Time slot ALOHA adaptive access method based on information age

Abstract

The invention provides a time slot ALOHA adaptive access method which allows an age gain threshold value and a sending probability to dynamically change along with a time slot under a multi-packet receiving mechanism. According to the method, age gain initial distribution is given, and the following steps are executed in each time slot: each time slot initial access point sets a sending probability and an age gain threshold by taking maximization of a current time slot AoI reduction amount expected value as a target according to the estimated age gain distribution; the users whose real-time age gains are greater than or equal to a set threshold in each time slot are accessed to a channel according to a set sending probability, if the number of the users simultaneously transmitted in the time slot is less than or equal to the packet acceptance gamma of the receiving end, the transmission is successful, otherwise, all the users fail; the last access point of each time slot records the observation information of the number of users transmitted at the same time in the time slot; and each time slot end access point estimates the age gain distribution of the next time slot beginning based on the Bayesian update theory according to the age gain distribution estimated by the time slot beginning, the observation information in the time slot and the data arrival probability.

Description

Technical Field

[0001] The invention relates to the technical field of wireless network communication, in particular to a time slot ALOHA adaptive access method based on information age. Background Art

[0002] With the continuous development of communication technology, the number of terminals in the Internet of Things is increasing, and the requirements for real-time transmission are becoming increasingly stringent. In the Internet of Things scenario, terminal users need to send data updates to access points in real time so that they can make decisions based on the received information in a timely manner. As an important performance indicator that describes the freshness of the information received by the receiver, the optimization of Age of Information (AoI) has become a research hotspot. Due to the mutual interference between users, the priority sorting of channel access for different users by age information can achieve better system information age performance. Despite this, previous studies lacked the exploration of how to design an age-based adaptive random access method under the physical layer multiple-packet reception (MPR) mechanism. Under the single-packet reception mechanism, the design of access parameters in the AAT method proposed by Chen et al. is based on the optimization of throughput rather than information age, so there is a large room for optimization in terms of information age performance. Therefore, it is of great significance to set reasonable time-varying access parameters under the MPR mechanism to adapt to the dynamically changing interference environment in the system. Summary of the invention

[0003] The present invention aims to provide a time slot ALOHA adaptive access method based on information age, which can provide excellent system mean AoI performance under the MPR mechanism. The technical solution to achieve the purpose of the present invention is: after the initial distribution of age gain is given, the following steps are performed in each time slot:

[0004] Step 1: The initial AP of each time slot sets the transmission probability and age gain threshold according to the estimated age gain distribution, with the goal of maximizing the expected value of the AoI reduction in the current time slot;

[0005] Step 2: Users whose real-time age gain in each time slot is greater than or equal to the set threshold access the channel with the set transmission probability. If the number of users transmitting simultaneously in the time slot is less than or equal to the packet acceptance capacity γ of the AP, the transmission is successful, otherwise all fails;

[0006] Step 3: At the end of each time slot, the AP records the observation information of the number of users transmitting simultaneously in that time slot;

[0007] Step 4: At the end of each time slot, the AP estimates the age gain distribution at the beginning of the next time slot based on the Bayesian update theory according to the estimated age gain distribution at the beginning of the time slot, the observation information in the time slot, and the data arrival probability.

[0008] Compared with the prior art, the present invention has the following significant advantages: the present invention takes into account the data non-saturation model and the MPR mechanism, and can achieve excellent system mean AoI performance under different parameters with lower complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the application scenario of the present invention;

[0010] Figure 2 A flow chart of the time slot ALOHA adaptive access method implemented by the present invention;

[0011] Figure 3-4 The figure is a graph showing the system mean AoI curve under different data arrival probabilities and MPR capabilities when the slotted ALOHA adaptive access method is implemented in the present invention. DETAILED DESCRIPTION

[0012] The present invention focuses on the uplink scenario consisting of N (N≥2) users with the same priority and 1 access point. In this scenario, the time axis is divided into time slots k∈{1,2,...,K} of equal length, and each user and AP can accurately locate the boundary of the time slot. Assume that any user At the initial moment of each time slot k, a data packet is generated independently with probability λ, and each user only retains the latest generated data packet. The real-time AoI of user i at the local and AP end in any time slot k is marked as and And set the initial value If user i generates a new data packet at the initial time of time slot k, then update Otherwise update like Figure 1 As shown in the figure, it is assumed that the N users transmit data to the AP through a shared channel, and the data packet receiving capacity of the AP is 1≤γ≤N, that is, when the number of data packets sent simultaneously in each time slot is less than or equal to γ, all are successful, otherwise all fail. It is assumed that at the end of any time slot, the AP sends the transmission feedback of the time slot to each user through an error-free and delay-free control channel. The real-time age gain of user i in any time slot k is defined as Mark the probability that the AP estimates that the real-time AoI value of any user end in the system is x and the real-time AoI value of the AP end is y at the initial moment of any time slot k is f k (x,y),x≥0,y≥1,y≥x.

[0013] Figure 2 Flow chart of the time slot ALOHA adaptive access method implemented by the present invention. Figure 2 As shown, a time slot ALOHA adaptive access method based on information age is performed in each time slot after the initial distribution of age gain is given:

[0014] Step 1: The AP at time slot k sets the transmission probability and age gain threshold according to the estimated age gain distribution:

[0015] Step 1-1: Calculate the probability that the real-time age gain of any user in the system estimated by the AP at the initial time of time slot k is g

[0016] Step 1-2: Set the age gain threshold for time slot k as follows:

[0017]

[0018] Step 1-3: Set the transmission probability of time slot k as follows:

[0019]

[0020] The parameter z is solved by the following fixed point iteration:

[0021]

[0022] The initial value of the iteration z(0) can be any real number in [1,γ].

[0023] Step 2: Users meeting the threshold condition in time slot k access the channel according to the transmission probability: the set of users meeting the threshold condition Any user in k The data packet is sent, and the real-time AoI of any AP that successfully transmits user j will become The real-time AoI of the AP side for other users will increase by 1.

[0024] Step 3: At the end of time slot k, the AP records the observation information of the number of users transmitting simultaneously in this time slot: mark the channel state that the AP can observe in time slot k as c k , and defined as follows:

[0025]

[0026] Among them, r k represents the number of users transmitting in time slot k.

[0027] Step 4: The AP at the end of time slot k estimates the distribution of age gain at the beginning of the next time slot based on the Bayesian update theory according to the estimated age gain distribution at the beginning of the time slot, the observation information in the time slot, and the data arrival probability:

[0028] Step 4-1: Calculate the probability π of any user in the system meeting the threshold condition as estimated by the AP at the initial time of time slot k k :

[0029]

[0030] Step 4-2: Based on the observation information c k Calculate the minimum number of users n that meet the threshold condition min :

[0031]

[0032] Step 4-3: Calculate the observation information c when the number of users who meet the threshold condition is n k The conditional probability η c,n :

[0033]

[0034] Step 4-4: Calculate the conditional probability β that at the initial time of time slot k, any user end real-time AoI value is x, the AP end real-time AoI value is y, and the channel state is c under the condition that at the initial time of time slot k, any user end real-time AoI value is x, the AP end real-time AoI value is y, and the channel state is c x,y,c,x′,y′ According to whether the real-time age gain of any user i reaches the threshold and whether user i successfully transmits the data packet in time slot k, β x,y,c,x′,y′ The calculation of can be divided into the following four cases: (1) And user i successfully transmits the data packet in time slot k, that is, y′-x′<Γ k ,x∈{x′+1,0},y=x′+1:

[0035] β x,y,c,x′,y′ =0. (8)

[0036] (2) When And user i fails to successfully transmit the data packet in time slot k, that is, y′-x′<Γ k ,x∈{x′+1,0},y=y′+1:

[0037]

[0038] (3) When And user i successfully transmits the data packet in time slot k, that is, y′-x′≥Γ k ,x∈{x′+1,0},y=x′+1:

[0039]

[0040] (4) When And user i fails to transmit the data packet in time slot k, that is, y′-x′≥Γ k ,x∈{x′+1,0},y=y′+1:

[0041]

[0042] Among them, 1(·) is the indicator function.

[0043] Step 4-5: Update f k+1 (x,y) is as follows:

[0044]

[0045] The present invention adopts MATLAB software to implement the method, sets the number of devices in the network N=100, and the simulation time K=100000 time slots.

[0046] Figure 3-4 Under the premise that other parameters remain unchanged, the data arrival probability λ and the MPR capacity γ are changed in turn. The results show that the method proposed in the present invention has relatively excellent system mean AoI performance under various parameters, thereby verifying the effectiveness of the present invention.

Claims

1. A time slot ALOHA adaptive access method based on Age of Information (AoI), wherein the scenario includes N users with the same priority and 1 access point (AP), characterized in that: Given the initial distribution of age gains, the following steps are performed at each time slot: Step 1: The initial AP of each time slot sets the transmission probability and age gain threshold according to the estimated age gain distribution, with the goal of maximizing the expected value of the AoI reduction in the current time slot; Step 2: Users whose real-time age gain in each time slot is greater than or equal to the set threshold access the channel with the set transmission probability. If the number of users transmitting simultaneously in the time slot is less than or equal to the packet acceptance capacity γ of the AP, the transmission is successful, otherwise all fails; Step 3: At the end of each time slot, the AP records the observation information of the number of users transmitting simultaneously in that time slot; Step 4: At the end of each time slot, the AP estimates the age gain distribution at the beginning of the next time slot based on the Bayesian update theory according to the estimated age gain distribution at the beginning of the time slot, the observation information in the time slot, and the data arrival probability.

2. The time slot ALOHA adaptive access method based on information age according to claim 1, characterized in that: The present invention divides the time axis into time slots k∈{1,2,...,K} of equal length, and each user can accurately locate the boundary of the time slot; assuming that any user At the initial moment of each time slot k, a data packet is generated with probability λ. Each user sends the latest generated data packet to the AP through a shared channel, and the data packet receiving capacity of the AP end is 1≤γ≤N, that is, when the number of data packets sent simultaneously in each time slot is less than or equal to γ, all are successful, otherwise all fail; the real-time AoI of user i at any time slot k and the AP end are marked as and And set the initial value If user i generates a new data packet at the initial time of time slot k, then otherwise Define the real-time age gain of user i in any time slot k as Mark the probability that the AP estimates that the real-time AoI value of any user end in the system is x and the real-time AoI value of the AP end is y at the initial moment of any time slot k is f k (x,y),x≥0,y≥1,y≥x.

3. The time slot ALOHA adaptive access method based on information age according to claim 1, characterized in that: The probability of sending in any time slot k in step 1 is p k and age gain threshold Γ k The setting method is: Step 1-1: Calculate the probability that the real-time age gain of any user in the system estimated by the AP at the initial time of time slot k is g Step 1-2: Set the age gain threshold for time slot k as follows: Step 1-3: Set the transmission probability of time slot k as follows: The parameter z is solved by the following fixed point iteration: The initial value of the iteration z(0) can be any real number in [1,γ].

4. The time slot ALOHA adaptive access method based on information age according to claim 1, characterized in that: The specific process of user k accessing the channel in any time slot in step 2 is as follows: the set of users meeting the threshold condition Any user in k The data packet is sent, and the real-time AoI of any AP that successfully transmits user j will become The real-time AoI of the AP side for other users will increase by 1.

5. The time slot ALOHA adaptive access method based on information age according to claim 1, characterized in that: The specific process of the AP recording the observation information of the number of users transmitting simultaneously in any time slot k in step 3 is as follows: mark the channel state that the AP can observe in time slot k as c k , and defined as follows: Among them, r k represents the number of users transmitting in time slot k.

6. The time slot ALOHA adaptive access method based on information age according to claim 1, characterized in that: The AP at the end of any time slot k calculates the age gain distribution {f k+1 (x,y) x≥0,y≥1,y≥x The specific process of estimation is as follows: Step 4-1: Calculate the probability π of any user in the system meeting the threshold condition as estimated by the AP at the initial time of time slot k k : Step 4-2: Based on the observation information c k Calculate the minimum number of users n that meet the threshold condition min : Step 4-3: Calculate the observation information c when the number of users who meet the threshold condition is n k The conditional probability η c,n : Step 4-4: Calculate the conditional probability β that at the initial time of time slot k, any user end real-time AoI value is x, the AP end real-time AoI value is y, and the channel state is c under the condition that at the initial time of time slot k, any user end real-time AoI value is x, the AP end real-time AoI value is y, and the channel state is c x,y,c,x′,y′ ; According to whether the real-time age gain of any user i reaches the threshold and whether user i successfully transmits the data packet in time slot k, β x,y,c,x′,y′ The calculation of can be divided into the following four cases: (1) When And user i successfully transmits the data packet in time slot k, that is, y′-x′<Γ k ,x∈{x′+1,0},y=x′+1: β x,y,c,x′,y′ ＝0； (8) (2) When And user i fails to successfully transmit the data packet in time slot k, that is, y′-x′<Γ k ,x∈{x′+1,0},y=y′+1: (3) When And user i successfully transmits the data packet in time slot k, that is, y′-x′≥Γ k ,x∈{x′+1,0},y=x′+1: (4) When And user i fails to transmit the data packet in time slot k, that is, y′-x′≥Γ k ,x∈{x′+1,0},y=y′+1: Among them, 1(·) is the indicator function; Step 4-5: Update f k+1 (x,y) is as follows:

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