Aloha network transmission method for optimizing information age

Abstract

The application discloses an Aloha network transmission method for optimizing information age, comprising the following steps: S1, for a time slot V2X Aloha network based on limited retry limit, a queuing system is modeled as a double-server queue system; S2, the average AoI of the double-server queue system is characterized; S3, based on Markov modeling of the queue head state, the average service time and the steady-state probability of successfully transmitting a data packet are characterized; S4, the node transmission probability of minimizing AoI and the number of retransmissions are selected. The application uses randomly generated data packets, a large buffer can accommodate any number of data packets, and the average AoI performance is improved by using a limited number of retries.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless communication networks, and in particular to an Aloha network transmission method for optimizing information age. Background Art

[0002] With the rapid popularization of vehicles, vehicle-to-everything (V2X) communication has received extensive research attention. In V2X communication, vehicles are typically equipped with sensors that communicate with everything around them. Cellular systems (such as 5G systems) are considered a simple and scalable solution to facilitate V2X communication, and so-called cellular-V2X communication is widely used in various fields such as intelligent transportation systems. For intelligent transportation systems, traffic safety information is time-critical and should be updated with fresh information in a timely manner. To measure the freshness of updated information, the age of information (AoI) metric is widely used, where the AoI of a data packet is defined as the time since the most recently received data packet was generated. To ensure that the vehicle's updates are fresh enough, the average AoI of the data packets should be small.

[0003] Some existing approaches improve average AoI performance by implementing arbitrary generation strategies, bounded retry limit strategies for nodes with a single buffer, and infinite retry limit strategies for nodes with a single buffer. In these strategies, the waiting time for each node's buffer is assumed to be instantaneous, resulting in zero waiting time. However, in the Aloha network under consideration, this waiting time cannot be ignored. In an Aloha network with a retry limit, the behavior of head-of-queue (HOL) packets differs from that in arbitrary generation and threshold-based strategies. Therefore, a specialized Markov chain is required to accurately model the behavior of HOL packets. When the retry limit and buffer size are infinite, the average AoI can be obtained by considering queue processing and deriving the probability mass function (PGF) from the probability generating function (PGF) of the service time. However, in an Aloha network with a bounded retry limit and infinite buffer, calculating the PGF of the service time using the same approach becomes complex. This complexity arises from the intricate queue processing and packet loss in the system, which is more complex than in an Aloha network. Therefore, obtaining the average AoI for an Aloha network with bounded retry limits and unlimited buffers is a significant challenge. Summary of the Invention

[0004] In order to solve the problem that the existing technology cannot effectively obtain the average AoI of an Aloha network with limited retry limit and unlimited buffer, the present invention proposes an Aloha network transmission method that optimizes information age to solve the above problem.

[0005] This application discloses an Aloha network transmission method for optimizing information age, comprising the following steps:

[0006] S1. For a time-slotted V2X Aloha network with bounded retry constraints, the queuing system is modeled as a two-server queue system.

[0007] S2,characterizes the average AoI of the dual-server queue system modeled in S1;

[0008] S3. Markov modeling based on the queue head state to characterize the average service time and the steady-state probability of successful packet transmission;

[0009] S4. Based on the obtained characterization information, the node transmission probability and the number of retransmissions that minimize the AoI are selected.

[0010] Preferably, said S1 comprises the following steps:

[0011] In a slotted V2X Aloha network, n vehicles send information to a receiver, assuming that each vehicle node has a Bernoulli arrival process with parameter λ, where λ is the input rate of each vehicle node, defined as the long-term average number of data packets arriving at each vehicle node buffer per time slot;

[0012] In each time slot, as long as the buffer is not empty, each vehicle node will send its HOL data packet with probability q∈(0,1], and all HOL data packets are provided in the order of arrival, that is, first come first served;

[0013] At the receiver, the classic collision model is adopted, that is, the HOL packet can be successfully received if and only if there is no concurrent transmission from other nodes;

[0014] Each vehicle node adopts a retransmission limit M, that is, the HOL data packet will be discarded only when the number of unsuccessful transmissions reaches M. When M is infinite, the HOL data packet always stays in the vehicle node queue until the transmission is successful. When M is a finite value, the HOL data packet of each vehicle node is discarded with a certain probability;

[0015] The queue of each vehicle node is considered as a two-server queue system, where the probability of each HOL packet being dropped in each time slot is p d , otherwise the probability of successful transmission is 1-p d .

[0016] Preferably, said S2 comprises the following steps:

[0017] For a two-server queue system, if The average AoI is characterized as:

[0018]

[0019] Among them, λs =λ(1-p d ) is the input rate of successfully sent HOL data packets, is the average service time of a HOL data packet, is the average service time of a successfully sent HOL data packet, function Service time D T The probability generating function of The second derivative of at z=1.

[0020] Preferably, the Markov modeling based on the queue head state includes the following steps:

[0021] A discrete-time Markov chain is built for each vehicle node to simulate the behavior of each HOL packet:

[0022] A new HOL packet is initially in state T. If the transmission is successful, the HOL packet will stay in state T for one time slot. If the transmission is paused, the HOL packet will enter state R0. If the transmission fails, the HOL packet will enter state R1.

[0023] For the state R i (0≤i≤M-2) HOL data packets, if the transmission is suspended, the HOL data packets will be in state R i If the transmission is successful, the HOL packet will go to state T; if the transmission fails, the HOL packet will go to state R i+1 ;

[0024] For the state R M-1 As long as the transmission probability reaches q, the HOL packet will move to the initial state T because the number of transmission attempts has reached the retry limit M.

[0025] Preferably, characterizing the average service time and the steady-state probability of successfully transmitting a data packet comprises the following steps:

[0026] Service Time D T The probability generating function is:

[0027]

[0028] Probability Generating Function The second derivative of is:

[0029]

[0030] Where z is the input of the probability generation function, p is the probability of successfully transmitting a HOL packet, and q is the node transmission probability;

[0031] The average service time is represented by:

[0032]

[0033] The average service time of successfully transmitted HOL packets is characterized by:

[0034]

[0035] The steady-state probability of successfully transmitting a data packet is characterized as:

[0036]

[0037] Substituting equations (2) to (6) into equation (1) can obtain the exact average AoI.

[0038] Preferably, said S4 comprises the following steps:

[0039] According to the monotonicity of AoI with respect to the transmission probability q, the node transmission probability of AoI is set as:

[0040]

[0041] Among them, p S is the solution representing the intermediate value of the steady-state probability p of successfully transmitting a data packet;

[0042] Minimizing the number of retransmissions is to ensure that Equation (6) has a solution for the maximum retry limit M. The specific value of the retry limit M is found through bisection.

[0043] Beneficial effects of the present invention:

[0044] (1) The present invention differs from previous work on average AoI of Aloha networks in V2X communications in that it utilizes randomly generated data packets, has a large buffer that can accommodate any number of data packets, and employs a limited number of retries to improve average AoI performance.

[0045] (2) The present invention considers V2X communication as a dual-server queue system and derives the average AoI of the general dual-server queue system as the probability generation function (PGF) of the service time. To further determine the PGF of the service time, a dedicated Markov chain is constructed to simulate the behavior of HOL packets that are subject to a bounded retry limit strategy, which follows different rules compared to the arbitrary generation strategy and the threshold-based strategy.

[0046] (3) The present invention uses a special Markov chain to determine the PGF of service time and steady-state point. Compared with the bistable Aloha network with unlimited retry limit, the V2X Aloha network with limited retry limit has two or three steady-state points. According to the PGF of steady-state point and service time, the expression of average AoI of V2X Aloha network with retry limit is further obtained, and the optimal transmission scheme is obtained based on the expression.

[0047] (4) When the input rate is small, the transmission scheme proposed in the present invention is better than the Aloha network with an arbitrary generation strategy. In addition, when the packet loss probability is small, the transmission scheme proposed in the present invention is better than the Aloha network based on threshold retention, indicating that the Aloha network with retry limit is more suitable for cellular-V2X communication with the best AoI and packet loss probability trade-off. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic flow chart of an Aloha network transmission method for optimizing information age according to an embodiment of the present invention;

[0049] Figure 2 Schematic diagram of a dual-server system of a time-slotted V2X Aloha network with limited retry restrictions according to an embodiment of the present invention;

[0050] Figure 3 A state transition diagram of a HOL data packet in a slotted Aloha network with retransmission restrictions according to an embodiment of the present invention;

[0051] Figure 4 Schematic diagram of the relationship between the minimum average age, maximum throughput, and total input rate according to an embodiment of the present invention;

[0052] Figure 5 Schematic diagram of the relationship between the maximum throughput and the total input rate according to an embodiment of the present invention;

[0053] Figure 6 Schematic diagram of the relationship between the minimum average AoI and the packet loss probability according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to make the objectives, technical solutions and advantages of this application more clear, the application is further described in detail below with reference to the accompanying drawings and examples.

[0055] The present invention discloses an Aloha network transmission method for optimizing information age. This method addresses the following problems for a slotted V2X Aloha-based random access network with a finite retry limit: how to adaptively adjust system parameters to optimize the average AoI performance of the random access network for a given retry limit M; and how the optimal average AoI performance varies with the finite retry limit M. Specifically, by modeling the behavior of each head-of-line packet as a Markov chain, the network steady-state probability of successful transmission can be derived. Existing analysis shows that for a slotted V2X Aloha network with a finite retry limit M, the network has either three or one steady-state point. Based on this, it is concluded that the average AoI of the slotted V2X Aloha network is a function of the transmission probability of each vehicle node, the packet input rate of each vehicle node, and the retry limit M, and is proven to be a monotonically decreasing function of the transmission probability.

[0056] like Figure 1 As shown, in one embodiment, the method specifically includes the following steps:

[0057] S1. For a slotted V2X Aloha network with bounded retry constraints, the queuing system is modeled as a dual-server system.

[0058] In a slotted V2X Aloha network, n vehicles transmit information to a single receiver. Each vehicle node is assumed to have a Bernoulli arrival process with parameter λ, where λ is the input rate per vehicle node and is defined as the long-term average number of packets arriving at each vehicle node's buffer per time slot. Each vehicle node is equipped with a buffer to store received packets. In each time slot, as long as the buffer is not empty, each vehicle node transmits its HOL packet with probability q∈(0,1]. All HOL packets are served in the order of arrival, i.e., first-come, first-served (FCFS). At the receiver, the classical collision model rule applies: a HOL packet is successfully received if and only if there are no concurrent transmissions from other nodes.

[0059] Each vehicle node adopts a retransmission limit M, that is, the HOL packet will be discarded only when the number of unsuccessful transmissions reaches M. When M is infinite, the HOL packet always stays in the vehicle node queue until the transmission is successful. When M is a finite value, the HOL packet of each vehicle node is discarded with a certain probability, where the probability of each HOL packet being discarded in each time slot is p d , otherwise the probability of successful transmission is 1-p d . Considering the queue of each vehicle node as a dual-server queue system, each vehicle node can be modeled as a dual-server queue system, such as Figure 2 shown.

[0060] S2, the average AoI of the two-server queue system modeled from S1 is characterized.

[0061] Based on queuing for two-server queue system, if the average AoI is characterized as:

[0062]

[0063] where λ s is the input rate of HOL packets, d is the input rate of successful transmitted HOL packets, is the average service time of a HOL packet, is the average service time of a successfully transmitted HOL packet, and the function is the probability generating function of the service time D T . The second derivative of at z = 1.

[0064] S3, based on the Markov modeling of the queue head state, the average service time and the steady-state probability of successful transmission packets are characterized.

[0065] A discrete-time Markov chain is established for each vehicle node to simulate the behavior of each HOL packet. As shown in Figure 3 , a new HOL packet is initially in state T, and if the transmission is successful, the HOL packet will stay in state T for one time slot; if the transmission is suspended, the HOL packet will enter state R0; if the transmission fails, the HOL packet will enter state R1.

[0066] For a HOL packet in state R i (0≤i≤M-2), if the transmission is suspended, the HOL packet will stay in state R i for one time slot; if the transmission is successful, the HOL packet will move to state T; if the transmission fails, the HOL packet will move to state R i+1 .

[0067] For a HOL packet in state R M-1 , as long as the transmission probability reaches q, the HOL packet will move to the initial state T, because the number of transmission attempts has reached the retry limit M.

[0068] According to the state transition diagram shown in Figure 3 , the probability generating function of the service time D T is:

[0069]

[0070] The probability generating function The second derivative of is:

[0071]

[0072] Among them, z is the input of the probability generation function, p is the probability of successfully transmitting the HOL data packet, and q is the node transmission probability.

[0073] The average service time is represented by:

[0074]

[0075] The average service time of successfully transmitted HOL packets is characterized by:

[0076]

[0077] The steady-state probability of successfully transmitting a data packet is characterized as:

[0078]

[0079] Substituting equations (2) to (6) into equation (1), we can obtain the exact average AoI for M, λ, and q.

[0080] S4. Based on the obtained characterization information, the node transmission probability and the number of retransmissions that minimize the AoI are selected.

[0081] According to the monotonicity of AoI with respect to the transmission probability q, the node transmission probability of AoI is set as:

[0082]

[0083] Among them, p S is the solution representing the intermediate value of the steady-state probability p of successfully transmitting a data packet.

[0084] Minimizing the number of retransmissions is to ensure that Equation (6) has a solution for the maximum retry limit M. The specific value of the retry limit M is found through bisection.

[0085] In a specific embodiment, the first-come, first-served, limited retry limit (FCFS FRL) strategy proposed in this application is compared with four existing strategies, including the CFS unlimited retry limit (IRL) strategy, the last-in, first-out (LCFS) FRL strategy, the pure on-demand generation (GW) strategy, and the threshold-based strategy. In the pure GW strategy, each node is equipped with a single packet buffer and transmits a new packet immediately after it is generated. The pure GW strategy corresponds to the case where M=1 and q=1 in the embodiment of this application.

[0086] If the transmission discipline of the Aloha network is LCFS, the newly arrived packets will be prioritized and served first. In the FCFS FRL and LCFS FRL policies, the retry limit is set to the optimal retry limit M. * , as shown below:

[0087]

[0088] in, The minimum average age.

[0089] Figure 4 Shows how the minimum average age (AoI) of different strategies varies with the total input rate of the node Changes. Figure 4 , the average AoI performance of the FCFS FRL strategy is the same as that of the LCFS FRL strategy. This is because when When q is small, the impact of service priority is not significant and q = 1. When is large, the optimal M of the LCFS FRL policy is obtained under the conditions of M = 1 and q = 1, which is exactly equivalent to M = 1 and q = 1 of the FCFS FRL policy. It should be noted that the LCFS policy may disrupt the order of data packets received by the receiver. Therefore, this embodiment focuses on the performance of the FCFS FRL policy. When , the minimum average AoI of the FCFSFRL strategy is smaller than that of the pure GW strategy. Therefore, in order to optimize the average AoI when the total traffic input rate of the node is small, a larger retry limit is required to store incoming packets to avoid dropping too many packets. In particular, when The IRL strategy is optimal when When , the FRL strategy is optimal. On the other hand, when the total input rate of the node is large, the minimum average AoI of the FRL strategy is similar to that of the pure GW strategy.

[0090] Figure 5 Shows how the maximum throughput of different strategies varies with the total input rate of the node Changes. Figure 5 ,The maximum throughput performance of the FCFSFRL policy is the same as that of the FCFS IRL policy.,That is, to obtain the optimal throughput, the optimal retry limit is always infinite,,while the optimal retry limit that minimizes the average AoI is a finite value.

[0091] Figure 6 It shows how the average age (AoI) of different strategies varies with the packet drop probability. In the threshold-based strategy, each node can only transmit its packet when the AoI exceeds a certain threshold, and the threshold can be optimized to minimize the average AoI. Figure 6When the packet drop probability is low, the proposed strategy outperforms the pure on-demand (GW) strategy and the threshold-based strategy. However, when the packet drop probability is high, the threshold-based strategy can further improve the average AoI. In other words, the first-come, first-served limited retry limit (FCFS FRL) strategy proposed in this application performs better in terms of the trade-off between packet drop probability and AoI.

[0092] Unlike previous studies on the average AoI of Aloha networks in V2X communication, this embodiment models V2X communication as a two-server queuing system and derives the average AoI of a general two-server queuing system as the probability generating function (PGF) of the service time. This is achieved by considering the queuing process and establishing a relationship between the average AoI and the PGF of each time period. To further determine the PGF of the service time, this embodiment constructs a specialized Markov chain to simulate the behavior of HOL packets subject to a bounded retry limit policy. This behavior follows different rules than arbitrary generation policies and threshold-based policies. Using this specialized Markov chain, the PGF of the service time and steady-state points is determined. Compared to a bistable Aloha network with an infinite retry limit, a V2X Aloha network with a bounded retry limit has two or three steady-state points. Based on the steady-state points and the PGF of the service time, the average AoI of the retry-limited V2X Aloha network is further described.

[0093] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. An Aloha network transmission method for optimizing information age, characterized in that: The following steps are involved: S1. For a time-slotted V2X Aloha network with bounded retry constraints, the queuing system is modeled as a two-server queue system. S2,characterizes the average AoI of the dual-server queue system modeled in S1; For a two-server queue system, if , then the average AoI is characterized as: in, is the input rate of successfully sent HOL packets, is the input rate of each vehicle node, is the probability that each HOL packet is dropped in each time slot, is the average service time of a HOL data packet, is the average service time of a successfully sent HOL data packet, function Service time The probability generating function of exist The second derivative of at ; S3. Markov modeling based on the queue head state to characterize the average service time and the steady-state probability of successful packet transmission; Characterizing the average service time and the steady-state probability of successfully transmitting a data packet comprises the following steps: Service Hours The probability generating function is: Probability Generating Function The second derivative of is: in, is the input of the probability generating function, is the probability of successfully transmitting a HOL packet, is the node transmission probability, is the retry limit; The average service time is represented by: The average service time of successfully transmitted HOL packets is characterized by: The steady-state probability of successfully transmitting a data packet is characterized as: in, is the number of vehicles; Substituting equations (2) to (6) into equation (1), we can get the exact average AoI. S4. Based on the obtained characterization information, the node transmission probability and the number of retransmissions that minimize the AoI are selected.

2. The Aloha network transmission method for optimizing information age according to claim 1, characterized in that: Said S1 comprises the following steps: In a slotted V2X Aloha network, A vehicle sends information to a receiver, assuming that each vehicle node has a parameter Bernoulli arrival process, where is the input rate of each vehicle node, defined as the long-term average number of packets arriving at each vehicle node buffer per time slot; In each time slot, as long as the buffer is not empty, each vehicle node will Send its HOL data packets. All HOL data packets are provided in the order of arrival, that is, first come first served; At the receiver, the classic collision model is adopted, that is, the HOL packet can be successfully received if and only if there is no concurrent transmission from other nodes; Each vehicle node uses retransmission limit , that is, only when the number of unsuccessful transmissions reaches The HOL data packet will be discarded when When is infinite, the HOL data packet always stays in the vehicle node queue until the transmission is successful. When is a finite value, the HOL data packet of each vehicle node is discarded with a certain probability; The queue of each vehicle node is regarded as a two-server queue system, where the probability of each HOL packet being dropped in each time slot is , otherwise the probability of successful transmission is .

3. The Aloha network transmission method for optimizing information age according to claim 2, characterized in that: The Markov modeling based on the queue head state includes the following steps: A discrete-time Markov chain is built for each vehicle node to simulate the behavior of each HOL packet: A new HOL packet is initially in state T. If the transmission is successful, the HOL packet will stay in state T for one time slot; if the transmission is suspended, the HOL packet will enter state ; If the transmission fails, the HOL packet will enter the state ; For the state If the transmission is paused, the HOL packet will be in the state If the transmission is successful, the HOL packet will go to state T; if the transmission fails, the HOL packet will go to state ; For the state HOL data packets, as long as the transmission probability reaches , the HOL packet moves to the initial state T because the number of transmission attempts has reached the retry limit .

4. The Aloha network transmission method for optimizing information age according to claim 3, characterized in that: The S4 comprises the following steps: According to AoI, the transmission probability The monotonicity of AoI is set as: in, is the steady-state probability of successfully transmitting a data packet The solution representing the intermediate value of ; Minimizing the number of retransmissions is the maximum retry limit that makes Equation (6) have a solution , find the retry limit by bisection The specific value of .

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