Towards 5G

13Low-latency Radio-interface Perspectives for Small-cell 5G Networks

Toni Levanen,¹ Juho Pirskanen,² and Mikko Valkama¹

¹ Tampere University of Technology, Tampere, Finland

² Nokia Networks, Espoo, Finland

13.1 Introduction to Low-latency Radio-interface Design

Reducing radio access latency is one of the key targets of the future 5G systems [1, 2]. There are two main reasons for needing an ultra-low-latency radio interface in 5G. First of all, if we want to keep the amount of memory required for hybrid automatic repeat request (HARQ) and other physical-layer processes approximately the same as for current solutions, or at least to increase at a slower rate than the actual throughput, we have to decrease the time duration of the transmitted frames as the frequency allocation increases [2]. This unavoidably leads to reduced physical layer latency. Secondly, because new applications and use cases of the future wireless access – cloud services, augmented reality, self driving cars, and so on – require very low latency radio interfaces, we have to provide a physical layer numerology capable of achieving a physical layer (PHY) round-trip-time (RTT) of 1 ms or even less [3]. The 1-ms target is generally considered as a good standard when compared to the LTE-A PHY latencies of the order of 10 ms [4].

The PHY design is dictated by the channel environment and the expected propagation conditions related to the assumed carrier frequency and maximum cell size. Therefore, we start by introducing ...