WO2019127914A1

WO2019127914A1 - Point coordination wireless medium access method based on latest leaving moment and least heap

Info

Publication number: WO2019127914A1
Application number: PCT/CN2018/078950
Authority: WO
Inventors: 官权升; 余德成; 陈伟琦; 官权学
Original assignee: 华南理工大学
Priority date: 2017-12-29
Filing date: 2018-03-14
Publication date: 2019-07-04
Also published as: CN107959980B; CN107959980A

Abstract

Disclosed in the present invention is a point coordination wireless medium access method based on the latest leaving moment and the least heap. The method is different from a conventional MAC protocol, and in the method, medium access is controlled according to the degrees of urgency of data packets. The residual time delay is used as the measuring basis of the degrees of urgency; the station where the data packets having a short residual time delay is located first obtains a polling opportunity, thus greatly avoiding network resource wastes caused by loss of data packet sent overtime; in addition, a plurality of data frames can be sent during single polling, thus reducing a polling frame sending frequency, and improving the effective utilization rate of a channel.

Description

Coordination wireless medium access method based on point of latest departure time and minimum heap

Technical field

The present invention relates to the field of wireless medium access control in a wireless local area network, and in particular to a point-coordinated wireless medium access method based on a latest departure time and a minimum heap.

Background technique

The IEEE 802.11 wireless LAN standard plays a very important role in building a wireless broadband computing environment. Multimedia applications in wireless networks are often multi-user and require QoS support such as bandwidth, delay, jitter, and bit error rate guarantees. Since the traditional MAC layer does not support QoS functions and the physical layer is constantly changing state due to noise interference, it is a big challenge for 802.11 WLAN to guarantee QoS requirements. Therefore, improving the IEEE 802.11 MAC layer protocol to meet QoS requirements has great application significance.

The basic mode of IEEE 802.11 is DCF (Distributed Coordination Function). DCF does not provide QoS support. In addition, there is a polling-based PCF (Point Coordination Function) mode. The DCF is a basic medium access control (MAC) method used by 802.11, and the DCF is based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism. DCF can only provide best-effort services without QoS guarantees. Representative time-limited services (such as IP telephony, video conferencing audio or video) require specific bandwidth, delay, and jitter, but can tolerate some loss. However, in the DCF mode, all sites in the BSS compete for resources and channels with the same priority. This indiscriminate mechanism does not provide bandwidth, latency, and jitter guarantees for high-priority sites or multimedia traffic. There is no difference in the throughput or delay of different service flows. Multiple service flows use the same queue, so their delays are basically the same. PCF allows 802.11 networks to provide a mandatory "fair" access to the media. To some extent, the media access under the PCF uses a medium access control scheme similar to polling, and the transmission data is rotated to each station. The point coordinator controls media access, and the access point has corresponding functions to match the point coordinator. The site can only send data if the point coordinator allows it. The media access under the PCF uses a network protocol that the point coordinator polls.

The traditional 802.11 wireless LAN standard can only provide "Best-effort" services, which cannot meet the QoS of multimedia real-time services such as voice and video. To enhance the support of quality of service, the IEEE committee proposed IEEE 802.11e, which has different transmission priorities depending on the type of service. High priority for voice and video signals with high real-time requirements, and lower priority for data texts with low real-time requirements. High-priority services have more access than low-priority services. The opportunity of the channel. Compared with the traditional 802.11 wireless LAN standard, the QoS performance of IEEE 802.11e has been improved. However, from the definition of QoS, the wireless MAC protocol with QoS guarantee should give priority to more urgent data packets to access the channel. Due to the delay jitter caused by the state variability of the wireless link, and the number of route hops that different transmission paths pass through, the data frame of the low priority class defined by IEEE 802.11e is likely to be higher than that of the high priority class. Data frames with more urgent latency requirements. However, under IEEE 802.11e, data frames of high priority class are still sent preferentially, rather than data frames that are truly more urgent. On the other hand, once a data frame of a high priority class bursts, it will occupy channel resources for a long time, and a data frame of a low priority class has difficulty obtaining an access channel.

Summary of the invention

The object of the present invention is to provide a method for coordinating wireless medium access based on the latest departure time and the minimum heap, which improves the service quality of the wireless local area network, and the latest departure time is small. The data packet can be preferentially accessed to the channel. If the same station has multiple data packets with the latest departure time, continuous transmission can be realized.

The object of the present invention can be achieved by the following technical solutions:

A wireless medium access method is coordinated based on a point of latest departure time and a minimum heap, the method comprising the steps of:

S1: The data packet first enters the queue of the ordinary station, and calculates the local residual delay and the latest departure time. When the data packet enters the queue, the data is queued according to the latest departure time of the data packet, so that the latest departure time is smaller. The higher the position of the data packet in the queue;

S2, the preset single polling can transmit a maximum of N frames, and the station sends the association request frame to the AP (Access Point, the central scheduling point), and carries the latest leaving time of the first N frames, and the site self-recording has been sent at the latest. Leave the time information to the queue position of the AP. If the site sends the association request frame carrying the N latest departure time, the record location is N, and the AP maintains a minimum heap based on the latest departure time (the minimum heap is A sorted complete binary tree in which the data value of any non-terminal node is not greater than the values of its left and right child nodes, and one node of the smallest heap includes the site ID and the latest departure time of a frame, AP After receiving the association request frame, the latest leaving time and the site ID of the first N frames are combined into a maximum of N nodes, and the minimum heap is sequentially inserted, and the process is completed before the data starts to be exchanged;

S3, loop the following steps:

The minimum heap top node is sequentially popped out until the site ID of the top node is different. Assuming that the minimum heap pops up k nodes, and the site IDs of the k nodes are the same, the AP sends a poll frame to notify the site, and the site obtains Access to the channel and the ability to send k data frames;

Each time the station sends a data frame, the frame header carries the latest departure time of the next data packet in the station queue record position, and the record position is incremented by 1. If there is no data packet in the next bit of the record position, then the frame is in the frame. Mark the head;

After receiving the data frame, the AP extracts the latest leaving time of the frame header, and forms a node with the site ID to insert the minimum heap. If the frame header is marked as the next bit of the recording location, there is no data packet, then the specific flag of the current data packet is Good mark, after receiving the current data packet, the AP forms the new node with the maximum value of the latest departure time in the minimum heap plus a system minimum time unit (such as 1μs), inserts the minimum heap, and thus makes the AP first round. While consulting other sites, the site will not be permanently lost polling opportunities.

Further, in step S1, the calculation step of the local remaining delay is:

First calculate the global residual delay, that is, the maximum delay of the data packet from the current site to the destination site. For multi-hop links, let n be the total number of hops of the path, i be the number of hops that have been experienced, experience i hop, reach the first i stations, g _i is the global residual delay when the data packet arrives at the i-th station. When i=0, the 0th station is the source station, and the global residual delay g _i =g ₀ , g _{0 is} The maximum end-to-end delay of the service flow is preset, and the global residual delay of each hop is obtained step by step through the following formula:

Where TA _i is the time when the data packet arrives at the i-th station, and ATD _i is the actual departure time of the data packet at the i-th station, then ATD _i- TA _i is the actual stay time of the data packet at the i-th station, size For the size of the data packet, rate is the data transmission rate, and size/rate is the transmission delay of the data packet sent from the i-th station;

Then calculate the local residual delay, that is, the time allowed for the data packet to stay at the current station. For the multi-hop link, the average residual delay is used to calculate the local residual delay, and the data packet is in the remaining path. The maximum local residual delay for each hop in a single site is as follows:

Where n-i is the remaining hop count;

For a single-hop link, the remaining delay does not distinguish between the global residual delay and the local residual delay. The maximum remaining delay is the maximum end-to-end delay of the service flow.

Further, in step S1, the calculation method of the latest departure time is:

For a multi-hop link, the maximum local residual delay l _i of the data packet at the i-th station, ie the maximum stay time of the data packet at the i-th station, and the arrival time of the data packet at the i-th station TA _i , that is, the latest departure time of the data packet at the ith site can be obtained:

Compared with the prior art, the present invention has the following advantages and beneficial effects:

The present invention coordinates a wireless medium access method based on the latest departure time and the minimum heap point, and adds QoS performance to the MAC layer compared to IEEE 802.11 "best effort", and is different from IEEE 802.11e based on "class" implementation. The service differentiation is considered from a single data packet, so that the most urgent data packet is first accessed to the medium, which greatly avoids the waste of network resources for sending data packets due to timeout. At the same time, a single poll can send multiple data. The frame reduces the transmission frequency of the polling frame and improves the effective utilization of the channel.

DRAWINGS

FIG. 1 is a schematic flowchart of a method for coordinating a wireless medium access method based on a latest departure time and a minimum heap point according to an embodiment of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

Example:

The embodiment provides a coordinated wireless medium access method based on the latest departure time and the minimum heap. The flowchart of the method is as shown in FIG. 1 and includes the following steps:

The data packet of each service flow has a maximum limit of end-to-end delay. When the end-to-end delay of a packet exceeds its maximum value, the packet is discarded even after being received by the target station. Therefore, the maximum value of the end-to-end delay can also be understood as the maximum lifetime of the data packet. The maximum value of the end-to-end delay is set to meet the QoS requirements of the traffic flow, such as the traffic flow of the real-time voice conversation. Only when the voice information of Party A is transmitted to Party B in time within the specified time interval, can Party A and Party B of the call communicate normally. Once the information of one party is delayed, the two parties will not be able to communicate normally. The specified time interval is The maximum end-to-end delay, the maximum end-to-end delay is set by the service flow according to its actual QoS requirements. The remaining delay is the name of the packet, which is the maximum end-to-end delay of the packet minus the packet has been experienced. The less time the remaining delay of the data packet is, the more urgent it is to send it to the destination site. If it expires, even if the destination site receives it, the data packet will be discarded. The network performance is reduced. Therefore, the less the remaining delay of the data packet, the higher the urgency of the data packet. From the definition of QoS, the wireless MAC protocol with QoS guarantee should give priority to more urgent data packets. The opportunity to enter the channel, therefore, the remaining delay as a parameter of the MAC protocol is very suitable.

For a multi-hop link, let n be the total number of hops of the path, i be the number of hops that have been experienced, go through i-hop, reach the i-th station, and g _i is the global residual delay when the packet arrives at the i-th station. When i=0, the 0th station is the source station, and the global residual delay g _i =g ₀ , g _{0 is} the preset end-to-end delay maximum value of the service flow, and iteratively iteratively Find the global residual delay for each hop:

Where n-i is the remaining hop count;

S3, loop the following steps:

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, and any person skilled in the art can disclose the patent according to the present invention within the scope disclosed by the present patent. The technical solutions and their inventive patent concepts are equivalently replaced or changed, and are all within the scope of protection of the present invention.

Claims

A wireless medium access method is coordinated based on a point of latest departure time and a minimum heap, wherein the method comprises the following steps:

S1: The data packet first enters the queue of the ordinary station, and calculates the local residual delay and the latest departure time. When the data packet enters the queue, the data is queued according to the latest departure time of the data packet, so that the latest departure time is smaller. The higher the position of the data packet in the queue;

S2, the preset single polling can transmit a maximum of N frames, the station sends the association request frame to the AP, and carries the latest leaving time of the first N frames, and the station records the latest departure time information to the AP queue position. If the site sending association request frame carries N latest leaving moments, the recording location is N, and the AP maintains a minimum heap sorted by the latest leaving time. The node of the smallest heap includes the site ID and the most At the late departure time, after receiving the association request frame, the AP combines the latest departure time of the first N frames and the site ID to form a maximum of N nodes, and sequentially inserts the minimum heap, and the process is completed before the data starts to be exchanged;

S3, loop the following steps:

The minimum heap top node is sequentially popped out until the site ID of the top node is different. Assuming that the minimum heap pops up k nodes, and the site IDs of the k nodes are the same, the AP sends a poll frame to notify the site, and the site obtains Access to the channel and the ability to send k data frames;

Each time the station sends a data frame, the frame header carries the latest departure time of the next data packet in the station queue record position, and the record position is incremented by 1. If there is no data packet in the next bit of the record position, then the frame is in the frame. Mark the head;

After receiving the data frame, the AP extracts the latest leaving time of the frame header, and forms a node with the site ID to insert the minimum heap. If the frame header is marked as the next bit of the recording location, there is no data packet, then the specific flag of the current data packet is Well, after the AP receives the current data packet, the AP adds the maximum value of the latest departure time in the minimum heap plus a system minimum time unit to form a new node, and inserts the minimum heap, so that the AP first polls other sites. At the same time, the site will not be permanently lost polling opportunities.
The point-coordinated wireless medium access method based on the latest departure time and the minimum heap according to claim 1, wherein in step S1, the calculation step of the local residual delay is:

First calculate the global residual delay, that is, the maximum delay of the data packet from the current site to the destination site. For multi-hop links, let n be the total number of hops of the path, i be the number of hops that have been experienced, experience i hop, reach the first i stations, g i is the global residual delay when the data packet arrives at the i-th station. When i=0, the 0th station is the source station, and the global residual delay g i =g 0 , g 0 is The maximum end-to-end delay of the service flow is preset, and the global residual delay of each hop is obtained step by step through the following formula:

Where TA i is the time when the data packet arrives at the i-th station, and ATD i is the actual departure time of the data packet at the i-th station, then ATD i- TA i is the actual stay time of the data packet at the i-th station, size For the size of the data packet, rate is the data transmission rate, and size/rate is the transmission delay of the data packet sent from the i-th station;

Then calculate the local residual delay, that is, the time allowed for the data packet to stay at the current station. For the multi-hop link, the average residual delay is used to calculate the local residual delay, and the data packet is in the remaining path. The maximum local residual delay for each hop in a single site is as follows:

Where n-i is the remaining hop count;

For a single-hop link, the remaining delay does not distinguish between the global residual delay and the local residual delay. The maximum remaining delay is the maximum end-to-end delay of the service flow.
The point-coordinated wireless medium access method based on the latest departure time and the minimum heap according to claim 1, wherein in the step S1, the calculation method of the latest departure time is:

For a multi-hop link, the maximum local residual delay l i of the data packet at the i-th station, ie the maximum stay time of the data packet at the i-th station, and the arrival time of the data packet at the i-th station TA i , that is, the latest departure time of the data packet at the ith site can be obtained: