LoRa Interleaver and LoRa Communication System

Abstract

The present invention discloses a LoRa interleaver and a LoRa communication system. The LoRa interleaver includes a diagonal matrix interleaving block and a symbol interleaving block. The symbol interleaving block is an SF×CR matrix written by rows and read by columns. After one interleaving operation on the diagonal matrix interleaving block, CR LoRa symbols are obtained. The i-th of the CR LoRa symbols taken out from the diagonal matrix interleaving block is stored in the i-th row of the SF×CR matrix. After filling the SF rows of the symbol interleaving block matrix, the symbols are taken out by columns. The present invention can effectively improve the bit error rate performance of the LoRa communication system when dealing with LoRa interference signals with the same spreading factor.

Description

Technical Field

[0001] The present invention belongs to the technical field of interleaver, and particularly relates to a LoRa interleaver and a LoRa communication system. Background Art

[0002] With the proposal of the concept of Internet of Everything, the networking of intelligent devices has become the focus of attention. At present, Internet of Things technologies are mainly divided into two categories. One is short-distance communication technologies such as Wi-Fi, Bluetooth, ZigBee, etc. However, due to the disadvantages of short communication distance and high power consumption, they cannot be applied to application scenarios such as industry and agriculture that require large-scale deployment and low-cost maintenance. Therefore, in order to solve the problems encountered in the development of the Internet of Things, the Low Power Wide Area Network (LPWAN) technology has gradually come into view.

[0003] LoRa is a kind of low power wide area networks (LPWAN) communication technology. At present, the main LPWAN technologies include LoRa, SigFox, LTE, Cat-m, and NB-IoT, etc. Compared with other LPWAN technologies, LoRa not only has low cost and flexible deployment, but also has good anti-Doppler performance. More importantly, LoRa can flexibly adjust the transmission distance, receiving sensitivity, and transmission rate by increasing or decreasing the spreading factor (SF). Because of these advantages, LoRa has been gradually taken seriously and has become one of the most promising and popular LPWAN technologies.

[0004] At present, LoRa has been applied in many aspects, such as smart agriculture, smart factories, intelligent communities, etc. However, with the increase in LoRa communication systems and terminal nodes, interference between LoRa signals will inevitably occur. For LoRa signals with different spreading factors, this interference is much smaller than Gaussian white noise interference under the same signal-to-noise ratio. However, for LoRa signals with the same spreading factor, this interference is higher than Gaussian white noise interference under the same signal-to-noise ratio, resulting in a decline in the LoRa bit error rate performance.

[0005] However, current research on this issue mostly stays at analyzing the bit error rate performance under the interference of LoRa with the same spreading factor, or reasonably allocating LoRa parameters at the application layer of LoRa. For example, the bit error rate performance of the interference between LoRa signals has been studied and simulated, including both the interference of LoRa signals with the same spreading factor and the interference of LoRa signals with different spreading factors; another example is to use the golden section search and parabolic interpolation to optimize the transmission parameters of the LoRaWAN system in a high-density smart city traffic environment. The optimized distribution method of the spreading factor (SF) not only significantly improves the success rate, but also enables more nodes to use lower spreading, thereby reducing latency; another example is to optimize and improve the algorithm of the receiver to reduce the interference of LoRa signals with the same spreading factor. However, there is almost no research on the physical layer of LoRa for this problem yet.

[0006] The physical layer of LoRa consists of Hamming coding, interleaver, scrambling, Gray coding technology, and frequency shift chirp modulation (FSCM) technology, as Figure 1 shown.

[0007] Among them, Hamming code: LoRa uses Hamming code for encoding. The Hamming code encoding algorithm is simple and has low complexity. In the LoRa protocol specification, there are four code rates (CR): 4 / 5, 4 / 6, 4 / 7, 4 / 8, which can be freely selected. It should be noted that only the 4 / 7 and 4 / 8 code rates have error correction functions and can only correct one bit. Among them, the 4 / 8 code rate can correct one bit and detect two errors.

[0008] Interleaver: The interleaver is essentially a data scrambler, and its function is to scramble an input sequence and then output it. Specifically, as Figure 2 shown. Let the input sequence be X with a length of n, and its address N = 1, 2,... N. Let the output sequence be Y. Then the address M of each element in the input sequence corresponding to Y can be calculated by the following expression:

[0009] M = F π (N)

[0010] where F π is the interleaving function of the interleaver, and the corresponding deinterleaving can be expressed by the following formula:

[0011] N = F u (M)

[0012] where F u is the deinterleaving function.

[0013] During the transmission of LoRa signals, a symbol can represent SF bits. When a symbol is in error, there is a 50% probability that the SF bits represented by this symbol are in error. Therefore, when a symbol is in error, usually a series of bits are in error. However, Hamming codes can only correct one-bit errors. Without an interleaver to evenly disperse these errors into each codeword, it will be very difficult for Hamming codes to function effectively.

[0014] In summary, the LoRa interleaver is a very important module. In order to evenly disperse the number of bits in a symbol into each codeword, the LoRa interleaver is a diagonal matrix interleaver. The diagonal matrix interleaver can evenly distribute the bits in a codeword into each codeword. Taking SF = 7 and code rate 4 / 7 as an example, specifically as Figure 3 shown. Among them, (a0, a1,... a6) represents a codeword encoded by Hamming codes. The SF codewords are sequentially placed into the Figure 3 SF×CR matrix shown in the figure (along the diagonal) in the order shown in the figure, and then taken out column by column. For example, the first column taken out is (a0, b0, c0, d0, e0, f0, g0). After that, the SF bits taken out from each column are modulated into LoRa symbols for transmission. This is the principle of the LoRa interleaver. Summary of the Invention

[0015] The object of the present invention is to provide a LoRa interleaver and a LoRa communication system to reduce the impact of LoRa interference signals with the same spreading factor on LoRa communication.

[0016] To achieve the above object, the present invention provides a LoRa interleaver, which includes a diagonal matrix interleaving block and a symbol interleaving block. The symbol interleaving block is an SF×CR matrix written row by row and read column by column;

[0017] After one interleaving, the diagonal matrix interleaving block obtains CR LoRa symbols. The i-th of the CR LoRa symbols taken out by the diagonal matrix interleaving block is stored in the i-th row of the SF×CR matrix. After filling the SF rows of the symbol interleaving block matrix, it is taken out column by column.

[0018] Further, there is 1 diagonal matrix interleaving block, and 1 diagonal matrix interleaving block fills the SF rows of the symbol interleaving block matrix after SF times of interleaving.

[0019] Further, there are SF diagonal matrix interleaving blocks, and SF diagonal matrix interleaving blocks fill the SF rows of the symbol interleaving block matrix after one interleaving.

[0020] The present invention also provides a LoRa communication system, which adopts the above-mentioned LoRa interleaver.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] When the present invention deals with LoRa interference signals with the same spreading factor, it can effectively improve the bit error rate performance of the LoRa communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the LoRa physical layer composition;

[0024] Figure 2 It is a schematic diagram of an interleaver;

[0025] Figure 3 It is a schematic diagram of the result of the LoRa diagonal matrix interleaver;

[0026] Figure 4 It is a schematic diagram of an improved scheme for the LoRa interleaver;

[0027] Figure 5 It is a schematic diagram of the construction principle of a symbol interleaver;

[0028] Figure 6 It is a simulation result diagram of the bit error rate comparison under a Gaussian channel with a signal-to-interference ratio of 0 dB;

[0029] Figure 7 It is a simulation result diagram of the bit error rate comparison under a Rayleigh channel with a signal-to-interference ratio of 0 dB. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] An embodiment of the present invention proposes an improved scheme for the LoRa interleaver, specifically as Figure 4 shown. After diagonal matrix interleaving, a symbol interleaver is added, and the CR×SF symbols taken out by multiple diagonal matrix interleavers are interleaved again.

[0032] As can be seen from the background art, without changing the original interleaver, if two consecutive LoRa symbols are in error, it is very likely that the Hamming code cannot correct the error. Therefore, the present invention considers interleaving the symbols again.

[0033] The essence of diagonal matrix interleaving is to interleave bits, while the symbol interleaver scrambles the symbols to be modulated. The diagonal matrix interleaver extracts a column of bits and converts them into decimal numbers, which are called symbols. One diagonal matrix interleaving can obtain CR symbols, and symbol interleaving requires SF×CR symbols for interleaving.

[0034] The symbol interleaver is selected in the form of the simplest row-column interleaver. Specifically, the symbols to be modulated are first stored row by row in an SF×CR matrix, and then taken out column by column. The principle of the symbol interleaver is as Figure 5 shown. Figure 5 It is assumed that SF = 6 and CR = 4 / 6, where A0, A1, … A5 represent the CR symbols extracted from the first diagonal matrix interleaving block, B0, B1, … B5 represent the CR symbols extracted from the second diagonal matrix interleaving block, and so on.

[0035] Among them, A0, A1, … A5 and B0, B1, … B5 can be obtained by interleaving the same diagonal matrix interleaving block multiple times, or can be obtained by interleaving multiple diagonal matrix interleaving blocks simultaneously. The symbols obtained by interleaving SF diagonal matrices are all used for interleaving.

[0036] Correspondingly, deinterleaving is the reverse of the above operation.

[0037] The present invention also provides a LoRa communication system, which adopts the above-mentioned LoRa interleaver.

[0038] To verify the method proposed by the present invention, the bit error rate simulation of this scheme was carried out. In order to simulate the actual communication process, two common channels were selected: Gaussian channel and Rayleigh channel, and a LoRa signal interference source with the same spreading factor was set. The simulation conditions were spreading factor SF = 8, code rate CR = 4 / 8, bandwidth BW = 125KHz. A LoRa interference signal with the same spreading factor was transmitted near the receiver every 1S, and the signal-to-interference ratio was taken as 0dB. Finally, the bit error rate performance of the traditional LoRa communication system and the LoRa communication system with the improved interleaver proposed by us within ten minutes was statistically analyzed, specifically as Figure 6 and Figure 7 shown.

[0039] From Figure 6 and Figure 7 it can be seen that the LoRa interference signal with the same spreading factor has a great impact on the bit error rate of the LoRa communication system, and even the phenomenon of bit error rate flat layer appears. The improved LoRa interleaver has superior bit error rate performance compared with the traditional LoRa interleaver.

[0040] The results show that the improved interleaver proposed in the present invention can effectively improve the bit error rate performance of the LoRa communication system when dealing with LoRa interference signals with the same spreading factor.

[0041] In summary, the traditional LoRa communication system has poor bit error rate performance when facing LoRa interference signals with the same spreading factor. The innovation of the present invention lies in proposing an improved scheme for the LoRa interleaver. The final experimental results show that it can effectively improve the bit error rate performance of the LoRa communication system when dealing with LoRa interference signals with the same spreading factor.

[0042] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A LoRa interleaver, characterized in that, The LoRa interleaver includes a diagonal matrix interleaving block and a symbol interleaving block. The symbol interleaving block is an SF×CR matrix written by rows and read by columns; After one interleaving, the diagonal matrix interleaving block obtains CR LoRa symbols. The i-th of the CR LoRa symbols taken out by the diagonal matrix interleaving block is stored in the i-th row of the SF×CR matrix. After filling the SF rows of the symbol interleaving block matrix, the symbols are taken out by columns.

2. The LoRa interleaver according to claim 1, wherein There is 1 diagonal matrix interleaving block, and after SF times of interleaving, the 1 diagonal matrix interleaving block fills the SF rows of the symbol interleaving block matrix.

3. The LoRa interleaver according to claim 1, wherein There are SF diagonal matrix interleaving blocks, and after one interleaving, the SF diagonal matrix interleaving blocks fill the SF rows of the symbol interleaving block matrix.

4. A LoRa communication system, characterized in that, The LoRa communication system adopts the LoRa interleaver described in any one of claims 1 to 3.

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