CN213522375U - Promote loRa private protocol gateway sensitivity of receiving's device - Google Patents
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- CN213522375U CN213522375U CN202022585706.2U CN202022585706U CN213522375U CN 213522375 U CN213522375 U CN 213522375U CN 202022585706 U CN202022585706 U CN 202022585706U CN 213522375 U CN213522375 U CN 213522375U
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Abstract
The utility model discloses a promote device of loRa private agreement gateway sensitivity of reception, after loRa gateway equipment and terminal node equipment set up wireless communication, the gateway configures and acquires the RSSI value to the terminal according to predetermined radio frequency parameter setting table, sets for and preserves the parameter according to best RSSI value. And the RSSI value is acquired through a receiving through channel. The utility model discloses a set for optimum radio frequency configuration parameter to combine the RSSI value that tests to, carry out selective enlarging, decay and filtering to received signal through preceding stage LNA, attenuator and wave filter, thereby reduced the noise figure of loRa gateway receiver and reach the purpose that improves the reception sensitivity.
Description
Technical Field
The utility model belongs to the technical field of low-power consumption wide area network, concretely relates to method and device for promoting loRa private protocol gateway receiving sensitivity.
Background
The LoRa belongs to LPWAN (low-power Wide-Area Network) communication technology, and is an ultra-long-distance low-power wireless transmission scheme based on a spread spectrum technology. This solution changes the previous conflicting problems with respect to distance and power consumption. The working frequency range of LoRa is from 137MHz-1020MHz, and the LoRa is mainly operated in free frequency bands of the whole world, such as 169MHz, 433MHz, 868MHz and 915 MHz. Due to the unique modulation technology of the LoRa, under different system bandwidths and spreading factors, the receiving sensitivity of the LoRa receiver is different, the highest receiving sensitivity of the LoRa receiver can reach-148 dBm under the condition of an ideal channel, the link budget is 168dB, and therefore, the LoRa receiver is very long in transmission distance and is very suitable for various application scenarios of low power consumption and long-distance transmission. The LoRa private protocol gateway is different from a standard protocol gateway based on LoRaWAN or LinkWAN, the networking protocol of the LoRa private protocol gateway is designed by equipment manufacturers, the server is flexible to deploy, the domestic working frequency is 470-510MHz, the LoRa private protocol gateway can be freely configured, the data confidentiality is strong, the cost is low, and the LoRa private protocol gateway becomes the first choice of a small-size Internet of things project. As an information converter of the LoRa internet of things communication system, the LoRa private protocol gateway device is responsible for communication between the network server and the terminal node, and is a core device of the LoRa network system. The gateway device must have reliable radio frequency transceiving characteristics to ensure that the terminal device can reliably network and upload data.
In actual use, the performance of the LoRa gateway device is greatly affected by environmental factors, especially in urban residential areas with many high-rise buildings and dense urban areas, the propagation loss of signals is large, the effective communication distance of the LoRa communication system is severely limited, and due to the particularity of LoRa spread spectrum modulation, different system configurations can also have different effects on the communication performance of the device, and good stability cannot be guaranteed in a complex and variable environment. The transmission power of the LoRa gateway and the terminal is strictly limited by the national standard, and the effect of increasing the communication distance cannot be achieved by increasing the transmission power, so that under the same radio frequency parameter configuration (bandwidth, spreading factor, coding rate and the like), the stable and reliable communication of the device under the complex environment can be increased only by increasing the receiving sensitivity of the receiving end. And the communication performance of the LoRa spread spectrum system can be better improved by adopting dynamic parameter configuration and improving the sensitivity of a gateway receiving end.
Receive sensitivity refers to the minimum signal power that the receiver can receive with an acceptable signal-to-noise ratio. Improving the receiving sensitivity of the LoRa gateway can enable the gateway device to have stronger capacity of capturing weak signals. Therefore, with the increase of the propagation distance of the terminal transmitting signals, the signals are weakened, the gateway equipment with higher receiving sensitivity can still receive the data, and the stable connection is maintained, so that the communication distance is greatly increased. Chinese patent application No. 201910518480.3 discloses a method and apparatus for improving the receiving sensitivity of a radio device, which can be directly connected in series to the antenna interface of the original radio device, and includes several couplers, an amplifying and detecting circuit, a comparator, an amplifying circuit, a radio frequency switch and a filter. The utility model discloses a there is following not enough: 1. in a multi-gateway multi-terminal system, the transmission and reception of signals in the same area may affect the transceiving judgment of the device, which may cause that a receiving channel is opened when a wireless device connected to the device needs to transmit signals, thereby causing the loss of signals of a transmission line. 2. The device adjusts the receiving sensitivity by writing the received signal strength judgment threshold value into a chip and comparing the threshold value with the receiver received signal strength of a transmitting and receiving system (such as an LoRa spread spectrum communication system) which possibly has dynamic receiving sensitivity as a fixed value, and can cause error adjustment under the condition that the receiving sensitivity of equipment is changed. 3. The apparatus includes a transmit path including a radio frequency power amplifier, which amplifies the power of the transmit signal and is not suitable for use in devices that do not require amplification of the transmit signal.
Chinese patent application No. 201010230631.4 discloses a method and apparatus for improving receiver sensitivity, comprising: the receiving signal is input to the ADC through the antenna filter and the low noise amplifier, the ADC processes the receiving signal through the SNRBOOST technology, stray noise is suppressed out of band, the DDC filter filters the out-of-band stray noise of the receiving signal, and the ADC result of the receiving signal meets the requirement of the channel selectivity of a system receiver. The utility model discloses a there is following not enough: 1. the receiving channel has no protection circuit, which may cause the saturation of the back-end input signal, and the two parties of the receiving and the sending cannot communicate. 2. The device comprises a transmission path which comprises a radio frequency power amplifier, and the device has amplification effect on the transmission signal power and is not suitable for equipment without amplifying the transmission signal. 3. The analog signal is digitized in advance, and a signal demodulation method which cannot be applied to a specific communication system is generally adopted, and for example, demodulation of the LoRa signal is generally processed by a specific device baseband chip.
Chinese patent application No. 201510520477.7 discloses an apparatus and method for improving the receiving sensitivity of a radio frequency link. The device comprises a signal receiving module, a signal amplifying module and a signal processing module, wherein the device receives signals through the signal receiving module, sends the signals to the signal amplifying module, and sends the signals to the signal processing module after the signals are amplified. The signal amplification module comprises a radio frequency switch and at least two LNAs with non-overlapping working frequency bands. When the frequency of the received signal is not in the working frequency band of the ith low noise amplifier, so that the equipment cannot be accessed to the terminal network, the amplification module controls the selection switch to connect the receiving path to the (i + 1) th LNA until the equipment is successfully accessed to the network. The utility model discloses a there is following not enough: 1. LNAs exist in different operating frequency bands, requiring more LNA channels and increasing implementation complexity for wideband communication systems. 2. The post-stage non-fading regulation circuit may damage the receiver when the post-stage amplified signal is too strong.
Zhang Fuhong et al in "design and simulation of low noise amplifier in Wireless receiver" a text proposes a noise factor is less than 0.9dB, in-band gain is greater than 16dB, input-output voltage standing wave ratio is less than 1.5 low noise amplifier's design method, it is applied to the front end of the particular receiver and can improve the sensitivity of the receiver, the working frequency of this low noise amplifier is 2.575GHz-2.625GHz, can't be applied to LoRa working frequency channel. And no gain flatness design index is given, which may result in too large in-band gain difference, so that the receiving system cannot obtain more consistent sensitivity improvement characteristics under different working frequencies.
SUMMERY OF THE UTILITY MODEL
To above-mentioned all kinds of restrictions and not enough among the prior art, the utility model provides a promote method and device of loRa private protocol gateway receiving sensitivity. After wireless communication is established between the LoRa gateway equipment and the terminal node equipment, the gateway configures the terminal and obtains an RSSI value according to a preset radio frequency parameter setting table, and sets and stores parameters according to the optimal RSSI value. And the RSSI value is acquired through a receiving through channel. The utility model discloses still relate to a loRa private agreement gateway sensitivity of reception hoisting device, the device mainly by radio frequency switch, low noise power amplifier, digital adjustable attenuator, wave filter, electric capacity is constituteed. The received signal is amplified through an LNA amplification access, a primary digital adjustable attenuator is connected to the rear stage of the LNA and used for adjusting the amplitude of the signal, the attenuation amplitude of the adjustable attenuator is determined and controlled by a gateway according to the radio frequency parameters configured by a terminal, and the device is used for performing direct processing on a radio frequency transmitting signal. Generally, the utility model discloses a set for optimum radio frequency configuration parameter to combine the RSSI value that tests, carry out selective enlarging, decay and filtering to received signal through preceding stage LNA, attenuator and wave filter, thereby reduced the noise figure of loRa gateway receiver and reach the purpose that improves the reception sensitivity.
The technical implementation scheme of the utility model is as follows:
the utility model relates to a promote loRa private protocol gateway sensitivity of reception's method, the method specifically is: the method comprises the steps that terminal equipment matched with LoRa private protocol gateway equipment sends a network access request through LoRa communication, the gateway equipment receives the network access request, then communicates with the terminal equipment through a LoRa configuration channel, confirms whether the terminal equipment is successfully connected or not, after the terminal equipment is successfully connected, the gateway equipment carries out sequential configuration on the terminal equipment according to a preset radio frequency parameter configuration table, the radio frequency parameters comprise a working frequency band, a working bandwidth, a spreading factor and a coding rate, the gateway equipment actively obtains the ambient noise RSSI (received signal strength indicator) of the terminal equipment which currently establishes communication under a certain parameter, the RSSI when data are received last time and the theoretical highest receiving sensitivity under the current parameter, compares the optimal RSSI value with the theoretical highest receiving sensitivity, and sets and stores the parameter;
after the terminal accesses the network, the gateway equipment periodically acquires the RSSI value of a signal channel connected to the terminal equipment of the gateway equipment in real time through the through channel, and compares the RSSI value with a preset weak signal threshold value and a replacement parameter threshold value in sequence according to the measured value to judge whether to bypass a corresponding terminal receiving signal to an amplification path or to reconfigure terminal radio frequency parameters;
for the case of reconfiguring radio terminal parameters: if the gateway and the terminal equipment have the received signal quality deterioration caused by the variation factors such as the environment and the like in the communication process, the gateway end compares and judges the RSSI value of the terminal after dynamically detecting the RSSI value with the preset extremely low signal intensity threshold value of the radio frequency parameter needing to be reconfigured, if the signal threshold value range of the radio frequency parameter needing to be reconfigured is met, the gateway reconfigures the parameters of the terminal so as to search the optimal communication configuration parameters after the environment is changed, and the condition that the terminal is lost is avoided;
for the condition that the received signal is accessed to the receiving and amplifying channel, a digital adjustable attenuator is connected at the rear stage of an LNA circuit of the amplifying channel, the attenuation amplitude is determined by a gateway according to the currently set radio frequency parameters and is used for adjusting the strength of the amplified received signal, and the rear-stage circuit is prevented from being damaged due to the fact that the received signal is too strong; the attenuation amplitude setting of the attenuator of the latter stage is given by:
the value of the attenuator is determined according to the following equation:
RSLmax＝Txpwr+Txantgain-Pathloss+Rxantgain+LNAgain-Attloss
wherein RSLmaxFor maximum signal strength present at the input of the LoRa radio frequency chip, TxpwrAnd TxatngainRespectively transmit power and transmit antenna gain, RxantgainAnd LNAgainGain of receiving antenna and low noise amplifier, PathlossTo path loss, AttlossI.e. the value of the attenuator; through the calculation of the formula, a proper attenuation value is set to ensure the RSL of the systemmaxLess than 0 dBm.
The utility model discloses a further technique:
preferably, where the theoretical receive sensitivity is related to the Spreading Factor (SF) and the channel Bandwidth (BW), the calculation formula is as follows:
the RSSI refers to a signal strength indication function, which is measured in the bandwidth of a receiver and is used for judging the connection quality, and the larger the RSSI value is, the stronger the current signal strength is, and the better the connection quality is.
The utility model also comprises 1 device for improving receiving sensitivity of LoRa private protocol gateway, which mainly comprises a radio frequency switch, a filter, a LoRa radio frequency chip, a LNA circuit, an attenuator and a control unit circuit;
the radio frequency switches are provided with two, wherein the output end of one radio frequency switch is divided into two paths to be connected with the input end of the other radio frequency switch, one path is a receiving direct path, the other path is a receiving amplifying path, the receiving amplifying path comprises an LNA circuit, an attenuator and a filter, the received signal is amplified by the LNA circuit and then sent to the attenuator for proper attenuation, the signal after amplitude modulation by the attenuator is sent to the LoRa radio frequency chip after being filtered by the rear-stage band-pass filter to remove out-of-band interference signals, a DIO2 pin is led out of the LoRa radio frequency chip and is used for controlling the radio frequency switch to receive and transmit, the control unit selects a transmitting or receiving path by controlling the radio frequency switch, if the signal is a transmitting signal, the control unit gates the transmitting path to carry out through processing on the transmitting signal, and if the transmitting signal is the receiving signal, gates the receiving through path or the receiving amplifying path according to whether the receiving signal is a configuration signal or a strong signal or a normal communication signal.
The strongest received signal of the input end of the LoRa radio frequency chip is less than 0 dBm.
And the control unit controls the attenuation value of the attenuator through the output interface.
The device for receiving sensitivity is provided with capacitors in each signal transmission path, and the capacitance values of the capacitors are all 47 pF.
And the capacitors among the radio frequency switch, the LoRa radio frequency chip, the transmitting through path and the receiving through path are all filter capacitors.
And the capacitors between the radio frequency switch and the LNA and between the LNA and the attenuator are blocking capacitors.
To the content and the beneficial effect that the utility model relates to summarize as follows:
the LoRa private protocol gateway adopts a spread spectrum modulation technology and has different radio frequency link characteristics and different receiving sensitivities under different radio frequency configuration parameters. The characteristics to spread spectrum modulation system dynamic sensitivity, the utility model discloses a RSSI of detection terminal equipment installation use position at first realizes carrying out optimal configuration to the terminal. Compare other private agreement loRa network systems, the utility model provides a method just can guarantee after the system sets up communication that terminal equipment has better operating condition. On the basis of optimal configuration, the gateway device dynamically detects the RSSI value of the terminal device, and selects a receiving signal path or reconfigures the working parameters of the terminal by combining theoretical receiving sensitivity, a weak signal threshold and a change parameter setting threshold. The terminal equipment with poor received signal strength is reconfigured, and the stability of the system in long-term operation is improved through the dynamic adjustment mode. The method and the device can effectively reduce the power consumption of the system and reduce the communication overhead by carrying out the direct connection processing of the received signals on some terminal devices with good communication quality. And amplifying and adjusting the terminal signals meeting the conditions to reduce the noise coefficient of a receiving path and improve the receiving sensitivity of the LoRa private protocol gateway.
Through the combination of the above method and device, the improvement on the performance of the receiving end of the LoRa private protocol gateway is significant, and is specifically embodied in that: through promoting loRa gateway receiving sensitivity, improved the communication distance of loRa gateway under the complex environment, reduced data packet loss rate and error rate, improved the stability and the reliability of the long-term operation of loRa network.
Drawings
Fig. 1 shows a system architecture of a LoRa private protocol gateway;
FIG. 2 is a flow chart of an implementation of a method for setting optimal working parameters of a terminal for a gateway
FIG. 3 is a flow chart of path selection, attenuation control and dynamic modification of terminal operating parameters;
FIG. 4 is a schematic circuit diagram of the lifting device;
fig. 5 is a hardware configuration diagram of the LNA.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
A method and a device for improving receiving sensitivity of a LoRa private protocol gateway are provided. After wireless communication is established between the LoRa gateway equipment and the terminal node equipment, the gateway configures the terminal and obtains an RSSI value according to a preset radio frequency parameter setting table, and sets and stores parameters according to the optimal RSSI value. And the RSSI value is acquired through a receiving through channel. The utility model discloses still relate to a loRa private agreement gateway sensitivity of reception hoisting device, the device mainly by radio frequency switch, low noise power amplifier, digital adjustable attenuator, wave filter, electric capacity is constituteed. The received signal is amplified through an LNA amplification access, a primary digital adjustable attenuator is connected to the rear stage of the LNA and used for adjusting the amplitude of the signal, the attenuation amplitude of the adjustable attenuator is determined and controlled by a gateway according to the radio frequency parameters configured by a terminal, and the device is used for performing direct processing on a radio frequency transmitting signal. Generally, the utility model discloses a set for optimum radio frequency configuration parameter to combine the RSSI value that tests, carry out selective enlarging, decay and filtering to received signal through preceding stage LNA, attenuator and wave filter, thereby reduced the noise figure of loRa gateway receiver and reach the purpose that improves the reception sensitivity.
The technical implementation scheme of the utility model is as follows:
the utility model provides a promote loRa private protocol gateway receiving sensitivity's method and device, the utility model relates to loRa private protocol gateway equipment and supporting terminal equipment, concretely relates to loRa gateway equipment communicates with supporting terminal through private protocol. The LoRa private protocol is a custom protocol that is different from LoRaWAN and LinkWAN network protocols and system architectures. Fig. 1 shows a system architecture of an LoRa private protocol gateway, where the LoRa private protocol gateway is characterized by having an LoRa configuration channel and N LoRa communication channels, where N is greater than or equal to 2, each LoRa channel operates in 470-510MHz frequency band, and the transceiving antennas of each channel are independent of each other.
The utility model relates to a promote method of loRa private protocol gateway reception sensitivity, wherein the gateway sets up the terminal optimum working parameter method and realizes that the flow is shown in figure 2. The method specifically comprises the following steps: terminal equipment matched with the LoRa private protocol gateway equipment sends a network access request through LoRa communication, and the gateway equipment receives the network access request and then communicates with the terminal equipment through a LoRa configuration channel to confirm whether the terminal equipment is successfully connected. After the terminal device is successfully connected, the gateway device sequentially configures the terminal device according to a preset radio frequency parameter configuration table, wherein the radio frequency parameters comprise a working frequency band, a working bandwidth, a spreading factor and a coding rate. The gateway device actively acquires the ambient noise RSSI, the RSSI when receiving data last time and the theoretical highest receiving sensitivity under a certain parameter of the terminal device which establishes communication at present, compares the optimal RSSI value with the theoretical highest receiving sensitivity, and sets and stores the parameter. Wherein the LoRa theoretical receive sensitivity is related to the Spreading Factor (SF) and the channel Bandwidth (BW), and the calculation formula is as follows:
the RSSI refers to a signal strength indication function, which is measured in the bandwidth of a receiver and is used for judging the connection quality, and the larger the RSSI value is, the stronger the current signal strength is, and the better the connection quality is.
The flow of path selection, attenuation control and dynamic modification of terminal operating parameters is illustrated in fig. 3. After the terminal accesses the network, the gateway equipment periodically acquires the RSSI value of the signal channel connected to the terminal equipment of the gateway equipment in real time through the through channel, and compares the RSSI value with a preset weak signal threshold value and a replacement parameter threshold value in sequence according to the measured value to judge whether to bypass the corresponding terminal receiving signal to an amplification channel or to reconfigure the radio frequency parameters of the terminal.
For the case of reconfiguring radio terminal parameters: if the gateway and the terminal equipment have the received signal quality deterioration caused by the variation factors such as the environment and the like in the communication process, the gateway end compares and judges the RSSI value of the terminal after dynamically detecting the RSSI value with the preset extremely low signal intensity threshold value of the radio frequency parameter needing to be reconfigured, if the signal threshold value range of the radio frequency parameter needing to be reconfigured is met, the gateway reconfigures the parameters of the terminal so as to search the optimal communication configuration parameters after the environment is changed, and the condition that the terminal is lost is avoided.
For the condition of meeting the requirement of accessing the received signal to the receiving and amplifying channel, a digital adjustable attenuator is connected at the rear stage of an LNA circuit of the amplifying channel, the attenuation amplitude is determined by a gateway according to the currently set radio frequency parameters and is used for adjusting the strength of the amplified received signal, and the rear stage circuit is prevented from being damaged due to the fact that the received signal is too strong. The attenuation amplitude setting of the attenuator of the latter stage is given by:
the strongest received signal at the input end of the LoRa radio frequency chip should be less than 0dBm, and the LNA used in the system can provide a gain of more than 25dB, which may cause the received signal strength of the LoRa gateway and the terminal to be large in the case of near field communication, so that the receiver power inside the gateway is saturated and even the LoRa radio frequency chip is damaged. To prevent this, an attenuator is usually added between the LNA output and the LoRa rf chip input. The value of the attenuator is determined according to the following equation:
RSLmax＝Txpwr+Txantgain-Pathloss+Rxantgain+LNAgain-Attloss
wherein RSLmaxFor maximum signal strength present at the input of the LoRa radio frequency chip, TxpwrAnd TxatngainRespectively transmit power and transmit antenna gain, RxantgainAnd LNAgainGain of receiving antenna and low noise amplifier, PathlossTo path loss, AttlossI.e. the value of the attenuator. Through the calculation of the formula, a proper attenuation value is set to ensure the RSL of the systemmaxLess than 0 dBm.
The utility model discloses still include a receiver sensitivity hoisting device for receiving front end circuit. In the LoRa wireless communication system, the range of the received signal is determined by factors such as the magnitude of the transmission power, the transmitter antenna gain, the receiver antenna gain, the propagation channel attenuation, and the receiver sensitivity. The receiver sensitivity of the LoRa gateway is between-111 dBm to-148 dBm depending on the selected configuration parameters (e.g., center frequency, channel bandwidth), hardware settings, and acceptable system performance limits for any particular application. The utility model discloses to 470-510MHz frequency channels that loRa private protocol gateway used, but designed external LNA module in the receiving path of receiving antenna and loRa radio frequency chip, improved the receiving sensitivity through reducing receiver noise figure, increased communication range.
The circuit principle of the device is shown in figure 4. The circuit mainly comprises a switch selection circuit, a filter circuit, a 470-510MHz LNA circuit, an adjustable attenuation circuit and a control unit circuit. The control unit circuit selects a transmitting or receiving path by controlling the radio frequency switch. If the signal is a transmitting signal, the control unit circuit gates the transmitting path to carry out through processing on the transmitting signal, and if the signal is a receiving signal, the control unit circuit gates the through path or the receiving amplifying path according to whether the receiving signal is a configuration signal or a strong signal or a normal communication signal.
The control circuit consists of a control unit, a LoRa radio frequency chip and a logic gate circuit. The control unit controls the attenuation value of the attenuator and controls the switching of the receiving through path and the receiving amplifying path through the output interface. A DIO2 pin led out from the LoRa radio frequency chip is used for controlling transceiving conversion, the pin is in an idle state or a receiving state and is in a low output level, and in a transmitting mode, the pin is in a high level. The control part realizes the automatic control of receiving and transmitting through the connection relation of the logic circuit, improves the switching speed of a radio frequency receiving and transmitting channel, and reduces the software and hardware overhead of the LoRa gateway. The model of the AND gate chip of the control unit circuit is SN74LVC1G08, the model of the inverter chip is SN74AHC1G04, and the model of the OR gate chip is SN74AHCT1G 32. The radio frequency switch is PE42440, the attenuator is PE43704, and the LoRa radio frequency chip is SX 1268.
The device accesses the received signal in the normal communication mode into the receiving amplification path, amplifies the received signal by the LNA circuit and then sends the amplified signal into the adjustable attenuator for proper attenuation, so that the damage to a receiving chip caused by overlarge amplitude of the amplified signal is avoided, and the linearity requirement of a receiver is met. The signals after amplitude modulation by the attenuator are accessed into a rear-stage band-pass filter to filter out-of-band interference signals and then input into a demodulation pin of a radio frequency chip to be subjected to signal processing. The receiving sensitivity improving device has 6 capacitors communicated with each signal transmission path, and the capacitance values of the capacitors are 47 pF. The capacitors between the antenna and the radio frequency switch, between the radio frequency switch and the LoRa radio frequency chip, and between the transmitting through path and the receiving through path are all filter capacitors, and the capacitors are mainly used for filtering out low-frequency out-of-band interference signals and improving the electromagnetic interference resistance of the circuit. In a receiving amplification path, capacitors between the radio frequency switch and the LNA and between the LNA and the attenuator are blocking capacitors, and the main function is to isolate a direct current signal of the LNA biasing circuit from an alternating current signal path. The theoretical analysis of the receiving sensitivity of the receiving signal amplification path is as follows:
the receiving sensitivity calculation formula of the system is as follows:
NT0is the thermal noise floor of the receiver, where K is Boltzmann constant, and K is 1.38 × 10-23J/K, T0 is standard noise temperature, T0＝290K，NT0＝kT0And ≈ 174dBm/Hz, which is a constant. The above formula can be reduced to the following formula:
NF is the noise figure of the receiver, and measures how much the SNR of the output signal of a signal is reduced when the signal enters a system, and the calculation formula is as follows:
f is the noise factor, which can be calculated in a cascade system by the following equation:
according to the formula, the influence on the noise coefficient is larger for the receiving system as the front circuit unit is higher, so that the noise coefficient of the receiver can be effectively reduced by adding the low noise amplifier at the front stage to amplify the received signal. BW is the channel bandwidth of the system, Eb/Nt _ req is the ratio of the mean bit energy of the useful signal to the noise and interference power spectral density, also called the demodulation threshold, and is a measure of the quality factor of the digital modulation and coding scheme. The value of Eb/Nt _ req depends on the modulation scheme and demodulation algorithm of the system, and therefore Eb/Nt _ req is a fixed value for a specific communication system. Therefore, once the communication system and the bandwidth are determined, only NF playing a decisive role in the sensitivity of the system, and the device achieves the aim of improving the receiving sensitivity by reducing the noise coefficient of the LoRa gateway receiver.
The working frequency band of the low noise amplifier in the device is 470-510MHz, the in-band gain is 25dB, the gain flatness is less than 0.8dB, and the noise coefficient is less than 1 dB. The design of the LNA comprises impedance matching of input and output and design of a direct current bias circuit, gain flatness is increased through a parallel negative feedback technology, and the hardware structure of the LNA is shown in fig. 5. The LNA circuit specifically comprises an input port, an input matching network, an LNA monolithic integrated circuit, an output matching network, a feedback network, a bias circuit and an output port. The LNA monolithic integrated circuit is BGU 6104. The input port and the output port are designed by adopting standard 50 ohm impedance, and the bias circuit determines the static working point of the LNA monolithic integrated circuit. The input matching network has the function of matching the minimum input noise coefficient impedance point of the LNA monolithic integrated circuit with the input port impedance within the frequency range of 470-510MHz so as to achieve the purpose of minimum input noise. The output matching network is used for matching the maximum gain impedance point of the LNA monolithic integrated circuit with the impedance of an output port so as to achieve the purpose of maximizing the gain in the frequency band of 470-510 MHz. The feedback network is used to improve the gain flatness and overall stability of the LNA circuit.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the above embodiments, and that the foregoing embodiments and descriptions are provided only to illustrate the principles of the present invention without departing from the spirit and scope of the present invention. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (6)
1. A device for improving receiving sensitivity of a LoRa private protocol gateway is characterized by mainly comprising a radio frequency switch, a filter, a LoRa radio frequency chip, an LNA circuit, an attenuator and a control unit circuit;
the radio frequency switches are provided with two, wherein the output end of one radio frequency switch is divided into two paths to be connected with the input end of the other radio frequency switch, one path is a receiving direct path, the other path is a receiving amplifying path, the receiving amplifying path comprises an LNA circuit, an attenuator and a filter, the received signal is amplified by the LNA circuit and then sent to the attenuator for proper attenuation, the signal after amplitude modulation by the attenuator is sent to the LoRa radio frequency chip after being filtered by the rear-stage band-pass filter to remove out-of-band interference signals, a DIO2 pin is led out of the LoRa radio frequency chip and is used for controlling the radio frequency switch to receive and transmit, the control unit selects a transmitting or receiving path by controlling the radio frequency switch, if the signal is a transmitting signal, the control unit gates the transmitting path to carry out through processing on the transmitting signal, and if the transmitting signal is the receiving signal, gates the receiving through path or the receiving amplifying path according to whether the receiving signal is a configuration signal or a strong signal or a normal communication signal.
2. The apparatus of claim 1, wherein the strongest received signal at the input of the LoRa rf chip is less than 0 dBm.
3. The apparatus of claim 1, wherein the control unit controls the attenuator attenuation value through the output interface.
4. The apparatus for improving the receiving sensitivity of the LoRa proprietary protocol gateway of claim 1, wherein the apparatus for improving the receiving sensitivity is provided with a capacitor in each signal transmission path, and the capacitance value of the capacitor is 47 pF.
5. The apparatus of claim 4, wherein the capacitors between the radio frequency switch and the LoRa radio frequency chip, the transmit pass-through path and the receive pass-through path are filter capacitors.
6. The apparatus of claim 4, wherein the capacitors between the RF switch and the LNA and between the LNA and the attenuator are blocking capacitors.
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