-RS resources to be used in performing CSI measurements in a second subframe. For example, the first subframe may be dynamically configured as a non-regular CSI-RS subframe that is not included in a plurality of regular CSI-RS subframes in which the wireless device <NUM> is configured to perform the CSI measurements. Wireless device <NUM> may receive an indication from network node <NUM> that CSI-RS is included in the non-regular CSI-RS subframe.

<FIG> illustrates an example of CSI-RS allocation <NUM> for a wireless device over a subset of PRBs. The subset of PRBs may include a fraction of the PRBs within the system bandwidth to reduce the required CSI-RS REs for a large number of antennas. As shown in FIGURE <NUM>, a first subset of PRBs <NUM> may be distinguished from a second subset of PRBs <NUM>.

According to certain embodiments, the first subset of PRBs <NUM> may comprise even number PRBs and the second subset of PRBS <NUM> may comprise odd-numbered PRBs. Accordingly, the wireless device may be signaled with identifying information indicating that wireless device is to measure channels from a serving cell using REs containing CSI-RS in even-numbered PRBs (i.e. PRB <NUM>, PRB2,. ) or in odd-numbered PRBs (i.e. PRB <NUM>, PRB <NUM>,. ) in a CSI-RS subframe.

The subsets of PRBs can be semi-statically configured for a wireless device as part of CSI measurement restriction. The measurement restriction can be semi-statically configured to a wireless device. For example, a wireless device may be configured to measure CSI over the even number PRBs <NUM> as shown in <FIG>. The wireless device then measures CSI based on only the CSI-RS transmitted in the even-numbered PRBs in CSI-RS subframes for both periodic and aperiodic CSI reports.

The wireless devices in one group (e.g. group A) may assume the CSI-RS REs in the other set of PRBs (i.e. odd-numbered PRBs as depicted in <FIG>) are reserved and are not used for PDSCH transmission. In one embodiment, the two groups of wireless devices may have the same CSI-RS resource configuration. For example, the two groups of wireless devices may have the same number of CSI-RS ports and the same CSI-RS REs in the subframe.

In certain embodiments, when the two groups of wireless devices have a different number of CSI-RS ports such as, for example, one group with eight ports and the other with sixteen ports, the wireless devices in the group with smaller number of CSI-RS ports may be configured with additional zero-power CSI-RS on the REs that are configured for CSI-RS for the other group. <FIG> illustrates an example CSI-RS configuration over two subsets of PRBs with different number of CSI-RS ports. Wireless devices in Group A may be configured with <NUM> port CSI-RS, while wireless devices in Group B are configured with <NUM> port CSI-RS and also <NUM> port zero power CSI-RS.

According to certain embodiments, wireless devices in group A and wireless devices in group B may be associated with different cells. Returning to <FIG>, in certain other embodiments, the first subset of PRBs <NUM> may be associated with a first cell and the second subset of PRBS <NUM> may be associated with a second cell.

In another embodiment, the first subset of PRBs <NUM> may be associated with a first CSI process and the second subset of PRBs <NUM> may be associated with a second process. For example, when a wireless device is configured with two CSI processes, CSI process A and CSI process B, the wireless device may be configured to measure CSI for CSI process A in one set of PRBs <NUM> and for CSI process B in the other set of PRBs <NUM>.

In still another embodiment, the first subset of PRBs <NUM> may be associated with a first type of CSI report while the second subset of PRBs <NUM> are associated with a different type of CSI report. For example, when a wireless device <NUM> is configured with both Class A and Class B types of CSI reports, the wireless device may be configured to measure CSI for Class A type of reporting on one set of PRBs <NUM> (depicted as even-numbered PRBs in <FIG>) and for Class B type of CSI reporting on another set of PRBs <NUM> (depicted as odd-numbered PRBs in <FIG>). Dynamic signaling, such as for example in the case of aperiodic CSI reports, may be used to indicate whether a Class A or Class B type of CSI should be reported.

In still another embodiment, the first subset of PRBs <NUM> may be associated with a first subset of antenna ports while the second subset of PRBs <NUM> is associated with a second subset of antenna ports. For example, a wireless device may be configured to measure channels on a subset of the configured antenna ports on one set of PRBs <NUM> and another subset of antenna ports on a different set of PRBs <NUM>.

<FIG> illustrates an example CSI-RS resource allocation <NUM> where thirty-two CSI-RS ports are allocated over two PRBs that each includes sixteen ports. Stated differently, <FIG> illustrates an example of a system with thirty-two antenna ports, where antenna ports <NUM> to <NUM> (Group A) are allocated to PRB <NUM> and antenna ports <NUM>-<NUM> (Group B) are allocated to PRB <NUM>. In this case, a wireless device may still report a single thirty-two port CSI based on the CSI-RS resource.

Although even and odd-numbered PRBs are used in the above examples, other ways of partitioning the bandwidth are also possible for measurement restriction. For example, even and odd PRBs, the measurement restriction may be applied to every M (M><NUM>) PRBs. <FIG> illustrates a second example of CSI-RS allocation <NUM> for a wireless device over a subset of PRBs. As depicted, a wireless device may be configured to measure CSI over alternating blocks of two adjacent PRBs. A wireless device belonging to group A <NUM> is configured to measure CSI in PRBs <NUM>, <NUM>, <NUM>, <NUM>,. , N-<NUM>, N-<NUM>. Conversely, another wireless device belonging to group B <NUM> is configured to measure CSI in PRBs <NUM>, <NUM>, <NUM>, <NUM>,. , N-<NUM>, N-<NUM>.

In another example, the measurement restriction may be applied to the Precoding Resource block Groups (PRGs). For example, a wireless device may be restricted to measure only certain PRGs.

In certain embodiments, a wireless device may be configured for subband CQI reporting and CSI-RS measurement restriction, and the wireless device may use a subset of the subbands in the system bandwidth to calculate CSI. The network node restricts the wireless device's CSI-RS measurements by indicating to the wireless device which subbands the wireless device can use to calculate CSI ('valid subbands'). In this case, wideband CSI is only calculated using the valid subbands, and subband CSI reports such as subband CQI or PMI for the subbands not indicated as valid subbands are either not included by the wireless device in CSI reporting or are set to fixed, specified values. The measurement indication can be semi-statically indicated through RRC signaling, or may be dynamically signaled in a downlink control channel. In some embodiments, the wireless device may be configured for subband channel measurement restriction only for channel measurements, or only for subband interference measurement restriction, or the wireless device may be configured for both subband interference and channel measurement restriction.

In another embodiment when a wireless device is configured for subband CQI reporting and CSI-RS measurement restriction, the wireless device may not assume that CSI-RS are present in more than one subband. The wireless device then calculates CSI (for example CQI, RI, and PMI) for each subband independently of the other subbands. Optionally, the wireless device may then calculate a wideband CQI value that allows minimum quantization error for each subband when the differential CQIs are reported for each subband. A single value for RI and PMI may be reported in some reporting modes, in which case the reported RI and PMI correspond to the subband with highest CQI.

<FIG> illustrates an example method <NUM> by a network node for restricting CSI measurement, according to certain embodiments. In a particular embodiment, the network node may include network node <NUM> described below with respect to <FIG> and <FIG>.

The method may begin at step <NUM> when network node <NUM> signals information identifying a first subset of CSI-RS resources to be used in performing CSI measurements to a wireless device. According to certain embodiments, the information may be signaled to a wireless device, which may include wireless device <NUM> described below with respect to <FIG> and <FIG> in particular embodiments. The information may also be signaled in semi-static signaling or in dynamic signaling, according to various embodiments. According to a particular embodiment, the information may be signaled as downlink control information (DCI). Additionally, the DCI may be signaled in a common control channel search space or a UE-specific search space. According to certain embodiments, the first subset of CSI-RS resources may be associated with a first portion of a frequency band that is less than all of the frequency band. According to a particular embodiment, the frequency band may include a system bandwidth in a CSI-RS subframe.

According to a particular embodiment, the frequency band may consist of a plurality of PRBs. For example, a first portion of the frequency band may consist of a first subset of PRBs in the frequency band, and the first subset of CSI-RS resources may include CSI-RS resources in the first subset of PRBs. A second subset of CSI-RS resources that are different from the first subset of CSI-RS resources may be associated with a second subset of PRBs that are not to be used when performing CSI measurements. In another embodiment, the second subset of CSI-RS resources may be associated with a second portion of the frequency band less than the entire frequency band, and the second subset of CSI-RS resources may also be used in performing CSI measurements.

In a particular embodiment, for example, the information identifying the first subset of CSI-RS resources may include one or more parameters identifying the first subset of PRBs.

According to another particular embodiment, the information identifying the first subset of CSI-RS resources may include a set of antenna ports. In such an embodiment, wireless device <NUM> may perform the CSI measurements in the first subset of CSI-RS resources associated with the set of antenna ports.

According to a particular embodiment, the information identifying the first subset of CSI-RS resources may additionally or alternatively include a set of even-number PRBs or a set of odd number PRBs in the frequency band. Wireless device <NUM> may perform the CSI measurements on the first subset of CSI-RS resources configured on the set of even number PRBs or the set of odd number PRBs. According to a particular embodiment, the information identifying the first subset of CSI-RS resources may include every M PRBs in the frequency band, where M is greater than one. According to another particular embodiment, the information identifying the first subset of CSI-RS resources may include a subset of precoding resource block groups (PRGs).

At step <NUM>, network node <NUM> receives CSI feedback from wireless device <NUM>. The CSI feedback may include one or more values associated with the CSI measurements performed in the first subset of CSI-RS resources by wireless device <NUM>. CSI measurements in the first subset of CSI-RS resources that is associated with the first portion of the frequency band.

According to certain embodiments, the CSI feedback may also include one or more values associated with the CSI measurements performed in the second subset of CSI-RS resources, where a second subset of CSI-RS resources is identified. In a particular embodiment, the information identifying the first subset of CSI-RS resources may be associated with a first CSI reporting type, and the CSI feedback may include a report of the first CSI reporting type. Likewise, the second subset of CSI-RS resources may be associated with a second CSI reporting type, and the CSI feedback may include a report of the second CSI reporting type. In a particular embodiment, the first type of CSI report may be associated with a first set of PRBS while the second type of CSI report is associated with a second set of PRBs.

According to a particular embodiment, the information signaled in step <NUM> may identify a first subframe in which the CSI measurements are to be performed. Additionally, network node <NUM> may also signal information identifying a second subset of CSI-RS resources to be used in performing CSI measurements in a second subframe. In a particular embodiment, the first subframe may be dynamically configured as a non-regular CSI-RS subframe that is not included in a plurality of regular CSI-RS subframes in which the wireless device <NUM> is configured to perform the CSI measurements. Network node <NUM> may signal an indication to wireless device <NUM> that CSI-RS is included in the non-regular CSI-RS subframe.

As described above with respect to <FIG>, the information identifying a first subset of CSI-RS resources may identify a subset of PRBs that is a fraction of the PRBs within the system bandwidth. According to the various embodiments described above, the first subset of PRBs <NUM> may comprise even number PRBs and the second subset of PRBS <NUM> may comprise odd-numbered PRBs. Thus, the network node may signal identifying information indicating that wireless device is to measure channels from a serving cell using REs containing CSI-RS in even-numbered PRBs (i.e. PRB <NUM>, PRB2,. ) or in odd-numbered PRBs (i.e. PRB <NUM>, PRB <NUM>,. ) in a CSI-RS subframe.

In certain other embodiments, the first subset of PRBs <NUM> may be associated with a first cell and the second subset of PRBS <NUM> may be associated with a second cell. Additionally or alternatively, the first subset of PRBs <NUM> may be associated with a first CSI process and the second subset of PRBs <NUM> may be associated with a second process. In still another embodiment, the first subset of PRBs <NUM> may be associated with a first type of CSI report while the second subset of PRBs <NUM> are associated with a different type of CSI report. In still another embodiment, the first subset of PRBs <NUM> may be associated with a first subset of antenna ports while the second subset of PRBs <NUM> is associated with a second subset of antenna ports.

According to certain embodiments, a wireless device may be configured to measure CSI over the full set of the configured antenna ports in some CSI-RS subframes while measuring CSI over a subset of the antenna ports in some other subframes. <FIG> illustrates an example of CSI measurement restriction <NUM> on a subset of antenna ports. As depicted, CSI measurements on eight out of thirty-two antenna ports are performed in some CSI-RS subframes while on all thirty-two ports in other subframes. The subframes over which CSI for a subset of antenna ports is measured can be semi-statically configured.

In certain embodiments, two CSI-RS subframe configurations, each with different number of antenna ports, can be signaled to a wireless device. One subframe configuration can be used for both periodic CSI feedback (e.g. thirty-two port CSI-RS subframes) and the other can be used for only aperiodic feedback (e.g. the eight port CSI-RS subframes). In the subframe configured with eight ports, only eight port CSI-RS resource may be configured and only <NUM> port CSI-RS may be transmitted.

In certain other embodiments, only thirty-two ports CSI-RS subframes may be configured for a wireless device, but a wireless device may be requested to measure CSI based on only a subset of the thirty-two antenna ports in some subframes. In a particular embodiment, the subset of antenna ports may be preconfigured. In a particular embodiment, the request for CSI measurement on a subset of antenna ports may be dynamically indicated or signaled in uplink scheduling grant. In a particular embodiment, the CSI feedback for the subset of the antenna ports may be based on either a codebook of the subset of antenna ports (e.g. an eight port codebook) or a codebook of full antenna ports (e.g. thirty-two ports). In a particular embodiment where the codebook of full antenna ports is used for CSI feedback for the subset of the antenna ports that are configured, then the wireless device can assume that the ports except the subset of antenna ports configured for CSI feedback are muted, wherein no CSI-RS transmission in the ports except the subset of antenna ports configured for CSI feedback.

<FIG> illustrates another example method <NUM> by a wireless device for restricting CSI measurement, according to certain embodiments. In a particular embodiment, the wireless device may include wireless device <NUM> described below with respect to <FIG> and <FIG>.

The method may begin at step <NUM> when wireless device <NUM> receives a CSI-RS resource configuration for a plurality of antenna ports and an associated codebook configuration for CSI feedback.

At step <NUM>, the wireless device <NUM> identifies a first subset of the plurality of antenna ports over which CSI measurements and feedback are to be performed in a first subframe. According to certain embodiments, the CSI feedback with the first subset of antenna ports is based on a codebook corresponding to the antenna port layout of the first subset of antenna ports. According to other embodiments, the CSI feedback with the first subset of antenna ports is based on the codebook configured for the plurality of antenna ports. According to a particular embodiment, the first subset of antenna ports may be received from a network node. The network node may include network node <NUM> described below with respect to <FIG> and <FIG>. The information may be received in semi-static signaling or in dynamic signaling, according to various embodiments.

At step <NUM>, wireless device <NUM> performs CSI measurements over the first subset of antenna ports in the first subframe. Wireless device <NUM> may assume that any antenna ports outside the first subset of antenna ports are muted when the codebook configured for the antenna ports is used.

According to a particular embodiment, the wireless device may also receive information identifying a second subset of antenna ports over which CSI measurements are to be performed in a second subframe. The second subset of antenna ports may include the first subset of antenna ports in certain embodiments. In such a scenario, the wireless device <NUM> may additionally perform CSI measurements over the second subset of antenna ports in the second subframe.

<FIG> illustrates another example method <NUM> by a network node for restricting CSI measurement, according to certain embodiments. In a particular embodiment, the network node may include network node <NUM> described below with respect to <FIG> and <FIG>.

The method may begin at step <NUM> when network node <NUM> signals a CSI-RS resource configuration for a plurality of antenna ports and an associated codebook configuration for CSI feedback.

At step <NUM>, network node <NUM> signals, to a wireless device, a first subset of a plurality of antenna ports over which CSI measurements and feedback are to be performed in a first subframe. According to certain embodiments, the CSI feedback with the first subset of the plurality of antenna ports is based on a codebook corresponding to the antenna port layout of the first subset of antenna ports. According to other embodiments, the CSI feedback with the first subset of antenna ports is based on the codebook configured for the plurality of antenna ports. According to a particular embodiment, the first subset of antenna ports may be signaled to a wireless device such as wireless device <NUM> described below with respect to <FIG> and <FIG>. The information may be signaled in semi-static signaling or in dynamic signaling, according to various embodiments.

At step <NUM>, network node <NUM> receives, from wireless device <NUM>, CSI feedback that is associated with the CSI measurements performed over the first subset of the plurality of antenna ports in the first subframe.

According to a particular embodiment, network node <NUM> may also signal information identifying a second subset of the plurality of antenna ports over which CSI measurements are to be performed in a second subframe. The second subset of antenna ports may be the plurality of antenna ports in certain embodiments. In such a scenario, network node <NUM> may additionally receive CSI feedback associated with the CSI measurements performed over the second subset of antenna ports in the second subframe.

Certain embodiments may provide methods and systems for performing CSI measurements for a scheduled CSI transmission occurring in a subframe that is not configured for CSI-RS. <FIG> illustrates an example of a scheduled CSI-RS transmission occurring in non-regular CSI-RS subframes <NUM>, according to certain embodiments. Specifically, as shown, CSI-RS transmissions in subframes i and j are dynamically scheduled and are not part of the regular semi-statically configured CSI-RS subframes.

A wireless device may be dynamically signaled as to whether or not CSI-RS is present in a subframe. The dynamic signaling can be done through a downlink DCI message. In various embodiments, the DCI may be a message targeted to all wireless devices in a cell, a message targeted to a group of wireless devices, or a message targeted to each individual wireless device.

According to certain embodiments, the DCI message may contain information including CSI-RS resource configuration in the subframe. Additionally or alternatively, the DCI message may contain information including CSI-RS transmit power ratio to PDSCH. The CSI-RS information may be preconfigured semi-statically with a number of CSI-RS resource configurations, and an indicator may be included in the DCI message to indicate which CSI-RS resource configuration is used for the dynamically scheduled CSI-RS transmission.

Where the DCI is targeted to all or a group of wireless devices, the DCI may be carried on a PDCCH transmitted in the common search space with a known common Radio Network Temporary Identifier (RNTI), CSI-RS-RNTI, for all or a group of wireless devices to decode and recognize the message. According to certain embodiments, the DCI may have the same bit length as DCI format <NUM> in the common search space so that there is no additional search required. Only CRC (Cyclic Redundancy Code) verification with an additional RNTI, for example, CSI-RS RNTI, is needed.

Where the DCI message is targeted to individual wireless devices, only wireless devices having downlink data scheduled in the subframe or wireless devices that need to measure CSI in the subframe may be signaled. In this case, the CSI-RS indication or scheduling is included in the data scheduling message. For wireless devices having data scheduled in the subframe, the dynamic signaling indicates to the wireless devices the presence of CSI-RS and thus the wireless devices may assume that the CSI-RS REs in the subframe are not available for PDSCH transmission. As such, proper rate matching is enabled for the CSI-RS REs.

<FIG> illustrates an example of dynamic scheduling <NUM> of CSI-RS transmission and CSI feedback with scheduling message to individual wireless devices, according to certain embodiments. As depicted, CSI-RS scheduling is signaled to only a first wireless device (depicted as UE1) in subframes SF i and SF j as there is no data scheduled to a second wireless device (depicted as UE2). In Subframe SF k, both UE1 and UE2 are signaled about the presence of CSI-RS in the subframe as both have DL scheduled data.

For wireless devices required to measure CSI in the subframe and provide feedback associated with the measured CSI, each of the wireless devices may also be signaled with an uplink grant (for example using DCI formats <NUM> or <NUM>) for the wireless device to report CSI in a later subframe in the uplink. In the example shown in <FIG>, UE1 is also requested in the UL scheduling grant to measure and report CSI based on the CSI-RS in the subframe.

In certain embodiments, a wireless device requested to measure and report CSI may also be indicated in its UL grant that CSI measurement restriction in frequency domain is used. For example, the CSI may be measured on the whole system bandwidth, in a particular embodiment. Alternatively, the CSI may be measured on a subset of predefined PRBs, in a particular embodiment, or the CSI may be measured on the same PRBs over which the PDSCH is scheduled for the wireless device in the same subframe if the wireless device has DL data scheduled in the subframe, in a particular embodiment.

In addition, according to certain embodiments, a wireless device that is requested to measure and report CSI may also be indicated in the UL grant one or more of the following: CSI reporting type, e.g. Class A, or Class B; and SU-MIMO CSI or MU-MIMO CSI.

<FIG> illustrates an example of SU-MIMO and MU-MIMO CSI feedback <NUM> with scheduled CSI-RS transmission, according to certain embodiments. As depicted, CSI-RS for SU-MIMO CSI measurements are scheduled on subframe SF k and subframe SF j, while CSI-RS for MU-MIMO CSI measurement is scheduled on subframe SF i.

One of the benefits of dynamically scheduled CSI-RS is that CSI-RS does not need to be transmitted periodically all the time as in the existing LTE systems. CSI-RS may be transmitted only when the network node has downlink data to transmit to a wireless device or a group of wireless devices. This may reduce CSI-RS resource overhead and interference and save eNB power. In addition, it is more flexible and may support CSI feedback with different granularities and different reporting types.

<FIG> is a block diagram illustrating an embodiment of a network <NUM> for flexible CSI-RS transmission, in accordance with certain embodiments. Network <NUM> includes one or more wireless devices 1310A-C, which may be interchangeably referred to as wireless devices <NUM> or UEs <NUM>, and network nodes 1315A-C, which may be interchangeably referred to as network nodes <NUM> or eNodeBs <NUM>. A wireless device <NUM> may communicate with network nodes <NUM> over a wireless interface. For example, wireless device 1310A may transmit wireless signals to one or more of network nodes <NUM>, and/or receive wireless signals from one or more of network nodes <NUM>. The wireless signals may contain voice traffic, data traffic, control signals, and/or any other suitable information. In some embodiments, an area of wireless signal coverage associated with a network node <NUM> may be referred to as a cell. In some embodiments, wireless devices <NUM> may have D2D capability. Thus, wireless devices <NUM> may be able to receive signals from and/or transmit signals directly to another wireless device <NUM>. For example, wireless device 1310A may be able to receive signals from and/or transmit signals to wireless device 1310B.

In certain embodiments, network nodes <NUM> may interface with a radio network controller (not depicted in <FIG>). The radio network controller may control network nodes <NUM> and may provide certain radio resource management functions, mobility management functions, and/or other suitable functions. In certain embodiments, the functions of the radio network controller may be included in network node <NUM>. The radio network controller may interface with a core network node. In certain embodiments, the radio network controller may interface with the core network node via an interconnecting network. The interconnecting network may refer to any interconnecting system capable of transmitting audio, video, signals, data, messages, or any combination of the preceding. The interconnecting network may include all or a portion of a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, or any other suitable communication link, including combinations thereof.

In some embodiments, the core network node may manage the establishment of communication sessions and various other functionalities for wireless devices <NUM>. Wireless devices <NUM> may exchange certain signals with the core network node using the non-access stratum layer. In non-access stratum signaling, signals between wireless devices <NUM> and the core network node may be transparently passed through the radio access network. In certain embodiments, network nodes <NUM> may interface with one or more network nodes over an internode interface. For example, network nodes 1315A and 1315B may interface over an X2 interface.

As described above, example embodiments of network <NUM> may include one or more wireless devices <NUM>, and one or more different types of network nodes capable of communicating (directly or indirectly) with wireless devices <NUM>. Wireless device <NUM> may refer to any type of wireless device communicating with a node and/or with another wireless device in a cellular or mobile communication system. Examples of wireless device <NUM> include a mobile phone, a smart phone, a PDA (Personal Digital Assistant), a portable computer (e.g., laptop, tablet), a sensor, a modem, a machine-type-communication (MTC) device / machine-to-machine (M2M) device, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, a D2D capable device, or another device that can provide wireless communication. A wireless device <NUM> may also be referred to as UE, a station (STA), a device, or a terminal in some embodiments. Also, in some embodiments, generic terminology, "radio network node" (or simply "network node") is used. It can be any kind of network node, which may comprise a Node B, base station (BS), multi-standard radio (MSR) radio node such as MSR BS, eNode B, network controller, radio network controller (RNC), base station controller (BSC), relay donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, RRU, RRH, nodes in distributed antenna system (DAS), core network node (e.g. MSC, MME etc.), O&M, OSS, SON, positioning node (e.g. E-SMLC), MDT, or any suitable network node. Example embodiments of network nodes <NUM>, wireless devices <NUM>, and other network nodes (such as radio network controller or core network node) are described in more detail with respect to <FIG>, <FIG>, and <FIG>, respectively.

Although <FIG> illustrates a particular arrangement of network <NUM>, the present disclosure contemplates that the various embodiments described herein may be applied to a variety of networks having any suitable configuration. For example, network <NUM> may include any suitable number of wireless devices <NUM> and network nodes <NUM>, as well as any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device (such as a landline telephone). Furthermore, although certain embodiments may be described as implemented in a LTE network, the embodiments may be implemented in any appropriate type of telecommunication system supporting any suitable communication standards and using any suitable components, and are applicable to any radio access technology (RAT) or multi-RAT systems in which the wireless device receives and/or transmits signals (e.g., data). For example, the various embodiments described herein may be applicable to LTE, LTE-Advanced, LTE-U UMTS, HSPA, GSM, cdma2000, WiMax, WiFi, another suitable radio access technology, or any suitable combination of one or more radio access technologies. Although certain embodiments may be described in the context of wireless transmissions in the downlink, the present disclosure contemplates that the various embodiments are equally applicable in the uplink and vice versa.

The techniques described herein are applicable to both LAA LTE and standalone LTE operation in license-exempt channels. The described techniques are generally applicable for transmissions from both network nodes <NUM> and wireless devices <NUM>.

<FIG> illustrate an example network node <NUM> for flexible CSI-RS transmission, according to certain embodiments. As described above, network node <NUM> may be any type of radio network node or any network node that communicates with a wireless device and/or with another network node. Examples of a network node <NUM> are provided above.

Network nodes <NUM> may be deployed throughout network <NUM> as a homogenous deployment, heterogeneous deployment, or mixed deployment. A homogeneous deployment may generally describe a deployment made up of the same (or similar) type of network nodes <NUM> and/or similar coverage and cell sizes and inter-site distances. A heterogeneous deployment may generally describe deployments using a variety of types of network nodes <NUM> having different cell sizes, transmit powers, capacities, and inter-site distances. For example, a heterogeneous deployment may include a plurality of low-power nodes placed throughout a macro-cell layout. Mixed deployments may include a mix of homogenous portions and heterogeneous portions.

Network node <NUM> may include one or more of transceiver <NUM>, processor <NUM>, memory <NUM>, and network interface <NUM>. In some embodiments, transceiver <NUM> facilitates transmitting wireless signals to and receiving wireless signals from wireless device <NUM> (e.g., via an antenna), processor <NUM> executes instructions to provide some or all of the functionality described above as being provided by a network node <NUM>, memory <NUM> stores the instructions executed by processor <NUM>, and network interface <NUM> communicates signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), core network nodes or radio network controllers, etc..

In certain embodiments, network node <NUM> may be capable of using multi-antenna techniques, and may be equipped with multiple antennas and capable of supporting MIMO techniques. The one or more antennas may have controllable polarization. In other words, each element may have two co-located sub elements with different polarizations (e.g., <NUM>-degree separation as in cross-polarization), so that different sets of beamforming weights will give the emitted wave different polarization.

Processor <NUM> may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of network node <NUM>. In some embodiments, processor <NUM> may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, processing circuitry, and/or other logic.

Memory <NUM> is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by a processor. Examples of memory <NUM> include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non-transitory computer-readable and/or computer-executable memory devices that store information.

In some embodiments, network interface <NUM> is communicatively coupled to processor <NUM> and may refer to any suitable device operable to receive input for network node <NUM>, send output from network node <NUM>, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface <NUM> may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

Other embodiments of network node <NUM> may include additional components beyond those shown in <FIG> that may be responsible for providing certain aspects of the radio network node's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solutions described above). The various different types of network nodes may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components. Additionally, the terms first and second are provided for example purposes only and may be interchanged.

<FIG> illustrates an example wireless device <NUM> for flexible CSI-RS transmission, in accordance with certain embodiments. As depicted, wireless device <NUM> includes transceiver <NUM>, processor <NUM>, and memory <NUM>. In some embodiments, transceiver <NUM> facilitates transmitting wireless signals to and receiving wireless signals from network node <NUM> (e.g., via an antenna), processor <NUM> executes instructions to provide some or all of the functionality described above as being provided by wireless device <NUM>, and memory <NUM> stores the instructions executed by processor <NUM>. Examples of a network node <NUM> are provided above.

Processor <NUM> may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of wireless device <NUM>. In some embodiments, processor <NUM> may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic.

Other embodiments of wireless device <NUM> may include additional components beyond those shown in <FIG> that may be responsible for providing certain aspects of the wireless device's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above).

In certain embodiments, the methods for flexible CSI-RS transmission as described above may be performed by a virtual computing device. <FIG> illustrates an example virtual computing device <NUM> for flexible CSI-RS transmission, according to certain embodiments. In certain embodiments, virtual computing device <NUM> may include modules for performing steps similar to those of method illustrated and described in <FIG>. For example, virtual computing device <NUM> may include at a receiving module <NUM>, a performing module <NUM>, and any other suitable modules for flexible CSI-RS transmission. In some embodiments, one or more of the modules may be implemented using one or more processors <NUM> of <FIG>. In certain embodiments, the functions of two or more of the various modules may be combined into a single module.

The receiving module <NUM> may perform the receiving functions of virtual computing device <NUM>. For example, in a particular embodiment, receiving module <NUM> may receive, from network node <NUM>, information identifying a first subset of CSI-RS resources to be used in performing CSI measurements. The first subset of CSI-RS may be associated with a first portion of a frequency band that is less than all of the frequency band.

The performing module <NUM> may perform the performing functions of virtual computing device <NUM>. For example, in a particular embodiment, performing module <NUM> may perform CSI measurements in the first subset of CSI-RS resources being associated with the first portion of the frequency band.

Other embodiments of virtual computing device <NUM> may include additional components beyond those shown in <FIG> that may be responsible for providing certain aspects of the wireless device's <NUM> functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solutions described above). The various different types of wireless devices <NUM> may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

<FIG> illustrates another example virtual computing device <NUM> for flexible CSI-RS transmission, according to certain embodiments. In certain embodiments, virtual computing device <NUM> may include modules for performing steps similar to those of method illustrated and described in <FIG>. For example, virtual computing device <NUM> may include at an receiving module <NUM>, a identifying module <NUM>, performing module <NUM>, and any other suitable modules for flexible CSI-RS transmission. In some embodiments, one or more of the modules may be implemented using one or more processors <NUM> of <FIG>. In certain embodiments, the functions of two or more of the various modules may be combined into a single module.

The receiving module <NUM> may perform the receiving functions of virtual computing device <NUM>. For example, in a particular embodiment, receiving module <NUM> may receive a CSI-RS resource configuration for a plurality of antenna ports and an associated codebook configuration for CSI feedback.

The identifying module <NUM> may perform the identifying functions of virtual computing device <NUM>. For example, in a particular embodiment, identifying module <NUM> may identify a first subset of antenna ports over which CSI measurements are to be performed in a first subframe.

The performing module <NUM> may perform the performing functions of virtual computing device <NUM>. For example, in a particular embodiment, performing module <NUM> may perform CSI measurements over the first subset of antenna ports in the first subframe.

<FIG> illustrates yet another example virtual computing device <NUM> for flexible CSI-RS transmission, according to certain embodiments. In certain embodiments, virtual computing device <NUM> may include modules for performing steps similar to those of method illustrated and described in <FIG>. For example, virtual computing device <NUM> may include at a signaling module <NUM>, a receiving module <NUM>, and any other suitable modules for flexible CSI-RS transmission. In some embodiments, one or more of the modules may be implemented using one or more processors <NUM> of <FIG>. In certain embodiments, the functions of two or more of the various modules may be combined into a single module.

The signaling module <NUM> may perform the signaling functions of virtual computing device <NUM>. For example, in a particular embodiment, signaling module <NUM> may signal, to a wireless device <NUM>, information identifying a first subset of CSI-RS resources to be used in performing CSI measurements. The first subset of CSI-RS resources may be associated with a first portion of a frequency band that is less than all of the frequency band. As another example, in a particular embodiment, signaling module <NUM> may signal, to wireless device <NUM>, a first subset of antenna ports over which CSI measurements are to be performed in a first subframe.

The receiving module <NUM> may perform the receiving functions of virtual computing device <NUM>. For example, in a particular embodiment, receiving module <NUM> may receive, from the wireless device <NUM>, CSI feedback associated with the CSI measurements performed using the first subset of CSI-RS resources. As another example, in a particular embodiment, receiving module <NUM> may receive, from wireless device <NUM>, CSI feedback associated with the CSI measurements performed over the first subset of antenna ports.

Other embodiments of virtual computing device <NUM> may include additional components beyond those shown in <FIG> that may be responsible for providing certain aspects of the network node's <NUM> functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solutions described above). The various different types of network nodes <NUM> may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

<FIG> illustrates another example virtual computing device <NUM> for flexible CSI-RS transmission, according to certain embodiments. In certain embodiments, virtual computing device <NUM> may include modules for performing steps similar to those of method illustrated and described in <FIG>. For example, virtual computing device <NUM> may include at a first signaling module <NUM>, a second signaling module <NUM>, a receiving module <NUM>, and any other suitable modules for flexible CSI-RS transmission. In some embodiments, one or more of the modules may be implemented using one or more processors <NUM> of <FIG>. In certain embodiments, the functions of two or more of the various modules may be combined into a single module.

The first signaling module <NUM> may perform certain of the signaling functions of virtual computing device <NUM>. For example, in a particular embodiment, first signaling module <NUM> may signal a CSI-RS resource configuration for a plurality of antenna ports and an associated codebook configuration for CSI feedback. The second signaling module <NUM> may perform certain other of the signaling functions of virtual computing device <NUM>. For example, in a particular embodiment, second signaling module <NUM> may signal, to a wireless device, a first subset of antenna ports over which CSI measurements are to be performed in a first subframe.

The receiving module <NUM> may perform the receiving functions of virtual computing device <NUM>. For example, in a particular embodiment, receiving module <NUM> may receive, from the wireless, CSI feedback associated with the CSI measurements performed over the first subset of antenna port.

Other embodiments of virtual computing device <NUM> may include additional components beyond those shown in <FIG> that may be responsible for providing certain aspects of the network node <NUM>'s functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solutions described above). The various different types of network nodes <NUM> may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

<FIG> illustrates an exemplary radio network controller or core network node, in accordance with certain embodiments. Examples of network nodes can include a mobile switching center (MSC), a serving GPRS support node (SGSN), a mobility management entity (MME), a radio network controller (RNC), a base station controller (BSC), and so on. The radio network controller or core network node <NUM> includes processor <NUM>, memory <NUM>, and network interface <NUM>. In some embodiments, processor <NUM> executes instructions to provide some or all of the functionality described above as being provided by the network node, memory <NUM> stores the instructions executed by processor <NUM>, and network interface <NUM> communicates signals to any suitable node, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), network nodes <NUM>, radio network controllers or core network nodes <NUM>, etc..

Processor <NUM> may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of the radio network controller or core network node <NUM>. In some embodiments, processor <NUM> may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic.

In some embodiments, network interface <NUM> is communicatively coupled to processor <NUM> and may refer to any suitable device operable to receive input for the network node, send output from the network node, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface <NUM> may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

Other embodiments of the network node may include additional components beyond those shown in <FIG> that may be responsible for providing certain aspects of the network node's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above).

Claim 1:
A method (<NUM>) by a wireless device (<NUM>) for restricting channel state information, CSI, measurement comprises:
receiving (<NUM>), from a network node (<NUM>), information identifying a first subset of channel state information-reference signal, CSI-RS, resources comprising one or more parameters identifying a first subset of physical resource blocks, PRBs, (<NUM>) and a first subset of antenna ports to be used in performing CSI measurements, the first subset of antenna ports being associated with a first portion of a frequency band that is less than all of the frequency band, wherein the information received from the network node further identifies a first CSI reporting type of a plurality of CSI reporting types for reporting the CSI associated with the first subset of CSI-RS resources;
performing (<NUM>) CSI measurements in the first subset of antenna ports associated with the first portion of the frequency band; and
transmitting, to the network node and based on the information, a first CSI report of the first CSI reporting type of the plurality of CSI reporting types, the first CSI report comprising one or more values associated with the CSI measurements performed in the first subset of CSI-RS resources.