LoRa和LoRaWANR技术概述.pdf

LoRa and LoRaWAN: A Technical Overview

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Technical Paper

Proprietary

February 11, 2020

Semtech

December 2019

Semtech

LoRa is an RF modulation technology for low-power, wide area networks (LPWANs). The name, LoRa, is a

reference to the extremely long-range data links that this technology enables. Created by Semtech to

standardize LPWANs, LoRa provides for long-range communications: up to three miles (five kilometers)

in urban areas, and up to 10 miles (15 kilometers) or more in rural areas (line of sight). A key

characteristic of the LoRa-based solutions is ultra-low power requirements, which allows for the

creation of battery-operated devices that can last for up to 10 years. Deployed in a star topology, a

network based on the open LoRaWAN protocol is perfect for applications that require long-range or

and latency issues. They often offer both LoRaWAN and Cat-M1, which are complementary

technologies. LoRaWAN accommodates the need for longer battery life, with a trade-off of longer

latency and smaller packet sizes. In contrast Cat-M1 can be used for larger payloads with less latency

than LoRaWAN can accommodate.

December 2019

Semtech

Figure 2 highlights some important advantages of deploying a LoRaWAN network:

Let’s look into these advantages in a little more depth.

With respect to range, a single LoRa-based gateway can receive and transmit signals over a distance of

for many, many years.

December 2019

Semtech

When it comes to capacity, a LoRaWAN network can support millions of messages. However, the number

of messages supported in any given deployment depends upon the number of gateways that are installed.

. If the network includes 10 such gateways, the network can support roughly 100,000 devices

and one million messages. If more capacity is required, all that is needed is to add additional gateways to

the network.

And then, there is cost. Given the capabilities of LoRa-based end nodes and gateways, only a few

gateways – configured in a star network – are required to serve a multitude of end nodes. This means

bandwidth channel of either 125 KHz or 500 KHz (for uplink channels), and 500 KHz (for downlink

channels). Additionally, LoRa uses orthogonal spreading factors. This allows the network to preserve the

battery life of connected end nodes by making adaptive optimizations of an individual end node’s power

levels and data rates. For example, an end device located close to a gateway should transmit data at a

low spreading factor, since very little link budget is needed. However, an end device located several

miles from a gateway will need to transmit with a much higher spreading factor. This higher spreading

factor provides increased processing gain, and higher reception sensitivity, although the data rate will,

necessarily, be lower.

LoRa is purely a physical (PHY), or “bits” layer implementation, as defined by the OSI seven-layer

Network Model, depicted in Figure 3. Instead of cabling, the air is used as a medium for transporting

December 2019

Semtech

“faster” signal is created that has higher frequency components than the original data signal. This means

that the signal bandwidth is spread beyond the bandwidth of the original signal. In RF terminology, the

bits of the code sequence are called chips (in order to distinguish between the longer, un-coded, bits of

the original data signal). When the transmitted signal arrives at the RF receiver, it is multiplied with an

identical copy of the spreading code used in the RF transmitter, resulting in a replica of the original data

signal.