An On-Demand Retransmission Method for Industrial Wireless Networks Based on Non-Orthogonal Multiple Access

Abstract

The present invention relates to industrial wireless network technology and non-orthogonal multiple access technology, and specifically to an on-demand retransmission method for industrial wireless networks based on non-orthogonal multiple access. The present invention is applicable to a single-channel star topology network composed of access devices and field devices, and each field device needs to periodically send data packets to the access device. According to the periodic transmission requirements, the present invention designs a superframe structure that supports non-orthogonal multiple access and reliable retransmission. By introducing power-domain non-orthogonal multiple access technology, parallel transmission of multiple field devices within a single time slot and single channel is achieved. At the same time, combined with the automatic on-demand retransmission mechanism, the optimal time slot and power level are allocated to the field devices to be transmitted in each round of retransmission according to the packet error rate and available communication resources of each field device. The present invention can significantly improve the utilization rate of the superframe, thereby enhancing the transmission reliability of the network.

Description

Technical Field

[0001] The present invention relates to industrial wireless network technology and non - orthogonal multiple access technology, and more specifically to an on - demand re - transmission method for industrial wireless networks based on non - orthogonal multiple access. Background Art

[0002] Compared with traditional wired networks, industrial wireless networks have the advantages of low cost, flexible structure design, simple installation, etc., and are thus considered to be one of the important enabling technologies for Industry 4.0. In addition, industrial wireless networks provide a broader application scenario for mobile terminals (such as automated guided vehicles). However, the complexity and unpredictability of the industrial environment make it difficult for wireless technology to meet the demanding performance requirements of industrial applications. For example, deterministic communication with low latency and high reliability.

[0003] As Figure 1 shown, non - orthogonal multiple access technology allows multiple users to simultaneously send data packets to the same receiver on the same frequency band. By introducing the power domain, non - orthogonal multiple access technology can achieve parallel transmission of different signals on an orthogonal time - frequency resource block with the help of successive interference cancellation technology, thereby improving spectrum utilization and achieving low - latency transmission. On the other hand, although non - orthogonal multiple access technology is an effective means to reduce latency and increase channel capacity, interference in the industrial environment can cause data packet transmission failures, making it difficult to meet reliability requirements. A feasible solution is to introduce a re - transmission method. By reasonably designing the super - frame structure, field devices can transmit data packets multiple times within a frame, thereby improving the transmission success rate and achieving highly reliable transmission. Summary of the Invention

[0004] The present invention combines non - orthogonal multiple access technology with an automatic on - demand re - transmission mechanism for the first time, and proposes a re - transmission method for industrial wireless networks based on non - orthogonal multiple access. The invention can effectively improve the utilization efficiency of communication resources, and further ensure highly reliable and low - latency uplink transmission of wireless networks.

[0005] For a single - channel star - shaped topology network composed of access devices and field devices, non - orthogonal multiple access technology and successive interference cancellation technology are introduced. The super - frame structure is designed according to the automatic on - demand re - transmission mechanism, and the transmission time slot and power are allocated for the data packets to be transmitted based on the packet error rate and available communication resources of the field devices that need to transmit data packets, so as to maximize transmission reliability.

[0006] The technical solution adopted by the present invention to achieve the above - mentioned purpose is as follows:

[0007] An on - demand re - transmission method for industrial wireless networks based on non - orthogonal multiple access, comprising the following steps:

[0008] Multiple field devices are enabled to transmit in parallel on a time-frequency resource block through a non-orthogonal multiple access method and a successive interference cancellation method;

[0009] Through a superframe structure, field devices can send data packets multiple times within a superframe, and according to the packet error rates and available communication resources of each field device, combined with an automatic retransmission on demand mechanism, dynamically allocate transmission time slots and power levels for the data packets to be transmitted, so as to maximize the number of successfully transmitted data packets within the frame and the transmission reliability.

[0010] The non-orthogonal multiple access method and the successive interference cancellation method are specifically as follows:

[0011] The non-orthogonal multiple access method further divides a time-frequency resource block into k power levels set in advance, enabling at most k field devices to transmit data to the access device in parallel;

[0012] The access device configures a k-SIC receiver, and through the successive interference cancellation method SIC, realizes the decoding of k parallel transmission data packets. During the decoding stage of the k-SIC receiver, decoding is performed in the order of received power from high to low. When the signal-to-interference-plus-noise ratio of the received data packet is greater than or equal to the given threshold γ, the decoding is successful, otherwise the decoding fails. When a data packet decoding fails, the decoding stage stops immediately, and the undecoded data packets are regarded as transmission failures.

[0013] The superframe structure is specifically as follows:

[0014] The superframe length is the data cycle L of the field device. The superframe consists of a beacon period and a data transmission period. Among them, the data transmission period includes a data first transmission period, an acknowledgment signal transmission period, and a data retransmission period.

[0015] The specific composition periods of the superframe are as follows:

[0016] Beacon period: Used for the access device to broadcast beacons to N field devices. The beacons are used for time synchronization and inform the field devices of the schedule of the data first transmission period, including time slots and power levels;

[0017] Data first transmission period: Used for each field device to send a data packet to the access device, with a length of time slots;

[0018] Acknowledgment signal transmission period: Used for the access device to send a negative acknowledgment frame NACK to the field device. The access device allocates time slots and power levels to the field devices that need to retransmit data packets by updating the content of the schedule in the NACK, with a length of 1 time slot;

[0019] Data retransmission period: Used for field devices to retransmit data packets. According to the content of the scheduling table in the NACK sent by the access device, the field devices that have not successfully transmitted calculate the transmission power based on the allocated power level and their own channel gain, and send the data packets in the specified time slot.

[0020] The transmission success and transmission reliability are specifically as follows:

[0021] Let the packet error rates of N field devices be p 1 , p 2 ,..., p N , then for the i-th field device FD i to have a successful transmission, two conditions need to be met: (1) According to the decoding order from high to low received power, the data packets sent by field devices with a higher power level than FD i in the same time slot are successfully decoded; (2) The data packet sent by FD i is successfully decoded;

[0022] The transmission reliability is the ratio of the number of successfully transmitted data packets to the total number of data packets within a superframe.

[0023] The power allocation of field devices is as follows:

[0024] Set the power threshold sequence of the k-SIC receiver as where σ 2 is the power of the channel noise, is the m-th power level, 1 ≤ m ≤ k. If the i-th field device FD i is assigned to the m-th power level in the first time slot, and the channel gain of FD i is h i , then the power of the data packet transmitted by FD i is

[0025] The specific automatic retransmission on demand mechanism is as follows:

[0026] During the data retransmission period, the access device broadcasts NACK to the field devices at the end of each round of retransmission, informing the field devices that have failed to transmit data packets of the scheduling table in the next round of retransmission. Let the number of data packets N ω that need to be retransmitted and the number of remaining time slots L maxω in the superframe be the number of data packets that have failed to be transmitted and the number of remaining time slots after the ω-th retransmission respectively, where ω = 0, 1,...;

[0027] The generation of the access device's scheduling table includes the following situations:

[0028] Situation 1: When N ω > k and That is, the remaining time slots of the superframe are sufficient to complete one retransmission. The access device sorts the field devices according to the packet error rate from small to large, and allocates a resource block to each field device, and the occupied time slot length is

[0029] Case 2: When N ω > k and That is, the remaining time slots of the superframe are not sufficient to complete one retransmission. The access device sorts the field devices according to the packet error rate from small to large, and selects the first kL maxω field devices, and allocates the remaining resource blocks to these kL maxω field devices;

[0030] Case 3: When N ω ≤ k, that is, the field devices that need to be retransmitted can be transmitted in parallel within one time slot. The access device sorts the field devices according to the packet error rate from small to large, and allocates the resource blocks to each field device.

[0031] When in Case 1 and Case 2, the access device allocates resource blocks according to Principle 2. When in Case 3, the access device allocates resource blocks according to Principle 1, where:

[0032] The said Principle 1 and Principle 2 are:

[0033] Principle 1: The transmitted data packets are at different power levels within the same time slot: within one time slot, if the packet error rates of n (n ≤ k) field devices satisfy p 1 ≤ p 2 ≤... ≤ p n , then the power level to which the i-th data packet belongs is i, i = 1, 2,..., n;

[0034] Principle 2:: The transmitted data packets are in different time slots: within T time slots, if the packet error rates of kT field devices satisfy p 1 ≤ p 2 ≤... ≤ p kT , then the time slot l to which the i-th data packet belongs is l = (i mod T) + 1, and the power level m is

[0035] The present invention has the following beneficial effects and advantages:

[0036] 1. The present invention combines non-orthogonal multiple access technology with an automatic on-demand retransmission mechanism. Among them, the non-orthogonal multiple access technology realizes the parallel transmission of multiple field devices on one orthogonal resource block, and the on-demand retransmission mechanism dynamically updates the data packets to be retransmitted in each round according to the packet loss situation in the previous round, greatly avoiding the waste of time slots caused by repeated transmissions. The present invention not only improves the spectrum utilization rate and channel capacity, but also increases the number of successful transmissions, making it possible to achieve low-latency and high-reliability communication required by industrial wireless.

[0037] 2. The present invention maximizes transmission reliability by finding a feasible power allocation strategy and an optimal retransmission scheduling scheme. This is actually equivalent to the problem of maximizing the number of successful transmissions in a superframe, that is, maximizing the number of successful transmissions in each round of retransmission.

[0038] 3. In each round of retransmission, the access device updates the scheduling table according to the packet error rate of the field devices that have not been successfully transmitted, and allocates the optimal time slot and power level for each field device that has not been successfully transmitted. Theoretical proof shows that the present invention can maximize the number of successful transmissions in each round of retransmission, that is, maximize transmission reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of non - orthogonal multiple access technology;

[0040] Figure 2 It is a schematic diagram of the superframe structure;

[0041] Figure 3 It is a schematic diagram of an industrial wireless network;

[0042] Figure 4 It is an example diagram of a round of retransmission algorithm. DETAILED DESCRIPTION OF THE INVENTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] The present invention mainly includes four parts: industrial wireless network modeling, superframe structure design, power allocation strategy and retransmission scheduling scheme, and the working mechanism of the on - demand retransmission method for wireless networks based on non - orthogonal multiple access.

[0045] 1. Industrial wireless network modeling

[0046] The network model considered by this method is as Figure 3 shown, which is a single - channel star - shaped topology structure composed of an access device and field devices. The access device is connected to all field devices wirelessly and is responsible for generating and broadcasting beacons, NACK signals, and receiving the uplink data packets sent by the field devices. The access device is configured with a k - SIC receiver, indicating that up to k data packets can be transmitted in parallel on a time - frequency resource block, where k is the number of field devices that can be transmitted in parallel. N field devices are installed in the industrial site and are connected to sensors, and are responsible for sending data packets according to the instructions of the scheduling table.

[0047] 2. Superframe structure design

[0048] As Figure 2 shown, the superframe structure is specifically as follows:

[0049] The superframe length is the data cycle L of the field device. The superframe consists of a beacon period and a data transmission period. The data transmission period includes a data first transmission period, an acknowledgment signal transmission period, and a data retransmission period.

[0050] · Beacon period: Used for the access device to broadcast beacons to N field devices. The main function of the beacon is time synchronization and to inform the field devices of the schedule of the data first transmission period, including time slots and power levels.

[0051] · Data first transmission period: Used for each field device to send a data packet to the access device, with a length of time slots.

[0052] · Acknowledgment signal transmission period: Used for the access device to send NACK (Negative Acknowledgment) to the field device. The access device allocates time slots and power levels to the field devices that need to retransmit data packets by updating the content of the schedule in the NACK, with a length of 1 time slot.

[0053] · Data retransmission period: Used for the field device to retransmit the data packet. According to the schedule content in the NACK sent by the access device, the field device that fails to transmit successfully calculates the transmission power based on the allocated power level and its own channel gain, and sends the data packet in the specified time slot.

[0054] 3. Power allocation strategy and retransmission scheduling scheme

[0055] Considering the complex industrial environment, we let the packet error rate of the i-th field device FD i be p i , where i = 1, 2,..., N. That is, the probability that FD i arrives at the receiving end and is successfully decoded follows a Bernoulli distribution with parameter 1 - p i . Then, for FD i to transmit successfully, two conditions need to be met: (1) According to the decoding order from high to low received power, the data packets sent by field devices with higher power levels than FD i in the same time slot need to be successfully decoded, and (2) the data packet sent by FD i also needs to be successfully decoded. If a transmission fails, FD i will wait for a retransmission opportunity. During the ω-th round of retransmission, we use N ω to represent the number of data packets that need to be retransmitted, and the corresponding packet error rate is N ω = 0 indicates that all data packets are successfully transmitted in this superframe. Let L maxω represent the remaining time slots in the ω-th round of retransmission, and L ω represent the number of time slots used in the ω-th round of retransmission. Then P ilm represents the FD for transmitting a data packet at the m-th power level in the l-th time slot i required transmission power.

[0056] Our goal is to find a joint scheme for power allocation and retransmission scheduling to maximize transmission reliability, which is actually equivalent to maximizing the number of successful transmissions in a superframe. Further, it is to maximize the number of successful transmissions in each round of retransmission.

[0057] To solve the power allocation problem, if the threshold of the signal-to-interference-plus-noise ratio is γ, we set the power threshold sequence of the k-SIC receiver as 1 ≤ m ≤ k - 1, where σ 2 is the power of the channel noise, is the m-th power level, 1 ≤ m ≤ k. Then, if it wants to be successfully decoded at the receiving end, P ilm needs to satisfy

[0058] To solve the problem of the optimal retransmission scheduling scheme, we set the following two principles.

[0059] Principle 3.1: The transmitted data packets are at different power levels in the same time slot. In a time slot, if the packet error rates of n (n ≤ k) field devices satisfy p 1 ≤ p 2 ≤... ≤ p n , then the power level to which the i-th data packet belongs is i, i = 1, 2,..., n.

[0060] Principle 3.2: The transmitted data packets are in different time slots. In T time slots, if the packet error rates of kT field devices satisfy p 1 ≤ p 2 ≤... ≤ p kT , then the time slot l to which the i-th data packet belongs is l = (i mod T) + 1, and the power level m is

[0061] 4. Working mechanism of the on-demand retransmission method for industrial wireless networks based on non-orthogonal multiple access

[0062] According to Principle 3.1 and Principle 3.2, we can obtain the optimal scheduling scheme for each round of retransmission, as Figure 4 shown. The specific steps are as follows:

[0063] Step 1, the access device collects the N ω packets that have not been successfully transmitted and their corresponding packet error rates;

[0064] Step 2, the access device sorts the packet error rates from small to large to make it satisfy

[0065] In the third step, the access device calculates the number of remaining time slots L in the superframe maxω and the number of time slots required for retransmission

[0066] In the fourth step, the access device calculates the number of time slots required for this retransmission

[0067] In the fifth step, initialize i = 1.

[0068] In the sixth step, the access device updates the scheduling table as follows:

[0069] Loop l from 1 to L ω ;

[0070] m from 1 to k;

[0071] The time slot to which the i-th device belongs is l, and the power level is m;

[0072] i = i + 1;

[0073] If i > N ω , the loop ends;

[0074] In the seventh step, the access device broadcasts the new scheduling table (contained in the NACK) to the field devices.

[0075] In the eighth step, the field devices calculate the transmission power according to the scheduling table and send data packets to the access device.

[0076] In the ninth step, ω = ω + 1. If N ω is 0, indicating that all packet transmissions are successful, then stop retransmission, otherwise return to the first step.

Claims

1. An on-demand retransmission method for industrial wireless networks based on non-orthogonal multiple access, characterized in that, it includes the following steps: By using non-orthogonal multiple access method and successive interference cancellation method, multiple field devices transmit in parallel on a time-frequency resource block; Through the superframe structure, the field devices send data packets multiple times within a superframe, and according to the packet error rate and available communication resources of each field device, combined with the automatic on-demand retransmission mechanism, dynamically allocate transmission time slots and power levels for the data packets to be transmitted; The non-orthogonal multiple access method and successive interference cancellation method are specifically as follows: The non-orthogonal multiple access method further divides a time-frequency resource block into k power levels set in advance, so that at most k field devices transmit data to the access device in parallel; The access device configures a k-SIC receiver, and through the successive interference cancellation method SIC, realizes the decoding of k parallel transmission data packets. During the decoding stage of the k-SIC receiver, decoding is performed in the order of received power from high to low. When the signal-to-interference-plus-noise ratio of the received data packet is greater than or equal to the given threshold γ, the decoding is successful, otherwise the decoding fails. When a data packet decoding fails, the decoding stage stops immediately, and the data packets that have not been decoded are regarded as transmission failures; The power allocation of the field device is: Set the power threshold sequence of the k-SIC receiver to where σ 2 is the power of the channel noise, is the m-th power level, 1 ≤ m ≤ k, γ is the threshold of the signal-to-interference-plus-noise ratio. If the i-th field device FD i is assigned to the m-th power level in the l-th time slot, and the channel gain of FD i is h i , then the power for FD i to transmit a data packet is 2. An on-demand retransmission method for industrial wireless networks based on non-orthogonal multiple access according to claim 1, characterized in that, the superframe structure is specifically as follows: The superframe length is the data period L of the field device. The superframe consists of a beacon period and a data transmission period. Among them, the data transmission period includes a data first transmission period, an acknowledgment signal transmission period, and a data retransmission period.

3. An on-demand retransmission method for industrial wireless networks based on non-orthogonal multiple access according to claim 2, characterized in that, the constituent periods of the superframe are specifically as follows: Beacon period: Used for the access device to broadcast beacons to N field devices. The beacons are used for time synchronization and inform the field devices of the schedule of the data first transmission period, including time slots and power levels; Data first transmission period: used for each field device to send a data packet to the access device, with a length of time slots; Acknowledgment signal transmission period: Used for the access device to send negative acknowledgment frames NACK to the field devices. The access device allocates time slots and power levels to the field devices that need to retransmit data packets by updating the content of the schedule in the NACK, and the length is 1 time slot; Data retransmission period: Used for the field devices to retransmit data packets. According to the content of the schedule in the NACK sent by the access device, the field devices that have not successfully transmitted calculate the transmission power according to the allocated power level and their own channel gains, and send data packets in the specified time slots.

4. An on-demand retransmission method for industrial wireless networks based on non-orthogonal multiple access according to claim 1, characterized in that, the transmission success and transmission reliability are specifically as follows: Let the packet error rates of N field devices be p 1 , p 2 ,..., p N . Then, for the transmission of the i-th field device FD i to be successful, two conditions need to be met: (1) According to the decoding order from high to low received power, the data packets sent by field devices with higher power levels than FD i in the same time slot are successfully decoded; (2) The data packet sent by FD i is successfully decoded; The transmission reliability is the ratio of the number of successfully transmitted data packets to the total number of data packets within a superframe.

5. An on-demand retransmission method for industrial wireless networks based on non-orthogonal multiple access according to claim 1, characterized in that, the automatic on-demand retransmission mechanism is specifically as follows: During the data retransmission period, the access device broadcasts a NACK to the field device at the end of each round of retransmission, informing the field device that the transmitted data packet has failed of the scheduling table in the next round of retransmission, and making the number N of data packets to be retransmitted ω and the number L of remaining time slots in the superframe maxω are the number of data packets that have failed to be transmitted and the number of remaining time slots after the ω-th retransmission respectively, where ω = 0, 1,...; The generation of the schedule of the access device includes the following situations: Case 1: When N ω > k and that is, the remaining time slots of the superframe are sufficient to complete one retransmission. The access device sorts the packet error rates of the field devices from small to large, and allocates a resource block to each field device, and the occupied time slot length is Case 2: When N ω > k and that is, the remaining time slots in the superframe are not enough to complete a retransmission. The access device sorts the packet error rates of the field devices from small to large and selects the first kL maxω field devices. For these kL maxω field devices, the remaining resource blocks are allocated; Case 3: When N ω ≤ k, that is, the field devices that need to retransmit can transmit in parallel within one time slot. The access device sorts the field devices according to the packet error rate from small to large, and allocates resource blocks to each field device.

6. An on-demand retransmission method for an industrial wireless network based on non-orthogonal multiple access according to claim 5, characterized in that, when in the said Case 1 and Case 2, the access device allocates resource blocks according to Principle 2, and when in Case 3, the access device allocates resource blocks according to Principle 1, where: the said Principle 1 and Principle 2 are: Principle 1: The transmitted data packets are at different power levels in the same time slot: In a time slot, if the packet error rates of n (n ≤ k) field devices satisfy p 1 ≤ p 2 ≤... ≤ p n , then the power level to which the i-th data packet belongs is i, where i = 1, 2,..., n; Principle 2: The transmitted data packets are on different time slots: within T time slots, if the packet error rates of kT field devices satisfy p 1 ≤ p 2 ≤...≤ p kT , then the time slot l to which the i-th data packet belongs is l = (i mod T) + 1, and the power level m is

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