Internet of Things Gateway platform and applications

The promise of efficient and intelligent use of resources enabled by IoT has raised the expectations of the technical as well as the consumer community. However, it’s not always possible to connect the IoT nodes directly to the public internet due to power or computational limitations. IoT gateways help connect Things to broader internet by using connectivity technologies suitable for resource limited Things. There are a myriad of technologies and protocols available to communicate between Things, Gateways and Cloud Applications. It is not trivial to make the correct choices for a specific application. In this paper, we present a flexible architecture for the IoT Gateway Platform known as ‘Wireless Bridge’, which supports different wireless technologies. We will also discuss various connectivity technologies and protocols available for IoT-based applications.

IoT is a network of connected objects (Things) with embedded electronics that allows the network to sense, report and control objects remotely and sometimes make simple decisions. IoT seeks to connect every device/Thing that we interact with, including those which are generally not connected to the network.

While the premise of connection to the internet increases with reach of IoT, it also poses unique challenges. One such challenge is that many IoT nodes have limited memory, storage and computation capabilities and are not able to connect to the IP-based networks directly. An IoT gateway fills this gap by acting as a bridge between IP-based public networks. It also provides additional security, storage and processing services allowing the end nodes to be cost-effective and power-efficient. The IoT space is very fragmented and there is a significant amount of literature available on this subject. This paper aims to provide a holistic view of all available protocols and connectivity technologies.

Challenges in designing an IoT gateway

1. Node connectivity: We need to select a short-range radiofrequency (RF) technology to connect to the IoT nodes. This selection is dependent on various parameters like frequency band, modulation scheme, channel number, data-rate, latency, robustness, etc.

2. Backend connectivity: The IoT gateway may use short-range radio technology to connect to the IoT nodes but a long-distance link is needed to connect to the internet. This selection is based on bandwidth requirements, available connectivity options in the area and criticality of the application.

3. Management server: IoT nodes are not generally accessed (through the gateway) on the internet as standalone entities. It’s more common to have a central server managing the nodes, while an IoT gateway facilitates this communication. We need to identify protocols for communication with the management server.

4. Local intelligence: The IoT gateway can make most of the decisions locally and send only the filtered data to the cloud. This can make the system more efficient. The gateway decision logic may be programmed by the server for flexibility.

5. Power considerations: The power source of the gateway also affects our decisions relating to the above points. As sensor networks become more prevalent and embedded in Things, they would need to be as unobtrusive as possible and scavenge power from their environment.

6. Security: This is a factor that can make or break the success of large-scale IoT networks. As these networks become part of an application (some of them critical in nature), security will assume paramount importance.

7. Serviceability: There must be a provision to service and to update the IoT gateway (and nodes) in the field. There should not be sole dependence on remote serviceability and we should have additional connectivity options to service the installation.

In the current landscape, many communication technologies are available such as Bluetooth, Wi-Fi, NFC and ZigBee. There are also several new emerging networking options such as Sub-GHz, Thread, ANT and Z-Wave that can be readily used for IoT applications.

Depending on the application, factors such as operating range, power consumption, data rate, operating frequency and battery life will dictate the choice of one or more from a combination of the technologies. Table 1 below draws a comparison of features of the major communication technologies on offer today.

Backend connectivity

Connectivity to the management server (backend) involves the selection of backhaul connectivity technology as well as protocols for connecting to the backend. Backhaul connectivity refers to the long-range connection of the IoT gateway to the ISP endpoint. Cellular technologies like 3G/4G/LTE are the most popular options. PLC (Power Line Communication) can be used for smart street lights or other similar applications. Optical fibres can be used for applications requiring high bandwidth. For remote areas not covered by cellular connectivity, options such as satellite links or microwave can be used.

Communication protocol

There are many communication protocols that can be used by the IoT gateway to communicate with the cloud application. Some of the popular protocols are:

• Plain HTTP: This is by far the most ubiquitous protocol. It’s widely accepted by servers and is backed by Internet Standards, and has the least compatibility issues and maps with the RESTful APIs.
• CoAP: Constrained Application Protocol is a binary version of HTTP. It has very concise headers and supported binary data format. It can be used on top of TCP or other transport as well. CoAP packets can be easily translated to a HTTP packet.
• Web sockets: This is a new protocol backed by World Wide Web Standards. It has the same addressing and handshake mechanism as used by HTTP. It’s especially suited to shared hosting environments and gateways operating behind proxies.
• MQTT: Another popular protocol running (optionally) on top of TCP. It works in a subscriber model. It is more suited to broadcasting messages to interested gateways.
• AMQP: This is the most suitable protocol for gateway server communication. It acts as a storing queue and ensures that packets are not lost, even in cases of temporary outage.
• XMPP: Extensible Messaging and Presence Protocol is a popular protocol used by chat clients for real-time communication and has standardised a lot of parameters.

Figure 1: STMicroelectronics Wireless Bridge Solution.

IoT gateway platform architecture

Wireless Bridge IoT gateway: Wireless Bridge is an STM32-based IoT Gateway Platform as shown in Figure 1 having different connectivity technologies. The system comprises Bluetooth, Wi-Fi, Sub-GHz and near-field communication. Wi-Fi is used for exchanging Things or Node data with the Cloud Platform through the IoT Gateway Platform. Bluetooth is used for communicating the Things or Node data with the Android app through Gateway Platform and Sub-GHz is used for exchanging data between Gateway Platform and Things. An Application layer is added on the Gateway solution that acts as bridge between the Cloud Application and Things.

Key communication elements

• Sub-GHz module: The communication between the Gateway and Things is based on 6LoWPAN using SPIRIT1 module. SPIRIT1 module is an ultralow-power and fully integrated RF module operating respectively in the 868 MHz/915 MHz ISM bands.
• Wi-Fi module: The Wi-Fi module connects the Wireless Bridge Gateway with the cloud application. The SPWF01Sx intelligent Wi-Fi module is a standalone plug-and-play 802.11 b/g/n solution with integrated power amplifier and an STM32 32-bit microcontroller.
• Near field communication: The Gateway has a CR95HF transceiver used as an NFC reader/writer device to communicate with the NFC Passive Tag on the Things for configuration purposes.
• Bluetooth module: The SPBT2632Cxx Bluetooth module provides a complete RF platform in a small form factor. It is used in home automation applications for communicating with Bluetooth devices and smartphones.

Things architecture

‘Things’ in this solution are based on the Multi Sensors-RF platform, which has 2 parts (STEVAL-IDI002V2 and STEVAL-IDI003V2). STEVAL-IDI002V2 is the master board consisting of an STM32L1, Dynamic NFC Tag (M24LR) and Sub-GHz. STM32L1 runs Contiki3x-based 6LoWPAN for connectivity with Gateway.

STEVAL-IDI003V2 consists of multiple sensors such as accelerometer, pressure, humidity, microphone and light sensor.

Figure 2: RF Sensor Node (Thing).

The IoT gateway has local and remote connectivity options to access sensor data and an actuator on the nodes (Figure 4).

• Web access: A remote user can view sensor data and send command for the actuators using the web interface provided by the Management Server.
• Android application: A local user can access the nodes using the Bluetooth connectivity on smartphones by pairing with the Wireless Bridge Gateway.

Design of Management Server application

We designed a cloud application that works as a bridge between sensor/actuator Things or Nodes and the end user as shown in Figure 3. The cloud application enables provisioning, control and configuration of the nodes. The cloud application has two major parts: a device module and a web module. The device module interacts with the sensor/actuator nodes and the web module handles the web and mobile clients which are used by end users. The modules interact with each other using shared objects or a cloud service bus. The cloud application has security features which allow it to work with the registered nodes only so that data integrity is not compromised. The cloud application exposes standard REST-based APIs that can be consumed by ‘Things’ via Gateway.

Figure 3: Cloud application for node management.

Applications of the Internet of Things

Smart home

These applications allow users to monitor and control security devices and home appliances remotely and conserve energy when the appliance is not required.

Smart city

Wirelessly connected meters enable remote meter reading along with applications like differential tariffs and two-way metering. Monitoring of parameters such as ambient light and traffic can allow us to control and conserve energy.

Industrial

The IoT can play an important role in monitoring and optimisation of industrial processes. The availability of low power sensor nodes opens new avenues in the industrial automation where human presence is possible.

Conclusion

We proposed a general-purpose IoT gateway working with smartphone and cloud application connected to Things on 6LoWPAN network. High-quality open source mesh networking stacks such as Contiki have helped the proliferation of IoT. Security still remains a challenging subject to be explored. The existing security techniques are holding well, but as IoT networks become more prevalent we would unearth more challenges. Advances in the semiconductor manufacturing process, decreasing cost and better power management along with energy harvesting would be another gate opener in the IoT space.

Figure 4: IoT gateway interfaces.

Technology	Standard	Band	Range	Power	Data rate	IoT applications
Bluetooth	Bluetooth 4.x specification	2.4 GHz	Medium 50–150 m (Smart)	Medium Low (BLE)	Medium 1 Mbps	Wearable devices Sensors nodes IoT application
Wi-Fi	802.11b/g/n/ac	2.5/5 GHz	Medium 50 m	High	High 500 Mbps to 1 Gbps	IP camera Gateway devices
NFC	ISO/IEC 18000-3	13.56 MHz	Low 10 cm	Low	Low 100–420 kbps	Access management BT/Wi-Fi pairing e-tickets payment
Sub GHz	802.15.4 6LowPAN	868 MHz/ 915 MHz	High	Low	Low 500 kbps	Smart street light Energy meters Smart building
ZigBee	802.15.4	2.4 GHz	10–100 m	Low	Low 250 kbps	Smart street light Smart building
Z-Wave	ITU-T G.9959	900 MHz	30 m	Low	9.6/40/100 kbps	Home automation
Thread	802.15.4 and 6LowPAN	2.4 GHz	N/A	Low	250 kbps	Home automation

Table 1: Comparison of Wireless Connectivity Technologies.