5G air interface design based on Universal Filtered (UF-)OFDM

In this paper we discuss 5G air interface design with respect to waveforms, multiple access and frame structure. We start by introducing the 5G system level requirements and expected scenarios. 5G will be driven by supporting very heterogeneous service and device classes. A unified frame structure for handling those heterogeneous traffic types is presented. Multiple access for 5G will make use of strict synchronicity where it is justifiable and will drop it where signalling overhead and energy consumption will demand for. In order to serve this unified frame structure best, the choice of the underlying waveform is discussed. CP-OFDM has its limitations in spectral properties and in conjunction with relaxed time-frequency alignment. The most discussed contender so far is Filter-Bank based Multi-Carrier (FBMC), with better spectral properties but new drawbacks introduced by offset-QAM and long filter lengths. Hence, a new alternative is required: Universal-Filtered OFDM (UF-OFDM), also known as Universal Filtered Multi-Carrier (UFMC), is a recent technology close to OFDM. UF-OFDM, according to encouraging results so far, summarized in this paper, fits best to the 5G system requirements. A further feature of the Unified Frame Structure is the usage of multiple signal layers. Here, users can be separated e.g. based on their interleavers, as done in Interleave-Division Multiple-Access (IDMA). This will introduce an additional degree of freedom for the system, improve robustness against crosstalk and helps to exploit the capacity of the multiple access channel (MAC). Altogether, the proposed new concepts offer an emboldening approach for dealing with the new challenges, faced by 5G wireless system designers.