"When considering the wireless connection of the IoT sensor, developers typically think of Wi-Fi, Zigbee or Bluetooth. But the reality is that the application often requires lower power consumption, longer coverage, different The use mode and lower data rate are beyond the scope of these technologies. Designers are not as high as the relevant cost, potential delay and rework issues from beginning to implement the relevant cost, potential delay and rework issues, and use ready-made modules to achieve various types. Relatively new low-power WAN (LPWAN).
These LPWANs include Sigfox, Lorawan, and new Radiocrafts Industrial Internet of Radiot, which all aims to connect relatively simple working in medium sampling rates, and can send short and scarce from long distance (longer than 50 km) Sudden data. Such applications typically specify a very stringent power constraint condition that is the purpose of maximizing the battery life of the sensor located in remote or inconvenient venues. Ideally, the sensor placed in such a place relying on the button battery or the AAA battery will be reliably working for up to 10 years.
This article will discuss the design requirements of typical remote field sensation and the characteristics of SIGFOX, Lorawan and Riiot. The appropriate modules provided by PI Supply, SIGFOX, and Radiocrafts will then be described, and how to use these modules.
LPWAN features
LPWAN's narrow bandwidth is one of its low power work (Figure 1). According to the basic principles of the information theory, the signal bandwidth and signal-to-noise ratio (SNR) are closely related to the error rate of information transmission. The larger the SNR, the narrower the bandwidth, the lower the error rate.
With this relationship, LPWAN achieves a highly reliable long-distance information transmission at low output power. By adopting relatively low data rates, the LPWAN system also reduces signal bandwidth requirements. As a result, the LPWAN system can realize a communication distance of thousands of meters.
The second key feature of the LPWAN system is that it uses the International Levive Industry, Science and Medicine (ISM) frequency band (886 - 906 MHz) frequency. According to Equation 1, the free space path loss can be reduced in these frequencies (longer) at a given transmit power, and the effective coverage is improved:
Formula 1
in:
D = distance
λ = wavelength
At lower frequencies, radio frequency (RF) absorbed by obstacles (such as walls and buildings), so that the LPWAN system has excellent penetration capacity in urban environments.
ISM-based design does not require a license, but still need to comply with global power and electromagnetic compatibility regulations for ISM bands.
LPWAN example
Although there are a variety of LPWAN schemes to choose, for developers seeking to quickly develop sensor-based Internet of Things applications, Lorawan, Sigfox and recently launched RIIOT are three sensible options. Each solution has pre-configured radio and sensor interface modules, which can be easily imported into its design, and there are also development kits to help quickly complete settings and application development.
The Lorawan Network is based on open standards managed by the LORA alliance and the proprietary spread spectrum radio technology with Semtech Corp. The network uses a star topology that allows a single node to communicate with multiple gateways, thereby achieving roaming. It supports two-way communication between gateways and nodes, allowing the gateway to relate messages from one node to another, and transmitted to cloud-based servers.
Lorawan can implement data rates of 300 bps to 50 kbps, can handle up to 243 bytes of messages payload and use 125 kHz or 250 kHz signal bandwidth. It supports adaptive data rates to maintain signal reliability under variation, and achieve 5 km coverage in urban environments, the sight (LOS) can reach 20 km. Users can develop nodes and access to commercial operations networks, or use their own gateway and return network to establish a private network.
SIGFOX is a proprietary agreement developed and managed by SIGFOX, which authorizes technology to chip developers and allows users to access their networks through the Gateway base station. SIGFOX can maintain the data rate at 600 bps at 100 Hz (Hz) signal bandwidth, so that the maximum coverage can be achieved. Under 40 km under accessible line of view, 10 km can be reached in urban environments. Its lightweight protocol limits the uplink message package to 26 bytes (up to 12 bytes of user data), so the transmitter is only short-lived. The node can only send 140 messages per day, and the gateway will only send a downlink message 4 times a day after receiving the uplink message of the node. Therefore, the node radio is very short, and most of the time is in sleep mode to minimize power consumption.
Although the LPWAN radio is a low power type, low-power is a relative term in the real world. For example, Radiocrafts's SIGFOX module products have two different power seals. The RC1692HP-SSM high power sensor interface module communicates with the host microcontroller via the UART and provides SPI, I2C, analog, and GPIO ports (Figure 2). This module is powered by 2.8 to 3.6 V.
In Sleep mode, the module consumes 1 μA current. In the activity mode connected to the sensor, the current consumed when the current consumes less than 20 μA, and the current consumed at the time of transmission is less than 292 mA.
The lower power consumption RC1682-SSM module is for the European market, consumes less current, only 58 mA.
RIIOT is one of the latest LPWAN solutions for developers. It is built on the IEEE 802.15.4g / e physical layer (PHY) standard, which was originally developed for intelligent metering and process control applications. It adds RF and Media Access Control (MAC) features to support low power consumption, long distance, and advanced security. Communication is conducted through bidirement of star network, providing a predictable network delay of less than 15 ms to support near real-time control applications.
RIIOT has two data rates (5 kbps and 50 kbps) and two power levels so that developers can optimize and weigh battery life, data rates, and coverage, it is best to meet demand. In the case of low power, high data rates, the RIIOT network can achieve 5 km barrier-free sponsoring and 200 m cities coverage, and the burst transmission time is 3.5 ms (MS). At higher output power and lower data rate, 60 km barrier-free hindrance and 2 km city coverage can be realized, and the burst transmission time is 45 ms. Typical leaf nodes have a sleep current of 0.7 microam (μA).
Building a RIIOT network involves three main elements: nodes, gateways and network controller software. A single leaf node uses modules like Radiocrafts RC1880CEF-SPR, which integrates an analog-to-digital converter (ADC) and GPIO, I2C, SPI, and UART interfaces. These nodes can wirelessly communicate with Linux PCs that use compatible RC1880CEF-GPR modules or USB adapters. A circuit board with the RC1880CEF-GPR module can be inserted into the PC expansion slot, and the USB adapter is connected via the PC's USB port.
To completely become the RIIOT gateway, developers must install the third component -Riiot network controller middleware. The software not only manages the network (including wireless firmware update to the leaf node), but also converts the data and commands to JSON objects to simplify the connection with the cloud.
A key content that increases over the basic standard IEEE 202.15.4 is to implement end-to-end security on data transfer. SIGFOX does not support encryption, LoraWan supports encryption in the wireless link between the node and the gateway, and RIIOT further improves security.
With RIIOT, each node has a unique security key such that the message is always in an encrypted state from the cloud application that is interactive with it. The gateway only transmits the encrypted message without having to access its content.
Use modules and suits to speed up design: RIIOT
For developers who want to implement the LPWAN IoT, you can use one of the many pre-configured RF and sensor interface modules for different networks to speed up design work. Such modules have solved all thorny problems in RF design, power consumption minimization, and protocol implementation, so it is basically inserted into the communication device of the host processor. In addition, these modules have been pre-certified, compliant with the regulatory requirements of the ISM band. Although developers still need to conduct certifications to their final products, due to the verification of radio components, eventually certification will become easier and determined.
These modules also help speed design by providing built-in sensor interfaces and control logic. For example, RADIOCRAFTS's RC1880CEF-SPR has an interface for an ADC analog input, a GPIO for the switch, an I2C and SPI for a sensor, and a UART for connecting to a host processor (Fig. 4). Developers can import this module into the design, solve the needs of the system's wireless communication and sensor interfaces. This module can program the setting, control, and sampling of the sensor to simplify the task of the application processor. Sensor and communication look like a read and write operation of the memory to the application code.
Development kits (such as RC1880-RIIOT-DK) help developers quickly establish a complete end-to-end RIIOT network for experiments. The kit includes leaf nodes, gateway modules, and system software for building a complete network. It also includes software tools for programming the leaf node with a C language to process the connected sensors.
Module and Development Kit for Lorawan and Sigfox
Lorawan has a ready-made pre-configured module to easily implement an Internet of Things system. PI Supply's PIS-1019 Rak811 LoraWan module is a good example (Figure 5).
This device provides a serial port for the host microcontroller so that the host microcontroller uses a standard AT command to control the module. To help create a complete network, the PIS-1019 PIS-1037 development kit contains a gateway concentrator module that converts the host PCIe controller into a gateway / router access point (Figure 6).
Radiocrafts also have a complete SIGFOX development kit, such as RC1692HP-SSM-DK kits for RC1692HP-SSM RF modules and RC-1682-SSM DK for RC1682-SSM RF modules. These kits are available, supporting SIGFOX radio module testing and development. These kits have temperature and humidity sensors, acceleration gauges, and Hall effect sensors.
However, developers using SIGFOX cannot choose to create their own network. SIGFOX is responsible for the operation and maintenance of system gateways and backhaul, and users need to pay for use. However, these modules are equipped with precoding ID and encryption keys. Once registered, only a very small amount of settings can begin to transfer data to SIGFOX cloud.
Summarize
For designers who want to connect low data rate sensors to the Internet of Things to connect to the Internet of Things, RIIOT, Lorawan and Sigfox, etc., Riiot, Lorawan, and Sigfox, etc., the LPWAN solutions such as Wi-Fi, ZigBee, or a cellular network. Each solution has its own advantages, but all programs can solve the various applications from smart meters to intelligent agriculture.
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