Millimetre-Wave Air-Interface for 5G: Challenges and Design Principles

The rapidly advances in wireless communications and market trends have made it imperative for the mobile communications industry to explore millimetre-wave (mm-wave) bands. By exploiting the larger available bandwidths and a massive number of antenna elements in a small form factor, a mm-wave based mobile communication network can deliver demanding services in terms of capacity, throughput, latency, and reliability. Therefore, mm-wave technology is envisaged to be a core component of the 5G multi-RAT ecosystem. mmMAGIC (Millimetre-Wave Based Mobile Radio Access Network for Fifth Generation Integrated Communications) is a European project where research is performed on pivotal components aiming to develop novel radio access technologies for mobile communication in the frequency range 6-100 GHz. One of the key objectives in mmMAGIC is to design a novel mm-wave air interface that fulfils the key performance indicators (KPIs) related to societal and operational 5G system requirements. However, the design of a mm-wave air interface is a challenging task. The propagation characteristics for communication over mm-wave frequencies differ quite a lot from these below 6 GHz. Furthermore, with increasing frequency, signals suffer severe RF impairments, such as phase noise. In addition, the electronics become less energy efficient and the larger bandwidth leads to very high demand on signal processing capacity. Therefore, the success of a mm-wave air interface relies on an efficient design that overcomes such mm-wave specific challenges. The mmMAGIC project has identified the main challenges, key requirements and design principles for mm-wave air interfaces to support a wide range of use cases. In this paper, five subtopics are investigated: waveforms, channel codes and re-transmission schemes, frame structure and numerology, multiple access and duplexing schemes, and initial access schemes. For each sub-topic, the technological KPIs and design principles are discussed, taking into account the the identified mm-wave specific challenges and extreme system requirements. The requirements and design principles will not only provide insights into efficient design of the mm-wave air-interface, but also help align various research activities in both industry and academia, paving the way for successful future 5G mobile communication networks.