Lora简述

一、LoRa®

LoRa® is the physical layer or the wireless modulation utilized to create the long range communication link.LoRa®是物理层或用于创建长距离通信链接的无线调制。

• Long Range
• Low Power
• Network capacity

二、LoRaWAN

• LoRaWAN是一个低功耗广域网网络(LPWAN)规范，适用于在地区、国家或全球网络中，使用电池供电的无线设备。

• LoRaWAN Specification定义了PHY与MAC协议

• LoRaWAN™ defines the communication protocol and system architecture for the network while the LoRa® physical layer enables the long-range communication link. LoRaWAN™定义了网络的通信协议和系统架构，LoRa®物理层实现了长距离的通信链接。
  

• LoRa® is based on chirp spread spectrum modulation, which maintains the same low power characteristics as FSK modulation but significantly increases the communication range.LoRa®以啁啾扩频调制为基础，它保持了与FSK调制相同的低功率特性，但大大增加了通信范围。

三、etwork Architecture

• loRaWAN网络架构是一个典型的星形拓扑结构。LoRaWAN网关可以看作是一个透明的“网桥”，连接前端终端设备(End Device)和后端中央服务器。网关与服务器通过标准IP连接，而终端设备采用单跳广播，与一个或多个网关通信，所有的节点均是双向通信。LoRaWAN协议的星形拓扑结构消除了同步开销和跳数，因而降低了功耗。
  

四、device Classes – Not All Nodes Are Created Equal

Bi-directional end-devices (Class A): End-devices of Class A allow for bi-directional communications whereby each end-device’s uplink transmission is followed by two short downlink receive windows. The transmission slot scheduled by the end-device is based on its own communication needs with a small variation based on a random time basis (ALOHA-type of protocol). This Class A operation is the lowest power end-device system for applications that only require downlink communication from the server shortly after the end-device has sent an uplink transmission. Downlink communications from the server at any other time will have to wait until the next scheduled uplink.
Class A设备执行的是一个非对称的双向通信机制，每一终端设备上行发送后会伴随打开两个下行接收窗口。终端设备的传输窗口是基于其自身通信需求，其微调是基于一个随机的时间基准（ALOHA协议）。Class A设备应用中功耗最低，在终端发送一个上行传输信号后才能与服务器进行下行通信，与服务器任何时候的下行通信都只能是在上行通信之后。

Bi-directional end-devices with scheduled receive slots (Class B): In addition to
the Class A random receive windows, Class B devices open extra receive windows at scheduled times. In order for the end-device to open its receive window at the scheduled time, it receives a time-synchronized beacon from the gateway. This allows the server to know when the end-device is listening.
Class B设备建立在Class A基础上，并会在预设时间中开放多余的接收窗口，为了达到这一目的，终端设备会同步从网关接收到一个Beacon，这一方式会让服务器知道终端设备正在“倾听”。

Bi-directional end-devices with maximal receive slots (Class C): End-devices of Class C have almost continuously open receive windows, only closed when transmitting
Class C设备同样基于Class A，在不需要发送数据的情况下，一直打开接收。

五、LoRa联盟

• LoRa联盟推广LoRaWANTM协议，可应用于IoT、智慧城市、智慧工业、智慧生活等领域。

六、End-Device Activation

• To participate in a LoRaWAN network, each end-device has to be personalized and activated.加入LoRaWAN网络，终端设备必须激活

• Activation of an end-device can be achieved in two ways, either via Over-The-Air Activation(OTAA) when an end-device is deployed or reset, or via Activation By Personalization(ABP) in which the two steps of end-device personalization and activation are done as one step.激活有两种方式，OTAA、ABP

• After activation, the following information is stored in the end-device: a device address(DevAddr), an application identifier(AppEUI), a network session key(NwkSKey), and an application session key(AppSKey).

6.1 Activation By Personalization（ABP）

6.1.1 DevAddr

The DevAddr consists of 32 bits identifies the end-device within the current network.

• the network identifier (NwkID) is separate addresses of territorially overlapping networks of different network operators and to remedy roaming issues。

• the network address (NwkAddr) of the end-device, can be arbitrarily assigned by the network manager.

6.1.2 Application identifier (AppEUI）

• The AppEUI is a global application ID in IEEE EUI64 address space that uniquely identifies the entity able to process the JoinReq frame
• The AppEUI is stored in the end-device before the activation procedure is executed

6.1.3 Network session key (NwkSKey)

• The NwkSKey is a network session key specific for the end-device
• It is used by both the network server and the end-device to calculate and verify the MIC of all data messages to ensure data integrity

6.1.4 Application session key (AppSKey)

• The AppSKey is an application session key specific for the end-device
• It is used by both the application server and the end-device to encrypt and decrypt the payload field of application-specific data messages.

激活方式	描述	所需参数
Over the Air Activation (OTAA)	模块通过加入网络（JOIN）操作，来获得网络安全密钥	DevEUI、AppEUI、AppKey，同时设置为OTAA激活方式。
Activation by Personalization (ABP)	模块本地已经保存网络会话密钥、应用加密密钥等，可以加入指定的LoRaWAN服务器	DevAddr、NwkSkey、AppSkey，同时设置为ABP激活