Patent Publication Number: US-2023156498-A1

Title: Npdcch monitoring restrictions for nbiot-ntn systems

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present disclosure relates to 5th Generation (5G) New Radio (NR) non-terrestrial network (NTN) operation, and relates more particularly to monitoring the downlink control signal in Narrow-Band Internet-of-Things (NB-IoT) for NTN. 
     2. Description of the Related Art 
     NB-IoT physical downlink control channel (NPDCCH) is used to carry Downlink Control Information (DCI). Some examples of information contained in DCI include uplink (UL) grant information and downlink (DL) scheduling information. 
     In legacy (traditional) terrestrial networks (TNs), an example of which is illustrated in  FIG.  1   , the propagation delay between UE and enB/gNB (which can be alternatively referenced as a “base station”) is less than 1 msec, as the distance between a user equipment (UE) and eNB would be around 40 KM for the NBIOT case. For NTNs, the propagation delay between UE and eNB would be much larger than 1 msec, as the distance between UE and a GEO satellite and GEO satellite to eNB/gNB would be around 35786 Km. Therefore, in IoT NTN networks, because of the large propagation delays, the duration for which the UE does not need to monitor any DL signal in response to UL transmission needs to be updated compared to traditional terrestrial networks. 
     Therefore, there is a need to optimize and update the DL monitoring restriction for the UE in IoT NTN networks to improve UE performance. 
     SUMMARY OF THE DISCLOSURE 
     According to an example embodiment of the present disclosure, a method of optimizing the monitoring time window conditions or restrictions of NPDCCH for NBIOT-NTN is provided, which optimization enables UE to reduce power consumption by no longer requiring monitoring of NPDCCH for a dispensable duration. 
     According to an example embodiment of the present disclosure, the changes that need to be made for NPDCCH monitoring restriction are provided for the case where UE does not need to monitor incoming DL signal which is transmitted by the gNB/eNB in response to UL transmissions. 
     For an example scenario involving NB-IoT Physical Uplink Shared Channel (NPUSCH) with the same hybrid automatic repeat request (HARQ) process when 2 HARQs are configured, if an NB-IoT UE is configured with higher layer parameter twoHARQ-ProcessesConfig., and if the UE has an NPUSCH transmission ending in subframe n, then at least one of: 1) the UE is not required to receive transmissions in the Type B half-duplex guard periods for FDD; and 2) the UE is not expected to receive an NPDCCH with DCI format N0/N1 for the same HARQ process ID as the NPUSCH transmission in any subframe starting from subframe n+1−n TA   UE  to subframe n+3+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     For an example scenario relating to monitoring restrictions involving subframe after NPUSCH processing, if the UE is not using higher layer parameter edt-Parameters or if the UE is using higher layer parameter edt-Parameters and 0≤I MCS ≤2, (I MCS  is the modulation and coding scheme field read from the DCI), then: if the NB-IoT UE has a NPUSCH transmission ending in subframe n, the UE is not required to monitor NPDCCH in any subframe starting from subframe n+1−n TA   UE  to subframe n+3+K mac , where n TA   UE ceil(N TA,UE-specific ). 
     For an example scenario relates to monitoring restrictions involving subframe after NPUSCH carrying Message 3 (Msg3), if the NB-IoT UE has an NPUSCH transmission for Msg3 ending in subframe n′with transport block size TBS Msg3 , whereas if maximum transport block size TBS Msg3,max  for Msg3 would have been selected the NPUSCH transmission would have ended in subframe n, the UE is not required to monitor NPDCCH in any subframe starting from subframe n′+1−n TA   UE  to subframe n+3+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     For an example scenario relating to Narrowband Physical Random-Access Channel (NPRACH) for scheduling request (SR) involved in a long NPRACH transmission, for an NB-IoT UE configured with higher layer parameter sr-WithoutHARQ-ACK-Config, if the transmission of a narrowband random access preamble for SR ends on subframe n, then: in case of frame structure type 1 with NPRACH format 0 and 1 when the number of NPRACH repetitions is greater than or equal to 64, or NPRACH format 2 when the number of NPRACH repetitions is greater than or equal to 16, the UE is not required to monitor NPDCCH UE-specific search space from subframe n−n TA   UE  to subframe n+40+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     For an example scenario relating to Narrowband Physical Random-Access Channel (NPRACH) for scheduling request (SR) involved in a short NPRACH transmission, for an NB-IoT UE configured with higher layer parameter sr-WithoutHARQ-ACK-Config, unless the transmission of a narrowband random access preamble for SR ends on subframe n, the UE is not required to monitor NPDCCH UE-specific search space from subframe n−n TA   UE  to subframe n+3+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a diagram illustrating an example propagation delay between UE and eNB/gNB in a terrestrial network (TN). 
         FIG.  2    is a diagram illustrating an example propagation delay between UE and eNB/gNB in NTN. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    is a diagram illustrating an example legacy terrestrial network (TN), which includes UE  1001 , eNB/gNB  1002 , evolved packet core (EPC)  1003 , internet of things (IoT) platform  1004 , and application server  1005 . In the example legacy TN shown in  FIG.  1   , the propagation delay between UE  1001  and eNB/gNB  1002  is typically less than 1 msec (as the distance between UE and eNB would be around 40 KM for the typical NBIOT scenario). 
       FIG.  2    illustrates an example propagation delay between UE and eNB/gNB in NTN, which NTN includes a GEO satellite  2001  and an eNB/gNB  1002 . For the NTN shown in  FIG.  2   , the propagation delay between UE  1001  and eNB/gNB  1002  would be much larger than 1 msec, as the total distance starting from UE  1001  to a GEO satellite  2001 , then to eNB/gNB  1002  would be around 35786 Km, for example. Considering the long propagation delays in NTN, the existing NPDCCH monitoring restrictions need to be optimized and updated where UE is not required to monitor NPDCCH. 
     In connection with  FIG.  2   , some parameters relevant to the NTN delay will be explained here. Feeder-link delay, denoted as t f , refers to one-way over-the-air (OTA) delay between the eNB/gNB  1002  and the satellite  2001 . Service-link delay, denoted as t s , refers to one-way OTA delay between the satellite  2001  and UE  1001 . Timing advance, TA, is a UE offset between the start of a received downlink subframe and a transmitted uplink subframe, which offset at the UE is necessary to ensure that downlink and uplink subframes are synchronized with the eNB. T TA  denotes the time length of the TA. K offset , which is in the unit of subframes, refers to an integer which is signaled (e.g., by the eNB/gNB) to the UE and is used by the UE to delay transmission time of a UL transmission which is triggered by a DL reception at the UE so that the causality of the UE operation is guaranteed. K offset  should always satisfy the condition K offset ≥T TA /1 ms. K max  is an integer which is signaled (e.g., by the eNB/gNB) to the UE and is used by the UE to calculate RTT between the UE and the eNB/gNB. 
     In the following sections, the proposed changes for optimizing the NPDCCH monitoring restrictions are discussed for various scenarios. UE-specific TA will be used by UE in connected mode before UL transmission. n TA   UE  is the UE-specific TA in the unit of subframes, and n TA   UE =ceil(N TA,UE-specific ) in msec (any floating value will be converted to upper integer value, e.g., ceil(3.23)=4). The estimate of UE to eNB/gNB (base station) round trip time (RTT) is equal to the sum of UE&#39;s T TA  and K mac , where UE&#39;s T TA  is represented by the following formula: 
         T   TA =( N   TA,UE-specific   +N   TA,common   +N   TA,offset ) ×T   s    
     In the above formula, the various variables are defined as follows:
 
a) N TA  is timing offset between uplink and downlink radio frames at the UE, expressed in units of T s . N TA  works in the same way as legacy terrestrial networks. It is part of closed-loop uplink timing correction procedure. The amount of timing advance is being estimated by the eNB and the value is being communicated to UE in timing advance command.
 
b) N TA,UE-specific  is UE-self-estimated TA to pre-compensate for the service link delay between the UE and the satellite. It is computed by the UE based on satellite-ephemeris-related higher-layers parameters if configured, otherwise N TA,UE-specific =0.
 
c) N TA,common  is network-controlled (or network-specified) common TA, and may include any timing offset considered necessary by the network (e.g., feeder link delay). It is derived from the higher-layer parameters TACommon, TACommonDrift, and TACommonDriftVariation if configured, otherwise N TA,common =0. These parameters are given to the UE in SIB31-NB.
 
d) N TA, offset  is Fixed timing advance offset, expressed in units of T s . For frame structure type 1, N TA,offset =0.
 
e) T s  is basic unit of time expressed in millisecond (msec). Therefore, the granularity of T TA  is 1 T s , i.e., 1 msec.
 
     In the present disclosure, several example optimization changes (relative to existing configuration restrictions in Terrestrial Network) are provided, e.g., to 3GPP TS36.213 version 16.6, to accommodate the impact of UE-eNB RTT. 
     EXAMPLE SCENARIO A 
     This example scenario involves NB-IoT Physical Uplink Shared Channel (NPUSCH) with the same hybrid automatic repeat request (HARQ) process when 2 HARQs are configured. As a point of reference, the existing configuration restrictions (e.g., 3GPP TS36.213 version 16.6) in a Terrestrial Network (TN) provide that, if an NB-IoT UE is configured with higher layer parameter twoHARQ-ProcessesConfig., and if the UE has an NPUSCH transmission ending in subframe n, then: 1) the UE is not required to receive transmissions in the Type B half-duplex guard periods for frequency division duplex (FDD); and 2) the UE is not expected to receive an NB-IoT Physical Downlink Control Channel (NPDCCH) with downlink control information (DCI) format N0/N1 for the same HARQ process ID as the NPUSCH transmission in any subframe starting from subframe n+1 to subframe n+3. 
     In contrast, for NTN, the UE DL Acknowledgement (ACK)/Negative Acknowledgement (NACK) monitoring restrictions are modified for this example scenario. The HARQ-ACK timing in response to NPUSCH transmission is n+4+K mac . The DL subframe n+3+K mac  corresponds to the subframe immediately before HARQ-ACK. Also, it should be noted that the DL subframe n+1−n TA   UE  starts immediately after UL subframe n. Therefore, the below-described changes need to be applied to the existing specifications, e.g., to 3GPP TS36.213 version 16.6, to properly accommodate the RTT between the UE and eNB. If an NB-IoT UE is configured with higher layer parameter twoHARQ-ProcessesConfig., and if the UE has an NPUSCH transmission ending in subframe n, then at least one of: 1) the UE is not required to receive transmissions in the Type B half-duplex guard periods for FDD; and 2) the UE is not expected to receive an NPDCCH with DCI format N0/N1 for the same HARQ process ID as the NPUSCH transmission in any subframe starting from subframe n+1−n TA   UE  to subframe n+3+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     EXAMPLE SCENARIO B 
     This example scenario relates to monitoring restrictions involving subframe after NPUSCH processing. As a point of reference, the existing configuration restrictions (e.g., 3GPP TS36.213 version 16.6) in a Terrestrial Network (TN) provide that, if the UE is not using higher layer parameter edt-Parameters or if the UE is using higher layer parameter edt-Parameters and 0≤I MCS ≤2 , (I MCS  is the modulation and coding scheme field read from the DCI), then: if the NB-IoT UE has a NPUSCH transmission ending in subframe n , the UE is not required to monitor NPDCCH in any subframe starting from subframe n+1 to subframe n+3. 
     In contrast, for NTN, the UE DL monitoring restrictions are modified for this example scenario, i.e., the below-described changes need to be applied to the existing specifications, e.g., to 3GPP TS36.213 version 16.6, to properly accommodate the RTT between the UE and eNB. If the UE is not using higher layer parameter edt-Parameters or if the UE is using higher layer parameter edt-Parameters and 0≤I MCS ≤2, (I MCS  is the modulation and coding scheme field read from the DCI), then: if the NB-IoT UE has a NPUSCH transmission ending in subframe n , the UE is not required to monitor NPDCCH in any subframe starting from subframe n+1−n TA   UE  to subframe n+3+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     EXAMPLE SCENARIO C 
     This example scenario relates to monitoring restrictions involving subframe after NPUSCH carrying Message 3 (Msg3). As a point of reference, the existing configuration restrictions (e.g., 3GPP TS36.213 version 16.6) in a Terrestrial Network (TN) provide that, if the NB-IoT UE has an NPUSCH transmission for Msg3 ending in subframe n′with transport block size TBS Msg3 , whereas if maximum transport block size TBS Msg3,max  for Msg3 would have been selected the NPUSCH transmission would have ended in subframe n, the UE is not required to monitor NPDCCH in any subframe starting from subframe n′+1 to subframe n+3. 
     In contrast, for NTN, the UE DL monitoring restrictions are modified for this example scenario, i.e., the below-described changes need to be applied to the existing specifications, e.g., to 3GPP TS36.213 version 16.6, to properly accommodate the RTT between the UE and eNB. If the NB-IoT UE has an NPUSCH transmission for Msg3 ending in subframe n′with transport block size TBS Msg3 , whereas if maximum transport block size TBS Msg3,max  for Msg3 would have been selected the NPUSCH transmission would have ended in subframe n, the UE is not required to monitor NPDCCH in any subframe starting from subframe n′+1−n TA   UE  to subframe n+3+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     EXAMPLE SCENARIO D 
     This example scenario relates to Narrowband Physical Random-Access Channel (NPRACH) for scheduling request (SR) involved in long NPRACH transmission. As a point of reference, the existing configuration restrictions (e.g., 3GPP TS36.213 version 16.6) in a Terrestrial Network (TN) provide that, for an NB-IoT UE configured with higher layer parameter sr-WithoutHARQ-ACK-Config, if the transmission of a narrowband random access preamble for SR ends on subframe n, then: in case of frame structure type 1 with NPRACH format 0 and 1 when the number of NPRACH repetitions is greater than or equal to 64, or NPRACH format 2 when the number of NPRACH repetitions is greater than or equal to 16, the UE is not required to monitor NPDCCH UE-specific search space from subframe n to subframe n+40. 
     In contrast, for NTN, the UE DL monitoring restrictions are modified for this example scenario, i.e., the below-described changes need to be applied to the existing specifications, e.g., to 3GPP TS36.213 version 16.6, to properly accommodate the RTT between the UE and eNB. For an NB-IoT UE configured with higher layer parameter sr-WithoutHARQ-ACK-Config, if the transmission of a narrowband random access preamble for SR ends on subframe n, then: in case of frame structure type 1 with NPRACH format 0 and 1 when the number of NPRACH repetitions is greater than or equal to 64, or NPRACH format 2 when the number of NPRACH repetitions is greater than or equal to 16, the UE is not required to monitor NPDCCH UE-specific search space from subframe n−n TA   UE  to subframe n+40+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     EXAMPLE SCENARIO E 
     This example scenario relates to Narrowband Physical Random-Access Channel (NPRACH) for scheduling request (SR) involved in short NPRACH transmission. As a point of reference, the existing configuration restrictions (e.g., 3GPP TS36.213 version 16.6) in a Terrestrial Network (TN) provide that, for an NB-IoT UE configured with higher layer parameter sr-WithoutHARQ-ACK-Config, unless the transmission of a narrowband random access preamble for SR ends on subframe n, the UE is not required to monitor NPDCCH UE-specific search space from subframe n to subframe n+3. 
     In contrast, for NTN, the UE DL monitoring restrictions are modified for this example scenario, i.e., the below-described changes need to be applied to the existing specifications, e.g., to 3GPP TS36.213 version 16.6, to properly accommodate the RTT between the UE and eNB. For an NB-IoT UE configured with higher layer parameter sr-WithoutHARQ-ACK-Config, unless the transmission of a narrowband random access preamble for SR ends on subframe n, the UE is not required to monitor NPDCCH UE-specific search space from subframe n−n TA   UE  to subframe n+3+K mac , where n TA   UE =ceil(N TA,UE-specific ). 
     According to the example embodiments of the present disclosure, impact of K mac  timing is taken into consideration for optimizing the monitoring window for DL reception at UE. The disclosed example embodiments of system optimization will help UEs reduce power consumption as UEs will not be required to monitor for DL signal for a longer duration. 
     Although the example embodiments of the present disclosure have been described in the context of NB-IoT for NTN operation, the present disclosure is equally applicable to 5G NR NTN operation, e.g., LTE Machine Type Communication (LTE-M) technology, and  . 
     ABBREVIATIONS 
     
         
         3GPP: 3rd Generation Partnership Project 
         5GC: 5G Core 
         eNB: evolved Node B 
         FDD: frequency division duplex 
         gNB: next generation Node B 
         HARQ: Hybrid automatic repeat request 
         LTE: Long Term Evolution 
         MIB: Master Information Block 
         NPDCCH: NB-IoT Physical Downlink Control Channel 
         NPUSCH: NB-IoT Physical Uplink Shared Channel 
         NTN—Non Terrestrial Network 
         NR: 5G New Radio 
         PDCP: Packet Data Convergence Protocol 
         PHY: Physical layer 
         PNF: Physical Network Function 
         PRACH: Physical Random Access Channel 
         RAN: Radio Access Network 
         RAT: Radio Access Technology 
         RF: Radio Frequency 
         RLC: Radio Link Control 
         RRC: Radio Resource Control 
         RRM: Radio Resource Management 
         SIB: System Information Block 
         UE: User Equipment