Switching waveforms for uplink transmission in NR network

Methods and apparatus are provided for switching a waveform for UL transmissions in a communication network to optimize power usage of the UE. In exemplary embodiments, the UE can use either CP-OFDM waveform or DFT-S-OFDM waveform for UL transmissions. A mechanism is provided to prevent excessive switching in environments where the channel conditions are rapidly changing. Further, a signaling mechanism is provided for switching waveforms for UL transmissions using Layer 1 (L1) signaling to reduce the transmission time needed to switch between CP-OFDM and DFT-S-OFDM waveforms.

TECHNICAL FIELD

The present disclosure relates generally to uplink transmissions in a wireless communication network and, more particularly, to dynamic switching between waveforms for uplink transmissions in NR networks.

BACKGROUND

Long Term Evolution (LTE) networks use cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) for downlink (DL) transmission and discrete Fourier transform spread OFDM (DFT-S-OFDM) for uplink (UL) transmission. On the other hand, New Radio (NR) networks employ CP-OFDM for DL as in LTE and both CP-OFDM and DFT-S-OFDM for UL.

Having symmetry between DL and UL transmission schemes provides simplification on the overall design, especially with respect to the wireless backhaul and device-to-device communications. Additionally, NR has the option to use DFT-S-OFDM for UL transmission, which is beneficial in coverage-limited scenarios, but is limited to single transmission layer transmission only and has a lower peak-to-average power ratio (PAPR)/cubic metric than CP-OFDM for power reduction purposes. CP-OFDM, in contrast, can support up to four transmission layers, which helps to achieve higher data rates. The low PAPR/cubic metric in DFT-S-OFDM, however, is beneficial for UE power consumption. Other DFT-S-OFDM restrictions imply that only contiguous allocations in the frequency domain can be scheduled for the UE in the UL, so DFT-S-OFDM is less flexible in terms of resource utilization and scheduling.

In practice, a 5G NodeB (gNB) can select between CP-OFDM or DFT-S-OFDM and the user equipment (UE) should be capable to support both. However, the switching between these different waveforms is complex, involving both radio resource control (RRC) configuration and DL control information (DCI) format changes.

Table 1 shows the maximum power reduction (MPR) for different modulation schemes and different carrier bandwidths (BWs).

As seen in Table 1, the transmission power gain obtained from DFT-S-OFDM is about 2 to 2.5 dB. This power gain is the reason of DFT-S-OFDM is beneficial for coverage or power-limited scenarios. On the other hand, CP-OFDM can transmit on multiple transmission layers, making it beneficial in scenarios where power constraints are not an issue.

For UL transmissions using CP-OFDM, the total transmitted power is equally divided between each of the available layers. The maximum number of layers used by a user equipment (UE) in the UL is configured by the network (NW) via a semi-static RRC parameter even though the number of layers to use is highly dependent on fast changing channel conditions. For example, the maximum number of UL layers in NR is four and can be fully used when the channel conditions are good. In this case, the total UE transmitted power would be divided by four and allocated to each of the layers. But when the channel conditions change for the worse (e.g., when the UE approaches a cell edge), it may be possible that only a single transmission layer can be used. In this case, the total transmitted power for the single transmission layer is still one fourth of the total transmit power due to the maximum number of layers configured by the network so the total available transmit power is not fully utilized, which could lead inefficient use of resources due to higher error rates and more retransmissions.

Radio conditions can change rapidly and RRC reconfiguration can take a relatively long time, typically in the order of 30 to 40 msec. During the RRC reconfiguration, the UE is unable to transmit or receive. Thus, frequent RRC reconfiguration in order to optimize power usage degrades performance, and in worst case scenarios, may lead to disruption of service.

SUMMARY

The present disclosure relates generally to selection of a waveform for UL transmissions in a communication network to optimize power usage of the UE. In exemplary embodiments, the UE can use either CP-OFDM or DFT-S-OFDM for UL transmissions. A mechanism is provided to prevent excessive switching in environments where the channel conditions are rapidly changing. Further, a signaling mechanism is provided for changing waveforms using Layer 1 (L1) signaling to reduce the transmission time needed to transition between CP-OFDM or DFT-S-OFDM waveforms. The techniques described herein can be used for both codebook based UL transmission and for non-codebook based UL transmission.

A first aspect of the disclosure comprises methods implemented by a base station in a wireless communication network of switching between a DFT-S-OFDM waveform and a CP-OFDM waveform for UL transmissions. In one embodiment, the base station receives, at two or more successive time instances, information from a UE indicative of channel conditions between the UE and the base station at each of the successive time instances. For each of the two or more time instances, the base station determines whether the information indicates a need for a change of the current waveform for UL transmissions. The base station maintains a first count of time instances where the information indicates a need for a change of the current waveform. The base station switches between a DFT-S-OFDM waveform on a single transmission layer and a CP-OFDM waveform on single transmission layer or multiple transmission layers depending on the first count.

According to a second aspect of the disclosure, the base station signals the change in waveform using L1 signaling. According to this aspect, the base station configures a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from a UE to a base station. The base station configures a UE to operate in the first BWP using a DFT-S-OFDM waveform on a single transmission layer, and to operate in the second BWP using a CP-OFDM waveform on a single transmission layer or multiple transmission layers. After configuring the UE, the base station receives information from the UE indicative of channel conditions between the UE and the base station. The base station evaluates, based on the information from the UE, whether to switch between the DFT-S-OFDM waveform and the CP-OFDM waveform for UL transmissions. If it is determined that a change in waveform is needed, the base station sends to the UE, responsive to the evaluation, DCI over the DL control channel. The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform.

A third aspect of the disclosure comprises methods implemented by a UE capable of multi-layer transmission of switching between a DFT-S-OFDM waveform and a CP-OFDM waveform for UL transmissions. The UE configures a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from the UE to a base station. The UE configures the first BWP for a DFT-S-OFDM waveform using a single transmission layer for UL transmissions and configures the second BWP for a CP-OFDM waveform on a single transmission layer or multiple transmission layers for UL transmissions. The UE further sends, to a base station, information from which channel conditions between the UE and the base station can be determined. The UE thereafter receives, from the base station, DCI over the DL control channel. The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform based on the information. Responsive to the BWP indication, the UE switches from a current BWP to the target BWP responsive to the BWP indication.

A fourth aspect of the disclosure comprises a base station configured to switch between a DFT-S-OFDM waveform and a CP-OFDM waveform for UL transmissions. The base station comprises one or more antennas, a receiving unit, a determining unit, a counting unit and a switching unit. The receiving unit is configured to receive, at two or more successive time instances, information from a UE indicative of channel conditions between the UE and the base station at each of the successive time instances. The determining unit is configured to, for each of the two or more time instances, determine whether the information indicates a need for a change of the current waveform for UL transmissions. The counting unit is configured to maintain a first count of time instances where the information indicates a need for a change of the current waveform. The switching unit is configured to switch between a DFT-S-OFDM waveform on a single transmission layer and a CP-OFDM waveform on a single transmission layer or multiple transmission layers depending on the first count.

A fifth aspect of the disclosure comprises a base station configured to switch between a DFT-S-OFDM waveform and a CP-OFDM waveform for UL transmissions. The base station comprises one or more antennas, a BWP configuring unit, a first waveform configuring unit, a second waveform configuring unit, a receiving unit, an evaluation unit and a DCI sending unit. The BWP configuring unit is operative to configure a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from a UE to a base station. The first waveform configuring unit is operative to configure a UE to operate in the first BWP using a DFT-S-OFDM waveform on a single transmission layer. The second waveform configuring unit is operative to configure the UE to operate in the second BWP using a CP-OFDM waveform on a single transmission layer or multiple transmission layers. The receiving unit is configured to receive information from a UE indicative of channel conditions between the UE and the base station. The evaluation unit is configured to evaluate, based on the information from the UE, whether to switch between the DFT-S-OFDM waveform and the CP-OFDM waveform for UL transmissions. The DCI configuring unit is configured to send to the UE, responsive to the evaluation, DCI over the DL control channel. The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform.

A sixth aspect of the disclosure comprises a UE capable of multi-layer transmission configured to switch between a DFT-S-OFDM waveform and a CP-OFDM waveform for UL transmissions. The UE comprises one or more antennas, a BWP configuring unit, a first waveform configuring unit, a second waveform configuring unit, a sending unit, a receiving unit, and a switching unit. The BWP configuring unit configures a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from the UE to a base station. The first waveform configuring unit is operative to configure the first BWP for a DFT-S-OFDM waveform using a single transmission layer. The second waveform configuring unit is operative to configure the second BWP for a CP-OFDM waveform on a single transmission layer or multiple transmission layers. The sending unit is configured to send, to a base station, information from which channel conditions between the UE and the base station can be determined. The receiving unit is configured to receive, from the base station, DCI over the DL control channel, The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform based on the information. The switching unit is configured to switch from a current BWP to the target BWP responsive to the BWP indication.

A seventh of the disclosure comprises a base station configured to perform the method according to the first and second aspects. The base station comprises interface circuitry for communicating with a UE over a wireless communication channel and processing circuitry. In one embodiment, the processing circuitry is configured to receive, at two or more successive time instances, information from a UE indicative of channel conditions between the UE and the base station at each of the successive time instances. The processing circuitry is further configured to, for each of the two or more time instances, determine whether the information indicates a need for a change in the current waveform used for UL transmission. The processing circuitry is further configured to maintain a first count of time instances where the information indicates a need for a change in the current waveform, and to switch between a DFT-S-OFDM waveform on a single transmission layer and a CP-OFDM waveform on a single transmission layer or multiple transmission layers depending on the first count.

An eighth of the disclosure comprises a base station configured to perform the method according to the first and second aspects. The base station comprises interface circuitry for communicating with a UE over a wireless communication channel and a processing circuitry. The processing circuitry is operative to configure a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from a UE to a base station. The processing circuitry is further operative to configure a UE to operate in the first BWP using a DFT-S-OFDM waveform on a single transmission layer, and to configure the UE to operate in the second BWP using a CP-OFDM waveform on a single transmission layer or multiple transmission layers. The processing circuitry is configured to receive information from a UE indicative of channel conditions between the UE and the base station and to evaluate, based on the received information, whether to switch between the DFT-S-OFDM waveform and the CP-OFDM waveform for UL transmissions. The processing circuitry is further configured to send to the UE, responsive to the evaluation, DCI over the DL control channel. The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform.

A ninth of the disclosure comprises a UE configured to perform the method according to the first and second aspects. The UE comprises interface circuitry for communicating with a base station over a wireless communication channel and a processing circuitry. The processing circuitry is operative to configure a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from the UE to a base station. The processing circuitry is further operative to configure the UE to operate in the first BWP using a DFT-S-OFDM waveform on a single transmission layer, and to configure the UE to operate in the second BWP using a CP-OFDM waveform on a single transmission layer or multiple transmission layers. The processing circuitry is further configured to send, to a base station, information from which channel conditions between the UE and the base station can be determined. The processing circuitry is further configured to receive, from the base station, DCI over the DL control channel. The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform based on the information. The processing circuitry is further configured to switch from a current BWP to the target BWP responsive to the BWP indication. The processing circuitry is further configured to, responsive to the BWP indication, switches from a current BWP to the target BWP responsive to the BWP indication.

A tenth of the disclosure comprises a computer program product comprising executable instructions that configure a processing circuitry in a base station to perform the method according to the first aspect. The computer program product can be embodied in a carrier, such as an electronic signal, optical signal, radio signal, or computer readable storage medium.

An eleventh aspect of the disclosure comprises a computer program product comprising executable instructions that configure a processing circuitry in a base station to perform the method according to the second aspect. The computer program product can be embodied in a carrier, such as an electronic signal, optical signal, radio signal, or computer readable storage medium.

A twelfth aspect of the disclosure comprises a computer program product comprising executable instructions that configure a processing circuitry in a UE to perform the method according to the third aspect. The computer program product can be embodied in a carrier, such as an electronic signal, optical signal, radio signal, or computer readable storage medium.

DETAILED DESCRIPTION

Referring now to the drawings, an exemplary embodiment of the disclosure will be described in the context of a 5G or NR wireless communication network. Those skilled in the art will appreciate that the methods and apparatus herein described are not limited to use in 5G or NR networks, but may also be used in wireless communication networks where multiple beams within a single cell are used for communication with wireless devices in the cell.

FIG.1illustrates a wireless communication network10according to the NR standard currently being developed by Third Generation Partnership Project (3GPP). The wireless communication network10comprises one or more base stations20providing service to user equipment (UEs)50in respective cells15of the wireless communication network10. The base stations20are also referred to as Evolved NodesBs (eNBs) and gNodeBs (gNBs) in 3GPP standards. Although only one cell15and one base station20are shown inFIG.1, those skilled in the art will appreciate that a typical wireless communication network10comprises many cells15served by many base stations20.

The UEs50may comprise any type of equipment capable of communicating with the base station20over a wireless communication channel. For example, the UEs50may comprise cellular telephones, smart phones, laptop computers, notebook computers, tablets, machine-to-machine (M2M) devices (also known as machine type communication (MTC) devices), embedded devices, wireless sensors, or other types of wireless end user devices capable of communicating over wireless communication networks10.

NR networks employ CP-OFDM for DL as in LTE and both CP-OFDM and DFT-S_OFDM for UL. In the case that CP-OFDM is selected for UL transmissions, the UE50can transmit on up to four layers. In the case that DFT-S-OFDM is selected for UL transmissions, the UE50can transmit on a single transmission layer only. The maximum number of layers is configured by RRC and the transmit power of the UE50is divided equally between all layers based on the configured maximum number of layers. If more than one layer is configured by RRC, the full transmit power of the UE50is used only in when transmitting on the allowed maximum number of layers.

Radio conditions can change rapidly and RRC reconfiguration can take a relatively long time, typically in the order of 30 to 40 msec. During this delay, a UE50is not expected to receive DL signals or transmit UL signals until the new RRC configuration is concluded. While switching between DFT-S-OFDM and CP-OFDM enables the UE to make more optimal use of its available power, switching too frequently may cause noticeable degradation in performance.

FIG.2illustrates the areas where DFT-S-OFDM and CP-OFDM typically are used. When the UE50is close to the base station10, referred to herein as the near zone, channel conditions are likely to be good so that CP-OFDM and a single transmission layer or multiple transmission layers can be used for UL transmission. On the other hand, when the UE50is located far away from the base station20, referred to herein as the far zone, channel conditions are likely to be poor in comparison to the near zone so that DFT-S-OFDM and a single transmission layer is used for UL transmission. Between these two zones is an intermediate zone, referred to herein as the ping-pong zone, where channel conditions change frequently causing frequent RRC reconfigurations. The frequent switching between DFT-S-OFDM using a single transmission layer and CP-OFDM using a single transmission layer or multiple transmission layers increases the time the UE50is unable to transmit or receive signals, degrading performance and, in worse case scenarios, resulting in link failure.

One aspect of the present disclosure comprises techniques to avoid ping-ponging between DFT-S-OFDM using a single transmission layer and CP-OFDM using a single transmission layer or multiple transmission layers when a UE50is an area with frequently changing channel conditions (e.g., ping-pong zone). To avoid repeated and frequent switching (i.e., ping-ponging) between waveforms, the switching logic is modified to introduce hysteresis into the decision process for link adaptation. Conventionally, the base station20monitors the channel conditions between the UE50and the base station20and determines when to change waveforms based on the channel conditions. Other factors may also be considered such as the power headroom of the UE, buffer status of the UE, battery status of the UE, temperature of the UE, etc. In embodiments of the present disclosure, the base station20avoids ping-ponging in scenarios where the channel conditions are frequently changing by delaying the change in the waveform after the change in the channel conditions is detected. For example, after detecting a change in the channel conditions necessitating a change in the waveform used for UL transmissions, the base station20may delay the change in the waveform during a time window while it continues to monitor the channel conditions. If the channel conditions requiring the change in waveform dominate or prevail during this time window, the base station20instructs the UE50to change the waveform. On the other hand, if the channel conditions change back before the end of the time window, the base station20will continue using the current waveform.

In some embodiments, the channel conditions on the UL can be determined based on periodic link adaptation reports from the UE. The periodic LA reports may contain channel state information indicating conditions of the DL channel. In other embodiments, the channel conditions are determined from sounding reference signals (SRSs) transmitted by the UE on the UL.

An exemplary embodiment of the decision logic for link adaptation is described below for purposes of illustrating the principles of the present disclosure. Those skilled in the art will appreciate that this example is not intended to be limiting. In this example, it is assumed that CP-OFDM may be configured for a maximum of two transmission layers, while DFT-S-OFDM uses only a single transmission layer. Additionally, it is assumed that the UE50has or supports only two antenna ports.

FIG.4illustrates an exemplary procedure for link adaptation according to one example. The procedure uses a counter, referred to herein as a change counter, and a timer that defines the length of a time window. The time window, shown inFIG.3, defines the maximum number of time instances that will be considered for changing waveforms and introduces a time delay. The time window is flexible to any desired report periodicity or number of reports. In this example, a time window of 120 msec is used to avoid switching back and forth between DFT-S-OFDM and CP-OFDM.

After the base station20and UE50are synchronized, a default waveform is selected, and the change counter and timer are initialized to starting values, which in this example is “0” for the counter and “1” for the timer (S1). In the example below, time is measured as a number of time intervals, which may comprise a reporting interval for LA reports or measurement intervals for performing UL measurements on SRS signals.

Once the base station20and UE50are synchronized, the base station20begins receiving periodic link adaptation (LA) reports from the UE50(S2). In this example, the UE50sends the LA reports to the base station at 40 msec intervals. The LA reports may include, for example, one or more of Reference Signal Received Power (RSRP) measurements on DL signal transmitted by the base station20or other signal quality measurements, a rank indicator (RI) indicating a number of transmission layers that can be supported by the UE50, or a precoding Matrix indicator (PMI) indicating a selected precoding matrix for the UL transmission. The LA reports provide the base station20with information about the DL channel conditions. Assuming reciprocity, (e.g., for example in Time Division Duplex (TDD) systems), the channel conditions on the UL are assumed to be the same, or at least close. In this case, the decision to change waveforms is based on the LA reports.

Alternatively, the UE50may send SRSs at periodic intervals and the base station20performs UL measurements on the received SRSs. The UL measurements in this case provide the base station20with information about the UL channel conditions when reciprocity cannot be assumed. In this case, the base station20receives the SRSs and performs UL measurements at a predetermined measurement interval. The decision to change waveforms is based on the UL measurements.

In some embodiments, both LA reports and SRSs may be used to make link adaptation decisions. It will also be appreciated that channel conditions can also be determined based on other UL reference signal or demodulated signals. Thus, the procedure as herein described is adaptable to any manner of determining the current UL channel conditions.

Returning toFIG.4, when a LA report or SRS is received from the UE50, the base station20evaluates the LA reports and/or UL measurements on the SRS to determine whether channel conditions have changed so as to necessitate a change of the waveform (S3). If the LA reports and/or the UL measurements indicate that a change is needed, the base station20does not necessarily change waveforms immediately. Instead, the base station20will wait for a predetermined time period defined by the time window to make the decision to change the waveform for UL transmissions. If a predetermined number of successive LA reports or UL measurements provide a change indication within the time window, the base station20makes the decision to change waveforms (S10). When the LA report or UL measurement provides a change indication, the base station20increments the change counter (S7) and activates or increments a timer (S8) that defines the time window. The base station20compares the timer value to a predetermined maximum value (S9). In this example, the timer measures time by the number of reporting intervals for LA reports or measurement intervals for UL measurements. If the timer value is less than or equal to the maximum timer value, the base station20waits for the next LA report or UL measurement. If the timer value is greater than the predetermined maximum value, the base station20compares the value of the change counter to a threshold T (S10). If the counter value is less than or equal to the threshold T, the waveform is not changed the changed (S5). In the case, the base station resets the counter and timer to their starting values (S6) and waits for the next LA report or SRS. If the counter value is greater than the threshold T, a decision is made to change the waveform (S11), which in some embodiments requires an RRC reconfiguration (S12). In other embodiment described in more detail below, RRC reconfiguration is avoided by preconfiguring the UL resources with at least two bandwidth parts using different RRC configurations. In this case, the base station20sends DL control information (DCI) to the UE50indicating the BWP to use for UL transmission (S12). Because the different BWPs are preconfigured, RRC reconfiguration is not required.

If, the base station20determines at S3that the channel conditions have not changed so as to require a change in the waveform, the base station20makes a decision to continue using the current waveform (S5). In this case, the base station20resets the counter and timer to their initial values (S6) and waits for the next LA report or SRS transmission from the UE50.

The effect of the procedure inFIG.4is to reset the counter and restart the timer every time an LA report or SRS provides a negative change indication, also referred to herein as a “no change” indication. Additionally, the counter and timer are reset upon timer expiration (e.g., every 120 msec) unless the counter value reaches the threshold T. Thus, the waveform will not be changed unless a predetermined number of consecutive LA reports or SRSs provide a change indication.

DFT-S-OFDM can be considered as “safer” or more robust than CP-OFDM due to its coverage-extension characteristic. In unfavorable channel conditions, it is likely that DFT-S-OFDM preserves the link. Additionally, DFT-S-OFDM requires less power and reduces power consumption due to its lower PAPR, which impacts positively the UE power saving. Given these benefits, some embodiments may bias operation towards DFT-S-OFDM so that the UE100operates most of the time using DFT-S-OFDM and switches to CP-OFDM only under good channel conditions.

Table 2 below provides one example of initial counter and timer values depending on the current transmission waveform.

TABLE 2Initial Counter and Timer ValuesCurrent TX ModeCounterTimerThresholdDFT-S-OFDM012CP-OFDM212

In the example shown in Table 2, the counter is initialized to a value of 0 when the current waveform is DFT-S-OFDM using a single transmission layer and to a value of 2 when the current waveform is CP-OFDM using a single transmission layer or multiple transmission layers. In both cases the timer is initialized to 1 and the time window is assumed to be 120 msec. Also, the threshold T is set to a value of 2 for both waveforms. In this example, the base station20will not change from DFT-S-OFDM to CP-OFDM unless 3 consecutive LA reports or SRSs provide a change indication. That is, after receiving the first change indication after a counter reset, the base station20waits to receive 2 additional change indications (80 msec) within the time window of 120 msec. On the other hand, the base station20will change from CP-OFDM to DFT-S-OFDM immediately on receipt of the first LA report or SRS providing a change indication. Therefore, the change to DFT-S-OFDM has more weight than the change from DFT-S-OFDM to CP-OFDM. This behavior is beneficial in environments with rapidly changing channel conditions.

According to another aspect of the disclosure, method and apparatus are provided for dramatically reducing the transition time for switching between DFT-S-OFDM using a single transmission layer to CP-OFDM configured for a single transmission layer or multiple transmission layers. The reduction in transition time is achieved by configuring the UL resources with two or more BWPs.

In NR, BWPs were introduced in Release-15. A UE50can operate on a single BWP per serving cell at a time, and switch among multiple BWPs. Currently, up to 4 BWPs can be defined for both UL and DL. A BWP configuration contains not only RF parameters (bandwidth and frequency location of BWP, numerology and CP), but also a list of parameters for physical channels, signals and scheduling related configurations.

Switching between BWPs can be accomplished by sending a BWP identification (ID) in DCI from the base station20to the UE50as shown inFIG.5. BWP switching can also be RRC-based or timer-based. The present disclosure focuses on DCI-based BWP switching. Table 3 illustrates switching latency for different scenarios denoted 1-5 as described in the 3GPP contribution Discussion on BWP delay requirement, R4-1806543. This characteristic of DCI-based BWP switching can be taken advantage of in a variety of applications for the benefit of overall network performance where inferior performance is caused by slow RRC reconfiguration. The scenarios best fitted the present disclosure is scenario 5, where the switching delay is 2 msec.

In one embodiment, a first BWP, denoted BWP #0 is configured for UL transmission using a DFT-S-OFDM waveform on a single transmission layer. A second BWP, denoted BWP #1, is configured for UL transmission using a CP-OFDM waveform on a single transmission layer or multiple transmission layers. It is important to highlight that this approach uses 2 of 4 of the available BWPs. The remaining BWPs may be used for other purposes, such as power saving.

FIG.6illustrates the high-level configuration of the BWPs. BWP #0 is configured for the waveform that serves as a default and BWP #1 is configured for the other waveform. In one embodiment, CP-OFDM is used as a default waveform because DFT-S-OFDM is a UE capability and some UEs may not support DFT-S-OFDM. In this case, BWP #0 is configured for CP-OFDM using a single transmission layer or multiple transmission layers and BWP #1 is configured for DFT-S-OFDM using a single transmission layer. In other embodiments, DFT-S-OFDM is used as a default waveform.

FIG.7shows the RRC dependencies that are needed to configure the common part of the BWPs. It is worth noting that BWP #0 has more fields to be configured and the additional BWPs can be tailored based on the bwp-Common (parameters shared by all the BWPs) and the bwp-Dedicated (parameters to specific BWP). Thus, CP-OFDM is configured to support a single transmission layer or multiple transmission layers, maximum rank greater than 1 and multiple antenna ports for all the reference signals and DFT-S-OFDM for single transmission layer, maximum rank one and single antenna port for diverse reference signals. When DFT-S-OFDM is chosen, maximum transmitted power can be achieved for UL transmission.

As BWPs are scarce resources with a maximum of 4 in the current versions of the 3GPP specifications, it might not always be suitable to use BWPs switching so that the BWPs can be used for other purposes. For example, the BWPs may be needed for actual bandwidth change for the sake of power saving. Therefore, when the BWPs are used for other purposes, the base station20might chose to use the RRC Reconfiguration procedure for switching the waveform used for UL transmissions.

In the current versions of the specifications, DCI is typically accompanied with a DL assignment or UL grant. Currently, the standards do not allow for the transmission of DCI to the UE for switching BWP without a resource allocation. Therefore, in case there is no need of resource allocation for UE data traffic or control information (not counting pre-allocated resources such as PUCCH used for SRS/CSI), and the base station20knows based on historical info/NW internal assistance/NW external assistance/UE assistance/buffer status in UL or DL) that there will not be any data exchange in some time ahead (e.g., 100's of milliseconds), then the RRC Reconfiguration procedure can be used by the base station20to achieve the waveform change. Alternatively, in some embodiments, the base station20can allocate a small “dummy” resource in the UL just to be able to provide the DCI including the BWP indication.

In another aspect of the present disclosure, in addition to link budget, other factors may be considered in deciding whether to switch between DFT-S-OFDM and CP-OFDM. Exemplary factors to consider include power headroom, battery capacity, operating temperature, and buffer status. When the power headroom is low, the UE10may not be able to take advantage of multiple transmission layers. In this case, it may be preferable to switch to or remain in the DFT-S-OFDM waveform. When battery capacity is low, or overheating is detected, the UE may provide a power preference indication (PPI) or temperature indication to the base station20. In this case, it is also preferable to switch to or remain in the DFT-S-OFDM waveform. When the UE50has little UL data too send, as reflected by buffer status reports (BSRs) received by the base station20, the DFT-S-OFDM mode may be sufficient even when the UE50can support multiple transmission layers.

In the embodiments herein described, the borders of the ping-pong zone may be chosen such that a larger area is used for DFT-S-OFDM and thereby, the ping-pong-area is much closer to the base station. This can be realized by a weight function (as shown in Table 2), which biases the selection of the waveform. The biasing can be implemented in a dynamic matter and adjusted as the UE status changes. For example, the bias can be adjusted based on the power preference of the UE50. A stronger bias can be applied when the UE50is indicates a preference for power saving and a weaker bias can be used when power saving is not indicated.

FIG.8illustrates an exemplary method100implemented by a base station20of switching waveforms for UL transmissions from a UE50. In one embodiment, the base station20receives, at two or more successive time instances, information from a UE50indicative of channel conditions between the UE50and the base station20at each of the successive time instances (block110). For each of the two or more time instances, the base station20determines whether the information indicates a need for a change of a current waveform for UL transmissions (block120). The base station20maintains a first count of time instances where the information indicates a need for a change of the current waveform (block130). The base station20switches between a DFT-S-OFDM waveform on a single transmission layer and a CP-OFDM waveform on a single transmission layer or multiple transmission layers depending on the first count (block140).

In some embodiments of the method100, the first count is of a number of consecutive time instances where the information indicates a need for a change of the current waveform.

In some embodiments of the method100, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform comprises switching waveforms when the first count reaches a threshold.

In some embodiments of the method100, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform when the first count reaches a threshold comprises switching from the DFT-S-OFDM waveform to the CP-OFDM waveform when the first count reaches a first threshold,; and switching from the CP-OFDM waveform to DFT-S-OFDM waveform when the first count reaches a second threshold less than the first threshold.

In some embodiments of the method100, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform comprises switching modulation waveforms when the first count reaches a threshold within a time window.

Some embodiments of the method100further comprise initializing a timer to measure a duration of the time window and running the timer responsive to the receipt of information indicating a need for a change of the current waveform.

Some embodiments of the method100further comprise resetting the timer responsive to expiration of the timer, or receipt of information indicating no change of the current waveform.

Some embodiments of the method100further comprise resetting the first count responsive to expiration of the timer.

Some embodiments of the method100further comprise maintaining a second count of time instances where the information indicates no need for a change of the current waveform.

In some embodiments of the method100, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform further depends on the second count.

In some embodiments of the method100, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform depends on a comparison of the first count and the second count.

In some embodiments of the method100, the information comprises channel state information indicative of downlink channel conditions.

In some embodiments of the method100, the information further includes power headroom of the UE50.

In some embodiments of the method100, the information further includes at least one of battery status information, a power preference indication or a temperature indication to the base station20.

In some embodiments of the method100, switching between a DFT-S-OFDM waveform configured for a single transmission layer and a CP-OFDM waveform configured for a single transmission layer or multiple transmission layers comprises performing Bandwidth Part (BWP) switching when BWPs are configured for waveform switching, and performing a Radio Resource Control (RRC) reconfiguration when BWPs are not configured for waveform switching.

In some embodiments of the method100, switching between a DFT-S-OFDM waveform configured for a single transmission layer and a CP-OFDM waveform configured for a single transmission layer or multiple transmission layers comprises performing a Radio Resource Control (RRC) reconfiguration when no data exchange requiring a resource assignment is expected within a predetermined time period, and performing Bandwidth Part (BWP) switching when a data exchange requiring a resource assignment is expected within a predetermined time period.

FIG.9illustrates another exemplary method200implemented by the base station20of switching waveforms for UL transmissions from a UE50capable of multi-layer transmission. The base station20configures a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from a UE50to a base station20(block210). The base station20configures a UE50to operate in the first BWP using a DFT-S-OFDM waveform on a single transmission layer, and to operate in the second BWP using a CP-OFDM waveform on a single transmission layer or multiple transmission layers (blocks220,230). After configuring the UE50, the base station20receives information from a UE50indicative of channel conditions between the UE50and the base station20(block240). The base station20evaluates, based on the information from the UE50, whether to switch between the DFT-S-OFDM waveform and the CP-OFDM waveform for UL transmissions (block250). If it is determined that a change in waveform is needed, the base station20sends to the UE50, responsive to the evaluation, DCI over the DL control channel (block260). The DCI including an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform.

In some embodiments of the method200, receiving information from a UE50indicative of channel conditions between the UE50and the base station20comprises receiving, for each of the two or more time instances, information from a UE50indicative of channel conditions between the UE50and the base station20at each of the successive time instances.

In some embodiments of the method200, evaluating whether to switch between the DFT-S-OFDM waveform and the CP-OFDM waveform for uplink transmissions comprises, for each of the two or more time instances, determining whether the information indicates a need for a change of a current waveform, maintaining a first count of time instances where the information indicates a need for a change of the current waveform, and determining, depending on the first count, whether to switch between the DFT-S-OFDM waveform and the CP-OFDM waveform.

In some embodiments of the method200, the first count is of a number of consecutive time instances where the information indicates a need for a change of the current waveform.

In some embodiments of the method200, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform comprises switching waveforms when the first count reaches a threshold.

In some embodiments of the method200, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform when the first count reaches a threshold comprises switching from the DFT-S-OFDM waveform to the CP-OFDM waveform when the first count reaches a first threshold, and switching from the CP-OFDM waveform to DFT-S-OFDM waveform when the first count reaches a second threshold less than the first threshold.

In some embodiments of the method200, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform comprises switching modulation waveforms when the first count reaches a threshold within a time window.

Some embodiments of the method200further comprise initializing a timer to measure a duration of the time window and running the timer responsive to the receipt of information indicating a need for a change of the current waveform.

Some embodiments of the method200further comprise resetting the timer responsive to expiration of the timer, or receipt of information indicating no change of the current waveform.

Some embodiments of the method200further comprise resetting the first count responsive to expiration of the timer.

Some embodiments of the method200further comprise maintaining a second count of time instances where the information indicates no need for a change of the current waveform.

In some embodiments of the method200, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform further depends on the second count.

In some embodiments of the method200, switching between the DFT-S-OFDM waveform and the CP-OFDM waveform depends on a comparison of the first count and the second count.

In some embodiments of the method200, the information from which channel conditions is determined comprises at least one of channel state information indicative of downlink channel conditions, sounding reference signals.

Some embodiments of the method200further comprise receiving power headroom of the UE50and evaluating whether to switch waveforms further based on the power headroom of the UE50.

Some embodiments of the method200further comprise receiving at least one of battery status information, a power preference indication or a temperature indication from the UE and evaluating whether to switch waveforms further based on at least one of the battery status information, power preference indication or temperature indication.

FIG.10illustrates an exemplary method300implemented by a UE50capable of multi-layer transmission in a wireless communication network of switching waveforms for UL transmissions to a base station20. The UE50configures a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from the UE50to a base station20(block310). The UE50configures the first BWP for a DFT-S-OFDM waveform on a single transmission layer for UL transmissions and configures the second BWP for a CP-OFDM waveform on a single transmission layer or multiple transmission layers for UL transmissions (blocks320,330). The UE50further sends, to a base station20, information from which channel conditions between the UE50and the base station20can be determined (block340). The UE50thereafter receives, from the base station20, DCI over the DL control channel (block350). The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform based on the information. Responsive to the BWP indication, the UE50switches from a current BWP to the target BWP (block360).

In some embodiments of the method200, sending information to the base station20from which channel conditions between the UE50and the base station20can be determined comprises sending channel state information indicative of downlink channel conditions.

In some embodiments of the method200, sending information to the base station20from which channel conditions between the UE50and the base station20can be determined comprises sending sounding reference signals to the base station.

Some embodiments of the method300further comprise sending power headroom information to the base station20.

Some embodiments of the method300sending at least one of battery status information, a power preference indication or a temperature indication to the base station.

FIG.11illustrates a base station20configured to perform the method ofFIG.8. The base station20comprises one or more antennas22, a receiving unit24, a determining unit26, a counting unit28and a switching unit30. The various units24-30can be implemented by hardware and/or by software code that is executed by a processor or processing circuitry. The receiving unit24is configured to receive, at two or more successive time instances, information from a UE50indicative of channel conditions between the UE50and the base station at each of the successive time instances. The determining unit26is configured to, for each of the two or more time instances, determine whether the information indicates a need for a change of the current waveform for UL transmissions. The counting unit28is configured to maintain a first count of time instances where the information indicates a need for a change of the current waveform. The switching unit30is configured to switch between a DFT-S-OFDM waveform on a single transmission layer and a CP-OFDM waveform on a single transmission layer or multiple transmission layers depending on the first count.

FIG.12illustrates a base station20configured to perform the method ofFIG.9. The base station20comprises on or more antennas22, a BWP configuring unit32, a first waveform configuring unit34, a second waveform configuring unit36, a receiving unit38, an evaluation unit40and a DCI sending unit42. The various units32-42can be implemented by hardware and/or by software code that is executed by a processor or processing circuitry. The BWP configuring unit32is configured to configure a first BWP and a second BWP on UL resources used for UL transmissions from a UE50to a base station20. The first waveform configuring unit34is configured to configure a UE50to operate in the first BWP using a DFT-S-OFDM waveform on a single transmission layer. The second waveform configuring unit36is configured to configure the UE50to operate in the second BWP using a CP-OFDM waveform on a single transmission layer or multiple transmission layers. The receiving unit38is configured to receive information from a UE indicative of channel conditions between the UE and the base station. The evaluation unit40is configured to evaluate, based on the information from the UE50, whether to switch between the DFT-S-OFDM waveform and the CP-OFDM waveform for UL transmissions. The DCI configuring unit42is configured to send to the UE50, responsive to the evaluation, DCI over the DL control channel. The DCI includes an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform.

FIG.13illustrates a UE50in accordance with one or more embodiments. The UE50comprises one or more antennas52, a BWP configuring unit54, a first waveform configuring unit56, a second waveform configuring unit58, a sending unit60, a receiving unit62, and a switching unit64. The various units54-64can be implemented by hardware and/or by software code that is executed by one or more processors or processing circuitry. The BWP configuring unit54configures a first bandwidth part (BWP) and a second BWP on UL resources used for UL transmissions from the UE50to a base station20. The first waveform configuring unit56configuring the first BWP for a DFT-S-OFDM waveform using a single transmission layer. The second waveform configuring unit58configuring the second BWP for a CP-OFDM waveform on a single transmission layer or multiple transmission layers. The sending unit60is configured to send, to a base station, information from which channel conditions between the UE50and the base station can be determined. The receiving unit62is configured receive, from the base station, DCI over the DL control channel, The DCI including an indication of the BWP associated with a target waveform selected from among the DFT-S-OFDM waveform and the CP-OFDM waveform based on the information. The switching unit64is configured to switching from a current BWP to the target BWP responsive to the BWP indication.

FIG.14illustrates a base station500according to one embodiment that may be configured to perform the methods as herein described including the methods ofFIGS.8and9. The base station500comprises an antenna array510with multiple antenna elements515, an interface circuit520, a processing circuitry530, and memory540. The interface circuit520is coupled to the antennas515and comprises the radio frequency (RF) circuitry522needed for transmitting and receiving signals over a wireless communication channel. In one embodiment, the interface circuit520comprises a RF transceiver including a transmitter and receiver configured to operate according to the NR standard. The interface circuit520further comprises a network interface524to communication over wired or wireless links with other network nodes.

The processing circuitry530controls the overall operation of the radio node500and processes the signals transmitted to or received by the radio node500. Such processing includes coding and modulation of transmitted data signals, and the demodulation and decoding of received data signals. The processing circuitry530may comprise one or more microprocessors, hardware, firmware, or a combination thereof. Memory540comprises both volatile and non-volatile memory for storing computer program code and data needed by the processing circuitry530for operation. Memory540may comprise any tangible, non-transitory computer-readable storage medium for storing data including electronic, magnetic, optical, electromagnetic, or semiconductor data storage. Memory540stores a computer program550comprising executable instructions that configure the processing circuitry530to implement the methods one or more of the methods100and200according toFIGS.8and9respectively. A computer program550in this regard may comprise one or more code modules corresponding to the means or units described above. In general, computer program instructions and configuration information are stored in a non-volatile memory, such as a ROM, erasable programmable read only memory (EPROM) or flash memory. Temporary data generated during operation may be stored in a volatile memory, such as a random access memory (RAM). In some embodiments, computer program550for configuring the processing circuitry530as herein described may be stored in a removable memory, such as a portable compact disc, portable digital video disc, or other removable media. The computer program550may also be embodied in a carrier such as an electronic signal, optical signal, radio signal, or computer readable storage medium.

FIG.15illustrates a UE600according to one embodiment that may be configured to perform the methods as herein described including the methods ofFIGS.8and9. The UE600comprises an antenna array610with multiple antenna elements616, an interface circuit620, a processing circuitry630, and memory640. The interface circuit620is coupled to the antennas616and comprises the radio frequency (RF) circuitry622needed for transmitting and receiving signals over a wireless communication channel. In one embodiment, the interface comprises a RF transceiver including a transmitter and receiver configured to operate according to the NR standard.

The processing circuitry630controls the overall operation of the radio node600and processes the signals transmitted to or received by the radio node600. Such processing includes coding and modulation of transmitted data signals, and the demodulation and decoding of received data signals. The processing circuitry630may comprise one or more microprocessors, hardware, firmware, or a combination thereof. Memory640comprises both volatile and non-volatile memory for storing computer program code and data needed by the processing circuitry630for operation. Memory640may comprise any tangible, non-transitory computer-readable storage medium for storing data including electronic, magnetic, optical, electromagnetic, or semiconductor data storage. Memory640stores a computer program650comprising executable instructions that configure the processing circuitry630to implement the methods one or more of the methods100and200according toFIGS.8and9respectively. A computer program650in this regard may comprise one or more code modules corresponding to the means or units described above. In general, computer program instructions and configuration information are stored in a non-volatile memory, such as a ROM, erasable programmable read only memory (EPROM) or flash memory. Temporary data generated during operation may be stored in a volatile memory, such as a random access memory (RAM). In some embodiments, computer program650for configuring the processing circuitry630as herein described may be stored in a removable memory, such as a portable compact disc, portable digital video disc, or other removable media. The computer program650may also be embodied in a carrier such as an electronic signal, optical signal, radio signal, or computer readable storage medium.

The techniques as herein described avoid unnecessary switching between waveforms, which can degrade performance due to RRC reconfiguration. Additionally, techniques have been described to reduce the time delay for waveform switching using multiple BWPs configured to use different waveforms. Thus, the time delay to switch waveforms is reduced from about 30-40 msec to about 2 msec. Though described in the context of NR networks, the techniques can be adapted for other standards.

Additional information may be found in Appendix A, which is incorporated in its entirety by reference.