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Soft demodulation method of linear frequency modulation spread spectrum modulation technology

A chirp spread spectrum, modulation technology technology, applied in the direction of shaping network, baseband system, digital transmission system, etc. in transmitter/receiver, can solve the problems affecting communication performance, continuous burst error, communication channel interference, etc. achieve the effect of improving communication capabilities

Active Publication Date: 2020-04-07
CHINA UNIV OF GEOSCIENCES (WUHAN)
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

In the urban environment, the communication channel is easily interfered by other wireless communication devices. At the same time, due to the large number of obstacles such as urban buildings and trees, the multipath effect during communication is obvious, and a large number of continuous burst errors often occur when the receiver demodulates. , making LoRa's error correction module "failure", seriously affecting communication performance

Method used

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  • Soft demodulation method of linear frequency modulation spread spectrum modulation technology
  • Soft demodulation method of linear frequency modulation spread spectrum modulation technology
  • Soft demodulation method of linear frequency modulation spread spectrum modulation technology

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Embodiment 1

[0031] Please refer to figure 1 , the present embodiment provides a soft demodulation method of chirp spread spectrum modulation technology, including FFT transform processing and orthogonal dichotomous peak difference (ODPS) soft demodulation, wherein:

[0032] The specific process of the FFT transformation process is: the received signal s k (t)+n(t) filters out-of-band noise through a band-pass filter (BPF), and retains the signal frequency band s k (t); the signal s k (t) and an orthogonal base Chirp signal s i (t) After multiplication, the high-frequency components are filtered out through a low-pass filter, and then the filtered result is sampled at a BW sampling rate into a digital signal s 1 , the signal s k (t) with another quadrature base Chirp signal s Q (t) After multiplication, the high-frequency components are filtered out through a low-pass filter, and then the filtered result is sampled at a BW sampling rate into a digital signal s 2 ; Wherein, the digita...

Embodiment 2

[0038] This embodiment performs soft demodulation on a specific received signal, wherein the FFT transformation process is the same as that of Embodiment 1, please refer to figure 2 , the transformation results obtained by the FFT transformation process include: the full set of symbols S={000,001,010,011,100,101,110,111}, the full set of amplitudes A={0.75,1.11,0.54,3.5,0.42,1.01 , 0.86, 1.28}, spreading factor SF=3; ODPS soft demodulation process is:

[0039] First, find all subscript position records K i，0 ={k|x i =0} and K i，1 ={k|x i =1}, the result is:

[0040] K 0，0 = {0, 1, 2, 3}, K 0，1 = {4, 5, 6, 7};

[0041] K 1，0 = {0, 1, 4, 5}, K 0，1 ={2,3,6,7};

[0042] K 2，0 = {0, 2, 4, 6}, K 2，1 ={1,3,5,7};

[0043] Then, starting from i=0, take the subscript position record K 0，0 The maximum value in the corresponding amplitude a 3 =3.5, remove the subscript position record K 0，1 The maximum value in the corresponding amplitude a 7 =1.28, the ODPS soft demodul...

Embodiment 3

[0045] Please refer to image 3 , this embodiment builds an enhanced LoRa communication system based on Turbo code and CSS modulation technology, including Turbo encoding module, CSS modulation module, CSS soft demodulation module, and Turbo decoding module, wherein the signal sending end will be sent The signal is sent out after being processed by the Turbo encoding module and the CSS modulation module, and the signal is propagated in the channel. After receiving the signal in the channel, the signal receiving end obtains the restored signal through CSS soft demodulation and Turbo decoding; what needs to be explained is In this embodiment, the Turbo code with better error correction performance is used to replace the Hamming code in the original LoRa system, and the soft demodulation technology described in Embodiment 1 of the present invention is used in the CSS soft demodulation.

[0046] In this embodiment, matlab is used to simulate the bit error rate of the enhanced LoRa...

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Abstract

The invention provides a soft demodulation method of a linear frequency modulation spread spectrum modulation technology. The method comprises FFT transformation processing and orthogonal binary peakdifference soft demodulation, and the orthogonal binary peak difference soft demodulation process comprises the following steps: S1, respectively finding out a first symbol subscript set with the ithbit being 0 and a second symbol subscript set with the ith bit being 1 in a transformation result; S2, determining soft information of the ith bit after demodulation according to a first maximum amplitude in all amplitudes corresponding to the first symbol subscript set and a second maximum amplitude in all amplitudes corresponding to the second symbol subscript set; and S3, starting from i=0, increasing i progressively, and repeating the steps S1 and S2 until all bits are traversed. The method has the advantages that the problem that soft information is needed in the decoding process when Turbo codes, LDPC codes, Polar codes and the like are used for replacing Hamming codes in LoRa is solved; cascading conditions are provided for Turbo+CSS, LDPC+CSS, Polar+CSS and other physical layer schemes, a series of enhanced LoRa communication systems are constructed, and the communication capacity of LoRa is greatly improved.

Description

technical field [0001] The invention relates to the technical field of wireless communication, in particular to a soft demodulation method of linear frequency modulation spread spectrum modulation technology. Background technique [0002] LoRa is currently one of the most popular long-distance communication technologies, and its communication distance can reach a maximum of more than ten kilometers in air-to-air conditions; the reason why LoRa can achieve long-distance transmission lies in its excellent communication physical layer design. Semtech disclosed in the patent document (US20140219329A) applied for in 2014 that the LoRa physical layer uses Hamming code, Gray code, diagonal interleaving, scrambling and chirp spread spectrum modulation (Chirp Spread Spectrum, CSS), etc. Technology, unlike the traditional communication system that uses amplitude modulation, phase modulation or frequency modulation, LoRa uses CSS technology, combined with forward error correction techn...

Claims

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Application Information

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IPC IPC(8): H04L1/00H04L25/03
CPCH04L1/0061H04L1/0064H04L25/03318
Inventor 谢桂辉焦向开唐晓庆张帅
Owner CHINA UNIV OF GEOSCIENCES (WUHAN)
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