Multi-User Multi-IoT-Device Symbiotic Radio: A Novel Massive Access Scheme for Cellular IoT

TL;DR

This paper introduces a novel multi-user multi-IoT-device symbiotic radio system for cellular IoT, utilizing robust and DoA-based beamforming to enable massive access with reduced feedback overhead.

Contribution

It proposes a new SR system model for cellular IoT with joint decoding and robust beamforming, including a DoA-based design that reduces feedback requirements.

Findings

The proposed system supports massive IoT device access.

The DoA-based beamforming achieves similar performance to CSI-based methods with small angular spreads.

Simulation confirms the effectiveness of the robust and DoA-based beamforming approaches.

Abstract

Symbiotic radio (SR) is a promising technique to support cellular Internet-of-Things (IoT) by forming a mutualistic relationship between IoT and cellular transmissions. In this paper, we propose a novel multi-user multi-IoT-device SR system to enable massive access in cellular IoT. In the considered system, the base station (BS) transmits information to multiple cellular users, and a number of IoT devices simultaneously backscatter their information to these users via the cellular signal. The cellular users jointly decode the information from the BS and IoT devices. Noting that the reflective links from the IoT devices can be regarded as the channel uncertainty of the direct links, we apply the robust design method to design the beamforming vectors at the BS. Specifically, the transmit power is minimized under the cellular transmission outage probability constraints and IoT transmission sum rate constraints. The algorithm based on semi-definite programming and difference-of-convex programming is proposed to solve the power minimization problem. Moreover, we consider a special case where each cellular user is associated with several adjacent IoT devices and propose a direction of arrival (DoA)-based transmit beamforming design approach. The DoA-based approach requires only the DoA and angular spread (AS) of the direct links instead of the instantaneous channel state information (CSI) of the reflective link channels, leading to a significant reduction in the channel feedback overhead. Simulation results have substantiated the multi-user multi-IoT-device SR system and the effectiveness of the proposed beamforming approaches. It is shown that the DoA-based beamforming approach achieves comparable performance as the CSI-based approach in the special case when the ASs are small.