Patent Description:
In a legacy Long Term Evolution (LTE) system such as a release <NUM> (Rel. <NUM>) LTE-Advanced (LTE-A) system, a CSI acquisition scheme supporting zero-power (ZP) CSI-RS was introduced to cope with inter-cell interference that degrades accuracy of CSI acquisition. When a user equipment (UE) is configured with a ZP CSI-RS resource, the UE assumes that rate matching is applied to the resource element (RE), for example, a Physical Downlink Shared Channel (PDSCH) is not multiplexed to the REs for the ZP CSI-RS. Typically, the ZP CSI-RS resource is scheduled to align with the non-zero power (NZP) CSI-RS resources for the neighboring cells. Additionally, the Rel. <NUM> LTE standard supports only periodic CSI-RS transmission. The ZP CSI-RS resource is also used as an interference measurement resource (IMR). For instance, UE can measure all the interference power using ZP CSI-RS resource element (RE), in which desired signal is muted.

On the other hand, in a New Radio (NR) (Fifth Generation (<NUM>)) system, further flexibility on NZP CSI-RS is supported such as periodic/aperiodic/semi-persistent CSI-RS transmission. As a result, whether the CSI-RS is transmitted to the neighboring cell is dynamically changed. In order to achieve efficient resource utilization for the NZP CSI-RS, further flexibility is required for the ZP CSI-RS resource as well.

In addition, in a conventional resource configuration in the legacy LTE system, the ZP CSI-RS resource uses the REs for <NUM>-port CSI-RS. Therefore, if the NR system apply the conventional resource configuration, scheduling of the ZP CSI-RS resource may be restricted.

<NPL>
discuss several issues regarding CSI measurement and reporting in NR. <NPL> presents views on CSI acquisition schemes for downlink beam management
<NPL> discusses the design for CSI reporting and CSI-RS configurations, the control mechanism for CSI reporting and CSI-RS transmission, and the use cases for CSI-related dynamic configuration and indication, respectively. Patent Reference <CIT> discloses a method and an apparatus that indicate and identify a ZP-CSI-RS configuration. Document <CIT> relates to a method and device for performing or supporting NIB coordinated multi-point transmission in a wireless communication system. Document <CIT> relates to radio resource control signaling for configuring the UE to obtain and report CSI for those downlink channels.

According to the present invention, enhanced flexibility on the scheduling of ZP CSI-RS resources can be realized.

Embodiments will be described in detail below, with reference to the drawings.

<FIG> and <FIG> are a diagram showing a wireless communications system <NUM> according to one or more embodiments. The wireless communication system <NUM> includes a user equipment (UE) <NUM> and base stations (BSs) 20A and 20B. The wireless communication system <NUM> may be a New Radio (NR) system. The wireless communication system <NUM> is not limited to the specific configurations described herein and may be any type of wireless communication system such as an LTE/LTE-Advanced (LTE-A) system.

The BS <NUM> may communicate uplink (UL) and downlink (DL) signals with the UE <NUM> in a cell of the BS <NUM>. The DL and UL signals may include control information and user data. The BS <NUM> may be a gNodeB (gNB).

The BS <NUM> includes antennas, a communication interface to communicate with an adjacent BS <NUM> (for example, X2 interface), a communication interface to communicate with a core network (for example, S1 interface), and a CPU (Central Processing Unit) such as a processor or a circuit to process transmitted and received signals with the UE <NUM>. Operations of the BS <NUM> may be implemented by the processor processing or executing data and programs stored in a memory. However, the BS <NUM> is not limited to the hardware configuration set forth above and may be realized by other appropriate hardware configurations as understood by those of ordinary skill in the art. Numerous BSs <NUM> may be disposed so as to cover a broader service area of the wireless communication system <NUM>.

The UE <NUM> may communicate DL and UL signals that include control information and user data with the BS <NUM> using MIMO technology. The UE <NUM> may be a mobile station, a smartphone, a cellular phone, a tablet, a mobile router, or information processing apparatus having a radio communication function such as a wearable device.

The UE <NUM> includes a CPU such as a processor, a RAM (Random Access Memory), a flash memory, and a radio communication device to transmit/receive radio signals to/from the BS <NUM> and the UE <NUM>. For example, operations of the UE <NUM> described below may be implemented by the CPU processing or executing data and programs stored in a memory. However, the UE <NUM> is not limited to the hardware configuration set forth above and may be configured with, e.g., a circuit to achieve the processing described below.

In one or more embodiments of the present invention, the wireless communication system <NUM> supports a Channel State Information (CSI) acquisition scheme using a zero-power (ZP) CSI-Reference Signal (RS) for high accurate CSI estimation. Resource element(s) (RE(s)) designated as the ZP CSI-RS may be muted. This makes it possible to improve accuracy of the CSI estimation on the muted RE(s). For example, a non-zero-power (NZP) CSI-RS may be transmitted from a serving cell and any signals/channels may not be transmitted from neighboring cells (the ZP CSI-RS may be applied in the neighboring cells). As shown in <FIG>, the BS 20A (serving cell) may transmit the NZP CSI-RS. The BS 20B (neighboring cell) may transmit the ZP CSI-RS (muting). Then, the UE <NUM> may transmit CSI feedback to the BS 20A (serving cell) in response to the NZP CSI-RS.

In one or more embodiments, the wireless communication system <NUM> supports an interference measurement using the ZP CSI- RS for flexible interference measurement. The RE(s) designated as the ZP CSI-RS may be muted. This makes it possible to improve flexibility of the interference measurement on the muted RE(s). For example, any signals/channels may not be transmitted from a serving cell and signals/channels may be transmitted from neighboring cells (the ZP CSI-RS may be applied in the serving cell). As shown in <FIG>, the BS 20A may multiplex and transmit the ZP CSI-RS. The BS 20B (neighboring cell) may transmit a DL data signal. Then, the UE <NUM> may transmit CSI feedback to the BS 20A (serving cell) (or the ZP CSI-RS from the serving cell and the DL data signal from the neighboring cell interfere mutually. Here, usage of ZP CSI-RS is not limited to the measurement of inter-cell interference but applicable to some other measurements, e.g., inter-user interference measurement for multi-user (MU)-MIMO. In addition, ZP CSI-RS is not used only for measuring downlink signals but also used to measure uplink or sidelink signals.

Next, the CSI-RS resources according to one or more embodiments will be described below, with reference to <FIG>, <FIG>, and <FIG>.

<FIG> is a diagram showing REs allocated to the CSI-RS antenna ports (APs) in a resource block (RB) for a normal cyclic prefix and an extended cyclic prefix according to one or more embodiments. As shown in <FIG>, one axis designates Orthogonal Frequency Division Multiplexing (OFDM) symbols and the other axis designates subcarriers. Each block corresponds to the RE in the RB and the hatched REs with the number of APs are allocated to the CSI-RS APs. Furthermore, as shown in <FIG>, two REs are allocated to the CSI-RS APs when the BS designates two CSI-RS APs. Moreover, four REs are allocated to the CSI-RS APs when the BS designates four CSI-RS APs, and eight REs are allocated to the CSI-RS APs when the BS designates eight CSI-RS APs. Furthermore, the conventional ZP CSI-RS resource in the legacy LTE standard (e.g., Rel. <NUM> LTE) is notified using the REs mapped to the <NUM>-port CSI-RS (RE mapping for <NUM>-port CSI-RS). That is, the conventional ZP CSI-RS resources can be designated only in a unit of four REs.

<FIG> and <FIG> show mapping from a CSI-RS configuration to REs for the normal cyclic prefix and the extended cyclic prefix, respectively, according to one or more embodiments. The tables (CSI-RS configuration) as shown in <FIG> and <FIG> are used to report, to the UE, mapping of CSI-RS to REs in the RB. The table (CSI-RS configuration) in <FIG> and <FIG> is defined in Table <NUM>. <NUM>-<NUM> and <NUM>. <NUM>-<NUM> respectively of the 3GPP TS <NUM>.

For example, when mapping two CSI-RS APs for the normal cycle prefix as shown in <FIG>, twenty pairs of REs allocated to the CSI-RS APs are indicated. <FIG> shows a table corresponding to frame structure type <NUM> and <NUM> including indexes <NUM>-<NUM> for a CSI-RS configuration (mapping information). The BS transmits to the UE one of the indexes <NUM>-<NUM> for a CSI-RS configuration in <FIG> to report which one of the twenty pairs of REs allocated to the CSI-RS APs in <FIG> is used.

As described above, the conventional ZP CSI-RS resource in Rel. <NUM> LTE supports the RE mapping for <NUM>-port CSI-RS only. On the other hand, a ZP CSI-RS resource according to one or more embodiments of the present invention may be a flexible and configurable ZP CSI-RS resource. That is, the ZP CSI-RS resource according to one or more embodiments of the present invention may not be limited to the RE mapping for <NUM>-port CSI-RS.

<FIG> is a sequence diagram showing an example operation according to one or more embodiments.

As shown in <FIG>, at step S11, the BS <NUM> may transmit ZP CSI-RS resource configuration information to the UE <NUM> via higher layer signaling such as Radio Resource Control (RRC) signaling. As shown in <FIG>, the ZP CSI-RS resource configuration information includes at least one of a resource index, the number of the APs, multiplexing timing, a multiplexing frequency location, a RE multiplexing location, and a Reference Signal (RS) type.

Turning back to <FIG>, at step S12, the BS <NUM> may transmit periodic ZP CSI-RS, semi-persistent ZP CSI-RS, or an aperiodic ZP CSI-RS to the UE <NUM>.

At step S13, the UE <NUM> may assume (specify) ZP CSI-RS resource using the received ZP CSI-RS resource configuration information. Then, at step S14, the UE <NUM> may receive the ZP CSI-RS based on the assumed ZP CSI-RS resource.

The ZP CSI-RS resource configuration information will be described below in detail.

The resource index is an index that identifies each ZP CSI-RS resource.

In one or more embodiments of the present invention, the number of the APs indicates the number of the APs used for the ZP CSI-RS. As shown in <FIG>, the number of the APs may be <NUM>, <NUM>, <NUM>, <NUM>,. Thus, according to one or more embodiments of the present invention, the ZP CSI-RS resource is not limited to the RE mapping for <NUM>-port CSI-RS, and may be the RE mapping for <NUM>/<NUM>/<NUM>-port CSI-RS ZP CSI-RS. Accordingly, the UE <NUM> may be configured with the number of the APs for the ZP CSI-RS.

According to one or more embodiments , the ZP CSI-RS may be transmitted as a periodic ZP CSI-RS, a semi-persistent ZP CSI-RS, or an aperiodic ZP CSI-RS. In one or more embodiments, the multiplexing timing indicates time domain behavior of the ZP CSI-RS such as "periodic", "semi-persistent", and "aperiodic.

The multiplexing timing of the ZP CSI-RS resource configuration information designates periodicity and a timing offset (slot offset) for the periodic ZP CSI-RS or the semi-persistent ZP CSI-RS.

The BS <NUM> may transmit, to the UE10, the ZP CSI-RS resource configuration information including the multiplexing timing that designates the periodicity and the timing offset for the periodic or semi-persistent ZP CSI-RS using the RRC signaling. The UE receives the periodic or semi-persistent ZP CSI-RS based on a ZP CSI-RS resource specified using the periodicity and the timing offset.

For example, activation/deactivation of the ZP CSI-RS resource may be triggered using at least one of Media Access Control Control Element (MAC CE) and Downlink Control Information (DCI).

For example, when the aperiodic ZP CSI-RS is transmitted, on/off of the ZP CSI-RS resource may be triggered using at least one of the MAC CE and DCI. The UE <NUM> receives the DCI that triggers the aperiodic ZP CSI-RS and receives the aperiodic ZP CSI-RS based on a ZP CSI-RS resource specified using the DCI.

The multiplexing frequency band of the ZP CSI-RS may be a frequency band in which the ZP CSI-RS is multiplexed. The multiplexing frequency band of the ZP CSI-RS may be notified as a wideband, a subband, or a partial band. According to one or more embodiments, the multiplexing frequency band of the ZP CSI-RS may be notified to the UE <NUM>.

Frequency density of the ZP CSI-RS can be also configured. For example, the UE <NUM> can be configured with the increased or reduced density.

The CSI-RS configuration indicates a time/frequency-multiplexing location of the REs associated with the ZP CSI-RS in a slot (subframe). The time/frequency-multiplexing location may be a location of the REs mapped to the ZP CSI-RS by time/frequency-multiplexing in a slot. Thus, the ZP CSI-RS resource configuration information indicates a location in time and frequency domains of resource elements mapped to the ZP CSI-RS in a slot. According to one or more embodiments of the present invention, the BS <NUM> may notify the UE <NUM> of the CSI-RS configuration of the ZP CSI-RS.

As shown in <FIG>, in the RS type, for example, a Synchronization Signal (SS), a measurement RS/mobility RS (MRS), a Demodulation-Reference Signal (DM-RS), and a Sounding Reference Signal (SRS) other than the CSI-RS may be designated. The ZP CSI-RS resource may be configured with a configuration used for the SS, the MRS, the DM-RS, and the SRS.

For example, when the SS is designated in the RS type, the number of the APs, the multiplexing timing, and the multiplexing frequency location used for the SS may be designated and applied to the ZP CSI-RS resource (this can be called as ZP SS resource, ZP RS resource or ZP resource).

Furthermore, when the RE multiplexing location of the SRS is applied to the ZP resource, comb information and frequency hopping information may be notified to the UE <NUM>.

Thus, according to one or more embodiments of the present invention, as shown in <FIG>, in the ZP resource, the resource <NUM>, <NUM>, and <NUM> corresponding to the resource index "<NUM>", "<NUM>", and "<NUM>", respectively may have flexible parameters.

In <FIG>, for example, in the resource <NUM>, "<NUM>-port", "CSI-RS", "Periodic (<NUM> msec periodicity and <NUM> msec subframe offset)", and "Wideband" are designated in the number of the APs, RS type, the multiplexing timing, and the multiplexing frequency location, respectively. Furthermore, the ZP resource of the resource <NUM> may be notified using the RRC signaling.

In <FIG>, for example, in the resource <NUM>, "<NUM>-port", "CSI-RS", "Aperiodic", and "Subband (index x)" are designated in the number of the APs, RS type, the multiplexing timing, and the multiplexing frequency location, respectively. Furthermore, the ZP resource of the resource <NUM> may be dynamically triggered with the possible preliminary RRC configuration.

In <FIG>, for example, in the resource <NUM>, "DM-RS (AP <NUM>-<NUM>)", "Periodic", and "Wideband" are designated in the RS type, the multiplexing timing, and the multiplexing frequency location, respectively. The number of the APs used for the DM-RS may be applied to the number of the APs for the ZP CSI-RS. Furthermore, the ZP resource of the resource <NUM> may be notified using the RRC signaling.

According to one or more embodiments, the ZP resource may be configured with configuration information of NZP SS/RS resource other than the NZP CSI-RS resource.

According to the present invention, a plurality of the ZP resources are grouped. According to the invention, activation/deactivation of the ZP resources and on/off of the ZP resources dynamically triggered in each group.

Furthermore, according to one or more embodiments, rate matching may be performed without multiplexing the PDSCH on the ZP resource. Furthermore, according to one or more embodiments of the present invention, the PDSCH of the ZP resource may be rate-matched and punctured. The method of rate matching and puncturing can be switched, e.g., with RRC signaling.

Thus, according to one or more embodiments, enhanced flexibility on the scheduling of ZP resources can be realized.

As another example, the above methods of the flexible ZP resource allocation may be applied to an Interference Measurement Resource (IMR). For example, IMR can be configured with at least one of the resource index, number of APs, multiplexing timing, multiplexing frequency location, RE multiplexing location and RS type. That is, IMR configuration information includes at least one of the resource index, number of APs, multiplexing timing, multiplexing frequency location, RE multiplexing location and RS type. For example, IMR can be triggered dynamically.

As shown in <FIG>, at step S21, the BS <NUM> may transmit IMR configuration information to the UE <NUM> via higher layer signaling such as RRC signaling. As shown in <FIG>, the IMR configuration information includes at least one of a resource index, the number of the APs, multiplexing timing, a multiplexing frequency location, an RE multiplexing location, and a RS type.

Turning back to <FIG>, at step S22, the BS <NUM> may transmit periodic IMR, semi-persistent IMR, or an aperiodic IMR to the UE <NUM>.

At step S23, the UE <NUM> may assume (specify) an IMR resource using the received IMR resource configuration information. Then, at step S14, the UE <NUM> may receive the IMR based on the assumed IMR resource.

For example, the BS <NUM> transmits, to the UE <NUM>, the IMR configuration information using the RRC signaling. For example, when the IMR is transmitted as a periodic IMR or a semi-persistent IMR, the IMR configuration information designates periodicity and a timing offset for the periodic IMR or the semi-persistent IMR.

For example, when the IMR is transmitted as the semi-persistent IMR, the UE <NUM> receives at least one of MAC CE and DCI triggering activation and deactivation of the semi-persistent IMR.

For example, when the IMR is transmitted as the aperiodic IMR, the UE <NUM> receives DCI that triggers the aperiodic IMR. The UE <NUM> receives the IMR based on a IMR resource specified using the DCI.

For example, the IMR resource configuration information indicates a frequency band on which the IMR is multiplexed. The frequency band may be a wideband, a subband, or a partial band. For example, the IMR resource configuration information indicates frequency density of the IMR. For example, the IMR resource configuration information indicates a location in time and frequency domains of resource elements mapped to the IMR in a slot. For example, the IMR resource configuration information indicates the number of antenna ports of the BS used for transmission of the IMR.

For example, an IMR resource of the IMR is not multiplexed on a Physical Downlink Shared Channel (PDSCH) and the IMR resource is rate matched.

The BS <NUM> according to one or more embodiments will be described below with reference to <FIG> is a diagram illustrating a schematic configuration of the BS <NUM> according to one or more embodiments. The BS <NUM> may include a plurality of antennas (antenna element group) <NUM>, amplifier <NUM>, transceiver (transmitter/receiver) <NUM>, a baseband signal processor <NUM>, a call processor <NUM> and a transmission path interface <NUM>.

User data that is transmitted on the DL from the BS <NUM> to the UE <NUM> is input from the core network <NUM>, through the transmission path interface <NUM>, into the baseband signal processor <NUM>.

In the baseband signal processor <NUM>, signals are subjected to Packet Data Convergence Protocol (PDCP) layer processing, Radio Link Control (RLC) layer transmission processing such as division and coupling of user data and RLC retransmission control transmission processing, Medium Access Control (MAC) retransmission control, including, for example, HARQ transmission processing, scheduling, transport format selection, channel coding, inverse fast Fourier transform (IFFT) processing, and precoding processing. Then, the resultant signals are transferred to each transceiver <NUM>. As for signals of the DL control channel, transmission processing is performed, including channel coding and inverse fast Fourier transform, and the resultant signals are transmitted to each transceiver <NUM>.

The baseband signal processor <NUM> notifies each UE <NUM> of control information (system information) for communication in the cell by higher layer signaling (e.g., RRC signaling and broadcast channel). Information for communication in the cell includes, for example, UL or DL system bandwidth.

In each transceiver <NUM>, baseband signals that are precoded per antenna and output from the baseband signal processor <NUM> are subjected to frequency conversion processing into a radio frequency band. The amplifier <NUM> amplifies the radio frequency signals having been subjected to frequency conversion, and the resultant signals are transmitted from the antennas <NUM>.

As for data to be transmitted on the UL from the UE <NUM> to the BS <NUM>, radio frequency signals are received in each antennas <NUM>, amplified in the amplifier <NUM>, subjected to frequency conversion and converted into baseband signals in the transceiver <NUM>, and are input to the baseband signal processor <NUM>.

The baseband signal processor <NUM> performs FFT processing, IDFT processing, error correction decoding, MAC retransmission control reception processing, and RLC layer and PDCP layer reception processing on the user data included in the received baseband signals. Then, the resultant signals are transferred to the core network <NUM> through the transmission path interface <NUM>. The call processor <NUM> performs call processing such as setting up and releasing a communication channel, manages the state of the BS <NUM>, and manages the radio resources.

The UE <NUM> according to one or more embodiments will be described below with reference to <FIG> is a schematic configuration of the UE <NUM> according to one or more embodiments of the present invention. The UE <NUM> has a plurality of UE antennas <NUM>, amplifiers <NUM>, the circuit <NUM> comprising transceiver (transmitter/receiver) <NUM>, the controller <NUM>, and an application <NUM>.

As for DL, radio frequency signals received in the UE antennas <NUM> are amplified in the respective amplifiers <NUM>, and subjected to frequency conversion into baseband signals in the transceiver <NUM>. These baseband signals are subjected to reception processing such as FFT processing, error correction decoding and retransmission control and so on, in the controller <NUM>. The DL user data is transferred to the application <NUM>. The application <NUM> performs processing related to higher layers above the physical layer and the MAC layer. In the downlink data, broadcast information is also transferred to the application <NUM>.

On the other hand, UL user data is input from the application <NUM> to the controller <NUM>. In the controller <NUM>, retransmission control (Hybrid ARQ) transmission processing, channel coding, precoding, DFT processing, IFFT processing and so on are performed, and the resultant signals are transferred to each transceiver <NUM>. In the transceiver <NUM>, the baseband signals output from the controller <NUM> are converted into a radio frequency band. After that, the frequency-converted radio frequency signals are amplified in the amplifier <NUM>, and then, transmitted from the antenna <NUM>.

One or more embodiments may be used for each of the uplink and the downlink independently. One or more embodiments may be also used for both of the uplink and the downlink in common.

Although the present disclosure mainly described examples of a channel and signaling scheme based on NR, the present invention is not limited thereto. One or more embodiments of the present invention may apply to another channel and signaling scheme having the same functions as LTE/LTE-A and a newly defined channel and signaling scheme.

Although the present disclosure mainly described examples of channel estimation and CSI feedback scheme based on the RS, the present invention is not limited thereto. One or more embodiments of the present invention may apply to another synchronization signal, reference signal, and physical channel such as CSI-RS, synchronization signal (SS), measurement RS (MRS), mobility RS (MRS), and beam RS (BRS).

Although the present disclosure mainly described examples of various signaling methods, the signaling according to one or more embodiments may be explicitly or implicitly performed.

Although the present disclosure mainly described examples of various signaling methods, the signaling according to one or more embodiments may be the higher layer signaling such as the RRC signaling and/or the lower layer signaling such as Downlink Control Information (DCI) and MAC Control Element (CE). Furthermore, the signaling according to one or more embodiments may use a Master Information Block (MIB) and/or a System Information Block (SIB). For example, at least two of the RRC, the DCI, and the MAC CE may be used in combination as the signaling according to one or more embodiments.

Although the present disclosure described examples of the beamformed RS (RS transmission using the beam), whether the physical signal/channel is beamformed may be transparent for the UE. The beamformed RS and the beamformed signal may be called the RS and the signal, respectively. Furthermore, the beamformed RS may be referred to as a RS resource. Furthermore, the beam selection may be referred to as resource selection. Furthermore, the Beam Index may be referred to as a resource index (indicator) or an antenna port index.

The UE antennas according to one or more may apply to the UE including one dimensional antennas, planer antennas, and predetermined three dimensional antennas.

In one or more embodiments, the Resource Block (RB) and a subcarrier in the present disclosure may be replaced with each other. A subframe, a symbol, and a slot may be replaced with each other.

Claim 1:
A user equipment, UE, for a wireless communication system comprising:
a receiver that receives, from a base station, BS,
Zero Power, ZP, Channel State Information-Reference Signal, CSI-RS, resource configuration information, and
a plurality of ZP CSI-RS,
wherein the ZP CSI-RS is transmitted as a periodic ZP CSI-RS, a semi-persistent ZP CSI-RS, or an aperiodic ZP CSI-RS
wherein when the ZP CSI-RS is transmitted as the periodic ZP CSI-RS or the semi-persistent ZP CSI-RS, the ZP CSI-RS resource configuration information designates periodicity and a slot offset for the periodic ZP CSI-RS or the semi-persistent ZP CSI-RS,
wherein the receiver receives the plurality of ZP CSI-RS based on a plurality of ZP CSI-RS resources specified using the periodicity and the slot offset,
wherein when the plurality of ZP CSI-RS are transmitted as the aperiodic ZP CSI-RS, the receiver receives Downlink Control Information, DCI, that triggers activation of the aperiodic ZP CSI-RS, and the receiver receives the plurality of ZP CSI-RS based on a plurality of ZP CSI-RS resources specified using the DCI, and
characterized in that the plurality of the ZP CSI-RS resources of the aperiodic ZP CSI-RS are grouped into a first group and a second group and wherein all of the ZP CSI-RS resources within the first group and all of the ZP CSI-RS resources within the second group are activated/deactivated by being triggered by the DCI.