At the beginning of the projet
The technique of using a large number of antennas organized in a network to shape the multi-dimensional transmission is called Massive MIMO.
In the special case of millimeter waves systems, the large number of antennas is imposed by the need to achieve significant gains to compensate for propagation losses and allowing a control of the spatial dimensions of the channels.
At the beginning of the project, these two techniques M-MIMO and mmW was constituting the 2 technical pivots of the 5G systems providing better spectral and energy efficiency .
The study of performances of channel estimation strategy requires model which preserve the spatial consistency of the channel as i.e Quadriga  which is a spatially consistent evolution of the WINNER channel model.
 T. S. Rappaport et al., “Millimeter Wave Mobile Communications for 5G Cellular: It Will Work!,” in IEEE Access, vol. 1, pp. 335-349, 2013. doi: 10.1109/ACCESS.2013.2260813
 S. Jaeckel, L. Raschkowski, K. Börner and L. Thiele, “QuaDRiGa: A 3-D Multi-Cell Channel Model With Time Evolution for Enabling Virtual Field Trials,” in IEEE Transactions on Antennas and Propagation, vol. 62, no. 6, pp. 3242-3256, June 2014. doi: 10.1109/TAP.2014.2310220
- Since 2015, the work in the channel modelling community has confirmed the importance of the Ray tracing approach in such a mmWave scenario, as considered in M5HESTIA.
- The sparsity of the channel has been widely confirmed and especially in the measurements campaigns carried out by Aalto University we worked with.
- In M5HESTIA we choose from the beginning of the project to exploit a channel simulator based on physical modeling with ray tracing which also preserve natively the important spatial structure of the channel like it has been recently presented in  by Fuschini and al.
 F. Fuschini, M. Zoli, E. M. Vitucci, M. Barbiroli and V. Degli-Esposti, “A Study on Millimeter-Wave Multiuser Directional Beamforming Based on Measurements and Ray Tracing Simulations,” in IEEE Transactions on Antennas and Propagation, vol. 67, no. 4, pp. 2633-2644, April 2019