A Skew Shift Keying - Chirp Modulation and Demodulation Method

Abstract

The present invention discloses a skew keying - Chirp modulation and demodulation method. In the present invention, a data bit stream is mapped into a decimal transmission symbol, and then this symbol is mapped to the initial frequency of the transmitted signal to obtain the transmitted signal. At the receiving end, the received signal is first subjected to undersampling operation, followed by de - chirping operation, DFT operation, and maximum value extraction operation to obtain the index corresponding to the maximum value, thereby demodulating the decimal transmission symbol. Then, the decoded symbol is converted into a binary bit stream to obtain the demodulated bit stream. The method proposed by the present invention is applied to the LPWAN system. It can improve the robustness of the signal to noise by increasing the spreading factor to adapt to the extremely low signal - to - noise ratio environment; the receiver sensitivity of the general modulation scheme is low; and it can achieve simultaneous communication of multiple terminal devices under the same SF and frequency band by adjusting the frequency modulation coefficient, saving spectrum resources.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and in particular, to a skew shift keying-Chirp modulation and demodulation method. Background Art

[0002] As a wireless communication technology designed specifically for Internet of Things (IoT) applications, the Low Power Wide Area Network (LPWAN) technology has the advantages of low power consumption, low bandwidth, low cost, long distance, and large coverage capacity compared with traditional wireless communication technologies such as WiFi, ZigBee, and Bluetooth. It is suitable for IoT devices powered by batteries for long-distance and small-data-volume transmissions.

[0003] The LoRa technology is one of the emerging LPWAN technologies. It uses chirp spread spectrum modulation technology, which not only maintains the low-power consumption characteristic of frequency shift keying (FSK) modulation but also improves the anti-interference ability. The LoRa technology has an ultra-high receiving sensitivity (RSSI), with a receiving current of only 10 mA and a sleep current of 200 nA, which greatly extends the battery life. Many traditional wireless systems use frequency shift keying (FSK) modulation as the physical layer because it is a very effective modulation for achieving low power consumption.

[0004] Terminal devices using different spreading factors (SFs) of the LoRa technology can transmit simultaneously using the same frequency without interference. However, since the chirp slope of LoRa signals with the same spreading factor (SF) is the same, serious interference will occur between terminal devices using the same SF. Summary of the Invention

[0005] To solve the technical problems existing in the background art, the present invention proposes a skew shift keying-Chirp modulation and demodulation method.

[0006] A skew shift keying-Chirp modulation and demodulation method proposed by the present invention includes the following steps:

[0007] S1. Perform natural mapping on the binary data bit stream b0,..., b SF-1 to obtain the transmitted decimal symbol m;

[0008] S2. Map m to the initial frequency f0 of the chirp signal to obtain the linear spread spectrum modulation signal s m (t);

[0009] S3. Pass the modulation signal s m (t) through an additive white Gaussian noise (AWGN) channel to obtain the received signal r m (t);

[0010] S4. Use the received signal r m (t) to perform undersampling at the sampling frequency f s = BW to obtain the sampled received sequence r m (l);

[0011] S5. Use the received sequence r m (l) to obtain the de-chirped signal r m ′(l) through de-chirping operation;

[0012] S6. Use the de-chirped signal r m ′(l) to perform DFT operation to obtain R(q);

[0013] S7. Use R(q) to perform modulo operation to obtain

[0014] S8. Use to perform maximum value operation to obtain the index corresponding to its maximum value

[0015] S9. Use the index to inverse map into an SF-bit binary bit stream

[0016] Preferably, in S1, map the binary bit stream into a decimal number m, where

[0017] Preferably, in S2, the chirp signal s m (t) is specifically:

[0018]

[0019] where T = 2 SF / BW is the symbol period, μ = λ·BW / T is the chirp rate, λ (λ≥1) is the chirp coefficient, T0 = (1 - m / 2 SF )·T / λ is the frequency hopping time, and f0 = m·BW / 2 SF is the initial frequency.

[0020] Preferably, in S3, the received signal r m (t) is specifically:

[0021] r m (t) = s m (t) + n(t)

[0022] where n(t) is Gaussian noise with a mean of 0 and a variance of σ 2 .

[0023] Preferably, in S4, the number of sampling points for the undersampling is M, and the received sequence r after sampling m (l) is specifically:

[0024]

[0025] Preferably, in S4, the received sequence r after sampling m (l) is specifically:

[0026]

[0027] where the frequency modulation slope μ = λ·BW 2 / M, and the initial frequency f0 = m·BW / M;

[0028] Preferably, where e -j2πl = 1.

[0029] Preferably, in S5, the dechirped signal r m ′(l) is specifically:

[0030]

[0031] where, Preferably, in S6, the dechirped signal r m ′(l) is subjected to an M-point DFT operation to obtain R(q):

[0032]

[0033] where q = 0, 1,..., M - 1, is Gaussian noise.

[0034] Preferably, in S7, is specifically:

[0035]

[0036] Preferably, in S8, the index is specifically:

[0037]

[0038] In the present invention, the proposed offset keying-Chirp modulation and demodulation method maps the data bit stream into decimal transmission symbols, and then maps the symbols to the initial frequency of the transmitted signal to obtain the transmitted signal. At the receiving end, the received signal is first undersampled, and then de-chirped, DFT operation, and maximum value extraction operation are performed to obtain the index corresponding to the maximum value, thereby demodulating the decimal transmission symbol, and then converting the decoded symbol into a binary bit stream to obtain the demodulated bit stream. The method proposed by the present invention is applied to the LPWAN system, which can improve the robustness of the signal to noise by increasing the spreading factor to adapt to the extremely low signal-to-noise ratio environment; the receiver sensitivity of the general modulation scheme is low; multiple terminal devices can communicate simultaneously under the same SF and frequency band by adjusting the frequency modulation coefficient, saving spectrum resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 FIG. 6 is a schematic diagram of the transmitting end structure of an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention.

[0040] Figure 2 FIG. 10 is a schematic diagram of the receiving end structure of an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention.

[0041] Figure 3 FIG. 14 is a time-frequency diagram at different initial frequencies in an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention.

[0042] Figure 4 FIG. 18 is a performance curve diagram at different SFs in an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] As Figures 1 to 4 shown, Figure 1 FIG. 6 is a schematic diagram of the transmitting end structure of an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention, Figure 2 FIG. 10 is a schematic diagram of the receiving end structure of an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention, Figure 3 FIG. 14 is a time-frequency diagram at different initial frequencies in an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention, Figure 4 FIG. 18 is a performance curve diagram at different SFs in an embodiment of the offset keying-Chirp modulation and demodulation method proposed by the present invention.

[0044] An offset keying-Chirp modulation and demodulation method proposed by the present invention includes the following steps:

[0045] S1. Generate a binary data bit stream b0,...,b from the information source SF-1 and perform a natural mapping to obtain a transmitted decimal symbol m;

[0046] Specifically,

[0047] S2. Map m to the initial frequency f0 of a chirp signal to obtain a chirp spread spectrum modulation signal s m (t);

[0048] Specifically, the chirp signal s m (t) is specifically:

[0049]

[0050] where T = 2 SF / BW is the symbol period, μ = λ·BW / T is the frequency modulation slope, λ (λ≥1) is the frequency modulation coefficient, T0 = (1 - m / 2 SF )·T / λ is the frequency hopping moment, and f0 = m·BW / 2 SF is the initial frequency.

[0051] S3. Pass the modulation signal s m (t) through an additive white Gaussian noise (AWGN) channel to obtain a received signal r m (t);

[0052] Specifically, the received signal r m (t) is specifically:

[0053] r m (t) = s m (t) + n(t)

[0054] where n(t) is Gaussian noise with a mean of 0 and a variance of σ 2 .

[0055] S4. Undersample the received signal r m (t) at a sampling frequency f s = BW to obtain a sampled received sequence r m (l);

[0056] Specifically, the number of sampling points for the undersampling is M, and the sampled received sequence r m (l) is specifically:

[0057]

[0058] Substitute the frequency modulation slope μ = λ·BW 2 / M and the initial frequency f0 = m·BW / M into the above formula to obtain:

[0059] Since e -j2πl = 1, the above equations can be combined to obtain:

[0060]

[0061] S5. Use the received sequence r m (l) to obtain the de-chirped signal r m ′(l) through de-chirping operation;

[0062] Specifically, the de-chirped signal r m ′(l) is specifically:

[0063]

[0064] where,

[0065] S6. Use the de-chirped signal r m ′(l) to perform DFT operation to obtain R(q);

[0066] Specifically, perform M-point DFT operation on the de-chirped signal r m ′(l) to obtain R(q):

[0067]

[0068] where q = 0, 1,..., M - 1, is Gaussian noise.

[0069] S7. Use R(q) to perform modulo operation to obtain Specifically,

[0070]

[0071] S8. Use to perform maximum value operation to obtain the index corresponding to its maximum value

[0072] Specifically, the index is:

[0073]

[0074] S9. Use the index to inverse map into an SF-bit binary bit stream

[0075] So far, the demodulation is completed.

[0076] Figure 1 and2 Shows the transmission link system model of the present invention. In actual operation, such as Figure 1 shown, S1 and S2 are completed at the sending end. As Figure 2 shown, S3 - S9 are completed at the receiving end.

[0077] In this embodiment, the proposed skew - shift keying - Chirp modulation and demodulation method. The present invention maps the data bit stream into decimal transmission symbols, and then maps the symbols to the initial frequency of the transmitted signal to obtain the transmitted signal; at the receiving end, the received signal is first undersampled, and then de - chirping operation, DFT operation and maximum value extraction operation are performed to obtain the index corresponding to the maximum value, so as to demodulate the decimal transmission symbol, and then convert the decoded symbol into a binary bit stream to obtain the demodulated bit stream. The method proposed by the present invention not only maintains the characteristics of low power consumption and long distance, but also supports terminal devices to communicate simultaneously using the same SF. When applied to the LPWAN system, it can improve the robustness of the signal to noise by increasing the spreading factor to adapt to the extremely low signal - to - noise ratio environment; the receiver sensitivity of the general modulation scheme is low; by adjusting the frequency modulation coefficient, multiple terminal devices can communicate simultaneously under the same SF and frequency band, saving spectrum resources.

[0078] The modulation and demodulation method of this embodiment will be described in detail below with simulation experiments.

[0079] Table 1 Simulation parameters of the modulation and demodulation scheme

[0080]

[0081]

[0082] The simulation parameters are as shown in the above table. The simulation results are as Figure 3 shown. Figure 3 This is the BER - SNR performance curve of the modulation method for this simulation experiment. Among them, the black curve with pentagram marks represents the error - code performance with SF = 6 under the AWGN channel; the blue curve with star marks represents the error - code performance with SF = 7 under the AWGN channel; the red curve with up - triangle marks represents the error - code performance with SF = 8 under the AWGN channel; the green curve with plus marks represents the error - code performance with SF = 9 under the AWGN channel; the magenta curve with circle marks represents the error - code performance with SF = 10 under the AWGN channel; the black curve with cross marks represents the error - code performance with SF = 11 under the AWGN channel.

[0083] Specifically, when SF = 6, the demodulation signal-to-noise ratio threshold at a bit error rate of 10-5 is approximately -4 dB, and as SF increases, the demodulation signal-to-noise ratio threshold continuously decreases. For each increase of 1 in SF, the signal-to-noise ratio threshold decreases by approximately 3 dB. When SF = 11, the demodulation signal-to-noise ratio threshold is approximately -18 dB.

[0084] As described above, only the specific preferred embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered within the protection scope of the present invention.

Claims

1. An offset keying-Chirp modulation and demodulation method, characterized in that Comprising the following steps: S1. Use the binary data bit stream b0,..., b generated by the information source SF-1 to perform a natural mapping to obtain the transmitted decimal symbol m; S2. Map m to the initial frequency f0 of the chirp signal to obtain the linearly spread-spectrum modulation signal s m (t); S3. Use the modulation signal s m (t) to obtain the received signal r m (t) through an additive white Gaussian noise (AWGN) channel; S4. Use the received signal r m (t) to perform undersampling at the sampling frequency f s = BW, and obtain the sampled received sequence r m (l); S5. Using the received sequence r m (l) Obtaining a de-chirped signal r' through a de-chirping operation m (l); S6. Using the de-chirped signal r′ m (l) Perform a DFT operation to obtain R(q); S7. Obtain by performing a modulo operation using R(q) S8. Using to perform a maximum value extraction operation to obtain the index corresponding to its maximum value S9. Using an index Inverse-map it into the binary bit stream of the SF bits 2. The skew shift keying-Chirp modulation and demodulation method according to claim 1, wherein In S1, map the binary bit stream to a decimal number m, where 3. The skew shift keying-Chirp modulation and demodulation method according to claim 1, characterized in that In S2, the chirp signal s m (t) is specifically: where T = 2 SF / BW is the symbol period, μ = λ·BW / T is the frequency modulation slope, λ (λ≥1) is the frequency modulation coefficient, T0 = (1 - m / 2 SF )·T / λ is the frequency hopping time, f0 = m·BW / 2 SF is the initial frequency.

4. The skew keying-Chirp modulation and demodulation method according to claim 1, wherein In S3, the received signal r m (t) is specifically: r m r(t) = s m r(t) + n(t) where n(t) is Gaussian noise with a mean of 0 and a variance of σ 2 .

5. The skew keying-Chirp modulation and demodulation method according to claim 1, characterized in that, In S4, the number of sampling points of the undersampling is M, and the received sequence r m (l) is specifically:

6. The skew shift keying-Chirp modulation and demodulation method according to claim 5, characterized in that, In S4, the sampled received sequence r m (l) is specifically: where the frequency modulation slope μ = λ·BW 2 / M, and the initial frequency f0 = m·BW / M.

7. The skew keying-Chirp modulation and demodulation method according to claim 6, characterized in that, where e -j2πl = 1 8. The skew keying-Chirp modulation and demodulation method according to claim 5, characterized in that In S5, the de-chirped signal r′ m (l) is specifically: Among them, 9. The skew shift keying - Chirp modulation and demodulation method according to claim 5, wherein In S6, perform an M-point DFT operation on the de-chirped signal r′ m (l) to obtain R(q): where q = 0, 1, ..., M - 1, is Gaussian noise.

10. The skew shift keying - Chirp modulation and demodulation method according to claim 1, wherein In S7, Specifically:

11. The skew keying-Chirp modulation and demodulation method according to claim 1, characterized in that, In S8, the index Specifically:

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