Design and validation of a system for capturing LTE sounding reference signals as a carrier for ambient backscatter

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master_Zhang_Tianshu_2025.pdf (2.47 MB)

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School of Electrical Engineering | Master's thesis
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Date

2025-07-31

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Communications Engineering

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Degree programme

Master's Programme in Computer, Communication and Information Sciences

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en

Pages

57

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Abstract

Ambient backscatter communication presents a promising avenue for enabling ultra-low-power Internet of Things (IoT) devices by leveraging existing environmental radio frequency signals. This thesis explores the use of the LTE uplink Sounding Reference Signal (SRS) as a carrier for such systems, capitalizing on its predictable, configurable, and data-independent nature. The primary objective is to develop and validate a complete system for capturing and analyzing SRS transmissions from a commercial User Equipment (UE) to facilitate research in SRS-based backscatter communications. This work delivers two principal contributions. First, a custom OFDM receiver was developed in MATLAB, designed to perform offline synchronization, channel estimation, and signal analysis on captured SRS signals. Second, to create a real-world testbed, the open-source srsRAN 4G eNodeB software was significantly modified to enable the configuration and command of a commercial smartphone to transmit periodic, wideband SRS-a feature not available in the baseline software. A critical part of this effort involved identifying and resolving complex interoperability issues between scheduled SRS and other uplink channels (PUSCH and PUCCH) that initially caused connection failures. Experimental results using a commercial smartphone and a USRP-based eNodeB validate the entire system. The modified srsRAN testbed successfully configures the UE for stable SRS transmission, and the custom MATLAB receiver demonstrates its ability to synchronize with these over-the-air signals and accurately extract the channel state information. In conclusion, this thesis provides the foundational software infrastructure and practical methodology required to advance research and development of ambient backscatter systems that leverage LTE uplink signals.

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Supervisor

Ruttik, Kalle

Keywords

OFDM, sounding reference signal, SRS, srsRAN 4G, SDR, software-defined radio, ambient backscatter communications

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https://urn.fi/URN:NBN:fi:aalto-202508196301

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[dipl] Sähkötekniikan korkeakoulu / ELEC