LTE - the evolution continues
LTE is the technology behind 4G. It's also expected to be a vital component of future 5G systems. What will the next iteration of LTE bring?
LTE, the 4G technology, today brings unprecedented mobile broadband performance to hundreds of millions of users across the globe. We've discussed LTE as a vital component in future 5G systems, beyond 2020, in our recent 5G blog posts. Naturally, as being one of the leading LTE companies, Ericsson is very active in contributing to the enhancements of LTE. In this blog post, I would like to share with you some of our thinking around the future evolution of LTE, with focus on 3GPP release 13.
3GPP is the organization developing the LTE specifications. The first incarnation of LTE was in release 8, and from there, the specifications have been regularly updated, with new features that boost performance and address new use cases. Currently, release 12 is being finalized. Focus is now, gradually shifting, to which enhancements to include in the next release, release 13. The intention is to finalize release 13 by the end of 2015.
Spectrum is fundamental for all radio access and there seems to be an almost never-ending quest for more spectrum as the means to provide higher capacity and higher data rates. There are two main types of spectrum: licensed and unlicensed spectrum. Systems, like LTE, operate in licensed spectrum, where the operator has an exclusive license for a certain frequency range. Licensed spectrum is key to superior performance and quality-of-service, as the operator can control the interference situation in the network.
On the other hand, unlicensed spectrum is free, but subject to much more unpredictable interference situations and the quality-of-service cannot be guaranteed. Therefore, in the future, getting access to additional licensed spectrum is the highest priority, but, unlicensed spectrum can serve as a complement. With this in mind, Ericsson is proposing to extend LTE in release 13 so that unlicensed spectrum can be exploited for offloading best-effort traffic through the carrier-aggregation framework. Mobility, critical control signaling and services demanding high quality-of-services rely on the licensed spectrum while (parts of) less demanding traffic can be handled by the unlicensed spectrum.
Figure 1: carrier aggregation
In situations when obtaining additional (licensed) spectrum is not possible, other means must be used to boost data rates and system capacity. Multi-antenna techniques, including beamforming, is one possibility and since the beginning, has been an integral part of LTE. Often, only the azimuthal direction has been used for evaluations, but research has shown that exploiting also the elevation domain has the potential to significantly increase capacity in, for example, city centers with high-rise buildings. Therefore, we propose to explore the potential gains with elevation-domain beamforming in 3GPP. One example of an enhancement is pathloss measurements to multiple candidate beams to determine the beam best suitable to serve a particular terminal.
From an end-user perspective, not only data rates are of interest. The latency, that is, the time it takes to send a small packet through the network, is also relevant for the overall service experience. In fact, several services, for example, gaming, are more interested in low latency than high data rates. The latency is one of the key performance numbers visible to the end-user, often expressed as round-trip-time or “ping time”, for example when conducting a speedtest. Consequently, although LTE already is capable of delivering low latency and this, for many users, is a major difference between 3G and 4G, we think 3GPP should investigate means to lower this latency, even further, to improve end-user experience and facilitate new use cases. For example, “instant uplink access” could be supported through a small extension to the specifications where the terminal is provided with a grant, i.e. permission to transmit, in advance, instead of requesting permission when the uplink data arrives to the terminal.
With the overall vision of a Networked Society, the number of “communicating machines”, that is, machines sending or receiving data via LTE, is expected to increase dramatically. Machine-type communication is a very wide range of requirements, but in many cases the focus of the requirements is on low-cost, low-power, simple devices rather than high data rates and large amounts of data per device. Therefore, we would like to continue the work started in release 12 and we are aiming for further improving the support for massive machine communication.
Finally, mobility has been and continues to be, a cornerstone in LTE. The possibility for the devices to seamlessly move around without losing connection to the network is essential for most applications and an enabler for many new use cases. Therefore, it is crucial to ensure continued superior mobility when introducing new functionality in LTE.
I hope I have managed to give you some insight in our thinking around the LTE evolution in release 13. LTE is an important part of the vision of a Networked Society and a cornerstone of the overall 5G solution and will, as such, continue to evolve for many years to come.
Principal Researcher, Ericsson Research