Symbiotic Radio: Cognitive Backscattering Communications for Future Wireless Networks

Abstract

The heterogenous wireless services and exponentially growing traffic call for novel spectrum-and energy-efficient wireless communication technologies. Recently, a new technique, called symbiotic radio (SR), is proposed to exploit the benefits and address the drawbacks of cognitive radio (CR) and ambient backscattering communications (AmBC), leading to mutualism spectrum sharing and highly reliable backscattering communications. In particular, the secondary transmitter (STx) in SR transmits messages to the secondary receiver (SRx) over the RF signals originating from the primary transmitter (PTx) based on cognitive backscattering communications, thus the secondary system shares not only the radio spectrum, but also the power, and infrastructure with the primary system. In return, the secondary transmission provides beneficial multipath diversity to the primary system, therefore the two systems form mutualism spectrum sharing. More importantly, joint decoding is exploited at SRx to achieve highly reliable backscattering communications. In this article, to exploit the full potential of SR, we provide a systematic view for SR and address three fundamental tasks in SR: (1) enhancing the backscattering link via active load; (2) achieving highly reliable communications through joint decoding; and (3) capturing PTx's RF signals using reconfigurable intelligent surfaces. Emerging applications, design challenges and open research problems will also be discussed.

Reconfigurable intelligent surfaces for smart wireless environments: channel estimation, system design and applications in 6G networks

“…Such mutual interference in the above subsection can be avoided via forming the SR between the RISbased transmission and the active transmission [29,30,128], as the SR encourages these two kinds of transmission to collaborate with each other and achieve the mutualistic benefits together. Specifically, in SR, the active transmission system shares the spectrum and energy with the RIS-based transmission and enables the RIS to perform the reflection pattern modulation via reflecting the existing active signal.…”

“…By proactively varying the reflection coefficients of the RIS-based on specific reflection patterns, the intended receiver can detect these artificial variations and decode the embedded messages encoded by the RIS. Compared with conventional backscatter communications [24][25][26][27][28], the use of an extremely large number of REs at the RIS helps to enhance the desired RF source, and greatly improves the performance of backscatter communications [29]. Moreover, the collaboration between the RIS information transmission and active primary transmission yields mutually beneficial spectrum and energy sharing, and such system is also termed symbiotic radio (SR) [29,30].…”

Energy Efficiency Maximization for Symbiotic Radio Networks With Multiple Backscatter Devices

“…In order to support massive IoT connections, cognitive radio (CR) technology has been employed to let IoT devices (as secondary transmitters (STs)) share the same spectrum with incumbent primary transmitters (PTs) [2], [3], [4], [5]. However, the energy efficiency (EE) of a CR system is limited by the energyconsuming active radio frequency (RF) components used in the STs [2], [6].…”

“…Thus, the energy consumption of passive BackCom is significantly reduced as compared with active transmissions in CR. However, since the BDs have no knowledge of the information transmitted by the PT, the EE of BackCom will be limited by the strong interference caused by the PT [6].…”

“…To exploit the synergy between CR and BackCom, symbiotic radio (SR) has been proposed recently [6], where the PT and the primary receiver (PR) are designed to support both the primary and BackCom transmissions, and has attracted a lot of research interest. Depending on whether the BD symbol period is equal to or much longer than the PT symbol period, SR is classified into parasitic SR (PSR) and commensal SR (CSR), respectively [2].…”