Patent Publication Number: US-2023156792-A1

Title: Schemes to avoid periodic resource collisions

Description:
BACKGROUND 
     The 3GPP standard body released the C-V2X standard to support V2X (i.e., vehicle-to-everything) communication. NR V2X includes two modes of operation, identified as Mode 1 and Mode 2. Mode 1 deals with gNB (e.g., base station) scheduling, while Mode 2 deals with autonomous selection. M ode  2  does not require the support of cellular infrastructure, and vehicles can autonomously select their sub-channels for their V2V transmissions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some examples of circuits, apparatuses and/or methods will be described in the following by way of example only. In this context, reference will be made to the accompanying figures. 
         FIG.  1    is a time-frequency diagram illustrating the two step sensing and selection for V2X autonomous selection. 
         FIG.  2    is a diagram illustrating a potential collision problem in V2X autonomous selection for periodic transmission schemes. 
         FIG.  3 A  is diagram illustrating a discontinuous periodic transmission scheme to address the collision problem with a periodic transmission scheme with a V2X autonomous selection process according to an aspect. 
         FIG.  3 B  is a flow diagram illustrating the discontinuous periodic transmission scheme of  FIG.  3 A  according to an aspect. 
         FIG.  4    is a diagram illustrating a unique collision condition with V2X autonomous selection when a competing UE has an resource reservation period (RRP) that is an integer multiple of an evaluating UE according to an aspect. 
         FIG.  5    is a diagram illustrating a unique collision condition with V2X autonomous selection when an evaluating UE has an RRP that is an integer multiple of a competing UE according to an aspect. 
         FIG.  6    is a flow diagram illustrating differing corrective actions depending upon the relative RRPs of the evaluating UE and a competing UE in a V2X autonomous selection process using a discontinuous periodic transmission scheme according to an aspect. 
         FIGS.  7 A- 7 B  are diagrams illustrating discontinuous periodic transmission schemes in instances where multiple, non-contiguous resource blocks are scheduled in each transmission period according to various aspects. 
         FIGS.  8 A- 8 B  are diagrams illustrating discontinuous periodic transmission schemes in instances where multiple, non-contiguous resource blocks are scheduled in each transmission period according to various aspects. 
         FIG.  9    is a diagram that illustrates the signaling performed to “skip” a transmission period to effectuate the discontinuous periodic transmission. 
         FIG.  10    is a flow diagram illustrating functions of one or more processors of an evaluating UE performing a self-collision detection scheme using HARQ feedback information. 
         FIG.  11    is a block diagram illustrating a UE and various components thereof according to an aspect. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the disclosure. Several aspects of the disclosure are described below with reference to example applications for illustration. Numerous specific details, relationships, and methods are set forth to provide an understanding of the disclosure. The present disclosure is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the selected present disclosure. 
     As highlighted above, Mode 1 in NR V2X involves vehicle direct communication with one another, however, those communications are managed by a cellular infrastructure that selects the sub-channels and time slots or radio resources for each V2V transmission. In contrast, Mode 2 in NR V2X does not require the support of the cellular infrastructure, and vehicles autonomously select the sub-channels and time slots or radio resources for their V2V transmissions. In this framework, the 3GPP standard defines a distributed semi-persistent scheduling scheme that all the vehicles must implement. 
     C-V2X supports 10 MHz and 20 MHz channels. The channel is divided temporally into 1 ms sub-frames and into resource blocks (RBs) of 180 KHz each. The standard defines a sub-channel as a group of RBs in the same sub-frame. The sub-channels are used to transmit data and control information. Such data is transmitted in transport blocks (TBs) over physical sidelink shared channels (PSSCH), and the control information is transmitted in sidelink control information (SCI) messages over physical sidelink control channels (PSCCH). A TB contains a full packet and can occupy one or several sub-channels. Each TB has an SCI associated therewith, and both are transmitted in the same sub-frame. The SCI occupies a configurable number of RBs and configurable number of OFDM symbols and includes information such as the modulation and coding scheme (MCS) used to transmit the TB, and the RBs that the TB occupies, and the resource reservation period (RRP) for the semi-persistent scheduling scheme. The resource reservation period refers to the periodicity used by vehicles to transmit their packet, and the period or interval is specified in multiples of 100 ms (e.g., 100 ms, 200 ms, . . . 1000 ms). The information on the SCI is valuable, so the SCI must be correctly received to receive and decode the TB. 
     In Mode 2, vehicles autonomously select their sub-channels and time slots using a sensing based semi-persistent scheduling (SPS) scheme, wherein vehicles reserve the selected sub-channels and time slots for a number of consecutive packet transmissions, dictated by a reselection counter value. After such number of transmissions, new resources or sub-channels must be selected and reserved. The process by which a vehicle selects and reserves resources is a multi-step process, which can be appreciated with reference to  FIG.  1   . Note that  FIG.  1    technically illustrates an LTE two-step procedure, but for purposes of understanding the substance, it is sufficient for explanatory purposes. At a high level, in a sensing step (or sensing window shown in  FIG.  1   ) the UE listens to the channel, i.e., listening for channel information (SCI of other vehicles) in order to see what resources are already reserved. In a selection step candidate resources are identified and subsequently selected or reserved. 
     More particularly, whenever a new resource is to be selected, resources can be reserved by the vehicle in a time period called the selection window, as shown in  FIG.  1   . Within this time period the vehicle identifies the candidate single sub-frame resources (CSRs) to be reserved. A CSR is a group of adjacent sub-channels within the same sub-frame where the packet or SCI and TB resides. If “T” is the beginning time of a time window in which the new resource selection must be made (i.e., the selection window), the vehicle senses all packets in a preceding sensing window that includes 1000 subframes before T. The vehicle creates a list that includes all the CSRs in the sensing window (i.e., candidate CSRs), except for CSRs that satisfy two criteria: (1) the resource is indicated in a received SCI from another vehicle (indicating that another vehicle will utilize that resource at the same time, and (2) a measured average reference signal received power (RSRP) over the RBs used to transmit the TB associated with the SCI of the other vehicle is greater than a RSRP threshold. If both conditions are met, the vehicle excludes that particular CSR as a candidate CSR. The vehicle then may perform a resource selection for a transmission from the identified candidate resources (CSRs) in the selection window. 
     As discussed above, in those instances when a periodic resource reservation is made, when the vehicle UE initiates transmission on the selected resources, it does not monitor the sidelink channels due to the half-duplex system constraint, and consequently if another vehicle UE selects the same periodic resources for its own sidelink transmissions, such dueling sideline transmissions could possibly continuously collide with each other. This undesired collision condition is illustrated in  FIG.  2   , wherein UE  1  and UE 2  correspond to two different vehicles that are transmitting on the same selected time-frequency resources (i.e., the same sub-channel at the same time). 
     As shown in  FIG.  2   , a first UE  202  (e.g., UE 1  corresponding to a first vehicle) has a first periodic resource reservation  204  at a time t 1 , while a second UE  206  (e.g., UE 2  corresponding to a second vehicle) has a second periodic resource reservation  208  that occupies the same time-frequency resources as the first reservation  204 . Further, in the example of  FIG.  2   , both resource reservations  204 ,  208  have the same periodicity  210  and thus not only is there a collision at time t 1 , but the data collisions continue at times t 2 , t 3 , t 4 . etc. In light of the appreciated issues highlighted above, the present disclosure provides circuitry, a methodology and a non-transitory computer readable medium for discontinuous periodic transmission that addresses this issue. 
     In one aspect, the UE (referred to as the evaluating UE) intentionally does not transmit in one of the scheduled, reserved time periods (which may be referred to as a scheduled discontinuous time period), and instead performs a channel monitoring on the periodically reserved resources. If during the monitoring function, an SCI of another UE (referred to as a competing UE) is detected, some form of corrective action is selectively performed, wherein the form of corrective action is based on the resource reservation period (RPP) and in some instances on a data priority of the competing UE. For example, in one aspect in which data priority is not a factor or a consideration, the form of corrective action based on the RRP may depend upon whether RRPs of the evaluating UE and the competing UE are: (1) identical, (2) the competing UE&#39;s RRP is an integer multiple of the evaluating UE&#39;s RRP, or (3) the evaluating UE&#39;s RRP is an integer multiple of the competing UE&#39;s RRP.  FIG.  3 A- 5    illustrate the three conditions highlighted above to help understand how the corrective action may differ based on the relative RRPs. 
       FIG.  3 A  illustrates condition (1) above, wherein the evaluating UE  302  (e.g., UE 1 ) and the competing UE  304  (e.g., UE 2 ) have reserved the same time-frequency resources (e.g., resources  306  and  308  are the same). In addition, in this example, the reserved resources  306 ,  308  have the same periodicity  310 , meaning that the RRPs of the resources  306 ,  308  are identical. Therefore absent any corrective action, data collisions will occur and not be detected by either UE  302 ,  304 . In this example, UE  302  is the evaluating UE and elects to not transmit at a time period (i.e., t 3 ), and instead performs a monitoring operation  312  of the channel at that time period. By not transmitting at the otherwise scheduled time period (e.g., a scheduled discontinuous time period), the evaluating UE  302  is performing a discontinuous periodic transmission. If, at the monitoring time period t 3  an SCI of a competing UE is detected and decoded that indicates the same time-frequency resource having an identical RRP, the evaluating UE  302  stops transmitting on the colliding resources, and instead initiates a re-selection procedure, wherein the UE  302  performs the two-part sensing and selection procedure discussed supra with respect to  FIG.  1    to schedule other resources. This is seen in  FIG.  3 A  at  314 , wherein the transmission at time t 4  is not performed and instead a re-selection procedure is initiated. 
     The above example discussion ignores the issue of data priority. That is, in the example of  FIG.  3 A , the evaluating UE  302  discontinues transmission at t 4  independently of whether or not the priority of the data transmission of the evaluating UE  302  is higher or lower than that of the competing UE  304 . In one aspect, the evaluating UE  302  performs the monitoring operation  312  at t 3  and decodes an SCI indicating a colliding transmission with a competing UE having an identical RRP. The evaluating UE  302  then further evaluates the data transmission priority of the competing UE  304 , for example, by evaluating the decoded SCI of the competing UE  304 , and if the data transmission priority of the evaluating UE  302  is higher than the priority of the competing UE  304  data transmission, then the evaluating UE  302  does not discontinue transmission. In this case, despite the collision, because of the higher data priority, the evaluating UE  302  does not stop transmitting, but instead continues to transmit. 
     In one aspect, if each of the UEs are operating in accordance with the present disclosure, the competing UE  304  is sometimes operating as an evaluating UE and in such instance would detect the collision and higher data priority of the other competing UE, and in response would discontinue transmission and initiate a re-selection procedure. 
     Therefore as highlighted above in conjunction with  FIG.  3 A , the disclosure contemplates a UE, or one or more processors in a UE that, upon executing instructions are configured to perform discontinuous periodic communication  350  with another UE, as set forth in  FIG.  3 B . The process  350  may be the functions of an apparatus comprising the functions of one or more processors in an evaluating UE, may be a method, and/or may be non-transitory computer readable media containing instructions that when executed by one or more processor result in the functions described herein. At  352 , the one or more evaluating UE processors are configured to schedule resources for discontinuous periodic transmission. As highlighted above, such scheduling looks similar to that of UE 1   302  that schedules a monitoring operation at a scheduled discontinuous time period (e.g., t 3  of  FIG.  3 A ) that would otherwise be used for a data transmission. Such scheduling includes reservation of periodic time-frequency resources. Further details of such scheduling will be discussed infra. Such scheduling details are set forth in the SCI and may include the periodicity, data priority, as well as other parameters that characterize the discontinuous periodic communication. 
     Still referring to  FIG.  3 B , the one or more UE processors perform the monitoring operation according to one of various methods. In one option the monitoring operation is scheduled according to a random selection with a probability (A) that may be preconfigured or may be a function of other criteria, such as data priority. In another aspect the selection of the monitoring process timing may follow a predefined pattern, such that the nature of the discontinuous transmission itself has a periodicity. Further details of how and when such monitoring is executed will be discussed in further detail infra. 
     During the monitoring operation at  354 , the one or more UE processors monitor the channel for the SCI of other transmitting UEs (i.e., competing UEs) at  356 . If no other transmissions are detected, or if an SCI is detected, but upon decoding does not include reserved resources that would collide with the evaluating UE (NO at  356 ), the discontinuous periodic transmission is continued at  358  until the next scheduled monitoring event. If, however, an SCI of a competing UE is detected that does conflict with the reserved resources of the evaluating UE (YES at  356 ), the one or more UE processors (i.e., the evaluating UE) performs a corrective action at  360 . 
     In one aspect, the corrective action taken at  360  comprises discontinuing the periodic transmission by the evaluating UE, and then initiating a re-selection process, where the UE does the two step sensing and selection procedure discussed above in conjunction with  FIG.  1   . In another aspect, the corrective action can be selective, wherein the discontinuation of data transmission is contingent upon the relative data priority levels or some other criteria. For example, upon decoding the SCI of the competing UE, if the scheduled resources conflict, but the relative data priorities of the evaluating UE and the competing UE meet some predetermined relationship, the evaluating UE will not discontinue transmission despite the detection of the collisions. For example, if the data priority of the evaluating UE is greater than that of the competing UE, the transmission may continue. Alternative, other criteria may be employed to make the corrective action at  360  selective. 
     As discussed above, the type of corrective action taken by an evaluating UE may differ based on the RRP of the evaluating UE and the competing UE. Option (2) corresponds to the condition where the RRP of the competing UE is an integer multiple of the evaluating UE (e.g., if the period of the evaluating UE is 100 ms, the period of the competing UE is 100 ms X “N”, wherein N is an integer), and is illustrated in  FIG.  4   . As shown in  FIG.  4   , a competing UE  404  performs periodic transmission that exhibits a period that is an integer multiple of the period transmission of the evaluating UE  402 . In this example, the integer is 2, and thus the evaluating UE  402  transmits data twice as often as the competing UE  404 . As can be seen in  FIG.  4   , in such a situation, a collision will not occur for every evaluating UE transmission, but will occur for every competing UE transmission. In this example, a collision occurs at t 1 , but not at t 2 . When the evaluating UE  402  discontinues transmission and instead performs a monitoring operation  410  at t 3 , the evaluating UE  402  decodes the SCI of the competing UE  404  and sees that it has an RRP that is an integer multiple of the evaluating UE RRP (e.g., 100 ms compared to 200 ms). At this point, the evaluating UE may select a few different options for its corrective action. In one aspect the evaluating UE discontinues only those transmissions at colliding time periods (e.g.,  412  and  414 ), while continuing to transmit at the other, non-conflicting time periods. In this case, the evaluating UE  402  does not initiate a re-selection procedure, but instead just skips transmitting on the colliding resources. Alternatively, the evaluating UE  402  may elect to initiate a re-selection procedure. In yet another alternative aspect, upon identifying the condition, the evaluating UE  402  may employ other criteria in deciding whether to skip colliding resource time periods  412 ,  414  or initiate re-selection. For example if the data transmission priority for the evaluating UE  402  is “high” (e.g., above a predetermined threshold), re-selection might be initiated. Alternatively re-selection could be initiated if the priority is “low” according to some predetermined criteria or threshold. Any other substantive criteria could be employed and is appreciated to be contemplated by the present disclosure. 
     As highlighted above, if condition (3) exists, and the evaluating UEs RRP is an integer multiple of the competing UE&#39;s RRP, the situation looks like  FIG.  5   . As shown in  FIG.  5   , an evaluating UE  502  and a competing UE  504  both are performing periodic transmission and the scheduling of such will result in collisions due to occupying some of the same time-frequency resources. In this instance, the evaluating UE  502  will experience a collision at each and every transmission, while some fraction of transmissions of the competing UE  504  will experience a collision (based on the integer multiple of the RRP). When the evaluating UE  502  performs a monitoring operation  508  at t 3  instead of a data transmission and discovers the issue via the competing UE&#39;s SCI, the evaluating UE  502  may elect to discontinue transmission and instead initiate a re-selection process. Alternatively, upon detecting the condition the UE may choose to message the competing UE  504  with a request that the competing UE  504  skip the colliding resources in the certain periods where the collision would exist. In yet another alternative, the evaluating UE  502  may take into account its data priority and/or the data priority of the competing UE  504  in deciding which corrective action to take under such circumstances. For example if the data transmission priority of the competing UE is “high”, instead of requesting the competing UE  504  to skip transmissions in the colliding time periods, the evaluating UE  502  may elect to discontinue transmission and initiate a re-selection procedure. 
     In summary, the variations in corrective action based on the three differing relationships between the evaluating UE&#39;s RRP and the competing UE&#39;s RRP is set forth in  FIG.  6   .  FIG.  6    shows the functions performed by an evaluating UE&#39;s one or more processors. As shown in  FIG.  3   , when an affirmative answer is made at  356  to the query of whether an SCI is detected in the evaluating UE&#39;s reserved resources (YES at  356 ), a corrective action  360  is performed.  FIG.  6    provides greater detail regarding what the corrective action may entail depending on the relationship of the RRPs between the evaluating UE and the competing UE. 
     Initially, the one or more processors of the evaluating UE compares its RRP with that of the competing UE via its decoded SCI. If the RRPs are the same (YES at  662 ), each transmission of each UE will collide, as illustrated in  FIG.  3 A . In one aspect the evaluating UE checks to see if its data priority is lower than the data priority of the competing UE at  664 . If not (NO at  664 ), then the evaluating UE may elect to take no further corrective action at  666 . This might reflect a situation where the evaluating UE has much higher priority data than the competing UE, and if the competing UE is also performing discontinuous periodic transmission, it will detect the collision, stop transmission and perform re-selection. If the determination is made that the data priority of the evaluating UE is lower than that of the competing UE (YES at  664 ), the evaluating UE stops transmitting and performs a re-selection procedure at  668 . Note that the analysis at  664  regarding the data priority is optional (as represented by the dashed lines) and alternatively if the conclusion at  662  is affirmative (YES), the evaluating UE may proceed straight to  668 , discontinue transmission, and perform re-selection. 
     Still referring to  FIG.  6   , if the RRPs of the evaluating UE and the competing UE are not identical (NO at  662 ), a determination is made whether the RRP of the competing UE is an integer multiple of the evaluating UE at  670 . If it is (YES at  670 ), the situation illustrated in  FIG.  4    exists, and the evaluating UE queries whether its data priority is higher than the data priority of the competing UE at  672 . If the evaluating UE data priority is greater (YES at  672 ) no corrective action is taken at  674 . That is, while there are clearly data collisions at  412  and  414 , as shown in  FIG.  4   , because that evaluating UE&#39;s data priority is sufficiently high according to some predetermined standard, the evaluating UE may continue to transmit. If the competing UE is also performing discontinuous periodic transmission, it may detect the condition, and since it has a lower data priority, it may stop transmission and perform a re-selection. If the query at  672  is negative (NO at  672 ), the evaluating UE may elect one of two different options. In one case, the evaluating UE may stop transmitting solely with respect to the colliding resources at  676 , as illustrated in  FIG.  4   , where resources  412  and  414  are cancelled, but transmission continues for the other evaluating UE resources. In another aspect, if the evaluating UE data priority is not “high” according to some predefined criteria, the evaluating UE discontinues all data transmission and initiates a re-selection process at  678 . Again, the data priority analysis at  672  may be optional, as shown by the dashed lines 
     Still referring to  FIG.  6   , if the result of the query at  670  is negative (NO at  670 ), then another query is made whether the RRP of the evaluating UE is an integer multiple of the competing UE at  680 . If so (YES at  680 ), the situation is as illustrated in  FIG.  5   . Under these conditions the evaluating UE has two available options, wherein at  682  the evaluating UE stops transmission and performs a re-selection, or the evaluating UE sends a message to the competing UE to skip those transmissions associated with the colliding resources at  684 . If however, the query at  680  is answered in the negative (NO at  680 ), then a situation exists where RRPs of the evaluating UE and the competing UE are mutually prime. For example, this situation would exist if the RRP of the evaluating UE was 30 ms and the RRP of the competing UE was 100 ms. In another alternative, if the RRP of the competing UE is 0, which means the competing UE only uses the resources once, and is not performing periodic transmissions. In such case, no corrective action is taken at  674 . 
     In the examples provided in  FIGS.  3 - 5   , only a single set or block of resources are scheduled within each transmission period. In an alternative aspect, multiple, non-contiguous sets or blocks of resources may be scheduled for periodic transmission by a UE. This example is illustrated in  FIG.  7 A , where a first UE 1   702  and a second UE 2   704  are performing periodic transmission, wherein within each transmission period multiple, non-contiguous sets or blocks of time-frequency resources are scheduled for transmission. For example, the first UE 1   702  has a first resource block  706  and a second resource block  708 , while the second UE 2  has a first resource block  710  and a second resource block  712  scheduled within each transmission period. As illustrated in  FIG.  7 A , according to the scheduling, the first resource blocks  706 ,  710  of the UEs  702 ,  704  do not collide, but the second resource blocks  708 ,  712  do collide. 
     In one aspect, during a third time period  714 , the first UE 1   702  does not transmit, but instead performs a monitoring operation  716  where it listens to the channel for the SCI of other competing UEs. In this case, UE 1   702  detects the SCI of UE 2   704 , decodes it, and determines that the second resource blocks  708 ,  712  collide, and thus a corrective action must take place. In one aspect, as illustrated in  FIG.  7 A , the first UE 1   702  (i.e., the evaluating UE) stops all further transmissions on all the reserved resources, which in this case corresponds to both resource blocks  706 ,  708 , and performs a re-selection procedure. In an alternative aspect, as illustrated in  FIG.  7 B , in a similar situation wherein only a portion of the scheduled resources collide (i.e., resource blocks  708 ,  712  collide, but resource blocks  706 ,  710  do not collide), the evaluating UE  702  discontinues transmissions only on the collided resources in the subsequent transmission periods, and optionally performs a re-selection procedure solely for the colliding resources. 
     In the examples of  FIGS.  7 A- 7 B , the evaluating UE  702  performed its monitoring operation for each resource block  706 ,  708  within the same transmission period  714 . Alternatively, an evaluating UE may schedule and thus perform a monitoring operation for each of the resource blocks in different transmission periods. For example as illustrated in  FIG.  8 A , a first UE 1   802  transmits in each transmission period according to scheduled resource blocks  806 ,  808 , while a second UE 2   804  transmits in each transmission period according to scheduled resource blocks  810 ,  812 . As shown in  FIG.  8 A , the first resource blocks  806 ,  810  of the UEs  802 ,  804  do not collide, while the second resource blocks  808 ,  812  of the UEs  802 ,  804  do experience a collision. In contrast to  FIG.  7 A  where the evaluating UE  702  performs a monitoring operation for both blocks  706 ,  708  in the same transmission period  714 , in the aspect of  FIG.  8 A , the evaluating UE  802  monitors  815  for the first block  806  in a second transmission period  814 , and monitors  817  for the second block  808  in a third transmission period  816 . As illustrated, the evaluating UE  802  does not detect a conflicting resource with respect to block  806  in the second transmission period  814 , but does detect a collision with respect to the block  808  in the third transmission period  816 . In one aspect, as illustrated in  FIG.  8 A , the corrective action taken by the evaluating UE  802  is to discontinue transmission of all resources and perform a re-selection procedure for all the resources. 
     In an alternative aspect illustrated in  FIG.  8 B , a similar collision condition is detected, that is, a partial collision is detected. More particularly, a collision is detected for some (i.e., resource  808 ), but not all the resources (i.e., resources  806  and  808 ). In this aspect, the corrective action taken by the evaluating UE  802  is to discontinue transmission of only the colliding resource (i.e., resource  808 ) while continuing transmission of the other non-colliding resources, as shown in  FIG.  8 B . In yet another alternative, the corrective action may be conditioned upon other criteria. For example, a priority of the data associated with the reserved resource block may be considered. If the priority of the data associated with the colliding resource block is “high” (e.g., it exceeds a predetermined threshold), the colliding resource is re-scheduled, and if it is not a “high” priority, the evaluating UE  802  simply discontinues transmission on that colliding resource, and maintains transmission on the non-colliding resource. 
     In one aspect, this discontinuous periodic transmission scheme highlighted herein may be selectively enabled or disabled, and in another aspect it may be a fixed solution or may be configured or preconfigured per resource pool. Either alternative is contemplated by the present disclosure. 
     As discussed above, the problem associated with collisions in periodic transmission is addressed by an evaluating UE discontinuing its periodic transmission and performing a monitoring operation during the time period it would otherwise be transmitting in order to determine whether a competing UE exists that has reserved resources that will conflict with those of the evaluating UE in a manner discussed herein and illustrated in  FIGS.  3 A,  4 - 5 ,  7 A- 7 B and  8 A- 8 B . One or more ways in which the monitoring function is scheduled to form a discontinuous periodic transmission is described below. 
     In one aspect of the present disclosure, prior to each transmission on resources in a given period, the UE determines whether or not to transmit on the next transmission period, and if a determination is made to transmit, the UE populates its SCI field accordingly. In one aspect, the determination whether or not to transmit (or monitor) on the next transmission period is made based on a random selection of whether to monitor in the next period, wherein the random selection has a probability (A) that may be configured or preconfigured, or based on criteria such as data priority. For example, if the probability (A) is configured or preconfigured to be 10%, then the chance that the evaluating UE will choose to not transmit, but instead monitor during the next transmission period will be 10%. 
     In accordance with an alternative aspect, the probability (A) may depend on various criteria, for example, in one aspect the probability (A) may depend upon the data priority. For example, in one aspect, the probability (A) may be increased for high priority data to ensure reliable data transmissions, and decreased for low priority data. Alternatively, the probability (A) may be decreased for high priority data to achieve more continuous data transmissions, and increased for low priority data to avoid collisions with higher priority data in competing UEs. 
     In accordance with another alternative aspect, the probability (A) may depend upon collision history. If a relatively high number of collision were detected (according to some predetermined threshold or criteria) in a recent predefined time period, the probability (A) may be increased to monitor more frequently, and if the recent history showed no or infrequent collisions, the probability (A) may be decreased. In other aspects, multiple factors or criteria may be collectively considered in forming or otherwise configuring the probability (A). 
     In addition, for non-contiguous multiple resources reserved in each transmission period, such as that illustrated in  FIG.  8 A , the probability may be independently applied to each of the various scheduled resources in the time period. 
     In another aspect, the monitoring of the evaluating UE may follow a predetermined pattern or periodicity. For example, in one aspect, the periodic transmissions are discontinuous due to monitoring every “B” time periods. The value B may be (pre)configured or may be randomly selected from a set of preconfigured periods. For example, the set may be mutually prime number such as {2, 3, 5, 7, 11} which may avoid consecutive identical discontinuous resources from different UEs. In another aspect, the selection of the value B may depend upon data priority. For example, the value B may be selected to be a lower value for high priority data to monitor more often to ensure more reliable transmission, and B made larger for lower priority data. In another aspect, B may be higher for high priority data to ensure more continuous transmission for such data. In addition, in one aspect, once the periodicity B is selected, the starting point needs to be determined as well. In one aspect, the starting period of the discontinuous resource time period may be randomly selected between 0 and B−1. Alternatively, the starting point can be configured or preconfigured, or based on other criteria. 
     The above discussion discloses determining how often to make the otherwise periodic transmission discontinuous by scheduling the monitoring operation. The manner in which such discontinuous transmission is signaled can be performed in a variety of different ways. In one aspect, if the evaluating UE determines a discontinuous transmission in the next time period, the evaluating UE alters the RRP (i.e., the resource reservation period) field of the SCI to skip the next transmission time period. In one aspect, if the present RRP is set to 100 ms, the evaluating UE sets the RRP in the SCI that is associated with PSSCH one period before the discontinuous transmission to 200 ms (double the periodicity). In another example, if the RRP is set to 400 ms, the RRP for the SCI one period before the discontinuous transmission is set to 800 ms to double the periodicity and effectively “skip” that particular transmission period so it can be utilized to monitor the channel. One example of this feature is illustrated in  FIG.  9   , wherein the SCI field indicates one period for the normal periodic transmission, and then indicates “2× period” on the period prior to the monitoring operation  914 , to indicate that the transmission on the scheduled resources skips to the “next” transmission period after the discontinuous (monitoring) time period. 
     In another aspect, an additional bit may be employed in the SCI field to indicate a discontinuous transmission in the next transmission period. For example, if the extra bit is set to “0”, for example, the resource in the next transmission period is reserved and periodic transmission continues. If the extra bit is set to “1”, for example, the resource in the next transmission period is not reserved and monitoring may be performed, and the resource will be reserved for transmission in the period following the monitoring period. 
     In various aspects discussed above, a discontinuous periodic transmission scheme is disclosed, wherein an evaluating UE stops transmitting during a discontinuous time period to monitor the channel for potential collisions. In another aspect, periodic transmission is not discontinued, but instead a transmitting UE operates as an evaluating UE and performs a self-detection of collision operation by evaluating the feedback from one or more receiving UEs when HARQ feedback is enabled. Alternatively, the transmitting UE operates as an evaluating UE by looking for HARQ feedback on sideline feedback channel (PSFCH) resources that correspond to PSCCH and PSSCH transmissions by other transmitting UEs to inferentially ascertain collisions when HARQ feedback is disabled. 
     In one aspect, self-detection of a collision may be performed by a transmitting UE performing a periodic transmission. For example, in a sidelink unicast or groupcast transmission with HARQ feedback enabled, the transmitting UE can evaluate the received feedback over a number of evaluated feedback messages, and calculate what percentage of such messages are negative acknowledgements (NACKs). If the percentage of such NACKs exceeds a predetermined threshold, then it is determined that a collision exists with a competing UE with respect to the scheduled resources. 
     As is known, a unicast transmission is a one-to-one communication, wherein a transmitting UE is transmitting the periodic transmission to a single, specific receiving UE. In response to the unicast transmission, the transmitting UE receives a response to the sidelink data packet from the receiving UE when HARQ feedback is enabled. In general, a HARQ-ACK is a response that indicates whether a sidelink data packet was successfully received. Available HARQ-ACK responses include, inter alia, positive acknowledgement (ACK), negative acknowledgement (NACK), and DTX. As only an ACK indicates a successful receipt of the transmitted data, either a NACK or a DTX is deemed to be a “NACK” for purposes of this disclosure, and thus represent an unsuccessful transmission that may be due to a collision. Thus, in a periodic transmission, for successive transmissions of the data, receipt of NACK or DTX is counted as a “fail” while an ACK is treated as a “success.” If the percentage of “fails” is larger than a threshold, then the transmitting UE concludes that a collision exists with respect to the scheduled periodic resources. In such instances a corrective action is performed, for example, where the periodic transmission is discontinued and a re-selection procedure is initiated. 
     In one aspect the threshold used to conclude a collision has occurred is preconfigured or configured. In another aspect, the threshold may be based on a data quality-of-service (QoS) parameter or a data priority level. For example, if the QoS or data priority is high, the threshold may be lower to trigger a re-selection operation if there is only a remote possibility that a collision exists. 
     Referring to  FIG.  10   , a UE for self-detecting collisions  1000  in a periodic communication environment employing, for example, autonomous selection is provided. Such a UE is a transmitting UE that also operates as an evaluating UE to detect collisions with competing UEs.  FIG.  10    also may correspond to a method of performing self-detection of collisions in the above environment using or more processors, and further may entail non-transitory computer readable media containing instructions that when executed by one or more processors performs the method described herein. 
     In one aspect, the functionality  1000  begins at  1002 , wherein a query is made whether HARQ feedback is enabled in the UE. As the standard allows for HARQ feedback to be selectively enabled, the functionality  1000  provides for two different options. If HARQ feedback is enabled (YES at  1002 ), then the transmitting UE will receive ACK/NACK type feedback in response to the periodic transmissions. 
     Upon knowledge of HARQ feedback being enabled, the transmitting UE receives resources for periodic communication and schedules such resources with one or more feedback-based collision detection parameters at  1004 . Non-limiting examples of such feedback-based collision detection parameters may be as follows. One parameter may be a number of total transmissions  1006  in the periodic transmission. For example, if the transmitting UE is associated with a vehicle, it may be transmitting a vehicle velocity periodically a total number of 100 times, or 500 times, before it needs to reschedule. This information may also include a period to dictate how frequently such data is to be transmitted. Another feedback collision detection parameter may be a number of data collection transmissions  1008  for collecting NACK statistics. In one example, if the total number of periodic transmissions is 100, the number of transmissions to be used or evaluated for collecting NACK statistics may be 10. Thus the UE will evaluate the first 10 HARQ feedbacks with respect to the 100 transmissions and make its decision based on the 10 pieces of HARQ feedback data. 
     Still referring to  FIG.  10   , another feedback collision detection parameter may include a data collection format  1010 . For example, in the example already provided, the analysis of potential collision may be based on 10/100 transmissions. In one data format  1010  only the first 10 pieces of HARQ feedback data are considered. In another aspect, each subsequent set of 10 pieces of HARQ feedback information are evaluated throughout the entire transmission, such that transmissions  1 - 10  are evaluated, then 11-20, then 21-30, and so on. In another aspect, the data collection format may be a sliding window, where pieces of HARQ feedback information  1 - 10  are evaluated, then 5-15 are evaluated, then 10-20, then 15-25, and so on. The data collection format  1010  allows flexibility in customizing a manner in which the self-collision data analysis will be conducted. 
     Another feedback collision detection parameter is a threshold  1012 . For example, as NACK statistics are collected, the percentage of received NACKs can be compared to the threshold, and if the NACK percentage exceeds the threshold, a conclusion is made that a collision exists on the scheduled resources. For example, if 10 of the 100 transmissions are evaluated with respect to their HARQ feedback responses, and 2 of the 10 HARQ feedback responses were NACKs, then the NACK percentage is 20%. If the threshold  1012  is 30% a conclusion is made that no collision exists, whereas if the threshold is 10% a conclusion is made that a collision has occurred with a competing UE on the reserved resources. 
     Referring back to  FIG.  10   , once the reserved resources are scheduled with the feedback-based collision detection parameters at  1004 , a periodic transmission is initiated and takes place at  1014  by the transmitting UE. As the periodic transmission is taking place at  1014 , NACK statistics are collected at the transmitting UE at  1016  via the HARQ feedback, and such NACK statistics are collected according to one or more of the feedback-based collision detection parameters. The process  1000  continues to  1018 , wherein the NACK statistics are converted to a percentage, for example, and compared to the threshold  1012 . If the threshold is not exceeded (NO at  1018 ), a conclusion may be made that no collision presently exists with respect to the reserved resources, and if the periodic transmission is still continuing (NO at  1020 ), additional NACK statistics may be collected depending on the data collection format  1010 . If periodic transmission has completed (YES at  1020 ), then no corrective action is needed, as no resource collision has been detected. 
     Referring back to act  1018  of  FIG.  10   , if the computed NACK percentage does exceed the threshold (YES at  1018 ), then a conclusion is made that a collision has occurred and a corrective action is selectively performed at  1024 . In one aspect, the corrective action is to discontinue the periodic transmission and initiate a re-selection process. In one aspect, the corrective action may be selective based on various other criteria. 
     Returning to query  1002  in  FIG.  10   , if the HARQ feedback is not enabled (NO at  1002 ), then the transmitting UE will not be receiving HARQ feedback information. However, if other competing UEs are transmitting and employing HARQ feedback, then such information may be detected by the evaluating UE on a feedback channel, such as the physical sidelink feedback channel (PSFCH) at  1030 . If during a monitoring the PSFCH, HARQ feedback is detected (YES at  1032 ), then an inference can be made that the periodic transmission made by the evaluating UE is colliding with a transmission of a competing UE, and a corrective action is performed at  1024 . In one example, the corrective action is discontinuing the periodic transmission and initiating a re-selection process. If no HARQ feedback is detected on PSFCH, for example (NO at  1032 ), then a conclusion is made that no collision exists, and no corrective action is taken at  1034 . For example, the periodic transmission of the evaluating UE continues. 
     In the descriptions above, description is made in conjunction with several flow diagrams outlining example methods. In this description and in the appended claims, use of the term “determine” with reference to some entity (e.g., parameter, variable, and so on) in describing a method step or function is to be construed broadly. For example, “determine” is to be construed to encompass, for example, receiving and parsing a communication that encodes the entity or a value of an entity. “Determine” should be construed to encompass accessing and reading memory (e.g., lookup table, register, device memory, remote memory, and so on) that stores the entity or value for the entity. “Determine” should be construed to encompass computing or deriving the entity or value of the entity based on other quantities or entities. “Determine” should be construed to encompass any manner of deducing or identifying an entity or value of the entity. 
     As used herein, the term identify when used with reference to some entity or value of an entity is to be construed broadly as encompassing any manner of determining the entity or value of the entity. For example, the term identify is to be construed to encompass, for example, receiving and parsing a communication that encodes the entity or a value of the entity. The term identify should be construed to encompass accessing and reading memory (e.g., device queue, lookup table, register, device memory, remote memory, and so on) that stores the entity or value for the entity. 
     As used herein, the term select when used with reference to some entity or value of an entity is to be construed broadly as encompassing any manner of determining the entity or value of the entity from amongst a plurality or range of possible choices. For example, the term select is to be construed to encompass accessing and reading memory (e.g., lookup table, register, device memory, remote memory, and so on) that stores the entities or values for the entity and returning one entity or entity value from amongst those stored. The term select is to be construed as applying one or more constraints or rules to an input set of parameters to determine an appropriate entity or entity value. The term select is to be construed as broadly encompassing any manner of choosing an entity based on one or more parameters or conditions. 
     As used herein, the term derive when used with reference to some entity or value of an entity is to be construed broadly. “Derive” should be construed to encompass accessing and reading memory (e.g., lookup table, register, device memory, remote memory, and so on) that stores some initial value or foundational values and performing processing and/or logical/mathematical operations on the value or values to generate the derived entity or value for the entity. “Derive” should be construed to encompass computing or calculating the entity or value of the entity based on other quantities or entities. “Derive” should be construed to encompass any manner of deducing or identifying an entity or value of the entity. 
     As described herein, for purposes of discussion, each vehicle employing V2X communication principles are described as a UE (i.e., user equipment).  FIG.  11    illustrates a non-limiting example of a platform  1100  (or “device  1100 ”) in accordance with various aspects that may constitute circuitry that makes up a UE. In aspects, the computer platform  1100  may be suitable for use as UEs and/or any other element/device discussed herein. The platform  1100  may include any combinations of the components shown in the example. The components of platform  1100  may be implemented as integrated circuits (ICs), portions thereof, discrete electronic devices, or other modules, logic, hardware, software, firmware, or a combination thereof adapted in the computer platform  1100 , or as components otherwise incorporated within a chassis of a larger system. The block diagram of  FIG.  11    is intended to show a high level view of components of the computer platform  1100 . However, some of the components shown may be omitted, additional components may be present, and different arrangement of the components shown may occur in other implementations. 
     Application circuitry  1105  includes circuitry such as, but not limited to one or more processors (or processor cores), cache memory, and one or more of LDOs, interrupt controllers, serial interfaces such as SPI, I2C or universal programmable serial interface module, RTC, timer-counters including interval and watchdog timers, general purpose I/O, memory card controllers such as SD MMC or similar, USB interfaces, MIPI interfaces, and JTAG test access ports. The processors (or cores) of the application circuitry  1105  may be coupled with or may include memory/storage elements and may be configured to execute instructions stored in the memory/storage to enable various applications or operating systems to run on the system  1100 . In some implementations, the memory/storage elements may be on-chip memory circuitry, which may include any suitable volatile and/or non-volatile memory, such as DRAM, SRAM, EPROM, EEPROM, Flash memory, solid-state memory, and/or any other type of memory device technology, such as those discussed herein. 
     As examples, the processor(s) of application circuitry  1105  may include a general or special purpose processor, such as an A-series processor (e.g., the A13 Bionic), available from Apple® Inc., Cupertino, Calif. or any other such processor. The processors of the application circuitry  905  may also be one or more of Advanced Micro Devices (AMD) Ryzen® processor(s) or Accelerated Processing Units (APUs); Core processor(s) from Intel® Inc., Snapdragon™ processor(s) from Qualcomm® Technologies, Inc., Texas Instruments, Inc.® Open Multimedia Applications Platform (OMAP)™ processor(s); a MIPS-based design from MIPS Technologies, Inc. such as MIPS Warrior M-class, Warrior I-class, and Warrior P-class processors; an ARM-based design licensed from ARM Holdings, Ltd., such as the ARM Cortex-A, Cortex-R, and Cortex-M family of processors; or the like. In some implementations, the application circuitry  1105  may be a part of a system on a chip (SoC) in which the application circuitry  1105  and other components are formed into a single integrated circuit, or a single package. 
     The baseband circuitry  1110  may be implemented, for example, as a solder-down substrate including one or more integrated circuits, a single packaged integrated circuit soldered to a main circuit board or a multi-chip module containing two or more integrated circuits. 
     The platform  1100  may also include interface circuitry (not shown) that is used to connect external devices with the platform  1100 . The external devices connected to the platform  1100  via the interface circuitry include sensor circuitry  1121  and electro-mechanical components (EMCs)  1122 , as well as removable memory devices coupled to removable memory circuitry  1123 . 
     A battery  1130  may power the platform  1100 , and may have a power supply coupled to an electrical grid. The battery  1130  may be a lithium ion battery, a metal-air battery, such as a zinc-air battery, an aluminum-air battery, a lithium-air battery, and the like. In some implementations, such as in V2X applications, the battery  1130  may be a typical lead-acid automotive battery. 
     While the methods are illustrated and described above as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or examples of the disclosure herein. Also, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. In some examples, the methods illustrated above may be implemented in a computer readable medium using instructions stored in a memory. Many other examples and variations are possible within the scope of the claimed disclosure. 
     EXAMPLES 
     Example 1 is an evaluating user equipment (UE) that comprises a memory and one or more processors communicatively coupled to the memory. The one or more processors are configured to schedule resources for discontinuous periodic transmission having a scheduled discontinuous time period in which scheduled resources are not transmitted, and perform a monitoring operation at the scheduled discontinuous time period, the monitoring operation comprising a monitoring for a collision of scheduled resources of the evaluating UE with scheduled resources of a competing UE. The one or more processors are also configured to selectively perform a corrective action when a collision of scheduled resources of the evaluating UE with scheduled resources of the competing UE is detected during the monitoring operation. 
     Example 2 includes the subject matter of example 1, wherein when scheduling resources for discontinuous periodic transmission, the one or more processors are configured to determine whether the evaluating UE will transmit on a next transmission time period based on a random selection having a probability that the next transmission time period is a discontinuous time period and thus not scheduled for data transmission on the next transmission time period. 
     Example 3 includes the subject matter of example 2, wherein the probability is a preconfigured probability value. 
     Example 4 includes the subject matter of claim  2 , wherein the probability depends upon a data priority associated with the scheduled resources. 
     Example 5 includes the subject of example 4, wherein the probability is a high probability value greater than a nominal probability value if the data priority is greater than a predefined threshold. 
     Example 6 includes the subject matter of example 1, wherein when scheduling resources for discontinuous periodic transmission, the one or more processors are configured to determine whether the evaluating UE will transmit on a next transmission time period based on a predefined periodicity of the scheduled discontinuous time period in which scheduled resources are not transmitted. 
     Example 7 includes the subject matter of example 6, wherein the predefined periodicity is randomly selected from a set of preconfigured periods. 
     Example 8 includes the subject matter of example 6, wherein the predefined periodicity depends upon a data priority associated with the scheduled resources. 
     Example 9 includes the subject matter of example 1, wherein when scheduling resources for discontinuous periodic transmission, the one or more processors are configured to determine that a next period will be a discontinuous transmission period, and set a resource reservation period (RRP) field of a sidelink control information (SCI) message of the evaluating UE to a new value that doubles a period of periodic transmission with respect to a previous RRP field value of the evaluating UE. 
     Example 10 includes the subject matter of example 1, wherein when scheduling resources for discontinuous periodic transmission, the one or more processors are configured to determine that a next period will be a discontinuous transmission period, and set a bit in a sidelink control information (SCI) message field to a predetermined value that indicates that a scheduled resource in the next transmission period is not reserved for data transmission, but the scheduled resource in a transmission period following the next transmission period is reserved for data transmission. 
     Example 11 includes the subject matter of example 1, wherein when performing the monitoring operation at the scheduled discontinuous time period, the one or more processors are configured to evaluate one or more relevant frequency channels for sidelink control information (SCI) messages of one or more competing UEs, and for each SCI message detected in the relevant frequency channels, determine whether any scheduled resources of the one or more competing UEs collide with scheduled resources of the evaluating UE. 
     Example 12 includes the subject matter of example 1, wherein when selectively performing the corrective action when a collision is detected, the one or more processors are configured to evaluate whether a resource reservation period (RRP) of a competing UE is identical to an RRP of the evaluating RRP, and selectively stop discontinuous periodic transmission by the evaluating UE on the scheduled resources and perform a re-selection operation to reschedule resources for discontinuous periodic transmission on different reserved resources. 
     Example 13 includes the subject matter of example 12, wherein the one or more processors are further configured to determine whether a data priority of the evaluating UE is greater than a data priority of the competing UE, and take no corrective action if the data priority of the evaluating UE is greater than the data priority of the competing UE. 
     Example 14 includes the subject matter of example 1, wherein when selectively performing the corrective action when a collision is detected, the one or more processors are configured to evaluate whether a resource reservation period (RRP) of a competing UE is an integer multiple of the RRP of the evaluating UE, and selectively stop periodic transmission on only those reserved resources by the evaluating UE that collide with transmissions of the competing UE when the RRP of the competing UE is an integer multiple of the RRP of the evaluating UE. 
     Example 15 includes the subject matter of example 14, wherein the one or more processors are configured to determine whether a data priority of the evaluating UE is greater than a data priority of the competing UE, and take no corrective action if the data priority of the evaluating UE is greater than the data priority of the competing UE. 
     Example 16 includes the subject matter of example 1, wherein when selectively performing the corrective action when a collision is detected, the one or more processors are configured to evaluate whether a resource reservation period (RRP) of the evaluating UE is an integer multiple of the RRP of the competing UE, and send a message from the evaluating UE to the competing UE to skip periodic transmission on scheduled resources that collide with the scheduled resources of the evaluating UE when the RRP of the evaluating UE is an integer multiple of the RRP of the competing UE. 
     Example 17 includes the subject matter of example 1, wherein when selectively performing the corrective action when a collision is detected, the one or more processors are configured to evaluate whether a resource reservation period (RRP) of the evaluating UE is an integer multiple of the RRP of the competing UE, and stop discontinuous periodic transmission and perform a re-selection operation to reschedule resources for discontinuous periodic transmission on different reserved resources. 
     Example 18 is directed to a method of performing user equipment (UE) autonomous selection in an evaluating UE. The method comprises scheduling resources for discontinuous periodic transmission having a scheduled discontinuous time period in which scheduled resources are not transmitted using the one or more processors, and performing a monitoring operation at the scheduled discontinuous time period, the monitoring operation comprising a monitoring for a collision of scheduled resources of the evaluating UE with scheduled resources of a competing UE the one or more processors. The method also comprises selectively performing a corrective action when a collision of scheduled resources of the evaluating UE with scheduled resources of the competing UE is detected during the monitoring operation using the one or more processors. 
     Example 19 includes the subject matter of example 18, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining whether the evaluating UE will transmit on a next transmission time period based on a random selection having a probability that the next transmission time period is a discontinuous time period and thus not scheduled for data transmission on the next transmission time period. 
     Example 20 includes the subject matter of example 19, wherein the probability is a preconfigured probability value. 
     Example 21 includes the subject matter of example 19, wherein the probability depends upon a data priority associated with the scheduled resources. 
     Example 22 includes the subject matter of example 21, wherein the probability is a high probability value greater than a nominal probability value if the data priority is greater than predefined threshold. 
     Example 23 includes the subject matter of example 18, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining whether the evaluating UE will transmit on a next transmission time period based on a predefined periodicity of the scheduled discontinuous time period in which scheduled resources are not transmitted. 
     Example 24 includes the subject matter of example 23, wherein the predefined periodicity is randomly selected from a set of preconfigured periods. 
     Example 25 includes the subject matter of example 23, wherein the predefined periodicity depends upon a data priority associated with the scheduled resources. 
     Example 26 includes the subject matter of example 18, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining that a next period will be a discontinuous transmission period using the one or more processors, and setting a resource reservation period (RRP) field of a sidelink control information (SCI) message of the evaluating UE to a new value that doubles a period of periodic transmission with respect to a previous RRP field value of the evaluating UE using the one or more processors. 
     Example 27 includes the subject matter of example 18, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining that a next period will be a discontinuous transmission period, and setting a bit in a sidelink control information (SCI) message field to a predetermined value that indicates that a scheduled resource in the next transmission period is not reserved for data transmission, but the scheduled resource in a transmission period following the next transmission period is reserved for data transmission. 
     Example 28 includes the subject matter of example 18, wherein when performing the monitoring operation at the scheduled discontinuous time period, the method comprises evaluating one or more relevant frequency channels for sidelink control information (SCI) messages of one or more competing UEs, and for each SCI message detected in the relevant frequency channels, determining whether any scheduled resources of the one or more competing UEs collide with scheduled resources of the evaluating UE. 
     Example 29 includes the subject matter of example 18, wherein when selectively performing the corrective action when a collision is detected, the method comprises evaluating whether a resource reservation period (RRP) of a competing UE is identical to an RRP of the evaluating RRP, and selectively stopping discontinuous periodic transmission by the evaluating UE on the scheduled resources and perform a re-selection operation to reschedule resources for discontinuous periodic transmission on different reserved resources. 
     Example 30 includes the subject matter of example 29, and further comprises determining whether a data priority of the evaluating UE is greater than a data priority of the competing UE, and taking no corrective action if the data priority of the evaluating UE is greater than the data priority of the competing UE. 
     Example 31 includes the subject matter of example 18, wherein when selectively performing the corrective action when a collision is detected, the method comprises evaluating whether a resource reservation period (RRP) of a competing UE is an integer multiple of the RRP of the evaluating UE, and selectively stopping periodic transmission on only those reserved resources by the evaluating UE that collide with transmissions of the competing UE when the RRP of the competing UE is an integer multiple of the RRP of the evaluating UE. 
     Example 32 includes the subject matter of example 31, and further comprises determining whether a data priority of the evaluating UE is greater than a data priority of the competing UE, and taking no corrective action if the data priority of the evaluating UE is greater than the data priority of the competing UE. 
     Example 33 includes the subject matter of example 18, wherein when selectively performing the corrective action when a collision is detected, the method further comprises evaluating whether a resource reservation period (RRP) of the evaluating UE is an integer multiple of the RRP of the competing UE, and sending a message from the evaluating UE to the competing UE to skip periodic transmission on scheduled resources that collide with the scheduled resources of the evaluating UE when the RRP of the evaluating UE is an integer multiple of the RRP of the competing UE. 
     Example 34 includes the subject matter of example 18, wherein when selectively performing the corrective action when a collision is detected, the method comprises evaluating whether a resource reservation period (RRP) of the evaluating UE is an integer multiple of the RRP of the competing UE, and stopping discontinuous periodic transmission and perform a re-selection operation to reschedule resources for discontinuous periodic transmission on different reserved resources. 
     Example 35 is directed to a non-transitory computer readable medium containing instructions, wherein such instructions when executed by one or more processors is configured to perform a method of performing user equipment (UE) autonomous selection in an evaluating UE. Such method comprises scheduling resources for discontinuous periodic transmission having a scheduled discontinuous time period in which scheduled resources are not transmitted using one or more processors, performing a monitoring operation at the scheduled discontinuous time period, the monitoring operation comprising a monitoring for a collision of scheduled resources of the evaluating UE with scheduled resources of a competing UE using the one or more processors, and selectively performing a corrective action when a collision of scheduled resources of the evaluating UE with scheduled resources of the competing UE is detected during the monitoring operation using the one or more processors. 
     Example 36 includes the subject matter of example 35, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining whether the evaluating UE will transmit on a next transmission time period based on a random selection having a probability that the next transmission time period is a discontinuous time period and thus not scheduled for data transmission on the next transmission time period. 
     Example 37 includes the subject matter of example 36, wherein the probability is a preconfigured probability value. 
     Example 38 includes the subject matter of example 36, wherein the probability depends upon a data priority associated with the scheduled resources. 
     Example 39 includes the subject matter of example 38, wherein the probability is a high probability value greater than a nominal probability value if the data priority is greater than predefined threshold. 
     Example 40 includes the subject matter of example 35, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining whether the evaluating UE will transmit on a next transmission time period based on a predefined periodicity of the scheduled discontinuous time period in which scheduled resources are not transmitted. 
     Example 41 includes the subject matter of example 40, wherein the predefined periodicity is randomly selected from a set of preconfigured periods. 
     Example 42 includes the subject matter of example 40, wherein the predefined periodicity depends upon a data priority associated with the scheduled resources. 
     Example 43 includes the subject matter of example 35, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining that a next period will be a discontinuous transmission period using the one or more processors, and setting a resource reservation period (RRP) field of a sidelink control information (SCI) message of the evaluating UE to a new value that doubles a period of periodic transmission with respect to a previous RRP field value of the evaluating UE using the one or more processors. 
     Example 44 includes the subject matter of example 35, wherein when scheduling resources for discontinuous periodic transmission, the method comprises determining that a next period will be a discontinuous transmission period, and setting a bit in a sidelink control information (SCI) message field to a predetermined value that indicates that a scheduled resource in the next transmission period is not reserved for data transmission, but the scheduled resource in a transmission period following the next transmission period is reserved for data transmission. 
     Example 45 includes the subject matter of example 35, wherein when performing the monitoring operation at the scheduled discontinuous time period, the method comprises evaluating one or more relevant frequency channels for sidelink control information (SCI) messages of one or more competing UEs, and for each SCI message detected in the relevant frequency channels, determining whether any scheduled resources of the one or more competing UEs collide with scheduled resources of the evaluating UE. 
     Example 46 includes the subject matter of example 35, wherein when selectively performing the corrective action when a collision is detected, the method comprises evaluating whether a resource reservation period (RRP) of a competing UE is identical to an RRP of the evaluating RRP, and selectively stopping discontinuous periodic transmission by the evaluating UE on the scheduled resources and perform a re-selection operation to reschedule resources for discontinuous periodic transmission on different reserved resources. 
     Example 47 includes the subject matter of example 46, and further comprises determining whether a data priority of the evaluating UE is greater than a data priority of the competing UE, and taking no corrective action if the data priority of the evaluating UE is greater than the data priority of the competing UE. 
     Example 48 includes the subject matter of example 35, wherein when selectively performing the corrective action when a collision is detected, the method comprises evaluating whether a resource reservation period (RRP) of a competing UE is an integer multiple of the RRP of the evaluating UE, and selectively stopping periodic transmission on only those reserved resources by the evaluating UE that collide with transmissions of the competing UE when the RRP of the competing UE is an integer multiple of the RRP of the evaluating UE. 
     Example 49 includes the subject matter of example 48, and further comprises determining whether a data priority of the evaluating UE is greater than a data priority of the competing UE, and taking no corrective action if the data priority of the evaluating UE is greater than the data priority of the competing UE. 
     Example 50 includes the subject matter of example 35, wherein when selectively performing the corrective action when a collision is detected, the method further comprises evaluating whether a resource reservation period (RRP) of the evaluating UE is an integer multiple of the RRP of the competing UE, and sending a message from the evaluating UE to the competing UE to skip periodic transmission on scheduled resources that collide with the scheduled resources of the evaluating UE when the RRP of the evaluating UE is an integer multiple of the RRP of the competing UE. 
     Example 51 includes the subject matter of example 35, wherein when selectively performing the corrective action when a collision is detected, the method comprises evaluating whether a resource reservation period (RRP) of the evaluating UE is an integer multiple of the RRP of the competing UE, and stopping discontinuous periodic transmission and perform a re-selection operation to reschedule resources for discontinuous periodic transmission on different reserved resources. 
     The term “couple” is used throughout the specification. The term may cover connections, communications, or signal paths that enable a functional relationship consistent with the description of the present disclosure. For example, if device A generates a signal to control device B to perform an action, in a first example device A is coupled to device B, or in a second example device A is coupled to device B through intervening component C if intervening component C does not substantially alter the functional relationship between device A and device B such that device B is controlled by device A via the control signal generated by device A. 
     It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users.