[Paper Review] An IRS Backscatter Enabled Integrated Sensing, Communication and Computation System

Sai Xu, Yanan Du+3 more|arXiv (Cornell University)|Jul 20, 2022

Advanced Wireless Communication Technologies4 citations

TL;DR

This paper proposes a radio-frequency-chain-free uplink transmission (RFCF-UT) paradigm using intelligent reflecting surface (IRS) backscatter to enable integrated sensing, communication, and computation (ISCC). By treating IRS elements as dynamic QR-code-like modulators, a full-duplex base station scans reflected signals to extract data, achieving high spectral efficiency without active RF chains at user equipment, with simulation results validating superior weighted throughput capacity (WTC) over benchmark schemes.

ABSTRACT

This paper proposes to leverage intelligent reflecting surface (IRS) backscatter to realize radio-frequency-chain-free uplink-transmissions (RFCF-UT). In this communication paradigm, IRS works as an information carrier, whose elements are capable of adjusting their amplitudes and phases to collaboratively portray an electromagnetic image like a dynamic quick response (QR) code, rather than a familiar reflection device, while a full-duplex base station (BS) is used as a scanner to collect and recognize the information on IRS. To elaborate it, an integrated sensing, communication and computation system as an example is presented, in which a dual-functional radar-communication BS simultaneously detects the target and collects the data from user equipments each connected to an IRS. Based on the established model, partial and binary data offloading strategies are respectively considered. By defining a performance metric named weighted throughput capacity (WTC), two maximization problems of WTC are formulated. According to the coupling degree of optimization variables in the objective function and the constraints, each optimization problem is firstly decomposed into two subproblems. Then, the methods of linear programming, fractional programming, integer programming and alternative optimization are developed to solve the subproblems. The simulation results demonstrate the achievable WTC of the considered system, thereby validating RFCF-UT.

Motivation & Objective

• To eliminate the need for RF chains at user equipment by leveraging IRS as a passive information carrier.
• To design an integrated sensing, communication, and computation (ISCC) system where a dual-functional radar-communication (DFRC) base station supports both target detection and data collection via IRS backscatter.
• To optimize system performance through joint beamforming and data offloading strategies under energy and hardware constraints.
• To validate the feasibility and superiority of IRS backscatter over active antenna solutions in terms of weighted throughput capacity (WTC).

Proposed method

• Proposes a novel communication paradigm—radio-frequency-chain-free uplink transmissions (RFCF-UT)—where IRS elements modulate data via adjustable amplitude and phase shifts, functioning as a dynamic QR code.
• Employs a full-duplex DFRC base station to transmit signals and simultaneously receive echoes modulated by IRS, enabling simultaneous sensing and data collection.
• Models the ISCC system with partial and binary data offloading strategies, formulating two WTC maximization problems under coupled optimization variables.
• Develops a hybrid optimization framework combining linear programming (LP), fractional programming (FP), integer programming (IP), and alternating optimization (AO) to solve subproblems.
• Introduces discrete passive beamforming at IRS to approximate continuous beamforming, reducing hardware complexity while preserving performance.
• Uses weighted throughput capacity (WTC) as the key performance metric to balance communication, sensing, and computation gains.

Experimental results

Research questions

• RQ1 Can IRS backscatter effectively replace active RF chains at user equipment to enable RF-chain-free uplink transmissions?
• RQ2 How does the integration of sensing, communication, and computation via IRS backscatter impact system spectral efficiency and throughput capacity?
• RQ3 What is the performance gain of joint optimization of beamforming, data offloading, and beam selection compared to simplified schemes like MRT or reflective beamforming?
• RQ4 To what extent does discrete passive beamforming at IRS approximate continuous beamforming in terms of WTC performance?
• RQ5 How do system parameters such as number of IRS elements, transmit power, and number of base station antennas affect the achievable WTC?

Key findings

• The proposed Joint optimization scheme achieves the highest weighted throughput capacity (WTC), outperforming MRT, Discrete4, Discrete8, and reflective beamforming schemes.
• IRS backscatter achieves comparable or better WTC than active antennas (e.g., Antenna4, Antenna8) under the same transmit power, demonstrating its feasibility as a low-cost, passive alternative.
• Increasing the number of IRS elements improves WTC for Joint, MRT, Discrete4, and Discrete8 schemes due to enhanced spatial multiplexing and power reception, while Reflective beamforming shows a peak and then decline due to equal power allocation.
• Higher transmit power at the base station increases WTC across all schemes, confirming the system's power scalability.
• More transmitting antennas at the base station significantly improve WTC for Joint, MRT, Discrete4, and Discrete8, but have minimal impact on Reflective and Antenna-based schemes, indicating that spatial freedom is key to performance gains.
• Partial offloading consistently achieves higher WTC than binary offloading, as it allows flexible resource allocation, whereas binary offloading forces all users into a single mode (local or offloaded).