TDMA ACCESS METHOD AND DEVICE BASED ON MULTIPLE ACCESS POINTS

• US 20150244486A1
• Filed: 01/10/2013
• Published: 08/27/2015
• Est. Priority Date: 09/17/2012
• Status: Active Grant

• Current Assignee: Shenyang Institute of Automation of the Chinese
• Original Assignee: Shenyang Institute of Automation of the Chinese
• Inventors: Liang, Wei, Liu, Shuai, Zhang, Xiaoling, Yang, Yutuo, Yu, Haibin
• Granted Patent: US 9,780,898 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04B 7/2656 for structure of frame, burst
• CPC Class Codes: H04J 3/1694 Allocation of channels in TDM/TDMA networks, e.g. distributed multiplexers Passive Optical Networks H04Q11/0062
• CPC Class Codes: H04L 5/0055 Physical resource allocation for ACK/NACK for physical mapping arrangements in ARQ protocols H04L1/1861
• CPC Class Codes: H04W 16/18 Network planning tools
• CPC Class Codes: H04W 40/244 using a network of reference devices, e.g. beaconing
• CPC Class Codes: H04W 48/08 Access restriction or access information delivery, e.g. discovery data delivery signalling during connection H04W76/00
• CPC Class Codes: H04W 72/0446 Resources in time domain, e.g. slots or frames

Abstract

The present invention relates to a TDMA access method and device based on multiple access points. According to the problems that the existing method cannot simultaneously satisfy the demands of timeliness and reliability in actual industrial application and has low resource utilization rate, the present invention takes full consideration of the transmission characteristics and industrial automation application characteristics of wireless networks, and provides a TDMA access method and device based on multiple access points. The main ideas of the method in the present invention are: the multi-access point redundant communication manner is adopted to improve system reliability, beacon frames of multiple access points are utilized to perform time synchronization so as to improve synchronization precision, confirmation messages are fed back with regard to reliable access points to reduce the number of retransmissions, and a modularized multi-access point device design method is adopted to lower the difficulties of device maintenance and management.

Claims

1. A TDMA access method based on multiple access points, wherein the method comprises the following steps:

a multi-AP access device is commanded as the time source of the whole network and the STA utilizes beacon frames broadcasted by the multi-AP access device to perform time synchronization;

the multi-AP access device containing n access points (AP) is divided into k groups, and 1≦

k≦

n;

according to the quantity j of the APs within any group B_i={AP_i1, AP_i2, . . . AP_ij}, super-frames with length of m are divided into k sub-super-frames, in which the i_th sub-super-frame corresponds to the group B_i;

within the corresponding i_th sub-super-frame of the group B_i, time slots are reserved from the i_th sub-super-frame and the quantity of the reserved time slots is equal to the quantity j of the APs in the group B_i; and

with regard to the AP_ij within any group B_i (1≦

i≦

k), if formula ASN%m=(m/k)*(i−

1)+j is true, the AP_ij broadcasts the beacon frame within the time slot ASN, or else does not make any response, wherein the ASN is the present absolute time slot number and is counted from 1.

2. The TDMA access method based on multiple access points according to claim 1, wherein the beacon frames are broadcast frames sent by the APs and include network numbers, time slot stamps and network resource management.

3. The TDMA access method based on multiple access points according to claim 1, wherein the grouping principle of dividing the multi-AP access device containing n APs into k groups is as follows:

(1) the overlap section of each AP transmission range in the group is the minimum section;

(2) the union set of all AP transmission ranges in the group is capable of covering the whole network.

4. The TDMA access method based on multiple access points according to claim 1, wherein the calculation method of the quantity j of the APs in the group B_i={AP_i1, AP_i2, . . . AP_ij} is as follows:

if n%k==0, j=n/k;

or else, when 1≦

i≦

k−

1, j=└

n/k┘

;

when i=k, j=(n%k).

5. The TDMA access method based on multiple access points according to claim 1, wherein after the multi-AP access device receives the data packet of the STA, a method of replying ACK to the STA by a network management module is as follows:

if only one AP receives the data packet of the STA, the AP directly replies the ACK;

if multiple APs receive the data packet of the STA, each AP replies the ACK according to the packet receiving success rate and the received signal strength indication RSSI.

6. The TDMA access method based on multiple access points according to claim 1, wherein the principle of each AP for replying the ACK according to the packet receiving success rate and the received signal strength indication RSSI is as follows:

when multiple APs receive the data packet of the STA, search a communication link quality mapping table, find out the AP corresponding to the maximum packet receiving success rate of the STA and send ACK by the AP in the corresponding time slot;

with regard to multiple APs having the same packet receiving success rate, search the AP with the maximum RSSI value from these APs and send ACK by the AP in the corresponding time slot; and

with regard to multiple APs having the same packet receiving success rate and the same RSSI value, randomly choose one AP to reply ACK.

7. The TDMA access method based on multiple access points according to claim 6, wherein the communication link quality mapping table is a mapping table of communication link quality between each AP and all APs of the network in the gateway maintenance;

the mapping table comprises the packet receiving success rate and the RSSI value, which are updated continuously along with the communication process.

8. A device for realizing the method according to claim 1 comprises a station STA, access points AP, a gateway and a controller;

the STA is connected with field equipment in the industrial field and is responsible for acquiring field data and controlling the production process;

wherein STA is wirelessly connected with multiple access points AP in the multi-AP access device;

said multiple access points AP is in a wired connection with one gateway of the multi-AP access device;

said multi-AP access device is used for transmitting the sensor data of the field equipment acquired by the STA to the controller and transmitting the control information of the controller to an actuator on the field equipment.

9. The device according to claim 8, wherein multiple APs share one address and work in parallel.

10. The device according to claim 8, wherein the multi-AP access device comprises a TDMA module, a user datagram protocol communication module, a packet-filtering module, a buffer cache management module and a network management module;

the user datagram protocol communication module adopts an UDP (user datagram protocol) communication protocol and is used for transmitting the data packets from multiple APs;

the packet-filtering module is connected with the user datagram protocol communication module and used for filtering redundant duplication packets;

the buffer cache management module is connected with the user datagram protocol communication module and the packet-filtering module and used for managing and accessing the buffer cache;

the network management module is connected with the buffer cache management module and used for delivering the data packet to the gateway; and

the TDMA module is connected with the user datagram protocol communication module and the network management module, is used for organizing TDMA super-frame communication and comprises an ACK replying sub-module.