Exploring the magic of mm-waves for 5G
After two years of research in millimeter (mm)-waves, the mmMAGIC EU project in 5G has successfully closed. Researchers in the project developed and designed concepts for 5G mobile radio access technology (RAT) in the 6-100 GHz range and addressed the specific challenges of mm-wave mobile propagation.
The project developed and demonstrated key technical solutions for mm-waves, supporting European industry in driving 5G development with pre-alignment to 5G system design and engagement with standards, regulation and 5G PPP initiatives. Results from the mmMagic project will continue to have a significant impact on standards and regulations. Explore more below:
The mmMAGIC system concept
It is possible to get a holistic view of the project by looking at its system concept, which consists of 23 components and more than 43 solutions for the radio access architecture and radio interface, with insights from the radio channel properties and hardware impairments as shown in the figures below. More details can be found in project deliverable D6.6-Final mmMagic system concept.
One of the primary focus of the Millimetre-Wave Based Mobile Radio Access Network for Fifth Generation Integrated Communications (mmMAGIC) project was to understand mmWave channels., The project collected 22 channel measurement campaigns covering more than eight frequency bands in the range 6-100 GHz and considering several scenarios (indoor, outdoor to indoor, among others). The analysis and validation of this tremendous amount of data helped the project partners create a mmMAGIC channel model and, in particular, come to the important conclusion that Delay Spread is not frequency dependent, which challenges the current view in 3GPP.
Other contributions included:
- Developing an outdoor to indoor penetration model (partially adopted in ITU-R Doc).
- Detailing a modelling for ground reflection, blockage, spatial consistency, clusters and subpaths. The mmMAGIC blockage model was adopted by ITU-R in the revised recommendation P.526 to be published.
The impact of mmMAGIC on standards and regulation is highlighted by 16 contributions to 3GPP and 6 to ITU-R channel model. More details can be found in the project deliverable D2.2-Measurement Results and Final mmMAGIC Channel Models.
Antenna and hardware imperfections
Several solutions for the beam refinement and/or tracking were investigated, namely time division, frequency division, code division, and spatial division depending on the transceiver design.
For analog beamforming capability, only time division is recommended. Due to extensive use of beamforming in mm-waves, multiple access in the spatial domain (SDMA) is the recommended solution, which can also be applied to optimized scheduling between backhaul (self-backhaul) and access traffics and can also be used for an Integrated Access-Backhaul (IAB). However, for initial phase deployments in which analogue beamforming transceivers are likely to be used, TDMA will most likely be the first choice.
Major efforts were dedicated to modeling user equipment antennas, base stations antennas, and hardware impairments, that is, phase noise and power amplifier non-linearity, among others. The phase noise model was introduced in several 3GPP contributions, and the effect of hardware imperfections was also demonstrated at several events using the proposed radio interface.
The mmMAGIC radio interface is based on the following recommendations:
- A scalable OFDM waveform for all transmissions in uplink and downlink. The numerology is designed based on the LTE numerology, and the proposed frame structure includes: downlink only subframe, uplink only subframe, mixed subframe structures and mini-slot, aiming for low latency and fast turn-time.The waveform, numerology, and frame-structure were designed to be robust against phase noise and Peak-to-Average-Power-Ratio. The beamformed reference signals investigated in mmMAGIC include: Channel State Information (CSI) acquisition, Demodulated Reference Signal (DMRS) and Phase Tracking Reference Signal (PTRS) to mitigate phase noise. Whenever possible, it is desirable to avoid having always-on reference signals.
- The recommendation for the channel code is to use Low-Density Parity-Check (LDPC) for data transmission and polar codes for transmission of control information, with low complexity decoders. The initial access procedure is periodically repeated, and solutions are detailed for three phases: the cell discovery phase, the random-access phase, and the beam refinement and/or tracking phase. The project proposed adaptive and asynchronous retransmission protocols for single hop and multi-hop scenarios, which constitutes an enhancement of LTE-A. The final radio interface was evaluated using common link level and system level simulators and is summarized in the blog Developing mmWave mobile radio interface. Details are given in D4.1-Preliminary radio interface concepts for mm-wave mobile communications and D4.2-Final radio interface concepts and evaluations for mm-wave mobile communications.
To ensure system integration between LTE-A and 5G RAT, the system concept design is based on the logical architecture and protocol stack of LTE-A RAN. Multi-connectivity is a recommended solution based on the LTE-A dual connectivity with MCG/SCG-split bearer at the PDCP layer, which allows data flows between two nodes. Multi-connectivity will enable Radio Resource Control (RRC) diversity to route the control plane RRC messages using different nodes. Tight interworking with LTE-A enables the interworking between LTE and 5G RAT to provide seamless connectivity. The solution is based on, but not limited to, dual connectivity and handover. For enabling a service with a separate logical network on a shared infrastructure, multi-service support is carried through network slicing. Multi-node coordination, and active and inactive mode mobility were also explored. Read more at D3.2 and D5.2.
The mmMagic partners showed leadership by exploiting and disseminating their results in 24 project deliverables as well as in more than 70 scientific publications, several keynotes and workshops. In addition, the partners contributed to the development of the software platform QuaDRiGa incorporating the mmMAGIC channel model, as well as development of a visualization tool, contributions to standards and regulations, show-casing hardware experiments, and reporting 11 patents to the European Commission.