로라 (LoRa Alliance) - 저전력 원거리 통신망 연합

[단독]애완견 찾기·수도검침..IoT 전용 전국망 나온다    (관련 한국기사) 

로라(LoRaWAN)는  900MHz대 주파수를 사용하여 저전력 원거리 통신( Low Power Wide Area Network)을 지향하는 사물 인터넷 망으로  SigFox, Weightless-N (N-Wave) 등과 직접 경쟁할 뿐만 아니라 저가 LTE, 동일 주파수대의 WiFi와도 경쟁을 하고 있다. 로라의 데이타 통신 속도는 0.3 kbps to 50 kbp로 낮아 저전력이 가능하고 높은 속도를 필요로 하지 않는 사물간 통신에 활용가능하다.

LoRa® Technology

LoRaWAN™  는 저전력 원거리 네트워크 (LPWAN) 스펙의 하나이며, 지역적, 국가적 혹은 글로벌 네트워크에서 무선 배터리로 운용되는 사물을 위해 만들어졌다. LoRaWAN  보안되는 양방향 통신이나 차량 혹은 지역서비스같은 사물인터넷을 주요 타겟으로 한다. 이 표준은 복잡한 설치과정 없이 스마트 기기들 사이에서 지속적인 상호호환성을 제공할것이다. 사용자에게 자유를 줄것이며, 비니지스적으로 사물인터넷을 확장할수 있을 것이다. 

LoRaWAN network architecture is typically laid out in a star-of-stars topology in which gateways is a transparent bridge relaying messages between end-devices and a central network server in the backend. Gateways are connected to the network server via standard IP connections while end-devices use single-hop wireless communication to one or many gateways. All end-point communication is generally bi-directional, but also supports operation such as multicast enabling software upgrade over the air or other mass distribution messages to reduce the on air communication time.

Communication between end-devices and gateways is spread out on different frequency channels and data rates. The selection of the data rate is a trade-off between communication range and message duration. Due to the spread spectrum technology, communications with different data rates do not interfere with each other and create a set of "virtual" channels increasing the capacity of the gateway. LoRaWAN data rates range from 0.3 kbps to 50 kbps. To maximize both battery life of the end-devices and overall network capacity, the LoRaWAN network server is managing the data rate and RF output for each end-device individually by means of an adaptive data rate (ADR) scheme.

National wide networks targeting internet of things such as critical infrastructure, confidential personal data or critical functions for the society has a special need for secure communication. This has been solved by several layer of encryption:

• Unique Network key (EUI64) and ensure security on network level
• Unique Application key (EUI64) ensure end to end security on application level
• Device specific key (EUI128)

LoRaWAN has several different classes of end-point devices to address the different needs reflected in the wide range of applications:

• 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.
• 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.
• Bi-directional end-devices with maximal receive slots (Class C): End-devices of Class C have nearly continuously open receive windows, only closed when transmitting. Class C