MQTT-SN for Cellular IoT and Micromobility

Due to urbanization, environmental concerns, and changes in consumer behavior, mobility and micromobility applications are becoming increasingly commonplace. These applications — ranging from connected scooters and bikes to asset tracking and fleet management systems — demand an efficient, reliable, and scalable communication protocol. MQTT-SN (Message Queuing Telemetry Transport for Sensor Networks) is a perfect fit for these applications, particularly when leveraging cellular connectivity via LTE-M, NB-IoT, and even Non-Terrestrial Networks (NTN). This blog explores why MQTT-SN is well suited for these applications and the benefits and integration strategies for the protocol.

Understanding MQTT-SN

MQTT-SN is a version of the MQTT protocol designed to cater to the needs of wireless sensor networks and devices in constrained environments. While MQTT is already lightweight and efficient, MQTT-SN takes these characteristics further by optimizing the protocol for devices with limited resources.

Key features of MQTT-SN include:

• Small packet size: MQTT-SN minimizes packet overhead, a necessity for low-bandwidth and high-latency networks.

• Sleep mode: MQTT-SN is connectionless so devices can save power by entering sleep mode without needing to wake to maintain connections.

• Gateway architecture: MQTT-SN architecture uses gateways to bridge between MQTT-SN clients and MQTT brokers, providing flexibility in deployment and management.

• Short topic names: MQTT-SN employs short topic IDs to further reduce overhead, decreasing bandwidth and power requirements.

The Importance of Cellular Connectivity

Cellular connectivity, especially through LTE-M and NB-IoT, plays a crucial role in enabling widespread, reliable IoT applications. Each of these technologies brings unique advantages:

• LTE-M (Long-Term Evolution for Machines): This variant of LTE is designed for IoT applications requiring higher bandwidth and lower latency compared to other available options such as NB-IoT. It is ideal for mobility, asset tracking, and telematics use cases. LTE-M also supports voice services (VoLTE).

• NB-IoT (Narrowband IoT): Optimized for low-power, low-data-rate applications, NB-IoT excels in providing extended coverage, deep penetration, and long battery life. It is ideal for stationary or slowly moving devices, such as EV charging points and environmental sensors.

NTN (Non-Terrestrial Networks)

NTN adds a further category to consider. This includes satellite and high-altitude platform systems, extending IoT connectivity to remote and underserved areas. NTNs ensure that IoT devices can maintain connectivity even in the most challenging environments, such as rural and maritime regions.

Why MQTT-SN for Cellular Mobility

• Efficiency in low-bandwidth environments: Both NB-IoT and NTN often operate in environments where bandwidth is limited and connectivity can be patchy. As mentioned before, MQTT-SN's reduced packet size and efficient use of network resources make it an excellent choice. By minimizing overhead, MQTT-SN ensures that more of the available bandwidth is used for actual data transmission, enhancing the performance of IoT applications.

• Battery life optimization: MQTT-SN is connectionless which is particularly beneficial for NB-IoT applications, where devices are often battery-powered and need to operate for years without maintenance.

• Mobility support: LTE-M is specifically designed to support mobile applications, providing the necessary handover capabilities to maintain connectivity as devices move. MQTT-SN complements LTE-M by providing a protocol that can handle intermittent connectivity gracefully. When devices move out of coverage temporarily, MQTT-SN ensures that they can resume communication seamlessly once back in range.

• Scalability and flexibility: The gateway architecture of MQTT-SN allows for scalable and flexible deployments. Gateways can manage connections to MQTT brokers, handle protocol translation, and can also provide additional services such as security and data aggregation. This architecture is particularly useful in NTN scenarios, where gateways can manage communication between satellite links and ground-based networks.

Integrating MQTT-SN with Cellular Networks

Implementing MQTT-SN Gateways

Deploying MQTT-SN gateways is essential for managing the communication between sensor networks and MQTT brokers. These gateways handle the translation of MQTT-SN messages to MQTT, ensuring compatibility with existing MQTT infrastructure.

Edge Gateways

Placing gateways at the edge of the network, close to the sensors, minimizes latency and improves efficiency. Edge gateways can also perform local processing and filtering, reducing the amount of data sent over the cellular network.

Cloud Gateways

For applications where edge processing is not feasible, cloud-based gateways can be used. These gateways aggregate data from multiple devices and provide centralized management and analytics capabilities.

Optimizing Protocol Settings

Fine-tuning the protocol settings for MQTT-SN can further enhance performance with:

• Message retries and QoS: Adjust the quality of service (QoS) levels and retry mechanisms based on the network conditions. For instance, in NB-IoT networks with higher latency, using QoS 1 or 2 can ensure reliable delivery. MQTT-SN offers four QoS levels allowing efficiency or reliability of messaging to fit the needs of the application perfectly.

• Topic management: Use short topic IDs to reduce message size and improve efficiency. Additionally, consider hierarchical topic structures to organize data logically and facilitate subscription management.

Example Mobility Applications for MQTT-SN and Cellular Communication

Connected Scooters and Bikes

Micromobility services, such as shared scooters and bikes, rely on consistent communication for tracking, maintenance, and user interaction. By leveraging MQTT-SN over LTE-M, these services can achieve:

• Real-time tracking: LTE-M provides the necessary bandwidth and low latency for real-time location updates. MQTT-SN ensures efficient use of the network, minimizing data costs and improving responsiveness.

• Battery management: MQTT-SN's support for sleep modes allows devices to conserve battery when not in use, extending operational life and reducing maintenance requirements.

• Seamless connectivity: As scooters and bikes move through different network cells, LTE-M ensures continuous connectivity, while MQTT-SN handles interruptions as per the specific needs of the application.

Smarter Cities

As mobility applications interact more with smart cities, better coverage will be required for static and slow-moving applications that form part of this infrastructure. These benefits include:

• Deep coverage: NB-IoT provides excellent coverage in urban and rural areas, ensuring that sensors can transmit data even from challenging locations.

• Efficient data transmission: MQTT-SN minimizes the data overhead, allowing lots of sensors to operate with minimal bandwidth requirements.

Beyond the Smart City

For asset tracking and mobility applications in areas with little to no cellular coverage, NTN combined with MQTT-SN offers:

• Extended coverage: NTN provides connectivity in areas where terrestrial networks are unavailable. MQTT-SN's efficient use of bandwidth ensures reliable communication even over satellite links.

• Data aggregation: Edge gateways can collect data from multiple assets and send aggregated updates via satellite, reducing transmission costs and improving efficiency.

• Long battery life: Devices can operate on battery power for extended periods, with MQTT-SN ensuring that communication is maintained despite low power consumption.

Future Trends and Considerations

As IoT technology continues to evolve, several trends will further enhance the synergy between MQTT-SN and cellular, including:

• 5G Integration: The rollout of 5G networks (and beyond) will provide even greater bandwidth, lower latency, and improved reliability. MQTT-SN will benefit from these advancements, enabling greater scale, more sophisticated, and data-intensive IoT applications.

• Edge Computing: The proliferation of edge computing will allow more processing to be performed locally, reducing the amount of unnecessary data being sent to the enterprise. MQTT-SN gateways will play a crucial role in this architecture, providing local data processing and aggregation.

• Enhanced Security: As security becomes increasingly important, MQTT-SN will continue to evolve to support robust encryption, authentication, and authorization mechanisms, ensuring the integrity and confidentiality of IoT data.

MQTT-SN for Micromobility

MQTT-SN stands out as a highly efficient and adaptable protocol for mobility and micromobility applications, particularly when paired with cellular connectivity via LTE-M, and NB-IoT. Its ability to operate in low-bandwidth environments, support battery-powered devices, and handle intermittent connectivity makes it an ideal choice for a wide range of IoT scenarios.

By leveraging MQTT-SN, engineers and systems integrators can design and deploy scalable, reliable, and cost-effective IoT solutions that meet the demands of modern mobility and micromobility applications.