Section: New Results

Flexible Radio Front-End

Activities in this axis could globally be divided in three main topics: wake-up radio and wireless power transfer, RFID systems and combination of spatial modulation and full-duplex.

Wake-Up radio and wireless power transfer

The ubiquity of wireless sensor networks (WSN), as well as the rapid development of the Internet of Things (IoT), impel new approaches to reduce the energy consumption of the connected devices. The wake-up radio receivers (WuRx) were born in this context to reduce as much as possible the energy consumption of the radio communication part. We aim at proposing a low-cost, high-efficiency rectifier to improve a quasi-passive WuRx performance in terms of communication range. By optimizing the wideband matching circuit and the proposed rectifier's load impedance, the sensitivity was increased by 5 dB, corresponding to an increase of the communication range (13 meters in free space) [10].

We also studied an original solution to maximize the DC power collected in the case of a wireless power transfer (WPT) scenario. Using state-space model representation, the WPT System is considered as a feedback approach in order to maximize the amount of harvested energy. To do this, a global simulation is performed to show the importance of taking into account the propagation channel and the rectifier circuit aspects in the case of optimizing the waveform to increase the harvested energy. By using an optimized multi-sine signal with zero phase as the excitation, taking into account the characteristics of the channel and the physical contributions of the rectifier, we managed to obtain better output DC values compared to a single tone source or a multi-sine signal without optimization, with the same average power input [14].

We plan now to apply this optimized WPT technique to feed Wireless sensors in the particular case of ventilation ducts (HVAC) [24].

RFID

The ARA (Auvergne Rhone Alpes) RAFTING project mainly deals with the design and analysis of wire antennas for RFID tags in the context of wearable electronics. More specifically, an helical dipole antenna dedicated to the smart textile yarn applications has been designed. Moreover, the performance was analysized with respect to mechanical constraints, together with the extraction of accurate electrical models. This work was done in collaboration with Primo 1D company. In perspective, the integration of the NFC protocol together with RFID UHF and the integration of sensing capabilities is envisaged [6], [19], [7], [12], [21].

The Spie ICS- INSA Lyon chair on IoT has granted us for a PhD thesis on Scatter Radio and RFID tag-to-tag communications. Some seminal results have shown that it is actually possible to create a communication between two RFID tags, just using ambient radiowaves or a dedicated distant radio source, without the need of generating a signal from the tag itself. Theoretical and simulated performance have been studied.

Combination of spatial modulation and full-duplex

Spatial modulation (SM) as a new MIMO technique is based on transmitting part of the information by activating different emitting antennas. SM increases spectral efficiency and uses only one radio frequency chain. Moreover, for full-duplex (FD) communication systems, self-interference (SI) is always a central problem. Therefore, combining FD and SM can dramatically reduce the difficulty of SIC (Self-interference Cancellation) because of the single SI chain. A Full Duplex Spatial Modulation (FDSM) system is proposed and an active analog SIC is designed in this work. Moreover, the impact of SIC accuracy on the system performance is studied. The results demonstrate that the accuracy requirement will increase as the INR (Self-interference-to-noise Ratio) increases. The FDSM system is less sensitive than the FD system, which can get a better BER (Bit Error Rate) performance as errors increase. Furthermore, an SI detector is proposed to resolve the influence of the number of detected symbols.