Internet of Things Trends:

The widespread adoption of the Internet of Things, including almost every industry and across global infrastructure, catalyzes what many have described as an exponential era that will unleash massive productivity and commercial growth increases.

As with every technological innovation, there are teething problems. Currently, the Internet of Things' potential is limited by the wireless networking capacity needed to support billions of IoT connections.

Several competing wireless technologies have been implemented, but individually, they need the capacity or harmonization to support the broad range of Internet of Things devices, leading to a fragmented, end-user-friendly landscape.

LoRa Alliance: There is no single networking technology for IoT that delivers:

• Ubiquitous coverage
• Universal availability and compatibility
• Ability to support every type of IoT solution and use case
• Ability to be used as a personal area network (PAN), local area network (LAN), neighborhood area network (NAN), or vast area network (WAN)

5G promises to deliver the capacity required to support large volumes of IoT connections, but the full implementation of the fifth-generation cellular networking technologies is still many years off. In the meantime, stakeholders are exploring solutions for harmonizing IoT connectivity among the heterogeneous technologies that are currently in use.

This article will explore the efforts to create and implement Multiple Radio Access Technologies (Multi-RAT) that marry the differing networking technologies used by the Internet of Things, particularly LPWAB cellular networking technologies, including LoRa.

What is Multiple Radio Access Technology (Multi-RAT)?

Multiple Radio Access Technology (Multi-RAT) is a networking architecture that creates heterogeneous wireless networks that integrate numerous cellular and non-cellular technologies. This architecture supports massive IoT applications that connect many disparately located nodes using several networking technologies.

Radio Access Technology (RAT) is a technology used to support connectivity in a radio-based communication network. Devices such as cell phones can support multiple RATs in a single device.

Novel heterogeneous wireless networking architectures are being developed using RATs. In particular, Multi-RAT provides network selectivity among various RATs to transfer data to the internet, similar to the selection of access points in WiFi.

The networking technologies that can be combined currently with this technology include:

• 5G New Radio (5GNR)
• NB-IoT
• LTE
• GSM
• UMTS
• WiFi
• LoRa
• Bluetooth

The networks created from these technologies are highly targeted and adaptive, with multiple layers of cells focused on specific areas of service provision, including expanding capacity and coverage, responding to adverse propagation conditions, or saving energy and bandwidth.

Interest in multi-RAT has increased with the deployment of the fifth-generation cellular technology, 5G NR. This technology can be used to build multi-layer (macro and small cells) networks, expand network capacity with small cells, or offload to other networks.

Multi-RAT planning uses the various layers of cellular networking technology and device solutions where other cellular and non-cellular wireless technologies can coexist with a cellular network and handle its throughput (offloading). Other areas of harmonization and synchronization between disparate technologies include switching, coverage targets, backhaul, interference management, and antennas.

About heterogeneous wireless networks

These novel networks, heterogeneous wireless networks, combine multiple radio access technologies (RATs) in a single network.

Theoretically, any combination of wireless networking technologies, both cellular and non-cellular access technologies, can work together.

This type of connectivity is now being developed for the Internet of Things. Devices can already maintain internet connectivity via multiple RATs sequentially and simultaneously. Electronic engineers can also configure heterogeneous networks to minimize energy consumption or optimize coverage as participant nodes require.

Key challenges and considerations of the multi-RAT model

Multi-RAT networking is vulnerable to interference and congested regions in the network. This is because there can be issues with the algorithms used to select the radio technologies, especially if many devices need internet access. Access point/gateway availability is essential, as this is where all networking technologies obtain internet access. Critical limitations in multi-RAT networks include:

• Access point (or gateway) availability
• Distance to the nearest access point
• Signal quality of the access point or gateway
• Load experienced at the access point
• Number of users using a specific radio access technology

The routine use of cellular networking technology in these networks makes any need for retransmissions expensive and energy-inefficient. By integrating other networking technologies, we can communicate using multiple shorter, cheaper, low-energy hops between relay nodes rather than one long-distance point-to-point cellular transmission.

Protocols for interoperability between radio access technologies

Several emerging standards seek functional integration between IoT's diverse wireless communications technologies. An existing example is IEEE 802.21, which specifies media-independent handover between various wired and wireless networks.

Electronic engineers have developed complex algorithms that control selecting the best network based on various characteristics, including the constituent networks' performance, power consumption, and energy efficiency.

Software-defined networking (SDN) can manage multi-RAT networks

A fundamental limitation of multi-RAT networking for IoT is that each RAT has its own control and management layer. To achieve harmonized control of a diverse range of RATs in a single network, a single, unified management platform must be needed to prevent suboptimal network performance.

SDN-based network architecture can deliver end-to-end control of multiple RATs by providing QoS guarantees and a Service Level Agreement (SLA). This approach to network management uncouples software from the hardware of the different participating technologies and centralizes control on a single platform that facilitates unified configuration and control.

SDN networking can scale IoT networks. It provides the global view of the network needed to ensure that downstream nodes function optimally using the RATs available. SDN is also simplified, requiring only a single controller rather than a core network controller and separate RAN controllers.

The role of LPWANs in multi-RAT

Multi-RAT uses a combination of short-, medium-, and long-range radio solutions to meet the requirements of varied use cases and applications.

Low power, wide-area networking (LPWAN) technologies are coming to the fore as radio access technologies that can provide coverage and support for IoT connections in large conurbations at a low cost. The utility of LoRa and other LPWAN technologies is being actively investigated as a solution for supporting cellar RATs as part of a multi-RAT network.

LPWAN networking has proven to be an effective solution for connecting battery-powered devices or nodes that cannot use standard cellular networks for data transfer because of their high energy consumption. It is expected to be utilized alongside cellular networking, similar to WiFi.

LPWANs offer effective long-range communications with licensed and license-free options despite low power. Though all LPWAN solutions are low-power, it is essential to note that they use distinct technologies and have different advantages and limitations. For example, here is a comparison of LoRaWAN and NB-IoT:

LoRaWAN

An LP WAN that uses the unlicensed radio spectrum:

• LoRa was initially developed by Semtech using the Chirp Spread Spectrum (CSS) modulation technique.
• The LoRaWAN communication protocol outlines the network architecture that sits on top of the LoRa physical layer developed by Semtech in 2015.
• LoRaWAN networks include non-profit ventures such as The Things Network and commercial enterprises like Nova Labs(Helium Network) or Amazon Web Services (AWS) that deploy large-scale LoRaWAN networks.
• LoRa is expected to be the leading non-cellular LPWAN technology as soon as 2026. It is projected to support at least 1.3 billion IoT connections, over 25% of all LPWAN connections by this time.

NB-IoT

Cellular technology that uses licensed frequency bands

• This commercial LPWAN protocol developed by the 3rd Generation Partnership Project (3GPP).
• NB-IoT is developed explicitly for long-range, low power, low bitrate LPWAN connectivity for battery-powered IoT devices

Short-range IoT RATs such as Bluetooth and WiFi have been successfully integrated into Multi-RAT solutions. A similar arrangement also includes multiple cellular technologies on devices, providing a GPRS fall-back if LTE coverage fails.

The move to integrate these LPWANS alongside cellular and short-range RATs with dynamic switching between them is ambitious. But an accurate multi-RAT approach that includes LPWAN networking can provide benefits for IoT networking that include:

• Greater autonomy, with devices/nodes remaining battery-operated rather than reliant on battery power.
• Energy efficiency
• Reduced latency
• Accommodation of larger payload sizes
• Improved quality of service
• Lower costs

For example, a sensor-based device that sends readings that require small data transmission can use technology suited to low-bitrate transmissions (e.g., LoRaWAN), but if it needs to exchange larger amounts of data, an alternative connectivity technology can be automatically selected and used.

A closer look at the benefits of Multi-RAT networking

A multi-RAT approach to IoT networking is expected to deliver benefits in 6 key areas:

[A] Power Management

Multi-RAT networks can deliver significant energy savings, making them ideal for supporting battery-powered devices. Network switching to the most energy-efficient networking technology means that IoT devices can optimize their performance and only expend significant amounts of energy on the required communications.

The LoRa Alliance advocates the inclusion of LoRaWAN technology in multi-RAT networks because it is intrinsically low-power. The energy consumption of LoRa is primarily determined by the Time on Air (ToA) of a transmitting device, which is a combination of the payload and spreading factor. LoRa can optimize the transmit power and data rate according to the available channel conditions. Power can be increased if the signal-to-noise ratio is low, but it can also be scaled right back in favorable conditions.

This type of narrow bandwidth signaling with a simple MAC will significantly reduce the overall power consumption of IoT networks, especially if suitable cellular data is offloaded via a LoRaWAN.

NB-IoT can be readily integrated with cellular IoT networks as a low-power, cellular-based option. NB-IoT is a simplified version of the LTE standard. It saves energy by enabling devices to have a longer sleep time, reduced active radio time, and a power-saving mode where participant devices can completely disconnect from the network if they are not in use.

[B] Network coverage

Coverage is essential for the reliable connectivity that IoT nodes need in critical applications, especially in inaccessible or remote areas. The distance to the nearest access point or gateway is a key determinant of the reliability of a LoRaWAN IoT network.

LPWANs are already actively used in IoT as they are designed to facilitate long-range connectivity and enhance coverage.

• LoRa relies on an adequate distribution and proximity of gateways to be reliable and is typically deployed in a disparate, decentralized manner. There is currently no common infrastructure for LoRaWAN networking, and there are many private networks. Coverage of LoRa networks is simply extended by increasing the number of gateways in the network. The range can also be improved by modifying the data rate by changing the spreading factor.
• NB-IoT can maintain network connectivity by utilizing three Coverage Enhancement (CE) levels to maintain connectivity in remote or inaccessible areas. The coverage classes enable NB-IoT to narrow its bandwidth and increase its power consumption to achieve more excellent coverage where necessary.

[C] Payload

For typical sensor-based IoT devices, the payload size is generally small as they can only transmit a limited number of bytes at a time. However, simultaneous transmissions from large numbers of nodes or an increase in the size of data packets will increase the payload.

A multi-RAT solution enables a network to select from a range of available payload sizes. Differences in the management of payload size between different LPWANs can also be exploited. For example, LoRaWAN payload size will depend on the data rate used, whereas NB-IoT offers unlimited uplink and downlink data transmissions with zero duty cycle.

[D] Latency

To achieve the safe functioning of infrastructural projects like Smart Cities, the latency of IoT data transfer needs to be minimized. Latency is comprised of uplink latency, the delay between data being transmitted from a node and being received on a server, and data transfer in the opposite direction from server to node, known as downlink latency

5G cellular networking is expected to provide the extremely low latency that would be required for Intelligent Transport Systems and related projects.

In a multi-RAT model, the latency of the overall network provision is limited by the lowest latency of the participating technologies. The inclusion of LP WAN networking means that latency will increase for devices that choose to use this radio access technology for data transfer.

For LoRaWAN networking, uplink and downlink latency is determined by the class of participating device, duty cycle, and data rate. NB-IoT also has increased latency as devices routinely listen for cell information and complete a process of synchronization with the base station before transmitting.

[E] Quality of Service (QoS)

Packet loss and throughput are key QoS indicators for sensor-based IoT use cases. Nodes that can repeat transmission, increase their power output, or be dynamically controlled generally deliver a higher QoS. LP WANs typically do not offer a variety of QoS levels, meaning that the use of LP WAN technology in a multi-RAT network will be at the expense of QoS. NB-IoT is an exception as it has the same time-slotted synchronous protocol as LTE, so it can provide end-to-end QoS.

[F] Cost efficiency

A multi-RAT approach to IoT networking is going to be more expensive than a single radio provision. Deployment costs for multi-RAT networking for IoT include:

• Spectrum costs
• Hardware (including antennas)
• Backhaul
• Network operator costs
• End devices
• Batteries (including the costs of replacing and recharging them)
• Servicing

However, the enhanced performance and energy efficiency that can be achieved through an effective multi-RAT network, could translate into significant savings long term.

In conclusion

Multi-RAT networking is a proposed solution for meeting the capacity and performance demands of a rapidly climbing number of IoT connections. A multi-RAT approach has the potential to harness the benefits of both cellular and LP WAN networking to deliver the coverage and capacity that a diverse ecosystem of IoT devices and nodes needs. Though a multi-RAT approach to IoT networking is expensive, careful planning and implementation of this type of network can maximize benefits for end-user devices and recoup costs.