Device and method for transmitting and receiving message in vehicle-to-vehicle communication

Abstract

A device for periodically transmitting and receiving a message to and from a counterpart device in sidelink communication according to an embodiment of the present invention may comprise: a memory configured to store a code for periodically transmitting and receiving a message to and from the counterpart device; and a processor configured to execute the code to perform an operation for periodically transmitting and receiving a message to and from the counterpart device.

Description

Device and method for transmitting and receiving messages in inter-vehicle communication

[0001] The present invention relates to wireless communication technology, and more specifically, to an apparatus and method for transmitting and receiving messages via a side link.

[0002] The national research and development projects that supported this invention are as follows:

[0003] This work was supported by the Korea Planning & Evaluation Institute of Industrial Technology (KEIT) grant funded by the Korea government(MOTIE) (RS-2025-02413183, Development of centralized resource management-based Ultra-high-speed / Ultra reliable V2X communication module technology that guarantees QoS)

[0004] Sidelink refers to a communication method that establishes a direct link between terminals, allowing voice or data to be exchanged directly without passing through a base station. Sidelink is being considered as a solution to alleviate the burden on base stations caused by rapidly increasing data traffic.

[0005] V2X (vehicle-to-everything) refers to a communication technology that exchanges information with other vehicles, pedestrians, and infrastructure-enabled objects through wired or wireless communication. V2X may include V2V (vehicle-to-vehicle), V2I (vehicle-to-infrastructure), V2N (vehicle-to-network), and V2P (vehicle-to-pedestrian).

[0006] V2X technology is attracting attention as a key technology that improves traffic safety and efficiency by enabling real-time information exchange between vehicles, road infrastructure, pedestrians, and other vehicles. V2X communication is generally implemented through IEEE 802.11p-based vehicle ad-hoc networks (WAVE, Wireless Access in Vehicular Environments) or 3GPP-based cellular V2X (C-V2X). In these communication methods, effective channel sensing and time delay management are essential for reliable data transmission.

[0007] In V2X communication, since multiple vehicles share a common channel, channel sensing is required to prevent packet collisions and ensure efficient communication. IEEE 802.11p-based WAVE systems use the CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) method to sense channels and transmit data only when available. However, this method can suffer from reduced reliability due to rapid channel changes in high-speed moving environments, and transmission latency may increase due to contention, particularly in situations with high traffic. On the other hand, C-V2X utilizes Semi-Persistent Scheduling (SPS), a schedule-based resource allocation method that transmits and receives data at regular intervals without carrier sensing, but it may lack flexibility regarding dynamic traffic changes.

[0008] Delays in the channel sensing process can degrade the performance of V2X application services. For example, safety-related services such as the Emergency Vehicle Warning System (EVWS) or Collision Avoidance System require low latency and high reliability. However, in the CSMA / CA method, packet delivery may be delayed due to random delays during the backoff process, and in the C-V2X method, communication delays may occur because retransmission is required when free resources are scarce.

[0009] Therefore, for efficient V2X communication, new techniques are required to enhance channel sensing accuracy and minimize packet collisions and transmission delays. In particular, for vehicle safety services where real-time data exchange is critical, technical improvements are necessary to enable stable channel access even in dynamic network environments.

[0010] Accordingly, the present invention proposes a device or method for transmitting and receiving messages at a side link.

[0011] In addition, the present invention proposes a device or method for transmitting and receiving messages that can reduce delay time in a side link.

[0012] The problems of the present invention are not limited to those described above. Other problems not described above will be understood by a person skilled in the art from the description of the present invention below.

[0013] According to one embodiment of the present invention, in sidelink communication, a device for periodically transmitting and receiving messages with a counterpart device is proposed, the device includes a memory configured to store code for periodically transmitting and receiving messages with a counterpart device; and a processor configured to execute said code to perform an operation for periodically transmitting and receiving messages with said counterpart device, said operation including selecting a resource in a resource selection window for transmitting and receiving data, receiving a message from the counterpart device in said selected resource, or transmitting a message to the counterpart device, and a parameter indicating the end time of said resource selection window or the size of said resource selection window may be set to less than or equal to half of a resource reservation period (RRP).

[0014] Additionally or alternatively, a parameter indicating the end time of the resource selection window ensures that even if resource reselection is performed, the transmission period or interval of periodic request messages, or the transmission period or interval of periodic response messages, is equal to or smaller than the RRP.

[0015] Additionally or alternatively, the above operation includes configuring to change the set packet delay budget (PDB), and said changed PDB may be set to be smaller than the value determined by the following formula. The formula is as follows: the RRP + 2 * parameter indicating the start time of the resource selection window - parameter indicating the end time of the resource selection window.

[0016] Additionally or alternatively, the above operation may include performing resource reselection if the time length to the next resource capable of transmitting the response message generated in the upper layer is greater than the changed PDB.

[0017] Additionally or alternatively, the above operation may include transmitting the response message from the re-selected resource.

[0018] According to another embodiment of the present invention, a method for periodically transmitting and receiving messages with a counterpart device in sidelink communication is proposed, the method may include the step of selecting a resource in a resource selection window for transmitting and receiving data; and the step of receiving a message from the counterpart device in the selected resource or transmitting a message to the counterpart device, and a parameter indicating the end time of the resource selection window may be set to less than or equal to 1 / 2 of the resource reservation period (RRP).

[0019] Additionally or alternatively, a parameter indicating the end time of the resource selection window ensures that even if resource reselection is performed, the transmission period or interval of periodic request messages, or the transmission period or interval of periodic response messages, is equal to or smaller than the RRP.

[0020] Additionally or alternatively, the above method includes a step of configuring to change the set packet delay budget (PDB), and said changed PDB may be set to be smaller than a value determined by the following formula. The formula is as follows: said RRP + 2 * parameter indicating the start time of said resource selection window - parameter indicating the end time of said resource selection window.

[0021] Additionally or alternatively, the method may include a step of performing resource reselection if the time length to the next resource capable of transmitting the response message generated in the upper layer is greater than the changed PDB.

[0022] Additionally or alternatively, the method may include the step of transmitting the response message from the re-selected resource.

[0023] According to another embodiment of the present invention, a computer-readable medium is proposed for storing a computer program for performing the method described above.

[0024] The means of solution of the present invention described above are part of the embodiments of the present invention. Various means of solution other than the means of solution of the problem described above may be derived and understood based on the detailed description of the present invention to be explained below.

[0025] The present invention has the following effects.

[0026] The present invention can reduce latency in side link communication that exchanges request messages and response messages.

[0027] In addition, the present invention can reduce delay time within the scope of current standards without revising standards related to side links.

[0028] The effects of the present invention are not limited to those described above. Other effects not described above may be understood by a person skilled in the art from the description of the present invention below.

[0029] The accompanying drawings, which are included as part of the detailed description to aid in understanding the present invention, provide embodiments of the present invention and explain the contents of the present invention together with the detailed description.

[0030] Figure 1 illustrates a V2X communication environment.

[0031] Figure 2 is a figure illustrating the effect of the size of a resource selection window according to the prior art on delay.

[0032] Figure 3 is a diagram illustrating the problem of delay occurring due to resource selection according to conventional technology.

[0033] Figure 4 illustrates the resource reordering problem caused by resource reselection.

[0034] Figure 5 shows the difference between communication delay according to the prior art and communication delay when resource reselection according to the present invention is applied.

[0035] Figures 6 and 7 show simulation results according to the present invention.

[0036] FIG. 8 illustrates a flowchart of a method for selecting a resource and transmitting a message from a selected resource according to the present invention.

[0037] Figure 9 shows a block diagram of a transmitting device and a receiving device.

[0038] FIG. 1 illustrates a communication environment to which the present invention is applied.

[0039] V2X (Vehicle to Everything) refers to a communication system that includes wireless communication (V2V) between vehicles (2). V2V serves not only the basic role of informing surrounding vehicles of information such as the vehicle's location, direction, and speed, but also serves to inform them of potential hazards such as sudden braking and changes in direction.

[0040] Additionally, V2X refers to a system in which a vehicle communicates and shares with various elements on the road to enable autonomous driving, such as wireless communication between a vehicle and a network (3) (V2N), wireless communication between a vehicle and a roadside unit (RSU) (4), and wireless communication between a vehicle and traffic infrastructure (5) (V2I).

[0041] It can be used to notify each other of potential hazards through vehicle-to-vehicle communication, or to check information such as parking locations and signal change times through communication with traffic infrastructure like parking lots and traffic lights, and is considered an essential technology for perfect autonomous driving.

[0042] V2X is implemented via sidelink within 5G communication standards. Vehicles, namely the transmitting and receiving sides, transmit and receive information via sidelink.

[0043] In cellular V2X communication using periodic broadcasts, a Sensing-Based Semi-Persistent Scheduling (SPS) algorithm is executed for distributed resource allocation at each vehicle or each vehicle terminal. Since base stations may not exist in some areas, distributed scheduling is the default mode, which is called Sidelink Mode 2 in 5G NR (New Radio).

[0044] When a vehicle or vehicle terminal needs to select a resource in time slot n, the resource selection window is assumed to have a range of [n + T1, n + T2]. Here, T1 is the processing time required for the vehicle to calculate the resource location based on observations over the past 1,100 ms (for periodic transmission) or 100 ms (for non-periodic transmission). T2 must satisfy the range T2min ≤ T2 ≤ PDB (packet delay budget), which is determined by the implementation of the vehicle terminal (UE or OBU) or RSU.

[0045] The PDB is configured by the application and provided as a parameter to the scheduling algorithm. When a resource is selected in the resource selection window, the SPS allows that resource to be used multiple times.

[0046] The usage method is as follows:

[0047] The vehicle is a subframe t TX A packet can be transmitted at + (k - 1) · RRP (1 ≤ k ≤ RC). Here, t TX is a subframe in which the vehicle terminal first transmits a packet to a reserved resource, RRP (Resource Reservation Period) is the resource reservation period of the vehicle terminal, and RC (Resource Reselection Counter) is a resource reselection counter.

[0048] RRP is set to 1 to 99ms or multiples of 100ms, up to a maximum of 1000ms.

[0049] The RC value is set to a uniform random value.

[0050] If the RC value decreases to 0, the vehicle terminal has a probability of 1 - P keep Select a new resource again, or P keep The previous resource is used continuously with a probability of ≤ 0.8. This process serves to prevent resource collisions between multiple vehicle terminals.

[0051] However, regarding communication between such vehicle terminals, increased latency and reverse issues occur on the request message sender or the response message sender side, so I will explain this first.

[0052] When a vehicle terminal sends a request and another vehicle terminal responds to it, this interaction has causality.

[0053] When considering these causal interactions in a cellular V2X environment, the following two problems may occur.

[0054] 1. Scheduling delay

[0055] 2. Causal relation affecting interaction delay

[0056] The first problem is related to the fact that communication delay can be doubled compared to unidirectional broadcast applications.

[0057] Therefore, delays must be controlled more strictly.

[0058] For example, let's assume that each vehicle terminal has reserved resources to send messages at 100ms intervals (RRP = 100ms).

[0059] In this case, the delay until the requesting vehicle terminal receives a response may reach or exceed 200ms in the worst case.

[0060] In other words, the interaction delay (RTT) is expressed as follows.

[0061] [Mathematical Formula 1]

[0062]

[0063] Here, T t+r is the transmission and reception delay (transmission + reception delay) (e.g., the time it takes for a message transmitted from vehicle terminal A to be received at vehicle terminal B or vice versa), and this is assumed to be a value much smaller than T2.

[0064] T proc T is the time taken to process a message at the application layer (i.e., the time required to receive a request and generate a response), and T2 is the size of the resource selection window, so if vehicle terminals A and B select a resource close to the end of the resource selection window, the RTT may become longer.

[0065] In fact, measurement experiments using commercial V2X equipment confirm that this phenomenon occurs frequently.

[0066] If the RTT exceeds a message generation cycle of 100ms, vehicle terminal A may not receive a response message from vehicle terminal B before sending its next request message. In other words, a problem may occur where a new request message is sent without receiving a response message for a previous request message.

[0067] However, in real-time applications, it is more natural and desirable for the response message to arrive before the request message. In other words, it is ideal for a new request message to be generated or sent after the response message arrives.

[0068] One way to solve this problem is to reduce the size of the resource selection window, i.e., T2.

[0069] Reducing T2 is expected to decrease RTT because the time interval between when a message is generated at the upper layer and when it is transmitted at the access layer becomes shorter (see Equation 1).

[0070] Unfortunately, reducing T2 in Equation 1 alone cannot completely solve the problem.

[0071] This is because there is another factor that cannot be explained by mathematical formula 1.

[0072] This is a delay pathology caused by a resource topology sequence that violates the causality of interactions. Since each vehicle terminal independently reserves sidelink resources without considering the relative timing of these resources in potential interactions, there is a lack of resource synchronization between interacting vehicle terminals. Consequently, communication delays can increase depending on relative timing. Essentially, delay spikes can occur when the causality of interactions at the application layer is not reflected at the resource allocation (i.e., MAC) layer.

[0073] To understand this aspect, it is necessary to classify the resource topology between communicating vehicle terminals A and B into two types: forward order and reverse order. Let VnA be defined as the resource that first appears at vehicle terminal A after a request message Qn (creation), and VnB as the resource that appears at vehicle terminal B. For convenience, n is used as the sequence number of all events occurring between Qn and Qn+1 on both the requester and responder sides. Therefore, Rn is the response that first appears after Qn and before Qn+1.

[0074] Now, T proc ≪RRP and T t+rLet's assume that ≪RRP. Then, the characteristics of these two orders can be summarized as follows.

[0075] 1. Forward Order

[0076] (a) The event timeline is as follows.

[0077]

[0078] Here, means "precedes".

[0079] (b) To achieve RTT < RRP, T2 must be limited to RRP / 2 or less.

[0080] If T2 is not controlled, RTT may exceed RRP.

[0081] This is as described in FIG. 2. FIG. 2 is a figure illustrating the effect of the size of a resource selection window according to the prior art on delay.

[0082] 2. Reverse Order

[0083] (a) The event timeline is as follows.

[0084] and, here, This means that it is uncertain which occurs first among VnA and VnB, and Vn+1A and Vn+1B. Consequently, The following order may appear.

[0085] (b) The empirical RTT of vehicle A has the following range.

[0086] RRP < RTT < 2·RRP

[0087] In other words, no matter how T2 is set, RTT is at least greater than RRP and can increase up to 2RRP.

[0088] Reverse ordering refers to a resource topology that forces a response to a request to be sent after the next request.

[0089] In other words, it refers to the case where the following precedence relation exists in the timeline.

[0090]

[0091] In forward order, when T2 is large, the Round Trip Time (RTT) can exceed the Resource Reservation Period (RRP), as can be seen in Figure 2. However, this can be mitigated by using a small T2. For example, when T2 < RRP / 2, the following holds.

[0092] [Mathematical Formula 2]

[0093]

[0094] Here, t(x,y)=xy represents the time difference between two events x and y. This is a necessary condition for receiving a response before the next request is sent within a single RRP.

[0095] In forward order, interaction delay can be controlled to be below RRP, but in reverse order, it is impossible to achieve sub-RRP delay by simply adjusting T2.

[0096] In other words, the following relationship holds true in reverse order.

[0097]

[0098] On the other hand, in the forward order,

[0099]

[0100] The relationship is established.

[0101] In reverse order, since the response Rn cannot use VnB and must instead use Vn+1B, the RTT is bound to be greater than the RRP.

[0102] That is, RTT > t(Vn+1B,Qn) > t(Vn+1B,VnB) (Reason: Qn VnB)

[0103] Therefore, RTT > RRP holds true.

[0104] This relationship always holds regardless of T2.

[0105] In reverse order, RTT has the following upper limit.

[0106] RTT < t(Vn+1B,Rn) + t(VnA,Qn) < t(Vn+1B,VnB) + t(VnA,Qn) < RRP + t(VnA,Qn)

[0107] Therefore, since t(VnA, Qn) ≤ T2 ≤ RRP,

[0108] RTT ≤ 2·RRP holds.

[0109] That is, in reverse order, RTT can increase up to 2 times the RRP. However, this maximum delay time may be too long for real-time safety-critical communication and is very long compared to the minimum sidelink communication delay between interacting vehicles.

[0110] Figure 3 illustrates two resource topologies with examples and shows how a reverse order is formed during the SPS resource reselection process due to some unfortunate series of events. Figure 3 is a figure intended to illustrate the problem of delays occurring due to resource reselection according to the prior art.

[0111] Figure 3(b) shows an example where reverse ordering occurs due to a requesting vehicle. Requesting vehicle terminal A uses V1A, and then performs resource reselection as the RC value reaches 0. Assuming that the new resource V1*A is located near the right end within the resource selection window, A relationship is established. Here, "*" signifies the re-selected resource. Therefore, Q2 must use V2A. In this case, t(V2A, V1*A) = RRP. However, the resources on the responding vehicle terminal B side are not changed, and still Maintain the relationship. As a result, Four events occur within the RRP range, and RTT > t(V3B, Q2) > RRP.

[0112] Figure 3(c) describes a case where the responding vehicle B performs resource reselection to generate a reverse order. The resources of the responding vehicle B move from the left end to the right end of the resource selection window. In this case, It becomes, A reverse order occurs. Therefore, R2 must use V3B, and t(V3B, V2*B) = RRP. Due to this, Therefore, t(V3B, Q2) > RRP holds. If a new resource is located before Q2, this is not reverse order, and V1*B and Q2 are It forms a relationship like that. In this case, it becomes a forward order, and then The relationship that... is established.

[0113] However, unfortunately, the formation of reverse order is unavoidable. This is because probabilistic resource reallocation between vehicle terminals is continuously performed in the SPS to mitigate resource conflicts. Whenever the internal RC count reaches 0, the vehicle 1 - P keepResource reselection is performed with a probability of . Even if the resource topology between two interacting vehicle terminals is in forward order, resource reselection of one of the vehicle terminals may result in reverse order, as shown in (b) and (c) of FIG. 3.

[0114] In the following, a solution is proposed to address the large, variable, and unpredictable delay problem that occurs in the interaction communication between vehicle terminals using periodic resources in the NR sidelink. Specifically, based on the preceding discussion, the solution presented in this specification consists of two components.

[0115] The first approach is to reduce the T2 value to address the significant latency issue in forward resource order. As previously discussed, this method does not resolve the problem in reverse order.

[0116] Therefore, the second step is to detect the reverse order and correct it.

[0117] Since the first method is relatively simple, I would like to focus on the second method.

[0118] The root cause of the reverse ordering problem lies in the fact that while sidelink endpoints allocate resources independently, applications require bidirectional packet exchange to implement request-response interactions. Although the two peers could prevent reverse ordering by explicitly coordinating resource allocation, this would require an additional signaling protocol. Therefore, we consider a standard-compliant approach where the MAC layer on the responder side automatically eliminates the possibility of reverse ordering without additional scheduling. The proposed solution utilizes the responder's Packet Delay Budget (PDB) and other parameters to rapidly perform resource re-alignment whenever there is a risk of reverse ordering.

[0119] Accordingly, we intend to present the behavior of the responding vehicle terminal when the resource topology changes due to the SPS algorithm.

[0120] First, we propose a case where the requesting vehicle terminal performs resource reselection according to SPS, and second, a case where the responding vehicle terminal itself performs resource reselection according to SPS.

[0121] Figure 4 illustrates the resource reordering problem caused by resource reselection.

[0122] First, we will explain how to handle the reverse order caused by resource reselection of the requesting vehicle terminal.

[0123] In FIG. 4(a), vehicle terminals A and B begin interacting in a forward-ordered resource topology. It is assumed that a time reference for the request is established, and that after vehicle terminal A transmits Q1, it performs resource reselection and uses V2A for Q2. Consequently, the resource order between the two vehicle terminals is reversed: Is It proceeds in the order of . Since t(V3B, V2B) = RRP, we obtain RTT > t(V3B, Q2) > RRP. To accurately describe RTT based on SPS system parameters, timing-related variables are defined as follows: α = t(V1A, Q1), β = t(V1B, R1). In Fig. 4(a), the relationship between variables before resource reselection is given as follows.

[0124] T1(A) ≤ α ≤ T2(A), T1(B) ≤ β ≤ T2(B)

[0125] Therefore, it can be summarized as follows.

[0126] [Mathematical Formula 3]

[0127]

[0128] After the reverse order resulting from resource reselection, the following relationships are additionally formed.

[0129] [Mathematical Formula 4]

[0130]

[0131] Here, δ is the time that the response message R2 of the responding vehicle terminal B waits for the next available resource. That is, δ represents the time that the responding vehicle terminal B waits for the transmission of the response message R2 after the response message R2 is generated at the upper layer. In Fig. 4(a), δ is defined as follows.

[0132] δ = (α + β + RRP) - α′ - T proc

[0133] Here, T proc is the delay in processing the respondent's request. Through (4) and (5), the minimum value of δ is as follows.

[0134] [Mathematical Formula 5]

[0135]

[0136] This is explained solely by system parameters, regardless of α, β, α′, and δ. Alternatively, if the two vehicles have identical T1 and T2 values ​​for a common application, the minimum value of δ is as follows.

[0137] [Mathematical Formula 6]

[0138]

[0139] This is the case where reverse ordering occurs due to resource reselection by the requesting vehicle terminal. For convenience, the right-hand side can be referred to as δmin. T proc Since it depends on processing capacity, it is unrelated to the communication protocol and is a local parameter at the response vehicle terminal B. proc Since is expected to be minimized, T proc Set to 0. Otherwise, the responding vehicle terminal is T in Equation 6 proc This can be considered. Since δmin actually increases even when T2 is reduced to a small value, this is one of the reasons why a small T2 cannot resolve the reverse order.

[0140] The solution proposed in this specification modifies the reverse order by triggering resource reselection to break the condition of Equation 6. To this end, the PDB, which is a parameter of the resource allocation hierarchy, may be utilized. Specifically, resource reselection is triggered when a situation satisfying Equation 6 occurs. To this end, the following is required.

[0141] [Mathematical Formula 7]

[0142]

[0143] In the responding vehicle terminal B, resource reselection according to the inequality in Equation 7 always succeeds in eliminating delay spikes. In the relevant communication standard, PDB-triggered reselection is defined as a suitable but optional feature. The relevant communication standard states: “If the remaining PDB is not satisfied, the UE implementation ... decides whether to perform sidelink resource reselection” (3GPP TS 38.321

[0037] , 5.22.1.2). Below, we describe the results of verifying whether this approach works properly in commercial V2X devices using Equation 7 in experiments.

[0144] The important point is that Equation 7 is free from time-related conditions such as α, β, and α′. Consequently, the responding vehicle terminal does not need to communicate with the requesting vehicle terminal to query the values ​​of α and α′. Instead, by using only the application-specific T1 and T2 parameters, the responding vehicle terminal can modify the reverse order to the forward order.

[0145] If T2 is set to a small value, the changes required in the PDB are also small, resulting in minimal impact on the previously specified PDB value. However, below, we will also discuss the impact of using a larger T2 value.

[0146] Regarding the reduction of PDB requirements at the MAC layer, the impact on the system can be considered from two perspectives.

[0147] First, the PDB is an application function and is provided as a parameter to the MAC layer. Since the PDB requirement represents a worst-case latency limit, meeting it early is not an issue; conversely, exceeding or violating it can be problematic.

[0148] Second, setting the PDB value smaller can lead to an increase in resource reselection. If the PDB is reduced more drastically in Equation 7, resource reselection may become more frequent. In SPS-based systems, since an increase in resource reselection can affect the packet reception rate (PRR), it is important to minimize the reduction of the PDB requirement.

[0149] However, the experiment shown below will demonstrate that the proposal of this specification does not significantly increase the number of resource reselections. The core of the problem that this proposal aims to solve is not the frequency of resource reselection, but the duration of the delay spike.

[0150] Consider the second type of reverse ordering problem. This is the case where it occurs due to resource reselection by the responding vehicle terminal B. Refer to Figure 4(b). In this case, the responding vehicle terminal does not need to infer the reverse ordering condition indirectly.

[0151] That is, the responding vehicle terminal B can immediately determine whether the resource it has selected results in a reverse order. For example, in FIG. 4(b), the responding vehicle terminal B knows that Q2 will arrive one RRP after V1A. Therefore, when the responding vehicle terminal B performs resource reselection after transmitting R1, it will reject V2*B as illustrated. The reason is that the resource in question results in a reverse order:

[0152]

[0153] Instead, the responding vehicle terminal B will attempt to use a resource closer to the left edge of the selection window. However, the responding vehicle terminal B does not know the exact timing of Q2 or the value of α, which is an internal variable of the requesting vehicle terminal A. Therefore, the best strategy is to use a small T2 value to cause the selected resource to move to the left edge of the selection window.

[0154] Since T1 ≤ α, β, β′ ≤ T2, a small T2 value helps reduce α. This is It works to your advantage in establishing a relationship.

[0155] T proc and T t+r If other delay factors such as can be ignored, then if T2 < 50ms The relationship is guaranteed. If not, T2 must be reduced further appropriately.

[0156] In this case, the following resource order can be obtained:

[0157] , where t(V2B, V1*B) = RRP.

[0158] This is another reason why a small T2 value must be used in the proposed solution. Consequently, We obtain the order as follows, which is a forward order and satisfies the condition RTT < RRP.

[0159] In addition, resource realignment can be performed individually for each pair of vehicles. Since maneuver coordination generally occurs between the two vehicles, the complexity of the realignment will not be high.

[0160] Even in cases where there is a 1:N relationship in a single driving coordination session (e.g., communication between a leader and a member in platooning), there is no mutual interference because N pairs of vehicles can be processed individually.

[0161] The following describes the results of verifying whether the proposed method actually eliminates delay spikes by running the solution on a commercial device compliant with sidelink-related communication standards.

[0162] Two OBUs from Etipos Co., Ltd. were used for the measurement. These are 5G-V2X sidelink terminals compliant with 3GPP Release-16 and are implemented in software.

[0163] The following parameter values ​​were used for the measurement, and the T2 and PDB values ​​were changed to apply Equation 7 described above. However, since the device used did not allow for completely free adjustment of the two parameters, the following values ​​were used for the measurement experiment.

[0164] T2: 10ms and 100ms

[0165] PDB: 80ms, 90ms, 95ms, 100ms

[0166] The remaining parameters were used as shown in the following table.

[0167] [Table 1]

[0168]

[0169] Figure 5 shows the difference between communication delay according to the prior art and communication delay when resource reselection according to the present invention is applied. Specifically, Figure 5 shows the measurement results of V2V (vehicle-to-vehicle) interactive communication with the current SPS algorithm (reference value) and the proposed method applied.

[0170] For reference values ​​(T2 = 100ms, PDB = 100ms), there are frequently occurring unpredictable delay spikes, as shown in Figure 5 (a).

[0171] On the other hand, reducing T2 (Fig. 5 (b)) brings about the following two distinct effects.

[0172] (1) Basic delay decreased to about 20ms → This is the expected result, and

[0173] RTT T by the 2·T2 relationship proc and T t+r This can be verified if it is relatively very small.

[0174] (2) The frequency of delayed spikes is greatly reduced → However, it can be seen that simply reducing T2 alone cannot completely eliminate the spikes.

[0175] This is because the reverse ordering problem cannot be solved with only a small T2.

[0176] In fact, the remaining delay spikes were caused by reverse ordering.

[0177] On the other hand, using PDB-based resource reselection (utilizing Equation 7) combined with a small T2 can completely eliminate delay spikes. Figures 5(d) and 5(e) show the results using T2=10ms, PDB=90ms, and T2=10ms, PDB=80ms, respectively.

[0178] That is, PDB = 80ms satisfies the requirements of Equation 7 (since RRP is 100ms and T1 is a value close to 0 in Table 1), and as a result, the reverse order phenomenon is successfully eliminated.

[0179] Figure 5(c) is noteworthy in that it shows that delay spikes can be eliminated even with PDB values ​​larger than those required by Equation 7, which is a conservative condition. According to Equation 7, if the PDB value at given parameter values ​​(RRP, T1, T2) is less than RRP + 2T1 - T2 = 92ms (T1 = 1ms), PDB-based resource reselection is triggered to eliminate delay spikes. However, this is only a conservative threshold value that guarantees reselection. That is, in some cases, PDB-based reselection may occur even with PDB values ​​larger than the threshold value.

[0180] The reason is that although Equation 7 assumes the worst case (α′ = T2), Equation 5 allows for α′ < T2, and according to Equation 4, it is sufficient to satisfy α′ > α + β. For example, when RRP = 100ms, T1 = 1ms, and T2 = 10ms, the threshold value of PDB is 92ms, but when α = 1, β = 1, and α′ = 3, reselection can occur even at PDB = 95ms. This is because the time difference from the resource α + β to the next resource is RRP + (α + β) - α′ = 99ms, which exceeds the non-conservative PDB value of 95ms.

[0181] In conclusion, Figure 5 suggests that there is no need to unnecessarily lower the PDB value after Equation 7 is satisfied, and that similar latency performance is observed when the PDB value is 90ms or less. This will be confirmed in the simulation results below, and it will also show that while an excessively low PDB value may increase the frequency of resource reselection, the increase is minimal.

[0182] Table 2 summarizes the measured delay statistics. Reducing the PDB to 100ms or less significantly reduces the delay standard deviation, clearly demonstrating that delay spikes have been eliminated. On the other hand, when only T2 is reduced to 10ms from the base PDB value, the average delay time decreases slightly, but the effect of reducing the standard deviation is not very significant because delay spikes are not all eliminated.

[0183] Schemeμ[ms]σ[ms]Baseline (T2 = 100 ms, PDB = 100ms)102.4845.61T2 = 10 ms, PDB = 100ms27.2733.14T2 = 10 ms, PDB = 95ms15.703.78T2 = 10 ms, PDB = 90ms16.873.96T2 = 10 ms, PDB = 80ms16.264.23

[0184] To further confirm that Equation 7 completely eliminates delay spikes at other PDB values, it is necessary to test various PDB values. Additionally, we intend to explore the effects of T2 values ​​other than 10 ms and 100 ms. However, since the actual experimental apparatus used does not allow for free variation of these parameters, simulation was used. Furthermore, through simulation, we were able to statistically collect PDB trigger resets that are not apparent in commercial devices. 1,000 RTT samples were collected using a custom simulator with the same configuration as in Table 1, which are shown in Figures 6 and 7.

[0185] Figure 6(a) confirms that the dynamic change in delay begins to improve almost immediately as the PDB decreases from 100 ms. Figure 6(b) provides more detailed data. When the PDB value is 97 ms, an average delay and deviation similar to the PDB value set more conservatively in Equation 7 can be achieved.

[0186] Excessive resource reselection can degrade the predictability of resource usage in the SPS algorithm, which can lead to an increase in packet collisions and an adverse effect on the packet reception rate (PRR). This can affect application performance. Therefore, PDB-based resets must be minimized to minimize the impact on the PRR. Figure 6 shows that the increase in resource reselection is actually minimized, and the system remains stable until it reaches a very low PDB value according to the proposed method. Thus, the proposed resource reselection is not excessive, and the impact on the PRR of other vehicle terminals can be minimized.

[0187] Finally, the impact of the T2 value in Equation 7 was examined. Regarding the criteria for how small T2 should be, side-link standards specify T2min ≤ T2. For LTE V2X, the required minimum value of T2 is defined as 10 ms in 3GPP Release 15. In Release 16, T2min(prioTX) ≤ T2 ≤ 100, meaning T2min is determined by the priority of the packets to be transmitted. For NR V2X, lower latency configurations became possible. In 3GPP Release 16, T2min can be set to 1 ms, 5 ms, 10 ms, or 20 ms (i.e., sl-SelectionWindowList-r16) when using a 15 kHz subcarrier interval. Therefore, interactive applications requiring low latency can use these small T2 values. However, if a larger T2 value is desirable for any reason, Equation 7 indicates that the PDB must be reduced accordingly. This affects the mean lag, lag variance, and the number of resource reselections. Therefore, the effect of larger T2 values ​​on these performance metrics was investigated. Since excessively large T2 values ​​are contrary to the objective that the interaction lag should be less than the RRP, only T2 < 50 ms is considered in this specification. Additionally, it should be noted that PDB ≥ T2 was limited because PDB-triggered resource reselection is performed automatically when the selected resource is in slot n and PDB < n ≤ T2. Figure 7 shows the effect of T2 values ​​on the mean RTT and variance.

[0188] In Figure 7(a), it can be seen that the average lag (RTT) increases as T2 increases. Even at larger T2 values, the average lag stabilizes when the PDB is set to 85 ms or less. At these T2 values, the PDB value exceeds the conservative boundary of Equation 7. In Figure 7(b), when the PDB value exceeds 85 ms, high variability appears, indicating the presence of lag spikes. Reducing the PDB triggers resource reselection according to Equation 7, and the lag spikes are eliminated. In Figure 7(c), the increase in the number of resource reselections is the trade-off for the elimination of lag spikes, but the number is relatively small. This is because the lag spikes persist for a long time after they occur but are not frequent.

[0189] In summary, to address the issues of high RTT variability and delay spikes in interactive vehicle communication, we propose combining two measures. First, the size of the resource selection window (T2) should be set to T2 <= RRP / 2. This limits the size of the resource selection window in Equation 1 to maximize the probability that the requesting vehicle terminal receives a response before transmitting the next request. Second, to eliminate remaining delay spikes not removed by the first measure, PDB-triggered resource reselection should be enforced by setting PDB < δmin in Equation 7.

[0190] FIG. 8 illustrates a flowchart of a method for selecting a resource and transmitting and receiving a message from a selected resource according to the present invention. As previously explained, resource re-selection to reduce communication delay between a requesting vehicle terminal and a responding vehicle terminal can be performed by the responding vehicle terminal. Hereinafter, the method of FIG. 8 will be described as being performed by the responding vehicle terminal.

[0191] The responding vehicle terminal may be configured to select a resource from a resource selection window (S810). The responding vehicle terminal may be configured to select a resource for transmitting a response message to the requesting vehicle terminal. If an SPS algorithm or mechanism is used, the same resource is maintained for a set SPS period.

[0192] The responding vehicle terminal can determine whether the response message transmission time is greater than a threshold value (S820). The response message transmission time refers to the time from when the response message is generated or prepared at the upper layer until the point in time corresponding to the selected resource. As previously explained, in order to prevent the expected RTT from exceeding the RRP, that is, to reduce the delay time, the responding vehicle terminal may be configured to perform resource reselection if the response message transmission time is greater than the threshold value.

[0193] If the response message transmission time is equal to or less than the threshold value, the response vehicle terminal can be configured to transmit the response message from the selected resource (S830).

[0194] Then, the responding vehicle terminal can check whether the SPS cycle has ended (S840). If the SPS cycle has not ended, the responding vehicle terminal returns to S820 to transmit the response message again. If the SPS cycle has ended, the responding vehicle terminal can terminate the procedure for transmitting the response message according to the SPS.

[0195] Figure 9 illustrates a block diagram of a requesting vehicle terminal and a responding vehicle terminal.

[0196] The requesting vehicle terminal (21) refers to a device that transmits a request message among messages for V2X communication. However, since communication always involves transmission and reception, the requesting vehicle terminal (21) can receive messages, data, etc. For example, the requesting vehicle terminal (21) may be configured to receive a response message from the responding vehicle terminal (22).

[0197] The request vehicle terminal (21) may include a memory (211) for storing messages, data, information, etc., a processor (212) for processing messages, data, information, etc., and a transceiver (213) for transmitting or receiving messages, data, information, etc.

[0198] The response vehicle terminal (22) refers to a device that transmits a response message among the messages for V2X communication. The response vehicle terminal (22) can also transmit messages and data. For example, the response vehicle terminal (22) may be configured to receive a request message from the request vehicle terminal (21).

[0199] The response vehicle terminal (22) may include a memory (221) for storing messages, data, information, etc., a processor (222) for processing messages, data, information, etc., and a transceiver (223) for transmitting or receiving messages, data, information, etc.

[0200] In addition, the memory (211, 221) of each terminal (21, 22) may store code for processing or transmitting / receiving requests or response messages for resource reselection or for processing the request or response message according to the present invention described above.

[0201] The request vehicle terminal (21) and the response vehicle terminal (22) can each be mounted on equipment or devices for V2X communication, such as a vehicle or an RSU (road side unit).

[0202] The requesting vehicle terminal (21) can transmit a sidelink channel to the responding vehicle terminal (22) via a sidelink, and the responding vehicle terminal (22) can detect the sidelink channel to obtain necessary information. Additionally, the responding vehicle terminal (22) can transmit a sidelink channel to the requesting vehicle terminal (21) via a sidelink, and the requesting vehicle terminal (21) can detect the sidelink channel to obtain necessary information.

[0203] As explained earlier, the sidelink also consists of a control channel that directs the data channel and a data channel, and receiving the control channel is required to receive the data channel.

[0204] Meanwhile, as previously explained, resource reselection may be performed to reduce the communication delay between the requesting vehicle terminal (21) and the responding vehicle terminal (22). It has been explained that resource reselection is performed by the responding vehicle terminal (22). Below, the contents of the present invention described above are explained as the operation of the responding vehicle terminal (22), but the requesting vehicle terminal (21) can also perform the corresponding operation.

[0205] The response vehicle terminal (22) can be configured to periodically send and receive messages with the counterpart device in sidelink communication.

[0206] The response vehicle terminal (22) may include a memory (221), and the memory (221) may be configured to store code for periodically transmitting and receiving messages with the counterpart terminal. Additionally, the memory (221) may be configured to store code for resource reselection, and in particular, may store conditions that trigger resource reselection.

[0207] The response vehicle terminal (22) may include a processor (222), and the processor (222) may be configured to execute code stored in memory (221) to perform an operation for periodically sending and receiving messages with the counterpart terminal.

[0208] The operation of the processor (222) may include selecting a resource in a resource selection window for the transmission and reception of the data. Here, a parameter indicating the end time of the resource selection window, namely T2, may be set to less than or equal to half of the resource reservation period (RRP). This is intended to reduce delay. Additionally, the parameter indicating the end time of the resource selection window ensures that the transmission period or interval of periodic request messages, or the transmission period or interval of periodic response messages, is equal to or smaller than the RRP even if resource re-selection is performed. That is, it enables the expected sequential transmission and reception of request messages and response messages (forward order).

[0209] Additionally, the operation of the processor (222) may include receiving a message from a counterpart device at a selected resource or transmitting a message to a counterpart terminal. The response vehicle terminal (22) may further include a transceiver (223) and may be configured to transmit and receive messages to and from a counterpart terminal through the transceiver (223).

[0210] The operation of the processor (222) includes configuring to change the set packet delay budget (PDB), and the changed PDB may be set to be less than or equal to the value determined by the following formula.

[0211] [Mathematical Formula 8]

[0212] RRP + 2 * Parameter (T1) indicating the start time of the resource selection window - Parameter (T2) indicating the end time of the above resource selection window

[0213] Additionally, the operation of the processor (222) may include performing resource reselection when the time length to the next resource capable of transmitting the response message generated in the upper layer is greater than the changed PDB. This solves the problem of reverse ordering described above and prevents the delay from increasing beyond the RRP.

[0214] Additionally, the operation of the processor (222) may include transmitting a response message from the re-selected resource to the counterpart terminal.

[0215] In the above specification, it has been described that a vehicle terminal or each component included therein performs control for performing sidelink communication or resource reselection for sidelink communication; however, "terminal" and the components belonging thereto are merely names, and the scope of rights is not subordinate to them.

[0216] In addition, as another aspect of the present invention, the operation of the proposed technology described above may also be provided as code that can be implemented, practiced, or executed by a "computer" (a comprehensive concept including a system on chip (SoC) or a (micro)processor, etc.), or as a computer-readable storage medium or computer program product that stores or contains said code. The scope of the present invention may be extended to said code or to a computer-readable storage medium or computer program product that stores or contains said code.

[0217] The detailed description of the preferred embodiments of the present invention disclosed as described above is provided so that a person skilled in the art can implement and practice the present invention.

Claims

As a device for periodically transmitting and receiving messages with a counterpart device in sidelink communication, A memory configured to store code for periodically transmitting and receiving messages with the aforementioned counterpart device; and It includes a processor configured to execute the code to perform an operation for periodically transmitting and receiving messages with the aforementioned counterpart device, The above operation is Select a resource in the resource selection window for sending and receiving the above message, and It includes receiving a message from a counterpart device or transmitting a message to a counterpart device at the selected resource above, and A device in which a parameter indicating the end time of the above resource selection window is set to less than or equal to 1 / 2 of the resource reservation period (RRP). In paragraph 1, A device in which a parameter indicating the end point of the resource selection window above ensures that even if resource reselection is performed, the transmission period or interval of periodic request messages, or the transmission period or interval of periodic response messages, is equal to or smaller than the RRP. In paragraph 1, the above operation is Includes configuring to change the configured packet delay budget (PDB), The above modified PDB is set to be smaller than the value determined by the following formula, The above RRP + 2 * parameter indicating the start time of the above resource selection window - parameter indicating the end time of the above resource selection window , device. In paragraph 3, the above operation is A device comprising performing resource reselection when the time length to the next resource capable of transmitting a response message generated in the upper layer is greater than the changed PDB. In paragraph 4, the above operation is A device comprising transmitting the response message from the re-selected resource. As a method for periodically transmitting and receiving messages with a counterpart device in sidelink communication, A step of selecting a resource in a resource selection window for sending and receiving the above message; and The method includes the step of receiving a message from the counterpart device or transmitting a message to the counterpart device at the selected resource. A method in which a parameter indicating the end time of the above resource selection window is set to less than or equal to 1 / 2 of the resource reservation period (RRP). In paragraph 6, A method in which a parameter indicating the end point of the above resource selection window ensures that even if resource reselection is performed, the transmission period or interval of periodic request messages, or the transmission period or interval of periodic response messages, is equal to or smaller than the above RRP. In paragraph 6, Includes a step of configuring to change the configured packet delay budget (PDB), and The above modified PDB is set to be smaller than the value determined by the following formula, The above RRP + 2 * parameter indicating the start time of the above resource selection window - parameter indicating the end time of the above resource selection window, method. In paragraph 8, A method comprising the step of performing resource reselection when the time length to the next resource capable of transmitting a response message generated in the upper layer is greater than the changed PDB. In Paragraph 9, A method comprising the step of transmitting the response message from the re-selected resource. A computer-readable medium storing a computer program for performing a method according to any one of paragraphs 6 through 10.

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