[Paper Review] Survey on Symbiotic Radio: A Paradigm Shift in Spectrum Sharing and Coexistence

Muhammad Bilal Janjua, Hüseyin Arslan|arXiv (Cornell University)|Nov 17, 2021

Advanced MIMO Systems Optimization12 citations

TL;DR

This paper proposes symbiotic radio (SRad) as a novel paradigm for spectrum sharing and coexistence in future wireless networks, where passive communication systems (PCS) exploit signals from active communication systems (ACS) for transmission. By leveraging bio-inspired symbiosis—particularly mutualism and commensalism—SRad enables energy-efficient, low-complexity communication with performance gains in spectral and energy efficiency, especially in IoT and 6G scenarios.

ABSTRACT

Sixth-generation (6G) of mobile communication aims to connect this world digitally through green communication networks that provide secure, ubiquitous, and unlimited connectivity in an attempt to improve the overall quality of life.The driving force behind the development of these networks is the rapid evolution of Internet-of-Things (IoT), which has stimulated the proliferation of wireless applications in health,education, agriculture, utilities, etc. However, these applications are accompanied by the deployment of a massive number of IoT devices that require a significant radio spectrum for wireless connectivity. IoT devices usually have low data rate requirements and limited power provision but desirably a long life.Recently, the development of passive radio systems has opened new paradigms of spectrum sharing and coexistence. These systems utilize the radio resources and infrastructure of the active radio systems to perform their functionalities. By enabling the dependent coexistence, a new technology named symbiotic radio (SRad) enables the symbiotic relationships between the different radio systems ranging from mutual benefits or competition in terms of sharing the resources, in particular for IoT devices. This survey first provides the motivation for dependent coexistence and background of spectrum sharing through coexistence along with existing literature. Then, it describes the active and passive radio systems definition and a brief overview. Afterward, the history of symbiosis and the role of SRad technology in spectrum sharing and coexistence are defined while focusing on symbiotic communication. Lastly, we discuss research challenges, future directions, and applications scenarios.

Motivation & Objective

• Address the growing spectrum scarcity and energy constraints in massive IoT deployments by proposing a new spectrum sharing paradigm.
• Overcome limitations of traditional spectrum sharing mechanisms like cognitive radio and backscatter communication by introducing symbiotic radio as a bio-inspired alternative.
• Enable coexistence between dissimilar radio systems—particularly active and passive systems—through symbiotic relationships such as mutualism and commensalism.
• Investigate performance, security, and channel estimation challenges specific to SRad systems, especially in the context of reconfigurable intelligent surfaces (RIS) and 6G networks.
• Provide a comprehensive survey of SRad's system models, performance metrics, and application scenarios to guide future research and deployment.

Proposed method

• Propose a bio-inspired symbiotic radio (SRad) framework where passive communication systems (PCS) backscatter signals from active communication systems (ACS) for transmission, enabling spectrum and energy sharing.
• Classify symbiotic relationships into obligatory (e.g., ARS-PRS) and facultative (e.g., ARS-PRDS) coexistence based on system dependency, with a focus on dependent coexistence for performance gains.
• Model the cascaded and doubly faded channel of PCS, distinguishing it from direct-link channels in ACS, and emphasize the need for accurate channel state information (CSI) estimation.
• Integrate reconfigurable intelligent surfaces (RIS) into SRad to enhance signal strength and reliability, while acknowledging the increased complexity of RIS channel estimation.
• Propose performance metrics beyond traditional throughput, including mutualism gains in system capacity and spectral efficiency, especially when PCS devices act as multipath reflectors.
• Explore physical layer security techniques and authentication mechanisms to protect sensitive data in PCS, given the broadcast nature of backscattered signals and vulnerability to eavesdropping.

Experimental results

Research questions

• RQ1 How can symbiotic radio (SRad) enable efficient spectrum and energy sharing between active and passive radio systems in future 6G and IoT networks?
• RQ2 What are the key performance gains and system capacity improvements achievable through mutualistic and commensalistic symbiotic relationships in SRad systems?
• RQ3 How do channel modeling and estimation challenges in SRad differ from conventional active systems, particularly in the context of cascaded and doubly faded channels for PCS?
• RQ4 What are the security and privacy risks in SRad, and how can low-complexity physical layer security mechanisms be designed for energy-constrained PCS devices?
• RQ5 How can reconfigurable intelligent surfaces (RIS) be integrated into SRad to enhance performance, and what are the implications for channel estimation and system design?

Key findings

• Symbiotic radio enables significant spectral and energy efficiency gains by allowing passive devices to exploit existing active signals, reducing the need for dedicated spectrum and power.
• In mutualistic SRad, the addition of PCS devices can increase the overall system capacity and spectral efficiency, as the PCS acts as a constructive multipath reflector for the ACS.
• Channel estimation in SRad is more complex than in conventional systems due to the cascaded and doubly faded nature of the PCS channel, requiring specialized techniques beyond standard ACS methods.
• Security remains a critical challenge due to the broadcast nature of backscattered signals, necessitating lightweight authentication and physical layer security mechanisms for sensitive applications like healthcare.
• The integration of RIS into SRad enhances performance but exacerbates channel estimation challenges, making it an open and active research problem.
• SRad is positioned as a promising candidate for 6G and massive IoT, offering a paradigm shift in spectrum coexistence through bio-inspired symbiotic relationships that outperform traditional cognitive radio and backscatter systems in scalability and efficiency.