The widespread adoption of the Internet of Things including almost every industry and across global infrastructure is catalyzing what many have described as an exponential era that will unleash massive increases in productivity and commercial growth.
As with every technological innovation, there are teething problems, and currently, the potential of the Internet of Things is limited by the wireless networking capacity needed to support billions of IoT connections.
Several competing wireless technologies have been implemented, but individually they do not have the capacity or harmonization to support the broad range of internet of things devices, leading to a fragmented landscape that is not end-user-friendly.
According to theLoRa Alliance, there is no single networking technology for IoT that delivers:
- ubiquitous coverage
- universal availability and compatibility
- the ability to support every type of IoT solution and use case
- the ability to be used as a personal area network (PAN), local area network (LAN), neighborhood area network (NAN), or wide 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 that are being made towards creating and implementing Multiple Radio Access Technologies (Multi-RAT) that marry the differing networking technologies that are used by the Internet of Things, in particular, LPWAB cellular networking technologies including LoRa.
What is Multiple Radio Access Technology (Multi-RAT)?
Multiple Radio Access Technology (Multi-RAT) is a type of networking architecture that is used to create heterogeneous wireless networks that integrate multiple cellular and non-cellular technologies. Multi-RAT network architecture supports massive IoT applications to connect many disparately located nodes using several networking technologies.
A Radio Access Technology (RAT) is the type of technology that is used to support connectivity in a radio-based communication network. Devices such as cellphones 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 a variety of RATs to transfer data to the internet, similarly to the selection of access points in WiFi.
The networking technologies that can be combined currently with this technology include:
The networks that are created from these technologies are highly targeted and adaptive with multiple layers of cells that are focused on dealing with specific areas of service provision including, expansion of 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 which can be used to build multi-layer (macro and small cells) networks and expand network capacity with small cells or offloading to other networks.
Multi-RAT planning uses the various layers of cellular networking technology and devices 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 the disparate technologies include switching, coverage targets, backhaul, interference management, and the use of antennas.
About heterogeneous wireless networks
These novel networks bring together multiple radio access technologies (RATs) together in a single network. These networks are heterogeneous wireless networks.
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 required by participant nodes.
Key challenges and considerations of the multi-RAT model
Multi-RAT networking is vulnerable to congested regions in the network and interference. This is because there can be issues with the algorithms that are used to select the radio technologies that are used, especially if large numbers of devices need to gain internet access. Access point/gateway availability is essential, as this is where all networking technologies obtain internet access. Key limitations in multi-RAT networks include:
- access point (or gateway) availability
- distance to the nearest access point
- the signal quality of the access point or gateway
- the load experienced at the access point
- the 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. But by integrating other networking technologies they can achieve communication 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 to achieve functional integration between the diverse wireless communications technologies used by IoT. An existing example isIEEE 802.21 that specifies media independent handover, between a variety of wired and wireless networks.
Electronic engineers have developed complex algorithms that control the selection of the best network according to a variety of characteristics including the performance, power consumption, and energy efficiency of the constituent networks.
Software-Defined Networking (SDN) can manage multi-RAT networks
A key limitation of multi-RAT networking for IoT is that each individual RAT has its own control and management layer. To achieve harmonized control of a diverse range of RATs in a single network, there needs to be a single, unified management platform to prevent suboptimal network performance.
SDN-based network architecture can deliver end-to-end control of multiple RATs with the provision of 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 as it provides the global view of the network that is needed to ensure that downstream nodes function optimally using the RATs available to them. SDN is also simplified as they require 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 requirement 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 the 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 in a similar way to WiFi.
Despite being low power, LPWANs also offer effective long-range communications with licensed and license-free options available. Though all LPWAN solutions are low-power it is important to note that they use distinct technologies and have different advantages and limitations. For example, here is a comparison of LoRaWAN and NB-IoT:
- Is an LP WAN that uses the unlicensed radio spectrum
- LoRa was originally developed by Semtech using 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 The 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 by this time, over 25% of all LPWAN connections.
- Cellular technology that uses licensed frequency bands
- This is a commercial LPWAN protocol developed by the 3rd Generation Partnership Project (3GPP).
- NB-IoT is specifically developed 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 works with the inclusion of 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 a true multi-RAT approach that includes LPWAN networking can provide benefits for IoT networking that include:
- greater autonomy, with devices/nodes being able to remain 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 are small data transmission can use the technology that is 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 have the potential to 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 communications that require it.
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 also power can be scaled right back in favorable conditions.
Having this type of narrow bandwidth signaling with simple MAC will reduce the overall power consumption of IoT networks significantly especially if cellular data of suitable caliber is offloaded via a LoRaWAN.
As a low-power, cellular-based option, NB-IoT can be readily integrated with cellular IoT networks. NB-IoT is a simplified version of the LTE standard and 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 that are used in critical applications need, 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.
- LoRais reliant on an adequate distribution and proximity of gateways to be reliable and is typically deployed in a disparate, decentralized manner. There is no common infrastructure for LoRaWAN networking at present 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 increased by modifying the data rate by changing the spreading factor.
- NB-IoTcan maintain its 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 greater coverage where necessary.
For typical sensor-based IoT devices, the payload size is generally small as they only are capable of transmitting 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 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 being used, whereas NB-IoT offers unlimited uplink and downlink data transmissions with zero duty cycle.
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 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 generally 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)
- network operator costs
- end devices
- batteries (including the costs of replacing and recharging them)
However, the enhanced performance and energy efficiency that can be achieved through an effective multi-RAT network, could translate into significant savings long term.
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 need. Though a multi-RAT approach to IoT networking is expensive, careful planning and implementations of this type of network can maximize benefits for end-user devices and recoup costs.
Posted by George Hardesty on 22nd Dec 2021