[Paper Review] Full-Duplex Backscatter Interference Networks Based on Time-Hopping Spread Spectrum

Wanchun Liu, Kaibin Huang+2 more|arXiv (Cornell University)|Aug 31, 2016

Energy Harvesting in Wireless Networks14 references3 citations

TL;DR

This paper proposes a full-duplex backscatter communication network using time-hopping spread spectrum (TH-SS) to enable simultaneous two-way information transfer (IT) and one-way energy transfer (ET) in dense IoT environments. By leveraging TH-SS for multiple access and combining coherent/non-coherent detection, the scheme suppresses interference and achieves high spectral efficiency, with analytical performance metrics including bit-error rate, energy harvesting efficiency, and outage probability validated through stochastic geometry models.

ABSTRACT

Future Internet-of-Things (IoT) is expected to wirelessly connect billions of low-complexity devices. For wireless information transfer (WIT) in IoT, high density of IoT devices and their ad hoc communication result in strong interference which acts as a bottleneck on WIT. Furthermore, battery replacement for the massive number of IoT devices is difficult if not infeasible, making wireless energy transfer (WET) desirable. This motivates: (i) the design of full-duplex WIT to reduce latency and enable efficient spectrum utilization, and (ii) the implementation of passive IoT devices using backscatter antennas that enable WET from one device (reader) to another (tag). However, the resultant increase in the density of simultaneous links exacerbates the interference issue. This issue is addressed in this paper by proposing the design of full-duplex backscatter communication (BackCom) networks, where a novel multiple-access scheme based on time-hopping spread-spectrum (TH-SS) is designed to enable both one-way WET and two-way WIT in coexisting backscatter reader-tag links. Comprehensive performance analysis of BackCom networks is presented in this paper, including forward/backward bit-error rates and WET efficiency and outage probabilities, which accounts for energy harvesting at tags, non-coherent and coherent detection at tags and readers, respectively, and the effects of asynchronous transmissions.

Motivation & Objective

• Address the challenge of severe interference caused by high-density, ad hoc IoT device communications in future IoT networks.
• Overcome the impracticality of battery replacement for massive IoT devices by enabling wireless energy transfer (ET) via backscatter communication.
• Design a full-duplex backscatter network that supports simultaneous one-way ET and two-way IT in coexisting reader-tag links.
• Develop a novel multiple-access scheme based on time-hopping spread spectrum (TH-SS) to suppress co-channel interference and enable efficient spectrum utilization.
• Analyze key performance metrics including forward/backward bit-error rates, ET efficiency, and outage probabilities under asynchronous transmissions and fading channels.

Proposed method

• Propose a full-duplex backscatter communication (BackCom) network architecture where readers simultaneously transmit energy and receive backscattered signals from tags.
• Design a time-hopping spread-spectrum (TH-SS) multiple-access scheme to enable orthogonality among coexisting reader-tag links and reduce interference.
• Integrate coherent detection at the reader and non-coherent detection at the tag to support full-duplex operation with improved reliability.
• Model the network using stochastic geometry, assuming Poisson point processes for random device deployment and Rayleigh fading for channel propagation.
• Derive closed-form expressions for key performance metrics: forward/backward bit-error rates (BER), energy harvesting (EH) efficiency, and energy outage probability.
• Account for asynchronous transmissions, energy harvesting at tags, and the impact of channel fading and path loss (with path loss exponent λ) in the performance analysis.

Experimental results

Research questions

• RQ1 How can full-duplex backscatter communication be designed to support simultaneous two-way information transfer and one-way energy transfer in dense IoT networks?
• RQ2 What is the achievable bit-error rate performance of forward and backward links in a full-duplex TH-SS backscatter network under Rayleigh fading and asynchronous transmissions?
• RQ3 How does the time-hopping spread-spectrum scheme suppress multi-user interference in coexisting reader-tag links?
• RQ4 What is the energy harvesting efficiency and outage probability of tags in the proposed network, and how do path loss and transmission power affect them?
• RQ5 How do the design parameters—such as duty cycle, reflection coefficient, and power splitting ratio—impact the overall system performance?

Key findings

• The proposed TH-SS-based full-duplex BackCom network achieves significant interference suppression, enabling reliable two-way IT and one-way ET in high-density IoT deployments.
• The forward and backward bit-error rates are derived in closed form, showing that coherent detection at the reader and non-coherent detection at the tag jointly improve BER performance under fading conditions.
• Energy harvesting efficiency is maximized when the reader’s transmit power and time allocation are optimized, with analytical expressions derived for the expected energy transfer rate (ETR).
• The energy outage probability is derived as a function of transmission power, path loss, and channel fading, with explicit dependence on the signal-to-interference-plus-noise ratio (SINR) and time-hopping parameters.
• The performance analysis accounts for asynchronous transmissions and shows that the system maintains robustness even under imperfect synchronization.
• Numerical results confirm that the proposed scheme achieves lower BER and higher ET efficiency compared to conventional backscatter systems, especially in high-density scenarios.