Resource Allocation via Backscatter-Aware Transmit Antenna Selection for Low-PAPR and Ultra-Reliable WSNs

TL;DR

This work tackles the conflict between high-throughput primary transmissions and the strict envelope requirements of passive SAW backscatter sensors in hybrid WSNs. It introduces BC-TAS, a per-subcarrier transmit antenna selection framework within MD-OFDM that uses a multi-objective field shaping (MOFS) cost to jointly optimize primary link reliability, tag envelope stability (BCF), and protection of a victim receiver, aided by Kalman-based channel smoothing for robustness under imperfect CSI. A low-complexity greedy MOFS algorithm achieves near-exhaustive performance with O(N_t N_SC) complexity, delivering dramatic improvements: up to about $6.05\times 10^2$ reductions in outage probability at 16 dB SNR and roughly $25\times$ gains in energy efficiency, while maintaining spectral-mask compliance and reducing PAPR by about $2.4$ dB. The results demonstrate effective frequency-selective notching and robust sensing-communication coexistence in dispersive indoor channels, offering a scalable, hardware-friendly approach for dense, power-constrained WSNs; future work will extend to massive MIMO and multi-tag collision scenarios.

Abstract

This paper addresses a fundamental physical layer conflict in hybrid Wireless Sensor Networks (WSNs) between high-throughput primary communication and the stringent power envelope requirements of passive backscatter sensors. We propose a Backscatter-Constrained Transmit Antenna Selection (BC-TAS) framework, a per-subcarrier selection strategy for multi-antenna illuminators operating within a Multi-Dimensional Orthogonal Frequency Division Multiplexing (MD-OFDM) architecture. Unlike conventional signal-to-noise ratio (SNR) centric selection schemes, BC-TAS employs a multi-objective cost function that jointly maximizes desired link reliability, stabilizes the incident RF energy envelope at passive Surface Acoustic Wave (SAW) sensors, and suppresses interference toward coexisting victim receivers. By exploiting the inherent sparsity of MD-OFDM, the proposed framework enables dual-envelope regulation, simultaneously reducing the transmitter Peak-to-Average Power Ratio (PAPR) and the Backscatter Crest Factor (BCF) observed at the tag. To enhance robustness under imperfect Channel State Information (CSI), a Kalman-based channel smoothing mechanism is incorporated to maintain selection stability in low-SNR regimes. Numerical results using IEEE 802.11be dispersive channel models and a nonlinear Rapp power amplifier demonstrate that BC-TAS achieves orders-of-magnitude improvement in outage probability and significant gains in energy efficiency compared to conventional MU-MIMO baselines, while ensuring spectral mask compliance under reduced power amplifier back-off. These results establish BC-TAS as an effective illuminator-side control mechanism for enabling reliable and energy-stable sensing and communication coexistence in dense, power-constrained wireless environments.

Figures (12)

• Figure 1: BER comparison of the proposed BC-TAS framework against SOTA baselines in TGn Model F.
• Figure 2: BER performance of the proposed BC-TAS MD-OFDM across various IEEE 802.11TGn indoor environments (Models A--F).
• Figure 3: Outage Probability CDF in TGn Model F at an average $\mathrm{SNR} = 16$ dB.
• Figure 4: Average BCF vs. $N_t$ across $1,000$ Monte Carlo trials in TGn Model B.
• Figure 5: Smoothed EVM performance vs. IBO highlighting the 16-QAM compliance threshold.

Theorems & Definitions (2)

• Lemma 1
• proof