LoRa频率背后的技术是什么

LoRa frequency range

LoRa使用CSS (线性调频扩频) 使用扩频方法作为调制技术的调制. 所谓的线性调频脉冲作为符号发送, which increase or decrease in LoRa frequency continuously over time. The data transmission is then realized by the sequential sequence of these chirp pulses.

LoRa频率

Special properties

Since LoRa works in the ISM frequency bands (433 兆赫, 868 MHz and 915 兆赫), the radiated transmission power is limited. In order to have a larger radio range than conventional modulation types such as To achieve FSK (Frequency Shift Keying), the receiver sensitivity has been significantly improved with LoRa. The LoRa receiver can still successfully receive and decode a useful LoRa signal up to 20 dB below the noise level, which results in a receiver sensitivity of a maximum of -149 分贝. Compared to the maximum FSK sensitivity of approx. –125 dBm to -130 分贝, LoRa offers a significant improvement. With the FSK receiver, the signal can only be successfully decoded if the useful signal is approx.

LoRa-Frequency-and-signal strength

Thanks to the property that LoRa can still successfully receive a useful signal up to 20 dB below the noise level, the robustness to radio interference is significantly better than that of FSK. FSK systems only work correctly if the interference signal is at least 10 dB weaker than the useful signal. 在最好的情况下, LoRa systems can still receive the useful signal if the interference signal is 20 dB stronger than the useful signal.

Limitations

From the graphic above you can see that LoRa can receive about 30 dB weaker signals than with FSK. 然而, there are two restrictions that somewhat relativize this big difference.

• First, the LoRa modulation is broadband than the FSK modulation, which means that the noise level of the LoRa receiver is generally higher than that of the FSK receiver. 特别, doubling the bandwidth increases the noise level by 3 D b.
• Secondly, LoRa can only receive a useful signal up to 20 dB below the noise level at very slow data rates of ≤ 0.5 千比特 / s. As soon as the data rate is increased, either the negative signal-to-noise ratio increases further towards zero or the bandwidth has to be increased further, which in turn increases the noise level.

Comparison measurement between LoRa and FSK

To find out how good LoRa really is, a direct comparison between LoRa and FSK should be carried out. 以此目的, our previously used standard FSK transceivers (CC1020 and CC1101) are compared with the data from the LoRa / FSK transceiver SX1261.

Transceiver调制 

Max sensitivity according to the datasheet

Data rate接收- bandwidth
CC1020FSK-118 分贝2.4 kBit/s12.5 千赫
CC1101FSK-116 分贝0.6 kBit/s58 千赫
SX1261FSK-125 分贝0.6 kBit/s4 千赫
SX1261劳拉-149.2 分贝0.02 kBit/s8 千赫

According to the information from the datasheets, LoRa achieves at least a 24dB better maximum sensitivity than with the best FSK transceiver (SX1261). Compared to the old FSK transceivers (CC1020 and CC1101), the maximum sensitivity is even 31 要么 33 dB better. Since it can be assumed that the radio range can be doubled for every 10 dB more sensitivity, 一个 4 至 8 times the radio range should be possible with LoRa compared to FSK.

然而, it is also noticeable that the maximum LoRa sensitivity is achieved with an extremely slow data rate of only 0.02 千比特 / s. In order to obtain a direct, meaningful comparison between the different transceivers, the sensitivity of all transceivers is determined at the same data rate. According to Semtech’s manufacturer, LoRa would have to achieve about 7 至 10 dB more sensitivity at the same data rate as FSK.

Our own measurements have given the following results:

Data rate灵敏度
CC1020CC1101SX1261SX1261
FSKFSK dBmFSK劳拉
1.2 kBit/s-117 分贝-112 分贝-123 分贝-129 分贝
2.4 kBit/s-117 分贝-111 分贝-121 分贝-126 分贝
4.8 kBit/s-114 分贝-109 分贝-118 分贝-123 分贝
9.6 kBit/s-112 分贝-107 分贝-116 分贝-120 分贝

The SX1261 transceiver with LoRa modulation achieves 4 – 6 dB more sensitivity than with FSK modulation. In comparison to the CC1020 8 – 11 dB and in comparison to the CC1101 13 – 17 dB more sensitivity is achieved. It is striking that the lower the data rate is chosen, the more sensitivity gain can be achieved with LoRa.

Another view shows the energy-saving potential of LoRa. In order to achieve the same sensitivity as with FSK, approximately 4 times the data rate can be used with LoRa. The same radio telegram thus becomes 4 times shorter and the energy consumption also drops by a factor of 4.

结论:

As with all radio transceivers, the maximum LoRa sensitivity of -149 dBm is only achieved at the lowest data rate. This data rate for LoRa is only approx. 0.02 千比特 / s and is therefore unusable for many applications. 然而, if such low data rates can be used, 4 times the radio range is theoretically possible compared to modern FSK transceivers.

If the LoRa data rate is increased to 1.2 kBit / s to 10 kBit / s, LoRa achieves approx. 4-6 dB more sensitivity compared to modern FSK transceivers. Compared to older FSK transceivers such as the CC1101 or CC1020, the radio range can even be doubled or tripled with LoRa.

There is an interesting energy-saving option in applications where the current FSK sensitivity was sufficient. If the same sensitivity is to be achieved with LoRa, the data rate can be increased by a factor of 4 compared to FSK, whereby the energy consumption can also be reduced by a factor of 4.

For us, LoRa technology represents an interesting alternative for applications with data rates up to 10 千比特 / s, since the radio range can be increased massively compared to the older transceivers. Of particular interest to us is the possibility of connecting to the LoRaWAN network, as this means that IoT applications can be connected to the Internet practically anywhere.

With our LoRa moduleTRX433-70we are ready for future innovative LoRa projects.

Radio transmission with LoRa

The meter readings, switching commands and other information can be transmitted from the concentrator module to the router and back in a variety of ways. If the wired transmission is not possible or too expensive, radio transmission with LoRa can be an alternative for remote reading.

The LoRa radio standard

LoRa stands for Long Range, 即. high (无线电) range and is an alternative radio standard to the known technologies such as UMTS or LTE. In many countries, LoRa has already established itself as the basis for a communication standard in the so-called Internet of Things (物联网), for machine-to-machine (M2M) communication and for industry and smart city applications.

The LoRa radio standard, like other radio technologies, uses the free LoRa frequency bands from the license-free ISM bands (产业, Scientific and Medical). 在欧洲, these are the bands in the 433 和 868 MHz range. By using a special radio procedure, the so-called frequency spread, the technology is almost immune to interference. The range between transmitter and receiver is between 2 和 15 公里, depending on the environment and built-up area. Due to the high sensitivity of -137 分贝, high penetration of buildings can be achieved. The radio signals penetrate deep into the interior of buildings and basements. Especially at campsites where the metallic covers of the caravans and mobile homes often weaken the signal strength of WLAN, radio transmission with LoRa is superior here. The data rate at LoRa is between 0.3 和 50 千比特 / s.

Applications for LoRa

LoRa is mainly used in applications in which very little data is to be transmitted over a long distance in a very energy-saving manner. These data are usually measured values, status signals or manipulated values.

Differences between WLAN, LoRa and mobile radio

WLAN and mobile radio are designed to transmit large amounts of data. Relatively short ranges are accepted. 劳拉, 另一方面, is optimized for the transmission of small amounts of data over large distances. The following table shows some differences between the different radio standards.

 

无线局域网LoRACellular
Rang<100 米2.000-3.000(city)

>10.000 米 (country)

<300 米 (city)

<10.000 米 (country)

 

最高. data rate

6.933 Mbit/s50 kbit/s1.000 Mbit/s
CostsMediumLowVery high
LoRa频率2.4 GHz的

5 GHz的

60 GHz的

433 兆赫

868 兆赫

800 兆赫

900 兆赫

1.800 兆赫

2.100 兆赫

2.600 兆赫

最高. transmission power1.000 mW25 mW20-50 w (Base station)

200 Mw (Terminal devices)

广域网 (远程广域网)

Low Power WANs (LPWANs) are network concepts for the Internet of Things (物联网) and machine-to-machine communication (M2M). LPWANs are characterized by the fact that they can cover distances of up to 50 km and require very little energy. There are several technical approaches to realizing the LPWANs. One from ETSI: ETSI GS LTN, other names are LoRaWAN, Weightless and RPMA, which stands for Random Phase Multiple Access.

So that the bridgeable distance is not impaired too much by the free space attenuation, some of the LPWAN concepts mentioned use frequencies in ISM bands at 433 MHz and 868 兆赫. Few also work in the ISM band at 2.4 GHz的.

例如, as regards SigFox as LoRaWAN (Long Range Wide Area Network), it uses the ISM band at 868 兆赫 (美国 915 兆赫) in Europe. The bridgeable distance range is over 5 km in the urban area and over 15 km outside the city. There are also radio transceivers in the LoRa frequency range of 2.4 GHz with which a range of 10 km can be bridged. LoRa transmission is a combination of Chirp Spread Spectrum (CSS) and Software Defined Radio (SDR). A key advantage is that signals that are up to 20 dB below the noise level can still be detected. The LoRaWAN concept supports bidirectional communication, mobility and location-based services.

Characteristic values广域网
 

频率范围

 

ISM band, 433 兆赫, 868 兆赫 (我), 915 兆赫 (美国)

调制Chirp spread spectrum (CSS)
Channel British8*125 KHz (我),

64*125KHz,8*125KHz(美国)

 

Package size

 

Determined by the user

Datasheet Up/Down300 bit/s 50 kbit/s (我)

900 bit/s bis 100 kbit/s(美国)

 

topology

 

Star topology

 

距离

取决于 5 km in built-up areas

取决于 15 km in the rural area

 

The end devices are connected to a base station, which in turn receives the information encrypted from a backbone via TCP / IP and the SSL protocol.
To ensure that the battery life of the end components is as long as possible, all data rates and the RF output signals are managed by the LoRaWAN network and the end components are controlled via an adaptive data rate (ADR). There are three-terminal device classes: Class A devices can communicate bidirectionally and have a planned transmission window in the uplink, class B devices also have a planned transmission window in the downlink and the transmission window for class C devices is continuously open. The LoRaWAN technology is standardized by the LoRa Alliance.

劳拉万 – Framework for wireless networks

LoRaWan is a specification and describes a framework for wireless networks. It is used in networks with little data traffic, for example in sensor networks. 劳拉万 (LongRangeWideAreaNetwork) is a so-called LPWAN (Low Power Wide Area Network) 协议. This article shows the frequencies used by LoRaWan and the available classes of end devices.

LoRa frequency varies in different regions of the world. 然而, it is necessary here to get more information before starting up a LoRa device in order to set the correct frequency. The following table shows the correct frequencies for each country or continent:

LoRaWan is also treated like a star topology. Gateways forward messages from the end devices to a specific access server. The gateways are connected via the standard server via standard internet connections.

Bidirectional devices
There are three main bidirectional classes handled by End:

A级

The uplink data always originate from the end device. The uplink message is followed by 2 short reception windows for downlink messages. These downlink messages can also be included for confirmation messages as well as for device parameters. Since the communication between the terminal and the gateway will only ever be from the terminal, there may be a waiting time between the detailed new device parameters and the implementation of the terminal.

Between the actual transmission time contacts, Class A devices can put their LoRa module completely in an energy-saving mode. This will change energy efficiency.

Class B

Class B, others to class A’s fault windows, become further reception windows. Class B devices are synchronized via cyclically sent beacons. These beacons are used to communicate, and other reception windows are open at other times. The loss is that the latency can be determined in advance, the loss of energy consumption as a component number. 然而, the energy consumption remains low enough for battery-operated applications.

Class C

Class C significantly reduces the latency for the downlink, since the receiving window of the end device is always heard as long as the device itself does not give any messages. 为此原因, the trusted server can start a downlink transmission. A time change between class A and C is particularly important in battery-powered legal contracts, 例如, “firmware-over-the-airupdates.

RegionThe LoRa Frequency
欧洲863-870 兆赫

433 兆赫

我们902-928 兆赫
中国470-510 兆赫

779-787 兆赫

Australian915-928 兆赫
Indian865-867 兆赫
Asia433 兆赫
North America915 兆赫