Double Diagonal Matrix Interleaver and LoRa Communication System

Abstract

The present invention discloses a double diagonal matrix interleaver and a LoRa communication system. The interleaver places 2×SF Hamming code codewords into an SF×2CR matrix in a diagonal order with spaces in between, and then modulates the SF bits taken from each column into LoRa symbols for transmission. The bits in two consecutive LoRa symbols come from different Hamming code codewords; where CR represents the length of the Hamming code codeword. 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 interleaving, and particularly relates to a double diagonal matrix 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 network (LPWAN) communication technology. At present, the main LPWAN technologies include LoRa, SigFox, LTE, Cat-m, and NB-IoT. 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 is 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 coding. The Hamming code coding 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 of the input sequence corresponding in 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. 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 in the Figure 3 SF×CR matrix shown in the figure (along the diagonal) in the order shown, and then taken out column by column. For example, the first column taken out is (a0, b0, c0, d0, e0, f0, g0). Then, 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 purpose of the present invention is to provide a double diagonal matrix 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 purpose, the present invention provides a double diagonal matrix interleaver. This interleaver places 2×SF Hamming code codewords into the SF×2CR matrix in the diagonal order with gaps, and then modulates the SF bits taken out from each column into LoRa symbols for transmission. The bits in two consecutive LoRa symbols come from different Hamming code codewords; where CR represents the length of the Hamming code codeword.

[0017] The present invention also provides a LoRa communication system that uses the above double diagonal matrix interleaver.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] 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. Brief Description of the Drawings

[0020] Figure 1 Schematic diagram of the LoRa physical layer composition;

[0021] Figure 2 It is a schematic diagram of an interleaver;

[0022] Figure 3 It is a schematic diagram of the result of a LoRa diagonal matrix interleaver;

[0023] Figure 4 It is a schematic diagram of a double diagonal matrix interleaving structure;

[0024] Figure 5 It is a schematic diagram of the principle of double diagonal matrix interleaving design;

[0025] Figure 6 It is a comparative simulation result diagram under a Gaussian channel with a signal-to-interference ratio of 0 dB;

[0026] Figure 7 It is a comparative simulation result diagram under a Rayleigh channel with a signal-to-interference ratio of 0 dB. Detailed implementation

[0027] 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.

[0028] The present invention proposes a scheme for an improved interleaver to reduce the impact of LoRa interference signals with the same spreading factor on LoRa communication.

[0029] The double diagonal matrix interleaver in this embodiment places 2×SF Hamming code words in an SF×2CR matrix in diagonal order. Taking SF = 7 and CR = 4 / 7 as an example for illustration, the structure of the double diagonal matrix interleaver is as Figure 4 shown, (a0, a1,... a n-1 ) represents a Hamming code word, and the SF×2CR matrix has a total of 2×SF Hamming code words.

[0030] By doubling the interleaving depth, it can be seen that the bits in two consecutive LoRa symbols come from different Hamming code words. Therefore, when dealing with the interference of LoRa signals with the same spreading factor, even if consecutive LoRa symbol errors occur, correct error correction can be achieved. Figure 5 Explains the principle of designing the double diagonal matrix interleaving in this way.

[0031] Correspondingly, deinterleaving is the reverse of the above operation.

[0032] The present invention also provides a LoRa communication system, which adopts the above-mentioned double diagonal matrix interleaver.

[0033] To verify the present invention, the bit error rate of this solution was simulated. To simulate the actual communication process, the present invention selected two common channels: Gaussian channel and Rayleigh channel. The simulation conditions were that the spreading factor SF = 8, the code rate CR = 4 / 8, the 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 (the power ratio of the signal to the interference) 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 the present invention within ten minutes was statistically analyzed. Figure 6 and Figure 7 The figure shows the comparison of the bit error rate simulation results between the novel interleaver proposed by the present invention and the LoRa interleaver. It can be seen from the figure that the LoRa interference signal with the same spreading factor will seriously affect the communication of the normal LoRa system, and even the phenomenon of bit error rate flat layer appears. However, the improved LoRa interleaver has superior bit error rate performance compared with the traditional LoRa interleaver.

[0034] The results show that the improved interleaver proposed by the present invention can effectively improve the bit error rate performance of the LoRa communication system when dealing with the LoRa interference signal with the same spreading factor.

[0035] In summary, when the traditional LoRa communication system faces the LoRa interference signal with the same spreading factor, its bit error rate performance is poor. The innovation of the present invention lies in designing a novel interleaver to deal with the LoRa interference signal with the same spreading factor. The final experimental results show that although the interleaver doubles the interleaving length, it can effectively improve the bit error rate performance of the LoRa communication system when dealing with the LoRa interference signal with the same spreading factor.

[0036] 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 principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A double diagonal matrix interleaver, characterized in that, The interleaver places 2×SF Hamming code codewords into an SF×2CR matrix in a diagonal order with spaces in between. Then, the SF bits taken from each column are modulated into LoRa symbols for transmission. The bits in two consecutive LoRa symbols come from different Hamming code codewords; where CR represents the length of the Hamming code codeword.

2. A LoRa communication system, characterized in that, This LoRa communication system employs the double diagonal matrix interleaver described in Claim 1.

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