Internet of Things multiple access method based on information timeliness

Abstract

The invention provides an Internet of Things multiple access method based on information timeliness, which allows an age gain threshold and a frame length to dynamically change along with frames under a multi-packet receiving mechanism. According to the method, age gain initial distribution is given, and the following steps are executed in each frame: an initial access point of each frame sets a frame length and an age gain threshold by taking maximization of an expected value of a time slot average AoI reduction amount of a current frame as a target according to the estimated age gain distribution; the users of which the real-time age gain in each frame is greater than or equal to a set threshold independently select any time slot in the frame in an equal-probable manner to send data, if the number of the users simultaneously transmitted in the same time slot is less than or equal to the packet receiving capability gamma of the receiving end, the transmission is successful, and otherwise, all the users fail; each frame end access point records observation information of the number of users transmitted at the same time in each time slot in the frame; and each frame end access point estimates the age gain distribution of the next frame beginning based on Bayesian updating and combinatorial mathematics theories according to the estimated age gain distribution of the frame beginning, the observation information in the frame and the data arrival probability.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless network communications, and in particular to an Internet of Things multiple access method based on information timeliness. Background Art

[0002] In the IoT scenario, end 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 the age of information (AoI) has become a research hotspot. On the other hand, the frame slot ALOHA method is increasingly used in the field of communications. For example, the EPCGlobal organization has formally included it in the wireless radio frequency identification standard. Therefore, how to design an IoT multiple access method based on information timeliness to optimize AoI performance has received widespread attention. Due to mutual interference between users, the priority sorting of channel access for different users through 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 maximum likelihood estimation method used in the T-DFSA method proposed by Moradian et al. has reduced accuracy when the frame length is short and the observation information is less, and it is necessary to use simulation search to design the access parameters, which will cause a large overhead. 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 an IoT multiple access method based on information timeliness, 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 frame:

[0004] Step 1: At the beginning of each frame, the AP sets the frame length and age gain threshold according to the estimated age gain distribution to maximize the expected value of the average AoI reduction in the current frame time slot;

[0005] Step 2: Users whose real-time age gain in each frame is greater than or equal to the set threshold independently and equally select any time slot in the frame to send data. If the number of users transmitting simultaneously in the same time slot is less than or equal to the packet receiving capacity γ of the AP, the transmission is successful, otherwise all fails;

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

[0007] Step 4: At the end of each frame, the AP estimates the age gain distribution at the beginning of the next frame based on the estimated age gain distribution at the beginning of the frame, the observation information in the frame, and the data arrival probability, based on Bayesian updating and combinatorial mathematics theory.

[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 method for multiple access to the Internet of Things based on information timeliness implemented by the present invention;

[0011] Figure 3-4 The figure is a system mean AoI curve diagram of the Internet of Things multiple access method based on information timeliness under different data arrival probabilities and MPR capabilities implemented by 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 of equal length, and each user and AP can accurately locate the boundaries of the time slots. 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 2The flowchart of the method for multiple access to the Internet of Things based on information timeliness is shown in the figure. Figure 2 As shown, a method for multiple access to the Internet of Things based on information timeliness is provided. The method performs the following steps in each frame after an initial distribution of age gain is given:

[0014] Step 1-1: Based on the estimated age gain distribution, calculate the probability that the real-time age gain of any user in the system estimated by the AP at the initial time of frame t is g g≥0.

[0015] Step 1-2: Calculate the probability π that any user in the system meets the threshold condition at the initial time of frame t when a certain age gain threshold Γ is given t :

[0016] π t =∑ g≥Γ h t,g . (1)

[0017] Step 1-3: Assuming that whether each user is in a state that satisfies the threshold condition is independent of each other, the number of users n that meet the threshold condition t The probability of taking the value n can be calculated based on the existing parameters as follows:

[0018]

[0019] Step 1-4: Calculate an estimate of the expected average AoI reduction in the time slots within frame t as follows:

[0020]

[0021] Step 1-5: Set the age gain threshold Γ for frame t t as follows:

[0022]

[0023] Step 1-6: Set the frame length w of frame t t as follows:

[0024]

[0025] in, The parameter z is solved by the following fixed point iteration:

[0026]

[0027] The initial value of the iteration z(0) can be any real number in [1,γ].

[0028] Step 2: Users that meet the threshold condition in frame t independently and equally select any time slot in the frame for data transmission: In the initial time slot k of frame t t The set of users that meet the threshold condition Any user in the time slot set independently and equally select a time slot for data transmission. If data transmission is successful, the real-time AoI at the AP side will become The real-time AoI of the remaining unsuccessful users on the AP side will increase by 1.

[0029] Step 3: At the end of frame t, the AP records the observation information of the number of users transmitting simultaneously in each time slot in the frame: mark the channel state that the AP can observe in time slot k as c k , and defined as follows:

[0030]

[0031] Among them, r k represents the number of users transmitting in time slot k. All channel observation information of AP in frame t can be expressed as:

[0032]

[0033] Step 4: At the end of frame t, AP calculates the age gain distribution at the beginning of the next frame based on the Bayesian update and combinatorial mathematics theory according to the estimated age gain distribution at the beginning of the frame, the observation information in the frame, and the data arrival probability:

[0034] Step 4-1: Based on the observation information O t , calculate the number of successful time slots in frame t

[0035] and collision slot number

[0036] Step 4-2: Based on the observation information O t , calculate the number of users v that completed data update in the jth successful time slot in frame t j and the vectors they form

[0037] Step 4-3: Based on the observation information O t , calculate the total number of users who successfully transmitted in frame t And the total number of collision users

[0038] Step 4-4: Based on the observation information O t , calculate the lower bound of the number of active users in frame t

[0039] Step 4-5: Calculate the observation information when the number of active users meeting the threshold condition is n t The conditional probability η o,n :

[0040]

[0041] Among them, C suc , C col Respectively represent that when the observation information is O t Under the condition of , the total possible transmission selection number of successful users and collision users in frame t can be calculated as follows:

[0042]

[0043]

[0044] Step 4-6: Calculate the initial time slot k in frame t t Under the condition that the real-time AoI value of any user terminal is x′ and the real-time AoI value of the AP terminal is y′, in the initial time slot k of frame t+1 t+1 The conditional probability β that the real-time AoI value of any user end is x, the real-time AoI value of the AP end is y, and the observation information is o x,y,o,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 frame t, β x,y,o,x′,y′ The calculation of can be divided into the following four cases:

[0045] (1) When And user i successfully transmits the data packet in frame t, that is, y′-x′<Γ t ,x∈{0,1,...,w t -1,x′+w t},y=x′+w t :

[0046] β x,y,o,x′,y′ =0. (12)

[0047] (2) When And user i fails to successfully transmit the data packet in frame t, that is, y′-x′<Γ t ,x∈{0,1,...,w t -1,x′+w t},y=y′+w t :

[0048]

[0049] (3) When And user i successfully transmits the data packet in frame t, that is, y′-x′≥Γ t,x∈{0,1,...,w t -1,x′+w t},y=x′+w t :

[0050]

[0051] (4) When And user i fails to successfully transmit the data packet in frame t, that is, y′-x′≥Γ t ,x∈{0,1,...,w t -1,x′+w t},y=y′+w t :

[0052]

[0053] Step 4-7: Update f t+1 (x,y) is as follows:

[0054]

[0055] The present invention adopts MATLAB software to implement the method, sets the number of devices in the network N=100, and the simulation time T=100000 frames.

[0056] 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 method for multiple access to the Internet of Things based on information timeliness, wherein the scenario includes N users with the same priority and an access point (AP), characterized in that: Given the initial distribution of age gains, the following steps are performed in each frame: Step 1: At the beginning of each frame, the AP sets the frame length and age gain threshold according to the estimated age gain distribution to maximize the expected value of the reduction in the average age of information (AoI) of the current frame time slot; Step 2: Users whose real-time age gain in each frame is greater than or equal to the set threshold independently and equally select any time slot in the frame to send data. If the number of users transmitting simultaneously in the same time slot is less than or equal to the packet receiving capacity γ of the AP, the transmission is successful, otherwise all fails; Step 3: At the end of each frame, the AP records the observation information of the number of users transmitting simultaneously in each time slot within the frame; Step 4: At the end of each frame, the AP estimates the age gain distribution at the beginning of the next frame based on the estimated age gain distribution at the beginning of the frame, the observation information in the frame, and the data arrival probability, based on Bayesian updating and combinatorial mathematics theory.

2. The Internet of Things multiple access method based on information timeliness according to claim 1 is characterized in that: The present invention divides the time axis into time slots 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 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 frame t as f t (x,y),x≥0,y≥1,y≥x.

3. The Internet of Things multiple access method based on information timeliness according to claim 1 is characterized in that: The frame length w of any frame t in step 1 t and age gain threshold Γ t The setting method is: Step 1-1: Based on the estimated age gain distribution, calculate the probability that the real-time age gain of any user in the system estimated by the AP at the initial time of frame t is g Step 1-2: Calculate the probability π that any user in the system meets the threshold condition at the initial time of frame t when a certain age gain threshold Γ is given t : π t ＝∑ g≥Γ h t,g ； (1) Step 1-3: Assuming that whether each user is in a state that satisfies the threshold condition is independent of each other, the number of users n that meet the threshold condition t The probability of taking the value n can be calculated based on the existing parameters as follows: Step 1-4: Calculate an estimate of the expected average AoI reduction in the time slots within frame t as follows: Step 1-5: Set the age gain threshold Γ for frame t t as follows: Step 1-6: Set the frame length w of frame t t as follows: in, 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 Internet of Things multiple access method based on information timeliness according to claim 1 is characterized in that: The specific process of user access to the channel in any frame t in step 2 is as follows: t The set of users that meet the threshold condition Any user in the time slot set independently and equally select a time slot for data transmission; if a user j selects a time slot If data transmission is successful, the real-time AoI at the AP side in the next time slot will become The real-time AoI of the remaining unsuccessful users on the AP side will increase by 1.

5. The Internet of Things multiple access method based on information timeliness according to claim 1 is characterized in that: The specific process of the AP recording the observation information of the number of users transmitting simultaneously in each time slot in the frame at the end of any frame t 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; and all channel observation information of AP in frame t can be expressed as:

6. The Internet of Things multiple access method based on information timeliness according to claim 1 is characterized in that: At the end of any frame t, AP calculates the age gain distribution {f at the beginning of the next frame based on the estimated age gain distribution at the beginning of the frame, the observation information in the frame, and the data arrival probability, based on Bayesian updating and combinatorial mathematics theory. t+1 (x,y) x≥0,y≥1,y≥x The specific process of estimation is as follows: Step 4-1: Based on the observation information O t , calculate the number of successful time slots in frame t and collision slot number Step 4-2: Based on the observation information O t , calculate the number of users v that completed data update in the jth successful time slot in frame t j and the vectors they form Step 4-3: Based on the observation information O t , calculate the total number of users who successfully transmitted in frame t And the total number of collision users Step 4-4: Based on the observation information O t , calculate the lower bound of the number of active users in frame t Step 4-5: Calculate the observation information O when the number of active users that meet the threshold condition is n t The conditional probability η o,n : Among them, C suc , C col Respectively represent that when the observation information is O t Under the condition of , the total possible transmission selection number of successful users and collision users in frame t can be calculated as follows: Step 4-6: Calculate the initial time slot k in frame t t Under the condition that the real-time AoI value of any user terminal is x′ and the real-time AoI value of the AP terminal is y′, in the initial time slot k of frame t+1 t+1 The conditional probability β that the real-time AoI value of any user end is x, the real-time AoI value of the AP end is y, and the observation information is o x,y,o,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 frame t, β x,y,o,x′,y′ The calculation of can be divided into the following four cases: (1) When And user i successfully transmits the data packet in frame t, that is, y′-x′<Γ t ,x∈{0,1,...,w t -1,x′+w t },y=x′+w t : β x,y,o,x′,y′ ＝0； (12) (2) When And user i fails to successfully transmit the data packet in frame t, that is, y′-x′<Γ t ,x∈{0,1,...,w t -1,x′+w t },y=y′+w t : (3) When And user i successfully transmits the data packet in frame t, that is, y′-x′≥Γ t ,x∈{0,1,...,w t -1,x′+w t },y=x′+w t : (4) When And user i fails to successfully transmit the data packet in frame t, that is, y′-x′≥Γ t ,x∈{0,1,...,w t -1,x′+w t },y=y′+w t : Step 4-7: Update f t+1 (x,y) is as follows:

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