Uplink LoRa adaptive transmission method based on RIS differential index modulation

Abstract

The invention relates to an uplink LoRa adaptive transmission method based on RIS differential index modulation, and the method comprises the steps: introducing RIS and IM into the uplink transmission of LoRa, and carrying out the differential modulation of a joint IM entity in a space-time domain. The RIS is deployed near the LoRa node as part of a transmitter, and additional information is communicated by building RIS space-time blocks, thereby enhancing the uplink transmission link of the single antenna LoRa node with the gateway. Meanwhile, in order to further improve the performance of the system, an adaptive spreading factor (SF) selection strategy is introduced. According to the invention, under the design based on the RIS differential IM, the CSI demand is effectively eliminated, and the LoRa transmission rate is significantly improved.

Description

Technical Field

[0001] This application relates to the field of communications, and more specifically, to an uplink LoRa adaptive transmission method based on RIS differential index modulation. Background Technology

[0002] Long Range Communication (LoRa) is one of the most popular and widely adopted low-power wide-area network (LPWAN) technologies developed globally for the Internet of Things (IoT). While it offers wide coverage with extremely low power consumption, its low data transmission rate remains a significant limitation. Meanwhile, Reconfigurable Intelligent Surface (RIS) and Index Modulation (IM), as key emerging technologies in next-generation mobile communications, demonstrate outstanding capabilities in improving data rates and reducing energy consumption. Therefore, these technologies hold great potential for improving LoRa transmission performance. However, for wireless communication systems involving RIS, the receiver must obtain Channel State Information (CSI) through channel estimation, a process typically accompanied by significant pilot overhead. Although there are existing RIS-based incoherent IM research schemes, these methods implicitly require the RIS to have pre-obtained the complete CSI when optimizing the channel response by dynamically adjusting the RIS phase shift. Summary of the Invention

[0003] To overcome at least one deficiency in the prior art, this application provides an uplink LoRa adaptive transmission method based on RIS differential index modulation.

[0004] Firstly, an uplink LoRa adaptive transmission method based on RIS differential index modulation is provided, including: The transmitter communicates with the LoRa gateway based on the RIS array, and the RIS array is divided into... The frame is divided into multiple space-time transmission blocks (SLTs) when the transmitting end sends a signal; each SLT includes multiple time slots. Within any space-time transport block, the information bits consist of three parts: a first part, a second part, and a third part. The first part is mapped to the space-time domain and used to determine... The activation order of the sub-RIS is determined by the following steps: the second part is mapped to the signal domain to select the constellation symbol carried by the activated sub-RIS; the third part is mapped to the signal domain to generate... LoRa transmission symbol.

[0005] In one embodiment, The activation order of individual RIS units is determined in the following way: The bit length of the first part is: , Indicates rounding down; Set a non-negative integer starting from 0. ,in, For The number of sub-RIS index permutations is determined using the Lehmer code method to determine the final length. The sub-RIS index permutation sequence, i.e. The activation order of individual RIS.

[0006] In one embodiment, the constellation symbol carried by the activated sub-RIS is determined in the following manner: The bit length of the second part is: ,in, Modulation order for constellation symbols; Each activated subRIS carries a constellation symbol belonging to -PSK Constellation Collection.

[0007] In one embodiment, generating LoRa transmission symbols includes: The bit length of the third part is: ,in, The number of chips contained in a LoRa symbol. ,in, It is the spreading factor; Set spreading factor index set , for The first in One element, express The number of elements in; For each This corresponds to a minimum SNR threshold required to guarantee demodulation performance. ;for ,have ; Obtain the instantaneous signal-to-noise ratio (SNR) at the receiver. Then As spreading factor ,like Then As spreading factor ; According to the spreading factor calculate And determine the bit length of the third part. Generate LoRa transmission symbols.

[0008] In one embodiment, the method further includes: After receiving the signal, the receiving end performs processing on each receiving block. LoRa demodulation is performed sequentially over a consecutive LoRa symbol duration to obtain the estimated LoRa symbol. This corresponds to the input information in the third part, where, For the first One LoRa estimation symbol; LoRa estimation symbol Re-modulate LoRa to obtain the estimated LoRa CSS signal. ,in, For the first One LoRa CSS signal; The first in the received block Data and Multiply, for The transpose of gives the first . column vectors, The column vectors are concatenated column by column to obtain the matrix after removing the LoRa signal. ; For the matrix after removing the LoRa signal Using an ML detector or a spherical decoder, we can obtain... The activation order of each sub-RIS and the constellation symbol carried by each activated sub-RIS; Decode the activation order of the K sub-RIS to obtain the first part of the input information; decode the constellation symbol carried by each activated sub-RIS to obtain the second part of the input information.

[0009] Secondly, an uplink LoRa adaptive transmission system based on RIS differential index modulation is provided, including a transmitter and a receiver. The transmitter includes a single-antenna LoRa node and a RIS array, and the receiver includes multiple receiving antennas. The system is used to implement the above-mentioned uplink LoRa adaptive transmission method based on RIS differential index modulation.

[0010] Compared to existing technologies, this application offers the following advantages: The uplink LoRa adaptive transmission method based on RIS differential index modulation introduces RIS and IM into LoRa uplink transmission and uses differential modulation on the joint IM entity in the spatiotemporal domain. The RIS is deployed near the LoRa node as part of the transmitter, transmitting additional information by constructing RIS spatiotemporal blocks, thereby enhancing the uplink transmission link between the single-antenna LoRa node and the gateway. Simultaneously, to further improve system performance, an adaptive spreading factor (SF) selection strategy is introduced. Simulation results demonstrate that under the RIS differential IM-based design, the CSI requirement is effectively eliminated, and the LoRa transmission rate is significantly improved. Attached Figure Description

[0011] This application can be better understood by referring to the description given below in conjunction with the accompanying drawings, which, together with the detailed description below, are incorporated in and form part of this specification. In the drawings: Figure 1 The schematic diagram of the uplink LoRa adaptive transmission design based on RIS differential IM is shown. Figure 2 The prior art and the present application are shown in terms of BER and throughput performance, wherein (a) is the performance of the prior art and the present application in terms of BER, and (b) is the performance of the prior art and the present application in terms of throughput. Figure 3 The BER and throughput performance of this application under the adaptive spreading factor selection strategy are shown, where (a) is the BER performance of this application under the adaptive spreading factor selection strategy, and (b) is the throughput performance of this application under the adaptive spreading factor selection strategy. Detailed Implementation

[0012] Exemplary embodiments of the present application will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of the actual embodiments are described in the specification. However, it should be understood that many embodiment-specific decisions can be made in the development of any such actual embodiment to achieve the developer’s specific objectives, and these decisions may vary as the embodiments differ.

[0013] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the device structure closely related to the solution of this application is shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0014] It should be understood that this application is not limited to the described embodiments by virtue of the following description with reference to the accompanying drawings. In this document, embodiments may be combined with each other, features may be substituted or borrowed between different embodiments, and one or more features may be omitted in one embodiment, where feasible.

[0015] This application provides an uplink LoRa adaptive transmission method based on RIS differential index modulation, which mainly includes the following steps: The transmitter communicates with the LoRa gateway based on the RIS array, and the RIS array is divided into... The frame is divided into multiple space-time transmission blocks when the transmitting end sends a signal. Each space-time transmission block includes multiple time slots.

[0016] Figure 1 This diagram illustrates the uplink LoRa adaptive transmission design principle based on RIS differential IM. A single-antenna LoRa node utilizes... A passive reflective element RIS communicates with a LoRa gateway, wherein the gateway is equipped with There are one receiving antenna. The RIS is placed close to the LoRa node as part of the transmitter. Due to obstacles, there is no direct transmission link between the LoRa node and the gateway. When the LoRa node is close enough to the RIS, it can be assumed that the wireless transmission between them is unaffected by fading.

[0017] Inspired by Differential Spatial Modulation (DSM), this embodiment will utilize the RIS array's... 3D transfer vector mapping to Each time slot is used to construct the RIS space-time transport block. Specifically, the size is... The RIS array is divided into Each sub-RIS contains 1 sub-RIS, and each sub-RIS contains 1 Each array element, This indicates rounding down. During transmission, the frame is divided into several space-time transport blocks, each consisting of... It consists of several time slots. Each sub-RIS will be activated sequentially during a space-time transport block to carry the corresponding constellation symbol and support... The transmission of LoRa symbols will occupy [a certain amount of] space. One LoRa symbol duration. Therefore, one LoRa symbol duration. The content will include Each time slot. The index set of the sub-RIS is denoted as... The index set of the gateway receiving antenna is denoted as Meanwhile, the index set containing all possible RIS spacetime transport blocks is denoted as... Each space-time transport block consists of a sub-RIS activation sequence and a constellation symbol. The indexed sequence indicating the sub-RIS activation sequence is represented as follows: , The index set is denoted as , Represents a set The number of elements, i.e., the number of sub-RIS index permutations. (The last part is incomplete and likely refers to a specific sequence or pattern.) The constellation symbol within the duration of each LoRa symbol is represented as follows: , The index set is denoted as , Represents a set The number of elements.

[0018] Within any space-time transport block, the information bits consist of three parts: a first part, a second part, and a third part. The first part is mapped to the space-time domain and used to determine... The activation order of the sub-RIS, the second part is mapped to the signal domain, for use in During the duration of each LoRa symbol, the constellation symbol carried by the active sub-RIS is selected, and the third part is mapped to the signal domain for use in... LoRa transmission symbols are generated within a LoRa symbol duration.

[0019] In any number Within each space-time transport block, the information bits are composed of... It consists of three parts, among which... , To represent the factorial operation, Modulation order for constellation symbols, is the spreading factor.

[0020] It satisfies the following three restrictions: 1) Only one RIS element is activated in each time slot; 2) When containing continuous... Within each space-time transmission block of each time slot, each array element is activated only once; 3) the signal constellation is limited to equal-energy... -PSK.

[0021] In one embodiment, The activation order of individual RIS units is determined in the following way: The bit length of the first part is: , Indicates rounding down; Set a non-negative integer starting from 0. ,in, For The number of sub-RIS index permutations is determined using the Lehmer code method to determine the final length. The sub-RIS index permutation sequence, i.e. The activation order of individual RIS.

[0022] The index mapping process will input Bits correspond to the activation order of sub-RIS in the space-time transport block. This mapping relationship can be achieved through... It is represented by an indexed arrangement of sub-RIS. Typically, a lookup table is used as input. Bits provide a mapping to the corresponding sub-RIS index permutations. This is a simple and efficient method when the lookup table size is small. However, the size of the lookup table increases with the number of sub-RIS. The growth is exponential, at which point the method of index mapping through lookup tables is no longer applicable. Therefore, this embodiment adopts the Lehmer code method. Lehmer code is a permutation encoding method based on the factorial base system, also known as Lehmer encoding or Cantor expansion. It associates a permutation with a unique sequence of numbers, and is used to efficiently calculate the lexicographical rank of a permutation or generate permutations with a specific rank.

[0023] In one embodiment, the constellation symbol mapping process will input... Bits are mapped into the signal domain for use in... During the duration of each LoRa symbol, a constellation symbol is selected for the active sub-RIS. The constellation symbol carried by the active sub-RIS is determined as follows: The bit length of the second part is: ,in, Modulation order for constellation symbols; Each activated subRIS carries a constellation symbol belonging to -PSK Zodiac Collection .

[0024] For example, when When QPSK modulation is used, then Here, the bits corresponding to each sub-RIS can be determined according to the order of activation, the binary value can be calculated based on the bits, and the result can be determined based on the magnitude of the binary value. The element with the corresponding index in the sequence is used as the constellation symbol carried by the subRIS.

[0025] In one embodiment, the input Bit correspondence generation LoRa transmission symbols within the duration of a LoRa symbol. Depend on Decision. Different. Each corresponds to a specific SNR threshold. During transmission, to ensure reliable demodulation, the node's transmit power must ensure that the receiver's SNR does not fall below this threshold. Therefore, when the SNR is relatively low... When the data rate that can be provided is far higher than the business needs, the transmit power of the node will be wasted.

[0026] Therefore, in order to achieve more flexible and efficient transmission performance under different channel conditions, an adaptive SF selection strategy based on instantaneous SNR is introduced. In this embodiment, LoRa transmission symbols are generated within a LoRa symbol duration, including: The bit length of the third part is: ,in, The number of chips contained in a LoRa symbol. ,in, It is the spreading factor; Set spreading factor index set , for The first in One element, express The number of elements in; For each This corresponds to a minimum SNR threshold required to guarantee demodulation performance. ;for ,have ; Obtain the instantaneous signal-to-noise ratio (SNR) at the receiver. Then As spreading factor ,like Then As spreading factor ; According to the spreading factor calculate And determine the bit length of the third part. Generate LoRa transmission symbols.

[0027] The aforementioned adaptive strategy enables the system to dynamically adjust under different channel conditions. While ensuring communication reliability, it effectively improves spectrum efficiency and uplink throughput performance.

[0028] Theoretically, the bit transmission rate (BTR) of the LoRa uplink transmission scheme based on RIS differential IM in a single-node scenario can be expressed as:

[0029] in, The spreading factor for LoRa modulation. The transmission bandwidth for LoRa symbols.

[0030] After implementing IM, such as Figure 1 As shown, the system lasts for one LoRa symbol duration. The total number of bits transferred internally is Therefore, BTR in a single-node scenario can be achieved through... Calculated. During the symbol duration Inside, a LoRa symbol is formed by It consists of 10 chips, and the duration of each chip is 1000. Furthermore, in LoRa modulation, the chip duration is constant; therefore, the symbol duration of LoRa increases with the increase of SF, thus having... .

[0031] As can be seen from the above analysis, this transmission design not only inherits the noncoherent detection characteristics of traditional LoRa and does not require channel estimation, but also transmits additional information through space-time differential IM, thus having great potential to enhance the uplink transmission performance of LoRa systems.

[0032] Furthermore, this embodiment provides a low-complexity incoherent detection method that simplifies receiver operation design by decoupling LoRa symbol detection and RIS space-time block differential detection, and applies a tree search structure to differential detection, using spherical decoding to reduce complexity.

[0033] After the receiver receives the signal, each receiver block... LoRa demodulation is performed sequentially over a consecutive LoRa symbol duration to obtain the estimated LoRa symbol. This corresponds to the input information in the third part, where, For the first One LoRa estimation symbol; LoRa estimation symbol Re-modulate LoRa to obtain the estimated LoRa CSS signal. ,in, For the first One LoRa CSS signal; The first in the received block Data and Multiply, for The transpose of gives the first . column vectors, The column vectors are concatenated column by column to obtain the matrix after removing the LoRa signal. ; For the matrix after removing the LoRa signal Using an ML detector or a spherical decoder, we can obtain... The activation order of each sub-RIS and the constellation symbol carried by each activated sub-RIS; Here, when the constellation symbol modulation order Number of RIS When the value is small, an ML detector is used; as the constellation symbol modulation order increases... Number of RIS As the number of elements increases, the computational complexity of the ML detector grows exponentially. To address this ever-increasing complexity, a spherical decoder is employed, which avoids exhaustive search by limiting the search range to paths within the sphere.

[0034] Decode the activation order of the K sub-RIS to obtain the first part of the input information; decode the constellation symbol carried by each activated sub-RIS to obtain the second part of the input information.

[0035] This application also provides an uplink LoRa adaptive transmission system based on RIS differential index modulation, including a transmitter and a receiver. The transmitter includes a single-antenna LoRa node and a RIS array, and the receiver includes multiple receiving antennas. The system is used to implement the uplink LoRa adaptive transmission method based on RIS differential index modulation described in the foregoing embodiments.

[0036] To further verify the validity of this application, the following experimental analysis was conducted.

[0037] The BER and throughput performance of a single-node LoRa uplink transmission method based on RIS differential IM on a Rayleigh fading channel were evaluated to verify the effectiveness of the transmission and detection design in this application. In the simulation, throughput was defined as the number of correctly detected transmitted bits per unit time at the receiver, and similar to classic diversity unification and spatial modulation schemes, [the following was performed]. Consider it as SNR.

[0038] (1) Simulation parameter settings In the simulation experiment of this application, the LoRa symbol transmission bandwidth is set. 250 LoRa spreading factor The number of RIS reflective elements is 7. The number of sub-RIS is 48. The number of receiving antennas is 3. It is 6. -PSK constellation symbol modulation order The time-varying coefficient is 2. for .

[0039] (2) Analysis of simulation results Figure 2 The performance of the prior art and the present application in terms of BER and throughput is shown, where (a) shows the performance of the prior art and the present application in terms of BER, and (b) shows the performance of the prior art and the present application in terms of throughput. The prior art includes conventional LoRa (Conv. in the figure) and a RIS-assisted LoRa scheme only (RIS-assisted in the figure), and the number of RIS elements used in the two schemes is shown. All are uniformly set to 48, except that the RIS-assisted LoRa scheme uses 4DPSK, while this application uses 4PSK. Apart from this, the number of sub-RIS in this application... Set them to 3 and 4 respectively.

[0040] like Figure 2 As shown in (a), although the RIS-assisted LoRa scheme, like this application, does not require channel estimation, it has the same number of RIS array elements. and modulation order Under these conditions, this application demonstrates superior bit error rate performance compared to traditional LoRa and LoRa schemes with only RIS assistance. This is because, in addition to using the same method of controlling the propagation channel with RIS as the LoRa scheme with only RIS assistance, this application also reduces the possibility of error detection by transmitting information across multiple time slots and reducing the temporal isolation between different RIS elements, thus resulting in a lower BER. Furthermore, it can be seen that the number of elements contained in each sub-RIS has a slight impact on bit error rate performance. When the number of RIS elements... Same number of sub-RIS At the same time, due to In this case, RIS is divided into durations for each LoRa symbol. Sub-RIS with fewer reflective elements, therefore with Compared to the previous case, the gains from RIS may be reduced.

[0041] exist Figure 2 In (b) of the paper, consistent with expected results, this application demonstrates a significant throughput improvement compared to conventional LoRa and RIS-assisted LoRa schemes only. This application achieves this improvement within one LoRa symbol duration. The total number of bits transferred internally is It always has more features than LoRa solutions that only use RIS assistance. Bits, and with the number of sub-RIS As the throughput increases, the proposed scheme's advantage will become increasingly significant. However, designs based on spatiotemporal difference will be subject to... The influence of coherence time limits the number of LoRa symbols that can be transmitted during a space-time block, i.e., the number of sub-RIS. There are limitations. Therefore, practical designs should consider the trade-off between coherence time requirements and the data rate improvement brought by more subarrays.

[0042] Figure 3 The BER and throughput performance of this application under the adaptive spreading factor selection strategy are shown, where (a) is the BER performance of this application under the adaptive spreading factor selection strategy, and (b) is the throughput performance of this application under the adaptive spreading factor selection strategy. This further demonstrates the advantages of this strategy in improving the performance of the proposed scheme. Specifically, this application configures the following selection criteria... :when hour, Take 7; when hour, Take 9; when hour, Take 11. From the graph, we can observe that... The configuration with a symbol duration of 7 achieves the highest throughput. However, due to its shorter symbol duration, it is more sensitive to noise and interference, resulting in a significant degradation in BER in low SNR regions. In contrast, The setting of 11 provides the most reliable transmission performance and achieves the lowest BER, but its effective data rate is significantly reduced, making its throughput the lowest among all schemes.

[0043] With the above fixed Different solutions, adaptive The solution will be based on the instantaneous SNR. The value dynamically switches between 7, 9, and 11 to achieve a good balance between reliability and efficiency: a smaller value is selected when the SNR is high. To maximize throughput, a larger value is selected for low SNR. To ensure higher transmission reliability. Therefore, adaptive The proposed solution can significantly improve throughput while maintaining a moderate BER, compared to a fixed high BER. The configuration exhibits superior overall performance.

[0044] In summary, this application has the following technical effects: This application considers an uplink LoRa adaptive transmission design based on RIS differential IM and develops a corresponding low-complexity incoherent detection algorithm for this novel transmission design. With RIS enabled, differential IM modulation is performed by mapping the RIS transmission vector to a corresponding number of time slots to construct RIS space-time transport blocks, eliminating the need for explicit CSI for both the gateway and RIS, while simultaneously enhancing the uplink transmission link between the LoRa node and the gateway.

[0045] Furthermore, in conjunction with the proposed transmission structure, this application introduces an adaptive spreading factor selection strategy based on instantaneous SNR, enabling the system to dynamically balance data rate and transmission reliability according to channel conditions. Simulation results show that the new LoRa transmission and detection design not only inherits the incoherent detection characteristics of traditional LoRa, eliminating the need for channel estimation, but also transmits additional information through space-time differential IM, and combines adaptive... After the mechanism was implemented, the data rate in the LoRa uplink was significantly improved.

[0046] The above descriptions are merely various embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An uplink LoRa adaptive transmission method based on RIS differential index modulation, characterized in that, include: The transmitter communicates with the LoRa gateway based on the RIS array, and the RIS array is divided into... RIS (Rapid Strokes) When the transmitting end sends a signal, the frame is divided into multiple space-time transmission blocks, and each space-time transmission block includes multiple time slots; Within any space-time transport block, the information bits consist of three parts: a first part, a second part, and a third part. The first part is mapped to the space-time domain and used to determine... The activation order of the sub-RIS, the second part is mapped to the signal domain for selecting the constellation symbol carried by the activated sub-RIS, and the third part is mapped to the signal domain for generating... LoRa transmission symbol.

2. The method as described in claim 1, characterized in that, The The activation order of individual RIS units is determined in the following way: The bit length of the first part is: , Indicates rounding down; Set a non-negative integer starting from 0. ,in, For The number of sub-RIS index permutations is determined using the Lehmer code method to determine the final length. The sub-RIS index permutation sequence, i.e. The activation order of individual RIS.

3. The method as described in claim 1, characterized in that, The constellation symbol carried by the activated sub-RIS is determined in the following way: The bit length of the second part is: ,in, Modulation order for constellation symbols; Each activated subRIS carries a constellation symbol belonging to -PSK Constellation Collection.

4. The method as described in claim 1, characterized in that, The generation of LoRa transmission symbols includes: The bit length of the third part is: ,in, The number of chips contained in a LoRa symbol. ,in, It is the spreading factor; Set spreading factor index set , for The first in One element, express The number of elements in; For each This corresponds to a minimum SNR threshold required to guarantee demodulation performance. ;for ,have ; Obtain the instantaneous signal-to-noise ratio (SNR) at the receiver. Then As spreading factor ,like Then As spreading factor ; According to the spreading factor calculate And determine the bit length of the third part. Generate LoRa transmission symbols.

5. The method as described in claim 1, characterized in that, The method further includes: After receiving the signal, the receiving end performs processing on each receiving block. LoRa demodulation is performed sequentially over a consecutive LoRa symbol duration to obtain the estimated LoRa symbol. This corresponds to the input information in the third part, where, For the first One LoRa estimation symbol; LoRa estimation symbol Re-modulate LoRa to obtain the estimated LoRa CSS signal. ,in, For the first One LoRa CSS signal; The first in the received block Data and Multiply, for The transpose of gives the first . column vectors, The column vectors are concatenated column by column to obtain the matrix after removing the LoRa signal. ; For the matrix after removing the LoRa signal Using an ML detector or a spherical decoder, we can obtain... The activation order of each sub-RIS and the constellation symbol carried by each activated sub-RIS; Decode the activation order of the K sub-RIS to obtain the input information of the first part; decode the constellation symbol carried by each activated sub-RIS to obtain the input information of the second part.

6. An uplink LoRa adaptive transmission system based on RIS differential index modulation, characterized in that, The system includes a transmitter and a receiver. The transmitter includes a single-antenna LoRa node and a RIS array, and the receiver includes multiple receiving antennas. The system is used to implement the uplink LoRa adaptive transmission method based on RIS differential index modulation as described in any one of claims 1-5.

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