Method and apparatus for channel state information reference signal (CSI-RS)

Methods and apparatuses for CSI reporting mechanisms are provided. A user equipment (UE) includes a transceiver and a processor operably connected to the transceiver. The transceiver is configured to receive information indicating a channel state information reference signal (CSI-RS) resource configuration, uplink-related downlink control information (DCI), and a CSI-RS associated with a selected CSI-RS resource in a same subframe as the uplink-related DCI. The processor configured to determine, in response to a CSI request included in the uplink-related DCI, an aperiodic CSI in reference to the CSI-RS. The transceiver is further configured to report the aperiodic CSI by transmitting the aperiodic CSI on an uplink channel.

TECHNICAL FIELD

The present disclosure relates generally to transmission method and channel state information (CSI) reporting for multiple transmit antennas which includes two dimensional arrays. Such two dimensional arrays can be associated with a type of multiple-input multiple-output (MIMO) system often termed “full-dimension” MIMO (FD-MIMO) or massive MIMO or 3D-MIMO.

BACKGROUND

Wireless communication has been one of the most successful innovations in modern history. The demand of wireless data traffic is rapidly increasing due to the growing popularity among consumers and businesses of smart phones and other mobile data devices, such as tablets, “note pad” computers, net books, eBook readers, and machine type of devices. To meet the high growth in mobile data traffic and support new applications and deployments, improvements in radio interface efficiency and coverage is of paramount importance.

A mobile device or user equipment can measure the quality of the downlink channel and report this quality to a base station so that a determination can be made regarding whether or not various parameters should be adjusted during communication with the mobile device. Existing channel quality reporting processes in wireless communications systems do not sufficiently accommodate reporting of channel state information associated with large, two dimensional array transmit antennas or, in general, antenna array geometry which accommodates a large number of antenna elements.

SUMMARY

Various embodiments of the present disclosure provide methods and apparatuses for CSI reporting.

In one embodiment, a user equipment (UE) is provided. The UE includes a transceiver and a processor operably connected to the transceiver. The transceiver is configured to receive information indicating a channel state information reference signal (CSI-RS) resource configuration, uplink-related downlink control information (DCI), and a CSI-RS associated with a selected CSI-RS resource in a same subframe as the uplink-related DCI. The processor is configured to determine, in response to a CSI request included in the uplink-related DCI, an aperiodic CSI in reference to the CSI-RS. The transceiver is further configured to report the aperiodic CSI by transmitting the aperiodic CSI on an uplink channel.

In another embodiment, a base station (BS) is provided. The BS includes a processor and a transceiver operably connected to the processor. The processor is configured to generate configuration information to configure a user equipment (UE) with channel state information reference signal (CSI-RS) resource. The transceiver configured to transmit, to the UE, the CSI-RS resource configuration information, uplink-related downlink control information (DCI), and a CSI-RS associated with a selected CSI-RS resource in a same subframe as the uplink-related DCI. The transceiver is further configured to receive, from the UE, an aperiodic CSI reporting on an uplink channel. The aperiodic CSI reporting is determined in response to a CSI request included in the uplink-related DCI and in reference to the CSI-RS.

In another embodiment, a method for operating a UE is provided. The method includes receiving, by the UE, information indicating a channel state information reference signal (CSI-RS) resource configuration, an uplink-related downlink control information (DCI), and a CSI-RS associated with a selected CSI-RS resource in a same subframe as the uplink-related DCI; in response to receipt of a CSI request included in the uplink-related DCI, determining, by the UE, an aperiodic CSI in reference to the CSI-RS; and reporting the aperiodic CSI by transmitting the aperiodic CSI on an uplink channel.

The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE).

DETAILED DESCRIPTION

The following documents and standards descriptions are hereby incorporated by reference into the present disclosure as if fully set forth herein: 3GPP Technical Specification (TS) 36.211 version 12.4.0, “E-UTRA, Physical channels and modulation” (“REF 1”); 3GPP TS 36.212 version 12.3.0, “E-UTRA, Multiplexing and Channel coding” (“REF 2”); 3GPP TS 36.213 version 12.4.0, “E-UTRA, Physical Layer Procedures” (“REF 3”); 3GPP TS 36.321 version 12.4.0, “E-UTRA, Medium Access Control (MAC) Protocol Specification” (“REF 4”); and 3GPP TS 36.331 version 12.4.0, “E-UTRA, Radio Resource Control (RRC) Protocol Specification” (“REF 5”).

FIG. 1illustrates an example wireless network100according to various embodiments of the present disclosure. The embodiment of the wireless network100shown inFIG. 1is for illustration only. Other embodiments of the wireless network100could be used without departing from the scope of the present disclosure.

The wireless network100includes an eNodeB (eNB)101, an eNB102, and an eNB103. The eNB101communicates with the eNB102and the eNB103. The eNB101also communicates with at least one Internet Protocol (IP) network130, such as the Internet, a proprietary IP network, or other data network. Instead of “eNB”, an alternative term “gNB” (general Node B) can also be used. Depending on the network type, other well-known terms can be used instead of “eNB” or “BS,” such as “base station” or “access point.” For the sake of convenience, the terms “eNB” and “BS” are used in this patent document to refer to network infrastructure components that provide wireless access to remote terminals. Also, depending on the network type, other well-known terms can be used instead of “user equipment” or “UE,” such as “mobile station,” “subscriber station,” “remote terminal,” “wireless terminal,” or “user device.” For the sake of convenience, the terms “user equipment” and “UE” are used in this patent document to refer to remote wireless equipment that wirelessly accesses an eNB, whether the UE is a mobile device (such as a mobile telephone or smartphone) or is normally considered a stationary device (such as a desktop computer or vending machine).

The eNB102provides wireless broadband access to the network130for a first plurality of user equipments (UEs) within a coverage area120of the eNB102. The first plurality of UEs includes a UE111, which can be located in a small business (SB); a UE112, which can be located in an enterprise (E); a UE113, which can be located in a WiFi hotspot (HS); a UE114, which can be located in a first residence (R); a UE115, which can be located in a second residence (R); and a UE116, which can be a mobile device (M) like a cell phone, a wireless laptop, a wireless PDA, or the like. The eNB103provides wireless broadband access to the network130for a second plurality of UEs within a coverage area125of the eNB103. The second plurality of UEs includes the UE115and the UE116. In some embodiments, one or more of the eNBs101-103can communicate with each other and with the UEs111-116using 5G, LTE, LTE-A, WiMAX, or other advanced wireless communication techniques.

Dotted lines show the approximate extents of the coverage areas120and125, which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with eNBs, such as the coverage areas120and125, can have other shapes, including irregular shapes, depending upon the configuration of the eNBs and variations in the radio environment associated with natural and man-made obstructions.

As described in more detail below, one or more of eNB101, eNB102, and eNB103transmit to UEs111-116with precoder cycling and configure UEs111-116for CSI reporting as described in embodiments of the present disclosure. In various embodiments, one or more of UEs111-116receive and demodulate at least one transmission with precoder cycling as well as perform calculation and reporting for of CSI.

AlthoughFIG. 1illustrates one example of a wireless network100, various changes can be made toFIG. 1. For example, the wireless network100could include any number of eNBs and any number of UEs in any suitable arrangement. Also, the eNB101could communicate directly with any number of UEs and provide those UEs with wireless broadband access to the network130. Similarly, each eNB102-103could communicate directly with the network130and provide UEs with direct wireless broadband access to the network130. Further, the eNB101,102, and/or103could provide access to other or additional external networks, such as external telephone networks or other types of data networks.

FIGS. 2A and 2Billustrate example wireless transmit and receive paths according to the present disclosure. In the following description, a transmit path200can be described as being implemented in an eNB (such as eNB102), while a receive path250can be described as being implemented in a UE (such as UE116). However, it will be understood that the receive path250could be implemented in an eNB and that the transmit path200could be implemented in a UE. In some embodiments, the receive path250is configured to receive and demodulate at least one transmission with precoder cycling as well as support channel quality measurement and reporting as described in embodiments of the present disclosure.

The transmit path200includes a channel coding and modulation block205, a serial-to-parallel (S-to-P) block210, a size N Inverse Fast Fourier Transform (IFFT) block215, a parallel-to-serial (P-to-S) block220, an add cyclic prefix block225, and an up-converter (UC)230. The receive path250includes a down-converter (DC)255, a remove cyclic prefix block260, a serial-to-parallel (S-to-P) block265, a size N Fast Fourier Transform (FFT) block270, a parallel-to-serial (P-to-S) block275, and a channel decoding and demodulation block280.

In the transmit path200, the channel coding and modulation block205receives a set of information bits, applies coding (such as convolutional, Turbo, or low-density parity check (LDPC) coding), and modulates the input bits (such as with Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM)) to generate a sequence of frequency-domain modulation symbols. The serial-to-parallel block210converts (such as de-multiplexes) the serial modulated symbols to parallel data in order to generate N parallel symbol streams, where N is the IFFT/FFT size used in the eNB102and the UE116. The size N IFFT block215performs an IFFT operation on the N parallel symbol streams to generate time-domain output signals. The parallel-to-serial block220converts (such as multiplexes) the parallel time-domain output symbols from the size N IFFT block215in order to generate a serial time-domain signal. The ‘add cyclic prefix’ block225inserts a cyclic prefix to the time-domain signal. The up-converter230modulates (such as up-converts) the output of the ‘add cyclic prefix’ block225to an RF frequency for transmission via a wireless channel. The signal can also be filtered at baseband before conversion to the RF frequency.

A transmitted RF signal from the eNB102arrives at the UE116after passing through the wireless channel, and reverse operations to those at the eNB102are performed at the UE116. The down-converter255down-converts the received signal to a baseband frequency, and the remove cyclic prefix block260removes the cyclic prefix to generate a serial time-domain baseband signal. The serial-to-parallel block265converts the time-domain baseband signal to parallel time domain signals. The size N FFT block270performs an FFT algorithm to generate N parallel frequency-domain signals. The parallel-to-serial block275converts the parallel frequency-domain signals to a sequence of modulated data symbols. The channel decoding and demodulation block280demodulates and decodes the modulated symbols to recover the original input data stream.

As described in more detail below, the transmit path200or the receive path250can perform signaling for CSI reporting. Each of the eNBs101-103can implement a transmit path200that is analogous to transmitting in the downlink to UEs111-116and can implement a receive path250that is analogous to receiving in the uplink from UEs111-116. Similarly, each of UEs111-116can implement a transmit path200for transmitting in the uplink to eNBs101-103and can implement a receive path250for receiving in the downlink from eNBs101-103.

Each of the components inFIGS. 2A and 2Bcan be implemented using only hardware or using a combination of hardware and software/firmware. As a particular example, at least some of the components inFIGS. 2A and 2Bcan be implemented in software, while other components can be implemented by configurable hardware or a mixture of software and configurable hardware. For instance, the FFT block270and the IFFT block215can be implemented as configurable software algorithms, where the value of size N can be modified according to the implementation.

AlthoughFIGS. 2A and 2Billustrate examples of wireless transmit and receive paths, various changes can be made toFIGS. 2A and 2B. For example, various components inFIGS. 2A and 2Bcould be combined, further subdivided, or omitted and additional components could be added according to particular needs. Also,FIGS. 2A and 2Bare meant to illustrate examples of the types of transmit and receive paths that could be used in a wireless network. Other suitable architectures could be used to support wireless communications in a wireless network.

FIG. 3Aillustrates an example UE116according to the present disclosure. The embodiment of the UE116illustrated inFIG. 3Ais for illustration only, and the UEs111-115ofFIG. 1could have the same or similar configuration. However, UEs come in a wide variety of configurations, andFIG. 3Adoes not limit the scope of the present disclosure to any particular implementation of a UE.

The UE116includes an antenna305, a radio frequency (RF) transceiver310, transmit (TX) processing circuitry315, a microphone320, and receive (RX) processing circuitry325. The UE116also includes a speaker330, a processor340, an input/output (I/O) interface (IF)345, an input350, a display355, and a memory360. The memory360includes an operating system (OS) program361and one or more applications362.

The processor340is also coupled to the input350(e.g., keypad, touchscreen, button etc.) and the display355. The operator of the UE116can use the input350to enter data into the UE116. The display355can be a liquid crystal display or other display capable of rendering text and/or at least limited graphics, such as from web sites.

As described in more detail below, the UE116can perform signaling and calculation for CSI reporting. AlthoughFIG. 3Aillustrates one example of UE116, various changes can be made toFIG. 3A. For example, various components inFIG. 3Acould be combined, further subdivided, or omitted and additional components could be added according to particular needs. As a particular example, the processor340could be divided into multiple processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Also, whileFIG. 3Aillustrates the UE116configured as a mobile telephone or smartphone, UEs could be configured to operate as other types of mobile or stationary devices.

FIG. 3Billustrates an example eNB102according to the present disclosure. The embodiment of the eNB102shown inFIG. 3Bis for illustration only, and other eNBs ofFIG. 1could have the same or similar configuration. However, eNBs come in a wide variety of configurations, andFIG. 3Bdoes not limit the scope of the present disclosure to any particular implementation of an eNB. eNB101and eNB103can include the same or similar structure as eNB102.

As shown inFIG. 3B, the eNB102includes multiple antennas370a-370n, multiple RF transceivers372a-372n, transmit (TX) processing circuitry374, and receive (RX) processing circuitry376. In certain embodiments, one or more of the multiple antennas370a-370ninclude 2D antenna arrays. The eNB102also includes a controller/processor378, a memory380, and a backhaul or network interface382.

The RF transceivers372a-372nreceive, from the antennas370a-370n, incoming RF signals, such as signals transmitted by UEs or other eNBs. The RF transceivers372a-372ndown-convert the incoming RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuitry376, which generates processed baseband signals by filtering, decoding, and/or digitizing the baseband or IF signals. The RX processing circuitry376transmits the processed baseband signals to the controller/processor378for further processing.

The TX processing circuitry374receives analog or digital data (such as voice data, web data, e-mail, or interactive video game data) from the controller/processor378. The TX processing circuitry374encodes, multiplexes, and/or digitizes the outgoing baseband data to generate processed baseband or IF signals. The RF transceivers372a-372nreceive the outgoing processed baseband or IF signals from the TX processing circuitry374and up-converts the baseband or IF signals to RF signals that are transmitted via the antennas370a-370n.

The controller/processor378can include one or more processors or other processing devices that control the overall operation of the eNB102. For example, the controller/processor378could control the reception of forward channel signals and the transmission of reverse channel signals by the RF transceivers372a-372n, the RX processing circuitry376, and the TX processing circuitry374in accordance with well-known principles. The controller/processor378could support additional functions as well, such as more advanced wireless communication functions. In some embodiments, the controller/processor378includes at least one microprocessor or microcontroller.

The controller/processor378is also capable of executing programs and other processes resident in the memory380, such as an OS. The controller/processor378is also capable of supporting channel quality measurement and reporting for systems having 2D antenna arrays as described in embodiments of the present disclosure. In some embodiments, the controller/processor378supports communications between entities, such as web RTC. The controller/processor378can move data into or out of the memory380as required by an executing process.

The controller/processor378is also coupled to the backhaul or network interface382. The backhaul or network interface382allows the eNB102to communicate with other devices or systems over a backhaul connection or over a network. The interface382could support communications over any suitable wired or wireless connection(s). For example, when the eNB102is implemented as part of a cellular communication system (such as one supporting 5G or new radio access technology or NR, LTE, or LTE-A), the interface382could allow the eNB102to communicate with other eNBs over a wired or wireless backhaul connection. When the eNB102is implemented as an access point, the interface382could allow the eNB102to communicate over a wired or wireless local area network or over a wired or wireless connection to a larger network (such as the Internet). The interface382includes any suitable structure supporting communications over a wired or wireless connection, such as an Ethernet or RF transceiver.

The memory380is coupled to the controller/processor378. Part of the memory380could include a RAM, and another part of the memory380could include a Flash memory or other ROM. In certain embodiments, a plurality of instructions, such as a BIS algorithm is stored in memory. The plurality of instructions are configured to cause the controller/processor378to perform the BIS process and to decode a received signal after subtracting out at least one interfering signal determined by the BIS algorithm.

As described in more detail below, the transmit and receive paths of the eNB102(implemented using the RF transceivers372a-372n, TX processing circuitry374, and/or RX processing circuitry376) perform configuration and signaling for CSI reporting.

AlthoughFIG. 3Billustrates one example of an eNB102, various changes can be made toFIG. 3B. For example, the eNB102could include any number of each component shown inFIG. 3A. As a particular example, an access point could include a number of interfaces382, and the controller/processor378could support routing functions to route data between different network addresses. As another particular example, while shown as including a single instance of TX processing circuitry374and a single instance of RX processing circuitry376, the eNB102could include multiple instances of each (such as one per RF transceiver).

FIG. 4illustrates example two-dimensional (2D) antenna arrays constructed from 16 dual-polarized elements arranged in a 4×2 or 2×4 rectangular format which can be utilized in various embodiments of the present disclosure. In this illustrative embodiment, the 2D dual-polarized antenna port array includes Marows and Nacolumns where (Ma, Na)=(2,4) and (4,2). The embodiment of the 2D dual-polarized antenna port array shown inFIG. 4is for illustration only. Other embodiments of the 2D dual-polarized antenna port array could be used without departing from the scope of the present disclosure.

The example 2D dual-polarized antenna port array arrangement results in a total of 2MaNa=16 ports, each mapped to one CSI-RS port. The three indices400,410, and420are three examples in indexing the 16 antenna ports as a means of mapping antenna ports to precoding matrix elements. For row-first indexing400, antenna ports associated with the same polarization group are indexed in a row-first manner regardless of (Ma, Na). For longer-first indexing410, antenna ports associated with the same polarization group are indexed in a column-first manner when Ma>Na, but row-first manner when Ma≤Na. For shorter-first indexing420, antenna ports associated with the same polarization group are indexed in a row-first manner when Ma>Na, but column-first manner when Ma≤Na. Indexing400is therefore termed row-first indexing while indexing410longer-first indexing and indexing420shorter-first indexing.

In these illustrative embodiments, both Maand Nacan be configured by an eNB for a UE. In another example, rather than defining Maand Naas the number of rows and columns of the rectangular array of ports or port pattern, respectively, these two parameters can be defined as two-dimensional precoding codebook parameters. The values of Maand Napartly determine the manner in which a codebook (hence each precoding matrix element in the codebook) is mapped onto antenna ports of a one- or two-dimensional antenna array. This configuration can be performed with and without signaling the total number of antenna ports. When a UE is configured with a codebook, these parameters can be included either in a corresponding CSI process configuration or NZP (non-zero-power) CSI-RS resource configuration.

In LTE systems, precoding codebooks are utilized for CSI reporting. Two categories of CSI reporting modes are supported: PUSCH-based aperiodic CSI (A-CSI) and PUCCH-based periodic CSI (P-CSI). In each category, different modes are defined based on frequency selectivity of CQI and/or PMI, that is, whether wideband (one CSI parameter calculated for all the “set S subbands”) or subband (one CSI parameter calculated for each “set S subband”) reporting is performed. The supported CSI reporting modes are given in TABLE 1 and 2.

In Rel.12 LTE, dual-stage precoding codebook enumerated with a first and a second PMI values (i1and i2, respectively) are supported for 4 and 8 antenna ports. The first PMI value i1is associated with a group of four DFT beams/precoders. The second PMI value i2, on the other hand, selects one out of four beams/precoders indicated with i1, along with QPSK co-phasing between two polarization groups.

In Rel.13 LTE, a flexible codebook structure which accommodates 2D CSI-RS port patterns is supported for ‘CLASS A’ eMIMO-Type with 8, 12, and 16 antenna ports, where not only (N1,N2) are configurable, but also oversampling factors for both dimensions (O1,O2) and four types of codebook subset selections configured via RRC parameter codebook-Config. In addition, a single-stage beam selection codebook for 2, 4, or 8 antenna ports is also supported for ‘CLASS B’ eMIMO-Type.

Based on the above codebook, a resulting precoding matrix can be described in Equation 1. That is, the first stage precoder can be described as a Kronecker product of a first and a second precoding vector (or matrix), which can be associated with a first and a second dimension, respectively. This type is termed partial Kronecker Product (partial KP) codebook. The subscripts m and n in Wm,n(im,n) denote precoding stage (first or second stage) and dimension (first or second dimension), respectively. Each of the precoding matrices Wm,ncan be described as a function of an index which serves as a PMI component. As a result, the precoding matrix W can be described as a function of 3 PMI components i1,1, i1,2, i2. The first stage pertains to a long-term component. Therefore, the first stage is associated with long-term channel statistics such as angle-of-departure (AoD) profile and AoD spread. On the other hand, the second stage pertains to a short-term component which performs selection, co-phasing, or any linear operation to the first component precoder W1,1(i1,1)W1,2(i1,2). In the present disclosure, AB denotes the Kronecker product between two matrices A and B. The precoder W2(i2), therefore, performs a linear transformation of the long-term component such as a linear combination of a set of basis functions or vectors associated with the column vectors of W1,1(i1,1)W1,2(i1,2)).

W⁡(i1,1,i1,2,i2)=(W1,1⁡(i1,1)⊗W1,2⁡(i1,2))︸W1⁡(i1,1,i2,2)⁢W2⁡(i2)(Equation⁢⁢1)
Here, a UE measures a CSI-RS in a subframe designated to carry CSI-RS, calculates a CSI (including PMI, RI, and CQI where each of these three CSI parameters can include multiple components) based on the measurement, and reports the calculated CSI to a serving eNB102.

The above precoding description is especially suitable when the serving eNB transmits non-precoded CSI-RS (NP CSI-RS). That is, a cell-specific one-to-one mapping between CSI-RS port and TXRU (transceiver unit) is utilized. Here, different CSI-RS ports have the same wide beam width and direction and hence generally cell wide coverage. This use case can be realized when the eNB configures the UE with ‘CLASS A’ eMIMO-Type which corresponds to NP CSI-RS. Other than CQI and RI, CSI reports associated with ‘CLASS A’ or ‘nonPrecoded’ eMIMO-Type include (assuming the partial KP design inherent in the Rel.13 codebook described above) a three-component PMI {i1,1, i1,2, i2}.

Another type of CSI-RS applicable to FD-MIMO is beamformed CSI-RS (BF CSI-RS). For example, beamforming operation, either cell-specific or UE-specific, is applied on a non-zero-power (NZP) CSI-RS resource (including multiple ports). Here, at least at a given time/frequency CSI-RS ports have narrow beam widths and hence not cell wide coverage, and (at least from the eNB perspective) at least some CSI-RS port-resource combinations have different beam directions. This beamforming operation is intended to increase CSI-RS coverage or penetration. In addition, when UE-specific beamforming is applied to a CSI-RS resource (termed the UE-specific or UE-specifically beamformed CSI-RS), CSI-RS overhead reduction can be obtained when NZP CSI-RS resources are allocated efficiently through resource sharing (pooling) for multiple UEs either in time domain (for instance, aperiodic transmission), beam domain (UE-specific beamforming), or dynamic CSI-RS resource (re)configuration. When a UE is configured to receive BF CSI-RS from a serving eNB, the UE can be configured to report PMI parameters associated with W2(W2,1and/or W2,2) without W1(W1,1and/or W1,2) or, in general, associated with a single-stage precoder/codebook. This use case can be realized when the eNB configures the UE with ‘CLASS B’ eMIMO-Type which corresponds to BF CSI-RS. Other than CQI and RI, CSI reports associated with ‘CLASS B’ or ‘beamformed’ eMIMO-Type (with one CSI-RS resource and alternative codebook) include a one-component PMI n. Although a single PMI defined with respect to a distinct codebook, this PMI can be associated with the second-stage PMI component of ‘CLASS A’/‘nonPrecoded’ codebooks i2.

Therefore, given a precoding codebook (a set of precoding matrices W(i1,1,i1,2,i2)), a UE measures a CSI-RS in a subframe designated to carry CSI-RS, calculates/determines a CSI (including PMI, RI, and CQI where each of these three CSI parameters can include multiple components) based on the measurement, and reports the calculated CSI to a serving eNB. In particular, this PMI is an index of a recommended precoding matrix in the precoding codebook. Similar to that for the first type, different precoding codebooks can be used for different values of RI. The measured CSI-RS can be one of the two types: non-precoded (NP) CSI-RS and beamformed (BF) CSI-RS. As mentioned, in Rel.13, the support of these two types of CSI-RS is given in terms of two eMIMO-Types: ‘CLASS A’ (with one CSI-RS resource) and ‘CLASS B’ (with one or a plurality of CSI-RS resources), respectively.

In scenarios where DL long-term channel statistics can be measured through UL signals at a serving eNB, UE-specific BF CSI-RS can be readily used. This is typically feasible when UL-DL duplex distance is sufficiently small. When this condition does not hold, however, some UE feedback is necessary for the eNB to obtain an estimate of DL long-term channel statistics (or any of its representation thereof). To facilitate such a procedure, a first BF CSI-RS transmitted with periodicity T1(ms) and a second NP CSI-RS transmitted with periodicity T2(ms), where T1≤T2. This approach is termed hybrid CSI-RS. The implementation of hybrid CSI-RS is largely dependent on the definition of CSI process and NZP CSI-RS resource.

As discussed above, utilizing UE-specific BF CSI-RS reduces the number of ports configured to each UE by applying beamforming on NP CSI-RS. For instance, a serving eNB can apply wideband beamforming on a 16-port NP CSI-RS to form a 2-port BF CSI-RS for a served UE. If each UE is configured with 2-port BF CSI-RS, the resulting total CSI-RS overhead is reduced when the number of co-scheduled UEs is less than 8—assuming the same transmission rate for NP and BF CSI-RS. However, although not all the served UEs require data transmission in every subframe, the number of served UEs per cell tends to be much larger than 8. Due to the burstiness and stochasticity of data traffic, UE-specific BF CSI-RS uses or requires an efficient CSI-RS resource allocation mechanism to ensure that the total CSI-RS overhead can be minimized or, conversely, the number of served UEs per cell can be maximized.

Therefore, there is a need to enable an efficient CSI-RS resource allocation mechanism for UE-specific BF CSI-RS.

Terms such as ‘non-precoded’ (or ‘NP’) CSI-RS and ‘beamformed’ (or ‘BF’) CSI-RS are used throughout the present disclosure. The essence of the present disclosure does not change when different terms or names are used to refer to these two CSI-RS types. For example, ‘CSI-RS-A’ and ‘CSI-RS-B’ can refer to or be associated with these two CSI-RS types. Essentially these two CSI-RS types are a first CSI-RS and a second CSI-RS. In another example, CSI-RS resource type can be used to differentiate those two modes of operation instead of CSI-RS type. CSI-RS resources associated with these two types of CSI-RS can be referred to as ‘a first CSI-RS resource’ and ‘a second CSI-RS resource’, or ‘CSI-RS-A resource’ and ‘CSI-RS-B resource’. Subsequently, the labels ‘NP’ and ‘BF’ (or ‘np’ and ‘bf’) are examples and can be substituted with other labels such as ‘1’ and ‘2’, or ‘A’ and ‘B’, or TYPE1 and TYPE2, or CLASS-A and CLASS-B. In another example, a MIMO type or eMIMO-Type which can be associated with CSI reporting operation can be used to differentiate those two modes of operation instead of CSI-RS type. For example, a UE is configured with a MIMO type or eMIMO-Type associated with CSI reporting behaviors and, in addition, CSI measurement behaviors. Names of higher-layer or RRC parameters utilized in this invention disclosure are example and illustrative. Other names which serve same functionalities can be utilized.

The present disclosure includes at least four components: aperiodic CSI-RS (Ap-CSI-RS) mechanism, Ap-CSI-RS resource definition, Ap-CSI-RS resource selection or reconfiguration, and Ap-CSI-RS reference resource definition. Each of the four components can be used either by itself (without the other component) or in conjunction with at least one of the other four components.

For the first component (that is, aperiodic CSI-RS mechanism),FIG. 5illustrates an example mechanism500for aperiodic CSI-RS (Ap-CSI-RS). Ap-CSI-RS is characterized by two primary features. First, a pool of CSI-RS resources is defined and shared among multiple served UEs (510). A CSI-RS resource from this pool can be assigned to a UE only when the UE measures CSI (hence a resource can only be used when the resource is needed). The UE needs to measure CSI when its associated serving eNB chooses to receive a CSI reporting calculated based on a most recent channel. This leads to a second primary feature. Ap-CSI-RS assignment is done in conjunction with an aperiodic CSI request from the serving eNB to a served UE (in this example, termed UE-k). Therefore, Ap-CSI-RS resource information is included in a DCI of an UL grant which contains an A-CSI request to UE-k in subframe n (520). Along with the A-CSI request, the Ap-CSI-RS itself, which is placed in the same DL subframe n as the A-CSI trigger and the Ap-CSI-RS resource information. Alternatively, the Ap-CSI-RS can be placed in another subframe following subframe n (at the expense of CSI reporting delay). In response to the CSI request and the Ap-CSI-RS resource information in subframe n (assuming that the Ap-CSI-RS is placed in subframe n), UE-k measures the associated Ap-CSI-RS assigned by the eNB (530) and reports a requested A-CSI in subframe n+L (540) where L is specified and can be scenario-dependent. For instance, a default value of L is 4 following Rel.13 LTE. This mechanism can be applied to both NP and UE-specific BF CSI-RS.

Although NP CSI-RS is cell-specific, its resource configuration is UE-specific. When used for NP CSI-RS, Ap-CSI-RS mechanism facilitates NP CSI-RS overhead reduction as the NP CSI-RS can be transmitted only when necessary. In turn, a served UE is assigned a CSI-RS resource and can measure NP CSI-RS only when necessary (aperiodically) thereby reducing computational complexity and hence UE power consumption. If applied to NP CSI-RS, channel measurement restriction can be utilized together with class A CSI reporting since CSI measurement (in time and frequency) is performed within the subframe containing Ap-CSI-RS.

Likewise, Ap-CSI-RS facilitates CSI-RS overhead reduction when applied to UE-specific BF CSI-RS. This is because UE-specific BF CSI-RS can be transmitted only when necessary thereby reducing the total CSI-RS overhead across all UEs. In turn, a served UE is assigned a CSI-RS resource and can measure BF CSI-RS only when necessary (aperiodically) thereby reducing computational complexity and hence UE power consumption.

For the second component (that is, aperiodic CSI-RS resource definition), since Ap-CSI-RS is transmitted and measured aperiodically (whenever required), an Ap-CSI-RS resource is not characterized by subframe configuration which includes subframe offset and periodicity (as in the legacy CSI-RS resource). Instead, an Ap-CSI-RS resource is characterized by at least one of the following parameters: the number of assigned CSI-RS ports, a set of CSI-RS port numbers, and a CSI-RS pattern configuration. The second and third parameters are described as follows.

Regarding the second parameters, to define a set of CSI-RS port numbers assigned to a UE, a master set of (available) port numbers {Port0, Port0+1, . . . , Port0+NPORT,MAX−1} is needed. At least two options are available. A first option is to define a new master set of ports where a previously unused value of Port0(so that any value in the master set {Port0, Port0+1, . . . , Port0+NPORT,MAX−1} is also previously unused) is chosen. For example, by choosing Port0=200, a master set of ports {200,201, . . . ,199+NPORT,MAX}, different from the available CSI-RS ports in Rel.13 {15,16, . . . ,30}, is defined. A second option is to extend the existing CSI-RS ports (in Rel.13 LTE) by choosing Port0=15 and increase NPORT,MAXbeyond the current value of 16 which results in a master set of CSI-RS ports {15,16, . . . ,14+NPORT,MAX}. The second option allows usage of the legacy CSI-RS ports for Ap-CSI-RS whenever the ports are available.

For a given number of CSI-RS ports NPORT, an NPORT-port CSI-RS resource can be specified in terms of a port subset of the master set {Port0, Port0+1, . . . , Port0+NPORT,MAX−1}. At least two options are possible.

A first option for port subset selection follows the legacy Rel.13 LTE and assuming that the second master set option (see the previous paragraph), an NPORT-port CSI-RS resource is always associated with port numbers {15,16, . . . ,14+NPORT}. That is, the first CSI-RS port number is always 15 and the assigned CSI-RS port numbers are consecutive for any CSI-RS resource assignment. In this case, the set of CSI-RS port numbers is fixed for a given number of CSI-RS ports. Therefore, there is no need to indicate or signal port subset selection in Ap-CSI-RS resource configuration.

A second option for port subset selection which offers more flexible resource allocation and increased number of resource configurations is to allow a CSI-RS resource configuration to be associated with port numbers {Port(0), Port(1), . . . , Port(NPORT−1)} where Port(i) can be any port number taken from the master set. A constraint of Port(i)<Port(k), i>k can be further imposed. As an example, antenna ports {17,18,21,22} can be assigned to a UE for NPORT=4. For a given value of NPORT,MAXand NPORT, a total of Ncand=

(NPORT,MAXNPORT)⁢
candidates for CSI-RS port subset selection are available. Thus, if port subset selection is unrestricted, all these candidates are available. Alternatively, only a part of these available candidates can be used. In that case, a restricted subset of available candidates Ncand<

For this second port subset selection option, port subset selection is to be signaled and indicated in Ap-CSI-RS resource configuration. For this purpose, either a length-NPORT,MAXbitmap (indicating which port numbers are assigned to a UE) or a ┌log2Ncand┐-bit port subset indicator can be used. The bitmap is applicable for either unrestricted or restricted subset selection. The subset indicator, on the other hand, is suitable for restricted subset selection.

Regarding the third parameter, for a given number of CSI-RS ports NPORT, an NPORT-port CSI-RS resource can also be specified in terms of a T-F (time frequency) pattern configuration, termed CSI reference signal configuration in Table 6.10.5.2.1 of REF1, but referred to as pattern configuration in this disclosure. This pattern configuration indicates locations of CSI-RS REs in time and frequency within a subframe. In the legacy Rel.12 LTE, this is indicated by a 32-value RRC parameter resourceConfig-r10 or ‘CSI reference signal configuration’ in Table 6.10.5.2.1 of REF1).

Based on the above description of Ap-CSI-RS resource configuration, the following example Ap-CSI-RS resource pooling procedure can be described in a three-step procedure as follows. In a first step, a serving eNB starts from a master set of NPORT,MAXCSI-RS antenna port numbers {Port0, Port0+1, . . . , Port0+NPORT,MAX−1}. In a second step, if the first option of port subset selection is utilized, an aperiodic CSI-RS (Ap-CSI-RS) resource is characterized with the number of CSI-RS ports NPORTand a pattern configuration. If the second option of port subset selection is utilized, an aperiodic CSI-RS (Ap-CSI-RS) resource is characterized with the number of CSI-RS ports NPORT, a bitmap or an indicator associated with a set of antenna port numbers {Port(0), Port(1), . . . , Port(NPORT−1)}, and a pattern configuration. In a third step, the serving eNB assigns (at least) one NPORTCSI-RS resource to a served UE-k associated with the resource configuration in Step 2.

In addition to those three parameters, other configuration parameters can be incorporated in CSI-RS resource configuration (as a part of CSI-RS resource configuration) for aperiodic CSI-RS. Some examples are given as follows: energy-per-RE ratio relative to PDSCH; eMIMO-Type (either ‘nonPrecoded’/‘CLASS A’ or ‘beamformed’/‘CLASS B’); a parameter indicating whether the CSI-RS is NZP (non-zero-power) or ZP (zero-power); a parameter indicating whether the CSI-RS configuration is periodic or aperiodic.

For the third component (that is, aperiodic CSI-RS resource selection or reconfiguration), at least three options are possible for signaling each of the three parameters associated with CSI-RS resource configuration (number of antenna ports, T-F pattern configuration, and port subset configuration). A first option is to use RRC signaling per UE to perform semi-static (re)configuration of CSI-RS resource. Several served UEs can be configured to share a same CSI-RS resource assignment or have overlapping resource assignments. A second option is to use UL grant by incorporating the parameter in an associated DCI which carries A-CSI request (trigger). Therefore, CSI-RS resource configuration is signaled dynamically. A third option is to use either periodic or aperiodic resource (re)configuration using a similar principle to semi-persistent scheduling (SPS). That is, an UL grant is used to signal a reconfigured CSI-RS resource assignment to a served UE-k. This CSI-RS resource assignment can be accompanied with A-CSI request (trigger) or signaled by itself. This CSI-RS resource (re)configuration can either be performed every X ms where X can be configured via RRC signaling, or initiated with activation/deactivation procedure based on DL assignments or UL grants. If periodic resource reconfiguration is used, the value of X can be chosen large such as in the order of 200-ms or 320-ms.

The third option allows a more dynamic resource reconfiguration (which is not possible with the first option since RRC configuration incurs large delay) without incurring large DL signaling overhead (which is the case with the second option). Therefore, it allows a more efficient pooling of Ap-CSI-RS resources with reasonable DL signaling overhead. To set up a UE for the third option, an RRC configuration similar to the one for SPS-ConfigDL (TS 36.331 REF5) can be used. Only a few parameters are applicable (for example, parameters similar to semiPersistSchedIntervalDL and/or numberOfConfSPS-Processes).

Considering the aforementioned three signaling options, applicable to each of the three parameters, TABLE 3-A and 3-B describe several possible combinations for the first and the second options of port subset selection, respectively.

For each of the options in TABLE 3-A and 3-B, at least a CSI request field in the DCI of an UL grant (which includes an associated aperiodic CSI-RS) is needed to trigger A-CSI. The CSI request field can include one or multiple bits where each bit is associated with a cell. In addition, Ap-CSI-RS parameter(s) which need to be configured dynamically (a subset of the number of ports, T-F pattern configuration, and/or port subset) are also included in the DCI of the UL grant. These configuration parameters can be defined as separate parameters or jointly with the CSI request field.

When a UE is configured with K CSI-RS resources (or resource configurations), one CSI request field (which can include one or multiple bits) can be used for each of the K CSI-RS resources (or resource configurations). When k of these K CSI request fields are set to 1, CSI-RS associated with each of these k CSI-RS resources (or resource configurations) is transmitted in the DL subframe containing the UL grant.

When a UE is configured with two (possibly different) eMIMO-Type setups in one CSI process where each eMIMO-Type setup is associated with one or more CSI-RS resources (or resource configurations), one CSI request field (which can include one or multiple bits) can be used for each of the two eMIMO-Type setups. When either one or both CSI request fields are set to 1, CSI-RS associated with each triggered eMIMO-Type setup is transmitted in the DL subframe containing the UL grant.

When a combination of semi-static (RRC signaling) and either semi-persistent or dynamic signaling is used (such as Opt. 1.1, 1.2, or 1.3 in TABLE 3-A; Opt. 1.1.1, 1.1.2, 1.1.3, 1.2.1, 1.3.1, 1.2.2, or 1.3.3 in TABLE 3-B), at least one (NZP or ZP) CSI-RS resource configuration parameter is semi-statically configured and at least one CSI-RS resource configuration parameter is either semi-persistently or dynamically configured. In this case, the semi-static CSI-RS resource configuration effectively indicates that the UE is semi-statically configured with a plurality of (KA) CSI-RS resources (where KAis the number of possible CSI-RS resources or resource configurations associated with the semi-statically configured parameters). The second signaling—either semi-persistent or dynamic—selects one CSI-RS resource or a subset of CSI-RS resources from the KAsemi-statically configured CSI-RS resources. Therefore, instead of defining CSI-RS resources in terms of parameters, the semi-static (higher-layer or RRC) signaling can instead configure the UE a set of KACSI-RS resources and the semi-persistent or dynamic signaling can select one of out of KACSI-RS resources. Each of these CSI-RS resources can either be NZP or ZP.

In the present disclosure, several embodiments of CSI-RS resource (re)configuration scheme (referred above as semi-persistent resource reconfiguration) with at least one CSI-RS resource configuration parameter signaled using the third option are given. For each of the following embodiments, when a UE is configured with a plurality of CSI processes or component carriers, one CSI-RS resource (re)configuration (activation/release or activation/deactivation) can be associated with one CSI process or component carrier. Alternatively, one CSI-RS resource (re)configuration (activation/release or activation/deactivation) can be associated with a plurality of CSI processes or component carriers. Alternatively, one CSI-RS resource (re)configuration (activation/release or activation/deactivation) can be associated with all the CSI processes or component carriers.

In a first embodiment (embodiment 1.A), an activation-release/deactivation mechanism similar to semi-persistent scheduling is utilized to reconfigure CSI-RS resource. In this embodiment, UL grants or DL assignments on PDCCH or EPDCCH are used to reconfigure CSI-RS resource. Therefore, an UL grant or DL assignment used for this purpose includes at least one DCI field either for selecting one out of multiple choices of CSI-RS resource configuration (which are, for instance, configured via higher layer signaling as a part of CSI-RS resource configuration ASN.1 Information Element) or for setting the value of at least one CSI-RS resource configuration parameter. This field can be a part of an existing DCI format (such as DCI format 0 or 4 for UL grant, or format 1A, 2/2A/2B for DL assignment) or a new DCI format specifically designed for CSI-RS resource reconfiguration (activation/release or activation/deactivation). The UL grant (or DL assignment) is signaled to the UE via PDCCH or EPDCCH and masked by a special RNTI (such as CSI-RNTI).

FIG. 6describes an example eNB and UE operations600(in terms of timing diagram associated with eNB in601and UE in602) when at least one CSI-RS resource configuration parameter is signaled using the third option. For example, this corresponds to Opt. 1.3 or 3.3 in TABLE 3-A, or Opt. 1.1.3, 1.3.1, 1.3.3, or 3.3.3 in TABLE 3-B. In this embodiment, Ap-CSI-RS resource is reconfigured every X ms in subframe(s)610via an UL grant (or an UL-related grant or, alternatively, a DL assignment) which carries Ap-CSI-RS resource configuration information (including the DCI field mentioned above). This configuration information can be accompanied with an A-CSI request/trigger or signaled by itself. Upon receiving a DL subframe from610, a served UE-k reads the configuration information in630. Based on this configuration information, the eNB requests A-CSI to UE-k via an UL grant (containing A-CSI trigger) while transmitting Ap-CSI-RS within the same subframe(s)620. Upon receiving a DL subframe from640—containing an A-CSI request/trigger—UE-k measures the transmitted Ap-CSI-RS (in subframe n) according to the resource configuration information received in subframe(s)630, and performs CSI calculation. The resulting A-CSI is reported to the eNB in subframe(s)650. In the example inFIG. 6, the semi-persistently configured CSI-RS resource includes a set of the number of ports.

Although the above example assumes periodic resource reconfiguration (every X ms), aperiodic resource reconfiguration using activation and deactivation based on UL grant or DL assignment can also be used.

The above semi-persistent CSI-RS resource allocation mechanism, applied to NZP CSI-RS resource, can be described as follows. First, a UE receives a dynamic trigger/release containing a selection from multiple higher-layer-configured NZP CSI-RS resources. These multiple CSI-RS resources can be associated with a first set of configured parameters (set values of CSI-RS resource configuration parameters) or simply a list of KACSI-RS resources. Likewise, dynamic trigger or release can indicate either a ┌log(KA)1┐-bit DCI field or another set of parameters which, together with the first parameter set, further indicates the selected CSI-RS resource. In this embodiment, each NZP CSI-RS resource can be either periodic or aperiodic CSI-RS resource. Second, for an activation trigger received in subframe n, the transmission of the associated NZP CSI-RS resource will start no earlier than subframe n+Y1 where Y1>0. Third, for a release (deactivation) trigger received in subframe n, the transmission of the associated NZP CSI-RS resource will stop after subframe n+Y1 where Y1>0. Fourth, if an UL grant or UL grant-like mechanism is used to trigger CSI-RS which is placed or transmitted in a same subframe as the UL grant, the value of Y1 or Y2 can be aligned with that of A-CSI. The same holds if a DL grant is used instead.

In a second embodiment (embodiment 1.B), an activation-release/deactivation mechanism (similar to semi-persistent scheduling) is also utilized to reconfigure CSI-RS resource, but instead of using PDCCH, MAC control element (MAC CE) is used. Here, a new type of MAC CE can be defined for the purpose of reconfiguring CSI-RS resource. For example, this type of MAC CE can be termed “CSI-RS resource reconfiguration MAC control element (MAC CE)”. For each of the following embodiments using MAC CE, when a UE is configured with a plurality of CSI processes or component carriers, one CSI-RS resource activation/release can be associated with one CSI process or component carrier. Alternatively, one CSI-RS resource activation/release can be associated with a plurality of CSI processes or component carriers. Alternatively, one CSI-RS resource activation/release can be associated with all the CSI processes or component carriers.

This CSI-RS resource reconfiguration MAC CE is signaled to the UE via DL-SCH and included in a MAC PDU. Since the number of CSI-RS resource configuration parameters (as well as the length of each parameter) included in the MAC CE remains the same, the size of CSI-RS resource reconfiguration MAC CE can be fixed. Therefore, its associated MAC PDU sub-header includes solely of the 4 header fields R/F2/E/LCID (cf. REF4 section 6.1.2). The arrangement of CSI-RS resource configuration MAC CE can be illustrated in diagram700ofFIG. 7Awhere MAC CE 1 (701) is designated as a CSI-RS resource configuration MAC CE and associated with MAC PDU sub-header702. The 5-bit LCID (logical channel ID) indicates the type of logical channel. In this case, CSI-RS resource configuration MAC CE can utilize any of the reserved hypotheses (within 01011-10111—cf. Table 6.2.1-1 of REF4).

An example of a MAC CE design for CSI-RS resource reconfiguration is as follows. First, the MAC CE design includes at least one CSI-RS resource configuration parameter, each written as a binary (bit) sequence and arranged in an octet-aligned format. For instance, if all the three parameters mentioned above (number of ports, T-F pattern, and port number set) are configurable via a MAC CE, three fields are included in the CSI-RS resource configuration MAC CE. This is illustrated in diagram750ofFIG. 7Bwhere three fields752(number of CSI-RS ports NPORT, 2 bits-4 hypotheses),753(T-F pattern, 5 bits-32 hypotheses), and754(port number set, 8 bits-up to 256 hypotheses) are included in a MAC CE with a fixed size of two octets. A one-bit reserved field R (751) is added at the beginning to fit the three fields into a two-octet codeword. Alternatively, if port number set is not needed (for instance, configured via higher layer signaling, or simply fixed to {15,16, . . . ,14+NPORT}), only one octet may be needed.

The above semi-persistent CSI-RS resource allocation schemes (the first and the second embodiments) can also be used for ZP CSI-RS resource.

The above semi-persistent CSI-RS resource allocation schemes (the first and the second embodiments are used and applicable for aperiodic CSI-RS. Alternatively, these first and the second embodiments can also be applied to periodic CSI-RS (that which is associated with subframe configuration in CSI-RS resource configuration—such as subframe offset and periodicity). When applied to periodic CSI-RS, each of the two schemes can be used to start/activate or stop/deactivate CSI-RS measurement at a UE. For the first embodiment, a DCI field in an UL grant or a DL assignment is used to signal the start or the stop of CSI measurement associated with a selected CSI-RS resource. For the second embodiment, the CSI-RS resource reconfiguration MAC CE is used to signal the start or the stop of CSI measurement associated with a selected CSI-RS resource.

For either embodiment (1.A or 1.B), two possibilities exist. First, the size and content of the DCI field (first embodiment) or MAC CE (second embodiment) can be different from that used for aperiodic CSI-RS. In this case, the selected CSI-RS resource is configured for the UE via higher layer signaling. Therefore, the DCI field (first embodiment) or the MAC CE (second embodiment) simply signals START (activate) or STOP (deactivate). Second, the size and content of the DCI field (first embodiment) or MAC CE (second embodiment) are identical to that used for aperiodic CSI-RS. In this case, the selected CSI-RS resource is indicated in the DCI field (first embodiment) or the MAC CE (second embodiment)—selected out of a plurality of (KA) resources which are configured for the UE via higher-layer signaling—in the same manner as that for aperiodic CSI-RS (cf.FIGS. 7A and 7B).

For Ap-CSI-RS, several schemes exist in designing higher-layer (such as RRC) CSI-RS resource configuration.

In a first scheme, Rel.13 CSI-RS resource configuration (based on periodic CSI-RS resource configuration) is reused but unused configuration parameters such as CSI-RS subframe configuration (periodicity and subframe offset) are ignored when the CSI-RS resource is configured as aperiodic. For this embodiment, a parameter which indicates whether the CSI-RS resource is periodic or aperiodic (or whether aperiodic is ON) can be added inside the CSI-RS resource configuration information. This embodiment can be described in the following example ASN.1 setup in TABLE 4-A when the number of antenna ports and T-F pattern (resourceConfig) are configured semi-statically via RRC signaling. When CSI-RS-Alloc-r14 is set as {aperiodic}, subframeConfig-r10 is unused.

In a second scheme, a new CSI-RS resource configuration for aperiodic CSI-RS is used. For this embodiment, a parameter which indicates whether the CSI-RS resource is periodic or aperiodic (or whether aperiodic is ON) can be added to select between the legacy Rel.13 CSI-RS resource configuration (based on periodic CSI-RS resource configuration) and aperiodic CSI-RS resource configuration. This embodiment can be described in the example ASN.1 setup in TABLE 4-B when the number of antenna ports and T-F pattern (resourceConfig) are configured semi-statically via RRC signaling. In this case, either port subset is not configurable or configured dynamically or semi-dynamically. To choose between the legacy periodic CSI-RS resource configuration and the aperiodic CSI-RS configuration, a parameter aperiodicCSI-RS-r14 is used in the example description in TABLE 4-C.

In a third scheme, when a UE is configured with a plurality of CSI-RS resources (or resource configurations) in one CSI process, one selection parameter (between periodic and aperiodic CSI-RS resource configuration) can be introduced for each of the plurality of CSI-RS resources (or resource configurations). That is, each CSI-RS resource (or resource configuration) can be configured either as a periodic or an aperiodic CSI-RS resource.

In a fourth scheme, the selection parameter (between periodic and aperiodic CSI-RS resource configuration) can be introduced in the CSI process configuration. Therefore, if one CSI process is configured with a plurality of CSI-RS resources (or resource configurations), all or some of the CSI-RS resources (or resource configurations) associated with the CSI process share a same CSI-RS resource allocation (either periodic or aperiodic).

In a fifth scheme, when a UE is configured with two (possibly different) eMIMO-Type setups in one CSI process where each eMIMO-Type setup is associated with one or more CSI-RS resources (or resource configurations), one selection parameter (between periodic and aperiodic CSI-RS resource configuration) can be introduced for each of the two eMIMO-Type setups. Therefore, if one of the eMIMO-Type setups is configured with a plurality of CSI-RS resources (or resource configurations), all or some of the CSI-RS resources (or resource configurations) associated with the eMIMO-Type setup share a same CSI-RS resource allocation (either periodic or aperiodic).

In a third embodiment (embodiment 1.C), CSI-RS resource configuration or reconfiguration can include a combination between semi-static CSI-RS resource configuration, activation/deactivation CSI-RS resource configuration, and dynamic CSI-RS resource selection. This embodiment is illustrated in diagram800ofFIG. 8A. In this embodiment, an initial (first-step) CSI-RS resource configuration is performed in step810where a UE is configured with an aperiodic CSI-RS resource via higher-layer (RRC) signaling. In this initial resource configuration, a set of K NZP CSI-RS resources is defined or configured for the UE. This set of resources can be described by setting at least one CSI-RS resource parameter to a certain value (while not setting value for other CSI-RS resource parameters). Alternatively, the set of resources can be described by listing K combinations of values of a plurality of CSI-RS resource parameters.

A second-step CSI-RS resource configuration is performed in step820where a UE is configured with an aperiodic CSI-RS resource via activation/deactivation (activation/release) procedure using MAC control element (CE) signaling or UL-related DCIs (UL grants) or DL-related DCIs (DL grants)—as detailed above. In this initial resource configuration, a set of KA<K NZP CSI-RS resources is defined or configured for the UE. This set of resources (or resource configurations) can be described by setting at least one CSI-RS resource parameter to a certain value (which are not set in the first step, while not setting value for other remaining CSI-RS resource parameters). Alternatively, the set of resources can be described by listing KAcombinations of values of a plurality of CSI-RS resource parameters taken from a size-KAsubset of K resources defined or given in the first step.

Diagram850FIG. 8Bdepicts an example of MAC CE signaling where a size-KAsubset of K CSI-RS resources is selected and activated for a UE. Therefore, the number of used or required hypotheses or code points is

(KKA⁢)
which can be signaled with

⌈log2⁡(KKA⁢)⌉-bit
codeword. In this example, for illustrative purposes, K and KAare set to be 8 and 4, respectively, which result in a 7-bit codeword (852)—appended with 1 reserved bit (851) to form an octet. In another example where K and KAare set to be 8 and 2, respectively, which result in a 5-bit codeword and a 3 reserved bits. In general, the number of bits for the CSI-RS resource subset selection field can be fixed to the worst-case (maximum) value or can be made dependent on either K, KAor both K and KA.

The value of K can be configured via higher-layer signaling within a CSI-RS resource configuration. For example, this CSI-RS resource configuration can be an aperiodic CSI-RS resource configuration associated with CLASS B eMIMO-Type. Each of these K NZP CSI-RS resources is associated with a set of CSI-RS resource parameters such as T-F (time-frequency) pattern (5-bit resourceConfig in REF5, CSI Reference Signal Configuration in REF1), number of ports NPORTϵ {1,2,4,8} (antennaPortsCount in REF5), pC, and/or other parameters. Each of these K NZP CSI-RS resources is not associated with any subframe configuration parameters (such as periodicity and subframe offset).

The value of KAcan be fixed. For example, the value can be fixed to 4 or 2.

The value of KAcan also be made configurable. An example is that KAcan take value from the set {1, 2, . . . , min(K, KA,MAX)} where KA,MAXcan either be fixed (to, e.g. 4 or 2) or made dependent on UE capability. Another example is that KA=K when K≤2; and KAcan take value from the set {1, 2, . . . , min(K, KA,MAX)} where KA,MAXcan either be fixed (to, e.g. 4 or 2) or made dependent on UE capability when K>2.

When K=1 or KA=K, this second-step is by definition skipped.

The value of KAcan be configured via higher-layer signaling. For instance, an RRC parameter KAcan be defined in association or as a part of an aperiodic CSI-RS resource configuration. Alternatively, K4can be defined in association or as a part of the (CLASS B) eMIMO-Type information element. Alternatively, K4can be defined in association or as a part of the aperiodic CSI reporting configuration.

Alternatively, instead of signaling K4via higher-layer (RRC) signaling, K4can be signaled via MAC CE. This can be done in at least two manners. First, the value of KAis explicitly signaled together with CSI-RS resource subset selection as depicted in diagram860ofFIG. 8C. In this example, CSI-RS resource subset selection field (862) is signaled together with the value of KA(863). One reserved bit is added (861) for illustrative purposes. If the total number of bits for862and863exceeds 8, two octets can be used. In general, the number of bits for the CSI-RS resource subset selection field can be fixed to the worst-case (maximum) value or can be made dependent on the value of K.

Another variation of this embodiment is illustrated in diagram870ofFIG. 8Dwhere a length-K bitmap BK-1BK-2. . . B1B0is used. In this illustrative embodiment, the value of K is 8. If K is less than 8, (8-K) reserved bits can be appended. Here, the k-th bit denotes whether the k-th CSI-RS resource (out of the K higher-layer-configured CSI-RS resources) is activated or dormant. In particular, when Bk=0, the k-th CSI-RS resource is dormant (not activated). When Bk=1, the k-th CSI-RS resource is activated. In this case, the number of Bkwhose value(s) are 1 is equal to KA. Therefore, the value of KAis implicitly signaled in the bitmap871and variable (configurable via MAC CE). An example is that KA(the number of Bkwhose value(s) are 1) can take value from the set {1, 2, . . . , min(K, KA,MAX)} where KA,MAXcan either be fixed (to, e.g. 4 or 2) or made dependent on UE capability. Another example is that KA=K when K≤2; and KA(the number of Bkwhose value(s) are 1) can take value from the set {1, 2, . . . , min(K, KA,MAX)} where KA,MAXcan either be fixed (to, e.g. 4 or 2) or made dependent on UE capability when K>2.

If UL-related DCIs (UL grants) or DL-related DCIs (DL grants) are used for activation/release, the mechanism can be described as follows. First, a UE receives a dynamic trigger/release UL or DL grant indicating a selection/activation size-KAsubset of K NZP CSI-RS resources. This selection corresponds to a

⌈log2⁡(KKA⁢)⌉-bit
DCI field. Alternatively, at least one of these

(KKA⁢)
code points (hypotheses) can be signaled using some available (unused) or reserved code points in the DCI, while other code points (hypotheses) can be signaled using at least one additional bit in the DCI. This subset selection indicates that the associated size-KAsubset of K NZP CSI-RS resources are activated and the UE shall measure or monitor (be ready to measure) these NZP CSI-RS resources. In this embodiment, each NZP CSI-RS resource can be either periodic or aperiodic CSI-RS resource. Second, for an activation trigger received in subframe n, the transmission of the associated NZP CSI-RS resource will start no earlier than subframe n+Y1 where Y1>0. For a release (deactivation) trigger received in subframe n, the transmission of the associated NZP CSI-RS resource will stop after subframe n+Y1 where Y1>0. If an UL grant or UL grant-like mechanism is used to trigger CSI-RS which is placed or transmitted in a same subframe as the UL grant, the value of Y1 or Y2 can be aligned with that of A-CSI. The same holds if a DL grant is used instead.

To perform activation and release, either the MAC-CE-based or the UL/DL-grant-based mechanism (as described above), at least the following procedures are possible. The interpretation of the currently received value of ‘Activation Subset’ (indication of size-KAsubset of K NZP CSI-RS resources) can either depend on the most recent previously received one or independent of the most recent previously received one.

In a first procedure (P-1), if a UE receives a CSI-RS MAC CE indicating the ‘Activation Subset’=x, or a UL/DL activation/release grant whose DCI includes the ‘Activation Subset’ (indication of size-KAsubset of K NZP CSI-RS resources)=x, this can be interpreted as follows. If the most recent previously received CSI-RS MAC CE or the DCI of the most recent previously received UL/DL activation/release grant includes the ‘Activation Subset’=x (the same as the currently received one), the corresponding size-KAsubset of K NZP CSI-RS resources activated by the previous activation/release event are released. If the most recent previously received CSI-RS MAC CE or the DCI of the most recent previously received UL/DL activation/release grant includes the ‘Activation Subset’=y≠x (different from the currently received one), the size-KAsubset of K NZP CSI-RS resources corresponding to ‘Activation Subset’=x are activated (and, consequently, the size-KAsubset of K NZP CSI-RS resources corresponding to ‘Activation Subset’=y are also still activated). If there is no previously received CSI-RS MAC CE or UL/DL activation/release grant, the corresponding size-KAsubset of K NZP CSI-RS resources are activated.

In a second procedure (P-2), if a UE receives a CSI-RS MAC CE indicating the ‘Activation Subset’=x, or a UL/DL activation/release grant whose DCI includes the ‘Activation Subset’ (indication of size-KAsubset of K NZP CSI-RS resources)=x, this can be interpreted as follows. If the most recent previously received CSI-RS MAC CE or the DCI of the most recent previously received UL/DL activation/release grant includes the ‘Activation Subset’=x (the same as the currently received one), the size-KAsubset of K NZP CSI-RS resources corresponding to ‘Activation Subset’=x are still activated/active. If the most recent previously received CSI-RS MAC CE or the DCI of the most recent previously received UL/DL activation/release grant includes the ‘Activation Subset’=y≠x (different from the currently received one), the size-KAsubset of K NZP CSI-RS resources corresponding to ‘Activation Subset’=x are activated (and, consequently, the size-KAsubset of K NZP CSI-RS resources corresponding to ‘Activation Subset’=y are released). If there is no previously received CSI-RS MAC CE or UL/DL activation/release grant, the corresponding size-KAsubset of K NZP CSI-RS resources are activated.

In a third procedure (P-3), two additional code points (hypotheses) can be used to indicate either ‘Activation’ or ‘Release’/‘Deactivation’. If a UE receives a CSI-RS MAC CE indicating the ‘Activation Subset’=x, or a UL/DL activation/release grant whose DCI includes the ‘Activation Subset’ (indication of size-KAsubset of K NZP CSI-RS resources)=x, this can be interpreted as follows. If ‘Activation’ is indicated, the size-KAsubset of K NZP CSI-RS resources corresponding to ‘Activation Subset’=x are activated. If ‘Release’ or ‘Deactivation’ is indicated, the size-KAsubset of K NZP CSI-RS resources corresponding to ‘Activation Subset’=x are released.

In the first and the third procedures (P-1 and P-3), once a size-KAsubset of K NZP CSI-RS resources is activated, the size-KAsubset of K NZP CSI-RS resources will remain activated until a release/deactivation (either via two consecutive identical values of size-KAsubset of K NZP CSI-RS resources) associated with the same size-KAsubset of K NZP CSI-RS resources is received. In the second procedure (P-2), once a size-KAsubset of K NZP CSI-RS resources is activated, the size-KAsubset of K NZP CSI-RS resources will remain activated until another activation message including a size-KAsubset of K NZP CSI-RS resources different from the previous one is received. In all or some of the three procedures (P-1, P-2, and P-3), more than one size-KAsubset of K NZP CSI-RS resources can be activated within a given subframe. In the second procedure (P-2), it is possible for a UE not to have any size-KAsubset of K NZP CSI-RS resources activated in a given subframe. In the first and third procedures (P-1 and P-3), at least one size-KAsubset of K NZP CSI-RS resources activated in a given subframe.

Diagram900ofFIG. 9illustrates an example eNB and UE operations (in terms of timing diagram associated with eNB in901and UE in902) which applies to either the MAC-CE-based or the UL/DL-grant-based mechanism. In this embodiment, an activation/release message containing ‘Activation Subset’910is received by a UE. This configuration information can be accompanied with an A-CSI request/trigger or signaled by itself. Upon receiving a DL subframe from910, a served UE-k reads the activation/release message in930. Based on this information, the eNB requests A-CSI to UE-k via an UL grant (containing A-CSI trigger) while transmitting Ap-CSI-RS within the same subframe(s)920. Upon receiving a DL subframe from940—containing an A-CSI request/trigger—UE-k measures the transmitted Ap-CSI-RS (in subframe n) according to the resource configuration information received in subframe(s)930, and performs CSI calculation. The resulting A-CSI is reported to the eNB in subframe(s)950.

For each of the above embodiments for selecting/activating a size-KAsubset of K NZP CSI-RS resources using MAC CE, when a UE is configured with a plurality of CSI processes or component carriers, one CSI-RS resource activation/release can be associated with one CSI process or component carrier. Alternatively, one CSI-RS resource activation/release can be associated with a plurality of CSI processes or component carriers. Alternatively, one CSI-RS resource activation/release can be associated with all the CSI processes or component carriers.

In a third step illustrated in component830ofFIG. 8A, a UE is assigned one Ap-CSI-RS transmission wherein the CSI-RS resource configuration is selected from KAconfigurations given in the second step. This selected resource (or resource configuration) can be described by setting at least one CSI-RS resource parameter to a certain value (which are not set in the first and second steps). Alternatively, the selected resource can be described by indicating one combination of values of a plurality of CSI-RS resource parameters taken from a size-KAcombination of values of a plurality of CSI-RS resource parameters defined or given in the second step. This selection is signaled via the UL-related DCI (included in the UL grant) used for CSI request (A-CSI triggering)—either via PDCCH or EPDCCH.

The following examples can be constructed assuming that the number of CSI-RS ports NPORTis configured semi-statically (the first step, via higher-layer signaling) while a set of time-frequency patterns (known as “CSI reference signal configuration” in REF1) can be configured using activation/deactivation procedure (the second step). The set of port indices is not configurable. That is, for an NPORT-port CSI-RS, the set of port indices is always {15, 16, . . . , 14+NPORT}.

In a first example, the number of CSI-RS ports NPORTis included as an RRC parameter (such as ‘antennaPortsCount’) in the RRC configuration IE ‘CSI-RS-Config’ along with other CSI-RS parameters (such as pC) except for the time-frequency pattern ‘resourceConfig’. For aperiodic CSI-RS, subframe configuration is not present. In the second step, a set of KAvalues of ‘resourceConfig’, where KA=2, is configured via activation/deactivation mechanism. That is, 2 out of 32 possible values of ‘resourceConfig’ are selected for the UE in the second-step CSI-RS resource configuration. For this purpose, a 10-bit (5 bits per value) field is needed to signal the selection, either in a MAC CE (cf. example inFIG. 7A, where the MAC CE includes ‘resourceConfig’) or a DCI used for activation/deactivation. In the third step, one additional bit (per CSI process or “cell”, or for one CSI process or “cell”) is used in addition to the CSI request field in order to select one out of KA=2 values of ‘resourceConfig’ defined in the second step resource configuration. In general, for a given value of KA, ┌log2KA┐ bits (per CSI process or “cell”; or for one CSI process or “cell”) can be added for selecting one out of KAvalues. Alternatively, instead of adding ┌log2KA┐ bits for selecting one out of KAvalues, some existing code points in the UL-related DCI can be reused for this purpose thereby reducing the number of or removing the need for additional bits.

In a second example, the number of CSI-RS ports NPORTis included as an RRC parameter (such as ‘antennaPortsCount’) in the RRC configuration IE ‘CSI-RS-Config’ along with other CSI-RS parameters (such as pC). In addition, a set of K values of the time-frequency pattern ‘resourceConfig’, where K=8, is also included in the RRC configuration IE ‘CSI-RS-Config’. For aperiodic CSI-RS, subframe configuration is not present. In the second step, a set of KAvalues of ‘resourceConfig’, where KA=2, is configured via activation/deactivation mechanism. That is, 2 out of 8 possible values of ‘resourceConfig’ are selected for the UE in the second-step CSI-RS resource configuration. For this purpose, a 6-bit (3 bits per value) field is needed to signal the selection, either in a MAC CE (cf. example inFIG. 7A, where the MAC CE includes ‘resourceConfig’) or a DCI used for activation/deactivation. In the third step, one additional bit (per CSI process or “cell”) is used in addition to the CSI request field in order to select one out of KA=2 values of ‘resourceConfig’ defined in the second step resource configuration. In general, for a given value of KA, ┌log2KA┐ bits (per CSI process or “cell”; or for one CSI process or “cell”) can be added for selecting one out of KAvalues. Alternatively, instead of adding ┌log2KA┐ bits for selecting one out of KAvalues, some existing code points in the UL-related DCI can be reused for this purpose thereby reducing the number of or removing the need for additional bits.

In a third example (also applicable to the previous two examples), given a size-KAsubset of NZP CSI-RS resources currently activated for the UE (from the previous step), a ┌log2(KA)┐-bit CSI-RS resource selection field to select one out of KAactivated resources can be introduced in an UL-related DCI. Alternatively, at least one of the used or required KAcode points for signaling this selection can reuse code point(s) (either reserved code points or borrowed from other unused feature(s)) from the existing code point(s) in the DCI. If there are KAavailable code points, no additional bit needs to be introduced. Otherwise, the number of additional bits for CSI-RS resource selection can be reduced.

The fourth component (that is, aperiodic CSI-RS CSI reference resource) regulates the manner in which a UE measures aperiodic CSI-RS. As described inFIGS. 5 and 6(640and650), a UE performs aperiodic CSI reporting in subframe n=m+L upon decoding in subframe n either an uplink DCI format, or a Random Access Response Grant containing a CSI request field which is set to trigger a CSI report. It is further described that a CSI-RS (in this case, aperiodic CSI-RS) is transmitted within the same subframe containing the trigger (the CSI request field in either the associated uplink DCI format or a Random Access Response Grant) for the CSI report. In other words, the aperiodic CSI reporting performed in subframe m is a response of a CSI request field in subframe n−L. To calculate this CSI, CSI-RS located within a same subframe no later than the associated CSI reference resource (defined by a single downlink or special subframe n−nCQI_ref) is used. This CSI reference resource is located on or after the subframe containing the trigger (the CSI request field in either the associated uplink DCI format or a Random Access Response Grant) for the CSI report.

In particular, the following description for aperiodic CSI calculation in relation to CSI reference resource for some scenarios is given as follows (from REF3 section 7.2.3).

For a UE in transmission mode9or10and for a CSI process, if the UE is configured with parameter eMIMO-Type by higher layers, and eMIMO-Type is set to ‘CLASS A’, and one CSI-RS resource configured, or the UE is configured with parameter eMIMO-Type by higher layers, and eMIMO-Type is set to ‘CLASS B’, and parameter channelMeasRestriction is not 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 non-zero power CSI-RS (defined in [3]) within a configured CSI-RS resource associated with the CSI process.

For a UE in transmission mode9or10and for a CSI process, if the UE is configured with parameter eMIMO-Type by higher layers, and eMIMO-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 (defined in [3]) within a configured CSI-RS resource associated with the CSI process.

The CSI reference resource for a serving cell is defined as follows:For a non-BL/CE UE, in the frequency domain, the CSI reference resource is defined by the group of downlink physical resource blocks corresponding to the band to which the derived CQI value relates. For a BL/CE UE, in the frequency domain, the CSI reference resource includes all downlink physical resource blocks for any of the narrowband to which the derived CQI value relates.In the time domain and for a non-BL/CE UE,for a UE configured in transmission mode1-9or transmission mode10with a single configured CSI process for the serving cell, the CSI reference resource is defined by a single downlink or special subframe n−nCQI_ref,where for aperiodic CSI reporting, if the UE is not configured with the higher layer parameter csi-SubframePatternConfig-r12,nCQI_refis such that the reference resource is in the same valid downlink or valid special subframe as the corresponding CSI request in an uplink DCI format.nCQI_refequal to 4 and subframe n−nCQI_refcorresponds to a valid downlink or valid special subframe, where subframe n−nCQI_refis received after the subframe with the corresponding CSI request in a Random Access Response Grant.where for aperiodic CSI reporting, and the UE configured with the higher layer parameter csi-SubframePatternConfig-r12,for the UE configured in transmission mode1-9,nCQI_refis the smallest value greater than or equal to 4 and subframe n−CQI_refcorresponds to a valid downlink or valid special subframe, where subframe n−nCQI_refis received on or after the subframe with the corresponding CSI request in an uplink DCI format;nCQI_refis the smallest value greater than or equal to 4, and subframe n−nCQI_refcorresponds to a valid downlink or valid special subframe, where subframe n−nCQI_refis received after the subframe with the corresponding CSI request in an Random Access Response Grant;if there is no valid value for nCQI_refbased on the above conditions, then nCQI_refis the smallest value such that the reference resource is in a valid downlink or valid special subframe n−nCQI_refprior to the subframe with the corresponding CSI request, where subframe n−nCQI_refis the lowest indexed valid downlink or valid special subframe within a radio frame;for the UE configured in transmission mode10,nCQI refis the smallest value greater than or equal to 4, such that the value corresponds to a valid downlink or valid special subframe, and the corresponding CSI request is in an uplink DCI format;nCQI_refis the smallest value greater than or equal to 4, and subframe n−nCQI_refcorresponds to a valid downlink or valid special subframe, where subframe n−nCQI_refis received after the subframe with the corresponding CSI request in a Random Access Response Grant;

In the present disclosure, several embodiments for aperiodic CSI-RS location and CSI reference resource subframe are given below.

In one embodiment, when a UE is configured with aperiodic CSI-RS (for example, via any of the configuration embodiments discussed above), the non-zero-power CSI-RS used to calculate CSI is located in the subframe containing the trigger (the CSI request field in either the associated uplink DCI format or a Random Access Response Grant) for the CSI report. In addition, the CSI reference resource n−nCQI_refis defined by a same valid downlink or valid special subframe as the corresponding CSI request in an uplink DCI format. In this embodiment, nCQI_refis chosen to be the same as that for the legacy periodic CSI-RS. For a UE configured in transmission mode1-9or transmission mode10with a single configured CSI process for the serving cell, three possibilities exist. First, nCQI_refis equal to 4. Second, nCQI_refis the smallest value greater than or equal to 4, such that the value corresponds to a valid downlink or valid special subframe, and the corresponding CSI request is in an uplink DCI format. Third, nCQI_refis the smallest value greater than or equal to 4, and subframe n−nCQI_refcorresponds to a valid downlink or valid special subframe, where subframe n−nCQI_refis received after the subframe with the corresponding CSI request in a Random Access Response Grant.

In another embodiment, when a UE is configured with aperiodic CSI-RS (for example, via any of the configuration embodiments discussed above), the non-zero-power CSI-RS used to calculate CSI is located in the subframe containing the trigger (the CSI request field in either the associated uplink DCI format or a Random Access Response Grant) for the CSI report. In addition, the CSI reference resource n−nCQI_refis defined by a same valid downlink or valid special subframe as the corresponding CSI request in an uplink DCI format. In this embodiment, nCQI_refis chosen to be different from that for the legacy periodic CSI-RS. An additional X-subframe time is added to the UE processing time when a UE is configured with aperiodic CSI-RS. For instance X=1 can be chosen. In this case, for a UE configured in transmission mode1-9or transmission mode10(for LTE) with a single configured CSI process for the serving cell, three possibilities exist. First, nCQI_refis equal to 5. Second, nCQI_refis the smallest value greater than or equal to 5, such that the value corresponds to a valid downlink or valid special subframe, and the corresponding CSI request is in an uplink DCI format. Third, nCQI_refis the smallest value greater than or equal to 5, and subframe n−nCQI_refcorresponds to a valid downlink or valid special subframe, where subframe n−nCQI_refis received after the subframe with the corresponding CSI request in a Random Access Response Grant.

In a variation of this embodiment, the value of X (a subframe offset for nCQI_reffrom 4) is not fixed and can be configured via higher-layer (RRC) signaling for a given UE. For example, an RRC parameter SubframeOffsetApCSIRS can be used to configure the value of X from {0, 1, or 2}. Alternatively, the value of X can be made a UE capability.

FIG. 10illustrates a flowchart for an example method1000wherein a UE receives CSI-RS resource configuration information according to an embodiment of the present disclosure. For example, the method1000can be performed by the UE116.

The method1000begins with the UE receiving CSI-RS resource configuration information which includes K≥1 CSI-RS resources (step1001). This configuration information can be sent to the UE via higher-layer (such as RRC) signaling. Since this CSI-RS resource configuration corresponds to aperiodic CSI-RS, subframe configuration (which includes periodicity and subframe offset) can be absent from this configuration. In addition, this configuration information can correspond to CLASS B eMIMO-Type. In a subframe, the UE receives an UL-related DCI containing an aperiodic CSI (A-CSI) request (step1002) along with a CSI-RS associated with a selected CSI-RS resource. In reference to the CSI-RS, the UE calculates A-CSI (step1003) and transmits the A-CSI on an UL channel (step1004).

The selected CSI-RS resource is taken from the K CSI-RS resources assigned to the UE. When K=1, the selected CSI-RS resource is the same as the resource included in the CSI-RS resource configuration information. When K>1, the selection of one CSI-RS resource can be done in one or two steps. In the one-step selection, the UL-related DCI includes an indication of which one of the K CSI-RS resources is selected. On the two-step selection, N (<K) CSI-RS resources are first selected by activating N out of K configured resources. This is then followed by an indication (in the UL-related DCI) of which one of the N CSI-RS resources is selected. The activation of N out of K configured resources can be signaled via either MAC CE or L1 downlink control signaling.

FIG. 11illustrates a flowchart for an example method wherein a BS configures a UE (labeled as UE-k) with CSI-RS resource. For example, the method1100can be performed by the eNB102.

The method1100begins with the BS configuring UE-k with K≥1 CSI-RS resources (step1101). This information is included in CSI-RS resource configuration information. This configuration information can be sent to the UE via higher-layer (such as RRC) signaling. Since this CSI-RS resource configuration corresponds to aperiodic CSI-RS, subframe configuration (which includes periodicity and subframe offset) can be absent from this configuration. In addition, this configuration information can correspond to CLASS B eMIMO-Type. In a subframe, the BS transmits an UL-related DCI containing aperiodic CSI (A-CSI) request to UE-k along with a CSI-RS which is associated with a selected CSI-RS resource (step1102). After a few subframes, the BS receives the requested A-CSI reporting on an UL channel from UE-k (step1103).

The selected CSI-RS resource is taken from the K CSI-RS resources assigned to UE-k. When K=1, the selected CSI-RS resource is the same as the resource included in the CSI-RS resource configuration information. When K>1, the selection of one CSI-RS resource can be done in one or two steps. In the one-step selection, the UL-related DCI includes an indication of which one of the K CSI-RS resources is selected. On the two-step selection, N (<K) CSI-RS resources are first selected by activating N out of K configured resources. This is then followed by an indication (in the UL-related DCI) of which one of the N CSI-RS resources is selected. The activation of N out of K configured resources can be signaled via either MAC CE or L1 downlink control signaling.

AlthoughFIGS. 10 and 11illustrate examples of methods for receiving configuration information and configuring a UE, respectively, various changes could be made toFIGS. 10 and 11. For example, while shown as a series of steps, various steps in each figure could overlap, occur in parallel, occur in a different order, occur multiple times, or not be performed in one or more embodiments.

Although the present disclosure has been described with example embodiments, various changes and modifications can be suggested by or to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.