At the start of the project, the main goal of M5HESTIA crystalizes in four scientific and technological objectives, all dedicated to M-MIMO in the 60-GHz band.
Objective 1: Real-time HW implementation for Multi-User MIMO (MU-MIMO)
The objective is to implement an HW platform demonstrating that users, geographically attached to a given small cell, can be spatially discriminated thanks to the combination of “appropriate antenna design and digital processing techniques”. Indeed, we want to demonstrate that it is possible to simultaneously transmit towards isolated users, different signals by focusing millimetre-wave power in a given direction, optimising the radiated power while minimizing the interference between users. This corresponds to the so-called Multi-User MIMO (MU-MIMO) concept. Therefore the HW platform will implement eNodeB and user equipment. At Tx side, the demonstrator will integrate an adaptive antenna array (the total number of elements and the beamforming techniques will be defined during the project) implemented on RF and a digital board, the latter one integrating the digital/baseband processing. The digital board will be dynamically programmed to take into account real-time constraints, to target at the same time different users with different contents. Different SDMA schemes allowing for MU M-MIMO will be chosen for HW implementation among the studied algorithms (optimisation of the feedback compression, solution based on channel reciprocity, etc.) depending on the theoretical results obtained with realistic channel models and complexity issues.
Objective 2: design and demonstration of 60-GHz front-end radios for channel sounding and M-MIMO communications
Various advanced 60-GHz RF front-ends will be designed and prototyped for M-MIMO channel sounding and M-MIMO communications integrating analogue and digital beamforming. The front-end specifications and architectures are different for these two cases. However, the ultimate objective is to design a 60-GHz front-end with up to 64 IQ links. To mitigate the risks associated to this extremely challenging objective, various intermediate antenna systems, still at the state-of-the-art, will be implemented.
Objective 3: SIMO channel sounding, characterisation and modelling
An accurate and reliable knowledge of the transmission channel model is strategic for an optimised design of communication systems. The outdoor radio channel has been recently characterized and modelled for SISO channel in the FP7 project MiWeba. M5HESTIA proposes to model the M-MIMO channel at mmW, based in a first step, on literature and theoretical investigations, and, in a second step, on its own mmW SIMO channel measurements campaign. To the best of our knowledge, this work is pioneer at the international level. The results obtained will be used opportunely for a realistic description of the M-MIMO transmission channel (including the important effect of antenna arrays and RF/baseband architecture) for further studies on beamforming and precoding schemes.
Objective 4: Signal processing algorithm optimisation for mmW M-MIMO transmissions
Signal processing algorithms accounting for the mmW M-MIMO channel characteristics (including antenna and RF front-end) are of high importance to propose efficient communication strategies, especially to exploit the system spatial dimension for SDMA purpose. We will propose, develop and compare algorithms for M-MIMO transmissions optimised for mmW outdoor propagation in a multi-user context. The most promising solutions will be selected for implementation in the HW platform.