Passive sensor frequency conversion transmission method, system time division polling method and system

Abstract

The present invention belongs to the technical field of passive sensor networks, and specifically discloses a passive sensor variable frequency transmission method, a system time-division polling method and a system. In the system time-division polling method, a wireless base station transmits an excitation signal in a transmission cycle, and in a receiving cycle, the wireless base station receives the reflection frequencies of multiple passive sensors within its coverage area. The wireless base station presets the local oscillator frequency used by each passive sensor in the receiving cycle, and the difference between the reflection frequency of different passive sensors and their local oscillator frequency is a fixed value in the receiving cycle; the wireless base station switches the local oscillator frequency to the local oscillator frequency corresponding to different sensors in different time slices in the receiving cycle, and obtains the mixed frequency signals of different passive sensors in turn in each time slice and extracts their sensing data. By adopting this technical solution, the response signals of different passive sensors are processed batch by batch, and the perception and information interaction of multiple passive sensors in the area are realized, thereby improving communication efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of passive sensor networks, and relates to a passive sensor frequency conversion transmission method, a system time division polling method and a system. Background Art

[0002] In existing wireless communication systems, a superheterodyne method is generally used to convert low-frequency signals to high frequencies so that the signals can be transmitted in space in the form of electromagnetic waves, or to convert high-frequency electromagnetic wave signals in space to low frequencies for digital processing.

[0003] At present, the main way to achieve frequency conversion is to use the nonlinear characteristics of semiconductor components (mixers) to multiply the signal to be converted and the local oscillator signal generated by the local oscillator signal source to obtain the combined frequency and the difference frequency, that is, to achieve frequency conversion. However, this method is dependent on DC power. On the one hand, the local oscillator signal source must be supplied with DC power to work; on the other hand, the mixer can only achieve frequency conversion gain under the condition of providing DC power. Even if the mixer can achieve frequency conversion effect without DC power, the power requirement for the local oscillator signal is relatively high (10-15dBm). In most cases, an amplifier is required to actively amplify the local oscillator signal, and there is still a dependence on DC power.

[0004] Therefore, the frequency conversion system must be powered by wires or batteries to work, which requires laying cables or frequently replacing batteries during use, greatly reducing the convenience of use and reliability of the equipment.

[0005] In the existing passive frequency conversion technology solutions, each MDFC (Microwave Direct Frequency Conversion) passive sensor occupies an exclusive communication frequency. When the sensor is excited by a microwave signal, the sensor performs frequency conversion on the received signal and returns it to the excitation signal source at a preset frequency. In this way, the sensor can return a signal carrying independent information (sensor parameters, such as temperature, humidity, etc.) to the excitation signal source.

[0006] When the wireless base station needs to read the data of a sensor, it will stimulate the sensor by emitting microwaves, then receive its feedback signal at a predetermined frequency, and finally parse / read its data. After reading the data, the base station will stimulate / read the data of the next sensor at the next time interval. This solution can only obtain data from one sensor each time an excitation signal is emitted, which is very inefficient.

[0007] In this variable frequency information transmission technology, since each MDFC passive sensor occupies a dedicated communication frequency, when the wireless base station transmits an excitation signal, all sensors within the range will be excited at the same time and return signals carrying independent information (within different frequency ranges) at the same time. However, the receiving end cannot process and return multiple signals at the same time, and thus cannot guarantee the normal interaction of a large amount of sensor information. This objectively leads to an extremely limited number of passive sensors that can be covered by a base station, and low communication efficiency of the passive sensor network, which has become the biggest shortcoming restricting the application of passive Internet of Things. Summary of the invention

[0008] The purpose of the present invention is to provide a passive sensor frequency conversion transmission method, a system time division polling method and a system to solve the problem of low communication efficiency in a passive sensor network.

[0009] In order to achieve the above object, the basic scheme of the present invention is: a passive sensor variable frequency transmission method, comprising the following steps:

[0010] The antenna receives the microwave signal f0 radiated in the space, and the antenna transmits the microwave signal f0 to the MDFC signal conversion circuit;

[0011] The passive sensor collects the sensing quantity and converts it into electrical parameters and transmits it to the MDFC signal conversion circuit;

[0012] The MDFC signal conversion circuit is used to form a frequency modulated signal with f1 as the carrier and carrying the sensing information. The MDFC signal conversion circuit outputs the frequency modulated signal carrying the sensing information to the antenna, and then radiates it into space through the antenna.

[0013] The working principle and beneficial effects of this basic solution are as follows: the passive sensor converts the sensing quantity (such as temperature, vibration, etc.) into an electrical parameter, which affects the frequency of the f1 signal and forms a frequency-modulated signal with f1 as the carrier and carrying the sensing information. The frequency of the f1 signal is controlled by the components in the MDFC signal conversion circuit to ensure that it is modulated to a predetermined frequency. Each passive wireless sensor has a preset exclusive uplink frequency (f1) that is different from each other to avoid mutual interference between the sensor ends. Multiple passive sensors can transmit information simultaneously, improving the communication efficiency of the passive sensor network.

[0014] The present invention also provides a time division polling method for a frequency division type passive wireless sensor system, comprising the following steps:

[0015] During the transmission period, the wireless base station transmits an excitation signal;

[0016] In a receiving cycle, the wireless base station receives the reflected frequencies of multiple passive sensors within its coverage, wherein the reflected frequencies of different passive sensors are different from each other, and the wireless base station presets the local oscillator frequency used by each passive sensor in the receiving cycle, and the difference between the reflected frequencies of different passive sensors and their local oscillator frequencies is a fixed value in the receiving cycle;

[0017] The wireless base station switches the local oscillator frequency to the local oscillator frequencies corresponding to different sensors in different time slices within the receiving cycle, and obtains the mixed signals of different passive sensors in turn in each time slice and extracts the sensing data thereof.

[0018] The technical solution adopts a time-division method to process the response signals of different MDFC passive sensors in batches, realize the perception and information interaction of multiple MDFC sensors in a region, and improve the communication efficiency of the passive sensor network.

[0019] Furthermore, the method for determining the local oscillator frequency used by all passive sensors is:

[0020] Obtaining preset reflection frequency bands f1 to fn for passive sensors within the coverage of the wireless base station and the number n of passive sensors covered;

[0021] Subtract the reflection frequency band of the passive sensor from the fixed intermediate frequency fIF to obtain the local oscillator frequency fLO that should be used when receiving the signals of each passive sensor.

[0022] Obtain the mapping relationship between the passive sensor and the corresponding local oscillator frequency for easy use.

[0023] Furthermore, the maximum number of uplink signals that can be received by the wireless base station in each clock cycle is capacity matched with the number of passive sensors within the coverage of the wireless base station, the number of batches of excitation signals transmitted by the wireless base station is calculated, and the passive sensors within the coverage of the wireless base station are allocated to different batches;

[0024] Based on the batch number of the excitation signal transmitted by the wireless base station, the wireless base station transmits the excitation signal in batches, and obtains the reflection frequency of the corresponding batch of passive sensors within the jurisdiction, and then obtains the reflection frequency of all passive sensors.

[0025] The slicing method can greatly increase the number of covered passive sensors and meet the sensor data reception requirements for multiple passive sensors by transmitting excitation signals in batches.

[0026] Further, the number of batches of the base station transmitting the excitation signal is calculated, and the specific steps are as follows:

[0027] The clock period t of the wireless base station's receiving module is divided by the minimum time slice t supported by the system min, get the maximum number m of uplink signals that can be received in each clock cycle;

[0028] If m>n, n is the number of passive sensors within the coverage of the wireless base station, the wireless base station can obtain all sensor data by transmitting an excitation signal once, k=1; otherwise, divide n by m and round up to get k, k is the number of batches that the base station needs to transmit excitation signals, and obtain the uploaded information of all passive sensors within the coverage area in batches.

[0029] The calculation is simple and easy to operate.

[0030] Further, the method of obtaining the sensing data of the passive sensor is as follows:

[0031] The wireless base station transmits k excitation signals, and the passive sensors excited in sequence are 1: f1,...f m ,2:f m+1 ,...f 2m ,...,k:f km+1 ,...f (k+1)m , and obtain the local oscillator frequency fLO corresponding to each passive sensor;

[0032] After the wireless base station transmits the excitation signal each time, the receiving module of the wireless base station immediately switches to the local oscillator frequency fLO corresponding to each passive sensor in this batch in each time slice, so as to obtain the mixed signal of the predetermined passive sensor in each time slice and extract its sensing data.

[0033] All passive sensor data within the base station coverage area can be acquired with maximum efficiency through communication efficiency.

[0034] The present invention also provides a wireless base station, comprising a transmitting module, a receiving module and a digital processing module;

[0035] The transmitting module transmits an excitation signal to a plurality of passive sensors within its coverage area;

[0036] The receiving module receives the reflection frequencies of multiple passive sensors, wherein the reflection frequencies of different passive sensors are different from each other, and the receiving module is preset with the local oscillator frequency used by each passive sensor in the receiving cycle, and the difference between the reflection frequencies of different passive sensors and their local oscillator frequencies is a fixed value in the receiving cycle; the receiving module switches the local oscillator frequency to the local oscillator frequency corresponding to different sensors in different time slices in the receiving cycle, and obtains the mixed frequency signals of different passive sensors in turn in each time slice and outputs them to the digital processing module;

[0037] The digital processing module extracts sensor data.

[0038] The wireless base station can receive information from multiple passive sensors in batches to improve communication efficiency.

[0039] The present invention also provides a passive sensor, comprising an antenna, an MDFC signal conversion circuit and a passive sensor;

[0040] The antenna is connected to the passive sensor through the MDFC signal conversion circuit. The antenna receives the microwave signal f0 radiated in the space, performs passive frequency conversion processing, converts it into a signal with a frequency of f1, and then radiates it into the space through the antenna;

[0041] The passive sensor converts the sensing quantity into an electrical parameter to form a frequency modulated signal with f1 as the carrier and carrying the sensing information.

[0042] The sensor realizes frequency conversion processing of the signal. Each passive sensor is preset with an exclusive uplink frequency (f1) that is different from each other to avoid mutual interference between the sensor ends.

[0043] The present invention also provides a frequency division type MDFC passive wireless sensor system time division polling system, comprising the wireless base station described in the present invention and a plurality of passive sensors described in the present invention;

[0044] The wireless base station executes the system time-division polling method of the present invention, and the passive sensor executes the passive sensor variable frequency transmission method of the present invention.

[0045] By using this system, the response signals of different MDFC passive sensors are processed batch by batch, the perception and information interaction of multiple MDFC sensors in the area are realized, and the communication efficiency of the system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the structure of the passive sensor of the present invention;

[0047] Figure 2 It is a spectrum diagram of the passive sensor variable frequency transmission method of the present invention;

[0048] Figure 3 It is a structural schematic diagram of a time-division polling system of a frequency-division MDFC passive wireless sensor system of the present invention;

[0049] Figure 4 It is a schematic diagram of the structure of a wireless base station of the present invention;

[0050] Figure 5 It is a structural schematic diagram of a receiving module of a wireless base station of the present invention;

[0051] Figure 6 It is a schematic diagram of time-sharing polling of the wireless base station of the present invention. DETAILED DESCRIPTION

[0052] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0053] In the description of the present invention, it is necessary to understand that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0054] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0055] The present invention discloses a passive sensor frequency conversion transmission method, comprising the following steps:

[0056] The antenna receives the microwave signal f0 (downlink frequency band) radiated in the space, and transmits the microwave signal f0 to the MDFC signal conversion circuit. The MDFC signal conversion circuit performs passive frequency conversion processing on the signal and converts it into a signal with a frequency of f1 (uplink frequency band);

[0057] Passive sensors collect sensing quantities (such as temperature, vibration, etc.) and convert them into electrical parameters and transmit them to the MDFC signal conversion circuit;

[0058] The MDFC signal conversion circuit is used to form a frequency modulated signal with f1 (uplink frequency band) as the carrier and carrying the sensor information (such as Figure 2 As shown), the MDFC signal conversion circuit outputs the frequency modulated signal carrying the sensing information to the antenna, which is then radiated into space through the antenna.

[0059] The frequency of the f1 signal is controlled by the components in the MDFC signal conversion circuit to ensure that it is modulated to the predetermined frequency. Each passive wireless sensor has a preset exclusive uplink frequency (f1) that is different from each other to avoid mutual interference between the sensor ends. At the same time, it overcomes the dependence of sensors on DC power supply in traditional technical solutions and realizes passive sensing.

[0060] The present invention also provides a time-division polling method for a frequency-division passive wireless sensor system, which solves the problem of low communication efficiency in a passive sensor network, and processes the response signals of different MDFC passive sensors in batches in a time-division manner, thereby realizing the perception and information interaction of multiple MDFC sensors in a region. The time-division polling method for a frequency-division passive wireless sensor system comprises the following steps:

[0061] During the transmission period, the wireless base station transmits an excitation signal;

[0062] In a receiving cycle, the wireless base station receives the reflected frequencies of multiple passive sensors within its coverage, wherein the reflected frequencies of different passive sensors are different from each other, and the wireless base station presets the local oscillator frequency used by each passive sensor in the receiving cycle, and the difference between the reflected frequencies of different passive sensors and their local oscillator frequencies is a fixed value in the receiving cycle;

[0063] The wireless base station switches the local oscillator frequency to the local oscillator frequencies corresponding to different sensors in different time slices within the receiving cycle, and obtains the mixed signals of different passive sensors in turn in each time slice and extracts the sensing data thereof.

[0064] When the wireless base station radiates a signal with a frequency of f0 (downlink frequency band) into space, the passive sensors (1 to n) in the coverage area can receive the signal and then reflect the signal with carrier frequencies of f1 to f n The wireless base station receives the signal from the wireless base station and processes it to restore the original sensor information. Since there is only one RF receiving channel in the base station, it is necessary to adjust the receiving frequency in time and process the information of each sensor in time.

[0065] In a preferred embodiment of the present invention, the method for determining the local oscillator frequencies used by all passive sensors is:

[0066] Obtaining preset reflection frequency bands f1 to fn for passive sensors within the coverage of the wireless base station and the number n of passive sensors covered;

[0067] By subtracting the reflection frequency band (uplink frequency band) of the passive sensor from the fixed intermediate frequency fIF, the local oscillator frequency fLO that should be used when receiving the signals of each passive sensor is obtained, as shown in Table 1.

[0068] Table 1. Correspondence between sensor and local oscillator frequency band

[0069] sensor Reflection frequency band LO frequency band Passive sensor 1 <![CDATA[f1]]> <![CDATA[fLO1]]> ... ... ... Passive Sensor <![CDATA[f n ]]> <![CDATA[fLO n ]]>

[0070] In a preferred solution of the present invention, the maximum number of uplink signals that can be received by the wireless base station in each clock cycle is capacity matched with the number of passive sensors within the coverage of the wireless base station, the number of batches of excitation signals transmitted by the wireless base station is calculated, and the passive sensors within the coverage of the wireless base station are allocated to different batches;

[0071] Based on the batch number of the excitation signal transmitted by the wireless base station, the wireless base station transmits the excitation signal in batches, and obtains the reflection frequency of the corresponding batch of passive sensors within the jurisdiction, and then obtains the reflection frequency of all passive sensors.

[0072] In a preferred solution of the present invention, although the slicing method can greatly increase the number of covered passive sensors, it is subject to the minimum limit of time slicing and the limited capacity of the signal receiving processor on the base station side. If the number of passive sensors exceeds the single batch processing capacity of the base station side, it is still necessary to obtain sensor data in batches.

[0073] Calculate the number of batches of excitation signals transmitted by the base station. The specific steps are as follows:

[0074] The clock period t of the wireless base station's receiving module is divided by the minimum time slice t supported by the system min , get the maximum number m of uplink signals that can be received in each clock cycle;

[0075] If m>n, n is the number of passive sensors within the coverage of the wireless base station, the wireless base station can obtain all sensor data by transmitting an excitation signal once, k = 1; otherwise, divide n by m and round up to get k, k is the number of batches that the base station needs to transmit excitation signals, and obtain the uploaded information of all passive sensors within the scope of its jurisdiction in batches. For example, if m = 10 and n = 33, then k = 4, and the base station needs to transmit 4 excitation signals to obtain the uploaded information of all sensors within the scope of its jurisdiction in batches.

[0076] In a preferred embodiment of the present invention, the method for obtaining the sensing data of the passive sensor is as follows:

[0077] The wireless base station transmits k excitation signals, and the passive sensors excited in sequence are 1: f1,...f m ,2:f m+1 ,...f 2m ,...,k:f km+1 ,...f (k+1)m , and obtain the local oscillator frequency fLO corresponding to each passive sensor, as shown in Table 2;

[0078] Table 2. Passive sensor data acquired in batches

[0079]

[0080] According to fIF=fi n-fLO, to extract the reflection signal of a certain sensor, just mix fin (from the base station side, the mixed signal of multiple sensors received) with the local oscillator signal fL0 of the sensor to obtain the intermediate frequency signal fIF carrying the sensor information;

[0081] If the fin signal lasts for 10 time slices, then fin is mixed with fL01 in the first time slice and mixed with fL02 in the second time slice. The information of each sensor can be obtained by processing them in sequence.

[0082] After the wireless base station transmits the excitation signal each time, the receiving module of the wireless base station immediately switches to the local oscillator frequency fLO corresponding to each passive sensor in this batch in each time slice, so as to obtain the mixed signal of the predetermined passive sensor in each time slice and extract its sensing data.

[0083] Through the above processing method, all passive sensor data within the base station coverage can be obtained with maximum efficiency. The present invention greatly improves the efficiency of passive sensor information interaction through time-division polling technology, improves the perception ability of the passive Internet of Things and expands its application field, and greatly increases the number of passive sensors that can be supported by wireless base stations.

[0084] The present invention also provides a wireless base station, such as Figure 4 As shown, it includes a transmitting module, a receiving module and a digital processing module. The transmitting module transmits an excitation signal to multiple passive sensors within its coverage area.

[0085] The receiving module receives the reflection frequencies of multiple passive sensors, wherein the reflection frequencies of different passive sensors are different from each other. The receiving module is preset with the local oscillator frequency used by each passive sensor in the receiving cycle, and the difference between the reflection frequencies of different passive sensors and their local oscillator frequencies is a fixed value in the receiving cycle.

[0086] The receiving module switches the local oscillator frequency to the local oscillator frequency corresponding to different sensors in different time slices within the receiving cycle, obtains the mixed frequency signals of different passive sensors in turn in each time slice and outputs them to the digital processing module, which extracts the sensor data.

[0087] The receiving module adopts a superheterodyne architecture (such as Figure 5As shown in the figure, in the receiving module, the signal fin (i.e. the signal reflected by the passive sensor, in the predetermined frequency band) is filtered and amplified and enters the mixer. After being mixed with the local oscillator signal fLO, it becomes an intermediate frequency signal with a frequency of fIF. The relationship between the three frequencies is fIF=fi n-fLO. The intermediate frequency signal fIF is filtered out by the filter to remove the clutter interference and enter the digital processing module to restore the sensor information. Under the fixed fIF target, the fi n signal to be processed can be selected by adjusting fLO.

[0088] The present invention adopts the method of adjusting the local oscillator frequency fLO to adapt the fi n within the predetermined frequency range so that the sum of the two is a fixed frequency intermediate frequency signal fIF, that is, by switching different local oscillator frequencies fLO at different time slices, the predetermined frequency (f1~f n ) After mixing, it falls within the bandwidth of a fixed intermediate frequency filter and then undergoes digital processing. Other carrier signals are filtered out by the intermediate frequency filter after mixing and will not interfere with the predetermined frequency. Figure 6 As shown, in each time slice, different local oscillator frequencies are switched so that only a predetermined MDFC signal enters a fixed intermediate frequency filter and then undergoes digital processing in the time slice.

[0089] The present invention also provides a passive sensor, such as Figure 1 As shown, it includes an antenna, an MDFC signal conversion circuit and a passive sensor. The antenna is electrically connected to the passive sensor through the MDFC signal conversion circuit. The antenna receives the microwave signal f0 radiated in the space, performs passive frequency conversion processing, converts it into a signal with a frequency of f1, and then radiates it into the space through the antenna. The passive sensor converts the sensing quantity into an electrical parameter, forming a frequency-modulated signal with f1 as the carrier and carrying the sensing information.

[0090] The present invention also provides a frequency division type MDFC passive wireless sensor system time division polling system, such as Figure 3 As shown, it includes the wireless base station of the present invention and multiple passive sensors of the present invention. The wireless base station executes the system time division polling method of the present invention, and the passive sensor executes the passive sensor variable frequency transmission method of the present invention.

[0091] By using this system, the response signals of different MDFC passive sensors are processed batch by batch, the perception and information interaction of multiple MDFC sensors in the area are realized, and the communication efficiency of the system is improved.

[0092] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0093] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A time division polling method for a frequency division passive wireless sensor system, characterized in that: The steps include: During the transmission period, the wireless base station transmits an excitation signal; In a receiving cycle, the wireless base station receives the reflected frequencies of multiple passive sensors within its coverage, wherein the reflected frequencies of different passive sensors are different from each other, and the wireless base station presets the local oscillator frequency used by each passive sensor in the receiving cycle, and the difference between the reflected frequencies of different passive sensors and their local oscillator frequencies is a fixed value in the receiving cycle; The wireless base station switches the local oscillator frequency to the local oscillator frequency corresponding to different sensors in different time slices within the receiving cycle, obtains the mixed frequency signals of different passive sensors in turn in each time slice and extracts the sensing data; The maximum number of uplink signals that can be received by the wireless base station in each clock cycle is matched with the number of passive sensors within the coverage of the wireless base station, the number of batches of excitation signals transmitted by the wireless base station is calculated, and the passive sensors within the coverage of the wireless base station are allocated to different batches; Based on the number of batches of excitation signals transmitted by the wireless base station, the wireless base station transmits the excitation signals in batches, and obtains the reflection frequencies of the corresponding batches of passive sensors within the jurisdiction, and then obtains the reflection frequencies of all passive sensors; The passive sensor frequency conversion transmission method comprises the following steps: The antenna receives the microwave signal f0 radiated in the space, and the antenna transmits the microwave signal f0 to the MDFC signal conversion circuit; The passive sensor collects the sensing quantity and converts it into electrical parameters and transmits it to the MDFC signal conversion circuit; The MDFC signal conversion circuit is used to form a frequency modulated signal with f1 as the carrier and carrying the sensing information. The MDFC signal conversion circuit outputs the frequency modulated signal carrying the sensing information to the antenna, and then radiates it into space through the antenna.

2. The time division polling method for a frequency division type passive wireless sensor system according to claim 1, characterized in that: The method to determine the local oscillator frequency used by all passive sensors is: Obtaining preset reflection frequency bands f1 to fn for passive sensors within the coverage of the wireless base station and the number n of passive sensors covered; Subtract the reflection frequency band of the passive sensor from the fixed intermediate frequency fIF to obtain the local oscillator frequency fLO that should be used when receiving the signals of each passive sensor.

3. The time division polling method for a frequency division type passive wireless sensor system as claimed in claim 2, characterized in that: Calculate the number of batches of excitation signals transmitted by the base station. The specific steps are as follows: The clock period t of the wireless base station's receiving module is divided by the minimum time slice t supported by the system min , get the maximum number m of uplink signals that can be received in each clock cycle; If m>n, n is the number of passive sensors within the coverage of the wireless base station, the wireless base station can obtain all sensor data by transmitting an excitation signal once, k=1; otherwise, divide n by m and round up to get k, k is the number of batches that the base station needs to transmit excitation signals, and obtain the uploaded information of all passive sensors within the coverage area in batches.

4. The time division polling method of the frequency division type MDFC passive wireless sensor system as claimed in claim 3, characterized in that: The method for obtaining the sensing data of the passive sensor is as follows: The wireless base station transmits k excitation signals, and the passive sensors excited in sequence are 1: f1,...f m ,2:f m+1 ,...f 2m ,...,k:f (k-1)m+1 ,...f km , and obtain the local oscillator frequency fLO corresponding to each passive sensor; After the wireless base station transmits the excitation signal each time, the receiving module of the wireless base station immediately switches to the local oscillator frequency fLO corresponding to each passive sensor in this batch in each time slice, so as to obtain the mixed signal of the predetermined passive sensor in each time slice and extract its sensing data.

5. A wireless base station based on the method according to any one of claims 1 to 4, characterized in that: It includes a transmitting module, a receiving module and a digital processing module; The transmitting module transmits an excitation signal to a plurality of passive sensors within its coverage area; The receiving module receives the reflection frequencies of multiple passive sensors, wherein the reflection frequencies of different passive sensors are different from each other, and the receiving module is preset with the local oscillator frequency used by each passive sensor in the receiving cycle, and the difference between the reflection frequencies of different passive sensors and their local oscillator frequencies is a fixed value in the receiving cycle; the receiving module switches the local oscillator frequency to the local oscillator frequency corresponding to different sensors in different time slices in the receiving cycle, and obtains the mixed frequency signals of different passive sensors in turn in each time slice and outputs them to the digital processing module; The digital processing module extracts sensor data.

6. A passive sensor based on the method according to any one of claims 1 to 4, characterized in that: It includes antenna, MDFC signal conversion circuit and passive sensor; The antenna is connected to the passive sensor through the MDFC signal conversion circuit. The antenna receives the microwave signal f0 radiated in the space, performs passive frequency conversion processing, converts it into a signal with a frequency of f1, and then radiates it into the space through the antenna; The passive sensor converts the sensing quantity into an electrical parameter to form a frequency modulated signal with f1 as the carrier and carrying the sensing information.

7. A frequency division type MDFC passive wireless sensor system time division polling system, characterized in that: comprising the wireless base station according to claim 5 and a plurality of passive sensors according to claim 6; The wireless base station executes the method described in any one of claims 1 to 4, and the passive sensor executes the method described in claim 1.

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