From conversations with Ghyslain Pelletier and Paul Marinier

Operators have craved flexibility to accommodate the proliferation of devices and use cases emerging in our increasingly connected world. 5G promises to efficiently support significantly more use cases than any previous generation of wireless and provides a high level of versatility to serve each use case according to its specific needs. The solutions fueled by spectrum aggregation techniques, many pioneered and patented by InterDigital, have defined this fundamental capability of 5G.

What Is Spectrum Aggregation?

Spectrum aggregation helps operators achieve greater flexibility in wireless network deployments to accommodate more types of devices, new services and new use cases. This approach is shaped by two key concepts: carrier aggregation and dual connectivity, both of which enable operators to perform transmissions using different frequency resources. Operators typically receive licenses to operate within designated frequency bands, or carriers within a band, and spectrum aggregation technologies allow operators to simultaneously access and deploy their resources to maximize user data rates and system throughput.

Carrier aggregation occurs when an operator adds a carrier, or additional transmission frequencies, within or between frequency bands using the same node. This allows a user device to connect to a network using different frequencies in the same node.

In contrast, dual connectivity occurs when a mobile device or user equipment (UE) connects to two different nodes, generally for different purposes – i.e., one for reliable connection and control information and the other for high data rates. Dual connectivity helps ensure quality of service and reliability, while adding redundancy to a connection to make it more robust. These techniques are considered spectrum aggregation because they enable a mobile device to efficiently use multiple pieces of the spectrum .

The path to achieving 5G’s potential is shaped by spectrum aggregation solutions. These techniques help user devices simultaneously connect to multiple carriers and frequency bands while supporting communications with multiple synchronous or asynchronous nodes and schedulers. As 5G deployments begin and continue in various parts of the world, existing network systems must be able to simultaneously support transmissions from LTE and 5G NR (New Radio), and beyond.

Understanding InterDigital’s Innovations

Power Sharing

At a foundational level, every cellular transmission is expected to allocate the appropriate amount of power required by both the node, or base station, and the user device. The prevalence of dual connectivity has made power determination more complex because different connections, though made simultaneously, might have different power requirements for the user device, which is typically more power-constrained than the node. Through our research leadership and collaboration within industry consortia, InterDigital developed a power-sharing solution to address this common challenge and make dual connectivity more efficient for the user device.

Traditionally, the amount of power a user device expends on transmissions in the uplink is determined by the scheduling information it receives from the node in downlink. If a user device has two connections, it's possible that the transmissions occur simultaneously, and the device must then determine how much power it puts into each. Because the network sets the power requirements based on the scheduling information it sends in the downlink, the UE must frequently make tough choices to mitigate power allocation for two different nodes that may otherwise be unaware of each other or the requirements their transmission link is placing on the UE.

A conundrum arises when the sum of the power requirements of each node exceeds the maximum power a UE can transmit. At InterDigital, we dedicated research to develop a solution that enables the UE to mitigate and reconcile the scheduling requirement from both nodes if the total requirements exceed the UE’s maximum power availability.

Our solution is based on the understanding that both connections are necessary and neither connection should have priority access to all the available power of the UE. Through our expertise, we crafted a solution that uses a minimum level of power to maintain both connections, and when extra power is available, prioritize and allocate the resources between the connections. Our approach understands that one of the connections will take the higher priority if it's a more critical connection and follows a structure that keeps the system working and ensures connectivity is maintained at the most optimized level based on circumstances.

In practice, a lower frequency connection is used to carry the information that maintains the user's network connection and control plane, while the second connection might be to a higher frequency node, which may be used to achieve high data rates and throughput to transmit user data. In this scenario, even if the high-frequency connection happens to degrade significantly or fail, the UE won’t lose connectivity because the lower frequency connection is maintained.

Overall, power-distributed dual connectivity ensures greater reliability in lower frequency spectrum while maximizing throughput in higher frequency spectrum. This is because the power demands can be dynamically determined and allocated based on the demands of the UE.

This solution is especially impactful as we transition more fully into 5G. Because 4G and 5G can coexist in the same spectrum or geographic area, our solution allows users to use 4G connectivity to transmit according to 5G in the same frequency band, allowing network operators to reuse their LTE systems to deploy 5G data transfers. In this instance, although connectivity management is maintained at 4G levels, the data is transmitted according to 5G.

Control Plane Connection Management

As the telecoms industry gradually deploys standalone architecture 5G (5G SA), the solutions InterDigital has developed around power-sharing, dual connectivity, and control plane management provide a critical bridge between wireless generations. To ensure 4G and 5G can work together in the same UE, operators must be able to use 4G system protocols to configure some aspects and operations according to the 5G system. As such, InterDigital has developed methods to enable 4G networks to control the setup of transmissions according to 5G protocol. Using the “radio resource control protocol” for LTE, the control plane connection of 4G LTE communications is used to configure and control data transmissions for 5G.

In this instance, the exchange between 4G and 5G systems can happen via a variety of methods. The first could be described as a piggybacking of the information on a legacy connection, where the 4G control plane is extended to also be able to control 5G. The second creates a new signaling mechanism, extending the 4G connection to create a new control plane connection dependent upon signaling from 5G. Though the transmission is used to control the setup and configuration of 5G, the 4G connection manages the setup of the transmission and the signaling connection.

Radio Link Failure Handling

After enhancing connectivity and optimizing the control plane, it is important to determine how the system will respond if the connection degrades significantly or fails. Through our research, we developed a method to ensure that a failed connection doesn't necessarily disconnect a UE but instead enables the UE to determine when a connection has failed to help it reestablish a connection to that node or connect to a different cell. Because most network providers will rely on both 4G and 5G radio interfaces for the foreseeable future, our patented research made it possible for the network to use 4G to recover, restore, and reconfigure a failed 5G connection, a significant milestone in the evolution toward 5G.

Both 4G and 5G are based on orthogonal frequency division multiplexing (OFDM) transmission techniques, so even though 5G taps higher frequencies, operators can utilize existing 4G deployments for connectivity. One of the first contemplated deployments of 5G considered the reuse of 4G sites with the addition of a 5G carrier to support higher data rates – a deployment scenario made possible by InterDigital’s innovations in dual connectivity. Dual connectivity is a keystone technology in the transition from 4G to 5G because it allows operators to leverage both capabilities and reduce deployment costs by using existing 4G system and speeding up time for making the benefits of 5G available to market.