TECHNICAL FIELD

The present description generally relates to wireless communications and wireless communication networks, and more particularly relates to waveform indication in wireless communication networks.

BACKGROUND

Transmissions in radio communication systems is often organized in terms of frames (or sometimes subframes), where each frame is a group of transmission resources (e.g. radio time and frequency resources) that contains both (at least) one control field and (at least) one payload data field. Typically, the control field appears at the beginning of the frame and contains, e.g., information about how the data part of the frame is encoded and modulated. The control field may also contain information related to data transmission in the reverse link direction (i.e. data transmitted from the receiver of the control information), e.g. ACK/NACK reports or channel state information.

Half-Duplex

If a communication system does not use paired spectrum (different frequency bands for the two link directions), as millimeter-wave (mmWave) systems typically will not do, it is normally necessary to limit communication to half-duplex, i.e. transmission can at any one time instance occur only in one of the two link directions. Hence, time-division duplex (TDD) has to be used. One reason for this limitation is that a radio node, e.g. a radio network node or a user equipment that is transmitting saturates its own analog receiving circuitry due to strong overhearing between transmit and receive antennas. In half-duplex systems, it may be useful to have two fields for control information in every frame, one for one link direction, and one for the other. The two directions of a link will henceforth be referred to as Tx/Rx directions, or sometimes the two duplex directions. In other words, any given node uses one of the fields for transmission (Tx) and the other field for reception (Rx).

Precoded Multi-Carrier Signal

In precoded multi-carrier signaling a multi-carrier modulator (e.g. OFDM, but could be any other multi-carrier modulation scheme such as FBMC) is not directly fed with data in the frequency domain but data are first precoded and then applied to the subcarriers of the multi-carrier modulator. Such a scheme is illustrated inFIG. 1.

The precoding transformation can be any precoder that enables a certain desired property at the output of the multi-carrier modulator; very often the precoding is used to generate a low Peak-to-Average Power Ratio (PAPR) signal at the output of the multi-carrier modulator. If the multi-carrier modulator is an OFDM modulator, a common choice of precoder is the Discrete Fourier Transform (DFT). In this case, the precoded multi-carrier scheme is the well-known DFTS-OFDM signaling scheme used in the uplink in LTE networks.

If the multi-carrier modulator is FBMC, a choice that reduces PAPR at the output of the FBMC modulator is to perform precoding with a filter bank transformation.

In case of DFTS-OFDM, the output signal for block i can be written as (omitting the subscript i for simplicity)
y=FNHSFMx

with FMand FNthe DFT matrices of size M and N, respectively. M is the number of allocated subcarrier and N is the IDFT size of the OFDM modulator. The N×M matrix S maps the output of the spreading operations to the M allocated subcarriers and has exactly one 1 and otherwise only 0 in each column. For a contiguous mapping of the M subcarriers we have

S=[0L01IM0L02]

with the M×M identity matrix IMand

0L01⁢⁢and⁢⁢0L02
all zero matrices of size L01×M and L02×M, respectively. Non-contiguous mappings such as interleaved mapping are possible as well. The data vector to transmit is the M element vector x.

Typically, a guard interval is prefixed to y to enable simple frequency-domain equalization at the receiver. As shown inFIG. 2, the guard interval can either be a true guard interval (an L-element long zero vector) or a cyclic prefix (copy of the last L elements of y). In both cases, the signal with guard interval can be written as
{tilde over (y)}=Py=PFNHSFMx

with P the matrix inserting the true guard interval or cyclic prefix.

Frame Structure

A possible frame structure of a communication system is illustrated inFIG. 3. Any two nodes communicating may in principle arbitrarily select which of the two control fields should be used for Tx and for Rx (see left and right panels ofFIG. 3). However, such arbitrariness may require complicated negotiation procedures and hence it is often more practical to have a general rule for the system, e.g. that one of the fields is always used for DL Tx, i.e. Tx by radio network nodes, whereas the other field is always used for UL Tx, i.e. Tx by UEs (see left and right panels ofFIG. 4). Note also that frames on different links in the system should preferably be time-aligned, partly because this enables nodes to more freely and efficiently change communication partner (node) from one frame to another, without waiting for the another communication link to finish its frame.

Fields are in most transmission systems further divided into smaller units, e.g. in OFDM-based systems, the fields would be further divided into one or more OFDM symbols. Similar holds e.g. for systems based on DFTS-OFDM, FBMC, etc. Such units may be generally referred to as symbols. Some fields may consist of only a single symbol.

Other Signals and Fields In and Between Frames

It should be noted that within each of the three fields, there may typically also be other signals interspersed, e.g. reference signals (or pilot signals) to allow the receiver to perform channel estimation.

MCS and TBS Determination

For an initial transmission of an LTE PUSCH, an MCS index, IMCS, is signalled in the DCI to the UE. The UE uses the received IMCSas the row key to read off modulation order, Qm, and TBS index, ITBS, from an MCS table specified in TS 36.213. To determine the TBS, the UE first calculates the total number of allocated PRBs, NPRB. The UE then determines the TBS from a TBS table specified in TS 36.213 using ITBSas row key and NPRBas column key.

In case of retransmission, the radio network node (e.g. a eNB in LTE) can elect to signal a modulation order to the UE and the UE shall assume the TBS determined from DCI transported in the latest PDCCH for the same transport block using 0≤IMCS≤27 or 28.

The PUSCH TBSs are designed assuming 144 REs per PRB are available for carrying the PUSCH. The MCS table is designed assuming DFTS-OFDM waveform for PUSCH.

Rel-8 LTE PUSCH was designed to operate a synchronous HARQ protocol. For initial transmissions, the redundancy version is restricted to rvidx=0.

For NR PUSCH, it was proposed that the MCS table provides modulation order, Qm, and target code rate, R, instead of the TBS index ITBS. One such example for PUSCH with OFDM waveform is provided in Table 1 below. The target code rates are those agreed for LTE MCS table for 256 QAM support.

For 0≤IMCS≤27, the UE determines the TBS based on, for example,

TBS⁢=⁢8×⌈NPRB·NREDL,PRB·υ·Qm·R8⌉

wherev is number of layers the codeword is mapped ontoNREDL,PRBis the number of REs per slot/mini-slot available for carrying the PUSCH.

For 28≤IMCS≤31, the TBS is assumed to be determined from the DCI in the most recently received PDCCH for the same TB using 0≤IMCS≤27.

As discussed in the above, NREDL,PRBis assumed to be 144 in LTE. For NR to support various slot/mini-slot/PUSCH lengths, a more flexible framework for NREDL,PRBis to be used. One or more of the following components can be considered:

A default NREDL,PRBvalue may be defined in specs and can be applicable to, e.g., system information, paging and random access reply transmissions. For this purpose, NREDL,PRB=144 can be considered for 14-OS slot and NREDL,PRB=72 can be considered for 7-OS slot.

Some default NREDL,PRBvalues for different PUSCH transmission lengths can be specified in the specification.

The network can configure the UE to apply a specific NREDL,PRBto the PUSCH.

The network can configure a set of NREDL,PRBvalues (e.g., four values) to the UE. The DCI then contains an index to instruct the UE to apply one of the pre-configured NREDL,PRBvalue for the current PUSCH.

If code rates lower than those available in the MCS table are found to be necessary for a specific use case (e.g., URLLC), the network can configure/select a NREDL,PRBvalue that is substantially lower such that the allocated resources are used to carry a substantially smaller TB.

TABLE 1Example MCS table for NR PUSCH with OFDM waveform(The target code rates are those agreed forLTE MCS table for 256QAM support).MCS IndexModulationCode RateIMCSorder QmR × 102402120121932230832449426025437864434744908455394616104658116466126517136567146616156666166719176772186822196873208682.5218711228754238797248841258885268916.5278948282reserved294306318

RRC Configuration and Processing Delay

When the UE receives an RRC command, the UE is allowed a time window (shown inFIG. 5as RRC Procedure Delay) during which the UE can apply the RRC command at any time during the window. Due to this delay, the radio network node (e.g. eNodeB (eNB), gNodeB (gNB)) that is communicating with the UE will be uncertain about the RRC configuration of the UE during the time window. For example, if the UE is configured to transmit PUSCH using waveform type 1 and if it receives an RRC command indicating waveform type 2, during the time window corresponding to RRC processing delay, the network will be uncertain whether the PUSCH transmissions by the UE are type 1 or type 2. Type 1 can OFDM, type 2 can be DFTS-OFDM or vice versa.

Transmission Profiles

In the last RAN2 meeting the following was concluded in RAN2:

For LCP and to know which restrictions to use the MAC needs to be aware of more information than just TTI length (e.g. numerology). An abstraction based on index or profiles can be supported. Exact parameters are FFS.

The approach RAN2 is going for is to define transmission index/profiles for the uplink. The LCPs that map to a given profile. The configuration would in the end be RRC configured. Multiple LCP could be mapped to the same profile or a single LCP can be mapped to a profile. Currently there are in total 8 LCPs defined within RAN2. From a RAN1 point of view, it would be good to consider this in designs from the start and inform RAN2 about the applicable setup can be envisioned from RAN1. From a physical layer perspective, the gNB can set the number of symbols the PUSCH is located within together with its applicable MCS, TBS, etc. In that sense, the gNB could select the applicable settings that are suitable for a given profile and hence the UL grant would only need to indicate the associated profile with the specific transmission. Together with the profile one could automatically potentially consider having a parameter setting the received target SINR (P0) at the gNB that is profile dependent.

Other than the above consideration the main aspect for RAN1 to consider is how many profiles that should be supported. Given that there is 8 LCP currently defined going beyond 8 profiles does not seem to attractive. Similarly having two few profiles as 2 would be rather restrictive. Hence going for either 4 or 8 profile would be a suitable choice. This would lead to either 2 or 3 bits in the UL grant to indicate the associated transmission profile.

CORESETs and Search Space

NR uses OFDM in the downlink. The basic NR downlink physical resource can thus be seen as a time-frequency grid as illustrated inFIG. 6where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. Multiple sub-carrier spacings are supported in NR.FIG. 6illustrates the case where the sub-carrier spacing is 15 kHz.

PDCCHs (Physical Downlink Control Channels) are used in NR for downlink control information (DCI), e.g. downlink scheduling assignments and uplink scheduling grants. The PDCCHs are in general transmitted at the beginning of a slot and relate to data in the same or a later slot, but a UE can in principle be configured to monitor PDCCHs more often than once per slot, e.g. to handle mini-slot-based transmissions. Different formats (sizes) of the PDCCHs are possible to handle different DCI payload sizes and different aggregation levels (i.e. different code rate for a given payload size). A UE is configured (implicitly and/or explicitly) to blindly monitor (or search) for a number of PDCCH candidates of different aggregation levels and DCI payload sizes. Upon detecting a valid DCI message (i.e. the decoding of a candidate is successful and the DCI contains a ID the UE is told to monitor) the UE follows the DCI (e.g. receives the corresponding downlink data or transmits in the uplink). The blind decoding process comes at a cost in complexity in the UE but is required to provide flexible scheduling and handling of different DCI payload sizes.

The DCI could also be used in combination with RRC signaling to signal a quantity needed for transmission or reception. One example is signaling of resources to be used for feedback signaling in the uplink such as hybrid-ARQ acknowledgements. Indicating the complete location in the uplink may result in too large DCI overhead. Instead, a two-bit index can be transmitted as part of the DCI and used as an index into a table, selecting one out of four preconfigured (or predefined) entries. This way, the DCI overhead can be kept small while at the same time allow for a significant amount of flexibility to handle different deployment scenarios and operating conditions. The same approach could in principle be used for any control information, not only the hybrid-ARQ resources to be used in the uplink.

In NR, there are currently discussions on how to configure control resource regions where the UE can monitor for PDCCH transmissions and how a UE can be configured with multiple control resource regions. Some of these control regions may be used for sending common control messages that are intended for multiple UEs and some may be intended for UE-specific control messages. A control region could serve both common and UE-specific control messages. One difference in NR from LTE is that the carrier bandwidths may be larger and hence there are benefits seen in the control region not spanning the entire bandwidth of the carrier. Thus, it is expected that control regions will be limited in time and in frequency.

Control regions generally need to be dimensioned to ensure that multiple UEs can be signaled within the region. To do this, statistical multiplexing principles are used where the number of UEs that are assigned to a control region to search for control messages is much greater than the resource available in the control region. Therefore, the search spaces for different UEs are randomized so that statistical multiplexing can be used to minimize the blocking probability when any particular UE needs to be scheduled. Therefore, control regions are expected to be dimensioned to be able to signal PDCCHs for multiple UEs simultaneously and the number of UEs that are assigned to monitor the control region is expected to be greater than the number of UEs that can simultaneously be signaled.

In the following, a CORESET is a control resource set that is configured to the UE. A CORESET is a set of resource elements (REs) that spans a set of PRBs in frequency and OFDM symbols in time. A UE may be configured with one or more CORESETs which the UE should monitor for the potential reception of one or more PDCCHs. CORESETs for one UE or different UEs can in principle be (partly) overlapping. For simplicity, inFIGS. 8 and 9, it is assumed that the CORESETs are not partly overlapping.

Using the resources defined by a CORESET, blind decoding using one or more search spaces can be performed to detect the valid PDCCH(s), if any (seeFIG. 9). A number of resources in a CORESET form a control channel element, CCE. The UE attempts to blindly decode PDCCHs using one or more of these CCEs. Typically, different search spaces use different aggregation levels, where an aggregation level is the number of CCEs used by a PDCCH candidate. For example, the search space on aggregation level one monitor for PDCCH candidates consisting of a single CCE, the search space on aggregation level two monitor for PDCCH candidates consisting of pairs of CCEs, etc. Which CCEs (or set of CCEs) that constitute a PDCCH candidate in each search space is given by some rule.

In some cases, to receive common control messages, multiple UEs may monitor (or attempt to decode) control signaling in the same search space. Such a search space can be called a common search space where parameters associated with the search space (e.g. CCE locations, monitored aggregation levels, randomization/hashing function related parameters) are not linked to UE-specific parameters such as UEID or an RNTI assigned to the UE. To receive UE-specific control messages, UE may monitor (or attempt to decode) control signaling in a UE-specific search space. For a UE-specific search space at least one or more parameters associated with the search space (e.g. CCE locations, monitored aggregation levels, randomization/hashing function related parameters) are linked to UE-specific parameters such as UEID or an RNTI assigned to the UE.

SUMMARY

NR supports two waveforms at least in the uplink. One is OFDM and the other one is DFTS-OFDM. If waveform switching is done, for instance, via RRC signaling, there will be a period of uncertainty in conjunction with RRC signaling where the waveform the UE will use in the uplink is not known to the network. In LTE, this uncertainty period from the standard is 15 ms and in addition there may be some implementation based uncertainty from the network side.

According to some embodiments, the UE is made aware of which waveform to use in the uplink based at least in part on a characteristic of a downlink transmission. For example, the UE may use a default waveform for uplink transmissions in response to uplink grants received in a particular search space (e.g., a common search space).

According to one aspect, some embodiments include a method to be performed by a user equipment, UE. The method generally comprises receiving a downlink transmission from a radio network node, the downlink transmission having at least one characteristic, selecting one waveform from two or more waveforms for an upcoming uplink transmission to the radio network node, the waveform being selected based at least in part on the at least one characteristic of the downlink transmission, and transmitting the uplink transmission to the radio network node using the selected waveform.

In some embodiments, the downlink transmission may comprise a downlink control message. In some embodiments, the downlink control message may comprise an uplink grant.

In some embodiments, the at least one characteristic may be a search space in which the downlink control message is transmitted. The search space may be one of a common search space and a UE-specific search space.

In some embodiments, the at least one characteristic may be a control resources set in which the downlink control message is transmitted. The control resources set may be one of a first control resources set and a second control resources set.

In some embodiments, the at least one characteristic may be a modulation and coding scheme, MCS, index of the downlink control message.

In some embodiments, the at least one characteristic may be a radio network temporary identifier, RNTI, used to scramble the downlink control message.

In some embodiments, the at least one characteristic may be a format the downlink control message.

In some embodiments, the method may comprise, or further comprise, selecting one resource allocation from two or more resource allocations for the uplink transmission based at least in part on the at least one characteristic, and transmitting the uplink transmission to the radio network node using the selected resource allocation.

In some embodiments, the method may comprise, or further comprise, obtaining an identification of the two or more waveforms. In such embodiments, the method may comprise, or further comprise, receiving an identification of at least one of the two or more waveforms via radio resource control, RRC, signaling received from the radio network node.

According to another aspect, some embodiments include a UE configured, or operable, to perform one or more UE functionalities (e.g. steps, actions, etc.) as described herein.

In some embodiments, the UE may comprise a transceiver configured to communicate with one or more radio network nodes and/or with one or more other UEs, and processing circuitry operatively connected to the transceiver, the processing circuitry being configured to perform one or more UE functionalities as described herein. In some embodiments, the processing circuitry may comprise at least one processor and at least one memory storing instructions which, upon being executed by the processor, configure the processor to perform one or more UE functionalities as described herein.

In some embodiments, the UE may comprise one or more functional modules configured to perform one or more UE functionalities as described herein.

According to another aspect, some embodiments include a non-transitory computer-readable medium storing a computer program product comprising instructions which, upon being executed by processing circuitry (e.g., a processor) of the UE, configure the processing circuitry to perform one or more UE functionalities as described herein.

According to another aspect, some embodiments include a method to be performed by a radio network node. The method generally comprises transmitting a downlink transmission to a user equipment, the downlink transmission having at least one characteristic, and receiving an uplink transmission from the user equipment, the uplink transmission using a waveform selected from two or more waveforms based at least in part on the at least one characteristic of the downlink transmission.

In some embodiments, the downlink transmission may comprise a downlink control message. In some embodiments, the downlink control message may comprise an uplink grant.

In some embodiments, the at least one characteristic may be a search space in which the downlink control message is transmitted. The search space may be one of a common search space and a UE-specific search space.

In some embodiments, the at least one characteristic may be a control resources set in which the downlink control message is transmitted. The control resources set may be one of a first control resources set and a second control resources set.

In some embodiments, the at least one characteristic may be a modulation and coding scheme, MCS, index of the downlink control message.

In some embodiments, the at least one characteristic may be a radio network temporary identifier, RNTI, used to scramble the downlink control message.

In some embodiments, the at least one characteristic may be a format of the downlink control message.

In some embodiments, the method may comprise, or further comprise, determining the at least one characteristic of the downlink transmission based at least in part on the one of the two or more waveforms desired for the upcoming uplink transmission.

In some embodiments, the method may comprise, or further comprise, transmitting an identification of at least one of the two or more waveforms to the UE. In such embodiments, transmitting an identification of at least one of the two or more waveforms to the UE may be performed via RRC signaling.

According to another aspect, some embodiments include a radio network node configured, or operable, to perform one or more radio network node functionalities (e.g. steps, actions, etc.) as described herein.

In some embodiments, the radio network node may comprise a transceiver configured to communicate with one or more UEs, and a communication interface configured to communicate with one or more other radio network nodes and/or with one or more network nodes (including core network nodes), and processing circuitry operatively connected to the communication interface, the processing circuitry being configured to perform one or more radio network node functionalities as described herein. In some embodiments, the processing circuitry may comprise at least one processor and at least one memory storing instructions which, upon being executed by the processor, configure the processor to perform one or more radio network node functionalities as described herein.

In some embodiments, the radio network node may comprise one or more functional modules configured to perform one or more radio network node functionalities as described herein.

According to another aspect, some embodiments include a non-transitory computer-readable medium storing a computer program product comprising instructions which, upon being executed by processing circuitry (e.g., a processor) of the radio network node, configure the processing circuitry to perform one or more radio network node functionalities as described herein.

Some embodiments may remove uncertainty about the waveform type used by the UE during RRC reconfiguration of waveform type.

Other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

