5G for latency-critical IoT applications
5G not only promises increased data rates but also targets new use cases important to the IoT ecosystem. Therefore, one of its distinguishing features will be the provision of low-latency data communication for machine type applications.
We are investigating the use of 5G for latency-critical IoT applications in the collaborative research project, Fast Wireless, a German government funded initiative involving large and small companies, research institutes and universities.
Latency-critical 5G use cases
When it comes to IoT applications, latency relates to end-to-end communication, where in a centralized network topology, uplink (UL) consists of one fraction of the communication loop followed by downlink (DL) forming the other fraction of the loop. In the Fast Wireless project, we carried out a detailed analysis on the quality-of-service (QoS) requirements for three major latency-critical IoT use cases:
- Industrial automation
- Intelligent transport systems (ITS)
- Real-time professional audio
Although low latency is one common requirement for these use cases, they are quite different in terms of coverage, mobility and reliability requirements
We published the main findings from the use case requirements and their enabling technologies in the article, “Latency critical IoT applications in 5G: Perspective on the design of radio interface and network architecture,” IEEE Communication Magazine, vol. 55, no. 2, pp. 70–78, 2017.
Harmonized end-to-end 5G solution
In the Fast Wireless project, we aim to provide a harmonized end-to-end 5G solution, which not only meets QoS requirements of the specific use cases but is also flexible and configurable enough for additional IoT applications.
Among other working groups, design of a low latency radio access and system architecture constitute the two main working areas. The main concept and findings of these groups are highlighted in the following sections.
Low-latency radio access
One part of the project focuses on 5G radio concepts enabling low latency communication and includes both LTE-evolution and new radio (NR) design. In LTE Release 13, the concept of Fast uplink access has been specified which eliminates the need for explicit scheduling request and individual scheduling grants for minimizing latency. Through pre-allocation of radio resources, Fast uplink access can reduce the average radio round trip latency (i.e. UL + DL) to 9ms, which is a significant improvement compared to traditional LTE with the round-trip latency of 16ms. In addition, the use of shorter transmission time intervals (TTI), along with reduced processing times for data transmission and reception, can further reduce the latencies to around 2ms. This work on short TTI is being specified in LTE Release 14 and 15. In parallel to the LTE radio evolution which is restricted to have backward compatibility, we are also working on 5G NR, which is designed from scratch to enable very low latency radio access. For latency-critical applications with local deployments, NR allows up-scaled OFDM subcarrier spacing (also called numerology), which leads to shorter symbol durations and a new frame design enabling ultra-low latency. We believe that by an appropriate NR design configuration a round-trip latency below 1ms can be achieved, which you can see in the figure below.
Achievable round-trip latencies in LTE and NR
Besides the radio design, we have performed a comprehensive latency measurement campaign in an LTE network as part of the project and it was observed that a considerable portion of the overall latency budget is spent in today’s transport and core networks. These observations motivate the need for a carefully designed network architecture for latency-critical IoT applications and to study the impact of placing very demanding applications close to the edge in the cellular network system. Therefore, we also focus on the system architecture design, including technologies such as network slicing and mobile edge computing. Through network slicing and mobile edge computing, we can place the core network functionalities and application servers closer to radio access network for local deployment scenarios with latency-critical IoT applications. Since the 5G network is not only being developed for latency-critical use cases but rather targets various applications with different requirements, we are designing a flexible architecture to enable different use cases in an optimum fashion. The proposed architecture enabling an efficient inter-working between both LTE and NR used for different 5G use cases is shown below:
5G architecture showing interworking of LTE and NR
5G Proof-of-concept and collaborative research
Both the radio access principles and the proposed architecture are significant for 5G to provide connectivity in order to fulfill QoS requirements of latency-critical IoT applications. Besides developing the novel 5G concepts for latency critical applications, the Fast Wireless project envisions prototype implementations. This collaborative research within the Fast cluster is a platform to develop synergies among the traditional as well as new industrial players in the 5G era.
Facts about the Fast cluster framework
Fast Wireless is a project in the Fast cluster, a collaborative research cluster of around 80 partners spanning large multinational companies, SMEs, research institutes and universities. Fast is an acronym for ’Fast Actuators Sensors & Transceivers’. Initiated and lead by TU Dresden, and funded by the German federal ministry for education and research (BMBF), the Fast cluster is integrated in the framework of ‘Twenty20 - Partnership for Innovation’. The cluster comprises more than a dozen application-oriented projects on subject areas of connectivity, traffic, industry and health. For example, the application project Fast Traffic investigates vehicle-to-anything (V2X) communication and the project Fast Automation focuses on industrial communication for sensors and actuators. These applications commonly rely on technologies enabling low latency wireless communication, which is developed in the four base projects namely Fast Access, Fast Carnet, Fast Realtime and Fast Wireless. Thereby, the Fast Wireless project aims at providing wireless communication for latency-critical IoT applications.