A time slot estimation method based on beacon network

Abstract

The present invention relates to a time slot estimation method based on a beacon network, and belongs to the field of communication technology. The method comprises the following steps: S1: node power-on networking; S2: TDMA time slot division; S3: when entering the TDMA time slot, analyzing the beacon frame of the upper node; S4: the node estimates the time slot division of the next cycle based on the time slot information of the current cycle; S5: judging whether a frame can be sent and completed within the CSMA time slot. In the actual operation of the system, due to the limitations of the working environment, the nodes are usually placed in the electrical well room, and it is impossible to ensure that the network is always in a state of high-quality communication. When the node state is abnormal and the beacon frame cannot be received correctly, in order to maintain the normal communication process, the time slot estimation information can be used for security processing.

Description

Technical Field

[0001] The invention belongs to the technical field of communications and relates to a time slot estimation method based on a beacon network. Background Art

[0002] Broadband micro-power wireless communication technology is used to collect electricity consumption information of smart grid users. It is a distributed wireless network that automatically forms a network of multiple wireless nodes for communication. The nodes in the network have the functions of self-organization, self-management and self-maintenance. Each node can communicate with other nodes in its communication range in a direct communication manner, and can communicate with nodes outside the communication range by using one or more relay nodes, thus forming a wireless multi-hop network between nodes. The entire network forms a tree-like topology, with a structure like Figure 1 shown.

[0003] The communication module connected to the concentrator is the main communication module, called the central coordinator CCO (Central Coordinator), which is responsible for the transmission and reception of data between the concentrator and the collector or the concentrator and the electric energy meter. It also has functions such as networking control and network maintenance management. The communication module connected to the collector or the electric energy meter is divided into a proxy coordinator PCO (Proxy Coordinator) and a station STA (Station) according to its role in the network. The outermost node has no relay function and is called a station STA (Station), while the node that acts as a relay function is called a proxy coordinator PCO (Proxy Coordinator). Due to changes in the network topology, the roles of PCO and STA can be converted to each other.

[0004] The broadband micro-power communication network uses a channel access mechanism based on beacon frames. The CCO periodically sends beacon frames. The beacon frames contain planning information for beacon slots, TDMA slots, CSMA slots, bound CSMA slots and other time slots within the beacon period assigned by the CCO. Subnodes in the network must follow the time slots assigned by the CCO to access the channel. In general, time slots such as beacon slots and TDMA slots that are explicitly allocated to the CCO or specific STAs are collectively referred to as non-contention slots (TDMA slots); time slots such as CSMA slots and bound CSMA slots that do not specify users and need to be competed for by STAs in need are collectively referred to as contention slots (CSMA slots). The beacon period time slots are divided as follows: Figure 2 shown.

[0005] In the actual smart grid user power consumption information data collection application, the time slot division is as follows Figure 3As shown. In the TDMA time slot, a node in the network may not receive any beacon frames due to abnormalities in the upper node or its own state. If this node is a STA, it will not be able to obtain time slot information within two routing cycles, which will cause the node to change its agent and reselect the agent node. If this node is a PCO, it will not be able to send beacon frames if it does not obtain time slot information within two routing cycles, and the nodes below this node will initiate a proxy change. When the network scale becomes larger and anomalies occur, a large number of proxy change and proxy confirmation messages will appear in the entire network. The transmission of a large number of messages competes for limited time slot resources, increasing the probability of transmission failure, which further leads to more retransmission messages, seriously affecting the execution efficiency of other normal services. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a time slot estimation method based on a beacon network. When a node enters the network, it uses a specific field in the beacon frame to receive the beacon frame synchronization time slot information in the TDMA time slot, and estimates the time slot information of the next cycle in the CSMA time slot according to the time slot parameters of the current cycle. When entering the next cycle, if a beacon frame is received in the TDMA time slot, the estimated time slot information of the previous cycle is erased, and the time slot information carried in the beacon frame is used for synchronization. If the beacon frame is not received in the TDMA time slot due to network abnormalities, the time slot estimation information of the previous cycle is used, and the network is temporarily maintained by sending a discovery list message in the estimated CSMA time slot, waiting for the abnormality to be resolved or entering the offline process.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A time slot estimation method based on a beacon network, the method comprising the following steps:

[0009] S1: Nodes are powered on and networked;

[0010] S2: TDMA time slot division;

[0011] S3: When entering the TDMA time slot, analyze the beacon frame of the upper node;

[0012] S4: The node estimates the time slot division of the next cycle based on the time slot information of the current cycle;

[0013] S5: Determine whether a frame can be sent within the CSMA time slot.

[0014] Optionally, S1 is specifically as follows: the central controller CCO completes the entire networking process by arranging the sending of central beacons, proxy beacons, and discovery beacons to trigger network access requests from STAs layer by layer; a multi-level tree network is formed between nodes.

[0015] Optionally, in S2, CCO dynamically allocates time slots to all nodes in the entire network; when CCO allocates time slots within a cycle, they are divided into TDMA time slots and CSMA time slots; the front of the TDMA time slot is the central beacon time slot, followed by the proxy beacon time slot, the order of the proxy beacon time slots is sorted according to the hierarchy, and there is no distinction between the front and the back in the same hierarchy, and the last is the discovery beacon time slot; after the beacon time slot is the CSMA time slot.

[0016] Optionally, in S3, when entering the TDMA time slot, if the PCO / STA receiving end receives a beacon frame, the time slot estimation information of the previous cycle is deleted, and a new round of normal time slots is synchronized according to the time slot information in the beacon frame; the beacon frame used for time slot synchronization is an upper layer central beacon frame, a proxy beacon frame or a discovery beacon frame;

[0017] If the node does not receive any beacon frames in this cycle due to abnormalities in the upper node or its own state, the node cannot obtain the new round of time slot division information. In order to ensure normal communication and maintain the sub-network under this node, the estimated time slot information of the previous cycle is used;

[0018] If the beacon frame of the upper node is not received within two routing cycles, the proxy change is started and the proxy node is replaced. During the proxy change, the lower network needs to be maintained by sending a discovery list message within the estimated CSMA time slot. When the proxy change is completed, the lower nodes are changed together with the proxy node.

[0019] Optionally, in S4, the time slot estimation is completed within the CSMA time slot, and the node estimates the time slot division of the next cycle based on the time slot information of the current cycle; to ensure the correctness of the time slot estimation, define:

[0020] T TDMA =0.2T period

[0021] T CSMA =0.8T period

[0022] Among them, T period is the length of the beacon period, which can be adjusted according to the network scale; T TDMA is the length of the TDMA time slot, which accounts for 20% of the beacon period; T CSMA It is the length of the CSMA time slot, which accounts for eighty percent of the beacon period.

[0023] Optionally, in S5, the message sent in the CSMA time slot is transmitted in the corresponding CSMA time slot and cannot cross the time slot; it cannot cross to non-competitive time slots such as beacon time slots and TDMA time slots; when competing to send data frames in the CSMA time slot, determine whether a frame can be sent in the CSMA time slot; if the transmission cannot be completed in the CSMA time slot, it is necessary to add it to the buffer area and wait until the next CSMA time slot to give priority to processing the unfinished data.

[0024] The beneficial effects of the present invention are:

[0025] 1. In the actual operation of the system, due to the limitations of the working environment, the nodes are usually placed in the electrical well room, and it is impossible to ensure that the network is always in a state of high-quality communication. When the node state is abnormal and cannot correctly receive the beacon frame, in order to maintain the normal communication process, the time slot estimation information can be used for security processing.

[0026] 2. The time slot estimation uses a specific field in the beacon frame, without the need for additional message transmission. After receiving the beacon frame normally, the node can delete the estimation information without affecting the normal process.

[0027] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0029] Figure 1 This is the broadband micro-power network topology;

[0030] Figure 2 This is a schematic diagram of standard time slot division;

[0031] Figure 3 A schematic diagram of the system operation time slot division;

[0032] Figure 4 It is a schematic diagram of TDMA time slot division;

[0033] Figure 5 It is the flow chart of time slot protection;

[0034] Figure 6 This is a diagram of the beacon frame structure;

[0035] Figure 7 It is a physical block format;

[0036] Figure 8 It is a flowchart for the interaction of associated network access management messages;

[0037] Fig. 9 It is the time slot estimation diagram;

[0038] Fig.10 The overall flow chart for time slot estimation. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0040] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0041] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0042] Embodiment 1:

[0043] Beacon frame format

[0044] CCO divides TDMA beacon slots into central beacon slots, proxy beacon slots, and discovery beacon slots. The three roles of CCO, PCO, and STA maintain the same management of beacon slots. CCO allocates slots in the beacon cycle and fills the slot allocation entries in the beacon, which are sent through beacons to notify PCO, STA and other stations. The beacon frame structure is as follows: Figure 6 shown.

[0045] The length of the MPDU frame control field is 16 bytes. The format of the MPDU frame control field is shown in Table 1. The "delimiter type" is used to indicate the type of frame. Different frame types have different variable areas. The "delimiter type" of the beacon frame is 0.

[0046] Table 1 MPDU frame control field

[0047]

[0048]

[0049] The beacon frame is used by CCO for network management. The format of the variable area of ​​the beacon frame is shown in Figure 0. The beacon timestamp is the network reference time marked by the device sending the beacon when sending the beacon. The network reference time is maintained by CCO, and all network nodes need to keep synchronized with the network reference time of CCO.

[0050] Table 2 Variable area of ​​beacon frame

[0051]

[0052] There are four types of physical block formats for the payload, and the size of the physical block can be selected as 72 / 136 / 264 / 520 bytes. The payload of the beacon frame only supports one physical block. The physical block format is as follows: Figure 7 shown.

[0053] The beacon frame payload format is shown in Table 3. Among them, "beacon type" 1 indicates a proxy beacon, and 2 indicates a discovery beacon. "Beacon management information" includes the specific number of beacon entries and the header of each beacon entry, the length of the beacon entry, and the specific beacon entry content.

[0054] Table 3 Beacon frame payload fields

[0055]

[0056]

[0057] The time slot allocation entry carries the time slot information arranged by the CCO, as shown in Table 4.

[0058] Table 4: Timeslot Allocation Entry Format

[0059]

[0060]

[0061] Embodiment 2:

[0062] Node power-on networking

[0063] After the CCO is powered on, it first monitors the public frequency for a period of time to find out whether there is a neighbor network. If a network notification message from the neighbor network is received during the monitoring period, the message content is parsed and an unused working frequency is selected. After the selection is successful, beacon frames are periodically sent at the working frequency to start networking. If no neighbor network information is received during the monitoring period, the central beacon is periodically sent at the set working frequency after the monitoring is completed.

[0064] CCO periodically sends network notification messages on the public frequency to inform other networks that this working frequency is in use.

[0065] After the STA is powered on, it first scans the public frequency to find the network. It may receive multiple network notification messages. It selects the working frequency where the network is first discovered and continues scanning until a beacon frame is received. After receiving the beacon frame, it initiates an association request based on the "start association flag" in the frame content. When the STA accesses the network, it first needs to receive and evaluate the network message and select its proxy site. This proxy site can be a CCO or another STA site. The principle of selecting a proxy site is generally good channel quality.

[0066] After receiving the association request, CCO performs whitelist authentication on the node requesting access. After that, CCO informs STA of the result of the association request by sending an association confirmation message in the CSMA time slot. Nodes that directly access the network through CCO are the first level. After the node enters the network, CCO arranges the newly connected node to send a beacon to trigger the nodes around the newly connected node to initiate network access. New nodes that join the network through the first-level nodes become the second-level nodes, and the relay nodes are upgraded to PCOs. This cycle continues until all nodes join the network. CCO is level 0, and the maximum level of STA supports up to 15 levels, eventually forming a tree network topology.

[0067] The interaction process of the associated network management message is as follows: Figure 8 shown.

[0068] Embodiment 3:

[0069] Time slot allocation

[0070] At the beginning of each beacon cycle, CCO sends a central beacon. The central beacon carries the time slot allocation information of all nodes in this cycle. The time slot allocation requirements are as follows:

[0071] 1. STA sends discovery beacons at least twice every 170 seconds.

[0072] 2. The PCO must send a proxy beacon every cycle.

[0073] 3. The total duration of the beacon TDMA time slot does not exceed 20% of the beacon period.

[0074] 4. Give priority to newly connected nodes sending beacons to accelerate network stability.

[0075] 5. When there are fewer nodes, after CCO arranges time slots for all nodes, if the total length of beacon time slots still does not exceed 20% of the cycle, time slots will be arranged for all nodes.

[0076] 6. When there are many nodes, after CCO arranges time slots for all nodes, the total length of beacon time slots exceeds 20% of the cycle, then the time slots are arranged according to the requirement of "STA sends at least two discovery beacons every 170 seconds". The total number of time slots N per cycle is:

[0077]

[0078] Among them, NUM STA is the number of STAs, NUM PCO is the number of PCOs, T period is the beacon period length.

[0079] Embodiment 4:

[0080] Time slot synchronization and estimation

[0081] In the TDMA time slot, if the PCO / STA receiving end receives a beacon frame, it deletes the time slot estimation information of the previous cycle and synchronizes a new round of normal time slots according to the time slot information in the beacon frame.

[0082] T TDMA_END =BPST cur +BTSL*(NON_SLOT_NUM+1)

[0083] T CSMA_END =T TDMA_END +CSMATSL

[0084] Among them, T TDMA_END Indicates the end time of the TDMA time slot of the current cycle, T CSMA_END Indicates the end time of the CSMA time slot in the current cycle, BPST cur Indicates the start time of this beacon cycle, BTSL indicates the beacon slot length, NON_SLOT_NUM indicates the total number of non-central beacon slots, and CSMATSL indicates the CSMA slot length.

[0085] If the PCO / STA cannot receive the beacon frame due to node abnormality, in order to temporarily maintain network stability, the estimated information of the previous cycle needs to be used to divide the time slots of this cycle.

[0086] T TDMA_END =T TDMA_EST

[0087] TCSMA_END =T CSMA_EST

[0088] Among them, T TDMA_EST Indicates the estimated TDMA time slot end time, T CSMA_EST Indicates the estimated end time of the CSMA time slot

[0089] After the current period time slot division is completed, calculate the start time of the next beacon period:

[0090] BPST next =BPST cur +T period +10ms

[0091] Among them, BPST next Indicates the start time of the next beacon cycle, and 10ms means the periodic protection interval is 10 milliseconds.

[0092] The time slot estimation is completed within the CSMA time slot. The node estimates the time slot division of the next cycle based on the time slot information of the current cycle. In order to ensure the correctness of the time slot estimation, define:

[0093] T TDMA =0.2T period

[0094] T CSMA =0.8T period

[0095] Among them, T period is the length of the beacon period, which can be adjusted according to the network size. TDMA is the length of the TDMA time slot, which accounts for 20% of the beacon period. CSMA It is the length of the CSMA time slot, which accounts for eighty percent of the beacon period.

[0096] Then the estimated time of TDMA and CSMA time slots is:

[0097] T TDMA_EST =BPST next +0.2T period

[0098] T CSMA_EST =T TMDA_EST +0.8T period

[0099] Estimated time slots Fig. 9 shown.

[0100] The overall process of time slot estimation is as follows Fig.10 shown.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A time slot estimation method based on a beacon network, characterized in that: The method comprises the following steps: S1: Nodes are powered on and networked; After the CCO is powered on, it first monitors the public frequency for a period of time to find out whether there is a neighbor network; if it receives a network notification message from the neighbor network during the monitoring period, it parses the message content and selects an unused working frequency. After the selection is successful, it periodically sends beacon frames at the working frequency to start networking; if no neighbor network information is received during the monitoring period, it periodically sends central beacons at the set working frequency after the monitoring is completed; CCO periodically sends network notification messages at the public frequency to inform other networks that this working frequency is in use; after the STA is powered on, it first scans the public frequency to find a network. It may receive multiple network notification messages and select the working frequency where the network is first discovered to continue scanning until the network is found. After receiving the beacon frame, the CCO initiates an association request based on the "start association flag" in the frame content. After receiving the association request, the CCO performs whitelist authentication on the node requesting access. After that, the CCO informs the STA of the result of the association request by sending an association confirmation message in the CSMA time slot. The nodes that directly access the network through the CCO are the first level. After the node accesses the network, the CCO arranges the newly-accessed node to send a beacon to trigger the nodes around the newly-accessed node to initiate network access. The new node that joins the network through the first-level node becomes the second level, and the relay node is upgraded to the PCO. This cycle continues until all nodes join the network. The CCO is level 0, and the maximum level of the STA is 15, eventually forming a tree network topology. S2: TDMA time slot division; S3: When entering the TDMA time slot, analyze the beacon frame of the upper node; In the TDMA time slot, if the PCO / STA receiving end receives a beacon frame, it deletes the time slot estimation information of the previous cycle and synchronizes the new round of normal time slots according to the time slot information in the beacon frame; T TDMA_END =BPST cur +BTSL*(NON_SLOT_NUM+1) T CSMA_END =T TDMA_END +CSMATSL Among them, T TDMA_END Indicates the end time of the TDMA time slot of the current cycle, T CSMA_END Indicates the end time of the CSMA time slot in the current cycle, BPST cur Indicates the start time of this beacon cycle, BTSL indicates the length of the beacon slot, NON_SLOT_NUM indicates the total number of non-central beacon slots, and CSMATSL indicates the length of the CSMA slot; If the PCO / STA cannot receive the beacon frame due to a node anomaly, in order to temporarily maintain network stability, the estimated information of the previous cycle needs to be used to divide the time slots of this cycle; T TDMA_END =T TDMA_EST T CSMA_END =T CSMA_EST Among them, T TDMA_EST Indicates the estimated TDMA time slot end time, T CSMA_EST Indicates the estimated end time of the CSMA time slot; After the current period time slot division is completed, calculate the start time of the next beacon period: BPST next =BPST cur +T period +10ms Among them, BPST next Indicates the start time of the next beacon cycle, 10ms means the periodic protection interval is 10 milliseconds; S4: The node estimates the time slot division of the next cycle based on the time slot information of the current cycle; The time slot estimation is completed within the CSMA time slot. The node estimates the time slot division of the next cycle based on the time slot information of the current cycle. To ensure the correctness of the time slot estimation, define: T TDMA =0.2T period T CSMA =0.8T period Among them, T period is the length of the beacon period, which is adjusted according to the network size; T TDMA is the length of the TDMA time slot, which accounts for 20% of the beacon period; T CSMA is the CSMA slot length, which accounts for eighty percent of the beacon period; Then the estimated time of TDMA and CSMA time slots is: T TDMA_EST =BPST next +0.2T period T CSMA_EST =T TMDA_EST +0.8T period S5: Determine whether a frame can be sent within the CSMA time slot; In the S5, the message sent in the CSMA time slot is transmitted in the corresponding CSMA time slot and cannot cross the time slot; it cannot cross to non-competitive time slots such as beacon time slots and TDMA time slots; when competing to send data frames in the CSMA time slot, it is determined whether a frame can be sent in the CSMA time slot; if the transmission cannot be completed in the CSMA time slot, it is necessary to add the buffer area and wait until the next CSMA time slot to give priority to the unfinished data.

2. The time slot estimation method based on a beacon network according to claim 1, characterized in that: Specifically, S1 is as follows: the central controller CCO completes the entire networking process by arranging the sending of central beacons, proxy beacons, and discovery beacons to trigger network access requests from STAs at each level; a multi-level tree network is formed between nodes.

3. The time slot estimation method based on a beacon network according to claim 2, characterized in that: In S2, CCO dynamically allocates time slots for all nodes in the network; when CCO allocates time slots within a cycle, they are divided into TDMA time slots and CSMA time slots; the front of the TDMA time slots is the central beacon time slot, followed by the proxy beacon time slot, the order of the proxy beacon time slots is based on the hierarchy, and there is no distinction between the front and the back in the same hierarchy, and the last is the discovery beacon time slot; after the beacon time slot is the CSMA time slot.

4. The time slot estimation method based on a beacon network according to claim 3, characterized in that: S3 is: when entering the TDMA time slot, if the PCO / STA receiving end receives a beacon frame, the time slot estimation information of the previous cycle is deleted, and a new round of normal time slots is synchronized according to the time slot information in the beacon frame; the beacon frame used for time slot synchronization is the upper layer central beacon frame, proxy beacon frame or discovery beacon frame; If the node does not receive any beacon frames in this cycle due to abnormalities in the upper node or its own state, the node cannot obtain the new round of time slot division information. In order to ensure normal communication and maintain the sub-network under this node, the estimated time slot information of the previous cycle is used; If no beacon frame is received from the upper node during two routing cycles, the proxy change is started and the proxy node is replaced; During the proxy change, it is necessary to maintain the lower network by sending discovery list messages within the estimated CSMA time slot. When the proxy change is completed, the lower nodes follow the proxy node to change.

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