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What’s LoRa?
Source:Original | Author:C&T RF Antennas Inc | Publish time: 2018-11-08 | 827 Views | Share:


LoRa Introduction There are several wireless technologies in the Internet of Things applications that can form a local area network or a wide area network. The main wireless technology to form a LAN 2.4GHz WiFi, Bluetooth, Zigbee, etc., composed of wide area network wireless technology mainly 2G / 3G / 4G and so on. These wireless technologies, the advantages, and disadvantages are very obvious, can be summarized as shown below. Before the Low Power Wide Area Network (LPWAN) generation, it seems that there is only one choice between the long distance and the low power consumption. When using LPWAN technology, designers can do both, to achieve maximum distance communications and lower power consumption, while also saving additional repeater costs.

 

LoRa is one of the LPWAN communication technologies and is an ultra-long distance wireless transmission scheme based on spread spectrum technology adopted and promoted by Semtech. This scheme has changed the previous trade-offs about transmission distance and power consumption, providing users with a simple system that can realize long-distance, long battery life, and large capacity, and then expand the sensor network. At present, LoRa mainly in the global free band operation, including 433,868,915 MHz and so on.

LoRa technology has long-range, low power (long battery life), multi-node, low-cost features.

The following is a case of USA, from the sensitivity, link budget, coverage, transmission rate, send current, standby current, receive current, 2000mAh battery life, positioning, anti-jamming, topology, maximum number of terminal connections Compared the differences between Sigfox, LTE-M, ZigBee, WLAN, 802.11ah, and LoRa. Subsequent LoRa technology small science (below) will explain some of the above parameters.

LoRa network composition

LoRa network mainly by the terminal (built-in LoRa module), gateway (or base station), Server and cloud four parts. Application data can be bi-directional.

 

LoRa Alliance The LoRa Alliance is an open, nonprofit organization led by Semtech in March 2015, with members such as Activity in France, AUGTEK in China and Kpn in the Netherlands. Less than a year, the Union has developed more than 150 member companies, many of which IBM, Cisco, France Orange and other heavyweight manufacturers. Each chain in the industry chain (terminal hardware manufacturer, chip maker, module gateway manufacturer, software vendor, system integrator, network operator) has a large number of enterprises, the openness, competition, and cooperation of this technology Adequacy have contributed to the rapid development of LoRa and ecological prosperity.

Network deployment

LoRa network has been in the world for more pilot or deployment. According to the earlier data released by LoRa Alliance, nine countries have started to build networks and 56 countries have started piloting. China AUGTEK completed 284 base stations in the Beijing-Hangzhou Grand Canal, covering 1300Km watershed. US network operator Senet completed 50 base stations in North America in 2015, covering 15,000 square miles (about 38,850 square kilometers) The first phase of the completion of more than 200 base stations set up; France Telecom-Orange announced in early 2016 in France network; Royal Dutch telecommunications kpn announced that it will build a network in New Zealand, 2016 years ago to reach 50% coverage; India Tata announced in Mumbai and Telstra announced that it will be piloted in Melbourne ... ... (follow-up article will detail some of the companies use LoRa technology to make the application)

LoRaWAN agreement

LoRaWAN is a low power Wide Area Network (LPWAN) standard based on the open source MAC layer protocol introduced by the LoRa Alliance. This technology can provide local, national or global networks for battery-powered wireless devices. LoRaWAN is aimed at some of the core needs of the Internet of Things, such as secure two-way communication, mobile communication, and static location identification services. The technology without the need for local complex configuration, you can make intelligent devices to achieve seamless interoperability between the Internet to the field of users, developers and businesses free operation authority.

LoRaWAN network architecture is a typical star topology, in this network architecture, LoRa gateway is a transparent transmission of the relay, connecting the terminal equipment and back-end central server. Between the gateway and the server through the standard IP connection, the terminal device with a single hop with one or more gateway communication. All nodes and the gateway are two-way communication between, but also support the cloud upgrade and other operations to reduce the cloud communication time.

The communication between the terminal and the gateway is done on the basis of the different frequencies and the data transmission rate. The choice of the data rate needs to be weighed between the transmission distance and the message delay. As a result of spread spectrum technology, the different transmission rate of communication will not interfere with each other and will create a "virtual" frequency band to increase the gateway capacity. LoRaWAN has a data transfer rate range of 0.3 kbps to 37.5 kbps. To maximize the battery life of the end device and the overall network capacity, the LoRaWAN network server controls the data transfer rate and data rate by each Adaptive Data Rate (ADR) The RF output power of a terminal device. Nationally covered wide area networks aim at applications such as critical infrastructure, confidential personal data transmission, or social public services. On the secure communication, LoRaWAN generally use multi-layer encryption to solve: First, the unique network key (EU164), to ensure network layer security; Second, the unique application key (EU164), to ensure that the application layer terminal to the terminal Of the security; Third, belong to the equipment of the special key (EUI128). LoRaWAN network according to the actual application of the different, the terminal equipment is divided into A / B / C three categories: Class A: two-way communication terminal equipment. This type of terminal device allows two-way communication, each terminal device uplink transmission will be accompanied by two downstream receive window. The transmission slot of the terminal device is based on its own communication requirements, and its fine-tuning is based on a random time base (ALOHA protocol). Class A belongs to the terminal equipment in the application of the lowest power consumption, the terminal sends an uplink transmission signal, the server can quickly carry out downlink communications, at any time, the server downlink communication can only be in the uplink after the communication.

Class B: Bidirectional communication terminal device with preset receiving slot. This type of terminal device will be at the preset time to open the redundant receiving window, in order to achieve this purpose, the terminal will synchronize from the gateway to receive a Beacon, through the Beacon base station and module time synchronization. This way enables the server to know that the terminal device is receiving data.

Class C: Bidirectional communication terminal equipment with the largest receiving slot. This type of terminal device continues to open the receiving window, only when the transmission is closed.

LoRa technical points

In general, the transmission rate, operating frequency band, and network topology are the three main parameters that affect the characteristics of the sensor network. The choice of transmission rate will affect the transmission distance and battery life of the system; the choice of working frequency band to compromise the frequency band and the system design goals; and in the FSK system, the network topology is selected by the transmission distance requirements and the system needs nodes Number to decide. LoRa incorporates digital spread spectrum, digital signal processing, and forward error correction coding technology, with unprecedented performance. Previously, only those high-grade industrial radio communications would fuse these technologies, and with the introduction of LoRa, the field of embedded wireless communications has undergone a radical change.

The forward error correction coding technique adds some redundant information to the sequence of data to be transmitted so that the error symbols injected in the data transmission process are corrected at the receiving end in time. This technology reduces the need to create "self-repair" packets in the past and performs well in resolving burst errors caused by multipath fading. Once the packet packets are set up and injected with forwarding error correction coding to ensure reliability, these packets will be sent to the digital spread spectrum modulator. This modulator feeds each bit of the packet into an "expander", dividing each bit of time into a number of chips.

 Even if the noise is large, LoRa can handle the LoRa modem, which can be divided into a range of 64-4096 chips/bit, up to 4096 chips/bits in the highest spreading factor (12). In contrast, ZigBee can only be divided into 10-12 chips/bit.

By using high spreading factors, LoRa technology can transmit small-capacity data over a wide range of radio spectra. In fact, when you measure by the spectrum analyzer, these data look like noise, but the difference is that the noise is irrelevant, and the data is relevant, based on which the data can actually be extracted from the noise. The higher the spreading factor, the more data can be extracted from the noise. At a well-functioning GFSK receiver, the 8dB minimum signal-to-noise ratio (SNR) requires reliable demodulation of the signal. Using the configuration of AngelBlocks, LoRa demodulates a signal with a signal-to-noise ratio of -20dB, GFSK A result of the gap is 28dB, which is equivalent to the range and distance widened a lot. In the outdoor environment, the 6dB gap can be achieved twice the original transmission distance.


 

Super link budget, let the signal fly farther

In order to effectively compare the performance of the transmission range of different technologies, we use a quantitative indicator called "link budget". The link budget includes each variable that affects the strength of the receiver, including the transmit power plus the receiver sensitivity in its simplified architecture. AngelBlocks has a transmit power of 100mW (20dBm), a receiver sensitivity of -129dBm, and a total link budget of 149dB. In comparison, GFSK wireless technology with a sensitivity of -110 dBm (which is its excellent data) requires 5W of power (37dBm) to achieve the same link budget value. In practice, most GFSK wireless technology receiver sensitivity can reach -103dBm, in this case, the transmitter launch frequency must be 46dBm or about 36W, in order to achieve similar to LoRa link budget value.

 

Therefore, using LoRa technology we can get a wider transmission range and distance with low transmit power, which is what we need.

 

About LPWAN

Low Power Wide Area Network (LPWAN) is an integral part of the Internet of things, with low power consumption, wide coverage, strong penetration characteristics, suitable for every few minutes to send and receive a small amount Data applications, such as water transport location, street monitoring, parking monitoring and so on. LPWAN-related organizations The LoRa Alliance currently has 145 members worldwide and its lush ecosystems are highly interoperable with LoRaWAN-compliant devices. A communication gateway that fully conforms to the LoRaWAN standard can access thousands of wireless sensor nodes within 5 to 10 kilometers, and its efficiency is much higher than that of the traditional point-to-point polling communication mode, and can greatly reduce the node communication power.