5G Update Series: Ultra-Reliable Low Latency Communication (URLLC)

Ultra-reliable Low-latency Communications (URLLC) is a special use case of cellular communications that includes a set of features suited to low latency and ultra-high reliability applications. This includes mission critical applications, such as industrial automation, autonomous vehicles, smart grid, intelligent transportation/freight, and even augmented/virtual reality or remote medical or industrial procedures. It is commonly assumed that 5G will also usher in a new paradigm of machine-to-machine (M2M) communications and Massive Machine Type Communications (mMTC), with autonomous systems controlling, communicating, surveying, storing, and analyzing massive amounts of data.

The goals of URLLC is to have features and network functions that can operate within extreme reliability standards and with round-trip latencies between critical infrastructure and machines below 1 ms. In order to enable these features, there needs to be substantial changes to networking infrastructure and protocol, as the lowest latency targets of 4G LTE in 3GPP release 14 was 4 milliseconds. Moreover, prior cellular standards predominantly focused on throughput and connectivity, with latency and reliability as second-level considerations. Though established in the standard, there are few low-latency and high reliability networks presently deployed, and these networks tend to be privately owned and operated, or for use in government applications.

With upcoming 3GPP Release 16 (targeted Q1 2020 development), there will be a new 5G variant that focuses on reducing the latency and increasing the reliability of networks to enable a wide range of applications that previously had to rely on proprietary solutions typically using wired interconnect and protocols. Moreover, it is also likely that URLLC capabilities will also benefit the general data communications systems by reducing the travel time between edge-devices and data centers, critical to machine-learning applications, as well as enabling much more responsive network automation/orchestration features.

Though much of the onus for URLLC is on the network infrastructure and protocol/standards development, there are potential impacts in the radio domain for URLLC. Where networks have mostly focused on throughput and capacity, URLLC features will necessitate changes in the base station schedule, resource allocation, and policy functions, that may require trade-offs to the overall spectral efficiency and other RF and data communications performance factors. Another result is that radios and base station hardware may require design strategies that have previously been unnecessary, in order to reduce latency and enhance reliability. An example of this is developing beamforming antenna systems that can track fast moving user equipment (UE) and seamlessly hand-off the connection between network nodes in a robust fashion.

Moreover, there are a variety of end-to-end infrastructure considerations to take into account the latency and reliability between data centers, edge computing nodes, core network control/orchestration, and UE. An additional challenge to this is how to achieve some level of homogeneity in performance when the 5G network will be made up of legacy networks and various grades of 5G services comprised of physical and software components from a wide range of vendors and network operators. We will all learn more as 3GPP Release 16 comes out, and pioneering service providers begin developing URLLC solutions for the market.