Channel state information (CSI) acquisition for dynamic MIMO transmission

Certain aspects of the present disclosure provide techniques for dynamic switching of reference transmission schemes used by a UE for CSI measurement and reporting.

BACKGROUND

Field of the Disclosure

Aspects of the present disclosure relate generally to wireless communications systems, and more particularly, to supporting dynamic changes to transmission schemes used for channel state information (CSI) measurements.

Description of Related Art

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is new radio (NR), for example, 5G radio access. NR is a set of enhancements to the LTE mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL) as well as support beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in NR technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

BRIEF SUMMARY

Certain aspects of the present disclosure generally relate to methods and apparatus for supporting dynamic change to reference transmission schemes used by a user equipment (UE) for CSI measurement.

Certain aspects of the present disclosure provide a method for wireless communication that may be performed, for example, by a UE. The method generally includes determining a reference transmission scheme (TS) for channel state information (CSI) measurement based on signaling received from a base station (BS), performing CSI measurement based on the determination, and transmitting a CSI report based on the measurement.

Certain aspects of the present disclosure provide a method for wireless communication that may be performed, for example, by a base station (BS). The method generally includes providing signaling to a user equipment (UE) allowing the UE to determine a reference transmission scheme (TS) for channel state information (CSI) measurement and receiving a CSI report from the UE based on the measurement performed according to the reference TS.

Aspects generally include methods, apparatus, systems, computer readable mediums, and processing systems, as substantially described herein with reference to and as illustrated by the accompanying drawings.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for operations that may be performed in new radio (NR) applications (new radio access technology or 5G technology).

Aspects of the present disclosure provide techniques and apparatus for supporting dynamic reference transmission scheme signaling for CSI measurement.

Example Wireless Communications System

FIG. 1illustrates an example wireless network100in which aspects of the present disclosure may be performed. For example, the wireless network may be a new radio (NR) or 5G network. According to aspects of the present disclosure, a UE120may perform certain actions to determine reference transmission schemes for CSI-measurements. According to aspects of the present disclosure, a UE120may perform certain actions to determine reference transmission schemes for CSI-measurements. Similarly, base stations110may provide signaling to the UE allowing such determination.

As will be described in more detail herein, a UE may be in a zone including a serving TRP and one or more non-serving TRPs. The serving and non-serving TRPs may be managed by the same ANC (see e.g., ANC202managing three TRPs208inFIG. 2).

UEs120may be configured to perform the operations1100and other methods described herein and discussed in more detail below which may help improve DL-based mobility. Base station (BS)110may comprise a transmission reception point (TRP), Node B (NB), 5G NB, access point (AP), new radio (NR) BS, etc.). The NR network100may include the central unit.

As illustrated inFIG. 1, the wireless network100may include a number of BSs110and other network entities. ABS may be a station that communicates with UEs. Each BS110may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a Node B and/or a Node B subsystem serving this coverage area, depending on the context in which the term is used. In NR systems, the term “cell” and gNB, Node B, 5G NB, AP, NR BS, NR BS, or TRP may be interchangeable. In some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile base station. In some examples, the base stations may be interconnected to one another and/or to one or more other base stations or network nodes (not shown) in the wireless network100through various types of backhaul interfaces such as a direct physical connection, a virtual network, or the like using any suitable transport network.

While aspects of the examples described herein may be associated with LTE technologies, aspects of the present disclosure may be applicable with other wireless communications systems, such as NR.

NR may utilize OFDM with a CP on the uplink and downlink and include support for half-duplex operation using TDD. A single component carrier bandwidth of 100 MHz may be supported. NR resource blocks may span 12 sub-carriers with a sub-carrier bandwidth of 75 kHz over a 0.1 ms duration. Each radio frame may consist of 50 subframes with a length of 10 ms. Consequently, each subframe may have a length of 0.2 ms. Each subframe may indicate a link direction (i.e., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. UL and DL subframes for NR may be as described in more detail below with respect toFIGS. 6 and 7. Beamforming may be supported and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells. Alternatively, NR may support a different air interface, other than an OFDM-based. NR networks may include entities such CUs and/or DUs.

In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station) allocates resources for communication among some or all devices and equipment within its service area or cell. Within the present disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communication, subordinate entities utilize resources allocated by the scheduling entity. Base stations are not the only entities that may function as a scheduling entity. That is, in some examples, a UE may function as a scheduling entity, scheduling resources for one or more subordinate entities (e.g., one or more other UEs). In this example, the UE is functioning as a scheduling entity, and other UEs utilize resources scheduled by the UE for wireless communication. A UE may function as a scheduling entity in a peer-to-peer (P2P) network, and/or in a mesh network. In a mesh network example, UEs may optionally communicate directly with one another in addition to communicating with the scheduling entity.

FIG. 2illustrates an example logical architecture of a distributed radio access network (RAN)200, which may be implemented in the wireless communication system illustrated inFIG. 1. A 5G access node206may include an access node controller (ANC)202. The ANC may be a central unit (CU) of the distributed RAN200. The backhaul interface to the next generation core network (NG-CN)204may terminate at the ANC. The backhaul interface to neighboring next generation access nodes (NG-ANs) may terminate at the ANC. The ANC may include one or more TRPs208(which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, or some other term). As described above, a TRP may be used interchangeably with “cell.”

The architecture may enable cooperation between and among TRPs208. For example, cooperation may be preset within a TRP and/or across TRPs via the ANC202. According to aspects, no inter-TRP interface may be needed/present.

According to aspects, a dynamic configuration of split logical functions may be present within the architecture200. As will be described in more detail with reference toFIG. 5, the Radio Resource Control (RRC) layer, Packet Date Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, Medium Access Control (MAC) layer, and a Physical (PHY) layers may be adaptably placed at the DU or CU (e.g., TRP or ANC, respectively). According to certain aspects, a BS may include a central unit (CU) (e.g., ANC202) and/or one or more distributed units (e.g., one or more TRPS208).

FIG. 3illustrates an example physical architecture of a distributed RAN300, according to aspects of the present disclosure. A centralized core network unit (C-CU)302may host core network functions. The C-CU may be centrally deployed. C-CU functionality may be offloaded (e.g., to advanced wireless services (AWS)), in an effort to handle peak capacity.

A centralized RAN unit (C-RU)304may host one or more ANC functions. Optionally, the C-RU may host core network functions locally. The C-RU may have distributed deployment. The C-RU may be closer to the network edge.

FIG. 4illustrates example components of the BS110and UE120illustrated inFIG. 1, which may be used to implement aspects of the present disclosure. For example, UE120may be configured to coordinate waking up to perform cell searches with the occurrence of paging occasions (POs).

As described above, the BS may include a TRP. One or more components of the BS110and UE120play be used to practice aspects of the present disclosure. For example, antennas452, Tx/Rx222, processors466,458,464, and/or controller/processor480of the UE120and/or antennas434, processors460,420,438, and/or controller/processor440of the BS110may be used to perform the operations described herein and illustrated with reference toFIGS. 10-12.

FIG. 4shows a block diagram of a design of a BS110and a UE120, which may be one of the BSs and one of the UEs inFIG. 1. For a restricted association scenario, the base station110may be the macro BS110cinFIG. 1, and the UE120may be the UE120y. The base station110may also be a base station of some other type. The base station110may be equipped with antennas434athrough434t, and the UE120may be equipped with antennas452athrough452r.

The controllers/processors440and480may direct the operation at the base station110and the UE120, respectively. The processor440and/or other processors and modules at the base station110may perform or direct, e.g., the execution of the functional blocks illustrated inFIG. 12, and/or other processes for the techniques described herein. Processes for the techniques described herein. The processor480and/or other processors and modules at the UE120may also perform or direct, e.g., the execution of the functional blocks illustrated inFIGS. 10 and 11, and/or other processes for the techniques described herein. The memories442and482may store data and program codes for the BS110and the UE120, respectively. A scheduler444may schedule UEs for data transmission on the downlink and/or uplink.

FIG. 5illustrates a diagram500showing examples for implementing a communications protocol stack, according to aspects of the present disclosure. The illustrated communications protocol stacks may be implemented by devices operating in in a 5G system (e.g., a system that supports uplink-based mobility). Diagram500illustrates a communications protocol stack including a Radio Resource Control (RRC) layer510, a Packet Data Convergence Protocol (PDCP) layer515, a Radio Link Control (RLC) layer520, a Medium Access Control (MAC) layer525, and a Physical (PHY) layer530. In various examples the layers of a protocol stack may be implemented as separate modules of software, portions of a processor or ASIC, portions of non-collocated devices connected by a communications link, or various combinations thereof. Collocated and non-collocated implementations may be used, for example, in a protocol stack for a network access device (e.g., ANs, CUs, and/or DUs) or a UE.

A second option505-bshows a unified implementation of a protocol stack, in which the protocol stack is implemented in a single network access device (e.g., access node (AN), new radio base station (NR BS), a new radio Node-B (NR NB), a network node (NN), or the like.). In the second option, the RRC layer510, the PDCP layer515, the RLC layer520, the MAC layer525, and the PHY layer530may each be implemented by the AN. The second option505-bmay be useful in a femto cell deployment.

Regardless of whether a network access device implements part or all of a protocol stack, a UE may implement an entire protocol stack (e.g., the RRC layer510, the PDCP layer515, the RLC layer520, the MAC layer525, and the PHY layer530).

FIG. 6is a diagram600showing an example of a DL-centric subframe. The DL-centric subframe may include a control portion602. The control portion602may exist in the initial or beginning portion of the DL-centric subframe. The control portion602may include various scheduling information and/or control information corresponding to various portions of the DL-centric subframe. In some configurations, the control portion602may be a physical DL control channel (PDCCH), as indicated inFIG. 6. The DL-centric subframe may also include a DL data portion604. The DL data portion604may sometimes be referred to as the payload of the DL-centric subframe. The DL data portion604may include the communication resources utilized to communicate DL data from the scheduling entity (e.g., UE or BS) to the subordinate entity UE). In some configurations, the DL data portion604may be a physical DL shared channel (PDSCH).

The DL-centric subframe may also include a common UL portion606. The common UL portion606may sometimes be referred to as an UL burst, a common UL burst, and/or various other suitable terms. The common UL portion606may include feedback information corresponding to various other portions of the DL-centric subframe. For example, the common UL portion606may include feedback information corresponding to the control portion602. Non-limiting examples of feedback information may include an ACK signal, a NACK signal, a HARQ indicator, and/or various other suitable types of information. The common UL portion606may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information. As illustrated inFIG. 6, the end of the DL data portion604may be separated in time from the beginning of the common UL portion606. This time separation may sometimes be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the subordinate entity (e.g., UE)) to UL communication (e.g., transmission by the subordinate entity (e.g., UE)). One of ordinary skill in the art will understand that the foregoing is merely one example of a DL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

FIG. 7is a diagram700showing an example of an UL-centric subframe. The UL-centric subframe may include a control portion702. The control portion702may exist in the initial or beginning portion of the UL-centric subframe. The control portion702inFIG. 7may be similar to the control portion described above with reference toFIG. 6. The UL-centric subframe may also include an UL data portion704. The UL data portion704may sometimes be referred to as the payload of the UL-centric subframe. The UL portion may refer to die communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, the control portion702may be a physical UL control channel (PUCCH).

As illustrated inFIG. 7, the end of the control portion702may be separated in time from the beginning of the UL data portion704. This time separation may sometimes be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduling entity) to UL communication (e.g., transmission by the scheduling entity). The UL-centric subframe may also include a common UL portion706. The common UL portion706inFIG. 7may be similar to the common UL portion706described above with reference toFIG. 7. The common UL portion706may additional or alternative include information pertaining to channel quality indicator (CQI), sounding reference signals (SRSs), and various other suitable types of information. One of ordinary skill in the art will understand that the foregoing is merely one example of an UL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein. In one example, a frame may include both UL centric subframes and DL centric subframes. In this example, the ratio of UL centric subframes to DL subframes in a frame may be dynamically adjusted based on the amount of UL data and the amount of DL data that are transmitted. For example, if there is more UL data, then the ratio of UL centric subframes to DL subframes may be increased. Conversely, if there is more DL data, then the ratio of UL centric subframes to DL subframes may be decreased.

FIG. 8illustrates an example of a wireless communication system800supporting a number of zones, in accordance with aspects of the present disclosure. The wireless communication system800may include a number of zones (including, e.g., a first zone805-a(Zone1), a second zone805-b(Zone2), and a third zone805-c(Zone3)). A number of UEs may move within or between the zones.

A zone may include multiple cells, and the cells within a zone may be synchronized (e.g., the cells may share the same timing). Wireless communication system800may include examples of both non-overlapping zones (e.g., the first zone805-aand the second zone805-b) and overlapping zones (e.g., the first zone805-aand the third zone805-c). In some examples, the first zone805-aand the second zone805-bmay each include one or more macro cells, micro cells, or pico cells, and the third zone805-cmay include one or more femto cells.

By way of example, the UE850is shown to be located in the first zone805-a. If the UE850is operating with a radio resource configuration associated with transmitting pilot signals using a common set of resources, such as an RRC common state, the UE850may transmit a pilot signal using a common set of resources. Cells (e.g., ANs, DUs, etc.) within the first zone805-amay monitor the common set of resources for a pilot signal from the UE850. If the UE850is operating with a radio resource configuration associated with transmitting pilot signals using a dedicated set of resource, such as an RRC dedicated state, the UE850may transmit a pilot signal using a dedicated set of resources. Cells of a monitoring set of cells established for the UE850within the first zone805-a(e.g., a first cell810-a, a second cell810-b, and a third cell810-c) may monitor the dedicated set of resources for the pilot signal of the UE850.

According to aspects of the present disclosure, the UE850performs one or more operations without relying on a zone signal. For example, the UE may perform an inter-zone handover using synchronization signals associated with a cell/TRP as opposed to a zone synchronization signal.

Example Channel State Information (CSI) Acquisition for Dynamic MIMO Transmission

MIMO is seen as a key technology enabler for satisfying the NR coverage and capacity requirements, but not without tradeoffs. For example, the advantages of using MIMO come at the price of accurate channel state information (CSI) at the transmission/reception point (TRP).

In TDD systems, the CSI may be available at the TRP by exploiting the UL-DL channel reciprocity. In FDD systems, the CSI has to be obtained at the TRP via UE feedback based on DL channel estimation aided by DL reference signals (RS).

As shown in table900ofFIG. 9, ten different DL transmission modes (TMs) are specified in LTE. The TMs differ in terms of how CSI is acquired by the terminal (UE) and fed back to the network. What reference TS is assumed for CSI measurement determines what reference signals are assumed for demodulation. Typically, the TM or transmission scheme (TS) (associated with a transmission mode) is configured via RRC signaling (semi-statically configured) and only limited switching may be supported. For TMs 3-10, dynamic switching (fallback) to transmit diversity (secondary TS) is possible via L1 signaling.

It is challenging to support dynamic switching between TSs. Conventionally, if a UE is configured with a particular TM, it may be dynamically switched between its primary TS and transmit diversity, but switching between other types of TSs is not currently supported.

This is unfortunate given that, for example, dynamic switching between close- and open-loop MIMO might yield sizeable gains if it was supported. Generally, a UE may assume a specific reference TS for CSI measurement, which may be bound to the configured TM. The eNB may be configured to override the reported CQI if the reference TS (used for measurement) is different from the actual PDSCH TS. For example, for TMs 3-6 and TMs 7-10 w/PMI/RI reporting, the primary TS is assumed for CSI measurement, the CQI is overridden if PDSCH TS is to fall back to transmit diversity. For TMs 7-10 w/o PMI/RI reporting, transmit diversity is assumed for CSI measurement, the CQI is overridden if the primary TS is used for PDSCH transmission.

Aspects of the present disclosure, allow for signaling, by a BS, that allows a UE to determine what reference TS to use for CSI measurement.

FIG. 10illustrates example operations1000which may be performed by a UE, in accordance with aspects of the present disclosure. The UE may include one or more modules of UE120illustrated inFIG. 4.

At1002, the UE determines a reference transmission scheme (TS) for channel state information (CSI) measurement based on signaling received from a base station (BS). At1004, the UE performs CSI measurement based on the determination. At1006, the UE transmits a CSI report based on the measurement. In one example, the signaling comprises an explicit indication of a reference transmission scheme via higher layer signaling. In another example, the signaling comprises art explicit indication of a reference transmission scheme via Layer 1 signaling. In yet another example, the signaling comprises an implicit indication of a reference transmission scheme.

FIG. 11illustrates example operations1100which may be performed by a BS, in accordance with aspects of the present disclosure. The operations1100may be considered complementary (BS-side) operations to the UE-side operations1000shown inFIG. 11. The BS may include one or more modules of BS110illustrated inFIG. 4.

At1102, the BS provides signaling to a user equipment (UE) allowing the UE to determine a reference transmission scheme (TS) for channel state information (CSI) measurement. At1104, the BS receives a CSI report from the UE based on the measurement performed according to the reference TS.

In some cases, such signaling could be provided via an explicit indication of reference transmission scheme via higher-layer signaling. In some cases, a TS may be associated w/CSI-RS resource configuration. For example, a UE may be configured with one or multiple CSI-RS resources and, for each CSI-RS resource, a reference transmission scheme may be configured.

In some cases, a reference transmission scheme may be implicitly dynamically switched, for example, via triggering A-CSI reporting or setup/release of semi-persistent CSI reporting.

In some cases, a reference TS may be associated with a CSI process configuration. In such cases, a UE may be configured with one or multiple CSI processes. For each CSI process, a reference transmission scheme may be configured. In some cases, a UE may be configured with one or multiple CSI reporting. For each CSI reporting, a reference transmission scheme may be configured.

In some cases, a UE may be configured with multiple CSI processes which belong to multiple A-CSI triggering sets. For each CSI process, a reference transmission scheme may be configured (e.g., via higher layer signaling) for each A-CSI triggering set. As illustrated inFIG. 12, when a UE is triggered to report CSI for a A-CSI triggering set (e.g., via Layer 1 signaling), it may assume the reference transmission scheme associated with the CSI process in the A-CSI triggering set. The example inFIG. 12assumes three CSI processes, with different reference TSs assumed, depending on the corresponding trigger.

As illustrated inFIG. 13, in some cases an indication of a reference TS may be part of the aperiodic CSI triggering (e.g., a CSI request). In this example, the triggered A-CSI reporting may assume the indicated reference transmission scheme (e.g., indicated in the request. In some cases, to reduce the DCI payload size, a UE may be configured with a subset of reference transmission schemes via higher-layer signaling and the lower layer (e.g., Layer 1) signaling may indicate one of the schemes in the configured subset.

As illustrated inFIG. 14, in some cases, an indication of a reference TS may be part of semi-persistent CSI triggering. For example, upon receiving some type of setup signaling, a UE may assume the transmission scheme as indicated until some type of release signaling is received. As in the case described above, to reduce the DCI payload size, a UE may be configured with a subset of reference transmission schemes via higher-layer signaling and the lower layer (e.g., Layer 1) signaling may indicate one of the schemes in the configured subset.

FIG. 15illustrates an example of using setup/release signaling of reference transmission scheme for Periodic-CSI. Upon receiving setup signaling, a UE may assume the transmission scheme as indicated (CL-MIMO in the illustrated example) until a release signaling is received. The UE may then assume a default transmission scheme (OL-MIMO in the illustrated example) when a reference transmission scheme is released. The default transmission scheme can be either predefined in the specification or configured via higher signaling. Again, to reduce the DCI payload size, a UE may be configured with a subset of reference transmission schemes via higher-layer signaling; the setup signaling may indicate a scheme in the configured subset.

In some cases, a UE may be configured by higher-layer with a subset of reference transmission schemes as cycling candidates (and the UE may cycle through the candidates). At each P-CSI reporting instance, the UE may report CSI assuming a different one of the candidate transmission schemes.

As illustrated inFIG. 16, upon receiving a setup signaling, the UE may start cycling through the candidate reference transmission schemes. The first reference transmission scheme may be explicitly indicated (e.g., by the setup signaling) or may be implicitly indicated, for example, as the first (or last) one in the configured subset. In some cases, the starting reference TS may be derived based on the index of the DL subframe in which the setup signaling is received; or on the index of the UL subframe in which the CSI is reported.

When receiving release signaling, the UE may stop the reference transmission scheme cycling. For example, until receiving (subsequent) setup signaling, the UE may report CSI assuming the same transmission scheme as before receiving the release signaling or the UE may report CSI assuming the default transmission scheme which can be either predefined in the specification or configured by higher layer.

As noted above, implicit indication of reference transmission scheme may be dependent on a subframe index. For example, the reference transmission scheme may be implicitly indicated by the index of the (DL) subframe in which the A-CSI triggering or the semi-persistent CSI reporting setup signaling is received. In some cases, a UE may be configured with K reference transmission schemes {0, 1, . . . , K−1}. If the UE receives a A-CSI triggering in subframe n, the UE may assume the kth reference transmission scheme for CSI measurement, where k=n mod K.

In some cases, the index of the (DL) subframe in which the RS for CSI measurement is transmitted may be used as an implicit indication. For example, a UE may be configured with K reference transmission schemes {0, 1, . . . , K−1}. If the RS transmission happens in subframe n, the UE shall assume the kth reference transmission scheme for the CSI measurement based on that RS, where k=n mod K

In some cases, the index of the (UL) subframe in which the CSI is reported may be used as an implicit indication. For example, a UE may be configured with K reference transmission schemes {0, 1, . . . , K−1}. The UE shall assume the kth reference transmission scheme for the CSI reported in subframe n, where k=n mod K.

In addition to the indicated reference transmission scheme, the following parameters may also be indicated or associated with each reference transmission scheme: the number of REs assumed for CSI reporting, a type of control channel, and/or the ratio of PDSCH EPRE to CSI-RS EPRE. It may also be possible to provide CSI feedback in one report covering CSI information assuming two or more reference transmission schemes, for example, SU-MIMO vs. MUST.

Reference transmission schemes may also be dependent on periodic/aperiodic CSI reporting, for example, using different transmission schemes for P-CSI and A-CSI reporting. Instead of network configuring transmission scheme for CQI reporting, no matter Layer 1 or higher-layer signaling, it may also be possible for a UE to determine one transmission scheme and report it together with CSI. One example of this is that a UE may report either CL or OL CSI, according to the Doppler. In some cases a transmission scheme indicator (TSI), which may be similar to CRI) may be, for example, selected from a set of configured transmission schemes.