Multi-mode scattering communication system compatible with LoRa
阅读说明：本技术 兼容LoRa的多模式散射通信系统 (Multi-mode scattering communication system compatible with LoRa ) 是由 佘亚军 唐晓庆 张帅 张超 谢桂辉 于 2018-11-16 设计创作，主要内容包括：本发明提出了兼容LoRa的多模式散射通信系统,能够在同一个数字系统上实现多种散射通信体制,形成了多模式散射通信的通用架构。因此,本发明比背景技术方案更加通用、灵活、可重配置、兼容性高。本发明的方案一仅通过更换天线、更改数字基带处理器软件配置即可实现不同模式下的散射通信。本发明的方案二可实现相互独立通道的多模式散射通信,而且在不发生信道阻塞的情况下,多个通道可以同时通信。本发明的方案三,能够以分时复用的方式,实现多频天线所覆盖频段内的多种模式的散射通信。(The invention provides a LoRa-compatible multi-mode scattering communication system, which can realize various scattering communication systems on the same digital system and form a general framework of multi-mode scattering communication. Therefore, compared with the technical scheme of the background, the invention is more universal, flexible, reconfigurable and high in compatibility. According to the scheme of the invention, the scattering communication under different modes can be realized only by replacing the antenna and changing the software configuration of the digital baseband processor. The second scheme of the invention can realize the multi-mode scatter communication of mutually independent channels, and a plurality of channels can simultaneously communicate under the condition of no channel blockage. According to the third scheme, the multi-mode scattering communication in the frequency band covered by the multi-frequency antenna can be realized in a time-sharing multiplexing mode.)
1. A LoRa-compliant multimode scattering communication system, comprising:
a digital baseband processor;
m single-band antennas, wherein each single-band antenna corresponds to one or more communication modes, K communication modes are shared, K and M are integers greater than or equal to 2, and K is greater than or equal to M; the K communication modes comprise LoRa scattering communication;
the hardware matching component comprises an input connecting end and K output connecting ends, wherein the K output connecting ends are connected with the K single-band antennas in a one-to-one mode and used for selectively communicating one single-band antenna with the input connecting end under the control of a control signal;
the radio frequency switch is connected with the input connecting end through one switch connecting end, and the other switch connecting end is grounded through a matched impedance;
the digital baseband processor comprises the following modules which are realized by software or hardware:
the input controlled switch module and the output controlled switch module;
the data processing module is used for processing the data to be processed by adopting the corresponding communication mode, and finally generating a scattering modulation waveform for driving the radio frequency switch;
the communication mode selection module is respectively connected with each input controlled switch module and each output controlled switch module so as to control the synchronous conduction of the input controlled switch module and the output controlled switch module of one data processing module at a time and the non-conduction of the other input controlled switch modules;
the data processing module of the LoRa scattering communication is used for carrying out Whitening scrambling, Hamming error correction coding, Interleaving and De-Gray coding on a LoRa data frame in a programming or digital logic circuit mode according to a LoRa protocol specification to obtain a Symbol of CSS linear frequency modulation, and then carrying out CSS linear modulation on the obtained Symbol by adopting DDS direct digital frequency synthesis to obtain a digital square wave signal and serially transmitting the digital square wave signal to the radio frequency switch; the radio frequency switch is used for controlling the on-off state of the radio frequency switch according to the digital square wave signal so as to send out the signal.
2. A LoRa-compliant multimode scattering communication system, comprising:
a digital baseband processor;
m single-band antennas, wherein each single-band antenna corresponds to one or more communication modes, K communication modes are shared, K and M are integers greater than or equal to 2, and K is greater than or equal to M; the K communication modes comprise LoRa scattering communication;
one switch connecting end of each radio frequency switch is connected with a single-frequency-band antenna, and the other switch connecting end is grounded through a matched impedance;
the digital baseband processing contains the following modules which are realized by software or hardware:
the data processing module is used for processing data to be processed by adopting the corresponding communication mode and finally generating a scattering modulation waveform for driving the radio frequency switch;
the communication mode selection module is respectively connected with each input controlled switch module so as to control the on-off of the input controlled switch modules of one or more data processing modules each time;
the data processing module of the LoRa scattering communication is used for carrying out Whitening scrambling, Hamming error correction coding, Interleaving and De-Gray coding on a LoRa data frame in a programming or digital logic circuit mode according to a LoRa protocol specification to obtain a Symbol of CSS linear frequency modulation, and then carrying out CSS linear modulation on the obtained Symbol by adopting DDS direct digital frequency synthesis to obtain a digital square wave signal and serially transmitting the digital square wave signal to the radio frequency switch; the radio frequency switch is used for controlling the on-off state of the radio frequency switch according to the digital square wave signal so as to send out the signal.
3. A LoRa-compliant multimode scattering communication system, comprising:
a digital baseband processor;
the multi-band antenna meets the frequency band requirements of K communication modes, wherein K is an integer greater than or equal to 2; the corresponding K communication modes comprise LoRa scattering communication;
the radio frequency switch is characterized in that one switch connecting end of the radio frequency switch is connected with the multi-band antenna, and the other switch connecting end of the radio frequency switch is grounded through a matched impedance;
the digital baseband processing contains the following modules which are realized by software:
the data processing module is used for processing the data to be processed by adopting the corresponding communication mode, and finally generating a scattering modulation waveform for driving the radio frequency switch;
the communication mode selection module is respectively connected with each input controlled switch module and each output controlled switch module so as to control the synchronous conduction of the input controlled switch module and the output controlled switch module of one or more data processing modules at each time;
the data processing module of the LoRa scattering communication is used for carrying out Whitening scrambling, Hamming error correction coding, Interleaving and De-Gray coding on a LoRa data frame in a programming or digital logic circuit mode according to a LoRa protocol specification to obtain a Symbol of CSS linear frequency modulation, and then carrying out CSS linear modulation on the obtained Symbol by adopting DDS direct digital frequency synthesis to obtain a digital square wave signal and serially transmitting the digital square wave signal to the radio frequency switch; the radio frequency switch is used for controlling the on-off state of the radio frequency switch according to the digital square wave signal so as to send out the signal.
4. A LoRa-compatible multi-mode scattering communications system as claimed in claim 3, wherein each data processing module time-multiplexes the multi-band antenna.
5. The LoRa-compatible multi-mode scatterometry communication system of any of claims 1-3, wherein the digital baseband processor is any one or combination of MCU, FPGA and ASIC.
6. The LoRa-compliant multimode scattering communication system of any of claims 1-3, wherein the K communication modes further comprise: WiFi scatter communication, Bluetooth scatter communication and Zigbee scatter communication.
7. The LoRa-compatible multi-mode scattercommunications system of claim 4, in which Bluetooth scattercommunications and WiFi scattercommunications share an antenna and are time division multiplexed.
8. The LoRa-compatible multi-mode scattering communication system according to any one of claims 1-3, wherein the data processing of each data processing module for processing data to be processed in the corresponding communication mode, and the data processing for generating the scattering modulation waveform finally comprises: data encoding, baseband and modulation.
Technical Field
The present invention relates to the field of scattercommunications, and more particularly to a LoRa-compatible multi-mode scattercommunications system.
Background
A Passive WiFi scattering communication technology is proposed in a paper of Brissing Low Power to Wi-Fi Transmissions by Bryce Kellogg et al at the university of Washington, early 2017; in The
In 2018, the dawn celebration et al, seventh and ninth research institute of China ship re-engineering group corporation, proposed a passive WiFi scattering communication method and system based on MCU microprocessor and a LoRa scattering communication method and system based on DDS direct digital frequency synthesis. The schemes are simple and easy to implement, can be realized only in a digital domain, and can respectively realize the development and design of a WiFi scattering communication system and a LoRa scattering communication system on a low-cost MCU.
It can be seen that each communication system of the background art only supports a specific communication system (WiFi or LoRa), and therefore has a drawback of single communication mode.
Disclosure of Invention
The technical problem to be solved by the invention is to provide various compatible LoRa multi-mode scattering communication systems aiming at the technical defect that each communication system in the prior art has a single communication mode, so that various scattering communication systems can be realized on the same digital system, and a general framework of multi-mode scattering communication is formed.
In order to solve the technical problem, the invention adopts the following technical scheme: there is provided a LoRa compatible multi-mode scattering communication system, comprising:
a digital baseband processor;
m single-band antennas, wherein each single-band antenna corresponds to one or more communication modes, K communication modes are shared, K and M are integers greater than or equal to 2, and K is greater than or equal to M; the K communication modes comprise LoRa scattering communication and/or WiFi scattering communication;
the hardware matching component comprises an input connecting end and K output connecting ends, wherein the K output connecting ends are connected with the K single-band antennas in a one-to-one mode and used for selectively communicating one single-band antenna with the input connecting end under the control of a control signal;
the radio frequency switch is connected with the input connecting end through one switch connecting end, and the other switch connecting end is grounded through a matched impedance;
the digital baseband processor comprises the following modules which are realized by software or hardware:
the input controlled switch module and the output controlled switch module;
the data processing module is used for processing the data to be processed by adopting the corresponding communication mode, and finally generating a scattering modulation waveform for driving the radio frequency switch;
and the communication mode selection module is respectively connected with each input controlled switch module and each output controlled switch module so as to control the synchronous conduction of the input controlled switch module and the output controlled switch module of one data processing module at a time and the non-conduction of the other input controlled switch modules.
In order to solve the technical problem, the invention adopts the following technical scheme: there is provided a LoRa compatible multi-mode scattering communication system, comprising:
a digital baseband processor;
m single-band antennas, wherein each single-band antenna corresponds to one or more communication modes, K communication modes are shared, K and M are integers greater than or equal to 2, and K is greater than or equal to M; the K communication modes comprise LoRa scattering communication and/or WiFi scattering communication;
one switch connecting end of each radio frequency switch is connected with a single-frequency-band antenna, and the other switch connecting end is grounded through a matched impedance;
the digital baseband processing contains the following modules which are realized by software or hardware:
the data processing module is used for processing data to be processed by adopting the corresponding communication mode and finally generating a scattering modulation waveform for driving the radio frequency switch;
and the communication mode selection module is respectively connected with each input controlled switch module so as to control the on-off of the input controlled switch modules of one or more data processing modules at each time.
In order to solve the technical problem, the invention adopts the following technical scheme: there is provided a WiFi and/or LoRa compatible multi-mode scatterometry communication system, comprising:
a digital baseband processor;
the multi-band antenna meets the frequency band requirements of K communication modes, wherein K is an integer greater than or equal to 2; the corresponding K communication modes comprise LoRa scattering communication and/or WiFi scattering communication;
the radio frequency switch is characterized in that one switch connecting end of the radio frequency switch is connected with the multi-band antenna, and the other switch connecting end of the radio frequency switch is grounded through a matched impedance;
the digital baseband processing contains the following modules which are realized by software:
the data processing module is used for processing the data to be processed by adopting the corresponding communication mode, and finally generating a scattering modulation waveform for driving the radio frequency switch;
and the communication mode selection module is respectively connected with each input controlled switch module and each output controlled switch module so as to control the synchronous conduction of the input controlled switch module and the output controlled switch module of one or more data processing modules at each time.
Further, in the LoRa-compatible multimode scattering communication system, each data processing module time-multiplexes the multiband antenna.
Further, in the LoRa-compatible multimode scattering communication system of the present invention, the digital baseband processor is any one or a combination of MCU, FPGA and ASIC.
Further, in the LoRa-compatible multimode scattering communication system of the present invention, the K communication modes further include: bluetooth scatter communication and Zigbee scatter communication.
Further, in the LoRa-compatible multimode scattering communication system of the present invention, the K communication modes further include: bluetooth scattering communication and Zigbee scattering communication; the Bluetooth scattering communication and the WiFi scattering communication share one antenna, and the Bluetooth scattering communication and the WiFi scattering communication are multiplexed in a time-sharing mode.
Further, in the LoRa-compatible multi-mode scattering communication system of the present invention, each data processing module performs data processing on data to be processed in a corresponding communication mode, and the data processing for finally generating a scattering modulation waveform includes: data encoding, baseband and modulation.
Further, in the LoRa-compatible multimode scattercommunications system of the present invention, the WiFi scattercommunications method comprises the steps of:
s1, encapsulating wifi data to be sent into MPDUs, adding PLCP frame headers and PLCP lead codes, and encapsulating into PPDUs;
s2, calculating and filling length information according to the formed PPDU, CRC check of PLCP, and FCS frame check information;
s3, scrambling the PPDU processed in the step S2 according to a scrambling polynomial specified by IEEE802.11b standard;
s4, carrying out parallel/serial conversion on the scrambled PPDU to convert the byte information into bit information and carrying out differential code conversion;
s5, spreading the obtained differential bit information according to the spreading sequence specified in the ieee802.11b standard, wherein 11 chip bits are obtained after spreading 1 differential bit;
s6, modulating and transmitting data by the method of S61 or S62;
s61, modulating the chip bit information by adopting a digital virtual DBPSK modulation method, storing the sequence bits modulated by the digital virtual DBPSK in a data storage space processed by a digital baseband, finally transmitting the bit information by utilizing a serial communication interface processed by the digital baseband, and switching the absorption/reflection state of an antenna by controlling a radio frequency electronic switch device so as to transmit the data to be transmitted in a scattering communication mode;
s62, a logic circuit is connected between the radio frequency electronic switch device and the digital baseband processing, a serial communication interface of the digital baseband processing directly outputs 11Mbps chip bit as a first input of the logic circuit, a clock signal with frequency greater than 11MHz is used as a second input of the logic circuit, the output of the logic circuit is used as a modulation result of DBPSK and directly used for driving the radio frequency electronic switch device to switch the absorption/reflection state of an antenna, and therefore data to be transmitted are subjected to scatter communication in a mode conforming to the IEEE802.11b standard;
wherein, the steps S1, S2, S3, S4, S5 and S61 are located in the digital baseband processor.
Further, in the loRa multimode scattering communication system of the invention, the data processing module of the loRa scattering communication is used for performing Whitening scrambling, Hamming error correction coding, Interleaving and De-Gray coding on a loRa data frame in a programming or digital logic circuit mode according to a loRa protocol specification to obtain a Symbol of CSS linear frequency modulation, and then performing CSS linear modulation on the obtained Symbol by adopting DDS direct digital frequency synthesis to obtain a digital square wave signal and serially transmitting the digital square wave signal to the radio frequency switch; the radio frequency switch is used for controlling the on-off state of the radio frequency switch according to the digital square wave signal so as to send out the signal.
The LoRa-compatible multimode scattering communication system has the following beneficial effects: the invention provides a LoRa-compatible multi-mode scattering communication system, which can realize multiple scattering communication systems on the same digital system and form a general framework of multi-mode scattering communication. Compared with the prior art, the method has the advantages that: compared with the background technical scheme, the method is more universal, flexible, reconfigurable and high in compatibility. The invention provides a scheme I: the single frequency band scattering communication scheme of antenna matching can realize scattering communication under different modes only by replacing the antenna and changing the software configuration of the digital baseband processor. The invention provides a scheme II: the multi-antenna and multi-mode scattering communication scheme' can realize the multi-mode scattering communication of mutually independent channels, and a plurality of channels can simultaneously communicate under the condition of no channel blockage. The invention provides a scheme III: the multi-band antenna and the multi-mode scattering communication scheme can realize the scattering communication of multiple modes covered by the frequency band of the antenna in a time division multiplexing mode.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic diagram of a first embodiment of a system for WiFi and/or LoRa compliant multi-mode scatter communication;
FIG. 2 is a schematic diagram of a second embodiment of a system for WiFi and/or LoRa compliant multi-mode scatter communication;
FIG. 3 is a schematic diagram of a third embodiment of a system for WiFi and/or LoRa compliant multi-mode scatter communication;
FIG. 4 is a schematic diagram of a fourth embodiment of a system for WiFi and/or LoRa compliant multi-mode scatter communication;
FIG. 5 is a schematic diagram of the WiFi scattering communication method based on the MCU microprocessor of the present invention;
FIG. 6 is a schematic diagram of the data encapsulation of the present invention;
FIG. 7 is a schematic diagram of a data scrambler of the present invention;
FIG. 8 is a differential code conversion diagram of the present invention;
fig. 9 is a schematic diagram of chip bit information modulated using a digital virtual DBPSK modulation method;
FIG. 10 is a schematic diagram of another embodiment of a WiFi scatter communication method based on an MCU microprocessor of the present invention;
FIG. 11 is a schematic illustration of the modulation process of the embodiment of FIG. 10 of the present invention;
FIG. 12 is a schematic diagram of the LoRa scatter communication of the present invention;
fig. 13 is a graph showing a frequency change law of a CCS linear tone modulation waveform when SF is 2.
Detailed Description
For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
The invention provides a WiFi and/or LoRa compatible multi-mode scattering communication system, which is shown in figure 1. Firstly, a base station generates a single-frequency signal of a frequency band covered by a plurality of communication modes, and radiates the single-frequency electromagnetic signal to the surrounding space through an antenna. The scattering communication system encodes data to be transmitted according to a corresponding communication protocol, forms a baseband, outputs a digital modulation waveform, changes the reflection/absorption state of an antenna of the scattering communication system by driving a radio frequency switching device, thereby forming different types of communication data packets, and is finally received, demodulated and decoded by communication receivers in various modes.
The multi-mode scattering communication system provided by the invention is simple in composition, multi-mode scattering communication can be realized only by a digital baseband processor (which can be an MCU, an FPGA or an ASIC), a radio frequency switch, an antenna and a matching circuit thereof, and three common combination schemes are adopted:
referring to fig. 2, the WiFi and/or LoRa compatible multimode scattering communication system of the present embodiment includes: the antenna comprises a digital baseband processor, M single-band antennas, a hardware matching component, 1 radio frequency switch and 1 matching impedance.
Each single-frequency-band antenna corresponds to one or more communication modes, K communication modes are shared, K and M are integers greater than or equal to 2, and K is greater than or equal to M; the K communication modes include LoRa scattering communication, Zigbee scattering communication, Bluetooth scattering communication, and WiFi scattering communication, and the Zigbee scattering communication and the Bluetooth scattering communication share one antenna, and are time-division multiplexed with each other.
The hardware matching part comprises an input connecting end and K output connecting ends, and the K selection output ends are connected with the K single-band antennas in a one-to-one mode. The hardware matching component can be a hardware matching controlled switch and is used for selectively communicating a single-frequency-band antenna with the input connecting end under the control of a control signal; the hardware matching part can also be a socket, and when the antenna is selected to be used, the antenna is manually connected to the socket.
The radio frequency switch is connected with the input connecting end through one switch connecting end, and the other switch connecting end is grounded through a matched impedance; the matching impedance is matched to the antenna to effectively transmit the signal.
The digital baseband processing contains the following modules which are realized by software or hardware:
the data processing module is used for processing the data to be processed by adopting the corresponding communication mode, and finally generating a scattering modulation waveform for driving the radio frequency switch; the data processing comprises the processes of data coding, baseband, modulation and the like, and finally generates and outputs a path of scattering modulation waveform for driving an external radio frequency switching device;
and the communication mode selection module is respectively connected with each input controlled switch module and each output controlled switch module so as to control the synchronous conduction of the input controlled switch module and the output controlled switch module of one data processing module at a time and the non-conduction of the other input controlled switch modules.
It should be understood that, in this embodiment, the input controlled switch module, the data processing module, the communication mode selection module, and the output controlled switch module may be implemented by software of digital baseband processing, that is, by software programming, in other embodiments of the present invention, they may also be implemented by hardware in the digital baseband processor, for example, hardware logic circuits, for example, FGPA may be implemented by built-in hardware, and in still other embodiments of the present invention, they may also be implemented by a combination of hardware and software, and regarding these modules, they are also similar in the following embodiments, and will not be described in detail later. When the communication selection module controls the input controlled switch module and the output controlled switch module of one data processing module to be conducted, the digital baseband processor can also synchronously control the hardware selection switch to conduct the antenna of the data processing module, and other modules are not conducted.
The scheme is characterized in that: only one external radio frequency switching device is connected to only one single-frequency-band antenna.
Referring to fig. 3, the WiFi and/or LoRa compatible multimode scattering communication system of the present embodiment includes a digital baseband processor, M single-band antennas, M radio frequency switches, and M matching impedances.
Each single-frequency-band antenna corresponds to one or more communication modes, K communication modes are shared, K and M are integers greater than or equal to 2, and K is greater than or equal to M; the K communication modes include LoRa scattering communication, Zigbee scattering communication, Bluetooth scattering communication, and WiFi scattering communication, and the Zigbee scattering communication and the Bluetooth scattering communication share one antenna, but in other embodiments of the present invention, one antenna may be used for each.
One switch connecting end of each radio frequency switch is connected with a single-frequency-band antenna, and the other switch connecting end is grounded through a matched impedance; the matching impedance is matched to the antenna to effectively transmit the signal.
The digital baseband processing contains the following modules which are realized by software or hardware:
the data processing module is used for processing data to be processed by adopting the corresponding communication mode and finally generating a scattering modulation waveform for driving the radio frequency switch; the data processing comprises the processes of data coding, baseband, modulation and the like, and finally generates and outputs a path of scattering modulation waveform for driving an external radio frequency switching device;
and the communication mode selection module is respectively connected with each input controlled switch module so as to control the conduction of the input controlled switch modules of one or more data processing modules at a time.
It should be understood that in the present embodiment, when the communication selection module controls the input controlled switch module and the output controlled switch module of one or more data processing modules to be turned on, each antenna operates independently.
The scheme is characterized in that: there are multiple external radio frequency switching devices, each switching device accessing an antenna for a different communication function.
Referring to fig. 4, the WiFi and/or LoRa compatible multimode scattering communication system of the present embodiment includes a digital baseband processor, 1 multiband antenna, 1 rf switch, and 1 matching impedance.
The multi-band antenna meets the frequency band requirements of K communication modes, wherein K is an integer greater than or equal to 2; the K communication modes comprise LoRa scattering communication, Zigbee scattering communication, Bluetooth scattering communication and WiFi scattering communication.
One switch connecting end of the radio frequency switch is connected with the multi-band antenna, and the other switch connecting end is grounded through a matched impedance; the matching impedance is matched to the antenna to effectively transmit the signal.
The digital baseband processing contains the following modules which are realized by software or hardware:
the data processing module is used for processing the data to be processed by adopting the corresponding communication mode, and finally generating a scattering modulation waveform for driving the radio frequency switch;
and the communication mode selection module is respectively connected with each input controlled switch module and each output controlled switch module so as to control the synchronous conduction of the input controlled switch module and the output controlled switch module of one or more data processing modules at each time.
It should be understood that, in the present embodiment, when the communication selection module controls the input controlled switch module and the output controlled switch module of the plurality of data processing modules to be turned on, each data processing module time-division multiplexes the multiband antenna.
The scheme is characterized in that: there is only one external radio frequency switching device and a multiband antenna is connected.
Wifi scatter communication
The WiFi scattering communication can be realized by using a digital baseband processor (described as MCU in this embodiment, especially MCU with low power consumption), a radio frequency electronic switch device, an antenna, and an antenna impedance matching circuit, as shown in fig. 5.
When WiFi data does not need to be sent, the MCU is in a low power consumption state to save power supply energy. When WiFi data needs to be sent, the MCU is firstly awakened, meanwhile, the CLK oscillator is started to provide a clock for the system, and the MCU is in a relatively high power consumption state. Then the MCU internal program starts to run according to the following steps:
1) the program encapsulates the data to be transmitted into MPDU (MAC protocol data unit), adds PLCP frame header and PLCP preamble, and encapsulates them into PPDU (PLCP protocol data unit), which can be referred to fig. 6 specifically;
2) according to the formed PPDU, the length information is calculated and filled, the CRC check of the PLCP, and the FCS frame check information, and in this embodiment, the length information specifically refers to a data length, an IP packet length, and a length of the entire data frame.
3) The PPDU processed in step 2 is scrambled according to a scrambling polynomial specified in the ieee802.11b standard, and in particular, refer to fig. 7, where the transfer polynomial around the scrambler is g (Z) -Z-7 + Z-4+ 1.
4) The PPDU is subjected to parallel/serial conversion, namely, the byte information is converted into bit information, and differential code conversion is carried out at the same time. The transformation rules are as follows: for data before transformation, a rising edge represents 1, a falling edge represents 0, and when the transformation occurs, the data is unchanged when meeting 1, and when the data meets 0, the data is subjected to level jump, which can be specifically referred to fig. 8.
5) The obtained differential bit information is spread according to a spreading sequence specified in the ieee802.11b standard, that is, 11 chip bits are obtained after 1 differential bit is spread. The chip bits are as follows:
+1,–1,+1,+1,–1,+1,+1,+1,–1,–1,–1
6) and modulating the chip bit information by adopting a digital virtual DBPSK modulation method. For example, when the chip bit is 1 (i.e., chip 1), the virtual DBPSK modulation sequence bits are 1,0,1,0, which represents phase 0; when the chip bit is 0 (i.e. chip-1), the virtual DBPSK modulation sequence bit is 0,1,0,1, which represents the phase pi, and specifically refer to fig. 9. It should be noted that 1 chip bit may correspond to N modulation sequence bits (the integer N ≧ 2, where N ═ 4 is taken for illustration only).
7) And storing the sequence bits modulated by the digital virtual DBPSK in a data storage space of the MCU, finally transmitting the bit information by using a universal serial communication interface of the MCU, and switching the absorption/reflection state of the antenna by controlling a radio frequency electronic switch device so as to transmit the data to be transmitted in a scattering communication mode.
Regarding the bit rate in the two processes of spreading and modulating, it should be noted that:
1) because the barker code of 11 chips is adopted, the storage space required by the chip bit information after the spread spectrum is 11 times of the differential bit information;
2) since 1 chip bit corresponds to N modulation sequence bits, the memory space required for modulating the sequence bits is N times that of the chip bits;
3) according to the specification of the IEEE802.11b standard, the DBPSK modulated differential bit rate is 1Mbps, and then the chip bit rate after spreading is 11Mbps, so that the modulated sequence bit rate is Nx 11Mbps, which is the final transmission rate of the MCU universal serial communication interface. In the data processing module, serial output can be directly realized, and parallel output can also be realized, but a parallel-serial conversion module is additionally added.
Referring to fig. 10, in the 6 th step of digital virtual DBPSK modulation, in order to reduce the transmission rate of the MCU usb interface and achieve the purpose of frequency reduction and power consumption reduction, a modulation method in which the MCU incorporates a logic circuit (e.g., an xor gate, but the present invention is not limited thereto) is also proposed herein.
The modulation process is shown in fig. 11. The MCU universal serial communication interface directly outputs chip bits of 11Mbps as a first input of the XOR gate; the clock output of the oscillator (which may in principle be any frequency > 11MHz, for ease of explanation this example takes a clock frequency of 19.25 MHz) serves as the second input to the xor gate. The output of the xor gate is the result of the DBPSK modulation and is directly used to drive the rf electronic switching device to switch the absorption/reflection state of the antenna, so that the data to be transmitted is transmitted in a manner that complies with the ieee802.11b standard.
The modulation method of the MCU + logic circuit can reduce the transmission rate of the MCU universal serial communication interface to 11Mbps, so that the MCU master frequency and power consumption are reduced, and a wider, cheap and low-frequency MCU can be used for system design of passive WiFi, thereby reducing the design difficulty and manufacturing cost. Furthermore, the modulation method also makes the configuration of the clock frequency of the CLK oscillator more flexible and is not limited to integer multiples of 5.5 MHz.
Lora scatter communication
The method realizes the process of LoRa data frame- > Whitening scrambling- > Hamming error correction coding- > Interleaving- > De-Gray coding- > CSS linear frequency modulation digital virtual modulation- > DMA high-speed serial port output through programming of a digital baseband processor. Therefore, the development and design of the LoRa scattering communication system can be realized on the low-cost digital baseband processor without spending huge cost on IC stream chips.
In addition, the direct frequency synthesis process of the DDS in the scheme is improved, a rapid table look-up CSS scattering modulation method is provided, the generation speed of CSS scattering modulation waveforms is remarkably increased, and the LoRa scattering communication power consumption is further reduced.
The invention can realize LoRa scattering communication only by a digital baseband processor (which can be MCU, FPGA or ASIC), a radio frequency switch, an antenna and a matching circuit thereof, as shown in figure 12.
First, in a digital baseband processor, according to LoRaWANTM1.1Specification of Specification protocol, the method carries out Whitening scrambling, Hamming error correction coding, Interleaving and De-Gray coding on LoRa data frame by programming or digital logic circuit mode, and finally obtains Symbol.
According to the LoRa specification, the desirable value of Symbol is 2 when the spreading factor is SFSFA (0, 1, 2 … … 2)SF-1), for simplicity, illustrated with SF-2. As shown in fig. 13, the frequency change law of the CSS linear frequency modulation waveform is shown when the symbol values are 0,1, 2, and 3, respectively.
Further, for example, Symbol duration CSS modulation waveform is shown as sine wave in the figure with Symbol 2. The invention proposes that in the digital domain, a DDS direct frequency synthesis scheme is adopted, each Symbol realizes linear frequency modulation by updating a frequency control word, and the MSB highest bit of a phase accumulator is output, so that a digital square wave with the same frequency as a sine wave can be generated, as shown in the lowermost waveform in FIG. 3. The DDS direct frequency synthesis principle and its frequency control word, phase accumulator belong to the existing mature technology, and are not described herein again.
In the MCU, the above process may be implemented by calculating the value of each clock phase accumulator (multiple clocks are needed to send a Symbol) in time sequence, sequentially storing the MSB highest bit of the value in the MCU memory, and finally transmitting the MSB highest bit to the GPIO port or the high-speed serial port via DMA, and sequentially sending the obtained digital square wave signals to the rf switch. The radio frequency switch is used for controlling the switching state of the radio frequency switch according to the digital square wave signal (namely the square wave sequence), and sending out the signal in a scattering mode, so that LoRa scattering communication is realized. In this embodiment, when the digital square wave signal is at a high level, the radio frequency switch is turned on, and the antenna is in a matching absorption state; at low level, the radio frequency switch is off and the antenna is in a mismatched reflective state. The LoRa scatterer communication requires cooperation of surrounding base stations, which is common knowledge of LoRa scatterer communication and will not be described in detail here, but should be understood by those skilled in the art.
The step of calculating the value of the phase accumulator in each clock cycle by the MCU consumes a large amount of time, and the CSS linear frequency modulation method based on the fast table look-up is provided for the invention. The method firstly defines a CSS modulation square wave sequence with Symbol 0 as a reference in a Symbol period and stores the reference in an MCU memory (for example, an array Symbol _ baseline [ N ]]For convenience of calculation, N is 2SFInteger multiples of). When the CSS linear frequency modulation square wave sequence corresponding to different Symbol values Symbol is required to be calculated, the array pointer is shifted by Symbol multiplied by N/2SFTaking a square wave sequence formed by the whole indicated array element before the rest elements as a square wave sequence corresponding to the different Symbol values Symbol; wherein N is the number of elements of the array. Therefore, the method can remarkably reduce the calculation time of the CSS linear frequency modulation waveform sequence, thereby greatly reducing the power consumption of the LoRa scattering communication process.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.