Low Power Wide Area Network (LPWAN for short), that is, low-power wide-area network, is mainly used for communication between devices. This communication technology has the characteristics of wide network coverage and low terminal power consumption. It is more suitable for Large-scale IoT application deployment, specifically including NB-IoT, LoRa, Sigfox, and eMTC, among which NB-IoT and LoRa have been widely sought after in recent years.
In this issue, we will come to know the technology that is widely used-LoRa. (NB-IoT will be introduced in the next issue)
LoRa is a long-distance wireless transmission technology based on spread spectrum technology. In fact, it is also one of many LPWAN communication technologies. It was first adopted and promoted by the American Semtech company. This solution provides users with a simple wireless communication method that can realize long-distance and low power consumption. At present, LoRa mainly operates in the ISM frequency band, mainly including 433, 868, 915 MHz and so on. As a low-power wide-area network communication technology, LoRa wireless transmission technology has the advantages of stronger communication radio frequency distance and longer transmission distance under the same power consumption. The communication distance is 3-5 times that of traditional wireless technology.
Semtech has developed a complete set of LoRa communication chip solutions based on LoRa technology, including different types of LoRa chips for gateways and terminals. In order to promote other companies to participate in the LoRa ecology, in March 2015, Semtech joined forces with Actility, Cisco, IBM and other manufacturers to jointly initiate the establishment of the LoRa Alliance, and launched the constantly iterative LoRaWAN specification, which gave birth to a network consisting of nearly a thousand companies around the world. The wide-area networking standard system supported by manufacturers forms a broad industrial ecology.
There are two representative spread spectrum methods: direct sequence spread spectrum and frequency hopping spread spectrum. LoRa technology is a modulation method based on direct sequence spread spectrum. Direct Sequence Spread Spectrum (DSSS), referred to as Direct Spread (DS), is a widely used spread spectrum method.
LoRa basic technical indicators:
Transmission distance: up to 2~5km in towns and up to 15km in suburbs.
Working frequency: ISM frequency band includes 433MHz, 470MHz, 868MHz, 915MHz, etc.
Standards: IEEE 802.15.4g, LoRaWAN.
Based on spread spectrum technology, a variant of CSS has forward error correction (Forward Error Correction, FEC) capability, which belongs to Semtech's private patented technology.
Capacity: A LoRa gateway can connect thousands of LoRa nodes.
Battery Life: Up to 10 years.
Security: AES128 encryption.
Transmission rate: 18b/s~ 62.5kb/s.
LoRa has the following advantages:
01Low power consumption
LoRa applications are generally IoT devices, usually powered by batteries, and used for more than a few years, which requires LoRa to have extremely low power consumption. The realization of LoRa's low power consumption is mainly determined by two aspects: on the one hand, the chip needs to have low power consumption; on the other hand, the software communication protocol also needs to have low power consumption.
First of all, the power consumption of LoRa in hardware is very low. For example, the current of SX126X series hot start sleep mode is only 1.2uA, the receiving current at 125kHz is 4.6mA, and the sending current at 17dBm power is only 58mA.
Secondly, in terms of software communication protocols, LoRa does not have complex communication protocols like other wireless technologies. The data packets are very simple, and there is no need to send a large amount of handshake data. In order to achieve the purpose of saving power, the industry widely uses a Wake on Radio (WOR) method.
The chip enters the receiving (RX) mode periodically to listen for the wake-up preamble, and is in the sleep (Sleep) mode at other times. The receiving current of WOR is shown in the figure below. Most of the time it is in sleep mode, and only a small part of the time is woken up in receiving mode, so its overall power consumption is very low. For example, Ebyte's E22 and E32 modules all have WOR function, which can meet the low power consumption requirements very well.
02 long distance
In wireless communication, the standard to measure the communication distance is the link budget, which is equal to the transmit power minus the sensitivity. Sensitivity is a negative number, and the higher the sensitivity, the more negative, so the way to improve the link budget is to increase the transmit power and improve the sensitivity. However, the transmission power has strict requirements in various countries and regions, so the only way to increase the communication distance is to increase the sensitivity. The LoRa sensitivity has reached -123dBm when BW=125kHz, SF=7; when BW=7.81kHz, SF=12, the sensitivity has reached -149.1dBm. The sensitivity of Bluetooth is around -90dbm, and ZigBee is around -85dBm, so the transmission distance of LoRa is much longer than other wireless communication technologies. However, LoRa uses bandwidth in exchange for sensitivity, which will result in a very slow transmission rate, so LoRa is suitable for long-distance, low-speed, and small-volume applications.
LoRa can achieve long-distance transmission. In addition to the advantage of sensitivity, another very important factor is its super anti-interference ability.
LoRa can still communicate when the noise is lower than 20dB, which is not available in existing traditional communication technologies.
LoRa can normally demodulate the signal 20dB below the noise, while FSK theoretically needs to be 8dB above the noise to ensure demodulation. When the communication process encounters external electromagnetic signal interference, LoRa can continue to communicate stably, while traditional wireless technologies cannot communicate. Therefore, in some areas with serious channel interference, customers will choose LoRa technology as the core technology for stable communication. The reason why LoRa modulation has such a strong anti-interference ability is mainly because Chirp debugging can gather useful LoRa signals under the noise during coherent demodulation, and the noise is still noise after coherent demodulation.
In 2022, more than 6.5 million LoRa-based gateways and more than 280 million LoRa-based terminal nodes have been deployed worldwide. There are more than 170 LoRaWAN public network operators and the number is still increasing. According to ABI Research, by 2026, LoRa will account for more than 50% of global non-cellular low-power wide-area network connections. The number of domestic LoRa industry chain enterprises has reached more than 3,000, and it is still growing rapidly. The Chinese market is an extremely important part of LoRa's global ecological construction.
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