What is LoRa

Introduction to LoRa: What is LoRa Technology?

What is LoRa?

LoRa (Long Range) is an emerging wireless communication technology developed by US Semtech, an ultra-long-distance wireless transmission scheme based on spread spectrum technology. Lora changes the previous way of thinking about the compromise between transmission distance and power consumption. Provide users with a simple wireless communication solution that can achieve long distance, long battery life and large capacity.

LoRa Advantages

LoRa Network Composition

LoRa network is mainly composed of end point (built-in LoRa module), gateway (or base station), server and cloud.

Schematic diagram of LoRa network composition

LoRa Data Packet Parameter

Generally speaking, transmission rate, operating frequency band and network topology are the three main parameters that affect the characteristics of sensor networks. The choice of transmission rate will affect the transmission distance and battery life of the system; the choice of operating frequency band should compromise the frequency band and the design goal of the system; in the FSK system, the choice of network topology is determined by the transmission distance requirements and the number of nodes required by the system. LoRa Combines digital spread spectrum, digital signal processing and forward error correction coding technology, with unprecedented performance. Previously, only those high-level industrial radio communications would integrate these technologies, and with the introduction of LoRa, the situation in the field of embedded wireless communications has been completely changed.

Forward error correction coding technology adds some redundant information to the data sequence to be transmitted, so that the error symbols injected during the data transmission process will be corrected in time at the receiving end. This technique reduces the need to create "self-healing" data packets for retransmission in the past, and performs well in solving sudden errors caused by multipath fading. Once the data packets are established and injected with forward error correction coding to ensure reliability, these data packets will be sent to a digital spread spectrum modulator. This modulator feeds each bit of the packet data packet into a "spreader", dividing each bit time into a number of chips.

Even if the noise is very large, LoRa can calmly deal with the LoRa modem. After being configured, the divisible range is 64-4096 chips/bit, and the highest spreading factor (12) of 4096 chips/bit can be used. In contrast, ZigBee can only divide the range of 10-12 chips/bit.

By using a high spreading factor, LoRa technology can transmit small volumes of data over a wide range of radio spectrum. In fact, when you measure through a spectrum analyzer, the data looks like noise, but the difference is that the noise is irrelevant, while the data is correlated, 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 minimum signal-to-noise ratio (SNR) of 8dB needs to be reliably demodulated. By configuring AngelBlocks, LoRa can demodulate a signal with a signal-to-noise ratio of -20dB. The difference between GFSK and this result is 28dB, which is equivalent to a much larger range and distance. In an outdoor environment, a 6dB gap can achieve twice the original transmission distance.

Strong link budget, let the signal fly farther. To effectively compare the performance of the transmission range between different technologies, we use a quantitative indicator called "link budget". The link budget includes every variable that affects the signal strength of the receiver, and in its simplified system it includes transmit power plus receiver sensitivity. AngelBlocks has a transmit power of 100mW (20 dBm ), a receiver sensitivity of -129dBm, and a total link budget of 149dB. In comparison, GFSK wireless technology with a sensitivity of -110dBm (which is already 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 must transmit at a frequency of 46dBm or about 36W to achieve a link budget value similar to LoRa . Therefore, using LoRa technology we can obtain a wider transmission range and distance with low transmit power, this low-power wide-area technology is exactly what we need.

LoRa data packet has three key parameters: preamble, optional header, data payload, the next three parameters to do some brief description.

LoRa Data Packet Parameter

LoRa modulation pack and data transmission diagram

LoRa modulation pack and data transmission diagram

1. Preamble

The preamble is used to keep the receiver in sync with the incoming data stream. By default, the data packet contains a preamble of 12 symbol lengths. The preamble length is a variable that can be set programmatically, so the length of the preamble can be expanded. The transmit preamble length can be changed by setting the preamble register length between 6 and 65536. The length of the actual transmitted preamble ranges from 6 + 4 to 65535 + 4 symbols. The receiver performs preamble detection periodically. The preamble length of the receiver should be consistent with that of the transmitter. If the preamble length is unknown or is subject to change, set the receiver's preamble length to a maximum value.

2. Header

Depending on the mode of operation selected, two headers can be selected. On the RegModemConfig1 register, the header type is selected by setting the ImplicitHeaderModeOn bit. Explicit header mode: Explicit header mode is the default mode of operation. In this mode, the header contains information about the payload, including:

The header is sent according to the maximum error correction code (4/8). In addition, the header also contains its own CRC, allowing the receiver to discard invalid headers. Implicit header mode: In certain cases, if the payload length, coding rate and CRC are fixed or known, it is more effective to shorten the transmission time by calling the implicit header mode. In this case, it is necessary to manually set the payload length, error coding rate and CRC at both ends of the wireless link. Note: If the spreading factor SF is set to 6, only the implicit header mode can be used, the spreading factor will be explained in detail below.

3. LoRa modem

LoRa modulation and demodulation technology (hereinafter referred to as LoRa) uses a proprietary modulation and demodulation program to combine spread spectrum modulation with cyclic error correction coding technology. Compared with traditional modulation technology (FSK or OOK), this technology expands the wireless communication link. The coverage range improves the robustness of the link. It has stronger anti-interference. The suppression ability of the same channel GMSK interference signal reaches 20dB, so LoRa is used in frequency bands and hybrid communication networks with high spectrum utilization, which is convenient for expanding the coverage when the original modulation scheme in the network fails. LoRa was optimized by developers by adjusting three key design parameters, spreading factor, modulation bandwidth, and coding rate, to achieve a balance between link budget, immunity, spectrum footprint, and nominal data rate.

4. Spreading factor

LoRa spreading uses multiple information chips to represent each bit of payload information. The transmission speed of spread spectrum information is called symbol rate (Rs), and the ratio between the chip rate and the nominal symbol rate is the spreading factor, which indicates the number of symbols transmitted per information bit. Signals can also be received normally under the condition of negative signal to noise ratio, which improves the sensitivity, link budget and coverage. However, the relationship between different spreading factors is orthogonal, so the spreading factors at the sender and receiver must be the same.

Spreading factor (RegModulationCfg) Spreading factor (chip/symbol) LoRa demodulator signal to noise ratio (SNR)
6 64 -5 dB
7 128 -7.5 dB
8 256 -10 dB
9 512 -12.5 dB
10 1024 -15 dB
11 2048 -17.5 dB
12 4096 -20 dB

As can be seen from the above table, when the spreading factor is 12, data packets can be received at -20dB, indicating that the larger the spreading factor, the higher the sensitivity, and the slower the transmission speed.

5. Coding rate

LoRa uses cyclic error correction coding for forward error detection and error correction, but incurs transmission overhead. The data overhead generated by each transmission is as follows:

Encoding rate (RegTxCfg1) Cyclic coding rate Cost ratio
1 4/5 1.25
2 4/6 1.5
3 4/7 1.75
4 4/8 2

The larger the coding rate, the stronger the forward error correction, and the stronger the link anti-interference, but the transmission overhead will increase, thereby increasing the transmission time.

6. Signal bandwidth

The frequency components contained in a signal can be observed from the signal spectrogram. The difference between the highest frequency and the lowest frequency of the harmonics contained in a signal, that is, the frequency range owned by the signal, is defined as the bandwidth of the signal. The larger the frequency range of the signal, the wider the bandwidth of the signal.

Bandwidth (kHz) Spreading factor coding rate Nominal bit rate (bps)
7.8 12 4/5 18
10.4 12 4/5 24
15.6 12 4/5 37
20.8 12 4/5 49
31.2 12 4/5 73
41.7 12 4/5 98
62.5 12 4/5 146
125 12 4/5 293
250 12 4/5 586
500 12 4/5 1172

As can be seen in the above table, increasing the signal bandwidth, the larger the nominal bit rate of transmission, indicating that increasing the signal bandwidth can effectively increase the data rate to shorten the transmission time, but there will be drawbacks that will reduce the reception sensitivity and shorten the transmission distance.

LoRa (Low Range, low power wide area network communication technology) market size and industry development prospects show a growth trend. According to the data, the size of my country's LoRa market will be about 21.80 billion yuan in 2021, and it is expected to increase to about 28.30 billion yuan in 2022, with a growth rate of 30%. In addition, the shipments of LoRa chips used in the end point field in my country in 2021 are about 705.20 billion, and it is expected to increase to 952 billion in 2022, with a growth rate of 35%.

In addition, LoRaWAN ( LoRa Wide Area Network) was officially recognized by the International Telecommunication Union (ITU) as a global Internet of Things standard in December 2021, which is an important milestone in the development of LoRa and is expected to further promote the expansion of the LoRa market. Under such a background, the development space of enterprises in the upstream and downstream layout of the LoRa industry chain is increasing, especially enterprises producing core components have huge development potential.

LoRa and NB-IoT (Narrowband IoT Technology) have their own advantages. LoRa has lower power consumption and lower cost, which can meet the needs of different scenarios; while NB-IoT has greater bandwidth and wider signal coverage, which can achieve global Roaming. The two technologies can be mixed and networked to improve the IoT communication experience.

From this point of view, LoRa and NB-IoT will compete with each other in some Application Areas in the future, but can be used complementary in more Application Areas. The era of the Internet of Everything has arrived, the number of networked end points will continue to grow rapidly, and the future development prospects of the LoRa industry are broad.