Patent Publication Number: US-2020281012-A1

Title: Fast Transmission of Scheduling Request

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to uplink transmission in a wireless communication network and, more particularly, to the transmission of scheduling requests for uplink transmissions. 
     BACKGROUND 
     New radio (NR) standard under development by the Third Generation Partnership Project 3GPP is being designed to provide service for multiple use cases, such as Enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communication (URLLC), and Machine Type Communication (MTC). Each of these services has different technical requirements. For example, the general requirement for eMBB is high data rate with moderate latency and moderate coverage, while URLLC service requires a low latency and high reliability transmission with moderate data rates. 
     One of the solutions for providing low latency data transmission is shorter transmission time intervals. In NR, in addition to transmission in a slot, a mini-slot transmission is also allowed to reduce latency. A mini-slot may consist of any number of 1 to 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols. It should be noted that the concepts of slot and mini-slot are not specific to a specific service meaning that a mini-slot may be used for either eMBB, URLLC, or other services. 
     Assume a scenario where a user equipment (UE) that is transmitting data in the uplink (UL) in a slot basis (e.g., eMBB data) on the Physical Uplink Shared Channel (PUSCH), and in the middle of slot-based PUSCH transmission some low latency data (e.g., URLLC data) arrives in the UE buffer and has to be sent with very short latency. In this case, the UE needs to send a scheduling request (SR) to obtain a scheduling grant for the low latency data. 
     When the resources for an ongoing slot-based PUSCH and a new mini-slot based SR are colliding, the information in one or potentially both channels are lost. 
     SUMMARY 
     The present disclosure describes methods and apparatus to handle a scheduling request for data with low latency requirements that is triggered during a slot-based PUSCH transmission. The summary of proposed solutions are as follows:
         If the SR periodicity is below a certain threshold, which means that the UE can send it within acceptable delay, then the UE does not interrupt PUSCH transmission and sends SR in the next available SR occasion. On the other hand, if the SR periodicity is above that threshold, then the UE preempts the ongoing PUSCH transmission and send SR right away.   The threshold may be fixed or semi-statically configurable by the network.   If the SR corresponds to certain logical channels, the UE preempts PUSCH to send SR. Otherwise it should wait until the ongoing PUSCH transmission is over and send SR after.   Higher-layer signaling configures whether preemption is allowed or not.       

     One aspect of the disclosure comprise methods of fast SR transmissions implemented by a UE. In one embodiment, the method comprises determining, responsive to the arrival of new transmit data for transmission on an uplink shared channel, that a scheduling request to request uplink resources for transmission of the new transmit data will overlap a scheduled data transmission; preempting the scheduled data transmission to transmit the scheduling request; and transmitting the scheduling request to request uplink resources for the new transmit data. 
     Another aspect of the disclosure comprises a UE configured for fast SR transmissions. The UE is configured to determine, responsive to the arrival of new transmit data for transmission on an uplink shared channel, that a scheduling request to request uplink resources for transmission of the new transmit data will overlap a scheduled data transmission preempt the scheduled data transmission to transmit the scheduling request; and transmit the scheduling request to request uplink resources for the new transmit data. 
     Another aspect of the disclosure comprises a UE comprising an interface circuit for configured for communicating over a wireless communication channel with a base station and a processing circuit configured to implement fast SR transmission. The processing circuit configured to determine, responsive to the arrival of new transmit data for transmission on an uplink shared channel, that a scheduling request to request uplink resources for transmission of the new transmit data will overlap a scheduled data transmission; preempt the scheduled data transmission to transmit the scheduling request; and transmit the scheduling request to request uplink resources for the new transmit data. 
     Another aspect of the disclosure comprises a computer program product containing executable instructions that, when executed by a processing circuit in a user equipment in a wireless communication network, causes the user equipment to determine, responsive to the arrival of new transmit data for transmission on an uplink shared channel, that a scheduling request to request uplink resources for transmission of the new transmit data will overlap a scheduled data transmission preempt the scheduled data transmission to transmit the scheduling request; and transmit the scheduling request to request uplink resources for the new transmit data. In one embodiment, the computer program product is embodied in a non-transitory computer-readable medium. In other embodiments, the computer program product is embodied in a carrier, such as an electronic signal, optical signal, radio signal, or computer readable storage medium. 
     Another aspect of the disclosure comprises methods of fast SR transmissions implemented by a base station. In one embodiment, the method comprises receiving, from the user equipment ( 30 ,  200 ), a data transmission on an uplink shared channel; and blindly detecting a pre-emptive scheduling request from the user equipment ( 30 ,  200 ) on resources allocated for the data transmission. 
     Another aspect of the disclosure comprises a base station configured for fast SR transmissions. The base station is configured to receive, from the user equipment ( 30 ,  200 ), a data transmission on an uplink shared channel; and blindly detect a pre-emptive scheduling request from the user equipment ( 30 ,  200 ) on resources allocated for the data transmission. 
     Another aspect of the disclosure comprises a base station comprising an interface circuit configured for communicating over a wireless communication channel with a user equipment and a processing circuit configured to implement fast SR transmission. More particularly, the processing circuit is configured to receive, from the user equipment ( 30 ,  200 ), a data transmission on an uplink shared channel; and blindly detect a pre-emptive scheduling request from the user equipment ( 30 ,  200 ) on resources allocated for the data transmission. 
     Another aspect of the disclosure comprises a computer program product containing executable instructions that, when executed by a processing circuit in a base station in a wireless communication network, causes the base station to receive, from the user equipment ( 30 ,  200 ), a data transmission on an uplink shared channel; and blindly detect a pre-emptive scheduling request from the user equipment ( 30 ,  200 ) on resources allocated for the data transmission. In one embodiment, the computer program product is embodied in a non-transitory computer-readable medium. In other embodiments, the computer program product is embodied in a carrier, such as an electronic signal, optical signal, radio signal, or computer readable storage medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates communications between a base station and a UE in a wireless communication network. 
         FIG. 2  illustrates radio resources used for communications between a base station and a UE in a wireless communication network. 
         FIG. 3  illustrates SR transmission. 
         FIG. 4  illustrates an exemplary method of scheduling request transmission implemented by a UE. 
         FIGS. 5A and 5B  illustrate another exemplary method of scheduling request transmission implemented by a UE. 
         FIG. 6  illustrates an example UE configured according to embodiments of the present disclosure. 
         FIG. 7  illustrates an exemplary method of scheduling request transmission implemented by a base station. 
         FIG. 8  illustrates an example base station configured according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, an exemplary embodiment of the present disclosure will be described in the context of Fifth Generation (5G) and Next Radio (NR) communication network configured for eMBB communications, URLLC, and MTC. Those skilled in the art will appreciate that the techniques described herein are more generally applicable to any wireless communication network in which the UE performs radio link monitoring. The preemption techniques herein described can be easily adapted by those skilled in the art for use in communication networks based on other radio access technologies (RATs), such as Long Term Evolution (LTE) networks, Wideband Code Division Multiple Access (WCDMA) networks, Code Division Multiple Access (CDMA)  2000  networks, Wireless Fidelity (WiFi) networks, Worldwide Interoperability for Microwave Access (WiMAX) networks, Wireless Local Area Networks (LANs) (WLANs), Narrowband Internet of Things (NB-IoT) networks, or other wireless communication networks using shared uplink channels. 
       FIG. 1  illustrates communications between a base station  20  and a UE  30  in a wireless communication network  10 . The base station  20  is commonly referred to in applicable standards as a Node B (NB), Evolved Node B (eNB) or 5G Node B (gNB). The UE  30  comprises any type of wireless device that communicates over a wireless channel with the base station  20 . For example, the UE  30  may comprise a cellular telephone, smart phone, laptop computer, tablet, MTC device, or other device capable of communicating over the wireless channel with the base station  20 . 
     The base station  20  transmits control information to the UE  30  on the Physical Downlink Control Channel (PDCCH), and user data to the UE  30  on the Physical Downlink Shared Channel (PDSCH). The UE  30  transmits control information to the base station  20  on the Physical Uplink Control Channel (PUCCH), and user data to the base station  20  on the PUSCH. The base station  20  is responsible for scheduling UL transmissions from the UE  30  and for allocating resources for the UL transmissions. After scheduling an UL transmission and allocating resources, the base station  20  sends a scheduling grant (SG) to the UE  30  indicating the resources on which the UE  30  has been scheduled and the transmission format for the scheduled transmission. The uplink grant is sent to the UE  30  on the PDCCH. After receiving the uplink, the UE  30  determines the UL transmit power for the transmission and transmits data to the base station  20  on the PUSCH resources indicated in the SG. 
     The available radio resources for uplink transmissions can be viewed as a time-frequency grid  50  as shown in  FIG. 2 . In the time domain, the physical resources are divided into subframes. Each subframe includes a number of symbols (e.g., OFDM symbols for the downlink and SC-FDMA symbols for the uplink). For a normal Cyclic Prefix (CP) length, suitable for use in situations where multipath dispersion is not expected to be extremely severe, a subframe comprises fourteen symbols. A subframe comprises twelve symbols if an extended CP is used. In the frequency domain, the physical resources are divided into adjacent subcarriers with a spacing of 15 kHz. The number of subcarriers varies according to the allocated system bandwidth. A subframe typically comprises two time slots, which may be further subdivided into mini-slots. A mini-slot comprises one or more symbol periods in a time slot. The smallest element of the time-frequency grid  50  is a Resource Element (RE)  52 . 
       FIG. 3  illustrates uplink scheduling in 5G and NR networks. The UE  30  is allocated resources for sending SRs to the base station  20 . The SRs may be sent at a predetermined time interval referred to as the SR interval. The SR interval may, for example, comprise a predetermined number of subframes, time slots, or mini-slots. When data that needs to be transmitted arrives at the transmit buffer of the UE  30 , the UE  30  sends a SR to the base station  20  on the PUCCH to request resources for an uplink transmission on the PUSCH. In response to the SR, the base station  20  sends a SG to the UE  30  on the PDCCH. The SG indicates the PUSCH resources for the uplink transmission and the transport format for the data transmission. The UE  30  transmits the data on the allocated uplink resources. 
     In 5G and NR communication networks  10 , the UE  30  may be allocated different SR resources for different services or groups of services. For example, the UE  30  may be allocated a first set of SR resources for eMBB services and a second set of resources for URLLC services. The SR intervals for the first and second sets of SR resources may be different. For example, services requiring lower latency (e.g., URLLC services) may have a shorter SR interval than services with less stringent latency requirements. 
     In some instances, data for transmission to the base station  20  may arrive at the transmit buffer while lower priority data is being transmitted. In this case, the UE  30  needs to send a SR to the base station  20  to request resources for transmitting the higher priority data. Conventionally, the UE  30  transmits the SR at the next available opportunity. However, the next available opportunity may occur while a previously scheduled transmission is ongoing. Depending on Quality of Services (QoS) requirements, the UE  30  may not be able to wait for the competition of the scheduled transmission to send the SR. 
     In exemplary embodiments of the disclosure, a SR mechanism is provided to preempt a scheduled data transmission in order to send a SR. Preemption in this context can refer to at least two possible transmission scenarios that can potentially impact an on-going data transmission negatively. In a first scenario, the radio resources for transmitting the SR and the on-going UL transmission overlap in time domain but do not overlap in frequency domain. In this scenario, the UE  30  may continue the ongoing UL transmission while simultaneously transmitting the SR. However, given limited UE transmission power, the UE  30  may need to reduce the transmission power for the on-going UL transmission in order to have enough power for reliable SR transmission. For example, if the ongoing UL transmission is a PUSCH transmission, for lower order modulations, the power reduction can cause PUSCH transmission performance degradation. In addition, if the UE power amplifier phase changes, an earlier obtained channel estimate may no longer be valid making demodulation difficult/impossible. For higher order modulations, this power reduction can cause the magnitude reference for the demodulator to misalign and result in erroneous demodulation of all REs in the impacted OFDM symbol. As described above, phase changes may also occur that may cause several PUSCH transmission failures. In a second scenario, the radio resources for transmitting the SR and the on-going UL transmission overlap in both time and frequency domain. In this scenario, the preempting SR transmission will take away radio resources as well as power from the on-going UL transmission. The second scenario is more likely to cause failure of the on-going UL transmission than the first scenario. 
     Preemption Based on Priority 
     According to one aspect of the disclosure, whether the UE  30  preempts an ongoing PUSCH transmission to send SR depends on some measure of the priority of the service. As an example, if the SR corresponds to certain logical channels with high priority, the UE  30  preempts PUSCH to send SR, and otherwise waits until the ongoing PUSCH transmission is over and send SR after. The UE  30  typically does that if the SR request has a higher priority than PUSCH priority. The priority of SR may also depend on certain transmission profiles. 
     In one embodiment, the SR preemption of a PUSCH transmission would depend on the content of the PUSCH transmission. If the PUSCH transmission contains traffic of equal or higher priority of that of the SR, the SR does not preempt the PUSCH while if the PUSCH transmission contains lower priority traffic the SR can preempt the PUSCH transmission. 
     In one exemplary embodiment, a UE  30  can be configured with a first SR configuration corresponding to a first set of SR resources and a second SR configuration corresponding to a second set of SR resources. The first SR configuration is associated with at least a first logical channel or first group of logical channels, and the second SR configuration is associated with at least a second logical channel or group of logical channels. The second logical channel (or logical channel group) has higher priority than the first logical channel (or logical channel group). The first and/or second sets of SR resources may comprise PUCCH resources (e.g., short PUCCH resources) that occur periodically. 
     When a SR corresponding to the first logical channel is triggered (e.g., when the UE  30  determines that it has UL data that it needs to transmit and the data is mapped to first logical channel), the UE  30  determines a SR resource from the first set of SR resources such that a SR transmission by the UE  30  on that SR resource does not overlap in time with another ongoing UL transmission by the same UE  30 , and transmits a SR on that SR resource. When a SR corresponding to the second logical channel is triggered (e.g., when the UE  30  determines that it has UL data that it needs to transmit and the data is mapped to second logical channel), the UE  30  determines an earliest available SR resource from the second set of SR resources, and transmits SR on that SR resource. If the UE  30  has an ongoing UL transmission that overlaps in time with the earliest available SR resource, the UE  30  transmits the SR on that SR resource by preempting the ongoing UL transmission. 
     The earliest available SR resource may be determined in a number of different ways. For example, the earliest available SR resource may comprise:
         the earliest SR resource from the second set of SR resources after the SR corresponding to the second logical channel is triggered; or   the earliest SR resource from the second set of SR resources after the SR corresponding to the second logical channel is triggered, such that it does not overlap (either in time or time and frequency) with an ongoing PUCCH transmission (e.g., long PUCCH transmission) by the same UE  30 ; or   the earliest SR resource from the second set of SR resources after the SR corresponding to the second logical channel is triggered, such that it does not overlap with a OFDM symbol reserved for Demodulation Reference Signal (DMRS) transmission corresponding to an ongoing PUSCH transmission by the same UE  30 ; or   the earliest SR resource from the second set of SR resources after the SR corresponding to the second logical channel is triggered, such that it does not overlap with an ongoing PUSCH transmission by the same UE  30 , where the PUSCH transmission carries data mapped to a logical channel with equal or higher priority than the priority of the second logical channel.       

     The earliest available SR resource can be determined by any one or more of the above criteria. 
     When a SR is triggered for the UE  30  at time T 0  (e.g., corresponding to the first logical channel or the second logical channel), and if the first available SR resource (e.g., corresponding to the first SR configuration or the second SR configuration respectively as discussed above) after time T 0 +T_proc, overlaps with a new PUSCH transmission (i.e., the PUSCH transmission starts after time T 0 +T_proc), the UE  30  can transmit a new Buffer Status Report (BSR) in the new PUSCH transmission and reset the SR trigger. Here, T_proc is a processing delay allowance given to the UE  30 . The processing delay T_proc can be equal to the minimum allowed delay between reception of UL grant and corresponding PUSCH transmission). 
     Preemption Based on Periodicity of the SR Interval 
     According to one aspect of the disclosure, the UE  30  may preempt an ongoing PUSCH transmission to send a high priority SR or wait until the next occasion for SR transmission depending on SR periodicity. For example, if the SR periodicity is below a certain threshold, i.e., there are frequent SR opportunities so that the UE  30  can send the SR within acceptable delay, the UE  30  does not interrupt the PUSCH transmission and sends SR in the next available SR occasion. On the other hand, if the SR periodicity is above that threshold, i.e., very infrequent, the UE  30  preempts the ongoing PUSCH transmission and sends the SR at the earliest opportunity. In one embodiment, the threshold can be scaled according to the remaining transmission duration of the PUSCH when the SR is triggered. 
     In another embodiment, preemption may depend on the remaining duration of the ongoing PUSCH transmission. If the remaining time is large, e.g., scheduled by a slot-aggregation transmission, then it could correspond to a long waiting time for the next SR and preemption should be triggered. If the remaining time is small, then the next SR opportunity can be close, and a preemption should not be triggered. This also has the advantage of not destroying an already received majority part of the transport block. 
     In one embodiment, the UE  30  uses the periodicity of the SR interval and the remaining duration of the ongoing PUSCH transmission in combination to determine preemption. For example, if the SR periodicity is below a certain threshold and the remaining duration of the ongoing PUSCH transmission is short so that the UE  30  can send the SR within acceptable delay, the UE  30  does not interrupt the PUSCH transmission and sends SR in the next available SR occasion after the ongoing PUSCH transmission is complete. On the other hand, if the SR periodicity is below a certain threshold but the remaining duration of the ongoing PUSCH transmission is long so that the UE  30  cannot send the SR within acceptable delay, the UE  30  interrupts the PUSCH transmission and sends SR in the next available SR occasion after the ongoing PUSCH transmission is complete. 
     In one embodiment, frequent SR opportunities is interpreted by the UE  30  as an indication of stringent latency requirements and the UE  30  preempts ongoing PUSCH transmissions when the periodicity is less than the threshold (the opposite of the previous example). In this case, infrequent SR opportunities (an interval greater than the threshold) would indicate a delay-tolerant traffic and no need to preempt an ongoing PUSCH transmission. 
     In the embodiments described above, the threshold for SR periodicity above which the ongoing PUSCH preempted may be fixed or semi-statically configurable by the network  10 . Similarly, the time limit for the remaining duration may be fixed or semi-statically configurable by the network  10 . 
     In one embodiment the UE  30  is configured with a periodic SR opportunity with periodicity T_SR and a maximum allowable delay T_max until when an SR must be sent after it has been triggered at time t_ 0 . The SR opportunities occur at T_SR+nT_SR. When no other transmission is ongoing, the UE  30  can use the next SR resource at time T_SR+n′T_SR&gt;t_ 0  after the SR has been triggered. If another transmission is ongoing at the next SR opportunity, T_SR+n′T_SR, the UE  30  uses the next SR opportunity at T_SR+n′T_SR only if: 
     1) T_SR+(n′+1)T_SR&gt;t_ 0 +T_max (i.e., the next opportunity comes too late); and 
     2) the already ongoing data transmission is of lower priority than the SR trigger reason. 
     Otherwise, the UE  30  postpones the SR until the next SR opportunity at T_SR+(n′+1) T_SR. At SR opportunity T_SR+(n′+1)T_SR, the UE  30  applies the same procedure, i.e., it transmits the SR if there is no ongoing data transmission or the next SR opportunity, T_SR+(n′+2)T_SR&gt;T_SR+T_max, is too late and the ongoing data transmission is of lower priority. If a UE  30  postpones its SR transmission, the UE  30  can also send a buffer status report if it is scheduled on PUSCH after SR has been triggered. In this case, the UE  30  does not need to transmit an SR. 
     Static Configuration of Preemption 
     In another embodiment, semi-static signaling may be used to indicate whether the UE  30  is allowed to preempt an ongoing PUSCH transmission to transmit an SR. If allowed, an SR can in such a case always preempt an ongoing PUSCH transmission. Further the UE  30  may also be configured so that an SR of a short time duration can preempt an ongoing PUCCH transmission. This configuration maybe a separate configuration than the PUSCH configuration. 
     SR Configurations 
     Another aspect of the disclosure relates to SR configuration including supported periodicity values for SR and related signaling. Multiple SR configurations can be supported. Also, periodicity values as short as 1 OFDM can be supported. SR configuration can be configured by Radio Resource Control (RRC) signaling or other higher layer signaling. 
     For SR configured on long-PUCCH, in addition to the periodicities supported for LTE, some additional periodicities depending on slot duration for higher SCS cases can be supported as shown in Table 1 below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Supported long-PUCCH based SR periodicities for NR 
               
            
           
           
               
               
               
            
               
                   
                 Subcarrier 
                   
               
               
                   
                 spacing 
                 Supported SR periodicity 
               
               
                   
                 (kHz) 
                 (ms) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 15 
                 1, 2, 5, 10, 20, 40, 80 
               
               
                   
                 30 
                 0.5, 1, 2, 5, 10, 20, 40, 80 
               
               
                   
                 60 
                 0.25, 0.5, 1, 2, 5, 10, 20, 40, 80 
               
               
                   
                 120 
                 0.125, 0.25, 0.5, 1, 2, 5, 10, 20, 40, 80 
               
               
                   
                 240 
                 0.0625, 0.125, 0.25, 0.5, 1, 2, 5, 10, 20, 40, 80 
               
               
                   
                 480 
                 0.0625, 0.125, 0.25, 0.5, 1, 2, 5, 10, 20, 40, 80 
               
               
                   
                   
               
            
           
         
       
     
     Configuration of long-PUCCH based SR resources can follow the same approach as LTE, i.e., a SR periodicity and offset is mapped to a SR resource index signaled by higher layers (e.g., RRC signaling) to identify the slots for SR transmission. In addition, the PUCCH resource to be used for SR transmission can be configured by higher layers. For larger sub-carrier spacing (SCS), it may be enough to support SR offsets with coarser granularity than slot duration, especially for SR periodicities spanning multiple milliseconds, e.g., for 120 kHz SCS case. For SR periodicity of 10 ms, it may be sufficient to support offsets with 0.5 ms granularity instead of supporting every possible offset with 0.125 ms granularity. 
     For short-PUCCH based SR, in addition to identifying the slots containing SR resources, additional signaling can be used to identify the OFDM symbols within the slot that are configured as SR resources. To achieve this a bitmap with length same as the number of OFDM symbols per slot (i.e., 14 bits) can be used. This bitmap would enable most generic signaling to cover all possible cases. For example, for 30 kHz FDD, a UE can be configured with 2 short-PUCCH based SR configurations, one for regular traffic with 5 ms slot periodicity and last OFDM symbol in each slot (indicated by 00000000000001 in the bitmap) and another for latency sensitive traffic with 0.5 ms slot periodicity and all OFDM symbols in the slot (indicated by 11111111111111 in the bitmap). 
     As an example, SR resources can be configured as follows in an embodiment.
         For long-PUCCH based SR, higher layers configure the following:
           A SR configuration index (that corresponds to a SR periodicity and slot offset) which identifies the slots to be used for SR transmission.   A long-PUCCH resource index which identifies the long PUCCH resource to use for SR transmission within the identified slots.   
           For short-PUCCH based SR, higher layers configure the following:
           A SR configuration index (that corresponds to a SR periodicity and slot offset) which identifies the slots to be used for SR transmission.   A 14 bit bitmap (i.e., slot length) that identifies OFDM symbol(s) to be used for SR transmission within the slots identified by the SR configuration index   A short-PUCCH resource index which identifies the short-PUCCH resource to use for SR transmission within the identified OFDM symbols.   
           For SR periodicity, in addition to the periodicities supported for LTE, additional more frequent periodicities can be supported for higher SCS cases.
           For higher SCS, only a subset of SR offsets with coarser granularity than slot duration should be supported especially for SR periodicities spanning multiple milliseconds.   
               

     Another aspect to consider arises in cases where a short-PUCCH based SR is triggered but the UE has an ongoing long-PUCCH/PUSCH transmission and an SR resource is available for UE before the end of ongoing transmission. For such cases, UE should transmit SR in the first available SR resource without an ongoing transmission. If the UE has PUSCH immediately scheduled after the ongoing transmission, it can send a BSR on the PUSCH. 
     Base Station Processing 
     When there is on ongoing PUSCH transmission in a slot where a SR transmission opportunity for the UE exists, and SR pre-emption is allowed, the base station performs blind detection of the SR. In one embodiment, the base station  20  performs blind SR detection before processing the received PUSCH. In another embodiment, blind detection is performed while receiving the PUSCH transmission. In this case, the PUSCH is reprocessed responsive to the detection of an SR. 
     According to some embodiments, the base station performs blind detection by correlating the signal received on REs corresponding to a SR transmission opportunity and comparing the correlation result to a threshold to determine whether an SR is present. 
     According to another embodiment, the base station  20  performs blind detection by decoding the signal received on the REs corresponding to a SR transmission opportunity and performs error detection (e.g., CRC check) on the decoded signal to determine whether an SR is present. 
     In a further embodiment, after an SR is detected, the BS sets the symbols of the received data transmission corresponding to the REs on which the SR was received to zero such that these received REs do not affect the decoding and reception of the PUSCH. 
     Example Methods of Preemption 
     When UE  30  determines a need to preempt the on-going PUSCH transmission, several enhanced preemption methods may be used as described below. 
     When it is necessary to reduce transmission power for the on-going PUSCH transmission to accommodate the SR transmission, the UE  30  may reduce a number of transmitted PUSCH REs such that the remaining transmitted PUSCH REs retain the same transmission power per RE as that for PUSCH REs in the other OFDM symbols not impacted by preemption. As one non-limiting example, assume that the PUSCH transmission has 1200 REs in one OFDM symbol. If it is determined that a 10% power reduction is needed to transmit the SR, rather than reduce the transmit power in all REs, the UE  30  may transmit in fewer REs while maintaining the power per RE. In this example, the UE  30  reduces the number of REs for the ongoing data transmission to 1080 (1200×0.9=1080 REs), which it transmits with the same power per RE instead of transmitting 1200 REs with 90% power per RE. 
     Since channel coded bits may be transmitted in sequence in the frequency domain, The PUSCH REs to be removed from transmission can be spread out in frequency domain to avoid localized removal of PUSCH. Continuing with the previous non-limiting example, 120 REs need to be removed from the PUSCH transmission. Instead of removing RE #0, #1, . . . , #119, the REs to be removed are spread across the frequency domain by removing every 10th RE (e.g., RE #0, #10, #20, . . . , #1190). The REs do not need to be equally spaced in the frequency domain. The main point is to spread out the removed REs in the frequency domain. 
     When the radio resources of the SR and the PUSCH overlap, part of the removed REs can be used by the UE  30  to transmit the SR with the remaining removed REs spread over the non-overlapping part of the PUSCH. Continuing with the previous non-limiting example, assume that 120 REs need to be removed from the PUSCH transmission and the SR transmission overlaps with the PUSCH in the first 12 REs. That is, SR will be transmitted in REs #0, #1, . . . , #11. In this example, the remaining 120−12=108 REs are spread over 1200-12=1188 PUSCH REs not used for transmitting the SR. Thus, the UE  30  removes, for example, REs #22, #33, . . . , #1177. Other specific locations are possible since the main point is to spread out the removed REs in the portion of the frequency domain not overlapping with the SR transmission. 
       FIG. 4  illustrates an exemplary method  100  implemented by a UE  30  according to one embodiment. The method  100  begins when new transmit data arrives in the transmit buffer of the UE  30  that needs to be transmitted (block  105 ). For example, the new transmit data may comprises data for transmission on the PUSCH or other shared uplink channel. Responsive to the arrival of new transmit data for transmission on an uplink shared channel, the UE  30  determines that a scheduling request to request uplink resources for transmission of the new transmit data will overlap a scheduled data transmission (block  110 ). The scheduled data transmission may comprise a PUSCH transmission. Once it is determined that the transmission of the SR will overlap the scheduled data transmission (e.g., PUSCH transmission), the UE  30  preempts the scheduled data transmission to transmit the SR (block  115 ), and transmits the scheduling request to request uplink resources for the new transmit data (block  120 ). The transmission of the SR may use some of the resources allocated for the scheduled data transmission (i.e., preempted resources) that have been freed up by preempting the scheduled data transmission. 
     In some embodiments of the method  100 , the UE  30  may also preempt the scheduled data transmission to transmit the new transmit data (blocks  125  and  130 ). For example, the UE  30  may preempt a scheduled data transmission on the PUSCH of relatively lower priority data to transmit new transmit data of higher priority on the PUSCH. 
     In some embodiments of the method  100 , preemption of the scheduled transmission may optionally be conditioned on one or more predetermined criteria. In this case, the UE  30  determines that the one or more predetermined criteria are met before preempting the scheduled transmission. In one embodiment, the UE  30  preempts the scheduled data transmission responsive to determining that the new transmit data has higher priority than the scheduled uplink transmission. In another embodiment, the UE  30  preempts the scheduled data transmission responsive to determining that a periodicity of a SR interval meets a threshold requirement. In another embodiment, the UE  30  preempts the scheduled data transmission responsive to determining that a remaining duration of the scheduled transmission is less than a predetermined time limit. In another embodiment, the UE  30  preempts the scheduled data transmission responsive to determining that a periodicity of the SR interval is less than a threshold, and a remaining duration of the scheduled transmission is less than a predetermined time limit. In another embodiment, the UE  30  preempts the scheduled data transmission responsive to determining, based on configuration data, that preemption is allowed. 
     In one embodiment of the method  100 , the UE  30  preempts the scheduled data transmission depending on a priority of the new transmit data. For example, the UE  30  may preempt the scheduled data transmission responsive to determining that the new transmit data has higher priority than the scheduled uplink transmission. 
     In one embodiment of the method  100 , the UE  30  preempts the scheduled data transmission depending on a periodicity of a SR interval. For example, the UE  30  may preempt the scheduled data transmission responsive to determining that the periodicity of the SR interval meets a threshold requirement. As another example, the UE  30  may preempt the scheduled data transmission responsive to determining that the periodicity of the SR interval is less than a first threshold, and a remaining duration of the scheduled transmission is less than a predetermined time limit. 
     In some embodiments of the method  100 , preempting the scheduled data transmission to transmit the SR comprises reducing the transmit power allocated for the scheduled transmission. In order to reduce the transmit power for the scheduled data transmission, the UE  30  may reduce a number of resource elements allocated for the scheduled transmission while maintaining a power per resource element for the scheduled transmission. In this case, the UE  30  may use the preempted resource elements no longer being used for the scheduled uplink transmission. 
     In some embodiments of the method  100 , preempting the scheduled data transmission to transmit the scheduling request comprises reducing a number of resource elements allocated for the scheduled transmission. In this case, the UE  30  may use the preempted resource elements no longer being used for the scheduled uplink transmission. 
       FIGS. 5A and 5B  illustrate another exemplary method  150  where preemption of a scheduled transmission is conditioned on one or more predetermined criteria being met. The method  150  begins when new transmit data arrives in the transmit buffer of the UE  30  that needs to be transmitted (block  155 ). For example, the new transmit data may comprises data for transmission on the PUSCH or other shared uplink channel. Responsive to the arrival of new transmit data for transmission on an uplink shared channel, the UE  30  determines that a scheduling request to request uplink resources for transmission of the new transmit data will overlap a scheduled data transmission (block  160 ). The scheduled data transmission may comprise a PUSCH transmission. Once it is determined that the transmission of the SR will overlap the scheduled data transmission (e.g., PUSCH transmission), the UE  30  determines whether one or more predetermined criteria are met (block  165 ). The predetermined criteria may be based on one or more of the following: priority of the new transmit data, length of the SR interval, remaining duration of the scheduled data transmission, and a predetermined SR configuration. If the UE determines that the predetermined criteria is met (block  170 ), the UE  30  preempts the scheduled data transmission to transmit the SR (block  175 ), and transmits the scheduling request to request uplink resources for the new transmit data (block  180 ). The transmission of the SR may use some of the resources allocated for the scheduled data transmission (i.e., preempted resources) that were freed up by the preemption. If the predetermined criteria are not met, the UE  30  waits for the completion of the scheduled data transmission (block  185 ) and transmits the SR after the competition of the scheduled data transmission (block  190 ). 
     In some embodiments of method  150 , the UE  30  preempts the scheduled data transmission responsive to determining that the new transmit data has higher priority than the scheduled uplink transmission. 
     In another embodiment of method  150 , the UE  30  preempts the scheduled data transmission responsive to determining that a periodicity of a SR interval meets a threshold requirement. 
     In another embodiment of method  150 , the UE  30  preempts the scheduled data transmission responsive to determining that a remaining duration of the scheduled transmission is less than a predetermined time limit. 
     In another embodiment of method  150 , the UE  30  preempts the scheduled data transmission responsive to determining that a periodicity of the SR interval is less than a threshold, and a remaining duration of the scheduled transmission is less than a predetermined time limit. 
     In another embodiment of method  150 , the UE  30  preempts the scheduled data transmission responsive to determining, based on configuration data, that preemption is allowed. 
     In some embodiments of the method  150 , preempting the scheduled data transmission to transmit the SR comprises reducing the transmit power allocated for the scheduled transmission. In order to reduce the transmit power for the scheduled data transmission, the UE  30  may reduce a number of resource elements allocated for the scheduled transmission while maintaining a power per resource element for the scheduled transmission. In this case, the UE  30  may use the preempted resource elements no longer being used for the scheduled uplink transmission. 
     In some embodiments of the method  150 , preempting the scheduled data transmission to transmit the scheduling request comprises reducing a number of resource elements allocated for the scheduled transmission. In this case, the UE  30  may use the preempted resource elements no longer being used for the scheduled uplink transmission. 
       FIG. 6  illustrates an embodiment of a UE  200  configured to implement the fast SR transmission methods described above. The UE  200  comprises an interface circuit  210 , a processing circuit  230 , and memory  250 . 
     The interface circuit  210  is coupled to one or more antennas or antenna elements  220 . The interface circuit  210  includes the Radio Frequency (RF) components needed for communicating with the base station  20  over a wireless communication channel. Typically, the RF components includes transmit circuitry and receive circuitry adapted for communications according to the 5G and/or NR standards or other RAT. 
     The processing circuit  230  processes the signals transmitted to or received by the UE  200 . Such processing includes coding and modulation of transmitted signals, and the demodulation and decoding of received signals. The processing circuit  230  includes a conflict determining unit  235  for determining whether a SR triggered by the arrival of new transmit data overlaps a scheduled data transmission, a preemption unit  240  for preempting the scheduled data transmission to transmit the SR, and a transmitting unit  245  for transmitting the SR. In some embodiments, the preemption unit  240  also determines whether predetermined criteria for preemption are met. The processing circuit  230  may comprise one or more microprocessors, hardware, firmware, or a combination thereof. In one embodiment, the synchronization unit  415  and random access unit  425  are implemented by a single microprocessor. In other embodiments, the synchronization unit  415  and random access unit  425  are implemented using different microprocessors. 
     Memory  250  comprises both volatile and non-volatile memory for storing computer program code and data needed by the processing circuit  230  for operation. Memory  250  may comprise any tangible, non-transitory computer-readable storage medium for storing data including electronic, magnetic, optical, electromagnetic, or semiconductor data storage. Memory  250  stores a computer program  255  comprising executable instructions that configure the processing circuit  230  to implement methods  100  according to  FIG. 4  as described herein. In general, computer program instructions and configuration information are stored in a non-volatile memory, such as a read only memory (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 program  255  for configuring the processing circuit  230  as 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 program  255  may also be embodied in a carrier such as an electronic signal, optical signal, radio signal, or computer readable storage medium. 
       FIG. 7  illustrates an exemplary method  300  implemented by a base station  20  according to one embodiment. The base station  20  optionally schedules a data transmission from a UE  30  on an uplink shared channel (block  310 ). The scheduling includes the allocation of time/frequency resources for the data transmission. The allocated resources may encompass a SR transmission opportunity. The base station  20  subsequently receives a data transmission from the UE  30  on the uplink shared channel (block  320 ). Where the allocated resources encompass a SR transmission opportunity, the UE  30  may pre-empt the data transmission to transmit a SR on one or more resources allocated for the data transmission. When the UE  30  pre-empts the data transmission to transmit a SR, the base station  20  blindly detects the pre-emptive SR on the resources allocated for the data transmission (block  330 ). 
     In some embodiments of the method  300 , the base station  20  decodes the pre-empted data transmission based on the detection of the SR (block  340 ). As one example, the base station  20  sets symbols corresponding to resources on which the pre-emptive SR was received to zero. Setting the symbols to zero reduces the impact of the symbols corresponding to the SR on the decoding of the data transmission. 
     In some embodiments of the method  300 , the base station  20  detects the SR prior to decoding the data transmission on the PUSCH. 
     In some embodiments of the method  300 , the base station  20  blindly detects the pre-emptive scheduling request by correlating a received signal corresponding to a scheduling request transmission opportunity with a known signal (e.g. SR). 
     In other embodiments of the method  300 , the base station  20  blindly detects the pre-emptive scheduling request by decoding a received signal corresponding to a scheduling request transmission opportunity with a known signal and performing error detection on the decoded signal. 
     In other embodiments of the method  300 , the base station  20  transmits, responsive to the SR, an uplink grant to the UE  30  (block  350 ). 
       FIG. 8  illustrates an embodiment of a base station  400  configured to implement the fast SR transmission methods described above. The base station  400  comprises an interface circuit  410 , a processing circuit  430 , and memory  450 . 
     The interface circuit  410  is coupled to one or more antennas or antenna elements  420 . The interface circuit  410  includes the Radio Frequency (RF) components needed for communicating with the UE  30  over a wireless communication channel. Typically, the RF components includes transmit circuitry and receive circuitry adapted for communications according to the 5G and/or NR standards or other RAT. 
     The processing circuit  430  processes the signals transmitted to or received by the base station  400 . Such processing includes coding and modulation of transmitted signals, and the demodulation and decoding of received signals. The processing circuit  430  includes a receiving unit  435  for receiving a scheduled data transmission form a UE  20  on the PUSCH, and a detection unit  440  for blindly detecting a pre-emptive SR in the data transmission on resources allocated for the PUSCH data transmission. 
     Memory  450  comprises both volatile and non-volatile memory for storing computer program code and data needed by the processing circuit  430  for operation. Memory  450  may comprise any tangible, non-transitory computer-readable storage medium for storing data including electronic, magnetic, optical, electromagnetic, or semiconductor data storage. Memory  450  stores a computer program  455  comprising executable instructions that configure the processing circuit  430  to implement methods  300  according to  FIG. 7  as described herein. In general, computer program instructions and configuration information are stored in a non-volatile memory, such as a read only memory (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 program  455  for configuring the processing circuit  430  as 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 program  455  may also be embodied in a carrier such as an electronic signal, optical signal, radio signal, or computer readable storage medium.