Efficient retransmission scheduling method and system in TDMA (Time Division Multiple Access) system

Abstract

The invention discloses an efficient retransmission scheduling method and system in a time division multiple access (TDMA) system, and relates to the technical field of wireless communication. The method is dominated by a network coordinator (AP), and a superframe is divided into a main time division multiple access (TDMA) period and a shared retransmission time slot period sounding reference signal (SRS). In the main TDMA period, if no data is sent in the allocated uplink time slot, the device STA must send the NULL frame, so that the AP can reliably detect the uplink failure. And the AP detects a transmission failure event in real time when the TDMAP is carried out, incrementally constructs a retransmission scheduling table, immediately broadcasts an SRS-MAP frame after a main TDMA period is ended, and intensively executes conflict-free retransmission in an SRS period. According to the invention, the contradiction between the resource efficiency and the retransmission delay of the traditional TDMA system is solved, and the beneficial effects of high spectrum efficiency, low retransmission delay, reliable failure detection and self-adaption to network change are realized.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and specifically to an efficient retransmission scheduling method and system in a TDMA system. Background Technology

[0002] In industrial TDMA wireless systems, each device (STA) is typically allocated a dedicated transmission time slot to ensure deterministic communication. However, electromagnetic interference (EMI) and channel fading in industrial environments inevitably lead to data transmission failures and packet loss. How to handle retransmissions becomes a core challenge in TDMA system design.

[0003] In traditional technology, there are two main retransmission schemes: Time slot reservation scheme: as attached Figure 1 As shown, time for the "worst-case scenario" (e.g., the time for transmission plus three retransmissions) is reserved for each TDMA time slot. While this approach is reliable, it results in a catastrophic waste of spectrum resources in most scenarios where transmissions succeed on the first try, with 90% of the time slots potentially being wasted due to idle time.

[0004] Next superframe retransmission scheme: If the current transmission fails, it waits for the corresponding time slot of the next superframe before retransmitting. This introduces a delay of a complete superframe cycle (e.g., 10ms or 100ms), which is completely unacceptable for low-latency applications such as industrial control and motion synchronization.

[0005] Therefore, a pressing technical problem in this field is how to provide low-latency, fast retransmission opportunities for failure scenarios without reserving excessive redundant resources for "average cases" and thus causing waste. Existing technologies struggle to achieve a balance between "resource efficiency" and "retransmission latency." Summary of the Invention

[0006] The purpose of this invention is to address the difficulty in balancing resource efficiency and retransmission latency in existing TDMA retransmission mechanisms by providing an efficient retransmission scheduling method and system. This invention separates the "initial transmission" and "retransmission" in time and introduces a "shared retransmission slot period" (SRS) centrally scheduled by the AP (Access Point / Coordinator). This achieves a highly efficient (no redundancy) primary TDMA slot while providing an immediate, low-latency, and conflict-free retransmission opportunity for all failed transmissions (uplink and downlink).

[0007] To address the aforementioned technical problems, embodiments of the present invention provide the following technical solution: a retransmission scheduling method for wireless communication, applied to a TDMA system, wherein the method is executed by a network coordinator (AP), and includes the following steps: The superframe is divided in time into a main TDMA period for initial transmissions and a shared retransmission slots period SRS for retransmissions; In the main TDMA period, each device is allocated a dedicated time slot for initial data transmission and an immediate acknowledgement mechanism is used; In the shared retransmission slots period, retransmissions of all failed data frames in the main TDMA period are handled collectively.

[0008] Preferably, in the main TDMA period, a device transmits a null data frame in the allocated uplink time slot when no data is to be transmitted; the network coordinator AP determines whether the uplink transmission is successful by detecting whether a data frame or a null data frame is received, and determines the uplink transmission to be failed if no frame is received.

[0009] Preferably, the network coordinator AP detects all uplink and downlink transmission failure events in real time during the main TDMA period, and incrementally builds a retransmission schedule table, wherein the incremental building comprises: initializing an empty retransmission schedule table draft at the beginning of the main TDMA period; triggering a scheduler immediately upon detecting a transmission failure event, and deciding whether to add the failure event to the retransmission schedule table draft and pre-allocate a micro-slot in the shared retransmission slots period SRS according to an arbitration algorithm.

[0010] Preferably, the network coordinator AP broadcasts a final retransmission schedule table frame immediately after the end of the main TDMA period in a short inter-frame space, which explicitly defines the offset, duration and corresponding device identifier of each retransmission micro-slot in the shared retransmission slots period.

[0011] Preferably, when the number of detected failure events is greater than the number of retransmissions that can be accommodated in the shared retransmission slots period, the network coordinator AP makes a decision based on device priority, historical retransmission number or random number when executing the arbitration algorithm, to preferentially schedule the failure frames of high-priority devices.

[0012] Preferably, the network coordinator AP dynamically adjusts the total duration of the shared retransmission slots period in subsequent beacon frames based on the statistical network transmission failure rate, to adapt to changes in network quality.

[0013] The present application also proposes a wireless network coordinator for a TDMA system, the coordinator comprising a processor and a memory, the memory storing a computer program, the processor implementing the method as described above when executing the computer program.

[0014] The application also provides a wireless communication system comprising a network coordinator and at least one device, characterized in that the system is configured to implement the method according to any one of the preceding method claims.

[0015] Preferably, the device is configured to send a null frame in its allocated uplink time slot if there is no data to send, and to retransmit according to the schedule in the shared retransmission time slot period after receiving the retransmission schedule table frame.

[0016] The application also provides a computer readable storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the method according to any one of the preceding method claims.

[0017] The application has the following beneficial effects: 1. The application moves the retransmission out of the main TDMA period, so that the main time slot can be designed very compactly without any time redundancy, greatly improving the throughput of the network in the "good" state. Failed frames do not need to wait for the next superframe, but immediately obtain a retransmission opportunity in the SRS period within the same superframe, reducing the retransmission delay from the superframe level to the time slot level.

[0018] 2. The innovative "forced NULL frame" mechanism of the application enables the AP to deterministically detect uplink failures, solving the detection ambiguity problem in traditional TDMA. The SRS period itself is also a "micro-TDMA" centrally scheduled by the AP, ensuring that there will be no secondary collision between retransmissions, ensuring determinism. The "incremental scheduling" and "intelligent arbitration" algorithms of the AP ensure that the most critical devices can obtain retransmission resources preferentially; the "dynamic scaling" SRS period enables the system to automatically adapt to changes in network quality. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Efficiency comparison chart of the application and prior art TDMA retransmission.

[0020] Figure 2 Superframe structure and timing chart of the application.

[0021] Figure 3 AP side incremental scheduling timing chart. DETAILED DESCRIPTION

[0022] To make the technical problems, technical solutions and advantages of the application clearer, specific embodiments will be described in detail below with reference to the accompanying drawings.

[0023] The application provides a retransmission scheduling method for wireless communication, as shown in FIG. 1, which is dominated by a network coordinator (AP). The superframe structure defined by the AP is divided into at least two consecutive periods in time: Figure 2 ​Master TDMA Period (TDMAP): Contains multiple compact time slots allocated to specific STAs for the first transmission. Each time slot employs an "immediate acknowledgement" mechanism (e.g., transmission + SIFS + ACK).

[0024] Shared Re-transmission Slots Period (SRS): A dedicated period for collectively handling all failed data frames in the previous TDMAP.

[0025] The core innovation of the present invention lies in the three links of "bidirectional failure detection", "incremental scheduling", and "collective retransmission": 1. Bidirectional failure detection link (executed in TDMAP): AP-side detection: a) Downlink (DL) failure: AP sends data to STA, but does not receive ACK from STA within the time slot.

[0026] b) Uplink (UL) failure: STA does not receive either its Data frame or its NULL Data frame from AP within its allocated time slot (core innovation: agreement that STA must send NULL frame when there is no data).

[0027] STA-side detection: a) Uplink (UL) failure: STA sends Data or NULL frame, but does not receive ACK from AP within the time slot. STA caches the frame for retransmission.

[0028] 2. Incremental scheduling link (AP executes in real time in TDMAP): AP initializes an empty "retransmission scheduling table" (SRS-MAP draft) at the beginning of TDMAP.

[0029] During the TDMAP, whenever AP detects a DL or UL failure, AP's scheduler is immediately triggered.

[0030] AP's scheduler decides in real time whether to add this failed frame to the SRS-MAP draft and pre-allocate a micro-slot within SRS based on an arbitration algorithm (e.g., based on device priority, historical retransmission, or random number).

[0031] 3. Collective retransmission link (executed in SRS): After the last time slot of the master TDMA period ends, AP's scheduler updates the SRS-MAP draft based on the results of the last time slot.

[0032] After a SIFS (short interframe space), AP immediately broadcasts the final SRS-MAP frame.

[0033] SRS-MAP frame is a "mini-TDMA schedule", which defines [offset, duration, STA_ID] for each retransmission micro-slot in SRS period.

[0034] After all STAs (including AP itself) receive SRS-MAP, they strictly follow the schedule of the table to perform collision-free retransmission (or receive retransmission) in the allocated retransmission micro-slot.

[0035] In addition, the AP can also dynamically expand or reduce the total duration of the SRS period in the Beacon of the next superframe according to the statistical network failure rate to adapt to the changes in network quality.

[0036] In order to make the technical problems, technical solutions and advantages of the present application clearer, specific embodiments will be described in detail below with reference to the accompanying drawings.

[0037] Example 1: Uplink failure detection based on NULL frame To solve the industry problem that AP cannot distinguish between "STA has no data" and "STA sending failure", the present application provides: In the main TDMA period (TDMAP), any STA must send a Data frame if it has data to send when it is its turn to allocate the uplink time slot.

[0038] If the STA has no data to send, it must send a NULL Data frame (a short frame containing only the MAC header).

[0039] Therefore, for the AP, receiving Data or NULL frame in its time slot indicates "uplink success".

[0040] If the AP receives nothing (including ACK timeout) in the time slot, the AP can 100% determine that the uplink of the STA has failed (or the device has powered off), and record it in the failure list, and prepare to schedule SRS for it.

[0041] Example 2: Incremental scheduling and arbitration algorithm on the AP side Referring to the accompanying Figure 3 (Timing diagram), the "incremental scheduling" process of the AP is as follows: T=0(TDMAP starts): the AP initializes an empty SRS-MAP_Draft.

[0042] T=T1(Slot1, STA1, UL): the AP does not receive the NULL frame of STA1, and determines failure. The AP scheduler runs arbitration and adds {STA1, Slot1} to SRS-MAP_Draft.

[0043] T=T2 (Slot2, AP, DL): AP did not receive ACK from STA2, decision failed. AP scheduler runs arbitration and adds {AP→STA2, Slot2} to SRS-MAP_Draft.

[0044] T=T3 (Slot3, STA3, UL): AP received Data frame, decision succeeded. Scheduler does nothing. ... T=Tn (SlotN, last slot): End of this slot, AP finishes the last update to SRS-MAP_Draft, SRS-MAP is finalized.

[0046] T=Tn + SIFS: AP immediately broadcasts this SRS-MAP frame.

[0047] Arbitration algorithm implementation: When AP detects a failure, tries to add it to SRS-MAP_Draft, and the SRS period is full: AP compares the priority of the "new failure" with the "already in draft" devices.

[0048] If the new failure has higher priority, it "kicks out" the one with the lowest priority in the draft.

[0049] Priority can be based on: 1. Static configuration (e.g. security device > sensor); 2. Dynamic factors (e.g. device that has failed 3 times in a row > device that failed for the first time); 3. Random number (lottery).

[0050] Example 3: Dynamic SRS period AP continuously counts the "failure rate" (e.g. number of failed slots / total number of slots) in a time window.

[0051] When the failure rate goes up (e.g. network is disturbed), AP increases the total length of SRS period (e.g. from 5ms to 10ms) in the Beacon of the next superframe, to accommodate more retransmissions.

[0052] When the failure rate goes down (e.g. network quality is good), AP shortens the total length of SRS period in the Beacon, even to 0, to release valuable airtime to (e.g.) CSMA / CA period or shorten the total length of superframe.

[0053] The above-described embodiments are preferred embodiments of the present application. It should be noted that, for those skilled in the technical field, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as falling within the scope of the present application.

Claims

1. A retransmission scheduling method for wireless communication, applied to a TDMA system, characterized in that, The method is executed by the network coordinator (AP) and includes the following steps: The superframe is divided into a main TDMA period for initial transmission and a shared retransmission slot period (SRS) for retransmission. During the main TDMA cycle, a dedicated time slot is allocated to each device for the first data transmission, and an instant confirmation mechanism is adopted. During the shared retransmission time slot period, retransmission of all failed data frames in the main TDMA period is processed centrally.

2. The method according to claim 1, characterized in that, During the main TDMA cycle, when there is no data to send in the allocated uplink time slot, the device sends a no-data frame; the network coordinator AP determines whether the uplink is successful by detecting whether a data frame or no data frame is received. If no frame is received, the uplink transmission is determined to have failed.

3. The method according to claim 1, characterized in that, During the main TDMA cycle, the network coordinator (AP) detects all uplink and downlink transmission failure events in real time and incrementally builds a retransmission schedule table, wherein the incremental construction includes: An empty retransmission schedule table draft is initialized at the start of the main TDMA cycle; Whenever a transmission failure event is detected, the scheduler is immediately triggered to decide whether to add the failure event to the retransmission schedule table draft according to the arbitration algorithm, and to pre-allocate micro-slots within the shared retransmission time slot period (SRS).

4. The method according to claim 3, characterized in that, After the main TDMA cycle ends, the network coordinator (AP) immediately broadcasts the final retransmission scheduling table frame within a short inter-frame interval. This frame explicitly defines the offset, duration, and corresponding device identifier of each retransmission micro-slot within the shared retransmission time slot cycle.

5. The method according to claim 4, characterized in that, When the number of detected failure events exceeds the number of retransmissions that the shared retransmission time slot period can accommodate, the network coordinator AP makes a decision based on device priority, historical retransmission count, or random number when executing the arbitration algorithm.

6. The method according to claim 1, characterized in that, The network coordinator (AP) dynamically adjusts the total duration of the shared retransmission time slot period in subsequent beacon frames based on the statistical network transmission failure rate.

7. A wireless network coordinator for a TDMA system, characterized in that, The coordinator includes a processor and a memory, the memory storing a computer program, and the processor executing the computer program to implement the method as described in any one of claims 1 to 6.

8. A wireless communication system, comprising a network coordinator and at least one device, characterized in that, The system is configured to perform the method as described in any one of claims 1 to 6.

9. The system according to claim 8, characterized in that, The device is configured to send a no-data frame if no data is being sent in its allocated uplink time slot, and to retransmit strictly in accordance with the schedule during the shared retransmission time slot period after receiving the retransmission schedule table frame.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1 to 6.

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