After a year of rapid development, practitioners in the field of the Internet of Things are no stranger to low power wide area networks (LPWAN). As an early commercialized LPWAN technology, LoRa has been widely used both at home and abroad. This article is based on various types of products that LoRa has adopted in LoRa's commercial promotion in August Technology (AUGTEK), chairman of the National Association of Low-Power Wide Area Network Industry. The problem is compiled.
Getting to Know LoRa: Low-Power Wide Area Network Representative Technology
LoRa is one of low-power wide-area network communication technologies. It is a super long-distance wireless transmission technology based on spread spectrum technology adopted and popularized by Semtech and is a unique modulation format generated by Semtech's RF part. The core chips for the LoRa radio section are the SX1276 and SX1278. This kind of chip integrates small scale and high efficiency, and brings high receiving sensitivity to LoRa wireless module. The gateway chip uses the SX1301 with higher integration and more channels. The LoRa gateway developed with SX1301 as the core can form a multi-node complex IoT ad hoc network with a large number of LoRa modules.
From the technical point of view, LoRa is a spread spectrum technology, but it is not a direct sequence spread spectrum. Direct-sequence spreading increases the coding gain by modulating the carrier chip to transmit more spectrum. LoRa modulation, similar to multi-state FSK modulation, uses an unmodulated carrier for chirping to spread energy over a wider range of frequencies.
From the perspective of the network structure, LoRa modulation technology is a physical layer (PH Ylayer) protocol, which can be used in almost all network technologies. Although the Mesh network expands the scope of network coverage, it sacrifices network capacity, synchronization overhead, and battery life. With the advancement of LoRa technology link budget and coverage distance, Mesh networks are no longer suitable. Therefore, star networking is used to optimize the network structure, extend battery life, and simplify installation. LoRa gateways and modules are networked in a star network. LoRa modules can be networked in point-to-point polling mode. Of course, point-to-point polling efficiency is much lower than that of star networks.
LoRa Gateway: A Bridge Between Terminals and Servers
The LoRa gateway is located at the core position of the LoRa star network. It is an information bridge between the terminal and the server and is a multi-channel transceiver. LoRa gateways are sometimes referred to as LoRa base stations or LoRa concentrators. Although the definitions are different, they are actually the same meaning.
The LoRa gateway uses different spreading factors. The different spreading factors are orthogonal to each other, so theoretically multiple different spreading factor signals can be demodulated in the same channel. The gateway and the network server are connected via standard IP. The terminal communicates with one or more gateways through a single hop. All terminal communications are two-way communication and also support remote software upgrade. Several important features of the following gateways:
(1) Gateway classification: At present, the definition is different and the gateway type is also different. For example, according to different application scenarios, they can be divided into indoor gateways and outdoor gateways; according to different communication methods, they can be divided into full-duplex gateways and half-duplex gateways; and according to design standards, they can be divided into fully-compliant LoRa WAN protocol gateways and Does not fully comply with the LoRa WAN protocol gateway. AUGTEK next-generation gateways are outdoor, full-duplex, and fully compliant with the LoRa WAN protocol. The LoRa gateway and LoRa terminal that are fully compliant with the LoRa WAN protocol can realize interconnection and interworking, which is of great significance!
(2) Gateway capacity: The gateway capacity refers to the ability of the gateway to receive the number of data packets within a certain period of time. In theory, a single SX1301 chip has 8 channels and can receive up to 15 million packets per day in full compliance with the LoRa WAN protocol. If the frequency of an application is 1 packet/hour, a single SX1301 chip gateway can access 62,500 endpoints. Of course, this is only a theoretical value, and the number of gateway access terminals is ultimately related to the number of gateway channels, the frequency of terminal sending packets, the number of bytes sent, and the spreading factor.
(3) Gateway access point determinants: The number of nodes accessed by the LoRa gateway depends on the channel resources that the LoRa gateway can provide and the channel resources occupied by a single LoRa terminal. If the LoRa Gateway uses the Semtech standard reference design and the gateway uses the SX1301 chip, the number of channels is a fixed 8 uplink channels and 1 downlink channel. The number of physical channels determines that the channel resources that the LoRa gateway can provide are also determined. (Different gateway design, the number of channels is different, AUGTEK gateway can realize 8 uplinks and 4 downlinks.) The channel resources occupied by a single LoRa terminal are consistent with the time occupied by the terminal by the terminal, ie, the frequency of the terminal's sending, the number of bytes sent, and The spread factor of the LoRa terminal is closely related. When the LoRa terminal's packet sending frequency and the number of transmitted packets increase, the time that the terminal occupies the channel to send and receive will increase, and it will occupy more channel resources. When the LoRa terminal uses a larger spreading factor, the signal can be transmitted farther, but at the cost of transferring more bytes of information.
In addition to the gateway, we also need to focus on the LoRa terminal: The LoRa terminal is an integral part of the LoRa network and is typically composed of LoRa modules and sensors. LoRa terminals are battery powered and can be located remotely. Each terminal that conforms to the LoRa WAN protocol can communicate directly with a gateway that conforms to the LoRa WAN, enabling interoperability.
LoRa band selection
In theory, any frequency in the 150 MHz to 1 GHz band can be used. However, Semtech's LoRa chip cannot be used in all sub-GHz frequency bands. Some frequencies other than common frequency bands (such as 433MHz, 470MHz to 510MHz, 780MHz, and 868MHz and 915MHz commonly used in Europe and the United States belong to common frequency bands) do not work well. support. AUGTEK dominates the formulation of the LoRa WAN470~510MHz protocol standard and currently provides a 470-510MHz frequency band gateway in China.
Someone will question whether the LoRa gateway uses free bands and will it be vulnerable to frequency interference?
The ability to resist interference depends on the nature of the LoRa technology itself and the design of the gateway. LoRa technology itself boasts ultra-high Receiver Sensitivity (RSSI) and superior signal-to-noise ratio (SNR). Take AUGTEK's LoRa gateway and LoRa module as an example, its receiving sensitivity reaches a staggering -142dBm, and the superior SNR can make AUTTEK gateway and terminal work 20dB below the noise threshold. In addition, the AUGTEK gateway uses frequency hopping to perform frequency shift keying through a pseudo-random code sequence, so that the carrier frequency constantly hops and spreads spectrum to prevent fixed-frequency interference.
LoRa data transmission rate and data length
The LoRa WAN protocol defines a series of data transmission rates. Different chips can be selected for different speed ranges. For example, the SX1272 supports 0.3-38.4 kbps, and the SX1276 supports 0.018-38.4 kbps. At present, AUGTEK can achieve a transmission rate of 0.3-37.5 kbps.
The length of data sent or received by LoRa devices is limited. Theoretically speaking, the SX127x series chips have a 256Bytes FIFO and transmit or receive 256Bytes will work. However, the LoRa module does not have a payload length of 256 Bytes at any transfer rate. In the case of a low transmission rate, it takes a very long time to transfer 256 bytes at one time (it may take several seconds or even longer), which is not conducive to anti-jamming and interaction, so it is generally recommended in the technical processing to split a long data. Several small data are transmitted.
Getting to Know LoRa: Low-Power Wide Area Network Representative Technology
LoRa is one of low-power wide-area network communication technologies. It is a super long-distance wireless transmission technology based on spread spectrum technology adopted and popularized by Semtech and is a unique modulation format generated by Semtech's RF part. The core chips for the LoRa radio section are the SX1276 and SX1278. This kind of chip integrates small scale and high efficiency, and brings high receiving sensitivity to LoRa wireless module. The gateway chip uses the SX1301 with higher integration and more channels. The LoRa gateway developed with SX1301 as the core can form a multi-node complex IoT ad hoc network with a large number of LoRa modules.
From the technical point of view, LoRa is a spread spectrum technology, but it is not a direct sequence spread spectrum. Direct-sequence spreading increases the coding gain by modulating the carrier chip to transmit more spectrum. LoRa modulation, similar to multi-state FSK modulation, uses an unmodulated carrier for chirping to spread energy over a wider range of frequencies.
From the perspective of the network structure, LoRa modulation technology is a physical layer (PH Ylayer) protocol, which can be used in almost all network technologies. Although the Mesh network expands the scope of network coverage, it sacrifices network capacity, synchronization overhead, and battery life. With the advancement of LoRa technology link budget and coverage distance, Mesh networks are no longer suitable. Therefore, star networking is used to optimize the network structure, extend battery life, and simplify installation. LoRa gateways and modules are networked in a star network. LoRa modules can be networked in point-to-point polling mode. Of course, point-to-point polling efficiency is much lower than that of star networks.
LoRa Gateway: A Bridge Between Terminals and Servers
The LoRa gateway is located at the core position of the LoRa star network. It is an information bridge between the terminal and the server and is a multi-channel transceiver. LoRa gateways are sometimes referred to as LoRa base stations or LoRa concentrators. Although the definitions are different, they are actually the same meaning.
The LoRa gateway uses different spreading factors. The different spreading factors are orthogonal to each other, so theoretically multiple different spreading factor signals can be demodulated in the same channel. The gateway and the network server are connected via standard IP. The terminal communicates with one or more gateways through a single hop. All terminal communications are two-way communication and also support remote software upgrade. Several important features of the following gateways:
(1) Gateway classification: At present, the definition is different and the gateway type is also different. For example, according to different application scenarios, they can be divided into indoor gateways and outdoor gateways; according to different communication methods, they can be divided into full-duplex gateways and half-duplex gateways; and according to design standards, they can be divided into fully-compliant LoRa WAN protocol gateways and Does not fully comply with the LoRa WAN protocol gateway. AUGTEK next-generation gateways are outdoor, full-duplex, and fully compliant with the LoRa WAN protocol. The LoRa gateway and LoRa terminal that are fully compliant with the LoRa WAN protocol can realize interconnection and interworking, which is of great significance!
(2) Gateway capacity: The gateway capacity refers to the ability of the gateway to receive the number of data packets within a certain period of time. In theory, a single SX1301 chip has 8 channels and can receive up to 15 million packets per day in full compliance with the LoRa WAN protocol. If the frequency of an application is 1 packet/hour, a single SX1301 chip gateway can access 62,500 endpoints. Of course, this is only a theoretical value, and the number of gateway access terminals is ultimately related to the number of gateway channels, the frequency of terminal sending packets, the number of bytes sent, and the spreading factor.
(3) Gateway access point determinants: The number of nodes accessed by the LoRa gateway depends on the channel resources that the LoRa gateway can provide and the channel resources occupied by a single LoRa terminal. If the LoRa Gateway uses the Semtech standard reference design and the gateway uses the SX1301 chip, the number of channels is a fixed 8 uplink channels and 1 downlink channel. The number of physical channels determines that the channel resources that the LoRa gateway can provide are also determined. (Different gateway design, the number of channels is different, AUGTEK gateway can realize 8 uplinks and 4 downlinks.) The channel resources occupied by a single LoRa terminal are consistent with the time occupied by the terminal by the terminal, ie, the frequency of the terminal's sending, the number of bytes sent, and The spread factor of the LoRa terminal is closely related. When the LoRa terminal's packet sending frequency and the number of transmitted packets increase, the time that the terminal occupies the channel to send and receive will increase, and it will occupy more channel resources. When the LoRa terminal uses a larger spreading factor, the signal can be transmitted farther, but at the cost of transferring more bytes of information.
In addition to the gateway, we also need to focus on the LoRa terminal: The LoRa terminal is an integral part of the LoRa network and is typically composed of LoRa modules and sensors. LoRa terminals are battery powered and can be located remotely. Each terminal that conforms to the LoRa WAN protocol can communicate directly with a gateway that conforms to the LoRa WAN, enabling interoperability.
LoRa band selection
In theory, any frequency in the 150 MHz to 1 GHz band can be used. However, Semtech's LoRa chip cannot be used in all sub-GHz frequency bands. Some frequencies other than common frequency bands (such as 433MHz, 470MHz to 510MHz, 780MHz, and 868MHz and 915MHz commonly used in Europe and the United States belong to common frequency bands) do not work well. support. AUGTEK dominates the formulation of the LoRa WAN470~510MHz protocol standard and currently provides a 470-510MHz frequency band gateway in China.
Someone will question whether the LoRa gateway uses free bands and will it be vulnerable to frequency interference?
The ability to resist interference depends on the nature of the LoRa technology itself and the design of the gateway. LoRa technology itself boasts ultra-high Receiver Sensitivity (RSSI) and superior signal-to-noise ratio (SNR). Take AUGTEK's LoRa gateway and LoRa module as an example, its receiving sensitivity reaches a staggering -142dBm, and the superior SNR can make AUTTEK gateway and terminal work 20dB below the noise threshold. In addition, the AUGTEK gateway uses frequency hopping to perform frequency shift keying through a pseudo-random code sequence, so that the carrier frequency constantly hops and spreads spectrum to prevent fixed-frequency interference.
LoRa data transmission rate and data length
The LoRa WAN protocol defines a series of data transmission rates. Different chips can be selected for different speed ranges. For example, the SX1272 supports 0.3-38.4 kbps, and the SX1276 supports 0.018-38.4 kbps. At present, AUGTEK can achieve a transmission rate of 0.3-37.5 kbps.
The length of data sent or received by LoRa devices is limited. Theoretically speaking, the SX127x series chips have a 256Bytes FIFO and transmit or receive 256Bytes will work. However, the LoRa module does not have a payload length of 256 Bytes at any transfer rate. In the case of a low transmission rate, it takes a very long time to transfer 256 bytes at one time (it may take several seconds or even longer), which is not conducive to anti-jamming and interaction, so it is generally recommended in the technical processing to split a long data. Several small data are transmitted.
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