In-Band Full-duplex System for Inter-Satellite Link with Independent Transmit and Receive Steerable Antennas – FullSSAT

This 36-month project focuses on the study and design of an IBFD antenna system with TX and RX beamsteering capabilities and with shared radiating elements.
The Full-Duplex (FD) or In-Band Full-Duplex (IBFD) technique, which consists of transmitting and receiving at the same time and in the same frequency band, is considered to be one of the most promising way to double the data rate in terrestrial and space communications, or to optimize the spectral resources (5G-Advanced, 6G, ...). This technique has other potential advantages, such as introducing a first level of security on the physical layer (self-scrambling), the ability to listen and transmit simultaneously in the same frequency band (radio-cognitive), ...
The main obstacle to achieve an IBFD communication are the self-interference (SI) signals which couple from the transmitter of one radio device to its own receiver. Thus, to establish such kind of communication, various Self-Interference Cancellation (SIC) circuitry must be implemented at the different stages of the radio front-end: at the antenna/analog, and digital levels.
Since 2010, a very large number of papers and conference articles (> 8000) on IBFD has been published among the international microwave scientific community (antennas, RF, Micro/millimeter wave) and some very promising results in terms of the high levels of SIC obtained have been demonstrated. Special sessions on this topic are regularly organized, in which FullSSAT members were strongly involved (guest papers, session chairman, TPC, etc.). Moreover, to our knowledge, we are the first in France to work and to have obtained experimental results on IBFD techniques at the antenna level. Moreover, these results were obtained for space applications (CubeSat) and Ultra-Wide-Band domains where the specifications are particularly severe; indeed for Inter-Satellite Link, the total required SIC level should reach 120-130dB.
But, currently, none of the techniques proposed in the literature makes it possible to achieve efficient beamsteering while keeping the high level of isolation between Tx and Rx required for In-Band Full-Duplex communication mode. Fully digital or hybrid MIMO techniques have recently been put forward, but the most significant contributions in this area together with our own observations from measurements show that a substantial first level of SIC (between 40 minimum and 60 dB) must be obtained at the antenna or analog level in order to i) avoid saturation at the reception level (ADC), or even to protect it from possible degradation and ii) to strive reaching a total level of self-interference cancellation of at least 120dB. Some initial work has just been published on an IBFD antenna system with beam-steering capabilities, but the number of radiating elements is necessarily very low (i.e. 4) and the beam-steering functionality is strongly limited.
The aim of FullSSAT poject is to bring together various teams within the Lab-STICC that have already gained considerable experience in the space field and independently produced SIC demonstrators at antenna level (DH team) and digital level (SI3 team) in order to focus on the study and design of a compact, high-gain IBFD antenna system with beamsteering/beamforming functionality.
The FullSSAT project also aims to:
- optimize the efficiency of the antenna system (i.e. the ratio of the transmit and receive antenna gain versus the surface area of the radiating part by sharing the same antenna element between TX and RX (to avoid a loss in gain of 3 dB),
- To consolidate (e.g. by adding so-called "SoftNull" techniques) the achievement of SIC at antenna level by taking advantage in this IBFD context of Hybrid Beamforming by optimizing the combination of analog (Phased Array) and digital (DBF: Digital BeamForming) beamforming solutions,
- To combine these antenna-level SIC results with a digital SIC dedicated to beamsteering antenna system