CN114189254B - Ultra-low power consumption LoRa communication system and communication method based on single-frequency oscillator - Google Patents
Ultra-low power consumption LoRa communication system and communication method based on single-frequency oscillator Download PDFInfo
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Abstract
The invention provides an ultra-low power consumption LoRa communication system and method based on a single-frequency oscillator. During communication, the digital processor generates a corresponding LoRa baseband square wave signal according to the original data and is used as a control signal of the phase switching circuit; the single-frequency oscillating circuit generates a single-frequency signal with stable amplitude as an input of the phase switching circuit; and the phase switching circuit is used for switching the phase of the single-frequency signal output by the single-frequency oscillating circuit according to the high and low levels of the LoRa baseband square wave signal and outputting the single-frequency signal to an antenna. Compared with the traditional LoRa chip, the ultra-low power consumption LoRa communication system and the communication method provided by the invention have the advantages of low power consumption and low cost; compared with LoRa back scattering communication, the invention has the advantage of no need of a base station on the basis of keeping low power consumption and low cost.
Description
Technical Field
The invention relates to the field of electronic circuits, in particular to an ultra-low power consumption LoRa communication system and method based on a single-frequency oscillator.
Background
The LoRa adopts a spread spectrum modulation technology to realize high sensitivity, uses lower power consumption to realize long-distance wireless communication, and is suitable for long-distance, low-power consumption and low-rate application scenes of the Internet of things. In recent years, various groups are also laid out aiming at the LoRa industry, and a large number of industry applications of landing are developed in the vertical fields of smart cities, smart parks, smart buildings, smart security and the like, and the method has a very broad prospect. The existing LoRa communication technology is mainly divided into two types: the method adopts the traditional LoRa communication technology of Semtech SX1276/7/8/9 series chips, and adopts the LoRa back scattering communication technology proposed by Washington university in the United states.
According to the technical scheme shown in fig. 1, the conventional SX1276/7/8/9 serial chip integrates a radio frequency PLL, a multiplier and a DAC/ADC; in order to transmit the LoRa signal according to a certain power, a radio frequency analog circuit such as a VGA, a power amplifier and the like is also required to be integrated. Therefore, the LoRa chip has high cost (taking SX1278 as an example, the current selling price is 40-50@10pcs), and the power consumption is larger (20-125 mA).
In 2017, the university of washington computer scientists and electrical engineers in the united states have proposed a "remote back-scattering" LoRa communication system as shown in fig. 2, which achieves low power consumption, low cost LoRa data transmission by reflecting radio signals transmitted by base stations. In 2018, the seventh and ninth institute of middle ship group also proposed "passive LoRa" communication technology based thereon. This type of communication technology, while having cost and power consumption advantages, is not widely used because of the use of a backscatter communication mechanism, where a high-power base station must be additionally provided.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides an ultra-low power consumption LoRa communication system and a communication method based on a single-frequency oscillator.
According to a first aspect of the present invention, there is provided an ultra-low power consumption LoRa communication system based on a single frequency oscillator, comprising a digital processor, a single frequency oscillation circuit and a phase switching circuit; the digital processor is used for generating a corresponding LoRa baseband square wave signal according to the original data as a control signal of the phase switching circuit during communication; the single-frequency oscillating circuit is used for generating a single-frequency signal with stable amplitude and is used as the input of the phase switching circuit; the phase switching circuit is used for switching the phase of the single-frequency signal output by the single-frequency oscillating circuit according to the high and low levels of the LoRa baseband square wave signal and outputting the single-frequency signal to an antenna.
On the basis of the technical scheme, the invention can also make the following improvements.
Optionally, the single-frequency oscillation circuit includes a resistor R1, a resistor R2, a capacitor C1, a capacitor C2, a capacitor C3, a resonant inductor L1, a radio-frequency transistor Q1, and an XTAL1; an output end of the digital processor is connected with an enabling end of a resistor R2, the other end of the resistor R2 is electrically connected with a base electrode of the radio frequency transistor Q1 and grounded through the XTAL1, an emitter electrode of the radio frequency transistor Q1 is grounded through a capacitor C1 and the resistor R1 respectively, a collector electrode of the radio frequency transistor Q1 is electrically connected with a first end of a capacitor C3, a second end of the capacitor C3 is electrically connected with the phase switching circuit, the first end of the capacitor C3 is also grounded through a resonant inductor L1 and a capacitor C2, and a common termination power supply VCC of the resonant inductor L1 and the capacitor C2 is realized.
Optionally, the XTAL1 is a quartz crystal or a SAW resonator/filter, and the frequency of the XTAL1 is determined according to the LoRa communication frequency band; the rf transistor Q1 is model BFT15A.
Optionally, the phase switching circuit includes a radio frequency switching device and a signal delay device, the radio frequency switching device is a double pole double throw switch, the signal delay device is a λ/2 transmission line or a multistage LC equivalent circuit, the digital processor outputs the generated LoRa baseband square wave signal to the radio frequency switching device, the single frequency oscillating circuit outputs a single frequency signal with stable amplitude to the radio frequency switching device through the second end of the capacitor C3, and the signal delay device is connected to the radio frequency switching device to form a loop.
According to a second aspect of the present invention, there is provided an ultra-low power consumption LoRa communication method based on a single frequency oscillator, comprising: the LoRa communication system comprises a digital processor, a single-frequency oscillation circuit and a phase switching circuit, and the LoRa communication method comprises the following steps: during communication, the digital processor generates a corresponding LoRa baseband square wave signal according to the original data and is used as a control signal of the phase switching circuit; the single-frequency oscillating circuit generates a single-frequency signal with stable amplitude as an input of the phase switching circuit; and the phase switching circuit is used for switching the phase of the single-frequency signal output by the single-frequency oscillating circuit according to the high and low levels of the LoRa baseband square wave signal and outputting the single-frequency signal to an antenna.
Optionally, the digital processor generates a corresponding LoRa baseband square wave signal according to the original data, including: according to the direct digital frequency synthesis DDS principle, a fixed chirped spread spectrum CSS square wave sequence is obtained by Matlab calculation, the CSS square wave sequence comprises all components of a LoRa lead code, a synchronous symbol, down-chirping and symbol data, and a complete LoRa baseband square wave signal is synthesized by intercepting different fragments of the CSS square wave sequence.
Optionally, the digital processor generates a corresponding LoRa baseband square wave signal according to the original data, including: obtaining N symbol values N through data scrambling, coding and interleaving 0 ……N n-1 And calculates the total number of symbols Num to be transmitted sym =n+13; calculating the address offset Addr of each symbol value offset [i]And the number of DMA bits Num for each symbol value DMAbit [i]. Addr is added with offset [0]Load the source address of DMA while simultaneously saving Num DMAbit [0]Loading a DMA counter, starting DMA transmission, and entering a low power consumption mode; immediately after each DMA transfer is completed, the Addr of the next symbol is automatically loaded offset [i]And Num DMAbit [i]Until all symbols have been output.
Optionally, the calculating calculates an address offset Addr of each symbol value offset [i]And the number of DMA bits Num for each symbol value DMAbit [i]Comprising: when the CSS waveform with the symbol value of N needs to be output, the current pointer is increased by P multiplied by N/2 on the basis of the base address SF The offset of the bits, the CSS waveform when the LoRa preamble is n=0, the address offset corresponding to the down-chirp is 2×p, and the address offset of each symbol is:
where P is the number of bits required per symbol value period, SF is the spreading factor, taking into account that the down-chirp occupies 2 1 / 4 The number of DMA transfer bits per symbol value is:
optionally, the frequency of the single-frequency signal generated by the single-frequency oscillating circuit is f osc The center frequency of the LoRa baseband square wave signal generated by the digital processing device is f B The phase switching circuit outputs a center frequencyIs f LoRa ＝f osc +f B Is of the LoRa signal and center frequency f Interference ＝f osc －f B Is a good signal for the interference of the image of the LoRa signal.
The ultra-low power consumption LoRa communication system and the communication method based on the single frequency oscillator, provided by the invention, are mainly composed of a low power consumption digital processing device, the low power consumption single frequency oscillator and a phase switching circuit, and have the advantages of low power consumption and low cost compared with the traditional LoRa chip; compared with LoRa back scattering communication, the invention has the advantage of no need of a base station on the basis of keeping low power consumption and low cost.
Drawings
Fig. 1 is a schematic diagram of an internal system structure of a LoRa communication chip in prior art 1;
FIG. 2 is a schematic diagram of the LoRa communication system of prior art 2;
FIG. 3 is a schematic diagram of an ultra-low power consumption LoRa communication system based on a single frequency oscillator according to the present invention;
FIG. 4 is a schematic diagram of the synthesis of LoRa baseband signals by a digital processor such as MCU;
FIG. 5 is a flow chart of outputting LoRa baseband signals by digital processing devices such as low-power consumption MCU;
FIG. 6 is a schematic diagram of a specific circuit of an ultra-low power consumption LoRa communication system based on a single frequency oscillator according to the present invention;
fig. 7-1 is a schematic diagram of an output signal of a single-frequency oscillating circuit and a frequency spectrum thereof, fig. 7-2 is a schematic diagram of a control signal of a phase switching circuit and a frequency spectrum thereof, and fig. 7-3 is a schematic diagram of an output signal of a phase switching circuit and a frequency spectrum thereof.
Detailed Description
The following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples are illustrative of the invention and are not intended to limit the scope of the invention.
Based on the defects in the background technology, the invention provides an ultra-low power consumption LoRa communication system based on an oscillator, which is unnecessary to be matched with a base station on the basis of keeping low power consumption and low costThe LoRa data transmission can be realized. The ultra-low power consumption LoRa communication system mainly comprises three parts: a digital processor (for example, MCU), a single frequency oscillating circuit, and a phase switching circuit, as shown in fig. 3. Wherein the single-frequency oscillating circuit is used for generating a single-frequency signal with stable amplitude and the frequency is f osc . When the digital processors such as MCU and the like are in communication, corresponding LoRa baseband square waves are generated according to the original data, and the center frequency is f B . The phase switching circuit switches the phase (0 or pi) of the single-frequency signal output by the oscillating circuit according to the high and low levels of the LoRa baseband square wave, and outputs the single-frequency signal to the antenna.
Specifically, the digital processor such as MCU calculates a fixed CSS square wave sequence according to the direct digital frequency synthesis principle by using Matlab, where the CSS square wave sequence includes two up-chirps and one down-chirp, as shown in fig. 4. And then, the CSS square wave sequence is written into a memory of a digital processing device such as a low-power MCU. Because the CSS square wave sequence contains all elements of the LoRa lead code, the synchronous symbol, the down-chirp and the symbol data CSS waveform, the complete LoRa baseband square wave signal can be synthesized by cutting different fragments. The detailed flow of the LoRa baseband square wave signal synthesis scheme can be seen in fig. 5, and mainly comprises the following steps:
(1) the method comprises the steps of firstly, sequentially carrying out scrambling, error correction coding, anti-interference interleaving and Gray coding on original data by using resources such as computation, logic, peripheral (mainly DMA, SPI) and the like of digital processing devices such as low-power consumption MCU and the like to obtain N symbol values N 0 ……N n-1 And calculates the total number of symbols Num to be transmitted sym =n+13 (for example, a preamble of 8 symbols length).
(2) When the CSS waveform with the symbol value of N needs to be output, the current pointer is only increased by P multiplied by N/2 on the basis of the base address SF The offset of the bits is sufficient. While the LoRa preamble may be considered as a CSS waveform when n=0. In addition, the address offset corresponding to the down-chirp is 2×p. The address offset for each symbol is:
where P is the number of bits required for each symbol period and SF is the spreading factor. Considering that the down-chirp occupies 2 1 / 4 A symbol period, the number of DMA transfer bits per symbol unit is therefore:
(3) addr is added with offset [0]Load the source address of DMA while simultaneously saving Num DMAbit [0]The DMA counter is loaded. DMA transfer is then initiated and a low power mode is entered. Immediately after each DMA transfer is completed, the Addr of the next symbol is automatically loaded offset [i]And Num DMAbit [i]The whole flow is shown in fig. 5 until all symbols have been output.
The single-frequency oscillation circuit can be a low-power-consumption phase-locked loop (PLL) integrated circuit (chip) or a low-power-consumption single-frequency oscillation circuit based on discrete devices such as a transistor/MOS tube, a SAW resonator/a filter/a quartz crystal and the like, and is used for generating a radio frequency carrier signal with stable amplitude and single frequency, has low power consumption characteristics and has high direct current-radio frequency energy conversion efficiency as much as possible. Taking a crystal oscillation circuit/SAW surface acoustic wave resonant circuit as an example, the invention can adopt a b-e type circuit (also called Miller circuit) in the circuit form, as shown in figure 6.
As shown in fig. 6, the single-frequency oscillation circuit includes a resistor R1, a resistor R2, a capacitor C1, a capacitor C2, a capacitor C3, a resonant inductance L1, a radio-frequency transistor Q1, and XTAL1.
An output end of the digital processor is connected with an enabling end of a resistor R2, the other end of the resistor R2 is electrically connected with a base electrode of the radio frequency transistor Q1 and is grounded through the XTAL1, an emitter electrode of the radio frequency transistor Q1 is grounded through a capacitor C1 and the resistor R1 respectively, a collector electrode of the radio frequency transistor Q1 is electrically connected with a first end of a capacitor C3, a second end of the capacitor C3 is electrically connected with the phase switching circuit, the first end of the capacitor C3 is also grounded through a resonant inductor L1 and a capacitor C2, and a common termination power supply VCC of the resonant inductor L1 and the capacitor C2 is realized.
XTAL1 is a quartz crystal or SAW resonator/filter, whose frequency is mainly determined according to the LoRa communication frequency band, such as 315M band, 433M band, 470M band, 868M band, 915M band, etc. Q1 is a low-power-consumption radio-frequency transistor or a radio-frequency MOS transistor, and in the embodiment, Q1 is a radio-frequency transistor, and the model of the radio-frequency transistor is BFT15A. L1 is collector resonance inductance, R1 is emitter resistance, R2 is base resistance, C1 is emitter capacitance, C2 is power decoupling capacitance, and C3 is output coupling capacitance. EN is the enable, defaults to low to turn off the tank circuit to save power, and is only high during the LoRa communication.
The phase switching circuit comprises a radio frequency switching device and a signal delay device, the radio frequency switching device is a double-pole double-throw switch, the signal delay device is a lambda/2 transmission line or a multistage LC equivalent circuit, the digital processor outputs the generated LoRa baseband square wave signal to the radio frequency switching device, the single-frequency oscillating circuit outputs a single-frequency signal with stable amplitude to the radio frequency switching device through a second end of the capacitor C3, and the signal delay device is connected with the radio frequency switching device to form a loop.
Specifically, the phase switching circuit is used for changing the phase of the radio frequency carrier signal output by the single frequency oscillating circuit, so that the phase switching circuit can realize phase switching between 0 and pi according to the control signal. To achieve this function, a "radio frequency switching device+signal delay device" scheme may be employed, as shown in fig. 6. The radio frequency switch adopts ADG936 series of double pole double throw type, or can be combined by a plurality of single pole type switches. The signal delay device adopts a lambda/2 transmission line, and can be replaced by a multistage LC equivalent circuit.
The signal input to the phase switching circuit is the carrier wave of the oscillator (frequency f osc ) The control input is a LoRa baseband square wave (center frequency of fundamental frequency is f B ). When higher harmonics are ignored, the output is a LoRa signal (center frequency f LoRa ＝f osc +f B ) And image-disturbed LoRa signal (center frequency f Interference ＝f osc －f B ). The waveform of each signalFig. 7 shows a schematic spectrum diagram of waveforms and schematic spectrums corresponding to different points in fig. 7, specifically, fig. 7-1 shows an output signal of a single-frequency oscillating circuit and a schematic spectrum diagram thereof, fig. 7-2 shows a control signal of a phase switching circuit and a schematic spectrum diagram thereof, and fig. 7-3 shows an output signal of a phase switching circuit and a schematic spectrum diagram thereof.
The ultra-low power consumption LoRa communication system of the embodiment of the invention mainly comprises a low power consumption digital processing device, a low power consumption single-frequency oscillator and a phase switching circuit, wherein a method for synthesizing a complete LoRa baseband square wave signal by intercepting fragments of a specific CSS square wave sequence is provided based on the low power consumption digital processing device such as MCU; the low-power consumption single-frequency oscillator adopts a quartz crystal/SAW resonant circuit and outputs a single-frequency carrier wave with stable amplitude; the phase switching circuit controls the transmission delay of the carrier wave through the radio frequency switch to realize the switching of phases 0 and pi.
Compared with the prior art, the method has the advantages that:
1) The power consumption is low, and the total current consumption of the LoRa communication system provided by the invention is less than or equal to 200 mu A under the condition of 2V power supply, and is two orders of magnitude lower than that of a traditional LoRa chip.
2) The LoRa communication system provided by the invention mainly adopts an inexpensive crystal/SAW resonator and a radio frequency switch, and the cost is only 1/3-1/4 of that of a traditional LoRa chip.
3) Compared with the LoRa communication technology based on back scattering, the method provided by the invention can realize LoRa communication without additional base stations.
In the foregoing embodiments, the descriptions of the embodiments are focused on, and for those portions of one embodiment that are not described in detail, reference may be made to the related descriptions of other embodiments.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (8)
1. An ultra-low power consumption LoRa communication system based on a single-frequency oscillator is characterized by comprising a digital processor, a single-frequency oscillation circuit and a phase switching circuit;
the digital processor is used for generating a corresponding LoRa baseband square wave signal according to original data during communication, and comprises utilizing Matlab to calculate and obtain a fixed chirped spread spectrum CSS square wave sequence according to a direct digital frequency synthesis DDS principle, wherein the CSS square wave sequence comprises all components of a LoRa lead code, a synchronous symbol, down-chirping and symbol data, and a complete LoRa baseband square wave signal is synthesized by intercepting different segments of the CSS square wave sequence; the LoRa baseband square wave signal is used as a control signal of the phase switching circuit, and the digital processor is a low-power consumption MCU;
the single-frequency oscillating circuit is used for generating a single-frequency signal with stable amplitude and is used as the input of the phase switching circuit;
the phase switching circuit is used for switching the phase of the single-frequency signal output by the single-frequency oscillating circuit according to the high and low levels of the LoRa baseband square wave signal and outputting the single-frequency signal to an antenna.
2. The LoRa communication system of claim 1, wherein the single frequency oscillating circuit comprises a resistor R1, a resistor R2, a capacitor C1, a capacitor C2, a capacitor C3, a resonant inductance L1, a radio frequency transistor Q1 and XTAL1;
an output end of the digital processor is connected with an enabling end of a resistor R2, the other end of the resistor R2 is electrically connected with a base electrode of the radio frequency transistor Q1 and grounded through the XTAL1, an emitter electrode of the radio frequency transistor Q1 is grounded through a capacitor C1 and the resistor R1 respectively, a collector electrode of the radio frequency transistor Q1 is electrically connected with a first end of a capacitor C3, a second end of the capacitor C3 is electrically connected with the phase switching circuit, the first end of the capacitor C3 is also grounded through a resonant inductor L1 and a capacitor C2, and a common termination power supply VCC of the resonant inductor L1 and the capacitor C2 is realized.
3. The LoRa communication system of claim 2, wherein the XTAL1 is a quartz crystal or a SAW resonator/filter having a frequency determined according to the LoRa communication band; the rf transistor Q1 is model BFT15A.
4. The LoRa communication system of claim 2, wherein the phase switching circuit comprises a radio frequency switching device and a signal delay device, the radio frequency switching device is a double pole double throw switch, the signal delay device is a λ/2 transmission line or a multistage LC equivalent circuit, the digital processor outputs the generated LoRa baseband square wave signal to the radio frequency switching device, and the single frequency oscillating circuit outputs a single frequency signal with stable amplitude to the radio frequency switching device through the second end of the capacitor C3, and the signal delay device is connected to the radio frequency switching device to form a loop.
5. The utility model provides a loRa communication method of ultra-low power consumption loRa communication system based on single frequency oscillator, its characterized in that, loRa communication system includes digital processor, single frequency oscillation circuit and phase switching circuit, digital processor is low-power consumption MCU, and the loRa communication method includes:
during communication, the digital processor generates a corresponding LoRa baseband square wave signal according to original data, the method comprises the steps of synthesizing a DDS (direct digital synthesis) principle according to direct digital frequency, calculating by utilizing Matlab to obtain a fixed chirped spread spectrum CSS square wave sequence, wherein the CSS square wave sequence comprises all components of a LoRa lead code, a synchronous symbol, down-chirping and symbol data, and synthesizing a complete LoRa baseband square wave signal by intercepting different segments of the CSS square wave sequence; the LoRa baseband square wave signal is used as a control signal of the phase switching circuit;
the single-frequency oscillating circuit generates a single-frequency signal with stable amplitude as an input of the phase switching circuit;
and the phase switching circuit is used for switching the phase of the single-frequency signal output by the single-frequency oscillating circuit according to the high and low levels of the LoRa baseband square wave signal and outputting the single-frequency signal to an antenna.
6. The method of claim 5, wherein the digital processor generating a corresponding LoRa baseband square wave signal from raw data, comprising:
obtaining N symbol values N through data scrambling, coding and interleaving 0 ……N n-1 And calculates the total number of symbols Num to be transmitted sym ＝n+13；
Calculating the address offset Addr of each symbol value offset [i]And the number of DMA bits Num for each symbol value DMAbit [i]；
Addr is added with offset [0]Load the source address of DMA while simultaneously saving Num DMAbit [0]Loading a DMA counter, starting DMA transmission, and entering a low power consumption mode;
immediately after each DMA transfer is completed, the Addr of the next symbol is automatically loaded offset [i]And Num DMAbit [i]Until all symbols have been output.
7. The method of claim 6, wherein the calculating the address offset Addr for each symbol value offset [i]And the number of DMA bits Num for each symbol value DMAbit [i]Comprising:
when the CSS waveform with the symbol value of N needs to be output, the current pointer is increased by P multiplied by N/2 on the basis of the base address SF The offset of the bits, the CSS waveform when the LoRa preamble is n=0, the address offset corresponding to the down-chirp is 2×p, and the address offset of each symbol is:
wherein P is the number of bits required for each symbol value period and SF is spreadSpreading factor, taking into account that the down-chirp occupies 2 1 / 4 The number of DMA transfer bits per symbol value is:
8. the method of claim 5, wherein the single frequency signal generated by the single frequency oscillating circuit has a frequency f osc The center frequency of the LoRa baseband square wave signal generated by the digital processing device is f B The output center frequency of the phase switching circuit is f LoRa ＝f osc +f B Is of the LoRa signal and center frequency f Interference ＝f osc －f B Is a good signal for the interference of the image of the LoRa signal.
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