Air Interface

Task 3.2 Air Interface (M4 - M18) Task leader: UPV Participants: BBC, IRT, NOK, SEUK, UNIS, UPV This task will investigate novel transmitter and receiver designs in order to assess the performance of the most promising candidate 5G transmission techniques for 5G-Xcast in terms of increased capacity and coverage. Initially (during the first 3 months) the progress of international standardisation towards the definition of the 5G unicast air interface, next-generation broadcast systems, and enhancements of eMBMS within 3GPP Rel’14 will be analysed, and it will identify the most promising transmission technologies for the 5G broadcast air interface in close alignment with the 5G unicast air interface. At present, promising candidate waveforms for 5G are Filtered-Orthogonal Frequency Division Multiplexing (F-OFDM) and its Discrete Fourier Transform (DFT) spread variant. Here, filter design will be studied in order to make F-OFDM suitable for broadband video multicast/broadcast transmissions, as well as for narrowband, short-burst, sporadic traffic as e.g. generated by PWS. As 5G is expected to be operating based on large antenna arrays, this task will address the design of multi-antenna beamforming and precoding (spatial multiplexing) for single-cell PTM and for broadcast in SFNs, novel multiplexing techniques for both unicast PTP and multicast/broadcast PTM, PTM scalable content, and interference-aware transmission techniques. For example, the potential of advanced multi-antenna precoding/beamforming techniques or the application of NOMA to facilitate concurrent broadcast/multicast transmissions for different services in the same frequency band at the same time, perhaps in a mixed HPHT / LPLT scenario shall be analysed. Similar mechanism could also be applied to allow for coexistence of SFN and non-SFN transmission. In this context considerations on appropriate pilot pattern designs and frame structures are also relevant. The parameters to be determined include transmission time interval (TTI), signal bandwidth, subcarrier spacing, resource block size, number of data and control symbols within each TTI, etc. Other important topics include i) replacing symbol-level rateless coding, which is applied at the application layer in LTE eMBMS, with bit-level rateless coding at the PHY or MAC (Medium Access Control) layer in order to improve efficiency as well as reduce overhead and transmission latency; ii) interference cancellation, and adaptive regularization of Interference Rejection Combining (IRC) algorithms, the optimal combining scheme in an interference-limited scenario such as when local content is transmitted in non-SFN mode; iii) the enhancement of the time interleaving over several transmission time intervals (TTIs) to improve the resilience against signal fluctuation in time, since the 5G unicast air interface is expected to provide a very short TTI (<1 ms) in order to minimize the latency and processing delay. This is essential for PTM transmissions where retransmissions/HARQ (Hybrid Automatic Repeat Request) are not available.