CN113556825B

CN113556825B - Multi-attribute decision-based polling method in point coordination

Info

Publication number: CN113556825B
Application number: CN202110751915.6A
Authority: CN
Inventors: 任塨晔; 柏荣胜; 黄镠; 吕卫祥
Original assignee: 724 Research Institute Of China Shipbuilding Corp
Current assignee: 724 Research Institute Of China Shipbuilding Corp
Priority date: 2021-07-02
Filing date: 2021-07-02
Publication date: 2023-09-26
Anticipated expiration: 2041-07-02
Also published as: CN113556825A

Abstract

The invention provides a polling method based on multi-attribute decision in point coordination, which determines an STA polled by an AP at a specific moment in a PCF and a data packet additionally transmitted when the STA is polled. First, the AP calculates the urgency of transmitting the packet to each STA, which is related to the remaining validity period of the packet, the packet priority, and the packet length. Second, the AP calculates how urgent each STA is to be polled, which is related to the time the STA was last polled, the number of packets the STA is to transmit, and the average signal-to-noise ratio of the AP receiving the STA signal. The AP adopts a multi-attribute decision method of dynamic weighted summation to solve the two values, wherein each attribute weight is related to the position of the current moment in the PCF period. The AP determines the currently polled STA based on the urgency degree of sending the data packet to each STA and the urgency degree of each STA to be polled, and selects the data packet with the highest urgency degree in the corresponding transmission queue as the data packet sent by the current poll.

Description

Multi-attribute decision-based polling method in point coordination

Technical Field

The invention relates to a scheduling strategy in an infrastructure network, in particular to a polling method of an AP in a PCF.

Background

The IEEE Std 802.11-1999 edition proposes two channel access modes of the MAC layer in the wireless lan: the duty cycle of the entire basic service set (Basic Service Set, BSS) can also be divided into two periods of time by a distributed coordination function (Distributed Coordination Function, DCF) and a point coordination function (Point Coordination Function, PCF): DCF period and PCF period. In the DCF period, an Access Point (AP) and a mobile STAtion (STA) in the BSS Access a channel in a contention form using a carrier sense multiple Access/collision avoidance (Carrier Sense Multiple Access with Collision Avoidance, CSMA/CA) protocol. In the PCF period, the AP uses a polling method to control channel access of STAs in the whole BSS, and the non-polled STAs cannot transmit signals. The PCF mode avoids the delay caused by channel access collision, and helps to ensure the service quality of specific services.

To avoid sending too many frames at the time of polling, the IEEE Std 802.11-1999 standard combines polling, data transmission, and acknowledgement to be transmitted in one frame using an omni-directional antenna characteristic, thereby performing more polling in a limited time. Frames transmitted by the AP include CF-Poll (no Data), data+cf-Poll, data+cf-ack+cf-Poll, and CF-ack+cf-Poll (no Data), and frames transmitted by the STA include Data, data+cf-Ack, CF-Ack (no Data), and Null.

An important issue faced by APs operating in PCF mode is the rules for polling STAs. The polling rules for APs are not specified in the IEEE Std 802.11-1999 standard. The general approach is to poll the STAs sequentially in order and send the data packets sequentially in the order they enter the queuing sequence. This approach, while guaranteeing fairness among STAs (polled once every certain period), ignores the impact of the polling order on the quality of service. STAs often interact with remote servers for a variety of different types of traffic that also vary in quality of service requirements. For example, services such as live video, web browsing, online gaming, file downloading, etc. may be run simultaneously on the STA. The video live broadcast service has higher requirements on transmission rate and time delay, but can tolerate a certain packet loss rate, while the online game service has higher requirements on packet loss rate and time delay, but has lower requirements on transmission rate. In order to ensure the service quality of each service, the AP operating in PCF mode should determine the STA currently polled and the data packet sent when polling the STA according to the attribute of each data packet and the service type carried by the data packet.

The AP, in performing the polling decision, considers the following two problems in addition to the properties of the packet itself. In one aspect, the polling rules of the AP should take into account the characteristics of the wireless channel. The wireless channel has problems of interference, attenuation, etc., and packet interaction between the AP and the STA is not always successful. Under other conditions, the AP should preferentially poll STAs with better channel quality, thereby fully utilizing the limited PCF time period to transmit more information. On the other hand, the polling rule of the AP should consider the attribute of the STA. The STA, as a user side, also generates service data, which also has an important influence on the service quality of service. In other cases, the AP shall poll more STAs with more data packets to be sent and guarantee certain polling opportunities for other STAs.

Disclosure of Invention

The invention aims to solve the problem of polling decision of an AP working in a PCF mode in a wireless local area network, namely determining an STA polled by the AP at a specific moment in a PCF period and polling a data packet sent when the STA is polled. The invention adopts a multi-attribute decision method of dynamic weighted summation to solve the problem, comprehensively considers the factors of the residual validity period of the data packet, the priority of the data packet, the length of the data packet, the time from the STA to be polled last time, the number of the data packets to be sent by the STA, the average signal to noise ratio of the STA signals received by the AP and the like, can effectively improve the service quality of the service, and simultaneously ensures the fairness of each STA.

In order to solve the technical problems, the invention is realized by the following technical scheme: the AP considers the following factors when determining the STA to be polled and the data packet to be transmitted: the method comprises the steps of firstly determining the STA to be polled by adopting a dynamic weighting summation multi-attribute decision method, then determining the data packet transmitted when the STA is polled, and the weight of each attribute is related to the position of the current moment in a PCF period, wherein the specific steps comprise:

step 1: AP calculation is to STA _i Degree of urgency s for transmitting data packets _i，t ；

Step 2: AP calculates STA _i The degree of urgency v of being polled _i，t ；

Step 3: AP calculates polling STA _i Strength w of (2) _i，t ＝max{s _i，t ，v _i，t }；

Step 4: AP determination of currentTime polling STA _j′ Wherein i' =argmax _{i＝1，2，...，N} {w _i，t }；

Step 5: the AP determines whether there is a STA to send _i′ The AP sends a data+CF-Poll packet or a data+CF-ack+CF-Poll packet, if any, to the STA _i′ Wherein the data portion is the destination address is the STA _i′ And transmitting the data packet with the greatest urgency, otherwise, the AP transmits the CF-Poll packet or the CF-ack+CF-Poll packet to the STA _i′ 。

Let 1 AP and N (N is more than or equal to 1) STA in one BSS. The set of STAs is denoted S, s= { STAi }, i=1, 2. The AP maintains a transmission queue for each STA, respectively, in which data packets to be transmitted to each STA are stored. At time t, AP maintains with STA _i The corresponding transmission queue is marked as For a particular STA _i ，/>Each packet within has corresponding attributes including remaining validity period, priority, length, etc. When the AP polls the sta, these factors are comprehensively considered, and the data packet transmission that can improve the service quality most is determined. The problem can be modeled as a multi-attribute decision problem. And the multi-attribute decision is to aggregate various attributes of the decision object into a utility value, and the object with the highest utility value is the target of the decision. Defining AP to STA _i Degree of urgency s for transmitting data packets _i，t Is->Maximum utility value of each data packet. Also, the AP records the STA _i Related attributes of (1) including STA _i Time since last polled, STA _i The number of data packets to be sent and the AP receiving STA _i Average signal-to-noise ratio of the signals, which factors together determine the STA _i Quilt wheelDegree of urgency v of polling _i，t The problem can also be modeled as a multi-attribute decision problem. In summary, the polling decision of an AP is related to two factors: the AP transmits the urgency of the data packet to each STA and the urgency of each STA being polled. The AP considers both factors together and eventually determines the STA being polled and the data packets sent when polling the STA.

Because of the limited PCF period, the location of the current time within the PCF period also affects the polling decisions of the AP. When the PCF period is about to end, the AP should give priority to how to transmit more data packets in the remaining period or to guarantee the transmission quality in the remaining period at the time of decision. Therefore, the polling decision of the AP is a dynamic multi-attribute decision problem, that is, the position of the PCF time period at the current moment affects the decision result as well under the condition that other factors are unchanged.

At time t, the AP operates in PCF mode, and determines the STA to be polled and the data packet sent when polling the STA according to the following steps:

step 1: AP calculation is to STA _i Degree of urgency s for transmitting data packets _i，t (i＝1，2，...，N)：

(1) AP cullingAnd (3) data packets with residual validity periods less than or equal to zero. For->Data packet in->Definition of remaining validity period u _i，j，t ＝t _{remove，i，j}-t, wherein t_{remove，i，j} Representing the absolute time of failure of the packet, is marked by the source node at the time the packet was generated. AP calculation->The remaining validity period of each data packet of (2) and from +.>Middle knockout u _i，j，t A packet of less than or equal to 0, a transmission queue is obtained>j＝1，2，...，J _i，t (J _i，t ≥0)。

(2) For the followingEvery data packet in->The following three properties were calculated:

a) Remaining validity period u _i，j，t : some services require that the data packets be delivered to the destination node within a certain period of time. The source node marks the validity period when generating the data packet, and the service is valid when the data packet is sent to the destination node in the validity period. When the validity period of the packet has expired when it is not delivered to the destination node, the intermediate node (router, AP, etc.) discards the packet. Definition u _i，j，t ＝t _{remove，i，j}-t, wherein t_{remove，i，j} Representing the absolute time of failure of the packet, is marked by the source node at the time the packet was generated.

b) Priority p _i，j : the upper protocol determines the priority of the data packet according to a certain strategy when generating the data packet, p _i，j ∈[0，1]0 represents the lowest priority, and 1 represents the highest priority.

c) Length l _i，j : the packet length refers to the length of the upper layer protocol frame carried by the MAC layer in bytes. In the IEEE 802.11 standard, this length is referred to as a MAC layer service data unit (MAC Service Data Unit, MSDU).

(3) Because the dimension of the three attributes of the data packet and the influence on the urgency degree of the AP to transmit each data packet are different, normalization processing is required to be carried out on the three attributes when weighted summation multi-attribute decision is carried out, and normalized values are obtained and />

a) For u _i，j，t Is normalized by the method of: u (u) _i，j，t The smaller the current time is, the closer the current time is to the expiration time of the corresponding data packet, and the stronger the urgency of transmitting the data packet is. Meanwhile, the validity period (time from generation to expiration) of each data packet is different from each other, so the following normalization method is adopted:

wherein It represents the validity period length of the data packet, t _{generate，i，j} For data packet->An absolute time of generation at the source node. />Indicating the relative residence time of the packet. In the case where a packet does not fail, the longer the relative residence time, the higher the urgency for the AP to transmit the packet. f (f) _u，n (x) Is defined as

b) For p _i，j Is normalized by the method of: the range of priority values is 0,1]And the higher the priority, the higher the urgency of the AP to transmit the packet, and therefore the normalized value

c) For l _i，j Is normalized by the method of: because the wireless channel is more lossy and is more prone to interference, there is a certain packet loss rate for the data packet transmission. To increase the success rate of transmission, the node should send shorter packets preferentially. However, the difference of the lengths of the data packets of different services is large, and the average length of the data packets is required to be normalized. L-shaped memory _t For the average length of the data packets in all transmission queues in the AP, thenIndicating the relative length of the data packet. Calculate +.>

wherein

(4) Determining weights omega of three attributes according to current time t _u，t 、ω _p，t 、ω _l，t . Calculating the weight omega _u，t 、ω _p，t 、ω _l，t The boundary value of each attribute weight at the beginning of the PCF period is first determinedAnd boundary value at the end of PCF period +.> They first meet the following weight requirements: /> The AP prioritizes the remaining validity and priority of the packets at the beginning of the PCF and prioritizes the packet length near the end of the PCF to send as many packets as possible for the remaining period. The boundary value of the set weight satisfies the following relationship: /> Let the starting time of the current PCF period be t _start PCF time period length is T _pcf Omega is calculated according to the following formula _u，t 、ω _p，t 、ω _l，t ：

The above formula defines the law of variation of three attribute weights, wherein ω _u，t and ω_p，t Linearly decreasing with increasing t, ω _l，t The linear increase with increasing t reflects the change in the extent of influence of different attributes of the AP in decision-making over time.

(5) Based on the normalized valueCorresponding three attribute weights omega _u，t 、ω _p，t 、ω _l，t Obtaining AP transmission number by applying weighted summation methodPacket->Degree of urgency s _i，j，t The method comprises the following steps:

(6) By definition, an AP transmits to STAs _i Degree of urgency s for transmitting data packets _i，t Is thatMaximum utility value of each data packet in the network, i.e

Step 2: AP calculates STA _i The degree of urgency v of being polled _i，t (i＝1，2，...，N)：

(1) AP calculates corresponding STA _i Three attributes of (a):

a) Time c from last time being polled _i，t ：c _i，t ＝t-t _i, wherein t_i Representing the absolute time that STAi was last polled, this value is recorded by the AP;

b) Number of data packets to be transmitted r _i，t : at the STA _i The corresponding field in the format of the frame (data+cf-Ack, data, CF-Ack, null) sent to the AP records the transmit queue of the STA(/>Is the transmission queue of the rejected failed packet, < >>) The number of data packets contained therein (excluding the currently transmitted data packet), and the AP may record the packet after receiving the packetA value;

c) AP receiving STA _i Average signal to noise ratio q of signal _i，t : the AP records the last M received STAs _i Recovering the signal-to-noise ratio of the packet and calculating the average value to obtain q _i，t ；

(2) Normalizing the three attributes to obtain normalized values and />

a) For c _i，t Is normalized by the method of: the longer the time from the last time of polling, the higher the urgency of the corresponding STA to be polled, so that the data packet generated by the STA can be sent out in time. Record h _t For the average time interval that each STA is polled, thenRepresenting STA _i The relative time interval being polled is calculated using the formula +.>

wherein

b) For r _i，t Is normalized by the method of: STA (station) _i The more data packets to be transmitted, the STA _i The higher the urgency to be polled. R is recorded _t The number of data packets waiting to be transmitted is averaged for each STA, i.eThen->Representing STA _i Relative to the number of data packets waiting to be transmitted +.>

wherein f_r，n (x)＝f _c，n (x)；

c) For q _i，t Is normalized by the method of: STA received by AP _i The larger the average signal-to-noise ratio of the signal, meaning that the AP transmits to the STA _i Is wrapped by STA of (a) _i The greater the probability of correct reception, the more so that the AP polls the STA _i The higher the tendency of (2). Record q _max，t ＝max _{i＝1，2，...，N} {q _i，t }，q _min，t ＝min _{i＝1，2，...，N} {q _i，t And is calculated according to the following formula

(3) Determining weights omega of three attributes according to current time t _c，t 、ω _r，t 、ω _q，t . Calculating the weight omega _c，t 、ω _r，t 、ω _q，t The boundary value of each attribute weight at the beginning of the PCF period is first determinedAnd boundary value at the end of PCF period +.> They first meet the following weight requirements: /> The AP prioritizes the time each STA was polled last and the number of data packets to be transmitted at the beginning of the PCF, and prioritizes the average signal-to-noise ratio of the received STA signals near the end of the PCF to transmit as many packets as possible during the remaining period. The boundary value of the set weight satisfies the following relationship: />Let the starting time of the current PCF period be t _start PCF time period length is T _pcf Omega is calculated according to the following formula _c，t 、ω _r，t 、ω _q，t ：

The above formula defines the law of variation of three attribute weights, wherein ω _c，t and ω_r，t Linearly decreasing with increasing t, ω _q，t The linear increase with increasing t reflects the change in the extent of influence of different attributes of the AP in decision-making over time.

(4) Based on the normalized valueCorresponding three attribute weights omega _c，t 、ω _r，t 、ω _q，t Applying a weighted summation method to obtain the STA _i The degree of urgency v of being polled _i，t The method comprises the following steps:

step 3: for each STA _i The AP calculates the corresponding s _i，t and v_i，t They respectively characterize AP-polled STAs from different angles _i Is not limited by the degree of urgency of the driver. Defining AP polling STAs _i Strength w of (2) _i，t The following are provided:

w _i，t ＝max{s _i，t ，v _i，t } (18)

w _i，t comprehensive reflection of AP polling STA _i Is not limited by the degree of urgency of the driver.

Step 4: AP determines the current time to poll the STA _i′ Wherein i' =argmax _{i＝1，2，...，N} {w _i，t }。

Step 5: after determining the STA to be polled, the AP also needs to determine the data packet to send to the STA. JudgingWhether or not it is empty, if->If it is null, the AP sends either a CF-Poll frame (when the frame replied to by the last polled STA does not contain a Data portion) or a CF-ack+CF-Poll frame (when the frame replied to by the last polled STA contains a Data portion) to the STA _i′ Otherwise the AP sends either a data+CF-Poll frame (when the frame replied to by the last polled STA does not contain a Data portion) or a data+CF-ack+CF-Poll frame (when the frame replied to by the last polled STA contains a Data portion) to the STA _i′ The Data part is a Data packet-> wherein />So far, the decision process of the AP ends.

The invention has the following beneficial effects:

1. the invention can effectively reduce service time delay and improve service quality. The invention comprehensively considers two factors: the attributes of the data packets to be sent and the attributes of the STAs in the BSS are cached by the AP. The attributes of the data packets include the remaining validity period, priority, and length, and the attributes of the STA include the time since last poll, the number of data packets to be transmitted, and the average signal-to-noise ratio of the STA signal received by the AP.

2. The invention dynamically adjusts the weight of each attribute according to the position of the current moment in the PCF time period, and reflects the change of the influence degree of different attributes on the decision at different moments in the PCF.

3. The invention is simple and easy to operate, and does not introduce a large amount of computation load.

4. The invention is compatible with IEEE Std 802.11-2016 standard. The MAC frame header defined by the IEEE Std 802.11-2016 standard contains a QoS Control field. The STA may add the amount of Data packets to be sent in this field when sending a data+cf-Ack, data, CF-Ack, null frame, from which the AP may obtain this information.

Drawings

FIG. 1 is an AP poll decision flow chart;

FIG. 2 is an AP calculation s _i，t Is a flow chart of (2);

fig. 3 is an AP calculation v _i，t Is a flow chart of (a).

Detailed Description

The invention discloses a polling method based on multi-attribute decision in point coordination, which determines an STA polled by an AP at a specific moment and a data packet additionally transmitted when the STA is polled. The polling decision of an AP is related to two factors: the AP transmits the urgency of the data packet to each STA and the urgency of each STA being polled. The whole polling decision problem is modeled as a multi-attribute decision problem, and factors such as the remaining validity period of a data packet, the priority of the data packet, the length of the data packet, the time from the STA to be polled last time, the number of the data packets to be sent by the STA, the average signal to noise ratio of the AP receiving the STA signals and the like are considered. Considering the influence of the position of the current moment in the PCF period on the decision result, the multi-attribute decision problem is solved by adopting a dynamic weighted summation method. The invention discloses a step of executing polling decision by an AP, definition of each attribute, a normalization method, a weight determining method and the like. The invention is further described below with reference to the drawings and examples. The embodiments and the process are given in detail on the premise of the technical scheme of the invention, but the protection scope of the invention is not limited to the following embodiments.

When the AP executes the polling method of the present invention, the AP, STA or its running protocol needs to have the following functions:

1. when the application layer protocol of the source node generates a data packet, the generation time, the failure time and the priority of the data packet are required to be added into the data packet;

the AP needs to record the last time each STA is polled;

the AP needs to record the average time interval of all the STAs to be polled;

the MAC layer protocol supports the STA to announce the quantity of data packets to be sent to the AP, and the AP acquires and records the information from the reply frame whenever receiving the reply frame of the STA;

and 5, the AP needs to record the signal-to-noise ratio of the reply packet of each STA received for the last M times, and calculates to obtain the average signal-to-noise ratio.

The AP decision flow of the present invention is shown in fig. 1, which includes five steps:

step 1: AP calculation is to STA _i Degree of urgency s for transmitting data packets _i，t (i=1, 2,., n.), fig. 2 gives a detailed procedure of the calculation;

step 2: AP calculates STA _i The degree of urgency v of being polled _i，t (i=1, 2,., N), fig. 3 gives a detailed procedure of the calculation;

step 3: AP calculates polling STA _i Strength w of (2) _i，t ＝max{s _i，t ，v _i，t }(i＝1，2，...，N)；

Step 4: AP determines the current time to poll the STA _i′ Wherein i' =argmax _{i＝1，2，...，N} {w _i，t }；

Step 5: judgingWhether or not it is empty, if->If it is null, the AP sends either a CF-Poll frame (when the frame replied to by the last polled STA does not contain a Data portion) or a CF-ack+CF-Poll frame (when the frame replied to by the last polled STA contains a Data portion) to the STA _i′ Otherwise the AP sends either a data+CF-Poll frame (when the frame replied to by the last polled STA does not contain a Data portion) or a data+CF-ack+CF-Poll frame (when the frame replied to by the last polled STA contains a Data portion) to the STA _i′ Wherein the Data part is a Data packet-> So far, the decision process of the AP ends.

Let 1 BSS contain 1 AP and 4 (n=4) STAs. The whole BSS works in an alternating mode of DCF and PCF, the repetition period is 1s, and the DCF period and PCF period respectively occupy 500ms, namely T _dcf ＝T _pcf =500 ms. Let the current time be t _current =3800 ms, the ap operates in PCF mode, and the current PCF period is from t _start =3500 ms. At t _current At this time, the AP determines the STA to be polled and the data packet transmitted when the STA is polled according to the flow shown in fig. 1. The AP first performs step 1, calculates the power to the STA _i Degree of urgency s for transmitting data packets _i，t (i=1, 2,3, 4). Various attributes of the data packets to be sent to each STA by the AP are shown in table 1, where the failed data packets are removed. The attributes of each normalized packet are shown in table 2.

Table 1 AP various attributes of data packets to be transmitted to STAs

Table 2 normalized attributes of each packet

The attributes of each STA recorded by the AP are shown in table 3. The normalized properties of each STA are shown in Table 4, where h _t ＝245ms。

Table 3 AP various attributes of each STA recorded

Table 4 normalized attributes of each STA

The boundary values for the weights of the attributes are set as follows:

at t _current At time=3800 ms, the weights of the various attributes are calculated according to formulas (5) to (7), (14) to (16)

ω _u，t ＝0.34，ω _p，t ＝0.28，ω _l，t ＝0.38，ω _c，t ＝0.24，ω _r，t ＝0.28，ω _q，t ＝0.48 (21)

According to table 2, table 4 and formula (21), the degree of urgency s for the AP to transmit data packets to each STA is calculated _i，t Degree of urgency v to which STAs are polled _i，t And AP polls strong for STAsDegree w _i，t As shown in table 5. According to the rules described in FIG. 1, at t _current At time=3800 ms, the AP decides to poll STA3 and transmits the 1 st packet in the STA3 transmission queue at the time of polling.

Table 5 s for each STA _i，t 、v _i，t and w_i，t Value of

Claims

1. A polling method based on multi-attribute decision in point coordination is characterized in that: the AP considers the following factors when determining the STA to be polled and the data packet to be transmitted: the method comprises the steps of firstly determining the STA to be polled by adopting a dynamic weighting summation multi-attribute decision method, then determining the data packet transmitted when the STA is polled, and the weight of each attribute is related to the position of the current moment in a PCF period, wherein the step comprises the following steps:

step 1: AP calculation is to STA _i Degree of urgency s for transmitting data packets _i，t The process comprises the following steps:

(1) For and STA _i Corresponding transmission queueEvery data packet in->The following three attributes are calculated:

a) Remaining validity period u _i，j，t ：u _i，j，t ＝t _{remove，i，j}-t, wherein t_{remove，i，j} Representing the absolute time of failure of the data packet, marked by the source node when the data packet is generated;

b) Priority p _i，j : calibrated by upper layer protocol, p _i，j ∈[0，1]0 represents the lowest priority1 represents the highest priority;

c) Length l _i，j : the number of bytes of the MAC layer service data unit;

(2) Normalizing the three attributes to obtain normalized values and />

(3) Determining weights omega of three attributes according to current moment _u，t 、ω _p，t 、ω _l，t ：

(4) Computing AP transmitting data packetIs urgent of (3):

(5) Computing AP to STA _i The urgency of transmitting the data packet:

step 2: AP calculates STA _i The degree of urgency v of being polled _i，t The process comprises the following steps:

(1) AP calculates corresponding STA _i Three attributes of (a):

a) Time c from last time being polled _i，t ：c _i，t ＝t-t _i, wherein t_i Representing STA _i Absolute time of last polled;

b) Number of data packets to be transmitted r _i，t : the number r of data packets to be transmitted _i，t By STA _i Providing to the AP;

c) AP receiving STA _i Average signal of signalRatio of noise q _i，t : the AP records the last M received STAs _i Recovering the signal-to-noise ratio of the packet and calculating the average value to obtain q _i，t ；

(2) Normalizing the three attributes to obtain normalized values and />

(3) Determining weights omega of three attributes according to current moment _c，t 、ω _r，t 、ω _q，t ；

(4) Computing STA _i The degree of urgency v of being polled _i，t ：

Step 5: the AP determines whether there is a STA to send _i′ The AP sends a data+CF-Poll packet or a data+CF-ack+CF-Poll packet, if any, to the STA _i′ The data part is the data packet with the highest sending urgency wherein ,j represents the AP stored pending STA _i′ Packet sequence number, J in packet queue _i′，t Representing the waiting to be sent to the STA stored by the AP at the current moment _i′ T represents the total number of data packets at the current timeThe time stamp value, otherwise, the AP sends a CF-Poll packet or a CF-ack+CF-Poll packet to the STA _i′ 。

2.A method of multi-attribute decision-based polling in point coordination according to claim 1, wherein: the remaining validity period u _i，j，t Priority p _i，j And length l _i，j The normalization method of (2) comprises:

a) For u _i，j，t Is normalized by the method of: t is recorded _{generate，i，j} Is a data packetAt the absolute time of generation of the source node, t _{valid，i，j} For the validity period length of the data packet, t is _{valid，i，j} ＝t _{remove，i，j} -t _{generate，i，j} Calculate +.>

wherein ：

b) For p _i，j Is normalized by the method of:

c) For l _i，j Is normalized by the method of: l-shaped memory _t For the average length of the data packets in all transmission queues in the AP, the average length is calculated according to the following formula

wherein ：

3.a method of multi-attribute decision-based polling in point coordination according to claim 2, wherein: the remaining validity period u _i，j，t Priority p _i，j And length l _i，j Weight omega of (2) _u，t 、ω _p，t and ω_l，t In relation to the current instant t, comprising:

a) Let ω be _u，t 、ω _p，t 、ω _l，t The initial values at the beginning of the PCF period are respectivelyThe value at the end of the PCF period is +.>And satisfy->

b) Let the starting time of the current PCF period be t _start PCF time period length is T _pcf Omega is calculated according to the following formula _u，t 、ω _p，t 、ω _l，t ：

4. A method of multi-attribute decision-based polling in point coordination according to claim 3, wherein: said time c from last time being polled _i，t Number of data packets to be transmitted r _i，t And AP receiving STA _i Average signal to noise ratio q of signal _i，t The normalization method of (2) comprises:

a) For c _i，t Is normalized by the method of: record h _t For the average time interval that each STA is polled, it is calculated according to the following formula

wherein ：

b) For r _i，t Is normalized by the method of: r is recorded _t The number of data packets waiting to be transmitted for each STA is calculated according to the following formula

wherein f_r，n (x)＝f _c，n (x)；

c) For q _i，t Is normalized by the method of: record q _max，t ＝max _{i＝1，2，...，N} {q _i，t }，q _min，t ＝min _{i＝1，2，...，N} {q _i，t And is calculated according to the following formula

5.A method of multi-attribute decision-based polling in point coordination according to claim 3, wherein: said time c from last time being polled _i，t Number of data packets to be transmitted r _i，t And AP receiving STA _i Average signal to noise ratio q of signal _i，t Weight omega of (2) _c，t 、ω _r，t and ω_q，t In relation to the current instant t, the calculation method comprises:

a) Let ω be _c，t 、ω _r，t 、ω _q，t The initial values at the beginning of the PCF period are respectivelyThe value at the end of the PCF period is +.>And satisfy->

b) Let the starting time of the current PCF period be t _start PCF time periodTotal length T _pcf Omega is calculated according to the following formula _c，t 、ω _r，t 、ω _q，t ：