WO2013177958A1

WO2013177958A1 - Ofdm technology-based frequency domain polling method for wireless sensor network

Info

Publication number: WO2013177958A1
Application number: PCT/CN2013/070327
Authority: WO
Inventors: 梁炜; 于海斌; 林俊如; 张晓玲; 曾鹏; 李世明
Original assignee: 中国科学院沈阳自动化研究所
Priority date: 2012-05-29
Filing date: 2013-01-10
Publication date: 2013-12-05
Also published as: CN103457893A; CN103457893B

Abstract

The present invention relates to the industrial wireless network technology, and particularly to an OFDM technology-based frequency domain polling method for a wireless sensor network. The present invention comprises the steps of: initial polling configuration: an AP allocating a polling group ID and a subcarrier ID to a node which is newly added into a network; OFDM frequency domain polling: the AP sending a polling request message, and after the node receives the polling request message, the AP responding in a frequency domain using an OFDM subcarrier; and TDMA slot allocation and node data transmission: according to the response condition of each polled node, the AP allocating a TDMA slot to a node which needs data transmission; and after the node receives the TDMA slot allocation result, conducting the data transmission in a corresponding slot. The present invention is proposed on the premise of fully taking into account the application characteristics of an industrial wireless network, and can reduce the network protocol overhead, and improve the bandwidth utilization rate and effective network throughput, thereby improving network timeliness and scale.

Description

Frequency domain polling method for wireless sensor network based on OFDM technology

The invention relates to an industrial wireless network technology, in particular to a frequency domain polling method for a wireless sensor network based on OFDM technology. Background technique

Wireless network technology has begun to be used in the field of factory automation, and has gradually become a hot spot for development. Compared with the traditional wired bus technology, the wireless technology has the advantages of easy installation and easy maintenance, and can avoid the problem that the cable is easily aging due to the movement, and the power contact between the slip rings is easy to fail. Therefore, in the high-speed workshop-level factory automation, wireless technology has great application potential.

In wireless communication, multiple terminals sharing channel resources cause conflicts. In order to solve this problem, the IEEE 802.11 protocol proposes two methods, one is carrier-multiple access with collision avoidance in the Distributed Coordination Function (DCF) mode (CSMA/CA, Carrier Sense Multiple Access with Collision). The Avoidance mechanism, the other is the polling mechanism in the Point Coordination Function (PCF) mode.

The CSMA/CA mechanism in DCF mode uses a random collision backoff algorithm, which cannot meet the deterministic requirements of the workshop-level industrial wireless network for delay. In addition, shop-level industrial wireless networks often require larger network sizes, resulting in a greater number of nodes competing for channels. Under the above circumstances, the CSMA/CA mechanism is difficult to meet the needs of industrial applications in terms of real-time and reliability.

The polling mechanism in PCF mode ensures that each node can occupy the channel to transmit data only when it is allowed, so it can be avoided to a large extent.

Figure 1 shows the scheduling of access points of each node under the PCF polling mechanism. The access point (AP, Access Point) acts as a point coordinator and polls three nodes in sequence in the Contention-Free Period (CFP). The AP first broadcasts the beacon beacon and issues related information of the CFP phase. After receiving the beacon, the other node waits to receive the polling packet of the AP. After the short interframe space (SIFS, Short InterFrame Space), the AP sends the packet to the node 1. Polling packet, node 1 receives the polling packet and has data to send, and then sends it after SIFS time. Then, the AP sends a polling message to the node 2, and the station 2 does not respond if there is no data to be sent. The AP does not receive the response of the node 2 in the PCF Interframe Space (PIFS). 3 After sending the polling message, the station 3 sends the data in its cache to the AP after receiving the polling message.

The existing polling method has a large agreement overhead. The packets in the industrial wireless network are often short. The AP receives a packet from the node and the polling packet to be sent occupies a large amount of bandwidth, which leads to a large overhead of control packets. Especially when the node has no data to send, the round The inquiry failed. At this time, although the resource utilization of the polling mechanism is high, the polling text body occupies a large amount of bandwidth, which not only fails to improve the effective throughput of the network, but also causes a significant drop in network throughput when frequent polling failures occur. . In addition, when the network scale is large, the entire polling period is long due to the need to poll each node, and it is difficult to meet the real-time requirements of industrial applications.

In addition to the above two methods, it is possible to solve the conflict problem caused by the shared channel resources of multiple wireless communication terminals, and the following methods are also available:

The Time Division Multiple Access (TDMA) mechanism guarantees deterministic communication delays because of its effective avoidance of collision characteristics. In addition to the time synchronization overhead, the TDMA mechanism itself The overhead is small. However, in order to meet the reliability requirements of industrial wireless networks, the TDMA mechanism needs to allocate a large number of retransmission slots for each node in the time slot allocation process, and the usage rates of these retransmission slots are often low. Therefore, the resource allocation of the statically allocated TDMA mechanism is low. For a network with high reliability and real-time requirements, the network cannot accommodate more nodes, and it is difficult to meet the large-scale demand for industrial applications.

Orthogonal Frequency Division Multiplexing (OFDM) belongs to multi-carrier modulation technology. The principle is to divide the channel into several orthogonal sub-channels, and convert high-speed data signals into parallel low-speed sub-data streams, and modulate them into Transmission is performed on each subchannel. OFDM technology has been widely used in wireless communication, such as IEEE 802.11a/g, but the existing wireless communication technology only utilizes the data efficient transmission function of the physical layer of OFDM technology, and has not yet utilized OFDM technology to achieve low overhead and high bandwidth utilization. MAC layer function. Summary of the invention

The present invention proposes a frequency domain polling method for a wireless sensor network based on OFDM technology, which aims to solve the existing polling for industrial wireless networks, in view of the problems of large existing methods, low resource utilization, and inability to guarantee performance. The technical overhead, the low bandwidth utilization of the TDMA method, real-time and network size are difficult to guarantee.

To solve the above technical problem, the technical solution adopted by the present invention is: A frequency domain polling method for a wireless sensor network based on OFDM technology, which is characterized in that it comprises the following steps:

Polling initial configuration: The AP allocates a polling group ID and a subcarrier ID to nodes newly joining the network;

OFDM frequency domain polling: The AP sends a polling request message. After the node receives the polling request message, the AP responds with the OFDM subcarrier in the frequency domain.

TDMA time slot allocation and node data transmission: The AP allocates TDMA time slots for nodes that need data transmission according to the response situation of each polled node; after receiving the TDMA time slot allocation result, the node performs data transmission in the corresponding time slot. .

The implementation process of the polling initial configuration is as follows: After the node joins the network, the AP determines whether there are unallocated subcarriers in the existing polling group; if yes, randomly selects an unallocated subcarrier, and records and Identify the corresponding polling group ID and subcarrier ID; otherwise, generate a new polling group, the subcarriers in the new polling group are initialized to the unassigned state, and the node newly joining the network selects any child in the new polling group. Carrier, and record and identify the corresponding polling group ID and subcarrier ID.

The polling request message carries a polling request flag and a polling group ID information.

When the node receives the polling request message, it determines whether the polling group ID in the polling request message is the same as the polling group ID to which the node belongs; if different, indicating that the node is not in the polling range, the node does not Do any response; otherwise, after the node waits for one SIFS time, it transmits one or more symbols with the allocated subcarriers.

The responding by using the OFDM subcarrier in the frequency domain is specifically: the AP determines whether the subcarrier is in an active state by detecting energy on each subcarrier, and does not need to restore the original signal on the subcarrier, if the subcarrier is in an active state, Then, the node corresponding to the subcarrier has data to be sent, and the AP records the corresponding node; otherwise, it indicates that the node corresponding to the subcarrier has no data to be sent, and the AP does not perform any processing.

The TDMA time slot allocation and node data transmission specifically include the following implementation process:

The AP allocates a TDMA time slot for each node that has data to be transmitted, and broadcasts the time slot allocation result; after receiving the time slot allocation result, the node that needs to send data extracts its own time slot allocation information, and The corresponding time slot transmits data to the AP.

After all the nodes that have data to send complete the data transmission, the AP aggregates the acknowledgement packets that need to be replied to the nodes in the network.

After receiving the aggregated acknowledgment message, each node that needs to send data extracts an acknowledgment message corresponding to itself, and determines whether the AP correctly receives its own data.

The frequency domain polling method for wireless sensor networks based on OFDM technology proposed by the present invention is proposed under the premise of fully considering the application characteristics of industrial wireless networks, which can reduce network protocol overhead, improve bandwidth utilization and effective network throughput. Thereby improving the real-time and scale of the network. Specifically in:

1. The method based on OFDM frequency domain polling proposed by the method of the invention can poll multiple nodes in parallel at one time, which reduces the polling overhead and improves the effective throughput of the network;

2. The method of the invention designs a TDMA time slot allocation algorithm based on the result of frequency domain polling, realizes on-demand allocation of communication resources (time slots), improves bandwidth utilization, ensures real-time performance and reliability, and is suitable for large applications. Industrial wireless networks of scale. DRAWINGS

1 is a schematic diagram of the principle of a PCF polling mechanism in the prior art;

2 is a schematic diagram of initial distribution of network nodes in the present invention;

3 is a schematic diagram of OFDM polling timing in an embodiment of the present invention;

FIG. 4 is a schematic diagram of a node performing frequency domain response according to an embodiment of the present invention. detailed description

The invention will be further described in detail below with reference to the accompanying drawings.

The invention mainly relates to a frequency domain polling method for a wireless sensor network based on OFDM technology, and the main idea thereof is: realizing a frequency domain polling response by using an OFDM subcarrier, so that the AP can be in one or more physical symbol time Polling multiple sites at a time; after receiving the response of the node in the frequency domain, the AP does not need to accurately restore the original data sent by each node on each subcarrier, and only needs to detect subcarriers by threshold/peak detection or other technical means. Whether it is active; if it is active, it means that there is data to be transmitted, otherwise it means there is no data.

The method of the present invention includes polling initial configuration, OFDM frequency domain polling, TDMA time slot allocation, and node data transmission, and specifically includes the following steps:

Step (1) polling the initial configuration: the AP allocates a corresponding polling group identifier (ID, Identifier) and a subcarrier ID to the node newly joining the network;

Step (2) OFDM frequency domain polling: The AP sends a polling request message. After the node receives the polling message, the AP responds by using the OFDM subcarrier in the frequency domain.

Step (3) TDMA time slot allocation and node data transmission: The AP allocates a TDMA time slot for the node that needs data transmission according to the response condition of each polled node; after the node receives the TDMA time slot allocation result, the corresponding time slot Data transfer takes place.

The polling group ID is used to identify different polling groups. Although OFDM frequency domain polling can achieve parallel polling, the number of nodes polled in parallel is limited by the number of OFDM subcarriers. The polling group ID is used to group the nodes, and the node is required to respond only to the polling messages of the polling group to avoid the polling response between different groups. The collision, which expands the network scale.

The subcarrier ID is used to identify a subcarrier that the node returns a polling response. Nodes in the same polling group use different subcarrier IDs to avoid collisions in the polling response within the group.

The step (1) polls the initial configuration, and specifically includes the following implementation process:

(1.1) After the node joins the network, the AP determines whether there are unallocated subcarriers in the existing polling group; if so, randomly selects an unassigned subcarrier, and records and identifies the corresponding polling group ID and sub Carrier ID; otherwise, execute (1.2);

( 1.2) If there are no unassigned subcarriers in the existing polling group, a new polling group is generated and the corresponding polling group ID is assigned, and the subcarriers in the new polling group are initialized to be unallocated. State; the node joining the network selects any subcarrier from the newly generated polling group, and records and identifies the corresponding polling group ID and subcarrier ID.

The step (2) OFDM frequency domain polling specifically includes the following implementation process:

(2.1) The AP sends a polling request message, where the polling request carries the polling request flag and the polling group ID information;

(2.2) When the node receives the polling request message, it determines whether the polling group ID in the polling request message is the same as the polling group ID to which the node belongs; if different, it indicates that the node is not in the polling range. The node does not respond, otherwise it executes (2.3);

(2.3) After the node waits for one SIFS time, one or more symbols are transmitted by using the allocated subcarriers;

(2.4) The AP determines whether the subcarrier is in an active state by detecting the energy on each subcarrier, and does not need to restore the original signal on the subcarrier; if the subcarrier is in an active state, the node corresponding to the subcarrier needs to send data. The AP records the corresponding node; otherwise, it indicates that the node corresponding to the subcarrier has no data to be sent, and the AP does not perform any processing.

The step (3) TDMA time slot allocation and node data transmission specifically includes the following implementation process:

(3.1) The AP allocates a TDMA time slot for each node recorded in (2.4), and broadcasts the time slot allocation result;

(3.2) After receiving the slot allocation result, the node extracts its own slot allocation information and sends data to the AP in the corresponding time slot.

(3.3) After all nodes complete the data transmission, the AP aggregates the acknowledgment (ACK, ACKnowledgement) packets to be broadcast to the nodes in the network.

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The examples in the method of the present invention are intended to explain the present invention and do not limit the practical application of the present invention.

As shown in Figure 2, the initial distribution map of a network is randomly distributed in the plane area of 100mX 100m.

20 nodes, numbered ( ^ ^' ²⁰ ] ); AP is ⁷ ^, located at (50, 50). Nodes in the network can communicate directly with the AP, logically a star topology. The node communicates using 52 subcarriers of the OFDM physical layer, of which 48 subcarriers are available for the polling function. The ID corresponding to 48 subcarriers is recorded as 1 to 48.

In the polling initial configuration phase, the AP assigns a polling group ID and a subcarrier ID to each node. Assuming that the nodes join the network in sequence according to their numbers, when the node ^ joins the network, there is no polling group in the network. AP generates a polling group 0x01, identifying 48 subcarriers in the 0x01 polling group as unassigned, and assigning subcarrier 1 to the node, then the result of polling the initial configuration (polling group ID, subcarrier ID) of the node^ is (0x01, 0x01). At this time, the unassigned subcarriers in the 0x01 polling group are 2 to 48. When the node ^ joins the network, the polling group 0x01 is already in the network, and the subcarriers 2 to 48 are not allocated, and the AP selects the subcarrier 2 to be assigned to the node ^, then the node ^ polls the result of the initial configuration (the polling group ID, The subcarrier ID) is (0x01, 0x02). By analogy, in view of the fact that the number of nodes in this embodiment is smaller than the number of subcarriers, the result of polling the initial configuration (polling group ID, subcarrier ID) of node ^ ( ^{e [1} ' ^20] ) is (0x01, i) .

The OFDM frequency domain polling and TDMA slot allocation and node data transmission in this embodiment will be described below with reference to Figs. 3 and 4.

In the OFDM frequency domain polling phase, it is assumed that the node ^Ν ' ( ^{1 e} C ¹ ' ²⁰ ] ) belongs to the polling group 0x01, node ^,

^NN , and have data to send and both need to reply _ACK . The embodiment performs the following process: the AP broadcasts a polling request message, and the polling group ID in the polling request message is 0x01;

After receiving the polling request message, the node compares whether its own polling group ID is equal to 0x01. The nodes ₍ ^ [1,20] ) in this embodiment belong to the polling group _0χ01; however, since only nodes, ^Ν ^、, and data in the node ( ^ [1,20] _} need to be sent, the node ^, ^NN , and after receiving the polling request message, the SIFS time is sent by using its own subcarrier to send 1 symbol (symbol data); when the AP detects that the subcarriers of the nodes W ^N , ^N " and ^N , 9 are active, then AP known node W

^N , and have data to send;

The AP allocates slots 1, 2, 3, 4, and 5 to nodes ⁷ ^, ^NN , _14, and ₁₉ , respectively, and broadcasts the results of the slot allocation;

After the nodes ^, ^NN , and ₉ resolve the time slot allocation message broadcasted by the Ap broadcast, respectively, the corresponding time slots are extracted as 1, 2, 3, 4, and 5;

Nodes, ^NN N , ^^, and N ₁₉ send data to the AP in slots L ₂ , ₃ , 4 , and 5 respectively; the AP will all of nodes ^{iV V} 8 , N ^V B _l3 , ^ N" _{l4 ,} and ^ ^ Broadcast after ACK aggregation;

Node ^Ν ί4

N4 N _l3 and W

Determine whether the AP correctly receives its own data;

The polling process is over.

Claims

Claim

A frequency domain polling method for a wireless sensor network based on OFDM technology, comprising the steps of:

The frequency domain polling method for a wireless sensor network based on OFDM technology according to claim 1, wherein the initial configuration of the polling initial configuration is: after the node joins the network, the AP determines that the polling has been performed. Whether there are unassigned subcarriers in the group; if present, randomly select an unassigned subcarrier, and record and identify the corresponding polling group ID and subcarrier ID; otherwise, generate a new polling group, new round The subcarriers in the query group are all initialized to the unassigned state. The node newly joining the network selects any subcarrier in the new polling group, and records and identifies the corresponding polling group ID and subcarrier ID.

The frequency domain polling method for a wireless sensor network based on OFDM technology according to claim 1, wherein the polling request message is provided with a polling request flag and a polling group ID information.

The frequency domain polling method for a wireless sensor network based on OFDM technology according to claim 1, wherein when the node receives the polling request message, it determines the polling in the polling request message. Whether the group ID is the same as the polling group ID to which the node belongs; if it is different, indicating that the node is not in the polling range, the node does not respond; otherwise, after waiting for one SIFS time, the node sends one or more by using the allocated subcarrier. Symbols.

The method for frequency domain polling of a wireless sensor network based on OFDM technology according to claim 1, wherein the responding by using an OFDM subcarrier in a frequency domain is specifically: the AP detects the subcarriers on each subcarrier. Energy, determining whether the subcarrier is in an active state, and does not need to restore the original signal on the subcarrier. If the subcarrier is in an active state, the node corresponding to the subcarrier has data to be sent, and the AP records the corresponding node; otherwise, this indicates The node corresponding to the subcarrier has no data to send, and the AP does not perform any processing.

The frequency domain polling method for a wireless sensor network based on OFDM technology according to claim 1, wherein the TDMA time slot allocation and node data transmission specifically include the following implementation process:

The AP allocates a TDMA time slot for each node that has data to be transmitted, and broadcasts the time slot allocation result. After receiving the time slot allocation result, the node that needs to send data extracts its own time slot allocation information, and correspondingly Sending data to the AP within the time slot;